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2162d503-35a3-48cc-ab6e-1ee8c36ecaff | 2162d503-35a3-48cc-ab6e-1ee8c36ecaff | 2162d503-35a3-48cc-ab6e-1ee8c36ecaff | human | null | null | none | abstracts | An invariance principle for semimartingale reflecting Brownian motions
in domains with piecewise smooth boundaries | null | Semimartingale reflecting Brownian motions (SRBMs) living in the closures of domains with piecewise smooth boundaries are of interest in applied probability because of their role as heavy traffic approximations for some stochastic networks. In this paper, assuming certain conditions on the domains and directions of reflection, a perturbation result, or invariance principle, for SRBMs is proved. This provides sufficient conditions for a process that satisfies the definition of an SRBM, except for small random perturbations in the defining conditions, to be close in distribution to an SRBM. A crucial ingredient in the proof of this result is an oscillation inequality for solutions of a perturbed Skorokhod problem. We use the invariance principle to show weak existence of SRBMs under mild conditions. We also use the invariance principle, in conjunction with known uniqueness results for SRBMs, to give some sufficient conditions for validating approximations involving (i) SRBMs in convex polyhedrons with a constant reflection vector field on each face of the polyhedron, and (ii) SRBMs in bounded domains with piecewise smooth boundaries and possibly nonconstant reflection vector fields on the boundary surfaces. |
aae54d4a-b8e5-41f9-82d2-d37613f5ba11 | aae54d4a-b8e5-41f9-82d2-d37613f5ba11 | aae54d4a-b8e5-41f9-82d2-d37613f5ba11 | human | null | null | none | abstracts | Photoconductance of organic single-molecule contacts | null | We study the dc conductance of organic single-molecule contacts in the presence of external electromagnetic radiation (photoconductance). In agreement with previous predictions, we find that the radiation can lead to large enhancements of the conductance of such contacts by bringing off-resonant levels into resonance through photoassisted processes. In our analysis we make use of the simplifying fact that, under certain assumptions, the photoconductance can be expressed in terms of the transmission function in the absence of the radiation. The conductance enhancement is demonstrated for oligophenylene molecules between gold electrodes, whose electronic structure is calculated based on density-functional theory. It is shown that the exponential decay of the conductance with the length of the molecule can be replaced by a length-independent value in the presence of radiation. |
ef886ca6-f902-4cc2-ace4-d1fae263e360 | ef886ca6-f902-4cc2-ace4-d1fae263e360 | ef886ca6-f902-4cc2-ace4-d1fae263e360 | human | null | null | none | abstracts | The Sigma-D Relation for Planetary Nebulae: Preliminary Analysis | null | An analysis of the relation between radio surface brightness and diameter, so-called Sigma-D relation, for planetary nebulae (PNe) is presented: i) the theoretical Sigma-D relation for the evolution of bremsstrahlung surface brightness is derived; ii) contrary to the results obtained earlier for the Galactic supernova remnant (SNR) samples, our results show that the updated sample of Galactic PNe does not severely suffer from volume selection effect - Malmquist bias (same as for the extragalactic SNR samples) and; iii) we conclude that the empirical Sigma-D relation for PNe derived in this paper is not useful for valid determination of distances for all observed PNe with unknown distances. |
93424dfd-73e9-4cb1-81a2-b8436e4a928a | 93424dfd-73e9-4cb1-81a2-b8436e4a928a | 93424dfd-73e9-4cb1-81a2-b8436e4a928a | human | null | null | none | abstracts | Stopping effects in U+U collisions with a beam energy of 520 MeV/nucleon | null | A Relativistic Transport Model (ART1.0) is applied to simulate the stopping effects in tip-tip and body-body U+U collisions, at a beam kinetic energy of 520 MeV/nucleon. Our simulation results have demonstrated that both central collisions of the two extreme orientations can achieve full stopping, and also form a bulk of hot, dense nuclear matter with a sufficiently large volume and long duration, due to the largely deformed uranium nuclei. The nucleon sideward flow in the tip-tip collisions is nearly 3 times larger than that in body-body ones at normalized impact parameter $b/b_{max}<0.5$, and that the body-body central collisions have a largest negative nucleon elliptic flow $v_{2}=-12%$ in contrast to zero in tip-tip ones. Thus the extreme circumstance and the novel experimental observables in tip-tip and body-body collisions can provide a good condition and sensitive probe to study the nuclear EoS, respectively. The Cooling Storage Ring (CSR) External Target Facility (ETF) to be built at Lanzhou, China, delivering the uranium beam up to 520 MeV/nucleon is expected to make significant contribution to explore the nuclear equation of state (EoS). |
8e265546-3eda-48da-869f-02e7a720191c | 8e265546-3eda-48da-869f-02e7a720191c | 8e265546-3eda-48da-869f-02e7a720191c | human | null | null | none | abstracts | QED for fields obeying a square root operator equation | null | Instead of using local field equations - like the Dirac equation for spin-1/2 and the Klein-Gordon equation for spin-0 particles - one could try to use non-local field equations in order to describe scattering processes. The latter equations can be obtained by means of the relativistic energy together with the correspondence principle, resulting in equations with a square root operator. By coupling them to an electromagnetic field and expanding the square root (and taking into account terms of quadratic order in the electromagnetic coupling constant e), it is possible to calculate scattering matrix elements within the framework of quantum electrodynamics, e.g. like those for Compton scattering or for the scattering of two identical particles. This will be done here for the scalar case. These results are then compared with the corresponding ones based on the Klein-Gordon equation. A proposal of how to transfer these reflections to the spin-1/2 case is also presented. |
81f014d1-209a-4544-ba1e-50b7d277ccef | 81f014d1-209a-4544-ba1e-50b7d277ccef | 81f014d1-209a-4544-ba1e-50b7d277ccef | human | null | null | none | abstracts | Feedback from first radiation sources: H- photodissociation | null | During the epoch of reionization, the formation of radiation sources is accompanied by the growth of a H- photodissociating flux. We estimate the impact of this flux on the formation of molecular hydrogen and cooling in the first galaxies, assuming different types of radiation sources (e.g. Pop II and Pop III stars, miniquasars). We find that H- photodissociation reduces the formation of H2 molecules by a factor of ~1+1000k_s*x/(f_esc*delta), where x is the mean ionized fraction in the IGM, f_esc is the fraction of ionizing photons that escape from their progenitor halos, delta is the local gas overdensity and k_s is an order unity constant which depends on the type of radiation source. By the time a significant fraction of the universe becomes ionized, H- photodissociation may significantly reduce the H2 abundance and, with it, the primordial star formation rate, delaying the progress of reionization. |
c789f3d5-7fb6-45eb-bcf7-0b8bdc4bd1d0 | c789f3d5-7fb6-45eb-bcf7-0b8bdc4bd1d0 | c789f3d5-7fb6-45eb-bcf7-0b8bdc4bd1d0 | human | null | null | none | abstracts | The 3D +-J Ising model at the ferromagnetic transition line | null | We study the critical behavior of the three-dimensional $\pm J$ Ising model [with a random-exchange probability $P(J_{xy}) = p \delta(J_{xy} - J) + (1-p) \delta(J_{xy} + J)$] at the transition line between the paramagnetic and ferromagnetic phase, which extends from $p=1$ to a multicritical (Nishimori) point at $p=p_N\approx 0.767$. By a finite-size scaling analysis of Monte Carlo simulations at various values of $p$ in the region $p_N<p<1$, we provide strong numerical evidence that the critical behavior along the ferromagnetic transition line belongs to the same universality class as the three-dimensional randomly-dilute Ising model. We obtain the results $\nu=0.682(3)$ and $\eta=0.036(2)$ for the critical exponents, which are consistent with the estimates $\nu=0.683(2)$ and $\eta=0.036(1)$ at the transition of randomly-dilute Ising models. |
8964d6ec-35b7-4e4f-98ac-b6d7ec8535fb | 8964d6ec-35b7-4e4f-98ac-b6d7ec8535fb | 8964d6ec-35b7-4e4f-98ac-b6d7ec8535fb | human | null | null | none | abstracts | Star Formation in the Bok Globule CB54 | null | We present mid-infrared (10.4 \micron, 11.7 \micron, and 18.3 \micron) imaging intended to locate and characterize the suspected protostellar components within the Bok globule CB54. We detect and confirm the protostellar status for the near-infrared source CB54YC1-II. The mid-infrared luminosity for CB54YC1-II was found to be $L_{midir} \approx 8 L_\sun$, and we estimate a central source mass of $M_* \approx 0.8 M_\sun$ (for a mass accretion rate of ${\dot M}=10^{-6} M_\sun yr^{-1}$). CB54 harbors another near-infrared source (CB54YC1-I), which was not detected by our observations. The non-detection is consistent with CB54YC1-I being a highly extinguished embedded young A or B star or a background G or F giant. An alternative explanation for CB54YC1-I is that the source is an embedded protostar viewed at an extremely high inclination angle, and the near-infrared detections are not of the central protostar, but of light scattered by the accretion disk into our line of sight. In addition, we have discovered three new mid-infrared sources, which are spatially coincident with the previously known dense core in CB54. The source temperatures ($\sim100$K) and association of the mid-infrared sources with the dense core suggests that these mid-infrared objects may be embedded class 0 protostars. |
c6d52719-3681-4d3f-94ec-ed92400bdd99 | c6d52719-3681-4d3f-94ec-ed92400bdd99 | c6d52719-3681-4d3f-94ec-ed92400bdd99 | human | null | null | none | abstracts | Quantitative Resolution to some "Absolute Discrepancies" in Cancer
Theories: a View from Phage lambda Genetic Switch | null | Is it possible to understand cancer? Or more specifically, is it possible to understand cancer from genetic side? There already many answers in literature. The most optimistic one has claimed that it is mission-possible. Duesberg and his colleagues reviewed the impressive amount of research results on cancer accumulated over 100 years. It confirms the a general opinion that considering all available experimental results and clinical observations there is no cancer theory without major difficulties, including the prevailing gene-based cancer theories. They have then listed 9 "absolute discrepancies" for such cancer theory. In this letter the quantitative evidence against one of their major reasons for dismissing mutation cancer theory, by both in vivo experiment and a first principle computation, is explicitly pointed out. |
541b8099-0112-419a-903e-fddbd2ba0651 | 541b8099-0112-419a-903e-fddbd2ba0651 | 541b8099-0112-419a-903e-fddbd2ba0651 | human | null | null | none | abstracts | Reduced phase space and toric variety coordinatizations of Delzant
spaces | null | In this note we describe the natural coordinatizations of a Delzant space defined as a reduced phase space (symplectic geometry view-point) and give explicit formulas for the coordinate transformations. For each fixed point of the torus action on the Delzant polytope, we have a maximal coordinatization of an open cell in the Delzant space which contains the fixed point. This cell is equal to the domain of definition of one of the natural coordinatizations of the Delzant space as a toric variety (complex algebraic geometry view-point), and we give an explicit formula for the toric variety coordinates in terms of the reduced phase space coordinates. We use considerations in the maximal coordinate neighborhoods to give simple proofs of some of the basic facts about the Delzant space, as a reduced phase space, and as a toric variety. These can be viewed as a first application of the coordinatizations, and serve to make the presentation more self-contained. |
d3656e8d-97e2-4323-a696-4e1e2d514842 | d3656e8d-97e2-4323-a696-4e1e2d514842 | d3656e8d-97e2-4323-a696-4e1e2d514842 | human | null | null | none | abstracts | Measurement of B(D_S^+ --> ell^+ nu) and the Decay Constant f_D_{S^+} | null | We examine e+e- --> Ds- Ds*+ and Ds*- Ds+ interactions at 4170 MeV using the CLEO-c detector in order to measure the decay constant fDs+. We use the Ds+ --> l+ nu channel, where the l+ designates either a mu+ or a tau+, when the tau+ --> pi+ nu. Analyzing both modes independently, we determine B(Ds+ --> mu+ nu) = (0.594 +- 0.066 +- 0.031)%, and B(Ds+ --> tau+ nu) = (8.0 +- 1.3 +- 0.4)%. We also analyze them simultaneously to find an effective value of B{eff}(Ds+ --> mu+ nu) = (0.638 +- 0.059 +- 0.033)% and extract fDs = (274 +- 13 +- 7) MeV. Combining with our previous determination of B(D+ -> mu+ nu), we also find the ratio fDs/fD+ = 1.23 +- 0.11 +- 0.04. We compare to current theoretical estimates. Finally, we find B(Ds+ --> e+ nu) < 1.3 x10^{-4} at 90% confidence level. |
bf2a6d59-32c5-42a0-851d-541a0dc7784c | bf2a6d59-32c5-42a0-851d-541a0dc7784c | bf2a6d59-32c5-42a0-851d-541a0dc7784c | human | null | null | none | abstracts | Broadening the Higgs Boson with Right-Handed Neutrinos and a Higher
Dimension Operator at the Electroweak Scale | null | The existence of certain TeV suppressed higher-dimension operators may open up new decay channels for the Higgs boson to decay into lighter right-handed neutrinos. These channels may dominate over all other channels if the Higgs boson is light. For a Higgs boson mass larger than $2 m_W$ the new decays are subdominant yet still of interest. The right-handed neutrinos have macroscopic decay lengths and decay mostly into final states containing leptons and quarks. A distinguishing collider signature of this scenario is a pair of displaced vertices violating lepton number. A general operator analysis is performed using the minimal flavor violation hypothesis to illustrate that these novel decay processes can occur while remaining consistent with experimental constraints on lepton number violating processes. In this context the question of whether these new decay modes dominate is found to depend crucially on the approximate flavor symmetries of the right-handed neutrinos. |
63655021-9c63-450e-bac6-d148b50082d4 | 63655021-9c63-450e-bac6-d148b50082d4 | 63655021-9c63-450e-bac6-d148b50082d4 | human | null | null | none | abstracts | Multiple Unfoldings of Orbifold Singularities: Engineering Geometric
Analogies to Unification | null | Katz and Vafa showed how charged matter can arise geometrically by the deformation of ADE-type orbifold singularities in type IIa, M-theory, and F-theory compactifications. In this paper we use those same basic ingredients, used there to geometrically engineer specific matter representations, here to deform the compactification manifold itself in a way which naturally compliments many features of unified model building. We realize this idea explicitly by deforming a manifold engineered to give rise to an $SU_5$ grand unified model into a one giving rise to the Standard Model. In this framework, the relative local positions of the singularities giving rise to Standard Model fields are specified in terms of the values of a small number of complex structure moduli which deform the original manifold, greatly reducing the arbitrariness of their relative positions. |
fc039b38-9eb6-488a-bfd4-f51590c5572d | fc039b38-9eb6-488a-bfd4-f51590c5572d | fc039b38-9eb6-488a-bfd4-f51590c5572d | human | null | null | none | abstracts | Geometrically Engineering the Standard Model: Locally Unfolding Three
Families out of E8 | null | This paper extends and builds upon the results of an earlier paper, in which we described how to use the tools of geometrical engineering to deform geometrically-engineered grand unified models into ones with lower symmetry. This top-down unfolding has the advantage that the relative positions of singularities giving rise to the many `low energy' matter fields are related by only a few parameters which deform the geometry of the unified model. And because the relative positions of singularities are necessary to compute the superpotential, for example, this is a framework in which the arbitrariness of geometrically engineered models can be greatly reduced.
In our earlier paper, this picture was made concrete for the case of deforming the representations of an SU(5) model into their Standard Model content. In this paper we continue that discussion to show how a geometrically engineered 16 of SO(10) can be unfolded into the Standard Model, and how the three families of the Standard Model uniquely emerge from the unfolding of a single, isolated E8 singularity. |
e3fdba42-2b0d-4215-861d-d48229b2e0c8 | e3fdba42-2b0d-4215-861d-d48229b2e0c8 | e3fdba42-2b0d-4215-861d-d48229b2e0c8 | human | null | null | none | abstracts | Giant Planet Migration in Viscous Power-Law Discs | null | Many extra-solar planets discovered over the past decade are gas giants in tight orbits around their host stars. Due to the difficulties of forming these `hot Jupiters' in situ, they are generally assumed to have migrated to their present orbits through interactions with their nascent discs. In this paper, we present a systematic study of giant planet migration in power law discs. We find that the planetary migration rate is proportional to the disc surface density. This is inconsistent with the assumption that the migration rate is simply the viscous drift speed of the disc. However, this result can be obtained by balancing the angular momentum of the planet with the viscous torque in the disc. We have verified that this result is not affected by adjusting the resolution of the grid, the smoothing length used, or the time at which the planet is released to migrate. |
660d61a5-b544-4771-8038-098007040d52 | 660d61a5-b544-4771-8038-098007040d52 | 660d61a5-b544-4771-8038-098007040d52 | human | null | null | none | abstracts | Worldsheet Instantons and Torsion Curves, Part B: Mirror Symmetry | null | We apply mirror symmetry to the problem of counting holomorphic rational curves in a Calabi-Yau threefold X with Z_3 x Z_3 Wilson lines. As we found in Part A [hep-th/0703182], the integral homology group H_2(X,Z)=Z^3 + Z_3 + Z_3 contains torsion curves. Using the B-model on the mirror of X as well as its covering spaces, we compute the instanton numbers. We observe that X is self-mirror even at the quantum level. Using the self-mirror property, we derive the complete prepotential on X, going beyond the results of Part A. In particular, this yields the first example where the instanton number depends on the torsion part of its homology class. Another consequence is that the threefold X provides a non-toric example for the conjectured exchange of torsion subgroups in mirror manifolds. |
22e2239c-8c9c-40b9-af79-c8ad62d31601 | 22e2239c-8c9c-40b9-af79-c8ad62d31601 | 22e2239c-8c9c-40b9-af79-c8ad62d31601 | human | null | null | none | abstracts | Electromigrated nanoscale gaps for surface-enhanced Raman spectroscopy | null | Single-molecule detection with chemical specificity is a powerful and much desired tool for biology, chemistry, physics, and sensing technologies. Surface-enhanced spectroscopies enable single molecule studies, yet reliable substrates of adequate sensitivity are in short supply. We present a simple, scaleable substrate for surface-enhanced Raman spectroscopy (SERS) incorporating nanometer-scale electromigrated gaps between extended electrodes. Molecules in the nanogap active regions exhibit hallmarks of very high Raman sensitivity, including blinking and spectral diffusion. Electrodynamic simulations show plasmonic focusing, giving electromagnetic enhancements approaching those needed for single-molecule SERS. |
51acacb4-512e-4d76-aedd-5025af29e394 | 51acacb4-512e-4d76-aedd-5025af29e394 | 51acacb4-512e-4d76-aedd-5025af29e394 | human | null | null | none | abstracts | Dramatic Variability of X-ray Absorption Lines in the Black Hole
Candidate Cygnus X-1 | null | We report results from a 30 ks observation of Cygnus X-1 with the High Energy Transmission Grating Spectrometer (HETGS) on board the {\em Chandra X-ray Observatory}. Numerous absorption lines were detected in the HETGS spectrum. The lines are associated with highly ionized Ne, Na, Mg, Al, Si, S, and Fe, some of which have been seen in earlier HETGS observations. Surprisingly, however, we discovered dramatic variability of the lines over the duration of the present observation. For instance, the flux of the Ne X line at 12.14 \AA\ was about $5 \times 10^{-3}$ photons cm$^{-2}$ s$^{-1}$ in the early part of the observation but became subsequently undetectable, with a 99% upper limit of $0.06 \times 10^{-3}$ photons cm$^{-2}$ s$^{-1}$ on the flux of the line. This implies that the line weakened by nearly two orders of magnitude on a timescale of hours. The overall X-ray flux of the source did also vary during the observation but only by 20--30%. For Cyg X-1, the absorption lines are generally attributed to the absorption of X-rays by ionized stellar wind in the binary system. Therefore, they may provide valuable diagnostics on the physical condition of the wind. We discuss the implications of the results. |
7f9389fc-5240-4ddf-b657-8f62bc1ddd70 | 7f9389fc-5240-4ddf-b657-8f62bc1ddd70 | 7f9389fc-5240-4ddf-b657-8f62bc1ddd70 | human | null | null | none | abstracts | An Extrasolar Planet Census with a Space-based Microlensing Survey | null | A space-based gravitational microlensing exoplanet survey will provide a statistical census of exoplanets with masses down to 0.1 Earth-masses and orbital separations ranging from 0.5AU to infinity. This includes analogs to all the Solar System's planets except for Mercury, as well as most types of planets predicted by planet formation theories. Such a survey will provide results on the frequency of planets around all types of stars except those with short lifetimes. Close-in planets with separations < 0.5 AU are invisible to a space-based microlensing survey, but these can be found by Kepler. Other methods, including ground-based microlensing, cannot approach the comprehensive statistics on the mass and semi-major axis distribution of extrasolar planets that a space-based microlensing survey will provide. The terrestrial planet sensitivity of a ground-based microlensing survey is limited to the vicinity of the Einstein radius at 2-3 AU, and space-based imaging is needed to identify and determine the mass of the planetary host stars for the vast majority of planets discovered by microlensing. Thus, a space-based microlensing survey is likely to be the only way to gain a comprehensive understanding of the nature of planetary systems, which is needed to understand planet formation and habitability. The proposed Microlensing Planet Finder (MPF) mission is an example of a space-based microlensing survey that can accomplish these objectives with proven technology and a cost that fits comfortably under the NASA Discovery Program cost cap. |
ad167abf-46b8-4f74-bc94-8be4f97b9f36 | ad167abf-46b8-4f74-bc94-8be4f97b9f36 | ad167abf-46b8-4f74-bc94-8be4f97b9f36 | human | null | null | none | abstracts | USco1606-1935: An Unusually Wide Low-Mass Triple System? | null | We present photometric, astrometric, and spectroscopic observations of USco160611.9-193532 AB, a candidate ultrawide (~1600 AU), low-mass (M_tot~0.4 M_sun) multiple system in the nearby OB association Upper Scorpius. We conclude that both components are young, comoving members of the association; we also present high-resolution observations which show that the primary is itself a close binary system. If the Aab and B components are gravitationally bound, the system would fall into the small class of young multiple systems which have unusually wide separations as compared to field systems of similar mass. However, we demonstrate that physical association can not be assumed purely on probabilistic grounds for any individual candidate system in this separation range. Analysis of the association's two-point correlation function shows that there is a significant probability (25%) that at least one pair of low-mass association members will be separated in projection by <15", so analysis of the wide binary population in Upper Sco will require a systematic search for all wide systems; the detection of another such pair would represent an excess at the 98% confidence level. |
256b1459-456a-44e2-b6dc-ff36f5d1fb1a | 256b1459-456a-44e2-b6dc-ff36f5d1fb1a | 256b1459-456a-44e2-b6dc-ff36f5d1fb1a | human | null | null | none | abstracts | Rotation Measures of Extragalactic Sources Behind the Southern Galactic
Plane: New Insights into the Large-Scale Magnetic Field of the Inner Milky
Way | null | We present new Faraday rotation measures (RMs) for 148 extragalactic radio sources behind the southern Galactic plane (253o < l < 356o, |b| < 1.5o), and use these data in combination with published data to probe the large-scale structure of the Milky Way's magnetic field. We show that the magnitudes of these RMs oscillate with longitude in a manner that correlates with the locations of the Galactic spiral arms. The observed pattern in RMs requries the presence of at least one large-scale magnetic reversal in the fourth Galactic quadrant, located between the Sagittarius- Carina and Scutum-Crux spiral arms. To quantitatively compare our measurements to other recent studies, we consider all available extragalactic and pulsar RMs in the region we have surveyed, and jointly fit these data to simple models in which the large-scale field follows the spiral arms. In the best-fitting model, the magnetic field in the fourth Galactic quadrant is directed clockwise in the Sagittarius-Carina spiral arm (as viewed from the North Galactic pole), but is oriented counter- clockwise in the Scutum-Crux arm. This contrasts with recent analyses of pulsar RMs alone, in which the fourth-quadrant field was presumed to be directed counter-clockwise in the Sagittarius- Carina arm. Also in contrast to recent pulsar RM studies, our joint modeling of pulsar and extragalactic RMs demonstrates that large numbers of large-scale magnetic field reversals are not required to account for observations. |
cccae260-c1a7-4878-9998-076579b2048c | cccae260-c1a7-4878-9998-076579b2048c | cccae260-c1a7-4878-9998-076579b2048c | human | null | null | none | abstracts | On iterated image size for point-symmetric relations | null | Let $\Gamma =(V,E)$ be a point-symmetric reflexive relation and let $v\in V$ such that
$|\Gamma (v)|$ is finite (and hence $|\Gamma (x)|$ is finite for all $x$, by the transitive action of the group of automorphisms). Let $j\in \N$ be an integer such that $\Gamma ^j(v)\cap \Gamma ^{-}(v)=\{v\}$. Our main result states that
$$ |\Gamma ^{j} (v)|\ge | \Gamma ^{j-1} (v)| + |\Gamma (v)|-1.$$
As an application we have $ |\Gamma ^{j} (v)| \ge 1+(|\Gamma (v)|-1)j.$ The last result confirms a recent conjecture of Seymour in the case of vertex-symmetric graphs. Also it gives a short proof for the validity of the Caccetta-H\"aggkvist conjecture for vertex-symmetric graphs and generalizes an additive result of Shepherdson. |
cb7fd534-8a53-4113-af55-5a19e6b5c839 | cb7fd534-8a53-4113-af55-5a19e6b5c839 | cb7fd534-8a53-4113-af55-5a19e6b5c839 | human | null | null | none | abstracts | Entanglement increase from local interactions with
not-completely-positive maps | null | Simple examples are constructed that show the entanglement of two qubits being both increased and decreased by interactions on just one of them. One of the two qubits interacts with a third qubit, a control, that is never entangled or correlated with either of the two entangled qubits and is never entangled, but becomes correlated, with the system of those two qubits. The two entangled qubits do not interact, but their state can change from maximally entangled to separable or from separable to maximally entangled. Similar changes for the two qubits are made with a swap operation between one of the qubits and a control; then there are compensating changes of entanglement that involve the control. When the entanglement increases, the map that describes the change of the state of the two entangled qubits is not completely positive. Combination of two independent interactions that individually give exponential decay of the entanglement can cause the entanglement to not decay exponentially but, instead, go to zero at a finite time. |
2e8d67d2-f6c2-4a99-b07d-4088b720544c | 2e8d67d2-f6c2-4a99-b07d-4088b720544c | 2e8d67d2-f6c2-4a99-b07d-4088b720544c | human | null | null | none | abstracts | Extended solar emission - an analysis of the EGRET data | null | The Sun was recently predicted to be an extended source of gamma-ray emission, produced by inverse-Compton scattering of cosmic-ray electrons with the solar radiation. The emission was predicted to contribute to the diffuse extragalactic background even at large angular distances from the Sun. While this emission is expected to be readily detectable in future by GLAST, the situation for available EGRET data is more challenging. We present a detailed study of the EGRET database, using a time dependent analysis, accounting for the effect of the emission from 3C 279, the moon, and other sources, which interfere with the solar signal. The technique has been tested on the moon signal, with results consistent with previous work. We find clear evidence for emission from the Sun and its vicinity. The observations are compared with our model for the extended emission. |
8e94e898-bade-412d-8cd4-e6d41cd2b8b0 | 8e94e898-bade-412d-8cd4-e6d41cd2b8b0 | 8e94e898-bade-412d-8cd4-e6d41cd2b8b0 | human | null | null | none | abstracts | Mass and Temperature of the TWA 7 Debris Disk | null | We present photometric detections of dust emission at 850 and 450 micron around the pre-main sequence M1 dwarf TWA 7 using the SCUBA camera on the James Clerk Maxwell Telescope. These data confirm the presence of a cold dust disk around TWA 7, a member of the TW Hydrae Association. Based on the 850 micron flux, we estimate the mass of the disk to be 18 lunar masses (0.2 Earth masses) assuming a mass opacity of 1.7 cm^2/g with a temperature of 45 K. This makes the TWA 7 disk (d=55 pc) an order of magnitude more massive than the disk reported around AU Microscopii (GL 803), the closest (9.9 pc) debris disk detected around an M dwarf. This is consistent with TWA 7 being slightly younger than AU Mic. We find that the mid-IR and submillimeter data require the disk to be comprised of dust at a range of temperatures. A model in which the dust is at a single radius from the star, with a range of temperatures according to grain size, is as effective at fitting the emission spectrum as a model in which the dust is of uniform size, but has a range of temperatures according to distance. We discuss this disk in the context of known disks in the TW Hydrae Association and around low-mass stars; a comparison of masses of disks in the TWA reveals no trend in mass or evolutionary state (gas-rich vs. debris) as a function of spectral type. |
77690e24-aa8c-4438-8ba3-ba3614785c6b | 77690e24-aa8c-4438-8ba3-ba3614785c6b | 77690e24-aa8c-4438-8ba3-ba3614785c6b | human | null | null | none | abstracts | Annealed importance sampling of dileucine peptide | null | Annealed importance sampling is a means to assign equilibrium weights to a nonequilibrium sample that was generated by a simulated annealing protocol. The weights may then be used to calculate equilibrium averages, and also serve as an ``adiabatic signature'' of the chosen cooling schedule. In this paper we demonstrate the method on the 50-atom dileucine peptide, showing that equilibrium distributions are attained for manageable cooling schedules. For this system, as naively implemented here, the method is modestly more efficient than constant temperature simulation. However, the method is worth considering whenever any simulated heating or cooling is performed (as is often done at the beginning of a simulation project, or during an NMR structure calculation), as it is simple to implement and requires minimal additional CPU expense. Furthermore, the naive implementation presented here can be improved. |
c00565d8-89f5-4f29-81e3-6ee7089c2a1f | c00565d8-89f5-4f29-81e3-6ee7089c2a1f | c00565d8-89f5-4f29-81e3-6ee7089c2a1f | human | null | null | none | abstracts | A General Nonlinear Fokker-Planck Equation and its Associated Entropy | null | A recently introduced nonlinear Fokker-Planck equation, derived directly from a master equation, comes out as a very general tool to describe phenomenologically systems presenting complex behavior, like anomalous diffusion, in the presence of external forces. Such an equation is characterized by a nonlinear diffusion term that may present, in general, two distinct powers of the probability distribution. Herein, we calculate the stationary-state distributions of this equation in some special cases, and introduce associated classes of generalized entropies in order to satisfy the H-theorem. Within this approach, the parameters associated with the transition rates of the original master-equation are related to such generalized entropies, and are shown to obey some restrictions. Some particular cases are discussed. |
b6161eff-ae90-49b8-ac79-7cf52a1d1c43 | b6161eff-ae90-49b8-ac79-7cf52a1d1c43 | b6161eff-ae90-49b8-ac79-7cf52a1d1c43 | human | null | null | none | abstracts | Modeling Accretion Disk X-ray Continuum of Black Hole Candidates | null | We critically examine issues associated with determining the fundamental properties of the black hole and the surrounding accretion disk in an X-ray binary based on modeling the disk X-ray continuum of the source. We base our work mainly on two XMM-Newton observations of GX 339-4, because they provided high-quality data at low energies (below 1 keV) which are critical for reliably modeling the spectrum of the accretion disk. A key issue examined is the determination of the so-called "color correction factor", which is often empirically introduced to account for the deviation of the local disk spectrum from a blackbody (due to electron scattering). This factor cannot be pre-determined theoretically because it may vary with, e.g., mass accretion rate, among a number of important factors. We follow up on an earlier suggestion to estimate the color correction observationally by modeling the disk spectrum with saturated Compton scattering. We show that the spectra can be fitted well and the approach yields reasonable values for the color correction factor. For comparison, we have also attempted to fit the spectra with other models. We show that even the high-soft-state continuum (which is dominated by the disk emission) cannot be satisfactorily fitted by state-of-the-art disk models. We discuss the implication of the results. |
0157689b-1e8a-45f8-babd-9a10c01c3955 | 0157689b-1e8a-45f8-babd-9a10c01c3955 | 0157689b-1e8a-45f8-babd-9a10c01c3955 | human | null | null | none | abstracts | Inapproximability of Maximum Weighted Edge Biclique and Its Applications | null | Given a bipartite graph $G = (V_1,V_2,E)$ where edges take on {\it both} positive and negative weights from set $\mathcal{S}$, the {\it maximum weighted edge biclique} problem, or $\mathcal{S}$-MWEB for short, asks to find a bipartite subgraph whose sum of edge weights is maximized. This problem has various applications in bioinformatics, machine learning and databases and its (in)approximability remains open. In this paper, we show that for a wide range of choices of $\mathcal{S}$, specifically when $| \frac{\min\mathcal{S}} {\max \mathcal{S}} | \in \Omega(\eta^{\delta-1/2}) \cap O(\eta^{1/2-\delta})$ (where $\eta = \max\{|V_1|, |V_2|\}$, and $\delta \in (0,1/2]$), no polynomial time algorithm can approximate $\mathcal{S}$-MWEB within a factor of $n^{\epsilon}$ for some $\epsilon > 0$ unless $\mathsf{RP = NP}$. This hardness result gives justification of the heuristic approaches adopted for various applied problems in the aforementioned areas, and indicates that good approximation algorithms are unlikely to exist. Specifically, we give two applications by showing that: 1) finding statistically significant biclusters in the SAMBA model, proposed in \cite{Tan02} for the analysis of microarray data, is $n^{\epsilon}$-inapproximable; and 2) no polynomial time algorithm exists for the Minimum Description Length with Holes problem \cite{Bu05} unless $\mathsf{RP=NP}$. |
aa3e7902-d479-44dc-8d42-b212f63fd318 | aa3e7902-d479-44dc-8d42-b212f63fd318 | aa3e7902-d479-44dc-8d42-b212f63fd318 | human | null | null | none | abstracts | Density dependence of the symmetry energy and the nuclear equation of
state: A Dynamical and Statistical model perspective | null | The density dependence of the symmetry energy in the equation of state of isospin asymmetric nuclear matter is of significant importance for studying the structure of systems as diverse as the neutron-rich nuclei and the neutron stars. A number of reactions using the dynamical and the statistical models of multifragmentation, and the experimental isoscaling observable, is studied to extract information on the density dependence of the symmetry energy. It is observed that the dynamical and the statistical model calculations give consistent results assuming the sequential decay effect in dynamical model to be small. A comparison with several other independent studies is also made to obtain important constraint on the form of the density dependence of the symmetry energy. The comparison rules out an extremely " stiff " and " soft " form of the density dependence of the symmetry energy with important implications for astrophysical and nuclear physics studies. |
3508b2cf-bfd8-4b70-a0ad-ce6da88beec5 | 3508b2cf-bfd8-4b70-a0ad-ce6da88beec5 | 3508b2cf-bfd8-4b70-a0ad-ce6da88beec5 | human | null | null | none | abstracts | Competitive nucleation and the Ostwald rule in a generalized Potts model
with multiple metastable phases | null | We introduce a simple nearest-neighbor spin model with multiple metastable phases, the number and decay pathways of which are explicitly controlled by the parameters of the system. With this model we can construct, for example, a system which evolves through an arbitrarily long succession of metastable phases. We also construct systems in which different phases may nucleate competitively from a single initial phase. For such a system, we present a general method to extract from numerical simulations the individual nucleation rates of the nucleating phases. The results show that the Ostwald rule, which predicts which phase will nucleate, must be modified probabilistically when the new phases are almost equally stable. Finally, we show that the nucleation rate of a phase depends, among other things, on the number of other phases accessible from it. |
a8a72224-d23e-4ed3-96cc-9cdb417b9301 | a8a72224-d23e-4ed3-96cc-9cdb417b9301 | a8a72224-d23e-4ed3-96cc-9cdb417b9301 | human | null | null | none | abstracts | Application of Ewald summations to long-range dispersion forces | null | We present results illustrating the effects of using explicit summation terms for the $r^{-6}$ dispersion term on the interfacial properties of a Lennard-Jones fluid and SPC/E water. For the Lennard-Jones fluid, we find that the use of long-range summations, even with a short ``crossover radius,'' yields results that are consistent with simulations using large cutoff radii. Simulations of SPC/E water demonstrate that the long-range dispersion forces are of secondary importance to the Coulombic forces. In both cases, we find that the ratio of box size $L_{\parallel}$ to crossover radius $r_{\rm c}^{\mathbf k}$ plays an important role in determining the magnitude of the long-range dispersion correction, although its effect is secondary when Coulombic interactions are also present. |
19f5462e-0d1e-44a9-b465-08e72546c2b5 | 19f5462e-0d1e-44a9-b465-08e72546c2b5 | 19f5462e-0d1e-44a9-b465-08e72546c2b5 | human | null | null | none | abstracts | Possible non-thermal nature of the soft-excess emission in the cluster
of galaxies Sersic 159-03 | null | We present an analysis of new Suzaku data and archival data from XMM-Newton of the cluster of galaxies Sersic 159-03, which has a strong soft X-ray excess emission component. The Suzaku observation confirms the presence of the soft excess emission, but it does not confirm the presence of redshifted OVII lines in the cluster. Radial profiles and 2D maps derived from XMM-Newton observations show that the soft excess emission has a strong peak at the position of the central cD galaxy and the maps do not show any significant azimuthal variations. Although the soft excess emission can be fitted equally well with both thermal and non-thermal models, its spatial distribution is neither consistent with the models of intercluster warm-hot filaments, nor with models of clumpy warm intracluster gas associated with infalling groups. Using the data obtained by the XMM-Newton Reflection Grating Spectrometers we do not confirm the presence of the warm gas in the cluster centre with the expected properties assuming the soft excess is of thermal origin. The observed properties of the soft excess emission are consistent with the non-thermal interpretation. While the high density of relativistic electrons associated with the peak of the soft emission in the cluster centre might have been provided by an active galactic nucleus in the central cD galaxy, the underlying population might have been accelerated in diffuse shocks. |
9e6b6c98-0429-4e2c-8a84-98f19c889893 | 9e6b6c98-0429-4e2c-8a84-98f19c889893 | 9e6b6c98-0429-4e2c-8a84-98f19c889893 | human | null | null | none | abstracts | Geometric phase of an atom inside an adiabatic radio frequency potential | null | We investigate the geometric phase of an atom inside an adiabatic radio frequency (rf) potential created from a static magnetic field (B-field) and a time dependent rf field. The spatial motion of the atomic center of mass is shown to give rise to a geometric phase, or Berry's phase, to the adiabatically evolving atomic hyperfine spin along the local B-field. This phase is found to depend on both the static B-field along the semi-classical trajectory of the atomic center of mass and an ``effective magnetic field'' of the total B-field, including the oscillating rf field. Specific calculations are provided for several recent atom interferometry experiments and proposals utilizing adiabatic rf potentials. |
463cf7d9-45c9-4a32-819c-676dbfa2ef91 | 463cf7d9-45c9-4a32-819c-676dbfa2ef91 | 463cf7d9-45c9-4a32-819c-676dbfa2ef91 | human | null | null | none | abstracts | The Transition from the First Stars to the Second Stars in the Early
Universe | null | We observe a sharp transition from a singular, high-mass mode of star formation, to a low-mass dominated mode, in numerical simulations, at a metallicity of 10^-3 Zsolar. We incorporate a new method for including the radiative cooling from metals into adaptive mesh-refinement hydrodynamic simulations. Our results illustrate how metals, produced by the first stars, led to a transition from the high-mass star formation mode of Pop III stars, to the low-mass mode that dominates today. We ran hydrodynamic simulations with cosmological initial conditions in the standard LambdaCDM model, with metallicities, from zero to 10^-2 Zsolar, beginnning at redshift, z = 99. The simulations were run until a dense core forms at the center of a 5 x 10^5 Msolar dark matter halo, at z ~ 18. Analysis of the central 1 Msolar core reveals that the two simulations with the lowest metallicities, Z = 0 and 10^-4 Zsolar, contain one clump with 99% of the mass, while the two with metallicities, Z = 10^-3 and 10^-2 Zsolar, each contain two clumps that share most of the mass. The Z = 10^-3 Zsolar simulation also produced two low-mass proto-stellar objects with masses between 10^-2 and 10^-1 Msolar. Gas with Z >= 10^-3 Zsolar is able to cool to the temperature of the CMB, which sets a lower limit to the minimum fragmentation mass. This suggests that the second generation stars produced a spectrum of lower mass stars, but were still more massive on average than stars formed in the local universe. |
25ffe99a-f770-4b8c-9e00-db18f61d6141 | 25ffe99a-f770-4b8c-9e00-db18f61d6141 | 25ffe99a-f770-4b8c-9e00-db18f61d6141 | human | null | null | none | abstracts | Super Star Cluster Velocity Dispersions and Virial Masses in the M82
Nuclear Starburst | null | We use high-resolution near-infrared spectroscopy from Keck Observatory to measure the stellar velocity dispersions of 19 super star clusters (SSCs) in the nuclear starburst of M82. The clusters have ages on the order of 10 Myr, which is many times longer than the crossing times implied by their velocity dispersions and radii. We therefore apply the Virial Theorem to derive the kinematic mass for 15 of the SSCs. The SSCs have masses of 2 x 10^5 to 4 x 10^6 solar masses, with a total population mass of 1.4 x 10^7 solar masses. Comparison of the loci of the young M82 SSCs and old Milky Way globular clusters in a plot of radius versus velocity dispersion suggests that the SSCs are a population of potential globular clusters. We present the mass function for the SSCs, and find a power law fit with an index of gamma = -1.91 +/- 0.06. This result is nearly identical to the mass function of young SSCs in the Antennae galaxies. |
d92350a4-a95e-4013-8141-b34194b6974d | d92350a4-a95e-4013-8141-b34194b6974d | d92350a4-a95e-4013-8141-b34194b6974d | human | null | null | none | abstracts | Implementation of holonomic quantum computation through engineering and
manipulating environment | null | We consider an atom-field coupled system, in which two pairs of four-level atoms are respectively driven by laser fields and trapped in two distant cavities that are connected by an optical fiber. First, we show that an effective squeezing reservoir can be engineered under appropriate conditions. Then, we show that a two-qubit geometric CPHASE gate between the atoms in the two cavities can be implemented through adiabatically manipulating the engineered reservoir along a closed loop. This scheme that combines engineering environment with decoherence-free space and geometric phase quantum computation together has the remarkable feature: a CPHASE gate with arbitrary phase shift is implemented by simply changing the strength and relative phase of the driving fields. |
ddf750f9-7925-42e0-bc84-f38d6e825b0b | ddf750f9-7925-42e0-bc84-f38d6e825b0b | ddf750f9-7925-42e0-bc84-f38d6e825b0b | human | null | null | none | abstracts | Kinematic Decoupling of Globular Clusters with Extended
Horizontal-Branch | null | About 25% of the Milky Way globular clusters (GCs) exhibit unusually extended color distribution of stars in the horizontal-branch (HB) phase. This phenomenon is now best understood as due to the presence of helium enhanced second generation subpopulations, which has raised a possibility that these peculiar GCs might have a unique origin. Here we show that these GCs with extended HB are clearly distinct from other normal GCs in kinematics and mass. The GCs with extended HB are more massive than normal GCs, and are dominated by random motion with no correlation between kinematics and metallicity. Surprisingly, however, when they are excluded, most normal GCs in the inner halo show clear signs of dissipational collapse that apparently led to the formation of the disk. Normal GCs in the outer halo share their kinematic properties with the extended HB GCs, which is consistent with the accretion origin. Our result further suggests heterogeneous origins of GCs, and we anticipate this to be a starting point for more detailed investigations of Milky Way formation, including early mergers, collapse, and later accretion. |
1c0ecd7b-ee63-4a95-8efc-1517c1e808a9 | 1c0ecd7b-ee63-4a95-8efc-1517c1e808a9 | 1c0ecd7b-ee63-4a95-8efc-1517c1e808a9 | human | null | null | none | abstracts | Scalar potential model progress | null | Because observations of galaxies and clusters have been found inconsistent with General Relativity (GR), the focus of effort in developing a Scalar Potential Model (SPM) has been on the examination of galaxies and clusters. The SPM has been found to be consistent with cluster cellular structure, the flow of IGM from spiral galaxies to elliptical galaxies, intergalactic redshift without an expanding universe, discrete redshift, rotation curve (RC) data without dark matter, asymmetric RCs, galaxy central mass, galaxy central velocity dispersion, and the Pioneer Anomaly. In addition, the SPM suggests a model of past expansion, past contraction, and current expansion of the universe. GR corresponds to the SPM in the limit in which the effect of the Sources and Sinks approximate a flat scalar potential field such as between clusters and on the solar system scale, which is small relative to the distance to a Source. |
ec393f52-3fe7-4a8a-96b5-dbf6fc57604e | ec393f52-3fe7-4a8a-96b5-dbf6fc57604e | ec393f52-3fe7-4a8a-96b5-dbf6fc57604e | human | null | null | none | abstracts | Teleparallel Version of the Stationary Axisymmetric Solutions and their
Energy Contents | null | This work contains the teleparallel version of the stationary axisymmetric solutions. We obtain the tetrad and the torsion fields representing these solutions. The tensor, vector and axial-vector parts of the torsion tensor are evaluated. It is found that the axial-vector has component only along $\rho$ and $z$ directions. The three possibilities of the axial vector depending on the metric function $B$ are discussed. The vector related with spin has also been evaluated and the corresponding extra Hamiltonian is furnished. Further, we use the teleparallel version of M$\ddot{o}$ller prescription to find the energy-momentum distribution of the solutions. It is interesting to note that (for $\lambda=1$) energy and momentum densities in teleparallel theory are equal to the corresponding quantities in GR plus an additional quantity in each, which may become equal under certain conditions. Finally, we discuss the two special cases of the stationary axisymmetric solutions. |
c1600623-ac01-4770-9044-b4820cefbb74 | c1600623-ac01-4770-9044-b4820cefbb74 | c1600623-ac01-4770-9044-b4820cefbb74 | human | null | null | none | abstracts | Weighted percolation on directed networks | null | We present an analysis of the percolation transition for general node removal strategies valid for locally tree-like directed networks. On the basis of heuristic arguments we predict that, if the probability of removing node $i$ is $p_i$, the network disintegrates if $p_i$ is such that the largest eigenvalue of the matrix with entries $A_{ij}(1-p_i)$ is less than 1, where $A$ is the adjacency matrix of the network. The knowledge or applicability of a Markov network model is not required by our theory, thus making it applicable to situations not covered by previous works. We test our predicted percolation criterion against numerical results for different networks and node removal strategies. |
68e5ad0d-c00f-4804-ade9-a2677ec6a9ed | 68e5ad0d-c00f-4804-ade9-a2677ec6a9ed | 68e5ad0d-c00f-4804-ade9-a2677ec6a9ed | human | null | null | none | abstracts | Refuting the Pseudo Attack on the REESSE1+ Cryptosystem | null | We illustrate through example 1 and 2 that the condition at theorem 1 in [8] dissatisfies necessity, and the converse proposition of fact 1.1 in [8] does not hold, namely the condition Z/M - L/Ak < 1/(2 Ak^2) is not sufficient for f(i) + f(j) = f(k). Illuminate through an analysis and ex.3 that there is a logic error during deduction of fact 1.2, which causes each of fact 1.2, 1.3, 4 to be invalid. Demonstrate through ex.4 and 5 that each or the combination of qu+1 > qu * D at fact 4 and table 1 at fact 2.2 is not sufficient for f(i) + f(j) = f(k), property 1, 2, 3, 4, 5 each are invalid, and alg.1 based on fact 4 and alg.2 based on table 1 are disordered and wrong logically. Further, manifest through a repeated experiment and ex.5 that the data at table 2 is falsified, and the example in [8] is woven elaborately. We explain why Cx = Ax * W^f(x) (% M) is changed to Cx = (Ax * W^f(x))^d (% M) in REESSE1+ v2.1. To the signature fraud, we point out that [8] misunderstands the existence of T^-1 and Q^-1 % (M-1), and forging of Q can be easily avoided through moving H. Therefore, the conclusion of [8] that REESSE1+ is not secure at all (which connotes that [8] can extract a related private key from any public key in REESSE1+) is fully incorrect, and as long as the parameter Omega is fitly selected, REESSE1+ with Cx = Ax * W^f(x) (% M) is secure. |
c93a4fe4-5c88-4344-b89f-9bc10caeafb9 | c93a4fe4-5c88-4344-b89f-9bc10caeafb9 | c93a4fe4-5c88-4344-b89f-9bc10caeafb9 | human | null | null | none | abstracts | Phase structure of a surface model on dynamically triangulated spheres
with elastic skeletons | null | We find three distinct phases; a tubular phase, a planar phase, and the spherical phase, in a triangulated fluid surface model. It is also found that these phases are separated by discontinuous transitions. The fluid surface model is investigated within the framework of the conventional curvature model by using the canonical Monte Carlo simulations with dynamical triangulations. The mechanical strength of the surface is given only by skeletons, and no two-dimensional bending energy is assumed in the Hamiltonian. The skeletons are composed of elastic linear-chains and rigid junctions and form a compartmentalized structure on the surface, and for this reason the vertices of triangles can diffuse freely only inside the compartments. As a consequence, an inhomogeneous structure is introduced in the model; the surface strength inside the compartments is different from the surface strength on the compartments. However, the rotational symmetry is not influenced by the elastic skeletons; there is no specific direction on the surface. In addition to the three phases mentioned above, a collapsed phase is expected to exist in the low bending rigidity regime that was not studied here. The inhomogeneous structure and the fluidity of vertices are considered to be the origin of such variety of phases. |
888dbdb1-3163-4b1b-b2af-f47721dd2a56 | 888dbdb1-3163-4b1b-b2af-f47721dd2a56 | 888dbdb1-3163-4b1b-b2af-f47721dd2a56 | human | null | null | none | abstracts | Vortex Dynamics at the Initial Stage of Resistive Transition in
Superconductors with Fractal Cluster Structure | null | The effect of fractal normal-phase clusters on vortex dynamics in a percolative superconductor is considered. The superconductor contains percolative superconducting cluster carrying a transport current and clusters of a normal phase, acting as pinning centers. A prototype of such a structure is YBCO film, containing clusters of columnar defects, as well as the BSCCO/Ag sheathed tape, which is of practical interest for wire fabrication. Transition of the superconductor into a resistive state corresponds to the percolation transition from a pinned vortex state to a resistive state when the vortices are free to move. The dependencies of the free vortex density on the fractal dimension of the cluster boundary as well as the resistance on the transport current are obtained. It is revealed that a mixed state of the vortex glass type is realized in the superconducting system involved. The current-voltage characteristics of superconductors containing fractal clusters are obtained and their features are studied. |
26886937-cef0-48d0-9970-b1c1eab6b806 | 26886937-cef0-48d0-9970-b1c1eab6b806 | 26886937-cef0-48d0-9970-b1c1eab6b806 | human | null | null | none | abstracts | Fusion process studied with preequilibrium giant dipole resonance in
time dependent Hartree-Fock theory | null | The equilibration of macroscopic degrees of freedom during the fusion of heavy nuclei, like the charge and the shape, are studied in the Time-Dependent Hartree-Fock theory. The pre-equilibrium Giant Dipole Resonance (GDR) is used to probe the fusion path. It is shown that such isovector collective state is excited in N/Z asymmetric fusion and to a less extent in mass asymmetric systems. The characteristics of this GDR are governed by the structure of the fused system in its preequilibrium phase, like its deformation, rotation and vibration. In particular, we show that a lowering of the pre-equilibrium GDR energy is expected as compared to the statistical one. Revisiting experimental data, we extract an evidence of this lowering for the first time. We also quantify the fusion-evaporation enhancement due to gamma-ray emission from the pre-equilibrium GDR. This cooling mechanism along the fusion path may be suitable to synthesize in the future super heavy elements using radioactive beams with strong N/Z asymmetries in the entrance channel. |
0229252d-f0cd-4f07-aab3-9054acfb6e15 | 0229252d-f0cd-4f07-aab3-9054acfb6e15 | 0229252d-f0cd-4f07-aab3-9054acfb6e15 | human | null | null | none | abstracts | A unified analysis of the reactor neutrino program towards the
measurement of the theta_13 mixing angle | null | We present in this article a detailed quantitative discussion of the measurement of the leptonic mixing angle theta_13 through currently scheduled reactor neutrino oscillation experiments. We thus focus on Double Chooz (Phase I & II), Daya Bay (Phase I & II) and RENO experiments. We perform a unified analysis, including systematics, backgrounds and accurate experimental setup in each case. Each identified systematic error and background impact has been assessed on experimental setups following published data when available and extrapolating from Double Chooz acquired knowledge otherwise. After reviewing the experiments, we present a new analysis of their sensitivities to sin^2(2 theta_13) and study the impact of the different systematics based on the pulls approach. Through this generic statistical analysis we discuss the advantages and drawbacks of each experimental setup. |
0e13c7a5-b69b-427d-90dc-3d9d23e6787e | 0e13c7a5-b69b-427d-90dc-3d9d23e6787e | 0e13c7a5-b69b-427d-90dc-3d9d23e6787e | human | null | null | none | abstracts | Optimal Routing for Decode-and-Forward based Cooperation in Wireless
Networks | null | We investigate cooperative wireless relay networks in which the nodes can help each other in data transmission. We study different coding strategies in the single-source single-destination network with many relay nodes. Given the myriad of ways in which nodes can cooperate, there is a natural routing problem, i.e., determining an ordered set of nodes to relay the data from the source to the destination. We find that for a given route, the decode-and-forward strategy, which is an information theoretic cooperative coding strategy, achieves rates significantly higher than that achievable by the usual multi-hop coding strategy, which is a point-to-point non-cooperative coding strategy. We construct an algorithm to find an optimal route (in terms of rate maximizing) for the decode-and-forward strategy. Since the algorithm runs in factorial time in the worst case, we propose a heuristic algorithm that runs in polynomial time. The heuristic algorithm outputs an optimal route when the nodes transmit independent codewords. We implement these coding strategies using practical low density parity check codes to compare the performance of the strategies on different routes. |
0b03c368-af9d-4db9-8fbe-db1dedbb4df4 | 0b03c368-af9d-4db9-8fbe-db1dedbb4df4 | 0b03c368-af9d-4db9-8fbe-db1dedbb4df4 | human | null | null | none | abstracts | E_6 and the bipartite entanglement of three qutrits | null | Recent investigations have established an analogy between the entropy of four-dimensional supersymmetric black holes in string theory and entanglement in quantum information theory. Examples include: (1) N=2 STU black holes and the tripartite entanglement of three qubits (2-state systems), where the common symmetry is [SL(2)]^3 and (2) N=8 black holes and the tripartite entanglement of seven qubits where the common symmetry is E_7 which contains [SL(2)]^7. Here we present another example: N=8 black holes (or black strings) in five dimensions and the bipartite entanglement of three qutrits (3-state systems), where the common symmetry is E_6 which contains [SL(3)]^3. Both the black hole (or black string) entropy and the entanglement measure are provided by the Cartan cubic E_6 invariant. Similar analogies exist for ``magic'' N=2 supergravity black holes in both four and five dimensions. |
c282539b-03c5-47d4-936f-d64eb388b4b2 | c282539b-03c5-47d4-936f-d64eb388b4b2 | c282539b-03c5-47d4-936f-d64eb388b4b2 | human | null | null | none | abstracts | Stable oscillations of a predator-prey probabilistic cellular automaton:
a mean-field approach | null | We analyze a probabilistic cellular automaton describing the dynamics of coexistence of a predator-prey system. The individuals of each species are localized over the sites of a lattice and the local stochastic updating rules are inspired on the processes of the Lotka-Volterra model. Two levels of mean-field approximations are set up. The simple approximation is equivalent to an extended patch model, a simple metapopulation model with patches colonized by prey, patches colonized by predators and empty patches. This approximation is capable of describing the limited available space for species occupancy. The pair approximation is moreover able to describe two types of coexistence of prey and predators: one where population densities are constant in time and another displaying self-sustained time-oscillations of the population densities. The oscillations are associated with limit cycles and arise through a Hopf bifurcation. They are stable against changes in the initial conditions and, in this sense, they differ from the Lotka-Volterra cycles which depend on initial conditions. In this respect, the present model is biologically more realistic than the Lotka-Volterra model. |
97851709-b6a7-4897-a7d4-4459c9c947d7 | 97851709-b6a7-4897-a7d4-4459c9c947d7 | 97851709-b6a7-4897-a7d4-4459c9c947d7 | human | null | null | none | abstracts | SDSS J233325.92+152222.1 and the evolution of intermediate polars | null | Intermediate polars (IPs) are cataclysmic variables which contain magnetic white dwarfs with a rotational period shorter than the binary orbital period. Evolutionary theory predicts that IPs with long orbital periods evolve through the 2-3 hour period gap, but it is very uncertain what the properties of the resulting objects are. Whilst a relatively large number of long-period IPs are known, very few of these have short orbital periods. We present phase-resolved spectroscopy and photometry of SDSS J233325.92+152222.1 and classify it as the IP with the shortest known orbital period (83.12 +/- 0.09 min), which contains a white dwarf with a relatively long spin period (41.66 +/- 0.13 min). We estimate the white dwarf's magnetic moment to be mu(WD) \approx 2 x 10^33 G cm^3, which is not only similar to three of the other four confirmed short-period IPs but also to those of many of the long-period IPs. We suggest that long-period IPs conserve their magnetic moment as they evolve towards shorter orbital periods. Therefore the dominant population of long-period IPs, which have white dwarf spin periods roughly ten times shorter than their orbital periods, will likely end up as short-period IPs like SDSS J2333, with spin periods a large fraction of their orbital periods. |
6e9f606b-d996-4c23-9aa3-b09d9a2569d2 | 6e9f606b-d996-4c23-9aa3-b09d9a2569d2 | 6e9f606b-d996-4c23-9aa3-b09d9a2569d2 | human | null | null | none | abstracts | Complexity Considerations, cSAT Lower Bound | null | This article discusses completeness of Boolean Algebra as First Order Theory in Goedel's meaning. If Theory is complete then any possible transformation is equivalent to some transformation using axioms, predicates etc. defined for this theory. If formula is to be proved (or disproved) then it has to be reduced to axioms. If every transformation is deducible then also optimal transformation is deducible. If every transformation is exponential then optimal one is too, what allows to define lower bound for discussed problem to be exponential (outside P). Then we show algorithm for NDTM solving the same problem in O(n^c) (so problem is in NP), what proves that P \neq NP.
Article proves also that result of relativisation of P=NP question and oracle shown by Baker-Gill-Solovay distinguish between deterministic and non-deterministic calculation models. If there exists oracle A for which P^A=NP^A then A consists of infinite number of algorithms, DTMs, axioms and predicates, or like NDTM infinite number of simultaneous states. |
0447a2d2-756c-41e7-a6c7-f7ac67351378 | 0447a2d2-756c-41e7-a6c7-f7ac67351378 | 0447a2d2-756c-41e7-a6c7-f7ac67351378 | human | null | null | none | abstracts | Using decomposed household food acquisitions as inputs of a Kinetic
Dietary Exposure Model | null | Foods naturally contain a number of contaminants that may have different and long term toxic effects. This paper introduces a novel approach for the assessment of such chronic food risk that integrates the pharmacokinetic properties of a given contaminant. The estimation of such a Kinetic Dietary Exposure Model (KDEM) should be based on long term consumption data which, for the moment, can only be provided by Household Budget Surveys such as the SECODIP panel in France. A semi parametric model is proposed to decompose a series of household quantities into individual quantities which are then used as inputs of the KDEM. As an illustration, the risk assessment related to the presence of methyl mercury in seafood is revisited using this novel approach. |
a93f01d3-8ca1-4eaa-abfc-3e240e2d3cb8 | a93f01d3-8ca1-4eaa-abfc-3e240e2d3cb8 | a93f01d3-8ca1-4eaa-abfc-3e240e2d3cb8 | human | null | null | none | abstracts | Fractionally charged excitations on frustrated lattices | null | Systems of strongly correlated fermions on certain geometrically frustrated lattices at particular filling factors support excitations with fractional charges $\pm e/2$. We calculate quantum mechanical ground states, low--lying excitations and spectral functions of finite lattices by means of numerical diagonalization. The ground state of the most thoroughfully studied case, the criss-crossed checkerboard lattice, is degenerate and shows long--range order. Static fractional charges are confined by a weak linear force, most probably leading to bound states of large spatial extent. Consequently, the quasi-particle weight is reduced, which reflects the internal dynamics of the fractionally charged excitations. By using an additional parameter, we fine--tune the system to a special point at which fractional charges are manifestly deconfined--the so--called Rokhsar--Kivelson point. For a deeper understanding of the low--energy physics of these models and for numerical advantages, several conserved quantum numbers are identified. |
1fd214d2-e35a-4bd8-83f3-425f30944e50 | 1fd214d2-e35a-4bd8-83f3-425f30944e50 | 1fd214d2-e35a-4bd8-83f3-425f30944e50 | human | null | null | none | abstracts | Many-to-One Throughput Capacity of IEEE 802.11 Multi-hop Wireless
Networks | null | This paper investigates the many-to-one throughput capacity (and by symmetry, one-to-many throughput capacity) of IEEE 802.11 multi-hop networks. It has generally been assumed in prior studies that the many-to-one throughput capacity is upper-bounded by the link capacity L. Throughput capacity L is not achievable under 802.11. This paper introduces the notion of "canonical networks", which is a class of regularly-structured networks whose capacities can be analyzed more easily than unstructured networks. We show that the throughput capacity of canonical networks under 802.11 has an analytical upper bound of 3L/4 when the source nodes are two or more hops away from the sink; and simulated throughputs of 0.690L (0.740L) when the source nodes are many hops away. We conjecture that 3L/4 is also the upper bound for general networks. When all links have equal length, 2L/3 can be shown to be the upper bound for general networks. Our simulations show that 802.11 networks with random topologies operated with AODV routing can only achieve throughputs far below the upper bounds. Fortunately, by properly selecting routes near the gateway (or by properly positioning the relay nodes leading to the gateway) to fashion after the structure of canonical networks, the throughput can be improved significantly by more than 150%. Indeed, in a dense network, it is worthwhile to deactivate some of the relay nodes near the sink judiciously. |
066f3c90-e9b7-442d-acac-8aaae1cdbb83 | 066f3c90-e9b7-442d-acac-8aaae1cdbb83 | 066f3c90-e9b7-442d-acac-8aaae1cdbb83 | human | null | null | none | abstracts | Scanning Tunneling Spectroscopy in the Superconducting State and Vortex
Cores of the beta-pyrochlore KOs2O6 | null | We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (Tc = 9.6 K) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully-gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fields of 2 and 6 T display a hexagonal Abrikosov flux line lattice. From the shape of the vortex cores, we extract a coherence length of 31-40 {\AA}, in agreement with the value derived from the upper critical field Hc2. We observe a reduction in size of the vortex cores (and hence the coherence length) with increasing field which is consistent with the unexpectedly high and unsaturated upper critical field reported. |
8c43b50d-5a16-4f17-88ea-0056e54bc14a | 8c43b50d-5a16-4f17-88ea-0056e54bc14a | 8c43b50d-5a16-4f17-88ea-0056e54bc14a | human | null | null | none | abstracts | Non-resonant and Resonant X-ray Scattering Studies on Multiferroic
TbMn2O5 | null | Comprehensive x-ray scattering studies, including resonant scattering at Mn L-edge, Tb L- and M-edges, were performed on single crystals of TbMn2O5. X-ray intensities were observed at a forbidden Bragg position in the ferroelectric phases, in addition to the lattice and the magnetic modulation peaks. Temperature dependences of their intensities and the relation between the modulation wave vectors provide direct evidences of exchange striction induced ferroelectricity. Resonant x-ray scattering results demonstrate the presence of multiple magnetic orders by exhibiting their different temperature dependences. The commensurate-to-incommensurate phase transition around 24 K is attributed to discommensuration through phase slipping of the magnetic orders in spin frustrated geometries. We proposed that the low temperature incommensurate phase consists of the commensurate magnetic domains separated by anti-phase domain walls which reduce spontaneous polarizations abruptly at the transition. |
1dd6bc1e-fd15-479c-a865-774953e6c660 | 1dd6bc1e-fd15-479c-a865-774953e6c660 | 1dd6bc1e-fd15-479c-a865-774953e6c660 | human | null | null | none | abstracts | Self-diffusion and Interdiffusion in Al80Ni20 Melts: Simulation and
Experiment | null | A combination of experimental techniques and molecular dynamics (MD) computer simulation is used to investigate the diffusion dynamics in Al80Ni20 melts. Experimentally, the self-diffusion coefficient of Ni is measured by the long-capillary (LC) method and by quasielastic neutron scattering. The LC method yields also the interdiffusion coefficient. Whereas the experiments were done in the normal liquid state, the simulations provided the determination of both self-diffusion and interdiffusion constants in the undercooled regime as well. The simulation results show good agreement with the experimental data. In the temperature range 3000 K >= T >= 715 K, the interdiffusion coefficient is larger than the self-diffusion constants. Furthermore the simulation shows that this difference becomes larger in the undercooled regime. This result can be refered to a relatively strong temperature dependence of the thermodynamic factor \Phi, which describes the thermodynamic driving force for interdiffusion. The simulations also indicate that the Darken equation is a good approximation, even in the undercooled regime. This implies that dynamic cross correlations play a minor role for the temperature range under consideration. |
d233b5c7-6fb9-4397-95f8-43c55dae5272 | d233b5c7-6fb9-4397-95f8-43c55dae5272 | d233b5c7-6fb9-4397-95f8-43c55dae5272 | human | null | null | none | abstracts | The Formation of Globular Cluster Systems in Massive Elliptical
Galaxies: Globular Cluster Multimodality from Radial Variation of Stellar
Populations | null | The most massive elliptical galaxies show a prominent multi-modality in their globular cluster system color distributions. Understanding the mechanisms which lead to multiple globular cluster sub-populations is essential for a complete picture of massive galaxy formation. By assuming that globular cluster formation traces the total star formation and taking into account the radial variations in the composite stellar populations predicted by the Pipino & Matteucci (2004) multi-zone photo-chemical evolution code, we compute the distribution of globular cluster properties as a function of galactocentric radius. We compare our results to the spectroscopic measurements of globular clusters in nearby early-type galaxies by Puzia et al. (2006) and show that the observed multi-modality in globular cluster systems of massive ellipticals can be, at least partly, ascribed to the radial variation in the mix of stellar populations. Our model predicts the presence of a super-metal-rich population of globular clusters in the most massive elliptical galaxies, which is in very good agreement with the spectroscopic observations. Furthermore, we investigate the impact of other non-linear mechanisms that shape the metallicity distribution of globular cluster systems, in particular the role of merger-induced globular cluster formation and a non-linear color-metallicity transformation, and discuss their influence in the context of our model (abridged) |
21ef549d-e9b7-471c-80e2-660a8540eb19 | 21ef549d-e9b7-471c-80e2-660a8540eb19 | 21ef549d-e9b7-471c-80e2-660a8540eb19 | human | null | null | none | abstracts | Binaries, microquasars and GLAST | null | Radio and X-ray observations of the relativistic jets of microquasars show evidence for the acceleration of particles to very high energies. Signatures of non-thermal processes occurring closer in to the compact object can also be found. In addition, three binaries are now established emitters of high (> 100 MeV) and/or very high (> 100GeV) energy gamma-rays. High-energy emission can originate from a microquasar jet (accretion-powered) or from a shocked pulsar wind (rotation-powered). I discuss the impact GLAST will have in the very near future on studies of such binaries. GLAST is expected to shed new light on the link between accretion and ejection in microquasars and to enable to probe pulsar winds on small scales in rotation-powered binaries. |
6d905097-e72d-4c31-809d-b582d5a3fca0 | 6d905097-e72d-4c31-809d-b582d5a3fca0 | 6d905097-e72d-4c31-809d-b582d5a3fca0 | human | null | null | none | abstracts | Linearisation of finite abelian subgroups of the Cremona group of the
plane | null | This article gives the proof of results announced in [J. Blanc, Finite Abelian subgroups of the Cremona group of the plane, C.R. Acad. Sci. Paris, S\'er. I 344 (2007), 21-26.] and some description of automorphisms of rational surfaces.
Given a finite Abelian subgroup of the Cremona group of the plane, we provide a way to decide whether it is birationally conjugate to a group of automorphisms of a minimal surface.
In particular, we prove that a finite cyclic group of birational transformations of the plane is linearisable if and only if none of its non-trivial elements fix a curve of positive genus. For finite Abelian groups, there exists only one surprising exception, a group isomorphic to Z/2ZxZ/4Z, whose non-trivial elements do not fix a curve of positive genus but which is not conjugate to a group of automorphisms of a minimal rational surface.
We also give some descriptions of automorphisms (not necessarily of finite order) of del Pezzo surfaces and conic bundles. |
5320eeb5-f651-47aa-9c47-bb9e51867717 | 5320eeb5-f651-47aa-9c47-bb9e51867717 | 5320eeb5-f651-47aa-9c47-bb9e51867717 | human | null | null | none | abstracts | Oriented growth of pentacene films on vacuum-deposited
polytetrafluoroethylene layers aligned by rubbing technique | null | We investigated structure and morphology of PTFE layers deposited by vacuum process in dependence on deposition parameters: deposition rate, deposition temperature, electron activation energy and activation current. Pentacene (PnC) layers deposited on top of those PTFE films are used as a tool to demonstrate the orienting ability of the PTFE layers. The molecular structure of the PTFE films was investigated by use of infrared spectroscopy. By means of ellipsometry, values of refractive index between 1.33 and 1.36 have been obtained for PTFE films in dependence on deposition conditions. Using the cold friction technique orienting PTFE layers with unidirectional grooves are obtained. On top of these PTFE films oriented PnC layers were grown. The obtained order depends both on the PTFE layer thickness and on PnC growth temperature. |
3365b311-1c7e-437d-82c0-23934ce06129 | 3365b311-1c7e-437d-82c0-23934ce06129 | 3365b311-1c7e-437d-82c0-23934ce06129 | human | null | null | none | abstracts | On the Achievable Rate Regions for Interference Channels with Degraded
Message Sets | null | The interference channel with degraded message sets (IC-DMS) refers to a communication model in which two senders attempt to communicate with their respective receivers simultaneously through a common medium, and one of the senders has complete and a priori (non-causal) knowledge about the message being transmitted by the other. A coding scheme that collectively has advantages of cooperative coding, collaborative coding, and dirty paper coding, is developed for such a channel. With resorting to this coding scheme, achievable rate regions of the IC-DMS in both discrete memoryless and Gaussian cases are derived, which, in general, include several previously known rate regions. Numerical examples for the Gaussian case demonstrate that in the high-interference-gain regime, the derived achievable rate regions offer considerable improvements over these existing results. |
c2acca16-411a-4b1c-816f-7fd1f3408227 | c2acca16-411a-4b1c-816f-7fd1f3408227 | c2acca16-411a-4b1c-816f-7fd1f3408227 | human | null | null | none | abstracts | Hilbert functions of points on Schubert varieties in Orthogonal
Grassmannians | null | A solution is given to the following problem: how to compute the multiplicity, or more generally the Hilbert function, at a point on a Schubert variety in an orthogonal Grassmannian. Standard monomial theory is applied to translate the problem from geometry to combinatorics. The solution of the resulting combinatorial problem forms the bulk of the paper. This approach has been followed earlier to solve the same problem for the Grassmannian and the symplectic Grassmannian.
As an application, we present an interpretation of the multiplicity as the number of non-intersecting lattice paths of a certain kind.
Taking the Schubert variety to be of a special kind and the point to be the "identity coset," our problem specializes to a problem about Pfaffian ideals treatments of which by different methods exist in the literature. Also available in the literature is a geometric solution when the point is a "generic singularity." |
bf43db0b-1261-498f-8487-a7f861171306 | bf43db0b-1261-498f-8487-a7f861171306 | bf43db0b-1261-498f-8487-a7f861171306 | human | null | null | none | abstracts | Crossover behavior in fluids with Coulomb interactions | null | According to extensive experimental findings, the Ginzburg temperature $t_{G}$ for ionic fluids differs substantially from that of nonionic fluids [Schr\"oer W., Weig\"{a}rtner H. 2004 {\it Pure Appl. Chem.} {\bf 76} 19]. A theoretical investigation of this outcome is proposed here by a mean field analysis of the interplay of short and long range interactions on the value of $t_{G}$. We consider a quite general continuous charge-asymmetric model made of charged hard spheres with additional short-range interactions (without electrostatic interactions the model belongs to the same universality class as the 3D Ising model). The effective Landau-Ginzburg Hamiltonian of the full system near its gas-liquid critical point is derived from which the Ginzburg temperature is calculated as a function of the ionicity. The results obtained in this way for $t_{G}$ are in good qualitative and sufficient quantitative agreement with available experimental data. |
1665dc55-92af-4831-878d-4c752ecb1383 | 1665dc55-92af-4831-878d-4c752ecb1383 | 1665dc55-92af-4831-878d-4c752ecb1383 | human | null | null | none | abstracts | The old open clusters Berkeley 32 and King 11 | null | We have obtained CCD BVI imaging of the old open clusters Berkeley 32 and King 11. Using the synthetic colour-magnitude diagram method with three different sets of stellar evolution models of various metallicities, with and without overshooting, we have determined their age, distance, reddening, and indicative metallicity, as well as distance from the Galactic centre and height from the Galactic plane. The best parameters derived for Berkeley 32 are: subsolar metallicity (Z=0.008 represents the best choice, Z=0.006 or 0.01 are more marginally acceptable), age = 5.0-5.5 Gyr (models with overshooting; without overshooting the age is 4.2-4.4 Gyr with poorer agreement), (m-M)_0=12.4-12.6, E(B-V)=0.12-0.18 (with the lower value being more probable because it corresponds to the best metallicity), Rgc ~ 10.7-11 kpc, and |Z| ~ 231-254 pc. The best parameters for King 11 are: Z=0.01, age=3.5-4.75 Gyr, (m-M)_0=11.67-11.75, E(B-V)=1.03-1.06, Rgc ~ 9.2-10 kpc, and |Z| ~ 253-387 pc. |
1af57ad6-3bbd-46a4-9848-c8d831855108 | 1af57ad6-3bbd-46a4-9848-c8d831855108 | 1af57ad6-3bbd-46a4-9848-c8d831855108 | human | null | null | none | abstracts | The Genetic Programming Collaboration Network and its Communities | null | Useful information about scientific collaboration structures and patterns can be inferred from computer databases of published papers. The genetic programming bibliography is the most complete reference of papers on GP\@. In addition to locating publications, it contains coauthor and coeditor relationships from which a more complete picture of the field emerges. We treat these relationships as undirected small world graphs whose study reveals the community structure of the GP collaborative social network. Automatic analysis discovers new communities and highlights new facets of them. The investigation reveals many similarities between GP and coauthorship networks in other scientific fields but also some subtle differences such as a smaller central network component and a high clustering. |
95cc48a0-d7b8-4fe8-a641-bc1385ca46e0 | 95cc48a0-d7b8-4fe8-a641-bc1385ca46e0 | 95cc48a0-d7b8-4fe8-a641-bc1385ca46e0 | human | null | null | none | abstracts | Spontaneous Lorentz Violation: Non-Abelian Gauge Fields as
Pseudo-Goldstone Vector Bosons | null | We argue that non-Abelian gauge fields can be treated as the pseudo-Goldstone vector bosons caused by spontaneous Lorentz invariance violation (SLIV). To this end, the SLIV which evolves in a general Yang-Mills type theory with the nonlinear vector field constraint $Tr(% \boldsymbol{A}_{\mu }\boldsymbol{A}^{\mu})=\pm M^{2}$ ($M$ is a proposed SLIV scale) imposed is considered in detail. With an internal symmetry group $G$ having $D$ generators not only the pure Lorentz symmetry SO(1,3), but the larger accidental symmetry $SO(D,3D)$ of the SLIV constraint in itself appears to be spontaneously broken as well. As a result, while the pure Lorentz violation still generates only one genuine Goldstone vector boson, the accompanying pseudo-Goldstone vector bosons related to the $SO(D,3D)$ breaking also come into play in the final arrangement of the entire Goldstone vector field multiplet. Remarkably, they remain strictly massless, being protected by gauge invariance of the Yang-Mills theory involved. We show that, although this theory contains a plethora of Lorentz and $CPT$ violating couplings, they do not lead to physical SLIV effects which turn out to be strictly cancelled in all the lowest order processes considered. However, the physical Lorentz violation could appear if the internal gauge invariance were slightly broken at very small distances influenced by gravity. For the SLIV scale comparable with the Planck one the Lorentz violation could become directly observable at low energies. |
aa5faca1-1bfa-46bc-ba4e-bb50ff06af70 | aa5faca1-1bfa-46bc-ba4e-bb50ff06af70 | aa5faca1-1bfa-46bc-ba4e-bb50ff06af70 | human | null | null | none | abstracts | In-medium effects on particle production in heavy ion collisions | null | The effect of possible in-medium modifications of nucleon-nucleon ($NN$) cross sections on particle production is investigated in heavy ion collisions ($HIC$) at intermediate energies. In particular, using a fully covariant relativistic transport approach, we see that the density dependence of the {\it inelastic} cross sections appreciably affects the pion and kaon yields and their rapidity distributions. However, the $(\pi^{-}/\pi^{+})$- and $(K^{0}/K^{+})$-ratios depend only moderately on the in-medium behavior of the inelastic cross sections. This is particularly true for kaon yield ratios, since kaons are more uniformly produced in high density regions. Kaon potentials are also suitably evaluated in two schemes, a chiral perturbative approach and an effective meson-quark coupling method, with consistent results showing a similar repulsive contribution for $K^{+}$ and $K^{0}$. As a consequence we expect rather reduced effects on the yield ratios. We conclude that particle ratios appear to be robust observables for probing the nuclear equation of state ($EoS$) at high baryon density and, particularly, its isovector sector. |
9769aef3-6c6e-44da-bac4-9f5f5ea4a4ee | 9769aef3-6c6e-44da-bac4-9f5f5ea4a4ee | 9769aef3-6c6e-44da-bac4-9f5f5ea4a4ee | human | null | null | none | abstracts | Effective conservation of energy and momentum algorithm using switching
potentials suitable for molecular dynamics simulation of thermodynamical
systems | null | During a crossover via a switching mechanism from one 2-body potential to another as might be applied in modeling (chemical) reactions in the vicinity of bond formation, energy violations would occur due to finite step size which determines the trajectory of the particles relative to the potential interactions of the unbonded state by numerical (e.g. Verlet) integration. This problem is overcome by an algorithm which preserves the coordinates of the system for each move, but corrects for energy discrepancies by ensuring both energy and momentum conservation in the dynamics. The algorithm is tested for a hysteresis loop reaction model with an without the implementation of the algorithm. The tests involve checking the rate of energy flow out of the MD simulation box; in the equilibrium state, no net rate of flows within experimental error should be observed. The temperature and pressure of the box should also be invariant within the range of fluctuation of these quantities. It is demonstrated that the algorithm satisfies these criteria. |
04a3ab2a-e5c7-4cd5-bf3c-c6a684b516a0 | 04a3ab2a-e5c7-4cd5-bf3c-c6a684b516a0 | 04a3ab2a-e5c7-4cd5-bf3c-c6a684b516a0 | human | null | null | none | abstracts | Signal for space-time noncommutativity: the Z -> gamma gamma decay in
the renormalizable gauge sector of the theta-expanded NCSM | null | We propose the Z -> gamma gamma decay, a process strictly forbidden in the standard model, as a signal suitable for the search of noncommutativity of coordinates at very short distances. We compute the Z -> gamma gamma partial widthin the framework of the recently proposed renormalizable gauge sector of the noncommutative standard model. The one-loop renormalizability is obtained for the model containing the usual six representations of matter fields of the first generation. Even more, the noncommutative part is finite or free of divergences, showing that perhaps new interaction symmetry exists in the noncommutative gauge sector of the model. Discovery of such symmetry would be of tremendous importance in further search for the violation of the Lorentz invariance at very high energies. Experimental possibilities of Z -> gamma gamma decay are analyzed and a firm bound to the scale of the noncommutativity parameter is set around 1 TeV. |
e44aed55-9a28-46b5-b510-8782f65c2ae4 | e44aed55-9a28-46b5-b510-8782f65c2ae4 | e44aed55-9a28-46b5-b510-8782f65c2ae4 | human | null | null | none | abstracts | New Organic thermally stable materials for optoelectronics devices - A
linear spectroscopy study | null | Thermally stable polymers have attracted a lot of interest due to their potential use as the active component in electronic, optical and optoelectronic applications, such as light-emitting diodes, light emitting electrochemical cells, photodiodes, photovoltaic cells, field effect transistors, optocouplers and optically pumped lasers in solution and solid state.We report results of investigations into the use of thermal treatment of poly(p-phenylene vinylene) (PPV) films grown on a variety of substrates (quartz and glass). Film thickness, morphology and structural properties were investigated by a range of techniques in particular: atomic force microscope - AFM, DEKTAK method, Ellipsometry and UV-VIS spectroscopy. |
0d28cf03-b3fb-4422-8a17-5336b33558c8 | 0d28cf03-b3fb-4422-8a17-5336b33558c8 | 0d28cf03-b3fb-4422-8a17-5336b33558c8 | human | null | null | none | abstracts | On the potential of transit surveys in star clusters: Impact of
correlated noise and radial velocity follow-up | null | We present an extension of the formalism recently proposed by Pepper & Gaudi to evaluate the yield of transit surveys in homogeneous stellar systems, incorporating the impact of correlated noise on transit time-scales on the detectability of transits, and simultaneously incorporating the magnitude limits imposed by the need for radial velocity follow-up of transit candidates. New expressions are derived for the different contributions to the noise budget on transit time-scales and the least-squares detection statistic for box-shaped transits, and their behaviour as a function of stellar mass is re-examined. Correlated noise that is constant with apparent stellar magnitude implies a steep decrease in detection probability at the high mass end which, when considered jointly with the radial velocity requirements, can severely limit the potential of otherwise promising surveys in star clusters. However, we find that small-aperture, wide field surveys may detect hot Neptunes whose radial velocity signal can be measured with present-day instrumentation in very nearby (<100 pc) clusters. |
00378b3f-b639-4abe-8639-f00f41a89dd3 | 00378b3f-b639-4abe-8639-f00f41a89dd3 | 00378b3f-b639-4abe-8639-f00f41a89dd3 | human | null | null | none | abstracts | Neutron-Capture Elements in the Double-Enhanced Star HE 1305-0007: a New
s- and r-Process Paradigm | null | The star HE 1305-0007 is a metal-poor double-enhanced star with metallicity [Fe/H] $=-2.0$, which is just at the upper limit of the metallicity for the observed double-enhanced stars. Using a parametric model, we find that almost all s-elements were made in a single neutron exposure. This star should be a member of a post-common-envelope binary. After the s-process material has experienced only one neutron exposure in the nucleosynthesis region and is dredged-up to its envelope, the AGB evolution is terminated by the onset of common-envelope evolution. Based on the high radial-velocity of HE 1305-0007, we speculate that the star could be a runaway star from a binary system, in which the AIC event has occurred and produced the r-process elements. |
1e1e54a9-2250-4ba4-acea-cf0162353e4d | 1e1e54a9-2250-4ba4-acea-cf0162353e4d | 1e1e54a9-2250-4ba4-acea-cf0162353e4d | human | null | null | none | abstracts | 3D photospheric velocity field of a Supergranular cell | null | We investigate the plasma flow properties inside a Supergranular (SG) cell, in particular its interaction with small scale magnetic field structures. The SG cell has been identified using the magnetic network (CaII wing brightness) as proxy, applying the Two-Level Structure Tracking (TST) to high spatial, spectral and temporal resolution observations obtained by IBIS. The full 3D velocity vector field for the SG has been reconstructed at two different photospheric heights. In order to strengthen our findings, we also computed the mean radial flow of the SG by means of cork tracing. We also studied the behaviour of the horizontal and Line of Sight plasma flow cospatial with cluster of bright CaII structures of magnetic origin to better understand the interaction between photospheric convection and small scale magnetic features. The SG cell we investigated seems to be organized with an almost radial flow from its centre to the border. The large scale divergence structure is probably created by a compact region of constant up-flow close to the cell centre. On the edge of the SG, isolated regions of strong convergent flow are nearby or cospatial with extended clusters of bright CaII wing features forming the knots of the magnetic network. |
1ced5f1a-3cb2-4187-af0f-b44899715ac3 | 1ced5f1a-3cb2-4187-af0f-b44899715ac3 | 1ced5f1a-3cb2-4187-af0f-b44899715ac3 | human | null | null | none | abstracts | Substructures in WINGS clusters | null | We search for and characterize substructures in the projected distribution of galaxies observed in the wide field CCD images of the 77 nearby clusters of the WIde-field Nearby Galaxy-cluster Survey (WINGS). This sample is complete in X-ray flux in the redshift range 0.04<z<0.07. We search for substructures in WINGS clusters with DEDICA, an adaptive-kernel procedure. We test the procedure on Monte-Carlo simulations of the observed frames and determine the reliability for the detected structures. DEDICA identifies at least one reliable structure in the field of 55 clusters. 40 of these clusters have a total of 69 substructures at the same redshift of the cluster (redshift estimates of substructures are from color-magnitude diagrams). The fraction of clusters with subclusters (73%) is higher than in most studies. The presence of subclusters affects the relative luminosities of the brightest cluster galaxies (BCGs). Down to L ~ 10^11.2 L_Sun, our observed differential distribution of subcluster luminosities is consistent with the theoretical prediction of the differential mass function of substructures in cosmological simulations. |
6ec4ac2f-88fa-453f-ada0-d2924f490e12 | 6ec4ac2f-88fa-453f-ada0-d2924f490e12 | 6ec4ac2f-88fa-453f-ada0-d2924f490e12 | human | null | null | none | abstracts | Ising-like dynamics and frozen states in systems of ultrafine magnetic
particles | null | We use Monte-Carlo simulations to study aging phenomena and the occurence of spinglass phases in systems of single-domain ferromagnetic nanoparticles under the combined influence of dipolar interaction and anisotropy energy, for different combinations of positional and orientational disorder. We find that the magnetic moments oriente themselves preferably parallel to their anisotropy axes and changes of the total magnetization are solely achieved by 180 degree flips of the magnetic moments, as in Ising systems. Since the dipolar interaction favorizes the formation of antiparallel chain-like structures, antiparallel chain-like patterns are frozen in at low temperatures, leading to aging phenomena characteristic for spin-glasses. Contrary to the intuition, these aging effects are more pronounced in ordered than in disordered structures. |
9cdaf251-3e54-4230-b4f7-fcfec2c01eee | 9cdaf251-3e54-4230-b4f7-fcfec2c01eee | 9cdaf251-3e54-4230-b4f7-fcfec2c01eee | human | null | null | none | abstracts | Continuous interfaces with disorder: Even strong pinning is too weak in
2 dimensions | null | We consider statistical mechanics models of continuous height effective interfaces in the presence of a delta-pinning at height zero. There is a detailed mathematical understanding of the depinning transition in 2 dimensions without disorder. Then the variance of the interface height w.r.t. the Gibbs measure stays bounded uniformly in the volume for any positive pinning force and diverges like the logarithm of the pinning force when it tends to zero.
How does the presence of a quenched disorder term in the Hamiltonian modify this transition? We show that an arbitarily weak random field term is enough to beat an arbitrarily strong delta-pinning in 2 dimensions and will cause delocalization. The proof is based on a rigorous lower bound for the overlap between local magnetizations and random fields in finite volume. In 2 dimensions it implies growth faster than the volume which is a contradiction to localization. We also derive a simple complementary inequality which shows that in higher dimensions the fraction of pinned sites converges to one when the pinning force tends to infinity. |
f4b56fb9-271f-4508-ae9a-0b39651b7418 | f4b56fb9-271f-4508-ae9a-0b39651b7418 | f4b56fb9-271f-4508-ae9a-0b39651b7418 | human | null | null | none | abstracts | On the KK-theory of strongly self-absorbing C*-algebras | null | Let $\Dh$ and $A$ be unital and separable $C^{*}$-algebras; let $\Dh$ be strongly self-absorbing. It is known that any two unital $^*$-homomorphisms from $\Dh$ to $A \otimes \Dh$ are approximately unitarily equivalent. We show that, if $\Dh$ is also $K_{1}$-injective, they are even asymptotically unitarily equivalent. This in particular implies that any unital endomorphism of $\Dh$ is asymptotically inner. Moreover, the space of automorphisms of $\Dh$ is compactly-contractible (in the point-norm topology) in the sense that for any compact Hausdorff space $X$, the set of homotopy classes $[X,\Aut(\Dh)]$ reduces to a point. The respective statement holds for the space of unital endomorphisms of $\Dh$. As an application, we give a description of the Kasparov group $KK(\Dh, A\ot \Dh)$ in terms of $^*$-homomorphisms and asymptotic unitary equivalence. Along the way, we show that the Kasparov group $KK(\Dh, A\ot \Dh)$ is isomorphic to $K_0(A\ot \Dh)$. |
d6c48aca-f9f4-4111-8ec4-9c50f2621384 | d6c48aca-f9f4-4111-8ec4-9c50f2621384 | d6c48aca-f9f4-4111-8ec4-9c50f2621384 | human | null | null | none | abstracts | Dust Formation and Survival in Supernova Ejecta | null | The presence of dust at high redshift requires efficient condensation of grains in SN ejecta, in accordance with current theoretical models. Yet, observations of the few well studied SNe and SN remnants imply condensation efficiencies which are about two orders of magnitude smaller. Motivated by this tension, we have (i) revisited the model of Todini & Ferrara (2001) for dust formation in the ejecta of core collapse SNe and (ii) followed, for the first time, the evolution of newly condensed grains from the time of formation to their survival - through the passage of the reverse shock - in the SN remnant. We find that 0.1 - 0.6 M_sun of dust form in the ejecta of 12 - 40 M_sun stellar progenitors. Depending on the density of the surrounding ISM, between 2-20% of the initial dust mass survives the passage of the reverse shock, on time-scales of about 4-8 x 10^4 yr from the stellar explosion. Sputtering by the hot gas induces a shift of the dust size distribution towards smaller grains. The resulting dust extinction curve shows a good agreement with that derived by observations of a reddened QSO at z =6.2. Stochastic heating of small grains leads to a wide distribution of dust temperatures. This supports the idea that large amounts (~ 0.1 M_sun) of cold dust (T ~ 40K) can be present in SN remnants, without being in conflict with the observed IR emission. |
3b202abd-fa9f-4f97-b7bb-062d273111d1 | 3b202abd-fa9f-4f97-b7bb-062d273111d1 | 3b202abd-fa9f-4f97-b7bb-062d273111d1 | human | null | null | none | abstracts | Preferential interaction coefficient for nucleic acids and other
cylindrical poly-ions | null | The thermodynamics of nucleic acid processes is heavily affected by the electric double-layer of micro-ions around the polyions. We focus here on the Coulombic contribution to the salt-polyelectrolyte preferential interaction (Donnan) coefficient and we report extremely accurate analytical expressions valid in the range of low salt concentration (when polyion radius is smaller than the Debye length). The analysis is performed at Poisson-Boltzmann level, in cylindrical geometry, with emphasis on highly charged poly-ions (beyond ``counter-ion condensation''). The results hold for any electrolyte of the form $z_-$:$z_+$. We also obtain a remarkably accurate expression for the electric potential in the vicinity of the poly-ion. |
638ebd4d-6e94-45fa-a6b3-645f880f8c15 | 638ebd4d-6e94-45fa-a6b3-645f880f8c15 | 638ebd4d-6e94-45fa-a6b3-645f880f8c15 | human | null | null | none | abstracts | Analysis of the real estate market in Las Vegas: Bubble, seasonal
patterns, and prediction of the CSW indexes | null | We analyze 27 house price indexes of Las Vegas from Jun. 1983 to Mar. 2005, corresponding to 27 different zip codes. These analyses confirm the existence of a real-estate bubble, defined as a price acceleration faster than exponential, which is found however to be confined to a rather limited time interval in the recent past from approximately 2003 to mid-2004 and has progressively transformed into a more normal growth rate comparable to pre-bubble levels in 2005. There has been no bubble till 2002 except for a medium-sized surge in 1990. In addition, we have identified a strong yearly periodicity which provides a good potential for fine-tuned prediction from month to month. A monthly monitoring using a model that we have developed could confirm, by testing the intra-year structure, if indeed the market has returned to ``normal'' or if more turbulence is expected ahead. We predict the evolution of the indexes one year ahead, which is validated with new data up to Sep. 2006. The present analysis demonstrates the existence of very significant variations at the local scale, in the sense that the bubble in Las Vegas seems to have preceded the more global USA bubble and has ended approximately two years earlier (mid 2004 for Las Vegas compared with mid-2006 for the whole of the USA). |
c05422b8-3106-4437-9c76-cb277c63e364 | c05422b8-3106-4437-9c76-cb277c63e364 | c05422b8-3106-4437-9c76-cb277c63e364 | human | null | null | none | abstracts | Quantum criticality and disorder in the antiferromagnetic critical point
of NiS$_{2}$ pyrite | null | A quantum critical point (QCP) between the antiferromagnetic and the paramagnetic phases was realized by applying a hydrostatic pressure of ~ 7 GPa on single crystals of NiS_{2} pyrite with a low residual resistivity, rho_{0}, of 0.5 mu-Omega-cm. We found that the critical behavior of the resistivity, rho, in this clean system contrasts sharply with those observed in its disordered analogue, NiS_{2-x}Se_{x} solid-solution, demonstrating the unexpectedly drastic effect of disorder on the quantum criticality. Over a whole paramagnetic region investigated up to P = 9 GPa, a crossover temperature, defined as the onset of T^{2} dependence of rho, an indication of Fermi liquid, was suppressed to a substantially low temperature T sim 2 K and, instead, a non Fermi liquid behavior of rho, T^{3/2}-dependence, robustly showed up. |
e222b5ea-2f3f-486a-a95c-4e10915aff68 | e222b5ea-2f3f-486a-a95c-4e10915aff68 | e222b5ea-2f3f-486a-a95c-4e10915aff68 | human | null | null | none | abstracts | Local-field effects in radiatively broadened magneto-dielectric media:
negative refraction and absorption reduction | null | We give a microscopic derivation of the Clausius-Mossotti relations for a homogeneous and isotropic magneto-dielectric medium consisting of radiatively broadened atomic oscillators. To this end the diagram series of electromagnetic propagators is calculated exactly for an infinite bi-cubic lattice of dielectric and magnetic dipoles for a lattice constant small compared to the resonance wavelength $\lambda$. Modifications of transition frequencies and linewidth of the elementary oscillators are taken into account in a selfconsistent way by a proper incorporation of the singular self-interaction terms. We show that in radiatively broadened media sufficiently close to the free-space resonance the real part of the index of refraction approaches the value -2 in the limit of $\rho \lambda^3 \gg 1$, where $\rho$ is the number density of scatterers. Since at the same time the imaginary part vanishes as $1/\rho$ local field effects can have important consequences for realizing low-loss negative index materials. |
e3ba627c-b10e-4cae-a2e1-125d34d79f9f | e3ba627c-b10e-4cae-a2e1-125d34d79f9f | e3ba627c-b10e-4cae-a2e1-125d34d79f9f | human | null | null | none | abstracts | About curvature, conformal metrics and warped products | null | We consider the curvature of a family of warped products of two pseduo-Riemannian manifolds $(B,g_B)$ and $(F,g_F)$ furnished with metrics of the form $c^{2}g_B \oplus w^2 g_F$ and, in particular, of the type $w^{2 \mu}g_B \oplus w^2 g_F$, where $c, w \colon B \to (0,\infty)$ are smooth functions and $\mu$ is a real parameter. We obtain suitable expressions for the Ricci tensor and scalar curvature of such products that allow us to establish results about the existence of Einstein or constant scalar curvature structures in these categories. If $(B,g_B)$ is Riemannian, the latter question involves nonlinear elliptic partial differential equations with concave-convex nonlinearities and singular partial differential equations of the Lichnerowicz-York type among others. |
b796e0ba-3b6c-4b96-abeb-0cc4ba929f9b | b796e0ba-3b6c-4b96-abeb-0cc4ba929f9b | b796e0ba-3b6c-4b96-abeb-0cc4ba929f9b | human | null | null | none | abstracts | Investigation of Colour Reconnection in WW Events with the DELPHI
detector at LEP-2 | null | In the reaction e+e- -> WW -> (q_1 qbar_2)(q_3 qbar_4) the usual hadronization models treat the colour singlets q_1 qbar_2 and q_3 qbar_4 coming from two W bosons independently. However, since the final state partons may coexist in space and time, cross-talk between the two evolving hadronic systems may be possible during fragmentation through soft gluon exchange. This effect is known as Colour Reconnection. In this article the results of the investigation of Colour Reconnection effects in fully hadronic decays of W pairs in DELPHI at LEP are presented. Two complementary analyses were performed, studying the particle flow between jets and W mass estimators, with negligible correlation between them, and the results were combined and compared to models. In the framework of the SK-I model, the value for its kappa parameter most compatible with the data was found to be: kappa_{SK-I} = 2.2^{+2.5}_{-1.3} corresponding to the probability of reconnection P_{reco} to be in the range 0.31 < P_{reco} < 0.68 at 68% confidence level with its best value at 0.52. |
db6ea24e-81e8-4200-82f1-f7358365c649 | db6ea24e-81e8-4200-82f1-f7358365c649 | db6ea24e-81e8-4200-82f1-f7358365c649 | human | null | null | none | abstracts | Evolutionary Neural Gas (ENG): A Model of Self Organizing Network from
Input Categorization | null | Despite their claimed biological plausibility, most self organizing networks have strict topological constraints and consequently they cannot take into account a wide range of external stimuli. Furthermore their evolution is conditioned by deterministic laws which often are not correlated with the structural parameters and the global status of the network, as it should happen in a real biological system. In nature the environmental inputs are noise affected and fuzzy. Which thing sets the problem to investigate the possibility of emergent behaviour in a not strictly constrained net and subjected to different inputs. It is here presented a new model of Evolutionary Neural Gas (ENG) with any topological constraints, trained by probabilistic laws depending on the local distortion errors and the network dimension. The network is considered as a population of nodes that coexist in an ecosystem sharing local and global resources. Those particular features allow the network to quickly adapt to the environment, according to its dimensions. The ENG model analysis shows that the net evolves as a scale-free graph, and justifies in a deeply physical sense- the term gas here used. |
2ef14f64-3667-445f-b447-93706de32a7e | 2ef14f64-3667-445f-b447-93706de32a7e | 2ef14f64-3667-445f-b447-93706de32a7e | human | null | null | none | abstracts | D-\bar D mixing and rare D decays in the Littlest Higgs model with
non-unitarity matrix | null | We study the $D-\bar D$ mixing and rare D decays in the Littlest Higgs model. As the new weak singlet quark with the electric charge of 2/3 is introduced to cancel the quadratic divergence induced by the top-quark, the standard unitary $3\times 3$ Cabibbo-Kobayashi-Maskawa matrix is extended to a non-unitary $4\times 3$ matrix in the quark charged currents and Z-mediated flavor changing neutral currents are generated at tree level. In this model, we show that the $D-\bar D$ mixing parameter can be as large as the current experimental value and the decay branching ratio (BR) of $D\to X_u \ga$ is small but its direct CP asymmetry could be $O(10%)$. In addition, we find that the BRs of $D\to X_u \ell^{+} \ell^{-}$, $D\to X_u\nu \bar \nu$ and $D\to \mu^{+} \mu^{-}$ could be enhanced to be $O(10^{-9})$, $O(10^{-8})$ and $O(10^{-9})$, respectively. |
bca25963-8fc1-403f-a61b-2dd1ba3c40d5 | bca25963-8fc1-403f-a61b-2dd1ba3c40d5 | bca25963-8fc1-403f-a61b-2dd1ba3c40d5 | human | null | null | none | abstracts | Reconciling the X(3872) with the near-threshold enhancement in the
D^0\bar{D}^{*0} final state | null | We investigate the enhancement in the D^0\bar{D}^0\pi^0 final state with the mass M=3875.2\pm 0.7^{+0.3}_{-1.6}\pm 0.8 MeV found recently by the Belle Collaboration in the B\to K D^0\bar{D}^0\pi^0 decay and test the possibility that this is yet another manifestation of the well-established resonance X(3872). We perform a combined Flatte analysis of the data for the D^0\bar{D}^0\pi^0 mode, and for the \pi^+\pi^- J/\psi mode of the X(3872). Only if the X(3872) is a virtual state in the D^0\bar{D}^{*0} channel, the data on the new enhancement comply with those on the X(3872). In our fits, the mass distribution in the D^0\bar{D}^{*0} mode exhibits a peak at 2-3 MeV above the D^0\bar{D}^{*0} threshold, with a distinctive non-Breit-Wigner shape. |
a8389e9d-7626-4dac-8de5-6bf4d8e4c315 | a8389e9d-7626-4dac-8de5-6bf4d8e4c315 | a8389e9d-7626-4dac-8de5-6bf4d8e4c315 | human | null | null | none | abstracts | Plasmon Amplification through Stimulated Emission at Terahertz
Frequencies in Graphene | null | We show that plasmons in two-dimensional graphene can have net gain at terahertz frequencies. The coupling of the plasmons to interband electron-hole transitions in population inverted graphene layers can lead to plasmon amplification through the process of stimulated emission. We calculate plasmon gain for different electron-hole densities and temperatures and show that the gain values can exceed $10^{4}$ cm$^{-1}$ in the 1-10 terahertz frequency range, for electron-hole densities in the $10^{9}$-$10^{11}$ cm$^{-2}$ range, even when plasmon energy loss due to intraband scattering is considered. Plasmons are found to exhibit net gain for intraband scattering times shorter than 100 fs. Such high gain values could allow extremely compact terahertz amplifiers and oscillators that have dimensions in the 1-10 $\mu$m range. |
9fb590d4-194a-467c-a549-6d0e23e6d78f | 9fb590d4-194a-467c-a549-6d0e23e6d78f | 9fb590d4-194a-467c-a549-6d0e23e6d78f | human | null | null | none | abstracts | Solving The High Energy Evolution Equation Including Running Coupling
Corrections | null | We study the solution of the nonlinear BK evolution equation with the recently calculated running coupling corrections [hep-ph/0609105, hep-ph/0609090]. Performing a numerical solution we confirm the earlier result of [hep-ph/0408216] that the high energy evolution with the running coupling leads to a universal scaling behavior for the dipole scattering amplitude. The running coupling corrections calculated recently significantly change the shape of the scaling function as compared to the fixed coupling case leading to a considerable increase in the anomalous dimension and to a slow-down of the evolution with rapidity. The difference between the two recent calculations is due to an extra contribution to the evolution kernel, referred to as the subtraction term, which arises when running coupling corrections are included. These subtraction terms were neglected in both recent calculations. We evaluate numerically the subtraction terms for both calculations, and demonstrate that when the subtraction terms are added back to the evolution kernels obtained in the two works the resulting dipole amplitudes agree with each other! We then use the complete running coupling kernel including the subtraction term to find the numerical solution of the resulting full non-linear evolution equation with the running coupling corrections. Again the scaling regime is recovered at very large rapidity. |
6ece21be-f0b6-4cbe-8c6b-6654cf0c9170 | 6ece21be-f0b6-4cbe-8c6b-6654cf0c9170 | 6ece21be-f0b6-4cbe-8c6b-6654cf0c9170 | human | null | null | none | abstracts | Millimeter imaging of HD 163296: probing the disk structure and
kinematics | null | We present new multi-wavelength millimeter interferometric observations of the Herbig Ae star HD 163296 obtained with the IRAM/PBI, SMA and VLA arrays both in continuum and in the 12CO, 13CO and C18O emission lines. Gas and dust properties have been obtained comparing the observations with self-consistent disk models for the dust and CO emission. The circumstellar disk is resolved both in the continuum and in CO. We find strong evidence that the circumstellar material is in Keplerian rotation around a central star of 2.6 Msun. The disk inclination with respect to the line of sight is 46+-4 deg with a position angle of 128+-4 deg. The slope of the dust opacity measured between 0.87 and 7 mm (beta=1) confirms the presence of mm/cm-size grains in the disk midplane. The dust continuum emission is asymmetric and confined inside a radius of 200 AU while the CO emission extends up to 540 AU. The comparison between dust and CO temperature indicates that CO is present only in the disk interior. Finally, we obtain an increasing depletion of CO isotopomers from 12CO to 13CO and C18O. We argue that these results support the idea that the disk of HD 163296 is strongly evolved. In particular, we suggest that there is a strong depletion of dust relative to gas outside 200 AU; this may be due to the inward migration of large bodies that form in the outer disk or to clearing of a large gap in the dust distribution by a low mass companion. |
43d6dd09-f1a1-483d-a428-c3122cbe2e3e | 43d6dd09-f1a1-483d-a428-c3122cbe2e3e | 43d6dd09-f1a1-483d-a428-c3122cbe2e3e | human | null | null | none | abstracts | Spectropolarimetric observations of the Ca II 8498 A and 8542 A lines in
the quiet Sun | null | The Ca II infrared triplet is one of the few magnetically sensitive chromospheric lines available for ground-based observations. We present spectropolarimetric observations of the 8498 A and 8542 A lines in a quiet Sun region near a decaying active region and compare the results with a simulation of the lines in a high plasma-beta regime. Cluster analysis of Stokes V profile pairs shows that the two lines, despite arguably being formed fairly close, often do not have similar shapes. In the network, the local magnetic topology is more important in determining the shapes of the Stokes V profiles than the phase of the wave, contrary to what our simulations show. We also find that Stokes V asymmetries are very common in the network, and the histograms of the observed amplitude and area asymmetries differ significantly from the simulation. Both the network and internetwork show oscillatory behavior in the Ca II lines. It is stronger in the network, where shocking waves, similar to those in the high-beta simulation, are seen and large self-reversals in the intensity profiles are common. |
6b5f8b29-c370-49b7-a7b5-1ee612828c46 | 6b5f8b29-c370-49b7-a7b5-1ee612828c46 | 6b5f8b29-c370-49b7-a7b5-1ee612828c46 | human | null | null | none | abstracts | Number of moduli of irreducible families of plane curves with nodes and
cusps | null | Consider the family S of irreducible plane curves of degree n with d nodes and k cusps as singularities. Let W be an irreducible component of S. We consider the natural rational map from W to the moduli space of curves of genus g=(n-1)(n-2)/2-d-k. We define the "number of moduli of W" as the dimension of the image of W with respect to this map. If W has the expected dimension equal to 3n+g-1-k, then the number of moduli of W is at most equal to the min(3g-3, 3g-3+\rho-k), dove \rho is the Brill-Neother number of the linear series of degree n and dimension 2 on a smooth curve of genus g. We say that W has the expected number of moduli if the equality holds. In this paper we construct examples of families of irreducible plane curves with nodes and cusps as singularities having expected number of moduli and with non-positive Brill-Noether number. |
39a10090-9f6a-466d-9784-b862249b5a6b | 39a10090-9f6a-466d-9784-b862249b5a6b | 39a10090-9f6a-466d-9784-b862249b5a6b | human | null | null | none | abstracts | Search for Heavy Neutral MSSM Higgs Bosons with CMS: Reach and
Higgs-Mass Precision | null | The search for MSSM Higgs bosons will be an important goal at the LHC. We analyze the search reach of the CMS experiment for the heavy neutral MSSM Higgs bosons with an integrated luminosity of 30 or 60 fb^-1. This is done by combining the latest results for the CMS experimental sensitivities based on full simulation studies with state-of-the-art theoretical predictions of MSSM Higgs-boson properties. The results are interpreted in MSSM benchmark scenarios in terms of the parameters tan_beta and the Higgs-boson mass scale, M_A. We study the dependence of the 5 sigma discovery contours in the M_A-tan_beta plane on variations of the other supersymmetric parameters. The largest effects arise from a change in the higgsino mass parameter mu, which enters both via higher-order radiative corrections and via the kinematics of Higgs decays into supersymmetric particles. While the variation of $\mu$ can shift the prospective discovery reach (and correspondingly the ``LHC wedge'' region) by about Delta tan_beta = 10, we find that the discovery reach is rather stable with respect to the impact of other supersymmetric parameters. Within the discovery region we analyze the accuracy with which the masses of the heavy neutral Higgs bosons can be determined. We find that an accuracy of 1-4% should be achievable, which could make it possible in favourable regions of the MSSM parameter space to experimentally resolve the signals of the two heavy MSSM Higgs bosons at the LHC. |
079de142-0ef6-4a59-8434-dc4520c37c2f | 079de142-0ef6-4a59-8434-dc4520c37c2f | 079de142-0ef6-4a59-8434-dc4520c37c2f | human | null | null | none | abstracts | White dwarf masses derived from planetary nebulae modelling | null | We compare the mass distribution of central stars of planetary nebulae (CSPN) with those of their progeny, white dwarfs (WD). We use a dynamical method to measure masses with an uncertainty of 0.02 M$_\odot$. The CSPN mass distribution is sharply peaked at $0.61 \rm M_\odot$. The WD distribution peaks at lower masses ($0.58 \rm M_\odot$) and shows a much broader range of masses. Some of the difference can be explained if the early post-AGB evolution is faster than predicted by the Bl\"ocker tracks. Between 30 and 50 per cent of WD may avoid the PN phase because of too low mass. However, the discrepancy cannot be fully resolved and WD mass distributions may have been broadened by observational or model uncertainties. |
e7fcc770-078b-4cdb-b1e7-842ae6e3abe2 | e7fcc770-078b-4cdb-b1e7-842ae6e3abe2 | e7fcc770-078b-4cdb-b1e7-842ae6e3abe2 | human | null | null | none | abstracts | Uniqueness theorems for Cauchy integrals | null | If $\mu$ is a finite complex measure in the complex plane $\C$ we denote by $C^\mu$ its Cauchy integral defined in the sense of principal value. The measure $\mu$ is called reflectionless if it is continuous (has no atoms) and $C^\mu=0$ at $\mu$-almost every point. We show that if $\mu$ is reflectionless and its Cauchy maximal function $C^\mu_*$ is summable with respect to $|\mu|$ then $\mu$ is trivial. An example of a reflectionless measure whose maximal function belongs to the "weak" $L^1$ is also constructed, proving that the above result is sharp in its scale. We also give a partial geometric description of the set of reflectionless measures on the line and discuss connections of our results with the notion of sets of finite perimeter in the sense of De Giorgi. |
edeea3b2-f80e-4d6f-bc8c-8ad1dc91258f | edeea3b2-f80e-4d6f-bc8c-8ad1dc91258f | edeea3b2-f80e-4d6f-bc8c-8ad1dc91258f | human | null | null | none | abstracts | Temporal Evolution of Step-Edge Fluctuations Under Electromigration
Conditions | null | The temporal evolution of step-edge fluctuations under electromigration conditions is analysed using a continuum Langevin model. If the electromigration driving force acts in the step up/down direction, and step-edge diffusion is the dominant mass-transport mechanism, we find that significant deviations from the usual $t^{1/4}$ scaling of the terrace-width correlation function occurs for a critical time $\tau$ which is dependent upon the three energy scales in the problem: $k_{B}T$, the step stiffness, $\gamma$, and the bias associated with adatom hopping under the influence of an electromigration force, $\pm \Delta U$. For ($t < \tau$), the correlation function evolves as a superposition of $t^{1/4}$ and $t^{3/4}$ power laws. For $t \ge \tau$ a closed form expression can be derived. This behavior is confirmed by a Monte-Carlo simulation using a discrete model of the step dynamics. It is proposed that the magnitude of the electromigration force acting upon an atom at a step-edge can by estimated by a careful analysis of the statistical properties of step-edge fluctuations on the appropriate time-scale. |
56e037b4-e231-4da3-8357-fc777c11dd0c | 56e037b4-e231-4da3-8357-fc777c11dd0c | 56e037b4-e231-4da3-8357-fc777c11dd0c | human | null | null | none | abstracts | Probing dark energy with steerable wavelets through correlation of WMAP
and NVSS local morphological measures | null | Using local morphological measures on the sphere defined through a steerable wavelet analysis, we examine the three-year WMAP and the NVSS data for correlation induced by the integrated Sachs-Wolfe (ISW) effect. The steerable wavelet constructed from the second derivative of a Gaussian allows one to define three local morphological measures, namely the signed-intensity, orientation and elongation of local features. Detections of correlation between the WMAP and NVSS data are made with each of these morphological measures. The most significant detection is obtained in the correlation of the signed-intensity of local features at a significance of 99.9%. By inspecting signed-intensity sky maps, it is possible for the first time to see the correlation between the WMAP and NVSS data by eye. Foreground contamination and instrumental systematics in the WMAP data are ruled out as the source of all significant detections of correlation. Our results provide new insight on the ISW effect by probing the morphological nature of the correlation induced between the cosmic microwave background and large scale structure of the Universe. Given the current constraints on the flatness of the Universe, our detection of the ISW effect again provides direct and independent evidence for dark energy. Moreover, this new morphological analysis may be used in future to help us to better understand the nature of dark energy. |
d34bafa0-9101-4159-8a86-d6c9556e825c | d34bafa0-9101-4159-8a86-d6c9556e825c | d34bafa0-9101-4159-8a86-d6c9556e825c | human | null | null | none | abstracts | Black hole puncture initial data with realistic gravitational wave
content | null | We present improved post-Newtonian-inspired initial data for non-spinning black-hole binaries, suitable for numerical evolution with punctures. We revisit the work of Tichy et al. [W. Tichy, B. Bruegmann, M. Campanelli, and P. Diener, Phys. Rev. D 67, 064008 (2003)], explicitly calculating the remaining integral terms. These terms improve accuracy in the far zone and, for the first time, include realistic gravitational waves in the initial data. We investigate the behavior of these data both at the center of mass and in the far zone, demonstrating agreement of the transverse-traceless parts of the new metric with quadrupole-approximation waveforms. These data can be used for numerical evolutions, enabling a direct connection between the merger waveforms and the post-Newtonian inspiral waveforms. |
c3b02568-e914-4002-ba1a-ac1743b773b3 | c3b02568-e914-4002-ba1a-ac1743b773b3 | c3b02568-e914-4002-ba1a-ac1743b773b3 | human | null | null | none | abstracts | The $e^+ e^-\to K^+ K^- \pi^+\pi^-$, $K^+ K^- \pi^0\pi^0$ and $K^+ K^-
K^+ K^-$ Cross Sections Measured with Initial-State Radiation | null | We study the processes $e^+ e^-\to K^+ K^- \pi^+\pi^-\gamma$, $K^+K^-\pi^0\pi^0\gamma$ and $K^+ K^- K^+ K^-\gamma$, where the photon is radiated from the initial state. About 34600, 4400 and 2300 fully reconstructed events, respectively, are selected from 232 \invfb of \babar data. The invariant mass of the hadronic final state defines the effective \epem center-of-mass energy, so that the $K^+ K^- \pi^+\pi^-\gamma$ data can be compared with direct measurements of the $e^+ e^-\to K^+K^- \pipi$ reaction; no direct measurements exist for the $e^+ e^-\to K^+ K^- \pi^0\pi^0$ or $\epem\to K^+ K^- K^+ K^-$ reactions. Studying the structure of these events, we find contributions from a number of intermediate states, and we extract their cross sections where possible. In particular, we isolate the contribution from $e^+ e^-\to\phi(1020) f_{0}(980)$ and study its structure near threshold. In the charmonium region, we observe the $J/\psi$ in all three final states and several intermediate states, as well as the $\psi(2S)$ in some modes, and measure the corresponding branching fractions. We see no signal for the Y(4260) and obtain an upper limit of $\BR_{Y(4260)\to\phi\pi^+\pi^-}\cdot\Gamma^{Y}_{ee}<0.4 \ev$ at 90% C.L. |