Endurance testing of downstream cathodes on a low-power MPD thruster

A low-power MPD thruster with downstream cathode was tested for endurance with a series of hollow cathode designs. Failure modes and failure mechanisms were identified. A new hollow cathode (with rod inserts) has emerged which shows promise for long life. The downstream positioning of the cathode was also changed from an on-axis location to an off-axis location. Data are presented for a 1332-hour life test of this new hollow cathode located at the new off-axis location. Xenon propellant was used

The Turbulence Power Spectrum in Optically Thick Interstellar Clouds

The Fourier power spectrum is one of the most widely used statistical tools to analyze the nature of magnetohydrodynamic turbulence in the interstellar medium. Lazarian & Pogosyan (2004) predicted that the spectral slope should saturate to -3 for an optically thick medium and many observations exist in support of their prediction. However, there have not been any numerical studies to-date testing these results. We analyze the spatial power spectrum of MHD simulations with a wide range of sonic and Alfv\'enic Mach numbers, which include radiative transfer effects of the $^{13}$CO transition. We confirm numerically the predictions of Lazarian & Pogosyan (2004) that the spectral slope of line intensity maps of an optically thick medium saturates to -3. Furthermore, for very optically thin supersonic CO gas, where the density or CO abundance values are too low to excite emission in all but the densest shock compressed gas, we find that the spectral slope is shallower than expected from the column density. Finally, we find that mixed optically thin/thick CO gas, which has average optical depths on order of unity, shows mixed behavior: for super-Alfv\'enic turbulence, the integrated intensity power spectral slopes generally follow the same trend with sonic Mach number as the true column density power spectrum slopes. However, for sub-Alfv\'enic turbulence the spectral slopes are steeper with values near -3 which are similar to the very optically thick regime.Comment: accepted to Ap

Reduction of salmonella contamination in pork carcasses by vaccination

Two field studies and one laboratory challenge were performed to evaluate of vaccination with a live, avirulent Salmonella choleraesuis vaccine (Enterisol® SC-54) to provide cross protection, reduce the level of internal culture and fecal shedding of multiple serovars of Salmonella. Barns of grow-finish pigs were vaccinated orally, via drinking water, or left as matched controls in the field studies. Ileocecal lymph nodes and spiral colon fecal material were collected at the abattoir from field studies. Three week old pigs were vaccinated intranasally and challenged at five weeks of age in the laboratory study. Internal organ culture and fecal shedding were measured two weeks following challenge with S typhimurium. In all three studies, vaccinated pigs had significantly lower culture prevalence of non S choleraesuis serovars (p\u3c0.05), and reduced fecal shedding in following laboratory challenge (p\u3c0.05). A nominal (p=0.07) trend to improved growth rate following laboratory challenge with S typhimurium challenge was also detected

Reduction of Salmonella choleraesuis contamination in pork carcasses by vaccination

Salmonellosis is a common clinical and subclinical infection of pigs. The species adapted serovar S choleraesuis predominantly produces a septicemic disease in swine. Disease in other species, including humans, is rare compared to enteric type infections from non host adapted serovars such as S typhimurium. However, when host adapted serovars infect alternate species, disease can be severe. Vaccination with an avirulent live S choleraesuis vaccine, Enterisol® SC-54, significantly reduces prevalence and quantity of infection in pigs. Additionally, those pigs that remain culture positive have two logs or more reduction in the quantity of S choleraesuis present. Vaccination of pigs as young as one day of age is successful. Where these infections are of concern in the human population, vaccination of pigs may provide dramatic reductions of the organism swine, reducing risk in food items of swine origin

A summary of the ECAS performance and cost results for MHD systems

The potential is examined of various advanced power plant concepts using coal and coal-derived fuel. The results indicate that open cycle coal fired direct preheat MHD systems have potentially one of the highest coal-pile-to-bus-bar efficiencies and also one of the lowest costs of electricity (COE) of the systems studied. Closed cycle MHD systems may have the potential to approach the efficiency and COE of open cycle MHD. The 1200-1500 F liquid metal MHD systems studied do not appear to have the potential of exceeding the efficiency or competing with the COE of advanced steam plants