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arxiv_dataset-22001010.3612 | Explicit examples of equivalence relations and factors with prescribed
fundamental group and outer automorphism group
math.OA math.DS math.GR
In this paper we give a number of explicit constructions for II$_1$ factors
and II$_1$ equivalence relations that have prescribed fundamental group and
outer automorphism group. We construct factors and relations that have
uncountable fundamental group different from $\IRpos$. In fact, given any
II$_1$ equivalence relation, we construct a II$_1$ factor with the same
fundamental group. Given any locally compact unimodular second countable group
$G$, our construction gives a II$_1$ equivalence relation $\RelR$ whose outer
automorphism group is $G$. The same construction does not give a II$_1$ factor
with $G$ as outer automorphism group, but when $G$ is a compact group or if
$G=\SL^{\pm}_n\IR=\{g\in\GL_n\IR\mid \det(g)=\pm1\}$, then we still find a type
II$_1$ factor whose outer automorphism group is $G$.
| arxiv topic:math.OA math.DS math.GR |
arxiv_dataset-22011010.3712 | Potential contributions of noncontact atomic force microscopy for the
future Casimir force measurements
quant-ph
Surface electric noise, i.e., the non-uniform distribution of charges and
potentials on a surface, poses a great experimental challenge in modern
precision force measurements. Such a challenge is encountered in a number of
different experimental circumstances. The scientists employing atomic force
microscopy (AFM) have long focused their efforts to understand the
surface-related noise issues via variants of AFM techniques, such as Kelvin
probe force microscopy or electric force microscopy. Recently, the physicists
investigating quantum vacuum fluctuation phenomena between two closely-spaced
objects have also begun to collect experimental evidence indicating a presence
of surface effects neglected in their previous analyses. It now appears that
the two seemingly disparate science communities are encountering effects rooted
in the same surface phenomena. In this report, we suggest specific experimental
tasks to be performed in the near future that are crucial not only for
fostering needed collaborations between the two communities, but also for
providing valuable data on the surface effects in order to draw the most
realistic conclusion about the actual contribution of the Casimir force (or van
der Waals force) between a pair of real materials.
| arxiv topic:quant-ph |
arxiv_dataset-22021010.3812 | Random Projection Trees Revisited
cs.DS cs.CG math.DG stat.ML
The Random Projection Tree structures proposed in [Freund-Dasgupta STOC08]
are space partitioning data structures that automatically adapt to various
notions of intrinsic dimensionality of data. We prove new results for both the
RPTreeMax and the RPTreeMean data structures. Our result for RPTreeMax gives a
near-optimal bound on the number of levels required by this data structure to
reduce the size of its cells by a factor $s \geq 2$. We also prove a packing
lemma for this data structure. Our final result shows that low-dimensional
manifolds have bounded Local Covariance Dimension. As a consequence we show
that RPTreeMean adapts to manifold dimension as well.
| arxiv topic:cs.DS cs.CG math.DG stat.ML |
arxiv_dataset-22031010.3912 | Interface effects on an ultrathin Co film in multilayers based on the
organic semiconductor Alq3
cond-mat.mtrl-sci cond-mat.mes-hall
The effect of the AlOx barrier thickness on magnetic and morphological
properties of Ta/Co/(AlOx)/Alq3/Si hybrid structures was systematically studied
by means of atomic force microscopy, SQUID magnetometry and nuclear magnetic
resonance (NMR). All used techniques pointed out that the barrier thickness of
2 nm is required to obtain a magnetically good cobalt layer on top of Alq3.
59Co NMR measurements revealed that the AlOx barrier gives rise to the
formation of an interface layer with "defective" cobalt favouring growth of
"bulk" cobalt with good magnetic properties.
| arxiv topic:cond-mat.mtrl-sci cond-mat.mes-hall |
arxiv_dataset-22041010.4012 | Experimental Evidence of Fluctuation-Dissipation Theorem Violation in a
Superspin Glass
cond-mat.dis-nn
We present the experimental observation of the fluctuation-dissipation
theorem (FDT) violation in an assembly of interacting magnetic nanoparticles in
the low temperature superspin glass phase. The magnetic noise is measured with
a two-dimension electron gas Hall probe and compared to the out of phase ac
susceptibility of the same ferrofluid. For "intermediate" aging times of the
order of 1 h, the ratio of the effective temperature $T_{\rm eff}$ to the bath
temperature T grows from 1 to 6.5 when T is lowered from $T_g$ to 0.3 $T_g$,
regardless of the noise frequency. These values are comparable to those
measured in an atomic spin glass as well as those calculated for a Heisenberg
spin glass.
| arxiv topic:cond-mat.dis-nn |
arxiv_dataset-22051010.4112 | Sliding functor and polarization functor for multigraded modules
math.AC
We define "sliding functors", which are exact endofunctors of the category of
multi-graded modules over a polynomial ring. They preserve several invariants
of modules, especially the (usual) depth and Stanley depth. In a similar way,
we can also define the "polarization functor". While this idea has appeared in
papers of Bruns-Herzog and Sbarra, we give slightly different approach. Keeping
these functors in mind, we treat simplicial spheres of Bier-Murai type.
| arxiv topic:math.AC |
arxiv_dataset-22061010.4212 | Partitions of metric spaces with finite distance sets
math.CO math.DS math.FA
A metric space $\mathrm{M}=(M,\de)$ is {\em indivisible} if for every
colouring $\chi: M\to 2$ there exists $i\in 2$ and a copy $\mathrm{N}=(N, \de)$
of $\mathrm{M}$ in $\mathrm{M}$ so that $\chi(x)=i$ for all $x\in N$. The
metric space $\mathrm{M}$ is {\em homogeneus} if for every isometry $\alpha$ of
a finite subspace of $\mathrm{M}$ to a subspace of $\mathrm{M}$ there exists an
isometry of $\mathrm{M}$ onto $\mathrm{M}$ extending $\alpha$. A homogeneous
metric space $\mathrm{U}$ with set of distances $\mathcal{D}$ is an Urysohn
metric space if every finite metric space with set of distances a subset of
$\mathcal{D}$ has an isometry into $\mathrm{U}$. The main result of this paper
states that all countable Urysohn metric spaces with a finite set of distances
are indivisible.
| arxiv topic:math.CO math.DS math.FA |
arxiv_dataset-22071010.4312 | Spectroscopic confirmation of a galaxy at redshift z=8.6
astro-ph.CO
Galaxies had their most significant impact on the Universe when they
assembled their first generations of stars. Energetic photons emitted by young,
massive stars in primeval galaxies ionized the intergalactic medium surrounding
their host galaxies, cleared sight-lines along which the light of the young
galaxies could escape, and fundamentally altered the physical state of the
intergalactic gas in the Universe continuously until the present day.
Observations of the Cosmic Microwave Background, and of galaxies and quasars at
the highest redshifts, suggest that the Universe was reionised through a
complex process that was completed about a billion years after the Big Bang, by
redshift z~6. Detecting ionizing Ly-alpha photons from increasingly distant
galaxies places important constraints on the timing, location and nature of the
sources responsible for reionisation. Here we report the detection of Ly-a
photons emitted less than 600 million years after the Big Bang. UDFy-38135539
is at a redshift z=8.5549+-0.0002, which is greater than those of the
previously known most distant objects, at z=8.2 and z=6.97. We find that this
single source is unlikely to provide enough photons to ionize the volume
necessary for the emission line to escape, requiring a significant contribution
from other, probably fainter galaxies nearby.
| arxiv topic:astro-ph.CO |
arxiv_dataset-22081010.4412 | The Locality Problem in Quantum Measurements
quant-ph
The locality problem of quantum measurements is considered in the framework
of the algebraic approach. It is shown that contrary to the currently
widespread opinion one can reconcile the mathematical formalism of the quantum
theory with the assumption of the existence of a local physical reality
determining the results of local measurements. The key quantum experiments:
double-slit experiment on electron scattering, Wheeler's delayed-choice
experiment, the Einstein-Podolsky-Rosen paradox, and quantum teleportation are
discussed from the locality-problem point of view. A clear physical
interpretation for these experiments, which does not contradict the classical
ideas, is given.
| arxiv topic:quant-ph |
arxiv_dataset-22091010.4512 | Effective inhomogeneous inflation: curvature inhomogeneities of the
Einstein vacuum
gr-qc astro-ph.CO hep-th
We consider spatially averaged inhomogeneous universe models and argue that,
already in the absence of sources, an effective scalar field arises through
foliating and spatially averaging inhomogeneous geometrical curvature
invariants of the Einstein vacuum. This scalar field (the `morphon') acts as an
inflaton, if we prescribe a potential of some generic form. We show that, for
any initially negative average spatial curvature, the morphon is driven through
an inflationary phase and leads - on average - to a spatially flat, homogeneous
and isotropic universe model, providing initial conditions for pre-heating and,
by the same mechanism, a possibly natural self-exit.
| arxiv topic:gr-qc astro-ph.CO hep-th |
arxiv_dataset-22101010.4612 | Recovering Compressively Sampled Signals Using Partial Support
Information
cs.IT cs.SY math.IT math.OC
In this paper we study recovery conditions of weighted $\ell_1$ minimization
for signal reconstruction from compressed sensing measurements when partial
support information is available. We show that if at least 50% of the (partial)
support information is accurate, then weighted $\ell_1$ minimization is stable
and robust under weaker conditions than the analogous conditions for standard
$\ell_1$ minimization. Moreover, weighted $\ell_1$ minimization provides better
bounds on the reconstruction error in terms of the measurement noise and the
compressibility of the signal to be recovered. We illustrate our results with
extensive numerical experiments on synthetic data and real audio and video
signals.
| arxiv topic:cs.IT cs.SY math.IT math.OC |
arxiv_dataset-22111010.4712 | Dynamical approach to the Casimir effect
cond-mat.stat-mech
Casimir forces can appear between intrusions placed in different media driven
by several fluctuation mechanisms, either in equilibrium or out of it. Herein,
we develop a general formalism to obtain such forces from the dynamical
equations of the fluctuating medium, the statistical properties of the driving
noise, and the boundary conditions of the intrusions (which simulate the
interaction between the intrusions and the medium). As a result, an explicit
formula for the Casimir force over the intrusions is derived. This formalism
contains the thermal Casimir effect as a particular limit and generalizes the
study of the Casimir effect to such systems through their dynamical equations,
with no appeal to their Hamiltonian, if any exists. In particular, we study the
Casimir force between two infinite parallel plates with Dirichlet or Neumann
boundary conditions, immersed in several media with finite correlation lengths
(reaction--diffusion system, liquid crystals, and two coupled fields with
non-Hermitian evolution equations). The driving Gaussian noises have vanishing
or finite spatial or temporal correlation lengths; in the first case,
equilibrium is reobtained and finite correlations produce nonequilibrium
dynamics. The results obtained show that, generally, nonequilibrium dynamics
leads to Casimir forces, whereas Casimir forces are obtained in equilibrium
dynamics if the stress tensor is anisotropic.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-22121010.4812 | Polynomial Bottleneck Congestion Games with Optimal Price of Anarchy
cs.GT
We study {\em bottleneck congestion games} where the social cost is
determined by the worst congestion of any resource. These games directly relate
to network routing problems and also job-shop scheduling problems. In typical
bottleneck congestion games, the utility costs of the players are determined by
the worst congested resources that they use. However, the resulting Nash
equilibria are inefficient, since the price of anarchy is proportional on the
number of resources which can be high. Here we show that we can get smaller
price of anarchy with the bottleneck social cost metric. We introduce the {\em
polynomial bottleneck games} where the utility costs of the players are
polynomial functions of the congestion of the resources that they use. In
particular, the delay function for any resource $r$ is $C_{r}^\M$, where $C_r$
is the congestion measured as the number of players that use $r$, and $\M \geq
1$ is an integer constant that defines the degree of the polynomial. The
utility cost of a player is the sum of the individual delays of the resources
that it uses. The social cost of the game remains the same, namely, it is the
worst bottleneck resource congestion: $\max_{r} C_r$. We show that polynomial
bottleneck games are very efficient and give price of anarchy
$O(|R|^{1/(\M+1)})$, where $R$ is the set of resources. This price of anarchy
is tight, since we demonstrate a game with price of anarchy
$\Omega(|R|^{1/(\M+1)})$, for any $\M \geq 1$. We obtain our tight bounds by
using two proof techniques: {\em transformation}, which we use to convert
arbitrary games to simpler games, and {\em expansion}, which we use to bound
the price of anarchy in a simpler game.
| arxiv topic:cs.GT |
arxiv_dataset-22131010.4912 | Effective Maxwell equations from time-dependent density functional
theory
math-ph cond-mat.mtrl-sci math.MP
The behavior of interacting electrons in a perfect crystal under macroscopic
external electric and magnetic fields is studied. Effective Maxwell equations
for the macroscopic electric and magnetic fields are derived starting from
time-dependent density functional theory. Effective permittivity and
permeability coefficients are obtained.
| arxiv topic:math-ph cond-mat.mtrl-sci math.MP |
arxiv_dataset-22141010.5012 | On the persistence properties of solutions of nonlinear dispersive
equations in weighted Sobolev spaces
math.AP
We study persistence properties of solutions to some canonical dispersive
models, namely the semi-linear Schr\"odinger equation, the $k$-generalized
Korteweg-de Vries equation and the Benjamin-Ono equation, in weighted Sobolev
spaces $H^s(\R^n)\cap L^2(|x|^ldx),\;s,\,l>0$
| arxiv topic:math.AP |
arxiv_dataset-22151010.5112 | Sense and sensitivity of double beta decay experiments
hep-ex hep-ph
The search for neutrinoless double beta decay is a very active field in which
the number of proposals for next-generation experiments has proliferated. In
this paper we attempt to address both the sense and the sensitivity of such
proposals. Sensitivity comes first, by means of proposing a simple and
unambiguous statistical recipe to derive the sensitivity to a putative Majorana
neutrino mass, m_bb. In order to make sense of how the different experimental
approaches compare, we apply this recipe to a selection of proposals, comparing
the resulting sensitivities. We also propose a "physics-motivated range" (PMR)
of the nuclear matrix elements as a unifying criterium between the different
nuclear models. The expected performance of the proposals is parametrized in
terms of only four numbers: energy resolution, background rate (per unit time,
isotope mass and energy), detection efficiency, and bb isotope mass. For each
proposal, both a reference and an optimistic scenario for the experimental
performance are studied. In the reference scenario we find that all the
proposals will be able to partially explore the degenerate spectrum, without
fully covering it, although four of them (KamLAND-Zen, CUORE, NEXT and EXO)
will approach the 50 meV boundary. In the optimistic scenario, we find that
CUORE and the xenon-based proposals (KamLAND-Zen, EXO and NEXT) will explore a
significant fraction of the inverse hierarchy, with NEXT covering it almost
fully. For the long term future, we argue that Xe-based experiments may provide
the best case for a 1-ton scale experiment, given the potentially very low
backgrounds achievable and the expected scalability to large isotope masses.
| arxiv topic:hep-ex hep-ph |
arxiv_dataset-22161010.5212 | -Generic Computability, Turing Reducibility and Asymptotic Density
math.GR math.LO
Generic computability has been studied in group theory and we now study it in
the context of classical computability theory. A set A of natural numbers is
generically computable if there is a partial computable function f whose domain
has density 1 and which agrees with the characteristic function of A on its
domain. A set A is coarsely computable if there is a computable set C such that
the symmetric difference of A and C has density 0. We prove that there is a
c.e. set which is generically computable but not coarsely computable and vice
versa. We show that every nonzero Turing degree contains a set which is not
coarsely computable. We prove that there is a c.e. set of density 1 which has
no computable subset of density 1. As a corollary, there is a generically
computable set A such that no generic algorithm for A has computable domain. We
define a general notion of generic reducibility in the spirt of Turing
reducibility and show that there is a natural order-preserving embedding of the
Turing degrees into the generic degrees which is not surjective.
| arxiv topic:math.GR math.LO |
arxiv_dataset-22171010.5312 | Bulk and Surface Nanoscale Hole Density Inhomogeneity in
HgBa$_2$CuO$_{4+\delta}$ and Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ Cuprates
cond-mat.supr-con
It is well established that the hole density in the prototypical
superconductor La$_{2-x}$Sr$_x$CuO$_4$ is very inhomogeneous due to Sr-dopant
induced disorder. On the other hand, until recently it is widely believed that
the hole distribution in HgBa$_2$CuO$_{4+\delta}$ and
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ doped by interstitial oxygen is much more
uniform. Recent nuclear magnetic resonance measurements indicate, however, that
the charge inhomogeneity in HgBa$_2$CuO$_{4+\delta}$ is close to that in
La$_{2-x}$Sr$_x$CuO$_4$. Calculations performed in the present paper confirm
this observation. We also show that the charge inhomogeneity is most pronounced
at the surface layer that can be probed by scanning tunneling microscope. Our
simulations demonstrate that, despite having similar amplitudes of charge
inhomogeneity, the hole mean free path in HgBa$_2$CuO$_{4+\delta}$ is
substantially longer than that in La$_{2-x}$Sr$_x$CuO$_4$. The screening of
Coulomb repulsion in HgBa$_2$CuO$_{4+\delta}$ is also stronger. These two
reasons might explain the difference in superconducting critical temperatures
between these two compounds.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-22181010.5412 | On optimizing over lift-and-project closures
cs.RO math.OC
The lift-and-project closure is the relaxation obtained by computing all
lift-and-project cuts from the initial formulation of a mixed integer linear
program or equivalently by computing all mixed integer Gomory cuts read from
all tableau's corresponding to feasible and infeasible bases. In this paper, we
present an algorithm for approximating the value of the lift-and-project
closure. The originality of our method is that it is based on a very simple cut
generation linear programming problem which is obtained from the original
linear relaxation by simply modifying the bounds on the variables and
constraints. This separation LP can also be seen as the dual of the cut
generation LP used in disjunctive programming procedures with a particular
normalization. We study some properties of this separation LP in particular
relating it to the equivalence between lift-and-project cuts and Gomory cuts
shown by Balas and Perregaard. Finally, we present some computational
experiments and comparisons with recent related works.
| arxiv topic:cs.RO math.OC |
arxiv_dataset-22191010.5512 | The electroweak model with rarely interacted neutrinos
physics.gen-ph
The electroweak model, which lepton sector correspond to the contracted gauge
group $ SU(2;j)\times U(1), j \rightarrow 0 $, whereas boson and quark sectors
are standard one, is suggested. This model describe in a natural manner why
neutrinos so rarely interact with matter, as well as why neutrinos
cross-section increase with the energy. Dimensionfull parameter of the model is
interpreted as neutrino energy. Dimensionless contraction parameter $j$ for low
energy is connected with the Fermi constant of weak interactions and is
approximated as $j^2\approx 10^{-5}$.
| arxiv topic:physics.gen-ph |
arxiv_dataset-22201010.5612 | Future CMB Constraints on Early, Cold, or Stressed Dark Energy
astro-ph.CO
We investigate future constraints on early dark energy (EDE) achievable by
the Planck and CMBPol experiments, including cosmic microwave background (CMB)
lensing. For the dark energy, we include the possibility of clustering through
a sound speed c_s^2 <1 (cold dark energy) and anisotropic stresses
parameterized with a viscosity parameter c_vis^2. We discuss the degeneracies
between cosmological parameters and EDE parameters. In particular we show that
the presence of anisotropic stresses in EDE models can substantially undermine
the determination of the EDE sound speed parameter c_s^2. The constraints on
EDE primordial energy density are however unaffected. We also calculate the
future CMB constraints on neutrino masses and find that they are weakened by a
factor of 2 when allowing for the presence of EDE, and highly biased if it is
incorrectly ignored.
| arxiv topic:astro-ph.CO |
arxiv_dataset-22211010.5712 | Inequalities for non-equilibrium fluctuations of work
cond-mat.stat-mech physics.data-an
Five previously unknown inequalities relating equilibrium free energy
differences and non-equilibrium work fluctuations are derived, and lucid path
to derivation of many similar inequalities is presented. These results are
based upon combined exploitation of the Jarzynski equality and the
generalization of the scheme for producing uncertainty-type inequalities due to
H. Weyl. The inequalities may possibly lead to better understanding of behavior
of the equilibrium free-energy estimators from non-equilibrium experimental
data in many important applications concerning biological, chemical, and
physical molecular processes.
| arxiv topic:cond-mat.stat-mech physics.data-an |
arxiv_dataset-22221010.5812 | Characteristics of Gamma-Ray Loud Blazars in the VLBA Imaging and
Polarimetry Survey
astro-ph.CO
The radio properties of blazars detected by the Large Area Telescope (LAT) on
board the Fermi Gamma-ray Space Telescope have been observed as part of the
VLBA Imaging and Polarimetry Survey (VIPS). This large, flux-limited sample of
active galactic nuclei (AGN) provides insights into the mechanism that produces
strong gamma-ray emission. At lower flux levels, radio flux density does not
directly correlate with gamma-ray flux. We find that the LAT-detected BL Lacs
tend to be similar to the non-LAT BL Lacs, but that the LAT-detected FSRQs are
often significantly different from the non-LAT FSRQs. The differences between
the gamma-ray loud and quiet FSRQs can be explained by Doppler boosting; these
objects appear to require larger Doppler factors than those of the BL Lacs. It
is possible that the gamma-ray loud FSRQs are fundamentally different from the
gamma-ray quiet FSRQs. Strong polarization at the base of the jet appears to be
a signature for gamma-ray loud AGN.
| arxiv topic:astro-ph.CO |
arxiv_dataset-22231010.5912 | Polarimetric imaging with the GMRT
astro-ph.CO
We present the first set of polarimetric images made with the GMRT. These
were obtained as part of the program to commission the polarization mode at the
telescope. We find that the instrumental polarization leakage at the GMRT
varies with frequency. It is hence necessary to solve for the leakage as a
function of spectral channel. Once this is done however, it is possible to
calibrate these terms to better than 1% accuracy, making it feasible to study
sources that are polarized at the few percent level. We present 610 MHz
polarization images of two extended FR-II radio galaxies, viz. 3C 79 and 3C
265. These were selected from the sample of sources for which the total
polarization fraction at 610 MHz is known from the survey of Conway & Strom
(1984). We present high resolution polarization images of these two sources and
also find that the polarization fractions of the two sources as seen at the
GMRT are consistent with those reported by Conway & Strom (1984).
| arxiv topic:astro-ph.CO |
arxiv_dataset-22241010.6012 | Decoherence in a quantum harmonic oscillator monitored by a
Bose-Einstein condensate
quant-ph cond-mat.quant-gas
We investigate the dynamics of a quantum oscillator, whose evolution is
monitored by a Bose-Einstein condensate (BEC) trapped in a symmetric double
well potential. It is demonstrated that the oscillator may experience various
degrees of decoherence depending on the variable being measured and the state
in which the BEC is prepared. These range from a `coherent' regime in which
only the variances of the oscillator position and momentum are affected by
measurement, to a slow (power law) or rapid (Gaussian) decoherence of the mean
values themselves.
| arxiv topic:quant-ph cond-mat.quant-gas |
arxiv_dataset-22251010.6112 | Proceedings 12th International Workshop on Verification of
Infinite-State Systems
cs.FL cs.CC cs.LO cs.SE
The aim of the INFINITY workshop is to provide a forum for researchers
interested in the development of formal methods and algorithmic techniques for
the analysis of systems with infinitely many states, and their application in
automated verification of complex software and hardware systems.
| arxiv topic:cs.FL cs.CC cs.LO cs.SE |
arxiv_dataset-22261010.6212 | A Statistical Comparison of the Optical/UV and X-ray Afterglows of
Gamma-Ray Bursts using the Swift Ultra-violet Optical and X-ray Telescopes
astro-ph.HE
We present the systematic analysis of the UVOT and XRT light curves for a
sample of 26 Swift Gamma-Ray Bursts (GRBs). By comparing the optical/UV and
X-ray light curves, we found that they are remarkably different during the
first 500s after the BAT trigger, while they become more similar during the
middle phase of the afterglow, i.e. between 2000s and 20000s. If we take
literally the average properties of the sample, we find that the mean temporal
indices observed in the optical/UV and X-rays after 500s are consistent with a
forward-shock scenario, under the assumptions that electrons are in the slow
cooling regime, the external medium is of constant density and the synchrotron
cooling frequency is situated between the optical/UV and X-ray observing bands.
While this scenario describes well the averaged observed properties, some
individual GRB afterglows require different or additional assumptions, such as
the presence of late energy injection. We show that a chromatic break (a break
in the X-ray light curve that is not seen in the optical) is present in the
afterglows of 3 GRBs and demonstrate evidence for chromatic breaks in a further
4 GRBs. The average properties of these breaks cannot be explained in terms of
the passage of the synchrotron cooling frequency through the observed bands,
nor a simple change in the external density. It is difficult to reconcile
chromatic breaks in terms of a single component outflow and instead, more
complex jet structure or additional emission components are required.
| arxiv topic:astro-ph.HE |
arxiv_dataset-22271011.0008 | Universal Area Product Formulae for Rotating and Charged Black Holes in
Four and Higher Dimensions
hep-th gr-qc
We present explicit results for the product of all horizon areas for general
rotating multi-charge black holes, both in asymptotically flat and
asymptotically anti-de Sitter spacetimes in four and higher dimensions. The
expressions are universal, and depend only on the quantized charges, quantized
angular momenta and the cosmological constant. If the latter is also quantized
these universal results may provide a "looking glass" for probing the
microscopics of general black holes.
| arxiv topic:hep-th gr-qc |
arxiv_dataset-22281011.0108 | An Active Learning Algorithm for Ranking from Pairwise Preferences with
an Almost Optimal Query Complexity
cs.DS
We study the problem of learning to rank from pairwise preferences, and solve
a long-standing open problem that has led to development of many heuristics but
no provable results for our particular problem. Given a set $V$ of $n$
elements, we wish to linearly order them given pairwise preference labels. A
pairwise preference label is obtained as a response, typically from a human, to
the question "which if preferred, u or v?$ for two elements $u,v\in V$. We
assume possible non-transitivity paradoxes which may arise naturally due to
human mistakes or irrationality. The goal is to linearly order the elements
from the most preferred to the least preferred, while disagreeing with as few
pairwise preference labels as possible. Our performance is measured by two
parameters: The loss and the query complexity (number of pairwise preference
labels we obtain). This is a typical learning problem, with the exception that
the space from which the pairwise preferences is drawn is finite, consisting of
${n\choose 2}$ possibilities only. We present an active learning algorithm for
this problem, with query bounds significantly beating general (non active)
bounds for the same error guarantee, while almost achieving the information
theoretical lower bound. Our main construct is a decomposition of the input
s.t. (i) each block incurs high loss at optimum, and (ii) the optimal solution
respecting the decomposition is not much worse than the true opt. The
decomposition is done by adapting a recent result by Kenyon and Schudy for a
related combinatorial optimization problem to the query efficient setting. We
thus settle an open problem posed by learning-to-rank theoreticians and
practitioners: What is a provably correct way to sample preference labels? To
further show the power and practicality of our solution, we show how to use it
in concert with an SVM relaxation.
| arxiv topic:cs.DS |
arxiv_dataset-22291011.0208 | Network Diversity and Economic Development: a Comment
cs.SI physics.soc-ph
Network diversity yields context-dependent benefits that are not yet
fully-understood. I elaborate on a recently introduced distinction between tie
strength diversity and information source diversity, and explain when, how, and
why they matter. The issue whether there are benefits to specialization is the
key.
| arxiv topic:cs.SI physics.soc-ph |
arxiv_dataset-22301011.0308 | Entanglement dynamics of bipartite system in squeezed vacuum reservoirs
quant-ph
Entanglement plays a crucial role in quantum information protocols, thus the
dynamical behavior of entangled states is of a great importance. In this paper
we suggest a useful scheme that permits a direct measure of entanglement in a
two-qubit cavity system. It is realized in the cavity-QED technology utilizing
atoms as fying qubits. To quantify entanglement we use the concurrence. We
derive the conditions, which assure that the state remains entangled in spite
of the interaction with the reservoir. The phenomenon of sudden death
entanglement (ESD) in a bipartite system subjected to squeezed vacuum reservoir
is examined. We show that the sudden death time of the entangled states depends
on the initial preparation of the entangled state and the parameters of the
squeezed vacuum reservoir.
| arxiv topic:quant-ph |
arxiv_dataset-22311011.0408 | Three-point correlation functions from semiclassical circular strings
hep-th
The strong-coupling limit of three-point correlation functions of local
operators can be analyzed beyond the supergravity regime using vertex operators
representing spinning string states. When two of the vertex operators
correspond to heavy string states having large quantum numbers, while the third
operator corresponds to a light state with fixed charges, the correlator can be
computed in the large string tension limit by means of a semiclassical
approximation. We study the case when the heavy string states are circular
string solutions with one AdS_5 spin and three different angular momenta along
S^5, for several choices of the light string state.
| arxiv topic:hep-th |
arxiv_dataset-22321011.0508 | Equation of state for dark energy in $f(T)$ gravity
astro-ph.CO gr-qc
We study the cosmological evolutions of the equation of state for dark energy
$w_{\mathrm{DE}}$ in the exponential and logarithmic as well as their
combination $f(T)$ theories. We show that the crossing of the phantom divide
line of $w_{\mathrm{DE}} = -1$ can be realized in the combined $f(T)$ theory
even though it cannot be in the exponential or logarithmic $f(T)$ theory. In
particular, the crossing is from $w_{\mathrm{DE}} > -1$ to $w_{\mathrm{DE}} <
-1$, in the opposite manner from $f(R)$ gravity models. We also demonstrate
that this feature is favored by the recent observational data.
| arxiv topic:astro-ph.CO gr-qc |
arxiv_dataset-22331011.0608 | Improving the precision of classification trees
stat.AP
Besides serving as prediction models, classification trees are useful for
finding important predictor variables and identifying interesting subgroups in
the data. These functions can be compromised by weak split selection algorithms
that have variable selection biases or that fail to search beyond local main
effects at each node of the tree. The resulting models may include many
irrelevant variables or select too few of the important ones. Either
eventuality can lead to erroneous conclusions. Four techniques to improve the
precision of the models are proposed and their effectiveness compared with that
of other algorithms, including tree ensembles, on real and simulated data sets.
| arxiv topic:stat.AP |
arxiv_dataset-22341011.0708 | New superintegrable models with position-dependent mass from Bertrand's
Theorem on curved spaces
math-ph math.MP nlin.SI
A generalized version of Bertrand's theorem on spherically symmetric curved
spaces is presented. This result is based on the classification of
(3+1)-dimensional (Lorentzian) Bertrand spacetimes, that gives rise to two
families of Hamiltonian systems defined on certain 3-dimensional (Riemannian)
spaces. These two systems are shown to be either the Kepler or the oscillator
potentials on the corresponding Bertrand spaces, and both of them are maximally
superintegrable. Afterwards, the relationship between such Bertrand
Hamiltonians and position-dependent mass systems is explicitly established.
These results are illustrated through the example of a superintegrable
(nonlinear) oscillator on a Bertrand-Darboux space, whose quantization and
physical features are also briefly addressed.
| arxiv topic:math-ph math.MP nlin.SI |
arxiv_dataset-22351011.0808 | Quasi-diffraction production of white quark--gluon clusters at
superhigh-energy hadron collisions
hep-ph
We discuss a collective effect, which can be possible in hadron--hadron
collisions at superhigh energies, that is, a quasi-diffraction production of
several white clusters of quarks and gluons. Being transformed into hadrons,
such clusters are sources of the fastest particles, which move forward nearly
parallel to each other.
| arxiv topic:hep-ph |
arxiv_dataset-22361011.0908 | Quark masses and strong CP violation
hep-lat hep-ph
Two flavor QCD involves three independent mass parameters for which
non-perturbative effects are not universal. This precludes matching lattice and
perturbative results for non-degenerate quarks and eliminates a vanishing up
quark mass as a viable solution to the strong CP problem.
| arxiv topic:hep-lat hep-ph |
arxiv_dataset-22371011.1008 | Localized in-situ polymerization on graphene surfaces for stabilized
graphene dispersions
cond-mat.soft cond-mat.mes-hall cond-mat.mtrl-sci
We demonstrate a novel in situ polymerization technique to develop localized
polymer coatings on the surface of dispersed pristine graphene sheets. Graphene
sheets show great promise as strong, conductive fillers in polymer
nanocomposites; however, difficulties in dispersion quality and interfacial
strength between filler and matrix have been a persistent problem for
graphene-based nanocomposites, particularly for pristine graphene. To address
this problem, a physisorbed polymer layer is used to stabilize graphene sheets
in solution. To form this protective layer, an organic microenvironment is
formed around dispersed graphene sheets in surfactant solutions, and a nylon
6,10 or nylon 6,6 coating is created via interfacial polymerization. A similar
technique was originally developed to protect luminescent properties of carbon
nanotubes in solution. These coated graphene dispersions are
aggregation-resistant and may be reversibly redispersed in water even after
freeze-drying. The coated graphene holds promise for a number of applications,
including multifunctional graphene-polymer nanocomposites.
| arxiv topic:cond-mat.soft cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-22381011.1108 | Crossover from commensurate to incommensurate antiferromagnetism in
stoichiometric NaFeAs revealed by single-crystal 23Na,75As-NMR experiments
cond-mat.str-el cond-mat.supr-con
We report results of 23Na and 75As nuclear magnetic resonance (NMR)
experiments on a self-flux grown high-quality single crystal of stoichiometric
NaFeAs. The NMR spectra revealed a tetragonal to twinned-orthorhombic
structural phase transition at T_O = 57 K and an antiferromagnetic (AF)
transition at T_AF = 45 K. The divergent behavior of nuclear relaxation rate
near T_AF shows significant anisotropy, indicating that the critical slowing
down of stripe-type AF fluctuations are strongly anisotropic in spin space. The
NMR spectra at low enough temperatures consist of sharp peaks showing a
commensurate stripe AF order with a small moment \sim 0.3 muB. However, the
spectra just below T_AF exhibits highly asymmetric broadening pointing to an
incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs
shows a certain similarity to the behavior of SrFe2As2 under high pressure.
| arxiv topic:cond-mat.str-el cond-mat.supr-con |
arxiv_dataset-22391011.1208 | Heavy-light current-current correlators
hep-lat
The current-current correlator method has been used successfully to obtain
very accurate results for quark masses and the coupling alpha_s. The
calculations were done using Highly Improved Staggered Quarks (HISQ) and
heavy-heavy meson correlators. We now extend this work to the significantly
more challenging heavy-light case, reporting the first results here. The aim is
to determine nonperturbative Z factors for NRQCD heavy-light currents, but
first we test the method in the HISQ case where Z=1.
| arxiv topic:hep-lat |
arxiv_dataset-22401011.1308 | Kinetic formulation of irreversible evolution of the two-nucleus spin
systems
quant-ph
The time irreversible evolution of the two-nucleus spin systems interacting
with a magnetic field is analyzed in the framework of the subdynamics theory.
The spin systems are determined by the H(1) and C(13) nuclei. The investigation
is based on the complex spectral representation of the Liouvillian which gives
a rigorous description of irreversibility. The evolution of the density matrix
is analyzed for the short and long time region. Quantum Zeno effect is
discussed.
| arxiv topic:quant-ph |
arxiv_dataset-22411011.1408 | Interactions of nanorod particles in the strong coupling regime
cond-mat.mes-hall
The plasmon coupling in a nanorod dimer obeys the exponential size dependence
according to the Universal Plasmon Ruler Equation. However, it was shown
recently that such a model does not hold at short nanorod distance (Nano Lett.
2009, 9, 1651). Here we study the nanorod coupling in various cases, including
nanorod dimer with the asymmetrical lengths and symmetrical dimer with the
varying gap width. The asymmetrical nanorod dimer causes two plasmon modes: one
is the attractive lower- energy mode and the other the repulsive high-energy
mode. Using a simple coupled LC-resonator model, the position of dimer
resonance has been determined analytically. Moreover, we found that the plasmon
coupling of symmetrical cylindrical (or rectangular) nanorod dimer is governed
uniquely by gap width scaled for the (effective) rod radius rather than for the
rod length. A new Plasmon Ruler Equation without using the fitting parameters
has been proposed, which agrees well with the FDTD calculations. The method has
also been extended to study the plasmonic wave-guiding in a linear chain of
gold nanorod particles. A field decay length up to 2700nm with the lateral mode
size about 50nm (~wavelength/28) has been suggested.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-22421011.1508 | Forecast Bias Correction: A Second Order Method
cs.CE math.DS math.OC
The difference between a model forecast and actual observations is called
forecast bias. This bias is due to either incomplete model assumptions and/or
poorly known parameter values and initial/boundary conditions. In this paper we
discuss a method for estimating corrections to parameters and initial
conditions that would account for the forecast bias. A set of simple
experiments with the logistic ordinary differential equation is performed using
an iterative version of a first order version of our method to compare with the
second order version of the method.
| arxiv topic:cs.CE math.DS math.OC |
arxiv_dataset-22431011.1608 | Metric flips with Calabi ansatz
math.DG
We study the limiting behavior of the Kahler-Ricci flow on
$\mathbb{P}(\mathcal{O}_{\mathbb{P}^n} \oplus
\mathcal{O}_{\mathbb{P}^n}(-1)^{\oplus (m+1)})$, assuming the initial metric
satisfies the Calabi symmetry. We show that the flow either shrinks to a point,
collapses to $\mathbb{P}^n$ or contracts a subvariety of codimension m+1 in
Gromov-Hausdorff sense. We also show that the Kahler-Ricci flow resolves
certain type of conical singularities in Gromov-Hausdorff sense.
| arxiv topic:math.DG |
arxiv_dataset-22441011.1708 | CRAM: Compressed Random Access Memory
cs.DS
We present a new data structure called the \emph{Compressed Random Access
Memory} (CRAM) that can store a dynamic string $T$ of characters, e.g.,
representing the memory of a computer, in compressed form while achieving
asymptotically almost-optimal bounds (in terms of empirical entropy) on the
compression ratio. It allows short substrings of $T$ to be decompressed and
retrieved efficiently and, significantly, characters at arbitrary positions of
$T$ to be modified quickly during execution \emph{without decompressing the
entire string}. This can be regarded as a new type of data compression that can
update a compressed file directly. Moreover, at the cost of slightly increasing
the time spent per operation, the CRAM can be extended to also support
insertions and deletions. Our key observation that the empirical entropy of a
string does not change much after a small change to the string, as well as our
simple yet efficient method for maintaining an array of variable-length blocks
under length modifications, may be useful for many other applications as well.
| arxiv topic:cs.DS |
arxiv_dataset-22451011.1808 | Weights on bimodules
math.QA math.OA
The concept of a {\em weight} on a planar algebra was introduced in
\cite{DGG}. In this article we give an alternate characterization of weights on
a planar algebra in terms of `weight functions' on the vertices of the
principal graphs. Using this characterization we show that the property of
bifinite bimodules of having a `trivial perturbation class' is closed under
Connes fusion. We give a direct and constructive method of perturbing a
bifinite bimodule by a positive weight in such a way that the bimodule planar
algebra of the perturbed bimodule is isomorphic to the perturbation of the one
associated to the initial bimodule by the given weight.
| arxiv topic:math.QA math.OA |
arxiv_dataset-22461011.1908 | Effects of Varying the Three-Body Molecular Hydrogen Formation Rate in
Primordial Star Formation
astro-ph.CO
The transformation of atomic hydrogen to molecular hydrogen through
three-body reactions is a crucial stage in the collapse of primordial,
metal-free halos, where the first generation of stars (Population III stars) in
the Universe are formed. However, in the published literature, the rate
coefficient for this reaction is uncertain by nearly an order of magnitude. We
report on the results of both adaptive mesh refinement (AMR) and smoothed
particle hydrodynamics (SPH) simulations of the collapse of metal-free halos as
a function of the value of this rate coefficient. For each simulation method,
we have simulated a single halo three times, using three different values of
the rate coefficient. We find that while variation between halo realizations
may be greater than that caused by the three-body rate coefficient being used,
both the accretion physics onto Population III protostars as well as the
long-term stability of the disk and any potential fragmentation may depend
strongly on this rate coefficient.
| arxiv topic:astro-ph.CO |
arxiv_dataset-22471011.2008 | Integral Menger curvature for sets of arbitrary dimension and
codimension
math.AP math.MG
We propose a notion of integral Menger curvature for compact, $m$-dimensional
sets in $n$-dimensional Euclidean space and prove that finiteness of this
quantity implies that the set is $C^{1,\alpha}$ embedded manifold with the
H{\"o}lder norm and the size of maps depending only on the curvature. We
develop the ideas introduced by Strzelecki and von der Mosel [Adv. Math.
226(2011)] and use a similar strategy to prove our results.
| arxiv topic:math.AP math.MG |
arxiv_dataset-22481011.2108 | Convergence to equilibrium for a thin film equation on a cylindrical
surface
math.AP math-ph math.MP
The degenerate parabolic equation u_t + [u^3(u_xxx + u_x - sin x)]_x=0 models
the evolution of a thin liquid film on a stationary horizontal cylinder. It is
shown here that for each given mass there is a unique steady state, given by a
droplet hanging from the bottom of the cylinder that meets the dry region at
the top with zero contact angle. The droplet minimizes the energy and attracts
all strong solutions that satisfy certain energy and entropy inequalities. The
distance of any solution from the steady state decays no faster than a power
law.
| arxiv topic:math.AP math-ph math.MP |
arxiv_dataset-22491011.2208 | Dynamic Stimulation of Quantum Coherence in Lattice Bosons
cond-mat.quant-gas
Thermal fluctuations tend to destroy long-range phase correlations.
Consequently, bosons in a lattice will undergo a transition from a
phase-coherent superfluid as the temperature rises. Contrary to common
intuition, however, we show that non-equilibrium driving can be used to reverse
this thermal decoherence. This is possible because the energy distribution at
equilibrium is rarely optimal for the manifestation of a given quantum
property. We demonstrate this in the Bose-Hubbard model by calculating the
non-equilibrium spatial correlation function with periodic driving. We show
that the non-equilibrium phase boundary between coherent and incoherent states
at finite bath temperatures can be made qualitatively identical to the familiar
zero-temperature phase diagram, and we discuss the experimental manifestation
of this phenomenon in cold atoms.
| arxiv topic:cond-mat.quant-gas |
arxiv_dataset-22501011.2308 | Fires on trees
math.PR
We consider random dynamics on the edges of a uniform Cayley tree with $n$
vertices, in which edges are either inflammable, fireproof, or burt. Every
inflammable edge is replaced by a fireproof edge at unit rate, while fires
start at smaller rate $n^{-\alpha}$ on each inflammable edge, then propagate
through the neighboring inflammable edges and are only stopped at fireproof
edges. A vertex is called fireproof when all its adjacent edges are fireproof.
We show that as $n\to \infty$, the density of fireproof vertices converges to
$1$ when $\alpha>1/2$, to $0$ when $\alpha<1/2$, and to some non-degenerate
random variable when $\alpha=1/2$. We further study the connectivity of the
fireproof forest, in particular the existence of a giant component.
| arxiv topic:math.PR |
arxiv_dataset-22511011.2408 | Hankel operators on Fock spaces and related Bergman kernel estimates
math.FA
Hankel operators with anti-holomorphic symbols are studied for a large class
of weighted Fock spaces on $\cn$. The weights defining these Hilbert spaces are
radial and subject to a mild smoothness condition. In addition, it is assumed
that the weights decay at least as fast as the classical Gaussian weight. The
main result of the paper says that a Hankel operator on such a Fock space is
bounded if and only if the symbol belongs to a certain BMOA space, defined via
the Berezin transform. The latter space coincides with a corresponding Bloch
space which is defined by means of the Bergman metric. This characterization of
boundedness relies on certain precise estimates for the Bergman kernel and the
Bergman metric. Characterizations of compact Hankel operators and Schatten
class Hankel operators are also given. In the latter case, results on Carleson
measures and Toeplitz operators along with H\"{o}rmander's $L^2$ estimates for
the $\bar{\partial}$ operator are key ingredients in the proof.
| arxiv topic:math.FA |
arxiv_dataset-22521011.2508 | Ab-initio calculations for the beta-tin diamond transition in Silicon:
comparing theories with experiments
cond-mat.mtrl-sci
We investigate the pressure-induced metal-insulator transition from diamond
to beta-tin in bulk Silicon, using quantum Monte Carlo (QMC) and density
functional theory (DFT) approaches. We show that it is possible to efficiently
describe many-body effects, using a variational wave function with an optimized
Jastrow factor and a Slater determinant. Variational results are obtained with
a small computational cost and are further improved by performing diffusion
Monte Carlo calculations and an explicit optimization of molecular orbitals in
the determinant. Finite temperature corrections and zero point motion effects
are included by calculating phonon dispersions in both phases at the DFT level.
Our results indicate that the theoretical QMC (DFT) transition pressure is
significantly larger (smaller) than the accepted experimental value. We discuss
the limitation of DFT approaches due to the choice of the exchange and
correlation functionals and the difficulty to determine consistent
pseudopotentials within the QMC framework, a limitation that may significantly
affect the accuracy of the technique.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-22531011.2608 | Spectral distributions of adjacency and Laplacian matrices of random
graphs
math.PR
In this paper, we investigate the spectral properties of the adjacency and
the Laplacian matrices of random graphs. We prove that: (i) the law of large
numbers for the spectral norms and the largest eigenvalues of the adjacency and
the Laplacian matrices; (ii) under some further independent conditions, the
normalized largest eigenvalues of the Laplacian matrices are dense in a compact
interval almost surely; (iii) the empirical distributions of the eigenvalues of
the Laplacian matrices converge weakly to the free convolution of the standard
Gaussian distribution and the Wigner's semi-circular law; (iv) the empirical
distributions of the eigenvalues of the adjacency matrices converge weakly to
the Wigner's semi-circular law.
| arxiv topic:math.PR |
arxiv_dataset-22541011.2708 | Searching for Young M Dwarfs with GALEX
astro-ph.SR
The census of young moving groups in the solar neighborhood is significantly
incomplete in the low-mass regime. We have developed a new selection process to
find these missing members based on the GALEX All-Sky Imaging Survey. For stars
with spectral types >K5 and younger than 300~Myr, we show that near-UV and
far-UV emission is greatly enhanced above the quiescent photosphere, analogous
to the enhanced X-ray emission of young low-mass stars seen by ROSAT but
detectable to much larger distances with GALEX. By combining GALEX data with
optical (HST Guide Star Catalog) and near-IR (2MASS) photometry, we identified
an initial sample of 34 young M dwarf candidates in a 1000 sq.~deg.~region
around the 10-Myr TW Hydra Association (TWA). Low-resolution spectroscopy of 30
of these found 16 which had H_alpha in emission, which were then followed-up at
high resolution to search for spectroscopic evidence of youth and to measure
radial velocities. Four objects have low surface gravities, photometric
distances and space motions consistent with TWA, but the non-detection of Li
indicates they may be too old to belong to this moving group. One object (M3.5,
93 pc) appears to be the first known accreting low-mass member of the 15~Myr
Lower Centaurus Crux OB association. Two objects exhibit all the
characteristics of the known TWA members, and thus we designate them as TWA 31
(M4.2, 110 pc) and TWA 32 (M6.3, 53 pc). TWA 31 shows extremely broad (447
km/s) H_alpha emission, making it the sixth member of TWA found to have ongoing
accretion. TWA 32 is resolved into a 0.6" binary in Keck laser guide star
adaptive optics imaging. Our search should be sensitive down to spectral types
of at least M4-M5 in TWA and thus the small numbers of new member is puzzling.
This may indicate TWA has an atypical mass function or that the presence of Li
may be too restrictive a criteria for selecting young low-mass stars.
| arxiv topic:astro-ph.SR |
arxiv_dataset-22551011.2808 | Fundamental Properties of the Highly Ionized Plasmas in the Milky Way
astro-ph.GA
The cooling transition temperature gas in the interstellar medium (ISM),
traced by the high ions, Si IV, C IV, N V, and O VI, helps to constrain the
flow of energy from the hot ISM with T >10^6 K to the warm ISM with T< 2x10^4
K. We investigate the properties of this gas along the lines of sight to 38
stars in the Milky Way disk using 1.5-2.7 km/s resolution spectra of Si IV, C
IV, and N V absorption from the Space Telescope Imaging Spectrograph (STIS),
and 15 km/s resolution spectra of O VI absorption from the Far Ultraviolet
Spectroscopic Explorer (FUSE). The absorption by Si IV and C IV exhibits broad
and narrow components while only broad components are seen in N V and O VI. The
narrow components imply gas with T<7x10^4 K and trace two distinct types of
gas. The strong, saturated, and narrow Si IV and C IV components trace the gas
associated with the vicinities of O-type stars and their supershells. The
weaker narrow Si IV and C IV components trace gas in the general ISM that is
photoionized by the EUV radiation from cooling hot gas or has radiatively
cooled in a non-equilibrium manner from the transition temperature phase, but
rarely the warm ionized medium (WIM) probed by Al III. The broad Si IV, C IV, N
V, and O VI components trace collisionally ionized gas that is very likely
undergoing a cooling transition from the hot ISM to the warm ISM. The cooling
process possibly provides the regulation mechanism that produces N(C IV)/N(Si
IV) = 3.9 +/- 1.9. The cooling process also produces absorption lines where the
median and mean values of the line widths increase with the energy required to
create the ion.
| arxiv topic:astro-ph.GA |
arxiv_dataset-22561011.2908 | Dark Matter as a Relativistic Inertial Effect in Einstein Canonical
Gravity?
gr-qc astro-ph.GA hep-th
After the study of non-inertial frames in special relativity with emphasis on
the problem of clock synchronization (i.e. of how to define 3-space), an
overview is given of Einstein canonical gravity in the York canonical basis and
of its Hamiltonian Post-Minkowskian (PM) linearization in 3-orthogonal gauges.
It is shown that the York time (the trace of the extrinsic curvature of
3-spaces) is the inertial gauge variable describing the general relativistic
remnant of the clock synchronization gauge freedom. The dark matter implied by
the rotation curves of galaxies can be explained with a choice of the York time
implying a PM extension of the Newtonian celestial frame ICRS.
| arxiv topic:gr-qc astro-ph.GA hep-th |
arxiv_dataset-22571011.3008 | Piezoresistance in silicon at uniaxial compressive stresses up to 3 GPa
cond-mat.mtrl-sci
The room-temperature longitudinal piezoresistance of n-type and p-type
crystalline silicon along selected crystal axes is investigated under uniaxial
compressive stresses up to 3 GPa. While the conductance ($G$) of n-type silicon
eventually saturates at $\approx 45%$ of its zero-stress value ($G_0$) in
accordance with the charge transfer model, in p-type material $G/G_0$ increases
above a predicted limit of $\approx 4.5$ without any significant saturation,
even at 3 GPa. Calculation of $G/G_0$ using \textit{ab-initio} density
functional theory reveals that neither $G$ nor the mobility, when properly
averaged over the hole distribution, saturate at stresses lower than 3 GPa. The
lack of saturation has important consequences for strained silicon
technologies.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-22581011.3108 | Atmospheric Oxygen Binding and Hole Doping in Deformed Graphene on a
SiO2 Substrate
cond-mat.mtrl-sci cond-mat.soft
Using micro-Raman spectroscopy and scanning tunneling microscopy, we study
the relationship between structural distortion and electrical hole doping of
graphene on a silicon dioxide substrate. The observed upshift of the Raman G
band represents charge doping and not compressive strain. Two independent
factors control the doping: (1) the degree of graphene coupling to the
substrate, and (2) exposure to oxygen and moisture. Thermal annealing induces a
pronounced structural distortion due to close coupling to SiO2 and activates
the ability of diatomic oxygen to accept charge from graphene. Gas flow
experiments show that dry oxygen reversibly dopes graphene; doping becomes
stronger and more irreversible in the presence of moisture and over long
periods of time. We propose that oxygen molecular anions are stabilized by
water solvation and electrostatic binding to the silicon dioxide surface.
| arxiv topic:cond-mat.mtrl-sci cond-mat.soft |
arxiv_dataset-22591011.3208 | Rigidity of Graph Joins and Hendrickson's Conjecture
math.MG cs.DM
Whiteley \cite{wh} gives a complete characterization of the infinitesimal
flexes of complete bipartite frameworks. Our work generalizes a specific
infinitesimal flex to include joined graphs, a family of graphs that contain
the complete bipartite graphs. We use this characterization to identify new
families of counterexamples, including infinite families, in $\R^5$ and above
to Hendrickson's conjecture on generic global rigidity.
| arxiv topic:math.MG cs.DM |
arxiv_dataset-22601011.3308 | Electronic Correlation effects in superconducting picene from ab-initio
calculations
cond-mat.str-el cond-mat.supr-con
We show, by means of ab-initio calculations, that electron-electron
correlations play an important role in potassium-doped picene ($K_x$-picene),
recently characterized as a superconductor with $T_c = 18K$. The inclusion of
exchange interactions by means of hybrid functionals reproduces the correct gap
for the undoped compound and predicts an antiferromagnetic state for $x=3$,
where superconductivity has been observed. The latter finding is compatible
with a sizable value of the correlation strength, in agreement with simple
estimates. Our results highlight the similarity between potassium-doped picene
and alkali-doped fulleride superconductors.
| arxiv topic:cond-mat.str-el cond-mat.supr-con |
arxiv_dataset-22611011.3408 | Current and noise correlations in a double dot Cooper pair beam splitter
cond-mat.mes-hall
We consider a double quantum dot coupled to two normal leads and one
superconducting lead, modeling the Cooper pair beam splitter studied in two
recent experiments. Starting from a microscopic Hamiltonian we derive a general
expression for the branching current and the noise crossed correlations in
terms of single and two-particle Green's function of the dot electrons. We then
study numerically how these quantities depend on the energy configuration of
the dots and the presence of direct tunneling between them, isolating the
various processes which come into play. In absence of direct tunneling, the
antisymmetric case (the two levels have opposite energies with respect to the
superconducting chemical potential) optimizes the Crossed Andreev Reflection
(CAR) process while the symmetric case (the two levels have the same energies)
favors the Elastic Cotunneling (EC) process. Switching on the direct tunneling
tends to suppress the CAR process, leading to negative noise crossed
correlations over the whole voltage range for large enough direct tunneling.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-22621011.3508 | Entropy production and equilibration in Yang-Mills quantum mechanics
nucl-th quant-ph
The Husimi distribution provides for a coarse grained representation of the
phase space distribution of a quantum system, which may be used to track the
growth of entropy of the system. We present a general and systematic method of
solving the Husimi equation of motion for an isolated quantum system, and we
construct a coarse grained Hamiltonian whose expectation value is exactly
conserved. As an application, we numerically solve the Husimi equation of
motion for two-dimensional Yang-Mills quantum mechanics (the x-y model) and
calculate the time evolution of the coarse grained entropy of a highly excited
state. We show that the coarse grained entropy saturates to a value that
coincides with the microcanonical entropy corresponding to the energy of the
system.
| arxiv topic:nucl-th quant-ph |
arxiv_dataset-22631011.3608 | Photon spin operator and Pauli matrix
physics.optics quant-ph
Any polarization vector of a plane wave can be decomposed into a pair of
mutually orthogonal base vectors, known as a polarization basis. Regarding this
decomposition as a quasi-unitary transformation from a three-component vector
to a corresponding two-component spinor, one is led to a representation
formalism for the photon spin. The spin operator $\hat{\boldsymbol \gamma}$
defined on the space of unit spinors, referred to as the Jones space, has only
component along the wave vector and is represented by one of the Pauli matrices
in the commonly used polarization basis. It is deformed by the quasi-unitary
transformation from the spin operator that is defined on the space of unit
polarization vectors, referred to as the Pancharatnam space. On the basis of
this theory, it is shown that the Cartesian components of spin operator
$\hat{\boldsymbol \gamma}$ are mutually commutative and the spin angular
momentum in units of $\hbar$ is exactly the component of the Stokes vector
along the wave vector.
| arxiv topic:physics.optics quant-ph |
arxiv_dataset-22641011.3708 | Catalan structures and Catalan pairs
cs.DM
A Catalan pair is a pair of binary relations (S,R) satisfying certain axioms.
These objects are enumerated by the well-known Catalan numbers, and have been
introduced with the aim of giving a common language to most of the structures
counted by Catalan numbers. Here, we give a simple method to pass from the
recursive definition of a generic Catalan structure to the recursive definition
of the Catalan pair on the same structure, thus giving an automatic way to
interpret Catalan structures in terms of Catalan pairs. We apply our method to
many well-known Catalan structures, focusing on the meaning of the relations S
and R in each considered case.
| arxiv topic:cs.DM |
arxiv_dataset-22651011.3808 | Resonant Absorption as Mode Conversion? II. Temporal Ray Bundle
astro-ph.SR
A fast-wave pulse in a simple, cold, inhomogeneous MHD model plasma is
constructed by Fourier superposition over frequency of harmonic waves that are
singular at their respective Alfven resonances. The pulse partially reflects
before reaching the resonance layer, but also partially tunnels through to it
to mode convert to an Alfven wave. The exact absorption/conversion coefficient
for the pulse is shown to be given precisely by a function of transverse
wavenumber tabulated in Paper I of this sequence, and to be independent of
frequency and pulse width.
| arxiv topic:astro-ph.SR |
arxiv_dataset-22661011.3908 | Structure and spatial distribution of Ge nanocrystals subjected to fast
neutron irradiation
cond-mat.mes-hall
The influence of fast neutron irradiation on the structure and spatial
distribution of Ge nanocrystals (NC) embedded in an amorphous SiO2 matrix has
been studied. The investigation was conducted by means of laser Raman
Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and
X-ray photoelectron spectroscopy (XPS). The irradiation of NC-Ge samples by a
high dose of fast neutrons lead to a partial destruction of the nanocrystals.
Full reconstruction of crystallinity was achieved after annealing the radiation
damage at 800 deg. C, which resulted in full restoration of the RS spectrum.
HR-TEM images show, however, that the spatial distributions of NC-Ge changed as
a result of irradiation and annealing. A sharp decrease in NC distribution
towards the SiO2 surface has been observed. This was accompanied by XPS
detection of Ge oxides and elemental Ge within both the surface and subsurface
region.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-22671011.4008 | CleGo: A package for automated computation of Clebsch-Gordan
coefficients in Tensor Product Representations for Lie Algebras A - G
math-ph hep-ph hep-th math.MP
We present a program that allows for the computation of tensor products of
irreducible representations of Lie algebras A-G based on the explicit
construction of weight states. This straightforward approach (which is slower
and more memory-consumptive than the standard methods to just calculate
dimensions of the tensor product decomposition) produces Clebsch-Gordan
coefficients that are of interest for instance in discussing symmetry breaking
in model building for grand unified theories. For that purpose, multiple tensor
products have been implemented as well as means for analyzing the resulting
effective operators in particle physics.
| arxiv topic:math-ph hep-ph hep-th math.MP |
arxiv_dataset-22681011.4108 | Wave-type equations of low regularity
math.AP gr-qc math-ph math.MP
We prove local existence and uniqueness of the Cauchy problem for a large
class of tensorial second order linear hyperbolic partial differential
equations with coefficients of low regularity in a suitable class of
generalized functions.
| arxiv topic:math.AP gr-qc math-ph math.MP |
arxiv_dataset-22691011.4208 | Grauert's theorem for subanalytic open sets in real analytic manifolds
math.AG math.CV
By open neighbourhood of an open subset $\Omega$ of $\mathbb{R}^n$ we mean an
open subset $\Omega'$ of $\mathbb{C}^n$ such that
$\mathbb{R}^n\cap\Omega'=\Omega.$ A well known result of H. Grauert implies
that any open subset of $\mathbb{R}^n$ admits a fundamental system of Stein
open neighbourhoods in $\mathbb{C}^n$. Another way to state this property is to
say that each open subset of $\mathbb{R}^n$ is Stein. We shall prove a similar
result in the subanalytic category, so, under the assumption that $\Omega$ is a
subanalytic relatively compact open subset in a real analytic manifold, we show
that $\Omega$ admits a fundamental system of subanalytic Stein open
neighbourhoods in any of its complexifications.
| arxiv topic:math.AG math.CV |
arxiv_dataset-22701011.4308 | PRIMUS: Obscured Star Formation on the Red Sequence
astro-ph.CO
We quantify the fraction of galaxies at moderate redshifts (0.1<z<0.5) that
appear red-and-dead in the optical, but in fact contain obscured star formation
detectable in the infrared (IR), with the PRIsm MUlti-object Survey (PRIMUS).
PRIMUS has measured ~120,000 robust redshifts with a precision of
sigma_z/(1+z)~0.5% over 9.1 square degrees of the sky to the depth of i~23
(AB), up to redshift z~1. We specifically targeted 6.7 square degree fields
with existing deep IR imaging from the Spitzer Space Telescope from the SWIRE
and S-COSMOS surveys. We select in these fields an i band flux-limited sample
(i<20 mag in the SWIRE fields and i<21 mag in the S-COSMOS field) of 3310
red-sequence galaxies at 0.1<z<0.5 for which we can reliably classify obscured
star-forming and quiescent galaxies using IR color. Our sample constitutes the
largest galaxy sample at intermediate redshift to study obscured star formation
on the red sequence, and we present the first quantitative analysis of the
fraction of obscured star-forming galaxies as a function of luminosity. We find
that on average, at L ~ L*, about 15% of red-sequence galaxies have IR colors
consistent with star-forming galaxies. The percentage of obscured star-forming
galaxies increases by ~8% per mag with decreasing luminosity from the highest
luminosities to L~0.2L*. Our results suggest that a significant fraction of
red-sequence galaxies have ongoing star formation and that galaxy evolution
studies based on optical color therefore need to account for this complication.
| arxiv topic:astro-ph.CO |
arxiv_dataset-22711011.4408 | Review of lattice results concerning low energy particle physics
hep-lat hep-ph
We review lattice results relevant for pion and kaon physics with the aim of
making them easily accessible to the particle physics community. Specifically,
we review the determination of the light-quark masses, the form factor f_+(0),
relevant for the semileptonic K -> pi transition at zero momentum transfer as
well as the ratio f_K/f_pi of decay constants and discuss the consequences for
the elements V_{us} and V_{ud} of the CKM matrix. Furthermore, we describe the
results obtained on the lattice for some of the low-energy constants of
SU(2)_LxSU(2)_R and SU(3)_LxSU(3)_R Chiral Perturbation Theory and review the
determination of the B_K parameter of neutral kaon mixing. We introduce quality
criteria and use these when forming averages. Although subjective and
imperfect, these criteria may help the reader to judge different aspects of
current lattice computations. Our main results are summarized in section 1.2,
but we stress the importance of the detailed discussion that underlies these
results and constitutes the bulk of the present review.
| arxiv topic:hep-lat hep-ph |
arxiv_dataset-22721011.4508 | Star formation efficiency in the Barred Spiral Galaxy NGC 4303
astro-ph.CO
We present new $^{12}$CO(J=1-0) observations of the barred galaxy NGC 4303
using the Nobeyama 45m telescope (NRO45) and the Combined Array for Research in
Millimeter-wave Astronomy (CARMA). The H$\alpha$ images of barred spiral
galaxies often show active star formation in spiral arms, but less so in bars.
We quantify the difference by measuring star formation rate and efficiency at a
scale where local star formation is spatially resolved. Our CO map covers the
central 2$\farcm$3 region of the galaxy; the combination of NRO45 and CARMA
provides a high fidelity image, enabling accurate measurements of molecular gas
surface density. We find that star formation rate and efficiency are twice as
high in the spiral arms as in the bar. We discuss this difference in the
context of the Kennicutt-Schimidt (KS) law, which indicates a constant star
formation rate at a given gas surface density. The KS law breaks down at our
native resolution ($\sim$ 250 pc), and substantial smoothing (to 500 pc) is
necessary to reproduce the KS law, although with greater scatter.
| arxiv topic:astro-ph.CO |
arxiv_dataset-22731011.4608 | Forward Raman compression via photonic band gap in metals or warm dense
matter
physics.plasm-ph
The group velocity of a light pulse in photonic band gap material could
considerably deviate from the speed of light in vacuum. Different speeds of a
forward stoke and a pump pulse would enable the Raman compression in metals or
the warm dense matter. A small window of the parameter regime, where the
compression is feasible via the forward Raman scattering, is identified.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-22741011.4708 | Homotopy Normal Maps
math.AT
Normal maps between discrete groups $N\rightarrow G$ were characterized [FS]
as those which induce a compatible topological group structure on the homotopy
quotient $EN\times_N G$. Here we deal with topological group (or loop) maps
$N\rightarrow G$ being normal in the same sense as above and hence forming a
homotopical analogue to the inclusion of a topological normal subgroup in a
reasonable way.
We characterize these maps by a compatible simplicial loop space structure on
$Bar_\bullet(N,G)$, invariant under homotopy monoidal functors, e.g.
Localizations and Completions. In the course of characterizing homotopy
normality, we define a notion of a "homotopy action" similar to an $A_{\infty}$
action on a space, but phrased in terms of Segal's 'special $\Delta-$spaces'
and seem to be of importance on its own right. As an application of the
invariance of normal maps, we give a very short proof to a theorem of Dwyer and
Farjoun namely that a localization by a suspended map of a principal fibration
of connected spaces is again principal.
| arxiv topic:math.AT |
arxiv_dataset-22751011.4808 | Calorimetric Evidence for Nodes in the Overdoped
Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$
cond-mat.supr-con
We present low-temperature specific heat of the electron-doped
Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$, which does not show any indication of
an upturn down to 400 mK, the lowest measuring temperature. The lack of a
Schottky-like feature at low temperatures or in magnetic fields up to 9 Tesla
enables us to identify enhanced low-temperature quasiparticle excitations and
to study anisotropy in the linear term of the specific heat. Our results can
not be explained by a single or multiple isotropic superconducting gap, but are
consistent with multi-gap superconductivity with nodes on at least one Fermi
surface sheet.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-22761011.4908 | Single and Double Photonuclear Excitations in Pb+Pb Collisions at
sqrt(s_NN) = 2.76 TeV at the CERN Large Hadron Collider
hep-ph nucl-th
Cross sections are calculated for single and double photon exchange in
ultraperipheral Pb+Pb collisions at the LHC. The particle production is
simulated with the DPMJET event generator. Large cross sections are found for
particle production around mid-rapidity making these processes an important
background to hadronic nuclear interactions at both the trigger and analysis
levels.
| arxiv topic:hep-ph nucl-th |
arxiv_dataset-22771011.5008 | Properties of the poset of Dyck paths ordered by inclusion
math.CO
An expository summary of properties of the poset of Dyck paths ordered by
inclusion.
| arxiv topic:math.CO |
arxiv_dataset-22781011.5108 | Stochastic models of the chemostat
q-bio.QM math.PR
We consider the modeling of the dynamics of the chemostat at its very source.
The chemostat is classically represented as a system of ordinary differential
equations. Our goal is to establish a stochastic model that is valid at the
scale immediately preceding the one corresponding to the deterministic model.
At a microscopic scale we present a pure jump stochastic model that gives rise,
at the macroscopic scale, to the ordinary differential equation model. At an
intermediate scale, an approximation diffusion allows us to propose a model in
the form of a system of stochastic differential equations. We expound the
mechanism to switch from one model to another, together with the associated
simulation procedures. We also describe the domain of validity of the different
models.
| arxiv topic:q-bio.QM math.PR |
arxiv_dataset-22791011.5208 | Mass shift of sigma-Meson in Nuclear Matter
hep-ph
The propagation of sigma meson in nuclear matter is studied in the Walecka
model, assuming that the sigma couples to a pair of nucleon-antinucleon states
and to particle-hole states, including the in medium effect of sigma-omega
mixing. We have also considered, by completeness, the coupling of sigma to two
virtual pions. We have found that the sigma meson mass decreases respect to its
value in vacuum and that the contribution of the sigma omega mixing effect on
the mass shift is relatively small.
| arxiv topic:hep-ph |
arxiv_dataset-22801011.5308 | The link surgery of $S^2\times S^2$ and Scharlemann's manifolds
math.GT
Fintushel-Stern's knot surgery gave many pairs of exotic manifolds, which are
homeomorphic but non-diffeomorphic. We show that if an elliptic fibration has
two parallel, oppositely oriented vanishing circles (for example $S^2\times
S^2$ or Matsumoto's $S^4$), then the knot surgery gives rise to standard
manifolds. The diffeomorphism can give an alternative proof that Scharlemann's
manifold is standard (originally by Akbulut [Ak1]).
| arxiv topic:math.GT |
arxiv_dataset-22811011.5408 | Deterministic endless collective evolvement in active nematics
cond-mat.stat-mech cond-mat.soft
We propose a simple deterministic dynamic equation and reveal the mechanism
of large-scale endless evolvement of spatial density inhomogeneity in active
nematic. We determine the phase regions analytically. The interplay of density,
magnitude of nematic order, and nematic director is crucial for the
long-wave-length instability and the emergence of seemingly fluctuated
collective motions. Ordered nematic domains can absorb particles, grow and
divide endlessly. The present finding extends our understanding of the
large-scale and seemingly fluctuated organization in active fluids.
| arxiv topic:cond-mat.stat-mech cond-mat.soft |
arxiv_dataset-22821011.5508 | Light Stop Searches at the LHC in Events with two b-Jets and Missing
Energy
hep-ph hep-ex
We propose a new method to discover light top squarks (stops) in the
co-annihilation region at the Large Hadron Collider (LHC). The bino-like
neutralino is the lightest supersymmetric particle (LSP) and the lighter stop
is the next-to-LSP. Such scenarios can be consistent with electroweak
baryogenesis and also with dark matter constraints. We consider the production
of two stops in association with two b-quarks, including pure QCD as well as
mixed electroweak-QCD contributions. The stops decay into a charm quark and the
LSP. For a higgsino-like light chargino the electroweak contributions can
exceed the pure QCD prediction. We show the size of the electroweak
contributions as a function of the stop mass and present the LHC discovery
reach in the stop-neutralino mass plane.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-22831011.5608 | Standard Model Predictions for $D^0$-oscillations and CP-violation
hep-ph
We review the status of the standard model predictions for $D$-mixing and
CP-violation in mixing.
| arxiv topic:hep-ph |
arxiv_dataset-22841011.5708 | The Cosmological Constant Problem from the Point of View of String
Theory
hep-th
The quantum field theory prediction of the cosmological constant is 120
orders of magnitude higher than the observed value. This is known as the
cosmological constant problem. Here, we deal with the cosmological constant as
a scalar field generated by the reduced extra dimensions, following
Kaluza-Klein reduction, in the superstring theory frame, where the vacuum
energy is the minimum of this field. We find methods for calculating the
cosmological constant, whose value is much lower than those obtained with the
current methods of quantum field theory. We conclude that the small
cosmological constant value could be explained by the behavior of the mentioned
scalar field, and finally we discuss a possible explanation for the observed
accelerated expansion of the Universe.
| arxiv topic:hep-th |
arxiv_dataset-22851011.5808 | Dotted Version Vectors: Logical Clocks for Optimistic Replication
cs.DC
In cloud computing environments, a large number of users access data stored
in highly available storage systems. To provide good performance to
geographically disperse users and allow operation even in the presence of
failures or network partitions, these systems often rely on optimistic
replication solutions that guarantee only eventual consistency. In this
scenario, it is important to be able to accurately and efficiently identify
updates executed concurrently. In this paper, first we review, and expose
problems with current approaches to causality tracking in optimistic
replication: these either lose information about causality or do not scale, as
they require replicas to maintain information that grows linearly with the
number of clients or updates. Then, we propose a novel solution that fully
captures causality while being very concise in that it maintains information
that grows linearly only with the number of servers that register updates for a
given data element, bounded by the degree of replication.
| arxiv topic:cs.DC |
arxiv_dataset-22861011.5908 | Kepler photometry of the prototypical Blazhko star RR Lyr: An old friend
seen in a new light
astro-ph.SR
We present our analysis of the long cadence Kepler data for the well-studied
Blazhko star RR Lyr, gathered during the first two quarters of the satellite's
observations and covering a total of 127d. Besides being of great importance
for our understanding of RR Lyrae stars in general, these RR Lyr data can be
regarded as a case study for observations of bright stars with Kepler. Kepler
can perform high-precision photometry on targets like RR Lyr, as the saturated
flux is conserved to a very high degree. The Kepler data on RR Lyr are
revolutionary in several respects. Even with long-cadence sampling (one
measurement per 29.4 min), the unprecedented precision (< mmag) of the Kepler
photometry allows the study of the star's extreme light curve variations in
detail. The multiplet structures at the main frequency and its harmonics,
typical for Blazhko stars, are clearly detected up to the quintuplets. For the
first time, photometric data of RR Lyr reveal the presence of half-integer
frequencies, linked to a period doubling effect. This phenomenon may be
connected to the still unexplained Blazhko modulation. Moreover, with three
observed Blazhko cycles at our disposal, we observe that there is no exact
repetition in the light curve changes from one modulation cycle to the next for
RR Lyr. This may be due to additional periodicities in the star, or to
transient or quasi-periodic changes.
| arxiv topic:astro-ph.SR |
arxiv_dataset-22871011.6008 | Suppression of $T_c$ by Zn impurity in the electron-type
LaFe$_{0.925-y}$Co$_{0.075}$Zn$_y$AsO system
cond-mat.supr-con cond-mat.mtrl-sci
The effect of non-magnetic Zn impurity on superconductivity in electron-type
pnictide superconductor LaFe$_{0.925-y}$Co$_{0.075}$Zn$_y$AsO is studied
systematically. The optimally doped LaFe$_{0.925}$Co$_{0.075}$AsO without Zn
impurity exhibits superconductivity at $T_c^{mid}$ of 13.2 K, where $T_c^{mid}$
is defiend as the mid-point in the resistive transition. In the presence of Zn
impurity, the superconducting transition temperature, $T_c^{mid}$, is severely
suppressed. The result is consistent with the theoretic prediction on the
effect of non-magnetic impurity in the scenario of $s_{\pm}$ pairing, but it is
in sharp contrast to the previous report on the effect of Zn impurity in the
F-doped systems. The possible interpretation of the different effects of Zn
impurity on superconductivity in different systems is discussed.
| arxiv topic:cond-mat.supr-con cond-mat.mtrl-sci |
arxiv_dataset-22881011.6108 | A scheme for the extraction of WIMP-nucleon scattering cross sections
from total event rates
hep-ph astro-ph.CO
We propose a scheme that allows to analytically determine the three
elementary cross sections and connect the solutions to the relative sign
between the proton and the neutron spin scattering amplitudes once the
measurements of total event rate from three appropriate targets become
available. In this way it is thus possible to extract the maximum information
on the supersymmetric parameter space obtainable from direct detection
experiments, in the case that the dark matter particle is the lightest
neutralino. Our scheme is based on suitably normalized form of the isospin
momentum dependent structure functions entering in the spin-dependent elastic
neutralino-nucleus cross section. We compare these functions with the commonly
used ones and discuss their advantages: in particular, these allow in the
spin-dependent cross section to factorize the particle physics degrees of
freedom from the momentum transfer dependent nuclear structure functions as it
happens in the spin-independent cross section with the nuclear form factor.
| arxiv topic:hep-ph astro-ph.CO |
arxiv_dataset-22891011.6208 | Locally-finite connected-homogeneous digraphs
math.CO math.GR
A digraph is connected-homogeneous if any isomorphism between finite
connected induced subdigraphs extends to an automorphism of the digraph. We
consider locally-finite connected-homogeneous digraphs with more than one end.
In the case that the digraph embeds a triangle we give a complete
classification, obtaining a family of tree-like graphs constructed by gluing
together directed triangles. In the triangle-free case we show that these
digraphs are highly arc-transitive. We give a classification in the two-ended
case, showing that all examples arise from a simple construction given by
gluing along a directed line copies of some fixed finite directed complete
bipartite graph. When the digraph has infinitely many ends we show that the
descendants of a vertex form a tree, and the reachability graph (which is one
of the basic building blocks of the digraph) is one of: an even cycle, a
complete bipartite graph, the complement of a perfect matching, or an infinite
semiregular tree. We give examples showing that each of these possibilities is
realised as the reachability graph of some connected-homogeneous digraph, and
in the process we obtain a new family of highly arc-transitive digraphs without
property Z.
| arxiv topic:math.CO math.GR |
arxiv_dataset-22901011.6308 | A calculus for costed computations
cs.LO cs.DC
We develop a version of the pi-calculus, picost, where channels are
interpreted as resources which have costs associated with them. Code runs under
the financial responsibility of owners; they must pay to use resources, but may
profit by providing them. We provide a proof methodology for processes
described in picost based on bisimulations. The underlying behavioural theory
is justified via a contextual characterisation. We also demonstrate its
usefulness via examples.
| arxiv topic:cs.LO cs.DC |
arxiv_dataset-22911011.6408 | Merging Galaxy Cluster Abell 2255 in Mid-Infrared
astro-ph.CO
We present the mid-infrared (MIR) observation of a nearby galaxy cluster,
Abell 2255 by the AKARI space telescope. Using the AKARI's continuous
wavelength coverage between 3-24 micron and the wide field of view, we
investigate the properties of cluster member galaxies to see how the infall of
the galaxies, the cluster substructures, and the cluster-cluster merger
influence their evolution. We show that the excess of MIR (11 micron) flux is a
good indicator to discriminate galaxies at different evolutionary stages, and
divide galaxies into three classes accordingly : strong MIR-excess (N3-S11>0.2)
galaxies that include both unobscured and obscured star-forming galaxies, weak
MIR-excess (-2.0<N3-S11<-1.2) galaxies that are quiescent, old (>5 Gyr)
galaxies where the MIR emission arises mainly from the circumstellar dust
around AGB stars, and intermediate MIR-excess (-1.2<N3-S11<0.2) galaxies in
between the two classes that are less than a few Gyrs old past the prime star
formation activity. With the MIR-excess diagnostics, we investigate how local
and cluster-scale environments affect the individual galaxies. We derive the
total star formation rate of ~130 Msun/yr for A2255 using the strong MIR-excess
galaxies, which is consistent with other clusters of galaxies at similar
redshifts and with similar masses. We find no strong evidence that supports
enhanced star formation neither inside the cluster nor in the substructure
region. The intermediate MIR-excess galaxies, representing galaxies in
transition from star-forming galaxies to quiescent galaxies, are located
preferentially at the medium density region or cluster substructures. Our
findings suggest that galaxies are being transformed from star-forming galaxies
into red, quiescent galaxies from the infall region through near the core,
which can be well-explained by the ram-pressure stripping as previous
simulation suggests.
| arxiv topic:astro-ph.CO |
arxiv_dataset-22921011.6508 | Multi-Hop Bandwidth Management Protocol for Mobile Ad Hoc Networks
cs.NI
An admission control scheme should play the role of a coordinator for flows
in a data communication network, to provide the guarantees as the medium is
shared. The nodes of a wired network can monitor the medium to know the
available bandwidth at any point of time. But, in wireless ad hoc networks, a
node must consume the bandwidth of neighboring nodes, during a communication.
Hence, the consumption of bandwidth by a flow and the availability of resources
to any wireless node strictly depend upon the neighboring nodes within its
transmission range. We present a scalable and efficient admission control
scheme, Multi-hop Bandwidth Management Protocol (MBMP), to support the QoS
requirements in multi-hop ad hoc networks. We simulate several options to
design MBMP and compare the performances of these options through mathematical
analysis and simulation results, and compare its effectiveness with the
existing admission control schemes through extensive simulations.
| arxiv topic:cs.NI |
arxiv_dataset-22931011.6608 | Evolution of massive fields around a black hole in Horava gravity
gr-qc
We study the evolution of massive scalar field in the spacetime geometry of
Kehagias-Sfetsos(KS) black hole in deformed Horava-Lifshitz(HL) gravity by
numerical analysis. We find that the signature of HL theory is encoded in the
quasinormal mode(QNM) phase of the evolution of field. The QNM phase in the
evolution process lasts for a longer time in HL theory. QNMs involved in the
evolution of massive field are calculated and find that they have a higher
oscillation frequency and a lower damping rate than the Schwarzschild spacetime
case. We also study the relaxation of field in the intermediate and asymptotic
range and verified that behaviors of field in these phases are independent of
the HL parameter and is identical to the Schwarzschild case.
| arxiv topic:gr-qc |
arxiv_dataset-22941012.0032 | Testing of sequences by simulation
cs.DS
Let $\xi$ be a random integer vector, having uniform distribution
\[\mathbf{P} \{\xi = (i_1,i_2,...,i_n) = 1/n^n \} \ \hbox{for} \ 1 \leq
i_1,i_2,...,i_n\leq n.\] A realization $(i_1,i_2,...,i_n)$ of $\xi$ is called
\textit{good}, if its elements are different. We present algorithms
\textsc{Linear}, \textsc{Backward}, \textsc{Forward}, \textsc{Tree},
\textsc{Garbage}, \textsc{Bucket} which decide whether a given realization is
good. We analyse the number of comparisons and running time of these algorithms
using simulation gathering data on all possible inputs for small values of $n$
and generating random inputs for large values of $n$.
| arxiv topic:cs.DS |
arxiv_dataset-22951012.0132 | Extended weight semigroups of affine spherical homogeneous spaces of
non-simple semisimple algebraic groups
math.RT math.AG
The extended weight semigroup of a homogeneous space G/H of a connected
semisimple algebraic group G characterizes the spectra of the representations
of G on the spaces of regular sections of homogeneous linear bundles over G/H,
including the space of regular functions on G/H. We compute the extended weight
semigroups for all strictly irreducible affine spherical homogeneous spaces
G/H, where G is a simply connected non-simple semisimple complex algebraic
group and H a connected closed subgroup of it. In all the cases we also find
the highest weight functions corresponding to the indecomposable elements of
this semigroup. Among other things, our results complete the computation of the
weight semigroups for all strictly irreducible simply connected affine
spherical homogeneous spaces of semisimple complex algebraic groups.
| arxiv topic:math.RT math.AG |
arxiv_dataset-22961012.0232 | Kolmogorov-Loveland Sets and Advice Complexity Classes
cs.CC
Loveland complexity is a variant of Kolmogorov complexity, where it is asked
to output separately the bits of the desired string, instead of the string
itself. Similarly to the resource-bounded Kolmogorov sets we define Loveland
sets. We highlight a structural connection between resource-bounded Loveland
sets and some advice complexity classes. This structural connection enables us
to map to advice complexity classes some properties of Kolmogorov sets first
noticed by Hartmanis and thoroughly investigated in Longpr\'e's thesis: 1.
Non-inclusion properties of Loveland sets result in hierarchy properties on the
corresponding advice complexity classes; 2. Immunity properties of Loveland
sets result in the non-existence of natural proofs between the corresponding
advice complexity classes, in the sense of Razborov & Rudich.
| arxiv topic:cs.CC |
arxiv_dataset-22971012.0332 | Experimental investigation of the uncertainty principle in the presence
of quantum memory
quant-ph
Heisenberg's uncertainty principle provides a fundamental limitation on an
observer's ability to simultaneously predict the outcome when one of two
measurements is performed on a quantum system. However, if the observer has
access to a particle (stored in a quantum memory) which is entangled with the
system, his uncertainty is generally reduced. This effect has recently been
quantified by Berta et al. [Nature Physics 6, 659 (2010)] in a new, more
general uncertainty relation, formulated in terms of entropies. Using entangled
photon pairs, an optical delay line serving as a quantum memory and fast,
active feed-forward we experimentally probe the validity of this new relation.
The behaviour we find agrees with the predictions of quantum theory and
satisfies the new uncertainty relation. In particular, we find lower
uncertainties about the measurement outcomes than would be possible without the
entangled particle. This shows not only that the reduction in uncertainty
enabled by entanglement can be significant in practice, but also demonstrates
the use of the inequality to witness entanglement.
| arxiv topic:quant-ph |
arxiv_dataset-22981012.0432 | Effects of Curvature on Dynamics
physics.gen-ph physics.class-ph
In this article we discuss the effect of curvature on dynamics when a
physical system moves adiabatically in a curved space. These effects give a way
to measure the curvature of the space intrinsically without referring to higher
dimensional space. Two interesting examples, the Foucault Pendulum and the
perihelion shift of planetary orbits, are presented in a simple geometric way.
A paper model is presented to see the perihelion shift.
| arxiv topic:physics.gen-ph physics.class-ph |
arxiv_dataset-22991012.0532 | The influence of collective neutrino oscillations on a supernova
r-process
astro-ph.SR hep-ph nucl-th
Recently, it has been demonstrated that neutrinos in a supernova oscillate
collectively. This process occurs much deeper than the conventional
matter-induced MSW effect and hence may have an impact on nucleosynthesis. In
this paper we explore the effects of collective neutrino oscillations on the
r-process, using representative late-time neutrino spectra and outflow models.
We find that accurate modeling of the collective oscillations is essential for
this analysis. As an illustration, the often-used "single-angle" approximation
makes grossly inaccurate predictions for the yields in our setup. With the
proper multiangle treatment, the effect of the oscillations is found to be less
dramatic, but still significant. Since the oscillation patterns are sensitive
to the details of the emitted fluxes and the sign of the neutrino mass
hierarchy, so are the r-process yields. The magnitude of the effect also
depends sensitively on the astrophysical conditions - in particular on the
interplay between the time when nuclei begin to exist in significant numbers
and the time when the collective oscillation begins. A more definitive
understanding of the astrophysical conditions, and accurate modeling of the
collective oscillations for those conditions, is necessary.
| arxiv topic:astro-ph.SR hep-ph nucl-th |
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