Showing papers by "Stanford University published in 1987"

Some philosophical problems from the standpoint of artificial intelligence

Abstract: A computer program capable of acting intelligently in the world must have a general representation of the world in terms of which its inputs are interpreted. Designing such a program requires commitments about what knowledge is and how it is obtained. Thus, some of the major traditional problems of philosophy arise in artificial intelligence. More specifically, we want a computer program that decides what to do by inferring in a formal language that a certain strategy will achieve its assigned goal. This requires formalizing concepts of causality, ability, and knowledge. Such formalisms are also considered in philosophical logic. The first part of the paper begins with a philosophical point of view that seems to arise naturally once we take seriously the idea of actually making an intelligent machine. We go on to the notions of metaphysically and epistemo-logically adequate representations of the world and then to an explanation of can, causes, and knows in terms of a representation of the world by a system of interacting automata. A proposed resolution of the problem of freewill in a deterministic universe and of counterfactual conditional sentences is presented. The second part is mainly concerned with formalisms within which it can be proved that a strategy will achieve a goal. Concepts of situation, fluent, future operator, action, strategy, result of a strategy and knowledge are formalized. A method is given of constructing a sentence of first-order logic which will be true in all models of certain axioms if and only if a certain strategy will achieve a certain goal. The formalism of this paper represents an advance over McCarthy (1963) and Green (1969) in that it permits proof of the correctness of strategies that contain loops and strategies that involve the acquisition of knowledge; and it is also somewhat more concise. The third part discusses open problems in extending the formalism of part 2. The fourth part is a review of work in philosophical logic in relation to problems of artificial intelligence and a discussion of previous efforts to program ‘general intelligence’ from the point of view of this paper.

Signaling Games and Stable Equilibria

Abstract: Games in which one party conveys private information to a second through messages typically admit large numbers of sequential equilibria, as the second party may entertain a wealth of beliefs in response to out-of-equilibrium messages. By restricting those out-of equilibrium beliefs, one can sometimes eliminate many unintuitive equilibria. We present a number of formal restrictions of this sort, investigate their behavior in specific examples, and relate these restrictions to Kohlberg and Mertens` notion of stability.

Structure of the human class I histocompatibility antigen, HLA-A2.

Abstract: The class I histocompatibility antigen from human cell membranes has two structural motifs: the membrane-proximal end of the glycoprotein contains two domains with immunoglobulin-folds that are paired in a novel manner, and the region distal from the membrane is a platform of eight antiparallel beta-strands topped by alpha-helices. A large groove between the alpha-helices provides a binding site for processed foreign antigens. An unknown 'antigen' is found in this site in crystals of purified HLA-A2.

Managerial perspectives on risk and risk taking

Abstract: This paper explores the relation between decision theoretic conceptions of risk and the conceptions held by executives. It considers recent studies of risk attitudes and behavior among managers against the background of conceptions of risk derived from theories of choice. We conclude that managers take risks and exhibit risk preferences, but the processes that generate those observables are somewhat removed from the classical processes of choosing from among alternative actions in terms of the mean (expected value) and variance (risk) of the probability distributions over possible outcomes. We identify three major ways in which the conceptions of risk and risk taking held by these managers lead to orientations to risk that are different from what might be expected from a decision theory perspective: Managers are quite insensitive to estimates of the probabilities of possible outcomes; their decisions are particularly affected by the way their attention is focused on critical performance targets; and they ...

Better Bootstrap Confidence Intervals

Abstract: We consider the problem of setting approximate confidence intervals for a single parameter θ in a multiparameter family. The standard approximate intervals based on maximum likelihood theory, , can be quite misleading. In practice, tricks based on transformations, bias corrections, and so forth, are often used to improve their accuracy. The bootstrap confidence intervals discussed in this article automatically incorporate such tricks without requiring the statistician to think them through for each new application, at the price of a considerable increase in computational effort. The new intervals incorporate an improvement over previously suggested methods, which results in second-order correctness in a wide variety of problems. In addition to parametric families, bootstrap intervals are also developed for nonparametric situations.

A unified approach for motion and force control of robot manipulators: The operational space formulation

Abstract: A framework for the analysis and control of manipulator systems with respect to the dynamic behavior of their end-effectors is developed. First, issues related to the description of end-effector tasks that involve constrained motion and active force control are discussed. The fundamentals of the operational space formulation are then presented, and the unified approach for motion and force control is developed. The extension of this formulation to redundant manipulator systems is also presented, constructing the end-effector equations of motion and describing their behavior with respect to joint forces. These results are used in the development of a new and systematic approach for dealing with the problems arising at kinematic singularities. At a singular configuration, the manipulator is treated as a mechanism that is redundant with respect to the motion of the end-effector in the subspace of operational space orthogonal to the singular direction.

The foreign antigen binding site and T cell recognition regions of class I histocompatibility antigens

Abstract: Most of the polymorphic amino acids of the class I histocompatibility antigen, HLA-A2, are clustered on top of the molecule in a large groove identified as the recognition site for processed foreign antigens. Many residues critical for T-cell recognition of HLA are located in this site, in positions allowing them to serve as ligands to processed antigens. These findings have implications for how the products of the major histocompatibility complex (MHC) recognize foreign antigens.

Toward a universal law of generalization for psychological science

Abstract: A psychological space is established for any set of stimuli by determining metric distances between the stimuli such that the probability that a response learned to any stimulus will generalize to any other is an invariant monotonic function of the distance between them. To a good approximation, this probability of generalization (i) decays exponentially with this distance, and (ii) does so in accordance with one of two metrics, depending on the relation between the dimensions along which the stimuli vary. These empirical regularities are mathematically derivable from universal principles of natural kinds and probabilistic geometry that may, through evolutionary internalization, tend to govern the behaviors of all sentient organisms.

Prostate-Specific Antigen as a Serum Marker for Adenocarcinoma of the Prostate

Abstract: To compare the clinical usefulness of the serum markers prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP), we measured them by radioimmunoassay in 2200 serum samples from 699 patients, 378 of whom had prostatic cancer. PSA was elevated in 122 of 127 patients with newly diagnosed, untreated prostatic cancer, including 7 of 12 patients with unsuspected early disease and all of 115 with more advanced disease. The PSA level increased with advancing clinical stage and was proportional to the estimated volume of the tumor. The PAP concentration was elevated in only 57 of the patients with cancer and correlated less closely with tumor volume. PSA was increased in 86 percent and PAP in 14 percent of the patients with benign prostatic hyperplasia. After radical prostatectomy for cancer, PSA routinely fell to undetectable levels, with a half-life of 2.2 days. If initially elevated, PAP fell to normal levels within 24 hours but always remained detectable. In six patients followed postoperatively by means of repeated measurements, PSA--but not PAP--appeared to be useful in detecting residual and early recurrence of tumor and in monitoring responses to radiation therapy. Prostate massage increased the levels of both PSA and PAP approximately 1.5 to 2 times. Needle biopsy and transurethral resection increased both considerably. We conclude that PSA is more sensitive than PAP in the detection of prostatic cancer and will probably be more useful in monitoring responses and recurrence after therapy. However, since both PSA and PAP may be elevated in benign prostatic hyperplasia, neither marker is specific.

HLA-DQ beta gene contributes to susceptibility and resistance to insulin-dependent diabetes mellitus.

Abstract: Over half of the inherited predisposition to insulin-dependent diabetes mellitus maps to the region of chromosome 6 that contains the highly polymorphic HLA class II genes which determine immune responsiveness. Analysis of DNA sequences from diabetics indicates that alleles of HLA-DQ beta determine both disease susceptibility and resistance, and that the structure of the DQ molecule, in particular residue 57 of the beta-chain, specifies the autoimmune response against the insulin-producing islet cells.

Sex differences in unipolar depression: evidence and theory.

Abstract: A large body of evidence indicates that women are more likely than men to show unipolar depression. Five classes of explanations for these sex differences are examined and the evidence for each class is reviewed. Not one of these explanations adequately accounts for the magnitude of the sex differences in depression. Finally, a response set explanation for the sex differences in depression is proposed. According to this explanation, men are more likely to engage in distracting behaviors that dampen their mood when depressed, but women are more likely to amplify their moods by ruminating about their depressed states and the possible causes of these states. Regardless of the initial source of a depressive episode (i.e., biological or psychological) men's more active responses to their negative moods may be more adaptive on average than women's less active, more ruminative responses. The epidemiology of a disorder can provide important clues to its etiology. When a disorder only strikes persons from one geographical region, one social class, or one gender, we can ask what characteristics of the vulnerable group might be making its members vulnerable. A frequent finding in epidemiological studies of mental disorders is that women are more prone to unipolar affective disorders than are men (Boyd & Weissman, 1981; Weissman & Klerman, 1977). A number of different explanations have been proposed to account for women's greater vulnerability to depression. Previous reviews of these explanations (e.g., Weissman & Klerman, 1977) have been quite brief and uncritical. In this article, the evidence for sex differences in unipolar depression first is summarized, then the most prominent explanations proposed for these sex differences are discussed in detail. These explanations include those attributing the differences to the response biases of subjects, as well as biological, psychoanalytic, sex role, and learned helplessness explanations. Although most of the proposed explanations for sex differences in depression have received some empirical support, not one of them has been definitively supported and not one as yet accounts for the magnitude of sex differences in depression. In the final section of this article it is suggested that differences in the ways that men and women respond to their own depressive episodes, whatever the origin of these episodes, may be an important source of the sex differences observed in depression.

The relation of parenting style to adolescent school performance

Abstract: This article develops and tests a reformation of Baumrind's typology of authoritarian, permissive, and authoritative parenting styles in the context of adolescent school performance. Using a large and diverse sample of San Francisco Bay Area high school students (N = 7,836), we found that both authoritarian and permissive parenting styles were negatively associated with grades, and authoritative parenting was positively associated with grades. Parenting styles generally showed the expected relation to grades across gender, age, parental education, ethnic, and family structure categories. Authoritarian parenting tended to have a stronger association with grades than did the other 2 parenting styles, except among Hispanic males. The full typology best predicted grades among white students. Pure authoritative families (high on authoritative but not high on the other 2 indices) had the highest mean grades, while inconsistent families that combine authoritarian parenting with other parenting styles had the lowest grades.

Logical Foundations of Artificial Intelligence

Abstract: Typographical Conventions 1 Introduction 1.1 Bibliographical and Historical Remarks Exercises 2 Declarative Knowledge 2.1 Conceptualization 2.2 Predicate Calculus 2.3 Semantics 2.4 Blocks World Example 2.5 Circuits Example 2.6 Algebraic Examples 2.7 List Examples 2.8 Natural-Language Examples 2.9 Specialized Languages 2.10 Bibliographical and Historical Remarks Exercises 3 Inference 3.1 Derivability 3.2 Inference Procedures 3.3 Logical Implication 3.4 Provability 3.5 Proving Provability 3.6 Bibliographical and Historical Remarks Exercises 4 Resolution 4.1 Clausal Form 4.2 Unification 4.3 Resolution Principle 4.4 Resolution 4.5 Unsatisfiability 4.6 True-or-False Questions 4.7 Fill-in-the-Blank Questions 4.8 Circuits Example 4.9 Mathematics Example 4.10 Soundness and Completeness 4.11 Resolution and Equality 4.12 Bibliographical and Historical Remarks Exercises 5 Resolution Strategies 5.1 Deletion Strategies 5.2 Unit Resolution 5.3 Input Resolution 5.4 Linear Resolution 5.5 Set of Support Resolution 5.6 Ordered Resolution 5.7 Directed Resolution 5.8 Sequential Constraint Satisfaction 5.9 Bibliographical and Historical Remarks Exercises 6 Nonmonotonic Reasoning 6.1 The Closed-World Assumption 6.2 Predicate Completion 6.3 Taxonomic Hierarchies and Default Reasoning 6.4 Circumscription 6.5 More General Forms of Circumscription 6.6 Default Theories 6.7 Bibliographical and Historical Remarks Exercises 7 Induction 7.1 Induction 7.2 Concept Formation 7.3 Experiment Generation 7.4 Bibliographical and Historical Remarks Exercises 8 Reasoning with Uncertain Beliefs 8.1 Probabilities of Sentences 8.2 Using Bayes' Rule in Uncertain Reasoning 8.3 Uncertain Reasoning in Expert Systems 8.4 Probabilistic Logic 8.5 Probabilistic Entailment 8.6 Computations Appropriate for Small Matrices 8.7 Dealing with Large Matrices 8.8 Probabilities Conditioned on Specific Information 8.9 Bibliographical and Historical Remarks Exercises 9 Knowledge and Belief 9.1 Preliminaries 9.2 Sentential Logics of Belief 9.3 Proof Methods 9.4 Nested Beliefs 9.5 Quantifying-In 9.6 Proof Methods for Quantified Beliefs 9.7 Knowing What Something Is 9.8 Possible-Worlds Logics 9.9 Properties of Knowledge 9.10 Properties of Belief 9.11 Group Knowledge 9.12 Equality, Quantification, and Knowledge 9.13 Bibliographical and Historical Remarks Exercises 10 Metaknowledge and Metareasoning 10.1 Metalanguage 10.2 Clausal Form 10.3 Resolution Principle 10.4 Inference Procedures 10.5 Derivability and Belief 10.6 Metalevel Reasoning 10.7 Bilevel Reasoning 10.8 Reflection 10.9 Bibliographical and Historical Remarks Exercises 11 State and Change 11.1 States 11.2 Actions 11.3 The Frame Problem 11.4 Action Ordering 11.5 Conditionality 11.6 Bibliographical and Historical Remarks Exercises 12 Planning 12.1 Initial State 12.2 Goals 12.3 Actions 12.4 Plans 12.5 Green's Method 12.6 Action Blocks 12.7 Conditional Plans 12.8 Planning Direction 12.9 Unachievability Pruning 12.10 State Alignment 12.11 Frame-Axiom Suppression 12.12 Goal Regression 12.13 State Differences 12.14 Bibliographical and Historical Remarks Exercises 13 Intelligent-Agent Architecture 13.1 Tropistic Agents 13.2 Hysteretic Agents 13.3 Knowledge-Level Agents 13.4 Stepped Knowledge-Level Agents 13.5 Fidelity 13.6 Deliberate Agents 13.7 Bibliographical and Historical Remarks Exercises Answers to Exercises A.1 Introduction A.2 Declarative Knowledge A.3 Inference A.4 Resolution A.5 Resolution Strategies A.6 Nonmonotonic Reasoning A.7 Induction A.8 Reasoning with Uncertain Beliefs A.9 Knowledge and Belief A.10 Metaknowledge and Metareasoning A.11 State and Change A.12 Planning A.13 Intelligent-Agent Architecture References Index

Interleukin-1 stimulates the secretion of hypothalamic corticotropin-releasing factor.

Abstract: There is now evidence that the immune system, during times of infectious challenge, can stimulate the secretion of glucocorticoids, the adrenal steroids that mediate important aspects of the response to stress. Specifically, secretion of interleukin-1 (IL-1), a monocyte lymphokine secreted after infection, appears at least in part responsible for this effect. Glucocorticoids are secreted in response to a neuroendocrine cascade involving, first, the brain, then the pituitary, and finally the adrenal gland. In this report, human IL-1 is shown to activate the adrenocortical axis at the level of the brain, stimulating the release of the controlling hormone corticotropin-releasing factor (CRF) from the hypothalamus. Infusion of IL-1 induced a significant secretion of CRF into the circulation exiting the hypothalamus, whereas immunoneutralization of CRF blocked the stimulatory effect of IL-1 on glucocorticoid secretion. IL-1 appeared to have no acute direct stimulatory effects on the pituitary or adrenal components of this system. Furthermore, IL-1 did not cause a nonspecific release of other hypothalamic hormones. Thus, the lymphokine acts in a specific manner to activate the adrenocortical axis at the level of the brain; this effect appears to be unrelated to the known pyrogenic effects of IL-1 within the hypothalamus.

The Complexity of Markov Decision Processes

Abstract: We investigate the complexity of the classical problem of optimal policy computation in Markov decision processes. All three variants of the problem finite horizon, infinite horizon discounted, and infinite horizon average cost were known to be solvable in polynomial time by dynamic programming finite horizon problems, linear programming, or successive approximation techniques infinite horizon. We show that they are complete for P, and therefore most likely cannot be solved by highly parallel algorithms. We also show that, in contrast, the deterministic cases of all three problems can be solved very fast in parallel. The version with partially observed states is shown to be PSPACE-complete, and thus even less likely to be solved in polynomial time than the NP-complete problems; in fact, we show that, most likely, it is not possible to have an efficient on-line implementation involving polynomial time on-line computations and memory of an optimal policy, even if an arbitrary amount of precomputation is allowed. Finally, the variant of the problem in which there are no observations is shown to be NP-complete.

Why are children in the same family so different from one another

Abstract: One of the most important findings that has emerged from human behavioral genetics involves the environment rather than heredity, providing the best available evidence for the importance of environmental influences on personality, psychopathology, and cognition. The research also converges on the remarkable conclusion that these environmental influences make two children in the same family as different from one another as are pairs of children selected randomly from the population.The theme of the target article is that environmental differences between children in the same family (called “nonshared environment”) represent the major source of environmental variance for personality, psychopathology, and cognitive abilities. One example of the evidence that supports this conclusion involves correlations for pairs of adopted children reared in the same family from early in life. Because these children share family environment but not heredity, their correlation directly estimates the importance of shared family environment. For most psychological characteristics, correlations for adoptive “siblings” hover near zero, which implies that the relevant environmental influences are not shared by children in the same family. Although it has been thought that cognitive abilities represent an exception to this rule, recent data suggest that environmental variance that affects IQ is also of the nonshared variety after adolescence.The article has three goals: (1) To describe quantitative genetic methods and research that lead to the conclusion that nonshared environment is responsible for most environmental variation relevant to psychological development, (2) to discuss specific nonshared environmental influences that have been studied to date, and (3) to consider relationships between nonshared environmental influences and behavioral differences between children in the same family. The reason for presenting this article in BBS is to draw attention to the far-reaching implications of finding that psychologically relevant environmental influences make children in a family different from, not similar to, one another.

A Progressive Damage Model for Laminated Composites Containing Stress Concentrations

Abstract: A progressive damage model is presented for notched laminated composites subjected to tensile loading. The model is capable of assessing damage in laminates with arbitrary ply-orientations and of predicting the ultimate tensile strength of the notched laminates. The model consists of two parts, namely, the stress analysis and the failure analysis. Stresses and strains in laminates were analyzed on the basis of classical lamination theory with the consideration of material nonlinearity. Damage accumulation in laminates was evaluated by proposed failure criteria combined with a proposed property degradation model. A nonlinear finite element program, based on the model, was developed for lami nates containing a circular hole. Numerical results were compared with the experimental data on laminates containing an open circular hole. An excellent agreement was found be tween the analytical prediction and the experimental data.

Self: The power of simplicity

Abstract: Self is a new object-oriented language for exploratory programming based on a small number of simple and concrete ideas: prototypes, slots, and behavior. Prototypes combine inheritance and instantiation to provide a framework that is simpler and more flexible than most object-oriented languages. Slots unite variables and procedures into a single construct. This permits the inheritance hierarchy to take over the function of lexical scoping in conventional languages. Finally, because Self does not distinguish state from behavior, it narrows the gaps between ordinary objects, procedures, and closures. Self's simplicity and expressiveness offer new insights into object-oriented computation.

Gene transfer and molecular cloning of the rat nerve growth factor receptor.

Abstract: The amino-acid sequence of one form of the receptor for nerve growth factor defines a new class of growth factor receptors.

Disruption of the Dictyostelium myosin heavy chain gene by homologous recombination

Abstract: The phenomenon of homologous recombination, which allows specific gene conversion and gene insertion, can be a powerful system for the study of eukaryotic cell biology. Data are presented demonstrating that integration of a transfected plasmid by homologous recombination occurs in the motile eukaryotic cell Dictyostelium discoideum. A plasmid carrying a G418 resistance gene and the amino terminal half of the myosin heavy chain gene was used to transfect Dictyostelium. A large fraction of the resultant G418-resistant cells had the plasmid integrated into the single genomic copy of the heavy chain gene. These cells, which fail to express the native myosin but express the myosin fragment, are defective in cytokinesis and become large and multinucleate. In spite of the absence of native myosin, these cells, termed hmm cells, exhibit many forms of cell movement, including membrane ruffling, phagocytosis, and chemotaxis. The hmm cells can aggregate but are blocked at a later stage in the Dictyostelium developmental cycle. The hmm cells revert to the wild-type phenotype. Reversion of the hmm phenotype is due to excision and loss of the transforming plasmid. The revertant cells express native myosin, are G418 sensitive, and have a normal developmental cycle. These results constitute genetic proof that the intact myosin molecule is required for cytokinesis and not for karyokinesis.

New evidence on the state of stress of the San Andreas fault system

Abstract: Contemporary in situ tectonic stress indicators along the San Andreas fault system in central California show northeast-directed horizontal compression that is nearly perpendicular to the strike of the fault. Such compression explains recent uplift of the Coast Ranges and the numerous active reverse faults and folds that trend nearly parallel to the San Andreas and that are otherwise unexplainable in terms of strike-slip deformation. Fault-normal crustal compression in central California is proposed to result from the extremely low shear strength of the San Andreas and the slightly convergent relative motion between the Pacific and North American plates. Preliminary in situ stress data from the Cajon Pass scientific drill hole (located 3.6 kilometers northeast of the San Andreas in southern California near San Bernardino, California) are also consistent with a weak fault, as they show no right-lateral shear stress at approximately 2-kilometer depth on planes parallel to the San Andreas fault.

On a fully three-dimensional finite-strain viscoelastic damage model: Formulation and computational aspects

Abstract: A fully three-dimensional finite-strain viscoelastic model is developed, characterized by: (i) general anisotropic response, (ii) uncoupled bulk and deviatoric response over any range of deformations, (iii) general relaxation functions, and (iv) recovery of finite elasticity for very fast or very slow processes; in particular, classical models of rubber elasticity (e.g. Mooney-Rivlin). Continuum damage mechanics is employed to develop a simple isotropic damage mechanism, which incorporates softening behavior under deformation, and leads to progressive degradation of the storage modulus in a cyclic test with increasing amplitude (Mullins' effect). A numerical integration procedure is proposed which trivially satisfies objectivity and bypasses the use of midpoint configurations. The resulting algorithm can be exactly linearized in closed form, and leads to symmetric tangent moduli. Quasi-incompressible response is accounted for within the context of a three-field variational formulation of the Hu-Washizu type.

How Many Subjects?: Statistical Power Analysis in Research

Abstract: CHAPTER 1 Introduction CHAPTER 2 General Concepts CHAPTER 3 The Pivotal Case Intraclass Correlation CHAPTER 4 Equality of News Z- and T- tests, Balanced ANOVA CHAPTER 5 Correlation Coefficients CHAPTER 6 Linear Regression CHAPTER 7 Homogeneity of Variance Tests CHAPTER 8 Binomial Tests CHAPTER 9 Contingency Table Analysis CHAPTER 10 Conclusions