Showing papers by "Mitre Corporation published in 1988"

The landmark hierarchy: a new hierarchy for routing in very large networks

Abstract: Landmark Routing is a set of algorithms for routing in communications networks of arbitrary size. Landmark Routing is based on a new type of hierarchy, the Landmark Hierarchy. The Landmark Hierarchy exhibits path lengths and routing table sizes similar to those found in the traditional area or cluster hierarchy. The Landmark Hierarchy, however, is easier to dynamically configure using a distributed algorithm. It can therefore be used as the basis for algorithms that dynamically configure the hierarchy on the fly, thus allowing for very large, dynamic networks. This paper describes the Landmark Hierarchy, analyzes it, and compares it with the area hierarchy.

Minimal trellises for block codes

Abstract: Basic concepts in the study of trellises of block codes are defined. It is shown that minimal proper trellises exists for all block codes. Bounds on the size of such trellises are established. These bounds are shown to be exact for maximum distance separable codes and nearly so for perfect codes. >

Communications network system using full-juncture and partial-juncture station status information for alternate-path distance-vector routing

Abstract: Apparatus and method for routing messages in a communications network having a plurality of communications stations interconnected by a plurality of communication links, and having at least one destination station. Each communications station informs each neighboring communications station of the distance between itself and the destination station. Each communications station stores information identifying a first neighboring station through which it has a primary path to the destination station. The primary path is the shortest of all possible paths to the destination station. Each communications station that is connected to the destination station by at least one alternate path stores information identifying a second neighboring station through which it has an alternate path to the destination station.

Algorithm for the detection of fine clustered calcifications on film mammograms.

Abstract: An algorithmic process for the detection and marking of clustered calcifications in digitized film-screen mammograms has been applied to mammograms from 50 clinical cases sampled at two digitization levels, in both the craniocaudal and mediolateral views. In all but one case the detector accurately located suggestive clusters found by radiologists in normal screening. In five cases additional clusters were also found by the detector. The detector has a negligible false-positive rate for the detection of clustered calcifications, although it is sensitive to clusters of emulsion defects displayed as artifactual calcification densities in the original film. The detector is flexible in structure and is easily adapted to various calcification/cluster criteria. The detector shows considerable promise when applied to clinical examples but will require refinement before formal testing.

Pagenumber of complete bipartite graphs

Abstract: Given an ordering of the vertices of a graph around a circle, a page is a collection of edges forming noncrossing chords. A book embedding is a circular permutation of the vertices together with a partition of the edges into pages. The pagenumber t(G) (also called book thickness) is the minimum number of pages in a book embedding of G. We present a general construction showing t(Km,n) ⩽ ⌈(m + 2n)/4⌉, which we conjecture optimal. We prove a result suggesting this is optimal for m ⩾ 2n − 3. For the most difficult case m = n, we consider vertex permutations that are regular, i.e., place vertices from each partite set into runs of equal size. Book embeddings with such orderings require ⌈(7n − 2)/9⌉ pages, which is achievable. The general construction uses fewer pages, but with an irregular ordering.

A dual plane variation of the Hough transform for detecting non-concentric circles of different radii

Abstract: The Hough transform for circle detection requires the search of a 3-dimensional parameter space for circles of arbitrary radius. A technique has been developed which calculates intersection points of edge gradient vectors storing response weights in one plane and the product of weights and radii in another plane effectively eliminating the radius dimension of the parameter space. The result is a significant savings in both search time and storage in the parameter space accumulator.

Breast calcifications: analysis of imaging properties.

Abstract: The imaging characteristics of microcalcifications in both benign and malignant breast conditions were analyzed in 48 digitized film mammograms. Each case included in this analysis had findings considered suggestive of malignancy by the radiologist, with the underlying histologic structure determined by excisional biopsy. Imaging properties of each microcalcification--such as pixel intensity, relative location, distribution, size, and local neighborhood intensities--were recorded. This information was statistically analyzed at the population level according to such selection criteria as histologic type, size of calcification, and cluster size. Distribution ranges were determined for these criteria. Statistical differences between data from benign and malignant cases show the average distance between calcifications in malignant conditions was greater than in benign conditions, and tissue region averages surrounding calcifications associated with malignant conditions were consistently higher than those for ...

Simplified procedure for correcting both errors and erasures of Reed-Solomon code using 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 that is needed to decode a Reed-Solomon (RS) code. In the paper, 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 Reed-Solomon 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.

Ranging and processing system for mobile surveillance and data link

Abstract: The satellite system includes at least two satellites having on-board processing capability so that data messages may be exchanged and the position of mobiles may be determined with direct access from multiple ground control facilities. The satellites transmit data and poll individual mobiles upon command by one or more of the control facilities and receive replies from the mobiles including the mobiles' altitude and other data of interest to the control facility. The at least two satellites communicate with one another by means of a cross-link communication path. Computer processing apparatus is included on the satellites to compute the ranges between the mobiles and each of the satellites from the replies received from the mobiles, and to store and process messages. The position information and messages are transmitted to at least one of the control facilities. It is preferred that the control facilities employ TDMA or FDMA protocols in the uplinks to the satellites. The on-board processing makes it readily possible for a number of control facilities to gain access to the satellites directly rather than through a central earth station, and to increase the capacity of a discrete address polling system for a given allocation of radio frequency spectrum. A discrete address polling system is one where each mobile is polled on an individual basis by only responding to polls that contain its identification.

Parallel Implementation of the Quadratic Sieve

Abstract: A new version of the Quadratic Sieve algorithm, used for factoring large integers, has recently emerged. The new algorithm, called the Multiple Polynomial Quadratic Sieve, not only considerably improves the original Quadratic Sieve but also adds features that ideally suit a parallel implementation. The parallel implementation used for the new algorithm, a novel remote batching system, is also described.

Fault tolerance in a systolic residue arithmetic processor array

Abstract: The regularity of systolic arrays and the potential for redundancy in residue number systems are used to provide fault tolerance in VLSI systems. The fault tolerance is concurrent with normal circuit operation and allows a continuous flow of correct data when a fault occurs. There is no interruption of valid data flow while the circuits are reconfigured. The technique also obviates the need for ultrahigh-reliability switches and switching control circuits. A fault-tolerant implementation of a finite-impulse-response filter with five residue channels, two of which are redundant, demonstrates the technique. As long as not more than one cell in each processing block is faulty, the filter outputs contain no errors. >

The ISA expert system: a prototype system for failure diagnosis on the space station

Abstract: The Mission Operations Directorate (MOD) at the Johnson Space Center (JSC) is responsible for the safe operation and mission success of manned space flights. The MITRE Corporation, working with MOD, is developing requirements for the Operations Management System (OMS) to automate many aspects of flight control for the Space Station onboard systems. To help develop these requirements, the Integrated Status Assessment (ISA) expert system prototype was built to perform Station-wide failure diagnosis. This paper describes the OMS, how the ISA prototype was built, and how the prototype is being used to help define the OMS.Currently the Space Shuttle is managed on the ground using a hierarchy of control personnel. A flight director responsible for the overall Shuttle mission, a number of front room flight controllers are each responsible for a different system, and many back room controllers support various front room controllers. This system has been used since the early days of space flight and is very manpower intensive. A similar hierarchy is seen in an automated system for the Space Station. The back room controllers can be augmented with smart components and sensors on the Station and the front room controllers can have their jobs aided with expert systems. At the highest level is the OMS which works at the flight director level getting summary information from the various systems in the Station.The OMS will include onboard automation, ground based automation, onboard manual operations, and ground based operations. One of the functions of the OMS is to perform a Station-wide status assessment and failure diagnosis of the Station. This Station-wide view is very important because all of the systems interact with each other and a failure in one system will have impacts on the other systems.It became evident early in discussion with to the MOD flight controllers that prototypes would be very helpful in the process of gathering requirements for the OMS. The prototypes were used to gather additional requirements, to expose people to new ideas and technologies, and study the feasibility of these technologies for systems management.Because the task of assessing the status of space vehicles is a complex job that requires “expert” knowledge to find heuristic solutions to problems, an expert system approach was chosen to prototype the ISA system. The initial domain of the expert system was the KU band portion of the communications and tracking system (one of the onboard “core” Space Station Systems).The ISA prototype expert system consists of a knowledge base, an inference engine, and a user interface. The ISA system was designed as a hybrid expert system using different methodologies: object-oriented programming, rule-based programming using both shallow and deep reasoning, and qualitative modeling.The ISA prototype has been very successful in its goals. ISA has demonstrated new technology and ideas to the NASA operations community, helped define requirements for the OMS, and shown the feasibility of using hierarchical expert systems to monitor complex systems. The ISA prototype, along with other OMS prototypes, are being integrated in a test bed environment with other space station prototypes to form the Space Station Information System (SSIS) End-to-end Test Capability (ETC) which will have components all over the world. The results of the ETC will influence the Space Station design and be a test environment for software and hardware for years to come.

An overview of DOD-STD-1838A (proposed) the common APSE interface set: revision

Abstract: A five-year effort under the Ada Joint Program Office has developed a proposed standard for a host system interface as seen by tools running in an Ada Programming Support Environment (APSE). Standardization of this interface as DOD-STD-1838A will have a number of desirable effects for the Department of Defense, including tool portability, tool integration, data transportability, encouragement of a market in portable tools, and better programmer productivity.As the capability of tools to communicate with each other is a central requirement in APSEs, the Common APSE Interface Set (CAIS) has paid particular attention to facilitate such communication in a host-independent fashion. CAIS incorporates a well-integrated set of concepts tuned to the needs of writers and users of integrated tool sets.This paper covers several of these concepts: • the entity management system used in place of a traditional filing system,• object typing with inheritance,• process control including atomic transactions,• access control and security,• input/output methods,• support for distributed resource control, and• facilities for inter-system data transport.

The cascading problem for interconnected networks

Abstract: One potential problem that must be faced when using the interconnected accredited system approach of the trusted network interpretation is cascading. The authors introduce some proofs showing that a simple nesting condition is sufficient and sometimes necessary to prevent cascading. They give a Prolog program that finds all cascading paths. >

Integrated enclosure and adjustable electronic equipment mounting system

Abstract: A light-weight, integrated enclosure and fully-adjustable mounting and support system for transport and use of mobile electronic equipment in the field. A curved upper shell and flat base of sandwich panel construction are connected by reinforced plastic members to form a lightweight enclosure which can be mounted on a truck for transport. The fully adjustable mounting and support system includes rails mounted within the enclosure on which a series of frame elements are horizontally movable to accomodate electronic equipment of varying widths between the frame elements. The frame elements are also lightweight extrusions and include an elastomeric pad engaged in a vertical channel to provide infinite vertical adjustability in mounting the equipment to the frames. The enclosure is shaped for efficiently housing the equipment, reducing aerodynamic drag, and providing superior structural strength and stiffness. A conductive coating or screen may be applied to the enclosure to provide electromagnetic interference protection. An improved button fastener for attaching the structural members to the sandwich panel enclosure is also provided.

Concurrent error correction in systolic architectures

Abstract: It is shown how two features of systolic arrays in which the cells retain partial results rather than pass them on can be used to facilitate testing and fault localization with no modification of the systolic design; the monitoring is performed either by software in the host processor or by hardware following the system output. One feature is the ability to enter identical sequences of inputs into two adjacent processor elements; the other is the resemblance of the data flow to that of a scan design. In particular, a one-dimensional systolic architecture of interest is described and applied to a finite-impulse response filter. Both the error detection and correction coverages are considered in detail for the FIR filter. The concurrent error-correction technique is applicable only to operational reliability, but the concurrent error-detection technique is equally applicable to manufacturing tests, incoming tests, and periodic maintenance tests. A hardware implementation of the error-detection-and-correction technique is presented. The architecture is extended to a two-dimensional processor. >

Landmark hierarchy method for routing signals in a communications network

Abstract: A hierarchy of landmarks is established for the nodes in the network. Each node is assigned at least one hierarchy level designation and has a corresponding radius. An address is assigned to each of the nodes, the address including components representing landmarks wherein each landmark represented by the address component is within the radius of the landmark represented by the next lower address component. Each node maintains a routing table for routing entries to landmarks within the radii of which a node resides. A source node chooses a path toward the highest level landmark represented by the address components of a destination node until the path reaches a node within the radius of the landmark represented by the next lower level address component. This procedure is repeated for the remaining address components.

The Detection Of Calcification Clusters In Film-Screen Mammograms; A Detailed Algorithmic Approach

Abstract: An efficient algorithm has been developed for the detection of clustered micro-calcifications in digitized film-screen mammograms. The calcification cluster detection algorithm involves a decision-theoretic mechanism which identifies calcifications meeting specific size, density, and clustering criteria. The algorithm first utilizes a pixel testing and region grouping procedure to identify pixels with specific intensity characteristics. A region growing procedure is then applied to identify pixels belonging to contiguous structures. Each single- and multi-pixel structure is subsequently tested against criteria for size, shape, contrast, and intensity to determine if the composite structure matches the expected characteristics of mammographic calcifications. Detected calcifications are then tested to determine if they fall within a cluster meeting specific density constraints. Only calcifications located in such clusters are marked in the processed image. This algorithmic process has been applied to mammograms from 40 clinical cases in which a biopsy was performed based on the presence of suspicious calcifications. The algorithm accurately identified the suspicious calcifications in each situation; in several cases, it also detected other clusters which were so fine as not to be visible in clinical screening.

Performance of some Rake modems over the non-disturbed wide band HF channel

Abstract: The author presents performance evaluations for four Rake modems used to communicate over the wideband (e.g. 1 MHz) HF channel. Attention is confined to performance for the nondisturbed HF channel. Consideration is given to the impact of mode Doppler shift and multipath spread due to dispersion. The effects of additive noise, self-noise, and imperfect channel measurements are included. Results are presented for decision-directed, parallel probe, serial probe, and DPSK Rake modems. Performance to within 1-3 dB of the additive white Gaussian noise channel is predicted, depending upon the modem and the channel dispersion, if the Doppler shift of the modem can be tracked to within 0.1 Hz. >

Inference rules using local contexts

Abstract: We construct equivalent “localized” versions of a formula, adding assumptions simultaneously to various locations, where the particular location determines what is added. Inference rules that take advantage of localized formulas are presented for sequent calculi in which the left hand side of sequents can be used to accumulate the background assumptions (or “contexts”) of assertions. The intended application is to the automatic generation of tractable justifying lemmas for substitution operations for interactive proof development systems, especially those concerned with mathematical topics where manipulation of deeply embedded terms is desirable.

Diagnosing multiple failures using knowledge of component states

Abstract: A prototype, called the generic model-based diagnostic system (GMODS), has been implemented to detect and diagnose failures in launch system hardware at the Kennedy Space Center. GMODS diagnoses both single and multiple failures from a model of the structure and function of a physical system. The diagnostic algorithm extends the strategy proposed by J. de Kleer and B. Williams (1987) for efficiently diagnosing multiple failures. GMODS departs from previous work by using knowledge of component states to diagnose failures in components that operate in one of several states. The resulting approach also prunes suspects by using knowledge of the failed-state behavior of components. >

Human-Computer Interaction

Abstract: Human-Computer Interaction (HCI) is a term known since the early 1980s. In HCI, the user plays the central role, much more than the computer hardware or software by itself. It is a multi-disciplinary research field, populated by researchers and practitioners from areas like psychology and cognitive sciences, ergonomics, sociology, computer science, graphic design, business, and more. In order to build really usable interfaces, the knowledge and engagement of every single related field are basic prerequisites. We are taking a look on how selected areas have contributed to HCI in recent years.

An execution model for distributed object-oriented computation

Abstract: This paper describes an execution model being developed for distributed object-oriented in a message-passing multiple-instruction/multiple-data-stream (MIMD) environment. The objective is to execute an object-oriented program as concurrently as possible. Some opportunities for concurrency can be identified explicitly by the programmer. Others can be identified at compile time. There are some opportunities for concurrency, however, that can only be discovered at runtime because they are data-dependent. The model of execution we describe attempts to discover and exploit the data-dependent concurrency that exists in a given program execution.

Display aid for air traffic controllers

Abstract: The locations of aircraft on a first approach to a first runway are displayed on a line substantially parallel to a second approach to a second runway, the second runway converging with the first runway. The distances of aircraft on the first approach from a threshold of landing for the first runway are computed. These distances are used to draw a symbol of aircraft on the first approach onto the line parallel to the second approach at the distances from a threshold of landing for the second runway. The "mirror image" of aircraft displayed on the line parallel to the second approach will aid air traffic controllers in staggering aircraft approaching an airport on converging runways.

A wideband HF interference and noise model based on measured data

Abstract: Describes the first results of a high-resolution, wide-bandwidth North American HF band interference measurements program in terms of the correspondence of these results with a model for the interference derived from earlier European measurements. The preliminary conclusion is that the model is valid. The interference-dominated portion of the frequency distribution is approximately linear on a log-log plot which relates the fraction of the resolution cells occupied with interference at a power level to that power level. >

Augmenting tactical communications networks to enhance survivability

Abstract: A methodology that makes use of global- and local-topology-based criteria to enhance the stability of tactical communications networks is presented. The global criteria were described previously, but the local criteria are newly derived. The criteria are used to enhance the topological stability of tactical networks through recursive link reallocation. This process has application to both predeployment and real-time configuration of tactical networks. With its use, tactical communication networks can be augmented to improve overall system survivability by reducing the impact that individual resource losses have on the topological structure of the network. >

A user interface for a knowledge-based planning and scheduling system

Abstract: The objective of EMPRESS (expert mission planning and replanning scheduling system) is to support the planning and scheduling required to prepare science and application payloads for flight aboard the US Space Shuttle. EMPRESS was designed and implemented in Zetalisp on a 3600 series Symbolics LISP machine. Initially, EMPRESS was built as a concept demonstration system. The system has since been modified and expanded to ensure that the data have integrity. Issues underlying the design and development of the EMPRESS-I interface, results from a system usability assessment, and consequent modifications are described. >