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arxiv_dataset-19001005.246 | Properties of the Top Quark
hep-ex
The top quark was discoverd at the CDF and D0 experiments in 1995. As the
partner of the bottom quark its properties within the Standard Model are fully
defined. Only the mass is a free parameter. The measurement of the top quark
mass and the verification of the expected properties have been an important
topic of experimental top quark physics since. In this review the recent
results on top quark properties obtained by the Tevatron experiments CDF and D0
are summarised. At the advent of the LHC special emphasis is given to the basic
measurement methods and the dominating systematic uncertainties.
| arxiv topic:hep-ex |
arxiv_dataset-19011005.256 | Diameters, distortion and eigenvalues
math.GR math.FA math.MG
We study the relation between the diameter, the first positive eigenvalue of
the discrete $p$-Laplacian and the $\ell_p$-distortion of a finite graph. We
prove an inequality relating these three quantities and apply it to families of
Cayley and Schreier graphs. We also show that the $\ell_p$-distortion of Pascal
graphs, approximating the Sierpinski gasket, is bounded, which allows to obtain
estimates for the convergence to zero of the spectral gap as an application of
the main result.
| arxiv topic:math.GR math.FA math.MG |
arxiv_dataset-19021005.266 | Differential-Algebraic Integrability Analysis of the Generalized Riemann
Type and Korteweg-de Vries Hydrodynamical Equations
nlin.SI math-ph math.MP physics.flu-dyn
A differential-algebraic approach to studying the Lax type integrability of
the generalized Riemann type hydrodynamic equations at N = 3; 4 is devised. The
approach is also applied to studying the Lax type integrability of the well
known Korteweg-de Vries dynamical system.
| arxiv topic:nlin.SI math-ph math.MP physics.flu-dyn |
arxiv_dataset-19031005.276 | On the velocity autocorrelation function of a Brownian particle
cond-mat.stat-mech physics.flu-dyn
Memory effect of Brownian motion in an incompressible fluid is studied. The
reasoning is based on the Mori-Zwanzig formalism and a new formulation of the
Langevin force as a result of collisions between an effective and the Brownian
particles. Thus, the stochastic force autocorrelation function with finite
dispersion and the corresponding Brownian particle velocity autocorrelation
function are obtained.
| arxiv topic:cond-mat.stat-mech physics.flu-dyn |
arxiv_dataset-19041005.286 | Substellar Companions to Evolved Intermediate-Mass Stars: HD 145457 and
HD 180314
astro-ph.EP
We report the detections of two substellar companions orbiting around evolved
intermediate-mass stars from precise Doppler measurements at Subaru Telescope
and Okayama Astrophysical Observatory. HD 145457 is a K0 giant with a mass of
1.9 M_sun and has a planet of minimum mass m_2sini=2.9 M_J orbiting with period
of P=176 d and eccentricity of e=0.11. HD 180314 is also a K0 giant with 2.6
M_sun and hosts a substellar companion of m_2sin i=22 M_J, which falls in
brown-dwarf mass regime, in an orbit with P=396 d and e=0.26. HD 145457 b is
one of the innermost planets and HD 180314 b is the seventh candidate of
brown-dwarf-mass companion found around intermediate-mass evolved stars.
| arxiv topic:astro-ph.EP |
arxiv_dataset-19051005.296 | Measurement of the Anisotropy of Cosmic Ray Arrival Directions with
IceCube
astro-ph.HE
We report the first observation of an anisotropy in the arrival direction of
cosmic rays with energies in the multi TeV region in the Southern sky using
data from the IceCube detector. Between June 2007 and March 2008, the
partially-deployed IceCube detector was operated in a configuration with 1320
digital optical sensors distributed over 22 strings at depths between 1450 and
2450 meters inside the Antarctic ice. IceCube is a neutrino detector, but the
data are dominated by a large background of cosmic ray muons. Therefore, the
background data are suitable for high-statistics studies of cosmic rays in the
Southern sky. The data include 4.3 billion muons produced by downgoing cosmic
ray interactions in the atmosphere; these events were reconstructed with a
median angular resolution of 3 degrees and a median energy of $\sim20$ TeV.
Their arrival direction distribution exhibits an anisotropy in right ascension
with a first harmonic amplitude of $(6.4\pm0.2 $stat$. \pm 0.8
$syst$.)\times10^{-4}$.
| arxiv topic:astro-ph.HE |
arxiv_dataset-19061005.306 | The Herschel Virgo Cluster Survey: VII. Dust in cluster dwarf elliptical
galaxies
astro-ph.CO
We use the Science Demonstration Phase data of the Herschel Virgo Cluster
Survey to search for dust emission of early-type dwarf galaxies in the central
regions of the Virgo Cluster as an alternative way of identifying the
interstellar medium.We present the first possible far-infrared detection of
cluster early-type dwarf galaxies: VCC781 and VCC951 are detected at the 10
sigma level in the SPIRE 250 micron image. Both detected galaxies have dust
masses of the order of 10^5 Msun and average dust temperatures ~20K. The
detection rate (less than 1%) is quite high compared to the 1.7% detection rate
for Hi emission, considering that dwarfs in the central regions are more Hi
deficient. We conclude that the removal of interstellar dust from dwarf
galaxies resulting from ram pressure stripping, harassment, or tidal effects
must be as efficient as the removal of interstellar gas.
| arxiv topic:astro-ph.CO |
arxiv_dataset-19071005.316 | Funny Problems in Intuitive Topology
math.GN
The goal of this article is to introduce some beautiful known riddles in
intuitive topology; hoping to make at least some fun for the reader.
| arxiv topic:math.GN |
arxiv_dataset-19081005.326 | Dynamics of disentanglement, density matrix and coherence in neutrino
oscillations
hep-ph
In charged current weak interaction processes, neutrinos are produced in an
entangled state with the charged lepton. This correlated state is disentangled
by the measurement of the charged lepton in a detector at the production site.
We study the dynamical aspects of disentanglement, propagation and detection,
in particular the conditions under which the disentangled state is a coherent
superposition of mass eigenstates. The appearance and disappearance
far-detection processes are described from the time evolution of this
disentangled "collapsed" state. The familiar quantum mechanical interpretation
and factorization of the detection rate emerges when the quantum state is
disentangled on time scales \emph{much shorter} than the inverse oscillation
frequency, in which case the final detection rate factorizes in terms of the
usual quantum mechanical transition probability provided the final density of
states is insensitive to the neutrino energy difference. We suggest
\emph{possible} corrections for short-baseline experiments. If the charged
lepton is unobserved, neutrino oscillations and coherence are described in
terms of a reduced density matrix obtained by tracing out an un-observed
charged lepton. The diagonal elements in the mass basis describe the production
of mass eigenstates whereas the off diagonal ones provide a measure of
coherence. It is shown that coherences are of the same order of the diagonal
terms on time scales up to the inverse oscillation frequency, beyond which the
coherences oscillate as a result of the interference between mass eigenstates.
| arxiv topic:hep-ph |
arxiv_dataset-19091005.336 | Structure, spectra and variability of some GPS radio sources
astro-ph.CO
We report the results of multifrequency-VLBI observations of
GHz-Peaked-Spectrum (GPS) radio sources. The VLBI structure and component
spectra of some GPS sources are presented. Our VLBI results show that about 80%
of the GPS galaxies exhibit a compact double or CSO-like structure, while the
GPS quasars tend to show a core-jet. The component spectra of the GPS galaxies
are often steep/convex, and the core has a flat spectrum but it is usually
hidden or weak. In addition, we studied the variability of GPS sources by
comparing new flux density measures, acquired with the Urumqi 25m telescope at
4.85 GHz, with previous 87GB data. The results show that 44% of the GPS quasars
varied higher than 10% in passed 20 years, while the fraction is only 12% for
the GPS galaxies meaning that the GPS quasars are much more variable than GPS
galaxies. In total, 25% of GPS sources show >10% variability at 4.85 GHz in our
sample.
| arxiv topic:astro-ph.CO |
arxiv_dataset-19101005.346 | Embedding a Latin square with transversal into a projective space
math.CO
A Latin square of side n defines in a natural way a finite geometry on 3n
points, with three lines of size n and n^2 lines of size 3. A Latin square of
side n with a transversal similarly defines a finite geometry on 3n+1 points,
with three lines of size n, n^2-n lines of size 3, and n concurrent lines of
size 4. A collection of k mutually orthogonal Latin squares defines a geometry
on kn points, with k lines of size n and n^2 lines of size k. Extending work of
Bruen and Colbourn (J. Combin. Th. Ser. A 92 (2000), 88-94), we characterise
embeddings of these finite geometries into projective spaces over skew fields.
| arxiv topic:math.CO |
arxiv_dataset-19111005.356 | Foundations for a theory of complex matroids
math.CO
We explore a combinatorial theory of linear dependency in complex space,
"complex matroids", with foundations analogous to those for oriented matroids.
We give multiple equivalent axiomatizations of complex matroids, showing that
this theory captures properties of linear dependency, orthogonality, and
determinants over C in much the same way that oriented matroids capture the
same properties over R. In addition, our complex matroids come with a canonical
circle action analogous to the action of C* on a complex vector space. Our
phirotopes (analogues of determinants) are the same as those studied previously
by Below, Krummeck, and Richter-Gebert and by Delucchi. We further show that
complex matroids cannot have vector axioms analogous to those for oriented
matroids.
| arxiv topic:math.CO |
arxiv_dataset-19121005.366 | Lieb-Liniger gas in a constant force potential
cond-mat.quant-gas quant-ph
We use Gaudin's Fermi-Bose mapping operator to calculate exact solutions for
the Lieb-Liniger model in a linear (constant force) potential (the constructed
exact stationary solutions are referred to as the Lieb-Liniger-Airy wave
functions). The ground state properties of the gas in the wedge-like trapping
potential are calculated in the strongly interacting regime by using
Girardeau's Fermi-Bose mapping and the pseudopotential approach in the
$1/c$-approximation ($c$ denotes the strength of the interaction). We point out
that quantum dynamics of Lieb-Liniger wave packets in the linear potential can
be calculated by employing an $N$-dimensional Fourier transform as in the case
of free expansion.
| arxiv topic:cond-mat.quant-gas quant-ph |
arxiv_dataset-19131005.376 | Fast and slow two-fluid magnetic reconnection
astro-ph.SR physics.plasm-ph
We present a two-fluid magnetohydrodynamics (MHD) model of quasi-stationary,
two-dimensional magnetic reconnection in an incompressible plasma composed of
electrons and ions. We find two distinct regimes of slow and fast reconnection.
The presence of these two regimes can provide a possible explanation for the
initial slow build up and subsequent rapid release of magnetic energy
frequently observed in cosmic and laboratory plasmas.
| arxiv topic:astro-ph.SR physics.plasm-ph |
arxiv_dataset-19141005.386 | Coulomb-induced dynamic correlations in a double nanosystem
cond-mat.mes-hall
Time-dependent transport through two capacitively coupled quantum dots is
studied in the framework of the generalized master equation. The Coulomb
interaction is included within the exact diagonalization method. Each dot is
connected to two leads at different times, such that a steady state is
established in one dot before the coupling of the other dot to its leads. By
appropriately tuning the bias windows on each dot we find that in the final
steady state the transport may be suppressed or enhanced. These two cases are
explained by the redistribution of charge on the many-body states built on both
dots. We also predict and analyze the transient mutual charge sensing of the
dots.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-19151005.396 | Notes on Feynman Integrals and Renormalization
hep-th
I review various aspects of Feynman integrals, regularization and
renormalization. Following Bloch, I focus on a linear algebraic approach to the
Feynman rules, and I try to bring together several renormalization methods
found in the literature from a unifying point of view, using resolutions of
singularities. In the second part of the paper, I briefly sketch the work of
Belkale, Brosnan resp. Bloch, Esnault and Kreimer on the motivic nature of
Feynman integrals.
| arxiv topic:hep-th |
arxiv_dataset-19161005.406 | The Beam Thrust Cross Section for Drell-Yan at NNLL Order
hep-ph hep-ex nucl-th
At the LHC and Tevatron strong initial-state radiation (ISR) plays an
important role. It can significantly affect the partonic luminosity available
to the hard interaction or contaminate a signal with additional jets and soft
radiation. An ideal process to study ISR is isolated Drell-Yan production, pp
-> X l+l- without central jets, where the jet veto is provided by the hadronic
event shape beam thrust tau_B. Most hadron collider event shapes are designed
to study central jets. In contrast, requiring tau_B << 1 provides an inclusive
veto of central jets and measures the spectrum of ISR. For tau_B << 1 we carry
out a resummation of alpha_s^n ln^m tau_B corrections at
next-to-next-to-leading-logarithmic order. This is the first resummation at
this order for a hadron-hadron collider event shape. Measurements of tau_B at
the Tevatron and LHC can provide crucial tests of our understanding of ISR and
of tau_B's utility as a central jet veto.
| arxiv topic:hep-ph hep-ex nucl-th |
arxiv_dataset-19171005.416 | Quantum Simulation and Phase Diagram of the Transverse Field Ising Model
with Three Atomic Spins
quant-ph
We perform a quantum simulation of the Ising model with a transverse field
using a collection of three trapped atomic ion spins. By adiabatically
manipulating the Hamiltonian, we directly probe the ground state for a wide
range of fields and form of the Ising couplings, leading to a phase diagram of
magnetic order in this microscopic system. The technique is scalable to much
larger numbers of trapped ion spins, where phase transitions approaching the
thermodynamic limit can be studied in cases where theory becomes intractable.
| arxiv topic:quant-ph |
arxiv_dataset-19181005.426 | Mathieu Subspaces of Associative Algebras
math.RA math.AC
Motivated by the Mathieu conjecture [Ma], the image conjecture [Z3] and the
well-known Jacobian conjecture [K] (see also [BCW] and [E]), the notion of
Mathieu subspaces as a natural generalization of the notion of ideals has been
introduced recently in [Z4] for associative algebras. In this paper, we first
study algebraic elements in the radicals of Mathieu subspaces of associative
algebras over fields and prove some properties and characterizations of Mathieu
subspaces with algebraic radicals. We then give some characterizations or
classifications for strongly simple algebras (the algebras with no non-trivial
Mathieu subspaces) over arbitrary commutative rings, and for quasi-stable
algebras (the algebras all of whose subspaces that do not contain the identity
element of the algebra are Mathieu spaces) over arbitrary fields. Furthermore,
co-dimension one Mathieu subspaces and the minimal non-trivial Mathieu
subspaces of the matrix algebras over fields are also completely determined.
| arxiv topic:math.RA math.AC |
arxiv_dataset-19191005.436 | Questions of controllability and observability for nonuniformly sampled
discrete systems
math.DS math-ph math.MP
A joint characterisation of the controllability and observability of a
particular kind of discrete system has been developed. The key idea of the
procedure can be reduced to a correct choice of the sampling sequence. This
freedom, owing to the arbitrary choice of the sampling instants, is used to
improve the sensitivity of system controllability and observability, by
exploiting an adequate geometric structure. Some qualitative examples are
presented for illustrative purposes.
| arxiv topic:math.DS math-ph math.MP |
arxiv_dataset-19201005.446 | Production of doubly strange hypernuclei via {\Xi}- doorways in the
16O(K-, K+) reaction at 1.8 GeV/c
nucl-th
We examine theoretically production of doubly strange hypernuclei, 16 {\Xi}-C
and 16 {\Lambda}{\Lambda}C, in doublecharge exchange 16O(K-, K+) reactions
using a distorted-wave impulse approximation. The inclusive K+ spectrum at the
incident momentum pK- = 1.8 GeV/c and scattering angle {\theta}lab = 0^{\circ}
is estimated in a one-step mechanism, K-p \to K+{\Xi}- via {\Xi}- doorways
caused by a {\Xi}-p-{\Lambda}{\Lambda} coupling. The calculated spectrum in the
{\Xi}- bound region indicates that the integrated cross sections are on the
order of 7-12 nb/sr for significant 1- excited states with 14C(0+, 2+) \otimes
s{\Lambda}p{\Lambda} configurations in 16 {\Lambda}{\Lambda}C via the doorway
states of the spin-stretched 15N(1/2-, 3/2-) \otimes s{\Xi}- in 16 {\Xi}-C due
to a high momentum transfer q{\Xi}- \approx 400 MeV/c. The {\Xi}- admixture
probabilities of these states are on the order of 5-9%. However, populations of
the 0+ ground state with 14C(0+) \otimes s2{\Lambda} and the 2+ excited state
with 14C(2+) \otimes s2 {\Lambda} are very small. The sensitivity of the
spectrum on the {\Xi}N-{\Lambda}{\Lambda} coupling strength enables us to
extract the nature of {\Xi}N-{\Lambda}{\Lambda} dynamics in nuclei, and the
nuclear (K-, K+) reaction can extend our knowledge of the S = -2 world.
| arxiv topic:nucl-th |
arxiv_dataset-19211005.456 | Laser acceleration of a thin, inflated layer of heavy material by the
radiation pressure applied to a self-generated, imperfect plasma mirror
physics.plasm-ph
The production of energetic (multi-GeV) heavy ion beams by acceleration of
ultra-thin foils through the application of radiation pressure to a
self-generated, imperfect plasma mirror (photon absorption probability {\eta}
finite) is studied. To evaluate the foil dynamics a relativistic model was
developed for a constant and relativistic invariant value of the
phenomenological parameter {\eta}. The achievable efficiency of kinetic energy
transfer to the matter has been evaluated as function of the parameters
involved ({\eta}, the aimed average foil velocity in unit of the light speed
{\beta}, etc.). The expected collimation degree for the generated ion beams,
the associated energy range, the self-consistency of the model in view of the
{\eta} finite value and the survival to R-T instability were evaluated for
initially thin material disks.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-19221005.466 | The maximum number of rational points for a genus 4 curve over F_7 is 24
math.NT
In this paper we show that the maximum number of rational points possible for
a smooth, projective, absolutely irreducible genus 4 curve over a finite field
F_7 is 24. It is known that a genus 4 curve over F_7 can have at most 25
points. In this paper we prove that such a curve can have at most 24. On the
other hand we provide an explicit example of a genus 4 curve over F_7 having 24
points.
| arxiv topic:math.NT |
arxiv_dataset-19231005.476 | Texture control in a pseudospin Bose-Einstein condensate
cond-mat.quant-gas
We describe a wavefunction engineering approach to the formation of textures
in a two-component nonrotated Bose-Einstein condensate. By controlling the
phases of wavepackets that combine in a three-wave interference process, a
ballistically-expanding regular lattice-texture is generated, in which the
phases determine the component textures. A particular example is presented of a
lattice-texture composed of half-quantum vortices and spin-2 textures. We
demonstrate the lattice formation with numerical simulations of a viable
experiment, identifying the textures and relating their locations to a linear
theory of wavepacket interference.
| arxiv topic:cond-mat.quant-gas |
arxiv_dataset-19241005.486 | Thermo-mechanic-electrical coupling in phospholipid monolayers near the
critical point
physics.bio-ph cond-mat.soft
Lipid monolayers have been shown to represent a powerful tool in studying
mechanical and thermodynamic properties of lipid membranes as well as their
interaction with proteins. Using Einstein's theory of fluctuations we here
demonstrate, that an experimentally derived linear relationship both between
transition entropy S and area A as well as between transition entropy and
charge q implies a linear relationships between compressibility \kappa_T, heat
capacity c_\pi, thermal expansion coefficient \alpha_T and electric capacity
CT. We demonstrate that these couplings have strong predictive power as they
allow calculating electrical and thermal properties from mechanical
measurements. The precision of the prediction increases as the critical point
TC is approached.
| arxiv topic:physics.bio-ph cond-mat.soft |
arxiv_dataset-19251005.496 | Impact of Supernova feedback on the Tully-Fisher relation
astro-ph.CO
Recent observational results found a bend in the Tully-Fisher Relation in
such a way that low mass systems lay below the linear relation described by
more massive galaxies. We intend to investigate the origin of the observed
features in the stellar and baryonic Tully-Fisher relations and analyse the
role played by galactic outflows on their determination. Cosmological
hydrodynamical simulations which include Supernova feedback were performed in
order to follow the dynamical evolution of galaxies. We found that Supernova
feedback is a fundamental process in order to reproduce the observed trends in
the stellar Tully-Fisher relation. Simulated slow rotating systems tend to have
lower stellar masses than those predicted by the linear fit to the massive end
of the relation, consistently with observations. This feature is not present if
Supernova feedback is turned off. In the case of the baryonic Tully-Fisher
relation, we also detect a weaker tendency for smaller systems to lie below the
linear relation described by larger ones. This behaviour arises as a result of
the more efficient action of Supernovae in the regulation of the star formation
process and in the triggering of powerful galactic outflows in shallower
potential wells which may heat up and/or expel part of the gas reservoir.
| arxiv topic:astro-ph.CO |
arxiv_dataset-19261005.506 | Understanding the Tenets of Agile Software Engineering: Lecturing,
Exploration and Critical Thinking
cs.CY
The use of agile principles and practices in software development is becoming
a powerful force in today's workplace. In our quest to develop better products,
therefore, it is imperative that we strive to learn and understand the
application of Agile methods, principles and techniques to the software
development enterprise. Unfortunately, in many educational institutions courses
and projects that emphasize Agile Software Development are minimal. At best,
students have only limited exposure to the agile philosophy, principles and
practices at the graduate and undergraduate levels of education. In an effort
to address this concern, we offered a graduate-level course entitled "Agile
Software Engineering" in the Department of Computer Science at Virginia Tech in
Fall 2009. The primary objectives of the class were to introduce the values,
principles and practices underlying the agile philosophy, and to do so in an
atmosphere that encourages debate and critical thinking. The course was
designed around three central components: (1) teaching the essentials of how
one develops a product within an Agile framework, (2) having invited
presentation by notable industry experts, and (3) having students present and
discuss current research topics and issues. This paper describes our
experiences during the offering of that course, and in particular, the unique
perspectives of the class instructor, the teaching assistant and a student who
was enrolled in the class.
| arxiv topic:cs.CY |
arxiv_dataset-19271005.516 | Left-Right Symmetry at LHC
hep-ph
We revisit the issue of the limit on the scale of Left-Right symmetry
breaking. We focus on the minimal SU(2)_L x SU(2)_R x U(1)_B-L gauge theory
with the seesaw mechanism and discuss the two possibilities of defining
Left-Right symmetry as parity or charge conjugation. In the commonly adopted
case of parity, we perform a complete numerical study of the quark mass
matrices and the associated left and right mixing matrices without any
assumptions usually made in the literature about the ratio of vacuum
expectation values. We find that the usual lower limit on the mass of the
right-handed gauge boson from the K mass difference, M_WR>2.5TeV, is subject to
a possible small reduction due to the difference between right and left Cabibbo
angles. In the case of charge conjugation the limit on M_WR is somewhat more
robust. However, the more severe bounds from CP-violating observables are
absent in this case. In fact, the free phases can also resolve the present mild
discrepancy between the Standard Model and CP-violation in the $B$-sector.
Thus, even in the minimal case, both charged and neutral gauge bosons may be
accessible at the Large Hadron Collider with spectacular signatures of lepton
number violation.
| arxiv topic:hep-ph |
arxiv_dataset-19281005.526 | Exponential moments of first passage times and related quantities for
random walks
math.PR
For a zero-delayed random walk on the real line, let $\tau(x)$, $N(x)$ and
$\rho(x)$ denote the first passage time into the interval $(x,\infty)$, the
number of visits to the interval $(-\infty,x]$ and the last exit time from
$(-\infty,x]$, respectively. In the present paper, we provide ultimate criteria
for the finiteness of exponential moments of these quantities. Moreover,
whenever these moments are finite, we derive their asymptotic behaviour, as $x
\to \infty$.
| arxiv topic:math.PR |
arxiv_dataset-19291005.536 | Total cross sections for neutron-nucleus scattering
nucl-th hep-ph nucl-ex
Systematics of neutron scattering cross sections on various materials for
neutron energies up to several hundred MeV are important for ADSS applications.
Ramsauer model is well known and widely applied to understand systematics of
neutron nucleus total cross sections. In this work, we examined the role of
nuclear effective radius parameter (r$_0$) on Ramsauer model fits of neutron
total cross sections. We performed Ramsauer model global analysis of the
experimental neutron total cross sections reported by W. P. Abfalterer, F. B.
Bateman, {\it et. al.,}, from 20MeV to 550MeV for nuclei ranging from Be to U .
The global fit functions which can fit total cross section data over periodic
table are provided along with the required global set of parameters. The global
fits predict within $\pm 8%$ deviation to data, showing the scope for
improvement. It has been observed that a finer adjustment of r$_0$ parameter
alone can give very good Ramsauer model description of neutron total scattering
data within $\pm 4%$ deviation. The required r$_0$ values for Ramsauer model
fits are shown as a function of nuclear mass number and an empirical formula is
suggested for r$_0$ values as a function of mass number. In optical model
approach for neutron scattering, we have modified the real part of
Koning-Deleroche potentails to fit the neutron total cross sections using SCAT2
code. The modified potentails have a different energy dependence beyond 200MeV
of neutron energy and fit the total cross sections from Al to Pb.
| arxiv topic:nucl-th hep-ph nucl-ex |
arxiv_dataset-19301005.546 | Shape in an Atom of Space: Exploring quantum geometry phenomenology
gr-qc
A phenomenology for the deep spatial geometry of loop quantum gravity is
introduced. In the context of a simple model, an atom of space, it is shown how
purely combinatorial structures can affect observations. The angle operator is
used to develop a model of angular corrections to local, continuum flat-space
3-geometries. The physical effects involve neither breaking of local Lorentz
invariance nor Planck scale suppression, but rather reply on only the
combinatorics of SU(2) recoupling. Bhabha scattering is discussed as an example
of how the effects might be observationally accessible.
| arxiv topic:gr-qc |
arxiv_dataset-19311005.556 | Statistical constraints on binary black hole inspiral dynamics
gr-qc
We perform a statistical analysis of the binary black hole problem in the
post-Newtonian approximation by systematically sampling and evolving the
parameter space of initial configurations for quasi-circular inspirals. Through
a principal component analysis of spin and orbital angular momentum variables
we systematically look for uncorrelated quantities and find three of them which
are highly conserved in a statistical sense, both as functions of time and with
respect to variations in initial spin orientations. We also look for and find
the variables that account for the largest variations in the problem. We
present binary black hole simulations of the full Einstein equations analyzing
to what extent these results might carry over to the full theory in the
inspiral and merger regimes. Among other applications these results should be
useful both in semi-analytical and numerical building of templates of
gravitational waves for gravitational wave detectors.
| arxiv topic:gr-qc |
arxiv_dataset-19321005.5662 | On the contribution of backward jumps to instruction sequence
expressiveness
cs.LO
We investigate the expressiveness of backward jumps in a framework of
formalized sequential programming called program algebra. We show that - if
expressiveness is measured in terms of the computability of partial Boolean
functions - then backward jumps are superfluous. If we, however, want to
prevent explosion of the length of programs, then backward jumps are essential.
| arxiv topic:cs.LO |
arxiv_dataset-19331006.0025 | The WIMP capture process for dark stars in the early universe
astro-ph.CO astro-ph.SR hep-ph
The first stars to form in the universe may have been dark stars, powered by
dark matter annihilation instead of nuclear fusion. The initial amount of dark
matter gathered by the star gravitationally can sustain it only for a limited
period of time. It has been suggested that capture of additional dark matter
from the environment can prolong the dark star phase even to the present day.
Here we show that this capture process is ineffective to prolong the life of
the first generation of dark stars. We construct a Monte-Carlo simulation that
follows each Weakly Interacting Massive Particle (WIMP) in the dark matter halo
as its orbit responds to the formation and evolution of the dark star, as it
scatters off the star's nuclei, and as it annihilates inside the star. A rapid
depletion of the WIMPs on orbits that cross the star causes the demise of the
first generation of dark stars. We suggest that a second generation of dark
stars may in principle survive much longer through capture. We comment on the
effect of relaxing our assumptions.
| arxiv topic:astro-ph.CO astro-ph.SR hep-ph |
arxiv_dataset-19341006.0125 | Nonsequential Two-Photon Double Ionization of Atoms: Identifying the
Mechanism
quant-ph physics.atom-ph
We develop an approximate model for the process of direct (nonsequential)
two-photon double ionization of atoms. Employing the model, we calculate
(generalized) total cross sections as well as energy-resolved differential
cross sections of helium for photon energies ranging from 39 to 54 eV. A
comparison with results of \textit{ab initio} calculations reveals that the
agreement is at a quantitative level. We thus demonstrate that this complex
ionization process is fully described by the simple model, providing insight
into the underlying physical mechanism. Finally, we use the model to calculate
generalized cross sections for the two-photon double ionization of neon in the
nonsequential regime.
| arxiv topic:quant-ph physics.atom-ph |
arxiv_dataset-19351006.0225 | Massive runaway stars in the Large Magellanic Cloud
astro-ph.GA
The origin of massive field stars in the Large Magellanic Cloud (LMC) has
long been an enigma. The recent measurements of large offsets (~100 km/s)
between the heliocentric radial velocities of some very massive (O2-type) field
stars and the systemic LMC velocity provides a possible explanation of this
enigma and suggests that the field stars are runaway stars ejected from their
birth places at the very beginning of their parent cluster's dynamical
evolution. A straightforward way to prove this explanation is to measure the
proper motions of the field stars and to show that they are moving away from
one of the nearby star clusters or OB associations. This approach however is
complicated by the large distance to the LMC, which makes accurate proper
motion measurements difficult. We use an alternative approach for solving the
problem, based on the search for bow shocks produced by runaway stars. The
geometry of detected bow shocks would allow us to infer the direction of
stellar motion and thereby to determine their possible parent clusters. In this
paper we present the results of a search for bow shocks around six massive
field stars which were suggested in the literature as candidate runaway stars.
Using archival (Spitzer Space Telescope) data, we found a bow shock associated
with one of our program stars, the O2 V((f*)) star BI 237, which is the
first-ever detection of bow shocks in the LMC. Orientation of the bow shock
suggests that BI 237 was ejected from the OB association LH 82 (located at ~120
pc in projection from the star). A by-product of our search is the detection of
bow shocks generated by four OB stars in the field of the LMC and an arc-like
structure attached to the candidate luminous blue variable R81 (HD 269128). The
geometry of two of these bow shocks is consistent with the possibility that
their associated stars were ejected from the 30 Doradus star forming complex.
| arxiv topic:astro-ph.GA |
arxiv_dataset-19361006.0325 | Pure O-sequences and matroid h-vectors
math.CO math.AC
We study Stanley's long-standing conjecture that the h-vectors of matroid
simplicial complexes are pure O-sequences. Our method consists of a new and
more abstract approach, which shifts the focus from working on constructing
suitable artinian level monomial ideals, as often done in the past, to the
study of properties of pure O-sequences. We propose a conjecture on pure
O-sequences and settle it in small socle degrees. This allows us to prove
Stanley's conjecture for all matroids of rank 3. At the end of the paper, using
our method, we discuss a first possible approach to Stanley's conjecture in
full generality. Our technical work on pure O-sequences also uses very recent
results of the third author and collaborators.
| arxiv topic:math.CO math.AC |
arxiv_dataset-19371006.0425 | Correlations in impact-parameter space in saturation models
hep-ph
In order to get an estimate of the homogeneity of the distribution of matter
in a fast hadron, we compute the correlation of the saturation scales between
different impact parameters. We find that these correlations are quite strong:
The saturation scale is nearly uniform in a wide domain around each point in
impact-parameter space. We provide analytical expressions for the correlations,
which are supported by numerical simulations. Although the numerical
calculations are done for specific saturation models which are obtained from
QCD after drastic simplifications, we expect our analytical formulas to be
correct for full QCD in asymptotic limits, since their derivation requires only
a few general assumptions.
| arxiv topic:hep-ph |
arxiv_dataset-19381006.0525 | The Weil-\'etale fundamental group of a number field II
math.NT math.AG
We define the fundamental group underlying to Lichtenbaum's Weil-\'etale
cohomology for number rings. To this aim, we define the Weil-\'etale topos as a
refinement of the Weil-\'etale sites introduced in \cite{Lichtenbaum}. We show
that the (small) Weil-\'etale topos of a smooth projective curve defined in
this paper is equivalent to the natural definition given in
\cite{Lichtenbaum-finite-field}. Then we compute the Weil-\'etale fundamental
group of an open subscheme of the spectrum of a number ring. Our fundamental
group is a projective system of locally compact topological groups, which
represents first degree cohomology with coefficients in locally compact abelian
groups. We apply this result to compute the Weil-\'etale cohomology in low
degrees and to prove that the Weil-\'etale topos of a number ring satisfies the
expected properties of the conjectural Lichtenbaum topos.
| arxiv topic:math.NT math.AG |
arxiv_dataset-19391006.0625 | A search for Ejecta Nebulae around Wolf-Rayet Stars using the SHS
H$\alpha$ survey
astro-ph.GA
Recent large scale Galactic Plane H$\alpha$ surveys allow a re-examination of
the environs of Wolf-Rayet (WR) stars for the presence of a circumstellar
nebula. Using the morphologies of WR nebulae known to be composed of stellar
ejecta as a guide, we constructed ejecta nebula criteria similar to those of
Chu (1991) and searched for likely WR ejecta nebula in the SHS H$\alpha$
survey. A new Wolf-Rayet ejecta nebula around WR 8 is found and its morphology
discussed. The fraction of WR stars with ejecta type nebulae is roughly
consistent between the MilkyWay (MW) and LMC at around 5-6%, with the MW sample
dominated by nitrogen rich WR central stars (WN type) and the LMC stars having
a higher proportion of carbon rich WR central stars (WC type). We compare our
results with those of previous surveys, including those of Marston (1997) and
Miller & Chu (1993), and find broad consistency. We investigate several trends
in the sample: most of the clear examples of ejecta nebulae have WNh central
stars; and very few ejecta nebulae have binary central stars. Finally, the
possibly unique evolutionary status of the nebula around the binary star WR 71
is explored.
| arxiv topic:astro-ph.GA |
arxiv_dataset-19401006.0725 | Minimization of Ohmic losses for domain wall motion in a ferromagnetic
nanowire
cond-mat.mes-hall cond-mat.mtrl-sci
We study current-induced domain-wall motion in a narrow ferromagnetic wire.
We propose a way to move domain walls with a resonant time-dependent current
which dramatically decreases the Ohmic losses in the wire and allows to drive
the domain wall with higher speed without burning the wire. For any domain wall
velocity we find the time-dependence of the current needed to minimize the
Ohmic losses. Below a critical domain-wall velocity specified by the parameters
of the wire the minimal Ohmic losses are achieved by dc current. Furthermore,
we identify the wire parameters for which the losses reduction from its dc
value is the most dramatic.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-19411006.0825 | Evolutionary dynamics, intrinsic noise and cycles of co-operation
q-bio.PE cond-mat.stat-mech physics.soc-ph
We use analytical techniques based on an expansion in the inverse system size
to study the stochastic evolutionary dynamics of finite populations of players
interacting in a repeated prisoner's dilemma game. We show that a mechanism of
amplification of demographic noise can give rise to coherent oscillations in
parameter regimes where deterministic descriptions converge to fixed points
with complex eigenvalues. These quasi-cycles between co-operation and defection
have previously been observed in computer simulations; here we provide a
systematic and comprehensive analytical characterization of their properties.
We are able to predict their power spectra as a function of the mutation rate
and other model parameters, and to compare the relative magnitude of the cycles
induced by different types of underlying microscopic dynamics. We also extend
our analysis to the iterated prisoner's dilemma game with a win-stay lose-shift
strategy, appropriate in situations where players are subject to errors of the
trembling-hand type.
| arxiv topic:q-bio.PE cond-mat.stat-mech physics.soc-ph |
arxiv_dataset-19421006.0925 | Modelling the Autocovariance of the Power Spectrum of a Solar-Type
Oscillator
astro-ph.SR
Asteroseismology is able to conduct studies on the interiors of solar-type
stars from the analysis of stellar acoustic spectra. However, such an analysis
process often has to rely upon subjective choices made throughout. A recurring
problem is to determine whether a signal in the acoustic spectrum originates
from a radial or a dipolar oscillation mode. In order to overcome this problem,
we present a procedure for modelling and fitting the autocovariance of the
power spectrum which can be used to obtain global seismic parameters of
solar-type stars, doing so in an automated fashion without the need to make
subjective choices. From the set of retrievable global seismic parameters we
emphasize the mean small frequency separation and, depending on the intrinsic
characteristics of the power spectrum, the mean rotational frequency splitting.
Since this procedure is automated, it can serve as a useful tool in the
analysis of the more than one thousand solar-type stars expected to be observed
as part of the Kepler Asteroseismic Investigation (KAI). We apply the
aforementioned procedure to simulations of the Sun. Assuming different apparent
magnitudes, we address the issues of how accurately and how precisely we can
retrieve the several global seismic parameters were the Sun to be observed as
part of the KAI.
| arxiv topic:astro-ph.SR |
arxiv_dataset-19431006.1025 | Simultaneous Measurement of Torsional Oscillator and NMR of Very Dilute
3He in Solid 4He
cond-mat.other
We have investigated the NMR properties of dilute 3He impurities in solid 4He
contained in a torsional oscillator (TO) by the simultaneous measurement of the
NMR and the torsional oscillator response of the so-called supersolid 4He. From
measurements on samples with one hundred to a few hundred ppm of 3He, we have
found three different states of 3He. The first is the homogeneously distributed
isolated 3He atom in a solid matrix of 4He. The second is the 3He cluster in a
homogeneous 4He matrix, which appears below the phase separation temperature of
a solid mixture. The third is the 3He cluster in some nonuniform part of a 4He
crystal. We find that 3He atoms contained in the third component remain in a
nearby location even above the phase separation temperature. Based on the fact
that even a ppm of 3He affects the supersolid response in a TO below and above
the phase separation temperature, we propose that the nonuniform part of a
crystal that holds the third type of 3He and thus has a higher local
concentration of 3He plays an important role in the supersolid phenomenon in a
TO.
| arxiv topic:cond-mat.other |
arxiv_dataset-19441006.1125 | Periodic bounce orbits of prescribed energy
math.DS math.SG
We prove the existence of periodic bounce orbits of prescribed energy on an
open bounded domain in Euclidean space. We derive explicit bounds on the period
and the number of bounce points.
| arxiv topic:math.DS math.SG |
arxiv_dataset-19451006.1225 | Existence of axially symmetric static solutions of the Einstein-Vlasov
system
gr-qc
We prove the existence of static, asymptotically flat non-vacuum spacetimes
with axial symmetry where the matter is modeled as a collisionless gas. The
axially symmetric solutions of the resulting Einstein-Vlasov system are
obtained via the implicit function theorem by perturbing off a suitable
spherically symmetric steady state of the Vlasov-Poisson system.
| arxiv topic:gr-qc |
arxiv_dataset-19461006.1325 | Random subshifts of finite type
math.PR math.DS
Let $X$ be an irreducible shift of finite type (SFT) of positive entropy, and
let $B_n(X)$ be its set of words of length $n$. Define a random subset $\omega$
of $B_n(X)$ by independently choosing each word from $B_n(X)$ with some
probability $\alpha$. Let $X_{\omega}$ be the (random) SFT built from the set
$\omega$. For each $0\leq \alpha \leq1$ and $n$ tending to infinity, we compute
the limit of the likelihood that $X_{\omega}$ is empty, as well as the limiting
distribution of entropy for $X_{\omega}$. For $\alpha$ near 1 and $n$ tending
to infinity, we show that the likelihood that $X_{\omega}$ contains a unique
irreducible component of positive entropy converges exponentially to 1. These
results are obtained by studying certain sequences of random directed graphs.
This version of "random SFT" differs significantly from a previous notion by
the same name, which has appeared in the context of random dynamical systems
and bundled dynamical systems.
| arxiv topic:math.PR math.DS |
arxiv_dataset-19471006.1425 | Instability by Chern-Simons and/or Transgressions
hep-th
It was demonstrated recently that there is an upper bound of the Chern-Simons
coupling of the five-dimensional Einstein-Maxwell theory, beyond which the
electrically charged AdS_2 \times S^3 vacuum solution becomes unstable. We
generalize the result to a general class of gravity theories involving
Chern-Simons and/or transgression terms and find their upper bounds for
stability. We show that supergravities with AdS \times Sphere vacua satisfy the
bounds.
| arxiv topic:hep-th |
arxiv_dataset-19481006.1525 | Dynamic spin susceptibility of superconducting cuprates: A microscopic
theory of the magnetic resonance mode
cond-mat.str-el
A microscopic theory of the dynamic spin susceptibility (DSS) in the
superconducting state within the t-J model is presented. It is based on an
exact representation for the DSS obtained by applying the Mori-type projection
technique for the relaxation function in terms of Hubbard operators. The static
spin susceptibility is evaluated by a sum-rule-conserving generalized
mean-field approximation, while the self-energy is calculated in the
mode-coupling approximation. The spectrum of spin excitations is studied in the
underdoped and optimally doped regions. The DSS reveals a resonance mode (RM)
at the antiferromagnetic wave vector Q = \pi(1,1) at low temperatures due to a
strong suppression of the damping of spin excitations. This is explained by an
involvement of spin excitations in the decay process besides the particle-hole
continuum usually considered in random-phase-type approximations. The spin gap
in the spin-excitation spectrum at Q plays a dominant role in limiting the
decay in comparison with the superconducting gap which results in the
observation of the RM even above $T_c$ in the underdoped region. A good
agreement with inelastic neutron-scattering experiments on the RM in YBCO
compounds is found.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-19491006.1625 | Effects of Zeeman field on a Spin Bose-Metal phase
cond-mat.str-el
We consider Zeeman field effects on a Spin Bose-Metal (SBM) phase on a
two-leg triangular ladder. This phase was found in a spin-1/2 model with ring
exchanges [D. N. Sheng et. al., Phys. Rev. B {\bf 79}, 205112 (2009)], and was
also proposed to appear in an interacting electronic model with longer-ranged
repulsion [Lai et. al., Phys. Rev. B {\bf 81}, 045105 (2010)]. Using
bosonization of a spinon-gauge theory, we study the stability of the SBM phase
and its properties under the field. We also explore phases arising from
potential instabilities of the SBM; in all cases, we find a gap to spin-1
excitations while spin-nematic correlations are power law. We discuss
two-dimensional analogues of these phases where spinons can pair with their own
species.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-19501006.1725 | Ionization and Coulomb explosion of Xenon clusters by intense, few-cycle
laser pulses
physics.atm-clus physics.chem-ph physics.optics physics.plasm-ph
Intense, ultrashort pulses of 800 nm laser light (12 fs, $\sim$4 optical
cycles) of peak intensity 5$\times$10$^{14}$ W cm$^{-2}$ have been used to
irradiate gas-phase Xe$_n$ clusters ($n$=500-25,000) so as to induce multiple
ionization and subsequent Coulomb explosion. Energy distributions of exploding
ions are measured in the few-cycle domain that does not allow sufficient time
for the cluster to undergo Coulomb-driven expansion. This results in overall
dynamics that appear to be significantly different to those in the many-cycle
regime. One manifestation is that the maximum ion energies are measured to be
much lower than those obtained when longer pulses of the same intensity are
used. Ion yields are cluster-size independent but polarization dependent in
that they are significantly larger when the polarization is perpendicular to
the detection axis than along it. This unexpected behavior is qualitatively
rationalized in terms of a spatially anisotropic shielding effect induced by
the electronic charge cloud within the cluster.
| arxiv topic:physics.atm-clus physics.chem-ph physics.optics physics.plasm-ph |
arxiv_dataset-19511006.1825 | Kinetic Theory of Flocking: Derivation of Hydrodynamic Equations
physics.bio-ph cond-mat.stat-mech
It is shown how to explicitly coarse-grain the microscopic dynamics of the
Vicsek model for self-propelled agents. The macroscopic transport equations are
derived by means of an Enskog-type kinetic theory. Expressions for all
transport coefficients at large particle speed are given. The phase transition
from a disordered to a flocking state is studied numerically and analytically.
| arxiv topic:physics.bio-ph cond-mat.stat-mech |
arxiv_dataset-19521006.1925 | Secants of Lagrangian Grassmannians
math.AG
We study the dimensions of secant varieties of the Grassmannian of Lagrangian
subspaces in a symplectic vector space. We calculate these dimensions for third
and fourth secant varieties. Our result is obtained by providing a normal form
for four general points on such a Grassmannian and by explicitly calculating
the tangent spaces at these four points.
| arxiv topic:math.AG |
arxiv_dataset-19531006.2025 | Klapdor's claim for the observation of the neutrinoless double
beta-decay of Ge-76. Analysis and corrections
hep-ph hep-ex
Heidelberg-Moscow Collaboration experimental data [1-4] with the claim for
the observation of the neutrinoless double beta-decay of Ge-76 has been
carefully analyzed. The analysis gave an evidence that the observed 2039 kev
line in the full spectrum was produced by overlapping of three unresolved
peaks: ~2035.5 kev, ~2037.5 kev and ~2039.5 kev. It was indicated that the
2035.5 kev and 2039.5 kev peaks were produced by the double-coincidences of
gamma-quanta in the detectors. Existence of the two background gamma-peaks at
~2035.5 kev and ~2039.5 kev was confirmed by an analysis of the background
measurements with low-background Ge detectors with an active shielding [5-7].
The 2037.5 kev line could be the expected 2{\beta}0{\nu}-decay transition of
76Ge according to the results of the improved pulse-shape analysis. Position of
the line, 2037.56+/-0.56(stat)+/-1.2(syst) kev [4], was slightly below the
expected, E2{\beta}=2039.0+/-0.05 kev [8], but still within a limit for poor
statistics. The most accurate value of its intensity was extracted from the
51.39 kg \cdot y data with PSA: number of events 12.4+/-3.7 and T1/2=1.98 \cdot
1025 years [2,3].
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-19541006.2125 | Small But Slow World: How Network Topology and Burstiness Slow Down
Spreading
physics.soc-ph cs.SI nlin.AO physics.bio-ph
Communication networks show the small-world property of short paths, but the
spreading dynamics in them turns out slow. We follow the time evolution of
information propagation through communication networks by using the SI model
with empirical data on contact sequences. We introduce null models where the
sequences are randomly shuffled in different ways, enabling us to distinguish
between the contributions of different impeding effects. The slowing down of
spreading is found to be caused mostly by weight-topology correlations and the
bursty activity patterns of individuals.
| arxiv topic:physics.soc-ph cs.SI nlin.AO physics.bio-ph |
arxiv_dataset-19551006.2225 | Demonstration of Cluster State Shaping and Quantum Erasure for
Continuous Variables
quant-ph
We demonstrate experimentally how to remove an arbitrary node from a
continuous-variable cluster state and how to shorten any quantum wires of such
a state. These two basic operations, performed in an unconditional fashion, are
a manifestation of quantum erasure and can be employed to obtain various graph
states from an initial cluster state. Starting with a sufficiently large
cluster, the resulting graph states can then be used for universal quantum
information processing. In the experiment, all variations of this
cluster-shaping are demonstrated on a four-mode linear cluster state through
homodyne measurements and feedforward.
| arxiv topic:quant-ph |
arxiv_dataset-19561006.2325 | Radial oscillation of harmonic functions in the Korenblum class
math.CV
We study radial behavior of harmonic functions in the unit disk belonging to
the Korenblum class. We prove that functions which admit two-sided Korenblum
estimate either oscillate or have slow growth along almost all radii.
| arxiv topic:math.CV |
arxiv_dataset-19571006.2425 | An optimal algorithm for stochastic strongly-convex optimization
math.OC
We consider stochastic convex optimization with a strongly convex (but not
necessarily smooth) objective. We give an algorithm which performs only
gradient updates with optimal rate of convergence.
| arxiv topic:math.OC |
arxiv_dataset-19581006.2525 | Second-order hyperbolic Fuchsian systems. Gowdy spacetimes and the
Fuchsian numerical algorithm
gr-qc math.AP
This is the second part of a series devoted to the singular initial value
problem for second-order hyperbolic Fuchsian systems. In the first part, we
defined and investigated this general class of systems, and we established a
well-posedness theory in weighted Sobolev spaces. This theory is applied here
to the vacuum Einstein equations for Gowdy spacetimes admitting, by definition,
two Killing fields satisfying certain geometric conditions. We recover, by more
direct and simpler arguments, the well-posedness results established earlier by
Rendall and collaborators. In addition, in this paper we introduce a natural
approximation scheme, which we refer to as the Fuchsian numerical algorithm and
is directly motivated by our general theory. This algorithm provides highly
accurate, numerical approximations of the solution to the singular initial
value problem. In particular, for the class of Gowdy spacetimes under
consideration, various numerical experiments are presented which show the
interest and efficiency of the proposed method. Finally, as an application, we
numerically construct Gowdy spacetimes containing a smooth, incomplete,
non-compact Cauchy horizon.
| arxiv topic:gr-qc math.AP |
arxiv_dataset-19591006.2625 | Seed design framework for mapping SOLiD reads
q-bio.QM q-bio.GN
The advent of high-throughput sequencing technologies constituted a major
advance in genomic studies, offering new prospects in a wide range of
applications. We propose a rigorous and flexible algorithmic solution to
mapping SOLiD color-space reads to a reference genome. The solution relies on
an advanced method of seed design that uses a faithful probabilistic model of
read matches and, on the other hand, a novel seeding principle especially
adapted to read mapping. Our method can handle both lossy and lossless
frameworks and is able to distinguish, at the level of seed design, between
SNPs and reading errors. We illustrate our approach by several seed designs and
demonstrate their efficiency.
| arxiv topic:q-bio.QM q-bio.GN |
arxiv_dataset-19601006.2725 | The problem of singularities and chaos in cosmology
gr-qc
We consider different aspects of the problem of cosmological singularity such
as the BKL oscillatory approach to the singularity, the new features of the
cosmological dynamics in the neighbourhood of the singularity in
multidimensional and superstring cosmological models and their connections with
such a modern branch of mathematics as infinite-dimensional Lie algebras. The
chaoticity of the oscillatory approach to the cosmological singularity is also
discussed. The Conclusion contains some thoughts about the past and the future
of the Universe in the light of the oscillatory approach to the Big Bang and
the Big Crunch cosmological singularities.
| arxiv topic:gr-qc |
arxiv_dataset-19611006.2825 | Neutrino masses from clustering of red and blue galaxies: a test of
astrophysical uncertainties
astro-ph.CO hep-ex
Combining measurements of the galaxy power spectrum and the cosmic microwave
background (CMB) is a powerful means of constraining the summed mass of
neutrino species sum(m_nu), but is subject to systematic uncertainties due to
non-linear structure formation, redshift-space distortions and galaxy bias. We
empirically test the robustness of neutrino mass results to these effects by
separately analyzing power spectra of red and blue galaxies from the Sloan
Digital Sky Survey (SDSS-II) Data Release 7 (DR7), combined with the CMB
five-year Wilkinson Microwave Anisotropy Probe (WMAP5) data. We consider
fitting for a range of maximum wavenumber k using twelve different galaxy bias
models. For example, using a new model based on perturbation theory and
including redshift space distortions (Saito et al. 2009), the all-galaxy power
spectrum combined with WMAP5 for a wavenumber range of k<0.2 Mpc/h yields 95%
CL sum(m_nu)<0.46 eV. The red and blue galaxy power spectra give 0.41 and 0.63
eV respectively for this model. Using mock catalogues, we find the expected
difference in these limits assuming a true neutrino mass of zero is 0.10 + or -
0.14 eV. Thus the difference of 0.22 eV between upper limits on neutrino mass
for red and blue galaxies is approximately 1 sigma from the expected value. We
find similar results for the other models and k ranges tested. This indicates
good agreement for current data but hints at possible issues for
next-generation surveys. Being able to perform such systematic tests is
advantageous, and future surveys would benefit by including broad galaxy
populations and luminosities that enable such a decomposition.
| arxiv topic:astro-ph.CO hep-ex |
arxiv_dataset-19621006.2925 | Crystal nucleation of hard spheres using molecular dynamics, umbrella
sampling and forward flux sampling: A comparison of simulation techniques
cond-mat.soft
Over the last number of years several simulation methods have been introduced
to study rare events such as nucleation. In this paper we examine the crystal
nucleation rate of hard spheres using three such numerical techniques:
molecular dynamics, forward flux sampling and a Bennett-Chandler type theory
where the nucleation barrier is determined using umbrella sampling simulations.
The resulting nucleation rates are compared with the experimental rates of
Harland and Van Megen [J. L. Harland and W. van Megen, Phys. Rev. E 55, 3054
(1997)], Sinn et al. [C. Sinn et al., Prog. Colloid Polym. Sci. 118, 266
(2001)] and Schatzel and Ackerson [K. Schatzel and B.J. Ackerson, Phys. Rev. E,
48, 3766 (1993)] and the predicted rates for monodisperse and 5% polydisperse
hard spheres of Auer and Frenkel [S. Auer and D. Frenkel, Nature 409, 1020
(2001)]. When the rates are examined in long-time diffusion units, we find
agreement between all the theoretically predicted nucleation rates, however,
the experimental results display a markedly different behaviour for low
supersaturation. Additionally, we examined the pre-critical nuclei arising in
the molecular dynamics, forward flux sampling, and umbrella sampling
simulations. The structure of the nuclei appear independent of the simulation
method, and in all cases, the nuclei contain on average significantly more
face-centered-cubic ordered particles than hexagonal-close-packed ordered
particles.
| arxiv topic:cond-mat.soft |
arxiv_dataset-19631006.3025 | Some congruences for trinomial coefficients
math.NT
We prove several congruences for trinomial coefficients.
| arxiv topic:math.NT |
arxiv_dataset-19641006.3125 | The big de Rham-Witt complex
math.NT math.AG math.KT
This paper gives a new and direct construction of the multi-prime big de
Rham-Witt complex which is defined for every commutative and unital ring; the
original construction by the author and Madsen relied on the adjoint functor
theorem and accordingly was very indirect. (The construction given here also
corrects the 2-torsion which was not quite correct in the original version.)
The new construction is based on the theory of modules and derivations over a
lambda-ring which is developed first. The main result in this first part of the
paper is that the universal derivation of a lambda-ring is given by the
universal derivation of the underlying ring together with an additional
structure depending on the lambda-ring structure in question. In the case of
the ring of big Witt vectors, this additional structure gives rise to divided
Frobenius operators on the module of K\"ahler differentials. It is the
existence of these divided Frobenius operators that makes the new construction
of the big de Rham-Witt complex possible. It is further shown that the big de
Rham-Witt complex behaves well with respect to \'etale maps, and finally, the
big de Rham-Witt complex of the ring of integers is explicitly evaluated. The
latter complex may be interpreted as the complex of differentials along the
leaves of a foliation of Spec Z.
| arxiv topic:math.NT math.AG math.KT |
arxiv_dataset-19651006.3225 | On Stokes polarimeters for high precision CMB measurements and mm
Astronomy measurements
astro-ph.IM
Several on-going and future experiments use a Stokes polarimeter (i.e. a
rotating wave plate followed by a steady polarizer and by an unpolarized
detector) to measure the small polarized component of the Cosmic Microwave
Background. The expected signal is typically evaluated using the Mueller
formalism. In this work we carry-out the signal evaluation taking into account
the temperatures of the different optical devices present in the instrument,
their non- idealities, multiple internal reflections, and reflections between
different optical components. This analysis, which exploits a new description
of the radiation transmitted by a half wave plate, can be used to optimize the
experimental setup as well as each of its optical components. We conclude with
an example of application of our analysis, studying a cryogenic polarization
modulator developed for detecting the interstellar dust polarization.
| arxiv topic:astro-ph.IM |
arxiv_dataset-19661006.3325 | An Effective Field Theory Look at Deep Inelastic Scattering
hep-ph
This talk discusses the effective field theory view of deep inelastic
scattering. In such an approach, the standard factorization formula of a hard
coefficient multiplied by a parton distribution function arises from matching
of QCD onto an effective field theory. The DGLAP equations can then be viewed
as the standard renormalization group equations that determines the cut-off
dependence of the non-local operator whose forward matrix element is the parton
distribution function. As an example, the non-singlet quark splitting functions
is derived directly from the renormalization properties of the non-local
operator itself. This approach, although discussed in the literature, does not
appear to be well known to the larger high energy community. In this talk we
give a pedagogical introduction to this subject.
| arxiv topic:hep-ph |
arxiv_dataset-19671006.3425 | Power law in website ratings
cs.IR cs.IT math.IT physics.soc-ph
In the practical work of websites popularization, analysis of their
efficiency and downloading it is of key importance to take into account
web-ratings data. The main indicators of website traffic include the number of
unique hosts from which the analyzed website was addressed and the number of
granted web pages (hits) per unit time (for example, day, month or year). Of
certain interest is the ratio between the number of hits (S) and hosts (H). In
practice there is even used such a concept as "average number of viewed pages"
(S/H), which on default supposes a linear dependence of S on H. What actually
happens is that linear dependence is observed only as a partial case of power
dependence, and not always. Another new power law has been discovered on the
Internet, in particular, on the WWW.
| arxiv topic:cs.IR cs.IT math.IT physics.soc-ph |
arxiv_dataset-19681006.3525 | Light scattering from exoplanet oceans and atmospheres
astro-ph.EP
Orbital variation in reflected starlight from exoplanets could eventually be
used to detect surface oceans. Exoplanets with rough surfaces, or dominated by
atmospheric Rayleigh scattering, should reach peak brightness in full phase,
orbital longitude = 180 deg, whereas ocean planets with transparent atmospheres
should reach peak brightness in crescent phase near OL = 30 deg. Application of
Fresnel theory to a planet with no atmosphere covered by a calm ocean predicts
a peak polarization fraction of 1 at OL = 74 deg; however, our model shows that
clouds, wind-driven waves, aerosols, absorption, and Rayleigh scattering in the
atmosphere and within the water column, dilute the polarization fraction and
shift the peak to other OLs. Observing at longer wavelengths reduces the
obfuscation of the water polarization signature by Rayleigh scattering but does
not mitigate the other effects. Planets with thick Rayleigh scattering
atmospheres reach peak polarization near OL = 90 deg, but clouds and Lambertian
surface scattering dilute and shift this peak to smaller OL. A shifted Rayleigh
peak might be mistaken for a water signature unless data from multiple
wavelength bands are available. Our calculations suggest that polarization
alone may not positively identify the presence of an ocean under an Earth-like
atmosphere; however polarization adds another dimension which can be used, in
combination with unpolarized orbital light curves and contrast ratios, to
detect extrasolar oceans, atmospheric water aerosols, and water clouds.
Additionally, the presence and direction of the polarization vector could be
used to determine planet association with the star, and constrain orbit
inclination.
| arxiv topic:astro-ph.EP |
arxiv_dataset-19691006.3625 | Spectral Theory for Dissipation Mechanism of Wind Waves
physics.ao-ph physics.flu-dyn
A systematic and full description of the theory for a dissipation mechanism
of wind wave energy in a spectral representation is given. As a basis of the
theory, the fundamental is stated that the most general dissipation mechanism
for wind waves is provided by the viscosity due to interaction between wave
motions and turbulence of the water upper layer. The latter, in turn, is
supposed to be induced by the whole aggregate of dissipation processes taking
place at the air-sea interface. In the frame of phenomenological constructions
of nonlinear closure for Reynolds stresses, it is shown that the dissipation
function is generally a power series with respect to wave spectrum, starting
from a quadratic term. Attracting previous results of the author, a simplified
parameterization of the general theoretical result is done. Physical meaning
for parameters of the dissipation function and its compliance with the new
experimental facts established in this field for the last 5-10 years is
discussed. Summarized theoretical results were verified in the mathematical
shells of the well known numerical models for wind waves, WAM and WAEWATCH.
Evidence is given, illustrating a superiority of the proposed model
modifications. Prospects for elaboration of the theory are discussed.
| arxiv topic:physics.ao-ph physics.flu-dyn |
arxiv_dataset-19701006.3725 | Topological stability for conservative systems
math.DS
We prove that the C1-interior of the set of all topologically stable
C1-incompressible flows is contained in the set of Anosov incompressible flows.
Moreover, we obtain an analogous result for the discrete-time case.
| arxiv topic:math.DS |
arxiv_dataset-19711006.3825 | Parikh's Theorem: A simple and direct automaton construction
cs.FL
Parikh's theorem states that the Parikh image of a context-free language is
semilinear or, equivalently, that every context-free language has the same
Parikh image as some regular language. We present a very simple construction
that, given a context-free grammar, produces a finite automaton recognizing
such a regular language.
| arxiv topic:cs.FL |
arxiv_dataset-19721006.3925 | Optimal control models of the goal-oriented human locomotion
math.OC
In recent papers it has been suggested that human locomotion may be modeled
as an inverse optimal control problem. In this paradigm, the trajectories are
assumed to be solutions of an optimal control problem that has to be
determined. We discuss the modeling of both the dynamical system and the cost
to be minimized, and we analyze the corresponding optimal synthesis. The main
results describe the asymptotic behavior of the optimal trajectories as the
target point goes to infinity.
| arxiv topic:math.OC |
arxiv_dataset-19731006.4025 | Leptonic Electroweak Spin-Torsion Interactions
hep-th
In this paper we consider the most general field equations for a system of
two fermions of which one single-handed, showing that the spin-torsion
interactions among these spinors have a structure identical to that of the
electroweak forces among leptons; possible extensions are discussed.
| arxiv topic:hep-th |
arxiv_dataset-19741006.4125 | The Aharonov-Bohm effect in presence of dissipative environments
cond-mat.mes-hall
We study a particle on a ring in presence of various dissipative
environments. We develop and solve a variational scheme assuming low frequency
dominance. Our solution produces a renormalization group (RG) transformation to
all orders in the inverse dissipation strength, and in particular reproduces
known two loop results. Our RG leads to a weak dissipation parameter, for which
a weak coupling expansion for the position correlation function shows a 1/t^2
decay in imaginary time.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-19751006.4225 | Optimal Spectrum Sharing in MIMO Cognitive Radio Networks via
Semidefinite Programming
cs.NI
In this paper, we study the optimal secondary-link beamforming pattern that
balances between the SU's throughput and the interference it causes to PUs in
MIMO cognitive radio networks. In particular, we aim to maximize the throughput
of the SU, while keeping the interference temperature at the primary receivers
below a certain threshold.
Unlike traditional MIMO systems, SUs may not have the luxury of knowing the
channel state information (CSI) on the links to PUs. This presents a key
challenge for a secondary transmitter to steer interference away from primary
receivers. In this paper, we consider three scenarios, namely when the
secondary transmitter has complete, partial, or no knowledge about the channels
to the primary receivers. In particular, when complete CSI is not available,
the interference-temperature constraints are to be satisfied with high
probability, thus resulting in chance constraints that are typically hard to
deal with. Our contribution is fourfold. First, by analyzing the distributional
characteristics of MIMO channels, we propose a unified homogeneous QCQP
formulation that can be applied to all three scenarios. The homogeneous QCQP
formulation, though non-convex, is amenable to semidefinite programming (SDP)
relaxation methods. Secondly, we show that the SDP relaxation admits no gap
when the number of primary links is no larger than two. Thirdly, we propose a
randomized polynomial-time algorithm for constructing a near-optimal solution
to the QCQP problem when there are more than two primary links. Finally, we
show that when the secondary transmitter has no CSI on the links to primary
receivers, the optimal solution to the QCQP problem can be found by a simple
matrix eigenvalue-eigenvector computation, which can be done much more
efficiently than solving the QCQP directly.
| arxiv topic:cs.NI |
arxiv_dataset-19761006.4325 | Entanglement criteria for microscopic-macroscopic systems
quant-ph physics.optics
We discuss the conclusions that can be drawn on a recent experimental
micro-macro entanglement test [F. De Martini, F. Sciarrino, and C. Vitelli,
Phys. Rev. Lett. 100, 253601 (2008). The system under investigation is
generated through optical parametric amplification of one photon belonging to
an entangled pair. The adopted entanglement criterion makes it possible to
infer the presence of entanglement before losses, that occur on the macrostate,
under a specific assumption. In particular, an a priori knowledge of the system
that generates the micro-macro pair is necessary to exclude a class of
separable states that can reproduce the obtained experimental results. Finally,
we discuss the feasibility of a micro-macro "genuine" entanglement test on the
analyzed system by considering different strategies, which show that in
principle a fraction epsilon, proportional to the number of photons that
survive the lossy process, of the original entanglement persists in any losses
regime.
| arxiv topic:quant-ph physics.optics |
arxiv_dataset-19771006.4425 | On-the-fly Uniformization of Time-Inhomogeneous Infinite Markov
Population Models
math.PR cs.CE cs.NA
This paper presents an on-the-fly uniformization technique for the analysis
of time-inhomogeneous Markov population models. This technique is applicable to
models with infinite state spaces and unbounded rates, which are, for instance,
encountered in the realm of biochemical reaction networks. To deal with the
infinite state space, we dynamically maintain a finite subset of the states
where most of the probability mass is located. This approach yields an
underapproximation of the original, infinite system. We present experimental
results to show the applicability of our technique.
| arxiv topic:math.PR cs.CE cs.NA |
arxiv_dataset-19781006.4525 | Endperiodic Automorphisms of Surfaces and Foliations
math.GT
We extend the unpublished work of M. Handel and R. Miller on the
classification, up to isotopy, of endperiodic automorphisms of surfaces. We
give the Handel-Miller construction of the geodesic laminations, give an
axiomatic theory for pseudo-geodesic lamaniations, show the geodesic
laminations satisfy the axioms, and prove that paeudo-geodesic laminations
satisfying our axioms are ambiently isotopic to the geodesic laminations. The
axiomatic approach allows us to show that the given endperiodic automorphism is
isotopic to a smooth endperiodic automorphism preserving smooth laminations
ambiently isotopic to the original ones. Using the axioms, we also prove the
"transfer theorem" for foliations of 3-manifolds., namely that, if two depth
one foliations are transverse to a common one-dimensional foliation whose
monodromy on the noncompact leaves of the first foliation exhibits the nice
dynamics of Handel-Miller theory, then the transverse one-dimensional foliation
also induces monodromy on the noncompact leaves of the second foliation
exhibiting the same nice dynamics. Our theory also applies to surfaces with
infinitely many ends.
| arxiv topic:math.GT |
arxiv_dataset-19791006.4625 | Mixing Times in Quantum Walks on Two-Dimensional Grids
quant-ph cs.CC
Mixing properties of discrete-time quantum walks on two-dimensional grids
with torus-like boundary conditions are analyzed, focusing on their connection
to the complexity of the corresponding abstract search algorithm. In
particular, an exact expression for the stationary distribution of the coherent
walk over odd-sided lattices is obtained after solving the eigenproblem for the
evolution operator for this particular graph. The limiting distribution and
mixing time of a quantum walk with a coin operator modified as in the abstract
search algorithm are obtained numerically. On the basis of these results, the
relation between the mixing time of the modified walk and the running time of
the corresponding abstract search algorithm is discussed.
| arxiv topic:quant-ph cs.CC |
arxiv_dataset-19801006.4725 | De Sitter Relativity and Cosmological Principle
physics.gen-ph
The formalism of Fantappie-Arcidiacono Projective General Relativity - also
known as De Sitter Relativity - has recently been revised in order to make
possible cosmological models with expansion, similarly to ordinary Fridman
cosmology formulated within the context of General Relativity. In this article,
several consequences of interest in the current cosmological debate are
examined and discussed in a semiquantitative manner. Specifically:
re-examination of the Supernova Project results using this new formalism, with
a new estimate of the cosmological parameters; the ordinary matter to dark
matter densities ratio; the existence of a new fundamental constant having the
dimensions of an acceleration and its relation with dark matter.
| arxiv topic:physics.gen-ph |
arxiv_dataset-19811006.4825 | Hysteresis of atmospheric parameters of 12 RR Lyrae stars based on
multichannel simultaneous Stroemgren photometry
astro-ph.SR
RR Lyrae stars have been observed to improve the insight into the processes
at work in their atmospheres. Simultaneous Stroemgren-photometry allows to
obtain a rapid sequence of measurements in which photometric indices are
unaffected by non-optimum observing conditions. The indices y, b-y, and c_1 are
used with an established calibration to derive T_eff and to derive the gravity,
log g_BJ from the Balmer jump, throughout the pulsation cycle. By employing the
equations for stellar structure, additional parameters can be derived.
Stroemgren photometry and its calibration in terms of T_eff and log g can be
used to determine the run of R and the atmosphere pulsation velocity. We find
that the Balmer-line strengths are correlated with T_eff and that the strength
of the Ca_ii K line correlates well with the radius of the star and thus the
pulsation-dependent density of the atmosphere. The density in the stellar
atmosphere fluctuates as indicated by the changes in the gravity log g_BJ,
derived from c_1, between 2.3 and 4.5 dex. Also the Stroemgren metal index,
m_1, fluctuates. We find a disagreement between log g(T,L,M), the gravity
calculated from T_eff, L, and the mass M,and the gravity log g_BJ. This can be
used to reassess the mass and the absolute magnitude of an individual star.The
curves derived for the pulsational velocity V_pul differ from curves obtained
from spectra needed to apply the Baade-Wesselink method; we think these
differences are due to phase dependent differences in the optical depth levels
sampled in continuum photometry and in spectroscopy. We find an atmospheric
oscillation in these fundamental mode RR Lyrae stars of periodicity P/7.
| arxiv topic:astro-ph.SR |
arxiv_dataset-19821006.4925 | Simulating information creation in social Semantic Web applications
cs.CE
Appropriate ranking algorithms and incentive mechanisms are essential to the
creation of high-quality information by users of a social network. However,
evaluating such mechanisms in a quantifiable way is a difficult problem.
Studies of live social networks of limited utility, due to the subjective
nature of ranking and the lack of experimental control. Simulation provides a
valuable alternative: insofar as the simulation resembles the live social
network, fielding a new algorithm within a simulated network can predict the
effect it will have on the live network. In this paper, we propose a simulation
model based on the actor-conceptinstance model of semantic social networks,
then we evaluate the model against a number of common ranking algorithms.We
observe their effects on information creation in such a network, and we extend
our results to the evaluation of generic ranking algorithms and incentive
mechanisms.
| arxiv topic:cs.CE |
arxiv_dataset-19831006.5025 | Perturbations of Mathieu equations with parametric excitation of large
period
nlin.CD math.DS
We consider a linear differential system of Mathieu equations with periodic
coefficients over periodic closed orbits and we prove that, arbitrarily close
to this system, there is a linear differential system of Hamiltonian damped
Mathieu equations with periodic coefficients over periodic closed orbits such
that, all but a finite number of closed periodic coefficients, have unstable
solutions. The perturbations will be peformed in the periodic coefficients.
| arxiv topic:nlin.CD math.DS |
arxiv_dataset-19841006.5125 | Off-Axis Gamma-Ray Burst Afterglow Modeling Based On A Two-Dimensional
Axisymmetric Hydrodynamics Simulation
astro-ph.HE astro-ph.CO astro-ph.SR
Starting as highly relativistic collimated jets, gamma-ray burst outflows
gradually decelerate and become non-relativistic spherical blast waves.
Although detailed analytical solutions describing the afterglow emission
received by an on-axis observer during both the early and late phases of the
outflow evolution exist, a calculation of the received flux during the
intermediate phase and for an off-axis observer requires either a more
simplified analytical model or direct numerical simulations of the outflow
dynamics. In this paper we present light curves for off-axis observers covering
the long-term evolution of the blast wave calculated from a high resolution
two-dimensional relativistic hydrodynamics simulation using a synchrotron
radiation model. We compare our results to earlier analytical work and
calculate the consequence of the observer angle with respect to the jet axis
both for the detection of orphan afterglows and for jet break fits to the
observational data. We find that observable jet breaks can be delayed for up to
several weeks for off-axis observers, potentially leading to overestimation of
the beaming corrected total energy. When using our off-axis light curves to
create synthetic Swift X-ray data, we find that jet breaks are likely to remain
hidden in the data. We also confirm earlier results in the literature finding
that only a very small number of local Type Ibc supernovae can harbor an orphan
afterglow.
| arxiv topic:astro-ph.HE astro-ph.CO astro-ph.SR |
arxiv_dataset-19851006.5225 | Composition operators on Bergman-Orlicz spaces on the ball
math.FA math.CV
We give embedding theorems for weighted Bergman-Orlicz spaces on the ball and
then apply our results to the study of composition operators in this context.
As one of the motivations of this work, we show that there exist some weighted
Bergman-Orlicz spaces, different from $H^{\infinity}$, on which every
composition operator is bounded.
| arxiv topic:math.FA math.CV |
arxiv_dataset-19861006.5325 | Radio emission from dark matter annihilation in the Large Magellanic
Cloud
astro-ph.HE
The Large Magellanic Cloud, at only 50 kpc away from us and known to be dark
matter dominated, is clearly an interesting place where to search for dark
matter annihilation signals. In this paper, we estimate the synchrotron
emission due to WIMP annihilation in the halo of the LMC at two radio
frequencies, 1.4 and 4.8 GHz, and compare it to the observed emission, in order
to impose constraints in the WIMP mass vs. annihilation cross section plane. We
use available Faraday rotation data from background sources to estimate the
magnitude of the magnetic field in different regions of the LMC's disc, where
we calculate the radio signal due to dark matter annihilation. We account for
the e+ e- energy losses due to synchrotron, Inverse Compton Scattering and
bremsstrahlung, using the observed hydrogen and dust temperature distribution
on the LMC to estimate their efficiency. The extensive use of observations,
allied with conservative choices adopted in all the steps of the calculation,
allow us to obtain very realistic constraints.
| arxiv topic:astro-ph.HE |
arxiv_dataset-19871006.5425 | New limit on Lorentz and CPT-violating neutron spin interactions
physics.atom-ph hep-ph
We performed a search for neutron spin coupling to a Lorentz and
CPT-violating background field using a magnetometer with overlapping ensembles
of K and $^3$He atoms. The co-magnetometer is mounted on a rotary platform for
frequent reversal of its orientation. We measure sidereal oscillations in the
signal to search for anomalous spin coupling of extra-solar origin. We
determine the equatorial components of the background field interacting with
the neutron spin to be $\widetilde{b}^n_X = (0.1 \pm 1.6) \times 10^{-33}$ GeV
and $\widetilde{b}^n_Y = (2.5 \pm 1.6) \times 10^{-33}$ GeV, improving on the
previous limit by a factor of 30. This measurement represents the highest
energy resolution of any spin anisotropy experiment.
| arxiv topic:physics.atom-ph hep-ph |
arxiv_dataset-19881006.5525 | The experimental failure of macroscopic determinism: the case of an
electrocardiogram
quant-ph
Even if never elucidated, the question of determinism is a standing question
along the history of human thinking. A physical system evolves in a
deterministic way if its future is completely determined once we have fixed
some present characteristics of it, i.e., its initial conditions. The problem
addressed in the present paper is to test determinism in the macroscopic
domain. By imposing a very plausible ``separability'' assumption, we prove that
determinism enters in contradiction with the recorded outcomes of a given
electrocardiogram. The interest of this result comes from the fact such a basic
idea as determinism has never been experimentally tested up to now in the
macroscopic domain, and as far as we know not even in the quantum domain.
| arxiv topic:quant-ph |
arxiv_dataset-19891006.5625 | Renormalization flow in extreme value statistics
cond-mat.stat-mech math-ph math.MP
The renormalization group transformation for extreme value statistics of
independent, identically distributed variables, recently introduced to describe
finite size effects, is presented here in terms of a partial differential
equation (PDE). This yields a flow in function space and gives rise to the
known family of Fisher-Tippett limit distributions as fixed points, together
with the universal eigenfunctions around them. The PDE turns out to handle
correctly distributions even having discontinuities. Remarkably, the PDE admits
exact solutions in terms of eigenfunctions even farther from the fixed points.
In particular, such are unstable manifolds emanating from and returning to the
Gumbel fixed point, when the running eigenvalue and the perturbation strength
parameter obey a pair of coupled ordinary differential equations. Exact
renormalization trajectories corresponding to linear combinations of
eigenfunctions can also be given, and it is shown that such are all solutions
of the PDE. Explicit formulas for some invariant manifolds in the Fr\'echet and
Weibull cases are also presented. Finally, the similarity between
renormalization flows for extreme value statistics and the central limit
problem is stressed, whence follows the equivalence of the formulas for Weibull
distributions and the moment generating function of symmetric L\'evy stable
distributions.
| arxiv topic:cond-mat.stat-mech math-ph math.MP |
arxiv_dataset-19901006.5725 | Nonstable $K$--theory for extension algebras of the simple purely
infinite $C^*$--algebra by certain $C^{*}$--algebras
math.OA
Let $0\longrightarrow
\B\stackrel{j}{\longrightarrow}E\stackrel{\pi}{\longrightarrow}\A\longrightarrow
0$ be an extension of $\A$ by $\B$, where $\A$ is a unital simple purely
infinite $C^{*}$--algebra. When $\B$ is a simple separable essential ideal of
the unital $C^{*}$--algebra $E$ with $\RR(\B)=0$ and {\rm(PC)},
$K_{0}(E)=\{[p]\mid p$ is a projection in $E\setminus B\}$; When $B$ is a
stable $C^{*}$--algebra, $\U(C(X,E))/\U_0(C(X,E))\cong K_1(C(X,E))$ for any
compact Hausdorff space $X$.
| arxiv topic:math.OA |
arxiv_dataset-19911006.5825 | A refined Bogoliubov-Huang approach to helium II thermodynamics
cond-mat.stat-mech
The thermodynamics of a free Bose gas with effective temperature scale
$\tilde{T}$ and hard-sphere Bose gas with the $\tilde{T}$ scale are studied.
$\tilde{T}$ arises as the temperature experienced by a single particle in a
quantum gas with 2-body harmonic oscillator interaction $V_\textrm{osc}$, which
at low temperatures is expected to simulate, almost correctly, the attractive
part of the interatomic potential $V_\textrm{He}$ between $^{4}\textrm{He}$
atoms. The repulsive part of $V_\textrm{He}$ is simulated by a hard-sphere (HS)
potential. The thermodynamics of this system of HS bosons, with the $\tilde{T}$
temperature scale (HSET), is investigated, first, by the Bogoliubov-Huang
method and next by a modified version of this method, which takes approximate
account of those terms of the 2-body repulsion which are linear in the
zero-momentum Bose operators $a_0,\,\,a^*_0$ (originally rejected by
Bogoliubov). Theoretical heat capacity $C_V(T)$ exhibits good agreement, below
2.1 K, with the experimental heat capacity graph observed in $^{4}\textrm{He}$
at saturated vapour pressure. The phase transition to the low-temperature
phase, with a Bose-Einstein condensate, occurs in the HSET at $T_\lambda=$2.17
K, and is accompanied, in the modified HSET version, by a singularity of
$C_V(T)$. Other thermal properties of HSET, such as the momentum distribution
function, the fraction of atoms in the momentum condensate and normal fluid
density, agree qualitatively with those of $^{4}\textrm{He}$, but improve those
of the free Bose gas.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-19921006.5925 | The Effect of Variable Flavour Number Scheme Variations on PDFs and
Cross Sections
hep-ph
I consider variations in the definition of a General-Mass Variable Flavour
Number Scheme (GM-VFNS) for heavy flavour structure functions, both at
next-to-leading order (NLO) and at next-to-next-to leading order (NNLO). I also
define a new "optimal" scheme choice improving the smoothness of the transition
from one flavour number to the next. At both NLO and NNLO I investigate the
variation of the structure function for a fixed set of parton distribution
functions (PDFs) and also the change in the distributions when a new MSTW-type
global fit to data is performed for each GM-VFNS. At NLO the parton
distributions, and predictions using them at hadron colliders, can vary by ~2%
from the mean value. Use of the the Zero-Mass Variable Flavour Number Scheme,
which is simpler but only an approximation, leads to results a further couple
of percent or more outside this range. At NNLO there is far more stability with
varying GM-VFNS definition. Typical changes in PDFs and predictions are less
than 1%, with most variation at very small x values. This demonstrates that
mass-scheme variation is an additional and significant source of uncertainty
when considering parton distributions, but like other theoretical
uncertainties, it diminishes quickly as higher orders are included.
| arxiv topic:hep-ph |
arxiv_dataset-19931007.0062 | Calendars of India
physics.pop-ph physics.hist-ph
This short monograph is devoted to different historical calendars prevalent
in India from ancient times. They are classified and described with
astronomical and historical details. Relationship of the calendrical elements
to modern astronomical terminology has been explained. A proposal is outlined
for modifying the calendar for removing inconsistencies and improving its
accuracy.
| arxiv topic:physics.pop-ph physics.hist-ph |
arxiv_dataset-19941007.0162 | Weakly convex sets and modulus of nonconvexity
math.FA math.GN
We consider a definition of a weakly convex set which is a generalization of
the notion of a weakly convex set in the sense of Vial and a proximally smooth
set in the sense of Clarke, from the case of the Hilbert space to a class of
Banach spaces with the modulus of convexity of the second order. Using the new
definition of the weakly convex set with the given modulus of nonconvexity we
prove a new retraction theorem and we obtain new results about continuity of
the intersection of two continuous set-valued mappings (one of which has
nonconvex images) and new affirmative solutions of the splitting problem for
selections. We also investigate relationship between the new definition and the
definition of a proximally smooth set and a smooth set.
| arxiv topic:math.FA math.GN |
arxiv_dataset-19951007.0262 | Extension of plurisubharmonic functions with growth control
math.CV
Suppose that $X$ is an analytic subvariety of a Stein manifold $M$ and that
$\varphi$ is a plurisubharmonic (psh) function on $X$ which is dominated by a
continuous psh exhaustion function $u$ of $M$. Given any number $c>1$, we show
that $\varphi$ admits a psh extension to $M$ which is dominated by $cu$ on $M$.
We use this result to prove that any $\omega$-psh function on a subvariety of
the complex projective space is the restriction of a global $\omega$-psh
function, where $\omega$ is the Fubini-Study K\"ahler form.
| arxiv topic:math.CV |
arxiv_dataset-19961007.0362 | Theory and simulation of the confined Lebwohl-Lasher model
cond-mat.soft cond-mat.stat-mech
We discuss the Lebwohl-Lasher model of nematic liquid crystals in a confined
geometry, using Monte Carlo simulation and mean-field theory. A film of
material is sandwiched between two planar, parallel plates that couple to the
adjacent spins via a surface strength $\epsilon_s$. We consider the cases where
the favoured alignments at the two walls are the same (symmetric cell) or
different (asymmetric or hybrid cell). In the latter case, we demonstrate the
existence of a {\it single} phase transition in the slab for all values of the
cell thickness. This transition has been observed before in the regime of
narrow cells, where the two structures involved correspond to different
arrangements of the nematic director. By studying wider cells, we show that the
transition is in fact the usual isotropic-to-nematic (capillary) transition
under confinement in the case of antagonistic surface forces. We show results
for a wide range of values of film thickness, and discuss the phenomenology
using a mean-field model.
| arxiv topic:cond-mat.soft cond-mat.stat-mech |
arxiv_dataset-19971007.0462 | Blackbody radiation shift in 87Rb frequency standard
physics.atom-ph quant-ph
The operation of atomic clocks is generally carried out at room temperature,
whereas the definition of the second refers to the clock transition in an atom
at absolute zero. This implies that the clock transition frequency should be
corrected in practice for the effect of finite temperature of which the leading
contributor is the blackbody radiation (BBR) shift. Experimental measurements
of the BBR shifts are difficult. In this work, we have calculated the blackbody
radiation shift of the ground-state hyperfine microwave transition in 87Rb
using the relativistic all-order method and carried out detailed evaluation of
the accuracy of our final value. Particular care is taken to accurately account
for the contributions from highly-excited states. Our predicted value for the
Stark coefficient, k_S=-1.240(4)\times 10^{-10}\text{Hz/(V/m)}^{2} is three
times more accurate than the previous calculation [1].
| arxiv topic:physics.atom-ph quant-ph |
arxiv_dataset-19981007.0562 | Cliophysics: Socio-political Reliability Theory, Polity Duration and
African Political (In)stabilities
physics.soc-ph physics.data-an stat.AP
Quantification of historical sociological processes have recently gained
attention among theoreticians in the effort of providing a solid theoretical
understanding of the behaviors and regularities present in sociopolitical
dynamics. Here we present a reliability theory of polity processes with
emphases on individual political dynamics of African countries. We found that
the structural properties of polity failure rates successfully capture the risk
of political vulnerability and instabilities in which 87.50%, 75%, 71.43%, and
0% of the countries with monotonically increasing, unimodal, U-shaped and
monotonically decreasing polity failure rates, respectively, have high level of
state fragility indices. The quasi-U-shape relationship between average polity
duration and regime types corroborates historical precedents and explains the
stability of the autocracies and democracies.
| arxiv topic:physics.soc-ph physics.data-an stat.AP |
arxiv_dataset-19991007.0662 | Astronomical identification of CN-, the smallest observed molecular
anion
astro-ph.GA
We present the first astronomical detection of a diatomic negative ion, the
cyanide anion CN-, as well as quantum mechanical calculations of the excitation
of this anion through collisions with para-H2. CN- is identified through the
observation of the J = 2-1 and J = 3-2 rotational transitions in the C-star
envelope IRC +10216 with the IRAM 30-m telescope. The U-shaped line profiles
indicate that CN-, like the large anion C6H-, is formed in the outer regions of
the envelope. Chemical and excitation model calculations suggest that this
species forms from the reaction of large carbon anions with N atoms, rather
than from the radiative attachment of an electron to CN, as is the case for
large molecular anions. The unexpectedly large abundance derived for CN-, 0.25
% relative to CN, makes likely its detection in other astronomical sources. A
parallel search for the small anion C2H- remains so far unconclusive, despite
the previous tentative identification of the J = 1-0 rotational transition. The
abundance of C2H- in IRC +10216 is found to be vanishingly small, < 0.0014 %
relative to C2H.
| arxiv topic:astro-ph.GA |
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