Showing papers by "University of Rochester published in 1973"

Voltage Dependent Charge Movement in Skeletal Muscle: a Possible Step in Excitation–Contraction Coupling

Abstract: It is suggested that a link in excitation-contraction coupling involves the movement of a fixed amount of charge free to move between different locations across the membrane.

Stochastic Transport in a Disordered Solid. I. Theory

Abstract: A general theory of stochastic transport in disordered systems has been developed. The theory is based on a generalization of the Montroll-Weiss continuous-time random walk (CTRW) on a lattice. Starting from a general mobility formalism, specialized $\stackrel{\mathrm{\ifmmode\acute\else\textasciiacute\fi{}}}{\mathrm{t}}$o hopping conduction, an exact expression for the conductivity $\ensuremath{\sigma}(\ensuremath{\omega})$ for the CTRW process is derived. The frequency dependence of $\ensuremath{\sigma}(\ensuremath{\omega})$ is determined by the Fourier transform of the zeroth and second spatial moments of the function $\ensuremath{\psi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{s}},t)$, which is equal to the probability per unit time that the displacement and time between hops is $\stackrel{\ensuremath{\rightarrow}}{\mathrm{s}}$, $t$. The conductivity corresponding to characteristically different types of hopping distributions is discussed, as well as the basic approximation in adopting a CTRW on a lattice to transport in disordered solids.

Linear programming techniques for multidimensional analysis of preferences

Abstract: This paper offers a new methodology for analyzing individual differences in preference judgments with regard to a set of stimuli prespecified in a multidimensional attribute space. The individual is modelled as possessing an “ideal point” denoting his most preferred stimulus location in this space and a set of weights which reveal the relative saliences of the attributes. He prefers those stimuli which are “closer” to his ideal point (in terms of a weighted Euclidean distance measure). A linear programming model is proposed for “external analysis”i.e., estimation of the coordinates of his ideal point and the weights (involved in the Euclidean distance measure) by analyzing his paired comparison preference judgments on a set of stimuli, prespecified by their coordinate locations in the multidimensional space. A measure of “poorness of fit” is developed and the linear programming model minimizes this measure overall possible solutions. The approach is fully nonmetric, extremely flexible, and uses paired comparison judgments directly. The weights can either be constrained nonnegative or left unconstrained. Generalizations of the model to consider ordinal or interval preference data and to allow an orthogonal transformation of the attribute space are discussed. The methodology is extended to perform “internal analysis,”i.e., to determine the stimuli locations in addition to weights and ideal points by analyzing the preference judgments of all subjects simultaneously. Computational results show that the methodology for external analysis is “unbiased”—i.e., on an average it recovers the “true” ideal point and weights. These studies also indicate that the technique performs satisfactorily even when about 20 percent of the paired comparison judgments are incorrectly specified.

Currents Related to Movement of the Gating Particles of the Sodium Channels

Abstract: “…IT seems difficult to escape the conclusion that the changes in ionic permeability depend on the movement of some component of the membrane which behaves as though it had a large charge or dipole moment”1. With these words Hodgkin and Huxley predicted the existence of gating currents: charge movement associated with molecular rearrangements that attend the opening and closing of the ionic channels in response to changes in the membrane field. The polarity of gating current of the sodium channels can be easily predicted: following a positive step change of membrane voltage, positively charged gating particles would move outward through the membrane field from closed to open position (or negatively charged particles would move inward), yielding an outward current. On repolarization after a voltage step that opened the channels, gating current would be inward, as particles moved from open to closed position. Hodgkin and Huxley were unable to observe gating currents experimentally, and concluded that the density of ionic channels in the membrane must be low. A later attempt by Chandler and Meves2 to detect such currents was also unsuccessful, and they estimated that there are less than 100 sodium channels μm−2, a prediction that has been borne out by later estimates of sodium channel density3,4. We report here that by use of signal averaging techniques, we have observed small transient currents which we believe are the gating currents of the sodium channels.

Phase Transition in the Dicke Model of Superradiance

Abstract: A system of $N$ two-level atoms interacting with a quantized field, the so-called Dicke model of superradiance, is studied. By making use of a set of Glauber's coherent states for the field, the free energy of the system is calculated exactly in the thermodynamic limit. The results agree precisely with those obtained by Hepp and Lieb, who studied the same model using a different method. The exhibition of a phase transition of the system is presented mathematically in an elementary manner in our approach. The generalization to the case of finitely many radiation modes is also presented.

Spherical Model of Shallow Acceptor States in Semiconductors

Abstract: The effective-mass approximation for shallow acceptor states in cubic semiconductors with degenerate valence bands is reformulated. The Hamiltonian is written as the sum of a spherical term and a cubic corection, thus pointing out the relevance of the spherical symmetry in the acceptor problem and the strong similarity to the case of atoms with the spin-orbit interaction. Without the introduction of any explicit representation of the Hamiltonian, the present formulation yields a meaningful classification of the acceptor states and reduces the eigenvalue problem to simple radial Hamiltonians. These radial Hamiltonians are explicitly given for the most improtant acceptor states and are shown to apply also to the description of the exciton problem. The variational method is used in the numerical calculation. The resulting eigenvalues, eigenfunctions, and related quantities are given as functions of the relevant parameters. The theoretical ionization energies are compared with available experimental data.

Stochastic Transport in a Disordered Solid. II. Impurity Conduction

Abstract: In a previous paper, the authors have developed a general theory of stochastic transport in disordered systems. In the present paper, the theory is applied, in detail, to a prototype of transport in a disordered system - impurity conduction in semiconductors. The complete frequency dependence of the real and imaginary part of the conductivity is calculated. In particular, the calculation details the transition from an ${\ensuremath{\omega}}^{s}$ dependence to essentially dc behavior (at a finite frequency), where $s\ensuremath{\sim}0.6\ensuremath{-}0.8$, depending on temperature and concentration. The theoretical results for frequency, temperature, and concentration dependence of the conductivity are shown to be in good agreement with the measurements of Pollak and Geballe (PG). In addition, the ac conductivity data of PG interpreted with the present theory yield experimental evidence for the existence of two-channel hopping in $n$-type Si.

Generalized master equations for continuous-time random walks

Abstract: An equivalence is established between generalized master equations and continuous-time random walks by means of an explicit relationship betweenψ(t), which is the pausing time distribution in the theory of continuous-time random walks, andφ(t), which represents the memory in the kernel of a generalized master equation. The result of Bedeaux, Lakatos-Lindenburg, and Shuler concerning the equivalence of the Markovian master equation and a continuous-time random walk with an exponential distribution forψ(t) is recovered immediately. Some explicit examples ofφ(t) andψ(t) are also presented, including one which leads to the equation of telegraphy.

Random walks on lattices. IV. Continuous-time walks and influence of absorbing boundaries

Abstract: The general study of random walks on a lattice is developed further with emphasis on continuous-time walks with an asymmetric bias. Continuous time walks are characterized by random pauses between jumps, with a common pausing time distributionψ(t). An analytic solution in the form of an inverse Laplace transform for P(l, t), the probability of a walker being atl at timet if it started atlo att=0, is obtained in the presence of completely absorbing boundaries. Numerical results for P(l, t) are presented for characteristically different ψ(t), including one which leads to a non-Gaussian behavior for P(l, t) even for larget. Asymptotic results are obtained for the number of surviving walkers and the mean 〈l〉 showing the effect of the absorption at the boundary.

Estimating the weights for multiple attributes in a composite criterion using pairwise judgments

Abstract: This paper presents a new methodology for estimating the weights or saliences of subcriteria (attributes) in a composite criterion measure. The inputs to the estimation procedure consist of (i) a set of stimuli or objects with each stimulus defined by its subcriteria profile (set of attribute values) and (ii) the set of paired comparison dominance (e.g., preference) judgments on the stimuli made by a single judge (expert) in terms of the global criterion. A criterion of fit is developed and its optimization via linear programming is illustrated with an example. The procedure is generalized to estimate a common set of weights when the pairwise judgments on the stimuli are made by more than one judge. The procedure is computationally efficient and has been applied in developing a composite criterion of managerial success yielding high concurrent validity. This methodology can also be used to perform ordinal multiple regression—i.e., multiple regression with an ordinally scaled dependent variable and a set of intervally scaled predictor variables. The approach is further extended to “internal analysis” (unfolding) using the vector model of preference and to the additive model of “conjoint measurement.”

The epidemiology of anorexia nervosa

Abstract: All patients with anorexia nervosa were extracted from three psychiatric case registers— North-East Scotland, Camberwell, and Monroe County. The average incidence varied from 0·37 per 100,000 population per year in Monroe County to 1·6 per 100,000 in North-East Scotland, in all three areas the number of cases reported per year was increasing, and in Camberwell, but not in Monroe County or North-East Scotland, there was a significant excess of patients from middle-class backgrounds.

Chlorinated Dibenzo-p-dioxins: Potent Inducers of δ-Aminolevulinic Acid Synthetase and Aryl Hydrocarbon Hydroxylase : II. A Study of the Structure-Activity Relationship

Abstract: 2,3,7,8-Tetrachlorodibenzo-p-dioxin, an extremely potent toxin and teratogen formed during the commercial synthesis of the herbicide 2,4,5-trichlorophenoxyacetic acid, is a potent inducer of δ-aminolevulinic acid synthetase and aryl hydrocarbon hydroxylase in chick embryo liver. The induction of hydroxylase activity is more sensitive to low doses of the toxin than is the induction of δ-aminolevulinic acid synthetase; 2-fold induction is produced by 1.55 pmoles/egg (0.5 ng), and maximal induction by 155 pmoles/egg. Coordinate expression of the two enzymes is also dissociable by the administration of cycloheximide, which selectively inhibits induction of the synthetase. Fifteen halogenated dibenzo-p-dioxins were screened for their ability to induce the two enzymes, and a well-defined structure-activity relationship emerged; all the congeners that induced both enzymes had halogen atoms at a minimum of three of the four lateral ring positions and contained at least one nonhalogenated ring position. There is a perfect correspondence between the whole animal toxicity data on the dibenzo-p-dioxin congeners and their ability to induce both enzymes.

Radiating and nonradiating classical current distributions and the fields they generate

Abstract: Several general theorems are established relating to well-behaved, localized, monochromatic current distributions and the fields that they generate. In particular, a necessary and sufficient condition for such a current distribution to be nonradiating is established and a general expression for all nonradiating current distributions of this class is obtained.

Identification of a major basic protein in guinea pig eosinophil granules.

Abstract: Elucidation of the functions of the eosinophil might be accomplished by analysis of the granule constituents. We have purified eosinophils (93% or greater) from the peritoneal cavity of the guinea pig and have investigated a variety of methods to disrupt cells and liberate intact granules. Lysis in 0.34 M sucrose gave the best yield of granules and these had the characteristic morphology of eosinophil granules when examined by electron microscopy. Granules were solubilized by a variety of treatments and the solutions analyzed by polyacrylamide electrophoresis at pH 3 in 6 M urea. Comparison of the electrophoretic patterns of solubilized eosinophil and neutrophil granules revealed a difference: a major portion (53±3%; x ±1 SE) of the protein from the eosinophil granule migrated as a single component. This major band protein has a molecular weight between 6,000 and 12,000 daltons and a pI of 10 or greater. Analysis of eosinophil granule constituents on Sephadex G-50 revealed two main peaks; peak 1 possessed peroxidase activity and peak 2 contained the major band protein. These studies indicate that eosinophil granules contain a cationic protein of low molecular weight which lacks peroxidase activity and which accounts for greater than 50% of granule protein.

Perception of random dot interference patterns.

Abstract: THE observation that circular patterns are immediately perceived if a random dot pattern (Fig. 1a) is superimposed on itself and rotated slightly (Fig. 2a) indicates that the visual system detects local autocorrelations and integrates these to form a global circular percept1. By varying both the local and global parameters describing the interference patterns, the functional organisation of the visual system can be probed and new perceptual effects discovered.

Upper bounds on the values of masses in unified gauge theories

Abstract: Upper bounds are found for the masses of most of the new, unobserved particles in unified gauge theories by requiring that the partial-wave amplitudes satisfy unitarity bounds.

Effect of eye movements on backward masking and perceived location

Abstract: A typical trial of this masking experiment involves, in quick succession, presentation of five letters, evocation of an eye movement, and presentation of a spatially localized mask, either a visual-pattern mask or a metacontrast ring. The effect of the mask is to sappress the report of the letter that stimulates the same retinal location, even though the mask appears to cover or surround the letter whose position in real space it shares. Masking is. however, weaker when the eyes move than when they do not. An auxiliary experiment suggests that the spatial aspects of observable (reportable by S) stimulus persistence are unaffected by eye movements, and therefore that observable persistence differs from that susceptible to masking.