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
Nasa Tech Briefs

Designs and Materials for Better Coronagraph Occulting Masks

Optical density and phase profiles are achromatized over a broad wavelength range.New designs, and materials appropriate for such designs, are under investigation in an effort to develop coronagraph occulting masks having broad-band spectral characteristics superior to those currently employed. These designs and materials are applicable to all coronagraphs, both ground-based and spaceborne. This effort also offers potential benefits for the development of other optical masks and filters that are required (1) for precisely tailored spatial transmission profiles, (2) to be characterized by optical-density neutrality and phase neutrality (that is, to be characterized by constant optical density and constant phase over broad wavelength ranges), and/or (3) not to exhibit optical-density-dependent phase shifts.

Posted in: Briefs, Materials, Design processes, Optics, Sun and solar, Materials identification


Turbulence and the Stabilization Principle

Further results of research, reported in several previous NASA Tech Briefs articles, were obtained on a mathematical formalism for postinstability motions of a dynamical system characterized by exponential divergences of trajectories leading to chaos (including turbulence).

Posted in: Briefs, Physical Sciences, Trajectory control, Mathematical analysis, Aerodynamics, Spacecraft, Turbulence


Improved Cloud Condensation Nucleus Spectrometer

Droplets can be sampled over a wide range of supersaturations in a short time.An improved thermal-gradient cloud condensation nucleus spectrometer (CCNS) has been designed to provide several enhancements over prior thermal- gradient counters, including fast response and high-sensitivity detection covering a wide range of supersaturations. CCNSs are used in laboratory research on the relationships among aerosols, supersaturation of air, and the formation of clouds. The operational characteristics of prior counters are such that it takes long times to determine aerosol critical supersaturations. Hence, there is a need for a CCNS capable of rapid scanning through a wide range of supersaturations. The present improved CCNS satisfies this need.

Posted in: Briefs, Physical Sciences


Better Modeling of Electrostatic Discharge in an Insulator

A model based on Kohlrausch relaxation gives improved fits to experimental data. An improved mathematical model has been developed of the time dependence of buildup or decay of electric charge in a high-resistivity (nominally insulating) material. The model is intended primarily for use in extracting the DC electrical resistivity of such a material from voltage-vs.- current measurements performed repeatedly on a sample of the material over a time comparable to the longest characteristic times (typically of the order of months) that govern the evolution of relevant properties of the material. This model is an alternative to a prior simplistic macroscopic model that yields results differing from the results of the time-dependent measurements by two to three orders of magnitude.

Posted in: Briefs, Physical Sciences, Mathematical models, Measurements, Conductivity, Insulation


Terahertz Mapping of Microstructure and Thickness Variations

Previously, it was not possible to separate microstructural and thickness effects using electromagnetic methods. A noncontact method has been devised for mapping or imaging spatial variations in the thickness and microstructure of a layer of a dielectric material. The method involves (1) placement of the dielectric material on a metal substrate, (2) through-the-thickness pulse-echo measurements by use of electromagnetic waves in the terahertz frequency range with a raster scan in a plane parallel to the substrate surface that do not require coupling of any kind, and (3) appropriate processing of the digitized measurement data.

Posted in: Briefs, TSP, Physical Sciences, Measurements, Imaging and visualization, Materials properties


Efficient Algorithmic Interleaver for Turbo Decoder

Permutations are computed when needed, rather than stored in lookup tables. An efficient bit-interleaving algorithm for a turbo encoder differs from prior such algorithms in that it does not require memory to store permutation mappings and can work with constituent decoders that produce multiple bit reliabilities per decoding stage. The algorithm can be implemented in hardware: The original version of the algorithm applies to a serially concatenated pulse position modulation (SCPPM) decoder that has been implemented in a field-programmable gate array (FPGA). The specific decoder can perform within 1 dB of the Shannon capacity on a Poisson channel and is suitable for use in optical data communications at megabit-per-second speeds. A bit interleaver is an essential component of any turbolike decoder, and the bit interleaver embodied in the present algorithm is essential for obtaining the capacity approaching performance of the specific SCPPM decoder and the affected SCPPM scheme. The algorithm can also be adapted to turbo decoders for modulation/coding schemes other than SCPPM.

Posted in: Briefs, Information Sciences, Physical Sciences, Mathematical models, Computer software and hardware, Integrated circuits, Wireless communication systems, Reliability


Generalized Approach to Prognosis for an Engineering System

Software combines signal forecasting and prognostic reasoning methods to predict system failures.This new generalized approach to prognostics can provide an automated early failure prediction of an engineering system or its components, often in time to prevent occurrence of hard failures. This approach has been demonstrated in a proof-of-concept software prototype, shown to accurately predict anomalies in the Mars Explorer Rover’s (MER) power systems using archived and model data. The approach differs from other attempted prognostic solutions in that it can interpret any sensed system trend, and not just specific failure modes with previously developed physicsof- failure models. The software employs an iterative reasoning process that implements (1) methods of forecasting signals represented by streams of sensor, telemetric, and other monitoring data and (2) new artificial intelligence methods for performing prognostic reasoning. This approach affords the following capabilities:

Posted in: Briefs, TSP, Information Sciences, Failure modes and effects analysis, Artificial intelligence, Prognostics, Systems engineering


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