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9d97578f-3f86-40e2-bd12-751fefe66213 | 9d97578f-3f86-40e2-bd12-751fefe66213 | 9d97578f-3f86-40e2-bd12-751fefe66213 | human | null | null | none | abstracts | Discovery of X-ray emission from the young radio pulsar PSR J1357-6429 | null | We present the first X-ray detection of the very young pulsar PSR J1357-6429
(characteristic age of 7.3 kyr) using data from the XMM-Newton and Chandra
satellites. We find that the spectrum is well described by a power-law plus
blackbody model, with photon index Gamma=1.4 and blackbody temperature kT=160
eV. For the estimated distance of 2.5 kpc, this corresponds to a 2-10 keV
luminosity of about 1.2E+32 erg/s, thus the fraction of the spin-down energy
channeled by PSR J1357-6429 into X-ray emission is one of the lowest observed.
The Chandra data confirm the positional coincidence with the radio pulsar and
allow to set an upper limit of 3E+31 erg/s on the 2-10 keV luminosity of a
compact pulsar wind nebula. We do not detect any pulsed emission from the
source and determine an upper limit of 30% for the modulation amplitude of the
X-ray emission at the radio frequency of the pulsar.
|
e0bf458e-2d27-4a56-aa46-3c8f73190bcd | e0bf458e-2d27-4a56-aa46-3c8f73190bcd | e0bf458e-2d27-4a56-aa46-3c8f73190bcd | human | null | null | none | abstracts | Chandra Observations of Supernova 1987A | null | We have been monitoring Supernova (SN) 1987A with {\it Chandra X-Ray
Observatory} since 1999. We present a review of previous results from our {\it
Chandra} observations, and some preliminary results from new {\it Chandra} data
obtained in 2006 and 2007. High resolution imaging and spectroscopic studies of
SN 1987A with {\it Chandra} reveal that X-ray emission of SN 1987A originates
from the hot gas heated by interaction of the blast wave with the ring-like
dense circumstellar medium (CSM) that was produced by the massive progenitor's
equatorial stellar winds before the SN explosion. The blast wave is now
sweeping through dense CSM all around the inner ring, and thus SN 1987A is
rapidly brightening in soft X-rays. At the age of 20 yr (as of 2007 January),
X-ray luminosity of SN 1987A is $L_{\rm X}$ $\sim$ 2.4 $\times$ 10$^{36}$ ergs
s$^{-1}$ in the 0.5$-$10 keV band. X-ray emission is described by two-component
plane shock model with electron temperatures of $kT$ $\sim$ 0.3 and 2 keV. As
the shock front interacts with dense CSM all around the inner ring, the X-ray
remnant is now expanding at a much slower rate of $v$ $\sim$ 1400 km s$^{-1}$
than it was until 2004 ($v$ $\sim$ 6000 km s$^{-1}$).
|
78a18c37-a480-4cb4-ab85-9c674aedbbe5 | 78a18c37-a480-4cb4-ab85-9c674aedbbe5 | 78a18c37-a480-4cb4-ab85-9c674aedbbe5 | human | null | null | none | abstracts | Geometric Complexity Theory V: On deciding nonvanishing of a generalized
Littlewood-Richardson coefficient | null | This article has been withdrawn because it has been merged with the earlier
article GCT3 (arXiv: CS/0501076 [cs.CC]) in the series. The merged article is
now available as:
Geometric Complexity Theory III: on deciding nonvanishing of a
Littlewood-Richardson Coefficient, Journal of Algebraic Combinatorics, vol. 36,
issue 1, 2012, pp. 103-110. (Authors: Ketan Mulmuley, Hari Narayanan and Milind
Sohoni)
The new article in this GCT5 slot in the series is:
Geometric Complexity Theory V: Equivalence between blackbox derandomization
of polynomial identity testing and derandomization of Noether's Normalization
Lemma, in the Proceedings of FOCS 2012 (abstract), arXiv:1209.5993 [cs.CC]
(full version) (Author: Ketan Mulmuley)
|
d58157b5-89e1-4965-808d-1df408e537e0 | d58157b5-89e1-4965-808d-1df408e537e0 | d58157b5-89e1-4965-808d-1df408e537e0 | human | null | null | none | abstracts | Three Particle Correlations from STAR | null | Two-particle correlations have shown modification to the away-side shape in
central Au+Au collisions relative to $pp$, d+Au and peripheral Au+Au
collisions. Different scenarios can explain this modification including: large
angle gluon radiation, jets deflected by transverse flow, path length dependent
energy loss, Cerenkov gluon radiation of fast moving particles, and conical
flow generated by hydrodynamic Mach-cone shock-waves. Three-particle
correlations have the power to distinguish the scenarios with conical emission,
conical flow and Cerenkov radiation, from other scenarios. In addition, the
dependence of the observed shapes on the $p_T$ of the associated particles can
be used to distinguish conical emission from a sonic boom (Mach-cone) and from
QCD-Cerenkov radiation. We present results from STAR on 3-particle azimuthal
correlations for a high $p_T$ trigger particle with two softer particles.
Results are shown for $pp$, d+Au and high statistics Au+Au collisions at
$\sqrt{s_{NN}}$=200 GeV. An important aspect of the analysis is the subtraction
of combinatorial backgrounds. Systematic uncertainties due to this subtraction
and the flow harmonics v2 and v4 are investigated in detail. The implications
of the results for the presence or absence of conical flow from Mach-cones are
discussed.
|
a879642d-b2e5-44c0-bcb1-ff9c96bad103 | a879642d-b2e5-44c0-bcb1-ff9c96bad103 | a879642d-b2e5-44c0-bcb1-ff9c96bad103 | human | null | null | none | abstracts | The Return of a Static Universe and the End of Cosmology | null | We demonstrate that as we extrapolate the current $\Lambda$CDM universe
forward in time, all evidence of the Hubble expansion will disappear, so that
observers in our "island universe" will be fundamentally incapable of
determining the true nature of the universe, including the existence of the
highly dominant vacuum energy, the existence of the CMB, and the primordial
origin of light elements. With these pillars of the modern Big Bang gone, this
epoch will mark the end of cosmology and the return of a static universe. In
this sense, the coordinate system appropriate for future observers will perhaps
fittingly resemble the static coordinate system in which the de Sitter universe
was first presented.
|
40745a77-eb17-4625-96db-6b7175bf8271 | 40745a77-eb17-4625-96db-6b7175bf8271 | 40745a77-eb17-4625-96db-6b7175bf8271 | human | null | null | none | abstracts | Magnetohydrodynamic Rebound Shocks of Supernovae | null | We construct magnetohydrodynamic (MHD) similarity rebound shocks joining
`quasi-static' asymptotic solutions around the central degenerate core to
explore an MHD model for the evolution of random magnetic field in supernova
explosions. This provides a theoretical basis for further studying synchrotron
diagnostics, MHD shock acceleration of cosmic rays, and the nature of intense
magnetic field in compact objects. The magnetic field strength in space
approaches a limiting ratio, that is comparable to the ratio of the ejecta mass
driven out versus the progenitor mass, during this self-similar rebound MHD
shock evolution. The intense magnetic field of the remnant compact star as
compared to that of the progenitor star is mainly attributed to both the
gravitational core collapse and the radial distribution of magnetic field.
|
50c20ceb-fbc6-436f-a8e2-5d5667814d97 | 50c20ceb-fbc6-436f-a8e2-5d5667814d97 | 50c20ceb-fbc6-436f-a8e2-5d5667814d97 | human | null | null | none | abstracts | Are There Mach Cones in Heavy Ion Collisions? Three-Particle
Correlations from STAR | null | We present results from STAR on 3-particle azimuthal correlations for a
$3<p_T<4$ GeV/c trigger particle with two softer $1<p_T<2$ GeV/c particles.
Results are shown for pp, d+Au and high statistics Au+Au collisions at
$\sqrt{s_{NN}}=200 GeV$. We observe a 3-particle correlation in central Au+Au
collisions which may indicate the presence of conical emission. In addition,
the dependence of the observed signal angular position on the $p_T$ of the
associated particles can be used to distinguish conical flow from simple
QCD-\v{C}erenkov radiation. An important aspect of the analysis is the
subtraction of combinatorial backgrounds. Systematic uncertainties due to this
subtraction and the flow harmonics $v_2$ and $v_4$ are investigated in detail.
|
798b451f-518a-49b9-9f47-910fafe66fa0 | 798b451f-518a-49b9-9f47-910fafe66fa0 | 798b451f-518a-49b9-9f47-910fafe66fa0 | human | null | null | none | abstracts | Correlated modulation between the redshifted Fe K alpha line and the
continuum emission in NGC 3783 | null | It has been suggested that X-ray observations of rapidly variable Seyfert
galaxies may hold the key to probe the gas orbital motions in the innermost
regions of accretion discs around black holes and, thus, trace flow patterns
under the effect of the hole strong gravitational field. We explore this
possibility analizing XMM-Newton observations of the seyfert 1 galaxy NGC 3783.
A detiled time-resolved spectral analysis is performed down to the shortest
possible time-scales (few ks) using "excess maps" and cross-correlating light
curves in different energy bands. In addition to a constant core of the Fe K
alpha line, we detected a variable and redshifted Fe K alpha emission feature
between 5.3-6.1 keV. The line exhibits a modulation on a time-scale of 27 ks
that is similar to and in phase with a modulation of the 0.3-10 keV source
continuum. The time-scale of the correlated variability of the redshifted Fe
line and continuum agrees with the local dynamical time-scale of the accretion
disc at 10 r_g around a black hole of 10^7 M_sun. Given the shape of the
redshfted line emission and the overall X-ray variability pattern, the line is
likely to arise from the relativistic region near the black hole.
|
fcc94f78-d81b-4871-8439-f8f6b7afeb1a | fcc94f78-d81b-4871-8439-f8f6b7afeb1a | fcc94f78-d81b-4871-8439-f8f6b7afeb1a | human | null | null | none | abstracts | Isotopic Effects in Nuclear Reactions at Relativistic Energies | null | A systematic study of isotopic effects in the break-up of projectile
spectators at relativistic energies has been performed at the GSI laboratory
with the ALADiN spectrometer coupled to the LAND neutron detector. Besides a
primary beam of 124Sn, also secondary beams of 124La and 107Sn produced at the
FRS fragment separator have been used in order to extend the range of isotopic
compositions. The gross properties of projectile fragmentation are very similar
for all the studied systems but specific isotopic effects have been observed in
both neutron and charged particle production. The breakup temperatures obtained
from the double ratios of isotopic yields have been extracted and compared with
the limiting-temperature expectation.
|
6bcdaf53-2045-4c4e-b032-7f823c620ae3 | 6bcdaf53-2045-4c4e-b032-7f823c620ae3 | 6bcdaf53-2045-4c4e-b032-7f823c620ae3 | human | null | null | none | abstracts | Einstein vs Maxwell: Is gravitation a curvature of space, a field in
flat space, or both? | null | Starting with a field theoretic approach in Minkowski space, the
gravitational energy momentum tensor is derived from the Einstein equations in
a straightforward manner. This allows to present them as {\it acceleration
tensor} = const. $\times$ {\it total energy momentum tensor}. For flat space
cosmology the gravitational energy is negative and cancels the material energy.
In the relativistic theory of gravitation a bimetric coupling between the
Riemann and Minkowski metrics breaks general coordinate invariance. The case of
a positive cosmological constant is considered. A singularity free version of
the Schwarzschild black hole is solved analytically. In the interior the
components of the metric tensor quickly die out, but do not change sign,
leaving the role of time as usual. For cosmology the $\Lambda$CDM model is
covered, while there appears a form of inflation at early times. Here both the
total energy and the zero point energy vanish.
|
0c82de12-1e7c-478f-a613-401c8cfea68a | 0c82de12-1e7c-478f-a613-401c8cfea68a | 0c82de12-1e7c-478f-a613-401c8cfea68a | human | null | null | none | abstracts | Two new basaltic asteroids in the Outer Main Belt? | null | The identification of basaltic asteroids in the asteroid Main Belt and the
description of their surface mineralogy is necessary to understand the
diversity in the collection of basaltic meteorites. Basaltic asteroids can be
identified from their visible reflectance spectra and are classified as V-type
in the usual taxonomies. In this work, we report visible spectroscopic
observations of two candidate V-type asteroids, (7472) Kumakiri and (10537)
1991 RY16, located in the outer Main Belt (a > 2.85 UA). These candidate have
been previously identified by Roig and Gil-Hutton (2006, Icarus 183, 411) using
the Sloan Digital Sky Survey colors. The spectroscopic observations have been
obtained at the Calar Alto Observatory, Spain, during observational runs in
November and December 2006. The spectra of these two asteroids show the steep
slope shortwards of 0.70 microns and the deep absorption feature longwards of
0.75 microns that are characteristic of V-type asteroids. However, the presence
of a shallow but conspicuous absorption band around 0.65 microns opens some
questions about the actual mineralogy of these two asteroids. Such band has
never been observed before in basaltic asteroids with the intensity we detected
it. We discuss the possibility for this shallow absorption feature to be caused
by the presence of chromium on the asteroid surface. Our results indicate that,
together with (1459) Magnya, asteroids (7472) Kumakiri and (10537) 1991 RY16
may be the only traces of basaltic material found up to now in the outer Main
Belt.
|
d029d07a-0411-4a25-ad4c-aca9eb80d290 | d029d07a-0411-4a25-ad4c-aca9eb80d290 | d029d07a-0411-4a25-ad4c-aca9eb80d290 | human | null | null | none | abstracts | New algebraic aspects of perturbative and non-perturbative Quantum Field
Theory | null | In this expository article we review recent advances in our understanding of
the combinatorial and algebraic structure of perturbation theory in terms of
Feynman graphs, and Dyson-Schwinger equations. Starting from Lie and Hopf
algebras of Feynman graphs, perturbative renormalization is rephrased
algebraically. The Hochschild cohomology of these Hopf algebras leads the way
to Slavnov-Taylor identities and Dyson-Schwinger equations. We discuss recent
progress in solving simple Dyson-Schwinger equations in the high energy sector
using the algebraic machinery. Finally there is a short account on a relation
to algebraic geometry and number theory: understanding Feynman integrals as
periods of mixed (Tate) motives.
|
f4c2dec8-e5cb-4f80-949e-9cc7bc741831 | f4c2dec8-e5cb-4f80-949e-9cc7bc741831 | f4c2dec8-e5cb-4f80-949e-9cc7bc741831 | human | null | null | none | abstracts | The Determination of the Helicity of $W'$ Boson Couplings at the LHC | null | Apart from its mass and width, the most important property of a new charged
gauge boson, $W'$, is the helicity of its couplings to the SM fermions. Such
particles are expected to exist in many extensions of the Standard Model. In
this paper we explore the capability of the LHC to determine the $W'$ coupling
helicity at low integrated luminosities in the $\ell +E_T^{miss}$ discovery
channel. We find that measurements of the transverse mass distribution,
reconstructed from this final state in the $W-W'$ interference region, provides
the best determination of this quantity. To make such measurements requires
integrated luminosities of $\sim 10(60) fb^{-1}$ assuming $M_{W'}=1.5(2.5)$ TeV
and provided that the $W'$ couplings have Standard Model magnitude. This
helicity determination can be further strengthened by the use of various
discovery channel leptonic asymmetries, also measured in the same interference
regime, but with higher integrated luminosities.
|
99c580f2-2e1c-461e-b36f-1835893df6ae | 99c580f2-2e1c-461e-b36f-1835893df6ae | 99c580f2-2e1c-461e-b36f-1835893df6ae | human | null | null | none | abstracts | Interface dynamics of microscopic cavities in water | null | An analytical description of the interface motion of a collapsing
nanometer-sized spherical cavity in water is presented by a modification of the
Rayleigh-Plesset equation in conjunction with explicit solvent molecular
dynamics simulations. Quantitative agreement is found between the two
approaches for the time-dependent cavity radius $R(t)$ at different solvent
conditions while in the continuum picture the solvent viscosity has to be
corrected for curvature effects. The typical magnitude of the interface or
collapse velocity is found to be given by the ratio of surface tension and
fluid viscosity, $v\simeq\gamma/\eta$, while the curvature correction
accelerates collapse dynamics on length scales below the equilibrium crossover
scales ($\sim$1nm). The study offers a starting point for an efficient implicit
modeling of water dynamics in aqueous nanoassembly and protein systems in
nonequilibrium.
|
db5a7166-2fd1-4428-856b-6f0d6192e608 | db5a7166-2fd1-4428-856b-6f0d6192e608 | db5a7166-2fd1-4428-856b-6f0d6192e608 | human | null | null | none | abstracts | Superconducting states of the quasi-2D Holstein model: Effects of vertex
and non-local corrections | null | I investigate superconducting states in a quasi-2D Holstein model using the
dynamical cluster approximation (DCA). The effects of spatial fluctuations
(non-local corrections) are examined and approximations neglecting and
incorporating lowest-order vertex corrections are computed. The approximation
is expected to be valid for electron-phonon couplings of less than the
bandwidth. The phase diagram and superconducting order parameter are
calculated. Effects which can only be attributed to theories beyond
Migdal--Eliashberg theory are present. In particular, the order parameter shows
momentum dependence on the Fermi-surface with a modulated form and s-wave order
is suppressed at half-filling. The results are discussed in relation to
Hohenberg's theorem and the BCS approximation.
|
630a22dc-3292-41f7-bacb-1e65983a14e6 | 630a22dc-3292-41f7-bacb-1e65983a14e6 | 630a22dc-3292-41f7-bacb-1e65983a14e6 | human | null | null | none | abstracts | Renormalized quasiparticles in antiferromagnetic states of the Hubbard
model | null | We analyze the properties of the quasiparticle excitations of metallic
antiferromagnetic states in a strongly correlated electron system. The study is
based on dynamical mean field theory (DMFT) for the infinite dimensional
Hubbard model with antiferromagnetic symmetry breaking. Self-consistent
solutions of the DMFT equations are calculated using the numerical
renormalization group (NRG). The low energy behavior in these results is then
analyzed in terms of renormalized quasiparticles. The parameters for these
quasiparticles are calculated directly from the NRG derived self-energy, and
also from the low energy fixed point of the effective impurity. They are found
to be in good agreement. We show that the main low energy features of the $\bf
k$-resolved spectral density can be understood in terms of the quasiparticle
picture. We also find that Luttinger's theorem is satisfied for the total
electron number in the doped antiferromagnetic state.
|
2b6939d5-7a99-45cb-95df-d925f89de8d6 | 2b6939d5-7a99-45cb-95df-d925f89de8d6 | 2b6939d5-7a99-45cb-95df-d925f89de8d6 | human | null | null | none | abstracts | One-loop MHV Rules and Pure Yang-Mills | null | It has been known for some time that the standard MHV diagram formulation of
perturbative Yang-Mills theory is incomplete, as it misses rational terms in
one-loop scattering amplitudes of pure Yang-Mills. We propose that certain
Lorentz violating counterterms, when expressed in the field variables which
give rise to standard MHV vertices, produce precisely these missing terms.
These counterterms appear when Yang-Mills is treated with a regulator,
introduced by Thorn and collaborators, which arises in worldsheet formulations
of Yang-Mills theory in the lightcone gauge. As an illustration of our
proposal, we show that a simple one-loop, two-point counterterm is the
generating function for the infinite sequence of one-loop, all-plus helicity
amplitudes in pure Yang-Mills, in complete agreement with known expressions.
|
016020dc-f888-4b5a-b2bc-b55a8da6fe93 | 016020dc-f888-4b5a-b2bc-b55a8da6fe93 | 016020dc-f888-4b5a-b2bc-b55a8da6fe93 | human | null | null | none | abstracts | Non-perturbative conserving approximations and Luttinger's sum rule | null | Weak-coupling conserving approximations can be constructed by truncations of
the Luttinger-Ward functional and are well known as thermodynamically
consistent approaches which respect macroscopic conservation laws as well as
certain sum rules at zero temperature. These properties can also be shown for
variational approximations that are generated within the framework of the
self-energy-functional theory without a truncation of the diagram series.
Luttinger's sum rule represents an exception. We analyze the conditions under
which the sum rule holds within a non-perturbative conserving approximation.
Numerical examples are given for a simple but non-trivial dynamical two-site
approximation. The validity of the sum rule for finite Hubbard clusters and the
consequences for cluster extensions of the dynamical mean-field theory are
discussed.
|
a6860bb7-a658-4a6e-8819-d9322182d887 | a6860bb7-a658-4a6e-8819-d9322182d887 | a6860bb7-a658-4a6e-8819-d9322182d887 | human | null | null | none | abstracts | Entanglement of Subspaces and Error Correcting Codes | null | We introduce the notion of entanglement of subspaces as a measure that
quantify the entanglement of bipartite states in a randomly selected subspace.
We discuss its properties and in particular we show that for maximally
entangled subspaces it is additive. Furthermore, we show that maximally
entangled subspaces can play an important role in the study of quantum error
correction codes. We discuss both degenerate and non-degenerate codes and show
that the subspace spanned by the logical codewords of a non-degenerate code is
a 2k-totally (maximally) entangled subspace. As for non-degenerate codes, we
provide a mathematical definition in terms of subspaces and, as an example, we
analyze Shor's nine qubits code in terms of 22 mutually orthogonal subspaces.
|
3bb6b5e6-10f9-4d34-ab88-21ac7ff28c53 | 3bb6b5e6-10f9-4d34-ab88-21ac7ff28c53 | 3bb6b5e6-10f9-4d34-ab88-21ac7ff28c53 | human | null | null | none | abstracts | The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds VIII.
Serpens Observed with MIPS | null | We present maps of 1.5 square degrees of the Serpens dark cloud at 24, 70,
and 160\micron observed with the Spitzer Space Telescope MIPS Camera. More than
2400 compact sources have been extracted at 24um, nearly 100 at 70um, and 4 at
160um. We estimate completeness limits for our 24um survey from Monte Carlo
tests with artificial sources inserted into the Spitzer maps. We compare source
counts, colors, and magnitudes in the Serpens cloud to two reference data sets,
a 0.50 deg^2 set on a low-extinction region near the dark cloud, and a 5.3
deg^2 subset of the SWIRE ELAIS N1 data that was processed through our
pipeline. These results show that there is an easily identifiable population of
young stellar object candidates in the Serpens Cloud that is not present in
either of the reference data sets. We also show a comparison of visual
extinction and cool dust emission illustrating a close correlation between the
two, and find that the most embedded YSO candidates are located in the areas of
highest visual extinction.
|
b635c24a-5fb4-48f0-aa24-65ce813eaa6b | b635c24a-5fb4-48f0-aa24-65ce813eaa6b | b635c24a-5fb4-48f0-aa24-65ce813eaa6b | human | null | null | none | abstracts | Unravelling the sbottom spin at the CERN LHC | null | Establishing that a signal of new physics is undoubtly supersymmetric
requires not only the discovery of the supersymmetric partners but also probing
their spins and couplings. We show that the sbottom spin can be probed at the
CERN Large Hadron Collider using only angular correlations in sbottom pair
production with subsequent decay of sbottoms into bottom quark plus the
lightest neutralino, which allow us to distinguish a universal extra
dimensional interpretation with a fermionic heavy bottom quark from
supersymmetry with a bosonic bottom squark. We demonstrate that this channel
provides a clear indication of the sbottom spin provided the sbottom production
rate and branching ratio into bottom quark plus the lightest neutralino are
sufficiently large to have a clear signal above Standard Model backgrounds.
|
abeec449-9e17-4660-9813-9ff77735ab4f | abeec449-9e17-4660-9813-9ff77735ab4f | abeec449-9e17-4660-9813-9ff77735ab4f | human | null | null | none | abstracts | Modeling the three-point correlation function | null | We present new predictions for the galaxy three-point correlation function
(3PCF) using high-resolution dissipationless cosmological simulations of a flat
LCDM Universe which resolve galaxy-size halos and subhalos. We create realistic
mock galaxy catalogs by assigning luminosities and colors to dark matter halos
and subhalos, and we measure the reduced 3PCF as a function of luminosity and
color in both real and redshift space. As galaxy luminosity and color are
varied, we find small differences in the amplitude and shape dependence of the
reduced 3PCF, at a level qualitatively consistent with recent measurements from
the SDSS and 2dFGRS. We confirm that discrepancies between previous 3PCF
measurements can be explained in part by differences in binning choices. We
explore the degree to which a simple local bias model can fit the simulated
3PCF. The agreement between the model predictions and galaxy 3PCF measurements
lends further credence to the straightforward association of galaxies with CDM
halos and subhalos.
|
9bb937f0-f51e-4275-90e4-dc189fa1622c | 9bb937f0-f51e-4275-90e4-dc189fa1622c | 9bb937f0-f51e-4275-90e4-dc189fa1622c | human | null | null | none | abstracts | Multi-spectral Observations of Lunar Occultations: I. Resolving The Dust
Shell Around AFGL 5440 | null | We present observations and modeling of a lunar occultation of the
dust-enshrouded carbon star AFGL 5440. The observations were made over a
continuous range of wavelengths from 1 - 4um with a high-speed
spectrophotometer designed expressly for this purpose. We find that the
occultation fringes cannot be fit by any single-size model. We use the DUSTY
radiative transfer code to model a circumstellar shell and fit both the
observed occultation light curves and the spectral energy distribution
described in the literature. We find a strong constraint on the inner radius of
the dust shell, Tmax = 950 K +/- 50K, and optical depth at 5um of 0.5 +/- 0.1.
The observations are best fit by models with a density gradient of r^-2 or the
gradient derived by Ivezic & Elitzur for a radiatively driven hydrodynamic
outflow. Our models cannot fit the observed IRAS 60um flux without assuming a
substantial abundance of graphite or by assuming a substantially higher
mass-loss rate in the past.
|
93c917c5-e902-498f-94ad-828e6e5342ab | 93c917c5-e902-498f-94ad-828e6e5342ab | 93c917c5-e902-498f-94ad-828e6e5342ab | human | null | null | none | abstracts | Orbifold cohomology of abelian symplectic reductions and the case of
weighted projective spaces | null | These notes accompany a lecture about the topology of symplectic (and other)
quotients. The aim is two-fold: first to advertise the ease of computation in
the symplectic category; and second to give an account of some new computations
for weighted projective spaces. We start with a brief exposition of how
orbifolds arise in the symplectic category, and discuss the techniques used to
understand their topology. We then show how these results can be used to
compute the Chen-Ruan orbifold cohomology ring of abelian symplectic
reductions. We conclude by comparing the several rings associated to a weighted
projective space. We make these computations directly, avoiding any mention of
a stacky fan or of a labeled moment polytope.
|
18d5cd73-8cb8-4380-b4b3-a0c7890b048a | 18d5cd73-8cb8-4380-b4b3-a0c7890b048a | 18d5cd73-8cb8-4380-b4b3-a0c7890b048a | human | null | null | none | abstracts | Formation and Collisional Evolution of Kuiper Belt Objects | null | This chapter summarizes analytic theory and numerical calculations for the
formation and collisional evolution of KBOs at 20--150 AU. We describe the main
predictions of a baseline self-stirring model and show how dynamical
perturbations from a stellar flyby or stirring by a giant planet modify the
evolution. Although robust comparisons between observations and theory require
better KBO statistics and more comprehensive calculations, the data are broadly
consistent with KBO formation in a massive disk followed by substantial
collisional grinding and dynamical ejection. However, there are important
problems reconciling the results of coagulation and dynamical calculations.
Contrasting our current understanding of the evolution of KBOs and asteroids
suggests that additional observational constraints, such as the identification
of more dynamical families of KBOs (like the 2003 EL61 family), would provide
additional information on the relative roles of collisional grinding and
dynamical ejection in the Kuiper Belt. The uncertainties also motivate
calculations that combine collisional and dynamical evolution, a `unified'
calculation that should give us a better picture of KBO formation and
evolution.
|
c54cd1ae-a63e-49c6-8600-e7baf5755041 | c54cd1ae-a63e-49c6-8600-e7baf5755041 | c54cd1ae-a63e-49c6-8600-e7baf5755041 | human | null | null | none | abstracts | Stringy Instantons at Orbifold Singularities | null | We study the effects produced by D-brane instantons on the holomorphic
quantities of a D-brane gauge theory at an orbifold singularity. These effects
are not limited to reproducing the well known contributions of the gauge theory
instantons but also generate extra terms in the superpotential or the
prepotential. On these brane instantons there are some neutral fermionic
zero-modes in addition to the ones expected from broken supertranslations. They
are crucial in correctly reproducing effects which are dual to gauge theory
instantons, but they may make some other interesting contributions vanish. We
analyze how orientifold projections can remove these zero-modes and thus allow
for new superpotential terms. These terms contribute to the dynamics of the
effective gauge theory, for instance in the stabilization of runaway
directions.
|
91ffdb6a-58e2-4fe7-9719-7354cf122c14 | 91ffdb6a-58e2-4fe7-9719-7354cf122c14 | 91ffdb6a-58e2-4fe7-9719-7354cf122c14 | human | null | null | none | abstracts | REM near-IR and optical multiband observations of PKS2155-304 in 2005 | null | Spectral variability is the main tool for constraining emission models of BL
Lac objects. By means of systematic observations of the BL Lac prototype PKS
2155-304 in the infrared-optical band, we explore variability on the scales of
months, days and hours. We made our observations with the robotic 60 cm
telescope REM located at La Silla, Chile. VRIJHK filters were used. PKS
2155-304 was observed from May to December 2005. The wavelength interval
explored, the total number of photometric points and the short integration time
render our photometry substantially superior to previous ones for this source.
On the basis of the intensity and colour we distinguish three different states
of the source, each of duration of months, which include all those described in
the literature. In particular, we report the highest state ever detected in the
H band. The source varied by a factor of 4 in this band, much more than in the
V band (a factor ~2). The source softened with increasing intensity, contrary
to the general pattern observed in the UV-X-ray bands. On five nights of
November we had nearly continuous monitoring for 2-3 hours. A variability
episode with a time scale of ~24 h is well documented, a much more rapid flare
with t=1-2 h, is also apparent, but is supported by relatively few points.
|
7bf81ae2-2794-422e-8a1c-fd231ecd172c | 7bf81ae2-2794-422e-8a1c-fd231ecd172c | 7bf81ae2-2794-422e-8a1c-fd231ecd172c | human | null | null | none | abstracts | Supernova Polarization and the Type IIn Classification | null | While the members of the Type IIn category of supernovae are united by the
presence of strong multicomponent Balmer emission lines in their spectra, they
are quite heterogeneous with respect to other properties such as Balmer line
profiles, light curves, strength of radio emission, and intrinsic brightness.
We are now beginning to see variety among SNe IIn in their polarimetric
characteristics as well, some but not all of which may be due to inclination
angle effects. The increasing number of known "hybrid" SNe with IIn-like
emission lines suggests that circumstellar material may be more common around
all types of SNe than previously thought. Investigation of the correlations
between spectropolarimetric signatures and other IIn attributes will help us
address the question of classification of "interacting SNe" and the possibility
of distinguishing different groups within the diverse IIn subclass.
|
49dccba9-0f4c-40db-8d75-64197114e7c7 | 49dccba9-0f4c-40db-8d75-64197114e7c7 | 49dccba9-0f4c-40db-8d75-64197114e7c7 | human | null | null | none | abstracts | Near-Infrared Spectra of the Black Hole X-Ray Binary, A0620-00 | null | We present broadband NIR spectra of A0620-00 obtained with SpeX on the IRTF.
The spectrum is characterized by a blue continuum on which are superimposed
broad emission lines of HI and HeII and a host of narrower absorption lines of
neutral metals and molecules. Spectral type standard star spectra scaled to the
dereddened spectrum of A0620-00 in K exceed the A0620-00 spectrum in J and H
for all stars of spectral type K7V or earlier, demonstrating that the donor
star, unless later than K7V, cannot be the sole NIR flux source in A0620-00. In
addition, the atomic absorption lines in the K3V spectrum are too weak with
respect to those of A0620-00 even at 100% donor star contribution, restricting
the spectral type of the donor star in A0620-00 to later than K3V. Comparison
of the A0620-00 spectrum to scaled K star spectra indicates that the CO
absorption features are significantly weaker in A0620-00 than in field dwarf
stars. Fits of scaled model spectra of a Roche lobe-filling donor star to the
spectrum of A0620-00 show that the best match to the CO absorption lines is
obtained when the C abundance is reduced to [C/H] = -1.5. The donor star
contribution in the H waveband is determined to be 82+-2%. Combined with
previous published results from Froning & Robinson (2001) and Marsh et al.
(1994), this gives a precise mass for the black hole in A0620-00 of M_BH =
9.7+-0.6 M_solar.
|
28a15bc2-3bae-44c3-887c-9c1c0b649f81 | 28a15bc2-3bae-44c3-887c-9c1c0b649f81 | 28a15bc2-3bae-44c3-887c-9c1c0b649f81 | human | null | null | none | abstracts | Automated Generation of Layout and Control for Quantum Circuits | null | We present a computer-aided design flow for quantum circuits, complete with
automatic layout and control logic extraction. To motivate automated layout for
quantum circuits, we investigate grid-based layouts and show a performance
variance of four times as we vary grid structure and initial qubit placement.
We then propose two polynomial-time design heuristics: a greedy algorithm
suitable for small, congestion-free quantum circuits and a dataflow-based
analysis approach to placement and routing with implicit initial placement of
qubits. Finally, we show that our dataflow-based heuristic generates better
layouts than the state-of-the-art automated grid-based layout and scheduling
mechanism in terms of latency and potential pipelinability, but at the cost of
some area.
|
1461a7a8-efe4-4e9e-b55b-3dc720e571a8 | 1461a7a8-efe4-4e9e-b55b-3dc720e571a8 | 1461a7a8-efe4-4e9e-b55b-3dc720e571a8 | human | null | null | none | abstracts | Modeling the Spectral Energy Distribution and Variability of 3C 66A
during the WEBT campaign of 2003 -- 2004 | null | The BL Lac object 3C 66A was observed in an extensive multiwavelength
monitoring campaign from July 2003 till April 2004. The spectral energy
distribution (SED) was measured over the entire electromagnetic spectrum, with
flux measurements from radio to X-ray frequencies and upper limits in the very
high energy (VHE) gamma-ray regime. Here, we use a time-dependent leptonic jet
model to reproduce the SED and optical spectral variability observed during our
multiwavelength campaign. Our model simulations could successfully reproduce
the observed SED and optical light curves and predict an intrinsic cutoff value
for the VHE gamma-ray emission at ~ 4 GeV. The effect of the optical depth due
to the intergalactic infrared background radiation (IIBR) on the peak of the
high-energy component of 3C 66A was found to be negligible. Also, the presence
of a broad line region (BLR) in the case of 3C 66A may play an important role
in the emission of gamma-ray photons when the emission region is very close to
the central engine, but further out, the production mechanism of hard X-ray and
gamma-ray photons becomes rapidly dominated by synchrotron self-Compton
emission. We further discuss the possibility of an observable X-ray spectral
variability pattern. The simulated results do not predict observable hysteresis
patterns in the optical or soft X-ray regimes for major flares on multi-day
time scales.
|
e53762cb-25e7-47c1-abda-1b50ed05eeef | e53762cb-25e7-47c1-abda-1b50ed05eeef | e53762cb-25e7-47c1-abda-1b50ed05eeef | human | null | null | none | abstracts | The HARPS search for southern extra-solar planets. X. A m sin i = 11
Mearth planet around the nearby spotted M dwarf GJ 674 | null | Context: How planet properties depend on stellar mass is a key diagnostic of
planetary formation mechanisms. Aims: This motivates planet searches around
stars which are significantly more massive or less massive than the Sun, and in
particular our radial velocity search for planets around very-low mass stars.
Methods: As part of that program, we obtained measurements of GJ 674, an M2.5
dwarf at d=4.5 pc, which have a dispersion much in excess of their internal
errors. An intensive observing campaign demonstrates that the excess dispersion
is due to two superimposed coherent signals, with periods of 4.69 and 35 days.
Results: These data are well described by a 2-planet Keplerian model where each
planet has a ~11 Mearth minimum mass. A careful analysis of the (low level)
magnetic activity of GJ 674 however demonstrates that the 35-day period
coincides with the stellar rotation period. This signal therefore originates in
a spot inhomogeneity modulated by stellar rotation. The 4.69-day signal on the
other hand is caused by a bona-fide planet, GJ 674b. Conclusion: Its detection
adds to the growing number of Neptune-mass planets around M-dwarfs, and
reinforces the emerging conclusion that this mass domain is much more populated
than the jovian mass range. We discuss the metallicity distributions of M dwarf
with and without planets and find a low 11% probability that they are drawn
from the same parent distribution. Moreover, we find tentative evidence that
the host star metallicity correlates with the total mass of their planetary
system.
|
a4315e0a-d969-41e2-bd13-114b80d39c37 | a4315e0a-d969-41e2-bd13-114b80d39c37 | a4315e0a-d969-41e2-bd13-114b80d39c37 | human | null | null | none | abstracts | A Comparison between Anomalous 6-cm H$_2$CO Absorption and CO(1-0)
Emission in the L1204/S140 | null | We report observations of the dust cloud L1204 with the Onsala 25-m telescope
in the 6 cm (1$_{11}-1_{10}$) transition of \htco. The observed region includes
the
S140 H${\alpha}$ arc. This spectral line is seen here in absorption against
the cosmic microwave background, indicating the presence of widespread warm
molecular gas at intermediate densities. Overall, the distributions of H$_2$CO
and CO (taken from the literature) are fairly similar, though significant
differences exist at small scales. Most notably, while the CO peak is nearly
coincident with the S140 H${\alpha}$ arc, the maximum H$_2$CO absorption is
clearly separated from it by a full 10$'$ beam ($\sim$ 3 pc). We argue that
these differences result from differing abundances and excitation requirements.
The CO(1-0) line is more optically thick and more biased towards warm gas than
the H$_2$CO 6 cm line. On the other hand, formaldehyde is more easily
photodissociated and is, therefore, a poorer tracer of the molecular gas
located immediately behind Photon Dominated Regions.
|
c6b0d237-f40d-48ca-9451-83adde03d9f9 | c6b0d237-f40d-48ca-9451-83adde03d9f9 | c6b0d237-f40d-48ca-9451-83adde03d9f9 | human | null | null | none | abstracts | Mapping radii of metric spaces | null | It is known that every closed curve of length \leq 4 in R^n (n>0) can be
surrounded by a sphere of radius 1, and that this is the best bound. Letting S
denote the circle of circumference 4, with the arc-length metric, we here
express this fact by saying that the "mapping radius" of S in R^n is 1.
Tools are developed for estimating the mapping radius of a metric space X in
a metric space Y. In particular, it is shown that for X a bounded metric space,
the supremum of the mapping radii of X in all convex subsets of normed metric
spaces is equal to the infimum of the sup norms of all convex linear
combinations of the functions d(x,-): X --> R (x\in X).
Several explicit mapping radii are calculated, and open questions noted.
|
7796ab62-b858-47d8-96c5-481817a7ca71 | 7796ab62-b858-47d8-96c5-481817a7ca71 | 7796ab62-b858-47d8-96c5-481817a7ca71 | human | null | null | none | abstracts | HI velocity dispersion in NGC 1058 | null | We present excellent resolution and high sensitivity Very Large Array (VLA)
observations of the 21cm HI line emission from the face-on galaxy NGC 1058,
providing the first reliable study of the HI profile shapes throughout the
entire disk of an external galaxy. Our observations show an intriguing picture
of the interstellar medium; throughout this galaxy velocity-- dispersions range
between 4 to 15 km/sec but are not correlated with star formation, stars or the
gaseous spiral arms. The velocity dispersions decrease with radius, but this
global trend has a large scatter as there are several isolated, resolved
regions of high dispersion. The decline of star light with radius is much
steeper than that of the velocity dispersions or that of the energy in the gas
motions.
|
a97afc6f-2dac-414d-bd39-43b170a8a5ea | a97afc6f-2dac-414d-bd39-43b170a8a5ea | a97afc6f-2dac-414d-bd39-43b170a8a5ea | human | null | null | none | abstracts | Common Envelope Evolution Redux | null | Common envelopes form in dynamical time scale mass exchange, when the
envelope of a donor star engulfs a much denser companion, and the core of the
donor plus the dense companion star spiral inward through this dissipative
envelope. As conceived by Paczynski and Ostriker, this process must be
responsible for the creation of short-period binaries with degenerate
components, and, indeed, it has proven capable of accounting for short-period
binaries containing one white dwarf component. However, attempts to reconstruct
the evolutionary histories of close double white dwarfs have proven more
problematic, and point to the need for enhanced systemic mass loss, either
during the close of the first, slow episode of mass transfer that produced the
first white dwarf, or during the detached phase preceding the final, common
envelope episode. The survival of long-period interacting binaries with massive
white dwarfs, such as the recurrent novae T CrB and RS Oph, also presents
interpretative difficulties for simple energetic treatments of common envelope
evolution. Their existence implies that major terms are missing from usual
formulations of the energy budget for common envelope evolution. The most
plausible missing energy term is the energy released by recombination in the
common envelope, and, indeed, a simple reformulation the energy budget
explicitly including recombination resolves this issue.
|
6a164ec9-8fa2-4fc1-9214-2bf11baceb1c | 6a164ec9-8fa2-4fc1-9214-2bf11baceb1c | 6a164ec9-8fa2-4fc1-9214-2bf11baceb1c | human | null | null | none | abstracts | Epitaxial graphene | null | Graphene multilayers are grown epitaxially on single crystal silicon carbide.
This system is composed of several graphene layers of which the first layer is
electron doped due to the built-in electric field and the other layers are
essentially undoped. Unlike graphite the charge carriers show Dirac particle
properties (i.e. an anomalous Berry's phase, weak anti-localization and square
root field dependence of the Landau level energies). Epitaxial graphene shows
quasi-ballistic transport and long coherence lengths; properties which may
persists above cryogenic temperatures. Paradoxically, in contrast to exfoliated
graphene, the quantum Hall effect is not observed in high mobility epitaxial
graphene. It appears that the effect is suppressed due to absence of localized
states in the bulk of the material.Epitaxial graphene can be patterned using
standard lithography methods and characterized using a wide array of
techniques. These favorable features indicate that interconnected room
temperature ballistic devices may be feasible for low dissipation high-speed
nanoelectronics.
|
c54d7f8c-8563-4201-a0fe-ececb6dde856 | c54d7f8c-8563-4201-a0fe-ececb6dde856 | c54d7f8c-8563-4201-a0fe-ececb6dde856 | human | null | null | none | abstracts | Specific heat and bimodality in canonical and grand canonical versions
of the thermodynamic model | null | We address two issues in the thermodynamic model for nuclear disassembly.
Surprisingly large differences in results for specific heat were seen in
predictions from the canonical and grand canonical ensembles when the nuclear
system passes from liquid-gas co-existence to the pure gas phase. We are able
to pinpoint and understand the reasons for such and other discrepancies when
they appear. There is a subtle but important difference in the physics
addressed in the two models. In particular if we reformulate the parameters in
the canonical model to better approximate the physics addressed in the grand
canonical model, calculations for observables converge. Next we turn to the
issue of bimodality in the probability distribution of the largest fragment in
both canonical and grand canonical ensembles. We demonstrate that this
distribution is very closely related to average multiplicities. The
relationship of the bimodal distribution to phase transition is discussed.
|
7018d626-6d5b-47a3-bfff-d84aa4a65eb3 | 7018d626-6d5b-47a3-bfff-d84aa4a65eb3 | 7018d626-6d5b-47a3-bfff-d84aa4a65eb3 | human | null | null | none | abstracts | The core binary fractions of star clusters from realistic simulations | null | We investigate the evolution of binary fractions in star clusters using
N-body models of up to 100000 stars. Primordial binary frequencies in these
models range from 5% to 50%. Simulations are performed with the NBODY4 code and
include a full mass spectrum of stars, stellar evolution, binary evolution and
the tidal field of the Galaxy. We find that the overall binary fraction of a
cluster almost always remains close to the primordial value, except at late
times when a cluster is near dissolution. A critical exception occurs in the
central regions where we observe a marked increase in binary fraction with time
-- a simulation starting with 100000 stars and 5% binaries reached a core
binary frequency as high as 40% at the end of the core-collapse phase
(occurring at 16 Gyr with ~20000 stars remaining). Binaries are destroyed in
the core by a variety of processes as a cluster evolves, but the combination of
mass-segregation and creation of new binaries in exchange interactions produces
the observed increase in relative number. We also find that binaries are cycled
into and out of cluster cores in a manner that is analogous to convection in
stars. For models of 100000 stars we show that the evolution of the core-radius
up to the end of the initial phase of core-collapse is not affected by the
exact value of the primordial binary frequency (for frequencies of 10% or
less). We discuss the ramifications of our results for the likely primordial
binary content of globular clusters.
|
ce654490-b39f-43c8-863d-8441e335c6b0 | ce654490-b39f-43c8-863d-8441e335c6b0 | ce654490-b39f-43c8-863d-8441e335c6b0 | human | null | null | none | abstracts | Approaching the Heisenberg limit in an atom laser | null | We present experimental and theoretical results showing the improved beam
quality and reduced divergence of an atom laser produced by an optical Raman
transition, compared to one produced by an RF transition. We show that Raman
outcoupling can eliminate the diverging lens effect that the condensate has on
the outcoupled atoms. This substantially improves the beam quality of the atom
laser, and the improvement may be greater than a factor of ten for experiments
with tight trapping potentials. We show that Raman outcoupling can produce atom
lasers whose quality is only limited by the wavefunction shape of the
condensate that produces them, typically a factor of 1.3 above the Heisenberg
limit.
|
29eb6639-77fd-4e94-be57-e4405a6401e3 | 29eb6639-77fd-4e94-be57-e4405a6401e3 | 29eb6639-77fd-4e94-be57-e4405a6401e3 | human | null | null | none | abstracts | A practical Seedless Infrared-Safe Cone jet algorithm | null | Current cone jet algorithms, widely used at hadron colliders, take event
particles as seeds in an iterative search for stable cones. A longstanding
infrared (IR) unsafety issue in such algorithms is often assumed to be solvable
by adding extra `midpoint' seeds, but actually is just postponed to one order
higher in the coupling. A proper solution is to switch to an exact seedless
cone algorithm, one that provably identifies all stable cones. The only
existing approach takes N 2^N time to find jets among N particles, making it
unusable at hadron level. This can be reduced to N^2 ln(N) time, leading to
code (SISCone) whose speed is similar to that of public midpoint
implementations. Monte Carlo tests provide a strong cross-check of an
analytical proof of the IR safety of the new algorithm, and the absence of any
'R_{sep}' issue implies a good practical correspondence between parton and
hadron levels. Relative to a midpoint cone, the use of an IR safe seedless
algorithm leads to modest changes for inclusive jet spectra, mostly through
reduced sensitivity to the underlying event, and significant changes for some
multi-jet observables.
|
e08a78ed-403e-4371-890b-33d0f1c1e6f3 | e08a78ed-403e-4371-890b-33d0f1c1e6f3 | e08a78ed-403e-4371-890b-33d0f1c1e6f3 | human | null | null | none | abstracts | Isospin breaking in the yield of heavy meson pairs in e+e- annihilation
near threshold | null | We revisit the problem of interplay between the strong and the Coulomb
interaction in the charged-to-neutral yield ratio for $B {\bar B}$ and $D {\bar
D}$ pairs near their respective thresholds in $e^+e^-$ annihilation. We
consider here a realistic situation with a resonant interaction in the isospin
I=0 channel and a nonresonant strong scattering amplitude in the I=1 state. We
find that the yield ratio has a smooth behavior depending on the scattering
phase in the I=1 channel. The same approach is also applicable to the $K {\bar
K}$ production at the $\phi(1020)$ resonance, where the Coulomb effect in the
charged-to-neutral yield ratio is generally sensitive to the scattering phases
in both the isoscalar and the isovector channels. Furthermore, we apply the
same approach to the treatment of the effect of the isotopic mass difference
between the charged and neutral mesons and argue that the strong-scattering
effects generally result in a modification to the pure kinematical effect of
this mass difference.
|
0171a81d-39ee-4d2d-a197-6701744d59df | 0171a81d-39ee-4d2d-a197-6701744d59df | 0171a81d-39ee-4d2d-a197-6701744d59df | human | null | null | none | abstracts | On the number of topological types occurring in a parametrized family of
arrangements | null | Let ${\mathcal S}(\R)$ be an o-minimal structure over $\R$, $T \subset
\R^{k_1+k_2+\ell}$ a closed definable set, and $$ \displaylines{\pi_1:
\R^{k_1+k_2+\ell}\to \R^{k_1 + k_2}, \pi_2: \R^{k_1+k_2+\ell}\to \R^{\ell}, \
\pi_3: \R^{k_1 + k_2} \to \R^{k_2}} $$ the projection maps.
For any collection ${\mathcal A} = \{A_1,...,A_n\}$ of subsets of
$\R^{k_1+k_2}$, and $\z \in \R^{k_2}$, let $\A_\z$ denote the collection of
subsets of $\R^{k_1}$, $\{A_{1,\z},..., A_{n,\z}\}$, where $A_{i,\z} = A_i \cap
\pi_3^{-1}(\z), 1 \leq i \leq n$. We prove that there exists a constant $C =
C(T) > 0,$ such that for any family ${\mathcal A} = \{A_1,...,A_n\}$ of
definable sets, where each $A_i = \pi_1(T \cap \pi_2^{-1}(\y_i))$, for some
$\y_i \in \R^{\ell}$, the number of distinct stable homotopy types of $\A_\z,
\z \in \R^{k_2}$, is bounded by $ \displaystyle{C \cdot n^{(k_1+1)k_2},} $
while the number of distinct homotopy types is bounded by $ \displaystyle{C
\cdot n^{(k_1+3)k_2}.} $ This generalizes to the general o-minimal setting,
bounds of the same type proved in \cite{BV} for semi-algebraic and
semi-Pfaffian families. One main technical tool used in the proof of the above
results, is a topological comparison theorem which might be of independent
interest in the study of arrangements.
|
eb657ebc-6ac8-4a0f-93d4-0fb6ad89a5bb | eb657ebc-6ac8-4a0f-93d4-0fb6ad89a5bb | eb657ebc-6ac8-4a0f-93d4-0fb6ad89a5bb | human | null | null | none | abstracts | Generalized Twistor Transform And Dualities, With A New Description of
Particles With Spin, Beyond Free and Massless | null | A generalized twistor transform for spinning particles in 3+1 dimensions is
constructed that beautifully unifies many types of spinning systems by mapping
them to the same twistor, thus predicting an infinite set of duality relations
among spinning systems with different Hamiltonians. Usual 1T-physics is not
equipped to explain the duality relationships and unification between these
systems. We use 2T-physics in 4+2 dimensions to uncover new properties of
twistors, and expect that our approach will prove to be useful for practical
applications as well as for a deeper understanding of fundamental physics.
Unexpected structures for a new description of spinning particles emerge. A
unifying symmetry SU(2,3) that includes conformal symmetry SU(2,2)=SO(4,2) in
the massless case, turns out to be a fundamental property underlying the
dualities of a large set of spinning systems, including those that occur in
high spin theories. This may lead to new forms of string theory backgrounds as
well as to new methods for studying various corners of M theory. In this paper
we present the main concepts, and in a companion paper we give other details.
|
cfb31d0c-ace4-4c88-883d-c38afe1ba1ba | cfb31d0c-ace4-4c88-883d-c38afe1ba1ba | cfb31d0c-ace4-4c88-883d-c38afe1ba1ba | human | null | null | none | abstracts | Parametrized Post-Newtonian Expansion of Chern-Simons Gravity | null | We investigate the weak-field, post-Newtonian expansion to the solution of
the field equations in Chern-Simons gravity with a perfect fluid source. In
particular, we study the mapping of this solution to the parameterized
post-Newtonian formalism to 1 PN order in the metric. We find that the PPN
parameters of Chern-Simons gravity are identical to those of general
relativity, with the exception of the inclusion of a new term that is
proportional to the Chern-Simons coupling parameter and the curl of the PPN
vector potentials. We also find that the new term is naturally enhanced by the
non-linearity of spacetime and we provide a physical interpretation for it. By
mapping this correction to the gravito-electro-magnetic framework, we study the
corrections that this new term introduces to the acceleration of point
particles and the frame-dragging effect in gyroscopic precession. We find that
the Chern-Simons correction to these classical predictions could be used by
current and future experiments to place bounds on intrinsic parameters of
Chern-Simons gravity and, thus, string theory.
|
fb44dd29-c408-46aa-a32a-3c6652980b59 | fb44dd29-c408-46aa-a32a-3c6652980b59 | fb44dd29-c408-46aa-a32a-3c6652980b59 | human | null | null | none | abstracts | Scaling of Resistance and Electron Mean Free Path of Single-Walled
Carbon Nanotubes | null | We present an experimental investigation on the scaling of resistance in
individual single walled carbon nanotube devices with channel lengths that vary
four orders of magnitude on the same sample. The electron mean free path is
obtained from the linear scaling of resistance with length at various
temperatures. The low temperature mean free path is determined by impurity
scattering, while at high temperature the mean free path decreases with
increasing temperature, indicating that it is limited by electron-phonon
scattering. An unusually long mean free path at room temperature has been
experimentally confirmed. Exponentially increasing resistance with length at
extremely long length scales suggests anomalous localization effects.
|
7c57238f-a8ed-4ab7-a9d9-ecfc58879df2 | 7c57238f-a8ed-4ab7-a9d9-ecfc58879df2 | 7c57238f-a8ed-4ab7-a9d9-ecfc58879df2 | human | null | null | none | abstracts | Spline Single-Index Prediction Model | null | For the past two decades, single-index model, a special case of projection
pursuit regression, has proven to be an efficient way of coping with the high
dimensional problem in nonparametric regression. In this paper, based on weakly
dependent sample, we investigate the single-index prediction (SIP) model which
is robust against deviation from the single-index model. The single-index is
identified by the best approximation to the multivariate prediction function of
the response variable, regardless of whether the prediction function is a
genuine single-index function. A polynomial spline estimator is proposed for
the single-index prediction coefficients, and is shown to be root-n consistent
and asymptotically normal. An iterative optimization routine is used which is
sufficiently fast for the user to analyze large data of high dimension within
seconds. Simulation experiments have provided strong evidence that corroborates
with the asymptotic theory. Application of the proposed procedure to the rive
flow data of Iceland has yielded superior out-of-sample rolling forecasts.
|
e6c3a340-90e6-4c34-9707-d34da98c5aca | e6c3a340-90e6-4c34-9707-d34da98c5aca | e6c3a340-90e6-4c34-9707-d34da98c5aca | human | null | null | none | abstracts | Measurement of the Aerosol Phase Function at the Pierre Auger
Observatory | null | Air fluorescence detectors measure the energy of ultra-high energy cosmic
rays by collecting fluorescence light emitted from nitrogen molecules along the
extensive air shower cascade. To ensure a reliable energy determination, the
light signal needs to be corrected for atmospheric effects, which not only
attenuate the signal, but also produce a non-negligible background component
due to scattered Cherenkov light and multiple-scattered light. The correction
requires regular measurements of the aerosol attenuation length and the aerosol
phase function, defined as the probability of light scattered in a given
direction. At the Pierre Auger Observatory in Malargue, Argentina, the phase
function is measured on an hourly basis using two Aerosol Phase Function (APF)
light sources. These sources direct a UV light beam across the field of view of
the fluorescence detectors; the phase function can be extracted from the image
of the shots in the fluorescence detector cameras. This paper describes the
design, current status, standard operation procedure, and performance of the
APF system at the Pierre Auger Observatory.
|
6bfd908e-da50-4922-90bc-f961055040f6 | 6bfd908e-da50-4922-90bc-f961055040f6 | 6bfd908e-da50-4922-90bc-f961055040f6 | human | null | null | none | abstracts | The World as Evolving Information | null | This paper discusses the benefits of describing the world as information,
especially in the study of the evolution of life and cognition. Traditional
studies encounter problems because it is difficult to describe life and
cognition in terms of matter and energy, since their laws are valid only at the
physical scale. However, if matter and energy, as well as life and cognition,
are described in terms of information, evolution can be described consistently
as information becoming more complex.
The paper presents eight tentative laws of information, valid at multiple
scales, which are generalizations of Darwinian, cybernetic, thermodynamic,
psychological, philosophical, and complexity principles. These are further used
to discuss the notions of life, cognition and their evolution.
|
828ffcc8-dbb9-482f-9dd3-2d0cbba96417 | 828ffcc8-dbb9-482f-9dd3-2d0cbba96417 | 828ffcc8-dbb9-482f-9dd3-2d0cbba96417 | human | null | null | none | abstracts | Polymerization Force Driven Buckling of Microtubule Bundles Determines
the Wavelength of Patterns Formed in Tubulin Solutions | null | We present a model for the spontaneous formation of a striated pattern in
polymerizing microtubule solutions. It describes the buckling of a single
microtubule (MT) bundle within an elastic network formed by other similarly
aligned and buckling bundles and unaligned MTs. Phase contrast and polarization
microscopy studies of the temporal evolution of the pattern imply that the
polymerization of MTs within the bundles creates the driving compressional
force. Using the measured rate of buckling, the established MT force-velocity
curve and the pattern wavelength, we obtain reasonable estimates for the MT
bundle bending rigidity and the elastic constant of the network. The analysis
implies that the bundles buckle as solid rods.
|
6d2016e9-84bd-4a1f-99f6-0b663ce96d84 | 6d2016e9-84bd-4a1f-99f6-0b663ce96d84 | 6d2016e9-84bd-4a1f-99f6-0b663ce96d84 | human | null | null | none | abstracts | Neutron Inelastic Scattering Processes as Background for Double-Beta
Decay Experiments | null | We investigate several Pb$(n,n'\gamma$) and Ge$(n,n'\gamma$) reactions. We
measure $\gamma$-ray production from Pb$(n,n'\gamma$) reactions that can be a
significant background for double-beta decay experiments which use lead as a
massive inner shield. Particularly worrisome for Ge-based double-beta decay
experiments are the 2041-keV and 3062-keV $\gamma$ rays produced via
Pb$(n,n'\gamma$). The former is very close to the ^{76}Ge double-beta decay
endpoint energy and the latter has a double escape peak energy near the
endpoint. Excitation $\gamma$-ray lines from Ge$(n,n'\gamma$) reactions are
also observed. We consider the contribution of such backgrounds and their
impact on the sensitivity of next-generation searches for neutrinoless
double-beta decay using enriched germanium detectors.
|
ec8fd9c9-221a-471d-8d51-6aab539ca059 | ec8fd9c9-221a-471d-8d51-6aab539ca059 | ec8fd9c9-221a-471d-8d51-6aab539ca059 | human | null | null | none | abstracts | Periodic accretion from a circumbinary disk in the young binary UZ Tau E | null | Close pre-main-sequence binary stars are expected to clear central holes in
their protoplanetary disks, but the extent to which material can flow from the
circumbinary disk across the gap onto the individual circumstellar disks has
been unclear. In binaries with eccentric orbits, periodic perturbation of the
outer disk is predicted to induce mass flow across the gap, resulting in
accretion that varies with the binary period. This accretion may manifest
itself observationally as periodic changes in luminosity. Here we present a
search for such periodic accretion in the pre-main-sequence spectroscopic
binary UZ Tau E. We present BVRI photometry spanning three years; we find that
the brightness of UZ Tau E is clearly periodic, with a best-fit period of 19.16
+/- 0.04 days. This is consistent with the spectroscopic binary period of 19.13
days, refined here from analysis of new and existing radial velocity data. The
brightness of UZ Tau E shows significant random variability, but the overall
periodic pattern is a broad peak in enhanced brightness, spanning more than
half the binary orbital period. The variability of the H-alpha line is not as
clearly periodic, but given the sparseness of the data, some periodic component
is not ruled out. The photometric variations are in good agreement with
predictions from simulations of binaries with orbital parameters similar to
those of UZ Tau E, suggesting that periodic accretion does occur from
circumbinary disks, replenishing the inner disks and possibly extending the
timescale over which they might form planets.
|
0a1c4696-26f8-487d-81c8-d0c534a233f6 | 0a1c4696-26f8-487d-81c8-d0c534a233f6 | 0a1c4696-26f8-487d-81c8-d0c534a233f6 | human | null | null | none | abstracts | Effect of node deleting on network structure | null | The ever-increasing knowledge of the structure of various real-world networks
has uncovered their complex multi-mechanism-governed evolution processes.
Therefore, a better understanding of the structure and evolution of these
networked complex systems requires us to describe such processes in a more
detailed and realistic manner. In this paper, we introduce a new type of
network growth rule which comprises addition and deletion of nodes, and propose
an evolving network model to investigate the effect of node deleting on network
structure. It is found that, with the introduction of node deleting, network
structure is significantly transformed. In particular, degree distribution of
the network undergoes a transition from scale-free to exponential forms as the
intensity of node deleting increases. At the same time, nontrivial
disassortative degree correlation develops spontaneously as a natural result of
network evolution in the model. We also demonstrate that node deleting
introduced in the model does not destroy the connectedness of a growing network
so long as the increasing rate of edges is not excessively small. In addition,
it is found that node deleting will weaken but not eliminate the small-world
effect of a growing network, and generally it will decrease the clustering
coefficient in a network.
|
112a8ffb-e19f-4b4c-8784-0c427e1c1c53 | 112a8ffb-e19f-4b4c-8784-0c427e1c1c53 | 112a8ffb-e19f-4b4c-8784-0c427e1c1c53 | human | null | null | none | abstracts | VLBI observations of nineteen GHz-Peaked-Spectrum radio sources at 1.6
GHz | null | Aims and Methods: We present the results of VLBI observations of nineteen
GHz-Peaked-Spectrum (GPS) radio sources at 1.6 GHz. Of them, 15 sources are
selected from the Parkes Half Jansky (PHJ) sample (Snellen 2002), 4 others are
from our previous observation list. We aimed at imaging the structure of GPS
sources, searching for Compact Symmetric Objects (CSOs) and studying the
absorption for the convex radio spectra of GPS sources.
Results: We obtained total intensity 1.6 GHz VLBI images of 17 sources for
the first time. Of them, 80% show mini-double-lobe radio structure, indicating
that they are CSOs or candidates, and their host AGNs could be edge-on to us.
This result suggests that there is a high incidence of mini double-lobe sources
(or CSOs) in the PHJ sample. The sources J0323+0534, J1135-0021, J1352+0232,
J2058+0540, J2123-0112 and J2325-0344 with measured redshift, showing
double-lobe structure with sizes of <1 kpc, are classified as CSOs. Three
sources J1057+0012, J1600-0037 and J1753+2750 are considered as core-jet
sources according to their morphologies and flux variability.
|
bf13bd61-8dc3-4a66-be91-7bcde3bad010 | bf13bd61-8dc3-4a66-be91-7bcde3bad010 | bf13bd61-8dc3-4a66-be91-7bcde3bad010 | human | null | null | none | abstracts | Moment switching in nanotube magnetic force probes | null | A recent advance in improving the spatial resolution of magnetic force
microscopy (MFM) uses as sensor tips carbon nanotubes grown at the apex of
conventional silicon cantilever pyramids and coated with a thin ferromagnetic
layer. Magnetic images of high density vertically recorded media using these
tips exhibit a doubling of the spatial frequency under some conditions. Here we
demonstrate that this spatial frequency doubling is due to the switching of the
moment direction of the nanotube tip. This results in a signal which is
proportional to the absolute value of the signal normally observed in MFM. Our
modeling indicates that a significant fraction of the tip volume is involved in
the observed switching, and that it should be possible to image very high bit
densities with nanotube magnetic force sensors.
|
dd8a264f-1e1a-4792-974f-727071796f23 | dd8a264f-1e1a-4792-974f-727071796f23 | dd8a264f-1e1a-4792-974f-727071796f23 | human | null | null | none | abstracts | Possibility of Gapless Spin Liquid State by One-dimensionalization | null | Motivated by the observation of a gapless spin liquid state in
$\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, we analyze the anisotropic triangular
lattice $S=1/2$ Heisenberg model with the resonating valence bond mean-field
approximation. Paying attention to the small quasi-one-dimensional anisotropy
of the material, we take an approach from one-dimensional (1D) chains coupled
with frustrating zig-zag bonds. By calculating one-particle excitation spectra
changing anisotropy parameter $J'/J$ from the decoupled 1D chains to the
isotropic triangular lattice, we find almost gapless excitations in the wide
range from the 1D limit. This one-dimensionalization by frustration is
considered to be a candidate for the mechanism of the gapless spin liquid
state.
|
55a86b14-0078-4eba-9dcf-cdb05234c76c | 55a86b14-0078-4eba-9dcf-cdb05234c76c | 55a86b14-0078-4eba-9dcf-cdb05234c76c | human | null | null | none | abstracts | Effects of Dirac sea on pion propagation in asymmetric nuclear matter | null | We study pion propagation in asymmetric nuclear matter (ANM). One of the
interesting consequences of pion propagation in ANM is the mode splitting for
the different charged states of pions. First we describe the pion-nucleon
dynamics using the non-chiral model where one starts with pseudoscalar (PS)
$\pi$N coupling and the pseudovector (PV) representation is obtained via
suitable non-linear field transformations. For both of these cases the effect
of the Dirac sea is estimated. Subsequently, we present results using the
chiral effective Lagrangian where the short-distance behavior (Dirac vacuum) is
included by re-defining the field parameters as done in the modern effective
field theory approach developed recently. The results are compared with the
previous calculations for the case of symmetric nuclear matter (SNM). Closed
form analytical results are presented for the effective pion masses and
dispersion relations by making hard nucleon loop (HNL) approximation and
suitable density expansion.
|
ede017d9-2352-4221-b5cb-d010c08a338e | ede017d9-2352-4221-b5cb-d010c08a338e | ede017d9-2352-4221-b5cb-d010c08a338e | human | null | null | none | abstracts | Spin-orbit coupling effect on the persistent currents in mesoscopic ring
with an Anderson impurity | null | Based on the finite $U$ slave boson method, we have investigated the effect
of Rashba spin-orbit(SO) coupling on the persistent charge and spin currents in
mesoscopic ring with an Anderson impurity. It is shown that the Kondo effect
will decrease the magnitude of the persistent charge and spin currents in this
side-coupled Anderson impurity case. In the presence of SO coupling, the
persistent currents change drastically and oscillate with the strength of SO
coupling. The SO coupling will suppress the Kondo effect and restore the abrupt
jumps of the persistent currents. It is also found that a persistent spin
current circulating the ring can exist even without the charge current in this
system.
|
c9fec9b6-d8c9-4e5b-847d-5b494a5903c3 | c9fec9b6-d8c9-4e5b-847d-5b494a5903c3 | c9fec9b6-d8c9-4e5b-847d-5b494a5903c3 | human | null | null | none | abstracts | Fabrication of half metallicity in a ferromagnetic metal | null | We investigate the growth of half metallic phase in a ferromagnetic material
using state-of-the-art full potential linearized augmented plane wave method.
To address the issue, we have substituted Ti at the Ru-sites in SrRuO3, where
SrRuO3 is a ferromagnetic material. Calculated results establish Ti4+ valence
states (similar to SrTiO3), which was predicted experimentally. Thus, Ti
substitution dilutes the Ru-O-Ru connectivity, which is manifested in the
calculated results in the form of significant band narrowing leading to finite
gap between t2g and eg bands. At 75% substitution, a large gap (> 2 eV) appears
at the Fermi level, e_F in the up spin density of states, while the down spin
states contributes at e_F characterizing the system a half-metallic
ferromagnet. The t2g - eg gap can be tailored judiciously by tuning Ti
concentrations to minimize thermal effects, which is often the major bottleneck
to achieve high spin polarization at elevated temperatures in other materials.
This study, thus, provides a novel but simple way to fabricate half-metallicity
in ferromagnetic materials, which are potential candidates for spin-based
technology.
|
fba8097c-eb5d-4ee8-8b43-4ac3440cad05 | fba8097c-eb5d-4ee8-8b43-4ac3440cad05 | fba8097c-eb5d-4ee8-8b43-4ac3440cad05 | human | null | null | none | abstracts | Emergence of spatiotemporal chaos driven by far-field breakup of spiral
waves in the plankton ecological systems | null | Alexander B. Medvinsky \emph{et al} [A. B. Medvinsky, I. A. Tikhonova, R. R.
Aliev, B.-L. Li, Z.-S. Lin, and H. Malchow, Phys. Rev. E \textbf{64}, 021915
(2001)] and Marcus R. Garvie \emph{et al} [M. R. Garvie and C. Trenchea, SIAM
J. Control. Optim. \textbf{46}, 775-791 (2007)] shown that the minimal
spatially extended reaction-diffusion model of phytoplankton-zooplankton can
exhibit both regular, chaotic behavior, and spatiotemporal patterns in a patchy
environment. Based on that, the spatial plankton model is furtherly
investigated by means of computer simulations and theoretical analysis in the
present paper when its parameters would be expected in the case of mixed
Turing-Hopf bifurcation region. Our results show that the spiral waves exist in
that region and the spatiotemporal chaos emerge, which arise from the far-field
breakup of the spiral waves over large ranges of diffusion coefficients of
phytoplankton and zooplankton. Moreover, the spatiotemporal chaos arising from
the far-field breakup of spiral waves does not gradually involve the whole
space within that region. Our results are confirmed by means of computation
spectra and nonlinear bifurcation of wave trains. Finally, we give some
explanations about the spatially structured patterns from the community level.
|
4ecc493f-dc52-404c-9c61-f5c8c5c05465 | 4ecc493f-dc52-404c-9c61-f5c8c5c05465 | 4ecc493f-dc52-404c-9c61-f5c8c5c05465 | human | null | null | none | abstracts | On the pseudospectrum of elliptic quadratic differential operators | null | We study the pseudospectrum of a class of non-selfadjoint differential
operators. Our work consists in a detailed study of the microlocal properties,
which rule the spectral stability or instability phenomena appearing under
small perturbations for elliptic quadratic differential operators. The class of
elliptic quadratic differential operators stands for the class of operators
defined in the Weyl quantization by complex-valued elliptic quadratic symbols.
We establish in this paper a simple necessary and sufficient condition on the
Weyl symbol of these operators, which ensures the stability of their spectra.
When this condition is violated, we prove that it occurs some strong spectral
instabilities for the high energies of these operators, in some regions which
can be far away from their spectra. We give a precise geometrical description
of them, which explains the results obtained for these operators in some
numerical simulations giving the computation of false eigenvalues far from
their spectra by algorithms for eigenvalues computing.
|
7a75042e-e092-4e0c-86c3-05d167b29985 | 7a75042e-e092-4e0c-86c3-05d167b29985 | 7a75042e-e092-4e0c-86c3-05d167b29985 | human | null | null | none | abstracts | Fluctuation-dissipation relation on a Melde string in a turbulent flow,
considerations on a "dynamical temperature" | null | We report on measurements of the transverse fluctuations of a string in a
turbulent air jet flow. Harmonic modes are excited by the fluctuating drag
force, at different wave-numbers. This simple mechanical probe makes it
possible to measure excitations of the flow at specific scales, averaged over
space and time: it is a scale-resolved, global measurement. We also measure the
dissipation associated to the string motion, and we consider the ratio of the
fluctuations over dissipation (FDR). In an exploratory approach, we investigate
the concept of {\it effective temperature} defined through the FDR. We compare
our observations with other definitions of temperature in turbulence. From the
theory of Kolmogorov (1941), we derive the exponent -11/3 expected for the
spectrum of the fluctuations. This simple model and our experimental results
are in good agreement, over the range of wave-numbers, and Reynolds number
accessible ($74000 \leq Re \leq 170000$).
|
b8abebe2-3287-49b8-9b5c-6b5a051ab198 | b8abebe2-3287-49b8-9b5c-6b5a051ab198 | b8abebe2-3287-49b8-9b5c-6b5a051ab198 | human | null | null | none | abstracts | On generalized entropy measures and pathways | null | Product probability property, known in the literature as statistical
independence, is examined first. Then generalized entropies are introduced, all
of which give generalizations to Shannon entropy. It is shown that the nature
of the recursivity postulate automatically determines the logarithmic
functional form for Shannon entropy. Due to the logarithmic nature, Shannon
entropy naturally gives rise to additivity, when applied to situations having
product probability property. It is argued that the natural process is
non-additivity, important, for example, in statistical mechanics, even in
product probability property situations and additivity can hold due to the
involvement of a recursivity postulate leading to a logarithmic function.
Generalizations, including Mathai's generalized entropy are introduced and some
of the properties are examined. Situations are examined where Mathai's entropy
leads to pathway models, exponential and power law behavior and related
differential equations. Connection of Mathai's entropy to Kerridge's measure of
"inaccuracy" is also explored.
|
354b6ffb-ab7a-4d6a-8b1d-9016643135a2 | 354b6ffb-ab7a-4d6a-8b1d-9016643135a2 | 354b6ffb-ab7a-4d6a-8b1d-9016643135a2 | human | null | null | none | abstracts | Evolution of a band insulating phase from a correlated metallic phase | null | We investigate the evolution of the electronic structure in SrRu_(1-x)Ti_xO_3
as a function of x using high resolution photoemission spectroscopy, where
SrRuO3 is a weakly correlated metal and SrTiO3 is a band insulator. The surface
spectra exhibit a metal-insulator transition at x = 0.5 by opening up a soft
gap. A hard gap appears at higher x values consistent with the transport
properties. In contrast, the bulk spectra reveal a pseudogap at the Fermi
level, and unusual evolution exhibiting an apparent broadening of the coherent
feature and subsequent decrease in intensity of the lower Hubbard band with the
increase in x. Interestingly, the first principle approaches are found to be
sufficient to capture anomalous evolutions at high energy scale. Analysis of
the spectral lineshape indicates strong interplay between disorder and electron
correlation in the electronic properties of this system.
|
3a35c134-d3b2-4614-afc2-76e7c8a37276 | 3a35c134-d3b2-4614-afc2-76e7c8a37276 | 3a35c134-d3b2-4614-afc2-76e7c8a37276 | human | null | null | none | abstracts | Electroweak phase transitions in the MSSM with an extra $U(1)'$ | null | We investigate the possibility of electroweak phase transition in the minimal
supersymmetric standard model (MSSM) with an extra $U(1)'$. This model has two
Higgs doublets and a singlet, in addition to a singlet exotic quark superfield.
We find that at the one-loop level this model may accommodate the electroweak
phase transitions that are strongly first-order in a reasonably large region of
the parameter space. In the parameter region where the phase transitions take
place, we observe that the lightest scalar Higgs boson has a smaller mass when
the strength of the phase transition becomes weaker. Also, the other three
heavier neutral Higgs bosons get more large masses when the strength of the
phase transition becomes weaker.
|
6c90aab2-aacd-4f2e-8aec-20aca8f3d76c | 6c90aab2-aacd-4f2e-8aec-20aca8f3d76c | 6c90aab2-aacd-4f2e-8aec-20aca8f3d76c | human | null | null | none | abstracts | Solutions of fractional reaction-diffusion equations in terms of the
H-function | null | This paper deals with the investigation of the solution of an unified
fractional reaction-diffusion equation associated with the Caputo derivative as
the time-derivative and Riesz-Feller fractional derivative as the
space-derivative. The solution is derived by the application of the Laplace and
Fourier transforms in closed form in terms of the H-function. The results
derived are of general nature and include the results investigated earlier by
many authors, notably by Mainardi et al. (2001, 2005) for the fundamental
solution of the space-time fractional diffusion equation, and Saxena et al.
(2006a, b) for fractional reaction- diffusion equations. The advantage of using
Riesz-Feller derivative lies in the fact that the solution of the fractional
reaction-diffusion equation containing this derivative includes the fundamental
solution for space-time fractional diffusion, which itself is a generalization
of neutral fractional diffusion, space-fractional diffusion, and
time-fractional diffusion. These specialized types of diffusion can be
interpreted as spatial probability density functions evolving in time and are
expressible in terms of the H-functions in compact form.
|
79e22e6c-8f6f-43fe-a872-70cc57898d48 | 79e22e6c-8f6f-43fe-a872-70cc57898d48 | 79e22e6c-8f6f-43fe-a872-70cc57898d48 | human | null | null | none | abstracts | The effect of a fifth large-scale space-time dimension on the
conservation of energy in a four dimensional Universe | null | The effect of introducing a fifth large-scale space-time dimension to the
equations of orbital dynamics was analysed in an earlier paper by the authors.
The results showed good agreement with the observed flat rotation curves of
galaxies and the Pioneer Anomaly. This analysis did not require the
modification of Newtonian dynamics, but rather only their restatement in a five
dimensional framework. The same analysis derived a acceleration parameter ar,
which plays an important role in the restated equations of orbital dynamics,
and suggested a value for ar. In this companion paper, the principle of
conservation of energy is restated within the same five-dimensional framework.
The resulting analysis provides an alternative route to estimating the value of
ar, without reference to the equations of orbital dynamics, and based solely on
key cosmological constants and parameters, including the gravitational
constant, G. The same analysis suggests that: (i) the inverse square law of
gravity may itself be due to the conservation of energy at the boundary between
a four-dimensional universe and a fifth large-scale space-time dimension; and
(ii) there is a limiting case for the Tulley-Fisher relationship linking the
speed of light to the mass of the Universe.
|
94f6c9b0-8183-493f-8530-7aaaa335fb48 | 94f6c9b0-8183-493f-8530-7aaaa335fb48 | 94f6c9b0-8183-493f-8530-7aaaa335fb48 | human | null | null | none | abstracts | A Multiphilic Descriptor for Chemical Reactivity and Selectivity | null | In line with the local philicity concept proposed by Chattaraj et al.
(Chattaraj, P. K.; Maiti, B.; Sarkar, U. J. Phys. Chem. A. 2003, 107, 4973) and
a dual descriptor derived by Toro-Labbe and coworkers (Morell, C.; Grand, A.;
Toro-Labbe, A. J. Phys. Chem. A. 2005, 109, 205), we propose a multiphilic
descriptor. It is defined as the difference between nucleophilic (Wk+) and
electrophilic (Wk-) condensed philicity functions. This descriptor is capable
of simultaneously explaining the nucleophilicity and electrophilicity of the
given atomic sites in the molecule. Variation of these quantities along the
path of a soft reaction is also analyzed. Predictive ability of this descriptor
has been successfully tested on the selected systems and reactions.
Corresponding force profiles are also analyzed in some representative cases.
Also, to study the intra- and intermolecular reactivities another related
descriptor namely, the nucleophilicity excess (DelW-+) for a nucleophile, over
the electrophilicity in it has been defined and tested on all-metal aromatic
compounds.
|
449e797c-22f7-41c0-be1e-6120b26fc012 | 449e797c-22f7-41c0-be1e-6120b26fc012 | 449e797c-22f7-41c0-be1e-6120b26fc012 | human | null | null | none | abstracts | Influence of Phonon dimensionality on Electron Energy Relaxation | null | We studied experimentally the role of phonon dimensionality on
electron-phonon (e-p) interaction in thin copper wires evaporated either on
suspended silicon nitride membranes or on bulk substrates, at sub-Kelvin
temperatures. The power emitted from electrons to phonons was measured using
sensitive normal metal-insulator-superconductor (NIS) tunnel junction
thermometers. Membrane thicknesses ranging from 30 nm to 750 nm were used to
clearly see the onset of the effects of two-dimensional (2D) phonon system. We
observed for the first time that a 2D phonon spectrum clearly changes the
temperature dependence and strength of the e-p scattering rate, with the
interaction becoming stronger at the lowest temperatures below $\sim$ 0.5 K for
the 30 nm membranes.
|
ae3a9df3-d5bc-4bcd-a420-84e46f358f33 | ae3a9df3-d5bc-4bcd-a420-84e46f358f33 | ae3a9df3-d5bc-4bcd-a420-84e46f358f33 | human | null | null | none | abstracts | Synergistic Effects of MoDTC and ZDTP on Frictional Behaviour of
Tribofilms at the Nanometer Scale | null | The layered structure and the rheological properties of anti-wear films,
generated in a rolling/sliding contact from lubricants containing zinc
dialkyldithiophosphate (ZDTP) and/or molybdenum dialkyldithiocarbamate (MoDTC)
additives, have been studied by dynamic nanoindentation experiments coupled
with a simple modelling of the stiffness measurements. Local nano-friction
experiments were conducted with the same device in order to determine the
evolution of the friction coefficient as a function of the applied pressure for
the different lubricant formulations. For the MoDTC film, the applied pressure
in the friction test remains low (<0.5 GPa) and the apparent friction
coefficient is high ($\mu$ > 0.4). For the tribofilms containing MoDTC together
with ZDTP, which permits the applied pressure to increase up to a few GPa
through some accommodation process, a very low friction domain appears (0.01 <
$\mu$ < 0.05), located a few nanometers below the surface of the tribofilm.
This low friction coefficient is attributed to the presence of MoS2 planes
sliding over each other in a favourable configuration obtained when the
pressure is sufficiently high, which is made possible by the presence of ZDTP.
|
4e6dc2b9-0d91-44df-a71e-d2108603d4a1 | 4e6dc2b9-0d91-44df-a71e-d2108603d4a1 | 4e6dc2b9-0d91-44df-a71e-d2108603d4a1 | human | null | null | none | abstracts | Lattice Boltzmann inverse kinetic approach for the incompressible
Navier-Stokes equations | null | In spite of the large number of papers appeared in the past which are devoted
to the lattice Boltzmann (LB) methods, basic aspects of the theory still remain
unchallenged. An unsolved theoretical issue is related to the construction of a
discrete kinetic theory which yields \textit{exactly} the fluid equations,
i.e., is non-asymptotic (here denoted as \textit{LB inverse kinetic theory}).
The purpose of this paper is theoretical and aims at developing an inverse
kinetic approach of this type. In principle infinite solutions exist to this
problem but the freedom can be exploited in order to meet important
requirements. In particular, the discrete kinetic theory can be defined so that
it yields exactly the fluid equation also for arbitrary non-equilibrium (but
suitably smooth) kinetic distribution functions and arbitrarily close to the
boundary of the fluid domain. Unlike previous entropic LB methods the theorem
can be obtained without functional constraints on the class of the initial
distribution functions. Possible realizations of the theory and asymptotic
approximations are provided which permit to determine the fluid equations
\textit{with prescribed accuracy.} As a result, asymptotic accuracy estimates
of customary LB approaches and comparisons with the Chorin artificial
compressibility method are discussed.
|
a4efcbf1-8dc7-4305-bac4-5f8388540d92 | a4efcbf1-8dc7-4305-bac4-5f8388540d92 | a4efcbf1-8dc7-4305-bac4-5f8388540d92 | human | null | null | none | abstracts | Phonon-mediated decay of an atom in a surface-induced potential | null | We study phonon-mediated transitions between translational levels of an atom
in a surface-induced potential. We present a general master equation governing
the dynamics of the translational states of the atom. In the framework of the
Debye model, we derive compact expressions for the rates for both upward and
downward transitions. Numerical calculations for the transition rates are
performed for a deep silica-induced potential allowing for a large number of
bound levels as well as free states of a cesium atom. The total absorption rate
is shown to be determined mainly by the bound-to-bound transitions for deep
bound levels and by bound-to-free transitions for shallow bound levels.
Moreover, the phonon emission and absorption processes can be orders of
magnitude larger for deep bound levels as compared to the shallow bound ones.
We also study various types of transitions from free states. We show that, for
thermal atomic cesium with temperature in the range from 100 $\mu$K to 400
$\mu$K in the vicinity of a silica surface with temperature of 300 K, the
adsorption (free-to-bound decay) rate is about two times larger than the
heating (free-to-free upward decay) rate, while the cooling (free-to-free
downward decay) rate is negligible.
|
6be7aa6a-9057-4dce-ae9f-acca71bdf1c7 | 6be7aa6a-9057-4dce-ae9f-acca71bdf1c7 | 6be7aa6a-9057-4dce-ae9f-acca71bdf1c7 | human | null | null | none | abstracts | Experimental observation of structural crossover in binary mixtures of
colloidal hard spheres | null | Using confocal-microscopy we investigate the structure of binary mixtures of
colloidal hard spheres with size ratio q=0.61. As a function of the packing
fraction of the two particle species, we observe a marked change of the
dominant wavelength in the pair correlation function. This behavior is in
excellent agreement with a recently predicted structural crossover in such
mixtures. In addition, the repercussions of structural crossover on the
real-space structure of a binary fluid are analyzed. We suggest a relation
between crossover and the lateral extension of networks containing only equally
sized particles that are connected by nearest neighbor bonds. This is supported
by Monte-Carlo simulations which are performed at different packing fractions
and size ratios.
|
a9fad31f-1bc7-4cd0-8791-a4f9959e9e4a | a9fad31f-1bc7-4cd0-8791-a4f9959e9e4a | a9fad31f-1bc7-4cd0-8791-a4f9959e9e4a | human | null | null | none | abstracts | Diffuse X-ray Emission from the Carina Nebula Observed with Suzaku | null | A number of giant HII regions are associated with soft diffuse X-ray
emission. Among these, the Carina nebula possesses the brightest soft diffuse
emission. The required plasma temperature and thermal energy can be produced by
collisions or termination of fast winds from main-sequence or embedded young O
stars, but the extended emission is often observed from regions apart from
massive stellar clusters. The origin of the X-ray emission is unknown.
The XIS CCD camera onboard Suzaku has the best spectral resolution for
extended soft sources so far, and is therefore capable of measuring key
emission lines in the soft band. Suzaku observed the core and the eastern side
of the Carina nebula (Car-D1) in 2005 Aug and 2006 June, respectively. Spectra
of the south part of the core and Car-D1 similarly showed strong L-shell lines
of iron ions and K-shell lines of silicon ions, while in the north of the core
these lines were much weaker. Fitting the spectra with an absorbed thin-thermal
plasma model showed kT~0.2, 0.6 keV and NH~1-2e21 cm-2 with a factor of 2-3
abundance variation in oxygen, magnesium, silicon and iron. The plasma might
originate from an old supernova, or a super shell of multiple supernovae.
|
838be3c6-1e25-4312-baec-cf51c4c0cc0c | 838be3c6-1e25-4312-baec-cf51c4c0cc0c | 838be3c6-1e25-4312-baec-cf51c4c0cc0c | human | null | null | none | abstracts | The Colin de Verdi\`ere number and graphs of polytopes | null | The Colin de Verdi\`ere number $\mu(G)$ of a graph $G$ is the maximum corank
of a Colin de Verdi\`ere matrix for $G$ (that is, of a Schr\"odinger operator
on $G$ with a single negative eigenvalue). In 2001, Lov\'asz gave a
construction that associated to every convex 3-polytope a Colin de Verdi\`ere
matrix of corank 3 for its 1-skeleton.
We generalize the Lov\'asz construction to higher dimensions by interpreting
it as minus the Hessian matrix of the volume of the polar dual. As a corollary,
$\mu(G) \ge d$ if $G$ is the 1-skeleton of a convex $d$-polytope.
Determination of the signature of the Hessian of the volume is based on the
second Minkowski inequality for mixed volumes and on Bol's condition for
equality.
|
1cb02c46-ec7a-4fb4-aca3-787ff92d2793 | 1cb02c46-ec7a-4fb4-aca3-787ff92d2793 | 1cb02c46-ec7a-4fb4-aca3-787ff92d2793 | human | null | null | none | abstracts | FIRST-based survey of Compact Steep Spectrum sources, V.
Milliarcsecond-scale morphology of CSS objects | null | Multifrequency VLBA observations of the final group of ten objects in a
sample of FIRST-based compact steep spectrum (CSS) sources are presented. The
sample was selected to investigate whether objects of this kind could be relics
of radio-loud AGNs switched off at very early stages of their evolution or
possibly to indicate intermittent activity. Initial observations were made
using MERLIN at 5 GHz. The sources have now been observed with the VLBA at 1.7,
5 and 8.4 GHz in a snapshot mode with phase-referencing. The resulting maps are
presented along with unpublished 8.4-GHz VLA images of five sources. Some of
the sources discussed here show a complex radio morphology and therefore a
complicated past that, in some cases, might indicate intermittent activity. One
of the sources studied - 1045+352 - is known as a powerful radio and
infrared-luminous broad absorption line (BAL) quasar. It is a young CSS object
whose asymmetric two-sided morphology on a scale of several hundred parsecs,
extending in two different directions, may suggest intermittent activity. The
young age and compact structure of 1045+352 is consistent with the evolution
scenario of BAL quasars. It has also been confirmed that the submillimetre flux
of 1045+352 can be seriously contaminated by synchrotron emission.
|
fe287737-49f9-4369-b063-07cfb125001f | fe287737-49f9-4369-b063-07cfb125001f | fe287737-49f9-4369-b063-07cfb125001f | human | null | null | none | abstracts | Investigation of relaxation phenomena in high-temperature
superconductors HoBa2Cu3O7-d at the action of pulsed magnetic fields | null | It is used the mechanical method of Abrikosov vortex stimulated dynamics
investigation in superconductors. With its help it was studied relaxation
phenomena in vortex matter of high-temperature superconductors. It established
that pulsed magnetic fields change the course of relaxation processes taking
place in vortex matter. The study of the influence of magnetic pulses differing
by their durations and amplitudes on vortex system of isotropic
high-temperature superconductors system HoBa2Cu3O7-d showed the presence of
threshold phenomena. The small duration pulses does not change the course of
relaxation processes taking place in vortex matter. When the duration of pulses
exceeds some critical value (threshold), then their influence change the course
of relaxation process which is revealed by stepwise change of relaxing
mechanical moment . These investigations showed that the time for formatting of
Abrikosov vortex lattice in HoBa2Cu3O7-d is of the order of 20 microsec. which
on the order of value exceeds the time necessary for formation of a single
vortex observed in type II superconductors.
|
6f54b6f1-796c-4ace-9478-cc057af9e79f | 6f54b6f1-796c-4ace-9478-cc057af9e79f | 6f54b6f1-796c-4ace-9478-cc057af9e79f | human | null | null | none | abstracts | Spin and pseudospin symmetries and the equivalent spectra of
relativistic spin-1/2 and spin-0 particles | null | We show that the conditions which originate the spin and pseudospin
symmetries in the Dirac equation are the same that produce equivalent energy
spectra of relativistic spin-1/2 and spin-0 particles in the presence of vector
and scalar potentials. The conclusions do not depend on the particular shapes
of the potentials and can be important in different fields of physics. When
both scalar and vector potentials are spherical, these conditions for
isospectrality imply that the spin-orbit and Darwin terms of either the upper
component or the lower component of the Dirac spinor vanish, making it
equivalent, as far as energy is concerned, to a spin-0 state. In this case,
besides energy, a scalar particle will also have the same orbital angular
momentum as the (conserved) orbital angular momentum of either the upper or
lower component of the corresponding spin-1/2 particle. We point out a few
possible applications of this result.
|
03e7d7f1-961b-4ecd-8916-564356f6d827 | 03e7d7f1-961b-4ecd-8916-564356f6d827 | 03e7d7f1-961b-4ecd-8916-564356f6d827 | human | null | null | none | abstracts | General asymptotic solutions of the Einstein equations and phase
transitions in quantum gravity | null | We discuss generic properties of classical and quantum theories of gravity
with a scalar field which are revealed at the vicinity of the cosmological
singularity. When the potential of the scalar field is exponential and
unbounded from below, the general solution of the Einstein equations has
quasi-isotropic asymptotics near the singularity instead of the usual
anisotropic Belinskii - Khalatnikov - Lifshitz (BKL) asymptotics. Depending on
the strength of scalar field potential, there exist two phases of quantum
gravity with scalar field: one with essentially anisotropic behavior of field
correlation functions near the cosmological singularity, and another with
quasi-isotropic behavior. The ``phase transition'' between the two phases is
interpreted as the condensation of gravitons.
|
c54dd23b-1346-41e8-bb6d-cd0b08257787 | c54dd23b-1346-41e8-bb6d-cd0b08257787 | c54dd23b-1346-41e8-bb6d-cd0b08257787 | human | null | null | none | abstracts | Trigonometric parallaxes of high velocity halo white dwarf candidates | null | The status of 38 halo white dwarf candidates identified by Oppenheimer et al.
(2001) has been intensively discussed by various authors. In analyses
undertaken to date, trigonometric parallaxes are crucial missing data. Distance
measurements are mandatory to kinematically segregate halo object from disk
objects and hence enable a more reliable estimate of the local density of halo
dark matter residing in such objects.
We present trigonometric parallax measurements for 15 candidate halo white
dwarfs (WDs) selected from the Oppenheimer et al. (2001) list. We observed the
stars using the ESO 1.56-m Danish Telescope and ESO 2.2-m telescope from August
2001 to July 2004. Parallaxes with accuracies of 1--2 mas were determined
yielding relative errors on distances of $\sim5$% for 6 objects, $\sim12$% for
3 objects, and $\sim20$% for two more objects. Four stars appear to be too
distant (probably farther than 100 pc) to have measurable parallaxes in our
observations. Distances, absolute magnitudes and revised space velocities were
derived for the 15 halo WDs from the Oppenheimer et al. (2001) list. Halo
membership is confirmed unambiguously for 6 objects while 5 objects may be
thick disk members and 4 objects are too distant to draw any conclusion based
solely on kinematics. Comparing our trigonometric parallaxes with photometric
parallaxes used in previous work reveals an overestimation of distance as
derived from photometric techniques. This new data set can be used to revise
the halo white dwarf space density, and that analysis will be presented in a
subsequent publication.
|
c8998bee-16ed-424f-aa05-884f21aac576 | c8998bee-16ed-424f-aa05-884f21aac576 | c8998bee-16ed-424f-aa05-884f21aac576 | human | null | null | none | abstracts | AMR simulations of the low T/|W| bar-mode instability of neutron stars | null | It has been recently argued through numerical work that rotating stars with a
high degree of differential rotation are dynamically unstable against bar-mode
deformation, even for values of the ratio of rotational kinetic energy to
gravitational potential energy as low as O(0.01). This may have implications
for gravitational wave astronomy in high-frequency sources such as core
collapse supernovae. In this paper we present high-resolution simulations,
performed with an adaptive mesh refinement hydrodynamics code, of such low
T/|W| bar-mode instability. The complex morphological features involved in the
nonlinear dynamics of the instability are revealed in our simulations, which
show that the excitation of Kelvin-Helmholtz-like fluid modes outside the
corotation radius of the star leads to the saturation of the bar-mode
deformation. While the overall trends reported in an earlier investigation are
confirmed by our work, we also find that numerical resolution plays an
important role during the long-term, nonlinear behaviour of the instability,
which has implications on the dynamics of rotating stars and on the attainable
amplitudes of the associated gravitational wave signals.
|
688c8cd2-bc14-409b-86b8-ccebd696d9d7 | 688c8cd2-bc14-409b-86b8-ccebd696d9d7 | 688c8cd2-bc14-409b-86b8-ccebd696d9d7 | human | null | null | none | abstracts | Torsional oscillations of longitudinally inhomogeneous coronal loops | null | We explore the effect of an inhomogeneous mass density field on frequencies
and wave profiles of torsional Alfven oscillations in solar coronal loops.
Dispersion relations for torsional oscillations are derived analytically in
limits of weak and strong inhomogeneities. These analytical results are
verified by numerical solutions, which are valid for a wide range of
inhomogeneity strength. It is shown that the inhomogeneous mass density field
leads to the reduction of a wave frequency of torsional oscillations, in
comparison to that of estimated from mass density at the loop apex. This
frequency reduction results from the decrease of an average Alfven speed as far
as the inhomogeneous loop is denser at its footpoints. The derived dispersion
relations and wave profiles are important for potential observations of
torsional oscillations which result in periodic variations of spectral line
widths. Torsional oscillations offer an additional powerful tool for a
development of coronal seismology.
|
e4b76652-0b33-46fd-a190-6f0be3c35b09 | e4b76652-0b33-46fd-a190-6f0be3c35b09 | e4b76652-0b33-46fd-a190-6f0be3c35b09 | human | null | null | none | abstracts | Pseudo-random Puncturing: A Technique to Lower the Error Floor of Turbo
Codes | null | It has been observed that particular rate-1/2 partially systematic parallel
concatenated convolutional codes (PCCCs) can achieve a lower error floor than
that of their rate-1/3 parent codes. Nevertheless, good puncturing patterns can
only be identified by means of an exhaustive search, whilst convergence towards
low bit error probabilities can be problematic when the systematic output of a
rate-1/2 partially systematic PCCC is heavily punctured. In this paper, we
present and study a family of rate-1/2 partially systematic PCCCs, which we
call pseudo-randomly punctured codes. We evaluate their bit error rate
performance and we show that they always yield a lower error floor than that of
their rate-1/3 parent codes. Furthermore, we compare analytic results to
simulations and we demonstrate that their performance converges towards the
error floor region, owning to the moderate puncturing of their systematic
output. Consequently, we propose pseudo-random puncturing as a means of
improving the bandwidth efficiency of a PCCC and simultaneously lowering its
error floor.
|
1be350d5-7555-44ea-8c37-ee412403dc8c | 1be350d5-7555-44ea-8c37-ee412403dc8c | 1be350d5-7555-44ea-8c37-ee412403dc8c | human | null | null | none | abstracts | The Arctic Circle Revisited | null | The problem of limit shapes in the six-vertex model with domain wall boundary
conditions is addressed by considering a specially tailored bulk correlation
function, the emptiness formation probability. A closed expression of this
correlation function is given, both in terms of certain determinant and
multiple integral, which allows for a systematic treatment of the limit shapes
of the model for full range of values of vertex weights. Specifically, we show
that for vertex weights corresponding to the free-fermion line on the phase
diagram, the emptiness formation probability is related to a one-matrix model
with a triple logarithmic singularity, or Triple Penner model. The saddle-point
analysis of this model leads to the Arctic Circle Theorem, and its
generalization to the Arctic Ellipses, known previously from domino tilings.
|
6fb92c80-2577-4100-a790-ac9f0227700a | 6fb92c80-2577-4100-a790-ac9f0227700a | 6fb92c80-2577-4100-a790-ac9f0227700a | human | null | null | none | abstracts | Generalized Nariai Solutions for Yang-type Monopoles | null | A detailed study of the geometries that emerge by a gravitating generalized
Yang monopole in even dimensions is carried out. In particular, those which
present black hole and cosmological horizons. This two-horizon system is
thermally unstable. The process of thermalization will drive both horizons to
coalesce. This limit is what is profusely studied in this paper. It is shown
that eventhough coordinate distance shrinks to zero, physical distance does
not. So, there is some remaining space which geometry has been computed and
identified as a generalized Nariai solution. The thermal properties of this new
spacetime are then calculated. Topics, as the elliptical relation between radii
of spheres in the geometry or a discussion about whether a mass-type term
should be present in the line element or not, are also included.
|
b22d4223-ce68-42d0-8d34-7f0a0d2ffde0 | b22d4223-ce68-42d0-8d34-7f0a0d2ffde0 | b22d4223-ce68-42d0-8d34-7f0a0d2ffde0 | human | null | null | none | abstracts | Metal-insulator transition in the low-dimensional organic conductor
(TMTSF)2FSO3 probed by infrared microspectroscopy | null | We present measurements of the infrared response of the quasi-one-dimensional
organic conductor (TMTSF)2$SO3 along (E||a) and perpendicular (E||b') to the
stacking axis as a function of temperature. Above the metal-insulator
transition related to the anion ordering the optical conductivity spectra show
a Drude-like response. Below the transition an energy gap of about 1500 cm-1
(185 meV) opens, leading to the corresponding charge transfer band in the
optical conductivity spectra. The analysis of the infrared-active vibrations
gives evidence for the long-range crystal structure modulation below the
transition temperature and for the short-range order fluctuations of the
lattice modulation above the transition temperature. Also we report about a new
infrared mode at around 710 cm-1 with a peculiar temperature behavior, which
has so far not been observed in any other (TMTSF)2X salt showing a
metal-insulator transition. A qualitative model based on the coupling between
the TMTSF molecule vibration and the reorientation of electrical dipole moment
of the FSO3 anion is proposed, in order to explain the anomalous behavior of
the new mode.
|
bf06b7f5-e75b-4c3f-972d-260b679cbdcc | bf06b7f5-e75b-4c3f-972d-260b679cbdcc | bf06b7f5-e75b-4c3f-972d-260b679cbdcc | human | null | null | none | abstracts | Shaped angular dependence of the spin transfer torque and microwave
generation without magnetic field | null | The generation of oscillations in the microwave frequency range is one of the
most important applications expected from spintronics devices exploiting the
spin transfer phenomenon. We report transport and microwave power measurements
on specially designed nanopillars for which a non-standard angular dependence
of the spin transfer torque (wavy variation) is predicted by theoretical
models. We observe a new kind of current-induced dynamics that is characterized
by large angle precessions in the absence of any applied field, as this is also
predicted by simulation with such a wavy angular dependence of the torque. This
type of non-standard nanopillars can represent an interesting way for the
implementation of spin transfer oscillators since they are able to generate
microwave oscillations without applied magnetic field. We also emphasize the
theoretical implications of our results on the angular dependence of the
torque.
|
cc815d3c-088e-4b56-88c5-5bee6a8f8531 | cc815d3c-088e-4b56-88c5-5bee6a8f8531 | cc815d3c-088e-4b56-88c5-5bee6a8f8531 | human | null | null | none | abstracts | Reality of linear and angular momentum expectation values in bound
states | null | In quantum mechanics textbooks the momentum operator is defined in the
Cartesian coordinates and rarely the form of the momentum operator in spherical
polar coordinates is discussed. Consequently one always generalizes the
Cartesian prescription to other coordinates and falls in a trap. In this work
we introduce the difficulties one faces when the question of the momentum
operator in spherical polar coordinate comes. We have tried to point out most
of the elementary quantum mechanical results, related to the momentum operator,
which has coordinate dependence. We explicitly calculate the momentum
expectation values in various bound states and show that the expectation value
really turns out to be zero, a consequence of the fact that the momentum
expectation value is real. We comment briefly on the status of the angular
variables in quantum mechanics and the problems related in interpreting them as
dynamical variables. At the end, we calculate the Heisenberg's equation of
motion for the radial component of the momentum for the Hydrogen atom.
|
9316c9a9-dcf5-45bb-a958-71fa85de700d | 9316c9a9-dcf5-45bb-a958-71fa85de700d | 9316c9a9-dcf5-45bb-a958-71fa85de700d | human | null | null | none | abstracts | Rich methane premixed laminar flames doped by light unsaturated
hydrocarbons - Part I : allene and propyne | null | The structure of three laminar premixed rich flames has been investigated: a
pure methane flame and two methane flames doped by allene and propyne,
respectively. The gases of the three flames contain 20.9% (molar) of methane
and 33.4% of oxygen, corresponding to an equivalence ratio of 1.25 for the pure
methane flame. In both doped flames, 2.49% of C3H4 was added, corresponding to
a ratio C3H4/CH4 of 12% and an equivalence ratio of 1.55. The three flames have
been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant,
with a gas velocity at the burner of 36 cm/s at 333 K. The concentration
profiles of stable species were measured by gas chromatography after sampling
with a quartz microprobe. Quantified species included carbon monoxide and
dioxide, methane, oxygen, hydrogen, ethane, ethylene, acetylene, propyne,
allene, propene, propane, 1,2-butadiene, 1,3-butadiene, 1-butene, isobutene,
1-butyne, vinylacetylene, and benzene. The temperature was measured using a
PtRh (6%)-PtRh (30%) thermocouple settled inside the enclosure and ranged from
700 K close to the burner up to 1850 K. In order to model these new results,
some improvements have been made to a mechanism previously developed in our
laboratory for the reactions of C3-C4 unsaturated hydrocarbons. The main
reaction pathways of consumption of allene and propyne and of formation of C6
aromatic species have been derived from flow rate analyses.
|
aa6c30c2-b63d-4809-b57b-3b995fd8deda | aa6c30c2-b63d-4809-b57b-3b995fd8deda | aa6c30c2-b63d-4809-b57b-3b995fd8deda | human | null | null | none | abstracts | The lifetime of unstable particles in electromagnetic fields | null | We show that the electromagnetic moments of unstable particles (resonances)
have an absorptive contribution which quantifies the change of the particle's
lifetime in an external electromagnetic field. To give an example we compute
here the imaginary part of the magnetic moment for the cases of the muon and
the neutron at leading order in the electroweak coupling. We also consider an
analogous effect for the strongly-decaying $\Delta$(1232) resonance. The result
for the muon is Im$ \mu = e G_F^2 m^3/768 \pi^3$, with $e$ the charge and $m$
the mass of the muon, $G_F$ the Fermi constant, which in an external magnetic
field of $B$ Tesla give rise to the relative change in the muon lifetime of
$3\times 10^{-15} B$. For neutron the effect is of a similar magnitude. We
speculate on the observable implications of this effect.
|
c0628665-afb4-49c0-ad16-7c85c93207e8 | c0628665-afb4-49c0-ad16-7c85c93207e8 | c0628665-afb4-49c0-ad16-7c85c93207e8 | human | null | null | none | abstracts | An equilibrium problem for the limiting eigenvalue distribution of
banded Toeplitz matrices | null | We study the limiting eigenvalue distribution of $n\times n$ banded Toeplitz
matrices as $n\to \infty$. From classical results of Schmidt-Spitzer and
Hirschman it is known that the eigenvalues accumulate on a special curve in the
complex plane and the normalized eigenvalue counting measure converges weakly
to a measure on this curve as $n\to\infty$. In this paper, we characterize the
limiting measure in terms of an equilibrium problem. The limiting measure is
one component of the unique vector of measures that minimes an energy
functional defined on admissible vectors of measures. In addition, we show that
each of the other components is the limiting measure of the normalized counting
measure on certain generalized eigenvalues.
|
b02fe561-dbe3-44cf-9c44-769b1d8f831f | b02fe561-dbe3-44cf-9c44-769b1d8f831f | b02fe561-dbe3-44cf-9c44-769b1d8f831f | human | null | null | none | abstracts | Exponential growth rates in a typed branching diffusion | null | We study the high temperature phase of a family of typed branching diffusions
initially studied in [Ast\'{e}risque 236 (1996) 133--154] and [Lecture Notes in
Math. 1729 (2000) 239--256 Springer, Berlin]. The primary aim is to establish
some almost-sure limit results for the long-term behavior of this particle
system, namely the speed at which the population of particles colonizes both
space and type dimensions, as well as the rate at which the population grows
within this asymptotic shape. Our approach will include identification of an
explicit two-phase mechanism by which particles can build up in sufficient
numbers with spatial positions near $-\gamma t$ and type positions near $\kappa
\sqrt{t}$ at large times $t$. The proofs involve the application of a variety
of martingale techniques--most importantly a ``spine'' construction involving a
change of measure with an additive martingale. In addition to the model's
intrinsic interest, the methodologies presented contain ideas that will adapt
to other branching settings. We also briefly discuss applications to traveling
wave solutions of an associated reaction--diffusion equation.
|
2bb9b712-d0e1-4bed-a7a5-c19f9d1dad0f | 2bb9b712-d0e1-4bed-a7a5-c19f9d1dad0f | 2bb9b712-d0e1-4bed-a7a5-c19f9d1dad0f | human | null | null | none | abstracts | The Exact Boundary Condition to Solve the Schrodinger Equation of Many
Electron System | null | In an attempt to bypass the sign problem in quantum Monte Carlo simulation of
electronic systems within the framework of fixed node approach, we derive the
exclusion principle "Two electrons can't be at the same external isopotential
surface simultaneously" using the first postulate of quantum mechanics. We
propose the exact Coulomb-Exchange nodal surface i.e. the exact boundary
condition to solve the non-relativistic Schrodinger equation for the
non-degenerate ground state of atoms and molecules. This boundary condition was
applied to compute the ground state energies of N, Ne, Li2, Be2, B2, C2, N2,
O2, F2, and H2O systems using diffusion Monte Carlo method. The ground state
energies thus obtained agree well with the exact estimate of non-relativistic
energies.
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90b07d14-8904-4309-9655-0d5d911dad98 | 90b07d14-8904-4309-9655-0d5d911dad98 | 90b07d14-8904-4309-9655-0d5d911dad98 | human | null | null | none | abstracts | Clustering features of $^9$Be, $^{14}$N, $^7$Be, and $^8$B nuclei in
relativistic fragmentation | null | Recent studies of clustering in light nuclei with an initial energy above 1 A
GeV in nuclear treack emulsion are overviewed. The results of investigations of
the relativistic $^9$Be nuclei fragmentation in emulsion, which entails the
production of He fragments, are presented. It is shown that most precise
angular measurements provided by this technique play a crucial role in the
restoration of the excitation spectrum of the $\alpha$ particle sysytem. In
peripheral interactions $^9$Be nuclei are dissociated practically totally
through the 0$^+$ and 2$^+$ states of the $^8$Be nucleus.
The results of investigations of the dissociation of a $^{14}$N nucleus of
momentum 2.86 A GeV/c in emulsion are presented as example of more complicated
system. The momentum and correlation characteristics of $\alpha$ particles for
the $^{14}$N$\to3\alpha+X$ channel in the laboratory system and the rest
systems of 3$\alpha$ particles were considered in detail.
Topology of charged fragments produced in peripheral relativistic
dissociation of radioactive $^8$B, $^7$Be nuclei in emulsion is studied.
|
48e3bb03-642f-4897-a0b1-4a8c8c63b0e0 | 48e3bb03-642f-4897-a0b1-4a8c8c63b0e0 | 48e3bb03-642f-4897-a0b1-4a8c8c63b0e0 | human | null | null | none | abstracts | Quantum non-local effects with Bose-Einstein condensates | null | We study theoretically the properties of two Bose-Einstein condensates in
different spin states, represented by a double Fock state. Individual
measurements of the spins of the particles are performed in transverse
directions, giving access to the relative phase of the condensates. Initially,
this phase is completely undefined, and the first measurements provide random
results. But a fixed value of this phase rapidly emerges under the effect of
the successive quantum measurements, giving rise to a quasi-classical situation
where all spins have parallel transverse orientations. If the number of
measurements reaches its maximum (the number of particles), quantum effects
show up again, giving rise to violations of Bell type inequalities. The
violation of BCHSH inequalities with an arbitrarily large number of spins may
be comparable (or even equal) to that obtained with two spins.
|
b56e1829-f8cc-42ed-aa49-5baba2466e86 | b56e1829-f8cc-42ed-aa49-5baba2466e86 | b56e1829-f8cc-42ed-aa49-5baba2466e86 | human | null | null | none | abstracts | Low mass visual binaries in the solar neighbourhood: The case of
HD141272 | null | We search for stellar and substellar companions of young nearby stars to
investigate stellar multiplicity and formation of stellar and substellar
companions. We detect common proper-motion companions of stars via multi-epoch
imaging. Their companionship is finally confirmed with photometry and
spectroscopy. Here we report the discovery of a new co-moving (13 sigma)
stellar companion ~17.8 arcsec (350 AU in projected separation) north of the
nearby star HD141272 (21 pc). With EMMI/NTT optical spectroscopy we determined
the spectral type of the companion to be M3+-0.5V. The derived spectral type as
well as the near infrared photometry of the companion are both fully consistent
with a 0.26+-0.07 Msol dwarf located at the distance of HD141272 (21 pc).
Furthermore the photometry data rules out the pre-main sequence status, since
the system is consistent with the ZAMS of the Pleiades.
|
f6e6da2e-0265-4e31-bd67-442eede5d1b8 | f6e6da2e-0265-4e31-bd67-442eede5d1b8 | f6e6da2e-0265-4e31-bd67-442eede5d1b8 | human | null | null | none | abstracts | Sterile neutrinos at the CNGS | null | We study the potential of the CNGS beam in constraining the parameter space
of a model with one sterile neutrino separated from three active ones by an
$\mathcal{O}(\eVq)$ mass-squared difference, $\Dmq_\Sbl$. We perform our
analysis using the OPERA detector as a reference (our analysis can be upgraded
including a detailed simulation of the ICARUS detector). We point out that the
channel with the largest potential to constrain the sterile neutrino parameter
space at the CNGS beam is $\nu_\mu \to \nu_\tau$. The reason for that is
twofold: first, the active-sterile mixing angle that governs this oscillation
is the less constrained by present experiments; second, this is the signal for
which both OPERA and ICARUS have been designed, and thus benefits from an
extremely low background. In our analysis we also took into account $\nu_\mu
\to \nu_e$ oscillations. We find that the CNGS potential to look for sterile
neutrinos is limited with nominal intensity of the beam, but it is
significantly enhanced with a factor 2 to 10 increase in the neutrino flux.
Data from both channels allow us, in this case, to constrain further the
four-neutrino model parameter space. Our results hold for any value of
$\Dmq_\Sbl \gtrsim 0.1 \eVq$, \textit{i.e.} when oscillations driven by this
mass-squared difference are averaged. We have also checked that the bound on
$\theta_{13}$ that can be put at the CNGS is not affected by the possible
existence of sterile neutrinos.
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218e79f5-ba00-41e2-ab78-bafd01ab2430 | 218e79f5-ba00-41e2-ab78-bafd01ab2430 | 218e79f5-ba00-41e2-ab78-bafd01ab2430 | human | null | null | none | abstracts | Evolution of the Carter constant for inspirals into a black hole: effect
of the black hole quadrupole | null | We analyze the effect of gravitational radiation reaction on generic orbits
around a body with an axisymmetric mass quadrupole moment Q to linear order in
Q, to the leading post-Newtonian order, and to linear order in the mass ratio.
This system admits three constants of the motion in absence of radiation
reaction: energy, angular momentum, and a third constant analogous to the
Carter constant. We compute instantaneous and time-averaged rates of change of
these three constants. For a point particle orbiting a black hole, Ryan has
computed the leading order evolution of the orbit's Carter constant, which is
linear in the spin. Our result, when combined with an interaction quadratic in
the spin (the coupling of the black hole's spin to its own radiation reaction
field), gives the next to leading order evolution. The effect of the
quadrupole, like that of the linear spin term, is to circularize eccentric
orbits and to drive the orbital plane towards antialignment with the symmetry
axis. In addition we consider a system of two point masses where one body has a
single mass multipole or current multipole. To linear order in the mass ratio,
to linear order in the multipole, and to the leading post-Newtonian order, we
show that there does not exist an analog of the Carter constant for such a
system (except for the cases of spin and mass quadrupole). With mild additional
assumptions, this result falsifies the conjecture that all vacuum, axisymmetric
spacetimes posess a third constant of geodesic motion.
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02ffd37a-1f71-4b4b-8322-e2d4c83c27c1 | 02ffd37a-1f71-4b4b-8322-e2d4c83c27c1 | 02ffd37a-1f71-4b4b-8322-e2d4c83c27c1 | human | null | null | none | abstracts | Simulation of Robustness against Lesions of Cortical Networks | null | Structure entails function and thus a structural description of the brain
will help to understand its function and may provide insights into many
properties of brain systems, from their robustness and recovery from damage, to
their dynamics and even their evolution. Advances in the analysis of complex
networks provide useful new approaches to understanding structural and
functional properties of brain networks. Structural properties of networks
recently described allow their characterization as small-world, random
(exponential) and scale-free. They complement the set of other properties that
have been explored in the context of brain connectivity, such as topology,
hodology, clustering, and hierarchical organization. Here we apply new network
analysis methods to cortical inter-areal connectivity networks for the cat and
macaque brains. We compare these corticocortical fibre networks to benchmark
rewired, small-world, scale-free and random networks, using two analysis
strategies, in which we measure the effects of the removal of nodes and
connections on the structural properties of the cortical networks. The brain
networks' structural decay is in most respects similar to that of scale-free
networks. The results implicate highly connected hub-nodes and bottleneck
connections as structural basis for some of the conditional robustness of brain
systems. This informs the understanding of the development of brain networks'
connectivity.
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fb303e5d-a9b2-4432-a356-d27f4ce87ab4 | fb303e5d-a9b2-4432-a356-d27f4ce87ab4 | fb303e5d-a9b2-4432-a356-d27f4ce87ab4 | human | null | null | none | abstracts | A Study of $B_{d}^0 \to J/\Psi \eta^{(\prime)}$ Decays in the pQCD
Approach | null | Motivated by the very recent measurement of the branching ratio of ${B_d^0}
\to J/\psi \eta$ decay, we calculate the branching ratios of ${B_d}^0 \to
J/\psi \eta$ and ${B_d}^0 \to J/\Psi \eta'$ decays in the perturbative QCD
(pQCD) approach. The pQCD predictions for the branching ratios of considered
decays are: $BR(B_d^0 \to J/\Psi \eta) = (1.96 ^{+9.68}_{-0.65}) \times
10^{-6}$, which is consistent with the first experimental measurement within
errors; while $BR(B_d^0 \to J/\Psi \eta') = (1.09 ^{+3.76}_{-0.25}) \times
10^{-6}$, very similar with $B_d^0 \to \jpsi \eta$ decay and can be tested by
the forthcoming LHC experiments. The measurements of these decay channels may
help us to understand the QCD dynamics in the corresponding energy scale,
especially the reliability of pQCD approach to these kinds of B meson decays.
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