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171.
The active and reactive load distribution between n paralleled single-phase uninterruptible power supply (UPS) inverters is equalized by virtue of n -1 load-sharing control loops. The approach permits the construction of UPS systems of any desired power rating at maximum utilization of the power components. The method of harmonic cancellation decreases the switching frequency of the power devices while maintaining good dynamic performance. The design details of a 45 kVA UPS inverter system with 150% steady-state overload capability are presented. The performance under various operating conditions is illustrated by oscillograms 相似文献
172.
The jejunal absorption of inorganic phosphate (P) was studied under basal conditions and during the intravenous infusion of synthetic salmon calcitonin (SCT) in normal subjects. Net P absorption increased as the intraluminal P concentration was raised. At intraluminal P concentrations equal to or above the plasma P level P absorption manifested first order kinetics. At intraluminal P concentrations below the plasma P level, net P absorption was non-linear presumably due to the movement of P from plasma to the lumen down a chemical gradient. A net secretion of water and electrolytes occurred in six normal subjects given SCT (250 ng/kg/hr) while saline infusion instead of SCT had no effect on jejunal absorption. Along with the secretory effect SCT reduced calcium and P absorption by 58% and 62% respectively, without any significant fall in the serum levels of calcium or P. The jejunal response to SCT was reproduced twice in a hypoparathyroid subject showing that endogenous parathyroid hormone was not involved in this effect. Calcium and P absorption were positively correlated with water movement suggesting that the observed changes in calcium and P absorption are due primarily to SCT-induced secretion of water. It is concluded that SCT induces a net secretion of water and ions while simultaneously reducing calcium and P absorption. 相似文献
173.
174.
TK Mutabingwa WM Eling JN Kitinya LN Malle A de Geus 《Canadian Metallurgical Quarterly》1993,45(6):274-279
The effect of malaria chemoprophylaxis during pregnancy on placenta malarial changes (PMCs) was investigated in 170 tissue sections. Women of 63 sections received daily proguanil (PROG), 61 once weekly chloroquine (CQ) and 46 the two drug combination (CQ+PROG). All were residents of a malaria hyperendemic area in Muheza District, Tanzania. Supervised prophylaxis started early in pregnancy till delivery. Parasitaemias and clinical episodes were detected early and radically treated. Overall, PMCs were mostly infrequent and light viz: fibrinous deposits (98%), fibrinoid necrosis (60%), leucocytic infiltrations (59%), macrophage containing pigment (16%), and malaria parasites (8%). The type, prevalence, and severity of the PMCs in the three prophylaxis groups were comparable. This was despite the fact that PROG and CQ+PROG were prophylactically more efficacious than CQ and despite the expectation that the prevalence and severity of the PMCs would be high in the CQ group. Prompt diagnosis and effective treatment of parasitaemias in this group contributed to the low prevalence and less severity. It is concluded that effective malaria chemoprophylaxis or prompt diagnosis and effective treatment of malaria parasitaemias have significant impact on the prevalence of PMCs. Due to various operational constraints in most developing countries, chemoprophylaxis remains the only feasible broad option for malaria control in pregnancy. 相似文献
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177.
An unusual case of chylothorax is described in a 4-year-old child after repair of a ventricular septal defect and ligation of a patent ductus arteriosus through a median sternotomy. Left chylothorax developed after a latent period of six days and was treated initially with continuous drainage and parenteral supplementation of proteins and lipids. Operative intervention with oversewing of the site of the leak in the anterior mediastinum proved necessary after three weeks. The anatomical variations of the thoracic duct are outlined to explain the occurrence of chylothorax after diverse intrathoracic operations. The physiological effects of a thoracic duct fistula and various aspects of management are reviewed. 相似文献
178.
Tyrosine kinases are involved in various intracellular signalling cascades of different cells: Genistein has been shown to inhibit tyrosine kinase in INS-1 cells, an insulin-secreting cell line (Verspohl et al., 1995). It is, however, not established how specific and selective the tyrosine kinase inhibitors and their controls are. The tyrosine kinase inhibitors genistein and tyrphostin 25 increased insulin release, but not their negative controls with isoflavonoid structure (daidzein and genistin). In addition to this short-term effect a long-term effect was investigated. Genistein (100 microM) time-dependently increased insulin mRNA levels in INS-1 cells. On the other hand the tyrosine kinase inhibitors tyrphostin 25 and lavendustin A (both at 100 microM), which are structurally different from genistein, failed to increase the insulin mRNA whereas daidzein and genistin, normally used as negative controls, increased insulin mRNA as potently as genistein did. However, an examination of the incubation medium revealed that genistin was degraded to genistein by about 50% probably by nonspecific glucosidases first seen after 2 hours of incubation; genistin, therefore, does not appear to be a proper control though often used in this way. In conclusion, the suitability of the compounds used in recent studies is doubtful since other effects than the inhibition of tyrosine kinases are possible. Whereas the involvement of tyrosine kinase in a short-term effect (insulin release) is obvious and clearly substantiated by using the established pharmacological tools (negative controls), the involvement of tyrosine kinases in long-term effects is not that clear; only compounds with isoflavonoid structure are effective independent whether they normally are thought to be inhibitors or negative controls. One has to be cautious in using the above-mentioned compounds in an uncritical way. 相似文献
179.
The effects of housing conditions on some functional properties of the GABAA benzodiazepine (BZD) receptor in the cerebral cortex were examined in the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines of rats. Compared to rats housed in pairs (P with P and NP with NP), P and NP rats housed individually had 44% (p < 0.005) and 32% (p < 0.01) lower values, respectively, for GABA-stimulated 36Cl- influx into cortical microsacs. The maximal effect (Vmax) of flunitrazepam (FNZ) to enhance GABA-stimulated 36Cl- uptake was 44% higher in individually housed P rats than pair-housed P rats (p < 0.05) and 51% higher than individually housed NP rats (p < 0.05). There was no difference between single and pair-housed NP rats for Vmax values of FNZ enhancement of GABA-stimulated 36Cl- influx. The results show housing conditions can alter some of the functional properties of the GABAA/BZD receptor in the P and NP lines of rats. The differential effect of housing conditions on FNZ enhancement of 36Cl- influx, observed between the lines, may be a result of higher levels of anxiety being produced by brief isolation in the P rat. 相似文献
180.
R Raghupathi SC Fernandez H Murai SP Trusko RW Scott WK Nishioka TK McIntosh 《Canadian Metallurgical Quarterly》1998,18(11):1259-1269
The proto-oncogene, BCL-2, has been suggested to participate in cell survival during development of, and after injury to, the CNS. Transgenic (TG) mice overexpressing human Bcl-2 (n = 21) and their wild-type (WT) littermates (n = 18) were subjected to lateral controlled cortical impact brain injury. Lateral controlled cortical impact brain injury resulted in the formation of a contusion in the injured cortex at 2 days, which developed into a well-defined cavity by 7 days in both WT and TG mice. At 7 days after injury, brain-injured TG mice had a significantly reduced cortical lesion (volume = 1.99 mm3) compared with that of the injured WT mice (volume = 5.1 mm3, P < 0.01). In contrast, overexpression of BCL-2 did not affect the extent of hippocampal cell death after lateral controlled cortical impact brain injury. Analysis of motor function revealed that both brain-injured WT and TG mice exhibited significant right-sided deficits at 2 and 7 days after injury (P < 0.05 compared with the uninjured controls). Although composite neuroscores (sum of scores from forelimb and hind limb flexion, lateral pulsion, and inclined plane tests) were not different between WT and TG brain-injured mice, TG mice had a slightly but significantly reduced deficit in the inclined plane test (P < 0.05 compared to the WT mice). These data suggest that the cell death regulatory gene, BCL-2, may play a protective role in the pathophysiology of traumatic brain injury. 相似文献