中跨横隔板对组合铁路桥梁静力和动力特性的影响(案例分析)

为高速列车而设计的中等跨度多肋铁路桥的桥梁上,混凝土桥面是提供横向刚度的主要构件,但横梁上的作用力是未知的。由于横梁需要现场操作和焊接,所以增加了桥梁的成本。研究了一种横隔板的影响,这种横隔板应用在法国的一个典型的多跨度铁路桥梁上。第一个目的是为了提出一种合适的建模方法,可以被用于评估在这种交通荷载呈横向分布的结构上应用横隔板的作用和有效性。第二个目的是为了探究应用横隔板的必要性。为解决这些问题,建立了一个三维模型和非线性材料本构关系,分析了带有横向横隔板的和不带横隔板的桥面在不同的静力荷载条件下(自重,UIC荷载,TGV)的反应。考虑到桥面的动力特性,TGV采用移动荷载模拟。在动力分析中还考虑到了火车的极限速度。静力和动力分析结果表明:横隔板可能并不是必须采用的,除非桥梁受到意外的侧向力作用。因此,在这些桥梁上也许可以不需要安装横隔板。     

Finite element analysis of free-edge stresses in composite laminates under mechanical an thermal loading

In this paper, a multi-particle finite element [Nguyen VT, Caron JF. A new finite element for free edge effect analysis in laminated composites. Comput Struct, accepted for publication] is applied for general laminated and is shown to be capable of simultaneously predicting global and local responses. The analysis of free-edge stresses of composite laminates subjected to mechanical and thermal loads is performed using this C^o${\mathbb{C}}^o$ eight-node layer-wise finite element after a classical bending validation. Laminates with finite dimensions are considered and three-dimensional out-of-plane stresses in the interior and near the free edges are evaluated. The results obtained with this finite element modelling are compared with those available in the literature. The present calculation provides accurate stresses and can be utilised as and operational tool to predict interlaminar stresses under the loads of mechanical and thermal combined.     

Time-dependent spectral analysis of epidemiological time-series with wavelets.

In the current context of global infectious disease risks, a better understanding of the dynamics of major epidemics is urgently needed. Time-series analysis has appeared as an interesting approach to explore the dynamics of numerous diseases. Classical time-series methods can only be used for stationary time-series (in which the statistical properties do not vary with time). However, epidemiological time-series are typically noisy, complex and strongly non-stationary. Given this specific nature, wavelet analysis appears particularly attractive because it is well suited to the analysis of non-stationary signals. Here, we review the basic properties of the wavelet approach as an appropriate and elegant method for time-series analysis in epidemiological studies. The wavelet decomposition offers several advantages that are discussed in this paper based on epidemiological examples. In particular, the wavelet approach permits analysis of transient relationships between two signals and is especially suitable for gradual change in force by exogenous variables.     

Image Decomposition into a Bounded Variation Component and an Oscillating Component

We construct an algorithm to split an image into a sum u + v of a bounded variation component and a component containing the textures and the noise. This decomposition is inspired from a recent work of Y. Meyer. We find this decomposition by minimizing a convex functional which depends on the two variables u and v, alternately in each variable. Each minimization is based on a projection algorithm to minimize the total variation. We carry out the mathematical study of our method. We present some numerical results. In particular, we show how the u component can be used in nontextured SAR image restoration.Jean-François Aujol graduated from 1 Ecole Normale Supérieure de Cachan in 2001. He was a PHD student in Mathematics at the University of Nice-Sophia-Antipolis (France). He was a member of the J.A. Dieudonné Laboratory at Nice, and also a member of the Ariana research group (CNRS/INRIA/UNSA) at Sophia-Antipolis (France). His research interests are calculus of variations, nonlinear partial differential equations, numerical analysis and mathematical image processing (and in particular classification, texture, decomposition model, restoration). He is Assistant Researcher at UCLA (Math Department).Gilles Aubert received the These dEtat es-sciences Mathematiques from the University of Paris 6, France, in 1986. He is currently professor of mathematics at the University of Nice-Sophia Antipolis and member of the J.A. Dieudonne Laboratory at Nice, France. His research interests are calculus of variations, nonlinear partial differential equations and numerical analysis; fields of applications including image processing and, in particular, restoration, segmentation, optical flow and reconstruction in medical imaging.Laure Blanc-Féraud received the Ph.D. degree in image restoration in 1989 and the Habilitation á Diriger des Recherches on inverse problems in image processing in 2000, from the University of Nice-Sophia Antipolis, France. She is currently director of research at CNRS in Sophia Antipolis. Her research interests are inverse problems in image processing by deterministic approach using calculus of variation and PDEs. She is also interested in stochastic models for parameter estimation and their relationship with the deterministic approach. She is currently working in the Ariana research group (I3S/INRIA) which is focussed on Earth observation.Antonin Chambolle studied mathematics and physics at the Ecole normale Supérieure in Paris and received the Ph.D. degree in applied mathematics from the Université de Paris-Dauphine in 1993. Since then he has been a CNRS researcher at the CEREMADE, Université de Paris-Dauphine, and, for a short period, a researcher at the SISSA, Trieste, Italy. His research interest include calculus of variations, with applications to shape optimization, mechanics and image processing.     

Introduction to the Special Section on Psychological and Behavioral Approaches to Occupational Health.

The history of the International Commission on Occupational Health is deeply bound to that of the 20th century. First and only international scientific society of such an importance, it was founded in 1906 to bring solutions to the problems caused by a great number of occupational injuries and diseases due to the developing of industry. With the passing years, from a small medical group it has become a multidisciplinary society, present in 90 countries, where researchers, government authorities, and practitioners are coexisting in a permanent exchange between practice and research. It is composed of international scientific committees, which organize regular conferences and meet every 3 years on the occasion of the great International Congress in Occupational Health. Owing to the changes due to the new technologies of work and to the globalization of economy, the orientation of its activities is in progress: larger opening toward developing countries and the phenomenon of development in general, emphasis on prevention in occupational health, and opening of a new field of research on the psychosocial factors and work organization. At the first conference on this theme, held in Copenhagen in August 1998, occupational health and occupational psychology specialists to meet. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monitoring of Transient Phenomena in Sliding Contact Application to Friction Brakes

This work focuses on the study of transient phenomena, in particular the non-uniformity and space–time variation of friction forces and surface temperature of a brake disc during stop-braking. Friction tests were conducted on a braking tribometer. The friction forces in the contact were measured using a 3D piezoelectric sensor, while the disc surface temperature was investigated by means of a high frequency fibre-optic two-colour pyrometer. An optical lap-top device was used to keep track of disc revolutions, and an original programme was written to plot the space–time variations of the measured parameters. This new original approach helps better understand the coupling between thermal and tribological phenomena occurring during braking.     

Effect of organic poultry purchase frequency on consumer attitudes toward organic poultry meat

Because of the growing consumers' interest in organic meat, consumers' (N = 976) attitude toward organic meat was evaluated. Most respondents (59%) occasionally purchased organic chicken. To determine the organic chicken consumer profile, the organic chicken consumption frequencies of different demographic groups were compared. The results show dependence on age (P= 0.039) and ethnicity (P = 0.015). Older respondents as well as respondents who identified themselves as Caucasians tended to buy organic chicken more frequently. However, many other socio-demographic factors were not correlated with organic chicken consumption: gender (P = 0.185), education (P = 0.235), household income (0.867), living with partner or not (P = 0.235), and number of children (P = 0.883). Taste was identified as the most important meat quality attribute (perceived as [very] important by 94% of the respondents). Other important meat quality criteria were: general appearance, overall health, price, nutritional value, and containing no medical residues. "Organically produced" appeared to not be that important compared with other criteria. When respondents bought organic chicken more often, the importance of most of the meat quality attributes shifted to higher levels of importance, except for the price where an adverse effect was shown. The main motivation factors to buy organic chicken were the perception that organic chicken has fewer residues (pesticides, hormones, antibiotics), is safer, and healthier. The high price for organic meats was the strongest limiting factor for organic meat purchases followed by poor availability. Approximately 41% of the non-buyers and 30% of the occasional buyers perceived organic meat as not or hardly likely to be available in their supermarket. PRACTICAL APPLICATION: This study obtained a better knowledge of consumers' attitudes and perception of organic chicken as well as the effect of various demographics on the likelihood of buying organic chicken. For marketing purposes of organic meats, it helps to know which attributes consumers perceive as important, where the consumer purchases organic chicken, and what the perceived availability of organic chicken is. Additionally, the motivation and deterrent factors are described indicating why the consumer does or does not purchase organic chicken. This information can be valuable to help promoting organic meats to the consumers.     

Modeling bio-atmospheric coupling of the nitrogen cycle through NOx emissions and NOy deposition

The tropospheric and terrestrial nitrogen cycles are connected to one another through the emissions of NO_x and NH_x from soils and vegetation and the subsequent redeposition of these compounds and their products elsewhere. These connections play an important role in the Earth system influencing tropospheric concentrations of NO_x, O₃, and CO₂. Estimates of the biogenic sources of NO_x, soil emissions and biomass burning, are amongst the most variable terms in the global budget of NO_x and are eclipsed only by lightning. A 3-D chemistry transport model, IMAGES, was used to examine how soil emissions and biomass burning influence tropospheric concentrations of NO_x and O₃ as well as NO_y deposition. Soil and biomass burning emissions of NO_x contributed the most to atmospheric NO_x concentrations closest to the surface and south of 30°N. The influence of these emissions on tropospheric O₃ and NO_x concentrations dissipated with height suggesting that these surface emissions are most important to surface ozone concentrations. The removal of either the soil or biomass burning source resulted in a 5-20% difference in tropospheric O₃ concentrations over large regions of the atmosphere. Both sources are also important contributors to N deposition, particularly south of 30°N which, in turn, can generate significant carbon storage. These exercises demonstrate both the importance and complexity of the connections between atmospheric chemistry and the terrestrial biosphere.     

Poly(lactic acid)/carbon nanotube nanocomposites with integrated degradation sensing

For the first time, an in-situ degradation monitoring system for biodegradable polymers is reported in present work. The proposed concept is based on a conductive biodegradable polymer composite, where carbon nanotubes (CNTs) are incorporated in poly(lactic acid) (PLA) in order to develop an intelligent biocomposite system that can sense biodegradation. Changes in electrical resistivity of the PLA/CNT nanocomposites were successfully correlated with degradation levels of the biopolymer. PLA/CNT nanocomposites demonstrated excellent degradation sensing abilities at CNT concentrations around the percolation threshold, with resistivity changes of about four orders of magnitude with biodegradation. In contrast to many other stimuli, biodegradation resulted in a reduction in resistivity due to an increased CNT network density after partial removal of the amorphous phase of the polymer matrix.