Effect of thruster pulse length on thruster-exhaust damage of S13G white thermal control coatings

Rocket exhaust products which strike thermal control surfaces cause changes in solar absorptance (Alpha Sub s) and thermal emittance (Epsilon) of these surfaces. A study was made of the effect of rocket pulse duration on exhaust damage to S13G white coatings. Two pulse lengths were used - 14 msec and 50 msec. An MMH/N204 bipropellant 5-lb thrust rocket was fired into a simulated space environment with a vacuum of 0.00001 torr, a liquid helium temperature enclosure, and solar radiation. The changes in solar absorptance and thermal emittance of S13G white coatings due to rocket exhaust were made in-situ for total firing times of 58 seconds with 14 msec pulses and 223.7 sec with 50 msec pulses. The solar absorptance of S13G increased 25 percent due to 223.7 sec of exposure to 50 msec pulses and the thermal emittance was unaffected. The ratio of Alpha Sub s/Epsilon therefore increased by 25 percent. The short 14 msec pulse exhaust exposure caused between 40 and 70 percent increase in solar absorptance and a decrease of between 13 and 18 percent in thermal emittance. The corresponding increase in Alpha Sub s/Epsilon ratio was between 80 and 100 percent. Ultraviolet radiation was present in the short pulse test and may have contributed to the large damage of that test

The Quilting Bee: A Research Metaphor

This paper uses the art of quilting as a metaphor for the research process. Two very different stories are revealed by Amish women at a quilting bee as they explore their purposes, thoughts, and experiences in producing their first quilts. The metaphor is used to contrast the goals, involvement of the researcher, and descriptions utilized by qualitative and quantitative researchers. The tales of these Amish women both contribute to an understanding of the art of quilting just as both qualitative and quantitative researchers have contributions to make to the field of education

Real Middle School Teachers

Effective middle school teachers are more than the sum total of their educational beliefs and practices. They are whole persons whose lives reflect receptivity to growth, treasured relationships, and the intertwining of their personal and professional lives. This article uses the children’s classic, The Velveteen Rabbit, as a metaphor to describe effective middle school teachers

Effective Middle School Teachers : Becoming Real

Problem. This study looks at four effective middle school teachers\u27 stories in order to understand the experiences and beliefs which impact their choice to use developmentally responsive classroom practices. There is general agreement in the literature concerning characteristics of effective middle school teachers, but little has been done to understand what influences these teachers to teach the way they do. Method. A qualitative case study design was used for this study. Two male and two female middle school teachers were observed and interviewed during the course of 1 school year. Each teacher\u27s life experiences, classroom practices, and beliefs are described in narrative form. An analysis of the four teachers\u27 practices and beliefs was conducted using the Carnegie Council on Adolescent Development\u27s Turning Points (1989) and the National Middle School Association\u27s This We Believe (1995). Further analysis of similarities and differences in the teachers\u27 lives led to the emergence of other themes. Results. The four teachers\u27 classroom practices and beliefs matched the descriptions of developmentally appropriate practices in Turning Points and This We Believe. Further analysis of similarities and differences in the teachers\u27 lives led to the emergence of other themes. Conclusions. The concept of Real as portrayed in The Velveteen Rabbit describes the lives of the four middle school teachers who participated in this study. These teachers love and give of themselves freely to others. They have experienced growing pains, but choose to look beyond the discomfort and allow it to mold and shape their lives. Though they are Real and recognize the contributions they are making to others, they continue to open themselves up to continued growth

Extremely High Energy Neutrinos and their Detection

We discuss in some detail the production of extremely high energy (EHE) neutrinos with energies above 10^18 eV. The most certain process for producing such neutrinos results from photopion production by EHE cosmic rays in the cosmic background photon field. However, using assumptions for the EHE cosmic ray source evolution which are consistent with results from the deep QSO survey in the radio and X-ray range, the resultant flux of neutrinos from this process is not strong enough for plausible detection. A measurable flux of EHE neutrinos may be present, however, if the highest energy cosmic rays which have recently been detected well beyond 10^20 eV are the result of the annihilation of topological defects which formed in the early universe. Neutrinos resulting from such decays reach energies of the grand unification (GUT) scale, and collisions of superhigh energy neutrinos with the cosmic background neutrinos initiate neutrino cascading which enhances the EHE neutrino flux at Earth. We have calculated the neutrino flux including this cascading effect for either massless or massive neutrinos and we find that these fluxes are conceivably detectable by air fluorescence detectors now in development. The neutrino-induced showers would be recognized by their starting deep in the atmosphere. We evaluate the feasibility of detecting EHE neutrinos this way using air fluorescence air shower detectors and derive the expected event rate. Other processes for producing deeply penetrating air showers constitute a negligible background.Comment: 33 pages, including 12 eps figures, LaTe

Correlation of creep rate with microstructural changes during high temperature creep

Creep tests were conducted on Haynes 188 cobalt-base alloy and alpha titanium. The tests on Haynes 188 were conducted at 1600 F and 1800 F for stresses from 3 to 20 ksi, and the as-received, mill-annealed results were compared to specimens given 5%, 10%, and 15% room temperature prestrains and then annealed one hour at 1800 F. The tests on alpha titanium were performed at 7,250 and 10,000 psi at 500 C. One creep test was done at 527 C and 10,000 psi to provide information on kinetics. Results for annealed titanium were compared to specimens given 10% and 20% room temperature prestrains followed by 100 hours recovery at 550 C. Electron microscopy was used to relate dislocation and precipitate structure to the creep behavior of the two materials. The results on Haynes 188 alloy reveal that the time to reach 0.5% creep strain at 1600 F increases with increasing prestrain for exposure times less than 1,000 hours, the increase at 15% prestrain being more than a factor of ten