486 research outputs found
Bounds on second generation scalar leptoquarks from the anomalous magnetic moment of the muon
We calculate the contribution of second generation scalar leptoquarks to the
anomalous magnetic moment of the muon (AMMM). In the near future, E-821 at
Brookhaven will reduce the experimental error on this parameter to , an improvement of 20 over its current value.
With this new experimental limit we obtain a lower mass limit of
\ GeV for the second generation scalar leptoquark, when its
Yukawa-like coupling \ to quarks and leptons is taken to be
of the order of the electroweak coupling .Comment: 5 pages, plain tex, 1 figure (not included available under request
Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors
We describe a theory of Mn local-moment magnetization relaxation due to p-d
kinetic-exchange coupling with the itinerant-spin subsystem in the
ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping
coefficient implied by this mechanism is calculated as a function of Mn moment
density, hole concentration, and quasiparticle lifetime. Comparison with
experimental ferromagnetic resonance data suggests that in annealed strongly
metallic samples, p-d coupling contributes significantly to the damping rate of
the magnetization precession at low temperatures. By combining the theoretical
Gilbert coefficient with the values of the magnetic anisotropy energy, we
estimate that the typical critical current for spin-transfer magnetization
switching in all-semiconductor trilayer devices can be as low as .Comment: 4 pages, 2 figures, submitted to Rapid Communication
Local influence of boundary conditions on a confined supercooled colloidal liquid
We study confined colloidal suspensions as a model system which approximates
the behavior of confined small molecule glass-formers. Dense colloidal
suspensions become glassier when confined between parallel glass plates. We use
confocal microscopy to study the motion of confined colloidal particles. In
particular, we examine the influence particles stuck to the glass plates have
on nearby free particles. Confinement appears to be the primary influence
slowing free particle motion, and proximity to stuck particles causes a
secondary reduction in the mobility of free particles. Overall, particle
mobility is fairly constant across the width of the sample chamber, but a
strong asymmetry in boundary conditions results in a slight gradient of
particle mobility.Comment: For conference proceedings, "Dynamics in Confinement", Grenoble,
March 201
Two-dimensional hole precession in an all-semiconductor spin field effect transistor
We present a theoretical study of a spin field-effect transistor realized in
a quantum well formed in a p--doped ferromagnetic-semiconductor-
nonmagnetic-semiconductor-ferromagnetic-semiconductor hybrid structure. Based
on an envelope-function approach for the hole bands in the various regions of
the transistor, we derive the complete theory of coherent transport through the
device, which includes both heavy- and light-hole subbands, proper modeling of
the mode matching at interfaces, integration over injection angles, Rashba spin
precession, interference effects due to multiple reflections, and gate-voltage
dependences. Numerical results for the device current as a function of
externally tunable parameters are in excellent agreement with approximate
analytical formulae.Comment: 9 pages, 11 figure
Assessing Contention Effects on MPI_Alltoall Communications
12 pagesInternational audienceOne of the most important collective communication patterns used in scientific applications is the complete exchange, also called All-to-All. Although efficient algorithms have been studied for specific networks, general solutions like those available in well-known MPI distributions (e.g. the MPI_Alltoall operation) are strongly influenced by the congestion of network resources. In this paper we present an integrated approach to model the performance of the All-to-All collective operation, which consists in identifying a contention signature that characterizes a given network environment, using it to augment a contention-free communication model. This approach, assessed by experimental results, allows an accurate prediction of the performance of the All-to-All operation over different network architectures with a small overhead
Green function techniques in the treatment of quantum transport at the molecular scale
The theoretical investigation of charge (and spin) transport at nanometer
length scales requires the use of advanced and powerful techniques able to deal
with the dynamical properties of the relevant physical systems, to explicitly
include out-of-equilibrium situations typical for electrical/heat transport as
well as to take into account interaction effects in a systematic way.
Equilibrium Green function techniques and their extension to non-equilibrium
situations via the Keldysh formalism build one of the pillars of current
state-of-the-art approaches to quantum transport which have been implemented in
both model Hamiltonian formulations and first-principle methodologies. We offer
a tutorial overview of the applications of Green functions to deal with some
fundamental aspects of charge transport at the nanoscale, mainly focusing on
applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references,
submitted to Springer series "Lecture Notes in Physics
AKT activity orchestrates marginal zone B cell development in mice and humans.
The signals controlling marginal zone (MZ) and follicular (FO) B cell development remain incompletely understood. Here, we show that AKT orchestrates MZ B cell formation in mice and humans. Genetic models that increase AKT signaling in B cells or abolish its impact on FoxO transcription factors highlight the AKT-FoxO axis as an on-off switch for MZ B cell formation in mice. In humans, splenic immunoglobulin (Ig) D <sup>+</sup> CD27 <sup>+</sup> B cells, proposed as an MZ B cell equivalent, display higher AKT signaling than naive IgD <sup>+</sup> CD27 <sup>-</sup> and memory IgD <sup>-</sup> CD27 <sup>+</sup> B cells and develop in an AKT-dependent manner from their precursors in vitro, underlining the conservation of this developmental pathway. Consistently, CD148 is identified as a receptor indicative of the level of AKT signaling in B cells, expressed at a higher level in MZ B cells than FO B cells in mice as well as humans
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