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Search Results: 1 - 10 of 3116 matches for " Yves Hermier "
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First direct determination of the Boltzmann constant by an optical method
Christophe Daussy,Mickael Guinet,Anne Amy-Klein,Khelifa Djerroud,Yves Hermier,Stephan Briaudeau,Christian J. Bordé,Christian Chardonnet
Physics , 2007, DOI: 10.1103/PhysRevLett.98.250801
Abstract: We have recorded the Doppler profile of a well-isolated rovibrational line in the \nu2 band of 14NH3. Ammonia gas was placed in an absorption cell thermalized by a water-ice bath. By extrapolating to zero pressure, we have deduced the Doppler width which gives a first measurement of the Boltzmann constant, kB, by laser spectroscopy. A relative uncertainty of 2x10-4 has been obtained. The present determination should be significantly improved in the near future and contribute to a new definition of the kelvin.
H2 and CH4 Sorption on Cu-BTC Metal Organic Frameworks at Pressures up to 15 MPa and Temperatures between 273 and 318 K  [PDF]
Yves Gensterblum
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2011, DOI: 10.4236/jsemat.2011.12004
Abstract: Sorption isotherms of methane and hydrogen on Cu3(BTC)2 have been measured in the temperature range from 273 to 318 K and at pressures up to 15 MPa. H2 excess sorption capacities of the Cu3(BTC)2 amounted to 3.9 mg/g at 14 MPa. Promising maximum CH4 excess sorption capacities on the same sample were reached at approximately 5 MPa. They amounted to 101, 100, 92 and 80 mg/g at 273, 278, 293 and 318 K, respectively. The sorbed phase density was essestially the same for all temperatures and amounted to ~600 kg/m3. Structural changes of the Cu3(BTC)2 samples after thermal activation and treatment with high pressure H2 and CH4 were tested. It was found that the initial micropore structure has virtually disappeared as evidenced by a decrease of the Langmuir specific surface area by a factor ~3 and CO2 micropore volume by a factor of ~4 for H2 and ~3 for CH4. This is in line with an increase in the average pore diameter from initially 9.2 to 15.7 for H2 and 12.8 for CH4.
Minkowskian Solution of General Relativity with Cosmological Constant and the Accelerating Universe  [PDF]
Yves Pierseaux
Journal of Modern Physics (JMP) , 2014, DOI: 10.4236/jmp.2014.516172
Abstract: A Minkowskian solution of the equation of General Relativity (as written by Einstein in 1915) is trivial because it simply means that both members of the equation are equal to zero. However, if alternatively, one considers the complete equation with a non-zero constant Λ (Einstein 1917), a Minkowskian solution is no longer trivial because it amounts to impose a constraint on the right hand side of the equation (i.e. a non-null stress-energy tensor). If furthermore one identifies (as usual) this tensor to the one of a perfect fluid, one finds that this fluid has a positive energy density and a negative pressure that depend on the three constants of the equation (i.e. gravitational constant G, cosmological constant Λ and velocity of light c). When doing that (§1), one has to consider the “Minkowskian Vacuum” as a physical object of GR (an enigmatic non-baryonic Minkowskian fluid). Can one build a model of this object on the basis of a dynamical equilibrium between the effective gravitational attraction due to the positive energy density versus the negative pressure repulsion? We propose to study such a model, where the (enigmatic) fluid is assumed to exist only in a limited sphere whose surface acts like a “test body” sensitive to the gravitational field created by the fluid. No static equilibrium exists, but a pseudoNewtonian “dynamical equilibrium” (§2) can be reached if the pseudoEuclidean fluid is in state of expansion. Up to there, we have simply constructed a model of an “abstract Universe” (i.e. the limited sphere: There is no fluid outside this sphere!) that gives to a (purely mathematical) constant Λ a concrete physical meaning. We discover finally that our expanding fluid has not only dynamical (gravitational) properties (§3) but also optical properties that are connected with Doppler Redshift (§4). Remembering that recent observations in Cosmology indicate that the “real Universe” seems to be “Flat” and in “Accelerated Expansion”; remembering also (after all) that the archetypal Flat Universe is simply a Minkowskian Universe, we logically wonder if the unexpected Minkowskian global solution, could not be also a significant cosmological model (conclusion).
Photon-correlation Fourier spectroscopy
Xavier Brokmann,Moungi Bawendi,Laurent Coolen,Jean-Pierre hermier
Physics , 2006, DOI: 10.1364/OE.14.006333
Abstract: We describe a method to probe the spectral fluctuations of a transition over broad ranges of frequencies and timescales with the high spectral resolution of Fourier spectroscopy, and a temporal resolution as high as the excited state lifetime, even in the limit of very low photocounting rates. The method derives from a simple relation between the fluorescence spectral dynamics of a single radiating dipole and its fluorescence intensity correlations at the outputs of a continuously scanning Michelson interferometer. These findings define an approach to investigate the fast fluorescence spectral dynamics of single molecules and other faint light sources beyond the time-resolution capabilities of standard spectroscopy experiments.
Measurement of the radiative and non-radiative decay rates of single CdSe nanocrystals through controlled modification of their spontaneous emission
X. Brokmann,L. Coolen,Maxime Dahan,J. P. Hermier
Physics , 2004, DOI: 10.1103/PhysRevLett.93.107403
Abstract: We present a simple method to measure the radiative and non-radiative recombination rates of individual fluorescent emitters at room temperature. By placing a single molecule successively close and far from a dielectric interface and simultaneously measuring its photoluminescence decay and its orientation, both the radiative and non-radiative recombination rates can be determined. For CdSe nanocrystals, our results demonstrate that the fluorescence quantum efficiency, determined at the single molecule level, is 98% in average, far above the value expected from conventional ensemble experiments. The bi-dimensionnal nature of the transition dipole is also directly evidenced from a single particle measurement.
PAPR Reduction Scheme with SOCP for MIMO-OFDM Systems  [PDF]
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2008, DOI: 10.4236/ijcns.2008.11005
Abstract: Combination of multiple-input multiple-output (MIMO) with orthogonal frequency division multiplexing (OFDM) has become a promising candidate for high performance wireless communications. However one major disadvantage of MIMO-OFDM systems lies in a prohibitively large peak-to-average power ratio (PAPR) of the transmitted signal on each antenna. In this paper we extend from SISO to MIMO systems a method based on allocating dedicated subcarriers for PAPR mitigation. These subcarriers are located on unused subcarriers of OFDM spectrum under the assumption they all fall under the power mask. This is originally implemented with a SOCP optimization algorithm applied before space time coding scheme. This jointly mitigates PAPR on each MIMO branch scheme. This approach does not degrade the bit-error-rate (BER) and the data bit rate and no side information (SI) transmission is required. Simulation results are presented in the IEEE 802.16 WiMAX standard contexts: an Alamouti space time code with two transmitted antennas and 256 OFDM subcarriers are considered where 56 of which are unused and allocated for PAPR reduction. PAPR gains up to 7dB are obtained depending on mean power increase limitation. Moreover, with a spectrum mask constraint, this method is standard compliant.
Contribution of Topographically Explicit Descriptors of Landscape Measures for Application in the Vector Data Environment  [PDF]
Auda Yves, Jomaa Ihab
Journal of Geographic Information System (JGIS) , 2010, DOI: 10.4236/jgis.2010.23023
Abstract: Digital terrain models (DTMs) are not commonly used to integrate for landscape spatial analysis. Two dimensional patchcorridormatrix models are prototypes in landscape spatial ecology analysis. Previous studies have motivated ecologists to integrate terrain models in landscape analysis through 1) adjusting areas and distance calculations prior computing landscape indices; 2) designing new indices to capture topography and 3) searching the possible relationship between topographic characteristics and vegetation patterns. This study presents new indices called Relative number of Topographic Faces (RTF) and Simplicity of topographic Faces (STF) that can be easily computed in a GIS environment, capturing topographical features of landscapes. Digital terrain model was first prepared and topographic units were extracted and installed in computing the suggested indices. Mountainous and rugged topography in Lebanon was chosen on a forested landscape for the purpose of this study. The indices were useful in monitoring changes of topographic features on patch and landscape level. Both indices are ecologically useful if integrated in landscape pattern analysis, especially in areas of rugged terrains.
Interdisciplinarity in Primary and Secondary School: Issues and Perspectives  [PDF]
Yves Lenoir, Abdelkrim Hasni
Creative Education (CE) , 2016, DOI: 10.4236/ce.2016.716233
Abstract: The article deals with three questions which feed the debates on the school interdisciplinarity. Firstly, why promote interdisciplinarity in basic education? To answer this question requires to make a fast historical reminder of the emergence and the evolution of the interdisciplinarity in the field of education, so as to highlight three distinct readings of interdisciplinarity before presenting four arguments which show the relevance of its use in teaching. Secondly, how can interdisciplinary practices be fostered in education? The results of various works lead us to draw four strong trends, ideal-typical, to which the teachers use in their practices. Thirdly, what are the educational questions and issues raised by such practices, and what challenges must we address to make sure they are properly applied? We then suggest six principles by which to found and describe what we understand by school interdisciplinarity. A definition of the school interdisciplinarity is then moved forward. To conclude, we call back to mind a few aspects which appear essential when contemplating the use of interdisciplinarity in school, what leads us to place this one with regard to the transdisciplinarity.
Identification of a Cam Clay Model through Shear-Box and Oedometer Tests. Application to Lateritical Soils from Senegal (West Africa)  [PDF]
Cheikhou Ndiaye, Yves Berthaud
Geomaterials (GM) , 2018, DOI: 10.4236/gm.2018.81001
Abstract: The main objective of this research is to study the mechanical behaviour of tropical soils using elasto-plastic constitutive equations in the so-called limit and critical states. Indeed, researchers of the Cambridge University had noticed that during their various experiments, the rate of volumetric deformation (\"\" ) of the sample tending to zero every time the rupture of the specimen is reached during a test performed on a clay specimen Roscoe et al., 1958. To better understand and clarify this mechanical behaviour, a description has been proposed in the (e, p, q) representation that means void ratio, volumetric stress (spherical pressure) and deviatoric stress. This frame of theoretical study and apprehension is called: the theory of the Critical State. One of the major problems met at the time of our present research is the non-availability of triaxial apparatus allowing us to achieve some tests on tropical soils (samples from Senegal in West Africa) and to describe the behaviour of these materials easily like the researchers of the university of Cambridge in the theory of the critical state. To by-pass this difficulty, we decided to consider two very classical and simple mechanical tests: shear-box and the oedometer test as well as the interrelationship of the results given by the tests and some theoretical calculations. This is a way to identify an elasto-plastic model (the modified Cam Clay model) without any triaxial experiment. Indeed it supposes the model to be suitable to describe the mechanical behaviour of the considered clays.
Natural Isotopic Signatures of Variations in Body Nitrogen Fluxes: A Compartmental Model Analysis
Nathalie Poupin,Fran?ois Mariotti,Jean-Fran?ois Huneau,Dominique Hermier,Hélène Fouillet
PLOS Computational Biology , 2014, DOI: doi/10.1371/journal.pcbi.1003865
Abstract: Body tissues are generally 15N-enriched over the diet, with a discrimination factor (Δ15N) that varies among tissues and individuals as a function of their nutritional and physiopathological condition. However, both 15N bioaccumulation and intra- and inter-individual Δ15N variations are still poorly understood, so that theoretical models are required to understand their underlying mechanisms. Using experimental Δ15N measurements in rats, we developed a multi-compartmental model that provides the first detailed representation of the complex functioning of the body's Δ15N system, by explicitly linking the sizes and Δ15N values of 21 nitrogen pools to the rates and isotope effects of 49 nitrogen metabolic fluxes. We have shown that (i) besides urea production, several metabolic pathways (e.g., protein synthesis, amino acid intracellular metabolism, urea recycling and intestinal absorption or secretion) are most probably associated with isotope fractionation and together contribute to 15N accumulation in tissues, (ii) the Δ15N of a tissue at steady-state is not affected by variations of its P turnover rate, but can vary according to the relative orientation of tissue free amino acids towards oxidation vs. protein synthesis, (iii) at the whole-body level, Δ15N variations result from variations in the body partitioning of nitrogen fluxes (e.g., urea production, urea recycling and amino acid exchanges), with or without changes in nitrogen balance, (iv) any deviation from the optimal amino acid intake, in terms of both quality and quantity, causes a global rise in tissue Δ15N, and (v) Δ15N variations differ between tissues depending on the metabolic changes involved, which can therefore be identified using simultaneous multi-tissue Δ15N measurements. This work provides proof of concept that Δ15N measurements constitute a new promising tool to investigate how metabolic fluxes are nutritionally or physiopathologically reorganized or altered. The existence of such natural and interpretable isotopic biomarkers promises interesting applications in nutrition and health.
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