Distributed Verification of Rare Properties using Importance Splitting Observers

Rare properties remain a challenge for statistical model checking (SMC) due to the quadratic scaling of variance with rarity. We address this with a variance reduction framework based on lightweight importance splitting observers. These expose the model-property automaton to allow the construction of score functions for high performance algorithms. The confidence intervals defined for importance splitting make it appealing for SMC, but optimising its performance in the standard way makes distribution inefficient. We show how it is possible to achieve equivalently good results in less time by distributing simpler algorithms. We first explore the challenges posed by importance splitting and present an algorithm optimised for distribution. We then define a specific bounded time logic that is compiled into memory-efficient observers to monitor executions. Finally, we demonstrate our framework on a number of challenging case studies

The Particle Based Moving Interface Method for Soft Matter Mechanics and Fluid/membrane Interactions with Applications to Biological Cells

The mechanics of the interaction between a fluid and a soft interface (such as an elastic membrane or shell) undergoing large deformations appears in many places, such as in biological systems or industrial processes. We present here an Eulerian approach that describes the mechanics of an interface and its interactions with a surrounding fluid via the so-called Navier boundary condition. The interface is modeled as a curvilinear surface with arbitrary mechanical properties across which discontinuities in pressure and tangential fluid velocity can naturally be enforced using a modified version of the extended finite element method. The tracking and evolution of the membrane is then handled with the Grid Based Particle method, and the handling of complex singular boundary conditions around sharp corner is accounted for with the use of an asymptotic/numerical matching method. We show that this method is ideal to describe large membrane deformations, enforce volume constraints, and Navier boundary conditions on the interface with velocity/pressure discontinuities. The method is applied to the study of the filtration of deformable particles through a fibrous network, and an the equivalent permeabilities with respect to the fluid and particles are estimated. The method is then adapted to the study of an elastic material in an Eulerian framework and is shown to be capable of handling arbitrarily large deformations, which is ideal for the study of biological problems

Prediction Models of Skin Temperatures and Heat Loss by Evaporation for Thermal Comfort in Buildings in Hot and Humid Climates in Cameroon

The aim of this study is to propose models for predicting skin temperatures and heat loss by evaporation for the inclusion in the calculations of thermal comfort indicators in hot and humid areas, more particularly in sub-Saharan Africa. This will make it possible to complete the thermal comfort data for this climatic region, which for lack of it still uses the standard based on Fanger models, established mainly for the temperate zone (ISO 7730). The experiments were carried out on a representative sample of 24 people (men and women) in experimental buildings, located in the Douala-Cameroon region, representative of the hot and humid zone, as considered by numerous thermal balance references encountered in the litterature. The measurements of the ambient parameters and of the physiological parameters were carried out according to the recommended standards. 1008 skin temperature measurement points were performed on 3 levels of metabolic activity, in order to provide 72 individual average skin temperature values. Analyzes, statistical validation tests and comparisons were performed. We are able to present the most suitable prediction models, other than those of Fanger, for thermal comfort conditions in air-conditioned buildings in hot and humid areas of sub-Saharan Africa. It appears that the skin of people living in these regions has a higher thermal inertia, less water loss by diffusion or a higher skin barrier than that of people in temperate regions

Parallel Program Performance Debugging with the Pandore II Environment

International audienceIn this paper, we present the overall design of Pandore II, an Environment dedicated to the experimentation of distribution of sequential programs for their execution on distributed memory parallel architectures. The emphasis is then put on two performance analysis tools integrated in this environment

Controlling and Assessing Correlations of Cost Matrices in Heterogeneous Scheduling

International audienceThis paper considers the problem of allocating independent tasks to unrelated machines such as to minimize the maximum completion time. Testing heuristics for this problem requires the generation of cost matrices that specify the execution time of each task on each machine. Numerous studies showed that the task and machine heterogeneities belong to the properties impacting heuristics performance the most. This study focuses on orthogonal properties, the average correlations between each pair of rows and each pair of columns, which is a proximity measure with uniform instances 1. Cost matrices generated with a novel generation method show the effect of these correlations on the performance of several heuristics from the literature. In particular, EFT performance depends on whether the tasks are more correlated than the machines and HLPT performs the best when both correlations are close to one

3D lithium ion batteries—from fundamentals to fabrication

3D microbatteries are proposed as a step change in the energy and power per footprint of surface mountable rechargeable batteries for microelectromechanical systems (MEMS) and other small electronic devices. Within a battery electrode, a 3D nanoarchitecture gives mesoporosity, increasing power by reducing the length of the diffusion path; in the separator region it can form the basis of a robust but porous solid, isolating the electrodes and immobilising an otherwise fluid electrolyte. 3D microarchitecture of the whole cell allows fabrication of interdigitated or interpenetrating networks that minimise the ionic path length between the electrodes in a thick cell. This article outlines the design principles for 3D microbatteries and estimates the geometrical and physical requirements of the materials. It then gives selected examples of recent progress in the techniques available for fabrication of 3D battery structures by successive deposition of electrodes, electrolytes and current collectors onto microstructured substrates by self-assembly methods

List and shelf schedules for independent parallel tasks to minimize the energy consumption with discrete or continuous speeds

International audienceScheduling independent tasks on a parallel platform is a widely-studied problem, in particular when the goal is to minimize the total execution time, or makespan (P||C_max problem in Graham's notations). Also, many applications do not consist of sequential tasks, but rather parallel tasks, either rigid, with a fixed degree of parallelism, or moldable, with a variable degree of parallelism (i.e., for which we can decide at the execution on how many processors they are executed). Furthermore, since the energy consumption of data centers is a growing concern, both from an environmental and economical point of view, minimizing the energy consumption of a schedule is a main challenge to be addressed. One can then decide, for each task, on how many processors it is executed, and at which speed the processors are operated, with the goal to minimize the total energy consumption. We further focus on co-schedules, where tasks are partitioned into shelves, and we prove that the problem of minimizing the energy consumption remains NP-complete when static energy is consumed during the whole duration of the application. We are however able to provide an optimal algorithm for the schedule within one shelf, i.e., for a set of tasks that start at the same time. Several approximation results are derived, both with discrete and continuous speed models, and extensive simulations are performed to show the performance of the proposed algorithms

Influence of Experience on Performance of Individual Surgeons in Thyroid Surgery: Prospective Cross Sectional Multicentre Study

Objective: To determine the association between surgeons’ experience and postoperative complications in thyroid surgery. Design: Prospective cross sectional multicentre study. Setting: High volume referral centres in five academic hospitals in France. Participants: All patients who underwent a thyroidectomy undertaken by every surgeon in these hospitals from 1 April 2008 to 31 December 2009. Main outcome measures: Presence of two permanent major complications (recurrent laryngeal nerve palsy or hypoparathyroidism), six months after thyroid surgery. We used mixed effects logistic regression to determine the association between length of experience and postoperative complications. Results: 28 surgeons completed 3574 thyroid procedures during a one year period. Overall rates of recurrent laryngeal nerve palsy and hypoparathyroidism were 2.08% (95% confidence interval 1.53% to 2.67%) and 2.69% (2.10% to 3.31%), respectively. In a multivariate analysis, 20 years or more of practice was associated with increased probability of both recurrent laryngeal nerve palsy (odds ratio 3.06 (1.07 to 8.80), P=0.04) and hypoparathyroidism (7.56 (1.79 to 31.99), P=0.01). Surgeons’ performance had a concave association with their length of experience (P=0.036) and age (P=0.035); surgeons aged 35 to 50 years had better outcomes than their younger and older colleagues. Conclusions: Optimum individual performance in thyroid surgery cannot be passively achieved or maintained by accumulating experience. Factors contributing to poor performance in very experienced surgeons should be explored further

Caen – 116 rue de la Délivrande

Dans le cadre d’un projet de construction de logements sociaux à Caen, rue de la Délivrande, les travaux de démolition des bâtiments existants ont permis la découverte d’un bunker de la Seconde Guerre mondiale. Les ouvriers ont d’abord cru avoir affaire à une simple cave, mais devant la difficulté à détruire un ouvrage en béton de 2 m d’épaisseur, il a fallu se rendre à l’évidence que celui-ci correspondait à un ouvrage militaire. Prévenu aussitôt par la société Logipays, le Service régional ..