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arxiv_dataset-1600912.0249 | Iterated integrals of superconnections
math.AT
Starting with a Z-graded superconnection on a graded vector bundle over a
smooth manifold M, we show how Chen's iterated integration of such a
superconnection over smooth simplices in M gives an A-infinity functor if and
only if the superconnection is flat. If the graded bundle is trivial, this
gives a twisting cochain.
Very similar results were obtained by K.T. Chen using similar methods. This
paper is intended to explain this from scratch beginning with the definition
and basic properties of a connection and ending with an exposition of Chen's
"formal connections" and a brief discussion of how this is related to higher
Reidemeister torsion.
| arxiv topic:math.AT |
arxiv_dataset-1601912.0349 | The state of cold quark matter: a model-independent view
astro-ph.HE astro-ph.SR hep-ph nucl-th
From a model-independent point of view, we address the possibility that quark
clustering could occur in cold quark matter at realistic baryon densities
because of the likely strong coupling between quarks in compact stars.
| arxiv topic:astro-ph.HE astro-ph.SR hep-ph nucl-th |
arxiv_dataset-1602912.0449 | Fit;o) - A M\"ossbauer spectrum fitting program
physics.comp-ph physics.data-an
Fit;o) is a M\"ossbauer fitting and analysis program written in Borland
Delphi. It has a complete graphical user interface that allows all actions to
be carried out via mouse clicks or key shortcut operations in a WYSIWYG
fashion. The program does not perform complete transmission integrals, and will
therefore not be suited for a complete analysis of all types of M\"ossbauer
spectra and e.g. low temperature spectra of ferrous silicates. Instead, the
program is intended for application on complex spectra resulting from typical
mineral samples, in which many phases and different crystallite sizes are often
present at the same time. The program provides the opportunity to fit the
spectra with Gaussian, Lorentzian, Split-Lorentzian, Pseudo-Voigt,
Pseudo-Lorentz and Pearson-VII line profiles for individual components of the
spectra. This feature is particularly useful when the sample contains
components, that are affected by effects of either relaxation or interaction
among particles. Fitted spectra may be printed, fits saved, data files exported
for graph creation in other programs, and analysis tables and reports may be
exported as plain text or LaTeX files. With Fit;o) even an inexperienced user
will soon be able to analyze and fit relatively complex M\"ossbauer spectra of
mineralogical samples quickly without programming knowledge.
| arxiv topic:physics.comp-ph physics.data-an |
arxiv_dataset-1603912.0549 | Modular Workflow Engine for Distributed Services using Lightweight Java
Clients
cs.SE cs.CE
In this article we introduce the concept and the first implementation of a
lightweight client-server-framework as middleware for distributed computing. On
the client side an installation without administrative rights or privileged
ports can turn any computer into a worker node. Only a Java runtime environment
and the JAR files comprising the workflow client are needed. To connect all
clients to the engine one open server port is sufficient. The engine submits
data to the clients and orchestrates their work by workflow descriptions from a
central database. Clients request new task descriptions periodically, thus the
system is robust against network failures. In the basic set-up, data up- and
downloads are handled via HTTP communication with the server. The performance
of the modular system could additionally be improved using dedicated file
servers or distributed network file systems.
We demonstrate the design features of the proposed engine in real-world
applications from mechanical engineering. We have used this system on a compute
cluster in design-of-experiment studies, parameter optimisations and robustness
validations of finite element structures.
| arxiv topic:cs.SE cs.CE |
arxiv_dataset-1604912.0649 | A d'Alembert Formula for Hopf Hypersurfaces
math.DG
A Hopf hypersurface in complex hyperbolic space CH^n is one in which the
complex structure applied to the normal vector is a principal direction at each
point. In this paper, Hopf hypersurfaces for which the corresponding principal
curvature is small (relative to the ambient sectional curvature) are studied by
means of a generalized Gauss map into a product of spheres, and it is shown
that the hypersurface may be recovered from the image of this map, via an
explicit formula.
| arxiv topic:math.DG |
arxiv_dataset-1605912.0749 | Quest for precision in hadronic cross sections at low energy: Monte
Carlo tools vs. experimental data
hep-ph hep-ex
We present the achievements of the last years of the experimental and
theoretical groups working on hadronic cross section measurements at the low
energy e+e- colliders in Beijing, Frascati, Ithaca, Novosibirsk, Stanford and
Tsukuba and on tau decays. We sketch the prospects in these fields for the
years to come. We emphasise the status and the precision of the Monte Carlo
generators used to analyse the hadronic cross section measurements obtained as
well with energy scans as with radiative return, to determine luminosities and
tau decays. The radiative corrections fully or approximately implemented in the
various codes and the contribution of the vacuum polarisation are discussed.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-1606912.0849 | Superfluid density of Ba(Fe$_{1-x}M_x$)$_2$As$_2$ from optical
experiments
cond-mat.supr-con
The temperature dependence of the $ab$-plane optical reflectivity of
Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$
single crystals is measured in a wide spectral range. Upon entering the
superconducting regime, the reflectivity in both compounds increases
considerably at low frequency, leading to a clear gap in the optical
conductivity below 100 cm$^{-1}$. From the analysis of the complex conductivity
spectra we obtain the penetration depth $\lambda(T)=(3500\pm 350)$ \AA for
Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and $(3000\pm 300)$ \AA for
Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$. The calculated superfluid density
$\rho_s$ of both compounds nicely fits the scaling relation $\rho_s=(125\pm
25)\sigma_{dc}T_c$.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-1607912.0949 | Unified dark energy and dark matter from a scalar field different from
quintessence
astro-ph.CO
We explore unification of dark matter and dark energy in a theory containing
a scalar field of non-Lagrangian type, obtained by direct insertion of a
kinetic term into the energy-momentum tensor. This scalar is different from
quintessence, having an equation of state between -1 and 0 and a zero sound
speed in its rest frame. We solve the equations of motion for an exponential
potential via a rewriting as an autonomous system, and demonstrate the
observational viability of the scenario, for sufficiently small exponential
potential parameter \lambda, by comparison to a compilation of kinematical
cosmological data.
| arxiv topic:astro-ph.CO |
arxiv_dataset-1608912.1049 | Delta-Interference of Two Friedel Resonances
cond-mat.mes-hall
When a single resonator is coupled to a continuous spectrum one obtains a
resonance of finite half-width. Such a resonance is known in many fields of
physics. The Friedel resonance is an example where a d-impurity is dissolved in
a simple metal. If two resonators are coupled to the continuous spectrum the
resonances interfere. For identical coupling and frequencies one obtains two
effective resonances. The effective coupling of one of them to the continuum
can be tuned to zero yielding a delta-like resonance.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-1609912.1149 | Vertex operator approach for form factors of Belavin's
$(Z/nZ)$-symmetric model
math-ph hep-th math.MP math.QA
Belavin's $(\mathbb{Z}/n\mathbb{Z})$-symmetric model is considered on the
basis of bosonization of vertex operators in the $A^{(1)}_{n-1}$ model and
vertex-face transformation. Free field representations of nonlocal tail
operators are constructed for off diagonal matrix elements with respect to the
ground state sectors. As a result, integral formulae for form factors of any
local operators in the $(\mathbb{Z}/n\mathbb{Z})$-symmetric model can be
obtained, in principle.
| arxiv topic:math-ph hep-th math.MP math.QA |
arxiv_dataset-1610912.1249 | The Lagrangian description of perfect fluids and modified gravity with
an extra force
astro-ph.GA gr-qc
We revisit the issue of the correct Lagrangian description of a perfect fluid
(pressure versus minus energy density) in relation with modified gravity
theories in which galactic luminous matter couples nonminimally to the Ricci
scalar. These Lagrangians are only equivalent when the fluid couples minimally
to gravity and not otherwise; in the presence of nonminimal coupling they give
rise to two distinct theories with different predictions.
| arxiv topic:astro-ph.GA gr-qc |
arxiv_dataset-1611912.1349 | New physics reach of CP violating observables in the decay B to K* l+ l-
hep-ph
We discuss theoretical and experimental preparations for an indirect new
physics search using the rare decay B to K*0 (to K pi) l+ l- focusing on CP
violating observables. The separation of new physics effects and hadronic
uncertainties is the key issue when using flavour observables in a new-physics
search. Our analysis is based on QCD factorization and soft-collinear effective
theory and critically examines the new physics reach of those observables via a
detailed error analysis due to scale dependences, form factors, and other input
parameters; we also explore the experimental sensitivities at LHCb using a
full-angular fit method; finally, we make the impact of the unknown Lambda/mb
corrections manifest in our theoretical predictions.
| arxiv topic:hep-ph |
arxiv_dataset-1612912.1449 | Charge creation and nucleation of longitudinal plasma wave in coupled
Josephson junctions
cond-mat.supr-con cond-mat.mes-hall
We study the phase dynamics in coupled Josephson junctions describing by
system of nonlinear differential equations. Results of detailed numerical
simulations of charge creation in the superconducting layers and the
longitudinal plasma wave (LPW) nucleation are presented. We demonstrate the
different time stages in the development of the LPW and present results of FFT
analysis at different values of bias current. The correspondence between the
breakpoint position on the outermost branch of current voltage characteristics
(CVC) and the growing region in time dependence of the electric charge in the
superconducting layer is established. The effects of noise in the bias current
and the external microwave radiation on the charge dynamics of the coupled
Josephson junctions are found. These effects introduce a way to regulate the
process of LPW nucleation in the stack of IJJ.
| arxiv topic:cond-mat.supr-con cond-mat.mes-hall |
arxiv_dataset-1613912.1549 | Entanglement-preserving frequency conversion in cold atoms
quant-ph
We propose a method that enables efficient frequency conversion of quantum
information based on recently demonstrated strong parametric coupling between
two single-photon pulses propagating in a slow-light atomic medium at different
group velocities. We show that an incoming single-photon state is efficiently
converted into another optical mode in a lossless and shape-conserving manner.
The persistence of initial quantum coherence and entanglement within frequency
conversion is also demonstrated. We first illustrate this result for the case
of small frequency difference of converted photons, and then discuss the
modified scheme for conversion of photon wavelengths in different spectral
ranges. Finally we analyze the generation of a narrow-band single-photon
frequency-entangled state.
| arxiv topic:quant-ph |
arxiv_dataset-1614912.1649 | Completeness of the WDS method in Checking Positivity of Integral Forms
cs.SC
Examples show that integral forms can be efficiently proved positive
semidefinite by the WDS method, but it was unknown that how many steps of
substitutions are needed, or furthermore, which integral forms is this method
applicable for. In this paper, we give upper bounds of step numbers of WDS
required in proving that an integral form is positive definite, positive
semidefinite, or not positive semidefinite, thus deducing that the WDS method
is complete.
| arxiv topic:cs.SC |
arxiv_dataset-1615912.1749 | Approximation Results for alpha-Rosen Fractions
math.NT
In this article we generalize Borel's classical approximation results for the
regular continued fraction expansion to the alpha-Rosen fraction expansion,
using a geometric method. We give a Haas-Series-type result about all possible
good approximations for the alpha for which the Legendre constant is larger
than the Hurwitz constant.
| arxiv topic:math.NT |
arxiv_dataset-1616912.1849 | Global Study of Electron-Quark Unparticle Interactions
hep-ph hep-ex
We perform a global fit on parity-conserving electron-quark interactions via
spin-1 unparticle exchange. Besides the peculiar features of unparticle
exchange due to non-integral values for the scaling dimension d_U and a
non-trivial phase factor exp (-id_U \pi) associated with a time-like unparticle
propagator, the energy dependence s^{-2 + d_U} of the unparticle contributions
in the scattering amplitudes are also taken into account. The high energy data
sets taken into consideration in our analysis are from (1) deep inelastic
scattering at high Q^2 from ZEUS and H1, (2) Drell-Yan production at Run II of
CDF and DO, and (3) e^+e^- --> hadrons at LEPII. The hadronic data at LEPII by
itself indicated a 3-4 sigma preference of new physics over the Standard Model.
However, when all data sets are combined, no preference for unparticle effects
can be given. We thus deduce an improved 95% confidence level limit on the
unparticle energy scale \Lambda_\U.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-1617912.1949 | Bipartite quantum channels using multipartite cluster-type entangled
coherent states
quant-ph
We propose a particular encoding for bipartite entangled states derived from
multipartite cluster-type entangled coherent states (CTECSs). We investigate
the effects of amplitude damping on the entanglement content of this bipartite
state, as well as its usefulness as a quantum channel for teleportation. We
find interesting relationships among the amplitude of the coherent states
constituting the CTECSs, the number of subsystems forming the logical qubits
(redundancy), and the extent to which amplitude damping affects the
entanglement of the channel. For instance, in the sense of sudden death of
entanglement, given a fixed value of the initial coherent state amplitude, the
entanglement life span is shortened if redundancy is increased.
| arxiv topic:quant-ph |
arxiv_dataset-1618912.2049 | Towards a consistent picture for quasi-1D organic superconductors
cond-mat.supr-con cond-mat.str-el
The electrical resistivity of the quasi-1D organic superconductor (TMTSF)2PF6
was recently measured at low temperature from the critical pressure needed to
suppress the spin-density-wave state up to a pressure where superconductivity
has almost disappeared. This data revealed a direct correlation between the
onset of superconductivity at Tc and the strength of a non-Fermi-liquid linear
term in the normal-state resistivity, going as r(T) = r0 + AT + BT2 at low
temperature, so that A goes to 0 as Tc goes to 0. Here we show that the
contribution of low-frequency antiferromagnetic fluctuations to the
spin-lattice relaxation rate is also correlated with this non-Fermi-liquid term
AT in the resistivity. These correlations suggest that anomalous scattering and
pairing have a common origin, both rooted in the low-frequency
antiferromagnetic fluctuations measured by NMR. A similar situation may also
prevail in the recently-discovered iron-pnictide superconductors.
| arxiv topic:cond-mat.supr-con cond-mat.str-el |
arxiv_dataset-1619912.2149 | Influence of detector motion in entanglement measurements with photons
quant-ph
We investigate how the polarization correlations of entangled photons
described by wave packets are modified when measured by moving detectors. For
this purpose, we analyze the Clauser-Horne-Shimony-Holt Bell inequality as a
function of the apparatus velocity. Our analysis is motivated by future
experiments with entangled photons designed to use satellites. This is a first
step towards the implementation of quantum information protocols in a global
scale.
| arxiv topic:quant-ph |
arxiv_dataset-1620912.2249 | The Landau gauge gluon propagator in 4D SU(2) lattice gauge theory
revisited: Gribov copies and scaling properties
hep-lat
Lattice results for the gluon propagator in SU(2) pure gauge theory obtained
on large lattices are presented. Simulated annealing is used throughout to fix
the Landau gauge. We concentrate on checks for Gribov copy effects and for
scaling properties. Our findings are similar to the ones in the SU(3) case,
supporting the decoupling-type infrared behaviour of the gluon propagator.
| arxiv topic:hep-lat |
arxiv_dataset-1621912.2349 | Algebraic totality, towards completeness
cs.LO math.LO
Finiteness spaces constitute a categorical model of Linear Logic (LL) whose
objects can be seen as linearly topologised spaces, (a class of topological
vector spaces introduced by Lefschetz in 1942) and morphisms as continuous
linear maps. First, we recall definitions of finiteness spaces and describe
their basic properties deduced from the general theory of linearly topologised
spaces. Then we give an interpretation of LL based on linear algebra. Second,
thanks to separation properties, we can introduce an algebraic notion of
totality candidate in the framework of linearly topologised spaces: a totality
candidate is a closed affine subspace which does not contain 0. We show that
finiteness spaces with totality candidates constitute a model of classical LL.
Finally, we give a barycentric simply typed lambda-calculus, with booleans
${\mathcal{B}}$ and a conditional operator, which can be interpreted in this
model. We prove completeness at type ${\mathcal{B}}^n\to{\mathcal{B}}$ for
every n by an algebraic method.
| arxiv topic:cs.LO math.LO |
arxiv_dataset-1622912.2449 | Noncommutative Geometry, Hodge Theorem and Holography
hep-th math-ph math.MP math.QA
Some time ago we presented an article (which was in fact the outline of a
research programme) in which we argued for the need to develop a nonommutative
version of topological quantum field theories (NCTQFT for short). Recent work
by C.J. Hogan et all, has demonstrated the possibility to get experimental
verification of holography; if this comes true, then that would indicate that
quantum gravity is indeed a TQFT. On the other hand there is accumulating
evidence that the underlying geometry of spacetime is a noncommutative
(abreviated to nc in the sequel) space, hence if one wants a unified theory of
all physical interactions including gravity that would mean that the right
framework would be NCTQFT. Towards this goal we present a modest achievement
which is a nc version of Hodge Theorem and the definition of the nc free
bosonic propagator.
| arxiv topic:hep-th math-ph math.MP math.QA |
arxiv_dataset-1623912.2549 | Formal Aspects of Grid Brokering
cs.DC cs.FL
Coordination in distributed environments, like Grids, involves selecting the
most appropriate services, resources or compositions to carry out the planned
activities. Such functionalities appear at various levels of the infrastructure
and in various means forming a blurry domain, where it is hard to see how the
participating components are related and what their relevant properties are. In
this paper we focus on a subset of these problems: resource brokering in Grid
middleware. This paper aims at establishing a semantical model for brokering
and related activities by defining brokering agents at three levels of the Grid
middleware for resource, host and broker selection. The main contribution of
this paper is the definition and decomposition of different brokering
components in Grids by providing a formal model using Abstract State Machines.
| arxiv topic:cs.DC cs.FL |
arxiv_dataset-1624912.2649 | Negative index of refraction, spacetime folding and perfect imaging in
transformation optics
physics.optics
Negative index of refraction has become an accepted part of transformation
optics, which is encountered in transformations that change the orientation of
the manifold. Based on this concept, various designs of perfect lenses have
been proposed, which all rely on a folding of space or spacetime, where the
maps from electromagnetic space to laboratory space are multi-valued. Recently,
a new concept for perfect imaging has been proposed by Leonhardt and Philbin,
which also uses multi-valued maps, but does neither include negative index of
refraction nor an amplification of evanescent modes. In this context it was
speculated that multi-valued maps should be seen as the basis of perfect
imaging rather than amplification of evanescent modes. It might be useful to
review the standard lens based on negative index of refraction from this point
of view. In this paper we show that a negative index of refraction is not an
inherent characteristic of transformation optics, but rather appears as a
specific choice of a sign ambiguity. Furthermore, we point out that the
transformation designed lens does not amplify evanescent modes, in contrast to
the Pendry-Veselago lens. Instead, evanescent modes at the image point are
produced by a duplicated source and thus no imaging of the near field takes
place.
| arxiv topic:physics.optics |
arxiv_dataset-1625912.2749 | Gravito-magnetic amplification in cosmology
astro-ph.CO gr-qc
Magnetic fields interact with gravitational waves in various ways. We
consider the coupling between the Weyl and the Maxwell fields in cosmology and
study the effects of the former on the latter. The approach is fully analytical
and the results are gauge-invariant. We show that the nature and the outcome of
the gravito-magnetic interaction depends on the electric properties of the
cosmic medium. When the conductivity is high, gravitational waves reduce the
standard (adiabatic) decay rate of the B-field, leading to its superadiabatic
amplification. In poorly conductive environments, on the other hand,
Weyl-curvature distortions can result into the resonant amplification of
large-scale cosmological magnetic fields. Driven by the gravitational waves,
these B-fields oscillate with an amplitude that is found to diverge when the
wavelengths of the two sources coincide. We present technical and physical
aspects of the gravito-magnetic interaction and discuss its potential
implications.
| arxiv topic:astro-ph.CO gr-qc |
arxiv_dataset-1626912.2849 | Density excitations of a harmonically trapped ideal gas
cond-mat.quant-gas
The dynamic structure factor of a harmonically trapped Bose gas has been
calculated well above the Bose-Einstein condensation temperature by treating
the gas cloud as a canonical ensemble of noninteracting classical particles.
The static structure factor is found to vanish as wavenumber squared in the
long-wavelength limit. We also incorporate a relaxation mechanism
phenomenologically by including a stochastic friction force to study the
dynamic structure factor. A significant temperature dependence of the
density-fluctuation spectra is found. The Debye-Waller factor has been
calculated for the trapped thermal cloud as function of wavenumber and of
particle number. A substantial difference is found between clouds of small and
large particle number.
| arxiv topic:cond-mat.quant-gas |
arxiv_dataset-1627912.2949 | Observational signatures for depletion in the Spite plateau: solving the
cosmological Li discrepancy?
astro-ph.SR astro-ph.CO
We present Li abundances for 73 stars in the metallicity range -3.5 < [Fe/H]
< -1.0 using improved IRFM temperatures (Casagrande et al. 2010) with precise
E(B-V) values obtained mostly from interstellar NaI D lines, and high-quality
equivalent widths (errors ~ 3%). At all metallicities we uncover a
fine-structure in the Li abundances of Spite plateau stars, which we trace to
Li depletion that depends on both metallicity and mass. Models including atomic
diffusion and turbulent mixing seem to reproduce the observed Li depletion
assuming a primordial Li abundance ALi = 2.64 dex (MARCS models) or 2.72
(Kurucz overshooting models), in good agreement with current predictions (ALi =
2.72) from standard BBN. We are currently expanding our sample to have a better
coverage of different evolutionary stages at the high and low metallicity ends,
in order to verify our findings.
| arxiv topic:astro-ph.SR astro-ph.CO |
arxiv_dataset-1628912.3049 | Dark Energy, Inertia and Mach's Principle
astro-ph.CO
Mach's Principle says that a particle's inertia is due to some interaction of
that particle with all the other masses in the universe. Here we explore the
possibility of the gravitational interaction energy of the background quantum
vacuum energy playing the role of a global Higg's field (described by a varying
cosmological constant) entirely contributing to the local inertial masses of
particles in the spirit of Mach's principle.
| arxiv topic:astro-ph.CO |
arxiv_dataset-1629912.3149 | Next-to-Leading Order Transport Coefficients from the Four-Particle
Irreducible Effective Action
hep-ph
Transport coefficients can be obtained from 2-point correlators using the
Kubo formulae. It has been shown that the full leading order result for
electrical conductivity and (QCD) shear viscosity is contained in the re-summed
2-point function that is obtained from the 3-loop 3PI re-summed effective
action. The theory produces all leading order contributions without the
necessity for power counting, and in this sense it provides a natural framework
for the calculation. In this article we study the 4-loop 4PI effective action
for a scalar theory with cubic and quartic interactions in the presence of
spontaneous symmetry breaking. We obtain a set of integral equations that
determine the re-summed 2-point vertex function. A next-to-leading order
contribution to the viscosity could be obtained from this set of coupled
equations.
| arxiv topic:hep-ph |
arxiv_dataset-1630912.3249 | Local Spacetime Physics from the Grassmannian
hep-th
A duality has recently been conjectured between all leading singularities of
n-particle N^(k-2)MHV scattering amplitudes in N=4 SYM and the residues of a
contour integral with a natural measure over the Grassmannian G(k,n). In this
note we show that a simple contour deformation converts the sum of Grassmannian
residues associated with the BCFW expansion of NMHV tree amplitudes to the CSW
expansion of the same amplitude. We propose that for general k the same
deformation yields the (k-2) parameter Risager expansion. We establish this
equivalence for all MHV-bar amplitudes and show that the Risager degrees of
freedom are non-trivially determined by the GL(k-2) "gauge" degrees of freedom
in the Grassmannian. The Risager expansion is known to recursively construct
the CSW expansion for all tree amplitudes, and given that the CSW expansion
follows directly from the (super) Yang-Mills Lagrangian in light-cone gauge,
this contour deformation allows us to directly see the emergence of local
space-time physics from the Grassmannian.
| arxiv topic:hep-th |
arxiv_dataset-1631912.3349 | Compactification driven Hilltop Inflation in Einstein-Yang-Mills
astro-ph.CO hep-th
Starting from Einstein-Yang-Mills in higher dimensions with an instanton on a
compact sphere, we dimensionally reduce to find an effective four-dimensional
action describing "hilltop" inflation. Using recent CMB data, we analyse the
parameter space of this model to search for viable set-ups. One unique feature
of this class of inflationary models is that the value of the inflaton field,
or alternatively, the size of the compact sphere, is stabilised dynamically
during the inflationary process.
| arxiv topic:astro-ph.CO hep-th |
arxiv_dataset-1632912.3449 | Galactic tide and secular orbital evolution
astro-ph.EP
Equation of motion for the galactic tide is treated for the case of a comet
situated in the Oort cloud of comets. We take into account that galactic
potential and mass density depend on a distance from the galactic equator and
on a distance from the rotational axis of the Galaxy. Secular evolution of
orbital elements is presented. New terms generated by the Sun's oscillation
about the galactic plane are considered. The inclusion of the new terms into
the equation of motion of the comet leads to orbital evolution which may be
significantly different from the conventional approach. The usage of the
secular time derivatives is limited to the cases when orbital period of the
comet is much less than i) the period of oscillations of the Sun around the
galactic equator, and, ii) the orbital period of the motion of the Sun around
the galactic center.
| arxiv topic:astro-ph.EP |
arxiv_dataset-1633912.3549 | Dual Gate Graphene FETs with fT of 50 GHz
cond-mat.mes-hall
A dual-gate graphene field-effect transistors is presented, which shows
improved RF performance by reducing the access resistance using electrostatic
doping. With a carrier mobility of 2700 cm2/Vs, a cutoff frequency of 50 GHz is
demonstrated in a 350-nm gate length device. This fT value is the highest
frequency reported to date for any graphene transistor, and it also exceeds
that of Si MOSFETs at the same gate length, illustrating the potential of
graphene for RF applications.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-1634912.3649 | Kelvin-Helmholtz instability in coronal magnetic flux tubes due to
azimuthal shear flows
astro-ph.SR
Transverse oscillations of coronal loops are often observed and have been
theoretically interpreted as kink magnetohydrodynamic (MHD) modes. Numerical
simulations by Terradas et al. (2008, ApJ 687, L115) suggest that shear flows
generated at the loop boundary during kink oscillations could give rise to a
Kelvin-Helmholtz instability (KHI). Here, we investigate the linear stage of
the KHI in a cylindrical magnetic flux tube in the presence of azimuthal shear
motions. We consider the basic, linearized MHD equations in the beta = 0
approximation, and apply them to a straight and homogeneous cylindrical flux
tube model embedded in a coronal environment. Azimuthal shear flows with a
sharp jump of the velocity at the cylinder boundary are included in the model.
We obtain an analytical expression for the dispersion relation of the unstable
MHD modes supported by the configuration, and compute analytical approximations
of the critical velocity shear and the KHI growth rate in the thin tube limit.
A parametric study of the KHI growth rates is performed by numerically solving
the full dispersion relation. We find that fluting-like modes can develop a KHI
in time-scales comparable to the period of kink oscillations of the flux tube.
The KHI growth rates increase with the value of the azimuthal wavenumber and
decrease with the longitudinal wavenumber. However, the presence of a small
azimuthal component of the magnetic field can suppress the KHI. Azimuthal
motions related to kink oscillations of untwisted coronal loops may trigger a
KHI, but this phenomenon has not been observed to date. We propose that the
azimuthal component of the magnetic field is responsible for suppressing the
KHI in a stable coronal loop. The required twist is small enough to prevent the
development of the pinch instability.
| arxiv topic:astro-ph.SR |
arxiv_dataset-1635912.3749 | Dynamical behavior of Darboux curves
math.DG math.DS
In 1872 G. Darboux defined a family of curves on surfaces of R^3 which are
preserved by the action of the Mobius group and share many properties with
geodesics. Here we characterize these curves under the view point of Lorentz
geometry and prove some general properties and make them explicit them on
simple surfaces, retrieving results of Pell (1900) and Santalo (1941).
| arxiv topic:math.DG math.DS |
arxiv_dataset-1636912.3849 | Hyperfine structure and nuclear hyperpolarization observed in the bound
exciton luminescence of Bi donors in natural Si
quant-ph
As the deepest group V donor in Si, Bi has by far the largest hyperfine
interaction, and also a large I=9/2 nuclear spin. At zero field this splits the
donor ground state into states having total spin 5 and 4, which are fully
resolved in the photoluminescence spectrum of Bi donor bound excitons. Under a
magnetic field, the 60 expected allowed transitions cannot be individually
resolved, but the effects of the nuclear spin distribution, -9/2 <= I_z <= 9/2,
are clearly observed. A strong hyperpolarization of the nuclear spin, with sign
opposite to the expected equilibrium polarization, is observed to result from
the nonresonant optical excitation. This is very similar to the recently
reported optical hyperpolarization of P donors observed by EPR at higher
magnetic fields. We introduce a new model to explain this effect, and predict
that it may be very fast.
| arxiv topic:quant-ph |
arxiv_dataset-1637912.3949 | Discovery of a Young Gamma-ray Pulsar Associated with an Extended TeV
Gamma-ray Source
astro-ph.HE
Since its launch in June 2008, the Large Area Telescope (LAT), onboard the
\emph{Fermi} Gamma-ray Space Telescope, has greatly added to our understanding
of gamma-ray pulsars. Its fine point spread function and large effective area,
combined with the time-differencing method, make it the first gamma-ray
instrument capable of discovering a new population of gamma-ray pulsars. We
will present the recent discovery of the youngest (~4600 yr) radio-quiet
gamma-ray pulsar discovered in a blind frequency search so far: PSR J1022-5746,
a pulsar associated with an extended TeV source. We also present
multiwavelength observations of the source, including X-ray observations.
| arxiv topic:astro-ph.HE |
arxiv_dataset-1638912.4049 | Local Functions : Algebras, Ideals, and Reduced Power Algebras
math.GM
A further significant extension is presented of the infinitely large class of
differential algebras of generalized functions which are the basic structures
in the nonlinear algebraic theory listed under 46F30 in the AMS Mathematical
Subject Classification. These algebras are constructed as {\it reduced powers},
when seen in terms of Model Theory. The major advantage of these differential
algebras of generalized functions is that they allow their elements to have
singularities on {\it dense} subsets of their domain of definition, and {\it
without} any restrictions on the respective generalized functions in the
neighbourhood of their singularities. Their applications have so far been in 1)
solving large classes of systems of nonlinear PDEs, 2) highly singular problems
in Differential Geometry, with respective applications in modern Physics,
including General Relativity and Quantum Gravity. These infinite classes of
algebras contain as a particular case the Colombeau algebras, since in the
latter algebras rather strongly limiting growth conditions, namely, of
polynomial type, are required on the generalized functions in the neighbourhood
of their singularities.
| arxiv topic:math.GM |
arxiv_dataset-1639912.4149 | Stars quenching stars: how photoionization by local sources regulates
gas cooling and galaxy formation
astro-ph.CO astro-ph.HE
Current models of galaxy formation lack an efficient and physically
constrained mechanism to regulate star formation (SF) in low and intermediate
mass galaxies. We argue that the missing ingredient could be the effect of
photoionization by local sources on the gas cooling. We show that the soft
X-ray and EUV flux generated by SF is able to efficiently remove the main
coolants (e.g., HeII, OV and FeIX) from the halo gas via direct
photoionization. As a consequence, the cooling and accretion time of the gas
surrounding star-forming galaxies may increase by one or two orders of
magnitude. For a given halo mass and redshift, the effect is directly related
to the value of the star formation rate (SFR). Our results suggest the
existence of a critical SFR above which "cold" mode accretion is stopped, even
for haloes with virial masses well below the critical shock-heating mass
suggested by previous studies.The evolution of the critical SFR with redshift,
for a given halo mass, resembles the respective steep evolution of the observed
SFR for z<1. This suggests that photoionization by local sources would be able
to regulate gas accretion and star formation, without the need for additional,
strong feedback processes.
| arxiv topic:astro-ph.CO astro-ph.HE |
arxiv_dataset-1640912.4249 | Acoustic cloaking and mirages with flying carpets
physics.optics math-ph math.MP
Carpets under consideration here, in the context of pressure acoustic waves
propagating in a compressible fluid, do not touch the ground: they levitate in
mid-air (or float in mid-water), which leads to approximate cloaking for an
object hidden underneath, or touching either sides of a square cylinder on, or
over, the ground. The tentlike carpets attached to the sides of a square
cylinder illustrate how the notion of a carpet on a wall naturally generalizes
to sides of other small compact objects. We then extend the concept of flying
carpets to circular cylinders. However, instead of reducing its scattering
cross-section like in acoustic cloaks, we rather mimic that of another
obstacle, say a square rigid cylinder. For instance, show that one can hide any
type of defects under such circular carpets, and yet they still scatter waves
just like a smaller cylinder on its own. Interestingly, all these carpets are
described by non-singular acoustic parameters. To exemplify this important
aspect, we propose a multi-layered carpet consisting of isotropic homogeneous
fluids with constant bulk modulus and varying density which works over a finite
range of wavelengths. We have discussed some applications, with the sonar boats
or radars cases as typical examples. For instance, we would like to render a
pipeline lying on the bottom of the sea or floating in mid-water undetectable
for a boat with a sonar at rest just above it on the surface of the sea.
Another possible application would be protecting parabolic antennas.
| arxiv topic:physics.optics math-ph math.MP |
arxiv_dataset-1641912.4349 | Not all pure entangled states are useful for sub shot-noise
interferometry
quant-ph cond-mat.quant-gas
We investigate the connection between the shot-noise limit in linear
interferometers and particle entanglement. In particular, we ask whether or not
sub shot-noise sensitivity can be reached with all pure entangled input states
of $N$ particles if they can be optimized with local operations. Results on the
optimal local transformations allow us to show that for $N=2$ all pure
entangled states can be made useful for sub shot-noise interferometry while for
$N>2$ this is not the case. We completely classify the useful entangled states
available in a bosonic two-mode interferometer. We apply our results to several
states, in particular to multi-particle singlet states and to cluster states.
The latter turn out to be practically useless for sub shot-noise
interferometry. Our results are based on the Cramer-Rao bound and the Fisher
information.
| arxiv topic:quant-ph cond-mat.quant-gas |
arxiv_dataset-1642912.4449 | Chromospheric Magnetic Reconnection caused by Photospheric Flux
Emergence: Implications for Jet-like Events Formation
astro-ph.SR
Magnetic reconnection in the low atmosphere, e.g. chromosphere, is
investigated in various physical environments. Its implications for the
origination of explosive events (small--scale jets) are discussed. A
2.5-dimensional resistive magnetohydrodynamic (MHD) model in Cartesian
coordinates is used. It is found that the temperature and velocity of the
outflow jets as a result of magnetic reconnection are strongly dependent on the
physical environments, e.g. the magnitude of the magnetic field strength and
the plasma density. If the magnetic field strength is weak and the density is
high, the temperature of the jets is very low (~10,000 K) as well as its
velocity (~40 km/s). However, if environments with stronger magnetic field
strength (20 G) and smaller density (electron density Ne=2x10^{10} cm^{-3}) are
considered, the outflow jets reach higher temperatures of up to 600,000 K and a
line-of-sight velocity of up to 130 km/s which is comparable with the
observational values of jet-like events.
| arxiv topic:astro-ph.SR |
arxiv_dataset-1643912.4549 | Spontaneous magnetization of the superintegrable chiral Potts model:
calculation of the determinant D_PQ
cond-mat.stat-mech
For the Ising model, the calculation of the spontaneous magnetization leads
to the problem of evaluating a determinant. Yang did this by calculating the
eigenvalues in the large-lattice limit. Montroll, Potts and Ward expressed it
as a Toeplitz determinant and used Szego's theorem: this is almost certainly
the route originally travelled by Onsager. For the corresponding problem in the
superintegrable chiral Potts model, neither approach appears to work: here we
show that the determinant D_PQ can be expressed as that of a product of two
Cauchy-like matrices. One can then use the elementary exact formula for the
Cauchy determinant. One of course regains the known result, originally
conjectured in 1989.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-1644912.4649 | The use of ideas of Information Theory for studying "language" and
intelligence in ants
cs.IT cs.AI math.IT nlin.AO
In this review we integrate results of long term experimental study on ant
"language" and intelligence which were fully based on fundamental ideas of
Information Theory, such as the Shannon entropy, the Kolmogorov complexity, and
the Shannon's equation connecting the length of a message ($l$) and its
frequency $(p)$, i.e. $l = - \log p$ for rational communication systems. This
approach, new for studying biological communication systems, enabled us to
obtain the following important results on ants' communication and intelligence:
i) to reveal "distant homing" in ants, that is, their ability to transfer
information about remote events; ii) to estimate the rate of information
transmission; iii) to reveal that ants are able to grasp regularities and to
use them for "compression" of information; iv) to reveal that ants are able to
transfer to each other the information about the number of objects; v) to
discover that ants can add and subtract small numbers. The obtained results
show that Information Theory is not only wonderful mathematical theory, but
many its results may be considered as Nature laws.
| arxiv topic:cs.IT cs.AI math.IT nlin.AO |
arxiv_dataset-1645912.4749 | Experimental demonstration of a Displacement noise Free Interferometry
scheme for gravitational wave detectors showing displacement noise reduction
at low frequencies
gr-qc
This paper reports an experimental demonstration of partial displacement
noise free laser interferometry in the gravitational wave detection band. The
used detuned Fabry-Perot cavity allows the isolation of the mimicked
gravitational wave signal from the displacement noise on the cavities input
mirror. By properly combining the reflected and transmitted signals from the
cavity a reduction of the displacement noise was achieved. Our results
represent the first experimental demonstration of this recently proposed
displacement noise free laser interferometry scheme. Overall we show that the
rejection ratio of the displacement noise to the gravitational wave signal was
improved in the frequency range of 10 Hz to 10 kHz with a typical factor of 60.
| arxiv topic:gr-qc |
arxiv_dataset-1646912.4849 | Implementation of Nano-scale Rectifiers: An Exact Study
cond-mat.mes-hall cond-mat.mtrl-sci
We propose the possibilities of designing nano-scale rectifiers using
mesoscopic rings. A single mesoscopic ring is used for half-wave rectification,
while full-wave rectification is achieved using two such rings and in both
cases each ring is threaded by a time varying magnetic flux $\phi$ which plays
a central role in the rectification action. Within a tight-binding framework,
all the calculations are done based on the Green's function formalism. We
present numerical results for the two-terminal conductance and current which
support the general features of half-wave and full-wave rectifications. The
analysis may be helpful in fabricating mesoscopic or nano-scale rectifiers.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-1647912.4949 | Design method for quasi-isotropic transformation materials based on
inverse Laplace's equation with sliding boundaries
physics.class-ph
The deformation method of transformation optics has been demonstrated to be a
useful tool, especially in designing arbitrary and nonsingular transformation
materials. Recently, there are emerging demands for isotropic material
parameters, arising from the broadband requirement of the designed devices. In
this work, the deformation method is further developed to design
quasi-isotropic/isotropic transformation materials. The variational functional
of the inverse Laplace's equation is investigated and found to involve the
smooth and quasi-conformal nature of coordinate transformation. Together with
the sliding boundary conditions, the inverse Laplace's equation can be utilized
to give transformations which are conformal or quasi-conformal, depending on
functionalities of interest. Examples of designing an arbitrary carpet cloak
and a waveguide with arbitrary cross sections are given to validate the
proposed idea. Compared with other quasi-conformal methods based on grid
generation tools, the proposed method unifies the design and validation of
transformation devices, and thus is much convenient.
| arxiv topic:physics.class-ph |
arxiv_dataset-1648912.5049 | Volovik effect in the $\pm$s-wave state for the iron-based
superconductors
cond-mat.supr-con cond-mat.str-el
We studied the field dependencies of specific heat coefficient $\gamma(H) =
\lim_{T \rightarrow 0} C(T,H)/T $ and thermal conductivity coefficient $\lim_{T
\rightarrow 0} \kappa(T ,H)/T$ of the $\pm$s-wave state in the mixed state. We
found that it is a generic feature of the two band s-wave state with the
unequal sizes of gaps, small $\Delta_S$ and large $\Delta_L$, that Doppler
shift of the quasiparticle excitations (Volovik effect) creates a finite
density of states, on the extended states outside of vortex cores, proportional
to $H$ in contrast to the $\sqrt{H}$ dependence of the d-wave state. Impurity
scattering effect on the $\pm$s-wave state, however, makes this generic
$H$-linear dependence sublinear approaching to the $\sqrt{H}$ behavior. Our
calculations of $\lim_{T \rightarrow 0} \kappa(T ,H)/T$ successfully fit the
experimental data of Ba(Fe$_{1-x}$Co$_x )_2$ As$_2$ with different Co-doping
$x$ by systematically varying the gap size ratio $R= |\Delta_S | / |\Delta_L
|$. We also resolve the dilemma of a substantial value of $\gamma(H \rightarrow
0)$ but almost zero value of $\lim_{T \rightarrow 0} \kappa(T ,H \rightarrow
0)/T$, observed in experiments.
| arxiv topic:cond-mat.supr-con cond-mat.str-el |
arxiv_dataset-1649912.5149 | Bounds on Shannon distinguishability in terms of partitioned measures
quant-ph
A family of quantum measures like the Shannon distinguishability is
presented. These measures are defined over the two classes of POVM measurements
and related to separate parts in the expression for mutual information. Changes
of Ky Fan's norms and the partitioned trace distances under the operation of
partial trace are discussed. Upper and lower bounds on the introduced
quantities are obtained in terms of partitioned trace distances and Uhlmann's
partial fidelities. These inequalities provide a kind of generalization of the
well-known bounds on the Shannon distinguishability. The notion of
cryptographic exponential indistinguishability for quantum states is revisited.
When exponentially fast convergence is required, all the metrics induced by
unitarily invariant norms are shown to be equivalent.
| arxiv topic:quant-ph |
arxiv_dataset-1650912.5249 | The Instantaneous Wall Viscosity in Pipe Flow of Power Law Fluids: Case
Study for a Theory of Turbulence in Time-Independent Non-Newtonian Fluids
physics.flu-dyn
This paper presents a new theory of turbulence in time-independent
non-Newtonian fluids. The wall layer is modelled in terms of unsteady exchange
of viscous momentum between the wall and the main stream, following the classic
visualisation of inrush-sweep-ejection/burst. The thickness of the wall layer
is found to be the same for Newtonian and purely viscous non-Newtonian fluids,
when normalised with the instantaneous wall parameters at the onset of
bursting. The results indicate that the mechanisms of turbulence in Newtonian
and time-independent fluids are identical when structural similarity relations
in turbulence are based on phase-locked parameters linked with the development
of secondary flows rather than on time-averaged wall parameters. This
similarity analysis collapses the local critical instantaneous friction factor
data of both Newtonian and non-Newtonian fluids at the point of bursting into a
single curve. The method greatly simplifies the analysis of turbulent transport
phenomena in non-Newtonian fluids.
Keywords: Turbulence, time-independent non-Newtonian, Power law, pipe flow,
wall layer
| arxiv topic:physics.flu-dyn |
arxiv_dataset-1651912.5349 | Parametrisations of elements of spinor and orthogonal groups using
exterior exponents
math-ph math.MP
We present new parametrizations of elements of spinor and orthogonal groups
of dimension 4 using Grassmann exterior algebra. Theory of spinor groups is an
important tool in theoretical and mathematical physics namely in the Dirac
equation for an electron.
| arxiv topic:math-ph math.MP |
arxiv_dataset-1652912.5449 | Time and Memory Efficient Lempel-Ziv Compression Using Suffix Arrays
cs.DS cs.IT math.IT
The well-known dictionary-based algorithms of the Lempel-Ziv (LZ) 77 family
are the basis of several universal lossless compression techniques. These
algorithms are asymmetric regarding encoding/decoding time and memory
requirements, with the former being much more demanding. In the past years,
considerable attention has been devoted to the problem of finding efficient
data structures to support these searches, aiming at optimizing the encoders in
terms of speed and memory. Hash tables, binary search trees and suffix trees
have been widely used for this purpose, as they allow fast search at the
expense of memory. Some recent research has focused on suffix arrays (SA), due
to their low memory requirements and linear construction algorithms. Previous
work has shown how the LZ77 decomposition can be computed using a single SA or
an SA with an auxiliary array with the longest common prefix information. The
SA-based algorithms use less memory than the tree-based encoders, allocating
the strictly necessary amount of memory, regardless of the contents of the text
to search/encode. In this paper, we improve on previous work by proposing
faster SA-based algorithms for LZ77 encoding and sub-string search, keeping
their low memory requirements. For some compression settings, on a large set of
benchmark files, our low-memory SA-based encoders are also faster than
tree-based encoders. This provides time and memory efficient LZ77 encoding,
being a possible replacement for trees on well known encoders like LZMA. Our
algorithm is also suited for text classification, because it provides a compact
way to describe text in a bag-of-words representation, as well as a fast
indexing mechanism that allows to quickly find all the sets of words that start
with a given symbol, over a static dictionary.
| arxiv topic:cs.DS cs.IT math.IT |
arxiv_dataset-16531001.0012 | The Statistics of Albedo and Heat Recirculation on Hot Exoplanets
astro-ph.EP
[Abridged] If both the day-side and night-side effective temperatures of a
planet can be measured, it is possible to estimate its Bond albedo, 0<A_B<1, as
well as its day-night heat redistribution efficiency, 0<epsilon<1. We attempt a
statistical analysis of the albedo and redistribution efficiency for 24
transiting exoplanets that have at least one published secondary eclipse. For
each planet, we show how to calculate a sub-stellar equilibrium temperature,
T_0, and associated uncertainty. We then use a simple model-independent
technique to estimate a planet's effective temperature from planet/star flux
ratios. We use thermal secondary eclipse measurements -those obtained at
lambda>0.8 micron- to estimate day-side effective temperatures, T_d, and
thermal phase variations -when available- to estimate night-side effective
temperature. We strongly rule out the "null hypothesis" of a single A_B and
epsilon for all 24 planets. If we allow each planet to have different
parameters, we find that low Bond albedos are favored (A_B<0.35 at 1 sigma
confidence), which is an independent confirmation of the low albedos inferred
from non-detection of reflected light. Our sample exhibits a wide variety of
redistribution efficiencies. When normalized by T_0, the day-side effective
temperatures of the 24 planets describe a uni-modal distribution. The
dimensionless quantity T_d/T_0 exhibits no trend with the presence or absence
of stratospheric inversions. There is also no clear trend between T_d/T_0 and
T_0. That said, the 6 planets with the greatest sub-stellar equilibrium
temperatures (T>2400 K) have low epsilon, as opposed to the 18 cooler planets,
which show a variety of recirculation efficiencies. This hints that the very
hottest transiting giant planets are qualitatively different from the merely
hot Jupiters.
| arxiv topic:astro-ph.EP |
arxiv_dataset-16541001.0112 | D=11 supergravity with manifest supersymmetry
hep-th
The complete supersymmetric action for eleven-dimensional supergravity is
presented. The action is polynomial in the scalar fermionic pure spinor
superfield, and contains only a minor modification to the recently proposed
three-point coupling.
| arxiv topic:hep-th |
arxiv_dataset-16551001.0212 | Quasi-isometric classification of non-geometric 3-manifold groups
math.GT math.GR
We describe the quasi-isometric classification of fundamental groups of
irreducible non-geometric 3-manifolds which do not have "too many" arithmetic
hyperbolic geometric components, thus completing the quasi-isometric
classification of 3--manifold groups in all but a few exceptional cases.
| arxiv topic:math.GT math.GR |
arxiv_dataset-16561001.0312 | The Method of Combinatorial Telescoping
math.CO math.NT
We present a method for proving q-series identities by combinatorial
telescoping, in the sense that one can transform a bijection or a
classification of combinatorial objects into a telescoping relation. We shall
illustrate this method by giving a combinatorial proof of Watson's identity
which implies the Rogers-Ramanujan identities.
| arxiv topic:math.CO math.NT |
arxiv_dataset-16571001.0412 | Identifying Bright Stars in Crowded Environments Using Velocity
Dispersion Measurements, and an Application to the Center of M32
astro-ph.GA astro-ph.CO
The identification of individual stars in crowded environments using
photometric information alone is confounded by source confusion. However, with
the addition of spectroscopic information it is possible to distinguish between
blends and areas where the light is dominated by a single star using the widths
of absorption features. We describe a procedure for identifying locations in
kinematically hot environments where the light is dominated by a single star,
and apply this method to spectra with 0.1 arcsec angular resolution covering
the 2.1 - 2.3 micron interval in the central regions of M32. Targets for
detailed investigation are selected as areas of localized brightness
enhancement. Three locations where at least 60% of the K-band light comes from
a single bright star, and another with light that is dominated by two stars
with very different velocities, are identified. The dominant stars are evolving
near the tip of the asymptotic giant branch (AGB), and have M5 III spectral
type. The lack of a dispersion in spectral-type suggests that the upper AGB
within the central arcsec of M32 has a dispersion in J-K of only a few
hundreths of a magnitude, in agreement with what is seen at larger radii. One
star has weaker atomic absorption lines than the others, such that [M/H] is 0.2
dex lower. Such a difference in metallicity is consistent with the metallicity
dispersion inferred from the width of the AGB in M32. The use of line width to
distinguish between blends involving many relatively faint stars, none of which
dominate the light output, and areas that are dominated by a single
intrinsically bright star could be extended to crowded environments in other
nearby galaxies.
| arxiv topic:astro-ph.GA astro-ph.CO |
arxiv_dataset-16581001.0512 | AO Vel: The role of multiplicity in the development of chemical
peculiarities in late B-type stars
astro-ph.SR
We present high-resolution, high signal-to-noise UVES spectra of AO Vel, a
quadruple system containing an eclipsing BpSi star. From these observations we
reconstruct the spectra of the individual components and perform an abundance
analysis of all four stellar members. We found that all components are
chemically peculiar with different abundances patters. In particular, the two
less massive stars show typical characteristics of HgMn stars. The two most
massive stars in the system show variable line profiles indicating the presence
of chemical spots. Given the youth of the system and the notable chemical
peculiarities of their components, this system could give important insights in
the origin of chemical anomalies.
| arxiv topic:astro-ph.SR |
arxiv_dataset-16591001.0612 | A Berry Esseen Theorem for the Lightbulb Process
math.PR math.ST stat.TH
In the so called lightbulb process, on days $r=1,..., n$, out of $n$
lightbulbs, all initially off, exactly $r$ bulbs, selected uniformly and
independent of the past, have their status changed from off to on, or vice
versa. With $X$ the number of bulbs on at the terminal time $n$, an even
integer, and $\mu=n/2, \sigma^2=Var(X)$, we have $$ \sup_{z \in \mathbb{R}}
|P(\frac{X-\mu}{\sigma} \le z)-P(Z \le z)| \le \frac{n}{2\sigma^2}
\bar{\Delta}_0 + 1.64 \frac{n}{\sigma^3}+ \frac{2}{\sigma} $$ where $Z$ is a
standard normal random variable, and $$ \bar{\Delta}_0 = 1/2\sqrt{n}} +
\frac{1}{2n} + 1/3 e^{-n/2} \qmq {for $n \ge 6$,} $$ yielding a bound of order
$O(n^{-1/2})$ as $n \to \infty$. A similar, though slightly larger bound holds
for $n$ odd. The results are shown using a version of Stein's method for
bounded, monotone size bias couplings. The argument for even $n$ depends on the
construction of a variable $X^s$ on the same space as $X$ that has the $X$-size
bias distribution, that is, that satisfies \beas E [X g(X)] =\mu E[g(X^s)]
\quad for all bounded continuous $g$, \enas and for which there exists a $B \ge
0$, in this case B=2, such that $X \le X^s \le X+B$ almost surely. The argument
for $n$ odd is similar to that for $n$ even, but one first couples $X$ closely
to $V$, a symmetrized version of $X$, for which a size bias coupling of $V$ to
$V^s$ can proceed as in the even case. In both the even and odd cases, the
crucial calculation of the variance of a conditional expectation requires
detailed information on the spectral decomposition of the lightbulb chain.
| arxiv topic:math.PR math.ST stat.TH |
arxiv_dataset-16601001.0712 | Indication of antiferromagnetic interaction between paramagnetic Co ions
in the diluted magnetic semiconductor Zn$_{1-x}$Co$_{x}$O
cond-mat.mtrl-sci cond-mat.str-el
The magnetic properties of Zn$_{1-x}$Co$_x$O ($x=0.07$ and 0.10) thin films,
which were homo-epitaxially grown on a ZnO(0001) substrates with varying
relatively high oxygen pressure, have been investigated using x-ray magnetic
circular dichroism (XMCD) at Co $2p$ core-level absorption edge. The line
shapes of the absorption spectra are the same in all the films and indicate
that the Co$^{2+}$ ions substitute for the Zn sites. The magnetic-field and
temperature dependences of the XMCD intensity are consistent with the
magnetization measurements, indicating that except for Co there are no
additional sources for the magnetic moment, and demonstrate the coexistence of
paramagnetic and ferromagnetic components in the homo-epitaxial
Zn$_{1-x}$Co$_{x}$O thin films, in contrast to the ferromagnetism in the
hetero-epitaxial Zn$_{1-x}$Co$_{x}$O films studied previously. The analysis of
the XMCD intensities using the Curie-Weiss law reveals the presence of
antiferromagnetic interaction between the paramagnetic Co ions. Missing XMCD
intensities and magnetization signals indicate that most of Co ions are
non-magnetic probably because they are strongly coupled antiferromagnetically
with each other. Annealing in a high vacuum reduces both the paramagnetic and
ferromagnetic signals. We attribute the reductions to thermal diffusion and
aggregation of Co ions with antiferromagnetic nanoclusters in
Zn$_{1-x}$Co$_{x}$O.
| arxiv topic:cond-mat.mtrl-sci cond-mat.str-el |
arxiv_dataset-16611001.0812 | Effects of the $\Lambda$(1405) on the Structure of Multi-Antikaonic
Nuclei
nucl-th
The effects of the $\Lambda$(1405) ($\Lambda^\ast$) on the structure of the
multi-antikaonic nucleus (MKN), in which several $K^-$ mesons are embedded to
form deeply bound states, are considered based on chiral symmetry combined with
a relativistic mean-field theory. It is shown that additional attraction
resulting from the $\Lambda^\ast$ pole has a sizable contribution to not only
the density profiles for the nucleons and $K^-$ mesons but also the ground
state energy of the $K^-$ mesons and binding energy of the MKN as the number of
the embedded $K^-$ mesons increases.
| arxiv topic:nucl-th |
arxiv_dataset-16621001.0912 | Fields in nonaffine bundles. IV. Harmonious non-Abelian currents in
string defects
hep-th
This article continues the study of the category of harmonious field models
that was recently introduced as a kinetically non-linear generalisation of the
well known harmonic category of multiscalar fields over a supporting brane
wordsheet in a target space with a curved Riemannian metric. Like the perfectly
harmonious case of which a familiar example is provided by ordinary barotropic
perfect fluids, another important subcategory is the simply harmonious case,
for which it is shown that as well as ``wiggle'' modes of the underlying brane
world sheet, and sound type longitudinal modes, there will also be transverse
shake modes that propagate at the speed of light. Models of this type are shown
to arise from a non-Abelian generalisation of the Witten mechanism for
conducting string formation by ordinary scalar fields with a suitable quartic
self coupling term in the action.
| arxiv topic:hep-th |
arxiv_dataset-16631001.1012 | Infinite Tensor Products of C_0(R): Towards a Group Algebra for R^\infty
math.OA math.FA
The construction of an infinite tensor product of the C*-algebra C_0(R) is
not obvious, because it is nonunital, and it has no nonzero projection. Based
on a choice of an approximate identity, we construct here an infinite tensor
product of C_0(R), denoted L_V. We use this to construct (partial) group
algebras for the full continuous unitary representation theory of the group
R^(N) = the infinite sequences with real entries, of which only finitely many
entries are nonzero. We obtain an interpretation of the Bochner-Minlos theorem
in R^(N) as the pure state space decomposition of the partial group algebras
which generate L_V. We analyze the representation theory of L_V, and show that
there is a bijection between a natural set of representations of L_V and the
continuous unitary representations of R^(N), but that there is an extra part
which essentially consists of the representation theory of a multiplicative
semigroup which depends on the initial choice of approximate identity.
| arxiv topic:math.OA math.FA |
arxiv_dataset-16641001.1112 | Relational mechanics of shape and scale
gr-qc
Relational particle mechanics models (RPM's) are useful models for the
problem of time in quantum gravity and other foundational issues in quantum
cosmology. Some concrete examples of scalefree RPM's have already been studied,
but it is the case with scale that is needed for the semiclassical and
dilational internal time approaches to the problem of time. In this paper, I
show that the scaled RPM's configuration spaces are the cones over the
scalefree RPM's configuration spaces, which are spheres in 1-d and complex
projective spaces in 2-d for plain shapes, and these quotiented by Z_2 for
oriented shapes. I extend the method of physical interpretation by tessellation
of the configuration space and the description in terms of geometrical
quantities to the cases with scale and/or orientation. I show that there is an
absence of monopole issues for RPM's and point out a difference between quantum
cosmological operator ordering and that used in molecular physics. I use up
RPM's freedom of the form of the potential to more closely parallel various
well-known cosmologies, and begin the investigation of the semiclassical
approach to the problem of time for such models.
| arxiv topic:gr-qc |
arxiv_dataset-16651001.1212 | Electromagnetic modes in cavities made of negative-index metamaterials
physics.optics
We discuss electromagnetic modes in cavities formed by metamaterials with
negative refraction and demonstrate that the straightforward approach to
substitute negative values of the electric permittivity and the magnetic
permeability leads to quasi-bound states with a negative quality factor. To
ensure positive quality factors and a consistent physical interpretation of the
quasi-bound states it is essential to include the frequency dispersion of the
permittivity and the permeability, as required by positive field energy and
causality. The basic mode equation and the boundary conditions including linear
frequency dispersion are derived. As an example we consider a disk-like cavity
with deformed cross sectional shape. The transition from the unphysical
nondispersive case with negative quality factors to the dispersive case with
positive quality factors is demonstrated numerically and in an analytical
perturbative treatment.
| arxiv topic:physics.optics |
arxiv_dataset-16661001.1312 | Scaling Trajectories in Civil Aircraft (1913-1997)
physics.soc-ph
Using entropy statistics we analyse scaling patterns in terms of changes in
the ratios among product characteristics of 143 designs in civil aircraft. Two
allegedly dominant designs, the piston propeller DC3 and the turbofan Boeing
707, are shown to have triggered a scaling trajectory at the level of the
respective firms. Along these trajectories different variables have been scaled
at different moments in time: this points to the versatility of a dominant
design which allows a firm to react to a variety of user needs. Scaling at the
level of the industry took off only after subsequently reengineered models were
introduced, like the piston propeller Douglas DC4 and the turbofan Boeing 767.
The two scaling trajectories in civil aircraft corresponding to the piston
propeller and the turbofan paradigm can be compared with a single, less
pronounced scaling trajectory in helicopter technology for which we have data
during the period 1940-1996. Management and policy implications can be
specified in terms of the phases of codification at the firm and the industry
level.
| arxiv topic:physics.soc-ph |
arxiv_dataset-16671001.1412 | Positive Definite Distributions and Normed Spaces
math.FA
We answer a question of Alex Koldobsky on isometric embeddings of finite
dimensional normed spaces.
| arxiv topic:math.FA |
arxiv_dataset-16681001.1512 | Measurements of scattering observables for the $pd$ break-up reaction
nucl-ex
High-precision measurements of the scattering observables such as cross
sections and analyzing powers for the proton-deuteron elastic and break-up
reactions have been performed at KVI in the last two decades and elsewhere to
investigate various aspects of the three-nucleon force (3NF) effects
simultaneously. In 2006 an experiment was performed to study these effects in
$\vec{p}+d$ break-up reaction at 135 MeV with the detection system, Big
Instrument for Nuclear polarization Analysis, BINA. BINA covers almost the
entire kinematical phase space of the break-up reaction. The results are
interpreted with the help of state-of-the-art Faddeev calculations and are
partly presented in this contribution.
| arxiv topic:nucl-ex |
arxiv_dataset-16691001.1612 | Energy-Dependent Harmonic Ratios of the Cyclotron Features of X0331+53
in the 2004-2005 Outburst
astro-ph.HE
We report on changes of the cyclotron resonance energies of the recurrent
transient pulsar, X0331+53 (V0332+53). The whole RXTE data acquired in the
2004-2005 outburst were utilized. The 3-80 keV source luminosity varied between
1.7x10^36 and 3.5x10^38 ers/s, assuming a distance of 7 kpc. We confirmed that
the fundamental cyclotron resonance energy changed from ~22 to ~27 keV in a
clear anti-correlation to the source luminosity, and without any hysteresis
effects between the rising and declining phases of the outburst. In contrast,
the second harmonic energy changed from ~49 to ~54 keV, implying a weaker
fractional change as a function of the luminosity. As a result, the observed
resonance energy ratio between the second harmonic and the fundamental was ~2.2
when the source was most luminous, whereas the ratio decreased to the nominal
value of 2.0 at the least luminous state. Although the significance of this
effect is model dependent, these results suggest that the fundamental and
second harmonic resonances represent different heights in the accretion column,
depending on the mass accretion rate.
| arxiv topic:astro-ph.HE |
arxiv_dataset-16701001.1712 | The covalent bond in Particle Spectroscopy
hep-ex
It is proposed that meson resonances are linear combinations of q-qbar and
meson-meson (MM); baryon resonances are combinations of qqq and meson-baryon
(MB). Mixing between these combinations arises via decays of confined states to
meson-meson or meson-baryon. There is a precise analogy with the covalent bond
in molecular physics; it helps to visualise what is happening physically. One
eigenstate is lowered by the mixing; the other moves up and normally increases
in width. Cusps arise at thresholds. At sharp thresholds due to S-wave
2-particle decays, these cusps play a conspicuous role in many sets of data.
| arxiv topic:hep-ex |
arxiv_dataset-16711001.1812 | A classification of sharp tridiagonal pairs
math.RA math.CO
Let $F$ denote a field and let $V$ denote a vector space over $F$ with finite
positive dimension. We consider a pair of linear transformations $A:V \to V$
and $A^*:V \to V$ that satisfy the following conditions: (i) each of $A,A^*$ is
diagonalizable; (ii) there exists an ordering $\lbrace V_i\rbrace_{i=0}^d$ of
the eigenspaces of $A$ such that $A^* V_i \subseteq V_{i-1} + V_{i} + V_{i+1}$
for $0 \leq i \leq d$, where $V_{-1}=0$ and $V_{d+1}=0$; (iii) there exists an
ordering $\lbrace V^*_i\rbrace_{i=0}^\delta$ of the eigenspaces of $A^*$ such
that $A V^*_i \subseteq V^*_{i-1} + V^*_{i} + V^*_{i+1}$ for $0 \leq i \leq
\delta$, where $V^*_{-1}=0$ and $V^*_{\delta+1}=0$; (iv) there is no subspace
$W$ of $V$ such that $AW \subseteq W$, $A^* W \subseteq W$, $W \neq 0$, $W \neq
V$. We call such a pair a {\it tridiagonal pair} on $V$. It is known that
$d=\delta$ and for $ 0 \leq i \leq d$ the dimensions of $V_i,V_{d-i},V^*_i,
V^*_{d-i}$ coincide. The pair $A,A^*$ is called {\it sharp} whenever ${\rm dim}
V_0=1$. It is known that if $F$ is algebraically closed then $A,A^*$ is
sharp. In this paper we classify up to isomorphism the sharp tridiagonal pairs.
As a corollary, we classify up to isomorphism the tridiagonal pairs over an
algebraically closed field. We obtain these classifications by proving the
$\mu$-conjecture.
| arxiv topic:math.RA math.CO |
arxiv_dataset-16721001.1912 | M\'ethode du point proximal: principe et applications aux algorithmes
it\'eratifs
cs.IT math.IT
This paper recalls the proximal point method. We study two iterative
algorithms: the Blahut-Arimoto algorithm for computing the capacity of
arbitrary discrete memoryless channels, as an example of an iterative algorithm
working with probability density estimates and the iterative decoding of the
Bit Interleaved Coded Modulation (BICM-ID). For these iterative algorithms, we
apply the proximal point method which allows new interpretations with improved
convergence rate.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-16731001.2012 | New Constraints on the Primordial Magnetic Field
astro-ph.CO gr-qc hep-ph
We present the newest statistical and numerical analysis of the matter and
cosmic microwave background power spectrum with effects of the primordial
magnetic field (PMF) included. New limits to the PMF strength and power
spectral index are obtained based upon the accumulated data for both the matter
and CMB power spectra on small angular scales. We find that a maximum develops
in the probability distribution for a magnitude of the PMF of $|B_\lambda| =
0.85 \pm 1.25(\pm 1\sigma)$ nG on a comoving scale of at 1 Mpc, corresponding
to upper limits of $\mathbf{< 2.10 nG} (68% \mathrm{CL})$ and $\mathbf{< 2.98
nG} (95% \mathrm{CL})$. While for the power spectral index we find
$n_\mathrm{B}= -2.37^{+0.88}_{-0.73}(\pm 1\sigma)$, corresponding to upper
limits of $ \mathbf{< -1.19} (68% \mathrm{CL})$ and $ \mathbf{< -0.25} (95%
\mathrm{CL})$. This result provides new constraints on models for magnetic
field generation and the physics of the early universe. We conclude that future
observational programs for the CMB and matter power spectrum will likely
provide not only upper limits but also lower limits to the PMF parameters.
| arxiv topic:astro-ph.CO gr-qc hep-ph |
arxiv_dataset-16741001.2112 | Outage Capacity of Bursty Amplify-and-Forward with Incremental Relaying
cs.IT math.IT
We derive the outage capacity of a bursty version of the amplify-and-forward
(BAF) protocol for small signal-to-noise ratios when incremental relaying is
used. We show that the ratio between the outage capacities of BAF and the
cut-set bound is independent of the relay position and that BAF is outage
optimal for certain conditions on the target rate R. This is in contrast to
decode-and-forward with incremental relaying, where the relay location strongly
determines the performance of the cooperative protocol. We further derive the
outage capacity for a network consisting of an arbitrary number of relay nodes.
In this case the relays transmit in subsequent partitions of the overall
transmission block and the destination accumulates signal-to-noise ratio until
it is able to decode.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-16751001.2212 | Identifying the progenitor set of present-day early-type galaxies: a
view from the standard model
astro-ph.CO
We present a comprehensive theoretical study, using a semi-analytical model
within the standard LCDM framework, of the photometric properties of the
progenitors of present-day early-type galaxies in the redshift range 0<z<1. We
explore progenitors of all morphologies and study their characteristics as a
function of the luminosity and local environment of the early-type remnant at
z=0. In agreement with previous studies, we find that, while larger early-types
are generally assembled later, their luminosity-weighted stellar ages are
typically older. In dense cluster-like environments, 70% of early-type systems
are `in place' by z=1 and evolve without interactions thereafter, while in the
field the corresponding value is 30%. Averaging across all environments at z~1,
less than 50% of the stellar mass which ends up in early-types today is
actually in early-type progenitors at this redshift, in agreement with recent
observational work. We develop probabilistic prescriptions which provide a
means of including spiral (i.e. non early-type) progenitors at intermediate and
high redshifts, based on their luminosity and optical colours. For example, we
find that, at intermediate redshifts (z~0.5), large (M_V<-21.5), red (B-V>0.7)
spirals have 75-95% chance of being an early-type progenitor, while the
corresponding probability for large blue spirals (M_B<-21.5, B-V<0.7) is
50-75%. The prescriptions developed here can be used to address, from the
perspective of the standard model, the issue of `progenitor bias', whereby the
exclusion of late-type progenitors in observational studies can lead to
inaccurate conclusions regarding the evolution of the early-type population
over cosmic time. (abridged)
| arxiv topic:astro-ph.CO |
arxiv_dataset-16761001.2312 | Heavy quarks in deep-inelastic scattering
hep-ph
We discuss a general framework for the inclusion of heavy quark mass
contributions to deep-inelastic structure functions and their perturbative
matching to structure functions computed in variable-mass schemes. Our approach
is based on the so-called FONLL method, previously introduced and applied to
heavy quark hadroproduction and photoproduction. We define our framework,
provide expressions up to second order in the strong coupling, and use them to
construct matched expressions for structure functions up to NNLO. After
checking explicitly the consistency of our results, we perform a study of the
phenomenological impact of heavy quark terms, and compare results obtained at
various perturbative orders, and with various prescriptions for the treatment
of subleading terms, specifically those related to threshold behaviour. We also
consider the heavy quark structure function F2c and discuss issues related to
the presence of mass singularities in their coefficient functions.
| arxiv topic:hep-ph |
arxiv_dataset-16771001.2412 | The solar X-ray continuum measured by RESIK
astro-ph.SR
The solar X-ray continuum emission at five wavelengths between 3.495
Angstroms and 4.220 Angstroms for 19 flares in a seven-month period in
2002--2003 was observed by the RESIK crystal spectrometer on CORONAS-F. In this
wavelength region, free--free and free--bound emissions have comparable fluxes.
With a pulse-height analyzer having settings close to optimal, the fluorescence
background was removed so that RESIK measured true solar continuum in these
bands with an uncertainty in the absolute calibration of plus or minus 20 per
cent. With an isothermal assumption, and temperature and emission measure
derived from the ratio of the two GOES channels, the observed continuum
emission normalized to an emission measure of 10^48 cm^-3 was compared with
theoretical continua using the CHIANTI atomic code. The accuracy of the RESIK
measurements allows photospheric and coronal abundance sets, important for the
free--bound continuum, to be discriminated. It is found that there is agreement
to about 25 per cent of the measured continua with those calculated from
CHIANTI assuming coronal abundances in which Mg, Si, Fe abundances are four
times photospheric.
| arxiv topic:astro-ph.SR |
arxiv_dataset-16781001.2512 | A Search for Unrecognized Carbon-Enhanced Metal-Poor Stars in the Galaxy
astro-ph.SR
We have developed a new procedure to search for carbon-enhanced metal-poor
(CEMP) stars from the Hamburg/ESO (HES) prism-survey plates. This method
employs an extended line index for the CH G-band, which we demonstrate to have
superior behavior when compared to the narrower G-band index formerly employed
to estimate G-band strengths for these spectra. Although CEMP stars have been
found previously among candidate metal-poor stars selected from the HES, the
selection on metallicity undersamples the population of
intermediate-metallicity CEMP stars (-2.5<=[Fe/H]<=-1.0); such stars are of
importance for constraining the onset of the s-process in metal-deficient
asymptotic giant-branch stars (thought to be associated with the origin of
carbon for roughly 80% of CEMP stars). The new candidates also include
substantial numbers of warmer carbon-enhanced stars, which were missed in
previous HES searches for carbon stars due to selection criteria that
emphasized stars with cooler temperatures.
A first subsample, biased towards brighter stars (B<15.5), has been extracted
from the scanned HES plates. After visual inspection, a list of 669 previously
unidentified candidate CEMP stars was compiled. Follow-up spectroscopy for a
pilot sample of 132 candidates was obtained with the Goodman spectrograph on
the SOAR 4.1m telescope. Our results show that most of the observed stars lie
in the targeted metallicity range, and possess prominent carbon absorption
features at 4300A. The success rate for the identification of new CEMP stars is
43% (13 out of 30) for [Fe/H]<-2.0. For stars with [Fe/H]<-2.5, the ratio
increases to 80% (4 out of 5 objects), including one star with [Fe/H]<-3.0.
| arxiv topic:astro-ph.SR |
arxiv_dataset-16791001.2612 | On distributed convex optimization under inequality and equality
constraints via primal-dual subgradient methods
math.OC cs.SY
We consider a general multi-agent convex optimization problem where the
agents are to collectively minimize a global objective function subject to a
global inequality constraint, a global equality constraint, and a global
constraint set. The objective function is defined by a sum of local objective
functions, while the global constraint set is produced by the intersection of
local constraint sets. In particular, we study two cases: one where the
equality constraint is absent, and the other where the local constraint sets
are identical. We devise two distributed primal-dual subgradient algorithms
which are based on the characterization of the primal-dual optimal solutions as
the saddle points of the Lagrangian and penalty functions. These algorithms can
be implemented over networks with changing topologies but satisfying a standard
connectivity property, and allow the agents to asymptotically agree on optimal
solutions and optimal values of the optimization problem under the Slater's
condition.
| arxiv topic:math.OC cs.SY |
arxiv_dataset-16801001.2712 | XMM-Newton unveils the complex iron K alpha region of Mrk 279
astro-ph.CO
We present the results of a ~160 ks-long XMM-Newton observation of the
Seyfert 1 galaxy Mrk 279. The spectrum shows evidence of both broad and narrow
emission features. The Fe K alpha line may be equally well explained by a
single broad Gaussian (FWHM~10,000 km/s) or by two components: an unresolved
core plus a very broad profile (FWHM~14,000 km/s). For the first time we
quantified, via the "locally optimally emitting cloud" model, the contribution
of the broad line region (BLR) to the absolute luminosity of the broad
component of the Fe K alpha at 6.4 keV. We find that the contribution of the
BLR is only ~3%. In the two-line component scenario, we also evaluated the
contribution of the highly ionized gas component, which produces the FeXXVI
line in the iron K region. This contribution to the narrow core of the Fe K
alpha line is marginal <0.1%. Most of the luminosity of the unresolved,
component of Fe K alpha may come from the obscuring torus, while the very-broad
associated component may come from the accretion disk. However, models of
reflection by cold gas are difficult to test because of the limited energy
band. The FeXXVI line at 6.9 keV is consistent to be produced in a high column
density (N_H~10^23 cm^{-2}), extremely ionized (log\xi~5.5-7) gas. This gas may
be a highly ionized outer layer of the torus.
| arxiv topic:astro-ph.CO |
arxiv_dataset-16811001.2812 | Face rings of simplicial complexes with singularities
math.AC math.AG math.CO
The face ring of a simplicial complex modulo m generic linear forms is shown
to have finite local cohomology if and only if the link of every face of
dimension m or more is `nonsingular', i.e., has the homology of a wedge of
spheres of the expected dimension. This is derived from an enumerative result
for local cohomology of face rings modulo generic linear forms, as compared
with local cohomology of the face ring itself. The enumerative result is
generalized in slightly weaker form to squarefree modules. A concept of
`Cohen-Macaulay in codimension c' is defined and characterized for arbitrary
finitely generated modules and coherent sheaves. For the face ring of an
r-dimensional complex Delta, it is equivalent to nonsingularity of Delta in
dimension r-c; for a coherent sheaf on projective space, this condition is
shown to be equivalent to the same condition on any single generic hyperplane
section. The characterization of nonsingularity in dimension m via finite local
cohomology thus generalizes from face rings to arbitrary graded modules.
| arxiv topic:math.AC math.AG math.CO |
arxiv_dataset-16821001.2912 | Dependence of elliptic flow on number of parton degrees of freedom
hep-ph nucl-th
We calculate the elliptic flow parameter $v_2$ for Au+Au collisions at
$\sqrt{s_{NN}}=200$ GeV employing the parton cascade BAMPS (Boltzmann Approach
of Multiparton Scatterings). Besides gluon interactions including the
bremsstrahlung process, interactions with quarks are considered in an
effective, but approximate way to investigate the dependence of the collective
flow on the number of parton degrees of freedom. We find that $v_2$ as a
function of the transverse momentum $p_T$ is sensitive to the number of parton
degrees of freedom, whereas the $p_T$ averaged $v_2$ does not. When including
quarks, $v_2(p_T)$ shifts to lower $p_T$, the parton transverse momentum
spectra become softer and the mean parton transverse momenta decrease.
| arxiv topic:hep-ph nucl-th |
arxiv_dataset-16831001.3012 | Modelling conflicts with cluster dynamics on networks
physics.soc-ph physics.comp-ph
We introduce cluster dynamical models of conflicts in which only the largest
cluster can be involved in an action. This mimics the situations in which an
attack is planned by a central body, and the largest attack force is used. We
study the model in its annealed random graph version, on a fixed network, and
on a network evolving through the actions. The sizes of actions are distributed
with a power-law tail, however, the exponent is non-universal and depends on
the frequency of actions and sparseness of the available connections between
units. Allowing the network reconstruction over time in a self-organized
manner, e.g., by adding the links based on previous liaisons between units, we
find that the power-law exponent depends on the evolution time of the network.
Its lower limit is given by the universal value 5/2, derived analytically for
the case of random fragmentation processes. In the temporal patterns behind the
size of actions we find long-range correlations in the time series of number of
clusters and non-trivial distribution of time that a unit waits between two
actions. In the case of an evolving network the distribution develops a
power-law tail, indicating that through the repeated actions, the system
develops internal structure which is not just more effective in terms of the
size of events, but also has a full hierarchy of units.
| arxiv topic:physics.soc-ph physics.comp-ph |
arxiv_dataset-16841001.3112 | Magnetic Avalanches in Molecular Nanomagnets
cond-mat.mes-hall cond-mat.mtrl-sci
The magnetization of the prototypical molecular magnet Mn12-acetate exhibits
a series of sharp steps at low temperatures due to quantum tunneling at
specific resonant values of magnetic field applied along the easy c-axis. An
abrupt reversal of the magnetic moment of such a crystal can also occur as an
avalanche, where the spin reversal proceeds along a "deflagration" front that
travels through the sample at subsonic speed. In this article we review
experimental results that have been obtained for the ignition temperature and
the speed of propagation of magnetic avalanches in molecular nanomagnets. Fits
of the data with the theory of magnetic deflagration yield overall qualitative
agreement. However, numerical discrepancies indicate that our understanding of
these avalanches is incomplete.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-16851001.3212 | Analytic Torsion of Z_2-graded Elliptic Complexes
math.DG hep-th
We define analytic torsion of Z_2-graded elliptic complexes as an element in
the graded determinant line of the cohomology of the complex, generalizing most
of the variants of Ray-Singer analytic torsion in the literature. It applies to
a myriad of new examples, including flat superconnection complexes, twisted
analytic and twisted holomorphic torsions, etc. The definition uses
pseudo-differential operators and residue traces. We also study properties of
analytic torsion for Z_2-graded elliptic complexes, including the behavior
under variation of the metric. For compact odd dimensional manifolds, the
analytic torsion is independent of the metric, whereas for even dimensional
manifolds, a relative version of the analytic torsion is independent of the
metric. Finally, the relation to topological field theories is studied.
| arxiv topic:math.DG hep-th |
arxiv_dataset-16861001.3312 | Eigenphase preserving two-channel SUSY transformations
math-ph math.MP
We propose a new kind of supersymmetric (SUSY) transformation in the case of
the two-channel scattering problem with equal thresholds, for partial waves of
the same parity. This two-fold transformation is based on two imaginary
factorization energies with opposite signs and with mutually conjugated
factorization solutions. We call it an eigenphase preserving SUSY
transformation as it relates two Hamiltonians, the scattering matrices of which
have identical eigenphase shifts. In contrast to known phase-equivalent
transformations, the mixing parameter is modified by the eigenphase preserving
transformation.
| arxiv topic:math-ph math.MP |
arxiv_dataset-16871001.3412 | A Deep HST Search for Escaping Lyman Continuum Flux at z~1.3: Evidence
for an Evolving Ionizing Emissivity
astro-ph.CO astro-ph.GA
We have obtained deep Hubble Space Telescope far-UV images of 15 starburst
galaxies at z~1.3 in the GOODS fields to search for escaping Lyman continuum
photons. These are the deepest far-UV images m_{AB}=28.7, 3\sigma, 1" diameter)
over this large an area (4.83 arcmin^2) and provide the best escape fraction
constraints for any galaxy at any redshift. We do not detect any individual
galaxies, with 3\sigma limits to the Lyman Continuum (~700 \AA) flux 50--149
times fainter (in f_nu) than the rest-frame UV (1500 \AA) continuum fluxes.
Correcting for the mean IGM attenuation (factor ~2), as well as an intrinsic
stellar Lyman Break (~3), these limits translate to relative escape fraction
limits of f_{esc,rel}<[0.03,0.21]. The stacked limit is
f_{esc,rel}(3\sigma)<0.02. We use a Monte Carlo simulation to properly account
for the expected distribution of IGM opacities. When including constraints from
previous surveys at z~1.3 we find that, at the 95% confidence level, no more
than 8% of star--forming galaxies at z~1.3 can have relative escape fractions
greater than 0.50. Alternatively, if the majority of galaxies have low, but
non-zero, escaping Lyman Continuum, the escape fraction can not be more than
0.04. Both the stacked limits, and the limits from the Monte Carlo simulation
suggest that the average ionizing emissivity (relative to non-ionizing UV
emissivity) at z~1.3 is significantly lower than has been observed in Lyman
Break Galaxies (LBGs) at z~3. If the ionizing emissivity of star-forming
galaxies is in fact increasing with redshift, it would help to explain the high
photoionization rates seen in the IGM at z>4 and reionization of the
intergalactic medium at z>6. [Abridged]
| arxiv topic:astro-ph.CO astro-ph.GA |
arxiv_dataset-16881001.3512 | Theory of Room Temperature Ferromagnet V(TCNE)_x (1.5 < x < 2): Role of
Hidden Flat Bands
cond-mat.str-el cond-mat.mtrl-sci
Theoretical studies on the possible origin of room temperature ferromagnetism
(ferromagnetic once crystallized) in the molecular transition metal complex,
V(TCNE)_x (1.5<x<2) have been carried out. For this family, there have been no
definite understanding of crystal structure so far because of sample quality,
though the effective valence of V is known to be close to +2. Proposing a new
crystal structure for the stoichiometric case of x=2, where the valence of each
TCNE molecule is -1 and resistivity shows insulating behavior, exchange
interaction among d-electrons on adjacent V atoms has been estimated based on
the cluster with 3 vanadium atoms and one TCNE molecule. It turns out that
Hund's coupling among d orbitals within the same V atoms and antiferromagnetic
coupling between d oribitals and LUMO of TCNE (bridging V atoms) due to
hybridization result in overall ferromagnetism (to be precise, ferrimagnetism).
This view based on localized electrons is supplemented by the band picture,
which indicates the existence of a flat band expected to lead to ferromagnetism
as well consistent with the localized view. The off-stoichiometric cases (x<2),
which still show ferromagnetism but semiconducting transport properties, have
been analyzed as due to Anderson localization.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-16891001.3612 | Mass Function of Binary Massive Black Holes in Active Galactic Nuclei
astro-ph.CO astro-ph.GA hep-ph
If the activity of active galactic nuclei (AGNs) is predominantly induced by
major galaxy mergers, then a significant fraction of AGNs should harbor binary
massive black holes in their centers. We study the mass function of binary
massive black holes in nearby AGNs based on the observed AGN black-hole mass
function and theory of evolution of binary massive black holes interacting with
a massive circumbinary disk in the framework of coevolution of massive black
holes and their host galaxies. The circumbinary disk is assumed to be steady,
axisymmetric, geometrically thin, self-regulated, self-gravitating but
non-fragmenting with a fraction of Eddington accretion rate, which is typically
one tenth of Eddington value. The timescale of orbital decay is {then}
estimated as ~10^8yr for equal mass black-hole, being independent of the black
hole mass, semi-major axis, and viscosity parameter but dependent on the
black-hole mass ratio, Eddington ratio, and mass-to-energy conversion
efficiency. This makes it possible for any binary massive black holes to merge
within a Hubble time by the binary-disk interaction. We find that (1.8+-0.6%)
for the equal mass ratio and (1.6+-0.4%) for the one-tenth mass ratio of the
total number of nearby AGNs have close binary massive black holes with orbital
period less than ten years in their centers, detectable with on-going highly
sensitive X-ray monitors such as Monitor of All-sky X-ray Image and/or
Swift/Burst Alert Telescope. Assuming that all binary massive black holes have
the equal mass ratio, about 20% of AGNs with black hole masses of
10^{6.5-7}M_sun has the close binaries and thus provides the best chance to
detect them.
| arxiv topic:astro-ph.CO astro-ph.GA hep-ph |
arxiv_dataset-16901001.3712 | Precipitation of water from aqueous mixtures with addition of
hydrophilic ions
cond-mat.soft cond-mat.stat-mech
We examine phase separation in aqueous mixtures at fixed amounts of
hydrophilic monovalent ions. When water is the minority component, preferential
solvation can stabilize water domains enriched with ions.
This ion-induced precipitation occurs in wide ranges of the temperature and
the average composition where the solvent would be in one-phase states without
ions. The volume fraction of such water domains is decreased to zero as the
interaction parameter $\chi$ (dependent on the temperature) is decreased toward
a critical value for each average composition.
| arxiv topic:cond-mat.soft cond-mat.stat-mech |
arxiv_dataset-16911001.3812 | Control of the amplification process in baseline XFEL undulator with
mechanical SASE switchers
physics.acc-ph
The magnetic gap of the baseline XFEL undulators can be varied mechanically
for wavelength tuning. In particular, the wavelength range 0.1 nm - 0.4 nm can
be covered by operating the European XFEL with the SASE2 undulator. The length
of the SASE2 undulator (256.2 m) is sufficient to independently generate three
pulses of different radiation wavelengths at saturation. Normally, if a SASE
FEL operates in saturation, the quality of the electron beam is too bad for
generation of SASE radiation in the subsequent part of undulator which is
resonant at a few times longer wavelength. The new method of SASE
undulator-switching based on the rapid switching of the FEL amplification
process proposed in this paper is an attempt to get around this obstacle. Using
mechanical SASE shutters installed within short magnetic chicanes in the
baseline undulator, it is possible to rapidly switch the FEL photon beam from
one wavelength to another, providing simultaneous multi-color capability.
Combining this method with a photon-beam distribution system can provide an
efficient way to generate a multi-user facility.
| arxiv topic:physics.acc-ph |
arxiv_dataset-16921001.3912 | Titchmarsh-Sims-Weyl theory for complex Hamiltonian systems on Sturmian
time scales
math.CA
We study non-self-adjoint Hamiltonian systems on Sturmian time scales,
defining Weyl-Sims sets, which replace the classical Weyl circles, and a
matrix-valued $M-$function on suitable cone-shaped domains in the complex
plane. Furthermore, we characterize realizations of the corresponding dynamic
operator and its adjoint, and construct their resolvents. Even-order scalar
equations and the Orr-Sommerfeld equation on time scales are given as examples
illustrating the theory, which are new even for difference equations. These
results unify previous discrete and continuous theories to dynamic equations on
Sturmian time scales.
| arxiv topic:math.CA |
arxiv_dataset-16931001.4012 | Monge's transport problem in the Heisenberg group
math.AP math.MG
We prove the existence of solutions to Monge transport problem between two
compactly supported Borel probability measures in the Heisenberg group equipped
with its Carnot-Caratheodory distance assuming that the initial measure is
absolutely continuous with respect to the Haar measure of the group.
| arxiv topic:math.AP math.MG |
arxiv_dataset-16941001.4112 | Elastic and non-linear stiffness of graphene: a simple approach
cond-mat.mtrl-sci cond-mat.mes-hall
The recent experiment [Science \textbf{321}, 385 (2008)] on the Young's
modulus and third-order elastic stiffness of graphene are well explained in a
very simple approach, where the graphene is described by a simplified system
and the force constant for the non-linear interaction is estimated from the
Tersoff-Brenner potential.
| arxiv topic:cond-mat.mtrl-sci cond-mat.mes-hall |
arxiv_dataset-16951001.4212 | Time-dependent corrections to effective rate and event statistics in
Michaelis-Menten kinetics
q-bio.QM cond-mat.stat-mech physics.chem-ph q-bio.MN
We generalize the concept of the geometric phase in stochastic kinetics to a
noncyclic evolution. Its application is demonstrated on kinetics of the
Michaelis-Menten reaction. It is shown that the nonperiodic geometric phase is
responsible for the correction to the Michaelis-Menten law when parameters,
such as a substrate concentration, are changing with time. We apply these ideas
to a model of chemical reactions in a bacterial culture of a growing size,
where the geometric correction qualitatively changes the outcome of the
reaction kinetics.
| arxiv topic:q-bio.QM cond-mat.stat-mech physics.chem-ph q-bio.MN |
arxiv_dataset-16961001.4312 | On characters and formal degrees of discrete series of affine Hecke
algebras of classical types
math.RT
We address two fundamental questions in the representation theory of affine
Hecke algebras of classical types. One is an inductive algorithm to compute
characters of tempered modules, and the other is the determination of the
constants in the formal degrees of discrete series (in the form conjectured by
Reeder \cite{Re}). The former is completely different than the Lusztig-Shoji
algorithm \cite{Sh, L}, and it is more effective in a number of cases. The main
idea in our proof is to introduce a new family of representations which behave
like tempered modules, but for which it is easier to analyze the effect of
parameter specializations. Our proof also requires a comparison of the
$C^{\ast}$-theoretic results of Opdam, Delorme, Slooten, Solleveld \cite{O, DO,
Sl2, OSa, OS}, and the geometric construction from \cite{K1,K2,CK}.
| arxiv topic:math.RT |
arxiv_dataset-16971001.4412 | Quantitative analysis of single particle trajectories: mean maximal
excursion method
cond-mat.stat-mech
An increasing number of experimental studies employ single particle tracking
to probe the physical environment in complex systems. We here propose and
discuss new methods to analyze the time series of the particle traces, in
particular, for subdiffusion phenomena. We discuss the statistical properties
of mean maximal excursions, i.e., the maximal distance covered by a test
particle up to time t. Compared to traditional methods focusing on the mean
squared displacement we show that the mean maximal excursion analysis performs
better in the determination of the anomalous diffusion exponent. We also
demonstrate that combination of regular moments with moments of the mean
maximal excursion method provides additional criteria to determine the exact
physical nature of the underlying stochastic subdiffusion processes. We put the
methods to test using experimental data as well as simulated time series from
different models for normal and anomalous dynamics, such as diffusion on
fractals, continuous time random walks, and fractional Brownian motion.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-16981001.4512 | The Importance of XUV Radiation as a Solution to the P V Mass Loss Rate
Discrepancy in O-Stars
astro-ph.SR astro-ph.HE
A controversy has developed regarding the stellar wind mass loss rates in
O-stars. The current consensus is that these winds may be clumped which implies
that all previously derived mass loss rates using density-squared diagnostics
are overestimated by a factor of ~ 2. However, arguments based on FUSE
observations of the P V resonance line doublet suggest that these rates should
be smaller by another order of magnitude, provided that P V is the dominant
phosphorous ion among these stars. Although a large mass loss rate reduction
would have a range of undesirable consequences, it does provide a
straightforward explanation of the unexpected symmetric and un-shifted X-ray
emission line profiles observed in high energy resolution spectra. But
acceptance of such a large reduction then leads to a contradiction with an
important observed X-ray property: the correlation between He-like ion source
radii and their equivalent X-ray continuum optical depth unity radii. Here we
examine the phosphorous ionization balance since the P V fractional abundance,
q(P V), is fundamental to understanding the magnitude of this mass loss
reduction. We find that strong "XUV" emission lines in the He II Lyman
continuum can significantly reduce q(P V). Furthermore, owing to the unique
energy distribution of these XUV lines, there is a negligible impact on the S V
fractional abundance (a key component in the FUSE mass loss argument). We
conclude that large reductions in O-star mass loss rates are not required, and
the X-ray optical depth unity relation remains valid.
| arxiv topic:astro-ph.SR astro-ph.HE |
arxiv_dataset-16991001.4612 | Damping in high-frequency metallic nanomechanical resonators
cond-mat.mes-hall cond-mat.mtrl-sci
We have studied damping in polycrystalline Al nanomechanical resonators by
measuring the temperature dependence of their resonance frequency and quality
factor over a temperature range of 0.1 - 4 K. Two regimes are clearly
distinguished with a crossover temperature of 1 K. Below 1 K we observe a
logarithmic temperature dependence of the frequency and linear dependence of
damping that cannot be explained by the existing standard models. We attribute
these phenomena to the effect of the two-level systems characterized by the
unexpectedly long (at least two orders of magnitude longer) relaxation times
and discuss possible microscopic models for such systems. We conclude that the
dynamics of the two-level systems is dominated by their interaction with
one-dimensional phonon modes of the resonators.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
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