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2.
Functional magnetic resonance imaging (fMRI) is capable of detecting task-induced blood oxygenation changes using susceptibility sensitive pulse sequences such as gradient-recalled echo-planar imaging (EPI). The local signal increases seen in the time course are believed to be due to an increase in oxygen delivery that is incommensurate with oxygen demands. To help isolate the sources of functional signal changes, the authors have incorporated various forms of diffusion weighting into EPI pulse sequences to characterize the apparent mobility of the functionally modulated protons. Results suggest that the majority of the functional signal at 1.5 T arises from protons that have apparent diffusion coefficients that are approximately four or five times higher than that of brain tissue. This implies that significant functional signal sources are either protons within the vascular space or protons from the perivascular space that is occupied by cerebrospinal fluid. 相似文献
3.
Hida H. Tsukada Y. Ogawa Y. Toyoshima H. Fujii M. Shibahara K. Kohno M. Nozaki T. 《Electron Devices, IEEE Transactions on》1989,36(10):2223-2230
The authors describe a novel design concept for enhancement (E) and depletion (D) mode FET formation using i-AlGaAs/n-GaAs doped-channel hetero-MISFET (DMT) and a novel self-aligned gate process technology for submicrometer-gate DMT-LSIs based on E/D logic gates. 0.5-μm gate E-DMTs (D-DMTs) with a lightly doped drain (LDD) structure show an average V t of 0.18 (-0.46) V, a V t standard deviation of 22.6 (24.9) mV, and a maximum transconductance of 450 (300) mS/mm. The V t shift is less than 50 mV with a decrease in gate length down to 0.5 μm. The gate forward turn-on voltage V f is more than 0.9 V, i.e. about 1.6 times that for MESFETs. This superiority in V f, preserved in the high-temperature range, leads to an improvement in noise margin tolerance by a factor of three. In addition, 31-stage ring oscillators operate with a power consumption of 20 (1.0) mW/gate and a propagation delay of 4.8 (14.5) ps/gate. Circuit simulation based on the experimental data predicts 140 ps/gate and 1 mW/gate for DMT direct-coupled FET logic circuits under standard loading conditions. DMTs and the technology developed here are very attractive for realizing low-power and/or high speed LSIs 相似文献
4.
Inaba S. Okano K. Matsuda S. Fujiwara M. Hokazono A. Adachi K. Ohuchi K. Suto H. Fukui H. Shimizu T. Mori S. Oguma H. Murakoshi A. Itani T. Iinuma T. Kudo T. Shibata H. Taniguchi S. Takayanagi M. Azuma A. Oyamatsu H. Suguro K. Katsumata Y. Toyoshima Y. Ishiuchi H. 《Electron Devices, IEEE Transactions on》2002,49(12):2263-2270
The 35 nm gate length CMOS devices with oxynitride gate dielectric and Ni salicide have been fabricated to study the feasibility of higher performance operation. Nitrogen concentration in gate oxynitride was optimized to reduce gate current I/sub g/ and to prevent boron penetration in the pFET. The thermal budget in the middle of the line (MOL) process was reduced enough to realize shallower junction depth in the S/D extension regions and to suppress gate poly-Si depletion. Finally, the current drives of 676 /spl mu/A//spl mu/m in nFET and 272 /spl mu/A//spl mu/m in pFET at V/sub dd/=0.85 V (at I/sub off/=100 nA//spl mu/m) were achieved and they are the best values for 35 nm gate length CMOS reported to date. 相似文献
5.
Three samples of LaCoO3 were prepared by two different methods and calcined at 800 or 1000 °C. They had BET areas of 1, 12, and 16 m2/g and all of them showed pure perovskite X-ray diffraction patterns with identical unit cell dimensions. In a series of experiments the oxide, having larger surface area, was stepwise reduced in hydrogen at temperatures between 60 and 500 °C. The XPS spectra, taken at room temperature after evacuation at 400 °C at each reduction level, showed that the surface concentration of Co° was very low up to 300 °C but increased sharply between 300 and 350 °C (9–75%). This concentration further increased to 100% after 10 min reduction at 450 °C, but upon heating in hydrogen for an additional 10 min at 500 °C it decreased again to 75%. In another series of experiments the mixed oxide was reoxidized after each reduction. A fresh sample was reduced to 350 and 400 °C by contacting with hydrogen for 1 hr and evacuated at temperatures between 400 and 500 °C. Both high evacuation temperatures and reduction at 400 °C during 1 hr produced a sharp decrease in Co° surface concentration. These results are consistent with the catalytic behavior of this perovskite reported earlier by E. A. Lombardo et al. (4–7). A model is proposed to interpret the reduction of LaCoO3. 相似文献
6.
Hidemitsu Hojo Wataru Toyoshima Masayasu Tamura Noriyuki Kawamura 《Polymer Engineering and Science》1974,14(9):604-609
Particulate-filled thermosetting composites are widely used, yet little systematic work has been done on their long-term strength characteristics. In this study short-term tensile, flexural, and impact tests as well as tensile creep-rupture tests were made for unfilled and filled epoxy to clarify the effects of filler size, filler content, and temperature. Fillers used were silica, alumina particles, and glass beads. Test temperatures were varied from 25 to 110°C. As a result of short-term testing, it was found that the Petch relation held between strength and filler size if brittle fracture occurred, while a strength and filler size if brittle fracture occurred, while a strengthening effect existed when ductile fracture occurred. On creeprupture testing, a strengthening is observed with filler size and content for silica and glass beads. The Arrhenius plot of rupture time for various filler sizes and contents converges to a characteristic point corresponding to the glass transition temperature of the material. Using this relation, a modified Larson-Miller master rupture curve is proposed which can predict the long-term strength of particulate-filled thermosetting composites as functions of rupture time, temperature, filler size, and content. 相似文献
7.
H Toyoshima S Hayashi N Tanabe K Miyanishi T Satoh Y Aizawa T Izumi 《Canadian Metallurgical Quarterly》1996,59(3-4):81-95
Epidemiological features, risk factors and preventive methods of sudden death (SD) derived from studies the authors have performed since 1987 together with colleagues in Niigata University School of Medicine were reviewed. When SD was defined as death occurring within 24 hours of the onset of symptoms, the annual incidence was 145/100,000 for people aged 15 years and older in Niigata Prefecture. The incidence increased sharply along with the advance of age, while the proportion of SD to natural death due to circulatory diseases was higher in younger people. Though diseases of the circulatory system made up approximately 90 percent of all causes of death, SD due to ischemic heart disease was less frequent in Japan than in western countries. SD showed various patterns in seasonal and "within-a-day" occurrences according to sex, age and cause of death. The months of the highest SD occurrence differed by occupation and matched the busiest work periods. A decrease in sleeping hours and mental stress experienced during the preceding week were related to the occurrence of both sudden death and non-fatal acute myocardial infarction. People having structural circulatory diseases were shown to be predisposed to SD when stress occurred, because fatal arrhythmia is easily induced by the above factors in such people. Health examinations were shown to have preventive effects, though limited, against SD. Differences in the resuscitated rates in cases where a witness was present and where one was not indicates that educating people about correct resuscitation methods is important to minimizing SD. 相似文献
8.
Effects of time averaging on optical scintillation in a ground-to-satellite atmospheric propagation 总被引:1,自引:0,他引:1
Temporal natures for a variance of turbulence-induced log-intensity fluctuations are obtained. The variance of the optical fluctuation is reduced when the optical signals are integrated in a photodetector, and we express the index of reduction (called the time-averaging factor) by using an autocovariance function of the optical fluctuation. The optical fluctuations for a ground-to-satellite path are caused by both atmospheric turbulence and the beam-pointing jitter error of the optical transmitter. The turbulence-induced optical scintillation can be discriminated from the fluctuation that is due to the beam-pointing jitter error. The compared result from the probability density function of the optical signal reveals good agreement. The temporal autocovariance functions of optical scintillation are obtained and used to calculate the time-averaging factor. The analytically expected effects of time averaging are verified by the experimental results. The estimations contribute to the link budget design for the optical tracking channel through atmospheric turbulence. 相似文献
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