Information Science

P-Code-Enhanced Encryption-Mode Processing of GPS Signals

This is an improved method of processing without knowledge of the encryption code. A method of processing signals in a Global Positioning System (GPS) receiver has been invented to enable the receiver to recover some of the information that is otherwise lost when GPS signals are encrypted at the transmitters. The need for this method arises because, at the option of the military, precision GPS code (P-code) is sometimes encrypted by a secret binary code, denoted the A code. Authorized users can recover the full signal with knowledge of the A-code. However, even in the absence of knowledge of the A-code, one can track the encrypted signal by use of an estimate of the A-code. The present invention is a method of making and using such an estimate. In comparison with prior such methods, this method makes it possible to recover more of the lost information and obtain greater accuracy.

Posted in: Information Sciences, Briefs, TSP

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Software for Automated Reading of STEP Files by I-DEAS™

A program called "readstep" enables the I-DEAS™ computer- aided-design (CAD) software to automatically read Standard for the Exchange of Product Model Data (STEP) files. (The STEP format is one of several used to transfer data between dissimilar CAD programs.) Prior to the development of "readstep," it was necessary to read STEP files into I-DEAS™ one at a time in a slow process that required repeated intervention by the user. In operation, "readstep" prompts the user for the location of the desired STEP files and the names of the I-DEAS™project and model file, then generates an I-DEAS™program file called "readstep.prg" and two Unix shell programs called "runner" and "controller." The program "runner" runs I-DEAS™ sessions that execute readstep.prg, while "controller" controls the execution of "runner" and edits readstep.prg if necessary. The user sets "runner" and "controller" into execution simultaneously, and then no further intervention by the user is required. When "runner" has finished, the user should see only parts from successfully read STEP files present in the model file. STEP files that could not be read successfully (e.g., because of format errors) should be regenerated before attempting to read them again.

Posted in: Information Sciences, Briefs, TSP

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Using a Portfolio of Algorithms for Planning and Scheduling

The Automated Scheduling and Planning Environment (ASPEN) software system, aspects of which have been reported in several previous NASA Tech Briefs articles, includes a subsystem that utilizes a portfolio of heuristic algorithms that work synergistically to solve problems. The nature of the synergy of the specific algorithms is that their likelihoods of success are negatively correlated: that is, when a combination of them is used to solve a problem, the probability that at least one of them will succeed is greater than the sum of probabilities of success of the individual algorithms operating independently of each other. In ASPEN, the portfolio of algorithms is used in a planning process of the iterative repair type, in which conflicts are detected and addressed one at a time until either no conflicts exist or a user-defined time limit has been exceeded. At each choice point (e.g., selection of conflict; selection of method of resolution of conflict; or choice of move, addition, or deletion) ASPEN makes a stochastic choice of a combination of algorithms from the portfolio. This approach makes it possible for the search to escape from looping and from solutions that are locally but not globally optimum.

Posted in: Information Sciences, Briefs, TSP

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Software for Better Documentation of Other Software

The Literate Programming Extraction Engine is a Practical Extraction and Reporting Language- (PERL-) based computer program that facilitates and simplifies the implementation of a concept of self- documented literate programming in a fashion tailored to the typical needs of scientists. The advantage for the programmer is that documentation and source code are written side-by-side in the same file, reducing the likelihood that the documentation will be inconsistent with the code and improving the verification that the code performs its intended functions. The advantage for the user is the knowledge that the documentation matches the software because they come from the same file. This program unifies the documentation process for a variety of programming languages, including C, C++, and several versions of FORTRAN. This program can process the documentation in any markup language, and incorporates the LaTeX typesetting software. The program includes sample Makefile scripts for automating both the code-compilation (when appropriate) and documentation-generation processes into a single command-line statement. Also included are macro instructions for the Emacs display-editor software, making it easy for a programmer to toggle between editing in a code or a documentation mode.

Posted in: Information Sciences, Briefs, TSP

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Self-Supervised Dynamical Systems

Mathematical models describe coupled motor and mental dynamics. Some progress has been made in a continuing effort to develop mathematical models of the behaviors of multi- agent systems known in biology, economics, and sociology (e.g., systems ranging from single or a few biomolecules to many interacting higher organisms). This effort at an earlier stage was reported in "Characteristics of Dynamics of Intelligent Systems" (NPO- 21037), NASA Tech Briefs, Vol. 26, No. 12 (December 2002), page 48.

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Integrated Formulation of Beacon-Based Exception Analysis for Multimissions

BEAM has become a broadly applicable, highly capable means of automated diagnosis. Further work on beacon-based exception analysis for multimissions (BEAM), a method of real-time, automated diagnosis of a complex electromechanical systems, has greatly expanded its capability and suitability of application. This expanded formulation, which fully integrates physical models and symbolic analysis, is described architecturally in the figure.

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Artifacts for Calibration of Submicron Width Measurements

Dimensional tolerances as small as 1 nm should be possible. Artifacts that are fabricated with the help of molecular-beam epitaxy (MBE) are undergoing development for use as dimensional calibration standards with submicron widths. Such standards are needed for calibrating instruments (principally, scanning electron microscopes and scanning probe microscopes) for measuring the widths of features in advanced integrated circuits. Dimensional calibration standards fabricated by an older process that involves lithography and etching of trenches in (110) surfaces of single-crystal silicon are generally reproducible to within dimensional tolerances of about 15 nm. It is anticipated that when the artifacts of the present type are fully developed, their critical dimensions will be reproducible to within 1 nm. These artifacts are expected to find increasing use in the semiconductor-device and integrated-circuit industries as the width tolerances on semiconductor devices shrink to a few nanometers during the next few years.

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