3,812 research outputs found
Strong spin relaxation length dependence on electric field gradients
We discuss the influence of electrical effects on spin transport, and in
particular the propagation and relaxation of spin polarized electrons in the
presence of inhomogeneous electric fields. We show that the spin relaxation
length strongly depends on electric field gradients, and that significant
suppression of electron spin polarization can occur as a result thereof. A
discussion in terms of a drift-diffusion picture, and self-consistent numerical
calculations based on a Boltzmann-Poisson approach shows that the spin
relaxation length in fact can be of the order of the charge screening length.Comment: 4 pages, 3 figures, to be presented at PASPSI
Isolation and Screening of Microorganisms for Their Ability to Reduce the Amount of Cholesterol in a Model System
ABSTRACT
The objective of this study was to isolate and screen the ability of microorganisms to reduce the amount of cholesterol in a model system supplemented with cholesterol. The cholesterol-degrading bacteria were isolated from samples of various fats and authentic strains were also used. Analyses were performed to determine the rate of cholesterol degradation in model system, effect of the medium pH on cholesterol reduction, and identification of cholesterol-degrading bacteria. Rhodococcus equi ATCC 21107, Rhodococcus equi ATCC 33706, Leuconostoc cremoris, Serratia maicescens ATCC 13880 and several bacterial isolates from fats were capable of degrading cholesterol in a model system supplemented with pure soluble cholesterol. Morphological and biochemical characteristics revealed that some of the bacterial isolates tentatively classified as belonged to the genus Pseudomona
Quantifier-Free Interpolation of a Theory of Arrays
The use of interpolants in model checking is becoming an enabling technology
to allow fast and robust verification of hardware and software. The application
of encodings based on the theory of arrays, however, is limited by the
impossibility of deriving quantifier- free interpolants in general. In this
paper, we show that it is possible to obtain quantifier-free interpolants for a
Skolemized version of the extensional theory of arrays. We prove this in two
ways: (1) non-constructively, by using the model theoretic notion of
amalgamation, which is known to be equivalent to admit quantifier-free
interpolation for universal theories; and (2) constructively, by designing an
interpolating procedure, based on solving equations between array updates.
(Interestingly, rewriting techniques are used in the key steps of the solver
and its proof of correctness.) To the best of our knowledge, this is the first
successful attempt of computing quantifier- free interpolants for a variant of
the theory of arrays with extensionality
Measurement of the fraction of t-tbar production via gluon-gluon fusion in p-pbar collisions at sqrt(s)=1.96 TeV
We present a measurement of the ratio of t-tbar production cross section via
gluon-gluon fusion to the total t-tbar production cross section in p-pbar
collisions at sqrt{s}=1.96 TeV at the Tevatron. Using a data sample with an
integrated luminosity of 955/pb recorded by the CDF II detector at Fermilab, we
select events based on the t-tbar decay to lepton+jets. Using an artificial
neural network technique we discriminate between t-tbar events produced via
q-qbar annihilation and gluon-gluon fusion, and find
Cf=(gg->ttbar)/(pp->ttbar)<0.33 at the 68% confidence level. This result is
combined with a previous measurement to obtain the most precise measurement of
this quantity, Cf=0.07+0.15-0.07.Comment: submitted to Phys. Rev.
Measurement of Resonance Parameters of Orbitally Excited Narrow B^0 Mesons
We report a measurement of resonance parameters of the orbitally excited
(L=1) narrow B^0 mesons in decays to B^{(*)+}\pi^- using 1.7/fb of data
collected by the CDF II detector at the Fermilab Tevatron. The mass and width
of the B^{*0}_2 state are measured to be m(B^{*0}_2) =
5740.2^{+1.7}_{-1.8}(stat.) ^{+0.9}_{-0.8}(syst.) MeV/c^2 and \Gamma(B^{*0}_2)
= 22.7^{+3.8}_{-3.2}(stat.) ^{+3.2}_{-10.2}(syst.) MeV/c^2. The mass difference
between the B^{*0}_2 and B^0_1 states is measured to be
14.9^{+2.2}_{-2.5}(stat.) ^{+1.2}_{-1.4}(syst.) MeV/c^2, resulting in a B^0_1
mass of 5725.3^{+1.6}_{-2.2}(stat.) ^{+1.4}_{-1.5}(syst.) MeV/c^2. This is
currently the most precise measurement of the masses of these states and the
first measurement of the B^{*0}_2 width.Comment: 7 pages, 1 figure, 1 table. Submitted to Phys.Rev.Let
Search for lepton flavor violating decays of a heavy neutral particle in p-pbar collisions at root(s)=1.8 TeV
We report on a search for a high mass, narrow width particle that decays
directly to e+mu, e+tau, or mu+tau. We use approximately 110 pb^-1 of data
collected with the Collider Detector at Fermilab from 1992 to 1995. No evidence
of lepton flavor violating decays is found. Limits are set on the production
and decay of sneutrinos with R-parity violating interactions.Comment: Figure 2 fixed. Reference 4 fixed. Minor changes to tex
Chronic heart block in dogs; a method for producing experimental heart failure
A method is described for the production of chronic atrioventricular block in dogs, by incision of the region of the bundle of His through the open right atrium during temporary caval occlusion. Exercise tolerances, chest x-ray films, electrocardiograms, phonocardiograms, cardiac outputs, intracardiac pressures, femoral pressures, and left ventricular coronary flows were obtained preoperatively and from 1 to 10 months postoperatively. The majority of the animals developed clinical, laboratory, and pathological evidence of congestive heart failure. All animals had generalized myocardial hypertrophy
Accelerated sources in de Sitter spacetime and the insufficiency of retarded fields
The scalar and electromagnetic fields produced by the geodesic and uniformly
accelerated discrete charges in de Sitter spacetime are constructed by
employing the conformal relation between de Sitter and Minkowski space.
A special attention is paid to new effects arising in spacetimes which, like
de Sitter space, have spacelike conformal infinities. Under the presence of
particle and event horizons, purely retarded fields (appropriately defined)
become necessarily singular or even cannot be constructed at the "creation
light cones" -- future light cones of the "points" at which the sources "enter"
the universe. We construct smooth (outside the sources) fields involving both
retarded and advanced effects, and analyze the fields in detail in case of (i)
scalar monopoles, (ii) electromagnetic monopoles, and (iii) electromagnetic
rigid and geodesic dipoles.Comment: 36 pages, 5 figures, LaTex2e; minor misprints corrected, one
reference added and some terminology change
Epistemic policy networks in the European Union’s CBRN risk mitigation policy
This paper offers insights into an innovative and currently flagship approach of the European Union (EU) to the mitigation of chemical, biological, radiological, and nuclear (CBRN) risks. Building on its long-time experience in the CBRN field, the EU has incorporated methods familiar to the students of international security governance: it is establishing regional networks of experts and expertise. CBRN Centers of Excellence, as they are officially called, aim to contribute to the security and safety culture in different parts of Africa, the Middle East, South East Asia, and South East Europe, in the broadly construed CBRN area. These regional networks represent a modern form of security cooperation, which can be conceptualized as an epistemic policy networks approach. It offers flexibility to the participating states, which have different incentives to get involved. At the same, however, the paper identifies potential limitations and challenges of epistemic policy networks in this form
Search for a Higgs Boson Decaying to Two W Bosons at CDF
We present a search for a Higgs boson decaying to two W bosons in ppbar collisions at sqrt(s)=1.96 TeV center-of-mass energy. The data sample corresponds to an integrated luminosity of 3.0 fb-1 collected with the CDF II detector. We find no evidence for production of a Higgs boson with mass between 110 and 200 GeV/c^2, and determine upper limits on the production cross section. For the mass of 160 GeV/c^2, where the analysis is most sensitive, the observed (expected) limit is 0.7 pb (0.9 pb) at 95% Bayesian credibility level which is 1.7 (2.2) times the standard model cross section
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