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71.
Studies of the fabrication of uranium oxide fuel pellets by the low-temperature sintering of nonstoichiometric oxide are described. Completer reversion to stoichiometric UO2 in the sintered pellets was attained by two methods: (1) Sintering in a nitrogen atmosphere which contained a small amount of hydrogen and (2) sintering in pure nitrogen and then exposing the pellets to hydrogen at the sintering temperature. Large variations in sinterability were found in commercially procured ceramic-grade UO2 powder. In studying these variations, it was discovered that fluorine was a powerful inhibitor of low-temperature sintering. This impurity could be readily removed by oxidation in air at 500°C. The data strongly indicated that the primary mechanism responsible for the removel of residual fluorine was pyrohydrolysis. It was found that a preliminary oxidation-reduction cycle activated the less-sinterable oxides so that in every case densities of at least 95% of theoretical were obtained by sintering at 1200°C. 相似文献
72.
The thermal decomposition of europium hydroxide in an air atmosphere was investigated by means of weight-loss measurements, infrared spectroscopy, X-ray diffraction analysis, and electron microscopy. These studies showed that EU(OH)° decomposed at temperatures between 225° and 300°C into EuOOH, which was stable up to about 425°C. Between 435° and 465°C this compound decomposed into cubic Eu2 O3 , which was stable until its inversion to the high-temperature monoclinic form. X-ray diffraction data were collected for Eu(OH)3 and EuOOH and showed that the trihydroxide has a hexagonal crystal structure and the oxyhydroxide is possibly orthorhombic. The Eu(OH)2 , EuOOH, and cubic EunOa powders contained particles up to several microns in size consisting of agglomerates of crystallites in the size range 200 to 400 A. The single monoclinic Eu2 O3 sample studied contained crystallites whose average size was greater than 2000 A. 相似文献
73.
Glucose was found to induce large amplitude oscillations of cytoplasmic Sr2+ and Ca2+ in individual pancreatic beta-cells exposed to the respective cation. Subsequent addition of 20 nM glucagon or other agents raising cAMP triggered pronounced transients superimposed upon the large amplitude oscillations. Hyperpolarization with diazoxide prevented both the large amplitude oscillations and the superimposed transients. After short exposure to carbachol or ATP there was a temporary, and after addition of the Ca2+-ATPase inhibitor thapsigargin a permanent, disappearance of the transients with persistence of the glucose-induced large amplitude oscillations. The Ca2+ channel blocker methoxyverapamil exhibited opposite specificity in preventing the large amplitude oscillations under conditions when the transients often remained. In the presence of methoxyverapamil the transients disappeared during diazoxide hyperpolarization and were restored by subsequent K+ depolarization, which also elevated the content of inositol 1,4,5-trisphosphate (IP3) by 45%. The glucagon-induced transients were obliterated by 12-O-tetradecanoylphorbol 13-acetate, insensitive to ryanodine and paradoxically inhibited by high concentrations of caffeine. The IP3-mediated intracellular ion mobilization induced by carbachol was amplified by glucagon. The results indicate that depolarization-dependent formation of IP3 causes intracellular Ca2+ mobilization in individual beta-cells when the IP3 receptors are sensitized by cAMP. This mechanism may be an important determinant for the electrophysiological burst activity in intact pancreatic islets due to the presence of endogenous glucagon. 相似文献
74.
In 4 experiments the role of coarse (low-pass filtered) and fine (high-pass filtered) spatial information in guiding visual processing was studied in a same-different task. The second of a pair of sequential patterns was either a normal image or the first 100 ms was restricted either coarse or fine information before a normal image was shown for the rest of the presentation. This 100-ms cue could be from the immediately succeeding image (relevant) or from other images in the set (irrelevant). Analysis of response times and errors showed relevant coarse- and fine-scale cues were usually equally effective, but any differences favored fine-scale versions. Irrelevant fine-scale cuing was significantly more disruptive than coarse-scale cuing. No evidence of preferential cuing by coarse-scale information occurred in any experiment. 相似文献
75.
With the advent of the World Wide Web (WWW), we are now on the cusp of a revolution in computer technology that will dramatically enhance medical education. An historical analogy might be Johann Gutenberg's invention of movable type in the 1400's-radically decreasing the cost, time, and expertise required to reproduce printed materials. Now, the WWW can decrease the cost of disseminating medical educational materials. When an educational module is authored for the Web, it can be placed on a computer \"server\" which in turn, distributes the program on the WWW to anyone with a computer and Internet access. Rapidly emerging standards are being developed to allow increasingly rich educational experiences on the Internet. With the introduction of HTML (hypertext markup language), a standardized method of placing text and graphics, as well as the connections between them, was created. 相似文献
76.
The purpose of this prospective study was to verify whether the percentage area of lung occupied by lowest attenuation values on high-resolution computed tomography (HRCT) scans reflects microscopic emphysema and to compare this quantification with the information yielded by the most widely used pulmonary function tests (PFT). Preoperative HRCT scans were obtained with 1-cm intervals in 38 subjects. With a semiautomatic evaluation procedure, the percentage areas occupied by attenuation values inferior to thresholds ranging from -900 Hounsfield units (HU) to -970 HU were calculated for the lobe or lung to be resected. Emphysema was microscopically quantified by using a computer-based method, measuring the perimeters and interwall distances of alveoli and alveolar ducts. The strongest correlation was found for -950 HU. As a second step, we evaluated possible correlations between PFT and microscopic measurements. Finally, considering the microscopic measurements as a standard, we tried to investigate their relationships with each of the PFT and with the relative area occupied by attenuation values lower than -950 HU for both lungs. This revealed that the diffusing capacity for carbon monoxide associated with HRCT quantification is sufficient to predict microscopic measurements. We concluded that the percentage area of lung occupied by attenuation values lower than -950 HU is a valid index of pulmonary emphysema. 相似文献
77.
Associations between coping responses, drinking motivations, expectations of meeting social and academic goals, and family of origin problem drinking and measures of college students' quantity/frequency of alcohol use and social complications of alcohol use were investigated in a sample of 218 college students. Positive associations were found between \"emotion-focused\" forms of coping such as detachment and the criterion measures, whereas \"problem-focused coping\" was not significantly associated with quantity/frequency of alcohol use or drinking complications. Positive correlations were also found between drinking motives, goal attainment expectancies and family models measures and the criterion measures. Regression models constructed for alcohol quantity/frequency and drinking complications implicated the total number of drinking motives, family models of problem drinking and the coping strategy of self-blame as strongly related to criterion measures. Positive social drinking motives and coping by seeking social support were implicated as possible protective factors. 相似文献
78.
G Liuzzo A Buffon LM Biasucci JR Gallimore G Caligiuri A Vitelli S Altamura G Ciliberto AG Rebuzzi F Crea MB Pepys A Maseri 《Canadian Metallurgical Quarterly》1998,98(22):2370-2376
BACKGROUND: Systemic markers of inflammation have been found in unstable angina. Disruption of culprit coronary stenoses may cause a greater inflammatory response in patients with unstable than those with stable angina. We assessed the time course of C-reactive protein (CRP), serum amyloid A protein (SAA), and interleukin-6 (IL-6) after single-vessel PTCA in 30 patients with stable and 56 patients with unstable angina (protocol A). We also studied 12 patients with stable and 15 with unstable angina after diagnostic coronary angiography (protocol B). METHODS AND RESULTS: Peripheral blood samples were taken before and 6, 24, 48, and 72 hours after PTCA or angiography. In protocol A, baseline CRP, SAA, and IL-6 levels were normal in 87% of stable and 29% of unstable patients. After PTCA, CRP, SAA, and IL-6 did not change in stable patients and unstable patients with normal baseline levels but increased in unstable patients with raised baseline levels (all P<0.001). In protocol B, CRP, SAA, and IL-6 did not change in stable angina patients after angiography but increased in unstable angina patients (all P<0.05). Baseline CRP and SAA levels correlated with their peak values after PTCA and angiography (all P<0.001). CONCLUSIONS: Our data suggest that plaque rupture per se is not the main cause of the acute-phase protein increase in unstable angina and that increased baseline levels of acute-phase proteins are a marker of the hyperresponsiveness of the inflammatory system even to small stimuli. Thus, an enhanced inflammatory response to nonspecific stimuli may be involved in the pathogenesis of unstable angina. 相似文献
79.
80.