817 research outputs found
A Statistical Mechanical Problem in Schwarzschild Spacetime
We use Fermi coordinates to calculate the canonical partition function for an
ideal gas in a circular geodesic orbit in Schwarzschild spacetime. To test the
validity of the results we prove theorems for limiting cases. We recover the
Newtonian gas law subject only to tidal forces in the Newtonian limit.
Additionally we recover the special relativistic gas law as the radius of the
orbit increases to infinity. We also discuss how the method can be extended to
the non ideal gas case.Comment: Corrected an equation misprint, added four references, and brief
comments on the system's center of mass and the thermodynamic limi
Bose-Einstein condensation for interacting scalar fields in curved spacetime
We consider the model of self-interacting complex scalar fields with a rigid
gauge invariance under an arbitrary gauge group . In order to analyze the
phenomenon of Bose-Einstein condensation finite temperature and the possibility
of a finite background charge is included. Different approaches to derive the
relevant high-temperature behaviour of the theory are presented.Comment: 28 pages, LaTe
From Forbidden Coronal Lines to Meaningful Coronal Magnetic Fields
We review methods to measure magnetic fields within the corona using the
polarized light in magnetic-dipole (M1) lines. We are particularly interested
in both the global magnetic-field evolution over a solar cycle, and the local
storage of magnetic free energy within coronal plasmas. We address commonly
held skepticisms concerning angular ambiguities and line-of-sight confusion. We
argue that ambiguities are in principle no worse than more familiar remotely
sensed photospheric vector-fields, and that the diagnosis of M1 line data would
benefit from simultaneous observations of EUV lines. Based on calculations and
data from eclipses, we discuss the most promising lines and different
approaches that might be used. We point to the S-like [Fe {\sc XI}] line (J=2
to J=1) at 789.2nm as a prime target line (for ATST for example) to augment the
hotter 1074.7 and 1079.8 nm Si-like lines of [Fe {\sc XIII}] currently observed
by the Coronal Multi-channel Polarimeter (CoMP). Significant breakthroughs will
be made possible with the new generation of coronagraphs, in three distinct
ways: (i) through single point inversions (which encompasses also the analysis
of MHD wave modes), (ii) using direct comparisons of synthetic MHD or
force-free models with polarization data, and (iii) using tomographic
techniques.Comment: Accepted by Solar Physics, April 201
Timescales of IP(3)-evoked Ca(2+) spikes emerge from Ca(2+) puffs only at the cellular level
The behavior of biological systems is determined by the properties of their component molecules, but the interactions are usually too complex to understand fully how molecular behavior generates cellular behavior. Ca(2+) signaling by inositol trisphosphate receptors (IP(3)R) offers an opportunity to understand this relationship because the cellular behavior is defined largely by Ca(2+)-mediated interactions between IP(3)R. Ca(2+) released by a cluster of IP(3)R (giving a local Ca(2+) puff) diffuses and ignites the behavior of neighboring clusters (to give repetitive global Ca(2+) spikes). We use total internal reflection fluorescence microscopy of two mammalian cell lines to define the temporal relationships between Ca(2+) puffs (interpuff intervals, IPI) and Ca(2+) spikes (interspike intervals) evoked by flash photolysis of caged IP(3). We find that IPI are much shorter than interspike intervals, that puff activity is stochastic with a recovery time that is much shorter than the refractory period of the cell, and that IPI are not periodic. We conclude that Ca(2+) spikes do not arise from oscillatory dynamics of IP(3)R clusters, but that repetitive Ca(2+) spiking with its longer timescales is an emergent property of the dynamics of the whole cluster array
Gravitons and Lightcone Fluctuations
Gravitons in a squeezed vacuum state, the natural result of quantum creation
in the early universe or by black holes, will introduce metric fluctuations.
These metric fluctuations will introduce fluctuations of the lightcone. It is
shown that when the various two-point functions of a quantized field are
averaged over the metric fluctuations, the lightcone singularity disappears for
distinct points. The metric averaged functions remain singular in the limit of
coincident points. The metric averaged retarded Green's function for a massless
field becomes a Gaussian which is nonzero both inside and outside of the
classical lightcone. This implies some photons propagate faster than the
classical light speed, whereas others propagate slower. The possible effects of
metric fluctuations upon one-loop quantum processes are discussed and
illustrated by the calculation of the one-loop electron self-energy.Comment: 18pp, LATEX, TUTP-94-1
Spinor Field in Bianchi type-I Universe: regular solutions
Self-consistent solutions to the nonlinear spinor field equations in General
Relativity has been studied for the case of Bianchi type-I (B-I) space-time. It
has been shown that, for some special type of nonliearity the model provides
regular solution, but this singularity-free solutions are attained at the cost
of broken dominant energy condition in Hawking-Penrose theorem. It has also
been shown that the introduction of -term in the Lagrangian generates
oscillations of the B-I model, which is not the case in absence of
term. Moreover, for the linear spinor field, the term provides
oscillatory solutions, those are regular everywhere, without violating dominant
energy condition.
Key words: Nonlinear spinor field (NLSF), Bianch type -I model (B-I),
term
PACS 98.80.C CosmologyComment: RevTex, 21 page
Topological entropy for some isotropic cosmological models
The chaotical dynamics is studied in different Friedmann-Robertson- Walker
cosmological models with scalar (inflaton) field and hydrodynamical matter. The
topological entropy is calculated for some particular cases. Suggested scheme
can be easily generalized for wide class of models. Different methods of
calculation of topological entropy are compared.Comment: Final version to appear in Phys. Rev D. Minor changes, typos
corrected; 29 pages with 2 eps figure
Contribution of noncanonical antigens to virulence and adaptive immunity in human infection with enterotoxigenic E. coli
Enterotoxigenic Escherichia coli (ETEC) contributes significantly to the substantial burden of infectious diarrhea among children living in low- and middle-income countries. In the absence of a vaccine for ETEC, children succumb to acute dehydration as well as nondiarrheal sequelae related to these infections, including malnutrition. The considerable diversity of ETEC genomes has complicated canonical vaccine development approaches defined by a subset of ETEC pathovar-specific antigens known as colonization factors (CFs). To identify additional conserved immunogens unique to this pathovar, we employed an “open-aperture” approach to capture all potential conserved ETEC surface antigens, in which we mined the genomic sequences of 89 ETEC isolates, bioinformatically selected potential surface-exposed pathovar-specific antigens conserved in more than 40% of the genomes (n = 118), and assembled the representative proteins onto microarrays, complemented with known or putative colonization factor subunit molecules (n = 52) and toxin subunits. These arrays were then used to interrogate samples from individuals with acute symptomatic ETEC infections. Surprisingly, in this approach, we found that immune responses were largely constrained to a small number of antigens, including individual colonization factor antigens and EtpA, an extracellular adhesin. In a Bangladeshi cohort of naturally infected children <2 years of age, both EtpA and a second antigen, EatA, elicited significant serologic responses that were associated with protection from symptomatic illness. In addition, children infected with ETEC isolates bearing either etpA or eatA genes were significantly more likely to develop symptomatic disease. These studies support a role for antigens not presently targeted by vaccines (noncanonical) in virulence and the development of adaptive immune responses during ETEC infections. These findings may inform vaccine design efforts to complement existing approaches
Ponderomotive entangling of atomic motions
We propose the use of ponderomotive forces to entangle the motions of
different atoms. Two situations are analyzed: one where the atoms belong to the
same optical cavity and interact with the same radiation field mode; the other
where each atom is placed in own optical cavity and the output field of one
cavity enters the other.Comment: Revtex file, five pages, two eps figure
Dynamically avoiding fine-tuning the cosmological constant: the "Relaxed Universe"
We demonstrate that there exists a large class of action functionals of the
scalar curvature and of the Gauss-Bonnet invariant which are able to relax
dynamically a large cosmological constant (CC), whatever it be its starting
value in the early universe. Hence, it is possible to understand, without
fine-tuning, the very small current value of the CC as compared to its
theoretically expected large value in quantum field theory and string theory.
In our framework, this relaxation appears as a pure gravitational effect, where
no ad hoc scalar fields are needed. The action involves a positive power of a
characteristic mass parameter, M, whose value can be, interestingly enough, of
the order of a typical particle physics mass of the Standard Model of the
strong and electroweak interactions or extensions thereof, including the
neutrino mass. The model universe emerging from this scenario (the "Relaxed
Universe") falls within the class of the so-called LXCDM models of the cosmic
evolution. Therefore, there is a "cosmon" entity X (represented by an effective
object, not a field), which in this case is generated by the effective
functional and is responsible for the dynamical adjustment of the cosmological
constant. This model universe successfully mimics the essential past epochs of
the standard (or "concordance") cosmological model (LCDM). Furthermore, it
provides interesting clues to the coincidence problem and it may even connect
naturally with primordial inflation.Comment: LaTeX, 63 pp, 8 figures. Extended discussion. Version accepted in
JCA
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