47 research outputs found
A Stochastic Model of Latently Infected Cell Reactivation and Viral Blip Generation in Treated HIV Patients
Motivated by viral persistence in HIV+ patients on long-term anti-retroviral treatment (ART), we present a stochastic model of HIV viral dynamics in the blood stream. We consider the hypothesis that the residual viremia in patients on ART can be explained principally by the activation of cells latently infected by HIV before the initiation of ART and that viral blips (clinically-observed short periods of detectable viral load) represent large deviations from the mean. We model the system as a continuous-time, multi-type branching process. Deriving equations for the probability generating function we use a novel numerical approach to extract the probability distributions for latent reservoir sizes and viral loads. We find that latent reservoir extinction-time distributions underscore the importance of considering reservoir dynamics beyond simply the half-life. We calculate blip amplitudes and frequencies by computing complete viral load probability distributions, and study the duration of viral blips via direct numerical simulation. We find that our model qualitatively reproduces short small-amplitude blips detected in clinical studies of treated HIV infection. Stochastic models of this type provide insight into treatment-outcome variability that cannot be found from deterministic models
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure
Why is Iridium the best substrate for single crystal diamond growth?
The synthesis of heteroepitaxial monocrystalline diamond films has been of technological and scientific interest for several decades. Using chemical vapor deposition techniques, polycrystalline diamond has been successfully grown on many substrates. However, iridium emerges in providing highly oriented films, significantly better than any other transition metals. In the present work we propose an ab initio density functional study of the interaction of diamond with different substrates used experimentally. The origin of iridium's specific behavior is investigated. The kinetics of carbon atoms in the substrate lattice is found to play a key role, determining the nucleation mechanisms and hence the quality of the final diamond film. (c) 2005 American Institute of Physics
Reactive gas pulsing process: a method to extend the composition range of sputtered iron oxynitride films
International audienc
Structural properties of iron oxynitride films obtained by reactive magnetron sputtering
International audienc
Caractérisation des films colorés de Fe-O-N élaborés par pulvérisation magnétron réactive
International audienc
Influence of Oxygen Flow Rate on the Properties of FeOXNY Films Obtained by Magnetron Sputtering at High Nitrogen Pressure
International audienceFe-O-N films were successfully deposited by magnetron sputtering of an iron target in Ar-N2-O2 reactive mixtures at high nitrogen partial pressure 1.11 Pa (Q(N2) = 8 sccm) using a constant flow rate of argon and an oxygen flow rate Q(O2) varying from 0 to 1.6 sccm. The chemical composition and the structural and microstructural nature of these films were characterized using Rutherford Backscattering Spectrometry, X-ray diffraction, and Conversion Electron Mössbauer Spectrometry, respectively. The results showed that the films deposited without oxygen are composed of a single phase of γ''-FeN, whereas the other films do not consist of pure oxides but oxidelike oxynitrides. With higher oxygen content, the films are well-crystallized in the α-Fe2O3 structure. At intermediate oxygen flow rate, the films are rather poorly crystallized and can be described as a mixture of oxide γ-Fe2O3/Fe3O4. In addition, the electrical behavior of the films evolved from a metallic one to a semiconductor one, which is in total agreement with other investigations. Comparatively to a previous study carried out at low nitrogen partial pressure (0.25 Pa), this behavior of films prepared at higher nitrogen partial pressure (1.11 Pa) could be caused by a catalytic effect of nitrogen on the crystallization of the hematite structure
Reconstitutions palĂ©oenvironnementales et enregistrement palĂ©oclimatique fini-carbonifĂšre Ă permien du bassin dâAutun (Nord-Est du Massif Central)
International audienceLes bassins sĂ©dimentaires tardi-orogĂ©niques fini-carbonifĂšres Ă permiens du Nord-Est du Massif Central (bassins dâAutun, de lâAumance, de Decize-La Machine et de Blanzy-Le Creusot) ont Ă©tĂ© principalement Ă©tudiĂ©s pour leur potentiel en ressources carbonĂ©es jusque dans les annĂ©es 1980. Le regain dâintĂ©rĂȘt quâils suscitent aujourdâhui sâappuie sur des aspects plus fondamentaux afin de mieux comprendre la pĂ©riode charniĂšre quâest la fin du PalĂ©ozoĂŻque. Les sĂ©ries sĂ©dimentaires prĂ©servĂ©es dans ces bassins continentaux enregistrent en effet le dĂ©mantĂšlement des reliefs hercyniens ainsi que lâĂ©volution climatique (transition icehouse-greenhouse) se produisant entre la fin de lâaccrĂ©tion de la PangĂ©e et le dĂ©but de sa dislocation, amorcĂ©e au MĂ©sozoĂŻque. Pour mener Ă bien les reconstitutions palĂ©oenvironnementales et palĂ©oclimatiques de cette pĂ©riode, une Ă©tude multidisciplinaire est proposĂ©e, couplant des approches sĂ©dimentologiques, pĂ©trologiques, gĂ©ochimiques, structurales et gĂ©ochronologiques de ces diffĂ©rents bassins, dont le calage stratigraphique est mal contraint. Le bassin dâAutun, comprenant les sĂ©ries stĂ©phaniennes et autuniennes du CarbonifĂšre terminal au Permien infĂ©rieur, a fait lâobjet dâune Ă©tude sĂ©dimentologique basĂ©e sur la description des carottes des forages dâIgornay (186 m) et de Chevrey (365 m), respectivement au Nord-Est et Ă lâOuest du bassin et traversant la base de la sĂ©rie autunienne. Nos observations permettent de rĂ©viser le modĂšle sĂ©dimentologique fluviatile et fluvio-lacustre initialement proposĂ© pour ces sĂ©ries, en mettant en Ă©vidence des faciĂšs essentiellement lacustres (argilites distales carbonĂ©es, varves, faciĂšs turbiditiques et deltaĂŻques, microbialites). Les analyses minĂ©ralogiques Ă haute rĂ©solution de lâassemblage argileux, complĂ©tĂ©es par la pyrolyse Rock-Eval et la gĂ©ochimie isotopique et Ă©lĂ©mentaire du carbone et de lâazote organiques ont Ă©tĂ© rĂ©alisĂ©es sur le forage dâIgornay. Des fluctuations significatives au cours du temps du cycle hydrologique, de lâaltĂ©ration des bassins versants oĂč le volcanisme est omniprĂ©sent et de la prĂ©servation de la matiĂšre organique sont mises en Ă©vidence. Ces fluctuations peuvent ĂȘtre reliĂ©es aux changements des palĂ©oenvironnements de dĂ©pĂŽt (lac proximal vs. lac distal) du bassin ainsi quâĂ des Ă©volutions palĂ©oclimatiques de plus grande Ă©chelle
Evaluation of the optoelectronic properties of ZnSnN2 thin films under different growth conditions and doping implantation of As and P at different concentrations
National audienc
Evaluation of the optoelectronic properties of ZnSnN2 thin films under different growth conditions and doping implantation of As and P at different concentrations
National audienc