Showing papers by "Stanford University published in 1968"

Human memory ; A proposed system and its control processes

Abstract: Publisher Summary This chapter presents a general theoretical framework of human memory and describes the results of a number of experiments designed to test specific models that can be derived from the overall theory. This general theoretical framework categorizes the memory system along two major dimensions. The first categorization distinguishes permanent, structural features of the system from control processes that can be readily modified or reprogrammed at the will of the subject. The second categorization divides memory into three structural components: the sensory register, the short-term store, and the long-term store. Incoming sensory information first enters the sensory register, where it resides for a very brief period of time, then decays and is lost. The short-term store is the subject's working memory; it receives selected inputs from the sensory register and also from long-term store. The chapter also discusses the control processes associated with the sensory register. The term control process refers to those processes that are not permanent features of memory, but are instead transient phenomena under the control of the subject; their appearance depends on several factors such as instructional set, the experimental task, and the past history of the subject.

Elastic-Plastic Deformation at Finite Strains

Abstract: : In some circumstances, elastic-plastic deformation occurs in which both components of strain are finite. Such situations fall outside the scope of classical plasticity theory which assumes either infinitesimal strains or plastic-rigid theory for large strains. The present theory modifies the kinematics to include finite elastic and plastic strain components. For situations requiring this generalization, dilatational influences are usually significant including thermo-mechanical coupling. This is introduced through the consideration of two coupled thermodynamic systems: one comprising thermo- elasticity at finite strain and the other the irreversible process of dissipation and absorption of plastic work. The present paper generalizes a previous theory to permit arbitrary deformation histories.

An Introduction to Harmonic Analysis

Abstract: 1. Fourier series on T 2. The convergence of Fourier series 3. The conjugate function 4. Interpolation of linear operators 5. Lacunary series and quasi-analytic classes 6. Fourier transforms on the line 7. Fourier analysis on locally compact Abelian groups 8. Commutative Banach algebras A. Vector-valued functions B. Probabilistic methods.

Saving and Uncertainty: The Precautionary Demand for Saving

Abstract: Publisher Summary This chapter discusses a two-period model developed to analyze rigorously the precautionary demand for saving. The precautionary demand for saving is usually described as the extra saving caused by future income being random rather than determinate. The effect of uncertainty on saving becomes obfuscated by generality. Many of the usual outlets for consumer saving, including saving deposits and government bonds, offer a fixed monetary rate of return. A multi-period model would be necessary to explore fully the effect of assets on the precautionary demand for saving. Until further progress is made with the more powerful inter-temporal models of optimization under uncertainty, the two-period model must be accepted along with its conclusion that states that under reasonable assumptions, there exists a positive precautionary demand for saving.

The ecology of arctic and alpine plants

Abstract: Summary ‘How are plants adapted to the low temperatures and other stresses of arctic and alpine environments ?’ At present it is not possible to answer this question completely. Much work remains to be done, particularly on low-temperature metabolism, frost resistance, and the environmental cues and requirements for flowering, dormancy, regrowth, and germination. However, in brief, we can say that plants are adapted to these severe environments by employing combinations of the following general characteristics: 1. Life form: perennial herb, prostrate shrub, or lichen. Perennial herbs have greatest part of biomass underground. 2. Seed dormancy: generally controlled by environment; seeds can remain dormant for long periods of time at low temperatures since they require temperatures well above freezing for germination. 3. Seedling establishment: rare and very slow; it is often several years before a seedling is safely established. 4. Chlorophyll content: in both alpine and arctic ecosystems not greatly different on a land-area basis from that in temperate herbaceous communities. Within a single species there is more chlorophyll in leaves of arctic populations than in those of alpine populations. 5. Photosynthesis and respiration: (a) These are at high rates for only a few weeks when temperatures and light are favourable. (b) Optimum photosynthesis rates are at lower temperatures than for ordinary plants; rates are both genetically and environmentally controlled with phenotypic plasticity very marked. (c) Dark respiration is higher at all temperatures than for ordinary plants; rate is both genetically and environmentally controlled, with phenotypic plasticity very pronounced, i.e. low-temperature environment increases the rate at all temperatures. (d) Alpine plants have higher light-saturation values in photosynthesis than do arctic or lowland plants; light saturation closely tied to temperature. (e) There is some evidence that alpine plants can carry on photosynthesis at lower carbon dioxide concentrations than can other plants. (f) Annual productivity is low, but daily productivity during growing season can be as high as that of most temperate herbaceous vegetation. Productivity can be increased by temperature, nutrients, or water. 6. Drought resistance: most drought stress in winter in exposed sites is due to frozen soils and dry winds. It is met by decreased water potentials, higher concentrations of soluble carbohydrates, and closed stomates. Little drought resistance in snowbank plants. Alpine plants adapted to summer drought stress can carry on photosynthesis at low water potentials; alpine or arctic plants of moist sites cannot do this. 7. Breaking of dormancy: controlled by mean temperatures near or above 0° C., and in some cases by photoperiod also. 8. Growth: very rapid even at low positive temperatures. Respiration greatly exceeds photosynthesis in early re-growth of perennials. Internal photosynthesis may occur in hollow stems of larger plants during early growth. Nitrogen and phosphorus often limiting in cold soil. 9. Food storage: characteristic of all alpine and arctic plants except annuals. Carbohydrates mostly stored underground in herbaceous perennials. Lipids in old leaves and stems of prostrate evergreen shrubs. Depleted in early growth, and usually restored after flowering. 10. Winter survival: survival and frost resistance are excellent after hardening. Cold resistance closely tied to content of soluble carbohydrates, particularly raffinose. 11. Flowering: flower buds are pre-formed the year before. Complete development and anthesis dependent upon temperature of the flowering year and also, in some cases, upon photoperiod. 12. Pollination: mostly insect-pollinated in alpine regions and even in Arctic, but to a lesser extent. Wind-pollination increasingly more important with increasing latitude. Diptera more important than bees in the Arctic and in the highest mountains. 13. Seed production: opportunistic, and dependent upon temperature during flowering period and latter half of growing season. 14. Vegetative reproduction: by rhizomes, bulbils, or layering. More common and important in Arctic than in alpine areas. 15. Onset of dormancy: triggered by photoperiod, low temperatures, and drought. Dormant plant extremely resistant to low temperatures.

The development of a menstrual distress questionnaire.

Abstract: The development of a Menstrual Distress Questionnaire (MDQ) is described. Each of 839 women rated their experience of 47 symptoms on a six-point scale separately for the menstrual, premenstrual, and intermenstrual phases of her most recent menstrual cycle and for her worst menstrual cycle. The 47 sy

An innovations approach to least-squares estimation--Part II: Linear smoothing in additive white noise

Abstract: The innovations approach to linear least-squares approximation problems is first to "whiten" the observed data by a causal and invertible operation, and then to treat the resulting simpler white-noise observations problem This technique was successfully used by Bode and Shannon to obtain a simple derivation of the classical Wiener filtering problem for stationary processes over a semi-infinite interval Here we shall extend the technique to handle nonstationary continuous-time processes over finite intervals In Part I we shall apply this method to obtain a simple derivation of the Kalman-Bucy recursive filtering formulas (for both continuous-time and discrete-time processes) and also some minor generalizations thereof

Fluorescence Spectroscopy of Proteins

Abstract: Fluorescence spectroscopy of proteins, analyzing polarity, distances between groups, flexibility and conformational transitions

The Foundations of Decision Analysis

Abstract: Decision analysis has emerged from theory to practice to form a discipline for balancing the many factors that bear upon a decision. Unusual features of the discipline are the treatment of uncertainty through subjective probability and of attitude toward risk through utility theory. Capturing the structure of problem relationships occupies a central position; the process can be visualized in a graphical problem space. These features are combined with other preference measures to produce a useful conceptual model for analyzing decisions, the decision analysis cycle. In its three phases?deterministic, probabilistic, and informational?the cycle progressively determines the importance of variables in deterministic, probabilistic, and economic environments. The ability to assign an economic value to the complete or partial elimination of uncertainty through experimentation is a particularly important characteristic. Recent applications in business and government indicate that the increased logical scope afforded by decision analysis offers new opportunities for rationality to those who wish it.

Optimum Form of a Modified Heine-Abarenkov Model Potential for the Theory of Simple Metals

Abstract: A modified form of the Heine-Abarenkov model potential is proposed. The core potential is replaced with a constant potential ${A}_{l}$ only for those angular momenta for which there are core wave functions. Also, the model radius ${R}_{l}$ is allowed to be different for each $l$ and to depend on energy. It is shown that this potential can be optimized using a variational procedure. The optimum model parameters are obtained by choosing an ${R}_{l}$ such that ${A}_{l}=\ensuremath{-}v({R}_{l})$. The optimized form of this modified model potential has several advantages. It provides a unique prescription for selecting model radii, and it eliminates the necessity of approximating the ${A}_{l}$ for $lg2$. Also, the form factors tend to decay rather than oscillate at short wavelengths. The linear extrapolation of ${A}_{l}$ versus $E$ proposed by Animalu is shown to be valid for most simple metals. Optimum model potential parameters are obtained, and form factors and depletion holes are evaluated for a group of simple metals using the optimized model potential.

Estimation by the nearest neighbor rule

Abstract: Let R^{\ast} denote the Bayes risk (minimum expected loss) for the problem of estimating \theta \varepsilon \Theta , given an observed random variable x , joint probability distribution F(x,\theta) , and loss function L . Consider the problem in which the only knowledge of F is that which can be inferred from samples (x_{1},\theta_{1}),(x_{2},\theta_{2}), \cdots ,(x_{n}, \theta_{n}) , where the (x_{i}, \theta_{i})'s are independently identically distributed according to F . Let the nearest neighbor estimate of the parameter \theta associated with an observation x be defined to be the parameter \theta_{n}^{'} associated with the nearest neighbor x_{n}^{'} to x . Let R be the large sample risk of the nearest neighbor rule. It will be shown, for a wide range of probability distributions, that R \leq 2R^{\ast} for metric loss functions and R = 2R^{\ast} for squared-error loss functions. A simple estimator using the nearest k neighbors yields R = R^{\ast} (1 + 1/k) in the squared-error loss case. In this sense, it can be said that at least haft the information in the infinite training set is contained in the nearest neighbor. This paper is an extension of earlier work[q from the problem of classification by the nearest neighbor rule to that of estimation. However, the unbounded loss functions in the estimation problem introduce additional problems concerning the convergence of the unconditional risk. Thus some work is devoted to the investigation of natural conditions on the underlying distribution assuring the desired convergence.

The interaction of a shock wave with a laminar boundary layer

Abstract: A finite-difference solution to the problem of the interaction between an impinging shock wave and the laminar boundary layer on a flat plate is presented. The boundary-layer equations are used to calculate the flow with the Prandtl-Meyer formula being used to determine the pressure. Two different methods for calculating the region of separated flow are discussed. Comparisons between this theory and experimental results show good agreement. The effects of the viscosity and heat-conduction relationships on the calculated results are determined. Diagrams show the influence of the Mach number and the displacement thickness of the boundary layer at the start of the interaction on the pressure distribution. The insulated plate and the plate with given temperature are considered.

Transport Properties of GaAs

Abstract: The transport properties of the electrons in GaAs have been investigated; i.e., the absolute values of the electron drift velocity, the diffusion coefficient, and the trapping time have been measured for the first time as a function of the electric field. To measure the velocity at the electron, the response of a reversed-bias Schottky barrier-$I\ensuremath{-}{n}^{+}$ GaAs device to a short pulse (0.1 nsec) of high-energy electrons was measured. The incident electrons create a sheet of charges in the semiconductor very close to the cathode. The electrons move across the diode under the influence of the applied electric field and induce a current in the contacts until they reach the anode. The width of the induced current pulse is a measure of the transit time of the electrons. With a knowledge of the width of the field region ($I$ layer), the drift velocity corresponding to the particular bias field can be accurately determined. The specimen used in this experiment consists of a slab of semi-insulating boat-grown GaAs cut in the [100] and [111] directions. Thin contacts were evaporated on each face; one, the cathode contact, less than 1000 \AA{} thick, forms the noninjecting Schottky barrier. The other, the anode, is ohmic. The experimental results are in excellent agreement with the Butcher-Fawcett theory, with a low-field mobility of 7500 ${\mathrm{cm}}^{2}$/V sec, a threshold field of 3300 V/cm, and an initial negative mobility of 2600 ${\mathrm{cm}}^{2}$/V sec. Signs, but no strong evidence, of the minimum velocity being reached up to the highest field used, 14 kV/cm, were observed. We have also measured by the same method the velocity-field relation over a range of ambient temperatures from 160 to 340\ifmmode^\circ\else\textdegree\fi{}K. From the measurement of the difference between the rise and the fall time of the induced current pulse, which is a measure of the spread of the electron layer created at the cathode by electron bombardment, it was possible to obtain the diffusion coefficient as a function of the electric field. The diffusion coefficient is sharply peaked (900 ${\mathrm{cm}}^{2}$/sec) at the threshold field and decrease to a value slightly less than 200 ${\mathrm{cm}}^{2}$/sec at high field. The experimental results are in considerable disagreement with the theoretical prediction. This disagreement may possibly be due to the velocity fluctuation arising from the rapid electron intervalley transfers which have not been taken into account in the theory by Butcher and Fawcett. Finally, measurement of the number of electrons trapped during the electron transit time across the specimen yields the variation of the trapping time as a function of the electric field.

The fixed charge problem

Abstract: : A fundamental unsolved problem in the programming area is one in which various activities have fixed charges (e.g., set-up time charges) if operating at a positive level. Properties of a general solution to this type problem are discussed in this paper. Under special circumstances it is shown that a fixed charge problem can be reduced to an ordinary linear programming problem.

Ion implantation in semiconductors—Part I: Range distribution theory and experiments

Abstract: Ion implantation in semiconductors provides a doping technique with several potential advantages over more conventional doping methods. Among the most important of these are: 1) the ability to introduce into a variety of substrates precise amounts of nearly any impurity element desired; 2) the ability to control doping profiles in three dimensions by modulating the energy, current, and position of the ion beam; and 3) the possibility of avoiding certain undesirable effects that accompany the high-temperature diffusion process. Ion implantation can also be used in conjunction with other fabrication techniques to produce device structures that no one process can produce simply by itself. Current research in the field is directed toward several problems that must be solved before the full impact of ion implantation on semiconductor technology can be soundly predicted. In particular, it is necessary to be able to predict the distribution profiles of the implanted ions accurately, to know which crystalline sites the implanted ions occupy, to know the nature of the damage centers that are introduced by the implantation process, and to determine the extent to which these defects can he removed by appropriate annealing procedures. Theoretical and experimental work pertinent to the problem of predicting impurity distribution profiles in ion-implanted material are reviewed here. A review of current research on the other problems listed will be given in Part II, together with the characteristics of a number of interesting semiconductor devices that have already been fabricated by ion implantation.

Genetic control of the antibody response in inbred mice transfer of response by spleen cells and linkage to the major histocompatibility (h-2) locus

Abstract: The transfer of spleen cells from (C3H x C57Bl/6) F(1) mice, capable of responding to (T,G)-A--L, into irradiated C3H parental recipients, normally incapable of responding to (T,G)-A--L, transfers the ability to make either a primary or secondary immune response to this synthetic polypeptide antigen. This localizes the genetic control of the ability to respond to the spleen cell population and indicates that the genetic control is exerted upon a process directly related to antibody formation. Studies with congenic strains of mice and linkage studies in segregating backcross populations show that the ability to respond to (T,G)-A--L and (H,G)-A--L is linked to the H-2 locus and can thus be localized to the IXth mouse linkage group. Note Added in Proof: Of the three possible recombinant animals noted in Tables IV and V, two were infertile. The third animal was not a recombinant, since progeny testing and reimmunization showed that this animal was an H-2(2)/H-2(k) heterozygote capable of responding well to (T,G)-A--L.

Poetic Closure: A Study of How Poems End

Abstract: In "Poetic Closure", distinguished literary scholar Barbara Herrnstein Smith explores the provocative question: How do poems end? To answer it, Smith examines numerous individual poems and examples of common poetic forms in order to reveal the relationship between closure and the overall structure and integrity of a poem. First published in 1968, Smith's book remains essential reading in poetic theory.

Correlation of histopathology with other prognostic indicators in Hodgkin's disease

Abstract: The Rye Conference histologic classification of Hodgkin's disease has been applied retrospectively to a series of 176 previously untreated cases of Hodgkin's disease. Three different pathologists independently and unanimously agreed in two-thirds of the cases on assignment of cases to one of the four categories: lymphocyte predominance, nodular sclerosis, mixed cellularity, and lymphocyte depletion. The classification was found to be effective in predicting prognosis even within clinical staging groups. Nodular sclerosis emerges as the largest histologic group and has a favorable prognosis. The usual manner of spread in Hodgkin's disease was to adjacent lymph node groups. Noncontiguous dissemination, when it occurred, was more than twice as frequent in the mixed cellularity and lymphocyte depletion types, compared to nodular sclerosis. Nodular sclerosis involving lung has shown a favorable prognosis, unlike mixed cellularity. Survival appears to be increased in all histologic categories after intensive wide-field megavoltage radiotherapy.