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Characteristics of Supercritical Transitional Mixing Layers

This report describes a study of threedimensional, temporal mixing layers between different fluids initially flowing at different velocities under supercritical conditions. The study involved direct numerical simulations by use of a validated mathematical model of high-pressurefluid behavior that has been described in a number of prior NASA Tech Briefs articles. In some cases, the fluids were heptane and nitrogen; in other cases, they were hydrogen and oxygen. In all these simulations, the mixing layers underwent transition to turbulence.

Posted in: Briefs, TSP

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Design Concepts for the ISS TransHab Module

Twelve reports present concepts for the design of structural and functional systems, subsystems, and components of the proposed TransHab module — an inflatable, lightweight habitation module that would be used by crewmembers of the International Space Station and would serve as a prototype of habitation modules for future spacecraft on long missions (e.g., missions to Mars). The TransHab module would be a unique hybrid structure that would combine the packaging and mass efficiencies of an inflatable structure with the advantages of a load-bearing hard structure. The governing design concept is one of a high degree of integration and multifunctionality of all parts of the Trans- Hab system. The reports include sketches (some containing estimated dimensions) and discussions of engineering requirements. There are also numerous discussions of human factors (psychological, social, and physiological) that affect many aspects of design. Although the reports address issues specific to the TransHab module, some of the concepts discussed may be applicable to the design of temporary or transportable housing for use on Earth.

Posted in: Mechanics, Briefs, TSP

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The Complexity of the Diagnosis Problem

A report presents a study of the complexity of an algorithm that performs model-based diagnosis of a complex hardware system. [In model-based diagnosis, an algorithm detects logical inconsistencies between observational data and a description (mathematical model) of the system.] In the study, the problem of detecting logical inconsistencies is transformed into the problem of finding prime implicants of a monotone Boolean function. This transformation enables utilization of the welldeveloped machinery of Boolean function theory, not directly accessible in the logical approach: one can work with monotone Boolean functions described by polynomial-size monotone circuits instead of attempting to deal with logical objects and performing exhaustive searches in order to extract all desired information. One especially notable result achieved in this study through the Boolean-function approach is the first analytical proof that the diagnosis problem is NP-complete. The report asserts that the discovery of the connection between diagnosis and the Boolean functions may afford new means to solve the diagnosis problem — in particular, to develop diagnostic algorithms that take super-polynomial amounts of time, in contrast to the exponential amounts of time heretofore needed to solve NP-complete problems.

Posted in: Briefs, TSP

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HEMT Amplifiers and Equipment for Their On-Wafer Testing

Power levels in CPW circuits can be measured without packaging. Power amplifiers comprising InP-based high-electron-mobility transistors (HEMTs) in coplanar-waveguide (CPW) circuits designed for operation at frequencies of hundreds of gigahertz, and a test set for on-wafer measurement of their power levels have been developed. These amplifiers utilize an advanced 35-nm HEMT monolithic microwave integrated-circuit (MMIC) technology and have potential utility as local- oscillator drivers and power sources in future submillimeter-wavelength heterodyne receivers and imaging systems. The test set can reduce development time by enabling rapid output power characterization, not only of these and similar amplifiers, but also of other coplanar-waveguide power circuits, without the necessity of packaging the circuits.

Posted in: Briefs

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Capillography of Mats of Nanofibers

These mats can be the basis of small devices and instruments. Capillography (from the Latin capillus, “hair”, and the Greek graphein, “to write”) is a recently conceived technique for forming mats of nanofibers into useful patterns. The concept was inspired by experiments on carpetlike mats of multiwalled carbon nanotubes. Capillography may have the potential to be a less-expensive, less- time-consuming alternative to electron- beam lithography as a means of nanoscale patterning for the fabrication of small devices and instruments.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Nano-Engineered Catalysts for Direct Methanol Fuel Cells

Small particle sizes and large surface areas can be produced economically and consistently. Nano-engineered catalysts, and a method of fabricating them, have been developed in a continuing effort to improve the performances of direct methanol fuel cells as candidate power sources to supplant primary and secondary batteries in a variety of portable electronic products. In order to realize the potential for high energy densities (as much as 1.5 W•h/g) of direct methanol fuel cells, it will be necessary to optimize the chemical compositions and geometric configurations of catalyst layers and electrode structures. High performance can be achieved when catalyst particles and electrode structures have the necessary small feature sizes (typically of the order of nanometers), large surface areas, optimal metal compositions, high porosity, and hydrophobicity.

Posted in: Materials, Briefs, TSP

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Polymer Electric Storage



Posted in: Blog

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