Finite size effects in a model for plasticity of amorphous composites

We discuss the plastic behavior of an amorphous matrix reinforced by hard particles. A mesoscopic depinning-like model accounting for Eshelby elastic interactions is implemented. Only the effect of a plastic disorder is considered. Numerical results show a complex size-dependence of the effective flow stress of the amorphous composite. In particular the departure from the mixing law shows opposite trends associated to the competing effects of the matrix and the reinforcing particles respectively. The reinforcing mechanisms and their effects on localization are discussed. Plastic strain is shown to gradually concentrate on the weakest band of the system. This correlation of the plastic behavior with the material structure is used to design a simple analytical model. The latter nicely captures reinforcement size effects in $-(\log N/N)^{1/2}$ observed numerically. Predictions of the effective flow stress accounting for further logarithmic corrections show a very good agreement with numerical results.Comment: 18 pages, 19 figure

Accounting representation and the slave trade: The Guide du Commerce of Gaignat de L\u27Aulnais

The Guide du commerce occupies a distinctive place in the French-language literature on accounting. Passed over by most specialists in the history of maritime trade and the slave trade, the manual has never been the subject of a documented historical study. The apparent realism of the examples, the luxury of details and their precision, all bear witness to a deep concern to go beyond a simple apprenticeship in bookkeeping. Promoting itself essentially as un guide du commerce, the volume offers strategic examples for small local businesses, as well as for those engaged in international trade. Yet, the realism also demonstrated the expertise of the author in the eyes of potential purchasers. Inspired by the work of Bottin [2001], we investigate the extent to which the manual reflects real-world practices and provides a faithful glimpse into the socio-economic context of the period. Two additional questions are discussed briefly in our conclusion. First, can the work of Gaignat constitute a source document for the history of la traite negriere? The second entails our early deliberations about the place of this volume in the history of the slave trade itself

Comptabilité et traite négrière. Le Guide du commerce de Gaignat de l'Aulnais (1718-1791)

Malgré un titre très général qui explique certainement le peu de place qui lui a été fait jusque-là dans l'histoire de la comptabilité, le Guide du commerce de Gaignat de l'Aulnais (1771) est vraisemblablement l'un des tout premiers manuels spécialisés de comptabilité, mais d'une spécialisation qui lui confère une place très particulière. Au-delà de quelques paragraphes consacrés aux matières commerciales traditionnelles — marchandises à échanger en divers pays, pratique du change, effets de commerce, poids et mesures, etc. — et d'une présentation relativement classique de la tenue des livres en partie simple et parties doubles, l'ouvrage est essentiellement consacré au commerce maritime et, plus particulièrement, à l'un de ses aspects les plus dramatiques : la traite négrière. L’essor consécutif d’une fiscalité complexe a fourni par la suite tant à ces juristes qu’aux comptables un rôle de plus en plus important qu’ils se partageaient. L’Etat, pour assurer sa quiétude quant à l’établissement de l’assiette fiscale, formalisera alors une profession comptable libérale connue aujourd’hui sous le titre d’expert-comptable.

Discreteness effects in a reacting system of particles with finite interaction radius

An autocatalytic reacting system with particles interacting at a finite distance is studied. We investigate the effects of the discrete-particle character of the model on properties like reaction rate, quenching phenomenon and front propagation, focusing on differences with respect to the continuous case. We introduce a renormalized reaction rate depending both on the interaction radius and the particle density, and we relate it to macroscopic observables (e.g., front speed and front thickness) of the system.Comment: 23 pages, 13 figure

Fronts dynamics in the presence of spatio-temporal structured noises

Front dynamics modeled by a reaction-diffusion equation are studied under the influence of spatio-temporal structured noises. An effective deterministic model is analytical derived where the noise parameters, intensity, correlation time and correlation length appear explicitely. The different effects of these parameters are discussed for the Ginzburg-Landau and Schl\"ogl models. We obtain an analytical expression for the front velocity as a function of the noise parameters. Numerical simulations results are in a good agreement with the theoretical predictions.Comment: 11 pages, 6 figures; REVTEX; to be published in Phys.Rev.E, july 200

Prevalence and occurrence of zoonotic bacterial pathogens in surface waters determined by quantitative PCR

The prevalence and concentrations of Campylobacter jejuni, Salmonella spp. and enterohaemorrhagic E. coli (EHEC) were investigated in surface waters in Brisbane, Australia using quantitative PCR (qPCR) based methodologies. Water samples were collected from Brisbane City Botanic Gardens (CBG) Pond, and two urban tidal creeks (i.e., Oxley Creek and Blunder Creek). Of the 32 water samples collected, 8 (25%), 1 (3%), 9 (28%), 14 (44%), and 15 (47%) were positive for C. jejuni mapA, Salmonella invA, EHEC O157 LPS, EHEC VT1, and EHEC VT2 genes, respectively. The presence/absence of the potential pathogens did not correlate with either E. coli or enterococci concentrations as determined by binary logistic regression. In conclusion, the high prevalence, and concentrations of potential zoonotic pathogens along with the concentrations of one or more fecal indicators in surface water samples indicate a poor level of microbial quality of surface water, and could represent a significant health risk to users. The results from the current study would provide valuable information to the water quality managers in terms of minimizing the risk from pathogens in surface waters

Cell distribution after intracoronary bone marrow stem cell delivery in damaged and undamaged myocardium: implications for clinical trials

International audienceABSTRACT : INTRODUCTION : Early randomized clinical trials of autologous bone marrow cardiac stem cell therapy have reported contradictory results highlighting the need for a better evaluation of protocol designs. This study was designed to quantify and compare whole body and heart cell distribution after intracoronary or peripheral intravenous injection of autologous bone marrow mononuclear cells in a porcine acute myocardial infarction model with late reperfusion. METHODS : Myocardial infarction was induced using balloon inflation in the left coronary artery in domestic pigs. At seven days post-myocardial infarction, 1 x 10(8) autologous bone marrow mononuclear cells were labeled with fluorescent marker and/or 99mTc radiotracer, and delivered using intracoronary or peripheral intravenous injection (leg vein). RESULTS : Scintigraphic analyses and Upsilon-emission radioactivity counting of harvested organs showed a significant cell fraction retained within the heart after intracoronary injection (6 +/- 1.7% of injected radioactivity at 24 hours), whereas following peripheral intravenous cell injection, no cardiac homing was observed at 24 hours and cells were mainly detected within the lungs. Importantly, no difference was observed in the percentage of retained cells within the myocardium in the presence or absence of myocardial infarction. Histological evaluation did not show arterial occlusion in both animal groups and confirmed the presence of bone marrow mononuclear cells within the injected myocardium area. CONCLUSIONS : Intravenous bone marrow mononuclear cell injection was ineffective to target myocardium. Myocardial cell distribution following intracoronary injection did not depend on myocardial infarction presence, a factor that could be useful for cardiac cell therapy in patients with chronic heart failure of non-ischemic origin or with ischemic myocardium without myocardial infarction

Cooee bitumen. II. Stability of linear asphaltene nanoaggregates

Asphaltene and smaller aromatic molecules tend to form linear nanoaggregates in bitumen.Over the years bitumen undergoes chemical aging and during this process, the size of the nanoaggregate increases. This increase is associated with an increase in viscosity and brittleness of the bitumen, eventually leading to road deterioration. This paper focuses on understanding the mechanisms behind nanoaggregate size and stability. We used molecular dynamics simulations to quantify the probability of having a nanoaggregate of a given size in the stationary regime. To model this complicated behavior, we chose first to consider the simple case where only asphaltene molecules are counted in a nanoaggregate. We used a master equation approach and a related statistical mechanics model. The linear asphaltene nanoaggregates behave as a rigid linear chain. The most complicated case where all aromatic molecules are counted in a nanoaggregate is then discussed. The linear aggregates where all aromatic molecules are counted seem to behave as a flexible linear chain.Comment: 31 pages, 9 figure