Collective motion of self-propelled particles interacting without cohesion

We present a comprehensive study of Vicsek-style self-propelled particle models in two and three space dimensions. The onset of collective motion in such stochastic models with only local alignment interactions is studied in detail and shown to be discontinuous (first-order like). The properties of the ordered, collectively moving phase are investigated. In a large domain of parameter space including the transition region, well-defined high-density and high-order propagating solitary structures are shown to dominate the dynamics. Far enough from the transition region, on the other hand, these objects are not present. A statistically-homogeneous ordered phase is then observed, which is characterized by anomalously-strong density fluctuations, superdiffusion, and strong intermittency.Comment: Submitted to Physical Review

Deformations of elliptic fibre bundles in positive characteristic

We study deformation theory of elliptic fibre bundles over curves in positive characteristics. As applications, we give examples of non-liftable elliptic surfaces in charactertic two and three, which answers a question of Katsura and Ueno. Also, we construct a class of elliptic fibrations, whose liftability is equivalent to a conjecture of F. Oort concerning the liftability of automorphisms of curves. Finally, we classify deformations of bielliptic surfaces.Comment: Many typos fixed (thanks to the referee). Minor improvements in presentatio

A minimal model for spontaneous cell polarization and edge activity in oscillating, rotating and migrating cells

How the cells break symmetry and organize their edge activity to move directionally is a fun- damental question in cell biology. Physical models of cell motility commonly rely on gradients of regulatory factors and/or feedback from the motion itself to describe polarization of edge activity. Theses approaches, however, fail to explain cell behavior prior to the onset of polarization. Our analysis using the model system of polarizing and moving fish epidermal keratocytes suggests a novel and simple principle of self-organization of cell activity in which local cell-edge dynamics depends on the distance from the cell center, but not on the orientation with respect to the front-back axis. We validate this principle with a stochastic model that faithfully reproduces a range of cell-migration behaviors. Our findings indicate that spontaneous polarization, persistent motion, and cell shape are emergent properties of the local cell-edge dynamics controlled by the distance from the cell center.Comment: 8 pages, 5 figure

Assessing land cover changes in the French Pyrenees since the 1940s A semi‐automatic GEOBIA approach using aerial photographs

International audienceAgro-pastoral landscapes of the Pyrenees are subject to fast spontaneous reforestation. The objective of this work is to assess the spatial patterns of land cover changes during the last 70 years in three study sites of the Pyrenees, and to compare the local dynamics in order to observe and to explain similarities and disparities

Kalman filter design for atmospheric tip/tilt, tip/tilt anisoplanatism and focus filtering on extremely large telescopes

This paper discusses Kalman filter design to correct for atmospheric tip/tilt, tip/tilt anisoplanatism and focus disturbances in laser guide star multi-conjugate adaptive optics. Model identification, controller design and computation, command oversampling and disturbance rejection are discussed via time domain analysis and control performance evaluation. End-to-end high-fidelity sky-coverage simulations are presented by Wang and co-authors in a companion paper

Rapid Effect of Treatment of Psoriatic Erythrocytes with the Synthetic Retinoid Acitretin to Increase 8-Azido Cyclic AMP Bindings to the RI Regulatory Subunit

We have recently demonstrated a deficiency in the cyclic adenosine monophosphate (cAMP) – dependent protein kinases (PKA), the intracellular mediator of AMP, in psoriasis. This enzyme defect is expressed in fibroblasts and in red blood cells isolated from psoriatic patients. In these cells, the abnormality noted in cAMP binding to PKA correlates well with the severity of the disease and is corrected by long-term treatment with etretinate. In this study, we determined the effect of oral administration of acitretin in four psoriatic patients on the altered cAMP binding observed with the RI regulatory subunit of PKA in erythrocytes prepared from these patients. Acitretin (30 mg/day) induced a rapid (within 1 h) increase in the ability of the RI regulatory subunit of erythrocytes to bind the 8-azido[32P]cAMP photoaffinity analogue of cAMP. The maximal plateau for this effect of acitretin was observed within 24 h of treatment and preceded the clinical improvement of the disease. The effect of acitretin was dose-dependent, with the maximal response observed at 40 mg acitretin/d. In addition, the rapid exposure (15 mm) of erythrocytes isolated from untreated patients exhibiting severe psoriasis to acitretin also promoted an increase in binding of 8-azido[32P]cAMP to the RI cAMP binding protein. Retinoic acid and 13-cis-retinoic acid were as efficient as acitretin in inducing the increase in binding of 8- azido[32P]cAMP to the RI regulatory subunit, whereas arotinoid was without effect. These results suggest that acitretin may act to modify PKA (the RI regulatory subunit) at the post-transcriptional level, and this may reflect, in part, on the mechanism of action of this synthetic retinoid. Further, monitoring this biochemical event may be helpful in determining the choice of retinoid therapy and in the management of its pharmacology

Atmospheric methane, record from greenland ice core over the last 1000 years

The atmospheric methane concentration in ancient times can be reconstructed by analysing air entrapped in bubbles of polar ice sheets. We present results from an ice core from Central Greenland (Eurocore) covering the last 1000 years. We observe variations of about 70 ppbv around the mean pre-industrial level, which is confirmed at about 700 ppbv on a global average. According to our data, the beginning of the anthropogenic methane increase can be set between 1750 and 1800. Changes in the oxidizing capacity of the atmosphere may contribute significantly to the pre-industrial methane concentration variations, but changes in methane emissions probably play a dominant role. Since methane release depends on a host of influences it is difficult to specify clearly the reasons for these emission changes. Methane concentrations correlate only partially with proxy-data of climatic factors which influence the wetland release (the main source in pre-industrial times). A good correlation between our data and a population record from China suggests that man may already have influenced the CH4-cycle significantly before industrialisation

Ancient Yersinia pestis genomes from across Western Europe reveal early diversification during the First Pandemic (541–750)

The first historically documented pandemic caused by Yersinia pestis began as the Justinianic Plague in 541 within the Roman Empire and continued as the so-called First Pandemic until 750. Although paleogenomic studies have previously identified the causative agent as Y. pestis, little is known about the bacterium’s spread, diversity, and genetic history over the course of the pandemic. To elucidate the microevolution of the bacterium during this time period, we screened human remains from 21 sites in Austria, Britain, Germany, France, and Spain for Y. pestis DNA and reconstructed eight genomes. We present a methodological approach assessing single-nucleotide polymorphisms (SNPs) in ancient bacterial genomes, facilitating qualitative analyses of low coverage genomes from a metagenomic background. Phylogenetic analysis on the eight reconstructed genomes reveals the existence of previously undocumented Y. pestis diversity during the sixth to eighth centuries, and provides evidence for the presence of multiple distinct Y. pestis strains in Europe. We offer genetic evidence for the presence of the Justinianic Plague in the British Isles, previously only hypothesized from ambiguous documentary accounts, as well as the parallel occurrence of multiple derived strains in central and southern France, Spain, and southern Germany. Four of the reported strains form a polytomy similar to others seen across the Y. pestis phylogeny, associated with the Second and Third Pandemics. We identified a deletion of a 45-kb genomic region in the most recent First Pandemic strains affecting two virulence factors, intriguingly overlapping with a deletion found in 17th- to 18th-century genomes of the Second Pandemic. © 2019 National Academy of Sciences. All rights reserved

The integral monodromy of hyperelliptic and trielliptic curves

We compute the \integ/\ell and \integ_\ell monodromy of every irreducible component of the moduli spaces of hyperelliptic and trielliptic curves. In particular, we provide a proof that the \integ/\ell monodromy of the moduli space of hyperelliptic curves of genus $g$ is the symplectic group \sp_{2g}(\integ/\ell). We prove that the \integ/\ell monodromy of the moduli space of trielliptic curves with signature $(r,s)$ is the special unitary group \su_{(r,s)}(\integ/\ell\tensor\integ[\zeta_3])