Cryogenic propellant management: Integration of design, performance and operational requirements

The integration of the design features of the Shuttle elements into a cryogenic propellant management system is described. The implementation and verification of the design/operational changes resulting from design deficiencies and/or element incompatibilities encountered subsequent to the critical design reviews are emphasized. Major topics include: subsystem designs to provide liquid oxygen (LO2) tank pressure stabilization, LO2 facility vent for ice prevention, liquid hydrogen (LH2) feedline high point bleed, pogo suppression on the Space Shuttle Main Engine (SSME), LO2 low level cutoff, Orbiter/engine propellant dump, and LO2 main feedline helium injection for geyser prevention

Bringing the Vagueness Doctrine on Campus

Although students have traditionally paid little attention to university disciplinary codes, recent campus disturbances have given these codes unprecedented significance. Those subjected to disciplinary proceedings have charged, among other things, that the provisions which regulate their behavior are too vague to inform them of what they may and may not do. Arguing that a broadly-worded code of conduct is necessary to govern, university administrators, however, have refused to make their regulations more precise

Defects Annealing of Si^+ Implanted GaAs at RT and 100°C

Annealing behavior of point defects near room temperature is studied by measuring the strain relaxation of Si+ implanted GaAs. Polished semi-insulating GaAs wafers were implanted with 300keV Si^+ at liquid nitrogen (LN_2) and room temperature (RT). The strain profile was obtained by the X-ray Double Crystal Diffraction (DCD) technique and kinematical fitting. The maximum strain of the samples stored at RT and elevated temperature 100°C in air, decreases with time, which indicates the reduction of point defects. Relaxation is exponential in time. At least two time constants of 0.24hrs and 24hrs are needed to fit the data, suggesting that two different processes are responsible for annealing defects. Time constants are obtained for different doses at RT and LN_2 implantation temperature, and found to be insensitive to both these quantities. The activation energy for defect migration is estimated using simple diffusion model

Misoriented Epitaxial Growth of (111)CoSi_2 on Offset (111)Si Substrates

Single crystal epitaxial films of CoSi_2 were grown by MBE on various (111)Si single crystal substrates, whose surfaces were purposely tilted towards the _g, direction by small angles ϕ_g,†, 0°, ≤ ϕ_g, ≤, 4° measured between the surface normal and the _g, direction of Si. The actual offset angle, ϕ_g was determined by back Laue reflection method. The average perpendicular strain of the CoSi_2 epilayer, ε┵, and the _f orientation of the epitaxial CoSi_2 film were determined by double crystal diffractometry. We find that the misorientation angle, a, measured between the Si _g, and CoSi_2 _f directions, increases linearly with the offset angle, ϕ_g, up to ϕ_g = 4°. A simple geometrical model is developed which predicts that α = ε┵ × tan ϕ_g. The model agrees quantitatively with the experimental data. The equivalent strain energy associated with the misorientation is approximated by that of a low angle tilt boundary. The misorientation angle α of the equilibrium state, determined by minimizing the total strain energy of the epitaxial film, is nonzero in general

Spectrometry: Report of panel

Spectroscopic measurements are required to define the spectral background and provide the detailed spectral information that is essential for the design of species-specific systems and the analysis of data obtained from them. This function of spectroscopic measurements is expected to be an important part of any tropospheric remote-sensing program, and both emission and absorption spectroscopy are relevant in this context. The data from such observations are of value to tropospheric science in their own right, during the initial phases while species-specific techniques and instruments are under development. In addition, there are a number of unresolved problems in tropospheric radiative transfer and spectroscopy which presently limit the accuracy and reliability of all remote sensing methods. Only through a supporting program of spectroscopic measurements can progress be made in improving the understanding of these aspects of radiative transfer and ultimately reaching the desired confidence in the accuracy to species-specific monitoring techniques

Characterization of high-energy heavy-ion implanted InP crystals by a variety of techniques

MeV ion implantation into InP compound semiconductor crystals with 5 MeV nitrogen ions has been investigated. The subsequent characterization was undertaken by a variety of techniques such as nuclear resonant reaction analysis, channeling Rutherford backscattering spectrometry, X-ray rocking curve measurement and cross-sectional transmission electron microscopy. These techniques have clearly revealed substantial changes in structural properties and radiation-induced damage distribution as well as the influence of post-implantation annealing in ^(15)N ion-implanted InP samples. The results from these measurements, which are presented in this paper, are shown to be consistent with each other, and have led to a coherent description of the effects of the implantation and subsequent annealing. In a practical sense this has demonstrated the complementary nature of the analytical capabilities of all of these techniques used for the investigation of the processes involved in high-energy heavy-ion implantation

Amorphization and recrystallization in MeV ion implanted InP crystals

A comprehensive study of MeV-^(15)N-ion-implanted InP by a variety of analytical techniques has revealed the physical processes involved in MeV ion implantation into III-V compound semiconductors as well as the influence of post-implantation annealing. It provides a coherent picture of implant distribution, structural transition, crystalline damage, and lattice strain in InP crystals induced by ion implantation and thermal annealing. The experimental results from the different measurements are summarized in this report. Mechanisms of amorphization by implantation and recrystallization through annealing in MeV-ion-implanted InP are proposed and discussed in light of the results obtained

An Analysis of the Reflection Component in the EPICS Model of Service Learning

Service learning is a pedagogy providing a structured environment for students to link service with course learning objectives. Key to the service learning experience is critical reflection. This gives students the opportunity to examine their coursework in the context of the service they provide to their community and, in a broader sense, the impact they can have on the world. Research has shown that students participating in service learning have a higher comprehension of the course material and also develop an awareness of their local community and the issues it faces. In engineering, there are many examples of service-learning programs ranging from freshman introductory courses to senior capstone courses. Despite their successes, an area that the engineering education community has yet to fully develop is the reflection component of service learning. This paper addresses the development of reflection activities and materials in the Engineering Projects in Community Service (EPICS) program at Purdue University. EPICS engages students in long-term design projects that provide technical solutions to problems faced by local community service organizations. It is a multidisciplinary (composed of students from 20 majors), vertically integrated (freshman-senior), engineering-based design course. Students design, build, test, and deploy projects meeting the specific needs of their community partners. Reflection has been integrated in the EPICS program through curricular activities and key milestones of the course. These activities guide students through the reflection process on a variety of topics. Critical reflection on the design process and teaming complement those on more traditional areas of ethics and social context to enhance a student\u27s service learning experience. This paper presents an overview of the reflection activities that have been developed, interpretations of student reflections from these activities, and plans to evolve the reflection component in EPICS

Formation of Buried Oxide in MeV Oxygen Implanted Silicon

We have studied the formation of buried oxide in MeV oxygen implanted Si. A continuous oxide layer is formed in the samples implanted with 2x10^(18)/cm^2 oxygen and annealed at 1300° C. The microstructures are studied by cross-sectional transmission electron microscopy and high resolution electron microscopy. Chemical information was obtained by electron energy loss spectroscopy. The effects of implantation temperature are studied. Implantation at a low substrate temperature leads to a well-defined buried SiO_2 layer, inhibits the formation of oxide precipitates in the silicon, and reduces silicon inclusions in the SiO_2

Basal topographic controls on rapid retreat of Humboldt Glacier, northern Greenland

This is the final version of the article. Available from CUP via the DOI in this record.Discharge from marine-terminating outlet glaciers accounts for up to half the recent mass loss from the Greenland ice sheet, yet the causal factors are not fully understood. Here we assess the factors controlling the behaviour of Humboldt Glacier (HG), allowing us to evaluate the influence of basal topography on outlet glacier response to external forcing since part of HG’s terminus occupies a large overdeepening. HG’s retreat accelerated dramatically after 1999, coinciding with summer atmospheric warming of up to 0.19°C a–1 and sea-ice decline. Retreat was an order of magnitude greater in the northern section of the terminus, underlain by a major basal trough, than in the southern section, where the bedrock is comparatively shallow. Velocity change following retreat was spatially non-uniform, potentially due to a pinning point near HG’s northern lateral margin. Consistent with observations, numerical modelling demonstrates an order-of-magnitude greater sensitivity to sea-ice buttressing and crevasse depth (used as a proxy for atmospheric warming) in the northern section. The trough extends up to 72 km inland, so it is likely to facilitate sustained retreat and ice loss from HG during the 21st century.Funding for this work was provided by a Durham Doctoral Studentship to J.R.C. Radio-echo sounding data were acquired and processed through UK Natural Environment Research Council (NERC) grant NE/H020667 to J.A.D. and P.C. and a G. Unger Vetlesen grant to the University of Texas Institute for Geophysics (UTIG). GrOGG laser altimetry was supported by NNXAD33G to D.D.B. This paper is UTIG contribution No. 2733. S.S.R.J. was supported by UK NERC fellowship NE/J018333/1