Spatial nucleation and crystal growth Final report, 1 Jun. 1964 - 30 Sep. 1967

Nucleation and growth processes in interstellar grain formatio

Changing perceptions of preservice teachers : innovations in middle schooling teacher education

For the past twenty years, the disengagement of early adolescents has been the focus of much of the literature related to middle schooling. In response, some universities in Australia have introduced teacher education programs that focus upon graduating specialised middle schooling teachers. Constructing such programs is at the centre of much debate and discussion, however, it is advocated that positive futures for early adolescents can be enhanced through quality middle schooling teacher education programs (Education Queensland, 2004). At a Queensland university campus, middle schooling elective units were introduced as part of the Bachelor of Education (primary) degree. The design of the units was to support preservice teachers to gain the theoretical and pedagogical knowledge to engage and promote early adolescent learning. An innovative approach to the delivery of the units was promoted by a partnership agreement between local schools and the campus. The partnership allowed preservice teachers to combine university classes with opportunities to visit exemplary classrooms to observe, participate and reflect upon middle school teaching practices. The aim of this study was to explore and describe the 38 first-year preservice teachers’ perceptions of their first middle schooling elective unit and to ascertain whether the combination of university classes and school-based experiences assisted their development of middle schooling concepts and approaches. Data were gathered using pre-test and post-test questionnaires combined with guided written reflections to record their views before, after and during the unit delivery. Results indicated that initially 34 preservice teachers had little understanding of middle schooling concepts and pedagogical practices, however, 11 participants recognised that bullying and peer pressure were issues experienced by early adolescents. The collation of the written reflections supported the combined delivery of the middle years unit further supporting the inclusion of school experiences with university delivered units

Background studies in gas ionizing x ray detectors

The background response of a gas ionizing proportional x ray detector is estimated by solving the one dimensional photon transport equation for two regions using Monte Carlo techniques. The solution was effected using the SSL VAX 780 and the CRAY XMP computers at Marshall Space Flight Center. The isotropic photon energy spectrum encompassing the range from 1 to 1000 KeV incident onto the first region, the shield, is taken so as to represent the measured spectrum at an altitude of 3 mb over Palastine, Texas. The differential energy spectrum deposited in the gas region, xenon, over the range of 0 to 100 KeV is written to an output file. In addition, the photon flux emerging from the shield region, tin, over the range of 1 to 1000 KeV is also tabulated and written to a separate file. Published tabular cross sections for photoelectric, elastic and inelastic Compton scattering as well as the total absorption coefficient are used. Histories of each incident photon as well as secondary photons from Compton and photoelectric interactions are followed until the photon either is absorbed or exits from the regions under consideration. The effect of shielding thickness upon the energy spectrum deposited in the xenon region for this background spectrum incident upon the tin shield was studied

X-ray fluorescence surface contaminant analyzer: A feasibility study

The bonding of liner material to the inner metal surfaces of solid rocket booster cases is adversely affected by minute amounts of impurities on the metal surface. Suitable non-destructive methods currently used for detecting these surface contaminants do not provide the means of identifying their elemental composition. The feasibility of using isotopic source excited energy dispersive X-ray fluorescence as a possible technique for elemental analysis of such contaminants is investigated. A survey is made of the elemental compositions of both D-6ac steel, a common construction material for the booster cases, and Conoco HD-2 grease, a common surface contamination. Source and detector choices that maximize signal to noise ratio in a Recessed Source Geometry are made. A Monte Carlo simulation is then made of the optimized device incorporating the latest available X-ray constants at the energy of the chosen source to determine the device's response to a D-6ac steel surface contained with Conoco HD-2 grease

Preservice teachers’ observations of their mentors’ teaching strategies for differentiated learning

Tensions exist between teacher-centred and learner-centred approaches with constructivism as being favoured for learning in the 21st Century. There is little evidence of teaching strategies being used in the field for differentiating student learning. In addition, preservice teachers need to learn about teaching strategies for which observations of their mentor teachers can provide practical applications. This study explores 16 preservice teachers’ observations of their mentors’ teaching strategies over a four-week professional experience. They provided a minimum of five written observations during this period. Findings indicated that these preservice teachers observed their mentors’ practices and recorded four key teaching strategies used to differentiate learning, namely: (1) designating facilitators for students’ learning, including teacher, peers, parents, and support staff such as teachers aides, (2) managing student groups, (3) contexts for learning, and (4) using a range of teaching aids (visual, auditory, games) and resources. Preservice teachers’ observations of their mentor teachers indicated that they can commence at early stages for identifying teaching strategies and how they work for differentiating student learning

Precision gage measures ultrahigh vacuum levels

Ionization gage in which internally generated X rays are minimized is described. This gage permits the measurement of gas pressures in ultrahigh systems of micro-pico torr /10-18/

An 8-cm electron bombardment thruster for auxiliary propulsion

Thruster size, beam current level, and specific impulse trade-offs are considered for mercury electron bombardment ion thrusters to be used for north-south station keeping of geosynchronous spacecraft. An 8-cm diameter thruster operating at 2750 seconds specific impulse at thrust levels of 4.4 mN (1 m1b) to 8.9 mN (2 m6b) with a design life of 20,000 hours and 10,000 cycles is being developed. The thruster will have a dished two-grid system capable of thrust vectoring of + or - 10 degrees in two orthogonal directions. A preliminary thruster has been fabricated and tested; thruster performance characteristics have been determined at 4.45, 6.68, and 8.90 millinewtons

High performance auxiliary-propulsion ion thruster with ion-machined accelerator grid

An improvement in thruster performance was achieved by reducing the diameter of the accelerator grid holes. The smaller accelerator grid holes resulted in a reduction in neutral mercury atoms escaping the discharge chamber, which in turn enhanced the discharge propellant utilization from approximately 68 percent to 92 percent. The accelerator grids were fabricated by ion machining with an 8-centimeter-diameter thruster, and the screen grid holes individually focused ion beamlets onto the blank accelerator grid. The resulting accelerator grid holes are less than 1.12 millimeters in diameter, while previously used accelerator grids had hole diameters of 1.69 millimeters. The thruster could be operated with the small-hole accelerator grid at neutralizer potential