1,540 research outputs found
Induced Parity-Breaking Term at Finite Chemical Potential and Temparature
We exactly calculated the parity-odd term of the effective action induced by
the fermions in 2+1 dimensions at finite chemical potential and finite
temperature. It shows that gauge invariance is still respected. A more gerneral
class of background configurations is considered. The knowledge of the reduced
1+1 determinant is required in order to draw exact conclusions about the gauge
invariance of the parity-odd term in this latter case.Comment: 8 pages, LATEX, no figure
Feedback control of spin systems
The feedback stabilization problem for ensembles of coupled spin 1/2 systems
is discussed from a control theoretic perspective. The noninvasive nature of
the bulk measurement allows for a fully unitary and deterministic closed loop.
The Lyapunov-based feedback design presented does not require spins that are
selectively addressable. With this method, it is possible to obtain control
inputs also for difficult tasks, like suppressing undesired couplings in
identical spin systems.Comment: 16 pages, 15 figure
First study of radiation hardness of lead tungstate crystals at low temperatures
The electromagnetic calorimeter of PANDA at the FAIR facility will rely on an
operation of lead tungstate (PWO) scintillation crystals at temperatures near
-25 deg.C to provide sufficient resolution for photons in the energy range from
8 GeV down to 10 MeV. Radiation hardness of PWO crystals was studied at the
IHEP (Protvino) irradiation facility in the temperature range from room
temperature down to -25 deg.C. These studies have indicated a significantly
different behaviour in the time evolution of the damaging processes well below
room temperature. Different signal loss levels at the same dose rate, but at
different temperatures were observed. The effect of a deep suppression of the
crystal recovery process at temperatures below
0 deg.C has been seen.Comment: 10 pages 7 figure
Lipid-laden bronchoalveolar macrophages in asthma and chronic cough
SummaryBackgroundThe presence of lipids in alveolar macrophages (AMs) may impair their phagocytic response, and determine airway inflammation and obstruction.ObjectiveTo determine the factors such as severity of asthma, chronic cough, airway inflammation and obesity that may influence the presence of lipids in lung macrophages.MethodsBronchoalveolar lavage fluid (BALF) was obtained from 38 asthmatics (21 severe and 17 mild/moderate), 16 subjects with chronic cough and 11 healthy control subjects. The presence of lipids in macrophages was detected using an Oil-red-O stain and an index of lipid-laden macrophages (LLMI) was obtained.ResultsLLMI scores were higher in healthy subjects (median 48 [IQR 10â61]) and the severe asthma group (37 [11.5â61]) compared to mild/moderate asthmatics (7 [0.5â37]; p < 0.05 each). Subjects reporting a history of gastro-oesophageal reflux disease (GORD) had higher LLMI values (41.5 [11.3â138] versus 13 [0â39.3], p = 0.02). There was no significant correlation between LLMI and chronic cough, BAL cell differential counts, FEV1, FEV1/FVC or body mass index (BMI).ConclusionsThe reduced LLMI in mild/moderate asthma may be related to lower incidence of GORD. However, this was not related to the degree of airflow obstruction, obesity or airway inflammation
Determination of the time-dependent reaction coefficient and the heat flux in a nonlinear inverse heat conduction problem
Diffusion processes with reaction generated by a nonlinear source are commonly encountered in practical applications related to ignition, pyrolysis and polymerization. In such processes, determining the intensity of reaction in time is of crucial importance for control and monitoring purposes. Therefore, this paper is devoted to such an identification problem of determining the time-dependent coefficient of a nonlinear heat source together with the unknown heat flux at an inaccessible boundary of a one-dimensional slab from temperature measurements at two sensor locations in the context of nonlinear transient heat conduction. Local existence and uniqueness results for the inverse coefficient problem are proved when the first three derivatives of the nonlinear source term are Lipschitz continuous functions. Furthermore, the conjugate gradient method (CGM) for separately reconstructing the reaction coefficient and the heat flux is developed. The ill-posedness is overcome by using the discrepancy principle to stop the iteration procedure of CGM when the input data is contaminated with noise. Numerical results show that the inverse solutions are accurate and stable
Phonon effects in molecular transistors: Quantum and classical treatment
We present a comprehensive theoretical treatment of the effect of
electron-phonon interactions in molecular transistors, including both quantal
and classical limits and we study both equilibrated and out of equilibrium
phonons. We present detailed results for conductance, noise and phonon
distribution in two regimes. One involves temperatures large as compared to the
rate of electronic transitions on and off the dot; in this limit our approach
yields classical rate equations, which are solved numerically for a wide range
of parameters. The other regime is that of low temperatures and weak
electron-phonon coupling where a perturbative approximation in the Keldysh
formulation can be applied. The interplay between the phonon-induced
renormalization of the density of states on the quantum dot and the
phonon-induced renormalization of the dot-lead coupling is found to be
important. Whether or not the phonons are able to equilibrate in a time rapid
compared to the transit time of an electron through the dot is found to affect
the conductance. Observable signatures of phonon equilibration are presented.
We also discuss the nature of the low-T to high-T crossover.Comment: 20 pages, 19 figures. Minor changes, version accepted for publication
in Phys. Rev.
The molecular epidemiology of human immunodeficiency virus type 1 in six cities in Britain and Ireland
The authors sequenced the p17 coding regions of the gag gene from 211 patients infected either through injecting drug use (IDU) or by sexual intercourse between men from six cities in Scotland, N. England, N. Ireland, and the Republic of Ireland. All sequences were of subtype 5. Phylogenetic analysis revealed substantial heterogeneity in the sequences from homosexual men. In contrast, sequence from over 80% of IDUs formed a relatively tight cluster, distinct both from those of published isolates and of the gay men. There was no large-scale clustering of sequences by city in either risk group, although a number of close associations between pairs of individuals were observed. From the known date of the HIV-1 epidemic among IDUs in Edinburgh, the rate of sequence divergence at synonymous sites is estimated to be about 0.8%. On this basis it has been estimated that the date of divergence of the sequences among homosexual men to be about 1975, which may correspond to the origin of the B subtype epidemic
Experimental study of the e+e- -> pi0 gamma process in the energy region sqrt(s)=0.60-0.97 GeV
Results of the study of the e+e-->pi0 gamma process with SND detector at
VEPP-2M collider in the c.m.s. energy range sqrt(s)=0.60-0.97 GeV are
presented. Using 36513 selected events corresponding to a total integrated
luminosity of 3.4 pb^-1 the e+e-->pi0 gamma cross section was measured. The
energy dependence of the cross section was analyzed in the framework of the
vector meson dominance model. The data are well described by a sum of
phi,omega,rho0->pi0 gamma decay contributions with measured decay
probabilities: Br(omega->pi0 gamma)=(9.34+-0.15+-0.31)% and Br(rho0->pi0
gamma)=(5.15+-1.16+-0.73)*10^-4 . The rho-omega relative interference phase is
phi(rho,omega}=(-10.2+-6.5+-2.5) degree
Proximity effects and characteristic lengths in ferromagnet-superconductor structures
We present an extensive theoretical investigation of the proximity effects
that occur in Ferromagnet/Superconductor () systems. We use a numerical
method to solve self consistently the Bogoliubov-de Gennes equations in the
continuum. We obtain the pair amplitude and the local density of states (DOS),
and use these results to extract the relevant lengths characterizing the
leakage of superconductivity into the magnet and to study spin splitting into
the superconductor. These phenomena are investigated as a function of
parameters such as temperature, magnet polarization, interfacial scattering,
sample size and Fermi wavevector mismatch, all of which turn out to have
important influence on the results. These comprehensive results should help
characterize and analyze future data and are shown to be in agreement with
existing experiments.Comment: 24 pages, including 26 figure
Study of Radiation Damage in Lead Tungstate Crystals Using Intense High Energy Beams
We report on the effects of radiation on the light output of lead tungstate
crystals. The crystals were irradiated by pure, intense high energy electron
and hadron beams as well as by a mixture of hadrons, neutrons and gammas. The
crystals were manufactured in Bogoroditsk, Apatity (both Russia), and Shanghai
(China). These studies were carried out at the 70-GeV proton accelerator in
Protvino
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