Showing papers by "Mitre Corporation published in 1989"

Constraint propagation algorithms for temporal reasoning: a revised report

Abstract: This paper revises and expands upon a paper presented by two of the present authors at AAAI 1986 [Vilain & Kautz 1986]. As with the original, this revised document considers computational aspects of interval-based and point-based temporal representations. Computing the consequences of temporal assertions is shown to be computationally intractable in the interval-based representation, but not in the point-based one. However, a fragment of the interval language can be expressed using the point language and benefits from the tractability of the latter. The present paper departs from the original primarily in correcting claims made there about the point algebra, and in presenting some closely related results of van Beek [1989].

Automatic determination of grain size for efficient parallel processing

Abstract: The authors propose a method for automatic determination and scheduling of modules from a sequential program.

180 degrees lumped element hybrid

Abstract: A technique for the design of 180 degrees lumped-element hybrids is described which yields electrical performance comparable to the transmission line version but takes up significantly smaller area of GaAs. Broader bandwidth can be obtained by cascading two lumped-element sections. This technique is applicable to other distributed devices such as the 90 degrees branch-line hybrid and the Wilkinson power divider. The layout of an actual hybrid designed for a center frequency of 7.95 GHz is shown. >

Application of stochastic control techniques to chaotic nonlinear systems

Abstract: A control algorithm based on stochastic control techniques is devised for chaotic nonlinear systems. The algorithm uses a state estimator based on the Kalman filter, and yields performance improvements in at least some regions of state space with respect to that obtainable by use of a controller utilizing only the conditional mean of the system state vector. The method is applied to two typical chaotic nonlinear systems (the Henon-Heiles system and the Lorenz system), and their behavior with control is explored numerically. >

Finite-state noiseless covert channels

Abstract: Covert channels in a multilevel secure computer system can be exploited by malicious software to compromise information. The maximum information rate of a known channel is determined by modeling the channel as a communications channel and calculating its capacity. The capacity of an important class of covert channels, finite-state noiseless channels with nonuniform transition times, is found by adapting a technique suggested by Shannon (1964). >

Chaos: a real phenomenon in power electronics

Abstract: An introductory tutorial on chaotic behavior in DC-DC convertors is presented. Chaos is characterized by an emipirical spectrum which has a continuous component, and may even have no discrete components. Chaotic behavior frequently occurs when a power converter operates in a protective mode such as in a short-circuit or overload condition. Chaotic behavior in power converters is described in terms of phase-plane (state-space) trajectories. A description is given of a particular form of buck regulator circuit without PWM (pulse-width modulation) drive and without current sensing, i.e. a form of ripple-regulator. Simulation and experimental data for the circuit are presented and discussed. Two other similar circuits exhibiting chaotic behavior are also considered. >

An FFT based technique for suppressing narrow-band interference in PN spread spectrum communications systems

Abstract: Analyses and performance predictions of an FFT-based narrowband interference suppression filter for use in PN (pseudonoise) spread-spectrum communications systems are presented. The received baseband signal is processed in fixed-length blocks, transformed to the frequency domain with an FFT, filtered there by using an appropriate weighting, and then transformed back to the time domain. A general expression for the symbol matched filter signal-to-noise ratio (SNR) is given in terms of signal parameters and filter weighting coefficients. An optimal (maximum SNR) filter scheme and several suboptimal thresholding algorithms are discussed. Performance predictions, based on a realistic high-frequency interference model, are presented for these algorithms and FFT-based architecture. >

Mandatory security in object-oriented database systems

Abstract: A multilevel secure object-oriented data model (using the ORION data model) is proposed for which mandatory security issues in the context of a database system is discussed. In particular the following issues are dealt with: (1) the security policy for the system, (2) handling polyinstantiation, and (3) handling the inference problem.A set of security properties that has been established in this paper is more complete than those that have been proposed previously. Finally we describe how certain security constraints are handled by our model.

Datalink controller interface

Abstract: A digital data link is provided between an air traffic controller at a ground station and the pilot of an aircraft through digital communication between a computer on that aircraft and a ground-based computer located at the ground station and including an associated display screen containing a spatial representation of the airspace around the aircraft as well as a representation of the location of the aircraft in that airspace. A pointing device is moved to cause movement of a cursor on the display screen, beginning at the representation of the aircraft, corresponding to the movement of the aircraft that the controller intends. In response to this cursor movement, there is generated on the screen a cursorline representative of the movement of the cursor and thus of the intended path of aircraft. The ground-based computer calculates, from the beginning and the end points of the cursorline, and the length of the cursorline, the intended heading of the aircraft and the distance to be flown. Digital data related to calculated intended heading and distance is transmitted to the aircraft computer.

Secure query-processing strategies

Abstract: Strategies for secure query processing multilevel-security database management systems are proposed. They are carried out by query modification, a technique that has been used for enforcing integrity constraints and providing view mechanisms. The technique consists of replacing the query the user presents with one that, when evaluated, will perform the desired function. In the case of a view mechanism, the names of views referenced in the query are replaced by the definitions of the views in terms of base relations. The basic strategy and two variants-adding environmental information and using graphs-are described. The performance of the strategies is examined. >

National Airspace System demand and capacity modeling

Abstract: The US Federal Aviation Administration (FAA) has undertaken an effort to model and analyze the performance of the National Airspace System (NAS), a system that encompasses the nationwide airport and airspace network in the United States. This effort and the resulting capability, called the National Airspace System Performance Analysis Capability (NASPAC), are based on operations research and computer-modeling techniques. The authors provide a detailed description of a discrete-event simulation model of the NAS developed as part of the NASPAC project. Special emphasis is placed on the model's representation of the airport and airspace entities that constitute the NAS and the airspace user demand. The authors present the results of an initial analysis of the possible impact of a proposed new airport at Denver, CO, and conclude with a discussion of the potential future direction of NASPAC. >

Fabrication of n(+)/p InP solar cells on silicon substrates

Abstract: InP films were grown by MOCVD on Si GaAs substrates (as well as on InP substrates, included as controls), and were used to fabricate solar cells, using the Spitzer et al. (1987) technique. Contact to the substrate was made with Al-Ti-Pd-Ag to the Si wafers and with Au-Zn alloy to the GaAs wafers, while contract to the front was made with Cr-Au-Ag. Air mass zero efficiencies were found to be 7.1 percent for Si-substrate cells and 9.4 percent for GaAs-substrate cells.

Dynamic address binding in communication networks

Abstract: A communications network comprising a plurality of destination stations and associated server stations, each destination station having a unique destination address, and a unique destination name containing no semantic information relating to an associated server station, each server station having a unique server address, and being capable of storing the destination address of each destination station with which it is associated, the server address being found by an algorithmic manipulation of the destination name of any destination station that is associated with the server station.

A distributed batching system for parallel processing

Abstract: We describe the design and implementation of a novel, network batching system that uses loosely coupled SUN workstations on an Ethernet The system allows one to use multiple SUNs in a variety of configurations for parallel computing

Real-time equalization of A/D converter nonlinearities

Abstract: A report is presented on a design, implemented with current technology, of a real-time compensator circuit. The author demonstrates the feasibility of using the phase-plane approach for real-time equalization of analog nonlinearities in the digital domain. It is shown that such compensation schemes have the potential to improve performance by removing slew-rate-dependent errors in the critical sample-hold circuits in sampling A/D converters. Linearity, as measured by the SFDR (spurious-free dynamic range), improved by more than 2 b over most of the Nyquist bandwidth for a 12-b, 5-MSps state-of-the-art A/D converter. >

Software storming: combining rapid prototyping and knowledge engineering

Abstract: A method for rapidly producing highly functional prototypes is described. This method, called software storming, involves experts in the initial design and implementation of a system during an intense development effort that combines knowledge engineering with the latest advances in software-development technology and workstation hardware The experiment described is a test of tools and techniques developed in the field of artificial intelligence as well as the first step in the development of software storming. Using this approach, the authors developed a software prototype which possesses significantly more functionality than a standard prototype, in less than four months. >

On the Vandermonde matrix

Abstract: (1989). On the Vandermonde Matrix. The American Mathematical Monthly: Vol. 96, No. 10, pp. 921-924.

Measured wideband HF mid-latitude channel characteristics

Abstract: The authors present the results of HF ionospheric channel measurements on a 2000-km midlatitude path between Florida and Massachusetts performed during September 1988 and February/March 1989 using a 1-MHz bandwidth direct-sequence-pseudonoise (DSPN) probing signal. The channel impulse response is extracted by correlating the received probe signal with a local DSPN reference. Doppler information is obtained by Fourier-transforming a succession of these impulse responses. The channel is characterized in terms of its time, its Doppler spread, and the autocorrelation and distribution functions of the received power. The data indicate that this particular channel can operate within 2 dB of the ideal matched-filter signal-to-noise ratio given (1) a decision-directed Rake modem without Doppler correction and (2) a low-overhead backlink for infrequent (a few times, a minute at most) and small (1- or 2-dB increments) transmit power adjustments. >

An engineering and policy analysis of fiber introduction into the residential subscriber loop

Abstract: An engineering model which provides a framework for evaluating alternative network architectures for providing fiber to the home is presented. The analysis employs this model to construct estimates of the average cost per subscriber of several network alternatives which have been proposed in the literature. The results identify two possible network architectures, the active double star and the passive double star, as particularly attractive alternatives. Sensitivity analyses provide detail on the critical contributors to overall costs. Several policy issues raised by the analysis, including the proper allocation of risk from fiber-to-the-home investments, are considered. >

An investigation of ARQ and hybrid FEC-ARQ on an experimental high latitude meteor burst channel

Abstract: A computer investigation of error-control-coding techniques and bit error patterns recorded on an experimental Northern latitude meteor burst link is presented. Automatic repeat request (ARQ) and hybrid forward error correction (FEC) with ARC are examined from the standpoint of probability of message delivery and encountered message delivery delays. It is demonstrated that FEC will yield substantial improvement in the number of messages deliverable within a specified time constraint. Potential gains in extending the usable time duration of a meteor burst channel are on the order of factors of four with successful message delivery percentages increased by factors of 50. >

Models of Multilevel Computer Security

Abstract: Publisher Summary Some multilevel access-control models are surveyed in the chapter. This survey includes more recent models and also presents a few models in greater depth. The first access-control models were for operating systems, and modeled the policy by which an operating system grants requests by processes for access to controllable segments of main memory. This chapter focuses on the design decisions behind these models, and their intended application to secure computer system development. Some new ideas arise in database system models, which impose additional structure on data objects, raising questions about how to assign labels. There is a brief discussion of network model. Mandatory access-control (MAC) system models are used with some success to help design secure computer systems. There are two levels at which the MAC approach can be used. One level is at an external interface, where objects are complex abstractions such as relations, views, virtual connections, or datagrams. The other level is at the interface to the underlying secure operating system kernel, if there is one, where objects are segments of memory. This is the level at which access control is enforced, and where one has the most assurance that a simple information-flow policy is implemented.

Proportional Integral Estimator

Abstract: The standard Kalman filter requires that the statistical characteristics of system signal and noise are completely known. In practice, this is almost impossible to achieve. Numerous adaptive techniques have been developed to compensate for inexact system modeling. While some are not good enough, others are ad hoc approaches requiring substantial computer resources. A novel adaptive technique is proposed by adding to the standard Kalman estimator, an integral term which provides additional smoothing effect and design flexibility. Optimal structures are derived by using the innovation method for continuous and discrete data Gaussian process models with linear dynamics. The proportional integral estimator (PIE) is simple to implement, but by adjusting contributions from the proportional linear term and the integral term of filter residual, it provides flexible adaptive features to suit design requirements, such as robustness to parameter variation and maneuvering target tracking. An application to a tracking system is presented and the behavior of error covariance matrix is examined. The example included for comparison of the standard Kalman filter and the PIE, indicates that while the results obtained by using the two filters are comparatively close, significant improvement is observed in response time and noise smoothing capability.

Lectin teratogenesis II: Demonstration of increased binding of concanavalin a to limb buds of rabbit embryos during the teratogenically sensitive period

Abstract: The plant lectin concanavalin A (con A) causes malformations of rabbit embryos when 160 micrograms (in 40 microliter) are injected into the exocoelom on gestational days 12-15 but does not cause malformations on days 10-11. The purpose of this study was to investigate the mechanism for increased susceptibility of day 12-15 embryos to con A teratogenicity. Light microscopy of day 11 embryos 15-20 hr after treatment with con A revealed no observable difference from controls. Day 13 embryos at similar times exhibited limb buds with large areas that were denuded of ectoderm. Concurrent addition of alpha-methyl-D-mannoside (alpha MM), a specific inhibitor of con A, to the injection solution of day 13 embryos resulted in limb buds that appeared normal. The regions of con A binding to day 11 and day 13 embryos were visualized through epifluorescent microscopy of untreated embryos stained with fluorescein-labelled con A. Day 11 embryos exhibited moderate fluorescence on the surface of limb buds and the pericardial region. Day 13 embryos exhibited strong fluorescence of limb bud surfaces; the pericardial region remained moderately fluorescent. Addition of alpha MM to the incubation medium resulted in no fluorescence above background. Visualization of con A receptors was accomplished by ultrastructural analysis of forelimb buds stained with ferritin-labelled con A. Ferritin label was observed only on the surfaces of the ectoderm and was sparse over all regions of day 11 limb buds. In contrast, ferritin label was moderately heavy in all regions of the day 13 limb buds. No labelling occurred when the ferritin-labelled con A was preincubated with alpha MM. These observations indicate that the number of exposed con A receptors on limb buds of teratogenically sensitive embryos (day 13) is increased, compared with the number of exposed receptors on limb buds of younger, insensitive (day 11) embryos. The increased number of exposed con A receptors on limb buds during the teratogenically sensitive period provides not only increased binding of the lectin to sensitive embryos but also a potential mechanism for the anomalous attachment of distal regions of the limb buds to the body wall.

Enhanced network survivability through balanced resource criticality

Abstract: The authors describe two entropy-based measures that can be used to assess how close a network design comes to being maximally survivable: normalized node entropy (NNE) and normalized link entropy (NLE). Maximum survivability is achieved when the enemy cannot identify critical points of failure and must remove a maximum number of nodes/links before the network becomes disconnected. The normalized node and link entropy measures provide the network designer with an indication of how well individual network resources have been used to produce a highly survivable network structure. For instance, an NNE value of unity occurs in network configurations where all nodes appear equally important to the interconnection structure, such as in a ring or a fully connected network. In contrast, star configurations have NNE values of zero, since the center node can be identified as most critical to maintaining the network's interconnection structure. >

A development framework for distributed artificial intelligence

Abstract: The authors describe distributed artificial intelligence (DAI) applications in which multiple organizations of agents solve multiple domain problems. They then describe work in progress on a DAI system development environment, called SOCIAL, which consists of three primary language-based components. The Knowledge Object Language defines models of knowledge representation and reasoning. The metaCourier language supplies the underlying functionality for interprocess communication and control access across heterogeneous computing environments. The metaAgents language defines models for agent organization coordination, control, and resource management. Applications agents and agent organizations will be constructed by combining metaAgents and metaCourier building blocks with task-specific functionality such as diagnostic or planning reasoning. This architecture hides implementation details of communications, control, and integration in distributed processing environments, enabling application developers to concentrate on the design and functionality of the intelligent agents and agent networks themselves. >

Algebraic-integer quantization an residue number system processing

Abstract: The algebraic-integer number representation, in which the signal sample is represented by a set of (typically four to eight) small integers, combines with residue number system (RNS) processing to produce processors composed of simple parallel channels. The analog samples must first be quantized into the algebraic-integer representation, and the final algebraic-integer result converted back to an analog or digital form. In between these two conversions, the algebraic-integer representation must be converted into and out of two levels of RNS parallelism. The authors address these quantization and conversion problems and demonstrate their solution by implementing a 128-tap algebraic-integer filter using the moduli 17 and 31, with four parallel channels per modulus. This processor performs equivalently to an integer processor with 19 bits of dynamic range. It is concluded that the algebraic-integer representation is best suited to control the dynamic range requirements of integer processors in situations where there is a high sensitivity to quantization and roundoff errors, especially when there is a matching nonuniform input distribution. >

Controlled signalling systems and covert channels

Abstract: Computer security is addressed from the perspective of the spies, who attempt to build covert channels and then exploit the ones of maximum capacity. The close connection between classical noninterference and the existence of positive-capacity covert channels is demonstrated. It is shown how to characterize the space of covert channels associated with a particular system. The capacity of the system is defined as the maximum of the capacities of all its channels, and optimal algorithms for covert communication are given. >

Digital Medical Imaging: Implementation Strategy for the Defense Medical Establishment

Abstract: In formulating an Implementation strategy for digital medical imaging, three interrelated thrusts have emerged for the Defense Medical Establishment. These thrusts- (1) Totally filmless medical imaging on the battlefield, (2) Teleradiology, and (3) DIN/PACS for peacetime military health care- have significant implications in their fully developed form as resource savers and quality improvers for the unique aspects of military health care .