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Search Results: 1 - 10 of 448599 matches for " J.-L. Bertaux "
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First climatology of polar mesospheric clouds from GOMOS/ENVISAT stellar occultation instrument
K. Pérot,A. Hauchecorne,F. Montmessin,J.-L. Bertaux
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: GOMOS (Global Ozone Monitoring by Occultation of Stars), on board the European platform ENVISAT launched in 2002, is a stellar occultation instrument combining four spectrometers and two fast photometers which measure light at 1 kHz sampling rate in the two visible channels 470–520 nm and 650–700 nm. On the day side, GOMOS does not measure only the light from the star, but also the solar light scattered by the atmospheric molecules. In the summer polar days, Polar Mesospheric Clouds (PMC) are clearly detected using the photometers signals, as the solar light scattered by the cloud particles in the instrument field of view. The sun-synchronous orbit of ENVISAT allows observing PMC in both hemispheres and the stellar occultation technique ensures a very good geometrical registration. Four years of data, from 2002 to 2006, are analyzed up to now. GOMOS data set consists of approximately 10 000 cloud observations all over the eight PMC seasons studied. The first climatology obtained by the analysis of this data set is presented, focusing on the seasonal and latitudinal coverage, represented by global maps. GOMOS photometers allow a very sensitive PMC detection, showing a frequency of occurrence of 100% in polar regions during the middle of the PMC season. According to this work mesospheric clouds seem to be more frequent in the Northern Hemisphere than in the Southern Hemisphere. The PMC altitude distribution was also calculated. The obtained median values are 82.7 km in the North and 83.2 km in the South.
First climatology of polar mesospheric clouds from GOMOS/ENVISAT stellar occultation instrument
K. Pérot, A. Hauchecorne, F. Montmessin, J.-L. Bertaux, L. Blanot, F. Dalaudier, D. Fussen,E. Kyr l
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2010,
Abstract: GOMOS (Global Ozone Monitoring by Occultation of Stars), on board the European platform ENVISAT launched in 2002, is a stellar occultation instrument combining four spectrometers and two fast photometers which measure light at 1 kHz sampling rate in the two visible channels 470–520 nm and 650–700 nm. On the day side, GOMOS does not measure only the light from the star, but also the solar light scattered by the atmospheric molecules. In the summer polar days, Polar Mesospheric Clouds (PMC) are clearly detected using the photometers signals, as the solar light scattered by the cloud particles in the instrument field of view. The sun-synchronous orbit of ENVISAT allows observing PMC in both hemispheres and the stellar occultation technique ensures a very good geometrical registration. Four years of data, from 2002 to 2006, are analyzed up to now. GOMOS data set consists of approximately 10 000 cloud observations all over the eight PMC seasons studied. The first climatology obtained by the analysis of this data set is presented, focusing on the seasonal and latitudinal coverage, represented by global maps. GOMOS photometers allow a very sensitive PMC detection, showing a frequency of occurrence of 100% in polar regions during the middle of the PMC season. According to this work mesospheric clouds seem to be more frequent in the Northern Hemisphere than in the Southern Hemisphere. The PMC altitude distribution was also calculated. The obtained median values are 82.7 km in the North and 83.2 km in the South.
Mid-latitude ozone monitoring with the GOMOS-ENVISAT experiment version 5: the noise issue
P. Keckhut, A. Hauchecorne, L. Blanot, K. Hocke, S. Godin-Beekmann, J.-L. Bertaux, G. Barrot, E. Kyr l , J. A. E. van Gijsel,A. Pazmino
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2010,
Abstract: The GOMOS ozone profiles have been analysed to evaluate the GOMOS ability to capture the long-term ozone evolution at mid-latitudes during the expected recovery phase of the ozone layer. Version 5 of the operational GOMOS ozone data has been compared with data from two of the longest ground-based instruments based on different techniques and already involved with many other previous space instrument validations. Comparisons between ground-based and GOMOS data confirm the occurrence of spurious retrievals mainly occurring since 2006. Using a selected set of data it is shown that some bad retrievals are induced by the increasing dark charge of the detectors combined with an inadequate method for its correction. This effect does not only induce a continuous bias, but is rather exhibiting a bimodal distribution including the correct profiles and the bad retrievals. For long-term analyses it is recommended filtering the data according to background light conditions and star temperature (spectrum shape). The new method of the dark charge estimate proposed to be implemented in the version 6 of the ESA algorithm seems to significantly reduce the occurrence of such effects and should allow to monitor stratospheric ozone using GOMOS data with greater confidence.
Membrane proteins: functional and structural studies using reconstituted proteoliposomes and 2-D crystals
Rigaud, J.-L.;
Brazilian Journal of Medical and Biological Research , 2002, DOI: 10.1590/S0100-879X2002000700001
Abstract: reconstitution of membrane proteins into lipid bilayers is a powerful tool to analyze functional as well as structural areas of membrane protein research. first, the proper incorporation of a purified membrane protein into closed lipid vesicles, to produce proteoliposomes, allows the investigation of transport and/or catalytic properties of any membrane protein without interference by other membrane components. second, the incorporation of a large amount of membrane proteins into lipid bilayers to grow crystals confined to two dimensions has recently opened a new way to solve their structure at high resolution using electron crystallography. however, reconstitution of membrane proteins into functional proteoliposomes or 2-d crystallization has been an empirical domain, which has been viewed for a long time more like "black magic" than science. nevertheless, in the last ten years, important progress has been made in acquiring knowledge of lipid-protein-detergent interactions and has permitted to build upon a set of basic principles that has limited the empirical approach of reconstitution experiments. reconstitution strategies have been improved and new strategies have been developed, facilitating the success rate of proteoliposome formation and 2-d crystallization. this review deals with the various strategies available to obtain proteoliposomes and 2-d crystals from detergent-solubilized proteins. it gives an overview of the methods that have been applied, which may be of help for reconstituting more proteins into lipid bilayers in a form suitable for functional studies at the molecular level and for high-resolution structural analysis.
What place for literature in the education of French-speaking countries? A comparison between Belgium, France, Quebec and Switzerland.
Dufays, J.-L.
L1 Educational Studies in Language and Literature , 2007,
Abstract: This contribution attempts a partial synthesis of a large international study (Collès, Dufays & Maeder, 2003), which explores the teaching and learning of Romance languages in France, French Belgium, French Switzerland and Quebec. Each author analysed in their country or region the official instructions related to primary and secondary school and the plans of action related to teachers' training. All dealt with the same questions. Considering those data, the analysis here focuses particularly on the section of the report concerning the teaching and learning of literature in French mother tongue lessons. Specifically, I address three questions:1. Over the last 50 years, what place and value has been given to literature in the official programs for primary and secondary schools in the 4 countries or regions, compared to the other subjects considered as part of teaching French?2. What are today's prescriptions as far as literature is concerned? In relation to the contemporary debate between different paradigms, is literature first handled in terms of skills or in terms of knowledge? Which values are these knowledges and skills bound to?
Membrane proteins: functional and structural studies using reconstituted proteoliposomes and 2-D crystals
Rigaud J.-L.
Brazilian Journal of Medical and Biological Research , 2002,
Abstract: Reconstitution of membrane proteins into lipid bilayers is a powerful tool to analyze functional as well as structural areas of membrane protein research. First, the proper incorporation of a purified membrane protein into closed lipid vesicles, to produce proteoliposomes, allows the investigation of transport and/or catalytic properties of any membrane protein without interference by other membrane components. Second, the incorporation of a large amount of membrane proteins into lipid bilayers to grow crystals confined to two dimensions has recently opened a new way to solve their structure at high resolution using electron crystallography. However, reconstitution of membrane proteins into functional proteoliposomes or 2-D crystallization has been an empirical domain, which has been viewed for a long time more like "black magic" than science. Nevertheless, in the last ten years, important progress has been made in acquiring knowledge of lipid-protein-detergent interactions and has permitted to build upon a set of basic principles that has limited the empirical approach of reconstitution experiments. Reconstitution strategies have been improved and new strategies have been developed, facilitating the success rate of proteoliposome formation and 2-D crystallization. This review deals with the various strategies available to obtain proteoliposomes and 2-D crystals from detergent-solubilized proteins. It gives an overview of the methods that have been applied, which may be of help for reconstituting more proteins into lipid bilayers in a form suitable for functional studies at the molecular level and for high-resolution structural analysis.
Retrievals from GOMOS stellar occultation measurements using characterization of modeling errors
V. F. Sofieva, J. Vira, E. Kyr l , J. Tamminen, V. Kan, F. Dalaudier, A. Hauchecorne, J.-L. Bertaux, D. Fussen, F. Vanhellemont, G. Barrot,O. Fanton d'Andon
Atmospheric Measurement Techniques (AMT) & Discussions (AMTD) , 2010,
Abstract: In this paper, we discuss the development of the inversion algorithm for the GOMOS (Global Ozone Monitoring by Occultation of Star) instrument on board the Envisat satellite. The proposed algorithm takes accurately into account the wavelength-dependent modeling errors, which are mainly due to the incomplete scintillation correction in the stratosphere. The special attention is paid to numerical efficiency of the algorithm. The developed method is tested on a large data set and its advantages are demonstrated. Its main advantage is a proper characterization of the uncertainties of the retrieved profiles of atmospheric constituents, which is of high importance for data assimilation, trend analyses and validation.
Le président Mobutu et le premier ministre sous l'Acte constitutionnel de la Transition: duel ou duo?
J.-L. Esambo Kangashe
Afrika Focus , 1998,
Abstract: Since the beginning of the democratic process in Mobutu's Zaire, in April 1990, a judicial and political debate has continued to divide the opinion on the power sharing within the executive.The Transitional Constitutional Act, a result of the political negotiations of the Palais du Peuple, was aimed at resolving the competence conflicts between the President of the Republic and the Prime Minister. This constitutional framework, however, was unable to avoid neither the possibility of a "duel" nor the avatars of an alleged "duo" between the two main representatives of the executive function.In the meantime, the frequent violations of the constitution by the head of state have shown that power sharing within a parliamentary system could not come to a compromise with the power practice under Mobutu.
Zur Diskussion des Filioque auf dern Konzil von Florenz
J.-L. VAN DIETEN
Byzantina Symmeikta , 2008,
Abstract: No abstract
Estimation of the aerosol radiative forcing at ground level, over land, and in cloudless atmosphere, from METEOSAT-7 observation: method and case study
T. Elias,J.-L. Roujean
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: A new method is proposed to estimate the spatial and temporal variability of the solar radiative flux reaching the surface over land (DSSF), as well as the Aerosol Radiative Forcing (ARF), in cloud-free atmosphere. The objective of regional applications of the method is attainable by using the visible broadband of METEOSAT-7 satellite instrument which scans Europe and Africa on a half-hourly basis. The method relies on a selection of best correspondence between METEOSAT-7 radiance and radiative transfer computations. The validation of DSSF is performed comparing retrievals with ground-based measurements acquired in two contrasted environments: an urban site near Paris and a continental background site located South East of France. The study is concentrated on aerosol episodes occurring around the 2003 summer heat wave, providing 42 cases of comparison for variable solar zenith angle (from 59° to 69°), variable aerosol type (biomass burning emissions and urban pollution), and variable aerosol optical thickness (a factor 6 in magnitude). The method reproduces measurements of DSSF within an accuracy assessment of 20 W m 2 (5% in relative) in 70% of the situations, and within 40 W m 2 in 90% of the situations, for the two case studies considered here. Considering aerosol is the main contributor in changing the measured radiance at the top of the atmosphere, DSSF temporal variability is assumed to be caused only by aerosols, and consequently ARF at ground level and over land is also retrieved: ARF is computed as the difference between DSSF and a parameterised aerosol-free reference level. Retrievals are linearly correlated with the ground-based measurements of the aerosol optical thickness (AOT): sensitivity is included between 120 and 160 W m 2 per unity of AOT at 440 nm. AOT being an instantaneous measure indicative of the aerosol columnar amount, we prove the feasibility to infer instantaneous aerosol radiative impact at the ground level over land with METEOSAT-7 visible channel.
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