Research study on materials processing in space experiment number M512

Adhesion of the melted metals to the adjacent solid metals, and cohesion of the liquid metal to itself appeared to be equally as strong in zero gravity as on earth. Similar cut edge bead periodicity in cut thin plate, and similar periodic chevron patterns in full penetration welds were seen. The most significant practical result is that the design of braze joints for near zero gravity can be very tolerant of dimensional gaps in the joint. This conclusion is based on a comparison of narrow, wide and variable gap widths. Brazing is very practical as a joining or repairing technique for metal structures at zero gravity. The operation of the hardware developed to locate successive small (0.6 cm) diameter cylinders in the focus of the battery powered EB unit, melt the various metal specimens and deploy some liquid metal drops to drift in space, was generally successful. However, the sphericity and surface roughness were far from those of ball bearings

Space shuttle orbit maneuvering engine reusable thrust chamber program

Tests were conducted on the regenerative cooled thrust chamber of the space shuttle orbit maneuvering engine. The conditions for the tests and the durations obtained are presented. The tests demonstrated thrust chamber operation over the nominal ranges of chamber pressure mixture ratio. Variations in auxiliary film coolant flowrate were also demonstrated. High pressure tests were conducted to demonstrate the thrust chamber operation at conditions approaching the design chamber pressure for the derivative space tug application

Examining the Impact of Service Times on Overall Guest Satisfaction Perception in the Casual Dining Environment

A mystery shopper study was used to examine the influence of service times on customer satisfaction. The impact of management emphasis on service quality was also examined. In the restaurants studied, service time influenced customer satisfaction. Management attention to service time improved performance in direct relationship to the level of emphasis

High efficiency GaAs-Ge tandem solar cells grown by MOCVD

High conversion efficiency and low weight are obviously desirable for solar cells intended for space applications. One promising structure is GaAs on Ge. The advantages of using Ge wafers as substrates include the following: they offer high efficiency by forming a two-junction tandem cell; low weight combined with superior strength allows usage of thin (3 mil) wafers; and they are a good substrate for GaAs, being lattice matched, thermal expansion matched, and available as large-area wafers

Test of Scientific Literacy Skills (TOSLS) indicates limited scientific thinking gains as a result of science and mathematics general education

A number of instruments designed to measure scientific literacy exist, but none has been used to assess improvements in undergraduates’ scientific thinking over their college career. This study utilized the Test of Scientific Literacy Skills (TOSLS) in a longitudinal fashion to measure scientific thinking gains of over 800 students from matriculation to graduation at a small liberal arts college. We found the TOSLS to be a useful assessment instrument. Our results indicated rather small benefits of science general education overall, though there were larger improvements for some demographic groups (i.e., women, first-generation college students). STEM majors showed much greater development in their scientific thinking skills than non-STEM majors, although they started at a more advanced level. Suggestions are made to rethink STEM general education, either in terms of content or with regard to pedagogy, in order to improve future citizens’ ability to deal with the scientific challenges society faces

Effects of Na2S and (NH4)2S edge passivation treatments on the dark current-voltage characteristics of GaAs pn diodes

We have investigated the dark current-voltage characteristics of GaAs pn homojunctions whose surfaces have been passivated with NuzS and (NH4)2S chemical treatments. Reductions in 2kTpcrimeter recombination currents by a factor of 3.2 were obtained for the two treatments. A shunt leakage, observed at low forward bias for the NazS treated devices, is virtually eliminated with the {NH4hS treatment. It is also shown that even the high quality, large area (0.25 cm1 ) pn diodes used in this study are dominated by 2kTedge currents before passivation