Special Coverage

Supercomputer Cooling System Uses Refrigerant to Replace Water
Computer Chips Calculate and Store in an Integrated Unit
Electron-to-Photon Communication for Quantum Computing
Mechanoresponsive Healing Polymers
Variable Permeability Magnetometer Systems and Methods for Aerospace Applications
Evaluation Standard for Robotic Research
Small Robot Has Outstanding Vertical Agility
Smart Optical Material Characterization System and Method
Lightweight, Flexible Thermal Protection System for Fire Protection

Thermodynamic Instability of InxGa1–xAs/GaAs Quantum Dots

A report describes experiments that generated evidence of thermodynamic instability of nanometer-size islands (quantum dots) in InxGa1–xAs grown on GaAs. InxGa1–xAs/GaAs specimens were grown by metal-organic chemical vapor deposition, using various partial pressures of AsH3. Examination of specimens by force microscopy, electron microscopy, and low-temperature photoluminescence spectroscopy revealed differences in island formation at different partial pressures of AsH3, including differences in (1) surface coverages of islands, (2) ratios between numbers of coherent and incoherent islands, (3) sizes and shapes of islands after annealing, and (4) thicknesses for the onset of the Stranski-Krastanow (S-K) transformation (in which quantum dots form spontaneously in a second semiconductor deposited on a lattice-mismatched first semiconductor once the second semiconductor reaches a critical thickness, which is typically a few molecular layers).

Posted in: Briefs, TSP, Physical Sciences, Microscopy, Spectroscopy, Thermodynamics, Nanotechnology, Semiconductors


Power Supply for Miniature Quadrupole Mass Spectrometer

This lightweight, low-power system is designed to operate unattended for a long time.A lightweight, low-power-consumption power supply has been developed to generate a combination of radio-frequency (RF) and dc voltages needed for the operation of a miniature quadrupole mass spectrometer that could operate unattended in the field for a long time, possibly using a battery as an energy source. More specifically, the circuit is designed to supply large, variable, frequency- and amplitude-stable RF voltages, variously floating or superimposed on positive or negative dc voltages, for application to primarily capacitive mass-spectrometer loads with capacitances of the order of 50 pF.

Posted in: Briefs, Test & Measurement, Integrated circuits, Electric power, Energy consumption, Test equipment and instrumentation


Computer Program Automates Thermal Analyses

This program reduces the costs of thermal analyses of hypersonic flight systems.A computer program (see figure) has been developed to serve as a time- and cost-effective means of automating thermal analyses of such hypersonic flight systems as the space shuttle orbiter, the National Aerospace Plane (NASP), and the crew return vehicle (CRV). Heretofore, thermal analyses of the space shuttle orbiter have been performed manually and have, therefore, been hindered by long cycle times and the risk of human error. The present thermal-analysis automation program, which represents an advance in the state of the art, is expected to enable the sizing and analysis of thermal protection systems (TPSs) of re-entry space vehicles (RSVs) while increasing the accuracy of the analyses, reducing the amounts of labor needed to perform the analyses, and reducing the costs of the analyses.

Posted in: Briefs, TSP, Physical Sciences, Computer software and hardware, Performance upgrades, Thermal testing, Hypersonic and supersonic aircraft, Spacecraft


Automated Generation of Acoustic-Propagation Computer Codes

Traditionally labor-intensive programming tasks are performed automatically by software.A computer program written within the Mathematica software system automatically generates FORTRAN computer codes that numerically simulate, with high accuracy, the acoustical physics of complex unbounded three-dimensional or bounded two-dimensional flow fields. The program is a significant contribution to the field of computational aeroacoustics (CAA), which combines the traditional disciplines of acoustics and computational fluid dynamics (CFD). The program was developed, as a first step, to accelerate and facilitate analysis of noise generated by turbofan aircraft engines. It can also be applied in many other endeavors that involve the generation, propagation, and/or scattering of electromagnetic as well as acoustic waves, or in which there are requirements to obtain highly accurate solutions of systems of hyperbolic partial differential equations that describe physical phenomena in complex environments. Prior to the development of this program, considerable programming effort was necessary even to obtain a low-accuracy computer code for a typical application. The code generated automatically by this program is far more accurate and efficient.

Posted in: Briefs, TSP, Physical Sciences, Computational fluid dynamics, Computer simulation, Acoustics, Aerodynamics


Rule-Based "Intelligent" Monitoring Software

This program helps to automate the analysis of batch or real-time data.Dryden Flight Research Center has developed a computer program that performs signal management for analysis in real time (SMART). This program, called "SMART," has been effectively used since 1991 in F-18, X-31, LASRE, and X-33 programs.

Posted in: Briefs, Physical Sciences, Artificial intelligence, Computer software and hardware, Sensors and actuators


Comprehensive Micromechanics-Analysis Code (MAC/GMC)

Composite-material structures with complex thermomechanical load histories can be analyzed.Micromechanics Analysis Code With Generalized Method of Cells (MAC/GMC) is a comprehensive, user-friendly, efficient computer program that predicts the elastic and inelastic thermomechanical responses of continuous and discontinuous composite materials with arbitrary internal microstructures and reinforcement shapes. This program enables the efficient analysis of composite structures subjected to complex thermomechanical load histories. MAC/GMC won second place in the 1997 NASA Software of the Year competition and has been applied in industrial, government, and academic settings to such diverse composite-material structures as turbine parts, tires, and even brain tissues.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Computer simulation, Composite materials


Software for Analyzing Forth Programs

Various parts of code can be categorized and quantified in selectable ways.Forth Source Code Analysis Tool Set (FSCATS) is a computer program that provides a wide range of capabilities for documenting, analyzing, and reverse-engineering computer programs written in the Forth programming language. FSCATS also aids in the management of software, estimating costs of software, and development of metrics for characterizing software.

Posted in: Briefs, Information Sciences, CAD, CAM, and CAE, Computer software and hardware


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