排序方式: 共有87条查询结果,搜索用时 296 毫秒
81.
Mamadou Sankh Stphane Bernard Maxime Wartel Stphane Pellerin Philippe Gillard 《等离子体物理论文集》2019,59(3):326-339
Spark discharges are widely used to ignite flammable gases, liquids, or dust. For a better understanding of the interaction between the spark discharge and the ignited media (gas, liquid, or dust), it is necessary to measure some key parameters of the spark, especially the space‐time variation of its temperature. Determination of temperature gradients would allow a more precise and realistic simulation of the ignition process. In fact, electrons and particles in the discharge zone get their energy with increasing temperature before interacting with particles of the media to ignite the flame. In this study, optical emission spectroscopy of the spark discharge between two tungsten electrodes was performed. Assuming excitation balance between the WI lines, a Boltzmann plot after an Abel inversion gives the excitation temperature and its space‐time variation. For a 100‐μs time discharge, at 80‐μs delay, we measured 7,000 K at the centre of the column zone, 4,100 K at the centre of the cathode zone, and 3,600 K at the centre of the anode zone. Assuming a singly ionized tungsten plasma and excitation equilibrium, we used also the Saha–Boltzmann equation to calculate the plasma composition. The electron density at the column zone was about 3 × 1017 cm?3, which is two orders of magnitude higher than in the rest of the spark. 相似文献
82.
Didier Bresch El Hassan Essoufi Mamadou Sy 《Journal of Mathematical Fluid Mechanics》2007,9(3):377-397
In this paper, we look at the influence of the choice of the Reynolds tensor on the derivation of some multiphasic incompressible
fluid models, called Kazhikhov–Smagulov type models. We show that a compatibility condition between the viscous tensor and
the diffusive term allows us to obtain similar models without assuming a small diffusive term as it was done for instance
by A. Kazhikhov and Sh. Smagulov. We begin with two examples: The first one concerning pollution and the last one concerning
a model of combustion at low Mach number. We give the compatibility condition that provides a class of models of the Kazhikhov–Smagulov
type. We prove that these models are globally well posed without assumptions between the density and the diffusion terms. 相似文献
83.
Samer Riachy Mamadou Mboup Jean-Pierre Richard 《Journal of Computational and Applied Mathematics》2011,236(6):1069-1089
We present an innovative method for multivariate numerical differentiation i.e. the estimation of partial derivatives of multidimensional noisy signals. Starting from a local model of the signal consisting of a truncated Taylor expansion, we express, through adequate differential algebraic manipulations, the desired partial derivative as a function of iterated integrals of the noisy signal. Iterated integrals provide noise filtering. The presented method leads to a family of estimators for each partial derivative of any order. We present a detailed study of some structural properties given in terms of recurrence relations between elements of a same family. These properties are next used to study the performance of the estimators. We show that some differential algebraic manipulations corresponding to a particular family of estimators lead implicitly to an orthogonal projection of the desired derivative in a Jacobi polynomial basis functions, yielding an interpretation in terms of the popular least squares. This interpretation allows one to (1) explain the presence of a spatial delay inherent to the estimators and (2) derive an explicit formula for the delay. We also show how one can devise, by a proper combination of different elementary estimators of a given order derivative, an estimator giving a delay of any prescribed value. The simulation results show that delay-free estimators are sensitive to noise. Robustness with respect to noise can be highly increased by utilizing voluntary-delayed estimators. A numerical implementation scheme is given in the form of finite impulse response digital filters. The effectiveness of our derivative estimators is attested by several numerical simulations. 相似文献
84.
Ndiaye AA Pflieger R Siboulet B Molina J Dufrêche JF Nikitenko SI 《The journal of physical chemistry. A》2012,116(20):4860-4867
The sonoluminescence (SL) spectra of OH(A(2)Σ(+)) excited state produced during the sonolysis of water sparged with argon were measured and analyzed at various ultrasonic frequencies (20, 204, 362, 609, and 1057 kHz) in order to determine the intrabubble conditions created by multibubble cavitation. The relative populations of the OH(A(2)Σ(+)) v' = 1-4 vibrational states as well as the vibronic temperatures (T(v), T(e)) have been calculated after deconvolution of the SL spectra. The results of this study provide evidence for nonequilibrium plasma formation during sonolysis of water in the presence of argon. At low ultrasonic frequency (20 kHz), a weakly excited plasma with Brau vibrational distribution is formed (T(e) ~ 0.7 eV and T(v) ~ 5000 K). By contrast, at high-frequency ultrasound, the plasma inside the collapsing bubbles exhibits Treanor behavior typical for strong vibrational excitation. The T(e) and T(v) values increase with ultrasonic frequency, reaching T(e) ~ 1 eV and T(v) ~ 9800 K at 1057 kHz. 相似文献
85.
Lo M Lefebvre JF Marcotte N Tonnelé C Beljonne D Lazzaroni R Clément S Richeter S 《Chemical communications (Cambridge, England)》2012,48(28):3460-3462
Cleavage reactions of 2,3-diamino-meso-tetraarylporphyrins and meso-tetraarylporphyrins fused to imidazole rings afforded secochlorins including stable free base derivatives. 相似文献
86.
Optical dye-dilution techniques can quantify kinetic parameters in a region of tissue, but currently rely on a two-step process-spatial reconstruction of the dye concentration, repeated at every time-point, and subsequent kinetic analysis of the time-dependent change in dye concentration. Inaccuracies, in this approach, are due mainly to the ill-posed nature of the spatial reconstruction problem, which propagates into kinetic analysis and result in errors in extracted dynamic parameters. We present a hybrid kinetic deconvolution optical reconstruction algorithm, effectively combining optical reconstruction and model-independent kinetic analysis into a single inverse problem that is better posed. Kinetic parameters of multiple tissue regions can be quantified simultaneously. As proof of principle, we provide numerical experiments in reflectance-based and fluorescence molecular tomography scenarios. 相似文献
87.
Vyacheslav S. Bryantsev Wibe A. de Jong Kevin C. Cossel Mamadou S. Diallo William A. III Goddard Gary S. Groenewold Winnie Chien Michael J. Van Stipdonk 《ChemInform》2008,39(41):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献