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N Taniguchi K Itoh S Nakamura T Obayashi F Kawai M Nakamura 《Canadian Metallurgical Quarterly》1997,157(4):1242-1245
PURPOSE: We determined the usefulness of ultrasonic frequency dependent attenuation in differentiating hyperechoic renal cell carcinoma from angiomyolipoma. MATERIALS AND METHODS: Frequency dependent attenuation values were determined in 29 renal cell carcinomas and 13 angiomyolipomas. RESULTS: Frequency dependent attenuation values were significantly lower in renal cell carcinomas than in angiomyolipomas (0.42 versus 0.76 dB./cm./MHz.). Two of the renal cell carcinomas were as hyperechoic as the angiomyolipomas but they were clearly differentiated by the low frequency dependent attenuation. Two other renal cell carcinomas exhibited high values because of the abundance of fibrous tissue. However, they were readily diagnosed by the typical low echoic B-mode images. Frequency dependent attenuation did not differ between histological types of renal cell carcinoma. One angiomyolipoma that was poor in fat and rich in muscle components had an exceptionally low frequency dependent attenuation. Therefore, frequency dependent attenuation values can be regarded as an inversion of computerized tomography numbers. CONCLUSIONS: Frequency dependent attenuation measurement is a promising diagnostic aid in differentiating hyperechoic renal cell carcinomas from angiomyolipomas. 相似文献
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Previous investigations have invariably observed strain rate related deformation effects as the fatigue frequency is raised to the ultrasonic range. Through room temperature tests on strain rate insensitive nickel-base superalloy single crystals of Mar-M200, we have shown that another effect of increasing the fatigue frequency to the ultrasonic range is in the suppression of the deleterious influence of environment. It was found that above a stress amplitude of 30,400 psi the fatigue lives of crystals ultrasonically fatiguedin air increase with decreasing stress in a manner which is functionally similar to, that of crystals conventionally fatiguedin vacuum. Similarly, the fracture surfaces of ultrasonically fatigued crystals have a dimpled appearance over most of their areas which is characteristic of locally ductile failure and identical to, the appearance of crystals failed at conventionally frequency in vacuum. These results, along with a kinetic analysis of gaseous adsorption, indicate that the major effect of increasing the fatigue frequency to the ultrasonic, range is in the suppression of the influence of oxygen in enhancing the rate of crack propagation. In addition, the short test times involved in running large numbers of cycles have allowed for the determination of the fatigue limit in a nickel-base superalloy. This is the first indication of no-fail behavior in this type of alloy. 相似文献
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A system has been developed that can generate recombinant baculovirus expression vectors at frequencies approaching 100%. This system provides a selection for recombinant viruses by using the essential gene downstream of the Autographa californica nuclear polyhedrosis virus (AcMNPV) polyhedrin expression locus. Two AcMNPV derivatives were constructed in which the expression locus and part of the downstream gene are flanked by restriction sites. The parental viruses are viable; however, restriction of the viral DNAs removes an essential piece of the viral genome. Transfer vectors carry a copy of the missing sequences downstream from the site into which foreign genes are inserted for expression; hence, recombination between a transfer vector and the restricted viral DNA can restore the integrity of the essential gene. Such recombination events also transfer any foreign gene present in the expression locus of the transfer vector to the viral genome. Recombinant viruses therefore have a selective advantage over nonrecombinant viral DNAs. Consequently, a high proportion of the viruses obtained by co-transfecting transfer vector DNA and restricted viral DNA of one of these new viruses expresses the target gene from the transfer vector. This system greatly reduces the time needed to make recombinant baculovirus expression vectors. 相似文献
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岩石中裂隙损伤对超声波衰减影响的实验研究 总被引:3,自引:0,他引:3
在分析岩石裂隙损伤声衰减基础上,形成了损伤参量D与衰减系数α的关系式,建立了表达缺陷尺度与数量分布特征的裂隙集合。运用能量法进行了玄武岩度件损伤声衰减与应力关系的实验研究。结果表明,品质因数下降量△Qp随应力比率变化的线性tgα1,能够用来反映岩石裂隙损伤繁衍的规律。本文还对工程岩声衰减检测应用进行探索。 相似文献
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Though it has been established that skinfold anthropometry has severe limitations as a method of deriving total body fat (TBF), the possibility that the problem might be related more to the assumptions implicit in densitometry has to be addressed. This paper suggests that smaller residual errors might be obtained if sums of skinfolds are regressed against TBF measured by a difference technique (IVNAA + 3H2O dilution), suggesting that the latter may perhaps be a better standard than densitometry. 相似文献
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Perceived location of tonal stimuli d and narrow noise bands presented in two-dimensional space varies in an orderly manner with changes in stimulus frequency. Hence, frequency has a referent in space that is most apparent during monaural listening. The assumption underlying the present study is that maximum sound pressure level measured at the ear canal entrance for the various frequencies serves as a prominent spectral cue for their spatial referents. Even in binaural localization, location judgments in the vertical plane are strongly influenced by spatial referents. We measured sound pressure levels at the left ear canal entrance for 1.0-kHz-wide noise bands, centered from 4.0 kHz through 10.0 kHz, presented at locations from 60 degrees through -45 degrees in the vertical plane; the horizontal plane coordinate was fixed at -90 degrees. On the basis of these measurements, we fabricated three different bandstop stimuli in which differently centered 2.0-kHz-wide frequency segments were filtered from a broadband noise. Unfiltered broadband noise served as the remaining stimulus. Localization accuracy differed significantly among stimulus conditions (p < .01). Where in the vertical plane most errors were made depended on which frequency segment was filtered from the broadband noise. 相似文献