18,766 research outputs found
Three-loop HTLpt thermodynamics at finite temperature and chemical potential
In this proceedings we present a state-of-the-art method of calculating
thermodynamic potential at finite temperature and finite chemical potential,
using Hard Thermal Loop perturbation theory (HTLpt) up to
next-to-next-leading-order (NNLO). The resulting thermodynamic potential
enables us to evaluate different thermodynamic quantities including pressure
and various quark number susceptibilities (QNS). Comparison between our
analytic results for those thermodynamic quantities with the available lattice
data shows a good agreement.Comment: 5 pages, 6 figures, conference proceedings of XXI DAE-BRNS HEP
Symposium, IIT Guwahati, December 2014; to appear in 'Springer Proceedings in
Physics Series
On the Inelastic Collapse of a Ball Bouncing on a Randomly Vibrating Platform
We study analytically the dynamics of a ball bouncing inelastically on a
randomly vibrating platform, as a simple toy model of inelastic collapse. Of
principal interest are the distributions of the number of flights n_f till the
collapse and the total time \tau_c elapsed before the collapse. In the strictly
elastic case, both distributions have power law tails characterised by
exponents which are universal, i.e., independent of the details of the platform
noise distribution. In the inelastic case, both distributions have exponential
tails: P(n_f) ~ exp[-\theta_1 n_f] and P(\tau_c) ~ exp[-\theta_2 \tau_c]. The
decay exponents \theta_1 and \theta_2 depend continuously on the coefficient of
restitution and are nonuniversal; however as one approches the elastic limit,
they vanish in a universal manner that we compute exactly. An explicit
expression for \theta_1 is provided for a particular case of the platform noise
distribution.Comment: 32 page
Perturbation Theory for Fractional Brownian Motion in Presence of Absorbing Boundaries
Fractional Brownian motion is a Gaussian process x(t) with zero mean and
two-time correlations ~ t^{2H} + s^{2H} - |t-s|^{2H}, where H, with
0<H<1 is called the Hurst exponent. For H = 1/2, x(t) is a Brownian motion,
while for H unequal 1/2, x(t) is a non-Markovian process. Here we study x(t) in
presence of an absorbing boundary at the origin and focus on the probability
density P(x,t) for the process to arrive at x at time t, starting near the
origin at time 0, given that it has never crossed the origin. It has a scaling
form P(x,t) ~ R(x/t^H)/t^H. Our objective is to compute the scaling function
R(y), which up to now was only known for the Markov case H=1/2. We develop a
systematic perturbation theory around this limit, setting H = 1/2 + epsilon, to
calculate the scaling function R(y) to first order in epsilon. We find that
R(y) behaves as R(y) ~ y^phi as y -> 0 (near the absorbing boundary), while
R(y) ~ y^gamma exp(-y^2/2) as y -> oo, with phi = 1 - 4 epsilon + O(epsilon^2)
and gamma = 1 - 2 epsilon + O(epsilon^2). Our epsilon-expansion result confirms
the scaling relation phi = (1-H)/H proposed in Ref. [28]. We verify our
findings via numerical simulations for H = 2/3. The tools developed here are
versatile, powerful, and adaptable to different situations.Comment: 16 pages, 8 figures; revised version 2 adds discussion on spatial
small-distance cutof
Spin susceptibility of underdoped cuprates: the case of Ortho-II YBa_2Cu_3O_{6.5}
Recent inelastic neutron scattering measurements found that the spin
susceptibility of detwinned and highly ordered ortho-II YBa_2Cu_3O_{6.5}
exhibits, in both the normal and superconducting states, one-dimensional
incommensurate modulations at low energies which were interpreted as a
signature of dynamic stripes. We propose an alternative model based on
quasiparticle transitions between the arcs of a truncated Fermi surface. Such
transitions are resonantly enhanced by scattering to the triplet spin
resonance. We show that the anisotropy in the experimental spin response is
consistent with this model if the gap at the saddle points is anisotropic.Comment: 5 fives, 3 postscript figure
Efficient calculation of local dose distribution for response modelling in proton and ion beams
We present an algorithm for fast and accurate computation of the local dose
distribution in MeV beams of protons, carbon ions or other heavy-charged
particles. It uses compound Poisson-process modelling of track interaction and
succesive convolutions for fast computation. It can handle mixed particle
fields over a wide range of fluences. Since the local dose distribution is the
essential part of several approaches to model detector efficiency or cellular
response it has potential use in ion-beam dosimetry and radiotherapy.Comment: 9 pages, 3 figure
Enumeration of chord diagrams on many intervals and their non-orientable analogs
Two types of connected chord diagrams with chord endpoints lying in a
collection of ordered and oriented real segments are considered here: the real
segments may contain additional bivalent vertices in one model but not in the
other. In the former case, we record in a generating function the number of
fatgraph boundary cycles containing a fixed number of bivalent vertices while
in the latter, we instead record the number of boundary cycles of each fixed
length. Second order, non-linear, algebraic partial differential equations are
derived which are satisfied by these generating functions in each case giving
efficient enumerative schemes. Moreover, these generating functions provide
multi-parameter families of solutions to the KP hierarchy. For each model,
there is furthermore a non-orientable analog, and each such model likewise has
its own associated differential equation. The enumerative problems we solve are
interpreted in terms of certain polygon gluings. As specific applications, we
discuss models of several interacting RNA molecules. We also study a matrix
integral which computes numbers of chord diagrams in both orientable and
non-orientable cases in the model with bivalent vertices, and the large-N limit
is computed using techniques of free probability.Comment: 23 pages, 7 figures; revised and extended versio
An interpolatory ansatz captures the physics of one-dimensional confined Fermi systems
Interacting one-dimensional quantum systems play a pivotal role in physics.
Exact solutions can be obtained for the homogeneous case using the Bethe ansatz
and bosonisation techniques. However, these approaches are not applicable when
external confinement is present. Recent theoretical advances beyond the Bethe
ansatz and bosonisation allow us to predict the behaviour of one-dimensional
confined systems with strong short-range interactions, and new experiments with
cold atomic Fermi gases have already confirmed these theories. Here we
demonstrate that a simple linear combination of the strongly interacting
solution with the well-known solution in the limit of vanishing interactions
provides a simple and accurate description of the system for all values of the
interaction strength. This indicates that one can indeed capture the physics of
confined one-dimensional systems by knowledge of the limits using wave
functions that are much easier to handle than the output of typical numerical
approaches. We demonstrate our scheme for experimentally relevant systems with
up to six particles. Moreover, we show that our method works also in the case
of mixed systems of particles with different masses. This is an important
feature because these systems are known to be non-integrable and thus not
solvable by the Bethe ansatz technique.Comment: 22 pages including methods and supplementary materials, 11 figures,
title slightly change
Constraining and Dark Energy with Gamma-Ray Bursts
An relationship with a small
scatter for current -ray burst (GRB) data was recently reported, where
is the beaming-corrected -ray energy and
is the peak energy in the local observer frame. By considering this
relationship for a sample of 12 GRBs with known redshift, peak energy, and
break time of afterglow light curves, we constrain the mass density of the
universe and the nature of dark energy. We find that the mass density
(at the confident level) for a flat
universe with a cosmological constant, and the parameter of an assumed
static dark-energy equation of state ().
Our results are consistent with those from type Ia supernovae. A larger sample
established by the upcoming {\em Swift} satellite is expected to provide
further constraints.Comment: 8 pages including 4 figures, to appear in ApJ Letters, typos
correcte
Occupational safety considerations with hydrazine fuels
A simple pharmacokinetic model and a specially designed dermal vapor exposure chamber which provides respiratory protection were used to determine the rate of penetration of hydrazine and 1,1-dimethylhydrazine (UDMH) vapor through the skin of rats. Parameters for the pharmacokinetic model were determined from intravenous and inhalation exposure data. The model was then used to estimate the skin permeation coefficient for hydrazine or UDMH vapor from the dermal-vapor exposure data. This analysis indicates that UDMH vapor has a relatively high permeability through skin (0.7 cm/hr), a value somewhat higher than was obtained for hydrazine by the same procedure (0.09 cm/hr). Based on these skin permeability results, a skin-only vapor exposure limit giving protection equivalent to the inhalation Threshold Limit Value (TLV) could be calculated. The current TLV's for UDMH and hydrazine are 0.5 and 0.1 ppm, respectively. The corresponding skin-only TLV equivalents, for personnel wearing respiratory protection, are 32 ppm for UDMH and 48 ppm for hydrazine. Should the proposed lowering to the TLV's for these compounds to 0.01 ppm be adopted, the equivalent skin-only TLV's would become 0.64 ppm for UDMH and 4.8 for hydrazine
Lattice vibrations and structural instability in Cesium near the cubic to tetragonal transition
Under pressure cesium undergoes a transition from a high-pressure fcc phase
(Cs-II) to a collapsed fcc phase (Cs-III) near 4.2GPa. At 4.4GPa there follows
a transition to the tetragonal Cs-IV phase. In order to investigate the lattice
vibrations in the fcc phase and seek a possible dynamical instability of the
lattice, the phonon spectra of fcc-Cs at volumes near the III-IV transition are
calculated using Savrasov's density functional linear-response LMTO method.
Compared with quasiharmonic model calculations including non-central
interatomic forces up to second neighbours, at the volume (
is the experimental volume of bcc-Cs with =6.048{\AA}), the
linear-response calculations show soft intermediate wavelength
phonons. Similar softening is also observed for
short wavelength and phonons and intermediate
wavelength phonons. The Born-von K\'{a}rm\'{a}n analysis of
dispersion curves indicates that the interplanar force constants exhibit
oscillating behaviours against plane spacing and the large softening of
intermediate wavelength phonons results from a
negative (110)-interplanar force-constant . The frequencies of the
phonons with around 1/3 become imaginary
and the fcc structure becomes dynamically unstable for volumes below .
It is suggested that superstructures corresponding to the
soft mode should be present as a precursor of tetragonal Cs-IV structure.Comment: 12 pages, 5 figure
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