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891.
HJ Voeller M Augustus V Madike GS Bova KC Carter EP Gelmann 《Canadian Metallurgical Quarterly》1997,57(20):4455-4459
Loss of heterozygosity at chromosome 8p21-22 is common in human prostate cancer, suggesting the presence of one or more tumor suppressor genes at this locus. A homeobox gene that is expressed specifically in adult human prostate, NKX3.1, the expression of which is regulated by androgen, maps to chromosome 8p21. Fine structure in situ mapping showed that NKX3.1 is proximal to MSR32 (macrophage scavenger receptor type II) and LPL (human lipoprotein lipase) and very close to NEFL (human neurofilament light chain) on 8p21. Single-strand conformational polymorphism analysis of 48 radical prostatectomy cancer specimens and 3 metastases for the entire coding region of NKX3.1 showed no tumor-specific sequence alterations in 50 specimens and total absence of the gene in 1 specimen known to have a biallelic deletion of 8p21. NKX3.1 was found to have a polymorphism at nucleotide 154 in codon 52 that resulted in a CGC-->TGC sequence change and an Arg-->Cys amino acid alteration (R52C). This polymorphism was present in 20% of DNA samples. If NKX3.1 is a target of the 8p21 LOH, it is not via disruption of the coding region of the gene. 相似文献
892.
The high-frequency properties of quantum well infrared photodetectors (QWIP's) based on a double-barrier single QW structure are studied theoretically. An analytical model of the QWIP is developed. The model takes into account the main processes responsible for the QWIP operation, namely, the electron tunneling from the emitter, capture of the electrons into the QW, their photoexcitation from the QW, and electron drift or ballistic transport across the QWIP structure. Analytical expressions for the QWIP responsivity as functions of the modulation frequency of infrared radiation, its power density, and the QWIP structural parameters are obtained from the rigorous self-consistent small-signal analysis. It is shown that there are two distinct ranges where the frequency dispersion of the responsivity is strong. At low frequencies, the responsivity dispersion is associated with the inertia of the process of recharging of the QW while at very high frequencies the dispersion is due to the electron transit-time effect. The influence of the electron transit-time effect on the QWIP admittance is also evaluated. The derivation of the QWIP high-frequency performance and, in particular, the estimates of 3-dB bandwidth show that the QWIP's have a great potential for devices utilizing both infrared radiation and millimeter or submillimeter wavelength microwave signals 相似文献
893.
A deterministic digital simulation model with finite sum of properly weighted sinusoids is used to simulate a frequency nonselective mobile channel with LOS component. Measurement data are used to optimise the parameters. Which are then used in the deterministic simulation model. The probability distribution and level cross rate (LCR) obtained from the measured data agree well with the analytical and simulation results 相似文献
894.
A Konstantinidou E Patsouris N Kavantzas PM Pavlopoulos V Bouropoulou P Davaris 《Canadian Metallurgical Quarterly》1997,142(5-6):311-316
Proliferating cell nuclear antigen (PCNA) expression has been proven to be a significant marker of cell proliferation in meningiomas, which correlates with growth rate and, as shown by several authors, possibly provides prognostic information concerning biologic behavior. However, the current method for determining PCNA labeling index (LI) is tedious and time consuming like all the nonautomated methods for evaluating cell kinetics, presenting high interobserver and interlaboratory variability and low reproducibility. In the present study, we introduce a semi-automated computer-assisted image analysis method for determining PCNA LI in 38 meningiomas, in parallel with the current nonautomated method. Image analysis technique permits unbiased cell counting, standardizes the degree of staining intensity and provides instant results. By calculating coefficient of variability, the method proved to be highly reproducible. The correlation between the results provided by the nonautomated and the semiautomated image analysis method showed a high agreement between them, with a correlation coefficient, r, of 0.82. In conclusion, we consider that image analysis contributes to the accuracy, reproducibility, and practicality of PCNA LI determination so that along with other useful parameters this significant marker may serve to predict the clinical behavior in meningiomas. 相似文献
895.
Proximal duodenal obstruction due to tuberculosis can masquarade as duodenal ulcer. Although commonest cause of duodenal obstruction is ulcer, other causes must be considered, particularly tuberculosis which is common in tropics. 相似文献
896.
OBJECTIVE: Experiences obtained with nonoperative treatment (NOT), i.e. total prohibition of per oral food intake for a minimum of 7 days, administration of combinations of broad-spectrum antibiotics, and parenteral hyperalimentation, are described in the management of esophageal perforations. SUMMARY BACKGROUND DATA: The place, value, and indication of NOT in the management of esophageal perforation has not yet been unequivocally defined. As a result, contradictory data have been published regarding the outcome of NOT. METHODS: During the past 15 years (1979 to 1994), 20 of 86 patients (23.3%) with esophageal perforation have been treated nonoperatively from the outset. In this group, perforations were located to the upper, middle, and lower third of the esophagus in 50%, 30%, and 20%, respectively. In the operative management group (OT)--in which conservative (drainage, endeprothesis), reconstructive (suture, reinforced suture), and radical (resection) surgical methods were applied--lesions were preponderantly located in the lower one third of the esophagus (56.1%--37/66). As to the interval between the perforation and the onset of treatment, 14 patients had been diagnosed within 24 hours, whereas in 6 cases treatment had been begun beyond 24 hours. RESULTS: NOT could be successfully carried out in 16 patients; the decision to use NOT had to be revised in 4 other cases (Table 1). Two patients were lost; the mortality rate was 10% (2 of 20). The rate of complications was lower in the NOT group (20%, or 4 of 20) than in the OT group (50%, or 33 of 66). CONCLUSIONS: NOT can be suggested for the treatment of intramural perforations. In the case of transmural perforation, this approach should be taken into consideration if the esophageal lesion is circumscribed, is not in neoplastic tissue, is not in the abdominal cavity, and is not accompanied by simultaneous obstructive esophageal disease; in addition, symptoms and signs of septicemia should be absent. 相似文献
897.
Electron transport and heating in a two-dimensional semiconductor superlattice with arbitrary orientation of the field (current)
relative to the crystallographic axes is investigated in the approximation of constant energy and velocity relaxation times
with electron-electron collisions taken into account. The nonlinear conductivity, average electron energies, and interrelationship
between field direction and the current excited by it in an unbounded superlattice, as well as the current-voltage characteristics
and the transverse electromotive force of a superlattice of finite width are found.
Fiz. Tekh. Poluprovodn. 31, 308–310 (March 1997) 相似文献
898.
The development and creating of new-generation full-scope simulator and new technology of simulation
N. N. Ponomarev-Stepnoi V. A. Lebedev M. M. Khudiykov S. D. Malkin V. V. Shalia I. D. Rakitin 《Nuclear Engineering and Design》1997,173(1-3)
Set out is a brief account of the two major accomplishments by the Russian Research Center ‘Kurchatov Institute’ in creating the full-scope simulators and mathematical modeling technologies. Presented are the basic specifications of one of the world's largest simulators—the full-scope simulator for the Leningrad NPP which is the new-generation one. Owing to the extended modeling scope accomplished is the possibility of training personnel to act in terms of not only the design-basis but rather beyond the design-basis accidents. To minimize the expenditures for creating the simulators, analyzers and other modeling and control means, the RRC ‘Kurchatov Institute' has created the unique technology of mathmodeling automation. Thanks to its versatility and application at its creation of the ELUD philosophy (easy to learn, use and develop) good use is made of this technology both in nuclear and thermal power engineering, as well as in gas industry. 相似文献
899.
A. V. Kurdyumov V. F. Britun V. B. Zelyavskii S. N. Gromyko T. S. Bartnitskaya L. A. Lyudvinskaya 《Powder Metallurgy and Metal Ceramics》1997,36(7-8):425-429
The structure of SiC–AlN powders is investigated by x-ray diffraction and transmission electron microscopy methods. The powders
were produced by joint carbon reduction and nitriding of silicon and aluminum oxide mixtures. The results show that a mixture
of solid solutions forms during joint SiC and AlN synthesis at 1700°C, with SiC forming β (3C) and α (2H) modifications with
different grain morphology. The fiber form is characteristic of β-SiC, whereas the grains of the solid solution based on SiC
have a predominantly equiaxed form. α-SiC grain dimensions are considerablys smaller than those of AlN.
Institute of Materials Science, National Academy of Sciences of Ukraine. Kiev Translated from Poroshkovaya Metallurgiya, Nos.
7–8, pp. 81–86, July–August, 1997. 相似文献
900.
Kang W.P. Wisitsora-at A. Davidson J.L. Kerns D.V. 《Electron Device Letters, IEEE》1998,19(10):379-381
A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp2 content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters 相似文献