794 research outputs found
Repeated games for eikonal equations, integral curvature flows and non-linear parabolic integro-differential equations
The main purpose of this paper is to approximate several non-local evolution
equations by zero-sum repeated games in the spirit of the previous works of
Kohn and the second author (2006 and 2009): general fully non-linear parabolic
integro-differential equations on the one hand, and the integral curvature flow
of an interface (Imbert, 2008) on the other hand. In order to do so, we start
by constructing such a game for eikonal equations whose speed has a
non-constant sign. This provides a (discrete) deterministic control
interpretation of these evolution equations. In all our games, two players
choose positions successively, and their final payoff is determined by their
positions and additional parameters of choice. Because of the non-locality of
the problems approximated, by contrast with local problems, their choices have
to "collect" information far from their current position. For integral
curvature flows, players choose hypersurfaces in the whole space and positions
on these hypersurfaces. For parabolic integro-differential equations, players
choose smooth functions on the whole space
Existence of solutions for a higher order non-local equation appearing in crack dynamics
In this paper, we prove the existence of non-negative solutions for a
non-local higher order degenerate parabolic equation arising in the modeling of
hydraulic fractures. The equation is similar to the well-known thin film
equation, but the Laplace operator is replaced by a Dirichlet-to-Neumann
operator, corresponding to the square root of the Laplace operator on a bounded
domain with Neumann boundary conditions (which can also be defined using the
periodic Hilbert transform). In our study, we have to deal with the usual
difficulty associated to higher order equations (e.g. lack of maximum
principle). However, there are important differences with, for instance, the
thin film equation: First, our equation is nonlocal; Also the natural energy
estimate is not as good as in the case of the thin film equation, and does not
yields, for instance, boundedness and continuity of the solutions (our case is
critical in dimension in that respect)
Magnetic Interactions and Transport in (Ga,Cr)As
The magnetic, transport, and structural properties of (Ga,Cr)As are reported.
Zincblende GaCrAs was grown by low-temperature molecular beam
epitaxy (MBE). At low concentrations, x0.1, the materials exhibit unusual
magnetic properties associated with the random magnetism of the alloy. At low
temperatures the magnetization M(B) increases rapidly with increasing field due
to the alignment of ferromagnetic units (polarons or clusters) having large
dipole moments of order 10-10. A standard model of
superparamagnetism is inadequate for describing both the field and temperature
dependence of the magnetization M(B,T). In order to explain M(B) at low
temperatures we employ a distributed magnetic moment (DMM) model in which
polarons or clusters of ions have a distribution of moments. It is also found
that the magnetic susceptibility increases for decreasing temperature but
saturates below T=4 K. The inverse susceptibility follows a linear-T
Curie-Weiss law and extrapolates to a magnetic transition temperature
=10 K. In magnetotransport measurements, a room temperature resistivity
of =0.1 cm and a hole concentration of cm
are found, indicating that Cr can also act as a acceptor similar to Mn. The
resistivity increases rapidly for decreasing temperature below room
temperature, and becomes strongly insulating at low temperatures. The
conductivity follows exp[-(T/T)] over a large range of
conductivity, possible evidence of tunneling between polarons or clusters.Comment: To appear in PRB 15 Mar 200
Goos-H\"{a}nchen and Imbert-Fedorov shifts of polarized vortex beams
We study, analytically and numerically, reflection and transmission of an
arbitrarily polarized vortex beam on an interface separating two dielectric
media and derive general expressions for linear and angular Goos-Hanchen and
Imbert-Fedorov shifts. We predict a novel vortex-induced Goos-Hanchen shift,
and also reveal direct connection between the spin-induced angular shifts and
the vortex-induced linear shifts.Comment: 4 pages, 2 figures, to appear in Optics Letter
Spontaneous splenic rupture in an active duty Marine upon return from Iraq: a case report
<p>Abstract</p> <p>Introduction</p> <p>Atraumatic splenic rupture is a rare event that has been associated with several infectious disease processes. In the active duty military population, potential exposure to these pathogens is significant. Here we discuss the case of an active duty Marine with spontaneous splenic rupture upon return from a six-month deployment in Iraq.</p> <p>Case presentation</p> <p>A previously healthy 30-year-old Caucasian male active duty Marine presented with abdominal pain, fever and diarrhea after deployment to Iraq in support of Operation Iraqi Freedom. Based on clinical and radiographic evidence, a diagnosis of spontaneous splenic rupture was ultimately suspected. After exploratory laparotomy with confirmation of rupture, splenectomy was performed, and the patient made a full, uneventful recovery. Histopathologic examination revealed mild splenomegaly with a ruptured capsule of undetermined cause.</p> <p>Conclusion</p> <p>Spontaneous splenic rupture is a rare event that may lead to life-threatening hemorrhage if not diagnosed and treated quickly. Although the cause of this patient's case was unknown, atraumatic splenic rupture has been associated with a variety of infectious diseases and demonstrates some risks the active duty military population may face while on deployment. Having an awareness of these pathogens and their role in splenic rupture, clinicians caring for military personnel must be prepared to recognize and treat this potentially fatal complication.</p
Coordinated optimization of visual cortical maps (II) Numerical studies
It is an attractive hypothesis that the spatial structure of visual cortical
architecture can be explained by the coordinated optimization of multiple
visual cortical maps representing orientation preference (OP), ocular dominance
(OD), spatial frequency, or direction preference. In part (I) of this study we
defined a class of analytically tractable coordinated optimization models and
solved representative examples in which a spatially complex organization of the
orientation preference map is induced by inter-map interactions. We found that
attractor solutions near symmetry breaking threshold predict a highly ordered
map layout and require a substantial OD bias for OP pinwheel stabilization.
Here we examine in numerical simulations whether such models exhibit
biologically more realistic spatially irregular solutions at a finite distance
from threshold and when transients towards attractor states are considered. We
also examine whether model behavior qualitatively changes when the spatial
periodicities of the two maps are detuned and when considering more than 2
feature dimensions. Our numerical results support the view that neither minimal
energy states nor intermediate transient states of our coordinated optimization
models successfully explain the spatially irregular architecture of the visual
cortex. We discuss several alternative scenarios and additional factors that
may improve the agreement between model solutions and biological observations.Comment: 55 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1102.335
Rotation, activity, and lithium abundance in cool binary stars
We have used two robotic telescopes to obtain time-series high-resolution
spectroscopy and V I and/or by photometry for a sample of 60 active stars.
Orbital solutions are presented for 26 SB2 and 19 SB1 systems with
unprecedented phase coverage and accuracy. The total of 6,609 R=55,000 echelle
spectra are also used to systematically determine effective temperatures,
gravities, metallicities, rotational velocities, lithium abundances and
absolute H{\alpha}-core fluxes as a function of time. The photometry is used to
infer unspotted brightness, V - I and/or b - y colors, spot-induced brightness
amplitudes and precise rotation periods. Our data are complemented by
literature data and are used to determine rotation-temperature-activity
relations for active binary components. We also relate lithium abundance to
rotation and surface temperature. We find that 74% of all known
rapidly-rotating active binary stars are synchronized and in circular orbits
but 26% are rotating asynchronously of which half have Prot > Porb and e > 0.
Because rotational synchronization is predicted to occur before orbital
circularization active binaries should undergo an extra spin-down besides tidal
dissipation. We suspect this to be due to a magnetically channeled wind with
its subsequent braking torque. We find a steep increase of rotation period with
decreasing effective temperature for active stars. For inactive, single giants
with Prot > 100 d, the relation is much weaker. Our data also indicate a
period-activity relation for H{\alpha} of the form RH{\alpha} \propto P - 0.24
for binaries and RH{\alpha} \propto P -0.14 for singles. Lithium abundances in
our sample increase with effective temperature. On average, binaries of
comparable effective temperature appear to exhibit 0.25 dex less surface
lithium than singles. We also find a trend of increased Li abundance with
rotational period of form log n(Li) \propto - 0.6 log Prot
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SEIS: Insight's Seismic Experiment for Internal Structure of Mars.
By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars' surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking's Mars seismic monitoring by a factor of ∼ 2500 at 1 Hz and ∼ 200 000 at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars' surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of M w ∼ 3 at 40 ∘ epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution.Electronic supplementary materialThe online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users
CD8+ T Cells from Human Neonates Are Biased toward an Innate Immune Response
To better understand why human neonates show a poor response to intracellular pathogens, we compared gene expression and histone modification profiles of neonatal naive CD8+ T cells with that of their adult counterparts. We found that neonatal lymphocytes have a distinct epigenomic landscape associated with a lower expression of genes involved in T cell receptor (TCR) signaling and cytotoxicity and a higher expression of genes involved in the cell cycle and innate immunity. Functional studies corroborated that neonatal CD8+ T cells are less cytotoxic, transcribe antimicrobial peptides, and produce reactive oxygen species. Altogether, our results show that neonatal CD8+ T cells have a specific genetic program biased toward the innate immune response. These findings will contribute to better diagnosis and management of the neonatal immune response.This project was specifically supported by a joint EcosNord-Anuies-SEP-Con-acyt project (M11S01). Work in the M.A.S. laboratory is supported by grantsfrom Consejo Nacional de Ciencia y Tecnologı ́a(CONACYT; CB-2011-01168182) and Programa de Mejoramiento del Profesorado (PROMEPSI-UAEM/13/342). Work in the S.S. laboratory is supported by recurrent fundingfrom the Inserm and Aix-Marseille University and by specific grants from theEuropean Union’s FP7 Program (agreement 282510-BLUEPRINT), the Associ-ation pour la Recherche contre le Cancer (ARC) (project SFI20111203756), andthe Aix-Marseille initiative d’excelence (A*MIDEX) project ANR-11-IDEX-0001-02. We thank Centro Estatal de la Transfusio ́n Sanguı ́nea in Cuernavaca for thedonation of leukocyte concentrates and the mothers and babies of HospitalGeneral Parres in Cuernavaca for the donation of cord blood. This study makesuse of data generated by the Blueprint and Roadmap consortia. A full list of theinvestigators who contributed to the generation of the data is availablefromwww.blueprint-epigenome.euandhttp://www.roadmapepigenomics.org/. Funding for the Blueprint project was provided by the European Union’sSeventh Framework Program (FP7/2007-2013) under grant agreement282510 – BLUEPRINT. The Roadmap consortium is financed by the NIH. Weare grateful to Professor C.I. Pogson for critical reading of the manuscript.S
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