Electrode erosion in arc discharges at atmospheric pressure

An experimental investigation was performed in an effort to measure and increase lifetime of electrodes in an arcjet thruster. The electrode erosion of various anode and cathode materials was measured after tests in an atmospheric pressure nitrogen arc discharge at powers less than 1 kW. A free-burning arc configuration and a constricted arc configuration were used to test the materials. Lanthanum hexaboride and thoriated tungsten had low cathode erosion rates while thoriated tungsten and pure tungsten had the lowest anode erosion rates of the materials tested. Anode cooling, reverse gas flow, and external magnetic fields were all found to reduce electrode mass loss

Hollow cathodes in high pressure arc discharges

An orified hallow cathode was tested at high pressure to improve lifetime and efficiency in arcjet thrusters. It is indicated that the arc would not operate with emission from the insert above 200 torr in nitrogen regardless of insert material, orifice diameter, or gas flow direction. Emission occurred from the insert in argon and xenon although it could not be ascertained whether diffuse or spot emission existed within the cathode. Over the extended range of configurations and operating parameters explored the desired diffuse emission mode could not be obtained at high enough pressures for orified hollow cathodes to operate in the range which is considered for arcjet applications

A bibliography of electrothermal thruster technology, 1984

Electrothermal propulsion concepts are briefly discussed as an introduction to a bibliography and author index. Nearly 700 citations are given for resistojets, thermal arcjets, pulsed electrothermal thrusters, microwave heated devices, solar thermal thrusters, and laser thermal thrusters

An Inexpensive Liquid Crystal Spectropolarimeter for the Dominion Astrophysical Observatory Plaskett Telescope

A new, inexpensive polarimetric unit has been constructed for the Dominion Astrophysical Observatory (DAO) 1.8-m Plaskett telescope. It is implemented as a plug-in module for the telescope's existing Cassegrain spectrograph, and enables medium resolution (R~10,000) circular spectropolarimetry of point sources. A dual-beam design together with fast switching of the wave plate at rates up to 100Hz, and synchronized with charge shuffling on the CCD, is used to significantly reduce instrumental effects and achieve high-precision spectropolarimetric measurements for a very low cost. The instrument is optimized to work in the wavelength range 4700 - 5300A to simultaneously detect polarization signals in the H beta line as well as nearby metallic lines. In this paper we describe the technical details of the instrument, our observing strategy and data reduction techniques, and present tests of its scientific performance.Comment: 32 pages, 15 figures. Accepted for publication in PAS

An investigation of the social support experiences of high-level sports performers

publication-status: Publishedtypes: Articleas accepted for publication© 2000 Human Kinetics, IncLock of consensus regarding the nature and conceptual definition of the social support construct has led to a plethora of different forms of measurement of this psychosocial variable, many with psychometric limitations. Beyond the psychometric limitations of some measures, in sport there is also a need for measures to be relevant to the specific experiences of sports performers. In order to gain a greater understanding of the social support experiences of sports people, 10 high-level sports performers were interviewed regarding their experiences of social support. Principles of the grounded theory (Glaser & Strauss, 1967) approach were adopted for analysis of their responses and insights. Four dimensions of support were generated, within each of which were comments relating to sport-specific support and comments relating to support not directly concerning the sport itself. The dimensions were labeled emotional, esteem, informational, and tangible. Example quotes are given to highlight each dimension of support, and implications for intervention are derived

Matching social support with stressors: Effects on factors underlying performance in tennis.

notes: Conceived and formulated by Rees, this original study works innovatively with Cutrona and Russell’s (1990) matching hypothesis. Its contribution to knowledge and method is two-fold. First, it demonstrates with data from 130 high-performance tennis players that social support can protect players from the negative impact of stress on performance. Second, it demonstrates that detailed matching of support with stressors, through a combination of considering the controllability or otherwise of the stressors, by employing context-specific measurement of social support, and by using confirmatory factor analyses and moderated hierarchical regression analyses, this detailed matching process can successfully detect hypothesised interactions.publication-status: Publishedtypes: ArticleCopyright © 2004 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Psychology of Sport and Exercise. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Psychology of Sport and Exercise, 2004, Vol. 5, Issue 3, pp. 319 – 337 DOI: 10.1016/S1469-0292(03)00018-9Objectives: This study: (a) examined the factor structure of a four-dimensional measure of social support designed specifically for this study; (b) matched social support dimensions with stressors in examining the main and stress-buffering effects of social support upon factors underlying performance in tennis. Method: 130 high level tennis players completed measures of social support, stressors, and performance factors. Results: Analyses of covariance structures largely provided support for the four-dimensional structure of the social support measure. Moderated hierarchical regression analyses revealed significant main and stress-buffering effects of the social support dimensions upon performance factors. Conclusions: The results illustrate the importance of matching specific types of sport-relevant social support with the needs elicited by the stressors under consideration. They also illustrate the need to pay close attention to the measurement instruments used in such studies. In this study, the finding of significant stress-buffering effects of social support may have been optimised through detailed attention to the measurement instruments chosen for the constructs under study. Applied implications would include developing an understanding of the beneficial role social support has to play in protecting players from the deleterious impact of stressors upon performance. Providers of support should, however, carefully match their support to the needs of the individual

Towards Quantum Gravity: A Framework for Probabilistic Theories with Non-Fixed Causal Structure

General relativity is a deterministic theory with non-fixed causal structure. Quantum theory is a probabilistic theory with fixed causal structure. In this paper we build a framework for probabilistic theories with non-fixed causal structure. This combines the radical elements of general relativity and quantum theory. The key idea in the construction is physical compression. A physical theory relates quantities. Thus, if we specify a sufficiently large set of quantities (this is the compressed set), we can calculate all the others. We apply three levels of physical compression. First, we apply it locally to quantities (actually probabilities) that might be measured in a particular region of spacetime. Then we consider composite regions. We find that there is a second level of physical compression for the composite region over and above the first level physical compression for the component regions. Each application of first and second level physical compression is quantified by a matrix. We find that these matrices themselves are related by the physical theory and can therefore be subject to compression. This is the third level of physical compression. This third level of physical compression gives rise to a new mathematical object which we call the causaloid. From the causaloid for a particular physical theory we can calculate verything the physical theory can calculate. This approach allows us to set up a framework for calculating probabilistic correlations in data without imposing a fixed causal structure (such as a background time). We show how to put quantum theory in this framework (thus providing a new formulation of this theory). We indicate how general relativity might be put into this framework and how the framework might be used to construct a theory of quantum gravity.Comment: 23 pages. For special issue of Journal of Physics A entitled "The quantum universe" in honour of Giancarlo Ghirard

Electric propulsion options for the SP-100 reference mission

Analyses were performed to characterize and compare electric propulsion systems for use on a space flight demonstration of the SP-100 nuclear power system. The component masses of resistojet, arcjet, and ion thruster systems were calculated using consistent assumptions and the maximum total impulse, velocity increment, and thrusting time were determined, subject to the constraint of the lift capability of a single Space Shuttle launch. From the study it was found that for most systems the propulsion system dry mass was less than 20 percent of the available mass for the propulsion system. The maximum velocity increment was found to be up to 2890 m/sec for resistojet, 3760 m/sec for arcjet, and 23 000 m/sec for ion thruster systems. The maximum thruster time was found to be 19, 47, and 853 days for resistojet, arcjet, and ion thruster systems, respectively

Background, current status, and prognosis of the ongoing slush hydrogen technology development program for the NASP

Among the Hydrogen Projects at the NASA Lewis Research Center (NASA LeRC), is the task of implementing and managing the Slush Hydrogen (SLH2) Technology Program for the United States' National AeroSpace Plane Joint Program Office (NASP JPO). The objectives of this NASA LeRC program are to provide verified numerical models of fluid production, storage, transfer, and feed systems and to provide verified design criteria for other engineered aspects of SLH2 systems germane to a NASP. The pursuit of these objectives is multidimensional, covers a range of problem areas, works these to different levels of depth, and takes advantage of the resources available in private industry, academia, and the U.S. Government. A summary of the NASA LeRC overall SLH2 program plan, is presented along with its implementation, the present level of effort in each of the program areas, some of the results already in hand, and the prognosis for the effort in the immediate future

Bohm's interpretation and maximally entangled states

Several no-go theorems showed the incompatibility between the locality assumption and quantum correlations obtained from maximally entangled spin states. We analyze these no-go theorems in the framework of Bohm's interpretation. The mechanism by which non-local correlations appear during the results of measurements performed on distant parts of entangled systems is explicitly put into evidence in terms of Bohmian trajectories. It is shown that a GHZ like contradiction of the type+1=-1 occurs for well-chosen initial positions of the Bohmian trajectories and that it is this essential non-classical feature that makes it possible to violate the locality condition.Comment: 18 page