Local and global avalanches in a 2D sheared granular medium

We present the experimental and numerical studies of a 2D sheared amorphous material constituted of bidisperse photo-elastic disks. We analyze the statistics of avalanches during shear including the local and global fluctuations in energy and changes in particle positions and orientations. We find scale free distributions for these global and local avalanches denoted by power-laws whose cut-offs vary with inter-particle friction and packing fraction. Different exponents are found for these power-laws depending on the quantity from which variations are extracted. An asymmetry in time of the avalanche shapes is evidenced along with the fact that avalanches are mainly triggered from the shear bands. A simple relation independent from the intensity, is found between the number of local avalanches and the global avalanches they form. We also compare these experimental and numerical results for both local and global fluctuations to predictions from meanfield and depinning theories

PRESSURE BROADENING AND SHIFTING COEFFICIENTS AS TESTS OF H2(D2)-He POTENTIAL ENERGY SURFACES

International audienceWe have calculated the helium-pressure broadening and shifting coefficients of the isotropic Raman Q(1) lines of the fundamental of H 2 and D 2. The quantum dynamical close coupling calculations were performed on five 3-dimensional PESs, namely: the pot3d potential of Bakr et al, 1 the so-called BMP PES, 2 the modified Muchnik and Russek PES, 3 the modified BMP PES, 1 and the Schaefer and Köhler PES. 4 The last one being the oldest one and obtained at the lowest-level of quantum chemical accuracy but has the advantage of covering interactions over a larger intramolecular interval. Moreover, the theoretical values it leads to 5,6,7 are in quite good agreement with experimental pressure broadening and shifting coeffients. 7,8,9,10 By decomposing the kinetic energy dependent pressure broadening cross-sections in an inelastic part and a dephasing one and by also looking at the isotropic contribution of the pressure shifting cross-sections allow us to bring to the fore the main differences that exist between the five PESs we have considered. The modBMP PES has been readily rejected because it is only a slight modification of the original BMP PES. The BMP and modMR PESs lead to thermally averaged values far from the experimental ones. The quantum chemical " state of the art " PES of Bakr et al provides shifting parameters in better agreement than the SK PES with experimental shifts but, the broadening parameters seem to be slightly more accurate with the SK PES. This last point should be confirmed by an accu-

Marked length spectrum rigidity for Anosov surfaces

Let $\Sigma$ be a smooth closed oriented surface of genus $\geq 2$. We prove that two metrics on $\Sigma$ with same marked length spectrum and Anosov geodesic flow are isometric via an isometry isotopic to the identity. The proof combines microlocal tools with the geometry of complex curves.Comment: v2: We correct and simplify the proof of Lemma 3.11. v3: Added a corollary on the centralizer of Anosov geodesic flows. 19 pages, 1 figur

Reconstitution of an active human CENP-E motor

CENP-E is a large kinesin motor protein which plays pivotal roles in mitosis by facilitating chromosome capture and alignment, and promoting microtubule flux in the spindle. So far, it has not been possible to obtain active human CENP-E to study its molecular properties. Xenopus CENP-E motor has been characterized in vitro and is used as a model motor; however, its protein sequence differs significantly from human CENP-E. Here, we characterize human CENP-E motility in vitro. Full-length CENP-E exhibits an increase in run length and longer residency times on microtubules when compared to CENP-E motor truncations, indicating that the C-terminal microtubule-binding site enhances the processivity when the full-length motor is active. In contrast with constitutively active human CENP-E truncations, full-length human CENP-E has a reduced microtubule landing rate in vitro, suggesting that the non-motor coiled-coil regions self-regulate motor activity. Together, we demonstrate that human CENP-E is a processive motor, providing a useful tool to study the mechanistic basis for how human CENP-E drives chromosome congression and spindle organization during human cell division

Tradeoffs in Community Properties Through Time in a Desert Rodent Community

Resource limitation represents an important constraint on ecological communities, which restricts the total abundance, biomass, and community energy flux a given community can support. However, the exact relationship among these three measures of biological activity remains unclear. Here we use a simple framework that links abundance and biomass with an energetic constraint. Under constant energetic availability, it is expected that changes in abundance and biomass can result from shifts in the distribution of individual masses. We test these predictions using long-term data from a desert rodent community. Total energy use for the community has not changed directionally for 25 years, but species composition has. As a result, the average body size has decreased by almost 50% and average abundance has doubled. These results lend support to the idea of resource limitation on desert rodent communities and demonstrate that systems are able to maintain community energy flux in the face of environmental change, through changes in composition and structure