9,263 research outputs found

    Development and flight history of SERT 2 spacecraft

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    A 25-year historical review of the Space Electric Rocket Test 2 (SERT 2) mission is presented. The Agena launch vehicle; the SERT 2 spacecraft; and mission-peculiar spacecraft hardware, including two ion thruster systems, are described. The 3 1/2-year development period, from 1966 to 1970, that was needed to design, fabricate, and qualify the ion thruster system and the supporting spacecraft components, is documented. Major testing of two ion thruster systems and related auxiliary experiments that were conducted in space after the 3 Feb. 1970, launch are reviewed. Extended ion thruster restarts from 1973 to 1981 are reported, in addition to cross-neutralization tests. Tests of a reflector erosion experiment were continued in 1989 to 1991. The continuing performance of spacecraft subsystems, including the solar arrays, over the 1970-1991 period is summarized. Finally, the knowledge of thruster-spacecraft interactions learned from SERT 2 is listed

    Solving the mystery of human sleep schedules one mutation at a time.

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    Sleep behavior remains one of the most enigmatic areas of life. The unanswered questions range from "why do we sleep?" to "how we can improve sleep in today's society?" Identification of mutations responsible for altered circadian regulation of human sleep lead to unique opportunities for probing these territories. In this review, we summarize causative circadian mutations found from familial genetic studies to date. We also describe how these mutations mechanistically affect circadian function and lead to altered sleep behaviors, including shifted or shortening of sleep patterns. In addition, we discuss how the investigation of mutations can not only expand our understanding of the molecular mechanisms regulating the circadian clock and sleep duration, but also bridge the pathways between clock/sleep and other human physiological conditions and ailments such as metabolic regulation and migraine headaches

    The LSND and MiniBooNE Oscillation Searches at High Δm2\Delta m^2

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    This paper reviews the results of the LSND and MiniBooNE experiments. The primary goal of each experiment was to effect sensitive searches for neutrino oscillations in the mass region with Δm2∼1\Delta m^2 \sim 1 eV2^2. The two experiments are complementary, and so the comparison of results can bring additional information with respect to models with sterile neutrinos. Both experiments obtained evidence for νˉμ→νˉe\bar \nu_\mu \rightarrow \bar \nu_e oscillations, and MiniBooNE also observed a νμ→νe\nu_\mu \rightarrow \nu_e excess. In this paper, we review the design, analysis, and results from these experiments. We then consider the results within the global context of sterile neutrino oscillation models. The final data sets require a more extended model than the simple single sterile neutrino model imagined at the time that LSND drew to a close and MiniBooNE began. We show that there are apparent incompatibilities between data sets in models with two sterile neutrinos. However, these incompatibilities may be explained with variations within the systematic error. Overall, models with two (or three) sterile neutrinos seem to succeed in fitting the global data, and they make interesting predictions for future experiments.Comment: Posted with permission from the Annual Review of Nuclear and Particle Science, Volume 63. \c{opyright} 2013 by Annual Reviews, http://www.annualreviews.or

    Measuring the area and number of ballast particle contacts at sleeper/ballast and ballast/subgrade interfaces

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    The number of railway ballast particles in contact with a sleeper may be relatively small. The discrete and non-uniform nature of these contacts may cause breakage and wear. This article explores the use of pressure paper to record the loading history of sleeper to ballast particle contacts over >3 million loading cycles in full size tests. The results demonstrate that the actual contact area may be less than 1% of the total, and that the number of individual contacts is in the hundreds. Under sleeper pads, a finer ballast grading, a shallower shoulder slope and changes to the sleeper material are found to increase the number and area of contacts

    Projective equivalence of ideals in Noetherian integral domains

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    Let I be a nonzero proper ideal in a Noetherian integral domain R. In this paper we establish the existence of a finite separable integral extension domain A of R and a positive integer m such that all the Rees integers of IA are equal to m. Moreover, if R has altitude one, then all the Rees integers of J = Rad(IA) are equal to one and the ideals J^m and IA have the same integral closure. Thus Rad(IA) = J is a projectively full radical ideal that is projectively equivalent to IA. In particular, if R is Dedekind, then there exists a Dedekind domain A having the following properties: (i) A is a finite separable integral extension of R; and (ii) there exists a radical ideal J of A and a positive integer m such that IA = J^m.Comment: 20 page
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