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991.
The Born scattering approximation has been widely used in seismology to study scattered waves, and to linearize the propagation problem for inversion. The standard Born theory requires the model be separated into a smooth, reference model and a perturbation. Scattering occurs from the pertubation. In the distorted Born approximation, when the reference model is inhomogeneous, the reference Green's functions are normally not known exactly, but the error in these Green's functions is rarely quantified. In this paper, we generalize Born scattering theory to include the errors in the Green's functions explicitly, and obtain scattering integrals from these errors. For forward modelling, there is no need to separate the model into a reference and perturbation part - approximate Green's functions in the true model can be used to calculate the scattered signals.
The theory is developed for inhomogeneous, anisotropic media. Asymptotic ray theory results are suitable approximate Green's functions for the generalized Born scattering theory. The error terms are simple, easily calculated and included in the scattering integrals. Various applications of generalized Born scattering theory have already appeared in the literature, e.g. quasi-shear ray coupling, and this paper is restricted to an improved and more complete theoretical development. Further applications will appear elsewhere. 相似文献
992.
本文对IGBT模块中功率芯片(IGBT和续流二极管)的优化设计进行了讨论。通过优化几个重要的工艺参数并改进器件的结构,IGBT不仅有足够的短路容量,而且正向压降与电流下降时间之间可实现最佳折衷。另外,续流二极管的反向恢复特性也有明显改善。通过采用衬底控制技术,IGBT模块的输出特性不受温度的影响,输出电流更稳,输出阻抗更高。本文详细介绍了整个设计考虑。 相似文献
993.
A. Cerdán Vidal A. R. Maurí Aucejo M. Llobat Estellés C. Pascual Martí J. Simeón Martí 《Fresenius' Journal of Analytical Chemistry》1994,350(12):706-711
The possibility of identification of substances which have similar spectral behaviour by means of Apparent Content Curves has been studied. This study is carried out with absorption, excitation and emission spectra of several amphetamines of widespread pharmaceutical use. Results obtained show that amphetamine, phenylpropanolamine, pseudoephedrine, phenylephrine, epinephrine, dopamine and methoxyamphetamine can be identified with a probability of >95%. 相似文献
994.
A simple and fast HPLC method for the determination of glycols is described. It is characterized by a reversed-phase separation using water as eluent and a refractive index detection. The method was applied to investigate the biodegradation of glycols in a laboratory activated sludge plant and to determine the content of glycols or alcohols in detergents. The detection limit is 4 mg/l ethylene glycol or propylene glycol in an aqueous sample. 相似文献
995.
Investigations of coated carbon fibres are reported using Raman spectroscopy. Relationships between different process parameters (for example precursor concentration, reactor temperature and various precursors) and the resulting types of carbon fibres are discussed. 相似文献
996.
J.-J. Sauvain L. F. de Alencastro J. Tarradellas R. Camenzind G. Karlaganis C. Vuilleumier 《Fresenius' Journal of Analytical Chemistry》1994,350(7-9):555-562
The analysis of PCB in transformer oils has been achieved with three HRGC/ECD based methods, proposed by the International Electrotechnical Commission (IEC/TC 10), by the Comité Européen de Normalisation (CEN/TC 19/WG 22) and by the Deutsches Institut für Normung (DIN 51 527). The same clean-up, described in the CEN/TC 19/WG 22, has been used for all the samples, allowing a comparison of the quantification procedure only. The total chlorine content has also been determined with X-ray fluorescence. These different methods of quantification are compared and their application for legislative purposes is discussed.Dedicated to Professor Dr Dieter Klockow on the occasion of his 60th birthday 相似文献
997.
Patricia Smichowski María Beatriz de la Calle Guntiñas Carmen Cámara 《Fresenius' Journal of Analytical Chemistry》1994,348(5-6):380-384
Summary A method is described for antimony preconcentration based on retention on a column of activated alumina. Recovery is 80% when no pH-control and 4 mol/l HCl as eluent are used. The preconcentration factor is 400. The method was applied to the determination of antimony in spiked tap and sea water. The analytical performance of the method is discussed. 相似文献
998.
TiCx-PECVD-layers were characterized by TEM. EDX analysis and electron diffraction. TiCx-layers deposited using benzene showed a columnar structure, at which the column size decreases with rising excess carbon content. TiCx-layers deposited using n-heptane presented a lamellar structure, at which the lamellar thickness diminishes with an increasing excess carbon content. In dependence on the layer thickness a periodic progress of the element contents was observed, at which a maximum for Ti and Cl correlates with a minimum for C. It was found that the incorporated chlorine is bonded to titanium. The lattice parameter depends on the chlorine content. Using TiCl4/H2/Ar-gas mixtures without any hydrocarbon, layers containing TiH2 are formed. 相似文献
999.
Demetrio Pitea Laura Bonati Elena Collina Ugo Cosentino Marina Lasagni Giorgio Moro Roberto Todeschini 《Fresenius' Journal of Analytical Chemistry》1994,348(1-2):111-120
Summary The role of multivariate analysis methods in evaluating, rationalizing, and working out complex environmental problems is discussed. The discussion is organized in two sections; a literature analysis of the application of chemometric methods to PCDD/PCDF data interpretation and source correlation and a review of the role of chemometric methods in analysing the results obtained by the Authors studying PCDD/PCDF formation and destruction mechanisms in MSW combustion processes. 相似文献
1000.