Operating characteristics of a hollow-cathode neutralizer for 5 and 8 centimeter-diameter electron bombardment mercury ion thrusters

Thin-tip 0.3-cm-outside-diameter hollow-cathode neutralizers were used to investigate causes of neutralizer tip erosion experienced in thruster endurance tests. Bell-jar tests indicated that neutralizers with new rolled tantalum foil inserts coated with an emissive mixture eroded very little over the neutral flow rates investigated (3 to 10 mA) for simulated 5- and 8-cm-diameter thruster neutralizer conditions. Tip erosion rates of neutralizers operated with no insert or emissive mixture increased by two orders of magnitude for both configurations as the neutral flow rate decreased. Spectroscopic analysis of the discharge plasma from neutralizers operated with inserts coated with the emissive mixture detected tungsten at all neutral flow rates for both thruster neutralizer conditions. The only source of tungsten was the tip. Therefore, detection of tungsten indicated neutralizer tip erosion. Barium, an element of the emissive mixture, was detected at low neutral flow rates for the 5-cm-diameter thruster neutralizer operating condition only

Texturing polymer surfaces by transfer casting

A technique for fabricating textured surfaces on polymers without altering their surface chemistries is described. A surface of a fluorocarbon polymer is exposed to a beam of ions to texture it. The polymer which is to be surface-roughened is then cast over the textured surface of the fluorocarbon polymer. After curing, the cast polymer is peeled off the textured fluorocarbon polymer, and the peeled off surface has negative replica of the textured surface. The microscopic surface texture provides large surface areas for adhesive bonding. In cardiovascular prosthesis applications the surfaces are relied on for the development of a thin adherent well nourished thrombus

Hollow cathodes with BaO impregnated, porous tungsten inserts and tips

The technology of impregnated materials is described and some inherently advantageous characteristics of impregnated cathodes are discussed. Thermionic emission measurements are presented for oxide coated and impregnated cathodes. Five cathode configurations with barium oxide impregnated porous tungsten inserts and/or tips have been fabricated and tested. Reliability, durability, and stability of operation are characterized. One of the cathodes has accumulated over 9000 operational hours, another has been cycled on and off more than 800 times

TORT LAW—THE WRONGFUL DEMISE OF BUT FOR CAUSATION

The observation by Professor Dobbs that “[t]he substantial factor test is not so much a test as an incantation” remains compelling. The continued and widespread use of “substantial factor” in lieu of “but for” as the predominate means of defining causation in any multiple defendant or multiple cause case is troubling. “Substantial factor” was never intended to supplant “but for” in such cases. This overuse and misunderstanding, which is otherwise accentuated by the Third Restatement’s causal set notion, poses the significant risk that causation can be found when the defendant’s conduct is neither a “but for” nor sufficient cause of the harm or injury. The result is an unacceptable dilution of the requisite nexus for legal responsibility. This Article inspects the origin and sources of substantial factor causation in Massachusetts jurisprudence as well as the approach advocated for by the Third Restatement, both informing and demonstrating the need for greater understanding and restraint as to the otherwise wholesale substitution of “substantial factor” for “but for” in multiple cause or multiple defendant cases