40 research outputs found
Schwinger's Dynamical Casimir Effect: Bulk Energy Contribution
Schwinger's Dynamical Casimir Effect is one of several candidate explanations
for sonoluminescence. Recently, several papers have claimed that Schwinger's
estimate of the Casimir energy involved is grossly inaccurate. In this letter,
we show that these calculations omit the crucial volume term. When the missing
term is correctly included one finds full agreement with Schwinger's result for
the Dynamical Casimir Effect. We have nothing new to say about sonoluminescence
itself except to affirm that the Casimir effect is energetically adequate as a
candidate explanation.Comment: 6 pages. Uses LaTeX with RevTeX package in two-column forma
A Novel Stochastic Multi-Scale Model of Francisella tularensis Infection to Predict Risk of Infection in a Laboratory
We present a multi-scale model of the within-phagocyte, within-host and population-level infection dynamics of Francisella tularensis, which extends the mechanistic one proposed by Wood et al. (2014). Our multi-scale model incorporates key aspects of the interaction between host phagocytes and extracellular bacteria, accounts for inter-phagocyte variability in the number of bacteria released upon phagocyte rupture, and allows one to compute the probability of response, and mean time until response, of an infected individual as a function of the initial infection dose. A Bayesian approach is applied to parameterize both the within-phagocyte and within-host models using infection data. Finally, we show how dose response probabilities at the individual level can be used to estimate the airborne propagation of Francisella tularensis in indoor settings (such as a microbiology laboratory) at the population level, by means of a deterministic zonal ventilation model
Particle creation in an oscillating spherical cavity
We study the creation of massless scalar particles from the quantum vacuum
due to the dynamical Casimir effect by spherical shell with oscillating radius.
In the case of a small amplitude of the oscillation, to solve the infinite set
of coupled differential equations for the instantaneous basis expansion
coefficients we use the method based on the time-dependent perturbation theory
of the quantum mechanics. To the first order of the amplitude we derive the
expressions for the number of the created particles for both parametric
resonance and non-resonance cases.Comment: 8 pages, LaTeX, no figure
Vacuum Polarization and Energy Conditions at a Planar Frequency Dependent Dielectric to Vacuum Interface
The form of the vacuum stress-tensor for the quantized scalar field at a
dielectric to vacuum interface is studied. The dielectric is modeled to have an
index of refraction that varies with frequency. We find that the stress-tensor
components, derived from the mode function expansion of the Wightman function,
are naturally regularized by the reflection and transmission coefficients of
the mode at the boundary. Additionally, the divergence of the vacuum energy
associated with a perfectly reflecting mirror is found to disappear for the
dielectric mirror at the expense of introducing a new energy density near the
surface which has the opposite sign. Thus the weak energy condition is always
violated in some region of the spacetime. For the dielectric mirror, the mean
vacuum energy density per unit plate area in a constant time hypersurface is
always found to be positive (or zero) and the averaged weak energy condition is
proven to hold for all observers with non-zero velocity along the normal
direction to the boundary. Both results are found to be generic features of the
vacuum stress-tensor and not necessarily dependent of the frequency dependence
of the dielectric.Comment: 16 pages, 4 figures, Revtex style Minor typographic corrections to
equations and tex
Sonoluminescence as a QED vacuum effect. II: Finite Volume Effects
In a companion paper [quant-ph/9904013] we have investigated several
variations of Schwinger's proposed mechanism for sonoluminescence. We
demonstrated that any realistic version of Schwinger's mechanism must depend on
extremely rapid (femtosecond) changes in refractive index, and discussed ways
in which this might be physically plausible. To keep that discussion tractable,
the technical computations in that paper were limited to the case of a
homogeneous dielectric medium. In this paper we investigate the additional
complications introduced by finite-volume effects. The basic physical scenario
remains the same, but we now deal with finite spherical bubbles, and so must
decompose the electromagnetic field into Spherical Harmonics and Bessel
functions. We demonstrate how to set up the formalism for calculating Bogolubov
coefficients in the sudden approximation, and show that we qualitatively retain
the results previously obtained using the homogeneous-dielectric (infinite
volume) approximation.Comment: 23 pages, LaTeX 209, ReV-TeX 3.2, five figure
Acoustic geometry for general relativistic barotropic irrotational fluid flow
"Acoustic spacetimes", in which techniques of differential geometry are used
to investigate sound propagation in moving fluids, have attracted considerable
attention over the last few decades. Most of the models currently considered in
the literature are based on non-relativistic barotropic irrotational fluids,
defined in a flat Newtonian background. The extension, first to special
relativistic barotropic fluid flow, and then to general relativistic barotropic
fluid flow in an arbitrary background, is less straightforward than it might at
first appear. In this article we provide a pedagogical and simple derivation of
the general relativistic "acoustic spacetime" in an arbitrary (d+1) dimensional
curved-space background.Comment: V1: 23 pages, zero figures; V2: now 24 pages, some clarifications, 2
references added. This version accepted for publication in the New Journal of
Physics. (Special issue on "Classical and Quantum Analogues for Gravitational
Phenomena and Related Effects"
Multi-variate model of TÂ cell clonotype competition and homeostasis
Diversity of the naive T cell repertoire is maintained by competition for stimuli provided by self-peptides bound to major histocompatibility complexes (self-pMHCs). We extend an existing bi-variate competition model to a multi-variate model of the dynamics of multiple T cell clonotypes which share stimuli. In order to understand the late-time behaviour of the system, we analyse: (i) the dynamics until the extinction of the first clonotype, (ii) the time to the first extinction event, (iii) the probability of extinction of each clonotype, and (iv) the size of the surviving clonotypes when the first extinction event takes place. We also find the probability distribution of the number of cell divisions per clonotype before its extinction. The mean size of a new clonotype at quasi-steady state is an increasing function of the stimulus available to it, and a decreasing function of the fraction of stimuli it shares with other clonotypes. Thus, the probability of, and time to, extinction of a new clonotype entering the pool of T cell clonotypes is determined by the extent of competition for stimuli it experiences and by its initial number of cells
Short distance and initial state effects in inflation: stress tensor and decoherence
We present a consistent low energy effective field theory framework for
parameterizing the effects of novel short distance physics in inflation, and
their possible observational signatures in the Cosmic Microwave Background. We
consider the class of general homogeneous, isotropic initial states for quantum
scalar fields in Robertson-Walker (RW) spacetimes, subject to the requirement
that their ultraviolet behavior be consistent with renormalizability of the
covariantly conserved stress tensor which couples to gravity. In the functional
Schr\"odinger picture such states are coherent, squeezed, mixed states
characterized by a Gaussian density matrix. This Gaussian has parameters which
approach those of the adiabatic vacuum at large wave number, and evolve in time
according to an effective classical Hamiltonian. The one complex parameter
family of squeezed states in de Sitter spacetime does not fall into
this UV allowed class, except for the special value of the parameter
corresponding to the Bunch-Davies state. We determine the finite contributions
to the inflationary power spectrum and stress tensor expectation value of
general UV allowed adiabatic states, and obtain quantitative limits on the
observability and backreaction effects of some recently proposed models of
short distance modifications of the initial state of inflation. For all UV
allowed states, the second order adiabatic basis provides a good description of
particles created in the expanding RW universe. Due to the absence of particle
creation for the massless, minimally coupled scalar field in de Sitter space,
there is no phase decoherence in the simplest free field inflationary models.
We apply adiabatic regularization to the renormalization of the decoherence
functional in cosmology to corroborate this result.Comment: 83 pages, 2 figures, minor changes in content and styl