Impact of water saturation on seismoelectric transfer functions: a laboratory study of coseismic phenomenon

Seismic waves propagating in a porous medium, under favourable conditions, generate measurable electromagnetic fields due to electrokinetic effects. It has been proposed, following experimental and numerical studies, that these so-called ‘seismoelectromagnetic' couplings depend on pore fluid properties. The theoretical frame describing these phenomena are based on the original Biot's theory, assuming that pores are fluid-filled. We study here the impact of a partially saturated medium on amplitudes of those seismoelectric couplings by comparing experimental data to an effective fluid model. We have built a 1-m-length-scale experiment designed for imbibition and drainage of an homogeneous silica sand; the experimental set-up includes a seismic source, accelerometers, electric dipoles and capacitance probes in order to monitor seismic and seismoelectric fields during water saturation. Apparent velocities and frequency spectra (in the kiloHertz range) are derived from seismic and electrical measurements during experiments in varying saturation conditions. Amplitudes of seismic and seismoelectric waves and their ratios (i.e. transfer functions) are discussed using a spectral analysis performed by continuous wavelet transform. The experiments reveal that amplitude ratios of seismic to coseismic electric signals remain rather constant as a function of the water saturation in the Sw=[0.2-0.9] range, consistently with theoretically predicted transfer function

Gathering in Dynamic Rings

The gathering problem requires a set of mobile agents, arbitrarily positioned at different nodes of a network to group within finite time at the same location, not fixed in advanced. The extensive existing literature on this problem shares the same fundamental assumption: the topological structure does not change during the rendezvous or the gathering; this is true also for those investigations that consider faulty nodes. In other words, they only consider static graphs. In this paper we start the investigation of gathering in dynamic graphs, that is networks where the topology changes continuously and at unpredictable locations. We study the feasibility of gathering mobile agents, identical and without explicit communication capabilities, in a dynamic ring of anonymous nodes; the class of dynamics we consider is the classic 1-interval-connectivity. We focus on the impact that factors such as chirality (i.e., a common sense of orientation) and cross detection (i.e., the ability to detect, when traversing an edge, whether some agent is traversing it in the other direction), have on the solvability of the problem. We provide a complete characterization of the classes of initial configurations from which the gathering problem is solvable in presence and in absence of cross detection and of chirality. The feasibility results of the characterization are all constructive: we provide distributed algorithms that allow the agents to gather. In particular, the protocols for gathering with cross detection are time optimal. We also show that cross detection is a powerful computational element. We prove that, without chirality, knowledge of the ring size is strictly more powerful than knowledge of the number of agents; on the other hand, with chirality, knowledge of n can be substituted by knowledge of k, yielding the same classes of feasible initial configurations

Hemodynamic and antifibrotic effects of a selective liver nitric oxide donor V-PYRRO/NO in bile duct ligated rats.

AIM: To assess whether a liver specific nitric oxide (NO) donor (V-PYRRO/NO) would prevent the development of portal hypertension and liver fibrosis in rats with bile duct ligation (BDL). METHODS: Treatment (placebo or V-PYRRO/NO 0.53 micromol/kg per hour) was administered i.v. to rats 2 d before BDL (D-2) and maintained until the day of hemodynamic measurement (D26). Intra-hepatic NO level was estimated by measuring liver cGMP level. Effects of V-PYRRO/NO on liver fibrosis and lipid peroxidation were also assessed. RESULTS: Compared to placebo treatment, V-PYRRO/NO improved splanchnic hemodynamics in BDL rats: portal pressure was significantly reduced by 27% (P<0.0001) and collateral circulation development was almost completely blocked (splenorenal shunt blood flow by 74%, P=0.007). Moreover, V-PYRRO/NO significantly prevented liver fibrosis development in BDL rats (by 30% in hepatic hydroxyproline content and 31% in the area of fibrosis, P<0.0001 respectively), this effect being probably due to a decrease in lipid peroxidation by 44% in the hepatic malondialdehyde level (P=0.007). Interestingly, we observed a significant and expected increase in liver cGMP, without any systemic hemodynamic effects (mean arterial pressure, vascular systemic resistance and cardiac output) in both sham-operated and BDL rats treated with V-PYRRO/NO. This result is in accordance with studies on V-PYRRO/NO metabolism showing a specific release of NO in the liver. CONCLUSION: Continuous administrations of V-PYRRO/NO in BDL rats improved liver fibrosis and splanchnic hemodynamics without any noxious systemic hemo-dynamic effects

R&D progress on second-generation crystals for Laue lens applications

The concept of a gamma-ray telescope based on a Laue lens offers the possibility to increase the sensitivity by more than an order of magnitude with respect to existing instruments. Laue lenses have been developed by our collaboration for several years : the main achievement of this R&D program was the CLAIRE lens prototype. Since then, the endeavour has been oriented towards the development of efficient diffracting elements (crystal slabs), the aim being to step from a technological Laue lens to a scientifically exploitable lens. The latest mission concept featuring a gamma-ray lens is the European Gamma-Ray Imager (GRI) which intends to make use of the Laue lens to cover energies from 200 keV to 1300 keV. Investigations of two promising materials, low mosaicity copper and gradient concentration silicon-germanium are presented in this paper. The measurements have been performed during three runs on beamline ID15A of the European Synchrotron Radiation Facility, and on the GAMS 4 instrument of the Institute Laue-Langevin (both in Grenoble, France) using highly monochromatic beam of energy close to 500 keV. Despite it was not perfectly homogeneous, the presented copper crystal exhibits peak reflectivity of 25% in accordance with theoretical predictions, and a mosaicity around 26 arcsec, the ideal range for the realization of a Laue lens such as GRI. Silicon-germanium featuring a constant gradient have been measured for the very first time at 500 keV. Two samples showed a quite homogeneous reflectivity reaching 26%, which is far from the 48% already observed in experimental crystals but a very encouraging beginning. This results have been used to estimate the performance of the GRI Laue lens design

The X-ray Flux Distribution of Sagittarius A* as Seen by Chandra

We present a statistical analysis of the X-ray flux distribution of Sgr A* from the Chandra X-ray Observatory's 3 Ms Sgr A* X-ray Visionary Project (XVP) in 2012. Our analysis indicates that the observed X-ray flux distribution can be decomposed into a steady quiescent component, represented by a Poisson process with rate $Q=(5.24\pm0.08)\times10^{-3}$ cts s$^{-1},$ and a variable component, represented by a power law process ($dN/dF\propto F^{-\xi},$ $\xi=1.92_{-0.02}^{+0.03}$). This slope matches our recently-reported distribution of flare luminosities. The variability may also be described by a log-normal process with a median unabsorbed 2-8 keV flux of $1.8^{+0.9}_{-0.6}\times10^{-14}$ erg s$^{-1}$ cm$^{-2}$ and a shape parameter $\sigma=2.4\pm0.2,$ but the power law provides a superior description of the data. In this decomposition of the flux distribution, all of the intrinsic X-ray variability of Sgr A* (spanning at least three orders of magnitude in flux) can be attributed to flaring activity, likely in the inner accretion flow. We confirm that at the faint end, the variable component contributes ~10% of the apparent quiescent flux, as previously indicated by our statistical analysis of X-ray flares in these Chandra observations. Our flux distribution provides a new and important observational constraint on theoretical models of Sgr A*, and we use simple radiation models to explore the extent to which a statistical comparison of the X-ray and infrared can provide insights into the physics of the X-ray emission mechanism.Comment: 13 pages, 7 figures, accepted for publication in ApJ. Comments welcom

The SIGMA rat brain templates and atlases for multimodal MRI data analysis and visualization

Preclinical imaging studies offer a unique access to the rat brain, allowing investigations that go beyond what is possible in human studies. Unfortunately, these techniques still suffer from a lack of dedicated and standardized neuroimaging tools, namely brain templates and descriptive atlases. Here, we present two rat brain MRI templates and their associated gray matter, white matter and cerebrospinal fluid probability maps, generated from ex vivo [Formula: see text]-weighted images (90 µm isotropic resolution) and in vivo T2-weighted images (150 µm isotropic resolution). In association with these templates, we also provide both anatomical and functional 3D brain atlases, respectively derived from the merging of the Waxholm and Tohoku atlases, and analysis of resting-state functional MRI data. Finally, we propose a complete set of preclinical MRI reference resources, compatible with common neuroimaging software, for the investigation of rat brain structures and functions.This work is part of the SIGMA project with the reference FCT-ANR/NEU-OSD/0258/2012, co-financed by the French public funding agency ANR (Agence Nationale pour laRecherche, APP Blanc International II 2012), the Portuguese FCT (Fundação para aCiência e Tecnologia) and the Portuguese North Regional Operational Program (ON.2—O Novo Norte) under the National Strategic Reference Framework (QREN), through theEuropean Regional Development Fund (FEDER) as well as the Projecto Estratégico co-funded by FCT (PEst-C/SAU/LA0026-/2013) and the European Regional DevelopmentFund COMPETE (FCOMP-01-0124-FEDER-037298). D.A.B. and A.N. were funded bygrants from FCT-ANR/NEU-OSD/0258/2012. R.M. was supported by the FCT fellow-ship grant with the reference PDE/BDE/113604/2015 from the PhDiHES program. A.C.was supported by a grant from the foundation NRJ. P.M. was funded by FundaçãoCalouste Gulbenkian (Portugal;‘Better mental health during ageing based on temporalprediction of individual brain ageing trajectories TEMPO’) with Grant Number P-139977. France Life Imaging is acknowledged for its support in funding the NeuroSpinplatform of preclinical MRI scanners. The authors also acknowledge and thank EdwardGanz, MD, for proof reading our work

Networks become navigable as nodes move and forget

We propose a dynamical process for network evolution, aiming at explaining the emergence of the small world phenomenon, i.e., the statistical observation that any pair of individuals are linked by a short chain of acquaintances computable by a simple decentralized routing algorithm, known as greedy routing. Previously proposed dynamical processes enabled to demonstrate experimentally (by simulations) that the small world phenomenon can emerge from local dynamics. However, the analysis of greedy routing using the probability distributions arising from these dynamics is quite complex because of mutual dependencies. In contrast, our process enables complete formal analysis. It is based on the combination of two simple processes: a random walk process, and an harmonic forgetting process. Both processes reflect natural behaviors of the individuals, viewed as nodes in the network of inter-individual acquaintances. We prove that, in k-dimensional lattices, the combination of these two processes generates long-range links mutually independently distributed as a k-harmonic distribution. We analyze the performances of greedy routing at the stationary regime of our process, and prove that the expected number of steps for routing from any source to any target in any multidimensional lattice is a polylogarithmic function of the distance between the two nodes in the lattice. Up to our knowledge, these results are the first formal proof that navigability in small worlds can emerge from a dynamical process for network evolution. Our dynamical process can find practical applications to the design of spatial gossip and resource location protocols.Comment: 21 pages, 1 figur

Probing dust grain evolution in IM Lupi's circumstellar disc. Multi-wavelength observations and modelling of the dust disc

We present a panchromatic study, involving a multiple technique approach, of the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). We have undertaken a comprehensive observational study of IM Lupi using photometry, spectroscopy, millimetre interferometry and multi-wavelength imaging. For the first time, the disc is resolved from optical and near-infrared wavelengths in scattered light, to the millimetre regime in thermal emission. Our data-set, in conjunction with existing photometric data, provides an extensive coverage of the spectral energy distribution, including a detailed spectrum of the silicate emission bands. We have performed a simultaneous modelling of the various observations, using the radiative transfer code MCFOST, and analysed a grid of models over a large fraction of the parameter space via Bayesian inference. We have constructed a model that can reproduce all of the observations of the disc. Our analysis illustrates the importance of combining a wide range of observations in order to fully constrain the disc model, with each observation providing a strong constraint only on some aspects of the disc structure and dust content. Quantitative evidence of dust evolution in the disc is obtained: grain growth up to millimetre-sized particles, vertical stratification of dust grains with micrometric grains close to the disc surface and larger grains which have settled towards the disc midplane, and possibly the formation of fluffy aggregates and/or ice mantles around grains.Comment: 20 pages, 13 figures. Accepted for publication in A&

The dynamics of stress: a longitudinal MRI study of rat brain structure and connectome

Stress is a well-established trigger for a number of neuropsychiatric disorders, as it alters both structure and function of several brain regions and its networks. Herein, we conduct a longitudinal neuroimaging study to assess how a chronic unpredictable stress protocol impacts the structure of the rat brain and its functional connectome in both high and low responders to stress. Our results reveal the changes that stress triggers in the brain, with structural atrophy affecting key regions such as the prelimbic, cingulate, insular and retrosplenial, somatosensory, motor, auditory and perirhinal/entorhinal cortices, the hippocampus, the dorsomedial striatum, nucleus accumbens, the septum, the bed nucleus of the stria terminalis, the thalamus and several brain stem nuclei. These structural changes are associated with increasing functional connectivity within a network composed by these regions. Moreover, using a clustering based on endocrine and behavioural outcomes, animals were classified as high and low responders to stress. We reveal that susceptible animals (high responders) develop local atrophy of the ventral tegmental area and an increase in functional connectivity between this area and the thalamus, further spreading to other areas that link the cognitive system with the fight-or-flight system. Through a longitudinal approach we were able to establish two distinct patterns, with functional changes occurring during the exposure to stress, but with an inflection point after the first week of stress when more prominent changes were seen. Finally, our study revealed differences in functional connectivity in a brainstem-limbic network that distinguishes resistant and susceptible responders before any exposure to stress, providing the first potential imaging-based predictive biomarkers of an individual's resilience/vulnerability to stressful conditions.This work is part of the Sigma project with the reference FCT-ANR/NEU-OSD/ 0258/2012 co-financed by the French public funding agency ANR (Agence National pour la Recherche, APP Blanc International II 2012), the Portuguese FCT (Fundação para a Ciência e Tecnologia) and by the Portuguese North Regional Operational Program (ON.2 – O Novo Norte) under the National Strategic Reference Framework (QREN), through the European Regional Development Fund (FEDER) as well as the Projecto Estratégico co-funded by FCT (PEst-C/SAU/LA0026-/2013) and the European Regional Development Fund COMPETE (FCOMP-01-0124-FEDER-037298). DAB and AN were funded by grants from FCT-ANR/NEU-OSD/0258/2012. RM is supported by the FCT fellowship grant with the reference PDE/BDE/113604/2015 from the PhDiHES program; AC was supported by a grant from the foundation NRJ. PM was funded by Fundação Calouste Gulbenkian (Portugal; ‘Better mental health during ageing based on temporal prediction of individual brain ageing trajectories (TEMPO)’), Grant Number P-139977. We thank Drs Patrício Costa and Pedro Moreira for support on the various statistical analyses.info:eu-repo/semantics/publishedVersio