Flight software development for the isothermal dendritic growth experiment

The Isothermal Dendritic Growth Experiment (IDGE) is a microgravity materials science experiment scheduled to fly in the cargo bay of the shuttle on the United States Microgravity Payload (USMP) carrier. The experiment will be operated by real-time control software which will not only monitor and control onboard experiment hardware, but will also communicate, via downlink data and uplink commands, with the Payload Operations Control Center (POCC) at NASA George C. Marshall Space Flight Center (MSFC). The software development approach being used to implement this system began with software functional requirements specification. This was accomplished using the Yourdon/DeMarco methodology as supplemented by the Ward/Mellor real-time extensions. The requirements specification in combination with software prototyping was then used to generate a detailed design consisting of structure charts, module prologues, and Program Design Language (PDL) specifications. This detailed design will next be used to code the software, followed finally by testing against the functional requirements. The result will be a modular real-time control software system with traceability through every phase of the development process

Evidance for an Oxygen Diffusion Model for the Electric Pulse Induced Resistance Change Effect in Oxides

Electric pulse induced resistance (EPIR) switching hysteresis loops for Pr0.7Ca0.7MnO3 (PCMO) perovskite oxide films were found to exhibit an additional sharp "shuttle peak" around the negative pulse maximum for films deposited in an oxygen deficient ambient. The device resistance hysteresis loop consists of stable high resistance and low resistance states, and transition regions between them. The resistance relaxation of the "shuttle peak" and its temperature behavior as well as the resistance relaxation in the transition regions were studied, and indicate that the resistance switching relates to oxygen diffusion with activation energy about 0.4eV. An oxygen diffusion model with the oxygen ions (vacancies) as the active agent is proposed for the non-volatile resistance switching effect in PCMO.Comment: 7 pages, 5 figure

Improving Regulation Through Incremental Adjustment

Claiming that existing regulation is excessive and irrational, regulatory critics have successfully convinced Congress and the White House to implement a plethora of procedural requirements to analyze a proposed regulation before it is promulgated. In our book, Risk Regulation at Risk: Restoring A Pragmatic Approach (2003), we argued that the previous initiatives address the possibility of regulatory failure on the wrong end of the regulatory policy implementation process. We suggested that one way of improving regulation would be to rely on incremental adjustments in regulation on the back end of the regulatory process. This article addresses in more detail the potential of two types of back-end processes (deadline extensions and waivers, exceptions, and variances) by examining five federal statutes (administered by EPA and OSHA) that provide opportunities for the two types of adjustments we are studying. We find that these adjustment provisions are generally consistent with the precautionary tilt of the statutes in which they are located because they still require the regulated entity to do the best it can to protect people and the environment. Where such protective mechanisms are absent, we urge that the statutes be amended to include them. We also consider the procedures by which requests for back-end adjustments are currently processed. We support the use of notice and comment procedures because more elaborate procedures are not necessary to promote rational decision-making, given the nature of the issues likely to be raised in back-end adjustment proceedings. We are concerned, however, about the extent to which effective public participation will occur under these procedures. We therefore endorse two steps to enhance the transparency of back-end adjustment decision-making: the establishment of electronic reading rooms and the issuance by agencies of annual reports on back-end adjustment

An ultrasonic flowmeter for gases by Donald A. Bender, Leon R. Glicksman, Carl R. Peterson.

An ultrasonic flowmeter is developed for use in natural gas mains. The characteristics of the application and the dynamic head device presently employed are described. The performance requirements, design, and prototype testing of the ultrasonic instrument are discussed. The viability of a unique metering technique using reflected acoustic pulses was experimentally demonstrated. The flowmeter developed herein requires access to one side of the gas line and is self calibrating. It was concluded that continued development will produce a unit suitable for use in commercial service

Predicting gas-flow distribution in pilot-scale fluidized beds using cfd simulations

Bubbling fluidized beds are used extensively in energy and chemical industries because of their excellent heat and mass transfer characteristics. Recently, CFD has been identified as a useful tool for predicting reactor performance, but application to large scales continues to be challenging because of limitations on computational resources. Given that the hydrodynamics can largely be characterized by bubbles rising through the bed, a more feasible approach for investigating large-scale reactors is to quantify bubble dynamics and specifically, gas distribution in different phases- visible bubble flow, bubble-through flow and dense-phase flow. In this study, 3D CFD simulations of bubbling fluidized beds are first conducted to establish the impact of scale (bed diameter) on the hydrodynamics. Using solids circulation and bubble statistics (1), it is established that wall effects cease to be significant in beds larger than 50 cm (bed aspect ratio less than 1). At this scale, simulations are then carried out for two distinct Geldart B particles and data is subsequently analyzed for gas-flow distribution in the bed. Bubble statistics are also compared with existing correlations and their relation to solids circulation and mixing is investigated. The physical model and numerical tool were developed and validated in previous studies (1,2), while 3D Bubble statistics are computed using MS3DATA (Multiphase Statistics using 3D Detection and Tracking Algorithm) (3). Accurate description of the gas-flow is crucial for large-scale combustor design since quantifying gas distribution will indicate both fuel rich zones as well as oxidant bypass through bubbles leading to inefficient performance. Please click Additional Files below to see the full abstract

Crossover Scaling in Dendritic Evolution at Low Undercooling

We examine scaling in two-dimensional simulations of dendritic growth at low undercooling, as well as in three-dimensional pivalic acid dendrites grown on NASA's USMP-4 Isothermal Dendritic Growth Experiment. We report new results on self-similar evolution in both the experiments and simulations. We find that the time dependent scaling of our low undercooling simulations displays a cross-over scaling from a regime different than that characterizing Laplacian growth to steady-state growth