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Search Results: 1 - 10 of 200760 matches for " P. Forget "
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A sea spray generation function for fetch-limited conditions
J. Piazzola,P. Forget,S. Despiau
Annales Geophysicae (ANGEO) , 2003,
Abstract: This paper presents a sea spray generation function for aerosols produced by bubbles bursting that accounts for the effects of fetch. This is achieved by introducing a fetch-dependent model for the whitecap fraction, which is valid for fetch-limited conditions, i.e. steady-state conditions of the wave field in the whitecap droplet flux derived by Monahan et al. (1986). The aerosol generation fluxes calculated by this method show an enhancement of the aerosol production with increasing fetch. However, the predicted generation fluxes are lower than those calculated by using the classical model for the whitecap fraction proposed by Monahan and O’Muircheartaigh (1980). The results are then compared to aerosol size distributions measured in a Mediterranean coastal site at various fetch lengths. The data confirm the role of fetch, through its influence on marine aerosol generation and subsequent particle dispersion. The aerosol size distributions are divided into "fine" and "coarse" fractions. Submicrometer particles decrease in concentration at larger fetch, while the concentrations of super micron aerosols increase with increasing fetch. Key words. Atmospheric composition and structure (aerosols and particles) Meteorology and atmospheric dynamics (waves and ties) Oceanography: physical (air-sea interactions)
The modulated antiferromagnetic structures in multiferroic FeVO4: a 57Fe M?ssbauer spectroscopy investigation
D. Colson,A. Forget,P. Bonville
Physics , 2014,
Abstract: We present a 57Fe M\"ossbauer spectroscopy study of the two incommensurate magnetic phases in the multiferroic material FeVO4. We devise lineshapes appropriate for planar elliptical and collinear modulated magnetic structures and show that they reproduce very well the M\"ossbauer spectra in FeVO4, in full qualitative agreement with a previous neutron diffraction study. Quantitatively, our spectra provide precise determinations of the characteristics of the elliptical and modulated structures which are in good agreement with the neutron diffraction results. We find that the hyperfine field elliptical modulation persists as T goes to 0, which we attribute to an anisotropy of the hyperfine interaction since a moment modulation is forbidden at T=0 for a spin only ion like Fe3+.
Two-dimensional spectroscopy using dual acousto-optic pulse shapers for complete polarization, phase and amplitude control
Tyagi P.,Saari J. I.,Crozatier V.,Forget N.
EPJ Web of Conferences , 2013, DOI: 10.1051/epjconf/20134111004
Abstract: We demonstrate a pulse-shaper capable of independent polarization, phase and amplitude control over each pulse. The set-up is compact and easily switchable between pump-probe and collinear geometries.
Vitamin D deficiency in a cohort of HIV-infected patients: clinical analysis
D Wilmes,P Forget,A Vincent,L Belkhir
Journal of the International AIDS Society , 2012, DOI: 10.7448/ias.15.6.18205
Abstract: Purpose of the study: Observational studies have noted very high rates of low serum 25-hydroxyvitamin D [25(OH)D3] levels in both general and HIV-infected populations. In HIV-infected patients, low 25(OH)D3 levels are secondary to a combination of usual risk factors and HIV-specific risk factors, like antiretroviral therapy [1]. The objective of our study is to analyse the magnitude of vitamin D deficiency or insufficiency and the role of various factors such as age, sex, ethnicity, season, and antiretroviral medications in our cohort of HIV-infected patients. Methods: We prospectively collected data on 25-hydroxyvitamin D levels sampled between January 2009 and June 2011 from our cohort of 930 HIV-infected patients. Vitamin D dosage was performed using immunoassay (‘Diasorin’ - Saluggia, Italy). We divided vitamin D levels into 3 categories: 25-hydroxyvitamin D levels <20 mg/nl were considered deficient, insufficient between 20 and 29 ng/ml. Levels ≥30 ng/ml were defined as normal [2]. Data on demographic features (age, ethnicity, season, heterosexuality vs homosexuality), clinical features and laboratory findings (CD4 cell count, viral load, HAART, BMI) were collected from patients’ medical records using our institutional database ‘Medical explorer v3r9, 2009’. Summary of results: Overall, 848 patients were included in our study (Table 1). Low levels of serum 25(OH)D3 were seen in 89.3% of the study population, from which 69.5% were deficient and 19.8% were insufficient. On univariate analysis, female sex, high BMI, black African, heterosexuality, undetectable viral load and antiretroviral treatment were all predictors of vitamin D deficiency and insufficiency. Treatment with efavirenz and tenofovir were the most associated with low vitamin D levels. On multivariate analysis (multiple linear regression model) only female sex (OR=1.14; 95% CI 0.84–0.96; p<0.001), dosage during winter months (OR=1.14; 95% CI 1–1.15; p<0.05) and HAART (OR=1.12; 95% CI 1.04–1.19; p=0.002) were identified as independent risk factors of low 25(OH)D3 levels. Conclusion: Vitamin D deficiency is frequent in HIV-infected populations (69.5%). Patients on antiretroviral therapy are at higher risk of vitamin D deficiency. In our cohort, black women and dosage during winter were also independent risk factors for low vitamin D levels.
Incommensurate spin density wave in Co-doped BaFe2As2
P. Bonville,F. Rullier-Albenque,D. Colson,A. Forget
Physics , 2010, DOI: 10.1209/0295-5075/89/67008
Abstract: 57Fe Mossbauer spectroscopy measurements are presented in the underdoped Ba(Fe{1-x}Cox)2As2 series for x=0.014 (T_c < 1.4K) and x=0.03 and 0.045 (T_c ~ 2 and 12K respectively). The spectral shapes in the so-called spin-density wave (SDW) phase are interpreted in terms of incommensurate modulation of the magnetic structure, and allow the shape of the modulation to be determined. In undoped BaFe2As2, the magnetic structure is commensurate, and we find that incommensurability is present at the lowest doping level (x=0.014). As Co doping increases, the low temperature modulation progressively loses its "squaredness" and tends to a sine-wave. The same trend occurs for a given doping level, as temperature increases. We find that a magnetic hyperfine component persists far above the SDW transition, its intensity being progressively tranferred to a paramagnetic component on heating.
Investigation of the magnetic fluctuations in Tb$_2$Sn$_2$O$_7$ ordered spin ice by high resolution energy-resolved neutron scattering
I. Mirebeau,H. Mutka,P. Bonville,A. Apetrei,A. Forget
Physics , 2008, DOI: 10.1103/PhysRevB.78.174416
Abstract: We have studied magnetically frustrated Tb$_2$Sn$_2$O$_7$ by neutron diffraction and high resolution energy-resolved neutron scattering. At 0.1 K, we observe short range magnetic correlations with a typical scale of 4 \AA, close to the near neighbor distance between Tb$^{3+}$ ions. %(3.686 \AA), This short range order coexists with ferromagnetic correlations and long range spin ice order at the scales of 18 and 190 \AA, respectively. Spin dynamics was investigated at a time scale down to 10$^{-9}$s, by energy-resolved experiments on a backscattering spectrometer. We observe a freezing of the spin dynamics for all length-scales, with a strong slowing down of the spin fluctuations when long range order settles in. We discuss the spin fluctuations remaining in the ground state in comparison with previous data obtained by muon spectroscopy.
The present and past climates of planet Mars
Forget F.
EPJ Web of Conferences , 2009, DOI: 10.1140/epjconf/e2009-0924-9
Abstract: Mars is a small planet with a thin atmosphere of almost pure carbon dioxide. To first order, the Martian meteorology can be compared with what one would expect on a cold, dry desert-like Earth. However, several phenomena make the Martian climate system more complex than it appears. First, as much as 30% of the carbon dioxide atmosphere condenses every winter at high latitude to form CO2 ice polar caps, inducing large surface pressure variations all over the planet and an atmospheric circulation without equivalent on Earth. Second, a highly variable amount of suspended dust lifted by the winds modifies the radiative properties of the atmosphere, with sometime global dust storms able to totally shroud the planet. Last, a peculiar water cycle occurs on Mars, with water vapor transported by the atmosphere between the polar caps and possibly subsurface reservoirs, allowing the formation of clouds, hazes and frost. Telescopic and spacecraft observations have shown us that this complex climate system is highly variable, seasonally and from year to year, but these variations remain poorly understood. In fact, the Martian climate system has probably experienced large variations related to the oscillations in the parameters of the orbit and rotation of Mars (obliquity) a few millions or even thousand of years ago. These oscillations affected surface temperatures and the water cycle, inducing the mobilization and accumulation of large ice deposits in various locations on the planets. In a much distant past, it is also likely that Mars may have been a completely different planet. The observations of the geology (dry riverbeds and deltas, lacustrine sediments) and mineralogy (clay, sulfate) of the oldest surface on Mars dating back to more than 3 billions years ago provide evidence that liquid water was then abundant on the surface, at least episodically. Mars may have been warmed by a thicker atmosphere containing greenhouse gas and clouds, high geothermal fluxes, or episodically by large asteroid impacts.
La mise en jeu des discours dans le débat télévisé [Staking discourse in televised debates]
Danielle Forget
?édille : Revista de Estudios Franceses , 2010,
Abstract: Partagé entre un enjeu local de circulation des interventions de chacun des participants et un enjeu global d’appropriation / désappropriation des dires collectifs, le débat télévisé est un lieu de convergence des discours. Ses conditions propres et l’avancée argumentative à laquelle il prétend font de la récursivité discursive une dimension structurante de ce type de pratique. En effet, je m’appuie sur des procédés de réitération (tels les emprunts discursifs et les artefacts ) à incidences interactionnelles et argumentatives pour faire appara tre les stratégies rhétoriques qu’il met en oeuvre, montrant ainsi que l’importation des discours collectifs, qu’elle soit directe ou allusive, contribue à la dimension idéologique tout en attestant le dynamisme discursif, au sens de renouvellement des contenussémantiques et, sur le plan pragmatique, des jeux de places entre intervenants.Televised debates are a place for sharing discourses, divided between actual interventions and competing ideas in the socialbackground. Their specific conditions and argumentative goal allow recursivity to be an essential configuration. This study aimsat characterizing rhetorical strategies which play a crucial role in the integration of collective discourses and ultimately contributeto the renewal of their ideological dimension, in the context of televised debates.
Pour une rhétorique du quotidien dans la littérature québécoise moderne
Danielle Forget
Caligrama : Revista de Estudos Romanicos , 2000,
Abstract: Resumo: Seja sob a forma quase oral dos monólogos de Clémence DesRochers seja na trama narrativa do romance Des Nouvelles d’édouard, uma retórica do cotidiano se perfila nas obras literárias quebequenses; ela se faz presente a fim de provocar no leitor uma distancia crítica. Por figuras de valor textual como o clichê e a ironia, ela oferece assim à reflex o uma transgress o das normas literárias e sugere uma ultrapassagem dos nossos reflexos de interpreta o. Palavras-chave: Literatura canadense; língua francesa; Clémence DesRochers; Michel Tremblay; retórica. Résumé: Que ce soit sous la forme quasi-orale des monologues de Clémence DesRochers, ou dans la trame narrative du roman de Michel Tremblay, Des Nouvelles d’édouard, une rhétorique du quotidien se profile dans les oeuvres littéraires québécoises; elle prend pour toile afin de provoquer chez le lecteur une distance critique. Par des figures à portée textuelle comme le clichê et l’ironie, elle offre alors à la réflexion une transgression des normes littéraires et suggère un dépassement de nos réflexes d’interprétation. Mots-clés: Littérature canadienne; langue fran aise; Clémence DesRochers; Michel Tremblay; rhétorique.Keywords: Canadian literature; French; Clémence DesRochers; Michel Tremblay; rhetoric.
On the probability of habitable planets
Francois Forget
Physics , 2012, DOI: 10.1017/S1473550413000128
Abstract: In the past 15 years, astronomers have revealed that a significant fraction of the stars should harbor planets and that it is likely that terrestrial planets are abundant in our galaxy. Among these planets, how many are habitable, i.e. suitable for life and its evolution? These questions have been discussed for years and we are slowly making progress. Liquid water remains the key criterion for habitability. It can exist in the interior of a variety of planetary bodies, but it is usually assumed that liquid water at the surface interacting with rocks and light is necessary for the emergence of a life able to modify its environment and evolve. A first key issue is thus to understand the climatic conditions allowing surface liquid water assuming a suitable atmosphere. This have been studied with global mean 1D models which has defined the "classical habitable zone", the range of orbital distances within which worlds can maintain liquid water on their surfaces (Kasting et al. 1993). A new generation of 3D climate models based on universal equations and tested on bodies in the solar system is now available to explore with accuracy climate regimes that could locally allow liquid water. A second key issue is now to better understand the processes which control the composition and the evolution of the atmospheres of exoplanets, and in particular the geophysical feedbacks that seems to be necessary to maintain a continuously habitable climate. From that point of view, it is not impossible that the Earth's case may be special and uncommon.
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