Using Bayes formula to estimate rates of rare events in transition path sampling simulations

Transition path sampling is a method for estimating the rates of rare events in molecular systems based on the gradual transformation of a path distribution containing a small fraction of reactive trajectories into a biased distribution in which these rare trajectories have become frequent. Then, a multistate reweighting scheme is implemented to postprocess data collected from the staged simulations. Herein, we show how Bayes formula allows to directly construct a biased sample containing an enhanced fraction of reactive trajectories and to concomitantly estimate the transition rate from this sample. The approach can remediate the convergence issues encountered in free energy perturbation or umbrella sampling simulations when the transformed distribution insufficiently overlaps with the reference distribution.Comment: 11 pages, 8 figure

Catastrophisme : objectivité et apprentissage institutionnel

Le sentiment « catastrophiste » consiste à dramatiser l’ampleur d’une situation critique en proposant un récit qui met en scène des victimes innocentes et des coupables négligents. Ce catastrophisme ambiant constitue un défi majeur pour les pouvoirs publics en charge de la sécurité publique car il induit chez les citoyens une demande sécuritaire croissante, laquelle pousse les pouvoirs publics à investir toujours plus dans la prévention des risques et la gestion des crises. Dans un contexte de rationalisation des dépenses publiques il apparaît nécessaire d’interroger et d’expliciter les ressorts sociaux du sentiment catastrophiste afin de fournir des propositions concrètes aux pouvoirs publics et en particulier au MEDDE pour une gestion plus pertinente et moins coûteuse des crises et des catastrophes

Low GWP Refrigerant and Partial Miscible Lubricant

Lubricant selection is based on several lubricant properties to satisfied compressor and system reliability, longevity and energy efficiency performances. The use of non-miscible or low soluble lubricant can bring some technical advantage for the compressor and the system. This paper presents investigations results on low GWP refrigerant alternatives for light commercial and commercial applications. The work also targets the reduction refrigerant charge associated with the compressor characteristics

Does Code Generation Promote or Prevent Optimizations?

International audienceThis paper addresses the problem of code optimization for Real-Time and Embedded Systems (RTES). Such systems are designed using Model-Based Development (MBD)approach that consists of performing three major steps: building models, generating code from them and compiling the generated code. Actually, during the code generation, an important part of the modeling language semantics which could be useful for optimization is lost, thus, making impossible some optimizations achievement. This paper shows how adding a new level of optimization at the model level results in a more compact code. It also discusses the impact of the code generation on optimization: whether this step promotes or prevents optimizations. We conclude on a proposal of a new MBD approach containing only steps that advance optimization: modeling and compiling steps

Toward optimized code generation through model-based optimization

International audienceModel-Based Development (MBD) provides an additional level of abstraction, the model, which lets engineers focus on the business aspect of the developed system. MBD permits automatic treatments of these models with dedicated tools like synthesis of system's application by automatic code generation. Real-Time and Embedded Systems (RTES) are often constrained by their environment and/or the resources they own in terms of memory, energy consumption with respect to performance requirements. Hence, an important problem to deal with in RTES development is linked to the optimization of their software part. Although automatic code generation and the use of optimizing compilers bring some answers to application optimization issue, we will show in this paper that optimization results may be enhanced by adding a new level of optimizations in the modeling process. Our arguments are illustrated with examples of the Unified Modeling Language (UML) state machines diagrams which are widely used for control aspect modeling of RTES. The well-known Gnu Compiler Collection (GCC) is used for this study. The paper concludes on a proposal of two step optimization approach that allows reusing as they are, existing compiler optimizations

Contribution of point sources to the soft gamma-ray Galactic emission

The nature of the soft gamma-ray (20-200 keV) Galactic emission has been a matter of debate for a long time. Previous experiments have tried to separate the point source contribution from the real interstellar emission, but with a rather poor spatial resolution, they concluded that the interstellar emission could be a large fraction of the total Galactic emission. INTEGRAL, having both high resolution and high sensitivity, is well suited to reassess more precisely this problem. Using the INTEGRAL core program Galactic Center Deep Exposure (GCDE), we estimate the contribution of detected point sources to the total Galactic flux.Comment: Proceedings of the 5th INTEGRAL Workshop, Munich 16-20 February 2004. ESA SP-55

The Amplitude of Non-Equilibrium Quantum Interference in Metallic Mesoscopic Systems

We study the influence of a DC bias voltage V on quantum interference corrections to the measured differential conductance in metallic mesoscopic wires and rings. The amplitude of both universal conductance fluctuations (UCF) and Aharonov-Bohm effect (ABE) is enhanced several times for voltages larger than the Thouless energy. The enhancement persists even in the presence of inelastic electron-electron scattering up to V ~ 1 mV. For larger voltages electron-phonon collisions lead to the amplitude decaying as a power law for the UCF and exponentially for the ABE. We obtain good agreement of the experimental data with a model which takes into account the decrease of the electron phase-coherence length due to electron-electron and electron-phonon scattering.Comment: New title, refined analysis. 7 pages, 3 figures, to be published in Europhysics Letter

Potential changes in forest composition could reduce impacts of climate change on boreal wildfires

There is general consensus that wildfires in boreal forests will increase throughout this century in response to more severe and frequent drought conditions induced by climate change. However, prediction models generally assume that the vegetation component will remain static over the next few decades. As deciduous species are less flammable than conifer species, it is reasonable to believe that a potential expansion of deciduous species in boreal forests, either occurring naturally or through landscape management, could offset some of the impacts of climate change on the occurrence of boreal wildfires. The objective of this study was to determine the potential of this offsetting effect through a simulation experiment conducted in eastern boreal North America. Predictions of future fire activity were made using multivariate adaptive regression splines (MARS) with fire behavior indices and ecological niche models as predictor variables so as to take into account the effects of changing climate and tree distribution on fire activity. A regional climate model (RCM) was used for predictions of future fire risk conditions. The experiment was conducted under two tree dispersal scenarios: the status quo scenario, in which the distribution of forest types does not differ from the present one, and the unlimited dispersal scenario, which allows forest types to expand their range to fully occupy their climatic niche. Our results show that future warming will create climate conditions that are more prone to fire occurrence. However, unlimited dispersal of southern restricted deciduous species could reduce the impact of climate change on future fire occurrence. Hence, the use of deciduous species could be a good option for an efficient strategic fire mitigation strategy aimed at reducing fire propagation in coniferous landscapes and increasing public safety in remote populated areas of eastern boreal Canada under climate change

Technical aspects of an impact acceleration traumatic brain injury rat model with potential suitability for both microdialysis and PtiO2 monitoring

This report describes technical adaptations of a traumatic brain injury (TBI) model-largely inspired by Marmarou-in order to monitor microdialysis data and PtiO2 (brain tissue oxygen) before, during and after injury. We particularly focalize on our model requirements which allows us to re-create some drastic pathological characteristics experienced by severely head-injured patients: impact on a closed skull, no ventilation immediately after impact, presence of diffuse axonal injuries and secondary brain insults from systemic origin...We notably give priority to minimize anaesthesia duration in order to tend to banish any neuroprotection. Our new model will henceforth allow a better understanding of neurochemical and biochemical alterations resulting from traumatic brain injury, using microdialysis and PtiO2 techniques already monitored in our Intensive Care Unit. Studies on efficiency and therapeutic window of neuroprotective pharmacological molecules are now conceivable to ameliorate severe head-injury treatment

Ablation of hepatocellular carcinoma by percutaneous ethanol injection: Imaging findings

Summary: Since PEI is a treatment based on imaging techniques, the radiologist should be familiar with the various findings that may be observed after PEI on US, CT, and MR images immediately after treatment and during later follow-up. Although US is well suited for performing PEI, contrast-enhanced CT currently is the most commonly used imaging method to evaluate the effect of PEI. Residual, nodular areas of contrast enhancement correlate well with residual tumor and warrant additional treatment. Although the findings on MR images obtained after PEI are more complex, MR imaging may be used as an alternative to C