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arxiv_dataset-400712.2079 | Phenomenological analysis of the nucleon spin contents and their scale
dependence
hep-ph hep-ex nucl-ex
In the past few years, a lot of evidences have been accumulated, which
indicate that the gluon polarization inside the nucleon is likely to be small
at least at the low renormalization scales. On the other hand, the recent
lattice QCD analyses suggest that the net orbital angular momentum carried by
the quarks is nearly zero. There is also some indication noticed by Brodsky and
Gardner based on the COMPASS observation of small single-spin asymmetry on the
isoscalar deuteron target, that the gluon orbital angular momentum inside the
nucleon is likely to be small. Naively combining all these observations, we are
led to a rather embarrassing conclusion that the nucleon constituents
altogether do not carry enough amount of angular momentum saturating the total
nucleon spin. We show that this somewhat confused state of affairs can be
cleared up only by paying careful attention to the scale dependencies of the
nucleon spin decomposition.
| arxiv topic:hep-ph hep-ex nucl-ex |
arxiv_dataset-401712.2179 | Study of GEM-like detectors with resistive electrodes for RICH
applications
physics.ins-det
We have developed prototypes of GEM-like detectors with resistive electrodes
to be used as RICH photodetectors equipped with CsI photocathodes. The main
advantages of these detectors are their intrinsic spark protection and
possibility to operate at high gain (~10E5) in many gases including poorly
quenched ones, allowing for the adoption of windowless configurations in which
the radiator gas is also used in the chamber. Results of systematic studies of
the resistive GEMs combined with CsI photocathodes are presented: its quantum
efficiency, rate characteristics, long-term stability, etc. On the basis of the
obtained results, we believe that the new detector will be a promising
candidate for upgrading the ALICE RICH detector
| arxiv topic:physics.ins-det |
arxiv_dataset-402712.2279 | A Cheerful Introduction to Forcing and the Continuum Hypothesis
math.LO math.GM
This is an introduction to the set-theoretic method of forcing, including its
application in proving the independence of the Continuum Hypothesis from the
Zermelo-Fraenkel axioms of set theory. I presuppose no particular mathematical
background beyond some familiarity with set theory and mathematical logic - in
particular, no algebra is presupposed, though it can be useful. The goal is to
have a document that makes this material accessible to mathematics graduate
students in all fields, and to philosophers with an interest in set theory and
mathematical logic but no other mathematical background.
| arxiv topic:math.LO math.GM |
arxiv_dataset-403712.2379 | Gribov copies and anomalous scaling
hep-ph hep-th
Nonperturbative and lattice methods indicate that Gribov copies modify the
infrared behavior of gauge theories and cause a suppression of gluon
propagation. We investigate whether this can be implemented in a modified
perturbation theory. The minimal modification proceeds via a nonlocal
generalization of the Fadeev-Popov ghost that automatically decouples from
physical states. The expected scale invariance of the physics associated with
Gribov copies leads to the emergence of a nontrivial infrared fixed point. For
a range of a scaling exponent the gauge bosons exhibit unparticlelike behavior
in the infrared. The confining regime of interest for QCD requires a larger
scaling exponent, but then the severity of ghost dominance upsets naive power
counting for the infrared scaling behavior of amplitudes.
| arxiv topic:hep-ph hep-th |
arxiv_dataset-404712.2479 | Spinning superstrings at two loops: strong-coupling corrections to
dimensions of large-twist SYM operators
hep-th
We consider folded spinning strings in AdS_5xS^5 (with one spin component S
in AdS_5 and J in S^5) corresponding to the Tr(D^S Z^J) operators in the sl(2)
sector of the N=4 SYM theory in the special scaling limit in which both the
string mass M ~ \sqrt \lambda \ln S and J are sent to infinity with their ratio
fixed. Expanding in the parameter \el= J/M we compute the 2-loop string sigma
model correction to the string energy and show that it agrees with the
expression proposed by Alday and Maldacena in arxiv:0708.0672. We suggest that
a resummation of the logarithmic \el^2 \ln^n \el terms is necessary in order to
establish an interpolation to the weakly coupled gauge theory results. In the
process, we set up a general framework for the calculation of higher loop
corrections to the energy of multi-spin string configurations. In particular,
we find that in addition to the direct 2-loop term in the string energy there
is a contribution from lower loop order due to a finite ``renormalization'' of
the relation between the parameters of the classical solution and the fixed
spins, i.e. the charges of the SO(2,4) x SO(6) symmetry.
| arxiv topic:hep-th |
arxiv_dataset-405712.2579 | On the Information of the Second Moments Between Random Variables Using
Mutually Unbiased Bases
cs.IT math.IT
The notation of mutually unbiased bases(MUB) was first introduced by Ivanovic
to reconstruct density matrixes\cite{Ivanovic}. The subject about how to use
MUB to analyze, process, and utilize the information of the second moments
between random variables is studied in this paper. In the first part, the
mathematical foundation will be built. It will be shown that the spectra of MUB
have complete information for the correlation matrixes of finite discrete
signals, and the nice properties of them. Roughly speaking, it will be shown
that each spectrum from MUB plays an equal role for finite discrete signals,
and the effect between any two spectra can be treated as a global constant
shift. These properties will be used to find some important and natural
characterizations of random vectors and random discrete operators/filters. For
a technical reason, it will be shown that any MUB spectra can be found as fast
as Fourier spectrum when the length of the signal is a prime number.
In the second part, some applications will be presented. First of all, a
protocol about how to increase the number of users in a basic digital
communication model will be studied, which has bring some deep insights about
how to encode the information into the second moments between random variables.
Secondly, the application of signal analysis will be studied. It is suggested
that complete "MUB" spectra analysis works well in any case, and people can
just choose the spectra they are interested in to do analysis. For instance,
single Fourier spectra analysis can be also applied in nonstationary case.
Finally, the application of MUB in dimensionality reduction will be considered,
when the prior knowledge of the data isn't reliable.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-406712.2679 | Diffusion on Ruffled Membrane Surfaces
cond-mat.soft cond-mat.stat-mech
We present a position Langevin equation for overdamped particle motion on
rough two-dimensional surfaces. A Brownian Dynamics algorithm is suggested to
evolve this equation numerically, allowing for the prediction of effective
(projected) diffusion coefficients over corrugated surfaces. In the case of
static surface roughness, we find that a simple area-scaling prediction for the
projected diffusion coefficient leads to seemingly quantitative agreement with
numerical results. To study the effect of dynamic surface evolution on the
diffusive process, we consider particle diffusion over a thermally fluctuating
elastic membrane. Surface fluctuation has the effect of increasing the
effective diffusivity toward a limiting annealed-surface value discussed
previously. We argue that protein motion over cell surfaces spans a variety of
physical regimes, making it impossible to identify a single approximation
scheme appropriate to all measurements of interest.
| arxiv topic:cond-mat.soft cond-mat.stat-mech |
arxiv_dataset-407712.2779 | Modeling Evolving Innovation Networks
physics.soc-ph
We develop a new framework for modeling innovation networks which evolve over
time. The nodes in the network represent firms, whereas the directed links
represent unilateral interactions between the firms. Both nodes and links
evolve according to their own dynamics and on different time scales. The model
assumes that firms produce knowledge based on the knowledge exchange with other
firms, which involves both costs and benefits for the participating firms. In
order to increase their knowledge production, firms follow different strategies
to create and/or to delete links with other firms. Dependent on the information
firms take into account for their decision, we find the emergence of different
network structures. We analyze the conditions for the existence of these
structures within a mathematical approach and underpin our findings by
extensive computer simulations which show the evolution of the networks and
their equilibrium state. In the discussion of the results, particular attention
is given to the emergence of direct and indirect reciprocity in knowledge
exchange, which refers to the emergence of cycles in the network structure. In
order to motivate our modeling framework, in the first part of the chapter we
give a broad overview of existing literature from economics and physics. This
shows that our framework bridges and extends two different lines of research,
namely the study of equilibrium networks with simple topologies and the dynamic
approach of hypercycle models.
| arxiv topic:physics.soc-ph |
arxiv_dataset-408712.2879 | Exploring Parameter Constraints on Quintessential Dark Energy: the
Pseudo-Nambu Goldstone Boson Model
astro-ph
We analyze the constraining power of future dark energy experiments for
Pseudo-Nambu Goldstone Boson (PNGB) quintessence. Following the Dark Energy
Task Force methodology, we forecast data for three experimental ``stages'':
Stage 2 represents in-progress projects relevant to dark energy; Stage 3 refers
to medium sized experiments; Stage 4 comprises larger projects. We determine
the posterior probability distribution for the parameters of the PNGB model
using Markov Chain Monte Carlo analysis. Utilizing data generated on a $\Lambda
CDM$ cosmology, we find that the relative power of the different data stages on
PNGB quintessence is roughly comparable to the DETF results for the $w_0-w_a$
parametrization of dark energy. We also generate data based on a PNGB
cosmological model that is consistent with a $\Lambda CDM$ fiducial model at
Stage 2. We find that Stage 4 data based on this PNGB fiducial model will rule
out a cosmological constant by at least $3 \sigma$.
| arxiv topic:astro-ph |
arxiv_dataset-409712.2979 | Radially-Inflowing Molecular Gas in NGC 1275 Deposited by a X-ray
Cooling Flow in the Perseus Cluster
astro-ph
We have imaged in CO(2-1) the molecular gas in NGC 1275 (Perseus A), the cD
galaxy at the center of the Perseus Cluster, at a spatial resolution of $\sim$1
kpc over a central region of radius $\sim$ 10 kpc. Per A is known to contain
$\sim$1.3x10$^{10}$ M$_\odot$ of molecular gas, which has been proposed to be
captured from mergers with or ram-pressure stripping of gas-rich galaxies, or
accreted from a X-ray cooling flow. The molecular gas detected in our image has
a total mass of $\sim$4x10$^9$ M$_\odot$, and for the first time can be seen to
be concentrated in three radial filaments with lengths ranging from at least
1.1-2.4 kpc all lying in the east-west directions spanning the center of the
galaxy to radii of $\sim$8 kpc. The eastern and outer western filaments exhibit
larger blueshifted velocities with decreasing radii, whereas the inner western
filament spans the systemic velocity of the galaxy. The molecular gas shows no
signature of orbital motion, and is therefore unlikely to have been captured
from gas-rich galaxies. Instead, we are able to reproduce the observed
kinematics of the two outer filaments as free-fall in the gravitational
potential of Per A, as would be expected if they originate from a X-ray cooling
flow. Indeed, all three filaments lie between two prominent X-ray cavities
carved out by radio jets from Per A, and closely resembles the spatial
distribution of the coolest X-ray gas in the cluster core. The inferred
mass-deposition rate into the two outermost filaments alone is roughly 75
M$_odot$ yr$^{-1}$. This cooling flow can provide a nearly continuous supply of
molecular gas to fuel the active nucleus in Per A.
| arxiv topic:astro-ph |
arxiv_dataset-410712.3079 | Block-diagonal semidefinite programming hierarchies for 0/1 programming
math.OC
Lovasz and Schrijver, and later Lasserre, proposed hierarchies of
semidefinite programming relaxations for general 0/1 linear programming
problems. In this paper these two constructions are revisited and two new,
block-diagonal hierarchies are proposed. They have the advantage of being
computationally less costly while being at least as strong as the
Lovasz-Schrijver hierarchy. Our construction is applied to the stable set
problem and experimental results for Paley graphs are reported.
| arxiv topic:math.OC |
arxiv_dataset-411712.3179 | Surface solitons in two-dimensional chirped photonic lattices
nlin.PS
We study surface modes in semi-infinite chirped two-dimensional photonic
lattices in the frame- work of an effective discrete nonlinear model. We
demonstrate that the lattice chirp can change dramatically the conditions for
the mode localization near the surface, and we find numerically the families of
surface modes, in linear lattices, and discrete surface solitons, in nonlinear
lattices. We demonstrate that, in a sharp contrast to one-dimensional discrete
surface solitons, in two-dimensional lattices the mode threshold power is
lowered by the action of both the surface and lattice chirp. By manipulating
with the lattice chirp, we can control the mode position and its localization.
| arxiv topic:nlin.PS |
arxiv_dataset-412712.3279 | Quantum Pump for Fractional Charge
cond-mat.mes-hall cond-mat.str-el
We propose a theoretical scenario for pumping of fractionally charged
quasi-particle in the context of $\nu=1/3$ fractional quantum Hall liquid. We
consider quasi-particle pumping across an anti-dot level tuned close to the
resonance. Fractional charge pumping is achieved by slow and periodic
modulation of coupling of the anti-dot level to left and right moving edges of
a Hall bar set-up. This is attained by periodically modulating the gate
voltages controlling the couplings. In order to obtain quantization of pumped
charge in the unit of the electronic charge fraction ($\nu e$) per pumping
cycle in the adiabatic limit, we argue that the only possibility is to tune the
quasi-particle operator to be irrelevant from being relevant in the
renormalization group sense, which can be accomplished by invoking quantum Hall
line junctions into the Hall bar geometry. We also comment on possibility for
experimental realization of the above scenario.
| arxiv topic:cond-mat.mes-hall cond-mat.str-el |
arxiv_dataset-413712.3379 | Expectation values and vacuum currents of quantum fields
hep-th gr-qc
Theory of expectation values is presented as an alternative to S-matrix
theory for quantum fields. This change of emphasis is conditioned by a
transition from the accelerator physics to astrophysics and cosmology. The
issues discussed are the time-loop formalism, the Schwinger - Keldysh diagrams,
the effective action, the vacuum currents, and the effect of particle creation.
| arxiv topic:hep-th gr-qc |
arxiv_dataset-414712.3479 | Gravity modes and mixed modes as probes of stellar cores in
main-sequence stars: from solar-like to beta Cep stars
astro-ph
We investigate how the frequencies of gravity modes depend on the detailed
properties of the chemical composition gradient that develops near the core of
main-sequence stars and, therefore, on the transport processes that are able to
modify the \mu profile in the central regions. We show that in main-sequence
models, similarly to the case of white dwarfs, the periods of high-order
gravity modes are accurately described by a uniform period spacing superposed
to an oscillatory component. The periodicity and amplitude of such component
are related, respectively, to the location and sharpness of the \mu gradient.
We briefly discuss and interpret, by means of this simple approximation, the
effect of turbulent mixing near the core on the periods of both high-order and
low-order g modes, as well as of modes of mixed pressure-gravity character.
| arxiv topic:astro-ph |
arxiv_dataset-415712.3579 | Where Centaurus A gets its X-ray knottiness
astro-ph
We report an X-ray spectral study of the transverse structure of the
Centaurus A jet using new data from the Chandra Cen A Very Large Project. We
find that the spectrum steepens with increasing distance from the jet axis, and
that this steepening can be attributed to a change in the average spectrum of
the knotty emission. Such a trend is unexpected if the knots are predominantly
a surface feature residing in a shear layer between faster and slower flows. We
suggest that the spectral steepening of the knot emission as a function of
distance from the jet axis is due to knot migration, implying a component of
transverse motion of knots within the flow.
| arxiv topic:astro-ph |
arxiv_dataset-416712.3679 | Negative refraction in (bi)-isotropic periodic arrangements of chiral
SRRs
physics.optics
Bi-isotropic and isotropic negative refractive index (NRI) 3D metamaterials
made from periodic arrangements of chiral split ring resonators (SRRs) are
proposed and demonstrated. An analytical theory for the characterization and
design of these metamaterials is provided and validated by careful full-wave
electromagnetic simulations. The reported results are expected to pave the way
to the design of practical 3D bi-isotropic and isotropic NRI metamaterials made
from a single kind of inclusions.
| arxiv topic:physics.optics |
arxiv_dataset-417712.3779 | Non-Gaussian Density Fluctuations from Entropically Generated Curvature
Perturbations in Ekpyrotic Models
hep-th astro-ph
We analyze the non-gaussian density perturbations generated in
ekpyrotic/cyclic models based on heterotic M-theory. In this picture, two
scalar fields produce nearly scale-invariant entropic perturbations during an
ekpyrotic phase that are converted into curvature modes {\it after the
ekpyrotic phase is complete} and just before the big bang. Both intrinsic
non-linearity in the entropy perturbation and the conversion process contribute
to non-gaussianity. The range of the non-gaussianity parameter $f_{NL}$ depends
on how gradual the conversion process is and the steepness of the scalar field
potential during the ekpyrotic phase. Although a wider range is possible, in
principle, natural values of the ekpyrotic parameters combined with a gradual
conversion process lead to values of $-60 \lesssim f_{NL} \lesssim +80$,
typically much greater than slow-roll inflation but within the current
observational bounds.
| arxiv topic:hep-th astro-ph |
arxiv_dataset-418712.3879 | Observation of Anomalous Phonon Softening in Bilayer Graphene
cond-mat.mes-hall
The interaction of electron-hole pairs with lattice vibrations exhibits a
wealth of intriguing physical phenomena. The Kohn anomaly is a renowned example
where electron-phonon coupling leads to non-analytic phonon dispersion at
specific momentum nesting the Fermi surface. Here we report evidence of another
type of phonon anomaly discovered by low temperature Raman spectroscopy in
bilayer graphene where the charge density is modulated by the electric field
effect. This anomaly, arising from charge-tunable modulations of particle-hole
pairs that are resonantly coupled to lattice vibrations, is predicted to
exhibit a logarithmic divergence in the long-wavelength optical-phonon energy.
In a non-uniform bilayer of graphene, the logarithmic divergence is abated by
charge density inhomogeneity leaving as a vestige an anomalous phonon
softening. The observed softening marks the first confirmation of the phonon
anomaly as a key signature of the resonant deformation-potential
electron-phonon coupling. The high sensitivity of the phonon softening to
charge density non-uniformity creates significant venues to explore the
interplay between fundamental interactions and disorder in the atomic layers.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-419712.3979 | On Dynamics of $\ell$- Volterra Quadratic Stochastic Operators
math.DS
We introduce a notion of $\ell$-Volterra quadratic stochastic operator
defined on $(m-1)$-dimensional simplex, where $\ell\in\{0,1,...,m\}$. The
$\ell$-Volterra operator is a Volterra operator iff $\ell=m$. We study
structure of the set of all $\ell$-Volterra operators and describe their
several fixed and periodic points. For $m=2$ and 3 we describe behavior of
trajectories of $(m-1)$-Volterra operators. The paper also contains many
remarks with comparisons of $\ell$-Volterra operators and Volterra ones.
| arxiv topic:math.DS |
arxiv_dataset-420712.4079 | Effect of the boundary condition on the vortex patterns in mesoscopic
three-dimensional superconductors - disk and sphere
cond-mat.supr-con cond-mat.mes-hall cond-mat.mtrl-sci
The vortex state of mesoscopic three-dimensional superconductors is
determined using a minimization procedure of the Ginzburg-Landau free energy.
We obtain the vortex pattern for a mesoscopic superconducting sphere and find
that vortex lines are naturally bent and are closest to each other at the
equatorial plane. For a superconducting disk with finite height, and under an
applied magnetic field perpendicular to its major surface, we find that our
method gives results consistent with previous calculations. The matching
fields, the magnetization and $H_{c3}$, are obtained for models that differ
according to their boundary properties. A change of the Ginzburg-Landau
parameters near the surface can substantially enhance $H_{c3}$ as shown here.
| arxiv topic:cond-mat.supr-con cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-421712.4179 | High-efficiency single photon detector combined with an ultra-small APD
module and a self-training discriminator for high-speed quantum cryptosystems
quant-ph
A single-photon avalanche detector (SPAD) for high-speed quantum-key
generation has successfully been developed. It has the highest photon detection
repetition frequency and the lowest dark count rate in the world, as a
board-mountable sub-system. The SPAD consists of an ultra-small dual-avalanche
photodiode (APD) module and a novel discriminator. The APD module design is
consistent with cooling capability and high-frequency characteristics. The new
module has a 3 GHz bandwidth enabling 1 GHz gate-pulse repetition. The
bandwidth is extended 15-fold relative to the most wideband peltier cooled APD
module. The discriminator has a self-training mechanism to compensate charge
pulse. Dark count rare of the SPAD is reduced 1/10th relative to the lowest
dark count single photon detector. The SPAD allows 3.2-fold multiplying the
quantum key generation rate in theoretical estimation.
| arxiv topic:quant-ph |
arxiv_dataset-422712.4279 | Disjointness is hard in the multi-party number on the forehead model
cs.CC
We show that disjointness requires randomized communication
Omega(n^{1/(k+1)}/2^{2^k}) in the general k-party number-on-the-forehead model
of complexity. The previous best lower bound for k >= 3 was log(n)/(k-1). Our
results give a separation between nondeterministic and randomized multiparty
number-on-the-forehead communication complexity for up to k=log log n - O(log
log log n) many players. Also by a reduction of Beame, Pitassi, and Segerlind,
these results imply subexponential lower bounds on the size of proofs needed to
refute certain unsatisfiable CNFs in a broad class of proof systems, including
tree-like Lovasz-Schrijver proofs.
| arxiv topic:cs.CC |
arxiv_dataset-423712.4379 | A Note on Overtwisted Contact Structures
math.GT
In this note, we use the recent work of Honda-Kazez-Matic [HKM] to prove that
a closed contact 3-manifold admitting a compatible open book decomposition with
a nontrivial monodromy which can be presented as a product of left handed Dehn
twists is overtwisted.
| arxiv topic:math.GT |
arxiv_dataset-424801.0073 | Initiation to mould calculus through the example of saddle-node
singularities
math.DS
This article proposes an initiation to \'Ecalle's mould calculus, a powerful
combinatorial tool which yields surprisingly explicit formulas for the
normalising series attached to an analytic germ of singular vector field. This
is illustrated on the case of saddle-node singularities, generated by
two-dimensional vector fields which are formally conjugate to Euler's vector
field $x^2\frac{\pa}{\pa x}+(x+y)\frac{\pa}{\pa y}$, and for which the formal
normalisation proves to be resurgent in $1/x$.
| arxiv topic:math.DS |
arxiv_dataset-425801.0173 | Exceptional sequences and derived autoequivalences
math.AG
We prove a general theorem that gives a non trivial relation in the group of
derived autoequivalences of a variety (or stack) X, under the assumption that
there exists a suitable functor from the derived category of another variety Y
admitting a full exceptional sequence. Applications include the case in which X
is Calabi-Yau and either X is a hypersurface in Y (this extends a previous
result by the author and R.L. Karp, where Y was a weighted projective space) or
Y is a hypersurface in X. The proof uses a resolution of the diagonal of Y
constructed from the exceptional sequence.
| arxiv topic:math.AG |
arxiv_dataset-426801.0273 | On a three-dimensional symmetric Ising tetrahedron, and contributions to
the theory of the dilogarithm and Clausen functions
math-ph math.MP
Perturbative quantum field theory for the Ising model at the three-loop level
yields a tetrahedral Feynman diagram C(a,b) with masses a and b and four other
lines with unit mass. The completely symmetric tetrahedron C^Tet \equiv C(1,1)
has been of interest from many points of view, with several representations and
conjectures having been given in the literature. We prove a conjectured
exponentially fast convergent sum for C(1,1), as well as a previously empirical
relation for C(1,1) as a remarkable difference of Clausen function values. Our
presentation includes Propositions extending the theory of the dilogarithm Li_2
and Clausen Cl_2 functions, as well as their relation to other special
functions of mathematical physics. The results strengthen connections between
Feynman diagram integrals, volumes in hyperbolic space, number theory, and
special functions and numbers, specifically including dilogarithms, Clausen
function values, and harmonic numbers.
| arxiv topic:math-ph math.MP |
arxiv_dataset-427801.0373 | van der Waals Interactions Between Thin Metallic Wires and Layers
cond-mat.mtrl-sci
Quantum Monte Carlo (QMC) methods have been used to obtain accurate
binding-energy data for pairs of parallel thin metallic wires and layers
modeled by 1D and 2D homogeneous electron gases. We compare our QMC binding
energies with results obtained within the random phase approximation, finding
significant quantitative differences and disagreement over the asymptotic
behavior for bilayers at low densities. We have calculated pair-correlation
functions for metallic biwire and bilayer systems. Our QMC data could be used
to investigate van der Waals energy functionals.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-428801.0473 | Semileptonic $B(B_s, B_c)$ decays in the light-cone QCD sum rules
hep-ph
Semileptonic $B$($B_s, B_c$) decays are investigated systematically in the
light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on
weak form factors with an adequate chiral current correlator, which turns out
to be particularly effective to control the pollution by higher twist
components of spectator mesons. The result for each channel depends on the
distribution amplitude of the the producing meson. The leading twist
distribution amplitudes of the related heavy mesons and charmonium are worked
out by a model approach in the reasonable way. A practical scenario is
suggested to understand the behavior of weak form factors in the whole
kinematically accessible ranges. The decay widths and branching ratios are
estimated for several $B$($B_c$) decay modes of current interest.
| arxiv topic:hep-ph |
arxiv_dataset-429801.0573 | Marginally Deformed Rolling Tachyon around the Tachyon Vacuum in Open
String Field Theory
hep-th
We investigate the string field theory around the tachyon vacuum. A pure
gauge form of the solution is constructed at the tachyon vacuum. For a special
choice of the gauge function for the pure gauge form, marginal deformation from
the tachyon vacuum is allowed due to the nontrivial roles of Schnabl's analytic
vacuum solution. We obtain an exact rolling tachyon solution which describes
the late time behaviors of D-brane decay.
| arxiv topic:hep-th |
arxiv_dataset-430801.0673 | Valence band orbital polarization in III-V ferromagnetic semiconductors
cond-mat.mtrl-sci cond-mat.mes-hall
The element-specific technique of x-ray magnetic circular dichroism (XMCD) is
used to directly determine the magnitude and character of the valence band
orbital magnetic moments in (III,Mn)As ferromagnetic semiconductors. A distinct
dichroism is observed at the As K absorption edge, yielding an As 4p orbital
magnetic moment of around -0.1 Bohr magnetons per valence band hole. This is
strongly influenced by strain, indicating its crucial influence on the magnetic
anisotropy. The dichroism at the Ga K edge is much weaker. The K edge XMCD
signals for Mn and As both have positive sign, which indicates the important
contribution of Mn 4p states to the Mn K edge spectra.
| arxiv topic:cond-mat.mtrl-sci cond-mat.mes-hall |
arxiv_dataset-431801.0773 | Stimulus dependence of the collective vibration of atoms in an
icosahedral cluster
cond-mat.mes-hall
Molecular dynamics calculations of the vibrational behavior of atoms in a
Lennard-Jones 147-atom cluster revealed that the relaxation and the stability
of the collective vibration of atoms in the cluster depend on the extent of the
mechanical disturbance. A relatively larger-scale perturbation will cause a
faster decay of the vibration magnitude, the potential and the kinetic energy
compared to the vibration stimulated by a small-scale stimulus.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-432801.0873 | Inequalities and Ehrhart $\delta$-Vectors
math.CO
For any lattice polytope $P$, we consider an associated polynomial
$\bar{\delta}_{P}(t)$ and describe its decomposition into a sum of two
polynomials satisfying certain symmetry conditions. As a consequence, we
improve upon known inequalities satisfied by the coefficients of the Ehrhart
$\delta$-vector of a lattice polytope. We also provide combinatorial proofs of
two results of Stanley that were previously established using techniques from
commutative algebra. Finally, we give a necessary numerical criterion for the
existence of a regular unimodular lattice triangulation of the boundary of a
lattice polytope.
| arxiv topic:math.CO |
arxiv_dataset-433801.0973 | The spectrum of charmed mesons from dynamical anisotropic lattices
hep-lat
We present our preliminary analysis for the chamonium and D$_s$ spectra
obtained from N$_f=2$ dynamical anisotropic lattices. We use 12$^3\times 80$
lattices with lattice spacing $a_t=7.35$ GeV$^{-1}$ and anisotropy of six.
Meson correlators are computed using all-to-all propagators together with
variational analysis.
| arxiv topic:hep-lat |
arxiv_dataset-434801.1073 | Emerging singularities in the bouncing loop cosmology
gr-qc hep-th
In this paper we calculate $\mathcal{O}(\mu^4)$ corrections from holonomies
in the Loop Quantum Gravity, usually not taken into account. Allowance of the
corrections of this kind is equivalent with the choice of the new quatization
scheme. Quantization ambiguities in the Loop Quantum Cosmology allow for this
additional freedom and presented corrections are consistent with the standard
approach. We apply these corrections to the flat FRW cosmological model and
calculate the modified Friedmann equation. We show that the bounce appears in
the models with the standard $\mathcal{O}(\mu^2)$ quantization scheme is
shifted to the higher energies $\rho_{\text{bounce}} = 3 \rho_{\text{c}}$. Also
a pole in the Hubble parameter appears for $\rho_{\text{pole}} = {3/2}
\rho_{\text{c}}$ corresponding to \emph{hyper-inflation/deflation} phases. This
pole represents a curvature singularity at which the scale factor is finite. In
this scenario the singularity and bounce co-exist. Moreover we find that an
ordinary bouncing solution appears only when quantum corrections in the lowest
order are considered. Higher order corrections can lead to the nonperturbative
effects.
| arxiv topic:gr-qc hep-th |
arxiv_dataset-435801.1173 | Comment on "Design of a broadband highly dispersive pure silica photonic
crystal fiber" by Subbaraman et al
physics.optics
In a recent paper, Subbaraman et al report a theoretical and numerical study
of highly dispersive pure silica photonic crystal fiber supporting
group-velocity dispersion exceeding -2*10^4 ps/nm/km. This comment argues that
the authors only consider one out of the two sides of the same coin, by not
taking the corresponding beating length into account.
| arxiv topic:physics.optics |
arxiv_dataset-436801.1273 | X-Ray Propagation in Tapered Waveguides: Simulation and Optimization
cond-mat.mtrl-sci
We use the parabolic wave equation to study the propagation of x-rays in
tapered waveguides by numercial simulation and optimization. The goal of the
study is to elucidate how beam concentration can be best achieved in x-ray
optical nanostructures. Such optimized waveguides can e.g. be used to
investigate single biomolecules. Here, we compare tapering geometries, which
can be parametrized by linear and third-order (Bezier-type) functions and can
be fabricated using standard e-beam litography units. These geometries can be
described in two and four-dimensional parameter spaces, respectively. In both
geometries, we observe a rugged structure of the optimization problem's ``gain
landscape''. Thus, the optimization of x-ray nanostructures in general will be
a highly nontrivial optimization problem.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-437801.1373 | Fractional flux quanta at intrinsic metallic interfaces of
noncentrosymmetric superconductors
cond-mat.supr-con
We examine intrinsic interfaces separating crystalline twin domains of
opposite spin-orbit coupling in a noncentrosymmetric superconductor such as
CePt3Si. At these interfaces, low-energy Andreev bound states occur as a
consequence of parity-mixed Cooper pairing, and a superconducting phase which
violates time reversal symmetry can be realized. This provides an environment
allowing flux lines with fractional flux quanta to be formed at the interface.
Their presence could have strong implications on the flux creep behavior in
such superconductors.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-438801.1473 | Compatibility of Einstein minimally coupled self interacting scalar
field theory with the solar system tests of gravity
gr-qc
We examine the compatibility of the Einstein minimally coupled
self-interacting scalar field theory with the local tests of gravity. We find
that apart from the trivial case of the Schwarzschild-de Sitter solution with
constant scalar field the theory does not admit any other static solution,
which is consistent with the solar system tests of gravity.
| arxiv topic:gr-qc |
arxiv_dataset-439801.1573 | Taking a shower in Youth Hostels: risks and delights of heterogeneity
physics.soc-ph cs.GT
Tuning one's shower in some hotels may turn into a challenging coordination
game with imperfect information. The temperature sensitivity increases with the
number of agents, making the problem possibly unlearnable. Because there is in
practice a finite number of possible tap positions, identical agents are
unlikely to reach even approximately their favorite water temperature. We show
that a population of agents with homogeneous strategies is evolutionary
unstable, which gives insights into the emergence of heterogeneity, the latter
being tempting but risky.
| arxiv topic:physics.soc-ph cs.GT |
arxiv_dataset-440801.1673 | Downsizing by Shutdown in Red Galaxies
astro-ph
We address the origin of the `downsizing' of elliptical galaxies, according
to which the stars in more massive galaxies formed earlier and over a shorter
period than those in less massive galaxies. We show that this could be the
natural result of a shutdown of star formation in dark matter haloes above a
critical mass of 10^12MSun. This is demonstrated using a semianalytic
simulation of galaxy formation within the standard hierarchical scenario of
structure formation. The assumed threshold mass is motivated by the prediction
of stable shock heating above this mass and the finding that such a shutdown
reproduces the observed distribution of galaxies in luminosity and colour.The
shutdown at a critical halo mass introduces a characteristic stellar mass for
the transition of galaxies into the `red sequence' of the galaxy
colour-magnitude diagram. Central galaxies of haloes that are more massive
today have reached this mass earlier and can therefore grow further along the
red sequence by dry mergers, ending up more massive and containing older stars.
Small galaxies formed in haloes below the critical mass can shutdown late, when
they fall into haloes above the critical mass and become satellites. While our
semianalytic simulation that incorporates an explicit shutdown reproduces
downsizing as inferred from the stellar ages of ellipticals, we explain why it
is much harder to detect downsizing using the mass functions of different
galaxy types.
| arxiv topic:astro-ph |
arxiv_dataset-441801.1773 | Generation of d-wave coupling in the two-dimensional Hubbard model from
functional renormalization
cond-mat.str-el hep-th
Within the two-dimensional repulsive t-t'-Hubbard model, an attractive
coupling in the d-wave pairing channel is induced by antiferromagnetic
fluctuations. We investigate this coupling using functional renormalization
group equations. The momentum dependent d-wave coupling can be bosonized by the
use of scale dependent field transformations. We propose an effective coarse
grained model for the Hubbard model which is based on the exchange of
antiferromagnetic and d-wave collective bosons.
| arxiv topic:cond-mat.str-el hep-th |
arxiv_dataset-442801.1873 | Noncommutative Riesz transforms -- a probabilistic approach
math.OA math.FA
For $2\le p<\infty$ we show the lower estimates
\[ \|A^{\frac 12}x\|_p \kl c(p)\max\{\pl \|\Gamma(x,x)^{{1/2}}\|_p,\pl
\|\Gamma(x^*,x^*)^{{1/2}}\|_p\} \] for the Riesz transform associated to a
semigroup $(T_t)$ of completely positive maps on a von Neumann algebra with
negative generator $T_t=e^{-tA}$, and gradient form \[ 2\Gamma(x,y)\lel
Ax^*y+x^*Ay-A(x^*y)\pl .\] As additional hypothesis we assume that $\Gamma^2\gl
0$ and the existence of a Markov dilation for $(T_t)$. We give applications to
quantum metric spaces and show the equivalence of semigroup Hardy norms and
martingale Hardy norms derived from the Markov dilation. In the limiting case
we obtain a viable definition of BMO spaces for general semigroups of
completely positive maps which can be used as an endpoint for interpolation.
For torsion free ordered groups we construct a connection between Riesz
transforms and the Hilbert transform induced by the order.
| arxiv topic:math.OA math.FA |
arxiv_dataset-443801.1973 | A non-universal transition to asymptotic freedom in low-energy quantum
gravity
hep-th gr-qc quant-ph
The model of low-energy quantum gravity by the author has the property of
asymptotic freedom at very short distances. The character of transition to
asymptotic freedom is studied here. It is shown that this transition is not
universal, but the one obeys the scaling rule: the range of this transition in
units of $r/E^{1/2}$, where $r$ is a distance between particles and $E$ is an
energy of the screening particle, is the same for any micro-particle. This
range for a proton is between $10^{-11} - 10^{-13}$ meter, while for an
electron it is approximately between $10^{-13} - 10^{-15}$ meter.
| arxiv topic:hep-th gr-qc quant-ph |
arxiv_dataset-444801.2073 | Time translation of quantum properties
quant-ph
Based on the notion of time translation, we develop a formalism to deal with
the logic of quantum properties at different times. In our formalism it is
possible to enlarge the usual notion of context to include composed properties
involving properties at different times. We compare our results with the theory
of consistent histories.
| arxiv topic:quant-ph |
arxiv_dataset-445801.2173 | Heavy quark diffusion in QCD and N=4 SYM at next-to-leading order
hep-ph
We present the full details of a calculation at next-to-leading order of the
momentum diffusion coefficient of a heavy quark in a hot, weakly coupled, QCD
plasma. Corrections arise at O(g_s); physically they represent interference
between overlapping scatterings, as well as soft, electric scale (p ~ gT) gauge
field physics, which we treat using the hard thermal loop (HTL) effective
theory. In 3-color, 3-flavor QCD, the momentum diffusion constant of a
fundamental representation heavy quark at NLO is kappa = (16\pi/3) alpha_s^2
T^3 (log(1/g) + 0.07428 + 1.9026 g). We extend the computation to a heavy
fundamental representation ``probe'' quark in large N_c, N=4 Super Yang-Mills
theory, where the result is kappa^{SYM}= (lambda^2 T^3)(6\pi)
(log(1/\sqrt{\lambda}) + 0.4304 + 0.8010 \sqrt{lambda}) (where lambda=g_s^2 N_c
is the t'Hooft coupling). In the absence of some resummation technique, the
convergence of perturbation theory is poor.
| arxiv topic:hep-ph |
arxiv_dataset-446801.2273 | Where are the hot ion lines in classical T Tauri stars formed?
astro-ph
Classical T Tauri stars show a plethora of in- and outflow signatures in a
variety of wavelengths bands. In order to constrain gas velocities and
temperatures we analyse the emission in the hot ion lines. We use all available
archival FUSE spectra of CTTS to measure the line widths, fluxes and shifts and
complement this sample with HST/GHRS and HST/STIS data. We present theoretical
estimates for temperatures reached in possible emission models like jets,
winds, disks and accretion funnels and look for correlations with X-ray lines
and absorption properties. We find line shifts in the range from -170 km/s and
+100 km/s. Most linewidths exceed the stellar rotational broadening. Those CTTS
with blue-shifted lines also show excess absorption in X-rays. CTTS single out
from MS stars by their large ratio of the O VII to O VI luminosities. No single
emission mechanism can be found for all objects. The properties of those stars
with blue-shifted lines are compatible with an origin in a shock-heated
dust-depleted outflow.
| arxiv topic:astro-ph |
arxiv_dataset-447801.2373 | Electron localization function for two-dimensional systems
cond-mat.str-el
The concept of the electron localization function (ELF) is extended to
two-dimensional (2D) electron systems. We show that the topological properties
of the ELF in 2D are considerably simpler than in molecules studied previously.
We compute the ELF and demonstrate its usefulness for various physical 2D
systems, focusing on semiconductor quantum dots that effectively correspond to
a confined 2D electron gas. The ELF visualizes the shell structure of harmonic
quantum dots and provides insight into electron bonding in quantum-dot
molecules. In external magnetic fields the ELF is found to be a useful measure
of vorticity when analyzing the properties of quantum-Hall droplets. We show
that the current-dependent term in the ELF expression is important in magnetic
fields.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-448801.2473 | The fidelity approach to the Hubbard model
cond-mat.stat-mech cond-mat.other quant-ph
We use the fidelity approach to quantum critical points to study the zero
temperature phase diagram of the one-dimensional Hubbard model. Using a variety
of analytical and numerical techniques, we analyze the fidelity metric in
various regions of the phase diagram, with particular care to the critical
points. Specifically we show that close to the Mott transition, taking place at
on-site repulsion U=0 and electron density n=1, the fidelity metric satisfies
an hyper-scaling form which we calculate. This implies that in general, as one
approaches the critical point U=0, n=1, the fidelity metric tends to a limit
which depends on the path of approach. At half filling, the fidelity metric is
expected to diverge as U^{-4} when U is sent to zero.
| arxiv topic:cond-mat.stat-mech cond-mat.other quant-ph |
arxiv_dataset-449801.2573 | Transient Emissions from Radio-Active Stars: Implications for Wide-Field
Radio Surveys
astro-ph
Variability is a common characteristic of magnetically active stars. Flaring
variability is usually interpreted as the observable consequence of transient
magnetic reconnection processes happening in the stellar outer atmosphere.
Stellar flares have been observed now across 11 decades in
wavelength/frequency/energy; such a large span implies that a range of physical
processes takes place during such events. Despite the fact that stellar radio
flares have long been recognized and studied, key unanswered questions remain.
I will highlight what, in my opinion, are some of these questions. I will also
describe recent results on stellar flare emissions at radio wavelengths,
discussing the nature of coherent and incoherent emissions and the prospects of
wide-field radio imaging telescopes for studying such events.
| arxiv topic:astro-ph |
arxiv_dataset-450801.2673 | Cosmological particle production in emergent rainbow spacetimes
gr-qc
We investigate cosmological particle production in spacetimes where Lorentz
invariance emerges in the infrared limit, but is explicitly broken in the
ultraviolet regime. Our specific model focuses on the boost subgroup that
supports CPT invariance and results in a momentum-dependent dispersion
relation. Motivated by previous studies on spacetimes emerging from a
microscopic substrate, we show how these modifications naturally lead to
momentum-dependent rainbow metrics. Firstly, we investigate the possibility of
reproducing cosmological particle production in spacetimes emerging from real
Bose gases. We have studied the influence of non-perturbative ultraviolet
corrections in time-dependent analogue spacetimes, leading to
momentum-dependent emergent rainbow spacetimes. Within certain limits the
analogy is sufficiently good to simulate relativistic quantum field theory in
time-dependent classical backgrounds, and the quantum effects are approximately
robust against the model-dependent modifications. Secondly, we analyze how
significantly the particle production process deviates from the common picture.
While very low-energy modes do not see the difference at all, some modes
"re-enter the Hubble horizon" during the inflationary epoch, and extreme
ultraviolet modes are completely insensitive to the expansion.
| arxiv topic:gr-qc |
arxiv_dataset-451801.2773 | Symmetry Extensions and Their Physical Reasons in the Kinetic and
Hydrodynamic Plasma Models
math-ph math.MP
Characteristic examples of continuous symmetries in hydrodynamic plasma
theory (partial differential equations) and in kinetic Vlasov-Maxwell models
(integro-differential equations) are considered. Possible symmetry extensions
conditional and extended symmetries are discussed. Physical reasons for these
symmetry extensions are clarified.
| arxiv topic:math-ph math.MP |
arxiv_dataset-452801.2873 | Measurement-based approach to entanglement generation in coupled quantum
dots
quant-ph
Measurements provide a novel mechanism for generating the entanglement
resource necessary for performing scalable quantum computation. Recently, we
proposed a method for performing parity measurements in a coupled quantum dot
system. In this paper we generalise this scheme and perform a comprehensive
analytic and numerical study of environmental factors. We calculate the effects
of possible error sources including non-ideal photon detectors, ineffective
spin-selective excitation and dot distinguishability (both spatial and
spectral). Furthermore, we present an experimental approach for verifying the
success of the parity measurement.
| arxiv topic:quant-ph |
arxiv_dataset-453801.2973 | A Model to Explain Varying $\Lambda$, $G$ and $\sigma^2$ Simultaneously
gr-qc astro-ph hep-th
Models with varying cosmical parameters, which were earlier regarded
constant, are getting attention. However, different models are usually invoked
to explain the evolution of different parameters. We argue that whatever
physical process is responsible for the evolution of one parameter, should also
be responsible for the evolution of others. This means that the different
parameters are coupled together somehow. Based on this guiding principle, we
investigate a Bianchi type I model with variable $\Lambda$ and $G$, in which
$\Lambda$, $G$ and the shear parameter $\sigma^2$, all are coupled. It is
interesting that the resulting model reduces to the FLRW model for large $t$
with $G$ approaching a constant.
| arxiv topic:gr-qc astro-ph hep-th |
arxiv_dataset-454801.3073 | Large Deviations Analysis for the Detection of 2D Hidden Gauss-Markov
Random Fields Using Sensor Networks
cs.IT math.IT
The detection of hidden two-dimensional Gauss-Markov random fields using
sensor networks is considered. Under a conditional autoregressive model, the
error exponent for the Neyman-Pearson detector satisfying a fixed level
constraint is obtained using the large deviations principle. For a symmetric
first order autoregressive model, the error exponent is given explicitly in
terms of the SNR and an edge dependence factor (field correlation). The
behavior of the error exponent as a function of correlation strength is seen to
divide into two regions depending on the value of the SNR. At high SNR,
uncorrelated observations maximize the error exponent for a given SNR, whereas
there is non-zero optimal correlation at low SNR. Based on the error exponent,
the energy efficiency (defined as the ratio of the total information gathered
to the total energy required) of ad hoc sensor network for detection is
examined for two sensor deployment models: an infinite area model and and
infinite density model. For a fixed sensor density, the energy efficiency
diminishes to zero at rate O(area^{-1/2}) as the area is increased. On the
other hand, non-zero efficiency is possible for increasing density depending on
the behavior of the physical correlation as a function of the link length.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-455801.3173 | The impact of encounters on the members of Local Group Analogs. A view
from GALEX
astro-ph
The bright galaxy population of the Local Group Analog (LGA) LGG 225 has been
imaged with the Galaxy Evolution Explorer (GALEX) through its Far- and Near-UV
wavebands. A significant fraction of the group members appear to underwent
recent/on-going interaction episodes that strongly disturbed overall galaxy
morphology. UV-bright regions, sites of intense star formation activity
accompanied by intense dust extinction, mark the galaxy outskirts forming
irregular structures and tails. Compared to the Local Group, LGG 225 seems thus
to be experiencing a more intense and active evolutionary phase.
| arxiv topic:astro-ph |
arxiv_dataset-456801.3273 | Reconciling the Metallicity Distributions of Gamma-ray Burst, Damped
Lyman-alpha, and Lyman-break Galaxies at z=3
astro-ph
We test the hypothesis that the host galaxies of long-duration gamma-ray
bursts (GRBs) as well as quasar-selected damped Lyman-alpha (DLA) systems are
drawn from the population of UV-selected star-forming, high-z galaxies
(generally referred to as Lyman-break galaxies). Specifically, we compare the
metallicity distributions of the GRB and DLA populations to simple models where
these galaxies are drawn randomly from the distribution of star-forming
galaxies according to their star-formation rate and HI cross-section
respectively. We find that it is possible to match both observational
distributions assuming very simple and constrained relations between
luminosity, metallicity and HI sizes. The simple model can be tested by
observing the luminosity distribution of GRB host galaxies and by measuring the
luminosity and impact parameters of DLA selected galaxies as a function of
metallicity. Our results support the expectation that GRB and DLA samples, in
contrast to magnitude limited surveys, provide an almost complete census of z=3
star-forming galaxies that are not heavily dust-obscured.
| arxiv topic:astro-ph |
arxiv_dataset-457801.3373 | Integrally closed and componentwise linear ideals
math.AC math.AG
In two dimensional regular local rings integrally closed ideals have a unique
factorization property and have a Cohen-Macaulay associated graded ring. In
higher dimension these properties do not hold for general integrally closed
ideals and the goal of the paper is to identify a subclass of integrally closed
ideals for which they do. We restrict our attention to 0-dimensional
homogeneous ideals in polynomial rings $R$ of arbitrary dimension and identify
a class of integrally closed ideals, the Goto-class $\G^*$, that is closed
under product and that has a suitable unique factorization property. Ideals in
$\G^*$ have a Cohen-Macaulay associated graded ring if either they are monomial
or $\dim R\leq 3$. Our approach is based on the study of the relationship
between the notions of integrally closed, contracted, full and componentwise
linear ideals.
| arxiv topic:math.AC math.AG |
arxiv_dataset-458801.3473 | A Modified K\"ahler-Ricci Flow
math.DG
In this note, a modified K\"ahler-Ricci flow is introduced and studied. The
main point is to show the flexibility of K\"ahler-Ricci flow and summarize some
useful techniques.
| arxiv topic:math.DG |
arxiv_dataset-459801.3573 | Stability analysis and \mu-synthesis control of brake systems
physics.class-ph math.DS
The concept of friction-induced brake vibrations, commonly known as judder,
is investigated. Judder vibration is based on the class of geometrically
induced or kinematic constraint instability. After presenting the modal
coupling mechanism and the associated dynamic model, a stability analysis as
well as a sensitivity analysis have been conducted in order to identify
physical parameters for a brake design avoiding friction-induced judder
instability. Next, in order to reduce the size of the instability regions in
relation to possible system parameter combinations, robust stability via
\mu-synthesis is applied. By comparing the unstable regions between the initial
and controlled brake system, some general indications emerge and it appears
that robust stability via \mu-synthesis has some effect on the instability of
the brake system.
| arxiv topic:physics.class-ph math.DS |
arxiv_dataset-460801.3673 | Variational Functionals for Excited States
quant-ph
Functionals that have local minima at the excited states of a non degenerate
Hamiltonian are presented. Then, improved mutually orthogonal approximants of
the ground and the first excited state are reported.
| arxiv topic:quant-ph |
arxiv_dataset-461801.3773 | Graph-Based Classification of Self-Dual Additive Codes over Finite
Fields
cs.IT math.CO math.IT quant-ph
Quantum stabilizer states over GF(m) can be represented as self-dual additive
codes over GF(m^2). These codes can be represented as weighted graphs, and
orbits of graphs under the generalized local complementation operation
correspond to equivalence classes of codes. We have previously used this fact
to classify self-dual additive codes over GF(4). In this paper we classify
self-dual additive codes over GF(9), GF(16), and GF(25). Assuming that the
classical MDS conjecture holds, we are able to classify all self-dual additive
MDS codes over GF(9) by using an extension technique. We prove that the minimum
distance of a self-dual additive code is related to the minimum vertex degree
in the associated graph orbit. Circulant graph codes are introduced, and a
computer search reveals that this set contains many strong codes. We show that
some of these codes have highly regular graph representations.
| arxiv topic:cs.IT math.CO math.IT quant-ph |
arxiv_dataset-462801.3873 | 2-Cocycles of Original Deformative Schr\"{o}dinger-Virasoro Algebras
math.RA
Both original and twisted Schr\"{o}dinger-Virasoro algebras also their
deformations were introduced and investigated in a series of papers by Henkel,
Roger and Unterberger. In the present paper we aim to determine the 2-cocycles
of original deformative Schr\"{o}dinger-Virasoro algebras.
| arxiv topic:math.RA |
arxiv_dataset-463801.3973 | Boom and bust in continuous time evolving economic model
q-fin.GN physics.soc-ph
We show that a simple model of a spatially resolved evolving economic system,
which has a steady state under simultaneous updating, shows stable oscillations
in price when updated asynchronously. The oscillations arise from a gradual
decline of the mean price due to competition among sellers competing for the
same resource. This lowers profitability and hence population but is followed
by a sharp rise as speculative sellers invade the large un-inhabited areas.
This cycle then begins again.
| arxiv topic:q-fin.GN physics.soc-ph |
arxiv_dataset-464801.4073 | Magnetoelectric Control of Domain Walls in a Ferrite Garnet Film
cond-mat.mtrl-sci
The effect of magnetic domain boundaries displacement induced by electric
field is observed in epitaxial ferrite garnet films (on substrates with the
(210) crystallographic orientation). The effect is odd with respect to the
electric field (the direction of wall displacement changes with the polarity of
the voltage) and even with respect to the magnetization in domains. The
inhomogeneous magnetoelectric interaction as a possible mechanism of the effect
is proposed.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-465801.4173 | Timing and spectral properties of the accreting millisecond pulsar SWIFT
J1756.9-2508
astro-ph
SWIFT J1756.9-2508 is one of the few accreting millisecond pulsars (AMPs)
discovered to date. We report here the results of our analysis of its aperiodic
X-ray variability, as measured with the Rossi X-ray Timing Explorer during the
2007 outburst of the source. We detect strong (~35%) flat-topped broadband
noise throughout the outburst with low characteristic frequencies (~0.1 Hz).
This makes SWIFT J1756.9-2508 similar to the rest of AMPs and to other low
luminosity accreting neutron stars when they are in their hard states, and
enables us to classify this AMP as an atoll source in the extreme island state.
We also find a hard tail in its energy spectrum extending up to 100 keV, fully
consistent with such source and state classification.
| arxiv topic:astro-ph |
arxiv_dataset-466801.4273 | On the importance of the wind emission to the optical continuum of OB
supergiants
astro-ph
Thermal wind emission in the form of free-free and free-bound emission is
known to show up in the infrared and radio continuum of hot and massive stars.
For OB supergiants with moderate mass loss rates and a wind velocity
distribution with \beta = 0.8...1.0, no influence of the wind to the optical
continuum, i.e. for \lambda < 1 micron, is expected. Investigations of stellar
and wind parameters of OB supergiants over the last few years suggest, however,
that for many objects \beta is much higher than 1.0, reaching values up to 3.5.
We investigate the influence of the free-free and free-bound emission on the
emerging radiation, especially at optical wavelengths, from OB supergiants
having wind velocity distributions with \beta > 1. For the case of a
spherically symmetric, isothermal wind in local thermodynamical equilibrium
(LTE) we calculate the free-free and free-bound processes and the emerging wind
and total continuum spectra. We localize the generation region of the optical
wind continuum and especially focus on the influence of a \beta-type wind
velocity distribution with \beta > 1 on the formation of the wind continuum at
optical wavelengths. The optical wind continuum is found to be generated within
about 2 R_* which is exactly the wind region where \beta strongly influences
the density distribution. We find that for \beta > 1, the continuum of a
typical OB supergiant can indeed be contaminated with thermal wind emission,
even at optical wavelengths. The strong increase in the optical wind emission
is dominantly produced by free-bound processes.
| arxiv topic:astro-ph |
arxiv_dataset-467801.4373 | Evolution of massive stars at very low metallicity including rotation
and binary interactions
astro-ph
We discuss recent models on the evolution of massive stars at very low
metallicity including the effects of rotation, magnetic fields and binarity.
Very metal poor stars lose very little mass and angular momentum during the
main sequence evolution, and rotation plays a dominant role in their evolution.
In rapidly rotating massive stars, the rotationally induced mixing time scale
can be even shorter than the nuclear time scale throughout the main sequence.
The consequent quasi-chemically homogeneous evolution greatly differs from the
standard massive star evolution that leads to formation of red giants with
strong chemical stratification. Interesting outcomes of such a new mode of
evolution include the formation of rapidly rotating massive Wolf-Rayet stars
that emit large amounts of ionizing photons, the formation of a long gamma-ray
bursts and a hypernovae, and the production of large amounts of primary
nitrogen. We show that binary interactions can further enhance the effects of
rotation, as mass accretion in a close binary spins up the secondary.
| arxiv topic:astro-ph |
arxiv_dataset-468801.4473 | Microlensing of the X-ray, UV and optical emission regions of quasars:
Simulations of the time-scales and amplitude variations of microlensing
events
astro-ph
We consider the influence of microlensing on different spectral bands of
lensed QSOs. We assumed that the emitting X-ray, UV and optical regions are
different in size, but that the continuum emission in these spectral bands is
originating from an accretion disc. Estimations of the time scales for
microlensing and flux amplification in different bands are given. We found that
the microlensing duration should be shorter in the X-ray (several months) than
in UV/optical emitting region (several years). This result indicates that
monitoring of the X-ray variations in lensed QSOs that show a 'flux anomaly'
can clarify the source of this anomaly.
| arxiv topic:astro-ph |
arxiv_dataset-469801.4573 | How to use magnetic field information for coronal loop identification?
astro-ph
The structure of the solar corona is dominated by the magnetic field because
the magnetic pressure is about four orders of magnitude higher than the plasma
pressure. Due to the high conductivity the emitting coronal plasma (visible
e.g. in SOHO/EIT) outlines the magnetic field lines. The gradient of the
emitting plasma structures is significantly lower parallel to the magnetic
field lines than in the perpendicular direction. Consequently information
regarding the coronal magnetic field can be used for the interpretation of
coronal plasma structures. We extrapolate the coronal magnetic field from
photospheric magnetic field measurements into the corona. The extrapolation
method depends on assumptions regarding coronal currents, e.g. potential fields
(current free) or force-free fields (current parallel to magnetic field). As a
next step we project the reconstructed 3D magnetic field lines on an EIT-image
and compare with the emitting plasma structures. Coronal loops are identified
as closed magnetic field lines with a high emissivity in EIT and a small
gradient of the emissivity along the magnetic field.
| arxiv topic:astro-ph |
arxiv_dataset-470801.4673 | Gamma ray and Neutrino fluxes from a cosmological dark matter simulation
astro-ph
In this paper, we estimate the gamma-ray and neutrino fluxes coming from dark
matter annihilation in a Milky Way framework provided by a recent N-BODY
HORIZON simulation. We first study the characteristics of the simulation and
highlight the mass distribution within the galactic halo. The general dark
matter density has a typical $r^{-3}$ power law for large radii, but the inner
behaviour is poorly constrained below the resolution of the simulation ($\sim
200$ pc). We identify clumps and subclumps and analyze their distribution, as
well as their internal structure. Inside the clumps, the power law is rather
universal, $r^{-2.5}$ in the outer part with again strong uncertainties for
smaller radii, especially for light clumps. We show a full-sky map of the
astrophysical contribution to the gamma-ray or neutrino fluxes in this N-body
framework. Using quite model independent and general assumptions for the high
energy physics part, we evaluate the possible absolute fluxes and show some
benchmark regions for the experiments GLAST, EGRET, and a km3 size extension of
ANTARES like the KM3NeT project. While individual clumps seem to be beyond
detection reach, the galactic center region is promising and GLAST could be
sensitive to the geometry and the structure of its dark matter distribution.
The detection by a km3 version of ANTARES is, however, more challenging due to
a higher energy threshold. We also point out that the lack of resolution leaves
the inner structure of subhalos poorly constrained. Using the same clump
spectrum and mass fraction, a clump luminosity boost of order ten can be
achieved with a steeper profile in the inner part of the sub-halos.
| arxiv topic:astro-ph |
arxiv_dataset-471801.4773 | Effective structure theorems for symplectic spaces via height
math.NT
Given a $2k$-dimensional symplectic space $(Z,F)$ in $N$ variables, $1 < 2k
\leq N$, over a global field $K$, we prove the existence of a symplectic basis
for $(Z,F)$ of bounded height. This can be viewed as a version of Siegel's
lemma for a symplectic space. As corollaries of our main result, we prove the
existence of a small-height decomposition of $(Z,F)$ into hyperbolic planes, as
well as the existence of two generating flags of totally isotropic subspaces.
These present analogues of known results for quadratic spaces. A distinctive
feature of our argument is that it works simultaneously for essentially any
field with a product formula, algebraically closed or not. In fact, we prove an
even more general version of these statements, where canonical height is
replaced with twisted height. All bounds on height are explicit.
| arxiv topic:math.NT |
arxiv_dataset-472801.4873 | Counting nodal domains on surfaces of revolution
nlin.CD nlin.SI
We consider eigenfunctions of the Laplace-Beltrami operator on special
surfaces of revolution. For this separable system, the nodal domains of the
(real) eigenfunctions form a checker-board pattern, and their number $\nu_n$ is
proportional to the product of the angular and the "surface" quantum numbers.
Arranging the wave functions by increasing values of the Laplace-Beltrami
spectrum, we obtain the nodal sequence, whose statistical properties we study.
In particular we investigate the distribution of the normalized counts
$\frac{\nu_n}{n}$ for sequences of eigenfunctions with $K \le n\le K + \Delta
K$ where $K,\Delta K \in \mathbb{N}$. We show that the distribution approaches
a limit as $K,\Delta K\to\infty$ (the classical limit), and study the leading
corrections in the semi-classical limit. With this information, we derive the
central result of this work: the nodal sequence of a mirror-symmetric surface
is sufficient to uniquely determine its shape (modulo scaling).
| arxiv topic:nlin.CD nlin.SI |
arxiv_dataset-473802.0003 | On mobile sets in the binary hypercube
math.CO cs.IT math.IT
If two distance-3 codes have the same neighborhood, then each of them is
called a mobile set. In the (4k+3)-dimensional binary hypercube, there exists a
mobile set of cardinality 2*6^k that cannot be split into mobile sets of
smaller cardinalities or represented as a natural extension of a mobile set in
a hypercube of smaller dimension. Keywords: mobile set; 1-perfect code.
| arxiv topic:math.CO cs.IT math.IT |
arxiv_dataset-474802.0103 | Curvature corrections to the low energy effective theory in 6D
regularized braneworlds
hep-th astro-ph gr-qc
We study the effective gravitational theory on a brane in a six-dimensional
Einstein-Maxwell model of flux compactification, regularizing a conical defect
as a codimension-one brane. We employ the gradient expansion technique valid at
low energies. A lowest order analysis showed that standard four-dimensional
Einstein gravity is reproduced on the brane. We extend this study to include
second order corrections in the effective equations, and show that the
correction term is given by a quadratic energy-momentum tensor. Taking the
thin-brane limit where the regularized brane shrinks to the pole, we find that
the second order metric diverges logarithmically on the brane, giving rise to
divergences in the brane effective action. Away from the branes, the effective
action is however well-defined.
| arxiv topic:hep-th astro-ph gr-qc |
arxiv_dataset-475802.0203 | The Little Randall-Sundrum Model at the Large Hadron Collider
hep-ph hep-ex hep-th
We present a predictive warped model of flavor that is cut off at an
ultraviolet scale O(10^3) TeV. This "Little Randall-Sundrum (LRS)" model is a
volume-truncation, by a factor $y \approx 6$, of the RS scenario and is
holographically dual to dynamics with number of colors larger by $y$. The LRS
couplings between Kaluza-Klein states and the Standard Model fields, including
the proton constituents, are explicitly calculable without ad hoc assumptions.
Assuming separate gauge and flavor dynamics, a number of unwanted contributions
to precision electroweak, $Z b\bar b$ and flavor observables are suppressed in
the LRS framework, compared with the corresponding RS case. An important
consequence of the LRS truncation, independent of precise details, is a
significant enhancement of the clean (golden) di-lepton LHC signals, by O(y^3),
due to a larger "$\rho$-photon" mixing and a smaller inter-composite coupling.
| arxiv topic:hep-ph hep-ex hep-th |
arxiv_dataset-476802.0303 | The Taiwanese-American Occultation Survey: The Multi-Telescope Robotic
Observatory
astro-ph
The Taiwanese-American Occultation Survey (TAOS) operates four fully
automatic telescopes to search for occultations of stars by Kuiper Belt
Objects. It is a versatile facility that is also useful for the study of
initial optical GRB afterglows. This paper provides a detailed description of
the TAOS multi-telescope system, control software, and high-speed imaging.
| arxiv topic:astro-ph |
arxiv_dataset-477802.0403 | Self-Control of Traffic Lights and Vehicle Flows in Urban Road Networks
physics.soc-ph physics.flu-dyn
Based on fluid-dynamic and many-particle (car-following) simulations of
traffic flows in (urban) networks, we study the problem of coordinating
incompatible traffic flows at intersections. Inspired by the observation of
self-organized oscillations of pedestrian flows at bottlenecks [D. Helbing and
P. Moln\'ar, Phys. Eev. E 51 (1995) 4282--4286], we propose a self-organization
approach to traffic light control. The problem can be treated as multi-agent
problem with interactions between vehicles and traffic lights. Specifically,
our approach assumes a priority-based control of traffic lights by the vehicle
flows themselves, taking into account short-sighted anticipation of vehicle
flows and platoons. The considered local interactions lead to emergent
coordination patterns such as ``green waves'' and achieve an efficient,
decentralized traffic light control. While the proposed self-control adapts
flexibly to local flow conditions and often leads to non-cyclical switching
patterns with changing service sequences of different traffic flows, an almost
periodic service may evolve under certain conditions and suggests the existence
of a spontaneous synchronization of traffic lights despite the varying delays
due to variable vehicle queues and travel times. The self-organized traffic
light control is based on an optimization and a stabilization rule, each of
which performs poorly at high utilizations of the road network, while their
proper combination reaches a superior performance. The result is a considerable
reduction not only in the average travel times, but also of their variation.
Similar control approaches could be applied to the coordination of logistic and
production processes.
| arxiv topic:physics.soc-ph physics.flu-dyn |
arxiv_dataset-478802.0503 | An X-ray Survey of Wolf-Rayet Stars in the Magellanic Clouds. I. The
Chandra ACIS Dataset
astro-ph
Wolf-Rayet (WR) stars are evolved massive stars with strong fast stellar
winds. WR stars in our Galaxy have shown three possible sources of X-ray
emission associated with their winds: shocks in the winds, colliding stellar
winds, and wind-blown bubbles; however, quantitative analyses of observations
are often hampered by uncertainties in distances and heavy foreground
absorption. These problems are mitigated in the Magellanic Clouds (MCs), which
are at known distances and have small foreground and internal extinction. We
have therefore started a survey of X-ray emission associated with WR stars in
the MCs using archival Chandra, ROSAT, and XMM-Newton observations. In the
first paper of this series, we report the results for 70 WR stars in the MCs
using 192 archival Chandra ACIS observations. X-ray emission is detected from
29 WR stars. We have investigated their X-ray spectral properties,
luminosities, and temporal variability. These X-ray sources all have
luminosities greater than a few times 10^32 ergs s^-1, with spectra indicative
of highly absorbed emission from a thin plasma at high temperatures typical of
colliding winds in WR+OB binary systems. Significant X-ray variability with
periods ranging from a few hours up to ~20 days is seen associated with several
WR stars. In most of these cases, the X-ray variability can be linked to the
orbital motion of the WR star in a binary system, further supporting the
colliding wind scenario for the origin of the X-ray emission from these stars.
| arxiv topic:astro-ph |
arxiv_dataset-479802.0603 | Trusted-HB: a low-cost version of HB+ secure against Man-in-The-Middle
attacks
cs.CR
Since the introduction at Crypto'05 by Juels and Weis of the protocol HB+, a
lightweight protocol secure against active attacks but only in a detection
based-model, many works have tried to enhance its security. We propose here a
new approach to achieve resistance against Man-in-The-Middle attacks. Our
requirements - in terms of extra communications and hardware - are surprisingly
low.
| arxiv topic:cs.CR |
arxiv_dataset-480802.0703 | From star clusters to dwarf galaxies: The properties of dynamically hot
stellar systems
astro-ph
(Abridged) Objects with radii of 10 to 100 pc and masses in the range from
10^6 to 10^8 M_sun have been discovered during the past decade. These so-called
ultra compact dwarf galaxies (UCDs) constitute a transition between classical
star clusters and elliptical galaxies in terms of radii, relaxation times and
V-band mass-to-light (M/L_V) ratios. Using new data, we find that the mass
interval from 10^6 to 10^7 M_sun is of special interest, because within this
range typical half-light radii and dynamical mass-to-light ratios begin to
increase compared to globular clusters, the highest stellar densities are
reached and typical median two-body relaxation times surpass a Hubble time. The
M/L_V ratios of the UCDs turn out to be incompatible with the predictions from
simple stellar population (SSP) models when using the canonical stellar initial
mass function (IMF), although SSPs probably are good approximations to the real
stellar populations in UCDs and the SSP models allow to account for metallicity
effects on the M/L_V ratio. This provides evidence for the UCDs either having
formed with an IMF different from the canonical one or containing dark matter.
We emphasise that almost all pressure-supported stellar systems ranging from
star clusters to massive elliptical galaxies have M/L_V ratios less than 10
M_sun/L_sun, and that only dSph satellite galaxies have M/L_V ratios greater
than 100 M_sun/L_sun and therewith form exceptional systems.
| arxiv topic:astro-ph |
arxiv_dataset-481802.0803 | Quasar spectral energy distribution in EUV restored from associated
absorbers: indications to the HeII opacity of the quasar accretion disk wind
astro-ph
(abridged) Aims. To reconstruct the spectral shape of the quasar ionizing
radiation in the extreme-UV range (1Ryd <= E < 10Ryd) from the analysis of
narrow absorption lines (NAL) of the associated systems. Methods. Computational
technique for inverse spectroscopic problems - Monte Carlo Inversion augmented
by procedure of the spectral shape recovering and modified to account for the
incomplete coverage of the light source. Results. The ionizing spectra
responsible for the ionization structure of the NAL systems require an
intensity depression at E > 4Ryd which is attributed to the HeII Lyman
continuum opacity (tau^HeII_c ~ 1). A most likely source of this opacity is a
quasar accretion disk wind. The corresponding column density of HI in the wind
is estimated as a few times 10^16 cm^-2. This amount of neutral hydrogen should
cause a weak continuum depression at lamb <= 912A (rest-frame), and a broad and
shallow absorption in HI Ly-alpha. If metallicity of the wind is high enough,
other resonance lines of OVI, NeVI-NeVIII, etc. are expected. In the analyzed
QSO spectra we do observe broad (stretching over 1000s km/s) and shallow (tau
<< 1) absorption troughs of HI Ly-alpha and OVI 1031,1037A...
| arxiv topic:astro-ph |
arxiv_dataset-482802.0903 | High-fidelity gates in a Josephson qubit
quant-ph
We demonstrate new experimental procedures for measuring small errors in a
superconducting quantum bit (qubit). By carefully separating out gate and
measurement errors, we construct a complete error budget and demonstrate single
qubit gate fidelities of 0.98, limited by energy relaxation. We also introduce
a new metrology tool -- a Ramsey interference error filter -- that can measure
the occupation probability of the state $\ket{2}$ down to $10^{-4}$, a
magnitude near the fault tolerant threshold.
| arxiv topic:quant-ph |
arxiv_dataset-483802.1003 | Spin-transfer switching and low-field precession in exchange-biased spin
valve nano-pillars
cond-mat.mtrl-sci
Using a three-dimensional focused-ion beam lithography process we have
fabricated nanopillar devices which show spin transfer torque switching at zero
external magnetic fields. Under a small in-plane external bias field, a
field-dependent peak in the differential resistance versus current is observed
similar to that reported in asymmetrical nanopillar devices. This is
interpreted as evidence for the low-field excitation of spin waves which in our
case is attributed to a spin-scattering asymmetry enhanced by the IrMn exchange
bias layer coupled to a relatively thin CoFe fixed layer.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-484802.1103 | Testing polynomial covariate effects in linear and generalized linear
mixed models
stat.AP
An important feature of linear mixed models and generalized linear mixed
models is that the conditional mean of the response given the random effects,
after transformed by a link function, is linearly related to the fixed
covariate effects and random effects. Therefore, it is of practical importance
to test the adequacy of this assumption, particularly the assumption of linear
covariate effects. In this paper, we review procedures that can be used for
testing polynomial covariate effects in these popular models. Specifically,
four types of hypothesis testing approaches are reviewed, i.e. R tests,
likelihood ratio tests, score tests and residual-based tests. Derivation and
performance of each testing procedure will be discussed, including a small
simulation study for comparing the likelihood ratio tests with the score tests.
| arxiv topic:stat.AP |
arxiv_dataset-485802.1203 | Chemical consequences of low star formation rates: stochastically
sampling the IMF
astro-ph
When estimating the abundances which result from a given star formation
event, it is customary to treat the IMF as a series of weight factors to be
applied to the stellar yields, as a function of mass, implicitly assuming one
is dealing with an infinite population. However, when the stellar population is
small, the standard procedure would imply the inclusion of fractional numbers
of stars at certain masses. We study the effects of small number statistics on
the resulting abundances by performing an statistical sampling of the IMF to
form a stellar population out of discrete numbers of stars. A chemical
evolution code then follows the evolution of the population, and traces the
resulting abundances. The process is repeated to obtain an statistical
distribution of the resulting abundances and their evolution. We explore the
manner in which different elements are affected, and how different abundances
converge to the infinite population limit as the total mass increases. We
include a discussion of our results in the context of dwarf spheroidal galaxies
and show the recently reported internal dispersions in abundance ratios for
dSph galaxies might be partly explained through the stochastic effects
introduced by a low star formation rate, which can account for dispersions of
over 2 dex in [C/O], [N/O], [C/Fe], [N/Fe] and [O/Fe].
| arxiv topic:astro-ph |
arxiv_dataset-486802.1303 | On GCD-morphic sequences
math.CO cs.DM
This note is a response to one of the problems posed by Kwa\'sniewski in
[1,2], see also [3] i.e. GCD-morphic Problem III. We show that any GCD-morphic
sequence $F$ is at the point product of primary GCD-morphic sequences and any
GCD-morphic sequence is encoded by natural number valued sequence satisfying
condition (C1). The problem of general importance - for example in number
theory was formulated in [1,2] while investigating a new class of DAG's and
their correspondent p.o. sets encoded uniquely by sequences with
combinatorially interpretable properties.
| arxiv topic:math.CO cs.DM |
arxiv_dataset-487802.1403 | Atmospheric dynamics of red supergiant stars and applications to
Interferometry
astro-ph
We have written a 3D radiative transfer code that computes emerging spectra
and intensity maps. We derive from radiative hydrodynamic (RHD) simulations of
RSG stars carried out with CO5BOLD (Freytag et al. 2002) observables expected
for red supergiant stars (RSG) especially for interferometric observations,
with emphasis on small scale structures. We show that the convection-related
surface structures are detectable in the H band with today's interferometers
and that the diameter measurement should not be too dependent on the adopted
model. The simulations are a great improvement over parametric models for the
interpretation of interferometric observations.
| arxiv topic:astro-ph |
arxiv_dataset-488802.1503 | Rotational dynamics of a soft filament: wrapping transition and
propulsive forces
physics.flu-dyn cond-mat.soft
We analyze experimentally the shape of a long elastic filament rotating in a
viscous liquid. We identify a continuous but sharp transition from a straight
to an helical shape, resulting from the competition between viscous stresses
and elastic forces. This induced helicity generates a propulsive force along
the axis of rotation. In addition, we show that the shape transition is
associated with an unstable branch in the force-torque relation. A linearized
model of the fluid-structure interaction is proposed to account for all the
features of the non-linear filament dynamics.
| arxiv topic:physics.flu-dyn cond-mat.soft |
arxiv_dataset-489802.1603 | Helioseismology of Sunspots: Confronting Observations with
Three-Dimensional MHD Simulations of Wave Propagation
astro-ph
The propagation of solar waves through the sunspot of AR 9787 is observed
using temporal cross-correlations of SOHO/MDI Dopplergrams. We then use
three-dimensional MHD numerical simulations to compute the propagation of wave
packets through self-similar magneto-hydrostatic sunspot models. The
simulations are set up in such a way as to allow a comparison with observed
cross-covariances (except in the immediate vicinity of the sunspot). We find
that the simulation and the f-mode observations are in good agreement when the
model sunspot has a peak field strength of 3 kG at the photosphere, less so for
lower field strengths. Constraining the sunspot model with helioseismology is
only possible because the direct effect of the magnetic field on the waves has
been fully taken into account. Our work shows that the full-waveform modeling
of sunspots is feasible.
| arxiv topic:astro-ph |
arxiv_dataset-490802.1703 | Lagrangian Floer theory on compact toric manifolds I
math.SG math-ph math.AG math.MP
The present authors introduced the notion of \emph{weakly unobstructed}
Lagrangian submanifolds and constructed their \emph{potential function}
$\mathfrak{PO}$ purely in terms of $A$-model data in [FOOO2]. In this paper, we
carry out explicit calculations involving $\mathfrak{PO}$ on toric manifolds
and study the relationship between this class of Lagrangian submanifolds with
the earlier work of Givental [Gi1] which advocates that quantum cohomology ring
is isomorphic to the Jacobian ring of a certain function, called the
Landau-Ginzburg superpotential. Combining this study with the results from
[FOOO2], we also apply the study to various examples to illustrate its
implications to symplectic topology of Lagrangian fibers of toric manifolds. In
particular we relate it to Hamiltonian displacement property of Lagrangian
fibers and to Entov-Polterovich's symplectic quasi-states.
| arxiv topic:math.SG math-ph math.AG math.MP |
arxiv_dataset-491802.1803 | Pair Formation in a t-J Model
cond-mat.str-el
We have investigated the formation of bound state of two electrons in
different kind of lattices using a t-J-U model.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-492802.1903 | How performing a mental arithmetic task modify the regulation of centre
of foot pressure displacements during bipedal quiet standing
q-bio.NC
We investigated the effect of performing a mental arithmetic task with two
levels of difficulty on the regulation of centre of foot pressure (COP)
displacements during bipedal quiet standing in young healthy individuals. There
was also a control condition in which no concurrent task was required. A
space-time-domain analysis showed decreased COP displacements, along the
antero-posterior axis, when participants concurrently performed the most
difficult mental arithmetic task. Frequency-domain and stabilogram-diffusion
analyses further suggested these decreased COP displacements to be associated
with an increased stiffness and a reduction of the exploratory behaviours in
the short term, respectively.
| arxiv topic:q-bio.NC |
arxiv_dataset-493802.2003 | Self-energy renormalization around the flux phase in the $t-J$ model:
Possible implications in underdoped cuprates
cond-mat.str-el cond-mat.supr-con
The flux phase predicted by the $t-J$ model in the large-N limit exhibits
features that make it a candidate for describing the pseudogap regime of
cuprates. However certain properties, as for instance the prediction of well
defined quasiparticle peaks, speak against this scenario. We have addressed
these issues by computing self-energy renormalizations in the vicinity to flux
phase. The calculated spectral functions show features similar to those
observed in experiments. At low doping, near the flux phase, the spectral
functions are anisotropic on the Fermi surface and very incoherent near the hot
spots. The temperature and doping evolution of self-energy and spectral
functions are discussed and compared with the experiment.
| arxiv topic:cond-mat.str-el cond-mat.supr-con |
arxiv_dataset-494802.2103 | A new abundance scale for the globular cluster 47 Tuc
astro-ph
We present chemical abundances for O, Na, Mg, Al, Si, Ca, Ti and Fe in eight
red giants and one turnoff star in the metal rich globular cluster 47 Tuc,
based on spectroscopy with the MIKE high resolution spectrograph on the
Magellan 6.5-m Clay telescope. A robust line by line differential abundance
analysis technique, relative to the K-giant Arcturus, was used to reduce
systematic errors from atmospheric and atomic parameters. Our derived mean LTE
[Fe/H] of -0.76 +- 0.01 +- 0.04 dex (random and systematic error, respectively)
is more metal poor by about 0.1 dex than recent literature results. The
chemical element ratios in this nearby globular cluster most closely resemble
those of the Galactic bulge, although there is a non-negligible overlap with
the composition of thick-disk stars. We find that the [Al/Fe] and [Na/Fe]
ratios coincide with the upper boundary of the trends seen in the bulge and
thick disk. There is only a small intrinsic scatter in the majority of the
abundance ratios, indicating that 47 Tuc is mostly a rather chemically
homogeneous system.
| arxiv topic:astro-ph |
arxiv_dataset-495802.2203 | Self-dual gravity is completely integrable
math-ph gr-qc hep-th math.MP nlin.SI
We discover multi-Hamiltonian structure of complex Monge-Ampere equation
(CMA) set in a real first-order two-component form. Therefore, by Magri's
theorem this is a completely integrable system in four real dimensions. We
start with Lagrangian and Hamiltonian densities and obtain a symplectic form
and the Hamiltonian operator that determines the Dirac bracket. We have
calculated all point symmetries of two-component CMA system and Hamiltonians of
the symmetry flows. We have found two new real recursion operators for
symmetries which commute with the operator of a symmetry condition on solutions
of the CMA system. These operators form two Lax pairs for the two-component
system. The recursion operators, being applied to the first Hamiltonian
operator, generate infinitely many real Hamiltonian structures. We show how to
construct an infinite hierarchy of higher commuting flows together with the
corresponding infinite chain of their Hamiltonians.
| arxiv topic:math-ph gr-qc hep-th math.MP nlin.SI |
arxiv_dataset-496802.2303 | Theory of smeared quantum phase transitions
cond-mat.str-el cond-mat.stat-mech
We present an analytical strong-disorder renormalization group theory of the
quantum phase transition in the dissipative random transverse-field Ising
chain. For Ohmic dissipation, we solve the renormalization flow equations
analytically, yielding asymptotically exact results for the low-temperature
properties of the system. We find that the interplay between quantum
fluctuations and Ohmic dissipation destroys the quantum critical point by
smearing. We also determine the phase diagram and the behavior of observables
in the vicinity of the smeared quantum phase transition.
| arxiv topic:cond-mat.str-el cond-mat.stat-mech |
arxiv_dataset-497802.2403 | On the relation between the neutrino flux from Centaurus A and the
associated diffuse neutrino flux
astro-ph hep-ph
Based on recent results obtained by the Pierre Auger Observatory (PAO), it
has been hypothesized that Centaurus A (Cen A) is a source of ultra-high-energy
cosmic rays (UHECRs) and associated neutrinos. We point out that the diffuse
neutrino flux may be used to constrain the source model if one assumes that the
ratio between the UHECR and neutrino fluxes outputted by Cen A is
representative for other sources. Under this assumption we investigate the
relation between the neutrino flux from Cen A and the diffuse neutrino flux.
Assuming furthermore that Cen A is the source of two UHECR events observed by
PAO, we estimate the all-sky diffuse neutrino flux to be ~200-5000 times larger
than the neutrino flux from Cen A. As a result, the diffuse neutrino fluxes
associated with some of the recently proposed models of UHECR-related neutrino
production in Cen A are above existing limits. Regardless of the underlying
source model, our results indicate that the detection of neutrinos from Cen A
without the accompanying diffuse flux would mean that Cen A is an exceptionally
efficient neutrino source.
| arxiv topic:astro-ph hep-ph |
arxiv_dataset-498802.2503 | Island formation without attractive interactions
cond-mat.stat-mech cond-mat.mtrl-sci
We show that adsorbates on surfaces can form islands even if there are no
attractive interactions. Instead strong repulsion between adsorbates at short
distances can lead to islands, because such islands increase the entropy of the
adsorbates that are not part of the islands. We suggest that this mechanism
cause the observed island formation in O/Pt(111), but it may be important for
many other systems as well.
| arxiv topic:cond-mat.stat-mech cond-mat.mtrl-sci |
arxiv_dataset-499802.2603 | A Markov Basis for Conditional Test of Common Diagonal Effect in
Quasi-Independence Model for Square Contingency Tables
stat.ME
In two-way contingency tables we sometimes find that frequencies along the
diagonal cells are relatively larger(or smaller) compared to off-diagonal
cells, particularly in square tables with the common categories for the rows
and the columns. In this case the quasi-independence model with an additional
parameter for each of the diagonal cells is usually fitted to the data. A
simpler model than the quasi-independence model is to assume a common
additional parameter for all the diagonal cells. We consider testing the
goodness of fit of the common diagonal effect by Markov chain Monte Carlo
(MCMC) method. We derive an explicit form of a Markov basis for performing the
conditional test of the common diagonal effect. Once a Markov basis is given,
MCMC procedure can be easily implemented by techniques of algebraic statistics.
We illustrate the procedure with some real data sets.
| arxiv topic:stat.ME |
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