3D simulations of supernova remnants evolution including non-linear particle acceleration

If a sizeable fraction of the energy of supernova remnant shocks is channeled into energetic particles (commonly identified with Galactic cosmic rays), then the morphological evolution of the remnants must be distinctly modified. Evidence of such modifications has been recently obtained with the Chandra and XMM-Newton X-ray satellites. To investigate these effects, we coupled a semi-analytical kinetic model of shock acceleration with a 3D hydrodynamic code (by means of an effective adiabatic index). This enables us to study the time-dependent compression of the region between the forward and reverse shocks due to the back reaction of accelerated particles, concomitantly with the development of the Rayleigh-Taylor hydrodynamic instability at the contact discontinuity. Density profiles depend critically on the injection level η of particles: for η ≲ 10-4 modifications are weak and progressive, for η ˜ 10-3 modifications are strong and immediate. Nevertheless, the extension of the Rayleigh-Taylor unstable region does not depend on the injection rate. A first comparison of our simulations with observations of Tycho's remnant strengthens the case for efficient acceleration of protons at the forward shock

Inverse problem and Bertrand's theorem

The Bertrand's theorem can be formulated as the solution of an inverse problem for a classical unidimensional motion. We show that the solutions of these problems, if restricted to a given class, can be obtained by solving a numerical equation. This permit a particulary compact and elegant proof of Bertrand's theorem.Comment: 11 pages, 3 figure

Optical-fiber-microsphere for remote fluorescence correlation spectroscopy

International audienceFluorescence correlation spectroscopy (FCS) is a versatile method that would greatly benefit to remote optical-fiber fluorescence sensors. However, the current state-of-the-art struggles with high background and low detection sensitivities that prevent the extension of fiber-based FCS down to the single-molecule level. Here we report the use of an optical fiber combined with a latex microsphere to perform FCS analysis. The sensitivity of the technique is demonstrated at the single molecule level thanks to a photonic nanojet effect. This offers new opportunities for reducing the bulky microscope setup and extending FCS to remote or in vivo applications

Approximation of conformal mappings using conformally equivalent triangular lattices

Consider discrete conformal maps defined on the basis of two conformally equivalent triangle meshes, that is edge lengths are related by scale factors associated to the vertices. Given a smooth conformal map $f$, we show that it can be approximated by such discrete conformal maps $f^\epsilon$. In particular, let $T$ be an infinite regular triangulation of the plane with congruent triangles and only acute angles (i.e.\ $<\pi/2$). We scale this tiling by $\epsilon>0$ and approximate a compact subset of the domain of $f$ with a portion of it. For $\epsilon$ small enough we prove that there exists a conformally equivalent triangle mesh whose scale factors are given by $\log|f'|$ on the boundary. Furthermore we show that the corresponding discrete conformal maps $f^\epsilon$ converge to $f$ uniformly in $C^1$ with error of order $\epsilon$.Comment: 14 pages, 3 figures; v2 typos corrected, revised introduction, some proofs extende

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What can genetics tell us about the history of a human-mediated introduction of the golden-striped salamander south of its native range?

The golden-striped salamander is a streamside species endemic to the northwestern corner of the Iberian Peninsula. In the first half of the twentieth century, an undisclosed number of individuals of this species were reportedly captured in Buçaco, Central Portugal, and deliberately introduced in Sintra Mountains, 170 km south of its native distribution range. The discovery of a breeding population of this salamander in Sintra during 2015 prompted this work: we used neutral genetic markers, the mitochondrial DNA cytochrome b (cytb), and seven microsatellite loci to elucidate on the relict/human-introduced nature of Sintra population, identify the potential source population, and infer the severity of founder effect. Our results support a human-mediated introduction. First, sequencing analysis of cytb showed the presence of a unique haplotype (h31) in Sintra, which was detected only in Buçaco and in two additional populations located close to Mondego river. Second, microsatellite analysis showed that Sintra is more closely related to populations in between Douro and Mondego rivers (Central Portugal), instead of its geographically closest populations (southernmost), as would be expected if Sintra was a relict population isolated in an interglacial refuge. Third, Sintra presents both reduced levels of genetic variability and effective population size when compared to native populations, particularly to those of Central Portugal. Consistent with an isolated population funded by a small number of individuals (inferred herein to be ca. 10–11 salamanders), Sintra forms a geographically coherent genetic unit that is significantly differentiated from the extant native C. lusitanica populations. Although our data provide supporting evidence for Buçaco as a likely source population, as documented in the literature, overall, we cannot unequivocally exclude other populations close to Mondego river as a potential source of the introduced individuals in Sintra.info:eu-repo/semantics/acceptedVersio

Frequency parametrization to numerically predict flutter in turbomachinery

In the quest for performance, modern turbomachinery designs are increasingly proner to flutter hazards. Unfortunately, their prediction is currently too expensive and inaccurate for industrial purpose. A significant step towards faster methods would consist in substituting a sequential algorithm to the classical iterative ones encountered in loose coupling strategies. The approach proposed here makes it possible through the use of a meta-model taking into account the sensitivity to design variables. This parametrized method is evaluated on a standard well referenced turbine configuration

Structure of molecular packing probed by polarization-resolved nonlinear four-wave mixing and coherent anti-Stokes Raman-scattering microscopy

International audienceWe report a method that is able to provide refined structural information on molecular packing in biomolecular assemblies using polarization-resolved four-wavemixing and coherent anti-Stokes Raman-scattering microscopy. These third-order nonlinear processes allow quantifying high orders of symmetry which are exploited here to reveal a high level of detail in the angular disorder behavior at the molecular scale in lipid membranes

A switch from horizontal compression to vertical extension in the Vrancea slab explained by the volume reduction of serpentine dehydration

The Vrancea slab, Romania, is a subducted remnant of the Tethyan lithosphere characterized by a significant intermediate-depth seismicity (60–170 km). A recent study showed a correlation between this seismicity and major dehydration reactions, involving serpentine minerals up to 130 km depth, and high-pressure hydrated talc deeper. Here we investigate the potential link between the triggering mechanisms and the retrieved focal mechanisms of 940 earthquakes, which allows interpreting the depth distribution of the stress field. We observe a switch from horizontal compression to vertical extension between 100 and 130 km depth, where the Clapeyron slope of serpentine dehydration is negative. The negative volume change within dehydrating serpentinized faults, expected mostly sub-horizontal in the verticalized slab, could well explain the vertical extension recorded by the intermediate-depth seismicity. This apparent slab pull is accompanied with a rotation of the main compressive stress, which could favour slab detachments in active subduction zones