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Showing papers by "Mitre Corporation published in 1984"


Journal ArticleDOI
TL;DR: In this correspondence it is shown that some binary Huffman codes contain a codeword that resynchronizes the decoder regardless of the synchronization slippage preceding thatcodeword.
Abstract: A problem associated with the use of variable-length source codes is that loss of synchronization may lead to extended errors in the decoded text. In this correspondence it is shown that some binary Huffman codes contain a codeword that resynchronizes the decoder regardless of the synchronization slippage preceding that codeword. Such codes are self-synchronizing in a probabilistic sense, yet require no additional system overhead. Some sufficient conditions are found for the existence or nonexistence of self-synchronizing Huffman codes for many classes of source probabilities. One of our results shows that many common languages can be encoded with self-synchronizing Huffman codes.

180 citations


Proceedings ArticleDOI
01 Apr 1984
TL;DR: Computer networks employ encryption several purposes, including private communication, message authentication, and digital signatures, which depend not only on the strength the cryptographic algorithms, but also on the procedures for key management.
Abstract: Computer networks employ encryption several purposes, including private communication, message authentication, and digital signatures. The correctness and security of these applications depend not only on the strength the cryptographic algorithms, but also on the procedures for key management.

74 citations


Journal ArticleDOI
TL;DR: Small memory codes are found which are optimized in the free-distance sense on the Gaussian channel which provide up to 4.8 dB of coding gain with 32 states over uncoded 8-PSK, a scheme having the same spectral efficiency as the codes described.
Abstract: Convolutional coding coupled with 16-PSK modulation is investigated for bandwidth efficient transmission. Rate 3/4, small memory codes are found which are optimized in the free-distance sense on the Gaussian channel. These codes provide up to 4.8 dB of coding gain with 32 states over uncoded 8-PSK, a scheme having the same spectral efficiency as the codes described. The performance is compared with earlier findings of Ungerboeck and some recent results on R = 2/3 coded 8-PSK. In addition, we present results of a channel transmission study to assess the performance of the four-state code on the band-limited nonlinear channel, and find that performance of the coded scheme degrades comparably with uncoded 8-PSK, i.e., coding gain is roughly preserved.

54 citations


Journal ArticleDOI
K. Brayer1
01 Nov 1984
TL;DR: In this paper, an adaptive computer communication routing algorithm is described, its application in space including a space segment design is presented, its actual implementation in real physical hardware is discussed, and system performance results as parameters are varied are presented.
Abstract: A potentially valuable implementation of a satellite computer communication packet switched network is one which is survivable and distributed. That is, a system which dynamically adapts to changing network element connectivities, changing interconnections of users, and is not dependent on any central unit for its own internal command and control. A laboratory prototype of such a system has been constructed of a group of computers which when given communication circuits between them will, acting autonomously, create a computer communication packet switching network and which will continually adapt to changes in connectivity. In this paper, an adaptive computer communication routing algorithm is described, its application in space including a space segment design is presented, its actual implementation in real physical hardware is discussed, and system performance results as parameters are varied are presented.

44 citations


Proceedings ArticleDOI
01 Apr 1984
TL;DR: The integrity-lock approach offers a "near-term" solution to the problems of database security, and makes use of existing technology emphasizing the use of encryption, and minimizing as much as possible the amount of trusted code required to insure the security of the data.
Abstract: This paper presents the integrity-lock approach to database security. The integrity-lock approach offers a "near-term" solution to the problems of database security. It makes use of existing technology emphasizing the use of encryption, and minimizing as much as possible the amount of trusted code required to insure the security of the data. The paper presumes the existence of an "off-the-shelf" database management system to perform most of the normal database management functions, and underlying secure operating system. Multiple variations of the integrity-lock approach are presented, with an accompanying description of the strengths and weaknesses of each approach. Finally, the paper suggests possible methods of offsetting some of the threaks to which the integrity-lock is vulnerable.

44 citations


Journal ArticleDOI
TL;DR: In this paper, the applicability of a nontactile acoustic sensing system, which provides range information about the distance between a sensor and the workpiece, is evaluated for the three-dimensional surface characterization task.
Abstract: Robotic seam tracking systems require three-dimensional information about the seam geometry. The applicability of a nontactile acoustic sensing system, which provides range information about the distance between a sensor and the workpiece, is evaluated for the three-dimensional surface characterization task. An algorithm for executing a two-dimensional surface height sampling of an unknown workpiece is developed and evaluated through digital simulation and hardware experimentation. The algorithm incorporates the limitations of the sensor's aperture size and uses only the range information provided by the sensing system. A recovery strategy is included if the sensor's aperture has been exceeded and range information is not available. The sampling procedure is found to be applicable for piecewise constant surfaces and surfaces with slight curvature. The effectiveness of the acoustic sensing system's surface characterization can be enhanced by using a priori knowledge of the workpiece. The sensing system appears to be promising for such industrial operations as part location and inspection.

37 citations


Journal ArticleDOI
H. Ma1, M. Poole
TL;DR: This paper provides performance analyses of a broad spectrum of error-correcting codes in an antijam communication system under worst-case partial-band noise jamming conditions and demonstrates the coding advantages available for systems operating with and without frequency diversity.
Abstract: This paper provides performance analyses of a broad spectrum of error-correcting codes in an antijam communication system under worst-case partial-band noise jamming conditions. These analyses demonstrate the coding advantages available for systems operating with and without frequency diversity. Utilizing both the exact approach (where possible) and upper-bounding approaches (Chernoff and union bounds), the decoded bit error rates for typical error-correcting codes (binary and M -ary, block and convolutional) have been obtained, and these codes have been compared according to the E_{b}/N_{0} required to achieve a bit error rate of 10-5. The best performance is achieved with the use of M -ary signaling and optimum diversity with M -ary codes, such as Reed-Solomon block codes, dual- k convolutional codes, convolutional orthogonal codes, or concatenated codes.

34 citations


Journal ArticleDOI
TL;DR: On souligne des preuves formelles de la concavite de rendement and de the convexite du temps de reponse dans des rapports techniques.

32 citations


Journal ArticleDOI
TL;DR: The Cospas-Sarsat project aims to develop a scheme in which a small battery-powered transmitter on a ship or aircraft would be activated, manually or automatically, in an accident, to emit a low-power omnidirectional signal that would be picked up by a satellite.
Abstract: The Cospas-Sarsat project aims to develop a scheme in which a small battery-powered transmitter on a ship or aircraft would be activated, manually or automatically, in an accident. Once activated, the transmitter, or beacon, would emit a low-power omnidirectional signal that would be picked up by a satellite. The satellite would relay the distress signal to an earth station, which in turn would send the message over conventional communication lines to a rescue center. Concurrently with development work on this project, and experiment with high-orbit geostationary search-and-rescue satellites is in progress. The geostationary experiment is aimed exclusively at the commercial maritime industry and is considering only the technical aspects of the beacon-to-satellite and satellite-to-earth links under uniform, controlled conditions. This program is using satellites and earth stations of Inmarsat, the 31-nation consortium that offers satellite communication services to merchant ships and offshore oil rigs.

28 citations


Journal ArticleDOI
TL;DR: It is shown that certain requirements for the use of Ada packages which cannot be expressed in Ada can be express in algebraic specification languages, and that such specifications can then be implemented in Ada.
Abstract: Our experience with design of Ada1 software has indicated that a methodology, based on formal algebra, can be developed which integrates the design and management of reusable components with Ada systems design. The methodology requires the use of a specification language, also based on formal algebra, to extend Ada's expressive power for this purpose. We show that certain requirements for the use of Ada packages which cannot be expressed in Ada can be expressed in algebraic specification languages, and that such specifications can then be implemented in Ada.

25 citations


Proceedings ArticleDOI
01 Apr 1984
TL;DR: The SCOMP system was developed by Honeywell FSD and is targeted at the Al class of the DoD Trusted Computer System Evaluation Criteria [CSC8S] as discussed by the authors.
Abstract: This paper reports on the analysis and evaluation of the SCOMP kernel verification. The SCOMP system was developed by Honeywell FSD and is targeted at the Al class of the DoD Trusted Computer System Evaluation Criteria [CSC8S]. It is currently under evaluation by the Department.of Defense Computer Security Center (DoDCSC). The work reported on here is significant in that the SCOMP system is the first commercially-available formally verified operating system. Furthermore, it is the first, system to be evaluated against.the A1 requirements for formal design specification and verification. The methods and procedures used for this analysis and evaluation will be of interest to future system designers, verifiers, and evaluators. The results of the verification, in particular the types of assurances that were gained, will also be discussed.

Journal ArticleDOI
TL;DR: Toxicological and carcinogenic effects were not clearly induced by the hair dye formulations and body weights and survival differed little between appropriate male and female treatment and control groups.
Abstract: The chronic toxicologic and carcinogenic potential of two oxidative and twelve non-oxidative hair dyes has been evaluated. The dyes were skin painted up to 3 times weekly on groups of 60 male and 60 female Eppley Swiss mice. Treatments were carried out for 20 months followed by terminal sacrifice. Nine months after treatments were initiated an intermediate sacrifice of ten mice per sex per group was carried out. Body weights and survival differed little between appropriate male and female treatment and control groups. Differences between treated and control groups in absolute and relative liver and kidney weights and in hematological and urinary values were not considered to be indicative of toxicologic effects. Microscopic examinations of the skin revealed occasional hyperplasia, necrosis, ulceration and other lesions not significantly increased by dye treatment. Chronic inflammation of the skin was observed in the control and treated mice and was significantly increased by one non-oxidative dye....

Journal ArticleDOI
R. Clapp1
TL;DR: In this article, the R-2R concept was modified to allow a full circle of array elements to be mapped onto a full-circle of beam ports, resulting in 360 degrees of simultaneous antenna beams, which can be used both for transmission and reception.
Abstract: The R.2R lens is a remarkable microwave device that provides perfect focusing, giving multiple simultaneous antenna beams from a circular or cylindrical array. However, the perfect focusing of the R-2R brings with it a serious limitation on angular coverage as a result of the angular doubling that enters when the array elements in the antenna are connected to the launcher elements on the lens periphery. We have now found a way to modify the R-2R concept so that a full circle of array elements can be mapped onto a full circle of beam ports. The new mapping makes use of hybrid junctions and either four or six physical lenses. The interconnections result in 360\deg of simultaneous antenna beams, each of which can be used both for transmission and for reception.

Journal ArticleDOI
TL;DR: Using the symmetry relations of the complex probability function (CPF), the algorithm developed by Humlíček (1979) to compute this function over the upper half plane can be extended to cover the entire complex plane.
Abstract: Using the symmetry relations of the complex probability function (CPF), the algorithm developed by Humlicek (1979) to compute this function over the upper half plane can be extended to cover the entire complex plane. Using the Humlicek algorithm the real and imaginary components of the CPF can be computed over the whole complex plane. Because of the relation between the CPF and other interesting mathematical functions, fast and accurate computer programs can be written to compute them. Such functions include the derivatives of the CPF, the complex error function, the complex Fresnel integrals, and the complex Dawson's functions. Fortran implementations of these functions are included in the Appendix.

Journal ArticleDOI
TL;DR: In this article, the authors investigate the multicollinearity among the property characteristics (regressor variables) and examine the stability of the estimated regression coefficients over time using ridge regression techniques.
Abstract: The use of multiple regression analysis as a tool of real estate valuation has received considerable attention in recent years. The primary objectives of this study are to investigate the multicollinearity among the property characteristics (regressor variables) and examine the stability of the estimated regression coefficients over time. Ridge regression techniques are used to partially adjust for the presence of collinearity. The results indicate that the ridge regression model provides a consistent set of properly signed, statistically significant regression coefficients throughout the sample period. Furthermore, ridge regression techniques are shown to have certain advantages over those of ordinary least squares for establishing logical and consistent values for specific property characteristics.

Journal ArticleDOI
Jose Nabielsky1
01 Jun 1984
TL;DR: This paper documents the efforts to connect the network front-ends to the 10 Mbps Ethernet,TM and presents some quantitative and qualitative results that may prove useful to those who, like us, are implementing a distributed-function architecture built upon a high-speed local area network.
Abstract: This paper documents our efforts to connect our network front-ends to the 10 Mbps Ethernet,TM and presents some quantitative and qualitative results that may prove useful to those who, like us, are implementing a distributed-function architecture built upon a high-speed local area network.

Journal ArticleDOI
TL;DR: In this article, the development of an integrated two-stage liquefaction process was traced, which involved conversion of a solvent refined coal (SRC) extract in an L.C. Finer second stage.

Journal ArticleDOI
22 Jun 1984-Science
TL;DR: A reliable and enduring C3l) system will be needed for a long time to come, even if a freeze on strategic nuclear forces is accomplished or other arms control successes achieved.
Abstract: Command, control, communications, and intelligence (C/sup 3/I) for nuclear forces are essential elements in the deterrence of nuclear war. The present C/sup 3/I system has vulnerabilities associated with its reliability, survivability, and endurance under attack, thereby weakening deterrence by increasing the ambiguity in our capabilities. Development of a reliable and enduring C/sup 3/I system would reduce this ambiguity. Its reliable, positive control of nuclear forces would give the national leadership more time to assess situations, ensure discriminate retaliation, and improve our ability to manage crises in general. These capabilities could help to stop a war rapidly should one start. A reliable and enduring C/sup 3/I system will be needed for a long time to come, even if a freeze on strategic nuclear forces is accomplished or other arms-control successes achieved. Indeed, C/sup 3/I may be the best source today of confidence-building measures to reduce tensions and the threat of nuclear catastrophe. 14 references, 5 figures.

Journal ArticleDOI
TL;DR: In this paper, the magnitude of error of differential reflectivity relative to antenna performance is illustrated by calculations from theory in a dual-receiver system operating with alternating horizontal and vertical polarization.
Abstract: The measurement capability of a polarization diversity radar is limited by several characteristics of the system and particularly by the performance of the antenna, which is characterized by the integrated cancellation ratio or integrated cross-polarization ratio. With reference to a transmitted or received signal of a desired polarization, these ratios describe the relative magnitude of the corresponding signal of opposite polarization generated as a result of antenna imperfections. In a single-receiver system operating with alternating horizontal and vertical polarization, the antenna performance tends to limit the accuracy with which the differential reflectivity can be measured. If the antenna pattern can be measured at orthogonal polarizations, then some of the bias introduced by antenna error can be removed from the resulting measurements. In this paper the magnitude of error of differential reflectivity relative to antenna performance is illustrated by calculations from theory. In a dual-r...

Proceedings Article
01 Jan 1984
TL;DR: The LOX Expert System (LES) as mentioned in this paper was developed as a tool for the constraint-based monitoring and analysis of propellant loading at the Kennedy Space Center (KSC).
Abstract: The LOX Expert System (LES), now being developed as a tool for the constraint-based monitoring and analysis of propellant loading at the Kennedy Space Center (KSC), is discussed. The loading of LOX at the KSC and its control and monitoring by the Launch Processing System are summarized, and the relevant problem for LES is presented. The LES database is briefly described, and the interaction of LES with KNOBS, a constraint- and frame-oriented knowledge-based system developed as a demonstration system in aid of tactical air mission planning, is the context of launch processing is discussed in detail. The design and fault isolation techniques of LES are also discussed.

Journal ArticleDOI
TL;DR: In this article, a cooperative word-meaning selector is proposed, which allows the computer to use various knowledge sources as it ''understands'' text, such as syntax, surface semantics, general world knowledge, and various types of contextual knowledge.
Abstract: An understander reading or listening to someone speak has to repeatedly solve the problem of word-meaning ambiguity, the selection of the intended meaning of a word from the set of its possible meanings. For example, the problem of pronominal reference can be considered as a choosing of the intended referent from the collection of entities which have already been mentioned or which can be inferred. Human understanders apply rules of syntax, surface semantics, general world knowledge, and various types of contextual knowledge to resolve word-sense or pronominal ambiguity as they process language. We describe a mechanism, called a cooperative word-meaning selector, which allows the computer to use various knowledge sources as it ``understands'' text. The word-meaning selector is part of a conceptual analyzer which forms the natural-language interface for a pair of multiprocess language processing systems. The first, called DSAM (distributable script applier mechanism), reads and summarizes newspaper articles making heavy reference to situational scripts. The second, ACE (academic counseling experiment), is a conversational program which automates certain parts of the academic counseling task. In each of these systems, a variety of knowledge sources, each managed by a distinct ``expert'' process, is brought to bear to enable the word-meaning selector to form the most plausible reading of a sentence containing ambiguous words.

Journal ArticleDOI
TL;DR: A wide variety of EMI sources can be as simple as a pulsing automotive spark plug or as complex as an aircraft-to-aircraft radio transmission as discussed by the authors, but the compatibility between sensitive microwave receivers and the rest of the radio-frequency world has yet to be achieved.
Abstract: Radio signals from pulsars and distant galaxies are difficult enough to detect on their own, but the problems encountered in making accurate astronomical observations at microwave frequencies are greatly compounded by terrestrial sources of electromagnetic interference (EMI). This paper discusses a wide variety of EMI sources as they affect the operation of radio-astronomy telescopes. These sources can be as simple as a pulsing automotive spark plug or as complex as an aircraft-to-aircraft radio transmission. Various protective countermeasures can be taken; however, compatibility between sensitive microwave receivers and the rest of the radio-frequency (RF) world has yet to be achieved.

Journal ArticleDOI
TL;DR: In this article, the polarization structure in spectral lines in solar type stars is computed using the method described by McKenna (1981, 1984a) using the frequency redistribution function used for these calculations is a linear combination ofRII andRIII.
Abstract: The polarization structure in several spectral lines in solar type stars is computed using the method described by McKenna (1981, 1984a). The frequency redistribution function used for these calculations is a linear combination ofRII andRIII. The line profiles and polarization structures have been computed for several weak solar resonance lines includingKi λ 7664 A, Sri λ4607 A, Baii λ4554 A, for various polar angles along the stellar disk. Both the line profiles and polarization structures as well as the center to limb behavior of the line center polarization agree well with observations.

Journal ArticleDOI
Ersch Rotholz1
TL;DR: In this paper, a formula for the output phase noise of a mixer when both the radio frequency RF and local oscillator LO carriers are impaired by phase noise is derived, using test results obtained with three discrete carriers.
Abstract: A formula is derived for the output phase noise of a mixer when both the radio frequency RF and local oscillator LO carriers are impaired by phase noise. The calculation uses test results obtained with three discrete carriers. An application of the noise formula to frequency synthesis is included.

Journal ArticleDOI
TL;DR: In this paper, the line absorption probability distribution functions and the reemission coefficients are derived for the non-coherent scattering functions RIII and RIV, where the appropriate line profile function for RIII is shown to be a simple Voigt function, while forRIV, the line absorbing probability distribution function is more complex involving a linear combination of two Voigts functions and another more complex probability distribution.
Abstract: The line absorption probability distribution functions and the reemission coefficients are derived for the non-coherent scattering functionsRIII andRIV. The appropriate line profile function forRIII is shown to be a simple Voigt function, while forRIV, the line absorption probability distribution function is more complex involving a linear combination of two Voigt functions and another more complex probability distribution. The structure of the reemission coefficients forRIII andRIV is then discussed.


Journal ArticleDOI
TL;DR: It is concluded that tests are available which, when used in combinations such as have been proposed by various authors, are capable of correctly identifying carcinogens and noncarcinogens with high confidence.

Journal ArticleDOI
Yan-Shek Hoh1
TL;DR: In this article, the authors examined the extremely low frequency (ELF) radiation from a horizontal antenna in the earth-ionosphere waveguide and focused on the application to field predictions in the Navy's ELF program.
Abstract: This paper examines the extremely low frequency (ELF) radiation from a horizontal antenna in the earth-ionosphere waveguide. Attention is focused on the application to field predictions in the Navy's ELF program. The field expressions in the presence of an anisotropic ground are obtained by a heuristic approach based upon a linear relationship between the horizontal electric and magnetic field components. Phasing anomalies at the Wisconsin Test Facility (WTF) have been observed since 1974. A theoretical model of this phenomenon is derived on the basis of a mutual coupling mechanism between the two WTF antenna elements and characteristics observed in measured field strength data. The diurnal variation of the radiated field is studied in terms of the attenuation rate, phase velocity, and height of the ionospheric reflecting layers. The diffusivity characteristics of realistic ionosphere are analytically modeled. A comparison of the predicted field strength/phase with the measured data yields excellent agreement.

Journal ArticleDOI
TL;DR: This paper presents algorithms for the computation of performance measures when the DMP is allowed to be any positive real-valued number, and two algorithms are presented which are computationally more efficient and not as cumbersome to implement as the obvious interpolation technique.

Book ChapterDOI
01 Jan 1984
TL;DR: An equivalent variation of the Herlestam and Johannesson (“Swedish”) algorithm that allows a much cleaner, easier and algebraically more organized approach to the algorithm’s process is described.
Abstract: This paper presents an analysis of the Herlestam and Johannesson (“Swedish”) algorithm, which heuristically computes discrete logarithms in GF(2p) using an iterative procedure An equivalent variation of the algorithm that allows a much cleaner, easier and algebraically more organized approach to the algorithm’s process is described A further modification to the algorithm which yields specific performance improvements is given Analysis of these methods is made through probability distributions which are appropriately selected to model the heuristic’s performance The significance of the algorithm is addressed by further comparing these methods to a procedure in which movement between iterations is governed by a random process rather than by a directed criterion