id stringlengths 16 29 | text stringlengths 86 3.49k | source stringlengths 14 112 |
|---|---|---|
arxiv_dataset-900810.4421 | Dark Energy and Dark Matter in General Relativity with local scale
invariance
hep-ph astro-ph
We consider a generalization of Einstein's general theory of relativity such
that it respects local scale invariance. This requires the introduction of a
scalar and a vector field in the action. We show that the theory naturally
displays both dark energy and dark matter. We solve the resulting equations of
motion assuming an FRW metric. The solutions are found to be almost identical
to those corresponding to the standard $\Lambda$CDM model
| arxiv topic:hep-ph astro-ph |
arxiv_dataset-901810.4521 | Gravitational Radiation by Cosmic Strings in a Junction
hep-th astro-ph gr-qc
The formalism for computing the gravitational power radiation from
excitations on cosmic strings forming a junction is presented and applied to
the simple case of co-planar strings at a junction when the excitations are
generated along one string leg. The effects of polarization of the excitations
and of the back-reaction of the gravitational radiation on the small scale
structure of the strings are studied.
| arxiv topic:hep-th astro-ph gr-qc |
arxiv_dataset-902810.4621 | Globular Cluster Populations in Four Early-Type Poststarburst Galaxies
astro-ph
We present a study of the globular cluster systems of four early-type
poststarburst galaxies using deep g and I-band images from the ACS camera
aboard the Hubble Space Telescope (HST). All the galaxies feature shells
distributed around their main bodies and are thus likely merger remnants. The
color distribution of the globular clusters in all four galaxies shows a broad
peak centered on g-I ~ 1.4, while PGC 6240 and PGC 42871 show a significant
number of globular clusters with g-I ~ 1.0. The latter globular clusters are
interpreted as being of age ~ 500 Myr and likely having been formed in the
merger. The color of the redder peak is consistent with that expected for an
old metal-poor population that is very commonly found around normal galaxies.
However, all galaxies except PGC 10922 contain several globular clusters that
are significantly brighter than the maximum luminosity expected of a single old
metal-poor population. To test for multiple-age populations of overlapping g-I
color, we model the luminosity functions of the globular clusters as composites
of an old metal-poor subpopulation with a range of plausible specific
frequencies and an intermediate-age subpopulation of solar metallicity. We find
that three of the four sample galaxies show evidence for the presence of an
intermediate-age (~ 1 Gyr) globular cluster population, in addition to the old
metal-poor GC population seen in normal early-type galaxies. None of the
galaxies show a significant population of clusters consistent with an old,
metal-rich red cluster population that is typically seen in early-type
galaxies.
| arxiv topic:astro-ph |
arxiv_dataset-903810.4721 | Computation of the response functions of spiral waves in active media
nlin.PS
Rotating spiral waves are a form of self-organization observed in spatially
extended systems of physical, chemical, and biological nature. A small
perturbation causes gradual change in spatial location of spiral's rotation
center and frequency, i.e. drift. The response functions (RFs) of a spiral wave
are the eigenfunctions of the adjoint linearized operator corresponding to the
critical eigenvalues $\lambda = 0, \pm i\omega$. The RFs describe the spiral's
sensitivity to small perturbations in the way that a spiral is insensitive to
small perturbations where its RFs are close to zero. The velocity of a spiral's
drift is proportional to the convolution of RFs with the perturbation. Here we
develop a regular and generic method of computing the RFs of stationary
rotating spirals in reaction-diffusion equations. We demonstrate the method on
the FitzHugh-Nagumo system and also show convergence of the method with respect
to the computational parameters, i.e. discretization steps and size of the
medium. The obtained RFs are localized at the spiral's core.
| arxiv topic:nlin.PS |
arxiv_dataset-904810.4821 | Estimation of distributions, moments and quantiles in deconvolution
problems
math.ST stat.TH
When using the bootstrap in the presence of measurement error, we must first
estimate the target distribution function; we cannot directly resample, since
we do not have a sample from the target. These and other considerations
motivate the development of estimators of distributions, and of related
quantities such as moments and quantiles, in errors-in-variables settings. We
show that such estimators have curious and unexpected properties. For example,
if the distributions of the variable of interest, $W$, say, and of the
observation error are both centered at zero, then the rate of convergence of an
estimator of the distribution function of $W$ can be slower at the origin than
away from the origin. This is an intrinsic characteristic of the problem, not a
quirk of particular estimators; the property holds true for optimal estimators.
| arxiv topic:math.ST stat.TH |
arxiv_dataset-905810.4921 | Constraints on Neutrino Masses from Weak Lensing
astro-ph hep-ph
The weak lensing (WL) distortions of distant galaxy images are sensitive to
neutrino masses by probing the suppression effect on clustering strengths of
total matter in large-scale structure. We use the latest measurement of WL
correlations, the CFHTLS data, to explore constraints on neutrino masses. We
find that, while the WL data alone cannot place a stringent limit on neutrino
masses due to parameter degeneracies, the constraint can be significantly
improved when combined with other cosmological probes, the WMAP 5-year (WMAP5)
data and the distance measurements of type-Ia supernovae (SNe) and baryon
acoustic oscillations (BAO). The upper bounds on the sum of neutrino masses are
m_tot = 1.1, 0.76 and 0.54 eV (95% CL) for WL+WMAP5, WMAP5+SNe+BAO, and
WL+WMAP5+SNe+BAO, respectively, assuming a flat LCDM model with finite-mass
neutrinos. In deriving these constraints, our analysis includes the
non-Gaussian covariances of the WL correlation functions to properly take into
account significant correlations between different angles.
| arxiv topic:astro-ph hep-ph |
arxiv_dataset-906810.5021 | Exotic Collective Excitations at High Spin: Triaxial Rotation and
Octupole Condensation
nucl-ex
In this thesis work, two topics, triaxiality and reflection asymmetry, have
been discussed. Band structures in $^{163}$Tm were studied in a "thin" target
experiment as well as in a DSAM lifetime measurement. Two new excited bands
were shown to be characterized by a deformation larger than that of the yrast
sequence. These structures have been interpreted as Triaxial Strongly Deformed
bands associated with particle-hole excitations, rather than with wobbling.
Moreover, the Tilted-Axis Cranking calculations provide a natural explanation
for the presence of wobbling bands in the Lu isotopes and their absence in the
neighboring Tm, Hf and Ta nuclei. A series of so-called "unsafe" Coulomb
excitation experiments as well as one-neutron transfer measurements was carried
out to investigate the role of octupole correlations in the $^{238,240,242}$Pu
isotopes. Some striking differences exist between the level scheme and
deexcitation patterns seen in $^{240}$Pu, and to a lesser extent in $^{238}$Pu,
and those observed in $^{242}$Pu and in many other actinide nuclei such as
$^{232}$Th and $^{238}$U, for example. The differences can be linked to the
strength of octupole correlations, which are strongest in $^{240}$Pu. Further,
all the data find a natural explanation within the recently proposed
theoretical framework of octupole condensation.
| arxiv topic:nucl-ex |
arxiv_dataset-907810.5121 | Helical Metal Inside a Topological Band Insulator
cond-mat.mes-hall cond-mat.str-el
Topological defects, such as domain walls and vortices, have long fascinated
physicists. A novel twist is added in quantum systems like the B-phase of
superfluid helium He$_3$, where vortices are associated with low energy
excitations in the cores. Similarly, cosmic strings may be tied to propagating
fermion modes. Can analogous phenomena occur in crystalline solids that host a
plethora of topological defects? Here we show that indeed dislocation lines are
associated with one dimensional fermionic excitations in a `topological
insulator', a novel band insulator believed to be realized in the bulk material
Bi$_{0.9}$Sb$_{0.1}$. In contrast to fermionic excitations in a regular quantum
wire, these modes are topologically protected like the helical edge states of
the quantum spin-Hall insulator, and not scattered by disorder. Since
dislocations are ubiquitous in real materials, these excitations could dominate
spin and charge transport in topological insulators. Our results provide a
novel route to creating a potentially ideal quantum wire in a bulk solid.
| arxiv topic:cond-mat.mes-hall cond-mat.str-el |
arxiv_dataset-908810.5221 | Multiplexing of discrete chaotic signals in presence of noise
nlin.CD
In this paper, multiplexing of discrete chaotic signals in the presence of
noise is investigated. Existing methods are based on chaotic synchronization
which is susceptible to noise and parameter mismatch. Furthermore, these
methods fail for multiplexing more than two discrete chaotic signals. We
propose two novel methods to multiplex multiple discrete chaotic signals based
on the principle of symbolic sequence invariance in the presence of noise and
finite precision implementation of finding the initial condition of an
arbitrarily long symbolic sequence of a chaotic map.
| arxiv topic:nlin.CD |
arxiv_dataset-909810.5321 | Holography and Fermions at a Finite Chemical Potential
hep-th
We review the Sakai-Sugimoto model of holographic QCD at zero temperature and
finite chemical potential, comparing the results to those expected at
large-$N_c$ QCD, and those in a closely related holographic model. We find that
as the baryon chemical potential is increased above a critical value, there is
a phase transition to a nuclear matter phase, the details of which depend on
the model. We argue that the nuclear matter phase is necessarily inhomogeneous
to arbitrarily high density, which suggests an explanation of the "chiral
density wave" instability of the quark Fermi surface in large-$N_c$ QCD. Some
details of the instanton distribution in the holographic dual are reminiscent
of a Fermi surface. This short manuscript summarizes a talk given by M.R. at
"Theory Canada 4" conference, and is based largely (but not entirely) on the
results of \cite{Rozalietal2008}.
| arxiv topic:hep-th |
arxiv_dataset-910810.5421 | Calculation of Coefficients of the Optimal Quadrature Formulas in the
$W_2^{m,m-1}(0,1)$ Space
math.NA
In this paper problem of construction of optimal quadrature formulas in
$W_2^{(m,m-1)}(0,1)$ space is considered. Here by using Sobolev's algorithm
when $m=1,2$ we find the optimal coefficients of the quadrature formulas of the
form $$ \int\limits_0^1\phi(x)dx\cong
\sum\limits_{\beta=0}^NC_{\beta}\phi(x_{\beta}). $$
| arxiv topic:math.NA |
arxiv_dataset-911810.5521 | Reconnection Dynamics for Quantized Vortices
cond-mat.stat-mech cond-mat.supr-con
By analyzing trajectories of solid hydrogen tracers in superfluid $^4$He, we
identify tens of thousands of individual reconnection events between quantized
vortices. We characterize the dynamics by the minimum separation distance
$\delta(t)$ between the two reconnecting vortices both before and after the
events. Applying dimensional arguments, this separation has been predicted to
behave asymptotically as $\delta(t) \approx A(\kappa |t-t_0|)^{1/2}$, where
$\kappa=h/m$ is the quantum of circulation. The major finding of the
experiments and their analysis is strong support for this asymptotic form with
$\kappa$ as the dominant controlling feature, although there are significant
event to event fluctuations. At the three-parameter level the dynamics may be
about equally well-fit by two modified expressions: (a) an arbitrary power-law
expression of the form $\delta(t)=B|t-t_0|^{\alpha}$ and (b) a
correction-factor expression $\delta(t)=A(\kappa|t-t_0|)^{1/2}(1+c|t-t_0|)$. In
light of possible physical interpretations we regard the correction-factor
expression (b), which attributes the observed deviations from the predicted
asymptotic form to fluctuations in the local environment and in boundary
conditions, as best describing our experimental data. The observed dynamics
appear statistically time-reversible, which suggests that an effective
equilibrium has been established in quantum turbulence on the time scales
investigated. We discuss the impact of reconnection on velocity statistics in
quantum turbulence and, as regards classical turbulence, we argue that forms
analogous to (b) could well provide an alternative interpretation of the
observed deviations from Kolmogorov scaling exponents of the longitudinal
structure functions.
| arxiv topic:cond-mat.stat-mech cond-mat.supr-con |
arxiv_dataset-912810.5621 | Conformally Osserman manifolds
math.DG
An algebraic curvature tensor is called Osserman if the eigenvalues of the
associated Jacobi operator are constant on the unit sphere. A Riemannian
manifold is called conformally Osserman if its Weyl conformal curvature tensor
at every point is Osserman. We prove that a conformally Osserman manifold of
dimension $n \ne 3, 4, 16$ is locally conformally equivalent either to a
Euclidean space or to a rank-one symmetric space.
| arxiv topic:math.DG |
arxiv_dataset-913810.5721 | Status of CMS and preparations for first physics
hep-ex
The status of the CMS experiment is described. After a brief review of the
detector design and a short overview of the first 5 years of assembly, the
focus of this presentation will be the parallel activities of completing and
commissioning over the last 2 years and the readiness of CMS for the exciting
prospect of first LHC operation.
| arxiv topic:hep-ex |
arxiv_dataset-914811.0048 | Conjectural Equilibrium in Water-filling Games
cs.GT cs.MA
This paper considers a non-cooperative game in which competing users sharing
a frequency-selective interference channel selfishly optimize their power
allocation in order to improve their achievable rates. Previously, it was shown
that a user having the knowledge of its opponents' channel state information
can make foresighted decisions and substantially improve its performance
compared with the case in which it deploys the conventional iterative
water-filling algorithm, which does not exploit such knowledge. This paper
discusses how a foresighted user can acquire this knowledge by modeling its
experienced interference as a function of its own power allocation. To
characterize the outcome of the multi-user interaction, the conjectural
equilibrium is introduced, and the existence of this equilibrium for the
investigated water-filling game is proved. Interestingly, both the Nash
equilibrium and the Stackelberg equilibrium are shown to be special cases of
the generalization of conjectural equilibrium. We develop practical algorithms
to form accurate beliefs and search desirable power allocation strategies.
Numerical simulations indicate that a foresighted user without any a priori
knowledge of its competitors' private information can effectively learn the
required information, and induce the entire system to an operating point that
improves both its own achievable rate as well as the rates of the other
participants in the water-filling game.
| arxiv topic:cs.GT cs.MA |
arxiv_dataset-915811.0148 | Plans D'Experiences D'Information De Kullback-Leibler Minimale
stat.ME
Experimental designs are tools which can dramatically reduce the number of
simulations required by time-consuming computer codes. Because we don't know
the true relation between the response and inputs, designs should allow one to
fit a variety of models and should provide information about all portions of
the experimental region. One strategy for selecting the values of the inputs at
which to observe the response is to choose these values so they are spread
evenly throughout the experimental region, according to "space-filling
designs". In this article, we suggest a new method based on comparing the
empirical distribution of the points in a design to the uniform distribution
with the Kullback-Leibler information. The considered approach consists in
estimating this difference or, reciprocally, the Shannon entropy. The entropy
is estimated by a Monte Carlo method where the density function is replaced by
its kernel density estimator or by using the nearest neighbor distances
| arxiv topic:stat.ME |
arxiv_dataset-916811.0248 | Neel order in the Hubbard model within spin-charge rotating reference
frame approach: crossover from weak to strong coupling
cond-mat.str-el
The antiferromagnetic phase of two-dimensional (2D) and three-dimensional
(3D) Hubbard model with nearest neighbors hopping is studied on a bipartite
cubic lattice by means of the quantum SU(2)xU(1) rotor approach that yields a
fully self-consistent treatment of the antiferromagnetic state that respects
the symmetry properties the model and satisfy the Mermin-Wagner theorem. The
collective variables for charge and spin are isolated in the form of the
space-time fluctuating U(1) phase field and rotating spin quantization axis
governed by the SU(2) symmetry, respectively. As a result interacting electrons
appear as a composite objects consisting of bare fermions with attached U(1)
and SU(2) gauge fields. An effective action consisting of a spin-charge rotor
and a fermionic fields is derived as a function of the Coulomb repulsion U and
hopping parameter t. At zero temperature, our theory describes the evolution
from a Slater (U<<t) to a Mott-Heisenberg (U>>t) antiferromagnet. The results
for zero-temperature sublatice magnetization (2D) and finite temperature (3D)
phase diagram of the antiferromagnetic Hubbard model as a function of the
crossover parameter U/t are presented and the role of the spin Berry phase in
the interaction driven crossover is analyzed.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-917811.0348 | Doppler maps and surface differential rotation of EI Eri from the
MUSICOS 1998 observations
astro-ph
We present time-series Doppler images of the rapidly-rotating active binary
star EI Eri from spectroscopic observations collected during the MUSICOS
multi-site campaign in 1998, since the critical rotation period of 1.947 days
makes it impossible to obtain time-resolved images from a single site. From the
surface reconstructions a weak solar-type differential rotation, as well as a
tiny poleward meridional flow are measured.
| arxiv topic:astro-ph |
arxiv_dataset-918811.0448 | Statistical properties of information flow in financial time series
q-fin.ST physics.data-an physics.soc-ph
This paper has been withdrawn by the authors.
| arxiv topic:q-fin.ST physics.data-an physics.soc-ph |
arxiv_dataset-919811.0548 | On $\omega_3$-chains in P($\omega_1$) mod finite
math.LO
We prove that if there exists a simplified $(\omega_1,2)$-morass, then there
is a ccc forcing which adds an $\omega_3$-chain in P($\omega_1$) mod finite and
a ccc forcing which adds a family of $\omega_3$-many strongly almost disjoint
functions from $\omega_1$ to $\omega$. The idea is to use a finite support
iteration of countable forcings which is not linear but three-dimensional.
| arxiv topic:math.LO |
arxiv_dataset-920811.0648 | Study of quark distribution amplitudes of 1S and 2S heavy quarkonium
states
hep-ph
In this paper, the quark distribution amplitudes of 1S and 2S heavy
quarkonium states are studied in terms of Gaussian-type wave functions. The
transverse momenta $p_\perp$ integrals of the formulae for the decay constant
are performed analytically. Then the quark distribution amplitudes are
obtained. In addition, the $\xi$-moments are also calculated. After fixing the
relevant parameters appearing in the quark distribution amplitude, the curves
of the quark distribution amplitude for 1S and 2S heavy quarkonium states are
plotted. Finally, the numerical results of this approach are compared with the
other theoretical predictions.
| arxiv topic:hep-ph |
arxiv_dataset-921811.0748 | Some equivalences between the auxiliary field method and the envelope
theory
quant-ph math-ph math.MP
The auxiliary field method has been recently proposed as an efficient
technique to compute analytical approximate solutions of eigenequations in
quantum mechanics. We show that the auxiliary field method is completely
equivalent to the envelope theory, which is another well-known procedure to
analytically solve eigenequations, although relying on different principles
\textit{a priori}. This equivalence leads to a deeper understanding of both
frameworks.
| arxiv topic:quant-ph math-ph math.MP |
arxiv_dataset-922811.0848 | On the global well-posedness of the one-dimensional Schrodinger map flow
math.DG math.AP
We establish the global well-posedness of the initial value problem for the
Schrodinger map flow for maps from the real line into Kahler manifolds and for
maps from the circle into Riemann surfaces. This partially resolves a
conjecture of W.-Y. Ding.
| arxiv topic:math.DG math.AP |
arxiv_dataset-923811.0948 | Multiple local whittle estimation in stationary systems
math.ST stat.TH
Moving from univariate to bivariate jointly dependent long-memory time series
introduces a phase parameter $(\gamma)$, at the frequency of principal
interest, zero; for short-memory series $\gamma=0$ automatically. The latter
case has also been stressed under long memory, along with the ``fractional
differencing'' case $\gamma=(\delta_2-\delta_1)\pi /2$, where $\delta_1$,
$\delta_2$ are the memory parameters of the two series. We develop time domain
conditions under which these are and are not relevant, and relate the
consequent properties of cross-autocovariances to ones of the (possibly
bilateral) moving average representation which, with martingale difference
innovations of arbitrary dimension, is used in asymptotic theory for local
Whittle parameter estimates depending on a single smoothing number.
Incorporating also a regression parameter $(\beta)$ which, when nonzero,
indicates cointegration, the consistency proof of these implicitly defined
estimates is nonstandard due to the $\beta$ estimate converging faster than the
others. We also establish joint asymptotic normality of the estimates, and
indicate how this outcome can apply in statistical inference on several
questions of interest. Issues of implemention are discussed, along with
implications of knowing $\beta$ and of correct or incorrect specification of
$\gamma$, and possible extensions to higher-dimensional systems and
nonstationary series.
| arxiv topic:math.ST stat.TH |
arxiv_dataset-924811.1048 | The noncommutative sine-Gordon breather
hep-th math-ph math.MP
As shown in [hep-th/0406065], there exists a noncommutative deformation of
the sine-Gordon model which remains (classically) integrable but features a
second scalar field. We employ the dressing method (adapted to the
Moyal-deformed situation) for constructing the deformed kink-antikink and
breather configurations. Explicit results and plots are presented for the
leading noncommutativity correction to the breather. Its temporal periodicity
is unchanged.
| arxiv topic:hep-th math-ph math.MP |
arxiv_dataset-925811.1148 | Strong correlation effects in single-wall carbon nanotubes
cond-mat.str-el
We present an overview of strong correlations in single-wall carbon
nanotubes, and an introduction to the techniques used to study them
theoretically. We concentrate on zigzag nanotubes, although universality
dictates that much ofthe theory can also be applied to armchair or chiral
nanotubes. We show how interaction effects lead to exotic low energy properties
and discuss future directions for studies on correlation effects in nanotubes.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-926811.1248 | Integrable boundary conditions for a non-abelian anyon chain with
$D(D_3)$ symmetry
math-ph cond-mat.mes-hall math.MP nlin.SI
A general formulation of the Boundary Quantum Inverse Scattering Method is
given which is applicable in cases where $R$-matrix solutions of the
Yang--Baxter equation do not have the property of crossing unitarity. Suitably
modified forms of the reflection equations are presented which permit the
construction of a family of commuting transfer matrices. As an example, we
apply the formalism to determine the most general solutions of the reflection
equations for a solution of the Yang-Baxter equation with underlying symmetry
given by the Drinfeld double $D(D_3)$ of the dihedral group $D_3$. This
$R$-matrix does not have the crossing unitarity property. In this manner we
derive integrable boundary conditions for an open chain model of interacting
non-abelian anyons.
| arxiv topic:math-ph cond-mat.mes-hall math.MP nlin.SI |
arxiv_dataset-927811.1348 | X-ray imaging of the dynamic magnetic vortex core deformation
cond-mat.other
Magnetic platelets with a vortex configuration are attracting considerable
attention. The discovery that excitation with small in-plane magnetic fields or
spin polarised currents can switch the polarisation of the vortex core did not
only open the possibility of using such systems in magnetic memories, but also
initiated the fundamental investigation of the core switching mechanism itself.
Micromagnetic models predict that the switching is mediated by a
vortex-antivortex pair, nucleated in a dynamically induced vortex core
deformation. In the same theoretical framework, a critical core velocity is
predicted, above which switching occurs. Although these models are extensively
studied and generally accepted, experimental support has been lacking until
now. In this work, we have used high-resolution time-resolved X-ray microscopy
to study the detailed dynamics in vortex structures. We could reveal the
dynamic vortex core deformation preceding the core switching. Also, the
threshold velocity could be measured, giving quantitative comparison with
micromagnetic models.
| arxiv topic:cond-mat.other |
arxiv_dataset-928811.1448 | An embedding theorem for Hilbert categories
math.CT math.QA quant-ph
We axiomatically define (pre-)Hilbert categories. The axioms resemble those
for monoidal Abelian categories with the addition of an involutive functor. We
then prove embedding theorems: any locally small pre-Hilbert category whose
monoidal unit is a simple generator embeds (weakly) monoidally into the
category of pre-Hilbert spaces and adjointable maps, preserving adjoint
morphisms and all finite (co)limits. An intermediate result that is important
in its own right is that the scalars in such a category necessarily form an
involutive field. In case of a Hilbert category, the embedding extends to the
category of Hilbert spaces and continuous linear maps. The axioms for
(pre-)Hilbert categories are weaker than the axioms found in other approaches
to axiomatizing 2-Hilbert spaces. Neither enrichment nor a complex base field
is presupposed. A comparison to other approaches will be made in the
introduction.
| arxiv topic:math.CT math.QA quant-ph |
arxiv_dataset-929811.1548 | Geometro-thermodynamics of tidal charged black holes
gr-qc astro-ph hep-th
Tidal charged spherically symmetric vacuum brane black holes are
characterized by their mass m and tidal charge q, an imprint of the
5-dimensional Weyl curvature. For q>0 they are formally identical to the
Reissner-Nordstr\"om black hole of general relativity. We study the
thermodynamics and thermodynamic geometries of tidal charged black holes and
discuss similarities and differences as compared to the Reissner-Nordstr\"om
black hole. As a similarity, we show that (for q>0) the heat capacity of the
tidal charged black hole diverges on a set of measure zero of the parameter
space, nevertheless both the regularity of the Ruppeiner metric and a
Poincar\'e stability analysis shows no phase transition at those points. The
thermodynamic state spaces being different indicates that the underlying
statistical models could be different. We find that the q<0 parameter range,
which enhances the localization of gravity on the brane, is thermodynamically
preferred. Finally we constrain for the first time the possible range of the
tidal charge from the thermodynamic limit on gravitational radiation efficiency
at black hole mergers.
| arxiv topic:gr-qc astro-ph hep-th |
arxiv_dataset-930811.1648 | Stationary transport in mesoscopic hybrid structures with contacts to
superconducting and normal wires. A Green's function approach for
multiterminal setups
cond-mat.mes-hall cond-mat.supr-con
We generalize the representation of the real time Green's functions
introduced by Langreth and Nordlander [Phys. Rev. B 43 2541 (1991)] and Meir
and Wingreen [Phys. Rev. Lett. 68 2512 (1992)] in stationary quantum transport
in order to study problems with hybrid structures containing normal (N) and
superconducting (S) pieces. We illustrate the treatment in a S-N junction under
a stationary bias and investigate in detail the behavior of the equilibrium
currents in a normal ring threaded by a magnetic flux with attached
superconducting wires at equilibrium. We analyze the flux sensitivity of the
Andreev states and we show that their response is equivalent to the one
corresponding to the Cooper pairs with momentum q=0 in an isolated
superconducting ring.
| arxiv topic:cond-mat.mes-hall cond-mat.supr-con |
arxiv_dataset-931811.1748 | Survival of branching random walks in random environment
math.PR
We study survival of nearest-neighbour branching random walks in random
environment (BRWRE) on ${\mathbb Z}$. A priori there are three different
regimes of survival: global survival, local survival, and strong local
survival. We show that local and strong local survival regimes coincide for
BRWRE and that they can be characterized with the spectral radius of the first
moment matrix of the process. These results are generalizations of the
classification of BRWRE in recurrent and transient regimes. Our main result is
a characterization of global survival that is given in terms of Lyapunov
exponents of an infinite product of i.i.d. $2\times 2$ random matrices.
| arxiv topic:math.PR |
arxiv_dataset-932811.1848 | Active Galactic Nuclei: Sources for ultra high energy cosmic rays?
astro-ph gr-qc hep-ph
The origin of ultra high energy cosmic rays promises to lead us to a deeper
understanding of the structure of matter. This is possible through the study of
particle collisions at center-of-mass energies in interactions far larger than
anything possible with the Large Hadron Collider, albeit at the substantial
cost of no control over the sources and interaction sites. For the extreme
energies we have to identify and understand the sources first, before trying to
use them as physics laboratories. Here we describe the current stage of this
exploration. The most promising contenders as sources are radio galaxies and
gamma ray bursts. The sky distribution of observed events yields a hint
favoring radio galaxies. Key in this quest are the intergalactic and galactic
magnetic fields, whose strength and structure are not yet fully understood.
Current data and statistics do not yet allow a final judgment. We outline how
we may progress in the near future.
| arxiv topic:astro-ph gr-qc hep-ph |
arxiv_dataset-933811.1948 | Exact solutions in the Dirac-Born-Infeld effective theory and the fate
of tachyon
hep-th
We show that the equation of motion from the Dirac-Born-Infeld effective
action of a general scalar field with some specific potentials admits exact
solutions after appropriate field redefinitions. Based on the exact solutions
and their energy-momentum tensors, we find that massive scalars and massless
scalars of oscillating modes in the DBI effective theory are not pressureless
generically for any possible momenta, which implies that the pressureless
"tachyon matter" forming at late time of the tachyon condensation process
should not really be some massive matter. It is more likely that the tachyon
field at late time behaves as a massless scalar of zero modes. At kinks, the
tachyon can be viewed as a massless scalar of a translational zero mode
describing a stable and static D-brane with one dimension lower. Near the
vacuum, the tachyon in regions without the caustic singularities can be viewed
as a massless scalar that has the same zero mode solution as a fundamental
string moving with a critical velocity. We find supporting evidences to this
conclusion by considering a DBI theory with modified tachyon potential, in
which the development of caustics near the vacuum may be avoided.
| arxiv topic:hep-th |
arxiv_dataset-934811.2048 | A note on conformal symmetry in projective superspace
hep-th
We describe a sufficient condition for actions constructed in projective
superspace to possess an SU(2) R-symmetry. We check directly that this
condition implies that the corresponding hyperkahler varieties, constructed by
means of the generalized Legendre transform, have a Swann bundle structure.
| arxiv topic:hep-th |
arxiv_dataset-935811.2148 | Extremely Red Objects in a hierarchical universe
astro-ph
We analyse whether hierarchical formation models based on Lambda cold dark
matter cosmology can produce enough massive red galaxies to match observations.
For this purpose, we compare with observations the predictions from two
published models for the abundance and redshift distribution of Extremely Red
Objects (EROs), which are red, massive galaxies observed at z >= 1. One of the
models invokes a "superwind" to regulate star formation in massive haloes and
the other suppresses cooling through "radio-mode" AGN feedback. The first one
underestimates the number counts of EROs by an order of magnitude, whereas the
radio-mode AGN feedback model gives excellent agreement with the number counts
of EROs and redshift distribution of K-selected galaxies. This study highlights
the need to consider AGN feedback in order to understand the formation and
evolution of massive galaxies at z >= 1.
| arxiv topic:astro-ph |
arxiv_dataset-936811.2248 | Dissipation and the Relaxation to Equilibrium
cond-mat.stat-mech
Using the recently derived Dissipation Theorem and a corollary of the
Transient Fluctuation Theorem (TFT), namely the Second Law Inequality, we
derive the unique time independent, equilibrium phase space distribution
function for an ergodic Hamiltonian system in contact with a remote heat bath.
We prove under very general conditions that any deviation from this equilibrium
distribution breaks the time independence of the distribution. Provided
temporal correlations decay, and the system is ergodic, we show that any
nonequilibrium distribution that is an even function of the momenta, eventually
relaxes (not necessarily monotonically) to the equilibrium distribution.
Finally we prove that the negative logarithm of the microscopic partition
function is equal to the thermodynamic Helmholtz free energy divided by the
thermodynamic temperature and Boltzmann's constant. Our results complement and
extend the findings of modern ergodic theory and show the importance of
dissipation in the process of relaxation towards equilibrium.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-937811.2348 | Search for double beta decay of Zinc and Tungsten with the help of
low-background ZnWO4 crystal scintillators
nucl-ex
Double beta processes in 64-Zn, 70-Zn, 180-W, and 186-W have been searched
for with the help of large volume (0.1-0.7 kg) low background ZnWO4 crystal
scintillators at the Gran Sasso National Laboratories of the INFN. Total time
of measurements exceeds 10 thousands hours. New improved half-life limits on
double electron capture and electron capture with positron emission in 64-Zn
have been set, in particular (all the limits are at 90% C.L.): T1/2(0nu2EC)>
1.1e20 yr, T1/2(2nuECbeta+)>7.0e20 yr, and T1/2(0nuECbeta+)>4.3e20 yr. The
different modes of double beta processes in 70-Zn, 180-W, and 186-W have been
restricted at the level of 1e17-1e20 yr.
| arxiv topic:nucl-ex |
arxiv_dataset-938811.2448 | Mauna Kea Sky Transparency from CFHT SkyProbe Data
astro-ph
Nighttime sky transparency statistics on Mauna Kea are reported based on data
from the Canada-France-Hawaii Telescope SkyProbe monitor. We focus on the
period beginning with the start of MegaCam wide-field optical imager operations
in 2003, and continuing for almost three years. Skies were clear enough to
observe on 76% of those nights; attenuations were less than 0.2 magnitudes up
to 60% of the time. An empirical model of cloud attenuation and duration is
presented allowing us to further characterize the photometric conditions. This
is a good fit tothe SkyProbe data, and indicates that Mauna Kea skies are truly
photometric (without cloud) an average of 56% of the time, with moderate
seasonal variation. Continuous monitoring of transparency during the night is
necessary to overcome fluctuations in attenuation due to thin cloud.
| arxiv topic:astro-ph |
arxiv_dataset-939811.2548 | Hyperdiscriminant polytopes, Chow polytopes, and Mabuchi energy
asymptotics
math.DG math.AG
Let X be a smooth, linearly normal algebraic variety. It is shown that the
Mabuchi energy of X restricted to the Bergman metrics is completely determined
by the X-hyperdiscriminant of format (n-1) and the Chow form of X. As a
corollary it is shown that the Mabuchi energy is bounded from below for all
degenerations in G if and only if the hyperdiscriminant polytope dominates the
Chow polytope for all maximal algebraic tori H of G .
| arxiv topic:math.DG math.AG |
arxiv_dataset-940811.2648 | $B\to S$ Transition Form Factors in the PQCD approach
hep-ph
Under two different scenarios for the light scalar mesons, we investigate the
transition form factors of $B(B_s)$ mesons decay into a scalar meson in the
perturbative QCD approach. In the large recoiling region, the form factors are
dominated by the short-distance dynamics and can be calculated using
perturbation theory. We adopt the dipole parametrization to recast the $q^2$
dependence of the form factors. Since the decay constants defined by the scalar
current are large, our predictions on the $B\to S$ form factors are much larger
than the $B\to P$ transitions, especially in the second scenario. Contributions
from various light-cone distribution amplitudes (LCDAs) are elaborated and we
find that the twist-3 LCDAs provide more than a half contributions to the form
factors. The two terms of the twist-2 LCDAs give destructive contributions in
the first scenario while they give constructive contributions in the second
scenario. With the form factors, we also predict the decay width and branching
ratios of the semileptonic $B\to Sl\bar\nu$ and $B\to Sl^+l^-$ decays. The
branching ratios of $B\to Sl\bar\nu$ channels are found to have the order of
$10^{-4}$ while those of $B\to Sl^+l^-$ have the order of $10^{-7}$. These
predictions can be tested by the future experiments.
| arxiv topic:hep-ph |
arxiv_dataset-941811.2748 | Scale-dependent bias induced by local non-Gaussianity: A comparison to
N-body simulations
astro-ph
We investigate the effect of primordial non-Gaussianity of the local f_NL
type on the auto- and cross-power spectrum of dark matter haloes using
simulations of the LCDM cosmology. We perform a series of large N-body
simulations of both positive and negative f_NL, spanning the range between 10
and 100. Theoretical models predict a scale-dependent bias correction \Delta
b(k,f_NL) that depends on the linear halo bias b(M). We measure the power
spectra for a range of halo mass and redshifts covering the relevant range of
existing galaxy and quasar populations. We show that auto and cross-correlation
analyses of bias are consistent with each other. We find that for low
wavenumbers with k<0.03 h/Mpc the theory and the simulations agree well with
each other for biased haloes with b(M)>1.5. We show that a scale-independent
bias correction improves the comparison between theory and simulations on
smaller scales, where the scale-dependent effect rapidly becomes negligible.
The current limits on f_NL from Slosar et al. (2008) come mostly from very
large scales k<0.01 h/Mpc and, therefore, remain valid. For the halo samples
with b(M)<1.5-2 we find that the scale- dependent bias from non-Gaussianity
actually exceeds the theoretical predictions. Our results are consistent with
the bias correction scaling linearly with f_NL.
| arxiv topic:astro-ph |
arxiv_dataset-942811.2848 | Fast decay of the velocity autocorrelation function in dense shear flow
of inelastic hard spheres
cond-mat.soft
We find in complementary experiments and event driven simulations of sheared
inelastic hard spheres that the velocity autocorrelation function $\psi(t)$
decays much faster than $t^{-3/2}$ obtained for a fluid of elastic spheres at
equilibrium. Particle displacements are measured in experiments inside a
gravity driven flow sheared by a rough wall. The average packing fraction
obtained in the experiments is 0.59, and the packing fraction in the
simulations is varied between 0.5 and 0.59. The motion is observed to be
diffusive over long times except in experiments where there is layering of
particles parallel to boundaries, and diffusion is inhibited between layers.
Regardless, a rapid decay of $\psi(t)$ is observed, indicating that this is a
feature of the sheared dissipative fluid, and is independent of the details of
the relative particle arrangements. An important implication of our study is
that the non-analytic contribution to the shear stress may not be present in a
sheared inelastic fluid, leading to a wider range of applicability of kinetic
theory approaches to dense granular matter.
| arxiv topic:cond-mat.soft |
arxiv_dataset-943811.2948 | A gracious exit from the matter-dominated phase in a quantum cosmic
phantom model
gr-qc
The most recent observational constraints coming from Planck, when combined
with other cosmological data, provide evidence for a phantom scenario. In this
work we consider a quantum cosmic phantom model where both the matter particles
and scalar field are associated with quantum potentials which make the
effective mass associated with the matter particles to vanish at the time of
matter-radiation equality, resulting in a cosmic system where a matter
dominance phase followed by an accelerating expansion is allowed.
| arxiv topic:gr-qc |
arxiv_dataset-944811.3048 | Bounds on Rayleigh-Benard convection with general thermal boundary
conditions. Part 1. Fixed Biot number boundaries
physics.flu-dyn
We investigate the influence of the thermal properties of the boundaries in
turbulent Rayleigh-Benard convection on analytical bounds on convective heat
transport. Using the Doering-Constantin background flow method, we
systematically formulate a bounding principle on the Nusselt-Rayleigh number
relationship for general mixed thermal boundary conditions of constant Biot
number \eta which continuously interpolates between the previously studied
fixed temperature ($\eta = 0$) and fixed flux ($\eta = \infty$) cases, and
derive explicit asymptotic and rigorous bounds. Introducing a control parameter
R as a measure of the driving which is in general different from the usual
Rayleigh number Ra, we find that for each $\eta > 0$, as R increases the bound
on the Nusselt number Nu approaches that for the fixed flux problem.
Specifically, for $0 < \eta \leq \infty$ and for sufficiently large R ($R > R_s
= O(\eta^{-2})$ for small \eta) the Nusselt number is bounded as $Nu \leq
c(\eta) R^{1/3} \leq C Ra^{1/2}$, where C is an \eta-independent constant. In
the $R \to \infty$ limit, the usual fixed temperature assumption is thus a
singular limit of this general bounding problem.
| arxiv topic:physics.flu-dyn |
arxiv_dataset-945811.3148 | Stochastic dynamics of model proteins on a directed graph
cond-mat.soft cond-mat.stat-mech
A method for reconstructing the energy landscape of simple polypeptidic
chains is described. We show that we can construct an equivalent representation
of the energy landscape by a suitable directed graph. Its topological and
dynamical features are shown to yield an effective estimate of the time scales
associated with the folding and with the equilibration processes. This
conclusion is drawn by comparing molecular dynamics simulations at constant
temperature with the dynamics on the graph, defined by a temperature dependent
Markov process. The main advantage of the graph representation is that its
dynamics can be naturally renormalized by collecting nodes into "hubs", while
redefining their connectivity. We show that both topological and dynamical
properties are preserved by the renormalization procedure. Moreover, we obtain
clear indications that the heteropolymers exhibit common topological
properties, at variance with the homopolymer, whose peculiar graph structure
stems from its spatial homogeneity. In order to obtain a clear distinction
between a "fast folder" and a "slow folder" in the heteropolymers one has to
look at kinetic features of the directed graph. We find that the average time
needed to the fast folder for reaching its native configuration is two orders
of magnitude smaller than its equilibration time, while for the bad folder
these time scales are comparable. Accordingly, we can conclude that the
strategy described in this paper can be successfully applied also to more
realistic models, by studying their renormalized dynamics on the directed
graph, rather than performing lengthy molecular dynamics simulations.
| arxiv topic:cond-mat.soft cond-mat.stat-mech |
arxiv_dataset-946811.3248 | Analytic Expressions for the Surface Brightness Profile of GRB Afterglow
Images
astro-ph
The exact profile of a gamma-ray burst (GRB) afterglow image on the plane of
the sky can provide important constraints on the underlying physics. In
particular, it can test whether the magnetic field in the emitting shocked
external medium decreases significantly with the distance behind the shock
front, or remains roughly constant. Moreover, it enables more accurate
measurements of the afterglow image size and the expected scintillation
properties. In this work analytic expressions are derived for the afterglow
image in power law segments (PLSs) of the afterglow synchrotron spectrum in
which the emission originates from a very thin layer just behind the shock,
while simple semi-analytic expressions are derived for the remaining PLSs in
which the emission arises from the bulk of the shocked fluid. In all cases the
expressions are for a general power law external density profile, and are
convenient to use in afterglow studies.
| arxiv topic:astro-ph |
arxiv_dataset-947811.3348 | On Electromagnetically Induced Transparency in the Degenerate
$\Lambda$-scheme
physics.optics
Using an experimental work on "stopped light" as an example, we show how a
classical phenomenon of linear optics - interference of polarized light - can
imitate the effect of electromagnetically induced transparency.
| arxiv topic:physics.optics |
arxiv_dataset-948811.3448 | Binar Sort: A Linear Generalized Sorting Algorithm
cs.DS
Sorting is a common and ubiquitous activity for computers. It is not
surprising that there exist a plethora of sorting algorithms. For all the
sorting algorithms, it is an accepted performance limit that sorting algorithms
are linearithmic or O(N lg N). The linearithmic lower bound in performance
stems from the fact that the sorting algorithms use the ordering property of
the data. The sorting algorithm uses comparison by the ordering property to
arrange the data elements from an initial permutation into a sorted
permutation.
Linear O(N) sorting algorithms exist, but use a priori knowledge of the data
to use a specific property of the data and thus have greater performance. In
contrast, the linearithmic sorting algorithms are generalized by using a
universal property of data-comparison, but have a linearithmic performance
lower bound. The trade-off in sorting algorithms is generality for performance
by the chosen property used to sort the data elements.
A general-purpose, linear sorting algorithm in the context of the trade-off
of performance for generality at first consideration seems implausible. But,
there is an implicit assumption that only the ordering property is universal.
But, as will be discussed and examined, it is not the only universal property
for data elements. The binar sort is a general-purpose sorting algorithm that
uses this other universal property to sort linearly.
| arxiv topic:cs.DS |
arxiv_dataset-949811.3548 | Topological characterization of flow structures in resistive
pressure-gradient-driven turbulence
physics.plasm-ph
Visualization of turbulent flows is a powerful tool to help understand the
turbulence dynamics and induced transport. However, it does not provide a
quantitative description of the observed structures. In this paper, an approach
to characterize quantitatively the topology of the flows is given. The
technique, which can be applied to any type of turbulence dynamics, is
illustrated through the example of resistive ballooning instabilities.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-950811.3648 | Revisiting Norm Estimation in Data Streams
cs.DS cs.CC
The problem of estimating the pth moment F_p (p nonnegative and real) in data
streams is as follows. There is a vector x which starts at 0, and many updates
of the form x_i <-- x_i + v come sequentially in a stream. The algorithm also
receives an error parameter 0 < eps < 1. The goal is then to output an
approximation with relative error at most eps to F_p = ||x||_p^p.
Previously, it was known that polylogarithmic space (in the vector length n)
was achievable if and only if p <= 2. We make several new contributions in this
regime, including:
(*) An optimal space algorithm for 0 < p < 2, which, unlike previous
algorithms which had optimal dependence on 1/eps but sub-optimal dependence on
n, does not rely on a generic pseudorandom generator.
(*) A near-optimal space algorithm for p = 0 with optimal update and query
time.
(*) A near-optimal space algorithm for the "distinct elements" problem (p = 0
and all updates have v = 1) with optimal update and query time.
(*) Improved L_2 --> L_2 dimensionality reduction in a stream.
(*) New 1-pass lower bounds to show optimality and near-optimality of our
algorithms, as well as of some previous algorithms (the "AMS sketch" for p = 2,
and the L_1-difference algorithm of Feigenbaum et al.).
As corollaries of our work, we also obtain a few separations in the
complexity of moment estimation problems: F_0 in 1 pass vs. 2 passes, p = 0 vs.
p > 0, and F_0 with strictly positive updates vs. arbitrary updates.
| arxiv topic:cs.DS cs.CC |
arxiv_dataset-951811.3748 | Covariant Light-Front Approach for $B_c$ transition form factors
hep-ph
In the covariant light-front quark model, we investigate the form factors of
$B_c$ decays into $D, D^*, D_s, D_s^*, \eta_c, J/\psi, B, B^*, B_s, B_s^*$
mesons. The form factors in the spacelike region $q^2<0$ are directly
evaluated. To extrapolate the form factors to the full kinematic region, we fit
the form factors by adopting a three-parameter form from the spacelike region.
$b\to u,d,s$ transition form factors at maximally recoiling point ($q^2=0$) are
smaller than $b\to c$ and $c\to d,s$ transition form factors, while the $b\to
d,s,c$ form factors at zero recoiling point are close to each other. In the
fitting procedure, we find the parameters for the form factors $A_2(B_c\to
B^*)$ and $A_2(B_c\to B^*_s)$ strongly depend on the decay constants of $B^*$
and $B_s^*$ mesons. Fortunately, the semileptonic and nonleptonic $B_c$ decays
are not sensitive to these form factors. With the form factors, we also
investigate the branching fractions, polarizations of the semileptonic $B_c\to
Ml\nu$ decays. Semileptonic $B_c\to (\eta_c,J/\psi)l\nu$ and $B_c\to
(B_s,B_s^*)l\nu$ decays have much larger branching fractions than $B_c\to
(D,D^*,B,B^*)l\nu$. In the three kinds of $B_c\to Vl\nu$ decays, contributions
from the longitudinal polarized vector is comparable with those from the
transversely polarized vector. These predictions will be tested at the ongoing
and forthcoming hadron colliders.
| arxiv topic:hep-ph |
arxiv_dataset-952811.3848 | S-numbers of elementary operators on C*-algebras
math.OA
We study the s-numbers of elementary operators acting on C*-algebras. The
main results are the following: If $\tau$ is any tensor norm and $a,b\in B(H)$
are such that the sequences $s(a),s(b)$ of their singular numbers belong to a
stable Calkin space $J$ then the sequence of approximation numbers of
$a\otimes_{\tau} b$ belongs to $J$. If $A$ is a C*-algebra, $J$ is a stable
Calkin space, $s$ is an s-number function, and $a_i, b_i \in A,$ $i=1,...,m$
are such that $s(\pi(a_i)), s(\pi(b_i)) \in J$, $i=1,...,m$ for some faithful
representation $\pi$ of $A$ then $s(\sum_{i=1}^{m} M_{a_i,b_i})\in J$. The
converse implication holds if and only if the ideal of compact elements of $A$
has finite spectrum. We also prove a quantitative version of a result of
Ylinen.
| arxiv topic:math.OA |
arxiv_dataset-953811.3948 | Note on Rotating Charged Black Holes in Einstein-Maxwell-Chern-Simons
Theory
hep-th gr-qc
We show that the general solution of Chong, Cvetic, Lu and Pope for
nonextremal rotating charged black holes in five-dimensional minimal gauged
supergravity, or equivalently in the Einstein-Maxwell-Chern-Simons theory with
a negative cosmological constant and with the Chern-Simons coefficient $ \nu=1
$, admits a simple description in a Kerr-Schild type framework with two scalar
functions. Next, assuming this framework as an ansatz, we obtain new analytic
solutions for slowly rotating charged black holes in the
Einstein-Maxwell-Chern-Simons theory with $ \nu\neq 1 .$ Using a covariant
superpotential derived from Noether identities within the
Katz-Bicak-Lynden-Bell approach, we calculate the mass and angular momenta for
the general supergravity solution as well as for the slowly rotating solution
with two independent rotation parameters. For the latter case, we also
calculate the gyromagnetic ratios and obtain simple analytic formulas,
involving both the parameters of the black holes and the Chern-Simons
coefficient.
| arxiv topic:hep-th gr-qc |
arxiv_dataset-954811.4048 | Toward Perfection: Kapellasite, Cu3Zn(OH)6Cl2, a New Model S = 1/2
Kagome Antiferromagnet
cond-mat.str-el cond-mat.mtrl-sci
The search for the resonating valence bond (RVB) state continues to underpin
many areas of condensed matter research. The RVB is made from the dimerisation
of spins on different sites into fluctuating singlets, and was proposed by
Anderson to be the reference state from which the transition to BCS
superconductivity occurs. Little is known about the state experimentally, due
to the scarcity of model materials. Theoretical work has put forward the S =
1/2 kagome antiferromagnet (KAFM) as a good candidate for the realization of
the RVB state. In this paper we introduce a new model system, the S = 1/2 KAFM
Kapellasite, Cu3Zn(OH)6Cl2. We show that its crystal structure is a good
approximation to a 2-dimensional kagome antiferromagnet and that susceptibility
data indicate a collapse of the magnetic moment below T = 25 K that is
compatible with the spins condensing into the non-magnetic RVB state.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-955811.4148 | Monoidal transformations of singularities in positive characteristic
math.AG
A sequence of monoidal transformations is defined, in terms of invariants,
for a singular hypersurface embedded in a smooth scheme of positive
characteristic. Some examples are added to illustrate the improvement of
singularities by this procedure.
| arxiv topic:math.AG |
arxiv_dataset-956811.4248 | Growth of GaAs nanowires on Au, Au / Pd, Ag, Ni, Ga, Cu, Al, Ti metal
films
cond-mat.mtrl-sci
GaAs nanowires were grown by metalorganic vapor phase epitaxy on evaporated
metal films (Au, Au / Pd, Ag, Ni, Ga, Cu, Al, Ti). The samples were
characterized by scanning electron microscope (SEM) and transmission electron
microscope (TEM). SEM images reveal that nanowires grow directly on the metals.
TEM characterization shows crystalline nanowire (nw) structure originating from
Au. Article presents state of the art about nanowire-metal interface growth and
enumerates nanowire contacting methods with metals.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-957811.4348 | Modelling the human pharyngeal airway: validation of numerical
simulations using in vitro experiments
physics.med-ph
In the presented study, a numerical model which predicts the flow-induced
collapse within the pharyngeal airway is validated using in vitro measurements.
Theoretical simplifications were considered to limit the computation time.
Systematic comparisons between simulations and measurements were performed on
an in vitro replica, which reflects asymmetries of the geometry and of the
tissue properties at the base of the tongue and in pathological conditions
(strong initial obstruction). First, partial obstruction is observed and
predicted. Moreover, the prediction accuracy of the numerical model is of 4.2%
concerning the deformation (mean quadratic error on the constriction area). It
shows the ability of the assumptions and method to predict accurately and
quickly a fluid-structure interaction.
| arxiv topic:physics.med-ph |
arxiv_dataset-958811.4448 | Four loop twist two, BFKL, wrapping and strings
hep-th hep-ph
The anomalous dimensions of twist two operators have to satisfy certain
consistency requirements derived from BFKL. For N=4 SYM it was shown that at
four loops, the anomalous dimensions derived from the all-loop asymptotic Bethe
ansatz do not pass this test. In this paper we obtain the remaining wrapping
part of these anomalous dimensions from string theory and show that these
contributions exactly cure the problem and lead to agreement with both LO and
NLO BFKL expectations.
| arxiv topic:hep-th hep-ph |
arxiv_dataset-959811.4548 | The inhomogeneous equation of state and the road towards the solution of
the cosmological constant problem
gr-qc
We present a cosmological model containing a cosmological constant $\Lambda$
and a component with an inhomogeneous equation of state. We study the form of
the inhomogeneous equation of state for which the model exhibits the relaxation
of the cosmological constant, i.e. it asymptotically tends to the de Sitter
regime characterized by a small positive effective cosmological constant. The
effect of the relaxation of the cosmological constant is observed both for
negative and positive values of $\Lambda$ and for a range of model parameters.
A special emphasis is put on the study of the details of the CC relaxation
mechanism and the robustness of the mechanism to the variation of model
parameters. It is found that within the studied model the effective
cosmological constant at large scale factor values is small because the
absolute value of the real cosmological constant is large.
| arxiv topic:gr-qc |
arxiv_dataset-960811.4648 | Nucleosynthesis Calculations from Core-Collapse Supernovae
astro-ph
We review some of the uncertainties in calculating nucleosynthetic yields,
focusing on the explosion mechanism. Current yield calculations tend to either
use a piston, energy injection, or enhancement of neutrino opacities to drive
an explosion. We show that the energy injection, or more accurately, an entropy
injection mechanism is best-suited to mimic our current understanding of the
convection-enhanced supernova engine. The enhanced neutrino-opacity technique
is in qualitative disagreement with simulations of core-collapse supernovae and
will likely produce errors in the yields. But piston-driven explosions are the
most discrepant. Piston-driven explosion severely underestimate the amount of
fallback, leading to order-of-magnitude errors in the yields of heavy elements.
To obtain yields accurate to the factor of a few level, we must use entropy or
energy injection and this has become the NuGrid collaboration approach.
| arxiv topic:astro-ph |
arxiv_dataset-961811.4748 | Gemini/GMOS search of massive binaries in the ionizing cluster of 30 Dor
astro-ph
If binaries are common among massive stars, it will have important
consequences for the derivation of fundamental properties like the cluster age,
IMF and dynamical mass. Making use of the multiplexing facilities of Gemini
Multi Object Spectrograph (GMOS) we were able to investigate the presence of
binary stars within the ionising cluster of 30 Doradus. From a seven epochs
observing campaign at Gemini South we detect a binary candidate rate of about
50%, which is consistent with an intrinsic 100% binary rate among massive
stars. We find that single epoch determinations of the velocity dispersion give
values around 30 km/s . After correcting the global velocity dispersion for the
binary orbital motions, the true cluster velocity dispersion is 8.3 km/s. This
value implies a virial mass of about 4.5E5 Msun or 8 percent of the mass
calculated using the single epoch value. The binary corrected virial mass
estimate is consistent with photometric mass determinations thus suggesting
that NGC 2070 is a firm candidate for a future globular cluster.
| arxiv topic:astro-ph |
arxiv_dataset-962812.0074 | Relative entropy of entanglement of rotationally invariant states
quant-ph
We calculate the relative entropy of entanglement for rotationally invariant
states of spin-1/2 and arbitrary spin-$j$ particles or of spin-1 particle and
spin-$j$ particle with integer $j$. A lower bound of relative entropy of
entanglement and an upper bound of distillable entanglement are presented for
rotationally invariant states of spin-1 particle and spin-$j$ particle with
half-integer $j$.
| arxiv topic:quant-ph |
arxiv_dataset-963812.0174 | Magnetic Moment Formulas of Baryons Determined by Quantum Numbers
physics.gen-ph physics.acc-ph
We propose that the magnetic moment formulas of baryons may be determined by
quantum numbers, and obtain three formulas. This is a new type of magnetic
moment formula, and agrees better with the experimental values. It is also
similar to corresponding mass formulas of hadrons.
| arxiv topic:physics.gen-ph physics.acc-ph |
arxiv_dataset-964812.0274 | Bose Einstein condensation on inhomogeneous amenable graphs
math.OA math-ph math.MP
We investigate the Bose-Einstein Condensation on nonhomogeneous amenable
networks for the model describing arrays of Josephson junctions. The resulting
topological model, whose Hamiltonian is the pure hopping one given by the
opposite of the adjacency operator, has also a mathematical interest in itself.
We show that for the nonhomogeneous networks like the comb graphs, particles
condensate in momentum and configuration space as well. In this case different
properties of the network, of geometric and probabilistic nature, such as the
volume growth, the shape of the ground state, and the transience, all play a
role in the condensation phenomena. The situation is quite different for
homogeneous networks where just one of these parameters, e.g. the volume
growth, is enough to determine the appearance of the condensation.
| arxiv topic:math.OA math-ph math.MP |
arxiv_dataset-965812.0374 | Asteroseismology of chemically peculiar stars
astro-ph
Pulsational variability is observed in several types of main sequence stars
with anomalous chemical abundances. In this contribution I summarize the
relationship between pulsations and chemical peculiarities, giving special
emphasis to rapid oscillations in magnetic Ap stars. These magneto-acoustic
pulsators provide unique opportunities to study the interaction of pulsations,
chemical inhomogeneities, and strong magnetic fields. Time-series monitoring of
rapidly oscillating Ap stars using high-resolution spectrometers at large
telescopes and ultra-precise space photometry has led to a number of important
breakthroughs in our understanding of these interesting objects. Interpretation
of the roAp frequency spectra has allowed constraining fundamental stellar
parameters and probing poorly known properties of the stellar interiors. At the
same time, investigation of the pulsational wave propagation in chemically
stratified atmospheres of roAp stars has been used as a novel asteroseismic
tool to study pulsations as a function of atmospheric height and to map in
detail the horizontal structure of the magnetically-distorted p-modes.
| arxiv topic:astro-ph |
arxiv_dataset-966812.0474 | Lh_c
hep-ph
The production cross-section of h_c, the 1P_1 charmonium state, can be
predicted in Non-Relativistic QCD (NRQCD) using heavy-quark symmetry. We show
that at the Large Hadron Collider a large cross-section for this resonance is
predicted and it should be possible to look for the h_c through it decay into
J/psi +pi even with the statistics that will be achieved within a few months of
run-time at the LHC.
| arxiv topic:hep-ph |
arxiv_dataset-967812.0574 | The Muisca Calendar: An approximation to the timekeeping system of the
ancient native people of the northeastern Andes of Colombia
physics.hist-ph
The aim of this project is to review and expand upon the model proposed by
Father Jose Domingo Duquesne de la Madrid (1745-1821) regarding the calendar of
the ancient Muisca culture of the central Colombia. This model was dismissed by
scholars in the late 19th century, calling it just a simple invention of a
clergyman; however, a detailed analysis of Duquesne's work shows that his
interpretation of the timekeeping system was based on information given to him
by indigenous informers. Based on his work, we can be derive somewhat
indirectly, some aspects of the calendar that apparently were not understood by
the priest. This confirms that such a system was not his own invention.
Ethnohistorical and archaeological evidence provide support for Duquesne's
calendar model. Massive Muisca ceremonies described by 16th century Spanish
chroniclers, is examined and; the occurrence of such ceremonies seem to match
the astronomical cycle of conjunctions of the planets Jupiter and Saturn, wich
also agrees with the 60-year span described by Duquesne as the Muisca Acrotom
Century. Archaeological artifacts, such as a carved stone found in the village
of Choachi (Cundinamarca) that shows numerical elements supports Duquesne's
model that suggests this stone was a calendar calculation tool for Muisca
priests.
| arxiv topic:physics.hist-ph |
arxiv_dataset-968812.0674 | BCS-BEC Crossover and Thermodynamics in Asymmetric Nuclear Matter with
Pairings in Isospin I=0 and I=1 Channels
nucl-th
The BCS-BEC crossover and phase diagram for asymmetric nuclear superfluid
with pairings in isospin I = 0 and I = 1 channels are investigated at mean
field level, by using a density dependent nucleon-nucleon potential. Induced by
the in-medium nucleon mass and density dependent coupling constants,
neutron-proton Cooper pairs could be in BEC state at sufficiently low density,
but there is no chance for the BEC formation of neutron-neutron and
proton-proton pairs at any density and asymmetry. We calculate the phase
diagram in asymmetry-temperature plane for weakly interacting nuclear
superfluid, and find that including the I = 1 channel changes significantly the
phase structure at low temperature. There appears a new phase with both I = 0
and I = 1 pairings at low temperature and low asymmetry, and the gapless state
in any phase with I = 1 pairing is washed out and all excited nucleons are
fully gapped.
| arxiv topic:nucl-th |
arxiv_dataset-969812.0774 | Superconductivity in LnFePO (Ln = La, Pr, and Nd) single crystals
cond-mat.supr-con
Single crystals of the compounds LaFePO, PrFePO, and NdFePO have been
prepared by means of a flux growth technique and studied by electrical
resistivity, magnetic susceptibility and specific heat measurements. We have
found that PrFePO and NdFePO display superconductivity with values of the
superconducting critical temperature T_c of 3.2 K and 3.1 K, respectively. The
effect of annealing on the properties of LaFePO, PrFePO, and NdFePO is also
reported. The LnFePO (Ln = lanthanide) compounds are isostructural with the
LnFeAsO_{1-x}F_x compounds that become superconducting with T_c values as high
as 55 K for Ln = Sm. A systematic comparison of the occurrence of
superconductivity in the series LnFePO and LnFeAsO_{1-x}F_x points to a
possible difference in the origin of the superconductivity in these two series
of compounds.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-970812.0874 | Stroke Fragmentation based on Geometry Features and HMM
cs.HC cs.CV
Stroke fragmentation is one of the key steps in pen-based interaction. In
this letter, we present a unified HMM-based stroke fragmentation technique that
can do segment point location and primitive type determination simultaneously.
The geometry features included are used to evaluate local features, and the HMM
model is utilized to measure the global drawing context. Experiments prove that
the model can efficiently represent smooth curves as well as strokes made up of
arbitrary lines and circular arcs.
| arxiv topic:cs.HC cs.CV |
arxiv_dataset-971812.0974 | Real space first-principles derived semiempirical pseudopotentials
applied to tunneling magnetoresistance
cond-mat.mes-hall
In this letter we present a real space density functional theory (DFT)
localized basis set semi-empirical pseudopotential (SEP) approach. The method
is applied to iron and magnesium oxide, where bulk SEP and local spin density
approximation (LSDA) band structure calculations are shown to agree within
approximately 0.1 eV. Subsequently we investigate the qualitative
transferability of bulk derived SEPs to Fe/MgO/Fe tunnel junctions. We find
that the SEP method is particularly well suited to address the tight binding
transferability problem because the transferability error at the interface can
be characterized not only in orbital space (via the interface local density of
states) but also in real space (via the system potential). To achieve a
quantitative parameterization, we introduce the notion of ghost semi-empirical
pseudopotentials extracted from the first-principles calculated Fe/MgO bonding
interface. Such interface corrections are shown to be particularly necessary
for barrier widths in the range of 1 nm, where interface states on opposite
sides of the barrier couple effectively and play a important role in the
transmission characteristics. In general the results underscore the need for
separate tight binding interface and bulk parameter sets when modeling
conduction through thin heterojunctions on the nanoscale.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-972812.1074 | Towards the Probabilistic Earth-System Model
physics.ao-ph
Multi-model ensembles provide a pragmatic approach to the representation of
model uncertainty in climate prediction. However, such representations are
inherently ad hoc, and, as shown, probability distributions of climate
variables based on current-generation multi-model ensembles, are not accurate.
Results from seasonal re-forecast studies suggest that climate model ensembles
based on stochastic-dynamic parametrisation are beginning to outperform
multi-model ensembles, and have the potential to become significantly more
skilful than multi-model ensembles.
The case is made for stochastic representations of model uncertainty in
future-generation climate prediction models. Firstly, a guiding characteristic
of the scientific method is an ability to characterise and predict uncertainty;
individual climate models are not currently able to do this. Secondly, through
the effects of noise-induced rectification, stochastic-dynamic parametrisation
may provide a (poor man's) surrogate to high resolution. Thirdly,
stochastic-dynamic parametrisations may be able to take advantage of the
inherent stochasticity of electron flow through certain types of low-energy
computer chips, currently under development.
These arguments have particular resonance for next-generation Earth-System
models, which purport to be comprehensive numerical representations of climate,
and where integrations at high resolution may be unaffordable.
| arxiv topic:physics.ao-ph |
arxiv_dataset-973812.1174 | Cosmic-ray electron signatures of dark matter
astro-ph
There is evidence for an excess in cosmic-ray electrons at about 500 GeV
energy, that may be related to dark-matter annihilation. I have calculated the
expected electron contributions from a pulsar and from Kaluza-Klein dark
matter, based on a realistic treatment of the electron propagation in the
Galaxy. Both pulsars and dark-matter clumps are quasi-pointlike and few, and
therefore their electron contributions at Earth generally have spectra that
deviate from the average spectrum one would calculate for a smooth source
distribution. I find that pulsars younger than about 10^5 years naturally cause
a narrow peak at a few hundred GeV in the locally observed electron spectrum,
similar to that observed. On the other hand, for a density n_c = 10 /kpc^3 of
dark-matter clumps the sharp cut-off in the contribution from Kaluza-Klein
particles is sometimes more pronounced, but often smoothed out and
indistinguishable from a pulsar source, and therefore the spectral shape of the
electron excess is insufficient to discriminate a dark-matter origin from more
conventional astrophysical explanations. The amplitude of variations in the
spectral feature caused by dark matter predominantly depends on the density of
dark-matter clumps, which is not well known.
| arxiv topic:astro-ph |
arxiv_dataset-974812.1274 | Probing the Mechanisms of Fibril Formation Using Lattice Models
q-bio.BM q-bio.OT
Using exhaustive Monte Carlo simulations we study the kinetics and mechanism
of fibril formation using lattice models as a function of temperature and the
number of chains. While these models are, at best, caricatures of peptides, we
show that a number of generic features thought to govern fibril assembly are
present in the toy model. The monomer, which contains eight beads made from
three letters (hydrophobic, polar, and charged), adopts a compact conformation
in the native state. The kinetics of fibril assembly occurs in three distinct
stages. In each stage there is a cascade of events that transforms the monomers
and oligomers to ordered structures. In the first "burst" stage highly mobile
oligomers of varying sizes form. The conversion to the aggregation-prone
conformation occurs within the oligomers during the second stage. As time
progresses, a dominant cluster emerges that contains a majority of the chains.
In the final stage, the aggregation-prone conformation particles serve as a
template onto which smaller oligomers or monomers can dock and undergo
conversion to fibril structures. The overall time for growth in the latter
stages is well described by the Lifshitz-Slyazov growth kinetics for
crystallization from super-saturated solutions.
| arxiv topic:q-bio.BM q-bio.OT |
arxiv_dataset-975812.1374 | Demystification of Taylor,Laurent coefficients of Lerch,Hurwitz Zeta
functions and Dirichlet L-Function at Unity and Zero and their Bounds
math.NT
Using elementary methods,we obtain simple,explicit expressions and bounds of
higher order derivatives of Hurwitz zeta function and consequently those of
Dirichlet L-function and also,of Lerch's Zeta function at unity (and at Zero
too)and also obtain their interrelations.We also state elementary complete
forms of approximate functional equations of Hurwitz zeta function and
Dirichlet L-function in the critical strip.
| arxiv topic:math.NT |
arxiv_dataset-976812.1474 | Entropic uncertainties for joint quantum measurements
quant-ph
We investigate the uncertainty associated with a joint quantum measurement of
two components of spin of a spin-1/2 particle and quantify this in terms of
entropy. We consider two entropic quantities: the joint entropy and the sum of
the marginal entropies, and obtain lower bounds for each of these quantities.
For the case of joint measurements where we measure each spin observable
equally well, these lower bounds are tight.
| arxiv topic:quant-ph |
arxiv_dataset-977812.1574 | Nonlinear gravitons in 4-D general relativity by expansion about the
Kodama state
gr-qc
In this paper we provide a possible realization of Penrose's idea of
nonlinear gravitons using a new description of nonmetric general relativity. In
the addressal of issues surrounding the normalizability of the Kodama state and
its reliability as a ground state for gravity, we expand the theory in
fluctuations about the Kodama state. This produces a theory of complex gravity
with a well-defined Hilbert space structure, whose quantization we carry out
both at the linearized level and in the full nonlinear theory. The results of
this paper demonstrate the preservation of the physical degrees of freedom of
the full nonlinear theory under linearization, as well provide a Hilbert space
of states of the former annihilated by the quantum Hamiltonian constraint.
| arxiv topic:gr-qc |
arxiv_dataset-978812.1674 | Monadic approach to Galois descent and cohomology
math.CT
We describe a simplified categorical approach to Galois descent theory. It is
well known that Galois descent is a special case of Grothendieck descent, and
that under mild additional conditions the category of Grothendieck descent data
coincides with the Eilenberg-Moore category of algebras over a suitable monad.
This also suggests using monads directly, and our monadic approach to Galois
descent makes no reference to Grothendieck descent theory at all. In order to
make Galois descent constructions perfectly clear, we also describe their
connections with some other related constructions of categorical algebra, and
make various explicit calculations, especially with 1-cocycles and
1-dimensional non-abelian cohomology, usually omitted in the literature.
| arxiv topic:math.CT |
arxiv_dataset-979812.1774 | UBVI CCD Photometry of the Old Open Cluster NGC 1193
astro-ph
We present UBVI photometry of the old open cluster NGC 1193. Color-magnitude
diagrams (CMDs) of this cluster show a well defined main sequence and a sparse
red giant branch. For the inner region of r<50 arcsec, three blue straggler
candidates are newly found in addition to the objects Kaluzny (1988) already
found. The color-color diagrams show that the reddening value toward NGC 1193
is E(B-V) =0.19 +/- 0.04. From the ultraviolet excess measurement, we derived
the metallicity to be [Fe/H]=-0.45 +/- 0.12. A distance modulus of (m-M)_0
=13.3 +/- 0.15 is obtained from zero age main sequence fitting with the
empirically calibrated Hyades isochrone of Pinsonneault et al. (2004). CMD
comparison with the Padova isochrones by Bertelli et al. (1994) gives an age of
log t =9.7 +/- 0.1.
| arxiv topic:astro-ph |
arxiv_dataset-980812.1874 | An experimental and kinetic modelling study of the oxidation of the four
isomers of butanol
physics.chem-ph
Butanol, an alcohol which can be produced from biomass sources, has received
recent interest as an alternative to gasoline for use in spark ignition engines
and as a possible blending compound with fossil diesel or biodiesel. Therefore,
the autoignition of the four isomers of butanol (1-butanol, 2-butanol,
iso-butanol, and tert-butanol) has been experimentally studied at high
temperatures in a shock tube and a kinetic mechanism for description of their
high-temperature oxidation has been developed. Ignition delay times for
butanol/oxygen/argon mixtures have been measured behind reflected shock waves
at temperatures and pressures ranging from approximately 1200 to 1800 K and 1
to 4 bar. Electronically excited OH emission and pressure measurements were
used to determine ignition delay times. A detailed kinetic mechanism has been
developed to describe the oxidation of the butanol isomers and validated by
comparison to the shock tube measurements. Reaction flux and sensitivity
analysis indicate that the consumption of 1 butanol and iso-butanol, the most
reactive isomers, takes place primarily by H-atom abstraction resulting in the
formation of radicals, the decomposition of which yields highly reactive
branching agents, H-atoms and OH radicals. Conversely, the consumption of tert
butanol and 2-butanol, the least reactive isomers, takes place primarily via
dehydration, resulting in the formation of alkenes, which lead to resonance
stabilized radicals with very low reactivity. To our knowledge, the ignition
delay measurements and oxidation mechanism presented here for 2-butanol,
iso-butanol, and tert butanol are the first of their kind..
| arxiv topic:physics.chem-ph |
arxiv_dataset-981812.1974 | Disk reflection signatures in the spectrum of the bright Z-source GX
340+0
astro-ph
We present the preliminary results of a 50 ks long XMM-Newton observation of
the bright Z-source GX 340+0. In this Letter we focus on the study of a broad
asymmetric emission line in the Fe K alpha energy band, whose shape is clearly
resolved and compatible with a relativistically smeared profile arising from
reflection on a hot accretion disk extending close to the central accreting
neutron star. By combining temporal and spectral analysis, we are able to
follow the evolution of the source along its Horizontal Branch. However,
despite a significant change in the continuum emission and luminosity, the line
profile does not show any strong correlated variation. This broad line is
produced by recombination of highly ionized iron (Fe XXV) at an inferred inner
radius close to 13 gravitational radii while the fit requires a high value for
the outer disk radius. The inclination of the source is extremely well
constrained at 35 deg, while the emissivity index is -2.50.
| arxiv topic:astro-ph |
arxiv_dataset-982812.2074 | Geometrical Diagnostics for Generalized Chaplygin Gas
astro-ph astro-ph.CO
A new diagnostic method, $Om$ is applied to generalized Chaplygin gas (GCG)
model as the unification of dark matter and dark energy. On the basis of the
recently observed data: the Union supernovae, the observational Hubble data,
the SDSS baryon acoustic peak and the five-year WMAP shift parameter, we show
the discriminations between GCG and $\Lambda$CDM model. Furthermore, it is
calculated that the current equation of state of dark energy $w_{0de}=-0.964$
according to GCG model.
| arxiv topic:astro-ph astro-ph.CO |
arxiv_dataset-983812.2174 | A discrete inhomogeneous model for the yeast cell cycle
q-bio.MN physics.bio-ph
We study the robustness and stability of the yeast cell regulatory network by
using a general inhomogeneous discrete model. We find that inhomogeneity, on
average, enhances the stability of the biggest attractor of the dynamics and
that the large size of the basin of attraction is robust against changes in the
parameters of inhomogeneity. We find that the most frequent orbit, which
represents the cell-cycle pathway, has a better biological meaning than the one
exhibited by the homogeneous model.
| arxiv topic:q-bio.MN physics.bio-ph |
arxiv_dataset-984812.2274 | Force-detected nuclear double resonance between statistical spin
polarizations
cond-mat.stat-mech
We demonstrate nuclear double resonance for nanometer-scale volumes of spins
where random fluctuations rather than Boltzmann polarization dominate. When the
Hartmann-Hahn condition is met in a cross-polarization experiment, flip-flops
occur between two species of spins and their fluctuations become coupled. We
use magnetic resonance force microscopy to measure this effect between 1H and
13C spins in 13C-enriched stearic acid. The development of a cross-polarization
technique for statistical ensembles adds an important tool for generating
chemical contrast in nanometer-scale magnetic resonance.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-985812.2374 | Cosmic Ray Positron and Electron Excess from Hidden-Fermion Dark Matter
Decays
hep-ph
The anomalies observed in recent cosmic ray experiments seem to strongly
constrain the nature of the dark matter. In this letter, we investigate a
possibility of the fermionic dark matter with a minimal extension of the
standard model. We found that the dark matter decays caused by the dimension
six operators can naturally explain the anomalies.
| arxiv topic:hep-ph |
arxiv_dataset-986812.2474 | Generation of entangled photon-pairs from a single quantum dot embedded
in a planar photonic-crystal cavity
cond-mat.other
We present a formal theory of single quantum-dot coupling to a planar
photonic crystal that supports quasi-degenerate cavity modes, and use this
theory to describe, and optimize, entangled-photon-pair generation via the
biexciton-exciton cascade. In the generated photon pairs, either both photons
are spontaneously emitted from the dot, or one photon is emitted from the
biexciton spontaneously and the other is emitted via the leaky-cavity mode. In
the strong-coupling regime, the generated photon pairs can be maximally
entangled, in qualitative agreement with the simple dressed-state predictions
of Johne {\em et al.} [Phys. Rev. Lett. vol. 100, 240404 (2008)]. We derive
useful and physically-intuitive analytical formulas for the spectrum of the
emitted photon pairs in the presence of exciton and biexciton broadening, which
is necessary to connect to experiments, and demonstrate the clear failure of
using a dressed-state approach. We also present a method for calculating and
optimizing the entanglement between the emitted photons, which can account for
post-sample spectral filtering. Pronounced entanglement values of greater than
80% are demonstrated using experimentally achievable parameters, even without
spectral filtering.
| arxiv topic:cond-mat.other |
arxiv_dataset-987812.2574 | Feature Selection By KDDA For SVM-Based MultiView Face Recognition
cs.CV cs.LG
Applications such as face recognition that deal with high-dimensional data
need a mapping technique that introduces representation of low-dimensional
features with enhanced discriminatory power and a proper classifier, able to
classify those complex features. Most of traditional Linear Discriminant
Analysis suffer from the disadvantage that their optimality criteria are not
directly related to the classification ability of the obtained feature
representation. Moreover, their classification accuracy is affected by the
"small sample size" problem which is often encountered in FR tasks. In this
short paper, we combine nonlinear kernel based mapping of data called KDDA with
Support Vector machine classifier to deal with both of the shortcomings in an
efficient and cost effective manner. The proposed here method is compared, in
terms of classification accuracy, to other commonly used FR methods on UMIST
face database. Results indicate that the performance of the proposed method is
overall superior to those of traditional FR approaches, such as the Eigenfaces,
Fisherfaces, and D-LDA methods and traditional linear classifiers.
| arxiv topic:cs.CV cs.LG |
arxiv_dataset-988812.2674 | Degenerate quantum codes and the quantum Hamming bound
quant-ph
The parameters of a nondegenerate quantum code must obey the Hamming bound.
An important open problem in quantum coding theory is whether or not the
parameters of a degenerate quantum code can violate this bound for
nondegenerate quantum codes. In this paper we show that Calderbank-Shor-Steane
(CSS) codes with alphabet $q\geq 5$ cannot beat the quantum Hamming bound. We
prove a quantum version of the Griesmer bound for the CSS codes which allows us
to strengthen the Rains' bound that an $[[n,k,d]]_2$ code cannot correct more
than $\floor{(n+1)/6}$ errors to $\floor{(n-k+1)/6}$. Additionally, we also
show that the general quantum codes $[[n,k,d]]_q$ with $k+d\leq
{(1-2eq^{-2})n}$ cannot beat the quantum Hamming bound.
| arxiv topic:quant-ph |
arxiv_dataset-989812.2774 | Two Mode Photon Bunching Effect as Witness of Quantum Criticality in
Circuit QED
quant-ph cond-mat.mes-hall
We suggest a scheme to probe critical phenomena at a quantum phase transition
(QPT) using the quantum correlation of two photonic modes simultaneously
coupled to a critical system. As an experimentally accessible physical
implementation, a circuit QED system is formed by a capacitively coupled
Josephson junction qubit array interacting with one superconducting
transmission line resonator (TLR). It realizes an Ising chain in the transverse
field (ICTF) which interacts with the two magnetic modes propagating in the
TLR. We demonstrate that in the vicinity of criticality the originally
independent fields tend to display photon bunching effects due to their
interaction with the ICTF. Thus, the occurrence of the QPT is reflected by the
quantum characteristics of the photonic fields.
| arxiv topic:quant-ph cond-mat.mes-hall |
arxiv_dataset-990812.2874 | A Data Model for Integrating Heterogeneous Medical Data in the
Health-e-Child Project
cs.DB
There has been much research activity in recent times about providing the
data infrastructures needed for the provision of personalised healthcare. In
particular the requirement of integrating multiple, potentially distributed,
heterogeneous data sources in the medical domain for the use of clinicians has
set challenging goals for the healthgrid community. The approach advocated in
this paper surrounds the provision of an Integrated Data Model plus links
to/from ontologies to homogenize biomedical (from genomic, through cellular,
disease, patient and population-related) data in the context of the EC
Framework 6 Health-e-Child project. Clinical requirements are identified, the
design approach in constructing the model is detailed and the integrated model
described in the context of examples taken from that project. Pointers are
given to future work relating the model to medical ontologies and challenges to
the use of fully integrated models and ontologies are identified.
| arxiv topic:cs.DB |
arxiv_dataset-991812.2974 | Resistance noise in electrically biased bilayer graphene
cond-mat.mes-hall
We demonstrate that the low-frequency resistance fluctuations, or noise, in
bilayer graphene is strongly connected to its band structure, and displays a
minimum when the gap between the conduction and valence band is zero. Using
double-gated bilayer graphene devices we have tuned the zero gap and charge
neutrality points independently, which offers a versatile mechanism to
investigate the low-energy band structure, charge localization and screening
properties of bilayer graphene.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-992812.3074 | Renormalization group flows for the second $\mathbb{Z}_{N}$
parafermionic field theory for $N$ even
hep-th cond-mat.stat-mech
Extending the results obtained in the case $N$ odd, the effect of slightly
relevant perturbations of the second parafermionic field theory with the
symmetry $\mathbb{Z}_{N}$, for $N$ even, are studied. The renormalization group
equations, and their infra red fixed points exhibit the same structure in both
cases. In addition to the standard flow from the $p$-th to the $(p-2)$-th
model, another fixed point corresponding to the $(p-1)$-th model is found.
| arxiv topic:hep-th cond-mat.stat-mech |
arxiv_dataset-993812.3174 | Discrimination of two mixed quantum states with maximum confidence and
minimum probability of inconclusive results
quant-ph
We study an optimized measurement that discriminates two mixed quantum states
with maximum confidence for each conclusive result, thereby keeping the overall
probability of inconclusive results as small as possible. When the rank of the
detection operators associated with the two different conclusive outcomes does
not exceed unity we obtain a general solution. As an application, we consider
the discrimination of two mixed qubit states. Moreover, for the case of
higher-rank detection operators we give a solution for particular states. The
relation of the optimized measurement to other discrimination schemes is also
discussed.
| arxiv topic:quant-ph |
arxiv_dataset-994812.3274 | Mass transport of impurities in a moderately dense granular gas
cond-mat.stat-mech
Transport coefficients associated with the mass flux of impurities immersed
in a moderately dense granular gas of hard disks or spheres described by the
inelastic Enskog equation are obtained by means of the Chapman-Enskog
expansion. The transport coefficients are determined as the solutions of a set
of coupled linear integral equations recently derived for polydisperse granular
mixtures [V. Garz\'o, J. W. Dufty and C. M. Hrenya, Phys. Rev. E {\bf 76},
031304 (2007)]. With the objective of obtaining theoretical expressions for the
transport coefficients that are sufficiently accurate for highly inelastic
collisions, we solve the above integral equations by using the second Sonine
approximation. As a complementary route, we numerically solve by means of the
direct simulation Monte Carlo method (DSMC) the inelastic Enskog equation to
get the kinetic diffusion coefficient $D_0$ for two and three dimensions. We
have observed in all our simulations that the disagreement, for arbitrarily
large inelasticity, in the values of both solutions (DSMC and second Sonine
approximation) is less than 4%. Moreover, we show that the second Sonine
approximation to $D_0$ yields a dramatic improvement (up to 50%) over the first
Sonine approximation for impurity particles lighter than the surrounding gas
and in the range of large inelasticity. The results reported in this paper are
of direct application in important problems in granular flows, such as
segregation driven by gravity and a thermal gradient. We analyze here the
segregation criteria that result from our theoretical expressions of the
transport coefficients.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-995812.3374 | A remarkable sequence of integers
math.NT math.CO
A survey of properties of a sequence of coefficients appearing in the
evaluation of a quartic definite integral is presented. These properties are of
analytical, combinatorial and number-theoretical nature.
| arxiv topic:math.NT math.CO |
arxiv_dataset-996812.3474 | Free particle on noncommutative plane -- a coherent state path integral
approach
math-ph hep-th math.MP
We formulate the coherent state path integral on a two dimensional
noncommutative plane using the fact that noncommuative quantum mechanics can be
viewed as a quantum system on the Hilbert space of Hilbert-Schmidt operators
acting on noncommutative configuration space. The propagation kernel for the
free particle shows ultra-violet cutoff which agrees with the earlier
investigations made in the literature but the approach differs substantially
from the earlier studies.
| arxiv topic:math-ph hep-th math.MP |
arxiv_dataset-997812.3574 | Interplay of anisotropy and frustration: triple transitions in a
triangular-lattice antiferromagnet
cond-mat.str-el cond-mat.stat-mech
The classical Heisenberg antiferromagnet on a triangular lattice with the
single-ion anisotropy of the easy-axis type is theoretically investigated. The
mean-field phase diagram in an external magnetic field is constructed. Three
finite-temperature Berezinskii-Kosterlitz-Thouless transitions are found by the
Monte Carlo simulations in zero field. The two upper transitions are related to
the breaking of the discrete ${\mathbb Z}_{6}$ symmetry group, while the lowest
transition is associated with a quasi-long-range ordering of transverse
components. The intermediate collinear phase between first and second
transitions is the sliding phase predicted by J. V. Jos\'e {\it et al}. [Phys.
Rev. B {\bf 16}, 1217 (1977)].
| arxiv topic:cond-mat.str-el cond-mat.stat-mech |
arxiv_dataset-998812.3674 | Monge-Amp\`ere equations in big cohomology classes
math.CV math.DG
We define non-pluripolar products of closed positive currents on a compact
Kaehler manifold. We show that a positive non-pluripolar measure can be written
in a unique way as the top degree self-intersection (in the non-pluripolar
sense) of a closed positive current in given big cohomology class. The solution
is shown to have minimal singularities in the sense of Demailly if the measure
is regular enough. These results are combined with a fixed point argument to
construct singular Kaehler-Einstein volume forms with minimal singularities on
varieties of general type.
| arxiv topic:math.CV math.DG |
arxiv_dataset-999812.3774 | Josephson-current induced conformational switching of a molecular
quantum dot
cond-mat.supr-con cond-mat.mes-hall
We discuss the behavior of a two-level system coupled to a quantum dot
contacted by superconducting source/drain electrodes, representing a simple
model for the conformational degree of freedom of a molecular dot or a break
junction. The Josephson current is shown to induce conformational changes,
including a complete reversal. For small bias voltage, periodic conformational
motions induced by Landau-Zener transitions between Andreev states are
predicted.
| arxiv topic:cond-mat.supr-con cond-mat.mes-hall |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.