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891.
A full wave moment method is applied to the analysis of aperture coupled microstrip antennas, in which all components of the electric and equivalent magnetic surface currents are considered. The electric current distributions on the rectangular patch for different coupling aperture positions are presented with their radiation patterns. The effects of the coupling aperture shape and size on the input impedance and radiation performance are also discussed. As an example of new radiators, slotted patches are studied, and it is shown that they can be used to achieve dual-frequency operation 相似文献
892.
Arata L.K. Dhawan A.P. Broderick J.P. Gaskil-Shipley M.F. Levy A.V. Volkow N.D. 《IEEE transactions on bio-medical engineering》1995,42(11):1069-1078
Model-based segmentation and analysis of brain images depends on anatomical knowledge which may be derived from conventional atlases. Classical anatomical atlases are based on the rigid spatial distribution provided by a single cadaver. Their use to segment internal anatomical brain structures in a high-resolution MR brain image does not provide any knowledge about the subject variability, and therefore they are not very efficient in analysis. The authors present a method to develop three-dimensional computerized composite models of brain structures to build a computerized anatomical atlas. The composite models are developed using the real MR brain images of human subjects which are registered through the principal axes transformation. The composite models provide probabilistic spatial distributions, which represent the variability of brain structures and can be easily updated for additional subjects. The authors demonstrate the use of such a composite model of ventricular structure to help segmentation of the ventricles and cerebrospinal fluid of MR brain images. Here, a composite model of ventricles using a set of 22 human subjects is developed and used in a model-based segmentation of ventricles, sulci, and white matter lesions. To illustrate the clinical usefulness, automatic volumetric measurements on ventricular size and cortical atrophy for an additional eight alcoholics and 10 normal subjects were made. The volumetric quantitative results indicated regional brain atrophy in chronic alcoholics 相似文献
893.
We develop an efficient method for the analysis of ultra-wide-band (UWB) electromagnetic pulses (e.g., double-exponential pulse) propagating through a waveguide or cold plasma (i.e., the ionosphere). First we show that the inverse Fourier-transform representations for the electric and magnetic fields satisfy second order, nonhomogeneous, ordinary, differential equations. These differential equations are solved analytically, thereby yielding closed-form expressions involving incomplete Lipschitz-Hankel integrals (ILHIs). The ILHIs are computed using efficient convergent and asymptotic series expansions. We demonstrate the usefulness of the ILHI expressions by comparing them with the fast Fourier-transform technique (FFT). Because of the long tails associated with UWB pulses, a large number of sample points are required in the FFT, to avoid aliasing errors. In contrast, the ILHI expressions provide accurate and efficient numerical results, regardless of the number of points computed. An asymptotic series representation for the ILHIs is also employed, to obtain a relatively simple, late-time approximation for the transient fields. This approximate late-time expression is shown to accurately model the waveform over a large portion of its time history 相似文献
894.
Harame D.L. Comfort J.H. Cressler J.D. Crabbe E.F. Sun J.Y.-C. Meyerson B.S. Tice T. 《Electron Devices, IEEE Transactions on》1995,42(3):455-468
A detailed review of SiGe epitaxial base technology is presented, which chronicles the progression of research from materials deposition through device and integration demonstrations, culminating in the first SiGe integrated circuit application. In part I of this paper, the requirements and processes for high-quality SiGe film preparation are discussed, with emphasis on fundamental principles. A detailed overview of SiGe HBT device design and implications for circuit applications is then presented 相似文献
895.
L Chan 《Canadian Metallurgical Quarterly》1995,6(5):335-340
Genetic manipulations of experimental animals have provided valuable information on lipoprotein metabolism in vivo. Somatic gene transfer is a novel method for introducing foreign genes into animals in vivo. Adenovirus-mediated transfer of genes for the LDL receptor, the receptor-associated protein, apolipoprotein A-I, apolipoprotein E, cholesterol 7 alpha-hydroxylase, and apolipoprotein B messenger RNA editing protein has resulted in high-level expression of these transgenes in mice and hamsters, and the production of interesting animal models of lipoprotein metabolism. Somatic gene transfer is a valuable tool for analyzing the role of transgenes in lipoprotein metabolism in vivo and for exploring the potential use of specific transgenes for human gene therapy. 相似文献
896.
Since foodborne diseases, especially those caused by bacteria, have become an increasingly important public health problem, the Authors conducted a survey in order to evaluate the organization of, and the intervention carried out by, six Public Health Services in the Lombardia region, after reports of foodborne diseases outbreaks. Lack of correct methodology was detected, not to mention the usual omission of epidemic curves and attack rates. Besides, too many microbiological tests were made and it took too much time to take care of and to report the outbreaks to Regional and National Health Authorities. Forty-one outbreaks were examined: 415 cases occurred (AR: 28.7%), most of which home-made food-related. In 25 outbreaks the suspected food vehicles were eggs or fish, but only 5 of them were confirmed by laboratory tests. Salmonella enterica, either serovar Eenteritidis or group D, appeared responsible for 26 of the outbreaks [corrected]. 相似文献
897.
898.
C Altman A Ladouch MJ Briantais T Rason E Martin L Jacques C Buffet 《Canadian Metallurgical Quarterly》1995,24(15):708-710
OBJECTIVES: Antral gastritis is frequent in alcoholics. The role of H. pylori in the pathogenesis of gastritis in these patients is not well known. The aim of our study was to study the role of H. pylori and cirrhosis in the pathogenesis of antral gastritis in alcoholic patients. METHODS: Seventy-nine patients were included in the study. All underwent upper gastrointestinal tract endoscopy with antral biopsies, independently of the presence of abdominal pain, and had serological examination for H. pylori antibodies. RESULTS: Cirrhosis and gastritis were present in 50 and 40 patients respectively, H. pylori serological assay and histological identification of the bacterium were positive in 35 (44%) and 19 (24%) patients respectively. Discrepancy between the 2 tests were observed more frequently in cirrhotic patients. A positive serology with a negative histologic examination for H. pylori was present for 18 cirrhotic and 4 noncirrhotic patients (p < 0.05). A gastritis without evidence of H. pylori was more frequent in cirrhotic than in noncirrhotic patients. H. pylori was histologically present in 11 of 29 cirrhotic patients and in 8 of the 11 noncirrhotic patients with a gastritis (p < 0.05). CONCLUSIONS: Discrepancies between histological examination and H. pylori serology in patients with cirrhosis might be due to the inhospitable environment for H. pylori in case of portal hypertension; the positive serology could be in relation with a past infection. 相似文献
899.
900.
Ferdinand P. Ferragu O. Lechien J.L. Lescop B. Magne S. Marty V. Rougeault S. Kotrotsios G. Neuman V. Depeursinge Y. Michel J.B. Van Uffelen M. Varelas D. Berthou H. Pierre G. Renouf C. Jarret B. Verbandt Y. Stevens W. Voet M.R.H. Toscano D. 《Lightwave Technology, Journal of》1995,13(7):1303-1313
Recent developments of stability control in mines, essentially based on Ge-doped fiber Bragg gratings (FBG) are reported including results about the different aspects of the system: accurate characterizations of FBG, sensor network topology and multiplexing method, user interface design and sensor packaging 相似文献