31,435 research outputs found
Analysis of hadronic invariant mass spectrum in inclusive charmless semileptonic B decays
We make an analysis of the hadronic invariant mass spectrum in inclusive
charmless semileptonic B meson decays in a QCD-based approach. The decay width
is studied as a function of the invariant mass cut. We examine their
sensitivities to the parameters of the theory. The theoretical uncertainties in
the determination of from the hadronic invariant mass spectrum are
investigated. A strategy for improving the theoretical accuracy in the value of
is described.Comment: 13 pages, 5 Postscript figure
Magnification of spin Hall effect in bilayer electron gas
Spin transport properties of a coupled bilayer electron gas with Rashba
spin-orbit coupling are studied. The definition of the spin currents in each
layer as well as the corresponding continuity-like equations in the bilayer
system are given. The curves of the spin Hall conductivities obtained in each
layer exhibit sharp cusps around a particular value of the tunnelling strength
and the conductivities undergo sign changes across this point. Our
investigation on the impurity effect manifests that an arbitrarily small
concentration of nonmagnetic impurities does not suppress the spin Hall
conductivity to zero in the bilayer system. Based on these features, an
experimental scheme is suggested to detect a magnification of the spin Hall
effect.Comment: Revtex 10 pages, 4 figures; largely extended versio
Evidence for Antiferromagnetic Order in LaCeCuO from Angular Magnetoresistance Measurements
We investigated the in-plane angular magnetoresistivity (AMR) of -phase LaCeCuO (LCCO) thin films () fabricated by a pulsed laser deposition technique. The in-plane
AMR with shows a twofold symmetry instead of the
fourfold behavior found in other electron-doped cuprates such as PrCeCuO and NdCeCuO. The twofold AMR
disappears above a certain temperature, . The is well above
for ( K), and decreases with increasing doping,
until it is no longer observed above at . This twofold AMR
below is suggested to originate from an antiferromagnetic or spin
density wave order.Comment: to be published in Phys. Rev. B, Vol. 80 (2009
First-principles modelling of magnetic excitations in Mn12
We have developed a fully microscopic theory of magnetic properties of the
prototype molecular magnet Mn12. First, the intra-molecular magnetic properties
have been studied by means of first-principles density functional-based
methods, with local correlation effects being taken into account within the
local density approximation plus U (LDA+U) approach. Using the magnetic force
theorem, we have calculated the interatomic isotropic and anisotropic exchange
interactions and full tensors of single-ion anisotropy for each Mn ion.
Dzyaloshinskii-Moriya (DM) interaction parameters turned out to be unusually
large, reflecting a low symmetry of magnetic pairs in molecules, in comparison
with bulk crystals. Based on these results we predict a distortion of
ferrimagnetic ordering due to DM interactions. Further, we use an exact
diagonalization approach allowing to work with as large Hilbert space dimension
as 10^8 without any particular symmetry (the case of the constructed magnetic
model). Based on the computational results for the excitation spectrum, we
propose a distinct interpretation of the experimental inelastic neutron
scattering spectra.Comment: 8 pages, 2 figures. To appear in Physical Review
MintHint: Automated Synthesis of Repair Hints
Being able to automatically repair programs is an extremely challenging task.
In this paper, we present MintHint, a novel technique for program repair that
is a departure from most of today's approaches. Instead of trying to fully
automate program repair, which is often an unachievable goal, MintHint performs
statistical correlation analysis to identify expressions that are likely to
occur in the repaired code and generates, using pattern-matching based
synthesis, repair hints from these expressions. Intuitively, these hints
suggest how to rectify a faulty statement and help developers find a complete,
actual repair. MintHint can address a variety of common faults, including
incorrect, spurious, and missing expressions.
We present a user study that shows that developers' productivity can improve
manyfold with the use of repair hints generated by MintHint -- compared to
having only traditional fault localization information. We also apply MintHint
to several faults of a widely used Unix utility program to further assess the
effectiveness of the approach. Our results show that MintHint performs well
even in situations where (1) the repair space searched does not contain the
exact repair, and (2) the operational specification obtained from the test
cases for repair is incomplete or even imprecise
Elastic-Net Regularization: Error estimates and Active Set Methods
This paper investigates theoretical properties and efficient numerical
algorithms for the so-called elastic-net regularization originating from
statistics, which enforces simultaneously l^1 and l^2 regularization. The
stability of the minimizer and its consistency are studied, and convergence
rates for both a priori and a posteriori parameter choice rules are
established. Two iterative numerical algorithms of active set type are
proposed, and their convergence properties are discussed. Numerical results are
presented to illustrate the features of the functional and algorithms
Nonperturbative QCD Contributions to the Semileptonic Decay Width of the B Meson
Nonperturbative QCD contributions to the inclusive semileptonic decay of the
B meson consist of the dynamic and kinematic components. We calculate the decay
width in an approach based on the light-cone expansion and the heavy quark
effective theory, which is able to include both components of nonperturbative
QCD contributions. The kinematic component results in the phase-space extension
and is shown to be quantitatively crucial, which could increase the decay width
significantly. We find that the semileptonic decay width is enhanced by
long-distance strong interactions by +(9\pm 6)%. This analysis is used to
determine the CKM matrix element |V_{cb}| with a controlled theoretical error.
Implications of the phase-space effects for the nonleptonic decay widths of b
hadrons are briefly discussed. The experimental evidence for the phase-space
effects is pointed out.Comment: 16 pages, Latex, 3 eps figures included, published version
(discussion extended, references updated, the main result unchanged
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Periodontitis-induced systemic inflammation exacerbates atherosclerosis partly via endothelial-mesenchymal transition in mice.
Growing evidence suggests close associations between periodontitis and atherosclerosis. To further understand the pathological relationships of these associations, we developed periodontitis with ligature placement around maxillary molars or ligature placement in conjunction with Porphyromonas gingivalis lipopolysaccharide injection at the ligature sites (ligature/P.g. LPS) in Apolipoprotein E knock out mice and studied the atherogenesis process in these animals. The mice were fed with high fat diet for 11 weeks and sacrificed for analyzing periodontitis, systemic inflammation, and atherosclerosis. Controls did not develop periodontitis or systemic inflammation and had minimal lipid deposition in the aortas, but mice receiving ligature or ligature/P.g. LPS showed severe periodontitis, systemic inflammation, and aortic plaque formation. The aortic plaque contained abundant macrophages and cells expressing both endothelial and mesenchymal cell markers. The severity of periodontitis was slightly higher in mice receiving ligature/P.g. LPS than ligature alone, and the magnitude of systemic inflammation and aortic plaque formation were also notably greater in the mice with ligature/P.g. LPS. These observations indicate that the development of atherosclerosis is due to systemic inflammation caused by severe periodontitis. In vitro, P.g. LPS enhanced the secretion of pro-inflammatory cytokines from macrophages and increased the adhesion of monocytes to endothelial cells by upregulating the expression of adhesion molecules from endothelial cells. Moreover, secretory proteins, such as TNF-α, from macrophages induced endothelial-mesenchymal transitions of the endothelial cells. Taken together, systemic inflammation induced by severe periodontitis might exacerbate atherosclerosis via, in part, causing aberrant functions of vascular endothelial cells and the activation of macrophages in mice
Evidence for a new magnetic field scale in CeCoIn5
The Nernst coefficient of CeCoIn5 displays a distinct anomaly at H_K ~ 23 T.
This feature is reminiscent of what is observed at 7.8 T in CeRu2Si2, a
well-established case of metamagnetic transition. New frequencies are observed
in de Haas-van Alphen oscillations when the field exceeds 23 T, which may
indicate a modification of the Fermi surface at this field.Comment: submitted to Physical Review Letter
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