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3f2479b9-c1aa-426c-ac75-4518f7bb70e5 | 3f2479b9-c1aa-426c-ac75-4518f7bb70e5 | 3f2479b9-c1aa-426c-ac75-4518f7bb70e5 | human | null | null | none | abstracts | Detecting and Characterizing Planetary Systems with Transit Timing | null | In the coming decades, research in extrasolar planets aims to advance two
goals: 1) detecting and characterizing low-mass planets increasingly similar to
the Earth, and 2) improving our understanding of planet formation. We present a
new planet detection method that is capable of making large advances towards
both of these objectives and describe a modest network of telescopes that is
able to make the requisite observations. In a system where a known planet
transits its host star, a second planet in that system will cause the time
between transits to vary. These transit timing variations can be used to infer
the orbital elements and mass of the perturbing planet even if it has a mass
that is smaller than the mass of the Earth. This detection technique
complements other techniques because it is most sensitive in mean-motion
resonances where, due to degeneracies, other techniques have reduced
sensitivity. Small ground-based observatories have already exceeded the
photometric precision necessary to detect sub-Earth mass planets. However, TTV
planet searches are currently limited by the relatively small number of
high-precision transit data and insufficient observing time on existing
telescopes. These issues will be compounded as the number of known transiting
planets suitable for TTV study will increase substantially in the near future.
A relatively modest investment in a ground-based network of small ($\sim 0.5
{\rm m}$ telescopes could provide the needed coverage and so dramatically
increase the effectiveness of transit timing observations.
|
e964cf72-4906-4b21-a0ce-c92f41803d9c | e964cf72-4906-4b21-a0ce-c92f41803d9c | e964cf72-4906-4b21-a0ce-c92f41803d9c | human | null | null | none | abstracts | d-wave superconductivity from electron-phonon interactions | null | I examine electron-phonon mediated superconductivity in the intermediate
coupling and phonon frequency regime of the quasi-2D Holstein model. I use an
extended Migdal-Eliashberg theory which includes vertex corrections and spatial
fluctuations. I find a d-wave superconducting state that is unique close to
half-filling. The order parameter undergoes a transition to s-wave
superconductivity on increasing filling. I explain how the inclusion of both
vertex corrections and spatial fluctuations is essential for the prediction of
a d-wave order parameter. I then discuss the effects of a large Coulomb
pseudopotential on the superconductivity (such as is found in contemporary
superconducting materials like the cuprates), which results in the destruction
of the s-wave states, while leaving the d-wave states unmodified.
|
ede2d3e5-1da2-4544-82cf-2993da2d2a6e | ede2d3e5-1da2-4544-82cf-2993da2d2a6e | ede2d3e5-1da2-4544-82cf-2993da2d2a6e | human | null | null | none | abstracts | A Finite Element framework for computation of protein normal modes and
mechanical response | null | A coarse-grained computational procedure based on the Finite Element Method
is proposed to calculate the normal modes and mechanical response of proteins
and their supramolecular assemblies. Motivated by the elastic network model,
proteins are modeled as homogeneous isotropic elastic solids with volume
defined by their solvent-excluded surface. The discretized Finite Element
representation is obtained using a surface simplification algorithm that
facilitates the generation of models of arbitrary prescribed spatial
resolution. The procedure is applied to compute the normal modes of a mutant of
T4 phage lysozyme and of filamentous actin, as well as the critical Euler
buckling load of the latter when subject to axial compression. Results compare
favorably with all-atom normal mode analysis, the Rotation Translation Blocks
procedure, and experiment. The proposed methodology establishes a computational
framework for the calculation of protein mechanical response that facilitates
the incorporation of specific atomic-level interactions into the model,
including aqueous-electrolyte-mediated electrostatic effects. The procedure is
equally applicable to proteins with known atomic coordinates as it is to
electron density maps of proteins, protein complexes, and supramolecular
assemblies of unknown atomic structure.
|
eb364d79-53d9-4053-97fb-17093b0021fe | eb364d79-53d9-4053-97fb-17093b0021fe | eb364d79-53d9-4053-97fb-17093b0021fe | human | null | null | none | abstracts | Sum-over-states vs quasiparticle pictures of coherent correlation
spectroscopy of excitons in semiconductors; femtosecond analogues of
multidimensional NMR | null | Two-dimensional correlation spectroscopy (2DCS) based on the nonlinear
optical response of excitons to sequences of ultrafast pulses, has the
potential to provide some unique insights into carrier dynamics in
semiconductors. The most prominent feature of 2DCS, cross peaks, can best be
understood using a sum-over-states picture involving the many-body eigenstates.
However, the optical response of semiconductors is usually calculated by
solving truncated equations of motion for dynamical variables, which result in
a quasiparticle picture. In this work we derive Green's function expressions
for the four wave mixing signals generated in various phase-matching directions
and use them to establish the connection between the two pictures. The formal
connection with Frenkel excitons (hard-core bosons) and vibrational excitons
(soft-core bosons) is pointed out.
|
fcf7a0f3-eb21-4c49-87e0-25a433806c65 | fcf7a0f3-eb21-4c49-87e0-25a433806c65 | fcf7a0f3-eb21-4c49-87e0-25a433806c65 | human | null | null | none | abstracts | Are constant loop widths an artifact of the background and the spatial
resolution? | null | We study the effect of the coronal background in the determination of the
diameter of EUV loops, and we analyze the suitability of the procedure followed
in a previous paper (L\'opez Fuentes, Klimchuk & D\'emoulin 2006) for
characterizing their expansion properties. For the analysis we create different
synthetic loops and we place them on real backgrounds from data obtained with
the Transition Region and Coronal Explorer (\textit{TRACE}). We apply to these
loops the same procedure followed in our previous works, and we compare the
results with real loop observations. We demonstrate that the procedure allows
us to distinguish constant width loops from loops that expand appreciably with
height, as predicted by simple force-free field models. This holds even for
loops near the resolution limit. The procedure can easily determine when loops
are below resolution limit and therefore not reliably measured. We find that
small-scale variations in the measured loop width are likely due to
imperfections in the background subtraction. The greatest errors occur in
especially narrow loops and in places where the background is especially bright
relative to the loop. We stress, however, that these effects do not impact the
ability to measure large-scale variations. The result that observed loops do
not expand systematically with height is robust.
|
7c77bbc0-d6ed-47e5-8db9-fcafdef9a7a5 | 7c77bbc0-d6ed-47e5-8db9-fcafdef9a7a5 | 7c77bbc0-d6ed-47e5-8db9-fcafdef9a7a5 | human | null | null | none | abstracts | A measure of the non-Gaussian character of a quantum state | null | We address the issue of quantifying the non-Gaussian character of a bosonic
quantum state and introduce a non-Gaussianity measure based on the
Hilbert-Schmidt distance between the state under examination and a reference
Gaussian state. We analyze in details the properties of the proposed measure
and exploit it to evaluate the non-Gaussianity of some relevant single- and
multi-mode quantum states. The evolution of non-Gaussianity is also analyzed
for quantum states undergoing the processes of Gaussification by loss and
de-Gaussification by photon-subtraction. The suggested measure is easily
computable for any state of a bosonic system and allows to define a
corresponding measure for the non-Gaussian character of a quantum operation.
|
95c2feea-9b61-402e-8331-29706c0bd2b5 | 95c2feea-9b61-402e-8331-29706c0bd2b5 | 95c2feea-9b61-402e-8331-29706c0bd2b5 | human | null | null | none | abstracts | Mapping the Youngest Galaxies to Redshift One | null | We describe results of a narrow band search for ultra-strong emission line
galaxies (USELs) with EW(H beta) > 30 A. 542 candidate galaxies are found in a
half square degree survey using two ~100 Angstrom 8150 A and 9140 A filters
with Subaru/SuprimeCam. Followup spectroscopy for randomly selected objects in
the sample with KeckII/DEIMOS shows they consist of [OIII] 5007, [OII] 3727,
and H alpha selected strong-emission line galaxies at intermediate redshifts (z
< 1), and Ly alpha emitting galaxies at high-redshift (z >> 5). We determine
the H beta luminosity functions and the star formation density of the USELs,
which is 5-10% of the value found from ultraviolet continuum objects at z=0-1,
suggesting they correspond to a major epoch in galaxy formation at these
redshifts. Many USELs show the temperature-sensitive [OIII] 4363 auroral lines
and about a dozen have oxygen abundances characteristic of eXtremely Metal Poor
Galaxies (XMPGs). These XMPGs are the most distant known today. Our high yield
rate of XMPGs suggests this is a powerful method for finding such populations.
The lowest metallicity measured in our sample is 12+log(O/H) = 7.06
(6.78-7.44), close to the minimum metallicity found in local galaxies. The
luminosities, metallicities and star formation rates of USELs are consistent
with the strong emitters being start-up intermediate mass galaxies and suggest
that galaxies are still forming in relatively chemically pristine sites at z <
1.
|
268deef1-2681-4edf-97d2-5f4d854fc1ca | 268deef1-2681-4edf-97d2-5f4d854fc1ca | 268deef1-2681-4edf-97d2-5f4d854fc1ca | human | null | null | none | abstracts | Discovery of extreme asymmetry in the debris disk surrounding HD 15115 | null | We report the first scattered light detection of a dusty debris disk
surrounding the F2V star HD 15115 using the Hubble Space Telescope in the
optical, and Keck adaptive optics in the near-infrared. The most remarkable
property of the HD 15115 disk relative to other debris disks is its extreme
length asymmetry. The east side of the disk is detected to ~315 AU radius,
whereas the west side of the disk has radius >550 AU. We find a blue optical to
near-infrared scattered light color relative to the star that indicates grain
scattering properties similar to the AU Mic debris disk. The existence of a
large debris disk surrounding HD 15115 adds further evidence for membership in
the Beta Pic moving group, which was previously argued based on kinematics
alone. Here we hypothesize that the extreme disk asymmetry is due to dynamical
perturbations from HIP 12545, an M star 0.5 degrees (0.38 pc) east of HD 15115
that shares a common proper motion vector, heliocentric distance, galactic
space velocity, and age.
|
1af9407f-32ec-46c4-a484-774190789cd0 | 1af9407f-32ec-46c4-a484-774190789cd0 | 1af9407f-32ec-46c4-a484-774190789cd0 | human | null | null | none | abstracts | The Mathematical Universe | null | I explore physics implications of the External Reality Hypothesis (ERH) that
there exists an external physical reality completely independent of us humans.
I argue that with a sufficiently broad definition of mathematics, it implies
the Mathematical Universe Hypothesis (MUH) that our physical world is an
abstract mathematical structure. I discuss various implications of the ERH and
MUH, ranging from standard physics topics like symmetries, irreducible
representations, units, free parameters, randomness and initial conditions to
broader issues like consciousness, parallel universes and Godel incompleteness.
I hypothesize that only computable and decidable (in Godel's sense) structures
exist, which alleviates the cosmological measure problem and help explain why
our physical laws appear so simple. I also comment on the intimate relation
between mathematical structures, computations, simulations and physical
systems.
|
18a7b7b7-bf2b-49e4-a71b-676106e124c2 | 18a7b7b7-bf2b-49e4-a71b-676106e124c2 | 18a7b7b7-bf2b-49e4-a71b-676106e124c2 | human | null | null | none | abstracts | Testing String Theory with CMB | null | Future detection/non-detection of tensor modes from inflation in CMB
observations presents a unique way to test certain features of string theory.
Current limit on the ratio of tensor to scalar perturbations, r=T/S, is r <
0.3, future detection may take place for r > 10^{-2}-10^{-3}. At present all
known string theory inflation models predict tensor modes well below the level
of detection. Therefore a possible experimental discovery of tensor modes may
present a challenge to string cosmology.
The strongest bound on r in string inflation follows from the observation
that in most of the models based on the KKLT construction, the value of the
Hubble constant H during inflation must be smaller than the gravitino mass. For
the gravitino mass in the usual range, m_{3/2} < O(1) TeV, this leads to an
extremely strong bound r < 10^{-24}. A discovery of tensor perturbations with r
> 10^{-3} would imply that the gravitinos in this class of models are
superheavy, m_{3/2} > 10^{13} GeV. This would have important implications for
particle phenomenology based on string theory.
|
2a9cff67-4106-481f-8cf9-04af3c1e130f | 2a9cff67-4106-481f-8cf9-04af3c1e130f | 2a9cff67-4106-481f-8cf9-04af3c1e130f | human | null | null | none | abstracts | Behavioral response to strong aversive stimuli: A neurodynamical model | null | In this paper a theoretical model of functioning of a neural circuit during a
behavioral response has been proposed. A neural circuit can be thought of as a
directed multigraph whose each vertex is a neuron and each edge is a synapse.
It has been assumed in this paper that the behavior of such circuits is
manifested through the collective behavior of neurons belonging to that
circuit. Behavioral information of each neuron is contained in the coefficients
of the fast Fourier transform (FFT) over the output spike train. Those
coefficients form a vector in a multidimensional vector space. Behavioral
dynamics of a neuronal network in response to strong aversive stimuli has been
studied in a vector space in which a suitable pseudometric has been defined.
The neurodynamical model of network behavior has been formulated in terms of
existing memory, synaptic plasticity and feelings. The model has an analogy in
classical electrostatics, by which the notion of force and potential energy has
been introduced. Since the model takes input from each neuron in a network and
produces a behavior as the output, it would be extremely difficult or may even
be impossible to implement. But with the help of the model a possible
explanation for an hitherto unexplained neurological observation in human brain
has been offered. The model is compatible with a recent model of sequential
behavioral dynamics. The model is based on electrophysiology, but its relevance
to hemodynamics has been outlined.
|
481879ff-66b8-45b8-a431-17a405ea7280 | 481879ff-66b8-45b8-a431-17a405ea7280 | 481879ff-66b8-45b8-a431-17a405ea7280 | human | null | null | none | abstracts | Galactic Wind Signatures around High Redshift Galaxies | null | We carry out cosmological chemodynamical simulations with different strengths
of supernova (SN) feedback and study how galactic winds from star-forming
galaxies affect the features of hydrogen (HI) and metal (CIV and OVI)
absorption systems in the intergalactic medium at high redshift. We find that
the outflows tend to escape to low density regions, and hardly affect the dense
filaments visible in HI absorption. As a result, the strength of HI absorption
near galaxies is not reduced by galactic winds, but even slightly increases. We
also find that a lack of HI absorption for lines of sight (LOS) close to
galaxies, as found by Adelberger et al., can be created by hot gas around the
galaxies induced by accretion shock heating. In contrast to HI, metal
absorption systems are sensitive to the presence of winds. The models without
feedback can produce the strong CIV and OVI absorption lines in LOS within 50
kpc from galaxies, while strong SN feedback is capable of creating strong CIV
and OVI lines out to about twice that distance. We also analyze the mean
transmissivity of HI, CIV, and OVI within 1 h$^{-1}$ Mpc from star-forming
galaxies. The probability distribution of the transmissivity of HI is
independent of the strength of SN feedback, but strong feedback produces LOS
with lower transmissivity of metal lines. Additionally, strong feedback can
produce strong OVI lines even in cases where HI absorption is weak. We conclude
that OVI is probably the best tracer for galactic winds at high redshift.
|
e0cf69da-4440-4b4f-aeb8-a938aa2bd0a8 | e0cf69da-4440-4b4f-aeb8-a938aa2bd0a8 | e0cf69da-4440-4b4f-aeb8-a938aa2bd0a8 | human | null | null | none | abstracts | An integral field spectroscopic survey for high redshift damped
Lyman-alpha galaxies | null | We search for galaxy counterparts to damped Lyman-alpha absorbers (DLAs) at
z>2 towards nine quasars, which have 14 DLAs and 8 sub-DLAs in their spectra.
We use integral field spectroscopy to search for Ly-alpha emission line objects
at the redshifts of the absorption systems. Besides recovering two previously
confirmed objects, we find six statistically significant candidate Ly-alpha
emission line objects. The candidates are identified as having wavelengths
close to the DLA line where the background quasar emission is absorbed. In
comparison with the six currently known Ly-alpha emitting DLA galaxies the
candidates have similar line fluxes and line widths, while velocity offsets
between the emission lines and systemic DLA redshifts are larger. The impact
parameters are larger than 10 kpc, and lower column density systems are found
at larger impact parameters. Assuming that a single gas cloud extends from the
QSO line of sight to the location of the candidate emission line, we find that
the average candidate DLA galaxy is surrounded by neutral gas with an
exponential scale length of ~5 kpc.
|
f8e99065-f557-4861-8a9c-0fff3c218ed5 | f8e99065-f557-4861-8a9c-0fff3c218ed5 | f8e99065-f557-4861-8a9c-0fff3c218ed5 | human | null | null | none | abstracts | Collective excitations in a magnetically doped quantized Hall
ferromagnet | null | A theory of collective states in a magnetically quantized two-dimensional
electron gas (2DEG) with half-filled Landau level (quantized Hall ferromagnet)
in the presence of magnetic 3d impurities is developed. The spectrum of bound
and delocalized spin-excitons as well as the renormalization of Zeeman
splitting of the impurity 3d levels due to the indirect exchange interaction
with the 2DEG are studied for the specific case of n-type GaAs doped with Mn
where the Lande` g-factors of impurity and 2DEG have opposite signs. If the
sign of the 2DEG g-factor is changed due to external influences, then impurity
related transitions to new ground state phases, presenting various spin-flip
and skyrmion-like textures, are possible. Conditions for existence of these
phases are discussed. PACS: 73.43.Lp, 73.21.Fg, 72.15.Rn
|
694891c7-f9e1-4ffc-bd1c-3d12e8156a8a | 694891c7-f9e1-4ffc-bd1c-3d12e8156a8a | 694891c7-f9e1-4ffc-bd1c-3d12e8156a8a | human | null | null | none | abstracts | Long Gamma-Ray Burst Progenitors: Boundary Conditions and Binary Models | null | The observed association of Long Gamma-Ray Bursts (LGRBs) with peculiar Type
Ic supernovae gives support to Woosley`s collapsar/hypernova model, in which
the GRB is produced by the collapse of the rapidly rotating core of a massive
star to a black hole. The association of LGRBs with small star-forming galaxies
suggests low-metallicity to be a condition for a massive star to evolve to the
collapsar stage. Both completely-mixed single star models and binary star
models are possible. In binary models the progenitor of the GRB is a massive
helium star with a close companion. We find that tidal synchronization during
core-helium burning is reached on a short timescale (less than a few
millennia). However, the strong core-envelope coupling in the subsequent
evolutionary stages is likely to rule out helium stars with main-sequence
companions as progenitors of hypernovae/GRBs. On the other hand, helium stars
in close binaries with a neutron-star or black-hole companion can, despite the
strong core-envelope coupling in the post-helium burning phase, retain
sufficient core angular momentum to produce a hypernova/GRB.
|
9596c4b3-e60d-451d-820f-fd919677be99 | 9596c4b3-e60d-451d-820f-fd919677be99 | 9596c4b3-e60d-451d-820f-fd919677be99 | human | null | null | none | abstracts | Multiscale model of electronic behavior and localization in stretched
dry DNA | null | When the DNA double helix is subjected to external forces it can stretch
elastically to elongations reaching 100% of its natural length. These
distortions, imposed at the mesoscopic or macroscopic scales, have a dramatic
effect on electronic properties at the atomic scale and on electrical transport
along DNA. Accordingly, a multiscale approach is necessary to capture the
electronic behavior of the stretched DNA helix. To construct such a model, we
begin with accurate density-functional-theory calculations for electronic
states in DNA bases and base pairs in various relative configurations
encountered in the equilibrium and stretched forms. These results are
complemented by semi-empirical quantum mechanical calculations for the states
of a small size [18 base pair poly(CG)-poly(CG)] dry, neutral DNA sequence,
using previously published models for stretched DNA. The calculated electronic
states are then used to parametrize an effective tight-binding model that can
describe electron hopping in the presence of environmental effects, such as the
presence of stray water molecules on the backbone or structural features of the
substrate. These effects introduce disorder in the model hamiltonian which
leads to electron localization. The localization length is smaller by several
orders of magnitude in stretched DNA relative to that in the unstretched
structure.
|
189d7c88-0c19-4dfd-aa0e-be73185e4bf8 | 189d7c88-0c19-4dfd-aa0e-be73185e4bf8 | 189d7c88-0c19-4dfd-aa0e-be73185e4bf8 | human | null | null | none | abstracts | Decoherence of Quantum-Enhanced Timing Accuracy | null | Quantum enhancement of optical pulse timing accuracy is investigated in the
Heisenberg picture. Effects of optical loss, group-velocity dispersion, and
Kerr nonlinearity on the position and momentum of an optical pulse are studied
via Heisenberg equations of motion. Using the developed formalism, the impact
of decoherence by optical loss on the use of adiabatic soliton control for
beating the timing standard quantum limit [Tsang, Phys. Rev. Lett. 97, 023902
(2006)] is analyzed theoretically and numerically. The analysis shows that an
appreciable enhancement can be achieved using current technology, despite an
increase in timing jitter mainly due to the Gordon-Haus effect. The decoherence
effect of optical loss on the transmission of quantum-enhanced timing
information is also studied, in order to identify situations in which the
enhancement is able to survive.
|
8b68554f-5bdc-4509-b964-caf246443b29 | 8b68554f-5bdc-4509-b964-caf246443b29 | 8b68554f-5bdc-4509-b964-caf246443b29 | human | null | null | none | abstracts | J/psi Production in an Equilibrating Partonic System | null | Any color singlet or octet ccbar pair is created at short distances and then
expands to a full size of J/psi. Such a dynamical evolution process is included
here in calculations for the J/psi number distribution as a function of
transverse momentum and rapidity in central Au-Au collisions at both RHIC and
LHC energies. The ccbar pairs are produced in the initial collision and in the
partonic system during the prethermal and thermal stages through the partonic
channels ab to ccbar [{2S+1}L_J] and ab to ccbar [{2S+1}L_J]x, and then they
dissociate in the latter two stages. Dissociation of ccbar in the medium occurs
via two reactions: (a) color singlet ccbar plus a gluon turns to color octet
ccbar, (b) color octet ccbar plus a gluon persists as color octet. There are
modest yields of ccbar in the prethermal stage at RHIC energy and through the
reactions ab to ccbar [{2S+1}L_J] at LHC energy for partons with large average
momentum in the prethermal stage at both collider energies and in the thermal
stage at LHC energy. Production from the partonic system competes with the
suppression of the initial yield in the deconfined medium. Consequently, a
bulge within -1.5<y<1.5 has been found for the J/psi number distribution and
the ratio of J/psi number distributions for Au-Au collisions to nucleon-nucleon
collisions. This bulge is caused by the partonic system and is thus an
indicator of a deconfined partonic medium. Based on this result we suggest the
rapidity region worth measuring in future experiments at RHIC and LHC to be
-3<y<3.
|
1ba29de0-c923-493a-b024-bbc1784a0bb0 | 1ba29de0-c923-493a-b024-bbc1784a0bb0 | 1ba29de0-c923-493a-b024-bbc1784a0bb0 | human | null | null | none | abstracts | Complete Set of Polarization Transfer Observables for the $^{12}{\rm
C}(p,n)$ Reaction at 296 MeV and 0$^{\circ}$ | null | A complete set of polarization transfer observables has been measured for the
$^{12}{\rm C}(p,n)$ reaction at $T_p=296 {\rm MeV}$ and $\theta_{\rm
lab}=0^{\circ}$. The total spin transfer $\Sigma(0^{\circ})$ and the observable
$f_1$ deduced from the measured polarization transfer observables indicate that
the spin--dipole resonance at $E_x \simeq 7 {\rm MeV}$ has greater $2^-$
strength than $1^-$ strength, which is consistent with recent experimental and
theoretical studies. The results also indicate a predominance of the spin-flip
and unnatural-parity transition strength in the continuum. The exchange tensor
interaction at a large momentum transfer of $Q \simeq 3.6 {\rm fm}^{-1}$ is
discussed.
|
b06c461d-e0ae-40ce-8acb-3f52ce19f8b6 | b06c461d-e0ae-40ce-8acb-3f52ce19f8b6 | b06c461d-e0ae-40ce-8acb-3f52ce19f8b6 | human | null | null | none | abstracts | Learning from compressed observations | null | The problem of statistical learning is to construct a predictor of a random
variable $Y$ as a function of a related random variable $X$ on the basis of an
i.i.d. training sample from the joint distribution of $(X,Y)$. Allowable
predictors are drawn from some specified class, and the goal is to approach
asymptotically the performance (expected loss) of the best predictor in the
class. We consider the setting in which one has perfect observation of the
$X$-part of the sample, while the $Y$-part has to be communicated at some
finite bit rate. The encoding of the $Y$-values is allowed to depend on the
$X$-values. Under suitable regularity conditions on the admissible predictors,
the underlying family of probability distributions and the loss function, we
give an information-theoretic characterization of achievable predictor
performance in terms of conditional distortion-rate functions. The ideas are
illustrated on the example of nonparametric regression in Gaussian noise.
|
c9602f57-cc77-4914-a627-64e2755516ff | c9602f57-cc77-4914-a627-64e2755516ff | c9602f57-cc77-4914-a627-64e2755516ff | human | null | null | none | abstracts | Hamiltonian formalism in Friedmann cosmology and its quantization | null | We propose a Hamiltonian formalism for a generalized
Friedmann-Roberson-Walker cosmology model in the presence of both a variable
equation of state (EOS) parameter $w(a)$ and a variable cosmological constant
$\Lambda(a)$, where $a$ is the scale factor. This Hamiltonian system containing
1 degree of freedom and without constraint, gives Friedmann equations as the
equation of motion, which describes a mechanical system with a variable mass
object moving in a potential field. After an appropriate transformation of the
scale factor, this system can be further simplified to an object with constant
mass moving in an effective potential field. In this framework, the $\Lambda$
cold dark matter model as the current standard model of cosmology corresponds
to a harmonic oscillator. We further generalize this formalism to take into
account the bulk viscosity and other cases. The Hamiltonian can be quantized
straightforwardly, but this is different from the approach of the
Wheeler-DeWitt equation in quantum cosmology.
|
b0e3a2cd-7cdf-425a-afa3-2e60aca35003 | b0e3a2cd-7cdf-425a-afa3-2e60aca35003 | b0e3a2cd-7cdf-425a-afa3-2e60aca35003 | human | null | null | none | abstracts | Optimal stimulus and noise distributions for information transmission
via suprathreshold stochastic resonance | null | Suprathreshold stochastic resonance (SSR) is a form of noise enhanced signal
transmission that occurs in a parallel array of independently noisy identical
threshold nonlinearities, including model neurons. Unlike most forms of
stochastic resonance, the output response to suprathreshold random input
signals of arbitrary magnitude is improved by the presence of even small
amounts of noise. In this paper the information transmission performance of SSR
in the limit of a large array size is considered. Using a relationship between
Shannon's mutual information and Fisher information, a sufficient condition for
optimality, i.e. channel capacity, is derived. It is shown that capacity is
achieved when the signal distribution is Jeffrey's prior, as formed from the
noise distribution, or when the noise distribution depends on the signal
distribution via a cosine relationship. These results provide theoretical
verification and justification for previous work in both computational
neuroscience and electronics.
|
3cf2db27-6082-46ed-9c11-1cde5022164b | 3cf2db27-6082-46ed-9c11-1cde5022164b | 3cf2db27-6082-46ed-9c11-1cde5022164b | human | null | null | none | abstracts | Three Different Types of Galaxy Alignment within Dark Matter Halos | null | Using a large galaxy group catalogue based on the Sloan Digital Sky Survey
Data Release 4 we measure three different types of intrinsic galaxy alignment
within groups: halo alignment between the orientation of the brightest group
galaxies (BGG) and the distribution of its satellite galaxies, radial alignment
between the orientation of a satellite galaxy and the direction towards its
BGG, and direct alignment between the orientation of the BGG and that of its
satellites. In agreement with previous studies we find that satellite galaxies
are preferentially located along the major axis. In addition, on scales r < 0.7
Rvir we find that red satellites are preferentially aligned radially with the
direction to the BGG. The orientations of blue satellites, however, are
perfectly consistent with being isotropic. Finally, on scales r < 0.1 \Rvir, we
find a weak but significant indication for direct alignment between satellites
and BGGs. We briefly discuss the implications for weak lensing measurements.
|
723241e6-5ae5-4b29-9185-98bbc46de8b7 | 723241e6-5ae5-4b29-9185-98bbc46de8b7 | 723241e6-5ae5-4b29-9185-98bbc46de8b7 | human | null | null | none | abstracts | A very massive runaway star from Cygnus OB2 | null | Aims: We analyze the available information on the star BD+43 3654 to
investigate the possibility that it may have had its origin in the massive OB
association Cygnus OB2.
Methods: We present new spectroscopic observations allowing a reliable
spectral classification of the star, and discuss existing MSX observations of
its associated bow shock and astrometric information not previously studied.
Results: Our observations reveal that BD+43 3654 is a very early and luminous
star of spectral type O4If, with an estimated mass of (70 +/- 15) solar masses
and an age of about 1.6 Myr. The high spatial resolution of the MSX
observations allows us to determine its direction of motion in the plane of the
sky by means of the symmetry axis of the well-defined bow shock, which matches
well the orientation expected from the proper motion. Tracing back its path
across the sky we find that BD+43 3654 was located near the central, densest
region of Cygnus OB2 at a time in the past similar to its estimated age.
Conclusions: BD+43 3654 turns out to be one of the three most massive runaway
stars known, and it most likely formed in the central region of Cygnus OB2. A
runaway formation mechanism by means of dynamical ejection is consistent with
our results.
|
9ea24e9c-880d-46ff-abb6-7cff858ff62a | 9ea24e9c-880d-46ff-abb6-7cff858ff62a | 9ea24e9c-880d-46ff-abb6-7cff858ff62a | human | null | null | none | abstracts | Optical spectrum of the post-AGB star HD56126 in the region 4010-8790 AA | null | We studied in detail the optical spectrum of the post-AGB star HD56126
(IRAS07134+1005). We use high resolution spectra (R=25000 and 60000) obtained
with the echelle spectrographs of the 6-m telescope. About one and a half
thousand absorptions of neutral atoms and ions, absorption bands of C_2, CN,
and CH molecules, and interstellar bands (DIBs) are identified in the 4010 to
8790 AA wavelength region, and the depths and radial velocities of these
spectral features are measured. Differences are revealed between the variations
of the radial velocities measured from spectral features of different
excitation. In addition to the well-known variability of the Halpha profile, we
found variations in the profiles of a number of FeII, YII, and BaII lines. We
also produce an atlas of the spectrum of HD56126 and its comparison staralpha
Per. The full version of the atlas is available in electronic form from
Web-address: http://www.sao.ru/hq/ssl/Atlas/Atlas.html
|
0487631a-8289-4a56-8520-6674bc4955ca | 0487631a-8289-4a56-8520-6674bc4955ca | 0487631a-8289-4a56-8520-6674bc4955ca | human | null | null | none | abstracts | Generation of Large Number-Path Entanglement Using Linear Optics and
Feed-Forward | null | We show how an idealised measurement procedure can condense photons from two
modes into one, and how, by feeding forward the results of the measurement, it
is possible to generate efficiently superpositions of components for which only
one mode is populated, commonly called ``N00N states''. For the basic
procedure, sources of number states leak onto a beam splitter, and the output
ports are monitored by photodetectors. We find that detecting a fixed fraction
of the input at one output port suffices to direct the remainder to the same
port with high probability, however large the initial state. When instead
photons are detected at both ports, Schr\"{o}dinger cat states are produced. We
describe a circuit for making the components of such a state orthogonal, and
another for subsequent conversion to a N00N state. Our approach scales
exponentially better than existing proposals. Important applications include
quantum imaging and metrology.
|
f62be744-2e6b-433e-ab29-e9408c794341 | f62be744-2e6b-433e-ab29-e9408c794341 | f62be744-2e6b-433e-ab29-e9408c794341 | human | null | null | none | abstracts | An Inverse $f(R)$ Gravitation for Cosmic Speed up, and Dark Energy
Equivalent | null | To explain the cosmic speed up, brought to light by the recent SNIa and CMB
observations, we propose the following: a) In a spacetime endowed with a FRW
metric, we choose an empirical scale factor that best explains the
observations. b) We assume a modified gravity, generated by an unspecified
field lagrangian, $f(R)$. c) We use the adopted empirical scale factor to work
back retroactively to obtain $f(R)$, hence the term `Inverse $f(R)$'. d) Next
we consider the classic GR and a conventional FRW universe that, in addition to
its known baryonic content, possesses a hypothetical `Dark Energy' component.
We compare the two scenarios, and find the density, the pressure, and the
equation of the state of the Dark Energy required to make up for the
differences between the conventional and the modified GR models.
|
b4a9223f-106f-4be6-aa97-a8fe9ad7f196 | b4a9223f-106f-4be6-aa97-a8fe9ad7f196 | b4a9223f-106f-4be6-aa97-a8fe9ad7f196 | human | null | null | none | abstracts | Monitoring spatially heterogeneous dynamics in a drying colloidal thin
film | null | We report on a new type of experiment that enables us to monitor spatially
and temporally heterogeneous dynamic properties in complex fluids. Our approach
is based on the analysis of near-field speckles produced by light diffusely
reflected from the superficial volume of a strongly scattering medium. By
periodic modulation of an incident speckle beam we obtain pixel-wise ensemble
averages of the structure function coefficient, a measure of the dynamic
activity. To illustrate the application of our approach we follow the different
stages in the drying process of a colloidal thin film. We show that we can
access ensemble averaged dynamic properties on length scales as small as ten
micrometers over the full field of view.
|
0d2a9b05-e995-4896-9208-9f1860b35808 | 0d2a9b05-e995-4896-9208-9f1860b35808 | 0d2a9b05-e995-4896-9208-9f1860b35808 | human | null | null | none | abstracts | Mapping the circumstellar SiO maser emission in R Leo | null | The study of the innermost circumstellar layers around AGB stars is crucial
to understand how these envelopes are formed and evolve. The SiO maser emission
occurs at a few stellar radii from the central star, providing direct
information on the stellar pulsation and on the chemical and physical
properties of these regions. Our data also shed light on several aspects of the
SiO maser pumping theory that are not well understood yet. We aim to determine}
the relative spatial distribution of the 43 GHz and 86 GHz SiO maser lines in
the oxygen-rich evolved star R Leo. We have imaged with milliarcsecond
resolution, by means of Very Long Baseline Interferometry, the 43 GHz (28SiO
v=1, 2 J=1-0 and 29SiO v=0 J=1-0) and 86 GHz (28SiO v=1 J=2-1 and 29SiO v=0
J=2-1) masing regions. We confirm previous results obtained in other
oxygen-rich envelopes. In particular, when comparing the 43 GHz emitting
regions, the 28SiO v=2 transition is produced in an inner layer, closer to the
central star. On the other hand, the 86 GHz line arises in a clearly farther
shell. We have also mapped for the first time the 29SiO v=0 J=1-0 emission in R
Leo. The already reported discrepancy between the observed distributions of the
different maser lines and the theoretical predictions is also found in R Leo.
|
e2a5bfca-65ad-475d-95f4-3bd9752947d4 | e2a5bfca-65ad-475d-95f4-3bd9752947d4 | e2a5bfca-65ad-475d-95f4-3bd9752947d4 | human | null | null | none | abstracts | Partially disordered state near ferromagnetic transition in MnSi | null | The polarized neutron scattering in helimagnetic MnSi at low $T$ reveals
existence of a partially disordered chiral state at ambient pressure in the
magnetic field applied along $<111>$ axis below the first order transition to
the non-chiral ferromagnetic state. This unexpected phenomenon is explained by
the analysis of the spin-wave spectrum. We demonstrate that the square of the
spin-wave gap becomes negative under magnetic field applied along $<111>$ and
$<110>$ but not along the $<100>$ direction. It is a result of competition
between the spin-wave interaction and cubic anisotropy. This negative sign
means an instability of the spin wave spectrum for the helix and leads to a
destruction of the helical order, giving rise to the partially disordered state
below the first order ferromagnetic transition.
|
25a95fbc-59e6-4b64-8cbd-9f4ec0ea99aa | 25a95fbc-59e6-4b64-8cbd-9f4ec0ea99aa | 25a95fbc-59e6-4b64-8cbd-9f4ec0ea99aa | human | null | null | none | abstracts | Fluctuations in glassy systems | null | We summarize a theoretical framework based on global time-reparametrization
invariance that explains the origin of dynamic fluctuations in glassy systems.
We introduce the main ideas without getting into much technical details. We
describe a number of consequences arising from this scenario that can be tested
numerically and experimentally distinguishing those that can also be explained
by other mechanisms from the ones that we believe, are special to our proposal.
We support our claims by presenting some numerical checks performed on the 3d
Edwards-Anderson spin-glass. Finally, we discuss up to which extent these ideas
apply to super-cooled liquids that have been studied in much more detail up to
present.
|
b84319ff-3f08-48ef-9c9f-692fb7181852 | b84319ff-3f08-48ef-9c9f-692fb7181852 | b84319ff-3f08-48ef-9c9f-692fb7181852 | human | null | null | none | abstracts | Statistical analysis of weighted networks | null | The purpose of this paper is to assess the statistical characterization of
weighted networks in terms of the generalization of the relevant parameters,
namely average path length, degree distribution and clustering coefficient.
Although the degree distribution and the average path length admit
straightforward generalizations, for the clustering coefficient several
different definitions have been proposed in the literature. We examined the
different definitions and identified the similarities and differences between
them. In order to elucidate the significance of different definitions of the
weighted clustering coefficient, we studied their dependence on the weights of
the connections. For this purpose, we introduce the relative perturbation norm
of the weights as an index to assess the weight distribution. This study
revealed new interesting statistical regularities in terms of the relative
perturbation norm useful for the statistical characterization of weighted
graphs.
|
b5eabe5b-dd7d-4414-956b-ba46efeb58a8 | b5eabe5b-dd7d-4414-956b-ba46efeb58a8 | b5eabe5b-dd7d-4414-956b-ba46efeb58a8 | human | null | null | none | abstracts | Strong Spherical Asymptotics for Rotor-Router Aggregation and the
Divisible Sandpile | null | The rotor-router model is a deterministic analogue of random walk. It can be
used to define a deterministic growth model analogous to internal DLA. We prove
that the asymptotic shape of this model is a Euclidean ball, in a sense which
is stronger than our earlier work. For the shape consisting of $n=\omega_d r^d$
sites, where $\omega_d$ is the volume of the unit ball in $\R^d$, we show that
the inradius of the set of occupied sites is at least $r-O(\log r)$, while the
outradius is at most $r+O(r^\alpha)$ for any $\alpha > 1-1/d$. For a related
model, the divisible sandpile, we show that the domain of occupied sites is a
Euclidean ball with error in the radius a constant independent of the total
mass. For the classical abelian sandpile model in two dimensions, with $n=\pi
r^2$ particles, we show that the inradius is at least $r/\sqrt{3}$, and the
outradius is at most $(r+o(r))/\sqrt{2}$. This improves on bounds of Le Borgne
and Rossin. Similar bounds apply in higher dimensions.
|
82de8f46-b09c-468d-bcfe-d7da254f0303 | 82de8f46-b09c-468d-bcfe-d7da254f0303 | 82de8f46-b09c-468d-bcfe-d7da254f0303 | human | null | null | none | abstracts | Fuzzballs with internal excitations | null | We construct general 2-charge D1-D5 horizon-free non-singular solutions of
IIB supergravity on T^4 and K3 describing fuzzballs with excitations in the
internal manifold; these excitations are characterized by arbitrary curves. The
solutions are obtained via dualities from F1-P solutions of heterotic and type
IIB on T^4 for the K3 and T^4 cases, respectively. We compute the holographic
data encoded in these solutions, and show that the internal excitations are
captured by vevs of chiral primaries associated with the middle cohomology of
T^4 or K3. We argue that each geometry is dual to a specific superposition of R
ground states determined in terms of the Fourier coefficients of the curves
defining the supergravity solution. We compute vevs of chiral primaries
associated with the middle cohomology and show that they indeed acquire vevs in
the superpositions corresponding to fuzzballs with internal excitations, in
accordance with the holographic results. We also address the question of
whether the fuzzball program can be implemented consistently within
supergravity.
|
d37444d5-4475-4f99-aa84-efa49c0f4ecd | d37444d5-4475-4f99-aa84-efa49c0f4ecd | d37444d5-4475-4f99-aa84-efa49c0f4ecd | human | null | null | none | abstracts | Rigorous derivation of the mean field Green functions of the two-band
Hubbard model of superconductivity | null | The Green function (GF) equation of motion technique for solving the
effective two-band Hubbard model of high-T_c superconductivity in cuprates
[N.M. Plakida et al., Phys. Rev. B, v. 51, 16599 (1995); JETP, v. 97, 331
(2003)] rests on the Hubbard operator (HO) algebra. We show that, if we take
into account the invariance to translations and spin reversal, the HO algebra
results in invariance properties of several specific correlation functions. The
use of these properties allows rigorous derivation and simplification of the
expressions of the frequency matrix (FM) and of the generalized mean field
approximation (GMFA) Green functions (GFs) of the model.
For the normal singlet hopping and anomalous exchange pairing correlation
functions which enter the FM and GMFA-GFs, an approximation procedure based on
the identification and elimination of exponentially small quantities is
described. It secures the reduction of the correlation order to GMFA-GF
expressions.
|
6ca22067-b09c-4286-a53f-27fa528e3a66 | 6ca22067-b09c-4286-a53f-27fa528e3a66 | 6ca22067-b09c-4286-a53f-27fa528e3a66 | human | null | null | none | abstracts | Geometry Effects at Atomic-Size Aluminium Contacts | null | We present electronic structure calculations for aluminium nanocontacts.
Addressing the neck of the contact, we compare characteristic geometries to
investigate the effects of the local aluminium coordination on the electronic
states. We find that the Al 3pz states are very sensitive against modifications
of the orbital overlap, which has serious consequences for the transport
properties. Stretching of the contact shifts states towards the Fermi energy,
leaving the system instable against ferromagnetic ordering. By spacial
restriction, hybridization is locally suppressed at nanocontacts and the charge
neutrality is violated. We discuss the influence of mechanical stress by means
of quantitative results for the charge transfer.
|
df050417-f74f-48a1-b367-372ce0f2b7a4 | df050417-f74f-48a1-b367-372ce0f2b7a4 | df050417-f74f-48a1-b367-372ce0f2b7a4 | human | null | null | none | abstracts | Current - voltage characteristics of break junctions of high-$T_c$
superconductors | null | The current-voltage ($I$-$V$) characteristics of break junctions of
polycrystalline La$_{1.85}$Sr$_{0.15}$CuO$_4$,
Y$_{0.75}$Lu$_{0.25}$Ba$_2$Cu$_3$O$_{7-\delta}$,
Bi$_{1.8}$Pb$_{0.3}$Sr$_{1.9}$Ca$_2$Cu$_3$O$_x$ and composite
YBa$_2$Cu$_3$O$_{7-\delta}$ + Ag are investigated. The experimental $I$-$V$
curves exhibit the specific peculiarities of
superconductor/normal-metal/superconductor junctions. The relation between an
$I$-$V$ characteristic of network of weak links and $I$-$V$ dependencies of
typical weak links is suggested to describe the experimental data. The $I$-$V$
curves of typical weak links are calculated by the K\"{u}mmel - Gunsenheimer -
Nicolsky model considering the multiple Andreev reflections.
|
1bec0511-4761-418a-8344-4d40784ac6c6 | 1bec0511-4761-418a-8344-4d40784ac6c6 | 1bec0511-4761-418a-8344-4d40784ac6c6 | human | null | null | none | abstracts | CP violation due to multi Froggatt-Nielsen fields | null | We study how to incorporate CP violation in the Froggatt--Nielsen (FN)
mechanism. To this end, we introduce non-renormalizable interactions with a
flavor democratic structure to the fermion mass generation sector. It is found
that at least two iso-singlet scalar fields with imposed a discrete symmetry
are necessary to generate CP violation due to the appearance of the relative
phase between their vacuum expectation values.
In the simplest model, ratios of quark masses and the
Cabibbo-Kobayashi-Maskawa (CKM) matrix including the CP violating phase are
determined by the CKM element |V_{us}| and the ratio of two vacuum expectation
values R=|R|e^{i*alpha} (a magnitude and a phase). It is demonstrated how the
angles phi_i (i=1--3) of the unitarity triangle and the CKM off-diagonal
elements |V_{ub}| and |V_{cb}| are predicted as a function of |V_{us}|, |R| and
\alpha. Although the predicted value of the CP violating phase does not agree
with the experimental data within the simplest model, the basic idea of our
scenario would be promising to construct a more realistic model of flavor and
CP violation.
|
360d0fcf-5d91-4156-a004-0b27dad5009f | 360d0fcf-5d91-4156-a004-0b27dad5009f | 360d0fcf-5d91-4156-a004-0b27dad5009f | human | null | null | none | abstracts | Rigorous Results for the Periodic Oscillation of an Adiabatic Piston | null | We study a heavy piston of mass $M$ that moves in one dimension. The piston
separates two gas chambers, each of which contains finitely many ideal, unit
mass gas particles moving in $d$ dimensions, where $ d\geq 1$. Using averaging
techniques, we prove that the actual motions of the piston converge in
probability to the predicted averaged behavior on the time scale $M^ {1/2} $
when $M$ tends to infinity while the total energy of the system is bounded and
the number of gas particles is fixed. Neishtadt and Sinai previously pointed
out that an averaging theorem due to Anosov should extend to this situation.
When $ d=1$, the gas particles move in just one dimension, and we prove that
the rate of convergence of the actual motions of the piston to its averaged
behavior is $\mathcal{O} (M^ {-1/2}) $ on the time scale $M^ {1/2} $. The
convergence is uniform over all initial conditions in a compact set. We also
investigate the piston system when the particle interactions have been
smoothed. The convergence to the averaged behavior again takes place uniformly,
both over initial conditions and over the amount of smoothing.
In addition, we prove generalizations of our results to $N$ pistons
separating $N+1$ gas chambers. We also provide a general discussion of
averaging theory and the proofs of a number of previously known averaging
results. In particular, we include a new proof of Anosov's averaging theorem
for smooth systems that is primarily due to Dolgopyat.
|
07fb21cd-dd78-4fa2-bc33-5bdb4c3488ad | 07fb21cd-dd78-4fa2-bc33-5bdb4c3488ad | 07fb21cd-dd78-4fa2-bc33-5bdb4c3488ad | human | null | null | none | abstracts | Thermal decomposition of norbornane (bicyclo[2.2.1]heptane) dissolved in
benzene. Experimental study and mechanism investigation | null | The thermal decomposition of norbornane (dissolved in benzene) has been
studied in a jet stirred reactor at temperatures between 873 and 973 K, at
residence times ranging from 1 to 4 s and at atmospheric pressure, leading to
conversions from 0.04 to 22.6%. 25 reaction products were identified and
quantified by gas chromatography, amongst which the main ones are hydrogen,
ethylene and 1,3-cyclopentadiene. A mechanism investigation of the thermal
decomposition of the norbornane - benzene binary mixture has been performed.
Reactions involved in the mechanism have been reviewed: unimolecular
initiations 1 by C-C bond scission of norbornane, fate of the generated
diradicals, reactions of transfer and propagation of norbornyl radicals,
reactions of benzene and cross-coupling reactions.
|
a231dfc4-1558-4a11-82b6-d1f6faa4a2a9 | a231dfc4-1558-4a11-82b6-d1f6faa4a2a9 | a231dfc4-1558-4a11-82b6-d1f6faa4a2a9 | human | null | null | none | abstracts | Detailed kinetic study of the ring opening of cycloalkanes by CBS-QB3
calculations | null | This work reports a theoretical study of the gas phase unimolecular
decomposition of cyclobutane, cyclopentane and cyclohexane by means of quantum
chemical calculations. A biradical mechanism has been envisaged for each
cycloalkane, and the main routes for the decomposition of the biradicals formed
have been investigated at the CBS-QB3 level of theory. Thermochemical data
(\delta H^0_f, S^0, C^0_p) for all the involved species have been obtained by
means of isodesmic reactions. The contribution of hindered rotors has also been
included. Activation barriers of each reaction have been analyzed to assess the
1 energetically most favorable pathways for the decomposition of biradicals.
Rate constants have been derived for all elementary reactions using transition
state theory at 1 atm and temperatures ranging from 600 to 2000 K. Global rate
constant for the decomposition of the cyclic alkanes in molecular products have
been calculated. Comparison between calculated and experimental results allowed
to validate the theoretical approach. An important result is that the
rotational barriers between the conformers, which are usually neglected, are of
importance in decomposition rate of the largest biradicals. Ring strain
energies (RSE) in transition states for ring opening have been estimated and
show that the main part of RSE contained in the cyclic reactants is removed
upon the activation process.
|
784161e7-90ec-455b-9ae5-59514b43a076 | 784161e7-90ec-455b-9ae5-59514b43a076 | 784161e7-90ec-455b-9ae5-59514b43a076 | human | null | null | none | abstracts | On thermal effects in solid state lasers: the case of ytterbium-doped
materials | null | A review of theoretical and experimental studies of thermal effects in
solid-state lasers is presented, with a special focus on diode-pumped
ytterbium-doped materials. A large part of this review provides however general
information applicable to any kind of solid-state laser. Our aim here is not to
make a list of the techniques that have been used to minimize thermal effects,
but instead to give an overview of the theoretical aspects underneath, and give
a state-of-the-art of the tools at the disposal of the laser scientist to
measure thermal effects. After a presentation of some general properties of
Yb-doped materials, we address the issue of evaluating the temperature map in
Yb-doped laser crystals, both theoretically and experimentally. This is the
first step before studying the complex problem of thermal lensing (part III).
We will focus on some newly discussed aspects, like the definition of the
thermo-optic coefficient: we will highlight some misleading interpretations of
thermal lensing experiments due to the use of the dn/dT parameter in a context
where it is not relevant. Part IV will be devoted to a state-of-the-art of
experimental techniques used to measure thermal lensing. Eventually, in part V,
we will give some concrete examples in Yb-doped materials, where their
peculiarities will be pointed out.
|
0ce3e7ab-958f-4776-99fb-8b62b6727ee3 | 0ce3e7ab-958f-4776-99fb-8b62b6727ee3 | 0ce3e7ab-958f-4776-99fb-8b62b6727ee3 | human | null | null | none | abstracts | Dimensional crossover of thermal conductance in nanowires | null | Dimensional dependence of thermal conductance at low temperatures in
nanowires is studied using the nonequilibrium Green's function (NEGF) method.
Our calculation shows a smooth dimensional crossover of thermal conductance in
nanowire from one-dimensional to three-dimensional behavior with the increase
of diameters. The results are consistent with the experimental findings that
the temperature dependence of thermal conductance at low temperature for
diameters from tens to hundreds nanometers will be close to Debye law. The
calculation also suggests that universal thermal conductance is only observable
in nanowires with small diameters. We also find that the interfacial thermal
conductance across Si and Ge nanowire is much lower than the corresponding
value in bulk materials.
|
51badf51-3272-4d44-a98d-acd3b61c97c2 | 51badf51-3272-4d44-a98d-acd3b61c97c2 | 51badf51-3272-4d44-a98d-acd3b61c97c2 | human | null | null | none | abstracts | Transient behavior of surface plasmon polaritons scattered at a
subwavelength groove | null | We present a numerical study and analytical model of the optical near-field
diffracted in the vicinity of subwavelength grooves milled in silver surfaces.
The Green's tensor approach permits computation of the phase and amplitude
dependence of the diffracted wave as a function of the groove geometry. It is
shown that the field diffracted along the interface by the groove is equivalent
to replacing the groove by an oscillating dipolar line source. An analytic
expression is derived from the Green's function formalism, that reproduces well
the asymptotic surface plasmon polariton (SPP) wave as well as the transient
surface wave in the near-zone close to the groove. The agreement between this
model and the full simulation is very good, showing that the transient
"near-zone" regime does not depend on the precise shape of the groove. Finally,
it is shown that a composite diffractive evanescent wave model that includes
the asymptotic SPP can describe the wavelength evolution in this transient
near-zone. Such a semi-analytical model may be useful for the design and
optimization of more elaborate photonic circuits whose behavior in large part
will be controlled by surface waves.
|
a5a7c76f-cab9-4198-a64b-f63f26553b66 | a5a7c76f-cab9-4198-a64b-f63f26553b66 | a5a7c76f-cab9-4198-a64b-f63f26553b66 | human | null | null | none | abstracts | Entropic Measure and Wasserstein Diffusion | null | We construct a new random probability measure on the sphere and on the unit
interval which in both cases has a Gibbs structure with the relative entropy
functional as Hamiltonian. It satisfies a quasi-invariance formula with respect
to the action of smooth diffeomorphism of the sphere and the interval
respectively. The associated integration by parts formula is used to construct
two classes of diffusion processes on probability measures (on the sphere or
the unit interval) by Dirichlet form methods. The first one is closely related
to Malliavin's Brownian motion on the homeomorphism group. The second one is a
probability valued stochastic perturbation of the heat flow, whose intrinsic
metric is the quadratic Wasserstein distance. It may be regarded as the
canonical diffusion process on the Wasserstein space.
|
569851f9-3799-47fb-ad85-cdeca1f4819b | 569851f9-3799-47fb-ad85-cdeca1f4819b | 569851f9-3799-47fb-ad85-cdeca1f4819b | human | null | null | none | abstracts | Second-Order Eikonal Corrections for A(e,e'p) | null | The first-order eikonal approximation is frequently adopted in interpreting
the results of $A(e,e'p)$ measurements. Glauber calculations, for example,
typically adopt the first-order eikonal approximation. We present an extension
of the relativistic eikonal approach to $A(e,e'p)$ which accounts for
second-order eikonal corrections. The numerical calculations are performed
within the relativistic optical model eikonal approximation. The nuclear
transparency results indicate that the effect of the second-order eikonal
corrections is rather modest, even at $Q^{2} \approx 0.2$ (GeV/c)$^2$. The same
applies to polarization observables, left-right asymmetries, and differential
cross sections at low missing momenta. At high missing momenta, however, the
second-order eikonal corrections are significant and bring the calculations in
closer agreement with the data and/or the exact results from models adopting
partial-wave expansions.
|
47b4dad6-7295-4cee-b7f6-a86db43473d7 | 47b4dad6-7295-4cee-b7f6-a86db43473d7 | 47b4dad6-7295-4cee-b7f6-a86db43473d7 | human | null | null | none | abstracts | AKARI Detection of the Infrared-Bright Supernova Remnant B0104-72.3 in
the Small Magellanic Cloud | null | We present a serendipitous detection of the infrared-bright supernova remnant
(SNR) B0104-72.3 in the Small Magellanic Cloud by the Infrared Camera (IRC)
onboard AKARI. An elongated, partially complete shell is detected in all four
observed IRC bands covering 2.6-15 um. The infrared shell surrounds radio,
optical, and X-ray emission associated with the SNR and is probably a radiative
SNR shell. This is the first detection of a SNR shell in this near/mid-infrared
waveband in the Small Magellanic Cloud. The IRC color indicates that the
infrared emission might be from shocked H2 molecules with some possible
contributions from ionic lines. We conclude that B0104-72.3 is a middle-aged
SNR interacting with molecular clouds, similar to the Galactic SNR IC 443. Our
results highlight the potential of AKARI IRC observations in studying SNRs,
especially for diagnosing SNR shocks.
|
23e4bdfa-0f53-497c-bdf9-48621778d567 | 23e4bdfa-0f53-497c-bdf9-48621778d567 | 23e4bdfa-0f53-497c-bdf9-48621778d567 | human | null | null | none | abstracts | On second order shape optimization methods for electrical impedance
tomography | null | This paper is devoted to the analysis of a second order method for recovering
the \emph{a priori} unknown shape of an inclusion $\omega$ inside a body
$\Omega$ from boundary measurement. This inverse problem - known as electrical
impedance tomography - has many important practical applications and hence has
focussed much attention during the last years. However, to our best knowledge,
no work has yet considered a second order approach for this problem. This paper
aims to fill that void: we investigate the existence of second order derivative
of the state $u$ with respect to perturbations of the shape of the interface
$\partial\omega$, then we choose a cost function in order to recover the
geometry of $\partial \omega$ and derive the expression of the derivatives
needed to implement the corresponding Newton method. We then investigate the
stability of the process and explain why this inverse problem is severely
ill-posed by proving the compactness of the Hessian at the global minimizer.
|
e0aa0462-2080-437d-8868-ec2f352e9e38 | e0aa0462-2080-437d-8868-ec2f352e9e38 | e0aa0462-2080-437d-8868-ec2f352e9e38 | human | null | null | none | abstracts | Interference effects in above-threshold ionization from diatomic
molecules: determining the internuclear separation | null | We calculate angle-resolved above-threshold ionization spectra for diatomic
molecules in linearly polarized laser fields, employing the strong-field
approximation. The interference structure resulting from the individual
contributions of the different scattering scenarios is discussed in detail,
with respect to the dependence on the internuclear distance and molecular
orientation. We show that, in general, the contributions from the processes in
which the electron is freed at one center and rescatters off the other obscure
the interference maxima and minima obtained from single-center processes.
However, around the boundary of the energy regions for which rescattering has a
classical counterpart, such processes play a negligible role and very clear
interference patterns are observed. In such energy regions, one is able to
infer the internuclear distance from the energy difference between adjacent
interference minima.
|
42e0ff3f-30b2-4a93-9218-bf98b8092edb | 42e0ff3f-30b2-4a93-9218-bf98b8092edb | 42e0ff3f-30b2-4a93-9218-bf98b8092edb | human | null | null | none | abstracts | Maximum solutions of normalized Ricci flows on 4-manifolds | null | We consider maximum solution $g(t)$, $t\in [0, +\infty)$, to the normalized
Ricci flow. Among other things, we prove that, if $(M, \omega) $ is a smooth
compact symplectic 4-manifold such that $b_2^+(M)>1$ and let
$g(t),t\in[0,\infty)$, be a solution to (1.3) on $M$ whose Ricci curvature
satisfies that $|\text{Ric}(g(t))|\leq 3$ and additionally $\chi(M)=3 \tau
(M)>0$, then there exists an $m\in \mathbb{N}$, and a sequence of points
$\{x_{j,k}\in M\}$, $j=1, ..., m$, satisfying that, by passing to a
subsequence, $$(M, g(t_{k}+t), x_{1,k},..., x_{m,k})
\stackrel{d_{GH}}\longrightarrow (\coprod_{j=1}^m N_j, g_{\infty},
x_{1,\infty}, ...,, x_{m,\infty}),$$ $t\in [0, \infty)$, in the $m$-pointed
Gromov-Hausdorff sense for any sequence $t_{k}\longrightarrow \infty$, where
$(N_{j}, g_{\infty})$, $j=1,..., m$, are complete complex hyperbolic orbifolds
of complex dimension 2 with at most finitely many isolated orbifold points.
Moreover, the convergence is $C^{\infty}$ in the non-singular part of
$\coprod_1^m N_{j}$ and
$\text{Vol}_{g_{0}}(M)=\sum_{j=1}^{m}\text{Vol}_{g_{\infty}}(N_{j})$, where
$\chi(M)$ (resp. $\tau(M)$) is the Euler characteristic (resp. signature) of
$M$.
|
43623089-bef9-42c1-932a-0d20f761e0ff | 43623089-bef9-42c1-932a-0d20f761e0ff | 43623089-bef9-42c1-932a-0d20f761e0ff | human | null | null | none | abstracts | Gravitational Wave Signals from Chaotic System: A Point Mass with A Disk | null | We study gravitational waves from a particle moving around a system of a
point mass with a disk in Newtonian gravitational theory. A particle motion in
this system can be chaotic when the gravitational contribution from a surface
density of a disk is comparable with that from a point mass. In such an orbit,
we sometimes find that there appears a phase of the orbit in which particle
motion becomes to be nearly regular (the so-called ``stagnant motion'') for a
finite time interval between more strongly chaotic phases. To study how these
different chaotic behaviours affect on observation of gravitational waves, we
investigate a correlation of the particle motion and the waves. We find that
such a difference in chaotic motions reflects on the wave forms and energy
spectra. The character of the waves in the stagnant motion is quite different
from that either in a regular motion or in a more strongly chaotic motion. This
suggests that we may make a distinction between different chaotic behaviours of
the orbit via the gravitational waves.
|
208bd12d-4cca-487a-9bde-5e843fb2d6e5 | 208bd12d-4cca-487a-9bde-5e843fb2d6e5 | 208bd12d-4cca-487a-9bde-5e843fb2d6e5 | human | null | null | none | abstracts | Two- and three-point Green's functions in two-dimensional Landau-gauge
Yang-Mills theory | null | The ghost and gluon propagator and the ghost-gluon and three-gluon vertex of
two-dimensional SU(2) Yang-Mills theory in (minimal) Landau gauge are studied
using lattice gauge theory. It is found that the results are qualitatively
similar to the ones in three and four dimensions. The propagators and the
Faddeev-Popov operator behave as expected from the Gribov-Zwanziger scenario.
In addition, finite volume effects affecting these Green's functions are
investigated systematically. The critical infrared exponents of the
propagators, as proposed in calculations using stochastic quantization and
Dyson-Schwinger equations, are confirmed quantitatively. For this purpose
lattices of volume up to (42.7 fm)^2 have been used.
|
c4acb179-9bc8-4ccb-b421-6f9ce9d810c0 | c4acb179-9bc8-4ccb-b421-6f9ce9d810c0 | c4acb179-9bc8-4ccb-b421-6f9ce9d810c0 | human | null | null | none | abstracts | Coupled electron and phonon transport in one-dimensional atomic
junctions | null | Employing the nonequilibrium Green's function method, we develop a fully
quantum mechanical model to study the coupled electron-phonon transport in
one-dimensional atomic junctions in the presence of a weak electron-phonon
interaction. This model enables us to study the electronic and phononic
transport on an equal footing. We derive the electrical and energy currents of
the coupled electron-phonon system and the energy exchange between them. As an
application, we study the heat dissipation in current carrying atomic junctions
within the self-consistent Born approximation, which guarantees energy current
conservation. We find that the inclusion of phonon transport is important in
determining the heat dissipation and temperature change of the atomic
junctions.
|
0e0be313-7e96-40c2-a434-76f57644c985 | 0e0be313-7e96-40c2-a434-76f57644c985 | 0e0be313-7e96-40c2-a434-76f57644c985 | human | null | null | none | abstracts | The First Law for Boosted Kaluza-Klein Black Holes | null | We study the thermodynamics of Kaluza-Klein black holes with momentum along
the compact dimension, but vanishing angular momentum. These black holes are
stationary, but non-rotating. We derive the first law for these spacetimes and
find that the parameter conjugate to variations in the length of the compact
direction is an effective tension, which generally differs from the ADM
tension. For the boosted black string, this effective tension is always
positive, while the ADM tension is negative for large boost parameter. We also
derive two Smarr formulas, one that follows from time translation invariance,
and a second one that holds only in the case of exact translation symmetry in
the compact dimension. Finally, we show that the `tension first law' derived by
Traschen and Fox in the static case has the form of a thermodynamic Gibbs-Duhem
relation and give its extension in the stationary, non-rotating case.
|
eb8b49c0-f93e-48d6-835f-377cb6e1a58b | eb8b49c0-f93e-48d6-835f-377cb6e1a58b | eb8b49c0-f93e-48d6-835f-377cb6e1a58b | human | null | null | none | abstracts | Revisiting the Issues On Netflow Sample and Export Performance | null | The high volume of packets and packet rates of traffic on some router links
makes it exceedingly difficult for routers to examine every packet in order to
keep detailed statistics about the traffic which is traversing the router.
Sampling is commonly applied on routers in order to limit the load incurred by
the collection of information that the router has to undertake when evaluating
flow information for monitoring purposes. The sampling process in nearly all
cases is a deterministic process of choosing 1 in every N packets on a
per-interface basis, and then forming the flow statistics based on the
collected sampled statistics. Even though this sampling may not be significant
for some statistics, such as packet rate, others can be severely distorted.
However, it is important to consider the sampling techniques and their relative
accuracy when applied to different traffic patterns. The main disadvantage of
sampling is the loss of accuracy in the collected trace when compared to the
original traffic stream. To date there has not been a detailed analysis of the
impact of sampling at a router in various traffic profiles and flow criteria.
In this paper, we assess the performance of the sampling process as used in
NetFlow in detail, and we discuss some techniques for the compensation of loss
of monitoring detail.
|
81eb1893-b25c-4fcb-b6d0-140510357d32 | 81eb1893-b25c-4fcb-b6d0-140510357d32 | 81eb1893-b25c-4fcb-b6d0-140510357d32 | human | null | null | none | abstracts | The tensor part of the Skyrme energy density functional. I. Spherical
nuclei | null | We perform a systematic study of the impact of the J^2 tensor term in the
Skyrme energy functional on properties of spherical nuclei. In the Skyrme
energy functional, the tensor terms originate both from zero-range central and
tensor forces. We build a set of 36 parameterizations, which covers a wide
range of the parameter space of the isoscalar and isovector tensor term
coupling constants, with a fit protocol very similar to that of the successful
SLy parameterizations. We analyze the impact of the tensor terms on a large
variety of observables in spherical mean-field calculations, such as the
spin-orbit splittings and single-particle spectra of doubly-magic nuclei, the
evolution of spin-orbit splittings along chains of semi-magic nuclei, mass
residuals of spherical nuclei, and known anomalies of charge radii. Our main
conclusion is that the currently used central and spin-orbit parts of the
Skyrme energy density functional are not flexible enough to allow for the
presence of large tensor terms.
|
f1da465b-20f4-4f29-b0e8-c00b3c82584a | f1da465b-20f4-4f29-b0e8-c00b3c82584a | f1da465b-20f4-4f29-b0e8-c00b3c82584a | human | null | null | none | abstracts | The HELLAS2XMM survey. X. The bolometric output of luminous obscured
quasars: The Spitzer perspective | null | Aims: We aim at estimating the spectral energy distributions (SEDs) and the
physical parameters related to the black holes harbored in eight high
X-ray-to-optical (F_X/F_R>10) obscured quasars at z>0.9 selected in the 2--10
keV band from the HELLAS2XMM survey.
Methods: We use IRAC and MIPS 24 micron observations, along with optical and
Ks-band photometry, to obtain the SEDs of the sources. The observed SEDs are
modeled using a combination of an elliptical template and torus emission (using
the phenomenological templates of Silva et al. 2004) for six sources associated
with passive galaxies; for two point-like sources, the empirical SEDs of red
quasars are adopted. The bolometric luminosities and the M_BH-L_K relation are
used to provide an estimate of the masses and Eddington ratios of the black
holes residing in these AGN.
Results: All of our sources are detected in the IRAC and MIPS (at 24 micron)
bands. The SED modeling described above is in good agreement with the observed
near- and mid-infrared data. The derived bolometric luminosities are in the
range ~10^45-10^47 erg s^-1, and the median 2--10 keV bolometric correction is
~25, consistent with the widely adopted value derived by Elvis et al. (1994).
For the objects with elliptical-like profiles in the K_s band, we derive high
stellar masses (0.8-6.2)X10^11 Mo, black hole masses in the range
(0.2-2.5)X10^9 Mo, and Eddington ratios L/L_Edd<0.1, suggesting a low-accretion
phase.
|
808e2d29-b76f-4228-9622-edc81b4a292c | 808e2d29-b76f-4228-9622-edc81b4a292c | 808e2d29-b76f-4228-9622-edc81b4a292c | human | null | null | none | abstracts | $p$-Adic Haar multiresolution analysis | null | In this paper, the notion of {\em $p$-adic multiresolution analysis (MRA)} is
introduced. We use a ``natural'' refinement equation whose solution (a
refinable function) is the characteristic function of the unit disc. This
equation reflects the fact that the characteristic function of the unit disc is
the sum of $p$ characteristic functions of disjoint discs of radius $p^{-1}$.
The case $p=2$ is studied in detail. Our MRA is a 2-adic analog of the real
Haar MRA. But in contrast to the real setting, the refinable function
generating our Haar MRA is periodic with period 1, which never holds for real
refinable functions. This fact implies that there exist infinity many different
2-adic orthonormal wavelet bases in ${\cL}^2(\bQ_2)$ generated by the same Haar
MRA. All of these bases are constructed. Since $p$-adic pseudo-differential
operators are closely related to wavelet-type bases, our bases can be
intensively used for applications.
|
1adf9475-566f-4e92-9dcf-c511badb9eb1 | 1adf9475-566f-4e92-9dcf-c511badb9eb1 | 1adf9475-566f-4e92-9dcf-c511badb9eb1 | human | null | null | none | abstracts | Vertical dynamics of disk galaxies in MOND | null | We investigate the possibility of discriminating between Modified Newtonian
Dynamics (MOND) and Newtonian gravity with dark matter, by studying the
vertical dynamics of disk galaxies. We consider models with the same circular
velocity in the equatorial plane (purely baryonic disks in MOND and the same
disks in Newtonian gravity embedded in spherical dark matter haloes), and we
construct their intrinsic and projected kinematical fields by solving the Jeans
equations under the assumption of a two-integral distribution function. We
found that the vertical velocity dispersion of deep-MOND disks can be much
larger than in the equivalent spherical Newtonian models. However, in the more
realistic case of high-surface density disks this effect is significantly
reduced, casting doubts on the possibility of discriminating between MOND and
Newtonian gravity with dark matter by using current observations.
|
03eb0d6c-7041-4295-9e05-6a1a62dbc3c4 | 03eb0d6c-7041-4295-9e05-6a1a62dbc3c4 | 03eb0d6c-7041-4295-9e05-6a1a62dbc3c4 | human | null | null | none | abstracts | Al'tshuler-Aronov correction to the conductivity of a large metallic
square network | null | We consider the correction $\Delta\sigma_\mathrm{ee}$ due to
electron-electron interaction to the conductivity of a weakly disordered metal
(Al'tshuler-Aronov correction). The correction is related to the spectral
determinant of the Laplace operator. The case of a large square metallic
network is considered. The variation of $\Delta\sigma_\mathrm{ee}(L_T)$ as a
function of the thermal length $L_T$ is found very similar to the variation of
the weak localization $\Delta\sigma_\mathrm{WL}(L_\phi)$ as a function of the
phase coherence length. Our result for $\Delta\sigma_\mathrm{ee}$ interpolates
between the known 1d and 2d results, but the interaction parameter entering the
expression of $\Delta\sigma_\mathrm{ee}$ keeps a 1d behaviour. Quite
surprisingly, the result is very close to the 2d logarithmic behaviour already
for $L_T\sim{a}/2$, where $a$ is the lattice parameter.
|
8a0c9fa6-b63d-481c-8e2d-0a037ca0fcf3 | 8a0c9fa6-b63d-481c-8e2d-0a037ca0fcf3 | 8a0c9fa6-b63d-481c-8e2d-0a037ca0fcf3 | human | null | null | none | abstracts | Quantifying social group evolution | null | The rich set of interactions between individuals in the society results in
complex community structure, capturing highly connected circles of friends,
families, or professional cliques in a social network. Thanks to frequent
changes in the activity and communication patterns of individuals, the
associated social and communication network is subject to constant evolution.
Our knowledge of the mechanisms governing the underlying community dynamics is
limited, but is essential for a deeper understanding of the development and
self-optimisation of the society as a whole. We have developed a new algorithm
based on clique percolation, that allows, for the first time, to investigate
the time dependence of overlapping communities on a large scale and as such, to
uncover basic relationships characterising community evolution. Our focus is on
networks capturing the collaboration between scientists and the calls between
mobile phone users. We find that large groups persist longer if they are
capable of dynamically altering their membership, suggesting that an ability to
change the composition results in better adaptability. The behaviour of small
groups displays the opposite tendency, the condition for stability being that
their composition remains unchanged. We also show that the knowledge of the
time commitment of the members to a given community can be used for estimating
the community's lifetime. These findings offer a new view on the fundamental
differences between the dynamics of small groups and large institutions.
|
0118c7cb-39d1-482b-8efd-a01bf127679f | 0118c7cb-39d1-482b-8efd-a01bf127679f | 0118c7cb-39d1-482b-8efd-a01bf127679f | human | null | null | none | abstracts | Weak and Strong Taylor methods for numerical solutions of stochastic
differential equations | null | We apply results of Malliavin-Thalmaier-Watanabe for strong and weak Taylor
expansions of solutions of perturbed stochastic differential equations (SDEs).
In particular, we work out weight expressions for the Taylor coefficients of
the expansion. The results are applied to LIBOR market models in order to deal
with the typical stochastic drift and with stochastic volatility. In contrast
to other accurate methods like numerical schemes for the full SDE, we obtain
easily tractable expressions for accurate pricing. In particular, we present an
easily tractable alternative to ``freezing the drift'' in LIBOR market models,
which has an accuracy similar to the full numerical scheme. Numerical examples
underline the results.
|
9406dc31-6d20-4e72-8f9c-15a7889636e7 | 9406dc31-6d20-4e72-8f9c-15a7889636e7 | 9406dc31-6d20-4e72-8f9c-15a7889636e7 | human | null | null | none | abstracts | The dynamical Casimir effect in braneworlds | null | In braneworld cosmology the expanding Universe is realized as a brane moving
through a warped higher-dimensional spacetime. Like a moving mirror causes the
creation of photons out of vacuum fluctuations, a moving brane leads to
graviton production. We show that, very generically, Kaluza-Klein (KK)
particles scale like stiff matter with the expansion of the Universe and can
therefore not represent the dark matter in a warped braneworld. We present
results for the production of massless and KK gravitons for bouncing branes in
five-dimensional anti de Sitter space. We find that for a realistic bounce the
back reaction from the generated gravitons will be most likely relevant. This
letter summarizes the main results and conclusions from numerical simulations
which are presented in detail in a long paper [M.Ruser and R. Durrer, Phys.
Rev. D 76, 104014 (2007), arXiv:0704.0790]
|
b91c02eb-2c89-4987-9705-f810578354fd | b91c02eb-2c89-4987-9705-f810578354fd | b91c02eb-2c89-4987-9705-f810578354fd | human | null | null | none | abstracts | Energy conservation and Onsager's conjecture for the Euler equations | null | Onsager conjectured that weak solutions of the Euler equations for
incompressible fluids in 3D conserve energy only if they have a certain minimal
smoothness, (of order of 1/3 fractional derivatives) and that they dissipate
energy if they are rougher. In this paper we prove that energy is conserved for
velocities in the function space $B^{1/3}_{3,c(\NN)}$. We show that this space
is sharp in a natural sense. We phrase the energy spectrum in terms of the
Littlewood-Paley decomposition and show that the energy flux is controlled by
local interactions. This locality is shown to hold also for the helicity flux;
moreover, every weak solution of the Euler equations that belongs to
$B^{2/3}_{3,c(\NN)}$ conserves helicity. In contrast, in two dimensions, the
strong locality of the enstrophy holds only in the ultraviolet range.
|
9d4b7be4-13e0-4b65-a014-70630e54caac | 9d4b7be4-13e0-4b65-a014-70630e54caac | 9d4b7be4-13e0-4b65-a014-70630e54caac | human | null | null | none | abstracts | Search for Heavy, Long-Lived Particles that Decay to Photons at CDF II | null | We present the first search for heavy, long-lived particles that decay to
photons at a hadron collider. We use a sample of photon+jet+missing transverse
energy events in p-pbar collisions at \sqrt{s}=1.96 TeV taken with the CDF II
detector. Candidate events are selected based on the arrival time of the photon
at the detector. Using an integrated luminosity of 570 pb-1 of collision data,
we observe 2 events, consistent with the background estimate of 1.3+-0.7
events. While our search strategy does not rely on model-specific dynamics, we
set cross section limits in a supersymmetric model with
\tilde{\chi}_1^0->\gamma\gravitino and place the world-best 95% C.L. lower
limit on the \tilde{\chi}_1^0 mass of 101 GeV/c^2 at \tau_{\tilde{\chi}_1^0} =
5 ns.
|
3fd5ee5f-67ec-4b90-a216-f54b9e6627ed | 3fd5ee5f-67ec-4b90-a216-f54b9e6627ed | 3fd5ee5f-67ec-4b90-a216-f54b9e6627ed | human | null | null | none | abstracts | Coherent control of atomic tunneling | null | We study the tunneling of a two-level atom in a double well potential while
the atom is coupled to a single electromagnetic field mode of a cavity. The
coupling between internal and external degrees of freedom, due to the
mechanical effect on the atom from photon emission into the cavity mode, can
dramatically change the tunneling behavior. We predict that in general the
tunneling process becomes quasiperiodic. In a certain regime of parameters a
collapse and revival of the tunneling occurs. Accessing the internal degrees of
freedom of the atom with a laser allows to coherently manipulate the atom
position, and in particular to prepare the atom in one of the two wells. The
effects described should be observable with atoms in an optical double well
trap.
|
7e2d5049-6889-4b42-b527-7aef95430dab | 7e2d5049-6889-4b42-b527-7aef95430dab | 7e2d5049-6889-4b42-b527-7aef95430dab | human | null | null | none | abstracts | Local de Broglie-Bohm Trajectories from Entangled Wavefunctions | null | We present a local interpretation of what is usually considered to be a
nonlocal de Broglie-Bohm trajectory prescription for an entangled singlet state
of massive particles. After reviewing various meanings of the term
``nonlocal'', we show that by using appropriately retarded wavefunctions (i.e.,
the locality loophole) this local model can violate Bell's inequality, without
making any appeal to detector inefficiencies.
We analyze a possible experimental configuration appropriate to massive
two-particle singlet wavefunctions and find that as long as the particles are
not ultra-relativistic, a locality loophole exists and Dirac wave(s) can
propagate from Alice or Bob's changing magnetic field, through space, to the
other detector, arriving before the particle and thereby allowing a local
interpretation to the 2-particle de Broglie-Bohm trajectories.
We also propose a physical effect due to changing magnetic fields in a
Stern-Gerlach EPR setup that will throw away events and create a detector
loophole in otherwise perfectly efficient detectors, an effect that is only
significant for near-luminal particles that might otherwise close the locality
loophole.
|
5a0614a8-9ac9-421b-8782-ac877092d039 | 5a0614a8-9ac9-421b-8782-ac877092d039 | 5a0614a8-9ac9-421b-8782-ac877092d039 | human | null | null | none | abstracts | Ground-based Microlensing Surveys | null | Microlensing is a proven extrasolar planet search method that has already
yielded the detection of four exoplanets. These detections have changed our
understanding of planet formation ``beyond the snowline'' by demonstrating that
Neptune-mass planets with separations of several AU are common. Microlensing is
sensitive to planets that are generally inaccessible to other methods, in
particular cool planets at or beyond the snowline, very low-mass (i.e.
terrestrial) planets, planets orbiting low-mass stars, free-floating planets,
and even planets in external galaxies. Such planets can provide critical
constraints on models of planet formation, and therefore the next generation of
extrasolar planet searches should include an aggressive and well-funded
microlensing component. When combined with the results from other complementary
surveys, next generation microlensing surveys can yield an accurate and
complete census of the frequency and properties of planets, and in particular
low-mass terrestrial planets.
|
5a7a33b9-c589-4ef2-a5c3-2a8befc0ad7a | 5a7a33b9-c589-4ef2-a5c3-2a8befc0ad7a | 5a7a33b9-c589-4ef2-a5c3-2a8befc0ad7a | human | null | null | none | abstracts | The luminous infrared composite Seyfert 2 galaxy NGC 7679 through the [O
III] 5007 emission line | null | NGC 7679 is a nearby luminous infrared Sy2 galaxy in which starburst and AGN
activities co-exist. The ionization structure is maintained by both the AGN
power-law continuum and starburst. The galaxy is a bright X-ray source
possessing a low X-ray column density N_H < 4 x 10^20 cm^{-2}. The Compton-thin
nature of such unabsorbed objects infers that the simple formulation of the
Unified model for SyGs is not applicable in their case. The main goal of this
article is to investigate both gas distribution and ionization structure in the
circumnuclear region of NGC 7679 in search for the presence of a hidden Sy1
nucleus, using the [O III] 5007 luminosity as a tracer of AGN activity. The [O
III] 5007 image of the NGC 7679 shows elliptical isophotes extended along the
PA ~ 80 deg in the direction to the counterpart galaxy NGC 7682. The maximum of
ionization by the AGN power-law continuum traced by [O III] 5007/Halpha ratio
is displaced by ~ 13 arcsec eastward from the nucleus. We conclude that the
dust and gas in the high ionization direction has a direct view to the central
AGN engine. This possibly results in dust/star-formation decay. A large
fraction of the unabsorbed Compton-thin Sy2s with [O III] luminosity > 10^41
erg s^{-1} possesses a hidden AGN source (abridged).
|
ae5c30db-977d-4c1d-8b1e-a154167a09a5 | ae5c30db-977d-4c1d-8b1e-a154167a09a5 | ae5c30db-977d-4c1d-8b1e-a154167a09a5 | human | null | null | none | abstracts | The Fermionic Density-functional at Feshbach Resonance | null | We consider a dilute gas of neutral unpolarized fermionic atoms at zero
temperature.The atoms interact via a short range (tunable) attractive
interaction. We demonstrate analytically a curious property of the gas at
unitarity. Namely, the correlation energy of the gas, evaluated by second order
perturbation theory, has the same density dependence as the first order
exchange energy, and the two almost exactly cancel each other at Feshbach
resonance irrespective of the shape of the potential, provided $(\mu r_s) >>
1$. Here $(\mu)^{-1}$ is the range of the two-body potential, and $r_s$ is
defined through the number density $n=3/(4\pi r_s^3)$. The implications of this
result for universality is discussed.
|
bc06b55b-ec22-4a78-8e60-01a37f5817a0 | bc06b55b-ec22-4a78-8e60-01a37f5817a0 | bc06b55b-ec22-4a78-8e60-01a37f5817a0 | human | null | null | none | abstracts | Suppression of 1/f noise in one-qubit systems | null | We investigate the generation of quantum operations for one-qubit systems
under classical noise with 1/f^\alpha power spectrum, where 2>\alpha > 0. We
present an efficient way to approximate the noise with a discrete multi-state
Markovian fluctuator. With this method, the average temporal evolution of the
qubit density matrix under 1/f^\alpha noise can be feasibly determined from
recently derived deterministic master equations. We obtain qubit operations
such as quantum memory and the NOT}gate to high fidelity by a gradient based
optimization algorithm. For the NOT gate, the computed fidelities are
qualitatively similar to those obtained earlier for random telegraph noise. In
the case of quantum memory however, we observe a nonmonotonic dependency of the
fidelity on the operation time, yielding a natural access rate of the memory.
|
0ea1f66b-2ebd-40a8-80b3-7e65f2dfa7b3 | 0ea1f66b-2ebd-40a8-80b3-7e65f2dfa7b3 | 0ea1f66b-2ebd-40a8-80b3-7e65f2dfa7b3 | human | null | null | none | abstracts | Collective behavior of stock price movements in an emerging market | null | To investigate the universality of the structure of interactions in different
markets, we analyze the cross-correlation matrix C of stock price fluctuations
in the National Stock Exchange (NSE) of India. We find that this emerging
market exhibits strong correlations in the movement of stock prices compared to
developed markets, such as the New York Stock Exchange (NYSE). This is shown to
be due to the dominant influence of a common market mode on the stock prices.
By comparison, interactions between related stocks, e.g., those belonging to
the same business sector, are much weaker. This lack of distinct sector
identity in emerging markets is explicitly shown by reconstructing the network
of mutually interacting stocks. Spectral analysis of C for NSE reveals that,
the few largest eigenvalues deviate from the bulk of the spectrum predicted by
random matrix theory, but they are far fewer in number compared to, e.g., NYSE.
We show this to be due to the relative weakness of intra-sector interactions
between stocks, compared to the market mode, by modeling stock price dynamics
with a two-factor model. Our results suggest that the emergence of an internal
structure comprising multiple groups of strongly coupled components is a
signature of market development.
|
7c5f1c8b-2031-408d-81c7-7a4abecafc60 | 7c5f1c8b-2031-408d-81c7-7a4abecafc60 | 7c5f1c8b-2031-408d-81c7-7a4abecafc60 | human | null | null | none | abstracts | Galaxy morphologies and environment in the Abell 901/902 supercluster
from COMBO-17 | null | We present a morphological study of galaxies in the A901/902 supercluster
from the COMBO-17 survey. A total of 570 galaxies with photometric redshifts in
the range 0.155 < z_phot < 0.185 are visually classified by three independent
classifiers to M_V=-18. These morphological classifications are compared to
local galaxy density, distance from the nearest cluster centre, local surface
mass density from weak lensing, and photometric classification. At high local
galaxy densities, log(Sigma_10 /Mpc^2) > 1.5, a classical morphology-density
relation is found. A correlation is also found between morphology and local
projected surface mass density, but no trend is observed with distance to the
nearest cluster. This supports the finding that local environment is more
important to galaxy morphology than global cluster properties. The breakdown of
the morphological catalogue by colour shows a dominance of blue galaxies in the
galaxies displaying late-type morphologies and a corresponding dominance of red
galaxies in the early-type population. Using the 17-band photometry from
COMBO-17, we further split the supercluster red sequence into old passive
galaxies and galaxies with young stars and dust according to the prescription
of Wolf et al. (2005). We find that the dusty star-forming population describes
an intermediate morphological group between late-type and early-type galaxies,
supporting the hypothesis that field and group spiral galaxies are transformed
into S0s and, perhaps, ellipticals during cluster infall.
|
d7c0652d-c52d-4242-9462-41c2da274402 | d7c0652d-c52d-4242-9462-41c2da274402 | d7c0652d-c52d-4242-9462-41c2da274402 | human | null | null | none | abstracts | Decoupling Supergravity from the Superstring | null | We consider the conditions necessary for obtaining perturbative maximal
supergravity in d dimensions as a decoupling limit of type II superstring
theory compactified on a (10 -- d)-torus. For dimensions d = 2 and d = 3 it is
possible to define a limit in which the only finite-mass states are the 256
massless states of maximal supergravity. However, in dimensions d > 3 there are
infinite towers of additional massless and finite-mass states. These correspond
to Kaluza--Klein charges, wound strings, Kaluza--Klein monopoles or branes
wrapping around cycles of the toroidal extra dimensions. We conclude that
perturbative supergravity cannot be decoupled from string theory in dimensions
d > 3. In particular, we conjecture that pure N = 8 supergravity in four
dimensions is in the Swampland.
|
d43e4ea3-ee2a-4a51-bddf-36ea6d781e6d | d43e4ea3-ee2a-4a51-bddf-36ea6d781e6d | d43e4ea3-ee2a-4a51-bddf-36ea6d781e6d | human | null | null | none | abstracts | Frobenius splitting and geometry of $G$-Schubert varieties | null | Let $X$ be an equivariant embedding of a connected reductive group $G$ over
an algebraically closed field $k$ of positive characteristic. Let $B$ denote a
Borel subgroup of $G$. A $G$-Schubert variety in $X$ is a subvariety of the
form $\diag(G) \cdot V$, where $V$ is a $B \times B$-orbit closure in $X$. In
the case where $X$ is the wonderful compactification of a group of adjoint
type, the $G$-Schubert varieties are the closures of Lusztig's $G$-stable
pieces. We prove that $X$ admits a Frobenius splitting which is compatible with
all $G$-Schubert varieties. Moreover, when $X$ is smooth, projective and
toroidal, then any $G$-Schubert variety in $X$ admits a stable Frobenius
splitting along an ample divisors. Although this indicates that $G$-Schubert
varieties have nice singularities we present an example of a non-normal
$G$-Schubert variety in the wonderful compactification of a group of type
$G_2$. Finally we also extend the Frobenius splitting results to the more
general class of $\mathcal R$-Schubert varieties.
|
e31a5e9f-4dac-40a1-87b4-0422a593f609 | e31a5e9f-4dac-40a1-87b4-0422a593f609 | e31a5e9f-4dac-40a1-87b4-0422a593f609 | human | null | null | none | abstracts | High Energy Variability Of Synchrotron-Self Compton Emitting Sources:
Why One Zone Models Do Not Work And How We Can Fix It | null | With the anticipated launch of GLAST, the existing X-ray telescopes, and the
enhanced capabilities of the new generation of TeV telescopes, developing tools
for modeling the variability of high energy sources such as blazars is becoming
a high priority. We point out the serious, innate problems one zone
synchrotron-self Compton models have in simulating high energy variability. We
then present the first steps toward a multi zone model where non-local, time
delayed Synchrotron-self Compton electron energy losses are taken into account.
By introducing only one additional parameter, the length of the system, our
code can simulate variability properly at Compton dominated stages, a situation
typical of flaring systems. As a first application, we were able to reproduce
variability similar to that observed in the case of the puzzling `orphan' TeV
flares that are not accompanied by a corresponding X-ray flare.
|
3f174f2b-0555-4b1b-86a4-9eedc21e0c47 | 3f174f2b-0555-4b1b-86a4-9eedc21e0c47 | 3f174f2b-0555-4b1b-86a4-9eedc21e0c47 | human | null | null | none | abstracts | Testing outer boundary treatments for the Einstein equations | null | Various methods of treating outer boundaries in numerical relativity are
compared using a simple test problem: a Schwarzschild black hole with an
outgoing gravitational wave perturbation. Numerical solutions computed using
different boundary treatments are compared to a `reference' numerical solution
obtained by placing the outer boundary at a very large radius. For each
boundary treatment, the full solutions including constraint violations and
extracted gravitational waves are compared to those of the reference solution,
thereby assessing the reflections caused by the artificial boundary. These
tests use a first-order generalized harmonic formulation of the Einstein
equations. Constraint-preserving boundary conditions for this system are
reviewed, and an improved boundary condition on the gauge degrees of freedom is
presented. Alternate boundary conditions evaluated here include freezing the
incoming characteristic fields, Sommerfeld boundary conditions, and the
constraint-preserving boundary conditions of Kreiss and Winicour. Rather
different approaches to boundary treatments, such as sponge layers and spatial
compactification, are also tested. Overall the best treatment found here
combines boundary conditions that preserve the constraints, freeze the
Newman-Penrose scalar Psi_0, and control gauge reflections.
|
b98dc8d1-7c3e-4271-98ea-d52df4b1a57c | b98dc8d1-7c3e-4271-98ea-d52df4b1a57c | b98dc8d1-7c3e-4271-98ea-d52df4b1a57c | human | null | null | none | abstracts | D-brane Instantons on the T^6/Z_3 orientifold | null | We give a detailed microscopic derivation of gauge and stringy instanton
generated superpotentials for gauge theories living on D3-branes at
Z_3-orientifold singularities. Gauge instantons are generated by D(-1)-branes
and lead to Affleck, Dine and Seiberg (ADS) like superpotentials in the
effective N=1 gauge theories with three generations of bifundamental and
anti/symmetric matter. Stringy instanton effects are generated by Euclidean
ED3-branes wrapping four-cycles on T^6/\Z_3. They give rise to Majorana masses
in one case and non-renormalizable superpotentials for the other cases. Finally
we determine the conditions under which ADS like superpotentials are generated
in N=1 gauge theories with adjoints, fundamentals, symmetric and antisymmetric
chiral matter.
|
265670f1-a22b-434a-a04a-d134146da72f | 265670f1-a22b-434a-a04a-d134146da72f | 265670f1-a22b-434a-a04a-d134146da72f | human | null | null | none | abstracts | Viscoplastic Properties and Tribological Behavior of Diamond-Like Carbon
Films Using Nanoindentation and Nanoscratch Tests | null | Diamond-Like Carbon (DLC) films have been shown to demonstrate various
tribological behaviors: in ultra-high vacuum (UHV), with either friction
coefficients as low as 0.01 or less and very mild wear, or very high friction
coefficients (>0.4) and drastic wear. These behaviors depend notably on gaseous
environment, hydrogen content of the film [1], and on its viscoplastic
properties [2,3]. A relation between superlow friction in UHV and
viscoplasticity has indeed been established for a-C:H films and confirmed for a
fluorinated sample (a-C:F:H). In this study, nanoindentation and nanoscratch
tests were conducted in ambient air, using a nanoindentation apparatus, in
order to evaluate tribological behaviors, as well as mechanical and
viscoplastic properties of different amorphous carbon films.
|
c7615c05-01d2-4906-b2d6-e7cb7e8d3c77 | c7615c05-01d2-4906-b2d6-e7cb7e8d3c77 | c7615c05-01d2-4906-b2d6-e7cb7e8d3c77 | human | null | null | none | abstracts | Optimal Synthesis of Multiple Algorithms | null | In this paper we give a definition of "algorithm," "finite algorithm,"
"equivalent algorithms," and what it means for a single algorithm to dominate a
set of algorithms. We define a derived algorithm which may have a smaller mean
execution time than any of its component algorithms. We give an explicit
expression for the mean execution time (when it exists) of the derived
algorithm. We give several illustrative examples of derived algorithms with two
component algorithms. We include mean execution time solutions for
two-algorithm processors whose joint density of execution times are of several
general forms. For the case in which the joint density for a two-algorithm
processor is a step function, we give a maximum-likelihood estimation scheme
with which to analyze empirical processing time data.
|
3dc8a78b-75df-4b4e-97fb-c9416bfa5750 | 3dc8a78b-75df-4b4e-97fb-c9416bfa5750 | 3dc8a78b-75df-4b4e-97fb-c9416bfa5750 | human | null | null | none | abstracts | New Close Binary Systems from the SDSS-I (Data Release Five) and the
Search for Magnetic White Dwarfs in Cataclysmic Variable Progenitor Systems | null | We present the latest catalog of more than 1200 spectroscopically-selected
close binary systems observed with the Sloan Digital Sky Survey through Data
Release Five. We use the catalog to search for magnetic white dwarfs in
cataclysmic variable progenitor systems. Given that approximately 25% of
cataclysmic variables contain a magnetic white dwarf, and that our large sample
of close binary systems should contain many progenitors of cataclysmic
variables, it is quite surprising that we find only two potential magnetic
white dwarfs in this sample. The candidate magnetic white dwarfs, if confirmed,
would possess relatively low magnetic field strengths (B_WD < 10 MG) that are
similar to those of intermediate-Polars but are much less than the average
field strength of the current Polar population. Additional observations of
these systems are required to definitively cast the white dwarfs as magnetic.
Even if these two systems prove to be the first evidence of detached magnetic
white dwarf + M dwarf binaries, there is still a large disparity between the
properties of the presently known cataclysmic variable population and the
presumed close binary progenitors.
|
f2866bcf-10a1-4779-9b46-bd63caa2372e | f2866bcf-10a1-4779-9b46-bd63caa2372e | f2866bcf-10a1-4779-9b46-bd63caa2372e | human | null | null | none | abstracts | Dynamical Casimir effect for gravitons in bouncing braneworlds | null | We consider a two-brane system in a five-dimensional anti-de Sitter
spacetime. We study particle creation due to the motion of the physical brane
which first approaches the second static brane (contraction) and then recedes
from it(expansion). The spectrum and the energy density of the generated
gravitons are calculated. We show that the massless gravitons have a blue
spectrum and that their energy density satisfies the nucleosynthesis bound with
very mild constraints on the parameters. We also show that the Kaluza-Klein
modes cannot provide the dark matter in an anti-de-Sitter braneworld. However,
for natural choices of parameters, backreaction from the Kaluza-Klein gravitons
may well become important. The main findings of this work have been published
in the form of a Letter [R. Durrer and M. Ruser, Phys. Rev. Lett. 99, 071601
(2007), arXiv:0704.0756].
|
8c0d729c-e384-49e5-9a02-f7e27c8f3731 | 8c0d729c-e384-49e5-9a02-f7e27c8f3731 | 8c0d729c-e384-49e5-9a02-f7e27c8f3731 | human | null | null | none | abstracts | Spectral analysis of Swift long GRBs with known redshift | null | We study the spectral and energetics properties of 47 long-duration gamma-ray
bursts (GRBs) with known redshift, all of them detected by the Swift satellite.
Due to the narrow energy range (15-150 keV) of the Swift-BAT detector, the
spectral fitting is reliable only for fitting models with 2 or 3 parameters. As
high uncertainty and correlation among the errors is expected, a careful
analysis of the errors is necessary. We fit both the power law (PL, 2
parameters) and cut--off power law (CPL, 3 parameters) models to the
time-integrated spectra of the 47 bursts, and present the corresponding
parameters, their uncertainties, and the correlations among the uncertainties.
The CPL model is reliable only for 29 bursts for which we estimate the nuf_nu
peak energy Epk. For these GRBs, we calculate the energy fluence and the rest-
frame isotropic-equivalent radiated energy, Eiso, as well as the propagated
uncertainties and correlations among them. We explore the distribution of our
homogeneous sample of GRBs on the rest-frame diagram E'pk vs Eiso. We confirm a
significant correlation between these two quantities (the "Amati" relation) and
we verify that, within the uncertainty limits, no outliers are present. We also
fit the spectra to a Band model with the high energy power law index frozen to
-2.3, obtaining a rather good agreement with the "Amati" relation of non-Swift
GRBs.
|
e1994aa0-855e-49c3-a836-3da469d65392 | e1994aa0-855e-49c3-a836-3da469d65392 | e1994aa0-855e-49c3-a836-3da469d65392 | human | null | null | none | abstracts | Constraints on the Interactions between Dark Matter and Baryons from the
X-ray Quantum Calorimetry Experiment | null | Although the rocket-based X-ray Quantum Calorimetry (XQC) experiment was
designed for X-ray spectroscopy, the minimal shielding of its calorimeters, its
low atmospheric overburden, and its low-threshold detectors make it among the
most sensitive instruments for detecting or constraining strong interactions
between dark matter particles and baryons. We use Monte Carlo simulations to
obtain the precise limits the XQC experiment places on spin-independent
interactions between dark matter and baryons, improving upon earlier analytical
estimates. We find that the XQC experiment rules out a wide range of
nucleon-scattering cross sections centered around one barn for dark matter
particles with masses between 0.01 and 10^5 GeV. Our analysis also provides new
constraints on cases where only a fraction of the dark matter strongly
interacts with baryons.
|
9baa293f-b510-4b4e-8019-5e00ef8c03ec | 9baa293f-b510-4b4e-8019-5e00ef8c03ec | 9baa293f-b510-4b4e-8019-5e00ef8c03ec | human | null | null | none | abstracts | Heavy-Light Semileptonic Decays in Staggered Chiral Perturbation Theory | null | We calculate the form factors for the semileptonic decays of heavy-light
pseudoscalar mesons in partially quenched staggered chiral perturbation theory
(\schpt), working to leading order in $1/m_Q$, where $m_Q$ is the heavy quark
mass. We take the light meson in the final state to be a pseudoscalar
corresponding to the exact chiral symmetry of staggered quarks. The treatment
assumes the validity of the standard prescription for representing the
staggered ``fourth root trick'' within \schpt by insertions of factors of 1/4
for each sea quark loop. Our calculation is based on an existing partially
quenched continuum chiral perturbation theory calculation with degenerate sea
quarks by Becirevic, Prelovsek and Zupan, which we generalize to the staggered
(and non-degenerate) case. As a by-product, we obtain the continuum partially
quenched results with non-degenerate sea quarks. We analyze the effects of
non-leading chiral terms, and find a relation among the coefficients governing
the analytic valence mass dependence at this order. Our results are useful in
analyzing lattice computations of form factors $B\to\pi$ and $D\to K$ when the
light quarks are simulated with the staggered action.
|
4b56b5f2-71dd-419a-9f65-be1ce53683a2 | 4b56b5f2-71dd-419a-9f65-be1ce53683a2 | 4b56b5f2-71dd-419a-9f65-be1ce53683a2 | human | null | null | none | abstracts | Scalar self-force on eccentric geodesics in Schwarzschild spacetime: a
time-domain computation | null | We calculate the self-force acting on a particle with scalar charge moving on
a generic geodesic around a Schwarzschild black hole. This calculation requires
an accurate computation of the retarded scalar field produced by the moving
charge; this is done numerically with the help of a fourth-order convergent
finite-difference scheme formulated in the time domain. The calculation also
requires a regularization procedure, because the retarded field is singular on
the particle's world line; this is handled mode-by-mode via the mode-sum
regularization scheme first introduced by Barack and Ori. This paper presents
the numerical method, various numerical tests, and a sample of results for
mildly eccentric orbits as well as ``zoom-whirl'' orbits.
|
85f60e37-e483-486c-8284-f4d315fd8371 | 85f60e37-e483-486c-8284-f4d315fd8371 | 85f60e37-e483-486c-8284-f4d315fd8371 | human | null | null | none | abstracts | Nonimmersions of RP^n implied by tmf, revisited | null | In a 2002 paper, the authors and Bruner used the new spectrum tmf to obtain
some new nonimmersions of real projective spaces. In this note, we
complete/correct two oversights in that paper.
The first is to note that in that paper a general nonimmersion result was
stated which yielded new nonimmersions for RP^n with n as small as 48, and yet
it was stated there that the first new result occurred when n=1536. Here we
give a simple proof of those overlooked results.
Secondly, we fill in a gap in the proof of the 2002 paper. There it was
claimed that an axial map f must satisfy f^*(X)=X_1+X_2. We realized recently
that this is not clear. However, here we show that it is true up multiplication
by a unit in the appropriate ring, and so we retrieve all the nonimmersion
results claimed in the original paper.
Finally, we present a complete determination of tmf^{8*}(RP^\infty\times
RP^\infty) and tmf^*(CP^\infty\times CP^\infty) in positive dimensions.
|
c55772f7-ea09-4cb2-b000-55b485966d25 | c55772f7-ea09-4cb2-b000-55b485966d25 | c55772f7-ea09-4cb2-b000-55b485966d25 | human | null | null | none | abstracts | Quantum Auctions | null | We present a quantum auction protocol using superpositions to represent bids
and distributed search to identify the winner(s). Measuring the final quantum
state gives the auction outcome while simultaneously destroying the
superposition. Thus non-winning bids are never revealed. Participants can use
entanglement to arrange for correlations among their bids, with the assurance
that this entanglement is not observable by others. The protocol is useful for
information hiding applications, such as partnership bidding with allocative
externality or concerns about revealing bidding preferences. The protocol
applies to a variety of auction types, e.g., first or second price, and to
auctions involving either a single item or arbitrary bundles of items (i.e.,
combinatorial auctions). We analyze the game-theoretical behavior of the
quantum protocol for the simple case of a sealed-bid quantum, and show how a
suitably designed adiabatic search reduces the possibilities for bidders to
game the auction. This design illustrates how incentive rather that
computational constraints affect quantum algorithm choices.
|
52fc6338-70db-47e0-8436-153143e33586 | 52fc6338-70db-47e0-8436-153143e33586 | 52fc6338-70db-47e0-8436-153143e33586 | human | null | null | none | abstracts | Hybrid-ARQ in Multihop Networks with Opportunistic Relay Selection | null | This paper develops a contention-based opportunistic feedback technique
towards relay selection in a dense wireless network. This technique enables the
forwarding of additional parity information from the selected relay to the
destination. For a given network, the effects of varying key parameters such as
the feedback probability are presented and discussed. A primary advantage of
the proposed technique is that relay selection can be performed in a
distributed way. Simulation results find its performance to closely match that
of centralized schemes that utilize GPS information, unlike the proposed
method. The proposed relay selection method is also found to achieve throughput
gains over a point-to-point transmission strategy.
|
6fbb57c2-59ff-4f15-b1f1-4d656701e71b | 6fbb57c2-59ff-4f15-b1f1-4d656701e71b | 6fbb57c2-59ff-4f15-b1f1-4d656701e71b | human | null | null | none | abstracts | Equation-free implementation of statistical moment closures | null | We present a general numerical scheme for the practical implementation of
statistical moment closures suitable for modeling complex, large-scale,
nonlinear systems. Building on recently developed equation-free methods, this
approach numerically integrates the closure dynamics, the equations of which
may not even be available in closed form. Although closure dynamics introduce
statistical assumptions of unknown validity, they can have significant
computational advantages as they typically have fewer degrees of freedom and
may be much less stiff than the original detailed model. The closure method can
in principle be applied to a wide class of nonlinear problems, including
strongly-coupled systems (either deterministic or stochastic) for which there
may be no scale separation. We demonstrate the equation-free approach for
implementing entropy-based Eyink-Levermore closures on a nonlinear stochastic
partial differential equation.
|
36ceb46b-ce00-4ee7-b70f-4575859f9c3f | 36ceb46b-ce00-4ee7-b70f-4575859f9c3f | 36ceb46b-ce00-4ee7-b70f-4575859f9c3f | human | null | null | none | abstracts | Opportunistic Relay Selection with Limited Feedback | null | It has been shown that a decentralized relay selection protocol based on
opportunistic feedback from the relays yields good throughput performance in
dense wireless networks. This selection strategy supports a hybrid-ARQ
transmission approach where relays forward parity information to the
destination in the event of a decoding error. Such an approach, however,
suffers a loss compared to centralized strategies that select relays with the
best channel gain to the destination. This paper closes the performance gap by
adding another level of channel feedback to the decentralized relay selection
problem. It is demonstrated that only one additional bit of feedback is
necessary for good throughput performance. The performance impact of varying
key parameters such as the number of relays and the channel feedback threshold
is discussed. An accompanying bit error rate analysis demonstrates the
importance of relay selection.
|
bd73f78c-31e8-4272-8a8c-55582e279dcf | bd73f78c-31e8-4272-8a8c-55582e279dcf | bd73f78c-31e8-4272-8a8c-55582e279dcf | human | null | null | none | abstracts | On a Conjecture of EM Stein on the Hilbert Transform on Vector Fields | null | Let $ v$ be a smooth vector field on the plane, that is a map from the plane
to the unit circle. We study sufficient conditions for the boundedness of the
Hilbert transform
\operatorname H_{v, \epsilon}f(x) := \text{p.v.}\int_{-\epsilon}^ \epsilon
f(x-yv(x)) \frac{dy}y where $ \epsilon $ is a suitably chosen parameter,
determined by the smoothness properties of the vector field. It is a
conjecture, due to E.\thinspace M.\thinspace Stein, that if $ v$ is Lipschitz,
there is a positive $ \epsilon $ for which the transform above is bounded on $
L ^{2}$. Our principal result gives a sufficient condition in terms of the
boundedness of a maximal function associated to $ v$. This sufficient condition
is that this new maximal function be bounded on some $ L ^{p}$, for some $
1<p<2$. We show that the maximal function is bounded from $ L ^{2}$ to weak $ L
^{2}$ for all Lipschitz maximal function. The relationship between our results
and other known sufficient conditions is explored.
|
fac79504-7e8f-457d-be7b-4c7fcf9870a9 | fac79504-7e8f-457d-be7b-4c7fcf9870a9 | fac79504-7e8f-457d-be7b-4c7fcf9870a9 | human | null | null | none | abstracts | Wide Field Surveys and Astronomical Discovery Space | null | I review the status of science with wide field surveys. For many decades
surveys have been the backbone of astronomy, and the main engine of discovery,
as we have mapped the sky at every possible wavelength. Surveys are an
efficient use of resources. They are important as a fundamental resource; to
map intrinsically large structures; to gain the necessary statistics to address
some problems; and to find very rare objects. I summarise major recent wide
field surveys - 2MASS, SDSS, 2dfGRS, and UKIDSS - and look at examples of the
exciting science they have produced, covering the structure of the Milky Way,
the measurement of cosmological parameters, the creation of a new field
studying substellar objects, and the ionisation history of the Universe. I then
look briefly at upcoming projects in the optical-IR survey arena - VISTA,
PanSTARRS, WISE, and LSST. Finally I ask, now we have opened up essentially all
wavelength windows, whether the exploration of survey discovery space is ended.
I examine other possible axes of discovery space, and find them mostly to be
too expensive to explore or otherwise unfruitful, with two exceptions : the
first is the time axis, which we have only just begun to explore properly; and
the second is the possibility of neutrino astrophysics.
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12aae02a-857c-46f9-af34-57151983c1e1 | 12aae02a-857c-46f9-af34-57151983c1e1 | 12aae02a-857c-46f9-af34-57151983c1e1 | human | null | null | none | abstracts | Jet interactions in massive X-ray binaries | null | Massive X-ray binaries are formed by a compact object that accretes matter
from the stellar wind of an early-type donor star. In some of these systems,
called microquasars, relativistic jets are launched from the surroundings of
the compact object. Such jets interact with the photon field of the companion
star, the stellar wind, and, at large distances, with the interstellar medium.
In this paper I will review the main results of such interactions with
particular emphasis on the production of high-energy photons and neutrinos. The
case of some specific systems, like LS I +61 303, will be discussed in some
detail. Prospects for future observations at different wavelengths of this type
of objects will be presented.
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ecb73b33-5e35-4b3f-b1f7-56702d66074c | ecb73b33-5e35-4b3f-b1f7-56702d66074c | ecb73b33-5e35-4b3f-b1f7-56702d66074c | human | null | null | none | abstracts | The Na I D resonance lines in main sequence late-type stars | null | We study the sodium D lines (D1: 5895.92 \AA; D2: 5889.95 \AA) in late-type
dwarf stars. The stars have spectral types between F6 and M5.5 (B-V between
0.457 and 1.807) and metallicity between [Fe/H] = -0.82 and 0.6. We obtained
medium resolution echelle spectra using the 2.15-m telescope at the argentinian
observatory CASLEO. The observations have been performed periodically since
1999. The spectra were calibrated in wavelength and in flux. A definition of
the pseudo-continuum level is found for all our observations. We also define a
continuum level for calibration purposes. The equivalent width of the D lines
is computed in detail for all our spectra and related to the colour index (B-V)
of the stars. When possible, we perform a careful comparison with previous
studies. Finally, we construct a spectral index (R_D') as the ratio between the
flux in the D lines, and the bolometric flux. We find that, once corrected for
the photospheric contribution, this index can be used as a chromospheric
activity indicator in stars with a high level of activity. Additionally, we
find that combining some of our results, we obtain a method to calibrate in
flux stars of unknown colour.
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f24dfd26-60cb-4a96-b099-e0f8218fb479 | f24dfd26-60cb-4a96-b099-e0f8218fb479 | f24dfd26-60cb-4a96-b099-e0f8218fb479 | human | null | null | none | abstracts | 3-D Simulations of Ergospheric Disk Driven Poynting Jets | null | This Letter reports on 3-dimensional simulations of Kerr black hole
magnetospheres that obey the general relativistic equations of perfect
magnetohydrodynamics (MHD). In particular, we study powerful Poynting flux
dominated jets that are driven from dense gas in the equatorial plane in the
ergosphere. The physics of which has been previously studied in the simplified
limit of an ergopsheric disk. For high spin black holes, $a/M > 0.95$, the
ergospheric disk is prominent in the 3-D simulations and is responsible for
greatly enhanced Poynting flux emission. Any large scale poloidal magnetic flux
that is trapped in the equatorial region leads to an enormous release of
electromagnetic energy that dwarfs the jet energy produced by magnetic flux
threading the event horizon. The implication is that magnetic flux threading
the equatorial plane of the ergosphere is a likely prerequisite for the central
engine of powerful FRII quasars.
|
ffa4ab34-e166-4219-9ea4-44b969db5830 | ffa4ab34-e166-4219-9ea4-44b969db5830 | ffa4ab34-e166-4219-9ea4-44b969db5830 | human | null | null | none | abstracts | Position-Velocity Diagrams for the Maser Emission coming from a
Keplerian Ring | null | We have studied the maser emission from a thin, planar, gaseous ring in
Keplerian rotation around a central mass observed edge-on. The absorption
coefficient within the ring is assumed to follow a power law dependence with
the distance from the central mass as, k=k0r^{-q}. We have calculated
position-velocity diagrams for the most intense maser features, for different
values of the exponent q. We have found that, depending on the value of q,
these diagrams can be qualitatively different. The most intense maser emission
at a given velocity can either come mainly from regions close to the inner or
outer edges of the amplifying ring or from the line perpendicular to the line
of sight and passing through the central mass (as is commonly assumed).
Particularly, when q>1 the position-velocity diagram is qualitatively similar
to the one observed for the water maser emission in the nucleus of the galaxy
NGC 4258. In the context of this simple model, we conclude that in this object
the absorption coefficient depends on the radius of the amplifying ring as a
decreasing function, in order to have significant emission coming from the
inner edge of the ring.
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9951b30b-cb28-4b63-9351-dc4b0ee5a89b | 9951b30b-cb28-4b63-9351-dc4b0ee5a89b | 9951b30b-cb28-4b63-9351-dc4b0ee5a89b | human | null | null | none | abstracts | Spin solid phases of spin 1 and spin 3/2 antiferromagnets on a cubic
lattice | null | We study spin S=1 and S=3/2 Heisenberg antiferromagnets on a cubic lattice
focusing on spin solid states. Using Schwinger boson formulation for spins, we
start in a U(1) spin liquid phase proximate to Neel phase and explore possible
confining paramagnetic phases as we transition away from the spin liquid by the
process of monopole condensation. Electromagnetic duality is used to rewrite
the theory in terms of monopoles. For spin 1 we find several candidate phases
of which the most natural one is a phase with spins organized into parallel
Haldane chains. For spin 3/2 we find that the most natural phase has spins
organized into parallel ladders. As a by-product, we also write a Landau theory
of the ordering in two special classical frustrated XY models on the cubic
lattice, one of which is the fully frustrated XY model. In a particular limit
our approach maps to a dimer model with 2S dimers coming out of every site, and
we find the same spin solid phases in this regime as well.
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528b85f8-eeac-4791-b31c-b5594c40c391 | 528b85f8-eeac-4791-b31c-b5594c40c391 | 528b85f8-eeac-4791-b31c-b5594c40c391 | human | null | null | none | abstracts | Braided quantum field theories and their symmetries | null | Braided quantum field theories proposed by Oeckl can provide a framework for
defining quantum field theories having Hopf algebra symmetries. In quantum
field theories, symmetries lead to non-perturbative relations among correlation
functions. We discuss Hopf algebra symmetries and such relations in braided
quantum field theories. We give the four algebraic conditions between Hopf
algebra symmetries and braided quantum field theories, which are required for
the relations to hold. As concrete examples, we apply our discussions to the
Poincare symmetries of two examples of noncommutative field theories. One is
the effective quantum field theory of three-dimensional quantum gravity coupled
with spinless particles given by Freidel and Livine, and the other is
noncommutative field theory on Moyal plane. We also comment on quantum field
theory on kappa-Minkowski spacetime.
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abe0ce2c-cc96-4e14-9400-6e698221abb2 | abe0ce2c-cc96-4e14-9400-6e698221abb2 | abe0ce2c-cc96-4e14-9400-6e698221abb2 | human | null | null | none | abstracts | Chromospheric Flares | null | In this topical review I revisit the "chromospheric flare." This should
currently be an outdated concept, because modern data seem to rule out the
possiblity of a major flare happening independently in the chromosphere alone,
but the chromosphere still plays a major observational role in many ways. It is
the source of the bulk of a flare's radiant energy - in particular the
visible/UV continuum radiation. It also provides tracers that guide us to the
coronal source of the energy, even though we do not yet understand the
propagation of the energy from its storage in the corona to its release in the
chromosphere. The formation of chromospheric radiations during a flare presents
several difficult and interesting physical problems.
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