Multi-objective reliability-based optimization with stochastic metamodels.

This paper addresses continuous optimization problems with multiple objectives and parameter uncertainty defined by probability distributions. First, a reliability-based formulation is proposed, defining the nondeterministic Pareto set as the minimal solutions such that user-defined probabilities of nondominance and constraint satisfaction are guaranteed. The formulation can be incorporated with minor modifications in a multiobjective evolutionary algorithm (here: the nondominated sorting genetic algorithm-II). Then, in the perspective of applying the method to large-scale structural engineering problems--for which the computational effort devoted to the optimization algorithm itself is negligible in comparison with the simulation--the second part of the study is concerned with the need to reduce the number of function evaluations while avoiding modification of the simulation code. Therefore, nonintrusive stochastic metamodels are developed in two steps. First, for a given sampling of the deterministic variables, a preliminary decomposition of the random responses (objectives and constraints) is performed through polynomial chaos expansion (PCE), allowing a representation of the responses by a limited set of coefficients. Then, a metamodel is carried out by kriging interpolation of the PCE coefficients with respect to the deterministic variables. The method has been tested successfully on seven analytical test cases and on the 10-bar truss benchmark, demonstrating the potential of the proposed approach to provide reliability-based Pareto solutions at a reasonable computational cost.

Surface structure, model and mechanism of an insect integument adapted to be damaged easily.

BACKGROUND: Several sawfly larvae of the Tenthredinidae (Hymenoptera) are called easy bleeders because their whole body integument, except the head capsule, disrupts very easily at a given spot, under a slight mechanical stress at this spot. The exuding haemolymph droplet acts as a feeding deterrent towards invertebrate predators. The present study aimed to describe the cuticle surface, to consider it from a mechanistic point of view, and to discuss potential consequences of the integument surface in the predator-prey relationships. RESULTS: The integument surface of sawfly larvae was investigated by light microscopy (LM) and scanning electron microscopy (SEM) which revealed that the cuticle of easy bleeders was densely covered by what we call "spider-like" microstructures. Such microstructures were not detected in non-easy bleeders. A model by finite elements of the cuticle layer was developed to get an insight into the potential function of the microstructures during easy bleeding. Cuticle parameters (i.e., size of the microstructures and thickness of the epi-versus procuticle) were measured on integument sections and used in the model. A shear force applied on the modelled cuticle surface led to higher stress values when microstructures were present, as compared to a plan surface. Furthermore, by measuring the diameter of a water droplet deposited on sawfly larvae, the integument of several sawfly species was determined as hydrophobic (e.g., more than Teflon(R)), which was related to the sawfly larvae's ability to bleed easily. CONCLUSION: Easy bleeders show spider-like microstructures on their cuticle surface. It is suggested that these microstructures may facilitate integument disruption as well as render the integument hydrophobic. This latter property would allow the exuding haemolymph to be maintained as a droplet at the integument surface.

Fulminant course of unilateral emphysematous pyelonephritis revealing a renal actinomycosis caused by Actinomyces meyeri, an unknown cause of septic shock.

The objective of this case report is to describe the first case of renal actinomycosis caused by Actinomyces meyeri presenting as severe emphysematous pyelonephritis and complicated by septic shock and multi-organ failure. Emphysematous pyelonephritis is a potentially life-threatening infection mostly described in diabetic patients and predominantly caused by uropathogenic bacteria. Actinomycosis is an uncommon chronic infection due to anaerobic gram-positive bacteria that unusually involves the urinary tract. We report the first case of emphysematous pyelonephritis caused by A. meyeri in a 75-year-old non-diabetic woman. The patient presented with an altered status, fever, nausea, and vomiting lasting for 2 days. A computed tomography scan revealed unilateral emphysematous pyelonephritis. She was rapidly admitted to intensive care unit for a septic shock with multiple organ dysfunctions. A conservative management consisting in renal percutaneous drainage, supportive measures, and prolonged adapted antibiotic therapy resulted in complete recovery. This case report illustrates that renal actinomycosis should be considered in case of emphysematous pyelonephritis given the good prognosis of this infection with conservative medical treatment.