Multidomain finite and discrete elements method for impact analysis of a concrete structure

This article focuses on a formulation for coupling discrete and finite element methods. The efficiency of the discrete element method for studying the fracture of heterogeneous media has been demonstrated, but it is limited by the number of elements. A multidomain analysis is thus proposed in order to reduce the computational effort. The structure is split into two subdomains, in each of which the method is adapted to the behavior of the structure under impact. The DEM is used to model the media close to the impacts. It easily takes into account the discontinuities. The remaining structure is modelled by the FEM. The aims of this paper are to present a method with rotations coupling and to propose a way to reduce spurious wave reflections; it presents an application on a rock impact on a concrete slab.     

Influence de la teneur en eau et de la température sur la conductivité thermique du béton cellulaire autoclavé

Résumé Pour mesurer simultanément sur quatre échantillons l'évolution de la conductivité thermique en fonction de la température, un dispositif expérimental spécifique, entièrement piloté par ordinateur, a été développé en intégrant quatre sondes à chocs thermiques ‘monotiges’ dans une étuve chaud/froid. Nous avons choisi d'explorer la gamme des températures comprises entre 0 et 60°C. Une série de teneurs en eau entre l'état saturé et l'état sec ont été réalisées par séchage progressif au four à micro-ondes. Sept échantillons de béton cellulaire autoclavé avec des masses volumiques allant de 270 à 630 kg m⁻³ ont été sélectionnés et leurs relations conductivité thermique-teneur en eau-température complètement déterminées. Sur la base de ces résultats, deux modèles d'estimation de la conductivité thermique du béton cellulaire autoclavé en fonction de ses caractéristiques et de son état hygrothermique ont pu être construits et validés; l'un nécessite la connaissance des propriétés thermiques de la ‘matrice solide’ microporeuse entourant la macroporosité cellulaire, l'autre se place à une autre échelle en considérant, cette fois, les propriétés du ‘grain’ solide non-poreux. Ces deux modèles présentent des caractères prédictifs équivalents et l'on choisira l'un ou l'autre suivant les données dont on dispose.

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Summary An experimental facility entirely controlled by a computer and using the ‘line source method” for measuring the thermal conductivity has been developed to characterize the evolution of this parameter with water content and temperature on four samples of autoclaved aerated concrete (AAC) blocks simultaneously. The temperature range studied was 0–60°C in steps of 10°C. A series of water contents from completely saturated to completely dry was established by progressive drying in a microwave oven. This technique ensures homogeneous distribution of the water inside the material. Seven samples of AAC blocks with densities between 270 kgm⁻³ and 630 kg m⁻³ were used and their overall temperature/water content/thermal conductivity relationships determined. A thermal conductivity estimation method has been developed and tested, on this database. We put forward the following procedure. 1. ‘Pure’ thermal conductivity, i.e., without taking into account the vaporization/condensation effects occurring in the porous space, has first to be estimated. For this purpose, one can simply do a linear interpolation between the thermal conductivities for the dry and saturated states, or two parallel models that we have constructed by electrical analogy can also be used. The first model achieves a separation between the microporous solid matrix and the macroporous cellular material. The second considers that the solid phase controls the heat flux inside the material through the contacts between this phase and the others: liquid and air. For these two models, formulas are given for determining the parameters and both give similar results. So, one or the other can be chosen depending on what kind of data are available. 2. Then, according to De Vries, the contribution of the ‘apparent’ thermal conductivity of the humid air has to be added. This parameter, depends only on temperature, and can be obtained from humid air physical properties tables. The factor f that characterizes the interaction of the porous structure with vapour diffusion must be known, and we give a relation between f and the saturation rate for AAC. With this method, for any temperature or water content, the results are within 10% of actual values, which is quite satisfactory, especially if one considers the errors that can occur if the influence of temperature is not taken into account.

     

Development of uranium carbide targets for the on-line production of neutron-rich isotopes

A number of on-line and off-line tests have been performed at the IRIS (investigation of radioactive isotopes at synchrocyclotron) facility in order to develop uranium carbide targets with a high density (11 g/cm³) for the on-line production of neutron-rich isotopes by fission of ²³⁸U. A 1 GeV proton beam was used to bombard two kinds of targets held at temperatures in the range of 1900–2100 °C. The first one was a target-ion source assembly slightly modified to withstand 3 months of continuous heating at a temperature of about 2050 °C. The second unit was of a new kind, where ionisation takes place in the target volume itself. A comparison of the on-line isotopic yields before and after heating for 3 months is here reported. The yields and release times of Rb, Cs and In are compared with the ones obtained from a standard reference target, as measured in previous experiments.     

Ribotyping: a tool for taxonomy and identification of the Nocardia asteroides complex species

Ribotyping has been evaluated as a taxonomic tool for studying bacteria belonging to the Nocardia asteroides complex. The probe used was obtained by PCR from DNA extracted from the type strain Nocardia asteroides ATCC 19247, a sequence that codes partly for 16S rRNA. Interpretation of hybridization after EcoRI restriction of total DNA of 21 strains of the N. asteroides complex allowed for the identification of only four different ribotypes: two related to N. asteroides sensu stricto, one related to N. farcinica and one related to N. nova. These results confirm the classification established by Tsukamura in 1982 (M. Tsukamura, Microbiol. Immunol. 26:1101-1119, 1982) as well as the heterogeneity of N. asteroides sensu stricto species. Ribotyping may also provide a major identification technique for the species belonging to the N. asteroides complex.     

An ontology of virtual humans

Most of the efforts concerning graphical representations of humans (Virtual Humans) have been focused on synthesizing geometry for static or animated shapes. The next step is to consider a human body not only as a 3D shape, but as an active semantic entity with features, functionalities, interaction skills, etc. We are currently working on an ontology-based approach to make Virtual Humans more active and understandable both for humans and machines. The ontology for Virtual Humans we are defining will provide the “semantic layer” required to reconstruct, stock, retrieve, reuse and share content and knowledge related to Virtual Humans.     

Blind maximum likelihood identification of Hammerstein systems

This paper is about the identification of discrete-time Hammerstein systems from output measurements only (blind identification). Assuming that the unobserved input is white Gaussian noise, that the static nonlinearity is invertible, and that the output is observed without errors, a Gaussian maximum likelihood estimator is constructed. Its asymptotic properties are analyzed and the Cramér–Rao lower bound is calculated. In practice, the latter can be computed accurately without using the strong law of large numbers. A two-step procedure is described that allows to find high quality initial estimates to start up the iterative Gauss–Newton based optimization scheme. The paper includes the illustration of the method on a simulation example. A theoretical analysis demonstrates that additive output measurement noise introduces a bias that is proportional to the variance of that additive, unmodeled noise source. The simulations support this result, and show that this bias is insignificant beyond a certain Signal-to-Noise Ratio (40 dB in the example).     

Review of validity research on the Stanford-Binet Intelligence Scale: Fourth Edition.

The Standord-Binet Intelligence Scale—Fourth Edition (SB—4; R. L. Thorndike et al, 1986) represents a significant departure from earlier versions of the scale. In the 5 yrs since its introduction into the field of intellectual assessment, a number of validity studies have been conducted with the SB—4. The results from these construct and criterion-related validity studies suggest that the SB—4 provides as valid a measure of general mental ability as existing tests. Support for the 4 factors hypothesized by the authors of the SB—4 is weaker. Research suggests that the SB—4 is a 2-factor test (Verbal, Nonverbal) for ages 2 through 6 yrs and a 3-factor test (Verbal, Nonverbal, Memory) for ages 7 yrs and older. Studies also suggest that the SB—4 can distinguish between groups of youngsters with differing intellectual abilities (e.g., mentally handicapped, gifted, neurologically impaired) and that the test correlates highly with scores on achievement tests. On the basis of validity information, recommendations for the use of the SB—4 are made. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physical modelling fire performance of wall-covering materials

A small-scale enclosure was constructed for characterizing the contribution of interior finish wall-lining materials to fire growth in compartments. The enclosure was based upon refinements to a design devised by scientists at the National Institute for Standards and Technology for quarter-scale modelling of room fire tests on interior-finish materials. A large volume of evidence is presented demonstrating how this small-scale enclosure could provide the information about surface flammability, heat release, smoke generation and contribution to fire growth that is required for a reasonable assessment of the fire performance of interior wall-finish materials.     

CPW-fed passive and active microstrip antennas

A numerical modelling based on the solution of coupled integral equations is used for the design ofCPW-fed microstrip antennas. This type of antennas shows properties close to those of aperture-coupled antennas fed by microstrip lines. Oscillating antennas and large bandwidth antennas working in the C-band are realized with the help of the theoretical model. Various shapes of excitation slots are studied and the slot-loop is shown to be a convenient feeding for the insertion of active devices.