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0704.0301 | Differential Recursion and Differentially Algebraic Functions | Moore introduced a class of real-valued "recursive" functions by analogy with
Kleene's formulation of the standard recursive functions. While his concise
definition inspired a new line of research on analog computation, it contains
some technical inaccuracies. Focusing on his "primitive recursive" functions,
we pin down what is problematic and discuss possible attempts to remove the
ambiguity regarding the behavior of the differential recursion operator on
partial functions. It turns out that in any case the purported relation to
differentially algebraic functions, and hence to Shannon's model of analog
computation, fails.
| cs.CC |
0704.0302 | Spline Single-Index Prediction Model | For the past two decades, single-index model, a special case of projection
pursuit regression, has proven to be an efficient way of coping with the high
dimensional problem in nonparametric regression. In this paper, based on weakly
dependent sample, we investigate the single-index prediction (SIP) model which
is robust against deviation from the single-index model. The single-index is
identified by the best approximation to the multivariate prediction function of
the response variable, regardless of whether the prediction function is a
genuine single-index function. A polynomial spline estimator is proposed for
the single-index prediction coefficients, and is shown to be root-n consistent
and asymptotically normal. An iterative optimization routine is used which is
sufficiently fast for the user to analyze large data of high dimension within
seconds. Simulation experiments have provided strong evidence that corroborates
with the asymptotic theory. Application of the proposed procedure to the rive
flow data of Iceland has yielded superior out-of-sample rolling forecasts.
| math.ST stat.TH |
0704.0303 | Measurement of the Aerosol Phase Function at the Pierre Auger
Observatory | Air fluorescence detectors measure the energy of ultra-high energy cosmic
rays by collecting fluorescence light emitted from nitrogen molecules along the
extensive air shower cascade. To ensure a reliable energy determination, the
light signal needs to be corrected for atmospheric effects, which not only
attenuate the signal, but also produce a non-negligible background component
due to scattered Cherenkov light and multiple-scattered light. The correction
requires regular measurements of the aerosol attenuation length and the aerosol
phase function, defined as the probability of light scattered in a given
direction. At the Pierre Auger Observatory in Malargue, Argentina, the phase
function is measured on an hourly basis using two Aerosol Phase Function (APF)
light sources. These sources direct a UV light beam across the field of view of
the fluorescence detectors; the phase function can be extracted from the image
of the shots in the fluorescence detector cameras. This paper describes the
design, current status, standard operation procedure, and performance of the
APF system at the Pierre Auger Observatory.
| astro-ph physics.ao-ph |
0704.0304 | The World as Evolving Information | This paper discusses the benefits of describing the world as information,
especially in the study of the evolution of life and cognition. Traditional
studies encounter problems because it is difficult to describe life and
cognition in terms of matter and energy, since their laws are valid only at the
physical scale. However, if matter and energy, as well as life and cognition,
are described in terms of information, evolution can be described consistently
as information becoming more complex.
The paper presents eight tentative laws of information, valid at multiple
scales, which are generalizations of Darwinian, cybernetic, thermodynamic,
psychological, philosophical, and complexity principles. These are further used
to discuss the notions of life, cognition and their evolution.
| cs.IT cs.AI math.IT q-bio.PE |
0704.0305 | Polymerization Force Driven Buckling of Microtubule Bundles Determines
the Wavelength of Patterns Formed in Tubulin Solutions | We present a model for the spontaneous formation of a striated pattern in
polymerizing microtubule solutions. It describes the buckling of a single
microtubule (MT) bundle within an elastic network formed by other similarly
aligned and buckling bundles and unaligned MTs. Phase contrast and polarization
microscopy studies of the temporal evolution of the pattern imply that the
polymerization of MTs within the bundles creates the driving compressional
force. Using the measured rate of buckling, the established MT force-velocity
curve and the pattern wavelength, we obtain reasonable estimates for the MT
bundle bending rigidity and the elastic constant of the network. The analysis
implies that the bundles buckle as solid rods.
| physics.bio-ph |
0704.0306 | Neutron Inelastic Scattering Processes as Background for Double-Beta
Decay Experiments | We investigate several Pb$(n,n'\gamma$) and Ge$(n,n'\gamma$) reactions. We
measure $\gamma$-ray production from Pb$(n,n'\gamma$) reactions that can be a
significant background for double-beta decay experiments which use lead as a
massive inner shield. Particularly worrisome for Ge-based double-beta decay
experiments are the 2041-keV and 3062-keV $\gamma$ rays produced via
Pb$(n,n'\gamma$). The former is very close to the ^{76}Ge double-beta decay
endpoint energy and the latter has a double escape peak energy near the
endpoint. Excitation $\gamma$-ray lines from Ge$(n,n'\gamma$) reactions are
also observed. We consider the contribution of such backgrounds and their
impact on the sensitivity of next-generation searches for neutrinoless
double-beta decay using enriched germanium detectors.
| nucl-ex hep-ex |
0704.0307 | Periodic accretion from a circumbinary disk in the young binary UZ Tau E | Close pre-main-sequence binary stars are expected to clear central holes in
their protoplanetary disks, but the extent to which material can flow from the
circumbinary disk across the gap onto the individual circumstellar disks has
been unclear. In binaries with eccentric orbits, periodic perturbation of the
outer disk is predicted to induce mass flow across the gap, resulting in
accretion that varies with the binary period. This accretion may manifest
itself observationally as periodic changes in luminosity. Here we present a
search for such periodic accretion in the pre-main-sequence spectroscopic
binary UZ Tau E. We present BVRI photometry spanning three years; we find that
the brightness of UZ Tau E is clearly periodic, with a best-fit period of 19.16
+/- 0.04 days. This is consistent with the spectroscopic binary period of 19.13
days, refined here from analysis of new and existing radial velocity data. The
brightness of UZ Tau E shows significant random variability, but the overall
periodic pattern is a broad peak in enhanced brightness, spanning more than
half the binary orbital period. The variability of the H-alpha line is not as
clearly periodic, but given the sparseness of the data, some periodic component
is not ruled out. The photometric variations are in good agreement with
predictions from simulations of binaries with orbital parameters similar to
those of UZ Tau E, suggesting that periodic accretion does occur from
circumbinary disks, replenishing the inner disks and possibly extending the
timescale over which they might form planets.
| astro-ph |
0704.0308 | Effect of node deleting on network structure | The ever-increasing knowledge of the structure of various real-world networks
has uncovered their complex multi-mechanism-governed evolution processes.
Therefore, a better understanding of the structure and evolution of these
networked complex systems requires us to describe such processes in a more
detailed and realistic manner. In this paper, we introduce a new type of
network growth rule which comprises addition and deletion of nodes, and propose
an evolving network model to investigate the effect of node deleting on network
structure. It is found that, with the introduction of node deleting, network
structure is significantly transformed. In particular, degree distribution of
the network undergoes a transition from scale-free to exponential forms as the
intensity of node deleting increases. At the same time, nontrivial
disassortative degree correlation develops spontaneously as a natural result of
network evolution in the model. We also demonstrate that node deleting
introduced in the model does not destroy the connectedness of a growing network
so long as the increasing rate of edges is not excessively small. In addition,
it is found that node deleting will weaken but not eliminate the small-world
effect of a growing network, and generally it will decrease the clustering
coefficient in a network.
| physics.soc-ph |
0704.0309 | The Complexity of HCP in Digraps with Degree Bound Two | The Hamiltonian cycle problem (HCP) in digraphs D with degree bound two is
solved by two mappings in this paper. The first bijection is between an
incidence matrix C_{nm} of simple digraph and an incidence matrix F of balanced
bipartite undirected graph G; The second mapping is from a perfect matching of
G to a cycle of D. It proves that the complexity of HCP in D is polynomial, and
finding a second non-isomorphism Hamiltonian cycle from a given Hamiltonian
digraph with degree bound two is also polynomial. Lastly it deduces P=NP base
on the results.
| cs.CC cs.DM |
0704.0310 | VLBI observations of nineteen GHz-Peaked-Spectrum radio sources at 1.6
GHz | Aims and Methods: We present the results of VLBI observations of nineteen
GHz-Peaked-Spectrum (GPS) radio sources at 1.6 GHz. Of them, 15 sources are
selected from the Parkes Half Jansky (PHJ) sample (Snellen 2002), 4 others are
from our previous observation list. We aimed at imaging the structure of GPS
sources, searching for Compact Symmetric Objects (CSOs) and studying the
absorption for the convex radio spectra of GPS sources.
Results: We obtained total intensity 1.6 GHz VLBI images of 17 sources for
the first time. Of them, 80% show mini-double-lobe radio structure, indicating
that they are CSOs or candidates, and their host AGNs could be edge-on to us.
This result suggests that there is a high incidence of mini double-lobe sources
(or CSOs) in the PHJ sample. The sources J0323+0534, J1135-0021, J1352+0232,
J2058+0540, J2123-0112 and J2325-0344 with measured redshift, showing
double-lobe structure with sizes of <1 kpc, are classified as CSOs. Three
sources J1057+0012, J1600-0037 and J1753+2750 are considered as core-jet
sources according to their morphologies and flux variability.
| astro-ph |
0704.0311 | Moment switching in nanotube magnetic force probes | A recent advance in improving the spatial resolution of magnetic force
microscopy (MFM) uses as sensor tips carbon nanotubes grown at the apex of
conventional silicon cantilever pyramids and coated with a thin ferromagnetic
layer. Magnetic images of high density vertically recorded media using these
tips exhibit a doubling of the spatial frequency under some conditions. Here we
demonstrate that this spatial frequency doubling is due to the switching of the
moment direction of the nanotube tip. This results in a signal which is
proportional to the absolute value of the signal normally observed in MFM. Our
modeling indicates that a significant fraction of the tip volume is involved in
the observed switching, and that it should be possible to image very high bit
densities with nanotube magnetic force sensors.
| cond-mat.mes-hall cond-mat.mtrl-sci |
0704.0312 | Power Spectra to 1% Accuracy between Dynamical Dark Energy Cosmologies | For dynamical dark energy cosmologies we carry out a series of N-body
gravitational simulations, achieving percent level accuracy in the relative
mass power spectra at any redshift. Such accuracy in the power spectrum is
necessary for next generation cosmological mass probes. Our matching procedure
reproduces the CMB distance to last scattering and delivers subpercent level
power spectra at z=0 and z~3. We discuss the physical implications for probing
dark energy with surveys of large scale structure.
| astro-ph |
0704.0313 | Possibility of Gapless Spin Liquid State by One-dimensionalization | Motivated by the observation of a gapless spin liquid state in
$\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, we analyze the anisotropic triangular
lattice $S=1/2$ Heisenberg model with the resonating valence bond mean-field
approximation. Paying attention to the small quasi-one-dimensional anisotropy
of the material, we take an approach from one-dimensional (1D) chains coupled
with frustrating zig-zag bonds. By calculating one-particle excitation spectra
changing anisotropy parameter $J'/J$ from the decoupled 1D chains to the
isotropic triangular lattice, we find almost gapless excitations in the wide
range from the 1D limit. This one-dimensionalization by frustration is
considered to be a candidate for the mechanism of the gapless spin liquid
state.
| cond-mat.str-el |
0704.0314 | Extra dimensions and Lorentz invariance violation | We consider effective model where photons interact with scalar field
corresponding to conformal excitations of the internal space (geometrical
moduli/gravexcitons). We demonstrate that this interaction results in a
modified dispersion relation for photons, and consequently, the photon group
velocity depends on the energy implying the propagation time delay effect. We
suggest to use the experimental bounds of the time delay of gamma ray bursts
(GRBs) photons propagation as an additional constrain for the gravexciton
parameters.
| hep-ph astro-ph hep-th |
0704.0315 | The small deviations of many-dimensional diffusion processes and
rarefaction by boundaries | We lead the algorithm of expansion of sojourn probability of many-dimensional
diffusion processes in small domain. The principal member of this expansion
defines normalizing coefficient for special limit theorems.
| math.PR math.AP |
0704.0316 | The Millennium Galaxy Catalogue: The local supermassive black hole mass
function in early- and late-type galaxies | We provide a new estimate of the local supermassive black hole mass function
using (i) the empirical relation between supermassive black hole mass and the
Sersic index of the host spheroidal stellar system and (ii) the measured
(spheroid) Sersic indices drawn from 10k galaxies in the Millennium Galaxy
Catalogue. The observational simplicity of our approach, and the direct
measurements of the black hole predictor quantity, i.e. the Sersic index, for
both elliptical galaxies and the bulges of disc galaxies makes it
straightforward to estimate accurate black hole masses in early- and late-type
galaxies alike. We have parameterised the supermassive black hole mass function
with a Schechter function and find, at the low-mass end, a logarithmic slope
(1+alpha) of ~0.7 for the full galaxy sample and ~1.0 for the early-type galaxy
sample. Considering spheroidal stellar systems brighter than M_B = -18 mag, and
integrating down to black hole masses of 10^6 M_sun, we find that the local
mass density of supermassive black holes in early-type galaxies rho_{bh,
early-type} = (3.5+/-1.2) x 10^5 h^3_{70} M_sun Mpc^{-3}, and in late-type
galaxies rho_{bh, late-type} = (1.0+/-0.5) x 10^5 h^3_{70} M_sun Mpc^{-3}. The
uncertainties are derived from Monte Carlo simulations which include
uncertainties in the M_bh-n relation, the catalogue of Sersic indices, the
galaxy weights and Malmquist bias. The combined, cosmological, supermassive
black hole mass density is thus Omega_{bh, total} = (3.2+/-1.2) x 10^{-6} h_70.
That is, using a new and independent method, we conclude that (0.007+/-0.003)
h^3_{70} per cent of the universe's baryons are presently locked up in
supermassive black holes at the centres of galaxies.
| astro-ph |
0704.0317 | Complete Shrinking Ricci Solitons have Finite Fundamental Group | We show that if a complete Riemannian manifold supports a vector field such
that the Ricci tensor plus the Lie derivative of the metric with respect to the
vector field has a positive lower bound, then the fundamental group is finite.
In particular, it follows that complete shrinking Ricci solitons and complete
smooth metric measure spaces with a positive lower bound on the Bakry-Emery
tensor have finite fundamental group. The method of proof is to generalize
arguments of Garcia-Rio and Fernandez-Lopez in the compact case.
| math.DG |
0704.0318 | Effects of Dirac sea on pion propagation in asymmetric nuclear matter | We study pion propagation in asymmetric nuclear matter (ANM). One of the
interesting consequences of pion propagation in ANM is the mode splitting for
the different charged states of pions. First we describe the pion-nucleon
dynamics using the non-chiral model where one starts with pseudoscalar (PS)
$\pi$N coupling and the pseudovector (PV) representation is obtained via
suitable non-linear field transformations. For both of these cases the effect
of the Dirac sea is estimated. Subsequently, we present results using the
chiral effective Lagrangian where the short-distance behavior (Dirac vacuum) is
included by re-defining the field parameters as done in the modern effective
field theory approach developed recently. The results are compared with the
previous calculations for the case of symmetric nuclear matter (SNM). Closed
form analytical results are presented for the effective pion masses and
dispersion relations by making hard nucleon loop (HNL) approximation and
suitable density expansion.
| nucl-th hep-ph |
0704.0319 | Spin-orbit coupling effect on the persistent currents in mesoscopic ring
with an Anderson impurity | Based on the finite $U$ slave boson method, we have investigated the effect
of Rashba spin-orbit(SO) coupling on the persistent charge and spin currents in
mesoscopic ring with an Anderson impurity. It is shown that the Kondo effect
will decrease the magnitude of the persistent charge and spin currents in this
side-coupled Anderson impurity case. In the presence of SO coupling, the
persistent currents change drastically and oscillate with the strength of SO
coupling. The SO coupling will suppress the Kondo effect and restore the abrupt
jumps of the persistent currents. It is also found that a persistent spin
current circulating the ring can exist even without the charge current in this
system.
| cond-mat.mes-hall |
0704.0320 | Probability distributions generated by fractional diffusion equations | Fractional calculus allows one to generalize the linear, one-dimensional,
diffusion equation by replacing either the first time derivative or the second
space derivative by a derivative of fractional order. The fundamental solutions
of these equations provide probability density functions, evolving on time or
variable in space, which are related to the class of stable distributions. This
property is a noteworthy generalization of what happens for the standard
diffusion equation and can be relevant in treating financial and economical
problems where the stable probability distributions play a key role.
| cond-mat.stat-mech |
0704.0321 | Fabrication of half metallicity in a ferromagnetic metal | We investigate the growth of half metallic phase in a ferromagnetic material
using state-of-the-art full potential linearized augmented plane wave method.
To address the issue, we have substituted Ti at the Ru-sites in SrRuO3, where
SrRuO3 is a ferromagnetic material. Calculated results establish Ti4+ valence
states (similar to SrTiO3), which was predicted experimentally. Thus, Ti
substitution dilutes the Ru-O-Ru connectivity, which is manifested in the
calculated results in the form of significant band narrowing leading to finite
gap between t2g and eg bands. At 75% substitution, a large gap (> 2 eV) appears
at the Fermi level, e_F in the up spin density of states, while the down spin
states contributes at e_F characterizing the system a half-metallic
ferromagnet. The t2g - eg gap can be tailored judiciously by tuning Ti
concentrations to minimize thermal effects, which is often the major bottleneck
to achieve high spin polarization at elevated temperatures in other materials.
This study, thus, provides a novel but simple way to fabricate half-metallicity
in ferromagnetic materials, which are potential candidates for spin-based
technology.
| cond-mat.str-el cond-mat.mtrl-sci |
0704.0322 | Emergence of spatiotemporal chaos driven by far-field breakup of spiral
waves in the plankton ecological systems | Alexander B. Medvinsky \emph{et al} [A. B. Medvinsky, I. A. Tikhonova, R. R.
Aliev, B.-L. Li, Z.-S. Lin, and H. Malchow, Phys. Rev. E \textbf{64}, 021915
(2001)] and Marcus R. Garvie \emph{et al} [M. R. Garvie and C. Trenchea, SIAM
J. Control. Optim. \textbf{46}, 775-791 (2007)] shown that the minimal
spatially extended reaction-diffusion model of phytoplankton-zooplankton can
exhibit both regular, chaotic behavior, and spatiotemporal patterns in a patchy
environment. Based on that, the spatial plankton model is furtherly
investigated by means of computer simulations and theoretical analysis in the
present paper when its parameters would be expected in the case of mixed
Turing-Hopf bifurcation region. Our results show that the spiral waves exist in
that region and the spatiotemporal chaos emerge, which arise from the far-field
breakup of the spiral waves over large ranges of diffusion coefficients of
phytoplankton and zooplankton. Moreover, the spatiotemporal chaos arising from
the far-field breakup of spiral waves does not gradually involve the whole
space within that region. Our results are confirmed by means of computation
spectra and nonlinear bifurcation of wave trains. Finally, we give some
explanations about the spatially structured patterns from the community level.
| nlin.PS nlin.CD q-bio.PE |
0704.0323 | General sequential quantum cloning | Some multipartite quantum states can be generated in a sequential manner
which may be implemented by various physical setups like microwave and optical
cavity QED, trapped ions, and quantum dots etc. We analyze the general N to M
qubits Universal Quantum Cloning Machine (UQCM) within a sequential generation
scheme. We show that the N to M sequential UQCM is available. The case of
d-level quantum states sequential cloning is also presented.
| quant-ph |
0704.0324 | On the pseudospectrum of elliptic quadratic differential operators | We study the pseudospectrum of a class of non-selfadjoint differential
operators. Our work consists in a detailed study of the microlocal properties,
which rule the spectral stability or instability phenomena appearing under
small perturbations for elliptic quadratic differential operators. The class of
elliptic quadratic differential operators stands for the class of operators
defined in the Weyl quantization by complex-valued elliptic quadratic symbols.
We establish in this paper a simple necessary and sufficient condition on the
Weyl symbol of these operators, which ensures the stability of their spectra.
When this condition is violated, we prove that it occurs some strong spectral
instabilities for the high energies of these operators, in some regions which
can be far away from their spectra. We give a precise geometrical description
of them, which explains the results obtained for these operators in some
numerical simulations giving the computation of false eigenvalues far from
their spectra by algorithms for eigenvalues computing.
| math.AP |
0704.0325 | Fluctuation-dissipation relation on a Melde string in a turbulent flow,
considerations on a "dynamical temperature" | We report on measurements of the transverse fluctuations of a string in a
turbulent air jet flow. Harmonic modes are excited by the fluctuating drag
force, at different wave-numbers. This simple mechanical probe makes it
possible to measure excitations of the flow at specific scales, averaged over
space and time: it is a scale-resolved, global measurement. We also measure the
dissipation associated to the string motion, and we consider the ratio of the
fluctuations over dissipation (FDR). In an exploratory approach, we investigate
the concept of {\it effective temperature} defined through the FDR. We compare
our observations with other definitions of temperature in turbulence. From the
theory of Kolmogorov (1941), we derive the exponent -11/3 expected for the
spectrum of the fluctuations. This simple model and our experimental results
are in good agreement, over the range of wave-numbers, and Reynolds number
accessible ($74000 \leq Re \leq 170000$).
| cond-mat.stat-mech physics.ins-det |
0704.0326 | On generalized entropy measures and pathways | Product probability property, known in the literature as statistical
independence, is examined first. Then generalized entropies are introduced, all
of which give generalizations to Shannon entropy. It is shown that the nature
of the recursivity postulate automatically determines the logarithmic
functional form for Shannon entropy. Due to the logarithmic nature, Shannon
entropy naturally gives rise to additivity, when applied to situations having
product probability property. It is argued that the natural process is
non-additivity, important, for example, in statistical mechanics, even in
product probability property situations and additivity can hold due to the
involvement of a recursivity postulate leading to a logarithmic function.
Generalizations, including Mathai's generalized entropy are introduced and some
of the properties are examined. Situations are examined where Mathai's entropy
leads to pathway models, exponential and power law behavior and related
differential equations. Connection of Mathai's entropy to Kerridge's measure of
"inaccuracy" is also explored.
| math.ST cond-mat.stat-mech stat.TH |
0704.0327 | Evolution of a band insulating phase from a correlated metallic phase | We investigate the evolution of the electronic structure in SrRu_(1-x)Ti_xO_3
as a function of x using high resolution photoemission spectroscopy, where
SrRuO3 is a weakly correlated metal and SrTiO3 is a band insulator. The surface
spectra exhibit a metal-insulator transition at x = 0.5 by opening up a soft
gap. A hard gap appears at higher x values consistent with the transport
properties. In contrast, the bulk spectra reveal a pseudogap at the Fermi
level, and unusual evolution exhibiting an apparent broadening of the coherent
feature and subsequent decrease in intensity of the lower Hubbard band with the
increase in x. Interestingly, the first principle approaches are found to be
sufficient to capture anomalous evolutions at high energy scale. Analysis of
the spectral lineshape indicates strong interplay between disorder and electron
correlation in the electronic properties of this system.
| cond-mat.str-el cond-mat.mtrl-sci |
0704.0328 | Electroweak phase transitions in the MSSM with an extra $U(1)'$ | We investigate the possibility of electroweak phase transition in the minimal
supersymmetric standard model (MSSM) with an extra $U(1)'$. This model has two
Higgs doublets and a singlet, in addition to a singlet exotic quark superfield.
We find that at the one-loop level this model may accommodate the electroweak
phase transitions that are strongly first-order in a reasonably large region of
the parameter space. In the parameter region where the phase transitions take
place, we observe that the lightest scalar Higgs boson has a smaller mass when
the strength of the phase transition becomes weaker. Also, the other three
heavier neutral Higgs bosons get more large masses when the strength of the
phase transition becomes weaker.
| hep-ph |
0704.0329 | Solutions of fractional reaction-diffusion equations in terms of the
H-function | This paper deals with the investigation of the solution of an unified
fractional reaction-diffusion equation associated with the Caputo derivative as
the time-derivative and Riesz-Feller fractional derivative as the
space-derivative. The solution is derived by the application of the Laplace and
Fourier transforms in closed form in terms of the H-function. The results
derived are of general nature and include the results investigated earlier by
many authors, notably by Mainardi et al. (2001, 2005) for the fundamental
solution of the space-time fractional diffusion equation, and Saxena et al.
(2006a, b) for fractional reaction- diffusion equations. The advantage of using
Riesz-Feller derivative lies in the fact that the solution of the fractional
reaction-diffusion equation containing this derivative includes the fundamental
solution for space-time fractional diffusion, which itself is a generalization
of neutral fractional diffusion, space-fractional diffusion, and
time-fractional diffusion. These specialized types of diffusion can be
interpreted as spatial probability density functions evolving in time and are
expressible in terms of the H-functions in compact form.
| math.PR math.CA math.ST stat.TH |
0704.0330 | Random Matrix Theory at Nonzero $\mu$ and $T$ | We review applications of random matrix theory to QCD at nonzero temperature
and chemical potential. The chiral phase transition of QCD and QCD-like
theories is discussed in terms of eigenvalues of the Dirac operator. We show
that for QCD at $\mu \ne 0$, which has a sign problem, the discontinuity in the
chiral condensate is due to an alternative to the Banks-Casher relation. The
severity of the sign problem is analyzed in the microscopic domain of QCD.
| hep-ph |
0704.0331 | Symmetries by base substitutions in the genetic code predict 2' or 3'
aminoacylation of tRNAs | This letter reports complete sets of two-fold symmetries between partitions
of the universal genetic code. By substituting bases at each position of the
codons according to a fixed rule, it happens that properties of the degeneracy
pattern or of tRNA aminoacylation specificity are exchanged.
| q-bio.OT |
0704.0332 | The effect of a fifth large-scale space-time dimension on the
conservation of energy in a four dimensional Universe | The effect of introducing a fifth large-scale space-time dimension to the
equations of orbital dynamics was analysed in an earlier paper by the authors.
The results showed good agreement with the observed flat rotation curves of
galaxies and the Pioneer Anomaly. This analysis did not require the
modification of Newtonian dynamics, but rather only their restatement in a five
dimensional framework. The same analysis derived a acceleration parameter ar,
which plays an important role in the restated equations of orbital dynamics,
and suggested a value for ar. In this companion paper, the principle of
conservation of energy is restated within the same five-dimensional framework.
The resulting analysis provides an alternative route to estimating the value of
ar, without reference to the equations of orbital dynamics, and based solely on
key cosmological constants and parameters, including the gravitational
constant, G. The same analysis suggests that: (i) the inverse square law of
gravity may itself be due to the conservation of energy at the boundary between
a four-dimensional universe and a fifth large-scale space-time dimension; and
(ii) there is a limiting case for the Tulley-Fisher relationship linking the
speed of light to the mass of the Universe.
| gr-qc |
0704.0333 | Optical properties of the Holstein-t-J model from dynamical mean-field
theory | We employ dynamical mean-field theory to study the optical conductivity
$\sigma(\omega)$ of one hole in the Holstein-t-J model. We provide an exact
solution for $\sigma(\omega)$ in the limit of infinite connectivity. We apply
our analysis to Nd$_{2-x}$Ce$_x$CuO$_4$. We show that our model can explain
many features of the optical conductivity in this compounds in terms of
magnetic/lattice polaron formation.
| cond-mat.str-el |
0704.0334 | A Multiphilic Descriptor for Chemical Reactivity and Selectivity | In line with the local philicity concept proposed by Chattaraj et al.
(Chattaraj, P. K.; Maiti, B.; Sarkar, U. J. Phys. Chem. A. 2003, 107, 4973) and
a dual descriptor derived by Toro-Labbe and coworkers (Morell, C.; Grand, A.;
Toro-Labbe, A. J. Phys. Chem. A. 2005, 109, 205), we propose a multiphilic
descriptor. It is defined as the difference between nucleophilic (Wk+) and
electrophilic (Wk-) condensed philicity functions. This descriptor is capable
of simultaneously explaining the nucleophilicity and electrophilicity of the
given atomic sites in the molecule. Variation of these quantities along the
path of a soft reaction is also analyzed. Predictive ability of this descriptor
has been successfully tested on the selected systems and reactions.
Corresponding force profiles are also analyzed in some representative cases.
Also, to study the intra- and intermolecular reactivities another related
descriptor namely, the nucleophilicity excess (DelW-+) for a nucleophile, over
the electrophilicity in it has been defined and tested on all-metal aromatic
compounds.
| physics.chem-ph |
0704.0335 | Approximation of the distribution of a stationary Markov process with
application to option pricing | We build a sequence of empirical measures on the space D(R_+,R^d) of
R^d-valued c\`adl\`ag functions on R_+ in order to approximate the law of a
stationary R^d-valued Markov and Feller process (X_t). We obtain some general
results of convergence of this sequence. Then, we apply them to Brownian
diffusions and solutions to L\'evy driven SDE's under some Lyapunov-type
stability assumptions. As a numerical application of this work, we show that
this procedure gives an efficient way of option pricing in stochastic
volatility models.
| math.PR q-fin.CP q-fin.PR |
0704.0336 | Influence of Phonon dimensionality on Electron Energy Relaxation | We studied experimentally the role of phonon dimensionality on
electron-phonon (e-p) interaction in thin copper wires evaporated either on
suspended silicon nitride membranes or on bulk substrates, at sub-Kelvin
temperatures. The power emitted from electrons to phonons was measured using
sensitive normal metal-insulator-superconductor (NIS) tunnel junction
thermometers. Membrane thicknesses ranging from 30 nm to 750 nm were used to
clearly see the onset of the effects of two-dimensional (2D) phonon system. We
observed for the first time that a 2D phonon spectrum clearly changes the
temperature dependence and strength of the e-p scattering rate, with the
interaction becoming stronger at the lowest temperatures below $\sim$ 0.5 K for
the 30 nm membranes.
| cond-mat.mes-hall |
0704.0337 | Bursting Dynamics of the 3D Euler Equations in Cylindrical Domains | A class of three-dimensional initial data characterized by uniformly large
vorticity is considered for the Euler equations of incompressible fluids. The
fast singular oscillating limits of the Euler equations are studied for
parametrically resonant cylinders. Resonances of fast swirling Beltrami waves
deplete the Euler nonlinearity. The resonant Euler equations are systems of
three-dimensional rigid body equations, coupled or not. Some cases of these
resonant systems have homoclinic cycles, and orbits in the vicinity of these
homoclinic cycles lead to bursts of the Euler solution measured in Sobolev
norms of order higher than that corresponding to the enstrophy.
| math.AP |
0704.0338 | Synergistic Effects of MoDTC and ZDTP on Frictional Behaviour of
Tribofilms at the Nanometer Scale | The layered structure and the rheological properties of anti-wear films,
generated in a rolling/sliding contact from lubricants containing zinc
dialkyldithiophosphate (ZDTP) and/or molybdenum dialkyldithiocarbamate (MoDTC)
additives, have been studied by dynamic nanoindentation experiments coupled
with a simple modelling of the stiffness measurements. Local nano-friction
experiments were conducted with the same device in order to determine the
evolution of the friction coefficient as a function of the applied pressure for
the different lubricant formulations. For the MoDTC film, the applied pressure
in the friction test remains low (<0.5 GPa) and the apparent friction
coefficient is high ($\mu$ > 0.4). For the tribofilms containing MoDTC together
with ZDTP, which permits the applied pressure to increase up to a few GPa
through some accommodation process, a very low friction domain appears (0.01 <
$\mu$ < 0.05), located a few nanometers below the surface of the tribofilm.
This low friction coefficient is attributed to the presence of MoS2 planes
sliding over each other in a favourable configuration obtained when the
pressure is sufficiently high, which is made possible by the presence of ZDTP.
| cond-mat.mtrl-sci |
0704.0339 | Lattice Boltzmann inverse kinetic approach for the incompressible
Navier-Stokes equations | In spite of the large number of papers appeared in the past which are devoted
to the lattice Boltzmann (LB) methods, basic aspects of the theory still remain
unchallenged. An unsolved theoretical issue is related to the construction of a
discrete kinetic theory which yields \textit{exactly} the fluid equations,
i.e., is non-asymptotic (here denoted as \textit{LB inverse kinetic theory}).
The purpose of this paper is theoretical and aims at developing an inverse
kinetic approach of this type. In principle infinite solutions exist to this
problem but the freedom can be exploited in order to meet important
requirements. In particular, the discrete kinetic theory can be defined so that
it yields exactly the fluid equation also for arbitrary non-equilibrium (but
suitably smooth) kinetic distribution functions and arbitrarily close to the
boundary of the fluid domain. Unlike previous entropic LB methods the theorem
can be obtained without functional constraints on the class of the initial
distribution functions. Possible realizations of the theory and asymptotic
approximations are provided which permit to determine the fluid equations
\textit{with prescribed accuracy.} As a result, asymptotic accuracy estimates
of customary LB approaches and comparisons with the Chorin artificial
compressibility method are discussed.
| physics.flu-dyn physics.comp-ph |
0704.0340 | Phonon-mediated decay of an atom in a surface-induced potential | We study phonon-mediated transitions between translational levels of an atom
in a surface-induced potential. We present a general master equation governing
the dynamics of the translational states of the atom. In the framework of the
Debye model, we derive compact expressions for the rates for both upward and
downward transitions. Numerical calculations for the transition rates are
performed for a deep silica-induced potential allowing for a large number of
bound levels as well as free states of a cesium atom. The total absorption rate
is shown to be determined mainly by the bound-to-bound transitions for deep
bound levels and by bound-to-free transitions for shallow bound levels.
Moreover, the phonon emission and absorption processes can be orders of
magnitude larger for deep bound levels as compared to the shallow bound ones.
We also study various types of transitions from free states. We show that, for
thermal atomic cesium with temperature in the range from 100 $\mu$K to 400
$\mu$K in the vicinity of a silica surface with temperature of 300 K, the
adsorption (free-to-bound decay) rate is about two times larger than the
heating (free-to-free upward decay) rate, while the cooling (free-to-free
downward decay) rate is negligible.
| quant-ph |
0704.0341 | Infrared Evolution Equations: Method and Applications | It is a brief review on composing and solving Infrared Evolution Equations.
They can be used in order to calculate amplitudes of high-energy reactions in
different kinematic regions in the double-logarithmic approximation.
| hep-ph |
0704.0342 | Cofibrations in the Category of Frolicher Spaces. Part I | Cofibrations are defined in the category of Fr\"olicher spaces by weakening
the analog of the classical definition to enable smooth homotopy extensions to
be more easily constructed, using flattened unit intervals. We later relate
smooth cofibrations to smooth neighborhood deformation retracts. The notion of
smooth neighborhood deformation retract gives rise to an analogous result that
a closed Fr\"olicher subspace $A$ of the Fr\"olicher space $X$ is a smooth
neighborhood deformation retract of $X$ if and only if the inclusion $i:
A\hookrightarrow X$ comes from a certain subclass of cofibrations. As an
application we construct the right Puppe sequence.
| math.AT |
0704.0343 | Experimental observation of structural crossover in binary mixtures of
colloidal hard spheres | Using confocal-microscopy we investigate the structure of binary mixtures of
colloidal hard spheres with size ratio q=0.61. As a function of the packing
fraction of the two particle species, we observe a marked change of the
dominant wavelength in the pair correlation function. This behavior is in
excellent agreement with a recently predicted structural crossover in such
mixtures. In addition, the repercussions of structural crossover on the
real-space structure of a binary fluid are analyzed. We suggest a relation
between crossover and the lateral extension of networks containing only equally
sized particles that are connected by nearest neighbor bonds. This is supported
by Monte-Carlo simulations which are performed at different packing fractions
and size ratios.
| cond-mat.soft cond-mat.dis-nn |
0704.0344 | The Blazar Spectral Sequence and GLAST | The present status and understanding of the "spectral sequence" of blazars is
discussed in the perspective of the upcoming GLAST launch. The vast improvement
in sensitivity will allow to i) determine more objectively the "average"
gamma-ray properties of classes objects ii) probe more deeply the ratio between
accretion power and jet power in different systems.
| astro-ph |
0704.0345 | A High Robustness and Low Cost Model for Cascading Failures | We study numerically the cascading failure problem by using artificially
created scale-free networks and the real network structure of the power grid.
The capacity for a vertex is assigned as a monotonically increasing function of
the load (or the betweenness centrality). Through the use of a simple
functional form with two free parameters, revealed is that it is indeed
possible to make networks more robust while spending less cost. We suggest that
our method to prevent cascade by protecting less vertices is particularly
important for the design of more robust real-world networks to cascading
failures.
| physics.soc-ph |
0704.0346 | Diffuse X-ray Emission from the Carina Nebula Observed with Suzaku | A number of giant HII regions are associated with soft diffuse X-ray
emission. Among these, the Carina nebula possesses the brightest soft diffuse
emission. The required plasma temperature and thermal energy can be produced by
collisions or termination of fast winds from main-sequence or embedded young O
stars, but the extended emission is often observed from regions apart from
massive stellar clusters. The origin of the X-ray emission is unknown.
The XIS CCD camera onboard Suzaku has the best spectral resolution for
extended soft sources so far, and is therefore capable of measuring key
emission lines in the soft band. Suzaku observed the core and the eastern side
of the Carina nebula (Car-D1) in 2005 Aug and 2006 June, respectively. Spectra
of the south part of the core and Car-D1 similarly showed strong L-shell lines
of iron ions and K-shell lines of silicon ions, while in the north of the core
these lines were much weaker. Fitting the spectra with an absorbed thin-thermal
plasma model showed kT~0.2, 0.6 keV and NH~1-2e21 cm-2 with a factor of 2-3
abundance variation in oxygen, magnesium, silicon and iron. The plasma might
originate from an old supernova, or a super shell of multiple supernovae.
| astro-ph |
0704.0347 | Resolvent estimates related with a class of dispersive equations | We present a simple proof of the resolvent estimates of elliptic Fourier
multipliers on the Euclidean space, and apply them to the analysis of
time-global and spatially-local smoothing estimates of a class of dispersive
equations. For this purpose we study in detail the properties of the
restriction of Fourier transform on the unit cotangent sphere associated with
the symbols of multipliers.
| math.AP math.CA |
0704.0348 | What can emission lines tell us? | 1 Generalities
2 Empirical diagnostics based on emission lines
3 Photoionization modelling
4 Pending questions
5 Appendix: Lists of useful lines and how to deal with them
| astro-ph |
0704.0349 | The Colin de Verdi\`ere number and graphs of polytopes | The Colin de Verdi\`ere number $\mu(G)$ of a graph $G$ is the maximum corank
of a Colin de Verdi\`ere matrix for $G$ (that is, of a Schr\"odinger operator
on $G$ with a single negative eigenvalue). In 2001, Lov\'asz gave a
construction that associated to every convex 3-polytope a Colin de Verdi\`ere
matrix of corank 3 for its 1-skeleton.
We generalize the Lov\'asz construction to higher dimensions by interpreting
it as minus the Hessian matrix of the volume of the polar dual. As a corollary,
$\mu(G) \ge d$ if $G$ is the 1-skeleton of a convex $d$-polytope.
Determination of the signature of the Hessian of the volume is based on the
second Minkowski inequality for mixed volumes and on Bol's condition for
equality.
| math.CO math.MG |
0704.0350 | Visible spectroscopic and photometric survey of Jupiter Trojans: final
results on dynamical families | We present the results of a visible spectroscopic and photometric survey of
Jupiter Trojans belonging to different dynamical families carried out at the
ESO-NTT telescope. We obtained data on 47 objects, 23 belonging to the L5 swarm
and 24 to the L4 one. These data together with those already published by
Fornasier et al. (2004a) and Dotto et al. (2006), constitute a total sample of
visible spectra for 80 objects. The survey allows us to investigate six
families (Aneas, Anchises, Misenus, Phereclos, Sarpedon, Panthoos) in the L5
cloud and four L4 families (Eurybates, Menelaus, 1986 WD and 1986 TS6). The
sample that we measured is dominated by D--type asteroids, with the exception
of the Eurybates family in the L4 swarm, where there is a dominance of C- and
P-type asteroids. All the spectra that we obtained are featureless with the
exception of some Eurybates members, where a drop--off of the reflectance is
detected shortward of 5200 A. Similar features are seen in main belt C-type
asteroids and commonly attributed to the intervalence charge transfer
transition in oxidized iron. Our sample comprises fainter and smaller Trojans
as compared to the literature's data and allows us to investigate the
properties of objects with estimated diameter smaller than 40--50 km. The
analysis of the spectral slopes and colors versus the estimated diameters shows
that the blue and red objects have indistinguishable size distribution. We
perform a statistical investigation of the Trojans's spectra property
distributions as a function of their orbital and physical parameters, and in
comparison with other classes of minor bodies in the outer Solar System.
Trojans at lower inclination appear significantly bluer than those at higher
inclination, but this effect is strongly driven by the Eurybates family.
| astro-ph |
0704.0351 | FIRST-based survey of Compact Steep Spectrum sources, V.
Milliarcsecond-scale morphology of CSS objects | Multifrequency VLBA observations of the final group of ten objects in a
sample of FIRST-based compact steep spectrum (CSS) sources are presented. The
sample was selected to investigate whether objects of this kind could be relics
of radio-loud AGNs switched off at very early stages of their evolution or
possibly to indicate intermittent activity. Initial observations were made
using MERLIN at 5 GHz. The sources have now been observed with the VLBA at 1.7,
5 and 8.4 GHz in a snapshot mode with phase-referencing. The resulting maps are
presented along with unpublished 8.4-GHz VLA images of five sources. Some of
the sources discussed here show a complex radio morphology and therefore a
complicated past that, in some cases, might indicate intermittent activity. One
of the sources studied - 1045+352 - is known as a powerful radio and
infrared-luminous broad absorption line (BAL) quasar. It is a young CSS object
whose asymmetric two-sided morphology on a scale of several hundred parsecs,
extending in two different directions, may suggest intermittent activity. The
young age and compact structure of 1045+352 is consistent with the evolution
scenario of BAL quasars. It has also been confirmed that the submillimetre flux
of 1045+352 can be seriously contaminated by synchrotron emission.
| astro-ph |
0704.0352 | Investigation of relaxation phenomena in high-temperature
superconductors HoBa2Cu3O7-d at the action of pulsed magnetic fields | It is used the mechanical method of Abrikosov vortex stimulated dynamics
investigation in superconductors. With its help it was studied relaxation
phenomena in vortex matter of high-temperature superconductors. It established
that pulsed magnetic fields change the course of relaxation processes taking
place in vortex matter. The study of the influence of magnetic pulses differing
by their durations and amplitudes on vortex system of isotropic
high-temperature superconductors system HoBa2Cu3O7-d showed the presence of
threshold phenomena. The small duration pulses does not change the course of
relaxation processes taking place in vortex matter. When the duration of pulses
exceeds some critical value (threshold), then their influence change the course
of relaxation process which is revealed by stepwise change of relaxing
mechanical moment . These investigations showed that the time for formatting of
Abrikosov vortex lattice in HoBa2Cu3O7-d is of the order of 20 microsec. which
on the order of value exceeds the time necessary for formation of a single
vortex observed in type II superconductors.
| cond-mat.soft cond-mat.supr-con |
0704.0353 | Spin and pseudospin symmetries and the equivalent spectra of
relativistic spin-1/2 and spin-0 particles | We show that the conditions which originate the spin and pseudospin
symmetries in the Dirac equation are the same that produce equivalent energy
spectra of relativistic spin-1/2 and spin-0 particles in the presence of vector
and scalar potentials. The conclusions do not depend on the particular shapes
of the potentials and can be important in different fields of physics. When
both scalar and vector potentials are spherical, these conditions for
isospectrality imply that the spin-orbit and Darwin terms of either the upper
component or the lower component of the Dirac spinor vanish, making it
equivalent, as far as energy is concerned, to a spin-0 state. In this case,
besides energy, a scalar particle will also have the same orbital angular
momentum as the (conserved) orbital angular momentum of either the upper or
lower component of the corresponding spin-1/2 particle. We point out a few
possible applications of this result.
| nucl-th quant-ph |
0704.0354 | General asymptotic solutions of the Einstein equations and phase
transitions in quantum gravity | We discuss generic properties of classical and quantum theories of gravity
with a scalar field which are revealed at the vicinity of the cosmological
singularity. When the potential of the scalar field is exponential and
unbounded from below, the general solution of the Einstein equations has
quasi-isotropic asymptotics near the singularity instead of the usual
anisotropic Belinskii - Khalatnikov - Lifshitz (BKL) asymptotics. Depending on
the strength of scalar field potential, there exist two phases of quantum
gravity with scalar field: one with essentially anisotropic behavior of field
correlation functions near the cosmological singularity, and another with
quasi-isotropic behavior. The ``phase transition'' between the two phases is
interpreted as the condensation of gravitons.
| hep-th gr-qc |
0704.0355 | Trigonometric parallaxes of high velocity halo white dwarf candidates | The status of 38 halo white dwarf candidates identified by Oppenheimer et al.
(2001) has been intensively discussed by various authors. In analyses
undertaken to date, trigonometric parallaxes are crucial missing data. Distance
measurements are mandatory to kinematically segregate halo object from disk
objects and hence enable a more reliable estimate of the local density of halo
dark matter residing in such objects.
We present trigonometric parallax measurements for 15 candidate halo white
dwarfs (WDs) selected from the Oppenheimer et al. (2001) list. We observed the
stars using the ESO 1.56-m Danish Telescope and ESO 2.2-m telescope from August
2001 to July 2004. Parallaxes with accuracies of 1--2 mas were determined
yielding relative errors on distances of $\sim5$% for 6 objects, $\sim12$% for
3 objects, and $\sim20$% for two more objects. Four stars appear to be too
distant (probably farther than 100 pc) to have measurable parallaxes in our
observations. Distances, absolute magnitudes and revised space velocities were
derived for the 15 halo WDs from the Oppenheimer et al. (2001) list. Halo
membership is confirmed unambiguously for 6 objects while 5 objects may be
thick disk members and 4 objects are too distant to draw any conclusion based
solely on kinematics. Comparing our trigonometric parallaxes with photometric
parallaxes used in previous work reveals an overestimation of distance as
derived from photometric techniques. This new data set can be used to revise
the halo white dwarf space density, and that analysis will be presented in a
subsequent publication.
| astro-ph |
0704.0356 | AMR simulations of the low T/|W| bar-mode instability of neutron stars | It has been recently argued through numerical work that rotating stars with a
high degree of differential rotation are dynamically unstable against bar-mode
deformation, even for values of the ratio of rotational kinetic energy to
gravitational potential energy as low as O(0.01). This may have implications
for gravitational wave astronomy in high-frequency sources such as core
collapse supernovae. In this paper we present high-resolution simulations,
performed with an adaptive mesh refinement hydrodynamics code, of such low
T/|W| bar-mode instability. The complex morphological features involved in the
nonlinear dynamics of the instability are revealed in our simulations, which
show that the excitation of Kelvin-Helmholtz-like fluid modes outside the
corotation radius of the star leads to the saturation of the bar-mode
deformation. While the overall trends reported in an earlier investigation are
confirmed by our work, we also find that numerical resolution plays an
important role during the long-term, nonlinear behaviour of the instability,
which has implications on the dynamics of rotating stars and on the attainable
amplitudes of the associated gravitational wave signals.
| astro-ph |
0704.0357 | Evolutionary games on minimally structured populations | Population structure induced by both spatial embedding and more general
networks of interaction, such as model social networks, have been shown to have
a fundamental effect on the dynamics and outcome of evolutionary games. These
effects have, however, proved to be sensitive to the details of the underlying
topology and dynamics. Here we introduce a minimal population structure that is
described by two distinct hierarchical levels of interaction. We believe this
model is able to identify effects of spatial structure that do not depend on
the details of the topology. We derive the dynamics governing the evolution of
a system starting from fundamental individual level stochastic processes
through two successive meanfield approximations. In our model of population
structure the topology of interactions is described by only two parameters: the
effective population size at the local scale and the relative strength of local
dynamics to global mixing. We demonstrate, for example, the existence of a
continuous transition leading to the dominance of cooperation in populations
with hierarchical levels of unstructured mixing as the benefit to cost ratio
becomes smaller then the local population size. Applying our model of spatial
structure to the repeated prisoner's dilemma we uncover a novel and
counterintuitive mechanism by which the constant influx of defectors sustains
cooperation. Further exploring the phase space of the repeated prisoner's
dilemma and also of the "rock-paper-scissor" game we find indications of rich
structure and are able to reproduce several effects observed in other models
with explicit spatial embedding, such as the maintenance of biodiversity and
the emergence of global oscillations.
| q-bio.PE q-bio.OT |
0704.0358 | Flavor Physics in SUSY at large tan(beta) | We discuss the phenomenological impact of a particularly interesting corner
of the MSSM: the large tan(beta) regime. The capabilities of leptonic and
hadronic Flavor Violating processes in shedding light on physics beyond the
Standard Model are reviewed. Moreover, we show that tests of Lepton
Universality in charged current processes can represent an interesting handle
to obtain relevant information on New Physics scenarios.
| hep-ph |
0704.0359 | Some properties of the complex Monge-Ampere operator in Cegrell's
classes and applications | In this article we will first prove a result about convergence in capacity.
Using the achieved result we will obtain a general decompositon theorem for
complex Monge-Ampere measues which will be used to prove a comparison principle
for the complex Monge-Ampere operator.
| math.CV |
0704.0360 | Torsional oscillations of longitudinally inhomogeneous coronal loops | We explore the effect of an inhomogeneous mass density field on frequencies
and wave profiles of torsional Alfven oscillations in solar coronal loops.
Dispersion relations for torsional oscillations are derived analytically in
limits of weak and strong inhomogeneities. These analytical results are
verified by numerical solutions, which are valid for a wide range of
inhomogeneity strength. It is shown that the inhomogeneous mass density field
leads to the reduction of a wave frequency of torsional oscillations, in
comparison to that of estimated from mass density at the loop apex. This
frequency reduction results from the decrease of an average Alfven speed as far
as the inhomogeneous loop is denser at its footpoints. The derived dispersion
relations and wave profiles are important for potential observations of
torsional oscillations which result in periodic variations of spectral line
widths. Torsional oscillations offer an additional powerful tool for a
development of coronal seismology.
| astro-ph |
0704.0361 | Pseudo-random Puncturing: A Technique to Lower the Error Floor of Turbo
Codes | It has been observed that particular rate-1/2 partially systematic parallel
concatenated convolutional codes (PCCCs) can achieve a lower error floor than
that of their rate-1/3 parent codes. Nevertheless, good puncturing patterns can
only be identified by means of an exhaustive search, whilst convergence towards
low bit error probabilities can be problematic when the systematic output of a
rate-1/2 partially systematic PCCC is heavily punctured. In this paper, we
present and study a family of rate-1/2 partially systematic PCCCs, which we
call pseudo-randomly punctured codes. We evaluate their bit error rate
performance and we show that they always yield a lower error floor than that of
their rate-1/3 parent codes. Furthermore, we compare analytic results to
simulations and we demonstrate that their performance converges towards the
error floor region, owning to the moderate puncturing of their systematic
output. Consequently, we propose pseudo-random puncturing as a means of
improving the bandwidth efficiency of a PCCC and simultaneously lowering its
error floor.
| cs.IT math.IT |
0704.0362 | The Arctic Circle Revisited | The problem of limit shapes in the six-vertex model with domain wall boundary
conditions is addressed by considering a specially tailored bulk correlation
function, the emptiness formation probability. A closed expression of this
correlation function is given, both in terms of certain determinant and
multiple integral, which allows for a systematic treatment of the limit shapes
of the model for full range of values of vertex weights. Specifically, we show
that for vertex weights corresponding to the free-fermion line on the phase
diagram, the emptiness formation probability is related to a one-matrix model
with a triple logarithmic singularity, or Triple Penner model. The saddle-point
analysis of this model leads to the Arctic Circle Theorem, and its
generalization to the Arctic Ellipses, known previously from domino tilings.
| math-ph hep-th math.MP |
0704.0363 | Time and motion in physics: the Reciprocity Principle, relativistic
invariance of the lengths of rulers and time dilatation | Ponderable objects moving in free space according to Newton's First Law
constitute both rulers and clocks when one such object is viewed from the rest
frame of another. Together with the Reciprocity Principle this is used to
demonstrate, in both Galilean and special relativity, the invariance of the
measured length of a ruler in motion. The different times: `proper', `improper'
and `apparent' appearing in different formulations of the relativistic time
dilatation relation are discussed and exemplified by experimental applications.
A non-intuitive `length expansion' effect predicted by the Reciprocity
Principle as a necessary consequence of time dilatation is pointed out
| physics.gen-ph |
0704.0364 | B --> rho K* decays and other rare vector-vector modes | The recent analyses of the following rare vector-vector decays of the B meson
are presented: rho K*, omega K*, omega rho, omega omega, and omega phi
charmless final states. The latest results indicate that the fraction of
longitudinal polarization is about 0.5 in penguin-dominated modes and close to
1 for tree-dominated modes.
| hep-ex |
0704.0365 | Extending the theory of phonon-mediated superconductivity in quasi-2D | I present results from an extended Migdal-Eliashberg theory of
electron-phonon interactions and superconductivity. The history of the
electron-phonon problem is introduced, and then study of the intermediate
parameter regime is justified from the energy scales in the cuprate
superconductors. The Holstein model is detailed, and limiting cases are
examined to demonstrate the need for an extended theory of superconductivity.
Results of the extended approximation are shown, including spectral functions
and phase diagrams. These are discussed with reference to Hohenberg's theorem,
the Bardeen-Cooper-Schrieffer theory and Coulomb repulsion.
| cond-mat.supr-con cond-mat.str-el |
0704.0366 | Generalized Nariai Solutions for Yang-type Monopoles | A detailed study of the geometries that emerge by a gravitating generalized
Yang monopole in even dimensions is carried out. In particular, those which
present black hole and cosmological horizons. This two-horizon system is
thermally unstable. The process of thermalization will drive both horizons to
coalesce. This limit is what is profusely studied in this paper. It is shown
that eventhough coordinate distance shrinks to zero, physical distance does
not. So, there is some remaining space which geometry has been computed and
identified as a generalized Nariai solution. The thermal properties of this new
spacetime are then calculated. Topics, as the elliptical relation between radii
of spheres in the geometry or a discussion about whether a mass-type term
should be present in the line element or not, are also included.
| gr-qc hep-th |
0704.0367 | Instanton representation of Plebanski gravity. Consistency of the
initital value constraints under time evolution | The instanton representation of Plebanski gravity provides as equations of
motion a Hodge self-duality condition and a set of `generalized' Maxwell's
equations, subject to gravitational degrees of freedom encoded in the initial
value constraints of general relativity. The main result of the present paper
will be to prove that this constraint surface is preserved under time
evolution. We carry this out not using the usual Dirac procedure, but rather
the Lagrangian equations of motion themsleves. Finally, we provide a comparison
with the Ashtekar formulation to place these results into overall context.
| gr-qc |
0704.0368 | Metal-insulator transition in the low-dimensional organic conductor
(TMTSF)2FSO3 probed by infrared microspectroscopy | We present measurements of the infrared response of the quasi-one-dimensional
organic conductor (TMTSF)2$SO3 along (E||a) and perpendicular (E||b') to the
stacking axis as a function of temperature. Above the metal-insulator
transition related to the anion ordering the optical conductivity spectra show
a Drude-like response. Below the transition an energy gap of about 1500 cm-1
(185 meV) opens, leading to the corresponding charge transfer band in the
optical conductivity spectra. The analysis of the infrared-active vibrations
gives evidence for the long-range crystal structure modulation below the
transition temperature and for the short-range order fluctuations of the
lattice modulation above the transition temperature. Also we report about a new
infrared mode at around 710 cm-1 with a peculiar temperature behavior, which
has so far not been observed in any other (TMTSF)2X salt showing a
metal-insulator transition. A qualitative model based on the coupling between
the TMTSF molecule vibration and the reorientation of electrical dipole moment
of the FSO3 anion is proposed, in order to explain the anomalous behavior of
the new mode.
| cond-mat.str-el |
0704.0369 | The effect of Topcolor Assisted Technicolor, and other models, on
Neutrino Oscillation | New physics beyond the Standard Model can lead to extra matter effects on
neutrino oscillation if the new interactions distinguish among the three
flavors of neutrino. In Ref.1, we argued that a long-baseline neutrino
oscillation experiment in which the Fermilab-NUMI beam in its high-energy mode
is aimed at the planned Hyper-Kamiokande detector would be capable of
constraining the size of those extra matter effects, provided the vacuum value
of \sin^2 2\theta_{23} is not too close to one. In this talk, we discuss how
such a constraint would translate into limits on the coupling constants and
masses of new particles in models such as topcolor assisted technicolor.
| hep-ph |
0704.0370 | Shaped angular dependence of the spin transfer torque and microwave
generation without magnetic field | The generation of oscillations in the microwave frequency range is one of the
most important applications expected from spintronics devices exploiting the
spin transfer phenomenon. We report transport and microwave power measurements
on specially designed nanopillars for which a non-standard angular dependence
of the spin transfer torque (wavy variation) is predicted by theoretical
models. We observe a new kind of current-induced dynamics that is characterized
by large angle precessions in the absence of any applied field, as this is also
predicted by simulation with such a wavy angular dependence of the torque. This
type of non-standard nanopillars can represent an interesting way for the
implementation of spin transfer oscillators since they are able to generate
microwave oscillations without applied magnetic field. We also emphasize the
theoretical implications of our results on the angular dependence of the
torque.
| cond-mat.mtrl-sci |
0704.0371 | Dark energy interacting with neutrinos and dark matter: a
phenomenological theory | A model for a flat homogeneous and isotropic Universe composed of dark
energy, dark matter, neutrinos, radiation and baryons is analyzed. The fields
of dark matter and neutrinos are supposed to interact with the dark energy. The
dark energy is considered to obey either the van der Waals or the Chaplygin
equations of state. The ratio between the pressure and the energy density of
the neutrinos varies with the red-shift simulating massive and non-relativistic
neutrinos at small red-shifts and non-massive relativistic neutrinos at high
red-shifts. The model can reproduce the expected red-shift behaviors of the
deceleration parameter and of the density parameters of each constituent.
| gr-qc |
0704.0372 | Levy-Lieb constrained-search formulation as a minimization of the
correlation functional | The constrained-search formulation of Levy and Lieb, which formally defines
the exact Hohenberg-Kohn functional for any N-representable electron density,
is here shown to be equivalent to the minimization of the correlation
functional with respect to the N-1 conditional probability density, where N is
number of electrons of the system. The consequences and implications of such a
result are here analyzed and discussed via a practical example.
| quant-ph |
0704.0373 | Reality of linear and angular momentum expectation values in bound
states | In quantum mechanics textbooks the momentum operator is defined in the
Cartesian coordinates and rarely the form of the momentum operator in spherical
polar coordinates is discussed. Consequently one always generalizes the
Cartesian prescription to other coordinates and falls in a trap. In this work
we introduce the difficulties one faces when the question of the momentum
operator in spherical polar coordinate comes. We have tried to point out most
of the elementary quantum mechanical results, related to the momentum operator,
which has coordinate dependence. We explicitly calculate the momentum
expectation values in various bound states and show that the expectation value
really turns out to be zero, a consequence of the fact that the momentum
expectation value is real. We comment briefly on the status of the angular
variables in quantum mechanics and the problems related in interpreting them as
dynamical variables. At the end, we calculate the Heisenberg's equation of
motion for the radial component of the momentum for the Hydrogen atom.
| quant-ph hep-th |
0704.0374 | Gravity-induced electric polarization of matter and planetary magnetic
fields | This paper has been withdrawn due to copyright reasons.
| physics.geo-ph |
0704.0375 | Rich methane premixed laminar flames doped by light unsaturated
hydrocarbons - Part I : allene and propyne | The structure of three laminar premixed rich flames has been investigated: a
pure methane flame and two methane flames doped by allene and propyne,
respectively. The gases of the three flames contain 20.9% (molar) of methane
and 33.4% of oxygen, corresponding to an equivalence ratio of 1.25 for the pure
methane flame. In both doped flames, 2.49% of C3H4 was added, corresponding to
a ratio C3H4/CH4 of 12% and an equivalence ratio of 1.55. The three flames have
been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant,
with a gas velocity at the burner of 36 cm/s at 333 K. The concentration
profiles of stable species were measured by gas chromatography after sampling
with a quartz microprobe. Quantified species included carbon monoxide and
dioxide, methane, oxygen, hydrogen, ethane, ethylene, acetylene, propyne,
allene, propene, propane, 1,2-butadiene, 1,3-butadiene, 1-butene, isobutene,
1-butyne, vinylacetylene, and benzene. The temperature was measured using a
PtRh (6%)-PtRh (30%) thermocouple settled inside the enclosure and ranged from
700 K close to the burner up to 1850 K. In order to model these new results,
some improvements have been made to a mechanism previously developed in our
laboratory for the reactions of C3-C4 unsaturated hydrocarbons. The main
reaction pathways of consumption of allene and propyne and of formation of C6
aromatic species have been derived from flow rate analyses.
| physics.chem-ph |
0704.0376 | Environmental noise reduction for holonomic quantum gates | We study the performance of holonomic quantum gates, driven by lasers, under
the effect of a dissipative environment modeled as a thermal bath of
oscillators. We show how to enhance the performance of the gates by suitable
choice of the loop in the manifold of the controllable parameters of the laser.
For a simplified, albeit realistic model, we find the surprising result that
for a long time evolution the performance of the gate (properly estimated in
terms of average fidelity) increases. On the basis of this result, we compare
holonomic gates with the so-called stimulated Raman adiabatic passage (STIRAP)
gates.
| quant-ph cond-mat.mes-hall |
0704.0377 | The lifetime of unstable particles in electromagnetic fields | We show that the electromagnetic moments of unstable particles (resonances)
have an absorptive contribution which quantifies the change of the particle's
lifetime in an external electromagnetic field. To give an example we compute
here the imaginary part of the magnetic moment for the cases of the muon and
the neutron at leading order in the electroweak coupling. We also consider an
analogous effect for the strongly-decaying $\Delta$(1232) resonance. The result
for the muon is Im$ \mu = e G_F^2 m^3/768 \pi^3$, with $e$ the charge and $m$
the mass of the muon, $G_F$ the Fermi constant, which in an external magnetic
field of $B$ Tesla give rise to the relative change in the muon lifetime of
$3\times 10^{-15} B$. For neutron the effect is of a similar magnitude. We
speculate on the observable implications of this effect.
| hep-ph hep-th nucl-th |
0704.0378 | An equilibrium problem for the limiting eigenvalue distribution of
banded Toeplitz matrices | We study the limiting eigenvalue distribution of $n\times n$ banded Toeplitz
matrices as $n\to \infty$. From classical results of Schmidt-Spitzer and
Hirschman it is known that the eigenvalues accumulate on a special curve in the
complex plane and the normalized eigenvalue counting measure converges weakly
to a measure on this curve as $n\to\infty$. In this paper, we characterize the
limiting measure in terms of an equilibrium problem. The limiting measure is
one component of the unique vector of measures that minimes an energy
functional defined on admissible vectors of measures. In addition, we show that
each of the other components is the limiting measure of the normalized counting
measure on certain generalized eigenvalues.
| math.CV math.CA |
0704.0379 | Capturing knots in polymers | This paper visualizes a knot reduction algorithm
| cond-mat.soft cond-mat.stat-mech |
0704.0380 | Exponential growth rates in a typed branching diffusion | We study the high temperature phase of a family of typed branching diffusions
initially studied in [Ast\'{e}risque 236 (1996) 133--154] and [Lecture Notes in
Math. 1729 (2000) 239--256 Springer, Berlin]. The primary aim is to establish
some almost-sure limit results for the long-term behavior of this particle
system, namely the speed at which the population of particles colonizes both
space and type dimensions, as well as the rate at which the population grows
within this asymptotic shape. Our approach will include identification of an
explicit two-phase mechanism by which particles can build up in sufficient
numbers with spatial positions near $-\gamma t$ and type positions near $\kappa
\sqrt{t}$ at large times $t$. The proofs involve the application of a variety
of martingale techniques--most importantly a ``spine'' construction involving a
change of measure with an additive martingale. In addition to the model's
intrinsic interest, the methodologies presented contain ideas that will adapt
to other branching settings. We also briefly discuss applications to traveling
wave solutions of an associated reaction--diffusion equation.
| math.PR |
0704.0381 | The collision velocity of the bullet cluster in conventional and
modified dynamics | We consider the orbit of the bullet cluster 1E 0657-56 in both CDM and MOND
using accurate mass models appropriate to each case in order to ascertain the
maximum plausible collision velocity. Impact velocities consistent with the
shock velocity (~ 4700km/s) occur naturally in MOND. CDM can generate collision
velocities of at most ~ 3800km/s, and is only consistent with the data provided
that the shock velocity has been substantially enhanced by hydrodynamical
effects.
| astro-ph |
0704.0382 | On Some Subgroup Chains Related to Kneser's Theorem | A recent result of Balandraud shows that for every subset S of an abelian
group G, there exists a non trivial subgroup H such that |TS| <= |T|+|S|-2
holds only if the stabilizer of TS contains H. Notice that Kneser's Theorem
says only that the stabilizer of TS must be a non-zero subgroup.
This strong form of Kneser's theorem follows from some nice properties of a
certain poset investigated by Balandraud. We consider an analogous poset for
nonabelian groups and, by using classical tools from Additive Number Theory,
extend some of the above results. In particular we obtain short proofs of
Balandraud's results in the abelian case.
| math.NT |
0704.0383 | The Exact Boundary Condition to Solve the Schrodinger Equation of Many
Electron System | In an attempt to bypass the sign problem in quantum Monte Carlo simulation of
electronic systems within the framework of fixed node approach, we derive the
exclusion principle "Two electrons can't be at the same external isopotential
surface simultaneously" using the first postulate of quantum mechanics. We
propose the exact Coulomb-Exchange nodal surface i.e. the exact boundary
condition to solve the non-relativistic Schrodinger equation for the
non-degenerate ground state of atoms and molecules. This boundary condition was
applied to compute the ground state energies of N, Ne, Li2, Be2, B2, C2, N2,
O2, F2, and H2O systems using diffusion Monte Carlo method. The ground state
energies thus obtained agree well with the exact estimate of non-relativistic
energies.
| cond-mat.str-el |
0704.0384 | Clustering features of $^9$Be, $^{14}$N, $^7$Be, and $^8$B nuclei in
relativistic fragmentation | Recent studies of clustering in light nuclei with an initial energy above 1 A
GeV in nuclear treack emulsion are overviewed. The results of investigations of
the relativistic $^9$Be nuclei fragmentation in emulsion, which entails the
production of He fragments, are presented. It is shown that most precise
angular measurements provided by this technique play a crucial role in the
restoration of the excitation spectrum of the $\alpha$ particle sysytem. In
peripheral interactions $^9$Be nuclei are dissociated practically totally
through the 0$^+$ and 2$^+$ states of the $^8$Be nucleus.
The results of investigations of the dissociation of a $^{14}$N nucleus of
momentum 2.86 A GeV/c in emulsion are presented as example of more complicated
system. The momentum and correlation characteristics of $\alpha$ particles for
the $^{14}$N$\to3\alpha+X$ channel in the laboratory system and the rest
systems of 3$\alpha$ particles were considered in detail.
Topology of charged fragments produced in peripheral relativistic
dissociation of radioactive $^8$B, $^7$Be nuclei in emulsion is studied.
| nucl-ex |
0704.0385 | Super-shell structures and pairing in ultracold trapped Fermi gases | We calculate level densities and pairing gaps for an ultracold dilute gas of
fermionic atoms in harmonic traps under the influence of mean field and
anharmonic quartic trap potentials. Super-shell structures, which were found in
Hartree-Fock calculations, are calculated analytically within periodic orbit
theory as well as from WKB calculations. For attractive interactions, the
underlying level densities are crucial for pairing and super-shell structures
in gaps are predicted.
| cond-mat.other |
0704.0386 | Quantum non-local effects with Bose-Einstein condensates | We study theoretically the properties of two Bose-Einstein condensates in
different spin states, represented by a double Fock state. Individual
measurements of the spins of the particles are performed in transverse
directions, giving access to the relative phase of the condensates. Initially,
this phase is completely undefined, and the first measurements provide random
results. But a fixed value of this phase rapidly emerges under the effect of
the successive quantum measurements, giving rise to a quasi-classical situation
where all spins have parallel transverse orientations. If the number of
measurements reaches its maximum (the number of particles), quantum effects
show up again, giving rise to violations of Bell type inequalities. The
violation of BCHSH inequalities with an arbitrarily large number of spins may
be comparable (or even equal) to that obtained with two spins.
| quant-ph cond-mat.other |
0704.0387 | Low mass visual binaries in the solar neighbourhood: The case of
HD141272 | We search for stellar and substellar companions of young nearby stars to
investigate stellar multiplicity and formation of stellar and substellar
companions. We detect common proper-motion companions of stars via multi-epoch
imaging. Their companionship is finally confirmed with photometry and
spectroscopy. Here we report the discovery of a new co-moving (13 sigma)
stellar companion ~17.8 arcsec (350 AU in projected separation) north of the
nearby star HD141272 (21 pc). With EMMI/NTT optical spectroscopy we determined
the spectral type of the companion to be M3+-0.5V. The derived spectral type as
well as the near infrared photometry of the companion are both fully consistent
with a 0.26+-0.07 Msol dwarf located at the distance of HD141272 (21 pc).
Furthermore the photometry data rules out the pre-main sequence status, since
the system is consistent with the ZAMS of the Pleiades.
| astro-ph |
0704.0388 | Sterile neutrinos at the CNGS | We study the potential of the CNGS beam in constraining the parameter space
of a model with one sterile neutrino separated from three active ones by an
$\mathcal{O}(\eVq)$ mass-squared difference, $\Dmq_\Sbl$. We perform our
analysis using the OPERA detector as a reference (our analysis can be upgraded
including a detailed simulation of the ICARUS detector). We point out that the
channel with the largest potential to constrain the sterile neutrino parameter
space at the CNGS beam is $\nu_\mu \to \nu_\tau$. The reason for that is
twofold: first, the active-sterile mixing angle that governs this oscillation
is the less constrained by present experiments; second, this is the signal for
which both OPERA and ICARUS have been designed, and thus benefits from an
extremely low background. In our analysis we also took into account $\nu_\mu
\to \nu_e$ oscillations. We find that the CNGS potential to look for sterile
neutrinos is limited with nominal intensity of the beam, but it is
significantly enhanced with a factor 2 to 10 increase in the neutrino flux.
Data from both channels allow us, in this case, to constrain further the
four-neutrino model parameter space. Our results hold for any value of
$\Dmq_\Sbl \gtrsim 0.1 \eVq$, \textit{i.e.} when oscillations driven by this
mass-squared difference are averaged. We have also checked that the bound on
$\theta_{13}$ that can be put at the CNGS is not affected by the possible
existence of sterile neutrinos.
| hep-ph |
0704.0389 | Evolution of the Carter constant for inspirals into a black hole: effect
of the black hole quadrupole | We analyze the effect of gravitational radiation reaction on generic orbits
around a body with an axisymmetric mass quadrupole moment Q to linear order in
Q, to the leading post-Newtonian order, and to linear order in the mass ratio.
This system admits three constants of the motion in absence of radiation
reaction: energy, angular momentum, and a third constant analogous to the
Carter constant. We compute instantaneous and time-averaged rates of change of
these three constants. For a point particle orbiting a black hole, Ryan has
computed the leading order evolution of the orbit's Carter constant, which is
linear in the spin. Our result, when combined with an interaction quadratic in
the spin (the coupling of the black hole's spin to its own radiation reaction
field), gives the next to leading order evolution. The effect of the
quadrupole, like that of the linear spin term, is to circularize eccentric
orbits and to drive the orbital plane towards antialignment with the symmetry
axis. In addition we consider a system of two point masses where one body has a
single mass multipole or current multipole. To linear order in the mass ratio,
to linear order in the multipole, and to the leading post-Newtonian order, we
show that there does not exist an analog of the Carter constant for such a
system (except for the cases of spin and mass quadrupole). With mild additional
assumptions, this result falsifies the conjecture that all vacuum, axisymmetric
spacetimes posess a third constant of geodesic motion.
| gr-qc |
0704.0390 | Dual billiards, Fagnano orbits and regular polygons | We study the notion of Fagnano orbits for dual polygonal billiards. We used
them to characterize regular polygons and we study the iteration of the
developing map.
| math.DS |
0704.0391 | Exactly solvable spin dynamics of an electron coupled to large number of
nuclei and the electron-nuclear spin echo in a quantum dot | The model considered in the paper is used nowadays to describe spin dynamics
of quantum dots after optical excitation. Based on the exact diagonalization of
a model Hamiltonian, we solve the problems of the electron spin polarization
decay and magnetic field dependence of the steady state polarization. The
important role of the nuclear state is shown and methods of its calculation for
different regimes of optical excitation are proposed. The effect of spin echo
observed after application of the magnetic field $\pi$-pulse is predicted.
| cond-mat.mes-hall |
0704.0392 | Simulation of Robustness against Lesions of Cortical Networks | Structure entails function and thus a structural description of the brain
will help to understand its function and may provide insights into many
properties of brain systems, from their robustness and recovery from damage, to
their dynamics and even their evolution. Advances in the analysis of complex
networks provide useful new approaches to understanding structural and
functional properties of brain networks. Structural properties of networks
recently described allow their characterization as small-world, random
(exponential) and scale-free. They complement the set of other properties that
have been explored in the context of brain connectivity, such as topology,
hodology, clustering, and hierarchical organization. Here we apply new network
analysis methods to cortical inter-areal connectivity networks for the cat and
macaque brains. We compare these corticocortical fibre networks to benchmark
rewired, small-world, scale-free and random networks, using two analysis
strategies, in which we measure the effects of the removal of nodes and
connections on the structural properties of the cortical networks. The brain
networks' structural decay is in most respects similar to that of scale-free
networks. The results implicate highly connected hub-nodes and bottleneck
connections as structural basis for some of the conditional robustness of brain
systems. This informs the understanding of the development of brain networks'
connectivity.
| q-bio.NC cond-mat.dis-nn physics.soc-ph |
0704.0393 | A thermodynamic model for the melting of supported metal nanoparticles | We construct a simple thermodynamic model to describe the melting of a
supported metal nanoparticle with a spherically curved free surface both with
and without surface melting. We use the model to investigate the results of
recent molecular dynamics simulations, which suggest the melting temperature of
a supported metal particle is the same as that of a free spherical particle
with the same surface curvature. Our model shows that this is only the case
when the contact angles of the supported solid and liquid particles are
similar. This is also the case for the temperature at which surface melting
begins.
| cond-mat.mtrl-sci |
0704.0394 | Average optimality for risk-sensitive control with general state space | This paper deals with discrete-time Markov control processes on a general
state space. A long-run risk-sensitive average cost criterion is used as a
performance measure. The one-step cost function is nonnegative and possibly
unbounded. Using the vanishing discount factor approach, the optimality
inequality and an optimal stationary strategy for the decision maker are
established.
| q-fin.RM math.PR |
0704.0395 | A Study of $B_{d}^0 \to J/\Psi \eta^{(\prime)}$ Decays in the pQCD
Approach | Motivated by the very recent measurement of the branching ratio of ${B_d^0}
\to J/\psi \eta$ decay, we calculate the branching ratios of ${B_d}^0 \to
J/\psi \eta$ and ${B_d}^0 \to J/\Psi \eta'$ decays in the perturbative QCD
(pQCD) approach. The pQCD predictions for the branching ratios of considered
decays are: $BR(B_d^0 \to J/\Psi \eta) = (1.96 ^{+9.68}_{-0.65}) \times
10^{-6}$, which is consistent with the first experimental measurement within
errors; while $BR(B_d^0 \to J/\Psi \eta') = (1.09 ^{+3.76}_{-0.25}) \times
10^{-6}$, very similar with $B_d^0 \to \jpsi \eta$ decay and can be tested by
the forthcoming LHC experiments. The measurements of these decay channels may
help us to understand the QCD dynamics in the corresponding energy scale,
especially the reliability of pQCD approach to these kinds of B meson decays.
| hep-ph |
0704.0396 | Finite-temperature phase transitions in a two-dimensional boson Hubbard
model | We study finite-temperature phase transitions in a two-dimensional boson
Hubbard model with zero-point quantum fluctuations via Monte Carlo simulations
of quantum rotor model, and construct the corresponding phase diagram.
Compressibility shows a thermally activated gapped behavior in the insulating
regime. Finite-size scaling of the superfluid stiffness clearly shows the
nature of the Kosterlitz-Thouless transition. The transition temperature,
$T_c$, confirms a scaling relation $T_c \propto \rho_0^x$ with $x=1.0$. Some
evidences of anomalous quantum behavior at low temperatures are presented.
| cond-mat.str-el |
0704.0397 | Conditional generation of path-entangled optical NOON states | We propose a measurement protocol to generate path-entangled NOON states
conditionally from two pulsed type II optical parametric oscillators. We
calculate the fidelity of the produced states and the success probability of
the protocol. The trigger detectors are assumed to have finite dead time, and
for short pulse trigger fields they are modeled as on/off detectors with finite
efficiency. Continuous-wave operation of the parametric oscillators is also
considered.
| quant-ph |
0704.0398 | Renewals for exponentially increasing lifetimes, with an application to
digital search trees | We show that the number of renewals up to time $t$ exhibits distributional
fluctuations as $t\to\infty$ if the underlying lifetimes increase at an
exponential rate in a distributional sense. This provides a probabilistic
explanation for the asymptotics of insertion depth in random trees generated by
a bit-comparison strategy from uniform input; we also obtain a representation
for the resulting family of limit laws along subsequences. Our approach can
also be used to obtain rates of convergence.
| math.PR |
0704.0399 | Hawking radiation of linear dilaton black holes | We compute exactly the semi-classical radiation spectrum for a class of
non-asymptotically flat charged dilaton black holes, the so-called linear
dilaton black holes. In the high frequency regime, the temperature for these
black holes generically agrees with the surface gravity result. In the special
case where the black hole is massless, we show that, although the surface
gravity remains finite, there is no radiation, in agreement with the fact that
massless objects cannot radiate.
| gr-qc hep-th |
0704.0400 | The S-Matrix of AdS/CFT and Yangian Symmetry | We review the algebraic construction of the S-matrix of AdS/CFT. We also
present its symmetry algebra which turns out to be a Yangian of the centrally
extended su(2|2) superalgebra.
| nlin.SI cond-mat.stat-mech hep-th |