March 1998

Briefs : Materials
Two Methods for Purifying Carbon Tetrachloride

Two methods have been developed to purify large batches of technical-grade carbon tetrachloride. The relatively impure carbon tetrachloride that had been purchased for use in infrared analysis of dissolved hydrocarbons proved that it could be purified. One method is spinning-band distillation, which...

Briefs : Manufacturing & Prototyping
Controlled-Orientation Short-Fiber Composite Bodies

A technique for depositing materials into position using a positive-displacement extruder to build up a body has been developed. This technique also includes a process to prepare composite materials through a solid free-body forming process containing directionally aligned short-fiber...

Briefs : Physical Sciences
Genetic Algorithms Help Design Dielectric Grating Filters

A computational method for designing all-dielectric grating electromagnetic filters involves a combination of (1) numerical simulation of filter performance via integral-equation solution of Maxwell's equations and (2) genetic algorithms to find acceptable combinations of filter-design...

Briefs : Materials
Nitrogen-Beam Source for Deposition of III/V Nitrides

A nitrogen-beam source has been developed to significantly improve the synthesis of wide-band-gap nitrides.

Briefs : Physical Sciences
Automated Dew-Point/Frost-Point Humidity Generator

The figure schematically illustrates an improved apparatus for generating a flow of gas with precise, stable humidity. Such flows are needed for calibration of dew-point, frost-point, and other humidity sensors.

Briefs : Electronics & Computers
Induced-Eddy-Current-Sensor Measurement of Semiconductor Performance

Recombination lifetime and minority-carrier lifetime are key performance parameters of semiconductor wafers used for microelectronics and solar cells. They are also particularly valuable for identifying low levels of impurities in wafers used for high-density integrated...

Briefs : Electronics & Computers
Radiative Measurement of Temperature in a MESFET Channel

A technique based on infrared-emission spectroscopy has been found to be useful for noncontact measurement of the temperature of a hot spot in the gate channel of a GaAs metal/semiconductor field-effect transistor (MESFET). Temperature measurements are important for the development of...

Briefs : Electronics & Computers
Rechargeable Microbatteries With Li Anodes Formed In Situ

Rechargeable, thin-film, lithium-based microbatteries of the proposed type would be manufactured in the discharged condition, and lithium anodes would be formed in situ during subsequent charging. In contrast, state-of-the-art rechargeable, thin-film, lithium-based microbatteries are...

Briefs : Electronics & Computers
Automated Cable-Analyzer System – ACAS

An instrumentation system automates the detection and location of faults in multiconductor electrical cables. It can accelerate diagnoses of aircraft, automotive, or industrial cables, while reducing the incidence of errors and of damage caused by test probes.

Briefs : Information Technology
LTI Approach to Adaptive Narrow-Band Feedforward Control

A unified theory of linear time-invariant (LTI) representations has been developed for use in the analysis and design of adaptive, narrow-band, feedforward controllers for systems characterized by harmonic regressors (the term "harmonic regressor" is defined below). Such controllers are...

Briefs : Software
Program for Design Analysis of Cache Memory

CACHESIM is a C-language computer program that simulates (1) cache-memory options associated with a computer hardware design concept and (2) related properties that can be expected to affect the overall performance of the computer, before the computer is constructed. Heretofore, the performance...

Briefs : Software
Software for Retrieval and Display of Planetary Data

The NASAView computer program provides access to, and display of, sets of scientific data in the Planetary Data System (PDS) archive. These data — totalling about 5 terabytes — were acquired during NASA's planetary-exploration missions and are stored along with descriptive information...

Briefs : Software
Program for Microanalysis of Composite Structures

Version 3.0 of the Boundary Element Solutions Technology Composite Modeling System (BESTCMS 3.0) is an advanced engineering software system for the microanalysis of fiber composite structures. BESTCMS is based on the BEST3D boundary-element program (COSMIC program LEW-15351). BESTCMS affords...

Briefs : Robotics, Automation & Control
Development of Small, Mobile, Special-Purpose Robots

A report presents a scenario for the proposed development of insectlike robots that would be equipped with microsensors and/or micromanipulators, and would be designed, variously, to crawl, burrow, swim, fly, or hop, to perform specific tasks in fields as diverse as exploration,...

Briefs : Robotics, Automation & Control
Adaptive Performance Optimization of Transport Aircraft

Adaptive performance optimization (APO) is an approach for improving aircraft performance without the need for extensive modifications of hardware. In this approach, one exploits existing redundant control-effector capabilities by providing for automatic reconfiguration of control-surface...

Briefs : Physical Sciences
Improving Distributions of Flux in Solar Thermal Receivers

A modification of design has been proposed to extend the longevity of cavity-type solar thermal receivers by improving the distribution of radiant solar flux in the cavities. A receiver of this type is used in conjunction with a solar concentrator, which is a mirror that focuses the...

Briefs : Physical Sciences
Weighted-Hyperbola Technique for Locating Pulsed Sources

The weighted-hyperbola technique is an iterative computational technique for processing data on the times of arrival of pulsed signals at more than four observing stations to determine location (in both space and time) of origin of the signals. (The location is overdetermined when data...

Briefs : Electronics & Computers
Dual-Channel Precision Signal-to-Noise Ratio Generator

During the development and testing of signal processing systems, it is useful to generate test signals in the laboratory in order to quantify system parameters such as dynamic range, processing gain, or frequency resolution. Furthermore, it is convenient to have two test signals that are...

Briefs : Manufacturing & Prototyping
Vertical Centrifugal Investment-Casting Machine

The need for improved investment castings at Marshall Space Flight Center's Rapid Prototyping Lab has led to the development of a simple machine for centrifugal investment casting of shells. This machine spins a radially symmetric shell about its own axis in a vertical orientation. This rotational...

Briefs : Information Technology
Training of Neural Networks by Modified Taguchi Techniques

Modified Taguchi techniques of robust design optimization are used in an innovative method of training artificial neural networks — for example the network shown in the figure. As in other neural-network-training methods, the synaptic weights (strengths of connections between neurons)...

Briefs : Manufacturing & Prototyping
Two-Sided Tools for Layup of Composite Sandwich Panels

A simple change in the design of tools used in manufacturing laminated-composite-material sandwich panels reduces the floor area needed to store the tools. To give meaning to a description of this modification, it is necessary to explain the basic function and original design of these tools:...

Briefs : Physical Sciences
Convex-Grating Spectrometer With Two Spherical Mirrors

The figure shows the basic optical configuration of an improved all-reflecting imaging spectrometer. This spectrometer would differ from older spectrometers in several respects, one being its convex spherical diffraction grating: heretofore, spectrometers have contained, variously, concave...

Briefs : Information Technology
Software for Assessing Effects of Designs on Operations

The Operations Impact Assessor (OIA) computer program facilitates rapid assessment of the effects of designs of spacecraft on spacecraft-processing operations at a launch site. OIA is a user-friendly, object-oriented, artificial-intelligence application program that features model-based...

Briefs : Electronics & Computers
Process for Fabrication of Micro Fluidic Structures

Through an innovative microfabrication process, enclosed microstructures are created for "laboratory on a chip" applications, such as medical diagnostics. These microstructures include capillaries, tunnels, pipettes, reaction vessels, and cavities. Using only conventional lithographic...

Briefs : Robotics, Automation & Control
Using a Jet Pump To Alter the Inlet Swirl of a Turbopump

An analysis of empirical data on low-frequency oscillations in the inlet flow of a turbopump has led to the conclusion that these oscillations could be reduced or eliminated with suitable design of a jet pump to alter the inlet swirl. The oscillations in question are of fluid-dynamic...

Briefs : Materials
Alumina/Ethanol Colloidal Suspensions for Seeding Hot Flows

The alumina for making a suspension according to this concept must be in the form of a highly pure (preferably >99.99 percent) powder with a suitable particle-size distribution — preferably monodisperse with a mean particle size of a fraction of a micron, as illustrated in the...

Briefs : Physical Sciences
Silicon Heat Exchanger for Use at Low Temperatures

A heat exchanger made largely from pieces of single-crystal silicon has been designed for use as a recuperator in a reverse-Brayton-cycle cryocooler. Its design is optimized for transferring heat between counterflows of neon at a mass flow rate of 0.7 g/s, with an inlet temperature of 300 K and...

Briefs : Electronics & Computers
Lightweight Dual-Beam Reflector Antenna

The figure illustrates a lightweight composite-material dual-beam reflector antenna for the SeaWinds spaceborne scatterometer instrument, which operates in the Ku band and is designed to measure wind velocities at the surface of the ocean. The design of the antenna could also be of interest for...

Briefs : Manufacturing & Prototyping
Fabrication of Thin-Film Type-S Thermocouples

Processes for fabricating thin-film type-S thermocouples on metal and silicon nitride substrates (see figure) have been developed. (A type-S thermocouple comprises one leg made of platinum and the other leg made of an alloy of platinum with a rhodium content of 10 percent.) Thin-film type-S...

Briefs : Information Technology
Improved Design of Adaptive Feedforward Tracking Systems

An improved method of analysis and design offers the potential to enhance the performances of adaptive feedforward tracking systems. The method can, in principle, make it possible to increase such performance measures as rates of convergence and noise-cancellation ratios, without need for...

Briefs : Mechanical & Fluid Systems
Flexible Actuators for Small, Mobile, Special-Purpose Robots

A report discusses flexible microactuators for a proposed generation of small, mobile, special-purpose robots. Aspects of this topic were discussed in two previous articles in NASA Tech Briefs: "Thin-Film, Light-Energized Bimorph Micromechanical Actuators" (NPO-19607), Vol. 20, No. 8...

Briefs : Electronics & Computers
Sight-to-Touch Translator

The sight-to-touch translator (ST3) is a conceptual electronic apparatus that would generate a tactile representation of visible objects in its vicinity. The ST3 would be worn by a blind person; the tactile display would help the wearer to visualize nearby obstacles and act to avoid them. Thus,...

Briefs : Software
Software for Tooth-Contact Analysis of Spiral Bevel Gears

The SBGTAPER computer program implements a method for design and generation of spiral bevel gears that feature tapered teeth with localized bearing contact and a low level of transmission errors. The influence of misalignment on transmission errors and shift of bearing contact were...

Briefs : Information Technology
Expressing Object-Oriented Concepts in Fortran 90

A methodology for object-oriented programming in Fortran 90 has been developed. The methodology provides for emulation of the most important object-oriented concepts of C++; namely, classes (including abstract data types, encapsulation, and function overloading), inheritance, and dynamic...

Briefs : Mechanical & Fluid Systems
Gas Buffer Seal

The figure presents a simplified view of a shaft seal that provides a small flow of neutral buffer gas to prevent contact between different gases contained in two adjacent regions along the shaft. In the original application, the shaft couples a hydrogen-burning turbine with a high-pressure oxygen pump, and helium is used as the...

Briefs : Electronics & Computers
Optical Horizontal-Displacement Sensors for Crane Payloads

Sensors made largely of commercially available optical and electronic components are being developed for use in measuring small horizontal displacements of payloads suspended below cranes at the ends of nominally vertical cables. The outputs of these sensors would be used in...

Briefs : Physical Sciences
Equations of State for Fluid Mixtures at High Pressures

A method that includes the use of modified equations of state has been developed to enable noniterative, efficient computation of the thermodynamic behaviors of gases and liquids at temperatures >100 K and pressures from 1 to 100 MPa. The method is intended to be particularly useful for...

Briefs : Materials
Coating SiC Fiber Tows With Polymer/Silicon Slurries

The figure schematically illustrates an apparatus and process in which a continuous tow of silicon carbide fibers is coated and infiltrated with a polymer/silicon slurry. A compact of such coated, infiltrated fiber tows is subsequently heated to a temperature > 1,200 °C in nitrogen to...

Briefs : Manufacturing & Prototyping
Removable Fillers for VPS Fabrication of Closed Channels

An improved process has been devised for making closed channels (e.g., coolant channels) in a heat-exchanger liner or a similar metal object. The process involves the following steps: First, grooves destined to become closed channels are machined into the object from one surface. Next, a...


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