411 research outputs found
Variational Principle for Mixed Classical-Quantum Systems
An extended variational principle providing the equations of motion for a
system consisting of interacting classical, quasiclassical and quantum
components is presented, and applied to the model of bilinear coupling. The
relevant dynamical variables are expressed in the form of a quantum state
vector which includes the action of the classical subsystem in its phase
factor. It is shown that the statistical ensemble of Brownian state vectors for
a quantum particle in a classical thermal environment can be described by a
density matrix evolving according to a nonlinear quantum Fokker-Planck
equation. Exact solutions of this equation are obtained for a two-level system
in the limit of high temperatures, considering both stationary and
nonstationary initial states. A treatment of the common time shared by the
quantum system and its classical environment, as a collective variable rather
than as a parameter, is presented in the Appendix.Comment: 16 pages, LaTex; added Figure 2 and Figure
Vacuum effects in a vibrating cavity: time refraction, dynamical Casimir effect, and effective Unruh acceleration
Two different quantum processes are considered in a perturbed vacuum cavity:
time refraction and dynamical Casimir effect. They are shown to be physically
equivalent, and are predicted to be unstable, leading to an exponential growth
in the number of photons created in the cavity. The concept of an effective
Unruh acceleration for these processes is also introduced, in order to make a
comparison in terms of radiation efficiency, with the Unruh radiation
associated with an accelerated frame in unbounded vacuum.Comment: 5 pages, version to appear in Physics Letters
Resonant transmission through an open quantum dot
We have measured the low-temperature transport properties of a quantum dot
formed in a one-dimensional channel. In zero magnetic field this device shows
quantized ballistic conductance plateaus with resonant tunneling peaks in each
transition region between plateaus. Studies of this structure as a function of
applied perpendicular magnetic field and source-drain bias indicate that
resonant structure deriving from tightly bound states is split by Coulomb
charging at zero magnetic field.Comment: To be published in Phys. Rev. B (1997). 8 LaTex pages with 5 figure
Finite temperature mobility of a particle coupled to a fermion environment
We study numerically the finite temperature and frequency mobility of a
particle coupled by a local interaction to a system of spinless fermions in one
dimension. We find that when the model is integrable (particle mass equal to
the mass of fermions) the static mobility diverges. Further, an enhanced
mobility is observed over a finite parameter range away from the integrable
point. We present a novel analysis of the finite temperature static mobility
based on a random matrix theory description of the many-body Hamiltonian.Comment: 11 pages (RevTeX), 5 Postscript files, compressed using uufile
Ethnic variations in upper gastrointestinal hospitalizations and deaths:the Scottish Health and Ethnicity Linkage Study
BACKGROUND: Upper gastrointestinal (GI) diseases are common, but there is a paucity of data describing variations by ethnic group and so a lack of understanding of potential health inequalities. We studied the incidence of specific upper GI hospitalization and death by ethnicity in Scotland.METHODS: Using the Scottish Health and Ethnicity Linkage Study, linking NHS hospitalizations and mortality to the Scottish Census 2001, we explored ethnic differences in incidence (2001-10) of oesophagitis, peptic ulcer disease, gallstone disease and pancreatitis. Relative Risks (RRs) and 95% confidence intervals were calculated using Poisson regression, multiplied by 100, stratified by sex and adjusted for age, country of birth (COB) and socio-economic position. The White Scottish population (100) was the reference population.RESULTS: Ethnic variations varied by outcome and sex, e.g. adjusted RRs (95% confidence intervals) for oesophagitis were comparatively higher in Bangladeshi women (209; 124-352) and lower in Chinese men (65; 51-84) and women (69; 55-88). For peptic ulcer disease, RRs were higher in Chinese men (171; 131-223). Pakistani women had higher RRs for gallstone disease (129; 112-148) and pancreatitis (147; 109-199). The risks of upper GI diseases were lower in Other White British and Other White [e.g. for peptic ulcer disease in men, respectively (74; 64-85) and (81; 69-94)].CONCLUSION: Risks of common upper GI diseases were comparatively lower in most White ethnic groups in Scotland. In non-White groups, however, risk varied by disease and ethnic group. These results require consideration in health policy, service planning and future research.</p
Fluctuations, dissipation and the dynamical Casimir effect
Vacuum fluctuations provide a fundamental source of dissipation for systems
coupled to quantum fields by radiation pressure. In the dynamical Casimir
effect, accelerating neutral bodies in free space give rise to the emission of
real photons while experiencing a damping force which plays the role of a
radiation reaction force. Analog models where non-stationary conditions for the
electromagnetic field simulate the presence of moving plates are currently
under experimental investigation. A dissipative force might also appear in the
case of uniform relative motion between two bodies, thus leading to a new kind
of friction mechanism without mechanical contact. In this paper, we review
recent advances on the dynamical Casimir and non-contact friction effects,
highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in
Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni,
David Roberts, and Felipe da Rosa. Minor changes, a reference adde
NuMorph: Tools for cortical cellular phenotyping in tissue-cleared whole-brain images
Tissue-clearing methods allow every cell in the mouse brain to be imaged without physical sectioning. However, the computational tools currently available for cell quantification in cleared tissue images have been limited to counting sparse cell populations in stereotypical mice. Here, we introduce NuMorph, a group of analysis tools to quantify all nuclei and nuclear markers within the mouse cortex after clearing and imaging by light-sheet microscopy. We apply NuMorph to investigate two distinct mouse models: a Topoisomerase 1 (Top1) model with severe neurodegenerative deficits and a Neurofibromin 1 (Nf1) model with a more subtle brain overgrowth phenotype. In each case, we identify differential effects of gene deletion on individual cell-type counts and distribution across cortical regions that manifest as alterations of gross brain morphology. These results underline the value of whole-brain imaging approaches, and the tools are widely applicable for studying brain structure phenotypes at cellular resolution
Resonances of low orders in the planetary system of HD37124
The full set of published radial velocity data (52 measurements from Keck +
58 ones from ELODIE + 17 ones from CORALIE) for the star HD37124 is analysed.
Two families of dynamically stable high-eccentricity orbital solutions for the
planetary system are found. In the first one, the outer planets c and d are
trapped in the 2/1 mean-motion resonance. The second family of solutions
corresponds to the 5/2 mean-motion resonance between these planets. In both
families, the planets are locked in (or close to) an apsidal corotation
resonance. In the case of the 2/1 MMR, it is an asymmetric apsidal corotation
(with the difference between the longitudes of periastra ), whereas in the case of the 5/2 MMR it is a symmetric antialigned
one ().
It remains also possible that the two outer planets are not trapped in an
orbital resonance. Then their orbital eccentricities should be relatively small
(less than, say, 0.15) and the ratio of their orbital periods is unlikely to
exceed .Comment: 28 pages, 10 figures, 3 tables; Accepted to Celestial Mechanics and
Dynamical Astronom
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
Understanding preventive behaviors among mid-Western African-American men: a pilot qualitative study of prostate screening
http://dx.doi.org/10.1016/j.jomh.2011.03.00
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