Showing papers by "University of Houston published in 1985"

The Elongation and Orientation of Cultured Endothelial Cells in Response to Shear Stress

Abstract: Vascular endothelial cells appear to be aligned with the flow in the immediate vicinity of the arterial wall and have a shape which is more ellipsoidal in regions of high shear and more polygonal in regions of low shear stress. In order to study quantitatively the nature of this response, bovine aortic endothelial cells grown on Thermanox plastic coverslips were exposed to shear stress levels of 10, 30, and 85 dynes/cm2 for periods up to 24 hr using a parallel plate flow chamber. A computer-based analysis system was used to quantify the degree of cell elongation with respect to the change in cell angle of orientation and with time. The results show that (i) endothelial cells orient with the flow direction under the influence of shear stress, (ii) the time required for cell alignment with flow direction is somewhat longer than that required for cell elongation, (iii) there is a strong correlation between the degree of alignment and endothelial cell shape, and (iv) endothelial cells become more elongated when exposed to higher shear stresses.

A United Approach to Optimal Real and Reactive Power Dispatch

Abstract: This paper presents a unified method for optimal real and reactive power dispatch for the economic operation of power systems. As in other methods, the problem is decomposed into a P-optimization module and a Q-optimization module, but in this method both modules use the same generation cost-objective function. The control variables are generator real power outputs for the real power module; and generator reactive power outputs, shunt capacitors/reactors, and transformer tap settings for the reactive power module. The constraints are the operating limits of the control variables, power line flows, and bus voltages. The optimization problem is solved using the gradient projection method (GPM) which is used for the first time in the power systems study. The GPM allows the use of functional constraints without the need of penalty functions or Lagrange multipliers among other advantages. Mathematical models are developed to represent the sensitivity tivity relationships between dependent and control variables for both, real and reactive power, optimization modules, and thus eliminate the use of B-coefficients. Results of two test systems are presented and compared with conventional methods.

Self-efficacy and the stages of self-change of smoking

Abstract: Efficacy expectations are postulated to mediate all behavior change. This study examined the construct of self-efficacy in the self-change of smoking behavior. A 31-item measure of self-efficacy was used that included ratings of both temptation (cue strength) and confidence (efficacy). The subjects were 957 volunteers representing five stages of self change: (1) immotives, (2) contemplators, (3) recent quitters, (4) long-term quitters, and (5) relapsers. Subjects were assessed initially and at a 3- to 5-month follow-up. The self-efficacy scale proved to be an extremely reliable and coherent instrument with identifiable but not clearly interpretable subcomponents. Groups of subjects demonstrated significant differences in total self-efficacy scores. Efficacy expectations demonstrated small but significant relationships with smoking history variables and the pros and cons of smoking, but not with demographic, life stress, or persistence measures. Subject's efficacy evaluations at the initial assessment were related to changes in status for recent quitters and contemplators at the follow-up. The relationship between temptation and efficacy ratings is complex and varies for subjects in the various stages of change. Correlations between total self-efficacy and temptation scores were largest for contemplators (r = −.65) and relapsers (r = −.67) and smallest for the recent quitters (r = −.18). Finally, the magnitude of the difference between temptation and efficacy increased with length of abstinence for subjects in maintenance.

Self-Efficacy and Classroom Learning

Abstract: This article discusses the role of perceived self-efficacy during classroom learning of cognitive skills. Self-efficacy refers to personal judgments of performance capabilities in a given domain of activity. Students enter classroom activities with various aptitudes and prior experiences, which affect their initial sense of self-efficacy for learning. During task engagement, students may assess self-efficacy by utilizing cues made cognitively salient by educational practices and which convey information about their capability to acquire knowledge and skills, such as performance outcomes, attributions, situational circumstances, outcome patterns, perceived model similarity, and persuader credibility. In turn, heightened learning self-efficacy enhances motivated learning, or motivation to acquire knowledge and skills. Research findings are presented showing how different educational practices affect self-efficacy. Future research needs to determine how students derive efficacy information from multiple cues, and to specify in finer detail how the cognitive processes involved in understanding instruction and appraising self-efficacy influence one another.

Measuring State Partisanship and Ideology with Survey Data

Abstract: The study of state politics has suffered because of the lack of good data on major political orientations at the state level. This paper briefly discusses this problem and the need for survey-based measures, and then presents sets of estimates of state partisanship and ideology. These are derived from aggregating CBS News-New York Times polls at the state level. Using fifty-one polls taken from 1974 through 1982, our estimates are based on over 76,000 respondents. The estimates are shown to have good overall validity and reliability, and should prove valuable in studies of comparative state elections and policymaking.

Structural and energetic effects of truncating long ranged interactions in ionic and polar fluids

Abstract: The effects of Coulomb potential truncation schemes used in computer simulations of ionic and polar fluids are examined by use of integral equation techniques. A renormalized HNC type equation capable of describing both ionic and polar molecular fluids with truncated interactions is derived and applied to several model systems of interest. Good agreement is found between the integral equation results and Monte Carlo simulations of the same potential for dilute solutions of ions in a dielectric continuum. Very large effects on the distribution functions result from truncation of the electrostatic interaction in dilute systems. Even in comparatively dense systems, unrealistic pair correlations near the cutoff distance result from some of the proposed truncation schemes. The effect of Coulomb potential truncation for a molecular model of pure water is also studied. Significant errors appear in the second neighbor region for commonly used truncation schemes; a simple switching function that zeros the potential and its first derivative yields results closest to the Coulomb potential without truncation.

The category concept: an extension to the entity-relationship model

Abstract: An enhanced version of the Entity-Relationship (ER) data model called the Entity-Category-Relationship (ECR) data model is presented. The principal extension is the introduction of the concept of a category. Categories permit the grouping of entities from different entity types according to the roles they play in a relationship, as well as the representation of ISA and generalization hierarchies. The structures of the ECR data model are defined, and a graphic representation technique for their display is presented. Language operations to define and use an ECR database are defined. Two realistic examples of the use of the ECR model for database design are demonstrated. The examples show how ECR structures can be directly mapped into relational and network structures. The definition of derived relationships on an ECR database gives the power to phrase higher order recursive queries in a first order query language.

Statistical properties of forced-choice psychometric functions: implications of probit analysis.

Abstract: Probit analysis was applied to the problem of threshold estimation from psychometric functions derived from the two-alternative forced-choice (2AFC) method of constant stimuli. Threshold estimates from 2AFC experiments are surprisingly poor: They are about twice as variable as corresponding estimates based on the traditional yes-no method of constant stimuli, and their asymmetrical confidence limits are not readily predicted from conventional standard error formulas. All of these faults are exacerbated in small samples. Computer simulations demonstrated that, for small samples, the probit analysis equations do not give a valid estimate of threshold variability. The variability of staircase estimates of threshold cannot be less than the variability of threshold estimates derived from the method of constant stimuli given an optimum placement of trials. Hence our findings also define the minimum variability of all staircase estimators under the assumptions of probit analysis.

Hyperacuity thresholds of 1 sec: theoretical predictions and empirical validation

Abstract: Bisection thresholds were measured as a function of the separation of the lines. For separations of less than 1.5 min, the addition of flanking lines facilitates bisection so that thresholds of less than 1 sec for discriminating the direction of offset could be reliably obtained. For larger separations an interval could be bisected to an accuracy of 1 part in 60. Experiments varying the length, luminance, and overlap of the lines suggest that different cues are used in these two regimes. A dual space-size analysis is presented that can account for these bisection thresholds over a wide range of experimental conditions. This quantitative analysis produces viewprints of the stimuli (analogous to the voiceprint of audition). Each viewprint shows the output of many spatial filters of different positions and sizes. A new filter shape is introduced that has advantages for modeling the visual system. The sensitivity of each filter is fixed by the contrast-response function. The analysis further shows that the limiting factors in spatial hyperacuity are both the contrast-response function and the spatial grain.

Participation in Goal Setting: Effects On Self-Efficacy and Skills of Learning-Disabled Children

Abstract: This experiment tested the hypothesis that participation in goal setting enhances self-efficacy and skills. Subjects were sixth-grade children who previously had been classified as learning disabled in mathematics. Children received subtraction training that included instruction and practice opportunities over several sessions. Some children set proximal performance goals each session, others had comparable proximal goals assigned, and children in a third condition received the training but no goals. Although proximal goals promoted motivation more than no goals, participation in goal setting led to the highest self-efficacy and subtraction skill. Implications for teaching are discussed.

Hopf Bifurcation in the presence of symmetry

Abstract: Using group theoretic techniques, we obtain a generalization of the Hopf Bifurcation Theorem to differential equations with symmetry, analogous to a static bifurcation theorem of Cicogna. We discuss the stability of the bifurcating branches, and show how group theory can often simplify stability calculations. The general theory is illustrated by three detailed examples: O(2) acting on R2, O(n) on Rn, and O(3) in any irreducible representation on spherical harmonics.

Ideology in the 1980 Election: Ideological Sophistication Does Matter

Abstract: The debate over the extent of ideological awareness in the American electorate has been characterized as an argument over whether the "ideology glass" is half empty or half full. This characterization results from the fact that analyses to date have employed various alternative indicators of ideology in isolation from each other. This paper presents an integrated assessment of ideological thinking in the American electorate. Specifically, it examines the effects of partisanship, ideological identification and policy preferences on the presidential vote in 1980 within the "levels of conceptualization." It concludes that when ideological sentiment is supported by the level of sophistication required to merit classification as an "ideologue" it has a substantial impact on candidate choice. Under all other conditions its impact is marginal, at best.

Ethnicity, survival, and delay in seeking treatment for symptoms of breast cancer.

Abstract: This study examined differences in 10-year survival rates from breast cancer among white, black, and Hispanic women controlling for the effects of age, socioeconomic status (SES), stage of disease, and delay in seeking treatment for symptoms. Breast cancer patients (n = 1983) treated at M. D. Anderson Hospital and Tumor Institute in Houston, Texas between 1949 and 1968, were followed for 10 years. Ethnicity, SES, stage of disease, and delay were all found to affect survival when considered separately. Black patients were less likely to survive than either white or Hispanic patients whose survival experience appeared to be similar. Multivariate analysis that used a Cox regression technique showed that ethnic differences remained when age, SES, stage, and delay were included in the model. In contrast, the authors could not detect an effect of delay on survival when ethnicity and all other variables were included. These data suggest that ethnic differences in breast cancer survival are not mediated by differences in delay in seeking treatment for breast cancer symptoms.

Algorithms for limited-view computed tomography: an annotated bibliography and a challenge.

Abstract: In many applications of computed tomography, it may not be possible to acquire projection data at all angles, as required by the most commonly used algorithm of convolution backprojection. In such a limited-data situation, we face an ill-posed problem in attempting to reconstruct an image from an incomplete set of projections. Many techniques have been proposed to tackle this situation, employing diverse theories such as signal recovery, image restoration, constrained deconvolution, and constrained optimization, as well as novel schemes such as iterative object-dependent algorithms incorporating a priori knowledge and use of multispectral radiation. We present an overview of such techniques and offer a challenge to all readers to reconstruct images from a set of limited-view data provided here.

Green's-function approach to nonlinear electronic transport for an electron-impurity-phonon system in a strong electric field.

Abstract: A Green's-function approach to nonlinear electronic transport in a static electric field is developed microscopically for the system composed of interacting electrons with impurities and phonons. The essential idea is to separate the center-of-mass motion from the relative motion of electrons. An electron temperature is introduced as a measurement of the internal energy of the relative electrons without reference to any distribution function. By allowing different temperatures for decoupled electrons and phonons in the initial state, we obtain the density matrix for the electron-lattice system to the first order of interaction but under arbitrarily strong electric field. The frictional force experienced by the center of mass of electrons and the energy transfer rate from electron system to phonon system are derived by means of the Green's-function technique, and the force- and energy-balance equations for steady state are obtained. These equations are applied to the calculations of the ratio of electron temperature to the lattice temperature and the electron resistivity as functions of drift velocity for impurity, acoustic-phonon, and optical-phonon scatterings. The dynamic nature of Coulomb screening by charge carriers is studied numerically. One of the interesting predictions is the possible cooling of electrons at low temperatures in samples with low impurity concentration.

Dual-band reactively loaded microstrip antenna

Abstract: A previously derived theory is applied to a microstrip antenna with a reactive load to produce a dual-band radiator. A model consisting of a rectangular patch radiator loaded with a variable length short-circuited coaxial stub was investigated experimentally. Comparisons of theoretical predictions and experimental data are made for the impedance and resonant frequencies as a function of the position of the load, the length of the stub, and the characteristic impedance of the stub.

Effects of the Knowledge Base on Children's Memory Strategies

Abstract: In this article, the importance of examining the linkage between knowledge and strategic factors in children's memory has been suggested. Indeed, it has been argued that a more complete analysis of the development of remembering in children requires a consideration of the operation of memory strategies in the context of the growing knowledge base. The effects of the knowledge base were analyzed in terms of concurrent influences on the use of strategies and long-term consequences for the development of increasingly skilled memory processing. The available evidence suggests that age-related changes in the contents of the knowledge system, as well as increases in the ease with which information can be accessed, contribute to the strategies that are used by children of different ages, and influence the development of efficient modes of processing. Continued research on the concurrent effects of the knowledge base should provide a more complete account of children's memory than that currently available, taking into consideration knowledge of the materials, understanding of the task demands, as well as overall strategic abilities. Similarly, research on the long-term developmental effects of the knowledge base on memory strategies should facilitate an understanding of the mechanisms by which memory processing becomes more efficient and less effortful. Ideally, studies that examine these issues should be longitudinal in scope (Ornstein et al., 1985a), but even cross-sectional research that explores the interrelationships between strategies and knowledge will facilitate an understanding of the development of memory in children.

Job Involvement Through the Life Course: A Panel Study of Three Age Groups

Abstract: Utilizing panel data for three age groups from the 1972-73 and 1977 Quality of Employment Surveys, this study investigates the interrelations of work experiences and subjective job involvement in three age groups that are indicative of different career stages. Whereas job involvement is quite volatile in the initial stage of the work career, it becomes more stable, supporting the "aging stability hypothesis," as workers grow older. Work experiences and rewards also change less as workers age, suggesting that the growing stability with age in job involvement occurs in the context of an increasingly stable work environment. Work autonomy exerts a significant influence on job involvement in all age groups. However, the fact that this intrinsic dimension of work has the strongest influence on involvement in the youngest cohort supports the contention that there is a highly formative stage in young adulthood, after which time the person becomes more resistant to environmental pressures to change. The findings also suggest that the effects ofjob involvement on occupational achievement may be specific to the middle stage of the career. The results of this study indicate the potential of applying a life-span developmental perspective to the study of the sources and consequences of job involvement.

Simulation of the diffusion-controlled reaction between superoxide and superoxide dismutase. I. Simple models.

Abstract: A two-stage Brownian dynamics simulation method is used to study the diffusion-influenced bimolecular reaction between superoxide and superoxide dismutase (SOD). The crystal structure of the dimeric enzyme is used in constructing detailed topographical and electrostatic models. Several electrostatic models are considered. In the most realistic, the excluded volume of the protein, which is impermeable to penetration by mobile ions, is assigned a dielectric constant of 2 and the surrounding “solvent” is assigned a value of 78. A finite difference method is used to solve the linearized Poisson–Boltzmann equation. For native SOD, the simulations reproduce the pronounced salt dependence of the rate constant observed experimentally. This salt dependence is attributed to electrostatic interactions between enzyme and substrate that are inherently attractive and amplified by the low dielectric constant of the protein interior. The simulation method is also applied to a modified enzyme, acylated SOD.

Construct validity of various memory testing procedures.

Abstract: The construct validity of Wechsler Memory Scale Logical Memory, Paired Associate Learning and Visual Reproduction subtests was evaluated, as well as the validity of the Benton Visual Retention Test, and the two memory factor scales of the Luria-Nebraska Neuropsychological Battery (LNNB). The results of a series of factor analyses based on test performances of 102 subjects indicated that delayed reproduction measures of visual memory were more valid than the traditional immediate reproduction administrations, which were more closely associated with visual-perceptual-motor abilities. Construct validity was also demonstrated for Logical Memory and Paired Associate Learning. Although both LNNB measures loaded on a memory factor, item heterogeneity and brief sampling of items raised serious questions about the clinical utility of these scales.