Modeling Na clusters in Ar matrices

We present a microscopic model for Na clusters embedded in raregas matrices. The valence electrons of the Na cluster are described by time-dependent density-functional theory at the level of the local-density approximation (LDA). Particular attention is paid to the semi-classical picture in terms of Vlasov-LDA. The Na ions and Argon atoms are handled as classical particles whereby the Ar atoms carry two degrees of freedom, position and dipole polarization. The interaction between Na ions and electrons is mediated through local pseudo-potentials. The coupling to the Ar atoms is described by (long-range) polarization potentials and (short-range) repulsive cores. The ingredients are taken from elsewhere developed standards. A final fine-tuning is performed using the NaAr molecule as benchmark. The model is then applied to embedded systems Na8ArN. By close comparison with quantum-mechanical results, we explore the capability of the Vlasov-LDA to describe such embedded clusters. We show that one can obtain a reasonable description by appropriate adjustments in the fine-tuning phase of the model.Comment: 17 pages, 7 figures, submitted to Annalen der Physi

Semiclassical theory of surface plasmons in spheroidal clusters

A microscopic theory of linear response based on the Vlasov equation is extended to systems having spheroidal equilibrium shape. The solution of the linearized Vlasov equation, which gives a semiclassical version of the random phase approximation, is studied for electrons moving in a deformed equilibrium mean field. The deformed field has been approximated by a cavity of spheroidal shape, both prolate and oblate. Contrary to spherical systems, there is now a coupling among excitations of different multipolarity induced by the interaction among constituents. Explicit calculations are performed for the dipole response of deformed clusters of different size. In all cases studied here the photoabsorption strength for prolate clusters always displays a typical double-peaked structure. For oblate clusters we find that the high--frequency component of the plasmon doublet can get fragmented in the medium size region ($N \sim 250$). This fragmentation is related to the presence of two kinds of three-dimensional electron orbits in oblate cavities. The possible scaling of our semiclassical equations with the valence electron number and density is investigated.Comment: 23 pages, 8 figures, revised version, includes discussion of scalin

Theory of inelastic lifetimes of low-energy electrons in metals

Electron dynamics in the bulk and at the surface of solid materials are well known to play a key role in a variety of physical and chemical phenomena. In this article we describe the main aspects of the interaction of low-energy electrons with solids, and report extensive calculations of inelastic lifetimes of both low-energy electrons in bulk materials and image-potential states at metal surfaces. New calculations of inelastic lifetimes in a homogeneous electron gas are presented, by using various well-known representations of the electronic response of the medium. Band-structure calculations, which have been recently carried out by the authors and collaborators, are reviewed, and future work is addressed.Comment: 28 pages, 18 figures, to appear in Chem. Phy

Identification and detection of transient phenomena from low signal-to-noise ratio radar signals : joint application to oceanographic and atmospheric sensing

L'observation de la dynamique de l'atmosphère et de la surface de l'océan peut être réalisée par télédétection radar. L'approche habituelle consiste, dans les deux cas, à calculer numériquement le spectre Doppler des échos temporels reçus à l'aide d'une transformée de Fourier discrète. Bien que satisfaisante pour la plupart des applications, cette méthode ne convient pas pour l'observation de phénomènes transitoires, plus courts que le temps d'intégration nécessaire à l'observation radar. Nous utilisons une technique alternative, basée sur une représentation autorégressive des séries temporelles radar et associée à la méthode dite à entropie maximale. Cette approche est appliquée à la mesure de courants de surface par radar côtier dans la bande des hautes fréquences, puis à celle de vent dans la basse atmosphère par radar en bande L. Dans les deux situations, nous montrons à l'aide de simulations numériques, de comparaisons avec d'autres instruments et d'études de cas que l'approche proposée conduit à des estimations fiables des grandeurs géophysiques (courants marins et vitesses de vent) pour des temps d'intégration brefs, là où la méthode conventionnelle échoue.Observations of atmospheric and ocean surface dynamics can be performed via radar remote sensing. The usual approach consists, in both cases, in numerically calculating the Doppler spectrum of the received temporal echoes using a discrete Fourier transform. Although satisfactory for most applications, this method is not suitable for observations of transient phenomena due to being shorter than the integration time required for radar observations. We use an alternative technique based on an autoregressive representation of the radar time series combined with the maximum entropy method. This approach is applied to coastal radar measurements of surface currents in the high frequency band as well as to L-band radar measurements of wind in the lower atmosphere. For both cases, through numerical simulations and case studies, we compare our approach with others that use different instruments. We show that for short integration times, where conventional methods fail, our proposed approach leads to reliable estimates of geophysical quantities (ocean currents and wind speeds)

Optimisation de l'esthétique dans le traitement de l'édentement unitaire au maxillaire antérieur : stratégies thérapeutiques

Nowadays, there are many patients who want an implant solution for the replacement of maxillary anterior edentulousness, in particular for a single edentulous sector. Developments, whether technological, surgical or prosthetic, make it possible to achieve new esthetic objectives. The objective of this thesis is to present the pre, per, and post operative means allowing to obtain an optimal esthetic result around a single implant in the anterior maxillary sector. After a presentation of the current esthetic standards described in the literature, these means will be presented through 4 main axes: the management of the implant positioning and the digital workflow, the preservation of the peri-implant tissues, their reconstructions. The prosthetic phase will then be developed in a dedicated part. The treatment of single tooth loss by implant solution must be considered as a whole to achieve an optimal esthetic result. This involves establishing and implementing a thoughtful and rigorous treatment plan.De nos jours, nombreux sont les patients qui désirent une solution implantaire pour le remplacement des édentements antérieurs maxillaires, notamment pour un secteur édenté unitaire. Les évolutions, qu'elles soient technologiques, chirurgicales ou prothétiques, permettent d'atteindre de nouveaux objectifs esthétiques. L’objectif de cette thèse est de présenter les moyens pré, per, et post opératoires permettant d’obtenir un résultat esthétique optimal autour d'un implant unitaire en secteur antérieur maxillaire. Après une présentation des standards esthétiques actuels décrits dans la littérature, ces moyens seront présentés au travers de 4 grands axes : la gestion du positionnement implantaire et le flux de travail numérique, la préservation des tissus péri-implantaires, leurs reconstructions. La phase prothétique sera ensuite développée dans une partie dédiée. Le traitement de l'édentement unitaire par solution implantaire doit être considéré dans sa globalité pour atteindre un résultat esthétique optimal. Il s'agit d’établir et de mettre en œuvre un plan de traitement réfléchi et rigoureux

CEVA Matrix Technology: A new alternative for pig medicated premixes

Specific problems are posed by medicated premixes : stability of the active ingredient, homogeneity of the medicated premix distribution in the feed and cross-contammation due to dust emission These problems can have two major consequences· a treatment failure and a risk for human health with selection of res1stant strains CEVA Matrix Technology, an exclusive CEVA Sante Ammale manufacturing process, matches all expectations of an effective and modern medicated premix. CEVA Matrix Technology consists of an innovative protective granulation technology. Most non-protected medicated premixes available in the market do not provide good stability and may not reach efficient concentration as the active ingredient is not protected enough. First, the CEVA Matrix Technology guarantees that the active ingredient is protected during manufacture (pelleting) and storage of the medicated feed without altenng its bioavailability. Secondly, the particle size of CEVA Matrix Technology premixes is similar to the feed in which it is to be blended. Therefore the active ingredient is mixed homogeneously into the feed and remains homogeneous even after transportation and storage. This perfect mixability ensures the right active ingredient concentration and dosage in feed every time. Consequently, treatment failure resulting from unequal dosage distribution of the active ingredient in the feed is considerably limited. Thirdly, CEVA Matrix Technology guarantees that the premix does not release dust. Therefore, it reduces risks such as cross contamination between two medicated feed batches in mills and inhalation of antimicrobial by users. It protects the workforce and reduces the risk of selecting resistant strams. This article validates all these points by comparing a tiamulin medicated premix manufactured with the CEVA Matrix Technology and some non-protected tiamulin.</p

Colistin: alternative for the treatment of swine colibacillosis with the respect of human health protection

From suckling up to slaughter, pigs experience frequently enteritis outbreaks caused by various pathogens, most of them from bacterial origin. Preliminary epidemiological studies have shown that Escherichia coli are the most often isolated bacteria during diarrhoeas. Quinolones and penicillins are the most frequently used treatments when colibacillosis is suspected. Many reports have shown these bacteria became frequently resistant when these antibiotics were massively used. Moreover, many cross resistances were demonstrated in these antibiotic families, leading to a major zootechnical and zoonotic concern.</p

Hierarchy-based Update Propagation in Decision Support Systems

International audienceSales forecasting systems are used by enterprise managers and executives to better understand the market trends and prepare appropriate business plans. These decision support systems usually use a data warehouse to store data and OLAP tools to visualize query results. A specific feature of sales forecasting systems regarding future predictions modification is backward propagation of updates, which is the computation of the impact of modifications on summaries over base data. In Data warehouses domain, some methods propagate updates in hierarchies when data sources are subject to modifications. However, very few works have been performed so far regarding update propagation from summaries to data sources. This paper proposes an algorithm named PAM algorithm, to efficiently propagate modifications on summaries. Experiments on an operational application (Anticipeo) have been performed to validate our algorithm

Geometrical and quantal fragmentation of optical response in Na

By comparing quantal and semi-classical calculations of optical response, we work out the part of the splitting of the plasmon spectra which is exclusively due to geometrical effects. We apply the analysis to the test case ${\rm Na}_{18}^{2+}$ which exhibits an interesting geometry with strong prolate quadrupole deformation and a pronounced asymmetry in addition. We find a new type of resonance splitting which is due to geometrical effects but goes beyond the simple and well known deformation splitting