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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.

Posted in: Briefs, TSP, Physical Sciences

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Improving Thin Foil X-Ray Mirrors

Resolution and diameter would be increased.A proposal has been made to develop improved thin foil, replicated conical mirrors for use in x-ray astrophysics. In the NASA astrophysical programs in which such mirrors are used, they are required to be lightweight, and to offer moderate angular resolution and high throughput to afford required sensitivity in the photon-energy band from 0.1 to 20 keV. In the proposed improvement program, emphasis would be placed on increasing resolution and diameter:

Posted in: Briefs, Physical Sciences

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First-Generation Integrated Free-Flying Micro-Spacecraft

The concept of free-flying micro-spacecraft was to develop a miniature spacecraft system fully integrated with a scientific sensor. A fleet of such tiny spacecraft would be deployed in space for multi-probe measurements of a three-dimensional phenomenon and to separate the spatial/temporal variations of that phenomenon. They would measure a parameter of interest, process the data onboard, and communicate the data in real time.

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DNS of a Transitional Supercritical C7H16/N2 Mixing Layer

This report discusses direct numerical simulations (DNS) of a mixing layer, between a nitrogen stream and a heptane stream initially flowing at different velocities, under supercritical conditions and undergoing a transition to turbulence. Thermodynamically, supercritical conditions prevail when either the temperature or the pressure exceeds its critical value; the critical regime is in particular characterized by the existence of a single phase. The governing conservation equations were formulated according to fluctuation-dissipation (FD) theory, in which the low-pressure typical transport properties (viscosity, diffusivity, and thermal conductivity) are complemented, at high pressure, by a thermal-diffusion factor.

Posted in: Briefs, Physical Sciences

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Built-in "Health Check" for Pressure Transducers

Calibrations could be verified approximately, without removing transducers to calibration laboratories. "Health check" would be built into pressure transducers, according to a proposal, to enable occasional, rapid, in situ testing of the transducers between normal pressure-measurement operations. The health check would include relatively simple devices that, upon command, would provide known stimuli to the transducers. The responses of the pressure transducers to these stimuli would be analyzed to quantify (at least approximately) deviations from the responses expected from previous rigorous calibrations. On the basis of such an analysis, a given pressure transducer could be removed from service, rigorously recalibrated, or continued in use with corrections applied for calibration drift. The use of the health check could provide timely warnings of pressure-transducer malfunctions and make it possible to retain confidence in the calibrations of pressure transducers while reducing the frequency with which they are replaced or subjected to full laboratory recalibration.

Posted in: Briefs, TSP, Physical Sciences

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All-Pressure Fluid-Drop Model Applied to a Binary Mixture

A report presents a computational study of the subcritical and supercritical behaviors of a drop of heptane surrounded by nitrogen, using the fluid-drop model described in "Model of a Drop of O2 Surrounded by H2 at High Pressure" (NPO-20220) and "The Lewis Number Under Supercritical Conditions" (NPO-20256), NASA Tech Briefs, Vol. 23, No. 3 (March 1999), pages 66-70. In this model, the differences between subcritical and supercritical behaviors are identified with length scales. The report compares results of the computations with data from microgravity experiments on large drops at temperatures and pressures in the sub- and supercritical regimes.

Posted in: Briefs, TSP, Physical Sciences

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Validation of All-Pressure Fluid-Drop Model

A report presents a computational study of the subcritical and supercritical behaviors of a drop of heptane surrounded by nitrogen. The subject matter is basically same as that of the report described in the preceding article, except that the Lewis-number issue is not addressed in detail; however, this article presents the full set of equations which lack in the former. As in the preceding case, the results of the computations are compared with data from microgravity experiments on drops of heptane evaporating in nitrogen at temperatures and pressures in the sub- and supercritical regimes, and conclusions are drawn regarding the accuracy of (1) the mathematical model used in the present study and (2) the limitation on accuracy of a traditional model (known as the d2 law) at supercritical pressures. The conclusions stated in the report are essentially a subset of the conclusions stated in the report described in the preceding article.

Posted in: Briefs, TSP, Physical Sciences

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