277 research outputs found
Linearizing torsion classes in the Picard group of algebraic curves over finite fields
We address the problem of computing in the group of -torsion rational
points of the jacobian variety of algebraic curves over finite fields, with a
view toward computing modular representations.Comment: To appear in Journal of Algebr
Random perfect lattices and the sphere packing problem
Motivated by the search for best lattice sphere packings in Euclidean spaces
of large dimensions we study randomly generated perfect lattices in moderately
large dimensions (up to d=19 included). Perfect lattices are relevant in the
solution of the problem of lattice sphere packing, because the best lattice
packing is a perfect lattice and because they can be generated easily by an
algorithm. Their number however grows super-exponentially with the dimension so
to get an idea of their properties we propose to study a randomized version of
the algorithm and to define a random ensemble with an effective temperature in
a way reminiscent of a Monte-Carlo simulation. We therefore study the
distribution of packing fractions and kissing numbers of these ensembles and
show how as the temperature is decreased the best know packers are easily
recovered. We find that, even at infinite temperature, the typical perfect
lattices are considerably denser than known families (like A_d and D_d) and we
propose two hypotheses between which we cannot distinguish in this paper: one
in which they improve Minkowsky's bound phi\sim 2^{-(0.84+-0.06) d}, and a
competitor, in which their packing fraction decreases super-exponentially,
namely phi\sim d^{-a d} but with a very small coefficient a=0.06+-0.04. We also
find properties of the random walk which are suggestive of a glassy system
already for moderately small dimensions. We also analyze local structure of
network of perfect lattices conjecturing that this is a scale-free network in
all dimensions with constant scaling exponent 2.6+-0.1.Comment: 19 pages, 22 figure
ROOOH: A missing piece of the puzzle for OH measurements in low-NO environments?
Abstract. Field campaigns have been carried out with the FAGE (fluorescence assay by
gas expansion) technique in remote biogenic environments in the last decade
to quantify the in situ concentrations of OH, the main oxidant in the
atmosphere. These data have revealed concentrations of OH radicals up to a
factor of 10 higher than predicted by models, whereby the disagreement
increases with decreasing NO concentration. This was interpreted as a major
lack in our understanding of the chemistry of biogenic VOCs (volatile organic
compounds), particularly isoprene, which are dominant in remote pristine
conditions. But interferences in these measurements of unknown origin have
also been discovered for some FAGE instruments: using a pre-injector, all
ambient OH is removed by fast reaction before entering the FAGE cell, and any
remaining OH signal can be attributed to an interference. This technique is
now systematically used for FAGE measurements, allowing the reliable
quantification of ambient OH concentrations along with the signal due to
interference OH. However, the disagreement between modelled and measured high
OH concentrations of earlier field campaigns as well as the origin of the
now-quantifiable background OH is still not understood. We present in this
paper the compelling idea that this interference, and thus the disagreement
between model and measurement in earlier field campaigns, might be at least
partially due to the unexpected decomposition of a new class of molecule,
ROOOH, within the FAGE instruments. This idea is based on experiments,
obtained with the FAGE set-up of the University of Lille, and supported by a
modelling study. Even though the occurrence of this interference will be
highly dependent on the design and measurement conditions of different FAGE
instruments, including ROOOH in atmospheric chemistry models might reflect a
missing piece of the puzzle in our understanding of OH in clean atmospheres.
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The BMV experiment : a novel apparatus to study the propagation of light in a transverse magnetic field
In this paper, we describe in detail the BMV (Bir\'efringence Magn\'etique du
Vide) experiment, a novel apparatus to study the propagation of light in a
transverse magnetic field. It is based on a very high finesse Fabry-Perot
cavity and on pulsed magnets specially designed for this purpose. We justify
our technical choices and we present the current status and perspectives.Comment: To be published in the European Physical Journal
Bis(monoacylglycero)phosphate regulates oxysterol binding protein-related protein 11 dependent sterol trafficking
Bis(Monoacylglycero) Phosphate (BMP) is a unique phospholipid localized in late endosomes, a critical cellular compartment in low density lipoprotein (LDL)-cholesterol metabolism. In previous work, we demonstrated the important role of BMP in the regulation of macrophage cholesterol homeostasis. BMP exerts a protective role against the pro-apoptotic effect of oxidized LDL (oxLDL) by reducing the production of deleterious oxysterols. As the intracellular sterol traffic in macrophages is in part regulated by oxysterol binding protein (OSBP) and OSBP-related proteins (ORPs), we investigated the role of ORP11, localized at the Golgi-late endosomes interface, in the BMP-mediated protection from oxLDL/oxysterol cytotoxicity. Stably silencing of ORP11 in mouse RAW264.7 macrophages via a shRNA lentiviruses system had no effect on BMP production. However, ORP11 knockdown abrogated the protective action of BMP against oxLDL induced apoptosis. In oxLDL treated control cells, BMP enrichment was associated with reduced generation of 7-oxysterols, while these oxysterol species were abundant in the ORP11 knock-down cells. Of note, BMP enrichment in ORP11 knock-down cells was associated with a drastic increase in free cholesterol and linked to a decrease of cholesterol efflux. The expression of ATP-binding cassette-transporter G1 (ABCG1) was also reduced in the ORP11 knock-down cells. These observations demonstrate a cooperative function of OPR11 and BMP, in intracellular cholesterol trafficking in cultured macrophages. We suggest that BMP favors the egress of cholesterol from late endosomes via an ORP11-dependent mechanism, resulting in a reduced production of cytotoxic 7-oxysterols.Peer reviewe
The RNA workbench: best practices for RNA and high-throughput sequencing bioinformatics in Galaxy
RNA-based regulation has become a major research topic in molecular biology. The analysis of epigenetic and expression data is therefore incomplete if RNA-based regulation is not taken into account. Thus, it is increasingly important but not yet standard to combine RNA-centric data and analysis tools with other types of experimental data such as RNA-seq or ChIP-seq. Here, we present the RNA workbench, a comprehensive set of analysis tools and consolidated workflows that enable the researcher to combine these two worlds. Based on the Galaxy framework the workbench guarantees simple access, easy extension, flexible adaption to personal and security needs, and sophisticated analyses that are independent of command-line knowledge. Currently, it includes more than 50 bioinformatics tools that are dedicated to different research areas of RNA biology including RNA structure analysis, RNA alignment, RNA annotation, RNA-protein interaction, ribosome profiling, RNA-seq analysis and RNA target prediction. The workbench is developed and maintained by experts in RNA bioinformatics and the Galaxy framework. Together with the growing community evolving around this workbench, we are committed to keep the workbench up-to-date for future standards and needs, providing researchers with a reliable and robust framework for RNA data analysis. Availability: The RNA workbench is available at https://github.com/bgruening/galaxy-rna-workbench
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