A Simple Geometrical Model for Solid Friction

We present a simple model for the friction of two solid bodies moving against each other. In a self consistent way we can obtain the dependence of the macroscopic friction force as a function of the driving velocity, the normal force and the ruggedness of the surfaces in contact. Our results are discussed in the context of friction laws used in earthquake models.Comment: 9 pages, plain TeX, preprint HLRZ 24/9

Rheology of granular flows across the transition from soft to rigid particles

International audienc

Metodologias para análise de incertezas paramétricas em conversores de potência

Le développement de la technologie des semi-conducteurs dans les trente dernières années a augmenté le nombre des nouvelles applications dans lesquelles les dispositifs d électronique de puissance sont utilisés. L'augmentation de la rapidité de commutation des transistors a permis que la conversion de puissance se produise de façon de plus en plus performante. Cet avantage apporte un nouveau challenge dans la phase de conception, lié à la Compatibilité Électromagnétique. En effet, les impulsions rapides de tension et courant dans les convertisseurs de puissance sont une source d émissions électromagnétiques conduites indésirables. Des méthodologies de modélisation précises, qui prennent en compte une grande partie des effets parasites, ont été développées pour évaluer le niveau de ces émissions conduites. Lorsque ces méthodologies sont confrontées aux mesures, les résultats sont en concordance dans une large gamme de fréquence, elles peuvent donc être considérées comme des outils fiables de pronostic. Néanmoins, la plupart des paramètres du modèle d un système électronique ne peuvent pas réellement être déterminés précisément : les conditions d opération sont souvent mal connues (variations de température ou d'humidité) ; les paramètres caractéristiques des composants présentent une certaine dispersion de production ; des interférences externes sont imprévisibles. Dans ce contexte, il est intéressant de développer des méthodologies de modélisation qui soient capables de prendre en compte des incertitudes paramétriques. Dans cette thèse, deux méthodologies d analyse d incertitudes, adaptées aux convertisseurs de puissance, sont proposées. Les incertitudes paramétriques sont modélisées en utilisant des fonctions de densité de probabilité et l objectif de l analyse proposée est de déterminer les moments statistiques, la fonction de densité de probabilité ou la limite supérieure probabiliste des émissions conduites d un convertisseur de puissance quelconque. Des techniques pour aborder les difficultés liées aux non-linéarités, au temps de simulation important et au nombre élevé de dimensions sont discutées. Les méthodologies proposées sont appliquées à des problèmes test et à des problèmes réels, et les résultats sont comparés aux méthodologies classiques. La précision des résultats des méthodologies proposées est similaire aux techniques classiques, mais le temps de calcul est considérablement réduit. Finalement, ce travail ouvre des possibilités de développements nouveaux pour l analyse des incertitudes des systèmes non-linéaires et à grande échelle.The development of semiconductor technology in the last decades has boosted numerous new applications in which power electronic devices have been employed. The fast switching of transistors has allowed power conversion to be performed with high efficiency. However, this improvement brought a new challenge in design: the Electromagnetic Compatibility. Both fast pulses of voltage and current, inside power converters, are a source of unwanted conducted electromagnetic emissions. High accurate modeling methodologies, which takes into account most of the parasitic phenomena, have been developed, in order to compute the level of conducted emissions of electronic devices. When these methods are confronted with measurement, they show good agreement in a large frequency range, and thus they are considered a trustful prediction tool for electronic systems design. Nevertheless, most of the parameters of the model of any electronic system, in reality, cannot be determined precisely, due to unknown operation conditions (i.e.: temperature or humidity variations), production dispersion of the components or unpredictable external interference. In this context, it is of great interest to develop modeling methodologies that are able to take into account parametric uncertainties. In this thesis, two methodologies for uncertainty analysis of power converters are proposed. In the first, namely Polynomials per Frequency, the parametric uncertainty is modeled using probability density functions and the objective of the proposed analysis is to determine the statistical moments, the probability density function or a probabilistic upper bound for the conducted emissions of an arbitrary power converter. In the second methodology, namely Adaptive Unscented Transform, techniques to tackle the difficulties of nonlinearity, long simulation time and high-dimensionality are discussed. The proposed methodologies are applied to benchmark and real-world problems and the results are confronted to classical approaches. The accuracy of the gotten results is similar to those obtained by classical methods, although the required computational time is significantly reduced. Finally, this work leaves many possibilities for further development in the field of uncertainty analysis of nonlinear and highdimensional systems.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Diphasic non-local model for granular surface flows

Considering recent results revealing the existence of multi-scale rigid clusters of grains embedded in granular surface flows, i.e. flows down an erodible bed, we describe here the surface flows rheology through a non-local constitutive law. The predictions of the resulting model are compared quantitatively to experimental results: The model succeeds to account for the counter-intuitive shape of the velocity profile observed in experiments, i.e. a velocity profile decreasing exponentially with depth in the static phase and remaining linear in the flowing layer with a velocity gradient independent of both the flowing layer thickness, the angle between the flow and the horizontal, and the coefficient of restitution of the grains. Moreover, the scalings observed in rotating drums are recovered, at least for small rotating speed.Comment: 7 pages, submitted to Europhys. Let

Advances in Zero-Sum Dynamic Games

International audienceThe survey presents recent results in the theory of two-person zero-sum repeated games and their connections with differential and continuous-time games. The emphasis is made on the following(1) A general model allows to deal simultaneously with stochastic and informational aspects.(2) All evaluations of the stage payoffs can be covered in the same framework (and not only the usual Cesàro and Abel means).(3) The model in discrete time can be seen and analyzed as a discretization of a continuous time game. Moreover, tools and ideas from repeated games are very fruitful for continuous time games and vice versa.(4) Numerous important conjectures have been answered (some in the negative).(5) New tools and original models have been proposed. As a consequence, the field (discrete versus continuous time, stochastic versus incomplete information models) has a much more unified structure, and research is extremely active

Renal Tumors of Childhood—A Histopathologic Pattern-Based Diagnostic Approach

Renal tumors comprise approximately 7% of all malignant pediatric tumors. This is a highly heterogeneous group of tumors, each with its own therapeutic management, outcome, and association with germline predispositions. Histopathology is the key in establishing the correct diagnosis, and therefore pathologists with expertise in pediatric oncology are needed for dealing with these rare tumors. While each tumor shows different histologic features, they do have considerable overlap in cell type and histologic pattern, making the diagnosis difficult to establish, if based on routine histology alone. To this end, ancillary techniques, such as immunohistochemistry and molecular analysis, can be of great importance for the correct diagnosis, resulting in appropriate treatment. To use ancillary techniques cost-effectively, we propose a pattern-based approach and provide recommendations to aid in deciding which panel of antibodies, supplemented by molecular characterization of a subset of genes, are required

Finite-time fluctuations in the degree statistics of growing networks

This paper presents a comprehensive analysis of the degree statistics in models for growing networks where new nodes enter one at a time and attach to one earlier node according to a stochastic rule. The models with uniform attachment, linear attachment (the Barab\'asi-Albert model), and generalized preferential attachment with initial attractiveness are successively considered. The main emphasis is on finite-size (i.e., finite-time) effects, which are shown to exhibit different behaviors in three regimes of the size-degree plane: stationary, finite-size scaling, large deviations.Comment: 33 pages, 7 figures, 1 tabl

Up-scaling, formative phases, and learning in the historical diffusion of energy technologies

The 20th century has witnessed wholesale transformation in the energy system marked by the pervasive diffusion of both energy supply and end-use technologies. Just as whole industries have grown, so too have unit sizes or capacities. Analysed in combination, these unit level and industry level growth patterns reveal some consistencies across very different energy technologies. First, the up-scaling or increase in unit size of an energy technology comes after an often prolonged period of experimentation with many smaller-scale units. Second, the peak growth phase of an industry can lag these increases in unit size by up to 20 years. Third, the rate and timing of up-scaling at the unit level is subject to countervailing influences of scale economies and heterogeneous market demand. These observed patterns have important implications for experience curve analyses based on time series data covering the up-scaling phases of energy technologies, as these are likely to conflate industry level learning effects with unit level scale effects. The historical diffusion of energy technologies also suggests that low carbon technology policies pushing for significant jumps in unit size before a ‘formative phase’ of experimentation with smaller-scale units are risky

Sultones and Sultines via a Julia-Kocienski Reaction of Epoxides

We thank the EPSRC/Syngenta for a CASE Ph.D. Studentship (to G.M.T.S. under grant EP/J50029X/1), the EPSRC UK National Mass Spectrometry Facility at Swansea University and the EPSRC UK National Crystallography Service Facility at Southampton University.37 We are indebted to Andrew Plant and Janice Black (Syngenta) for the initial suggestion of using the combination of LiN(SiMe3)2/CH2Cl2 and Matthew Reid (Syngenta) for NMR assistance

The UMBRELLA SIOP-RTSG 2016 Wilms tumour pathology and molecular biology protocol

On the basis of the results of previous national and international trials and studies, the Renal Tumour Study Group of the International Society of Paediatric Oncology (SIOP–RTSG) has developed a new study protocol for paediatric renal tumours: the UMBRELLA SIOP–RTSG 2016 protocol (the UMBRELLA protocol). Currently, the overall outcomes of patients with Wilms tumour are excellent, but subgroups with poor prognosis and increased relapse rates still exist. The identification of these subgroups is of utmost importance to improve treatment stratification, which might lead to reduction of the direct and late effects of chemotherapy. The UMBRELLA protocol aims to validate new prognostic factors, such as blastemal tumour volume and molecular markers, to further improve outcome. To achieve this aim, large, international, high-quality databases are needed, which dictate optimization and international harmonization of specimen handling and comprehensive sampling of biological material, refine definitions and improve logistics for expert review. To promote broad implementation of the UMBRELLA protocol, the updated SIOP–RTSG pathology and molecular biology protocol for Wilms tumours has been outlined, which is a consensus from the SIOP–RTSG pathology panel