Showing papers by "Stanford University published in 1980"

An Algorithm for Vector Quantizer Design

Abstract: An efficient and intuitive algorithm is presented for the design of vector quantizers based either on a known probabilistic model or on a long training sequence of data. The basic properties of the algorithm are discussed and demonstrated by examples. Quite general distortion measures and long blocklengths are allowed, as exemplified by the design of parameter vector quantizers of ten-dimensional vectors arising in Linear Predictive Coded (LPC) speech compression with a complicated distortion measure arising in LPC analysis that does not depend only on the error vector.

Measurement of patient outcome in arthritis.

Abstract: A structure for representation of patient outcome is presented, together with a method for outcome measurement and validation of the technique in rheumatoid arthritis. The paradigm represents outcome by five separate dimensions: death, discomfort, disability, drug (therapeutic) toxicity, and dollar cost. Each dimension represents an outcome directly related to patient welfare. Quantitation of these outcome dimensions may be performed at interview or by patient questionnaire. With standardized, validated questions, similar scores are achieved by both methods. The questionnaire technique is preferred since it is inexpensive and does not require interobserver validation. These techniques appear extremely useful for evaluation of long term outcome of patients with rheumatic diseases.

Aging, natural death, and the compression of morbidity.

Abstract: The average length of life has risen from 47 to 73 years in this century, but the maximum life span has not increased Therefore, survival curves have assumed an ever more rectangular form Eighty per cent of the years of life lost to nontraumatic, premature death have been eliminated, and most premature deaths are now due to the chronic diseases of the later years Present data allow calculation of the ideal average life span, approximately 85 years Chronic illness may presumably be postponed by changes in life style, and it has been shown that the physiologic and psychologic markers of aging may be modified Thus, the average age at first infirmity can be raised, thereby making the morbidity curve more rectangular Extension of adult vigor far into a fixed life span compresses the period of senescence near the end of life Health-research strategies to improve the quality of life require careful study of the variability of the phenomena of aging and how they may be modified

Exclusive Processes in Perturbative Quantum Chromodynamics

Abstract: We present a systematic analysis in perturbative quantum chromodynamics (QCD) of large-momentum-transfer exclusive processes. Predictions are given for the scaling behavior, angular dependence, helicity structure, and normalization of elastic and inelastic form factors and large-angle exclusive scattering amplitudes for hadrons and photons. We prove that these reactions are dominated by quark and gluon subprocesses at short distances, and thus that the dimensional-counting rules for the power-law falloff of these amplitudes with momentum transfer are rigorous predictions of QCD, modulo calculable logarithmic corrections from the behavior of the hadronic wave functions at short distances. These anomalous-dimension corrections are determined by evolution equations for process-independent meson and baryon "distribution amplitudes" $\ensuremath{\varphi}({x}_{i}, Q)$ which control the valence-quark distributions in high-momentum-transfer exclusive reactions. The analysis can be carried out systematically in powers of ${\ensuremath{\alpha}}_{s}({Q}^{2})$, the QCD running coupling constant. Although the calculations are most conveniently carried out using light-cone perturbation theory and the light-cone gauge, we also present a gauge-independent analysis and relate the distribution amplitude to a gauge-invariant Bethe-Salpeter amplitude.

Economies of scope and the scope of the enterprise

Abstract: This paper examines elements of an efficiency-based theory of the multiproduct firm. The theoretical framework developed by Williamson to explain vertical integration is extended to explain diversification. The proposition is advanced that a cost function displaying economies of scope has no direct implications for the scope of the business enterprise. However, if economies of scope are based upon the common and recurrent use of proprietary knowhow or the common and recurrent use of a specialized and indivisible physical asset, then multiproduct enterprise (diversification) is an efficient way of organizing economic activity. These propositions are first developed in a general context and then examined in the context of diversification in the U.S. Petroleum industry.

Gravitational Effects on and of Vacuum Decay

Abstract: It is possible for a classical field theory to have two stable homogeneous ground states, only one of which is an absolute energy minimum. In the quantum version of the theory, the ground state of higher energy is a false vacuum, rendered unstable by barrier penetration. There exists a well-established semiclassical theory of the decay of such false vacuums. In this paper, we extend this theory to include the effects of gravitation. Contrary to naive expectation, these are not always negligible, and may sometimes be of critical importance, especially in the late stages of the decay process.

Active stiffness control of a manipulator in cartesian coordinates

Abstract: A method of actively controlling the apparent stiffness of a manipulator end effecter is presented. The approach allows the programmer to specify the three transnational and three rotational stiffness of a frame located arbitrarily in hand coordinates. Control of the nominal position of the hand then permits simultaneous position and force control. Stiffness may be changed under program control to match varying task requirements. A rapid servo algorithm is made possible by transformation of the problem into joint space at run time. Applications examples are given.

Application of A-C Techniques to the Study of Lithium Diffusion in Tungsten Trioxide Thin Films

Abstract: The small signal a-c impedance of the cell Li]LiAsF6 (0.75M) in propylene carbonatel Lip V~O3 thin film on tin oxide covered glass substrate has been measured at room temperature as a function of frequency from 5  10 -4 Hz to 5 X l0 s Hz at various open-circuit voltages. The diffusion equations have been solved for the appropriate finite boundary conditions, and analysis of the impedance data by the complex plane method yields values for the chemical diffusion coefficient, the component diffusion coefficient, the partial ionic conductivity of lithium, and the thermodynamic enhancement factor for LiyWO3 as a function of y. The films of WO3 were prepared by vacuum evaporation and were largely amorphous to x-rays. The chemical diffusion coefficient has a value of 2.4  10 -12 cm2/sec at y _-- 0.1, increasing to 2.8 X 10 -11 cm2/sec at y ---- 0.26. At short times (t ~ 0.5 sec) the interracial charge transfer reaction is important, but at longer times the rate of lithium injection is determined by the diffusion kinetics.

Status organizing processes

Abstract: This chapter reviews theory and research on status organizing processes. A status organizing process is any process in which evaluations of and beliefs about the characteristics of actors become the basis of observable inequalities in face-to-face social interaction. The key concept in the study of status organizing processes is the status characteristic, any characteristic of actors around which evaluations of and beliefs about them come to be organized. Examples include age, sex, race, ethnicity, education, occupation, physical attractiveness, intelligence quotients, reading ability-but there are many others. In the present article we review (a) the current state of the theory of such processes; (b) relevant theoretical research as of September, 1979; (c) a selection of the relevant applied research, with particular reference to sex, race, and physical attractiveness; and (d) some of the interventions that have been devel­ oped to reduce undesired consequences of the process. The phenomenon with which a theory of status organizing processes is concerned is most commonly observed in the study of problem-solving groups whose members differ in status characteristics significant in the larger society. Such groups do not create a social organization de novo, out of the interaction of their members, but instead maintain external status differences inside the group. That informal problem-solving groups evolve inequalities in participa­ tion, evaluation, and influence was shown by Bales in the early fifties

Human sleep: its duration and organization depend on its circadian phase

Abstract: Two- to threefold variations in sleep length were observed in 12 subjects living on self-selected schedules in an environment free of time cues. The duration of polygraphically recorded sleep episodes was highly correlated with the circadian phase of the body temperature rhythm at bedtime and not with the length of prior wakefulness. Furthermore, the rate of REM (rapid eye movement) sleep accumulation , REM latency, bedtime selection, and self-rated alertness assessments were also correlated with the body temperature rhythm.

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.

A cryptanalytic time-memory trade-off

Abstract: A probabilistic method is presented which cryptanalyzes any N key cryptosystem in N^{2/3} operational with N^{2/3} words of memory (average values) after a precomputation which requires N operations. If the precomputation can be performed in a reasonable time period (e.g, several years), the additional computation required to recover each key compares very favorably with the N operations required by an exhaustive search and the N words of memory required by table lookup. When applied to the Data Encryption Standard (DES) used in block mode, it indicates that solutions should cost between 1 and 100 each. The method works in a chosen plaintext attack and, if cipher block chaining is not used, can also be used in a ciphertext-only attack.

Expression of a bacterial gene in mammalian cells

Abstract: Transfection of cultured monkey kidney cells with recombinant DNA constructed with a cloned Escherichia coli gene that codes for xanthine-guanine phosphoribosyltransferase and several different SV40 DNA-based vectors, results in the synthesis of readily measurable quantities of the bacterial enzyme. Moreover, the physiological defect in purine nucleotide synthesis characteristic of human Lesch-Nyhan cells can be overcome by the introduction of the bacterial gene into these cells.

Multidimensional scaling, tree-fitting, and clustering.

Abstract: American mathematical psychologists have developed computer-based methods for constructing representations of the psychological structure of a set of stimuli on the basis of pairwise measures of similarity or confusability. Applications to perceptual and semantic data illustrate how complementary aspects of the underlying psychological structure are revealed by different types of representations, including multidimensional spatial configurations and nondimensional tree-structures or clusterings.

Tests of the generality of self-efficacy theory.

Abstract: The present set of studies tested the explanatory and predictive generality of self-efficacy theory across additional treatment modalities and behavioral domains. Microanalysis of changes accompanying symbolic modeling indicates that this mode of treatment enhances coping behavior partly through its effects on perceived efficacy. Cognizing modeled mastery of threats increased phobics' self-percepts of efficacy, which, in turn, predicted their specific performance attainments on tasks of varying threat value. Examination of efficacy probes revealed that making efficacy judgments has no effect on subsequent avoidance behavior or on fear arousal. The close congruence found between changes in self-efficacy and different forms of coping behavior in the treatment of agoraphobia provides some evidence for the generality of efficacy theory across different areas of functioning. Microanalysis of anticipatory and performance fear arousal accompanying varying strengths of self-efficacy also lends support for the social learning conception of fear arousal in terms of perceived coping inefficacy.

A Deductive Approach to Program Synthesis

Abstract: Program synthesis is the systematic derivation of a program from a given specification. A deductive approach to program synthesis is presented for the construction of recursive programs. This approach regards program synthesis as a theorem-proving task and relies on a theorem-proving method that combines the features of transformation rules, unification, and mathematical induction within a single framework.

An Empirical Model of Labor Supply in a Life Cycle Setting

Abstract: This paper formulates and estimates a structural life cycle model of labor supply. Using theoretical characterizations derived from an economic model of life cycle behavior, a two-stage empirical analysis yields estimates of intertemporal and uncompensated substitution effects which provides the information needed to predict the response of hours of work to life cycle wage growth and shifts in the lifetime wage path. The empirical model developed here provides a natural framework for interpreting estimates found in other work on this topic. It also indicates how cross section specifications of hours of work can be modified to estimate parameters relevant for describing labor supply behavior in a lifetime setting.

A critique of cross-lagged correlation

Abstract: Comments that cross-lagged correlation (CLC) is not a useful procedure for the analysis of longitudinal panel data. In particular, the difference between CLCs is not a sound basis for causal inference. Demonstrations of the failure of CLC are based mainly on results for the 2-wave, 2-variable longit

The trilogy of mind: cognition, affection, and conation.

Abstract: The tripartite classification of mental activities into cognition, affection, and conation originated in the German faculty psychology of the eighteenth century, but was adopted by the association psychologists of the nineteenth century of Scotland, England, and America. Its influence extended into the twentieth century through the writings of William McDougall. It is proposed that the classificatory scheme is still useful in the assessment of contemporary emphases in psychology, such as the present prominence of cognitive psychology to the relative neglect of affection and conation.

Electron mobility in inversion and accumulation layers on thermally oxidized silicon surfaces

Abstract: Accurate modeling of MOS devices requires quantitative knowledge of carrier mobilities in surface inversion and accumulation layers. Optimization of device structures and accurate circuit simulation, particulary as technologies push toward fundamental limits, necessitate an understanding of how impurity doping levels, oxide charge densities, process techniques, and applied electric fields affect carrier surface mobilities. It is the purpose of this paper to present an extensive set experimental results on the behavior of electron surface mobility in thermally oxidized silicon structures. Empirical equations are developed which allow the calculation of electron mobility under a wide variety of substrate, process, and electrical conditions. The experimental results are interpreted in terms of the dominant physical mechanisms responsible for mobility degradation at the Si/SiO 2 interface. From the observed effects of process parameters on mobility roll-off under high vertical fields, conclusions are drawn about optimum process conditions for maximizing mobility. The implications of this work for performance limits of several types of MOS devices are described.

Multilocus structure of natural populations of hordeum spontaneum

Abstract: The association of alleles among different loci was studied in natural populations of Hordeum spontaneum, the evolutionary progenitor of cultivated barley. The variance of the number of heterozygous loci in two randomly chosen gametes affords a useful measure of such association. The behavior of this statistic in several particular models is described. Generally, linkage (gametic phase) disequilibrium tends to increase the variance above the value expected under complete independence. This increase is greatest when disequilibria are such as to maximize the sum of squares of the two-locus gametic frequencies.-When data on several loci per individual are available, the observed variance may be tested for its agreement with that expected under the hypothesis of complete interlocus independence, using the sampling theory of this model. When applied to allozyme data from 26 polymorphic populations of wild barley, this test demonstrated the presence of geographically widespread multilocus organization. On average, the variance was 80% higher than expected under random association. Gametic frequencies for four esterase loci in both of these populations of wild barley and two composite crosses of cultivated barley were analyzed. Most generations of the composites showed less multilocus structure, as measured by the indices of association, than the wild populations.