Sequential design of computer experiments for the estimation of a probability of failure

This paper deals with the problem of estimating the volume of the excursion set of a function $f:\mathbb{R}^d \to \mathbb{R}$ above a given threshold, under a probability measure on $\mathbb{R}^d$ that is assumed to be known. In the industrial world, this corresponds to the problem of estimating a probability of failure of a system. When only an expensive-to-simulate model of the system is available, the budget for simulations is usually severely limited and therefore classical Monte Carlo methods ought to be avoided. One of the main contributions of this article is to derive SUR (stepwise uncertainty reduction) strategies from a Bayesian-theoretic formulation of the problem of estimating a probability of failure. These sequential strategies use a Gaussian process model of $f$ and aim at performing evaluations of $f$ as efficiently as possible to infer the value of the probability of failure. We compare these strategies to other strategies also based on a Gaussian process model for estimating a probability of failure.Comment: This is an author-generated postprint version. The published version is available at http://www.springerlink.co

Family and Early Life Factors Associated With Changes in Overweight Status Between Ages 5 and 14 Years: Findings From The Mater University Study Of Pregnancy and its Outcomes

Objective To describe different patterns of overweight status between ages 5 and 14 y and examine the role of modifiable family and early life characteristics in explaining different patterns of change between these two ages. Design A population-based prospective birth cohort. Subjects A total of 2934 children (52% males) who were participants in the Mater-University study of pregnancy, Brisbane, and who were examined at ages 5 and 14 y. Main outcome measures Four patterns of change in overweight/obesity status between ages 5 and 14 y: (i) normal at both ages; (ii) normal at 5 y and overweight/obese at 14 y; (iii) overweight/obese at 5 y and normal at 14 y; (iv) overweight/obese at both ages. Results Of the 2934 participants, 2018 (68.8%) had a normal body mass index (BMI) at ages 5 and 14 y, 425 (14.5%) changed from a normal BMI at age 5 y to overweight or obese at age 14 y, 175 (6.0%) changed from being overweight or obese at age 5 y to normal weight at age 14 y and 316 (10.8%) were overweight or obese at both ages 5 and 14 y. Girls were more likely to make the transition from overweight or obese at age 5 y to normal at 14 y than their boy counterparts. Children whose parents were overweight or obese were more likely to change from having a normal BMI at age 5 y to being overweight at 14 y (fully adjusted RR: 6.17 (95% CI: 3.97, 9.59)) and were more likely to be overweight at both ages (7.44 (95% CI: 4.60, 12.02)). Birth weight and increase in weight over the first 6 months of life were both positively associated with being overweight at both ages. Other explanatory factors were not associated with the different overweight status transitions. Conclusions Parental overweight status is an important determinant of whether a child is overweight at either stage or changes from being not overweight at 5 y to becoming so at 14 y

Nutrient balance and body composition

International audienc

Solution analytique pour la distribution pour des patchs rectangulaires

International audienceThe aim of this paper is to provide a closed-form solution for the thermal stress distribution in a rectangular metal/composite bonded joint. This distribution depends on two directions, so it is suitable for studying bidimensional structures such as metallic plates reinforced with a rectangular composite patch. The solution is obtained using Fourier series. The relevance of the approach proposed in this paper is highlighted through various examples that clearly show that some coupling effects between the two directions of the problem take place. The influence of the nature of the composite plate used is analysed and discussed

Studying the thermoviscoelastic response of the Redux 312 adhesive. Part 2: Modeling

International audienceThe aim of this work is to propose a numerical model of a bonded joint that takes into account the thermoviscoelastic response of the adhesive to compute the stress distribution in the adhesive as well as in the adherends. The adhesive is assumed to obey a generalized Maxwell model. The effect of temperature is taken into account by considering that the branches of the model change with temperature. The numerical solution is obtained iteratively. The particular case of the Redux 312 adhesive is then considered as an example. The procedure is applied in various cases exhibiting an increasing complexity. Some significant differences are observed with the usual solution obtained within the framework of elasticity if the effects of both temperature and time are taken into account

Dietary inadequacies observed in homeless men visiting an emergency night shelter in Paris

International audienceObjective: To assess the dietary intake and the nutritional status of homeless men.Setting: A night emergency shelter in Paris, France.Design: Dietary survey (48-h) including alcohol intake and a questionnaire on age, duration of homelessness, smoking habits. Subjects were also weighed and measured.Subjects: Ninety-seven men aged 18-72 years (mean 43.3), of whom 54% were homeless for more than 18 months, 82% were smokers and 53% were regular and/or excessive drinkers.Results: The BMI distribution was shifted towards low values, the percentage of wasted persons being four times higher than in the reference population. The mean total energy intake was 2376 kcal (SD = 879) and included a high and highly variable percentage of energy derived from alcohol (12.0% (SD = 18.1)). Among drinkers, the mean ethanol intake was 90 g (SD = 102) and there was a significant negative correlation between ethanol and non-alcoholic energy intakes. The median intakes of potassium, calcium, zinc, vitamins 131, 132, and niacin were lower than European Population Reference Intakes but only the mean intake of vitamin B1 was significantly lower. Eighty percent of non-alcoholic energy was provided by charitable organisations. For most nutrients, the nutritional density of the shelter ration was not significantly different from the density of the foods purchased by the homeless.Conclusions: These data suggest that the content of some nutrients should be increased in existing food assistance programs for homeless people in France

Studying the thermoviscoelastic response of the Redux 312 adhesive. Part 1: Experimental characterization

International audienceThe aim of this study is to investigate the thermoviscoelastic behaviour of the Redux 312 structural adhesive. Two types of tests are performed on bulk specimens: dynamic tests over a wide range of temperature and stressrelaxation tests for five temperatures ranging between -50 and 70 °C. Dynamic tests clearly show that the shear modulus of the adhesive decreases with temperature. The parameters governing the Maxwell model used to model the viscoelastic properties of the adhesive are identified with the curves obtained with the stressrelaxation tests for the five different temperatures. The procedure used to identify these parameters takes into account the evolution of these parameters with temperature. Results obtained are presented and discussed throughout the paper

Experimental study of thermal stresses in a bonded joint

International audienceThis paper deals with the assessment of the thermal stress distribution in a composite/aluminium bonded joint. An aluminum specimen symmetrically reinforced with two composite patches is heated while both thermal and displacement fields are measured with an infrared camera and a CCD camera, respectively. The grid method is used to obtain the displacement fields in the composite patch. This displacement field is in good agreement with theoretical expectations. This enables us to deduce the longitudinal strain in the composite patch by fitting the displacement field with a suitable model and differentiating it. The shear stress peak which takes place in the adhesive near the free edge of the patch is finally estimated

Three dimensional stress analysis of a composite patch using stress functions

International audienceA stress function-based analysis is proposed to provide a simple and efficient approximation method of three-dimensional (3D) state of stress that exists near the free edge of bonded composite patches. In order to apply plane strain assumption in a composite patch, a linear superposition of sliced section from a bonded patch is used. In addition, to describe the load transfer mechanism from the substrate to the composite patch, a simple shear lag model is introduced. The 3D stress behavior at the free edge of the composite patch is modeled by Lekhnitskii stress functions, and the governing equations of the given composite patch are obtained by applying the principle of complementary virtual work. After a suitable expansion of the functions, the governing equations are transformed into two coupled ordinary differential equations, and they are solved by a general eigenvalue solution procedure. As the number of base functions increases, the interlaminar stresses converge. The interlaminar stresses reach maximum at the free edge and decrease sharply at the inner part of the patch. The interlaminar stresses are concentrated at the interface between the layers because of the mismatch of material properties and the geometric singularity. Since the proposed method accurately predicts the 3D stresses in a composite patch bonded on the metal substrate, it can be used as a simple and efficient analytical tool for designing such structural components