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291.
An analytic expression of fmax is derived based on a practical HBT circuit model where collector junction capacitance is split up into internal and external parts. It shows that for advanced HBTs, fmax is well characterized by the product of the base resistance and internal collector capacitance. In other words, the external collector capacitance has only a small impact on the determination of fmax. Good agreement between experimental results and numerical circuit simulation confirms the validity of the HBT circuit model. The influence of the external collector capacitance on maximum available gain is also described 相似文献
292.
A low threshold current density of ~100 A/cm2 has been obtained at 1.55 μm using a graded-index separate-confinement-heterostructure strained InGaAsP single-quantum-well laser. The design of the laser structure is based on results calculated from the viewpoint of effective carrier injection into the well 相似文献
293.
Event-related desynchronization (ERD) was studied in 10 young (mean age = 19.1) and 10 older (mean age = 62.8) subjects during a verbal recognition task. The attention load of the task varied according to the difficulty of discriminating between targets and distractors. EEG recorded from 29 electrodes was used to compute ERD from 14 source derivations in 125 ms intervals. Thereafter, it was displayed as spatiotemporal maps. The results show that attention influences the characteristics of EEG desynchronization. In young subjects, ERD is more pronounced and more widespread when the attentional load is high. In the elderly, differences between the two attention conditions are less marked. ANOVA reveals main effects of attention and time. The significant 'attention x time x age group' interaction confirms the presence of different brain activation patterns in the two age groups in relation to attention load. 相似文献
294.
K Alanko L Kanerva B Mohell-Talolahti R Jolanki T Estlander 《Canadian Metallurgical Quarterly》1996,35(4):647-648
The biotransformation of oxazepam by Bifidobacterium bifidum was studied. The major metabolite was purified by chromatographic methods and found to be desmethyldiazepam using NMR, IR and other physicochemical data. 相似文献
295.
296.
R Bookstein W Demers R Gregory D Maneval J Park K Wills 《Canadian Metallurgical Quarterly》1996,23(1):66-77
Tumor suppressor genes such as p53 contribute to the oncogenic process via loss-of-function mechanisms such as genetic mutation or complex formation with other cellular or viral proteins. p53 is mutated in approximately 50% of human tumors and has an important role in the genesis or progression of both colorectal and hepatocellular cancers. Colorectal cancer is leading cause of cancer mortality in the United States, whereas hepatocellular cancer is the leading worldwide cause of cancer death; the liver is a primary site of morbidity in both diseases. Because systemic tumor suppressor gene therapy is currently not feasible, we have chosen to develop a regional form of such therapy directed at primary or metastatic liver neoplasms. Gene replacement therapy with p53 is a promising new strategy to treat advanced human cancers. 相似文献
297.
298.
Face centered cubic metals and alloys have multiple slip systems and are characterized by high dislocation velocities. Nevertheless, these materials suffer from transgranular stress corrosion cracking (T-SCC), that occurs by environmentally-induced cleavage. Since plasticity precedes fracture in all T-SCC phenomena, the evolution of deformation patterning during T-SCC is an important element of the local microfracture mode. Experimental observations show that the presence of the SCC-causing environment during straining is promoting localized plastic deformation at the near-surface region and producing an entirely different deformation pattern compared with that developing in laboratory air. The deformation evolving in the presence of the SCC electrolyte is highly localized, exhibiting closely spaced, coarse slip bands. The amount of localized strain developing at the near-surface region prior to nucleation of stress corrosion cracks is equivalent to the strain required for ductile fracture of the material in air, suggesting the existence of a fundamental fracture criterion. The above phenomenology of the deformation evolution is considered in relation to T-SCC initiation and propagation. The T-SCC is suggested to be a macroscopically brittle but microscopically ductile fracture occurring by localized plastic flow. An environment-induced deformation localization mechanism is described where the role of the environment involves generation of vacancies and subsequent dislocation nucleation from the near-surface region at loads well below those required for normal yielding. The evolution of the localized deformation pattern during T-SCC is suggested to be an outcome of nonuniformity and periodicity in the dissolution process.Presented at Fourth Greek National Congress on Mechanics, 26–29 June 1995, held at Xanthi, Greece. 相似文献
299.
300.
Ligase chain reaction (LCR) is a ligation-mediated amplification technique of a target DNA sequence using oligonucleotides and thermostable ligase. LCR is useful for the detection of known DNA sequences and point mutations in a limited amount of DNA. We introduce the principle, development, and protocol of this simple and convenient technique for DNA analysis. 相似文献