Showing papers by "Mitre Corporation published in 1987"

Functionality and usability

Abstract: Instead of limiting functionality, usability complements functionality. It affects how and with what effectiveness a system is used, and even whether or not it is used at all.

The Interrogator: Protocol Secuity Analysis

Abstract: The Interrogator is a Prolog program that searches for security vulnerabilities in network protocols for automatic cryptographic key distribution. Given a formal specification of the protocol, it looks for message modification attacks that defeat the protocol objective. It is still under developement, but is has been able to rediscover a known vulnerability in a published protocol. It is implemented in LM-Prolog on a Lisp Machine, with a graphical user interface.

Artificial Intelligence for Society

Abstract: Based on papers presented at the Artificial Intelligence for Society conference held in July 1985, this volume forms the basis for discussing social, educational, economic, cultural and moral issues resulting from AI developments. It critically examines the relative neglect and AI and IT developments to enhance general human competences. The implications for society of adopting interactive technologies such as: intelligent knowledge based systems, expert systems, logic programming, computer assisted learning, computer based training, visual communication and interactive video systems are far reaching. As such this volume addresses issues crucial to practitioners in education, training, health and welfare, and provides a useful perspective for social scientists, computer professionals, artists and designers and all concerned with the impact of AI and IT developments.

A simplified procedure for correcting both errors and erasures of a Reed-Solomon code using the Euclidean algorithm

Abstract: It is well known that the Euclidean algorithm or its equivalent, continued fractions, can be used to find the error locator polynomial and the error evaluator polynomial in Berlekamp's key equation needed to decode a Reed-Solomon (RS) code. A simplified procedure is developed and proved to correct erasures as well as errors by replacing the initial condition of the Euclidean algorithm by the erasure locator polynomial and the Forney syndrome polynomial. By this means, the errata locator polynomial and the errata evaluator polynomial can be obtained, simultaneously and simply, by the Euclidean algorithm only. With this improved technique the complexity of time domain RS decoders for correcting both errors and erasures is reduced substantially from previous approaches. As a consequence, decoders for correcting both errors and erasures of RS codes can be made more modular, regular, simple, and naturally suitable for both VLSI and software implementation. An example illustrating this modified decoding procedure is given for a (15, 9) RS code.

Maternal factors in developmental toxicity

Abstract: The maternal organism provides the developing embryo with its physical environment, nutrients, and a mechanism for eliminating metabolic wastes. Since the physiological state of the pregnant female affects her ability to provide those requirements for the developing embryo, it is not surprising that there are maternal factors that can affect the wellbeing of the embryo. Extremes of maternal age in both humans and animals have been implicated in growth retardation, as well as autosomal trisomies. The influence of maternal size on fetal size is more pronounced among larger species with longer gestation periods such as humans and domestic animals. A clear relationship between the parity of the mother and potential developmental toxicity in humans has not been established due to the confounding influences of maternal age. Among laboratory rodents, however, it appears that offspring of multiparous animals are at increased risk of developmental toxicity. A variety of infectious agents, particularly viruses, have either been demonstrated or implicated as causes of developmental toxicity. In addition, hyperthermia is a possible confounding factor inherent with maternal infection. Although under experimental conditions hyperthermia is teratogenic in laboratory animals, a causative role for transient hyperthermia, which occurs during febrile states concomitant with infections, cannot be clearly established. Chronic maternal vascular disease states including essential hypertension, heart disease, or diabetes mellitus are likely to contribute to uteroplacental insufficiency and developmental toxicity. Poor maternal nutrition among humans contributes to growth retardation, but not to malformations. The production of "abnormal" maternal antibodies, such as are present in Rh incompatibility, can cause fetal wastage. An important maternal factor in humans is uteroplacental insufficiency, which can occur in normal states like twinning, as well as in abnormal conditions including reduced placental size, chronic maternal hypoxia, or uterine ischemia. Although all these maternal factors can contribute to developmental toxicity, they do not necessarily occur as isolated events. Some developmental toxicants exert deleterious effects within both the embryo and the maternal system.

Monopole element at the center of a circular ground plane whose radius is small or comparable to a wavelength

Abstract: The input impedance and directive gain of a monopole element at the center of a circular ground plane in free space are summarized for arbitrary element length and element radius with ground plane radii of zero to more than two wavelengths. Numerical results are obtained by utilizing various models and are compared with measurements. The models include a ground plane of zero extent, the integral equation method, method of moments, oblate spheroidal wave functions, and the method of moments combined with the geometric theory of diffraction (GTD).

Dependability Evaluation of Integrated Hardware/Software Systems

Abstract: A methodology for predicting the dependability (reliability and availability) of an integrated realtime hardware/software system using a semi-Markov process is described. This methodology was used to evaluate the reliability of the shuttle mission simulators at the NASA Johnson Space Center.

Automatic correction to misspelled names: a fourth-generation language approach

Abstract: Using an information theoretic likeness measure defined as an inner product on a data space created from a table of valid names, this 4GL procedure searches the database space for the nearest correctly spelled name.

A Statistical Exmination of Sky Cover Changes in the Contiguous United States

Abstract: The Sette Weather Chart constructed in 1939 with data from 1900 to 1936 was used to describe the climatology of cloudless days and to predict cloudless days in the United States for 14 regions. When the data for days having 0.1 sky cover or less were collected and analyzed for the period 1950 to 1982 and compared to the Sette period 1900 to 1936, there was a definite statistical decrease in the annual monthly average of cloudless days using 45 cities common to both periods. Using the most recent data a fuzzy k-means clustering analysis identified 17 largely contiguous regions from a sample of 65 cities and constructed a degree of belonging for each city to these regions. The resulting clusters were examined for their uniqueness with discriminant analysis The error rate estimation of the discriminant was evaluated with the resubstitution method, a holdout Method and the Lachenbruch crossvalidation procedure. The results of the study not only show a decrease in cloudless days but also regional chan...

On the linear span of binary sequences obtained from finite geometries

Abstract: A class of periodic binary sequences that are obtained from the incidence vectors of hyperplanes in finite geometries is defined, and a general method to determine their linear spans (the length of the shortest linear recursion over GF(2) satisfied by the sequence) is described. In particular, we show that the projective and affine hyperplane sequences of odd order both have full linear span. Another application involves the parity sequence of order n, which has period pn - 1 and linear span vL(s) where v = (pn - 1)/(p - 1) and L(s) is the linear span of a parity sequence of order 1. The determination of the linear span of the parity sequence of order 1 leads to an interesting open problem involving primes.

Computing k-shortest path lengths in euclidean networks

Abstract: In this paper, we examine the problem of finding k-shortest paths between an origin and destination pair when distances are Euclidean. Two versions of a generalized Dijkstra algorithm are compared. Computational results show that the advantage of the adaptive version (measured by total number of permanent labels) grows with both k and the network size. For large networks, the adaptive algorithm exhibits a 100:1 advantage in the number of permanent labels set.

Tactical Network Survivability through Connectivity Optimization

Abstract: The reduction of military C3 networks, composed of communications links and pro cessing nodes, into disconnected, stand-alone nodes is a primary goal of counter-C3 operations. This paper formulates a quantitative, graph-theory-based methodology for measuring C3 network connectivity. Extending past efforts that have been primarily geared towards simple node-pair analysis, this methodology investigates C3 network connectivity from a global, network-wide perspective. It provides a measure of how well nodes within the C3 network are initially interconnected, and to what degree they can maintain that connectivity in the face of counter-C3 operations.

Network security: Protocol reference model and the trusted computer system evaluation criteria

Abstract: Issues arising from the application of the Trusted Computer System Evaluation Criteria (TCSEC) to networks are discussed, particularly those requiring further research. The focus is on how to integrate many of the concepts in the Open Systems Interconnection (OSI) security addendum into the framework of the TCSEC. The discussion covers the protocol architectural issues of the trusted network with particular emphasis on the relationship among network protocols, protocol reference model, and network security. It is argued that application of the TCSEC to computer networks requires incorporation of a network protocol reference model as implemented in a protocol suite.

An optimized polarization sensitive Salisbury screen

Abstract: A transmission line equivalent circuit model for strip gratings is used to determine the performance of both conducting and resistive gratings. A polarization sensitive Salisbury screen is designed in which the space cloth is replaced by a resistive grating and the ground plane is replaced by a parallel conducting grating. The new Salisbury screen performs like the traditional screen for an incident E -field parallel to the strips, but is transparent for the perpendicular polarization.

An architecture for network-layer routing in OSI

Abstract: Work on the standardization of routing protocols for OSI is in progress. The envisioned set of routing protocols is expected to work in nearly all of the environments which constitute OSI networks. Behind these routing protocols is an architecture which outlines problems and goals, establishes a framework upon which to base the development of protocols, and provides a conceptual baseline for continued work on unsolved problems. This architecture defines routing in the OSI network layer, functionally partitions the problem into its components, defines a routing hierarchy and an address hierarchy and discusses their relationship, and discusses arms-length routing relationships between differently administered networks. This paper presents that architecture, and discusses problems which remain to be solved as work progresses towards a global OSI network.

Development of an air ground data exchange concept: Flight deck perspective

Abstract: The planned modernization of the U.S. National Airspace System (NAS) includes the development and use of a digital data link as a means to exchange information between aircraft and ground-based facilities. This report presents an operationally-oriented concept on how data link could be used for applications related directly to air traffic control. The specific goal is to establish the role that data link could play in the air-ground communications. Due regard is given to the unique characteristics of data link and voice communications, current principles of air traffic control, operational procedures, human factors/man-machine interfaces, and the integration of data link with other air and ground systems. The resulting concept is illustrated in the form of a paper-and-pencil simulation in which data link and voice communications during the course of a hypothetical flight are described.

Modeling Interference Effects for Land-Mobile and Air-Mobile Communications

Abstract: Analytic and computer models are presented that can provide an assessment of land-mobile and air-mobile communications performance in interference environments. The results obtained with these models, based on a communications region of operability criterion, include the effects of greater-than-free-space propagation path losses associated with low-elevation signal paths. The analytic models are used to examine the effects of higher order path loss on signal-to-interference contours for single and linearly distributed interference scenarios. The computer model can be used to investigate link performance for interference environments in which the link assets and each source of interference are arbitrarily located in three dimensions. A propagation submodel permits independent calculation of the loss over each link or interference signal path. Computer-generated plots are presented that illustrate the effect of antenna heights and frequency on the shape of the signal-to-interference (S/I) contours. Of particular interest is the effect on link region of operability when either the link transmitter or the sources of interference are at a higher altitude than the other.

Using Decision Trees to Derive the Complement of a Binary Function with Multiple-Valued Inputs

Abstract: An algorithm to minimize decision trees of Boolean functions with multiple-valued inputs is presented. The recursive algorithm is used to obtain a complement of a sum-of-products expression for a binary function with multiple-valued inputs. In the case where each input is p-valued, the algorithm produces at most pn−l products for n-variable functions, whereas Sasao's algorithm produces pn/2 products. This upper bound on the number of products is the best possible.

Formulation of a vector distance measure for the instantaneous-frequency distribution (IFD) of speech

Abstract: The instantaneous-frequency distribution (IFD) of the outputs of a filter bank of overlapping band-pass channels (or the equivalent DFT implementation) has been proposed [1] as a short-time spectral measure useful for representing speech. For application of the IFD in conventional tasks such as word recognition, an appropriate vectorization is needed on which a useful distance function can be defined. A number of recent studies have shown the cepstral representation to be generally most effective in terms of recognition accuracy. We propose a "pseudo-cepstral" format which treats the IFD as if it were a log-power spectrum, with a matrix-weighted squared-Euclidean distance function. Comparative results are given for two forms of IFD as well as two conventional cepstral transforms, in a small-scale word-recognition task with added white Gaussian noise. In addition, a statistic is derived which is highly correlated with recognition error rates, but requires far less computation than is involved in an actual recognition trial.

Consensus workshop on the evaluation of maternal and developmental toxicity work group I report: end points of maternal and developmental toxicity.

Abstract: It was concluded that this conference, sponsored by the EPA, has provided an opportunity to state current ideas regarding the utility of data from studies in developmental toxicology and that the deliberations have highlighted the need to consider fundamental relationships between maternal and developmental effects in a more comprehensive manner in the future.

An approach to design knowledge capture for the space station

Abstract: The design of NASA's space station has begun. During the design cycle, and after activation of the space station, the reoccurring need will exist to access not only designs, but also deeper knowledge about the designs, which is only hinted in the design definition. Areas benefiting from this knowledge include training, fault management, and onboard automation. NASA's Artificial Intelligence Office at Johnson Space Center and The MITRE Corporation have conceptualized an approach for capture and storage of design knowledge.

Authenticating Users by Word Association

Abstract: Testing word associations, as an extension of simple password entry, may be a practical means of verifying the identity of individual computer users. If each user specifies his/her own cue-response associations, then responses will be easy to remember. It should be easy for legitimate users to respond correctly to word association testing, but virtually impossible for potential intruders. Such testing should also prove easy for a computer to process.

Uncertainties in Building a Strategic Defense

Abstract: Building a strategic defense against nuclear ballistic missiles involves complex and uncertain functional, spatial, and temporal relations. Such a defensive system would evolve and grow over decades. It is too complex, dynamic, and interactive to be fully understood initially by design, analysis, and experiments. Uncertainties exist in the formulation of requirements and in the research and design of a defense architecture that can be implemented incrementally and be fully tested to operate reliably. The analysis and measurement of system survivability, performance, and cost-effectiveness are critical to this process. Similar complexities exist for an adversary's system that would suppress or use countermeasures against a missile defense. Problems and opportunities posed by these relations are described, with emphasis on the unique characteristics and vulnerabilities of space-based systems.