1,275 research outputs found
Massive spin 2 propagator on de Sitter space
We compute the Pauli-Jordan, Hadamard and Feynman propagators for the massive
metrical perturbations on de Sitter space. They are expressed both in terms of
mode sums and in invariant forms.Comment: 30 pages + 1 eps fi
Predictors of walking capacity in peripheral arterial disease patients
OBJECTIVE: To estimate walking capacity in intermittent claudication patients through a prediction model based on clinical characteristics and the walking impairment questionnaire.
METHODS: The sample included 133 intermittent claudication patients of both genders aged between 30 and 80 years. Data regarding clinical characteristics, the walking impairment questionnaire and treadmill walking test performance were obtained. Multiple regression modeling was conducted to predict claudication onset distance and total walking distance using clinical characteristics (age, height, mass, body mass index, ankle brachial index lower, gender, history of smoking and co-morbid conditions) and walking impairment questionnaire responses. Comparisons of claudication onset distance and total walking distance measured during treadmill tests and estimated by a regression equation were performed using paired t-tests.
RESULTS: Co-morbid conditions (diabetes and coronary artery disease) and questions related to difficulty in walking short distances (walking indoors - such as around your house and walking 5 blocks) and at low speed (walking 1 block at average speed - usual pace) resulted in the development of new prediction models high significant for claudication onset distance and total walking distance (p0.05) were observed.
CONCLUSION: The current study demonstrated that walking capacity can be adequately estimated based on co-morbid conditions and responses to the walking impairment questionnaire
Chiral supersymmetric pp-wave solutions of IIA supergravity
We describe solutions of type IIA (N=2, D=10) supergravity built under the
assumption of the existence of at least one residual chiral supersymmetry.
Their geometry is of pp-wave type. Explicit parametrization of the metric and
matter field components, in terms of Killing spinors and arbitrary functions,
is provided.Comment: LaTeX file, 10 page
Quantum charged fields in Rindler space
We study, using Rindler coordinates, the quantization of a charged scalar
field interacting with a constant, external, electric field. First we establish
the expression of the Schwinger vacuum decay rate, using the operator
formalism. Then we rederive it in the framework of the Feynman path integral
method. Our analysis reinforces the conjecture which identifies the zero
winding sector of the Minkowski propagator with the Rindler propagator.
Moreover we compute the expression of the Unruh's modes that allow to make
connection between Minkowskian and Rindlerian quantization scheme by purely
algebraic relations. We use these modes to study the physics of a charged two
level detector moving in an electric field whose transitions are due to the
exchange of charged quanta. In the limit where the Schwinger pair production
mechanism of the exchanged quanta becomes negligible we recover the Boltzman
equilibrium ratio for the population of the levels of the detector. Finally we
explicitly show how the detector can be taken as the large mass and charge
limit of an interacting fields system.Comment: 1 Tex file + 5 eps figure
Mimimal Length Uncertainty Principle and the Transplanckian Problem of Black Hole Physics
The minimal length uncertainty principle of Kempf, Mangano and Mann (KMM), as
derived from a mutilated quantum commutator between coordinate and momentum, is
applied to describe the modes and wave packets of Hawking particles evaporated
from a black hole. The transplanckian problem is successfully confronted in
that the Hawking particle no longer hugs the horizon at arbitrarily close
distances. Rather the mode of Schwarzschild frequency deviates from
the conventional trajectory when the coordinate is given by in units of the non local distance legislated
into the uncertainty relation. Wave packets straddle the horizon and spread out
to fill the whole non local region. The charge carried by the packet (in the
sense of the amount of "stuff" carried by the Klein--Gordon field) is not
conserved in the non--local region and rapidly decreases to zero as time
decreases. Read in the forward temporal direction, the non--local region thus
is the seat of production of the Hawking particle and its partner. The KMM
model was inspired by string theory for which the mutilated commutator has been
proposed to describe an effective theory of high momentum scattering of zero
mass modes. It is here interpreted in terms of dissipation which gives rise to
the Hawking particle into a reservoir of other modes (of as yet unknown
origin). On this basis it is conjectured that the Bekenstein--Hawking entropy
finds its origin in the fluctuations of fields extending over the non local
region.Comment: 12 pages (LateX), 1 figur
Uniformly Accelerated Charge in a Quantum Field: From Radiation Reaction to Unruh Effect
We present a stochastic theory for the nonequilibrium dynamics of charges
moving in a quantum scalar field based on the worldline influence functional
and the close-time-path (CTP or in-in) coarse-grained effective action method.
We summarize (1) the steps leading to a derivation of a modified
Abraham-Lorentz-Dirac equation whose solutions describe a causal semiclassical
theory free of runaway solutions and without pre-acceleration patholigies, and
(2) the transformation to a stochastic effective action which generates
Abraham-Lorentz-Dirac-Langevin equations depicting the fluctuations of a
particle's worldline around its semiclassical trajectory. We point out the
misconceptions in trying to directly relate radiation reaction to vacuum
fluctuations, and discuss how, in the framework that we have developed, an
array of phenomena, from classical radiation and radiation reaction to the
Unruh effect, are interrelated to each other as manifestations at the
classical, stochastic and quantum levels. Using this method we give a
derivation of the Unruh effect for the spacetime worldline coordinates of an
accelerating charge. Our stochastic particle-field model, which was inspired by
earlier work in cosmological backreaction, can be used as an analog to the
black hole backreaction problem describing the stochastic dynamics of a black
hole event horizon.Comment: Invited talk given by BLH at the International Assembly on
Relativistic Dynamics (IARD), June 2004, Saas Fee, Switzerland. 19 pages, 1
figur
Clustering and Alignment of Polymorphic Sequences for HLA-DRB1 Genotyping
Located on Chromosome 6p21, classical human leukocyte antigen genes are highly polymorphic. HLA alleles associate with a variety of phenotypes, such as narcolepsy, autoimmunity, as well as immunologic response to infectious disease. Moreover, high resolution genotyping of these loci is critical to achieving long-term survival of allogeneic transplants. Development of methods to obtain high resolution analysis of HLA genotypes will lead to improved understanding of how select alleles contribute to human health and disease risk. Genomic DNAs were obtained from a cohort of n = 383 subjects recruited as part of an Ulcerative Colitis study and analyzed for HLA-DRB1. HLA genotypes were determined using sequence specific oligonucleotide probes and by next-generation sequencing using the Roche/454 GSFLX instrument. The Clustering and Alignment of Polymorphic Sequences (CAPSeq) software application was developed to analyze next-generation sequencing data. The application generates HLA sequence specific 6-digit genotype information from next-generation sequencing data using MUMmer to align sequences and the R package diffusionMap to classify sequences into their respective allelic groups. The incorporation of Bootstrap Aggregating, Bagging to aid in sorting of sequences into allele classes resulted in improved genotyping accuracy. Using Bagging iterations equal to 60, the genotyping results obtained using CAPSeq when compared with sequence specific oligonucleotide probe characterized 4-digit genotypes exhibited high rates of concordance, matching at 759 out of 766 (99.1%) alleles. © 2013 Ringquist et al
Boundary conditions in the Unruh problem
We have analyzed the Unruh problem in the frame of quantum field theory and
have shown that the Unruh quantization scheme is valid in the double Rindler
wedge rather than in Minkowski spacetime. The double Rindler wedge is composed
of two disjoint regions (- and -wedges of Minkowski spacetime) which are
causally separated from each other. Moreover the Unruh construction implies
existence of boundary condition at the common edge of - and -wedges in
Minkowski spacetime. Such boundary condition may be interpreted as a
topological obstacle which gives rise to a superselection rule prohibiting any
correlations between - and - Unruh particles. Thus the part of the field
from the -wedge in no way can influence a Rindler observer living in the
-wedge and therefore elimination of the invisible "left" degrees of freedom
will take no effect for him. Hence averaging over states of the field in one
wedge can not lead to thermalization of the state in the other. This result is
proved both in the standard and algebraic formulations of quantum field theory
and we conclude that principles of quantum field theory does not give any
grounds for existence of the "Unruh effect".Comment: 31 pages,1 figur
- …