Gas-dynamic shock heating of post-flare loops due to retraction following localized, impulsive reconnection

We present a novel model in which shortening of a magnetic flux tube following localized, three-dimensional reconnection generates strong gas-dynamic shocks around its apex. The shortening releases magnetic energy by progressing away from the reconnection site at the Alfven speed. This launches inward flows along the field lines whose collision creates a pair of gas-dynamic shocks. The shocks raise both the mass density and temperature inside the newly shortened flux tube. Reconnecting field lines whose initial directions differ by more that 100 degrees can produce a concentrated knot of plasma hotter that 20 MK, consistent with observations. In spite of these high temperatures, the shocks convert less than 10% of the liberated magnetic energy into heat - the rest remains as kinetic energy of bulk motion. These gas-dynamic shocks arise only when the reconnection is impulsive and localized in all three dimensions; they are distinct from the slow magnetosonic shocks of the Petschek steady-state reconnection model

Elastic wave propagation in embankment dams

This study investigates the stresses produced in an embankment dam as a result of excitation due to elastic plane waves. A two dimensional finite element model is used to represent an embankment and its substructure. The model uses a quadrilateral element, formed from triangles with a condensed internal node, which gives a better prediction of stress direction than a constant strain triangle. The equations of motion are assembled with lumped mass and damping matrices, and solved by direct integration using a fourth order Runge-Kutta algorithm. For time-steps in the range of stability this algorithm is shown to be accurate and easy to use. It is shown that the range of stability is considerably reduced with the inclusion of damping, and so damping was not included in the models studied. Tests show that for a finite element grid to model elastic wave propagation it is essential for there to be at least eight elements per wavelength. If this requirement is violated the predicted stresses are seriously affected, and the results of previously published studies must be judged against this condition. The model grid is designed to meet this requirement for the propagation velocity typical of dam materials and the frequencies typical of seismic events. Two models, (a) homogeneous and (b) layered, are excited by P and S waves at several angles. The consequent distortions of static stress distributions are varied, but exhibit conditions that could lead to failure by slumping or by tensional cracking close to the crest. The severity of the stresses was greater in the cases of (a) S-waves, (b) angled waves, (c) layered models. The physical processes producing the stress distributions are examined. It is concluded that the stress distributions are dependent on the angle of incidence and are not capable of explanation in terms of natural modes of vibration only

The Development and Tryout of a Program Designed to Increase Students\u27 Multiplication Fact Fluency

Fluency skills are fundamental to the ability to complete relatively more complex problems using less mental energy. Most math curriculums do not stress the importance of automaticity of math facts. Variations in teaching styles and teaching modality seem to negate the true purpose for cementing and rapidly retrieving math facts. This study put to the test a program that was designed to increase students’ ability to retrieve multiplication facts fluently. The program exercised cognitive structures and enabled students to retrieve multiplication facts quickly. The results of a matched-pairs t-test indicated that after the students completed the course of the program, there was a statistically significant different in the students’ ability to retrieve multiplication facts accurately and speedily

A SLAM II simulation model for analyzing space station mission processing requirements

Space station mission processing is modeled via the SLAM 2 simulation language on an IBM 4381 mainframe and an IBM PC microcomputer with 620K RAM, two double-sided disk drives and an 8087 coprocessor chip. Using a time phased mission (payload) schedule and parameters associated with the mission, orbiter (space shuttle) and ground facility databases, estimates for ground facility utilization are computed. Simulation output associated with the science and applications database is used to assess alternative mission schedules

The effects of solid rocket motor effluents on selected surfaces and solid particle size, distribution, and composition for simulated shuttle booster separation motors

A series of three tests was conducted using solid rocket propellants to determine the effects a solid rocket plume would have on thermal protective surfaces (TPS). The surfaces tested were those which are baselined for the shuttle vehicle. The propellants used were to simulate the separation solid rocket motors (SSRM) that separate the solid rocket boosters (SRB) from the shuttle launch vehicle. Data cover: (1) the optical effects of the plume environment on spacecraft related surfaces, and (2) the solid particle size, distribution, and composition at TPS sample locations