Physical Sciences

Improved Spherical Energy Analyzer

An improved spherical energy analyzer (a type of electrostatic mass spectrometer) is under development for use in analyzing a beam of ions generated by a Hall thruster. The major improvement, relative to a commercial spherical energy analyzer, is the addition of a quadrupole stage (with refocusing electron optics) for separating ions of different charge states. The development work also includes efforts to make the instrument smaller and lighter than the commercial version in order to make it possible to translate and rotate the instrument through the ion beam inside a vacuum chamber that contains the Hall thruster.

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Redundant Oxygen-Deficiency Monitoring System

An oxygen-deficiency monitoring system (ODMS) has been developed for a ten-room facility in which the use of large amounts of nitrogen and helium could cause an oxygen deficiency severe enough to be hazardous to personnel. The ODMS comprises three subsystems, of which two monitor three rooms each, and one monitors four rooms. The ODMS generates alarms when the oxygen content of the air in a room falls below 19.5 mole percent. Each subsystem includes transport pumps that draw air continuously from each room through two tubes. Each subsystem includes two oxygen analyzers equipped with sampling pumps, plus two programmable-logic controllers (PLCs) and associated hardware that control electrically actuated valves that admit small fractions of the transport flows to the oxygen analyzers. The PLCs cause the valves to connect the two oxygen analyzers to two different sampling tubes, and then to switch the connections to a different pair of sampling tubes after an interval of about 10 seconds, and so forth until the air from all sampling points has been monitored, and then the sequence repeats. If one sampling tube, oxygen analyzer, pump, or PLC fails, it can be repaired while the system continues to operate, albeit at a reduced rate.

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Report on User's Guidefor Monthly Vector Wind Profile Model

A report briefly describes a user's guide for a computer program that constructs vector wind profiles on the basis of a statistical model. The monthly vector wind profiles are meant to be used (1) to estimate wind-dispersion-related dispersions of critical aerodynamic loads and corresponding aerospace-ascent-vehicle design parameters and (2) to analyze effects of monthly wind-profile dispersions on ascent trajectories and to design ascent autopilot systems to correct for these effects. The user's guide is also said to list output data to aid the user in the verification of test output.

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Sizes of Surface and Capped InxGa1-xAs/GaAs Quantum Dots

A report describes an experimental study of the sizes and concentrations of capped (buried) and surface In0.6Ga0.4As/GaAs quantum dots that were grown by metal-organic vapor deposition under the same conditions except for the inclusion or exclusion of capping. [InxGa1-xAs/GaAs quantum dots are lens-shaped islands (typically a few nanometers thick and tens of nanometers in diameter) of InxGa1-xAs grown on a GaAs substrate. As used here, "capping" signifies the growth of a layer of GaAs over the InxGa1-xAs islands.] In the experiments, the sizes of the capped In0.6Ga0.4As/GaAs islands were measured by transmission electron microscopy (TEM).

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Fuel Cell Would Generate Power From Martian Atmosphere

A report proposes the development of a thin-film fuel cell that would generate electric power from two minor constituents of the Martian atmosphere — O2 and CO. These compounds are generated continuously by photolysis of CO2, the major constituent. The fuel cell would include a cathode and an anode made of catalysts suitable for the selective low-temperature electrochemical reduction of O2 and oxidation of CO, respectively. It would also include a hygroscopic gel electrolyte.

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Improved Automate System for Transferring Liquid Helium

Consumption of liquid helium would be reduced by optimizing use of vapor for precooling.An improved automated system for transferring liquid helium from a supply tank to an end-use cryostat has been proposed. Like automated systems developed previously for the same purpose, this system would reduce the time that must be spent by technicians in replenishing cryostats in equipment required to operate for times longer than cryostat holding times. However, relative to prior automated liquid-helium-transfer systems, this system would operate in a more nearly optimum manner so as to reduce the consumption of liquid helium. Examples of equipment with which this system could be used include apparatuses for long-duration scientific experiments and large cooled electromagnets in medical imaging systems

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Algorithm for Computing Dynamics of Molecules

Equations of motion are solved more efficiently.The Newton-Euler Inverse Mass Operator (NEIMO) algorithm and software that implements the algorithm have been developed to reduce the amount of time needed to perform computational simulations of the dynamics of macromolecules. The NEIMO algorithm and the associated software are intended, in particular, for simulations of molecular motions at a space-time mesoscale, defined here as a length scale ranging from nanometers to micrometers and a time scale ranging from microseconds to milliseconds. Older molecular-dynamics algorithms and computer programs are not suitable for mesoscale simulations because they were formulated for the time scales, of the order of a microsecond or less, characteristic of such high-frequency degrees of freedom as stretching of molecular bonds.

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