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Search Results: 1 - 10 of 3492 matches for " Stephan Briaudeau "
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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.
Determination of the Boltzmann constant by laser spectroscopy as a basis for future measurements of the thermodynamic temperature
Cyril Lemarchand,Khelifa Djerroud,Beno?t Darquié,Olivier Lopez,Anne Amy-Klein,Christian Chardonnet,Christian J. Bordé,Stephan Briaudeau,Christophe Daussy
Physics , 2009, DOI: 10.1007/s10765-010-0755-3
Abstract: In this paper, we present the latest results on the measurement of the Boltzmann constant kB, by laser spectroscopy of ammonia at 10 ?m. The Doppler absorption profile of a ro-vibrational line of an NH3 gas sample at thermal and pressure equilibrium is measured as accurately as possible. The absorption cell is placed inside a large 1m3 thermostat filled with an ice-water mixture, which sets the temperature very close to 273.15 K. Analysing this profile, which is related to the Maxwell-Boltzmann molecular speed distribution, leads to a determination of the Boltzmann constant via a measurement of the Doppler width (proportional tosqrt(kBT)). A spectroscopic determination of the Boltzmann constant with an uncertainty as low as 37 ppm is obtained. Recent improvements with a new passive thermostat lead to a temperature accuracy, stability and homogeneity of the absorption cell better than 1 ppm over a day.
Measurement of the Boltzmann constant by the Doppler broadening technique at a 3,8x10-5 accuracy level
Khelifa Djerroud,Cyril Lemarchand,Alexandre Gauguet,Christophe Daussy,Stephan Briaudeau,Beno?t Darquié,Olivier Lopez,Anne Amy-Klein,Christian Chardonnet,Christian J. Bordé
Physics , 2009, DOI: 10.1016/j.crhy.2009.10.020
Abstract: In this paper, we describe an experiment performed at the Laboratoire de Physique des Lasers and dedicated to an optical measurement of the Boltzmann constant. With the proposed innovative technique, determining comes down to an ordinary frequency measurement. The method consists in measuring as accurately as possible the Doppler absorption profile of a rovibrational line of ammonia in thermal equilibrium. This profile is related to the Maxwell-Boltzmann molecular velocity distribution along the laser beam. A fit of the absorption line shape leads to a determination of the Doppler width proportional to sqrt(kT) and thus to a determination of the Boltzmann constant. The laser source is an ultra-stable CO2 laser with a wavelength . The absorption cell is placed in a thermostat keeping the temperature at 273.15 K within 1.4 mK. We were able to measure with a relative uncertainty as small as 3.8x10-5, which represents an improvement of an order of magnitude for an integration time comparable to our previous measurement published in 2007 [1]
A revised uncertainty budget for measuring the Boltzmann constant using the Doppler Broadening Technique on ammonia
Cyril Lemarchand,Sinda Mejri,Papa Lat Tabara Sow,Meriam Triki,Sean K. Tokunaga,Stephan Briaudeau,Christian Chardonnet,Beno?t Darquié,Christophe Daussy
Physics , 2013, DOI: 10.1088/0026-1394/50/6/623
Abstract: We report on our on-going effort to measure the Boltzmann constant, kB, using the Doppler Broadening Technique. The main systematic effects affecting the measurement are discussed. A revised error budget is presented in which the global uncertainty on systematic effects is reduced to 2.3 ppm. This corresponds to a reduction of more than one order of magnitude compared to our previous Boltzmann constant measurement. Means to reach a determination of kB at the part per million accuracy level are outlined.
Association between Magnetic Resonance Imaging and the Result of Medial Branch Blocks  [PDF]
Stephan Klessinger, Wolfgang Freund
Pain Studies and Treatment (PST) , 2017, DOI: 10.4236/pst.2017.51001
Abstract: The aim of this retrospective practice audit was to assess the correlation between painful zygapophysial joints and changes seen in magnetic resonance imaging (MRI). Patients with unilateral pain were tested with controlled medial branch blocks. The MRI scans of patients with a positive response were compared blinded with normal MRI scans. The dimensions of the joint were assessed and osteoarthritis was graded. Fifteen symptomatic patients and 15 asymptomatic patients were included and evaluated. Comparison of the joints showed that the maximum diameter of symptomatic joints was significantly larger, and the grading of osteoarthritis was significantly higher for symptomatic joints. No healthy patient was assigned a grade 3. Grades 2 and 3 were found significantly more often in symptomatic patients. Only one symptomatic joint was assigned grade 0. Grade 0 was found significantly more often in asympto-matic patients. The presented MRI technique has limited value as a diagnostic test for lumbar zygapophysial joint pain. It is not possible to detect a single symptomatic joint. However, the osteoarthritis grading for the lumbar zyg-apophysial joints might be helpful for finding predictors for negative response if the results of the rating are grade zero. Therefore, unnecessary medial branch blocks might be avoided.
Measuring the Boltzmann constant by mid-infrared laser spectroscopy of ammonia
S. Mejri,Papa Sow,O. Kozlova,C. Ayari,Sean Tokunaga,C. Chardonnet,S. Briaudeau,B. Darquié,F. Rohart,C. Daussy
Physics , 2015, DOI: 10.1088/0026-1394/52/5/S314
Abstract: We report on our ongoing effort to measure the Boltzmann constant, $k_B,$ using the Doppler broadening technique on ammonia. This paper presents some of the improvements made to the mid-infrared spectrometer including the use of a phase-stabilized quantum cascade laser, a lineshape analysis based on a refined physical model and an improved fitting program 2 increasing the confidence in our estimates of the relevant molecular parameters, and a first evaluation of the saturation parameter and its impact on the measurement of k B. A summary of the systematic effects contributing to the measurement is given and the optimal experimental conditions for mitigating those effects in order to reach a competitive measurement of $k_B$ at a part per million accuracy level are outlined.
T cell receptor variable β20-1 harbors a nucleotide binding pocket in the CDR2β loop  [PDF]
Stephan Watkins, Werner J. Pichler
Open Journal of Immunology (OJI) , 2013, DOI: 10.4236/oji.2013.33021
Abstract:

Novel aspects of T cells containing TCRVβ20-1 are numerous, ranging from pathogen specific reactivity to specific tissue homing, or possible T cell subsets. Recently, it was demonstrated that TCR itself could become reactive by binding to small molecules free of the pHLA interface. Our work here was to identify a natural ligand binding to an identified pocket on the CDR2β loop of these TCR. Using docking of suspected ligands, we were able to show Guanine and Adenine diand tri-nucleotides readily bind to the identified site. Comparing these with small molecule sites found on other TCR types, we show this interaction is novel. With further molecular dynamic simulations, these sites are shown to be plausible by conducting simple computational based solubility tests as cross validation. Combined with simple proliferative responses, the identified nucleotides are also shown to have functional consequences by inducing T cell proliferation for CD4/Vβ20-1 + T cells, while failing to induce proliferation in other T cell isolates. Merging computational and simple cell assays, this work establishes a role of nucleotides in T cells found to contain this TCR subtype.

Monitoring Endangered Species Populations: Gene Dispersal Can Have Pronounced Effects on the Relationship between Census Size and Genetic Diversity  [PDF]
Steven H. Rogstad, Stephan Pelikan
American Journal of Plant Sciences (AJPS) , 2013, DOI: 10.4236/ajps.2013.410238
Abstract:

Anthropogenic activities are increasing habitat fragmentation, as well as the number of threatened and endangered species. Thus, isolated fragments with natural remnant stands, or in situ or ex situ endangered species rescue populations, are on the rise. The most common method for assessing the “conservation health” of such populations is to determine or estimate the census size. However, while it is known that the census size of a population does not always correlate with its genetic diversity, methods for modeling how different factors can drive variation in the relationship of census size to genetic diversity in plant populations are needed. Here we use the computer program NEWGARDEN to investigate how the relationship of stand size versus genetic diversity (measured as both the percent of the founding alleles retained and FIT) can be extremely variable depending on founder number, founder density, and gene dispersal distances. Populations of endangered species that appear to have the same conservation health in terms of similar population numbers may differ greatly in their conservation health as indicated by the genetic diversity they retain. NEWGARDEN can be used to explore how different founding and intra- or interspecific life history characteristics can affect genetic diversity relative to census size. If proper historical data exist, NEWGARDEN can also be used to estimate the percent of founding genetic diversity remaining in a given stand.

Activating interactions of sulfanilamides with T cell receptors  [PDF]
Stephan Watkins, Werner J. Pichler
Open Journal of Immunology (OJI) , 2013, DOI: 10.4236/oji.2013.33019
Abstract:

Activation and expansion of drug reactive T cells are key features in drug hypersensitivity reactions. Drugs may interact directly with immune receptors such as the human leukocyte antigens (HLA) or the T-cell receptors (TCR) itself, the pharmacological interaction [p-i] concept. To analyze whether the drug sulfamethoxazole (SMX) interacts directly with the TCR and thereby contributing to signaling and T cell activation, we analyze two SMX specific T cell clones (TCC “1.3”and “H13”). Proliferation to SMX and 11 related sulfanilamides, Ca++ influx in drug stimulated T-cells and the inhibitory effect of non-reactive sulfanilamides on SMX stimulation were analyzed. In silico docking of SMX and related sulfanilamide to the TCR were used to identify possible drug binding sites, and correlated to in vitro data to find the correct docking. In Ca++ influx assays, reactions occurred as early as 14 sec after adding SMX to TCC and APC. The broadly reactive clone (“H13”) was stimulated by 5 additional sulfanilamide, while one TCC (“1.3”) was reactive exclusively with SMX but not other sulfanilamides. Competition experiments with sulfanilamide inhibited SMX induced Ca++ influx and proliferation of the TCC1.3 ina dose dependent way. Docking experiments with SMX and related sulfanilamides confirmed and explained the in vitro data as docking localized binding sites for SMX and the 5 stimulating sulfanilamides on the CDR2β domain of the clone H13, while the 6 non-stimulatory SA failed to bind. In TCC 1.3, SMX could be docked on the CDR3α of the TCR. The other, non-stimulatory but inhibitory SA could also be docked to the same site. The combined analysis of in vitro and in silico

Segmenting Salient Objects in 3D Point Clouds of Indoor Scenes Using Geodesic Distances  [PDF]
Shashank Bhatia, Stephan K. Chalup
Journal of Signal and Information Processing (JSIP) , 2013, DOI: 10.4236/jsip.2013.43B018
Abstract:

Visual attention mechanisms allow humans to extract relevant and important information from raw input percepts. Many applications in robotics and computer vision have modeled human visual attention mechanisms using a bottom-up data centric approach. In contrast, recent studies in cognitive science highlight advantages of a top-down approach to the attention mechanisms, especially in applications involving goal-directed search. In this paper, we propose a top-down approach for extracting salient objects/regions of space. The top-down methodology first isolates different objects in an unorganized point cloud, and compares each object for uniqueness. A measure of saliency using the properties of geodesic distance on the object’s surface is defined. Our method works on 3D point cloud data, and identifies salient objects of high curvature and unique silhouette. These being the most unique features of a scene, are robust to clutter, occlusions and view point changes. We provide the details of the proposed method and initial experimental results.

 

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