COMPLETE COMPUTATIONAL MODEL OF A HALL THRUSTER FROM THE ACCELERATION CHANNFL THROUGH THE PLUME

Abstract Two-and mnsional computational models describing both the internal' and extema12 physics of Hall thrusters have been developed at the Massachusetts Institute of Technology. Integration of these models would result in a single, stand-alone application characterizing thruster physics from the thruster interior through the plume region. The application would enhance the spacecraft design process by providing engineers with the ability to predict thruster performance and damage to the craft from plumeqcecmft interactions. This paper represents the first attempt at consolidation of the intemal and external computational models, exploring the issues critical to integration. 'Ihe key issue in integration is the compatibility between the source model produced by the acceleration channel code and the source model used by the threG dimensional plume code. Sensitivity analysis has been performed to de&mine the extent to which the source model affects the plume and the surrounding spgcecraft surface. Results on a realistic spacecraft geometry suggest that differences between the original source model and the model genemted by the acceleration channel code significantly affect satellite surface erosion rates. Enhancements have also been made to the source and sputtering models in the plume code. Results utilizing the improved source model have been validated against experimental data and suggest that the source axial ion temperature assumed in previous woe was over predicted. In addition, the sputtering model now includes the effect of the sputtering yield dependence upon particle angle of incidence. Future work includes a graphical user interface on Xwindows platforms, automatic source model generation, and code stream-lining and optimization

FERTILITY AND STERILITY

Objective: Myocardial ischemia and reperfusion (MI-R) leads to remote organ injury associated with oxidative stress. Melatonin is a well-known antioxidant and free-radical scavenger. This study was conducted to examine whether MI-R causes damage in the testes and sperm quality, and to investigate the possible protective effect of exogenous melatonin on these parameters in an in vivo rat model. Design: Experimental study. Setting: Experimental Research Center, Firat University Medical School, Elazig, Turkey. Patient(s): Eight-week-old male Wistar rats (n = 18). Intervention(s): To produce MI-R, a branch of descending left coronary artery was occluded for 30 minutes, followed by 120-minute reperfusion. Melatonin (10 mg/kg) or vehicle was given 10 minutes before ischemia via the jugular vein. Main Outcome Measure(s): Reproductive organ weights and epididymal sperm concentration, sperm motility, abnormal sperm rate, and testicular-tissue malondialdehyde (MDA) and glutathione (GSH) levels were examined after reperfusion. Result(s): MI-R significantly decreased epididymal sperm motility, and increased the tests-tissue level of MDA, compared to the control group. Administration of melatonin reversed the harmful effects of MI-R significantly. However, MI-R did not change sperm concentration, GSH levels, and reproductive organ weights. Conclusion(s): These findings indicate that MI-R leads to damage of testis and sperm motility, and melatonin protects againsts MI-R-induced reproductive-organ injury. These results may also encourage the use of antioxidants to reduce remove organ injury in the testis after MI-R

Effect of melatonin on epididymal sperm quality after testicular ischemia/reperfusion in rats

Objective: To determine the effect of melatonin, a pineal secretory product that prevents testicular ischemia/reperfusion (IR) injury through its antioxidative properties, on epididymal sperm quality in a rat testicular IR injury model. Design: Experimental study. Setting: University pharmacology laboratory. Animal(s): Fifty-six 8-week-old male Wistar albino rats. Intervention(s): Left testicular artery and vein occluded for 1 hour; before the bilateral orchiectomy, the organ was allowed to reperfuse 30 days. Melatonin (10 mg/kg IP) or vehicle (1% ethanol in saline) was administrated for 10 minutes before reperfusion and for 1 hour after reperfusion. Main Outcome Measure(s): After 24 hours of reperfusion, the rats were decapitated, and the testicular tissue samples were obtained for histologic examination. In addition, after 30 days of reperfusion, the epididymal sperm concentration, motility, and abnormal sperm rates were determined in the sperm collected from the epididymis. Result(s): A statistically significant decrease in sperm concentration resulted from IR as well as an increase in sperm abnormalities, but the sperm motility did not change. Melatonin treatment did not prevent the IR-induced reduction in sperm concentration. However, melatonin treatment statistically significantly decreased the sperm abnormalities when compared with the IR injured samples. Conclusion(s): Melatonin may improve sperm morphology for a protective effect in IR-induced testicular injury. Crown Copyright © 2010

Lycopene, an antioxidant carotenoid, attenuates testicular injury caused by ischemia/reperfusion in rats

Testicular torsion is a common syndrome that could lead to infertility. We investigated the therapeutic effects of lycopene, an antioxidant caretenoid, on testicular ischemia/reperfusion (IR) injury that resembles testicular torsion. Male Wistar albino rats were divided into three groups: sham (n = 6), IR (n = 18), and ischemia/reperfusion with lycopene (IRL, n = 18). Left testicular artery and vein was occluded for 1 h, followed by reperfusion of 3 h, 24 h or 30 days in IR and IRL animals. Either corn oil (vehicle) or lycopene (4 mg/kg) was administrated once daily by gavage to IR or IRL animals, respectively, 5 min after ischemia. Sham-operated animals were treated with vehicle by gavage 5 min after the operation. IR decreased sperm motility and concentration in both ipsilateral and contralateral testes and increased abnormal sperm rate in ipsilateral testis after 30 days of reperfusion. Treatment with lycopene increased the motility in bilateral testes and decreased the rate of abnormal sperm in ipsilateral testis to the sham level, but did not increase sperm concentration in bilateral testes. IR increased the activities of catalase and glutathione peroxidase and the level of reduced glutathione by 24 h of reperfusion, but malondialdehyde remained unchanged. Lycopene treatment restored the enzyme activities but not the reduced glutathione level. Lycopene treatment also ameliorated the IR-induced tissue damage in bilateral testes. In conclusion, the therapeutic antioxidant effect of lycopene on germ cells could serve as a promising intervention to oxidative stress-associated infertility problems, such as testicular torsion. © 2009 Tohoku University Medical Press

Sites of feline coronavirus persistence in healthy cats

Feline coronavirus (FCoV) is transmitted via the faecal-oral route and primarily infects enterocytes, but subsequently spreads by monocyte-associated viraemia. In some infected cats, virulent virus mutants induce feline infectious peritonitis (FIP), a fatal systemic disease that can develop in association with viraemia. Persistently infected, healthy carriers are believed to be important in the epidemiology of FIP, as they represent a constant source of FCoV, shed either persistently or intermittently in faeces. So far, the sites of virus persistence have not been determined definitely. The purpose of this study was to examine virus distribution and viral load in organs and gut compartments of specified-pathogen-free cats, orally infected with non-virulent type I FCoV, over different time periods and with or without detectable viraemia. The colon was identified as the major site of FCoV persistence and probable source for recurrent shedding, but the virus was shown also to persist in several other organs, mainly in tissue macrophages. These might represent additional sources for recurrent viraemia