New smoothing procedures in contact mechanics

AbstractThis paper presents recent methods to improve numerical simulation of contact problems by smoothing. The main idea is to combine contact surfaces regularization with an automatic adjustment of both penalty parameter and load step. The underlying goal is to provide handle situations frequently met in an industrial context

Radar target characterization by the polarimetric high resolution method

We consider in this paper the characterization of a radar target by the high resolution method (MUSIC) with polarization diversity. A stepped-frequency radar system is used and the target is modelled by the scattering centers . We propose a new high resolution method which exploits optimally the polarization of the received waves, the calculation time of this method is comparable to that of the scalar HR method . We show by simulation that the proposed method can not only give more informations about the target (polarization state), but also provide better performance than the classical scalar high resolution methods in terms of resolution of the scattering centers .Cet article s'inscrit dans le cadre de la caractérisation d'une cible radar par une méthode à haute résolution en incorporant la polarisation des ondes reçues. La cible radar est modélisée par des contributeurs élémentaires et le radar est à diversité de fréquence et de polarisation. On propose une nouvelle méthode généralisant la méthode MUSIC à la diversité de polarisation. Cette méthode permet d'exploiter pleinement l'information contenue dans les signaux vectoriels, tout en gardant un temps de calcul comparable à celui des méthodes ne tenant pas compte de l'aspect vectoriel des signaux reçus. Les simulations montrent que la prise en compte de la polarisation dans la méthode à haute résolution (MUSIC) permet non seulement de fournir plus d'information sur la cible, mais également d'améliorer sensiblement le pouvoir de résolution

Optimal processings design for synthetic aperture radar

Synthetic aperture radar (SAR) is a microwave imagery system capable ofproducing high resolution images by processing properly data collected by a relatively small antenna. In this papet the bi-dimensionnal received signal, using spatial coordinates, is formulated. The image is reconstructed by a two- dimensionnal filtering operation . We propose a straightforward derivation for the coherent sommation method (or bock-projection of range responses) and the 2-D azimuth matched filtering . The image quality is determined by that of the ambiguity fonction. This latter is analyzed and optimized for two performance criteria. First, for a matched filter receiver (maximal signal-to-noise ratio receiver), the optimal waveform is shown ta be a non linear FM pulse which autocorrelationfunction is a Taylor . The optimal azmiuth weighting fonction is related to that of Taylor by a Fourier transform . Second, for a Wiener filter (least mean-squares receiver), we show that the optimal waveform is the firstprolate spheroidal fonction . The single-hit measurement of the scattering matrix by mean of two optimal orthogonal waves is discussed . Resolutions, SNR as well as ambiguities, are specified .Le radar à visée latérale et à ouverture synthétique est un système d'imagerie micro-onde capable de produire des images de très haute résolution des terrains, et ceci à partir d'un traitement approprié des signaux reçus par une antenne de faible dimension, Dans cet article, nous présentons la formulation exacte du signal reçu, ainsi que les traitements associés afin de former l'image. On met en évidence l'équivalence entre la méthode de la sommation cohérente et le filtrage adapté bidimensionnel en azimut. La qualité de l'image ainsi formée est déterminée par celle de la fonction d'ambiguït

A genetic contribution from the Far East into Ashkenazi Jews via the ancient Silk Road

Contemporary Jews retain a genetic imprint from their Near Eastern ancestry, but obtained substantial genetic components from their neighboring populations during their history. Whether they received any genetic contribution from the Far East remains unknown, but frequent communication with the Chinese has been observed since the Silk Road period. To address this issue, mitochondrial DNA (mtDNA) variation from 55,595 Eurasians are analyzed. The existence of some eastern Eurasian haplotypes in eastern Ashkenazi Jews supports an East Asian genetic contribution, likely from Chinese. Further evidence indicates that this connection can be attributed to a gene flow event that occurred less than 1.4 kilo-years ago (kya), which falls within the time frame of the Silk Road scenario and fits well with historical records and archaeological discoveries. This observed genetic contribution from Chinese to Ashkenazi Jews demonstrates that the historical exchange between Ashkenazim and the Far East was not confined to the cultural sphere but also extended to an exchange of genes

Potential Energy Surface for H_2 Dissociation over Pd(100)

The potential energy surface (PES) of dissociative adsorption of H_2 on Pd(100) is investigated using density functional theory and the full-potential linear augmented plane wave (FP-LAPW) method. Several dissociation pathways are identified which have a vanishing energy barrier. A pronounced dependence of the potential energy on ``cartwheel'' rotations of the molecular axis is found. The calculated PES shows no indication of the presence of a precursor state in front of the surface. Both results indicate that steering effects determine the observed decrease of the sticking coefficient at low energies of the H_2 molecules. We show that the topology of the PES is related to the dependence of the covalent H(s)-Pd(d) interactions on the orientation of the H_2 molecule.Comment: RevTeX, 8 pages, 5 figures in uufiles forma

BONDING ANALYSIS IN SOLID STATE COMPOUNDS: BORON CARBON OF RARE EARTH METALS

The combination of boron and carbon elements with rare earth metals leads to the formation of materials having interestingphysical and structural properties. In theses compounds of formula MxByCz, The non-metal atoms form either two-dimensionalnetworks, or mon-dimensional zig-zag chains, or finite linear units of various length. The dimensionality of boron-carbonsublattice is related to the average valence electron count (VEC) per light atom (B or C). The bonding properties of rare earthmetal boron carbide compounds are analysed by means of extend Hückel tight-binding calculations. Results indicate that thesecompounds can be described in first approximation as being built of anionic units interacting with not fully oxidized metalliccations

Mitochondrial echoes of first settlement and genetic continuity in El Salvador

Background: From Paleo-Indian times to recent historical episodes, the Mesoamerican isthmus played an important role in the distribution and patterns of variability all around the double American continent. However, the amount of genetic information currently available on Central American continental populations is very scarce. In order to shed light on the role of Mesoamerica in the peopling of the New World, the present study focuses on the analysis of the mtDNA variation in a population sample from El Salvador. Methodology/Principal Findings: We have carried out DNA sequencing of the entire control region of the mitochondrial DNA (mtDNA) genome in 90 individuals from El Salvador. We have also compiled more than 3,985 control region profiles from the public domain and the literature in order to carry out inter-population comparisons. The results reveal a predominant Native American component in this region: by far, the most prevalent mtDNA haplogroup in this country (at ~90%) is A2, in contrast with other North, Meso- and South American populations. Haplogroup A2 shows a star-like phylogeny and is very diverse with a substantial proportion of mtDNAs (45%; sequence range 16090–16365) still unobserved in other American populations. Two different Bayesian approaches used to estimate admixture proportions in El Salvador shows that the majority of the mtDNAs observed come from North America. A preliminary founder analysis indicates that the settlement of El Salvador occurred about 13,400±5,200 Y.B.P.. The founder age of A2 in El Salvador is close to the overall age of A2 in America, which suggests that the colonization of this region occurred within a few thousand years of the initial expansion into the Americas. Conclusions/Significance: As a whole, the results are compatible with the hypothesis that today's A2 variability in El Salvador represents to a large extent the indigenous component of the region. Concordant with this hypothesis is also the observation of a very limited contribution from European and African women (~5%). This implies that the Atlantic slave trade had a very small demographic impact in El Salvador in contrast to its transformation of the gene pool in neighbouring populations from the Caribbean facade

Complete mitochondrial DNA sequences provide new insights into the Polynesian motif and the peopling of Madagascar

More than a decade of mitochondrial DNA (mtDNA) studies have given the 'Polynesian motif' renowned status as a marker for tracing the late-Holocene expansion of Austronesian speaking populations. Despite considerable research on the Polynesian motif in Oceania, there has been little equivalent work on the western edge of its expansion - leaving major issues unresolved regarding the motif's evolutionary history. This has also led to considerable uncertainty regarding the settlement of Madagascar. In this study, we assess mtDNA variation in 266 individuals from three Malagasy ethnic groups: the Mikea, Vezo, and Merina. Complete mtDNA genome sequencing reveals a new variant of the Polynesian motif in Madagascar; two coding region mutations define a Malagasy-specific sub-branch. This newly defined 'Malagasy motif' occurs at high frequency in all three ethnic groups (13-50%), and its phylogenetic position, geographic distribution, and estimated age all support a recent origin, but without conclusively identifying a specific source region. Nevertheless, the haplotype's limited diversity, similar to those of other mtDNA haplogroups found in our Malagasy groups, best supports a small number of initial settlers arriving to Madagascar through the same migratory process. Finally, the discovery of this lineage provides a set of new polymorphic positions to help localize the Austronesian ancestors of the Malagasy, as well as uncover the origin and evolution of the Polynesian motif itself

Resolving the ancestry of Austronesian-speaking populations

There are two very different interpretations of the prehistory of Island Southeast Asia (ISEA), with genetic evidence invoked in support of both. The “out-of-Taiwan” model proposes a major Late Holocene expansion of Neolithic Austronesian speakers from Taiwan. An alternative, proposing that Late Glacial/postglacial sea-level rises triggered largely autochthonous dispersals, accounts for some otherwise enigmatic genetic patterns, but fails to explain the Austronesian language dispersal. Combining mitochondrial DNA (mtDNA), Y-chromosome and genome-wide data, we performed the most comprehensive analysis of the region to date, obtaining highly consistent results across all three systems and allowing us to reconcile the models. We infer a primarily common ancestry for Taiwan/ISEA populations established before the Neolithic, but also detected clear signals of two minor Late Holocene migrations, probably representing Neolithic input from both Mainland Southeast Asia and South China, via Taiwan. This latter may therefore have mediated the Austronesian language dispersal, implying small-scale migration and language shift rather than large-scale expansion