86,422 research outputs found
International solar polar mission
The key configurations and characteristics of the two International Solar Polar Mission (ISPM) spacecraft are described. The primary mission objectives of the ISPM are to investigate, as a function of solar latitude, the properties of the solar corona, the solar wind, the sun/wind interface, the heliospheric magnetic field, solar and nonsolar cosmic rays, and the interstellar/interplanetary neutral gas and dust. In addition, instrumentation is included to detect the gamma ray bursts; it is hoped to pinpoint the sources of these bursts by using triangulation from each spacecraft and the Earth
International solar polar mission support
The primary objective of the International Solar Polar Mission (ISPM) is to investigate solar and interplanetary phenomena as a function of the solar latitude. The mission is to be accomplished by using a gravity assist at the planet Jupiter to send two spacecraft out of the ecliptic plane. Available trajectory information is supplied, and spaceborne experiments under consideration are discussed. An introduction to the key characteristics of both spacecraft is given, emphasizing communication equipment
Energy efficient aircraft engines
The three engine programs that constitute the propulsion portion of NASA's Aircraft Energy Efficiency Program are described, their status indicated, and anticipated improvements in SFC discussed. The three engine programs are (1) Engine Component Improvement--directed at current engines, (2) Energy Efficiency Engine directed at new turbofan engines, and (3) Advanced Turboprops--directed at technology for advanced turboprop--powered aircraft with cruise speeds to Mach 0.8. Unique propulsion system interactive ties to the airframe resulting from engine design features to reduce fuel consumption are discussed. Emphasis is placed on the advanced turboprop since it offers the largest potential fuel savings of the three propulsion programs and also has the strongest interactive ties to the airframe
Certain transformations and summations for generalized hypergeometric series with integral parameter differences
Certain transformation and summation formulas for generalized hypergeometric series with integral parameter differences are derived
Clausen's series 3F2(1) with integral parameter differences and transformations of the hypergeometric function 2F2(x)
We obtain summation formulas for the hypergeometric series 3 F 2(1) with at least one pair of numeratorial and denominatorial parameters differing by a negative integer. The results derived for the latter are used to obtain Kummer-type transformations for the generalized hypergeometric function 2 F 2(x) and reduction formulas for certain Kampé de Fériet functions. Certain summations for the partial sums of the Gauss hypergeometric series 2 F 1(1) are also obtained
Synchronization of Reed-Solomon codes
The synchronization capabilities of Reed-Solomon codes when an appropriate coset of the code is used instead of the code itself are examined. In this case an E-error correcting Reed-Solomon code is transformed into a code capable of determining that there are m symbols out of sync, if e symbol errors occurred, whenever m + e E. In the event that m = 0, i.e., the word is in sync, then decoder will correct any pattern of E - 1 on fewer symbol errors
Quasicontinuum Models of Interfacial Structure and Deformation
Microscopic models of the interaction between grain boundaries (GBs) and both
dislocations and cracks are of importance in understanding the role of
microstructure in altering the mechanical properties of a material. A recently
developed mixed atomistic and continuum method is extended to examine the
interaction between GBs, dislocations and cracks. These calculations elucidate
plausible microscopic mechanisms for these defect interactions and allow for
the quantitative evaluation of critical parameters such as the stress to
nucleate a dislocation at a step on a GB and the force needed to induce GB
migration.Comment: RevTex, 4 pages, 4 figure
Quasicontinuum simulation of fracture at the atomic scale
We study the problem of atomic scale fracture using the recently developed quasicontinuum method in which there is a systematic thinning of the atomic-level degrees of freedom in regions where they are not needed. Fracture is considered in two distinct settings. First, a study is made of cracks in single crystals, and second, we consider a crack advancing towards a grain boundary (GB) in its path. In the investigation of single crystal fracture, we evaluate the competition between simple cleavage and crack-tip dislocation emission. In addition, we examine the ability of analytic models to correctly predict fracture behaviour, and find that the existing analytical treatments are too restrictive in their treatment of nonlinearity near the crack tip. In the study of GB-crack interactions, we have found a number of interesting deformation mechanisms which attend the advance of the crack. These include the migration of the GB, the emission of dislocations from the GB, and deflection of the crack front along the GB itself. In each case, these mechanisms are rationalized on the basis of continuum mechanics arguments
A Production System Model of Capturing Reactive Moving Targets
Subjects manipulated a control stick to position a cursor over a moving target that reacted with a computer-generated escape strategy. The cursor movements were described at two levels of abstraction. At the upper level, a production system described transitions among four modes of activity; rapid acquisition, close following, a predictive mode, and herding. Within each mode, differential equations described trajectory-generating mechanisms. A simulation of this two-level model captures the targets in a manner resembling the episodic time histories of human subjects
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