156 research outputs found
Heats of formation of Zirconium binary transition metal alloys
AbstractD-band model is used to predict enthalpies of formation of binary transition metal alloys. One of the input parameters of the model namely bandwidth is optimized by refinement procedures based on ab initio calculations and reliable calometric data for Zr-, Hf- and Ti-compounds. Revised values of enthalpies of formation ÎHfor for Zr-binary transition metal compounds using new values of bandwidth WZrâ=7.24eV are substantially improved. This improvement can be applied for other problematic cases in order to ameliorate results of ÎHfor calculated by d-band model
Extraction de la signature veineuse dans le moyen (MWIR) et le proche infrarouge (NIR) : analyse de la thermorégulation du corps
Ce projet effectuĂ© dans le cadre d'une maĂźtrise Ă©merge suite Ă la demande croissante d'applications de l'infrarouge dans le domaine de la vision utilisĂ©e pour des recherches en bio-ingĂ©nierie. Il a pour objectif principal l'extraction de la signature veineuse de la main. Deux bandes spectrales infrarouges sont investiguĂ©es : la bande thermique du moyen infrarouge (MWIR, Mid-Wave InfraRed) et la bande du proche infrarouge (NIR, Near InfraRed). Dans la bande thermique, deux recherches sont menĂ©es. Tout d'abord, il est question d'Ă©tudier la biomĂ©trie des veines sur le dos de la main, oĂč l'on extrait la signature veineuse aprĂšs l'acquisition d'images thermiques. Nous avons optĂ© de travailler sur cette partie de la main et non pas sur la paume car les veines superficielles sont plus visibles dans cette zone lorsqu'on travaille dans l'infrarouge moyen. Les veines de la paume sont, en effet, plus profondes pour ĂȘtre visualisĂ©es dans cette zone spectrale. Par la suite, des outils de traitements d'images sont appliquĂ©s afin de distinguer les courbes veineuses du tissu. Toujours dans cette premiĂšre partie, une Ă©tude est rĂ©alisĂ©e sur le comportement thermophysiologique du corps humain en rĂ©action Ă des stimulations. Dans la bande du proche infrarouge, nous exploitons une propriĂ©tĂ© significative des composantes du sang en rĂ©ponse Ă une stimulation optique. La finalitĂ© pratique est de mettre en Ă©vidence la structure veineuse de la main par deux modes d'acquisition. Le premier est le mode par rĂ©flexion de lumiĂšre afin d'extraire la signature du dos de la main. Le second, est le mode par transmission pour extraire le rĂ©seau veineux digital. Encore une fois, dans cette partie, nous faisons l'extraction de la signature veineuse sur le dos de la main et non pas sur la paume pour deux raisons. La premiĂšre, c'est pour ĂȘtre consistant avec notre objectif d'obtenir des rĂ©sultats dans les deux zones spectrales sur la mĂȘme rĂ©gion corporelle, Ă savoir, le dos de la main. La deuxiĂšme raison est que le systĂšme d'acquisition dans le NIR doit ĂȘtre amĂ©liorĂ© afin de visualiser d'une maniĂšre exhaustive les fines veines au niveau de la paume. GrĂące Ă la mĂ©thode que nous avons dĂ©veloppĂ©e, des structures internes du corps humain non visibles Ă l'oeil nu peuvent ĂȘtre visualisĂ©es et dĂ©tectĂ©es. L'application mĂ©dicale de cette Ă©tude peut se rĂ©aliser dans la localisation des veines lors d'une perfusion ainsi que dans la prĂ©vention des maladies telles que les varices primitives, les caillots sanguins, etc. Ăgalement, une application dans le domaine de la biomĂ©trie est possible eu construisant une base de donnĂ©es de signatures veineuses des mains. Eu outre, ce mĂ©moire fournit au lecteur une base bibliographique consistante Ă laquelle il pourra se rĂ©fĂ©rer afin de mener Ă bien des recherches en vision infrarouge appliquĂ©e au corps humain
Stator current signal crossing for fault diagnosis of self-excited induction generators
This paper presents a novel method for modelling and diagnosis of electrical and mechanical faults in fixed-Speed Self-Excited Induction Generators (SEIGs) operating in autonomous mode in a small-scale wind energy system. The proposed method is validated using the finite element method. After the selection of the magnetising capacitors, the self-excitation process is performed under no-load conditions. Once the stator voltage is established, a symmetrical three-phase load is connected. The fault detection method introduced here is called Stator Current Signal Crossing (SCSC). The SCSC extracts a new signal from the stator currents, that enables the detection of stator inter turn shortcircuits, broken rotor bars, and dynamic eccentricity faults in SEIGs. A spectral analysis of SCSC using the Fast Fourier Transform (FFT) algorithm is used to precisely locate the induced fault components. What sets this fault-tracking method apart from its predecessors is its exceptional ability to detect faults of any magnitude by analysing the modulation of the SCSC signal. These faults are directly identified by the presence of distinct harmonics, each indicative of a specific type of fault. This study also focuses on the SEIG in a wind energy system, whereas previous works have mainly addressed the induction machine in motor mode. In contrast, previous methods involved analysing a single current signal and isolating specific harmonics from a wide frequency range. The effectiveness of the proposed fault detection method and the self-excitation process are illustrated by simulation results and spectral analysis
Induction motor mechanical defect diagnosis using DWT under different loading levels
The information extraction capability of the widely used signal processing tool, FFT for diagnosing induction machines, is commonly used at a constant load or at different levels. The loading level is a major influencing factor in the diagnostic process when the coupled load and the machine come with natural mechanical imperfections, and at a low load, the mechanical faults harmonics are strongly influenced. In this context, the main objective of this work is the detection of the mechanical faults and the study of the effect of the loading level on the induction motor diagnostic process. We have employed a diagnosis method based on discrete wavelet transform (DWT) for the multi-level decomposition of stator current and extracting the faultâs energy stored over a wide frequency range. The proposed approach has been experimentally tested on a faulty machine with dynamic eccentricity and a shaft misalignment for three loading levels. The proposed method is experimentally tested and the results are provided to verify the effectiveness of the fault detection and to point out the importance of the coupled load
New approach to Dynamical Monte Carlo Methods: application to an Epidemic Model
A new approach to Dynamical Monte Carlo Methods is introduced to simulate
markovian processes. We apply this approach to formulate and study an epidemic
Generalized SIRS model. The results are in excellent agreement with the forth
order Runge-Kutta Method in a region of deterministic solution. We also
demonstrate that purely local interactions reproduce a poissonian-like process
at mesoscopic level. The simulations for this case are checked
self-consistently using a stochastic version of the Euler Method.Comment: Written with Scientific WorkPlace 3.51 in REVTex4 format, 11 pages
with 2 figures in postscript forma
Expression and deployment of reaction policies
International audienceCurrent prevention techniques provide restrictive responses that may take a local reaction in a limited information system infrastructure. In this paper, an in depth and comprehensive approach is introduced for responding to intrusions in an efficient way. This approach considers not only the threat and the architecture of the monitored information system, but also the security policy. The proposed reaction workflow links the lowest level of the information system corresponding to intrusion detection mechanisms, including misuse and anomaly techniques, and access control techniques with the higher level of the security policy. This reaction workflow evaluates the intrusion alerts at three different levels, it then reacts against threats with appropriate counter measures in each level accordingly
Optimum Monte Carlo Simulations: Some Exact Results
We obtain exact results for the acceptance ratio and mean squared
displacement in Monte Carlo simulations of the simple harmonic oscillator in
dimensions. When the trial displacement is made uniformly in the radius, we
demonstrate that the results are independent of the dimensionality of the
space. We also study the dynamics of the process via a spectral analysis and we
obtain an accurate description for the relaxation time.Comment: 17 pages, 8 figures. submitted to J. Phys.
Simulations of a single membrane between two walls using a Monte Carlo method
Quantitative theory of interbilayer interactions is essential to interpret
x-ray scattering data and to elucidate these interactions for biologically
relevant systems. For this purpose Monte Carlo simulations have been performed
to obtain pressure P and positional fluctuations sigma. A new method, called
Fourier Monte-Carlo (FMC), that is based on a Fourier representation of the
displacement field, is developed and its superiority over the standard method
is demonstrated. The FMC method is applied to simulating a single membrane
between two hard walls, which models a stack of lipid bilayer membranes with
non-harmonic interactions. Finite size scaling is demonstrated and used to
obtain accurate values for P and sigma in the limit of a large continuous
membrane. The results are compared with perturbation theory approximations, and
numerical differences are found in the non-harmonic case. Therefore, the FMC
method, rather than the approximations, should be used for establishing the
connection between model potentials and observable quantities, as well as for
pure modeling purposes.Comment: 10 pages, 10 figure
Abord laparoscopique dâun volumineux kyste hĂ©patique simple : Ă propos dâun cas [A laparoscopic approach to a large simple hepatic cyst : a case report]
French Abstract :
La fenestration laparoscopique a rĂ©cemment Ă©tĂ© considĂ©rĂ©e comme une procĂ©dure stanÂdard pour les kystes hĂ©patiques symptomatiques non parasitaires. Lâobjectif de notre observation Ă©tait de montrer lâabord laparoscopique dâun volumineux kyste du dĂŽme hĂ©patique. Une femme de 54 ans sans antĂ©cĂ©dent pathologique qui consultait pour des douleurs chroniques de lâhypochondre droit. Les explorations radiologiques avaient obÂjectivĂ© un volumineux kyste hĂ©patique et une lithiase vĂ©siculaire non compliquĂ©e. La SĂ©rologie hydatique Ă©tait nĂ©gative. Le traitement consistait en une fenestration large par laparoscopie aprĂšs ponction prudente du kyste, afin dâĂ©liminer une pathologie paÂrasitaire et une aspiration dâenvirons 1,8 L dâun liquide brunĂątre, une cholĂ©cystectomie et lâextraction de la piĂšce opĂ©ratoire dans un sac. LâĂ©tude histologique Ă©tait en faveur dâun kyste hĂ©patique simple. La fenestration laparoscopique est le traitement de rĂ©fĂ©Ârence des kystes hĂ©patiques simples symptomatiques et ce dâautant que les kystes sont volumineux ou difficiles Ă ponctionner sous Ă©chographie.
English Abstract :
Laparoscopic fenestration has recently been considered a standard procedure for non parasitic symptomatic liver cysts.The objective of our observation was to show the laparoscopic approach of a large cyst of the hepatic dome. A 54-year-old woÂman with no pathological history who consulted for chronic pain in the right hypoÂchondrium. The radiological explorations had objectified a large hepatic cyst and an uncomplicated gall bladder lithiasis. Hydatid serology was negative. The treatment consisted of a wide fenestration by laparoscopy after careful puncture of the cyst in order to eliminate a parasitic pathology and an aspiration of around 1.8 liter of a brownish liquid, a cholecystectomy and the exteriorization of the cyst wall in an endobag. The histological study was in favor of a simple liver cyst. Laparoscopic feÂnestration is the reference treatment for symptomatic simple liver cysts, especially when the cysts are large or difficult to puncture under ultrasound
Experimental investigation of the natural and forced convection on solidification of Sn-3wt. %Pb alloy using a benchmark experiment
International audienceWe deal with the development of a solidification benchmark experiment in order to investigate the structure formation as well as solute macro-mesosegregation, by means of a well-controlled solidification experiment. The experiment consists in solidifying a rectangular ingot of Sn-3wt.%Pb alloy, by using two lateral heat exchangers which allow extraction of the heat flux from one or two vertical sides of the sample. The domain is a quasi two dimensional parallepipedic ingot (100x60x10) mm. The temperature difference ÎT between the two lateral sides is 40 K and the cooling rate CR= 0.03 K/s. The instrumentation consists in recording the instantaneous temperature maps by means of an array of 50 thermocouples in order to provide the time evolution of the isotherms. After each experiment the patterns of the segregations have been obtained by X-ray radiograph and confirmed by eutectic fraction measurements. The local solute distribution determined by means of induction coupled plasma analysis is provided. The originality of the present study is to examine the effect of the forced convection driven by a travelling magnetic field (TMF) induced by a linear inductor located on the bottom part of the sample. A periodically reversed stirring with a modulation frequency equal to 0.5 Hz stirring have been investigated. This study allows us to evaluate the evolution due to the forced convection induced by a TMF field, as well as its influence on the initial conditions, the solidification macrostructure and the segregation behavior. Measurements of the velocity field by ultrasonic Doppler velocimetry (UDV) method in a Ga-In-Sn pool were performed and transposed to the tin-lead alloy case before solidification. Post-mortem patterns of the macro-mesosegregations have been obtained by X-ray radiography. The results show the transport effects of the flow on both the macrosegregations and the channel formation. The reversal of the TMF produces a decrease of the level of mesosegregations, namely channel formation
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