Showing papers by "SRI International published in 1980"

Principles of Artificial Intelligence

Abstract: A classic introduction to artificial intelligence intended to bridge the gap between theory and practice, "Principles of Artificial Intelligence" describes fundamental AI ideas that underlie applications such as natural language processing, automatic programming, robotics, machine vision, automatic theorem proving, and intelligent data retrieval. Rather than focusing on the subject matter of the applications, the book is organized around general computational concepts involving the kinds of data structures used, the types of operations performed on the data structures, and the properties of the control strategies used. "Principles of Artificial Intelligence"evolved from the author's courses and seminars at Stanford University and University of Massachusetts, Amherst, and is suitable for text use in a senior or graduate AI course, or for individual study.

Reaching Agreement in the Presence of Faults

Abstract: The problem addressed here concerns a set of isolated processors, some unknown subset of which may be faulty, that communicate only by means of two-party messages. Each nonfaulty processor has a private value of information that must be communicated to each other nonfaulty processor. Nonfaulty processors always communicate honestly, whereas faulty processors may lie. The problem is to devise an algorithm in which processors communicate their own values and relay values received from others that allows each nonfaulty processor to infer a value for each other processor. The value inferred for a nonfaulty processor must be that processor's private value, and the value inferred for a faulty one must be consistent with the corresponding value inferred by each other nonfaulty processor.It is shown that the problem is solvable for, and only for, n ≥ 3m + 1, where m is the number of faulty processors and n is the total number. It is also shown that if faulty processors can refuse to pass on information but cannot falsely relay information, the problem is solvable for arbitrary n ≥ m ≥ 0. This weaker assumption can be approximated in practice using cryptographic methods.

Equations and rewrite rules: a survey

Abstract: Equations occur frequently in mathematics, logic and computer science. In this paper, we survey the main results concerning equations, and the methods available for reasoning about them and computing with them. The survey is self-contained and unified, using traditional abstract algebra. Reasoning about equations may involve deciding if an equation follows from a given set of equations (axioms), or if an equation is true in a given theory. When used in this manner, equations state properties that hold between objects. Equations may also be used as definitions; this use is well known in computer science: programs written in applicative languages, abstract interpreter definitions, and algebraic data type definitions are clearly of this nature. When these equations are regarded as oriented "rewrite rules," we may actually use them to compute. In addition to covering these topics, we discuss the problem of "solving" equations (the "unification" problem), the problem of proving termination of sets of rewrite rules, and the decidability and complexity of word problems and of combinations of equational theories. We restrict ourselves to first-order equations, and do not treat equations which define non-terminating computations or recent work on rewrite rules applied to equational congruence classes.

Allocated Academic Learning Time Revisited, or Beyond Time on Task:

Abstract: Clearly, student learning depends on how the available time is used, not just the amount of time available. Researchers at the Far West Laboratory initiated the idea of' Allocated Academic Learning Time in the Beginning Teacher Evaluation Study (BTES) (Fisher, Filby, Marliave, Cahen, Dishaw, Moore, & Berliner, 1978). Powell and Dishaw (in press), reporting data from the BTES, indicate that the Allocated Academic Learning Time for second graders ranged from 62-123 minutes per day, and for fifth graders from 49-105 minutes per day. The correlation of allocated learning time with achievement varied from one test

"Sometime" is sometimes "not never": on the temporal logic of programs

Abstract: Pnueli [15] has recently introduced the idea of using temporal logic [18] as the logical basis for proving correctness properties of concurrent programs. This has permitted an elegant unifying formulation of previous proof methods. In this paper, we attempt to clarify the logical foundations of the application of temporal logic to concurrent programs. In doing so, we will also clarify the relation between concurrency and nondeterminism, and identify some problems for further research.In this paper, we consider logics containing the temporal operators "henceforth" (or "always") and "eventually" (or "sometime"). We define the semantics of such a temporal logic in terms of an underlying model that abstracts the fundamental concepts common to almost all the models of computation which have been used. We are concerned mainly with the semantics of temporal logic, and will not discuss in any detail the actual rules for deducing theorems.We will describe two different temporal logics for reasoning about a computational model. The same formulas appear in both logics, but they are interpreted differently. The two interpretations correspond to two different ways of viewing time: as a continually branching set of possibilities, or as a single linear sequence of actual events. The temporal concepts of "sometime" and "not never" ("not always not") are equivalent in the theory of linear time, but not in the theory of branching time -- hence, our title. We will argue that the logic of linear time is better for reasoning about concurrent programs, and the logic of branching time is better for reasoning about nondeterministic programs.The logic of linear time was used by Pnueli in [15], while the logic of branching time seems to be the one used by most computer scientists for reasoning about temporal concepts. We have found this to cause some confusion among our colleagues, so one of our goals has been to clarify the formal foundations of Pnueli's work.The following section gives an intuitive discussion of temporal logic, and Section 3 formally defines the semantics of the two temporal logics. In Section 4, we prove that the two temporal logics are not equivalent, and discuss their differences. Section 5 discusses the problems of validity and completeness for the temporal logics. In Section 6, we show that there are some important properties of the computational model that cannot be expressed with the temporal operators "henceforth" and "eventually", and define more general operators.

Accurate three dimensional eye tracker

Abstract: A three dimensional eye tracker, for measuring as a function of time the point in three dimensional space on which the eye is fixed, includes a portion which functions as a two dimensional double Purkinje eye tracker for measuring movement of the eye in rotation and translation, an automatic optometer portion for measuring the refractive power of the eye, and a common optical path simultaneously to provide corrections for both portions of the instrument. The two dimensional eye tracker portion incorporates a means for directing a beam into the eye, thereby forming first and fourth Purkinje images, and measuring means responsive to the first and fourth Purkinje images to generate output signals indicative of eye rotation and translation. The automatic optometer portion alternately directs a light beam through different areas of the eye lens and includes a mechanism for altering the directed light beam until the image on the retina does not move. The common optical path for the light beams includes elements that stabilize the eye image in a way to make alignment of the subject in the instrument relatively easy and also to avoid errors both in measurement of refractive power and for direction of gaze due to translation and axial movement of the eye. Polarizers and mechanical stops are incorporated in the optometer portion to provide optical isolation between the eye tracker and the optometer portions, and electrical filtration is provided in both portions of the instrument further to avoid interference.

Free-radical oxidants in natural waters.

Abstract: Photooxidation of cumene (isopropylbenzene) and pyridine in dilute solution in natural waters gives products characteristic of reactions with alkylperoxy (RO(2).) and hydroxyl (HO.) radicals. On the basis of the rates of formation of the products, the average concentrations of RO(2). and HO. are estimated to be about 10(-9) and 10(-17) mole per liter, respectively. The concentration of RO(2). is large enough that, for some classes of reactive chemicals, oxidation can be an important process in natural waters.

An approach to acquiring and applying knowledge

Abstract: The problem addressed in this paper is how to enable a computer system to acquire facts about new domains from tutors who are experts in their respective fields, but who have little or no training in computer science. The information to be acquired is that needed to support question-answering activities. The basic acquisition approach is "learning by being told." We have been especially interested in exploring the notion of simultaneously learning not only new concepts, but also the linguistic constructions used to express those concepts. As a research vehicle we have developed a system that is preprogrammed with deductive algorithms and a fixed set of syntactic/semantic rules covering a small subset of English. It has been endowed with sufficient seed concepts and seed vocabulary to support effective tutorial interaction. Furthermore, the system is capable of learning new concepts and vocabulary, and can apply its acquired knowledge in a prescribed range of problem-solving situations.

The `Hoare logic' of concurrent programs

Abstract: Hoare's logical system for specifying and proving partial correctness properties of sequential programs is generalized to concurrent programs. The basic idea is to define the assertion {P} S {Q} to mean that if execution is begun anywhere in S with P true, then P will remain true until S terminates, and Q will be true if and when S terminates. The predicates P and Q may depend upon program control locations as well as upon the values of variables. A system of inference rules and axiom schemas is given, and a formal correctness proof for a simple program is outlined. We show that by specifying certain requirements for the unimplemented parts, correctness properties can be proved without completely implementing the program. The relation to Pnueli's temporal logic formalism is also discussed.

The Impact of the Mode of Information Presentation on Learning and Performance

Abstract: A logistics management game was modified to provide an information/decision system that would serve as a framework for experimentally investigating the impact of the mode of information presentation. Subjects played the game by making a series of weekly decisions during each of two playing sessions. The experimental treatments were varied between sessions to permit the testing of a set of hypotheses pertaining to the impact that information and its mode of presentation might have upon performance and the rate of performance change. Data on player decisions and simulated results performance were collected automatically by the modified gaming system while data on player backgrounds were collected via questionnaires. The experimental data provide some support for hypotheses relating to the superiority of display terminals and the influence of user background on exhibited learning. The data does not, however, provide solid support for hypotheses relating to the impact of additional information or of graphical forms of information presentation. Analysis of the experimental data suggests the need to consider individual and user-group differences in systems design. User background differences may also considerably complicate the design of graphical output for information systems. Experimental research involving human interaction with information systems is a very difficult undertaking. The experiences gained from this project and reported in this paper should aid other researchers in designing effective experiments. The findings discussed also point toward several areas offering potential for further research. Many different variables influence the development and use of computer-based information systems. This paper presents the results of an experiment designed to examine the impact of the amount of information provided, the mode of presentation of that information, and the differences in personal backgrounds on the performance and rate of performance change for users of a computer-based system.

Properties of hypolipidemic peroxisome proliferators in the lymphocyte [3H]thymidine and Salmonella mutagenesis assays.

Abstract: Several hypolipidemic peroxisome proliferators have demonstrated carcinogenic activity in rodent species. Six of these hypolipidemic drugs have now been examined for their ability to induce damage in cellular DNA. Damage to DNA was evaluated by alteration in rates of [ 3 H]thymidine incorporation into replicating DNA of in vitro cultures of proliferating lymphocytes and by mutagenic activity in the Salmonella /microsome assay. Both in the absence and presence of liver S-9 microsomal preparation, the hypolipidemic drugs ethyl-α- p -chlorophenoxyisobutyrate (clofibrate), 2-methyl-2-[ p -(1,2,3,4-tetrahydro-1-naphthyl)phenoxy]propionic acid (nafenopin), 1-methyl-4-piperidylbis( p -chlorophenoxy)acetate (SaH-42-348), 2-chloro-5-(3,5-dimethylpiperidinosulfonyl)benzoic acid (tibric acid), [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid (Wy-14,643), and [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio( N -β-hydroxyethyl)acetamide] (BR-931) suppressed the rate of [ 3 H]thymidine incorporation into replicating DNA in primary cultures of concanavalin A-stimulated C57BL/6J splenic lymphocytes. However, inhibition by hypolipidemic drugs of [ 3 H]-thymidine incorporation into replicating DNA was reversed by incubation of drug-treated lymphocytes for 3 hr in fresh culture medium without hypolipidemic drug. This was in contrast to lymphocytes treated with the known DNA-damaging carcinogens methylnitrosourea or benzo( a )pyrene, in which the rate of [ 3 H]thymidine incorporation into replicating DNA was increasingly suppressed during 3-hr incubation of treated lymphocytes without carcinogen. Furthermore, no mutagenic activity was detected in the Salmonella /microsome assay using Salmonella typhimurium strains TA98, TA100, TA1535, TA1537, and TA1538 for the drugs clofibrate, nafenopin, SaH 42-348, Wy-14,643, or BR-931 either in the absence or presence of liver S-9 microsomal preparation. Results obtained with the lymphocyte [ 3 H]thymidine and the Salmonella mutagenesis assays therefore suggest that the hypolipidemic drugs either in the absence or presence of liver microsomes do not interact with and damage cellular DNA. Whether mutagenic metabolites are generated by hypolipidemic drug-induced liver peroxisomes remains to be elucidated.

Polymers of di- (and higher functionality) ketene acetals and polyols

Abstract: This invention concerns ortho ester polymers having repeating mer units represented by the general formulas: ##STR1## The polymers are formed by a condensation reaction between ketene acetals having a functionality of two or more and hydroxyl containing compounds having a functionality of two or more. Unlike most conventional condensation reactions, the reaction between a ketene acetal and an alcohol proceeds without the evolution of small molecule by-products which must be removed by distillation in order to achieve high molecular weight. Hence, this new process produces high molecular weight poly (ortho esters) in short reaction times, at essentially room temperature and at atmospheric pressure. Furthermore, linear thermoplastic materials are produced when both the ketene acetal and alcohol have functionalities of two; and because no volatile materials are produced, void free, thermoset materials are produced when either or both the alcohol and ketene acetal have functionalities greater than two and crosslinking occurs. The polymers are bioerodible and are useful in the fabrication of devices and coatings for delivering beneficial agents.

Modified Heliocentric Coordinates for Particle Dynamics

Abstract: A modified heliocentric coordinate system is found for the dynamics of $n+1$ particles that is barycentric, diagonalizes the kinetic energy, and is symmetric in $n$ of the particles. The $n$ planetary vectors are based on Radau's canonical point between the center of mass and the heliocenter. These coordinates, described by Radau in 1868 and forgotten, are especially valuable for describing centrosymmetric molecular fragments $A{B}_{n}$, and useful also for the mass polarization in atoms.

How to Prove Algebraic Inductive Hypotheses Without Induction

Abstract: This paper proves the correctness of algebraic methods for deciding the equivalence of expressions by applying rewrite rules, and for proving inductive equational hypotheses without using induction; it also shows that the equations true in the initial algebra are just those provable by structural induction. The major results generalize, simplify and rigorize Musser's method for proving inductive hypotheses with the Knuth-Bendix algorithm; our approach uses a very general result, that (under certain conditions) an equation is true iff it is consistent. Finally, we show how these results can be extended to proving the correctness of an implementation of one data abstraction by another.

Spatiotemporal characteristics of visual mechanisms: excitatory-inhibitory model

Abstract: The stabilized spatiotemporal threshold response surface can be modeled as the linear difference between the threshold response surfaces of two mechanisms, each of which is simply the product of a spatial and temporal frequency response curve. With no free parameters, the resulting model is shown to be a good fit to available data.

Effects of blackbody radiation on highly excited atoms

Abstract: Transitions between energetically close-lying Rydberg states are characterized by large electric dipole matrix elements and frequencies low enough that at room temperature the photon occupation number is \ensuremath{\simeq} 10. Consequently the absorption of blackbody radiation and the stimulated emission produced by it lead to an efficient redistribution of population among nearby levels. In some cases dramatic effects are observed, for example, radiative lifetimes that are shortened to a small fraction of their $T=0$ values. In addition, the 300-K blackbody field of \ensuremath{\sim}10 V/cm produces ac Stark shifts of the Rydberg levels. Calculations of the population redistribution effects and ac Stark shifts are presented. Examples are given to illustrate that care must be taken in experiments with highly excited atoms to ensure that only one state is being observed rather than a distribution.

Method and apparatus for digital data compression

Abstract: Digital data compression method and means are disclosed which allow for transmission of digital data over a short time period and/or narrow bandwidth transmission line. Also a maximum amount of information may be stored on a movable recording medium using data compression method of this invention. Digital signals to be stored and/or transmitted first are compressed using a finite-impulse response digital compression filter which generates estimated signal values which are subtracted from actual signal values to provide a sequence of difference signals. The difference signals are encoded using a truncated Huffman type encoding method and means, and the encoded signals are transmitted to a remote receiver and/or are recorded. The receiver includes a decoder and digital reconstruction filter for exact reproduction of transmitted digital signals. The invention is well adapted for storage and/or transmission of three lead electrocardiogram (ECG) signals, recording and playback of music, and the like.

An overview of short-term tests for the mutagenic and carcinogenic potential of pesticides.

Abstract: In the last few years, marked progress has been made in the development of methods for evaluating the mutagenic and carcinogenic potential of pesticide chemicals. The correlation of genetic and related biological activity in short-term tests with carcinogenic activity in whole animals allows the utilization of short-term mutagenicity bioassays to prescreen chemicals for effects related to mutation induction and presumptive carcinogenicity. In addition, bioassays now available can measure directly the chemical transformation of normal cells in culture into cells capable of producing tumors when injected into animals. This paper will review briefly the major types of relevant short-term tests and will develop a rationale for a phased approach to the evaluation of the mutagenic and carcinogenic potential of environmental chemicals. This approach involves the sequential application of bioassays which are organized into a three-level matrix emphasizing first detection, then confirmation, and finally hazard assessment. Chemicals demonstrating positive results in the short-term detection systems and confirmatory bioassays are pursued in higher level whole animal define a negative result. The phased approach should facilitate a cost effective utilization of limited testing resources and provide protection for human health in proportion to the anticipated hazard. Results obtained in evaluating a series of thirty-eight pesticide chemicals according to the phased approach discussed in detail.

Theory and practice of controlled drug delivery from bioerodible polymers

Abstract: Drug release from bioerodible polymers is discussed in terms of three dissolution mechanisms. These are (1) watersoluble polymers insolubilized by degradable cross-links, (2) water insoluble polymers solubilized by ionization of pendant groups, and (3) water insoluble polymers solubilized by backbone cleavage.

Multiple-agent planning systems

Abstract: We analyze problems confronted by computer agents that synthesize plans that take into account (and employ) the plans of other, similar, cooperative agents. From the point of view of each of these agents, the others are dynamic entities that possess information about the world, have goals, make plans to achieve these goals, and execute these plans. Thus, each agent must represent not only the usual information about objects in the world and the preconditions and effects of its own actions, but it must also represent and reason about what other agents believe and what they may do. We describe a planning system that addresses these issues and show how it solves a sample problem.

Sintering of Si3N4-Y2O3-Al2O3

Abstract: Sintering kinetics of the system Si3N4-Y2O3-Al2O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si3N4 were studied with additions of 4 to 17 wt% Y2O3 and 4 wt% A12O3. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β′ -Si3N4 and glass or β′-Si3N4, α′-Si3N4, and glass. The compositions and amounts of the residual glassy phases are estimated.

Field responses of the western pine beetle1 and one of its predators to host- and beetle-produced compounds

Abstract: The responses of the western pine beetle (Dendroctonus brev-icomis LeConte) andTemnochila chlorodia (Mannerheim) to candidate attractants—exo- andendo-brevicomm, frontalin,trans-verbenol, ver-benone, and ponderosa pine turpentine and its major monoterpene components—were quantified by counts of beetles on traps baited with the various attractants, singly and in combinations released simultaneously. Combinations ofexo-brevicomin and frontalin plus a monoterpene or turpentine were the most attractive toD. brevicomis. The responses to these attractant combinations were reduced when verbenone plustrans-verbenol were present. All single compounds and binary mixtures, exceptexo-brevicomin plus frontalin, were much less attractive.exo-Brevicomin was most attractive toT. chlorodia, and this response appeared to decrease when verbenone plustrans-verbenol were present.