13 research outputs found
Diagnosis of chylous abdominal effusions: what is the triglyceride threshold value?
IntroductionChylous abdominal effusions are serious complications that can be triggered by various aetiologies. The biochemical diagnosis of chyle leakage in ascites or in peritoneal fluid capsules relies on the detection of chylomicrons. Assaying the fluidâs concentration of triglycerides is still the first-line tool. Given that only one comparative study has sought to quantify the value of the triglyceride assay for diagnosing chylous ascites in humans, our objective was to provide practical triglyceride thresholds.
Materials and methodsWe conducted a 9-year, retrospective, single-centre study of adult patients and compared a triglyceride assay with lipoprotein gel electrophoresis for the analysis of 90 non-recurring abdominal effusions (ascites and abdominal collections) of which 65 were chylous.
ResultsA triglyceride threshold of 0.4 mmol/L was associated with a sensitivity > 95%, and a threshold of 2.4 mmol/L was associated with a specificity > 95%. According to Youden index, the best threshold was 0.65 mmol/L with a sensitivity of 88 (77-95)%, a specificity of 72 (51-88)%, and, in our series, a positive predictive value of 89 (79-95)% and a negative predictive value of 69 (48-86)%.
ConclusionsIn our series, cut-off of 0.4 mmol/L could be used for ruling-out diagnosis of chylous effusions, while cut-off of 2.4 mmol/L could be used for reasonably confirming diagnosis
Caractérisation en régime dynamique des transferts de chaleur au contact glissant et imparfait de deux solides
The work presented in this thesis is a contribution to the study of heat transfer between two solid bodies in dry frictional contact. The problem of heat transfer across interfaces represents an essential part of the thermal modeling of many industrial devices and processes. Temperature levels can reach values that can cause damage in systems subjected to friction. Therefore, it is necessary to characterize the frictional interface before designing such systems. This study is interested in the macroscopic aspect of dry frictional contacts. The chosen model includes a coupling equation and three contact parameters ; (i) the heat flux generated by friction, (ii) the intrinsic partition coefficient of the generated heat flux, (iii) the contact resistance. The characterization of an interface with this model signifies the identification of these contact parameters through inverse methods. The originality of this work is the simultaneous estimation of the dynamic evolution of the contact parameters. Several estimation techniques by inversion of measurements have been tested. After a detailed sensitivity and correlation study, the method adopted is parametrization with time lag. This method minimizes the correlations between the parameters and provides a good accuracy of estimation. This technique is used to characterize these contact parameters on an experimental bench. With the objective of integrating a thermal-mechanical interaction into the study of dry frictional contact in future research, an innovative approach to thermal-mechanical coupling in a transient 1D configuration is presented. Using an analytical method, the deformation at a given position is calculated by the convolution product between a transferfunction and the temperature at another position. Through this relation, a method of thermomechanical characterization of materials by inversion of measurement was developed. In addition to the identification of the thermal diffusivity and the coefficient of thermal expansion, a procedure for the identification of the temperature by 'deconvolution' was also developed. Due to the high instability of the system, regularization techniques using the Tikhonov method and spectrum truncation were used. An experimental device has been assembled and instrumented for this purpose. The experimental results are in agreement with the literature and give good residuals.Le travail dĂ©veloppĂ© dans cette thĂšse est une contribution Ă l'Ă©tude du transfert de chaleur entre deux corps solides en contact frottant sec. Le problĂšme du transfert de chaleur Ă travers les interfaces reprĂ©sente une partie essentielle de la modĂ©lisation thermique de nombreux mĂ©canismes et procĂ©dĂ©s industriels. Les niveaux de tempĂ©rature peuvent atteindre des valeurs susceptibles dâoccasionner des dommages dans les systĂšmes soumis au frottement. Par consĂ©quent, il est nĂ©cessaire de caractĂ©riser lâinterface dâun frottement avant la conception de tels systĂšmes. Dans notre Ă©tude, nous nous sommes intĂ©ressĂ©s Ă lâaspect macroscopique des contacts frottants secs. Le modĂšle retenu comprend une Ă©quation de couplage et trois paramĂštres de contacts : (i) le flux gĂ©nĂ©rĂ© par frottement, (ii) le coefficient de partage intrinsĂšque du flux gĂ©nĂ©rĂ©, (iii) la rĂ©sistance de contact. La caractĂ©risation dâune interface Ă travers le modĂšle adoptĂ©, signifie lâidentification de ces paramĂštres de contact par le biais de mĂ©thodes inverses. LâoriginalitĂ© de ce travail consiste Ă estimer simultanĂ©ment lâĂ©volution dynamique des paramĂštres de contact. DiffĂ©rentes techniques dâestimations en inversion de mesures ont Ă©tĂ© testĂ©es. AprĂšs une Ă©tude de sensibilitĂ© et de corrĂ©lation approfondie, la mĂ©thode adoptĂ©e est la paramĂ©trisation avec dĂ©calage temporel. Cette mĂ©thode permet de minimiser les corrĂ©lations entre les paramĂštres et affiche un bon rĂ©sultat dâestimation. Cette technique est utilisĂ©e dans le but de caractĂ©riser ces paramĂštres de contact expĂ©rimentalement sur un banc dâessai dĂ©diĂ©. Dans la perspective dâintĂ©grer une interaction thermique-mĂ©canique Ă lâĂ©tude du contact frottant sec dans de futures recherches, une approche novatrice du couplage thermique et mĂ©canique Ă travers une configuration 1D transitoire est prĂ©sentĂ©e. GrĂące Ă une mĂ©thode analytique, la dĂ©formation Ă une position donnĂ©e est calculĂ©e par le produit de convolution entre une fonction de transfert et la tempĂ©rature Ă une autre position. Ainsi, cette relation, nous a permis de dĂ©velopper une mĂ©thode de caractĂ©risation thermomĂ©canique des matĂ©riaux par inversion de mesure. En plus de lâidentification de la diffusivitĂ© thermique et du coefficient de dilatation thermique, une procĂ©dure dâidentification de la tempĂ©rature par "dĂ©convolution" a Ă©tĂ© rĂ©alisĂ©e. Le systĂšme Ă©tant fortement instable, des techniques de rĂ©gularisation par la mĂ©thode de Tikhonov et de troncature de spectre sont utilisĂ©es. Un dispositif expĂ©rimental a Ă©tĂ© rĂ©alisĂ© et instrumentĂ© Ă cette fin. Les rĂ©sultats obtenus expĂ©rimentalement sont en accord avec la bibliographie et donnent de bon rĂ©sidus
Dynamic characterisation of heat transfer at sliding and imperfect contact of two solids
Le travail dĂ©veloppĂ© dans cette thĂšse est une contribution Ă l'Ă©tude du transfert de chaleur entre deux corps solides en contact frottant sec. Le problĂšme du transfert de chaleur Ă travers les interfaces reprĂ©sente une partie essentielle de la modĂ©lisation thermique de nombreux mĂ©canismes et procĂ©dĂ©s industriels. Les niveaux de tempĂ©rature peuvent atteindre des valeurs susceptibles dâoccasionner des dommages dans les systĂšmes soumis au frottement. Par consĂ©quent, il est nĂ©cessaire de caractĂ©riser lâinterface dâun frottement avant la conception de tels systĂšmes. Dans notre Ă©tude, nous nous sommes intĂ©ressĂ©s Ă lâaspect macroscopique des contacts frottants secs. Le modĂšle retenu comprend une Ă©quation de couplage et trois paramĂštres de contacts : (i) le flux gĂ©nĂ©rĂ© par frottement, (ii) le coefficient de partage intrinsĂšque du flux gĂ©nĂ©rĂ©, (iii) la rĂ©sistance de contact. La caractĂ©risation dâune interface Ă travers le modĂšle adoptĂ©, signifie lâidentification de ces paramĂštres de contact par le biais de mĂ©thodes inverses. LâoriginalitĂ© de ce travail consiste Ă estimer simultanĂ©ment lâĂ©volution dynamique des paramĂštres de contact. DiffĂ©rentes techniques dâestimations en inversion de mesures ont Ă©tĂ© testĂ©es. AprĂšs une Ă©tude de sensibilitĂ© et de corrĂ©lation approfondie, la mĂ©thode adoptĂ©e est la paramĂ©trisation avec dĂ©calage temporel. Cette mĂ©thode permet de minimiser les corrĂ©lations entre les paramĂštres et affiche un bon rĂ©sultat dâestimation. Cette technique est utilisĂ©e dans le but de caractĂ©riser ces paramĂštres de contact expĂ©rimentalement sur un banc dâessai dĂ©diĂ©. Dans la perspective dâintĂ©grer une interaction thermique-mĂ©canique Ă lâĂ©tude du contact frottant sec dans de futures recherches, une approche novatrice du couplage thermique et mĂ©canique Ă travers une configuration 1D transitoire est prĂ©sentĂ©e. GrĂące Ă une mĂ©thode analytique, la dĂ©formation Ă une position donnĂ©e est calculĂ©e par le produit de convolution entre une fonction de transfert et la tempĂ©rature Ă une autre position. Ainsi, cette relation, nous a permis de dĂ©velopper une mĂ©thode de caractĂ©risation thermomĂ©canique des matĂ©riaux par inversion de mesure. En plus de lâidentification de la diffusivitĂ© thermique et du coefficient de dilatation thermique, une procĂ©dure dâidentification de la tempĂ©rature par "dĂ©convolution" a Ă©tĂ© rĂ©alisĂ©e. Le systĂšme Ă©tant fortement instable, des techniques de rĂ©gularisation par la mĂ©thode de Tikhonov et de troncature de spectre sont utilisĂ©es. Un dispositif expĂ©rimental a Ă©tĂ© rĂ©alisĂ© et instrumentĂ© Ă cette fin. Les rĂ©sultats obtenus expĂ©rimentalement sont en accord avec la bibliographie et donnent de bon rĂ©sidus.The work presented in this thesis is a contribution to the study of heat transfer between two solid bodies in dry frictional contact. The problem of heat transfer across interfaces represents an essential part of the thermal modeling of many industrial devices and processes. Temperature levels can reach values that can cause damage in systems subjected to friction. Therefore, it is necessary to characterize the frictional interface before designing such systems. This study is interested in the macroscopic aspect of dry frictional contacts. The chosen model includes a coupling equation and three contact parameters ; (i) the heat flux generated by friction, (ii) the intrinsic partition coefficient of the generated heat flux, (iii) the contact resistance. The characterization of an interface with this model signifies the identification of these contact parameters through inverse methods. The originality of this work is the simultaneous estimation of the dynamic evolution of the contact parameters. Several estimation techniques by inversion of measurements have been tested. After a detailed sensitivity and correlation study, the method adopted is parametrization with time lag. This method minimizes the correlations between the parameters and provides a good accuracy of estimation. This technique is used to characterize these contact parameters on an experimental bench. With the objective of integrating a thermal-mechanical interaction into the study of dry frictional contact in future research, an innovative approach to thermal-mechanical coupling in a transient 1D configuration is presented. Using an analytical method, the deformation at a given position is calculated by the convolution product between a transferfunction and the temperature at another position. Through this relation, a method of thermomechanical characterization of materials by inversion of measurement was developed. In addition to the identification of the thermal diffusivity and the coefficient of thermal expansion, a procedure for the identification of the temperature by 'deconvolution' was also developed. Due to the high instability of the system, regularization techniques using the Tikhonov method and spectrum truncation were used. An experimental device has been assembled and instrumented for this purpose. The experimental results are in agreement with the literature and give good residuals
Multilevel inverter with optimal THD through the firefly algorithm
Reduction of the Total Harmonic Distortion (THD) in multilevel inverters requires resolution of complex nonlinear transcendental equations; in this paper we propose a combination of one of the best existing optimized hardware structures with the recent firefly algorithm, which was used to optimize the THD, through finding the best switching angles and guaranteeing the minimization of harmonics within a user defined bandwidth. The obtained THD through the simulation of the thirteen-level symmetric inverter has been reduced down to 5% (FFT of 60 harmonics). In order to validate the simulation results, a thirteen-level symmetric inverter prototype has been made, and practically experimented and tested with different loads. Consequently, the measured THD with resistive load was 4.7% on a bandwidth of 3 kHz. The main advantage of the achieved work is the reduction of the THD
Biochem-Env, une plateforme de biochimie pour la recherche en sciences environnementales et agronomiques
il s'agit d'un type de produit dont les mĂ©tadonnĂ©es ne correspondent pas aux mĂ©tadonnĂ©es attendues dans les autres types de produit : SOFTWAREBiochem-Env est une plateforme scientifique et technique qui permet : 1) le dĂ©veloppement dâoutils de caractĂ©risation biochimique de sols et de sĂ©diments (biomarqueurs enzymatiques, activitĂ© mĂ©taboliqueâŠ) ainsi que de la macrofaune terrestre et benthique (biomarqueurs enzymatiques, rĂ©serves Ă©nergĂ©tiquesâŠ), 2) lâanalyse de ces indicateurs biochimiques dans ces diffĂ©rentes matrices, et 3) lâexpertise, la formation et la veille scientifique et technologique sur ces indicateurs. Biochem-Env dĂ©veloppe Ă©galement un SystĂšme dâInformation Environnementale centrĂ© sur une base de donnĂ©es qui permet : 1) de gĂ©rer la traçabilitĂ© des Ă©chantillons, 2) de stocker et dâanalyser les donnĂ©es de caractĂ©risation biologique des matrices analysĂ©es
Seismic Vulnerability Assessment at Urban Scale: Case of Algerian buildings
International audienc