1,282 research outputs found
Load management strategy for Particle-In-Cell simulations in high energy particle acceleration
In the wake of the intense effort made for the experimental CILEX project,
numerical simulation cam- paigns have been carried out in order to finalize the
design of the facility and to identify optimal laser and plasma parameters.
These simulations bring, of course, important insight into the fundamental
physics at play. As a by-product, they also characterize the quality of our
theoretical and numerical models. In this paper, we compare the results given
by different codes and point out algorithmic lim- itations both in terms of
physical accuracy and computational performances. These limitations are illu-
strated in the context of electron laser wakefield acceleration (LWFA). The
main limitation we identify in state-of-the-art Particle-In-Cell (PIC) codes is
computational load imbalance. We propose an innovative algorithm to deal with
this specific issue as well as milestones towards a modern, accurate high-per-
formance PIC code for high energy particle acceleration
Principled Design and Implementation of Steerable Detectors
We provide a complete pipeline for the detection of patterns of interest in
an image. In our approach, the patterns are assumed to be adequately modeled by
a known template, and are located at unknown position and orientation. We
propose a continuous-domain additive image model, where the analyzed image is
the sum of the template and an isotropic background signal with self-similar
isotropic power-spectrum. The method is able to learn an optimal steerable
filter fulfilling the SNR criterion based on one single template and background
pair, that therefore strongly responds to the template, while optimally
decoupling from the background model. The proposed filter then allows for a
fast detection process, with the unknown orientation estimation through the use
of steerability properties. In practice, the implementation requires to
discretize the continuous-domain formulation on polar grids, which is performed
using radial B-splines. We demonstrate the practical usefulness of our method
on a variety of template approximation and pattern detection experiments
The Bay of Kiladha Project (Argolid, Greece): Bridging East and West
The project, a joint research program between the University of Geneva, under the aegis of the Swiss School of Archaeology in Greece, and the Greek Ephorate of Underwater Antiquities, aims at finding traces of prehistoric human activity in a small bay of the southern Argolid, near the Franchthi Cave, a major prehistoric site used from 40,000 years ago to 5,000 years ago. For most of these 35,000 years, because of global sea-level change in prehistory, the Bay of Kiladha was in fact a small coastal plain, where the sedentary farmers of the Neolithic period had probably their village.Research currently focuses on two parts of the bay: the Franchthi sector, close to the Cave (submerged Neolithic village) and the Lambayanna sector, just a few hundred meters to the north of Franchthi Cave (HA II fortified settlement)
RNA Control of HIV-1 Particle Size Polydispersity
HIV-1, an enveloped RNA virus, produces viral particles that are known to be
much more heterogeneous in size than is typical of non-enveloped viruses. We
present here a novel strategy to study HIV-1 Viral Like Particles (VLP)
assembly by measuring the size distribution of these purified VLPs and
subsequent viral cores thanks to Atomic Force Microscopy imaging and
statistical analysis. This strategy allowed us to identify whether the presence
of viral RNA acts as a modulator for VLPs and cores size heterogeneity in a
large population of particles. These results are analyzed in the light of a
recently proposed statistical physics model for the self-assembly process. In
particular, our results reveal that the modulation of size distribution by the
presence of viral RNA is qualitatively reproduced, suggesting therefore an
entropic origin for the modulation of RNA uptake by the nascent VLP
Surface rearrangement at complex adsorbate-substrate interfaces
On the basis of the information theory approach we propose a novel
statistical scheme for analyzing the evolution of coupled adsorbate-substrate
systems, in which the substrate undergoes the adsorbate-induced
transformations. A relation between the substrate morphology and the adsorbate
thermodynamic state is established. This allows one to estimate the surface
structure in terms of incomplete experimental information and the one
concerning the adsorbate thermodynamic response to the structural
modifications.Comment: 5 pages, 3 figure
Universal relaxation function in nonextensive systems
We have derived the dipolar relaxation function for a cluster model whose
volume distribution was obtained from the generalized maximum Tsallis
nonextensive entropy principle. The power law exponents of the relaxation
function are simply related to a global fractal parameter and for
large time to the entropy nonextensivity parameter . For intermediate times
the relaxation follows a stretched exponential behavior. The asymptotic power
law behaviors both in the time and the frequency domains coincide with those of
the Weron generalized dielectric function derived from an extension of the Levy
central limit theorem. They are in full agreement with the Jonscher
universality principle. Moreover our model gives a physical interpretation of
the mathematical parameters of the Weron stochastic theory and opens new paths
to understand the ubiquity of self-similarity and power laws in the relaxation
of large classes of materials in terms of their fractal and nonextensive
properties.Comment: Two figures. Submitted for publicatio
Effects of caffeine on cognitive and autonomic measures in heavy and light caffeine consumers
A phase I dose-escalation study of the immunocytokine EMD 521873 (Selectikine) in patients with advanced solid tumours
n/
Roles of Major Facilitator Superfamily Transporters in Phosphate Response in Drosophila
The major facilitator superfamily (MFS) transporter Pho84 and the type III transporter Pho89 are responsible for metabolic effects of inorganic phosphate in yeast. While the Pho89 ortholog Pit1 was also shown to be involved in phosphate-activated MAPK in mammalian cells, it is currently unknown, whether orthologs of Pho84 have a role in phosphate-sensing in metazoan species. We show here that the activation of MAPK by phosphate observed in mammals is conserved in Drosophila cells, and used this assay to characterize the roles of putative phosphate transporters. Surprisingly, while we found that RNAi-mediated knockdown of the fly Pho89 ortholog dPit had little effect on the activation of MAPK in Drosophila S2R+ cells by phosphate, two Pho84/SLC17A1–9 MFS orthologs (MFS10 and MFS13) specifically inhibited this response. Further, using a Xenopus oocyte assay, we show that MSF13 mediates uptake of [³³P]-orthophosphate in a sodium-dependent fashion. Consistent with a role in phosphate physiology, MSF13 is expressed highest in the Drosophila crop, midgut, Malpighian tubule, and hindgut. Altogether, our findings provide the first evidence that Pho84 orthologs mediate cellular effects of phosphate in metazoan cells. Finally, while phosphate is essential for Drosophila larval development, loss of MFS13 activity is compatible with viability indicating redundancy at the levels of the transporters.National Institutes of Health (U.S.) (NIDDK 5K08DK078361)Harvard Catalys
Extragalactic Magnetism with SOFIA (SALSA Legacy Program). VII. A tomographic view of far infrared and radio polarimetric observations through MHD simulations of galaxies
The structure of magnetic fields in galaxies remains poorly constrained,
despite the importance of magnetism in the evolution of galaxies. Radio
synchrotron and far-infrared dust polarization (FIR) polarimetric observations
are the best methods to measure galactic scale properties of magnetic fields in
galaxies beyond the Milky Way. We use synthetic polarimetric observations of a
simulated galaxy to identify and quantify the regions, scales, and interstellar
medium (ISM) phases probed at FIR and radio wavelengths. Our studied suite of
magnetohydrodynamical cosmological zoom-in simulations features
high-resolutions (10 pc full-cell size) and multiple magnetization models. Our
synthetic observations have a striking resemblance to those of observed
galaxies. We find that the total and polarized radio emission extends to
approximately double the altitude above the galactic disk (half-intensity disk
thickness of kpc)
relative to the FIR total and polarized emission that are concentrated in the
disk midplane ( kpc).
Radio emission traces magnetic fields at scales of pc, whereas
FIR emission probes magnetic fields at the smallest scales of our simulations.
These scales are comparable to our spatial resolution and well below the
spatial resolution ( pc) of existing FIR polarimetric measurements.
Finally, we confirm that synchrotron emission traces a combination of the warm
neutral and cold neutral gas phases, whereas FIR emission follows the densest
gas in the cold neutral phase in the simulation. These results are independent
of the ISM magnetic field strength. The complementarity we measure between
radio and FIR wavelengths motivates future multiwavelength polarimetric
observations to advance our knowledge of extragalactic magnetism.Comment: Submitted to ApJ. 32 pages, 15 figure
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