Showing papers by "University of Houston published in 1995"

On the identification of a vortex

Abstract: Considerable confusion surrounds the longstanding question of what constitutes a vortex, especially in a turbulent flow. This question, frequently misunderstood as academic, has recently acquired particular significance since coherent structures (CS) in turbulent flows are now commonly regarded as vortices. An objective definition of a vortex should permit the use of vortex dynamics concepts to educe CS, to explain formation and evolutionary dynamics of CS, to explore the role of CS in turbulence phenomena, and to develop viable turbulence models and control strategies for turbulence phenomena. We propose a definition of a vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor ${\bm {\cal S}}^2 + {\bm \Omega}^2$ are respectively the symmetric and antisymmetric parts of the velocity gradient tensor ${\bm \Delta}{\bm u}$. This definition captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers, unlike a pressure-minimum criterion. We compare our definition with prior schemes/definitions using exact and numerical solutions of the Euler and Navier–Stokes equations for a variety of laminar and turbulent flows. In contrast to definitions based on the positive second invariant of ${\bm \Delta}{\bm u}$ or the complex eigenvalues of ${\bm \Delta}{\bm u}$, our definition accurately identifies the vortex core in flows where the vortex geometry is intuitively clear.

Synthesizing the Implementation Literature: The Ambiguity-Conflict Model of Policy Implementation

Abstract: A review of the policy implementation literature finds the field split into two major schools, top-down and bottom-up. Previous attempts to reconcile these models are described, followed by an alternative model. This model reconciles these approaches by concentrating on the theoretical significance of ambiguity and conflict for policy implementation. A number offactors crucial to the implementation process are identified as varyingly dependent on a policy's ambiguity and conflict level. Four policy implementation paradigms are identified and the relevance of the existing literature to these conditions is discussed. The four paradigms are low conflict-low ambiguity (administrative implementation), high conflict-low ambiguity (political implementation), high conflict-high ambiguity (symbolic implementation), and low conflicthigh ambiguity (experimental implementation).

Electroencephalogram and visual evoked potential generation in a mathematical model of coupled cortical columns

Abstract: This study deals with neurophysiologically based models simulating electrical brain activity (i.e., the electroencephalogram or EEG, and evoked potentials or EPs). A previously developed lumped-parameter model of a single cortical column was implemented using a more accurate computational procedure. Anatomically acceptable values for the various model parameters were determined, and a multi-dimensional exploration of the model parameter-space was conducted. It was found that the model could produce a large variety of EEG-like waveforms and rhythms. Coupling two models, with delays in the interconnections to simulate the synaptic connections within and between cortical areas, made it possible to replicate the spatial distribution of alpha and beta activity. EPs were simulated by presenting pulses to the input of the coupled models. In general, the responses were more realistic than those produced using a single model. Our simulations also suggest that the scalp-recorded EP is at least partially due to a phase reordering of the ongoing activity.

Theory testing: Combining psychometric meta-analysis and structural equations modeling

Abstract: This paper presents an overview of a useful approach for theory testing in the social sciences that combines the principles of psychometric meta-analysis and structural equations modeling. In this approach to theory testing, the estimated true score correlations between the constructs of interest are established through the application of meta-analysis (Hunter & Schmidt, 1990), and structural equations modeling is then applied to the matrix of estimated true score correlations. The potential advantages and limitations of this approach are presented. The approach enables researchers to test complex theories involving several constructs that cannot all be measured in a single study. Decision points are identified, the options available to a researcher are enumerated, and the potential problems as well as the prospects of each are discussed.

Cardiac function in mice overexpressing the beta-adrenergic receptor kinase or a beta ARK inhibitor.

Abstract: Transgenic mice were created with cardiac-specific overexpression of the beta-adrenergic receptor kinase-1 (beta ARK1) or a beta ARK inhibitor. Animals overexpressing beta ARK1 demonstrated attenuation of isoproterenol-stimulated left ventricular contractility in vivo, dampening of myocardial adenylyl cyclase activity, and reduced functional coupling of beta-adrenergic receptors. Conversely, mice expressing the beta ARK inhibitor displayed enhanced cardiac contractility in vivo with or without isoproterenol. These animals demonstrate the important role of beta ARK in modulating in vivo myocardial function. Because increased amounts of beta ARK1 and diminished cardiac beta-adrenergic responsiveness characterize heart failure, these animals may provide experimental models to study the role of beta ARK in heart disease.

Information Systems Development and Data Modeling: Conceptual and Philosophical Foundations

Abstract: Data modelling was hypothesised to be the salvation of an organisation's data problems. This book aims to analyse the problems encountered and to present a comparative philosophical study of the various approaches. The authors explore the epistemology, ontology and rationality of each modelling approach, and describe the underlying assumptions embedded in them.

Spectacle lenses alter eye growth and the refractive status of young monkeys.

Abstract: The influence of visual experience on ocular development in higher primates is not well understood. To investigate the possible role of defocus in regulating ocular growth, spectacle lenses were used to optically simulate refractive anomalies in young monkeys (for example, myopia or nearsightedness). Both positive and negative lenses produced compensating ocular growth that reduced the lens-induced refractive errors and, at least for low lens powers, minimized any refractive-error differences between the two eyes. These results indicate that the developing primate visual system can detect the presence of refractive anomalies and alter each eye's growth to eliminate these refractive errors. Moreover, these results support the hypothesis that spectacle lenses can alter eye development in young children.

Critical Events: An Anthropological Perspective on Contemporary India

Abstract: Identifying key events in the history of contemporary India - Partition, sati, minority rights, the Bhopal industrial disaster, the nature of the Indian state - Veena Das describes the implications of these occurrences within the framework of anthropological knowledge. Her attempt here is to produce an ethnography of contemporary India which is sensitive to both world historical processes and the inner life of individuals. The critical events that Professor Das analyzes have all instituted new sorts of action which have, in turn, redefined traditional categories such as codes of purity and honour; the meaning of martyrdom; and the construction of a heroic life. The author shows how these new forms took shape and were appropriated by a variety of political actors such as caste groups, religious communities, women's groups, and the nation as a whole.

Physiological effects of inverse agonists in transgenic mice with myocardial overexpression of the β2-adrenoceptor

Abstract: G-protein-coupled receptors are thought to have an inactive conformation (R), requiring an agonist-induced conformational change for receptor/G-protein coupling. But new evidence suggests a two-state model in which receptors are in equilibrium between the inactive conformation (R), and a spontaneously active conformation (R*) that can couple to G protein in the absence of ligand (Fig. 1). Classic agonists have a high affinity for R* and increase the concentration of R*, whereas inverse agonists have a high affinity for R and decrease the concentration of R*. Neutral competitive antagonists have equal affinity for R and R* and do not displace the equilibrium, but can competitively antagonize the effects both of agonists and of inverse agonists. The lack of suitable in vivo model systems has restricted the evidence for the existence of inverse agonists to computer simulations and in vitro systems. We have used a transgenic mouse model in which there is such marked myocardial overexpression of beta 2-adrenoceptors that a significant population of spontaneously activated receptor (R*) is present, inducing a maximal response without agonist. We show that the beta 2-adrenoceptor ligand ICI-118,551 functions as an inverse agonist, providing evidence supporting the existence of inverse agonists and validating the two-state model of G-protein-coupled receptor activation.

Cloning of the putative tumour suppressor gene for hereditary multiple exostoses (EXT1)

Abstract: Hereditary multiple exostoses is an autosomal dominant disorder that is characterized by short stature and multiple, benign bone tumours. In a majority of families, the genetic defect (EXT1) is linked to the Langer-Giedion syndrome chromosomal region in 8q24.1. From this region we have cloned and characterized a cDNA which spans chromosomal breakpoints previously identified in two multiple exostoses patients. Furthermore, the gene harbours frameshift mutations in affected members of two EXT1 families. The cDNA has a coding region of 2,238 bp with no apparent homology to other known gene sequences and thus its function remains elusive. However, recent studies in sporadic and exostosis-derived chondrosarcomas suggest that the 8q24.1-encoded EXT1 gene may have tumour suppressor function.

Self-concept and advertising effectiveness: The influence of congruency, conspicuousness, and response mode

Abstract: It was hypothesized in this study that advertising appeals congruent with viewers' self-concept would be superior to incongruent appeals in terms of enhancing advertising effectiveness. Advertising effectiveness was operationalized as: brand memory, brand attitude, and purchase intentions. The sample consisted of 165 subjects who were exposed to four test stimuli (ads), two for automobiles and two for shampoos. One ad within a product class used an introvert appeal, and the other used an extrovert appeal. Congruence between self-concept and the brand image was determined by subjects' evaluations of themselves and the advertised brand. Ad-related tasks included remembering brand names and indicating preference and buying intention for each brand. The study results indicate that brand memory is not mediated by the extent to which advertising expressions are congruent with viewers' self-concept. However, brand preference and purchase intention were shown to be influenced by the self-congruency of an ad. © 1995 John Wiley & Sons, Inc.

Response linearity and kinetics of the cat retina: the bipolar cell component of the dark-adapted electroretinogram.

Abstract: The electroretinogram (ERG) of the dark-adapted cat eye in response to brief ganzfeld flashes of a wide range of intensities was recorded after intravitreal injection of n-methyl DL aspartate (NMDLA, cumulative intravitreal concentration of 1.3-3.9 mM) to suppress inner-retinal components, and after intravitreal DL or L-2-amino-4-phosphonobutyric acid (DL-APB, 1-3 mM; L-APB, 1.2 mM) and 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX, 40-60 μM), to suppress all post-receptoral neuronal responses. Rod PII, the ERG component arising from rod bipolar cells, was derived by subtracting records obtained after APB and CNQX from post-NMDLA records. When we measured the derived response at fixed times after the stimulus, we found that PII initially increased in proportion to stimulus intensity without any sign of a threshold. The leading edge of PII at early times after the stimulus, when the response was still small, was well described by V(t) = kI(t - t d ) 5 where k is a constant, I is the intensity of the stimulus, and t d is a brief delay of about 3 ms. Correspondingly, the time for the response to rise to an arbitrary small criterion voltage V crit was adequately fitted by t crit = t d + (V crit /kI) 1/5 . The time course of the leading edge of the PII response can be interpreted to indicate that the mechanism generating PII introduces three stages of temporal integration in addition to the three stages that are provided by the mechanism of the rod photoreceptors. This finding is consistent with the operation within the rod bipolar cell of a G-protein cascade similar to that in the rods.

The internal structure of an active sea-floor massive sulphide deposit

Abstract: THE hydrothermal circulation of sea water through permeable ocean crust results in rock–water interactions that lead to the formation of massive sulphide deposits. These are the modern analogues of many ancient ophiolite-hosted deposits1–4, such as those exposed in Cyprus. Here we report results obtained from drilling a series of holes into an actively forming sulphide deposit on the Mid-Atlantic Ridge. A complex assemblage of sulphide–anhydrite–silica breccias provides striking evidence that such hydrothermal mounds do not grow simply by the accumulation of sulphides on the sea floor. Indeed, the deposit grows largely as an in situ breccia pile, as successive episodes of hydrothermal activity each form new hydrothermal precipitates and cement earlier deposits. During inactive periods, the collapse of sulphide chimneys, dissolution of anhydrite, and disruption by faulting cause brecciation of the deposit. The abundance of anhydrite beneath the present region of focused hydrothermal venting reflects the high temperatures ( > 150 °C) currently maintained within the mound, and implies substantial entrainment of cold sea water into the interior of the deposit. These observations demonstrate the important role of anhydrite in the growth of massive sulphide deposits, despite its absence in those preserved on land.

Relative importance of personality and general mental ability in managers' judgments of applicant qualifications.

Abstract: Eighty-four managers who make hiring decisions in 1 of 6 occupations representative of J. L. Holland's (1973) 6 job typologies (medical technologist, insurance sales agent, carpenter, licensed practical nurse, reporter, and secretary) rated 39 hypothetical job applicants on 2 dependent variables, hirability and counterproductivity. Applicants were described on the Big Five personality factors (Emotional Stability, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness) and on general mental ability. Results showed that general mental ability and conscientiousness were the most important attributes related to applicants' hirability and that Emotional Stability, Conscientiousness, and Agreeableness were the most important attributes related to counterproductivity. In most respects, these results mirror meta-analytic reviews of validity studies, thereby confirming hypotheses.

Asymptotic stability of heteroclinic cycles in systems with symmetry

Abstract: Systems possessing symmetries often admit heteroclinic cycles that persist under perturbations that respect the symmetry. The asymptotic stability of such cycles has previously been studied on an ad hoc basis by many authors. Sufficient conditions, but usually not necessary conditions, for the stability of these cycles have been obtained via a variety of different techniques. We begin a systematic investigation into the asymptotic stability of such cycles. A general sufficient condition for asymptotic stability is obtained, together with algebraic criteria for deciding when this condition is also necessary. These criteria are always satisfied in R(3) and often satisfied in higher dimensions. We end by applying our results to several higher-dimensional examples that occur in mode interactions with O(2) symmetry.

Self-Efficacy and Addictive Behaviors

Abstract: It was not long after Bandura introduced the construct of self-efficacy in 1977 that scientists and practitioners in the addictive behaviors began to use the construct in their theorizing and research. Marlatt and Gordon (1979) found a key role for self-efficacy in their model of relapse. Condiotte and Lichtenstein (1981), DiClemente (1981), and Shiffman (1982) began using self-efficacy to understand the process of smoking cessation. Heather, Rollnick and Winton (1982) and Litman and colleagues (1979) began discussing how efficacy could be used as a predictor of relapse in alcohol-dependence treatment. Self-efficacy demonstrated both conceptual and practical utility, as well as heuristic value, in these initial studies. Since 1977, many studies have used the construct with smoking, alcohol problems, drug abuse, and eating disorders. Measures of self-efficacy continue to prove valuable in the assessment and treatment of these addictive behaviors, particularly in the area of maintenance or relapse (Di-Clemente, 1986). However, questions and controversies surround the use and usefulness of self-efficacy with addictive behaviors. This chapter summarizes the issues that arise when applying self-efficacy to the addictive behaviors, as well as review studies that have used the construct with smoking, alcohol, drug abuse, and eating disorders.

A molecular mechanics/grid method for evaluation of ligand–receptor interactions

Abstract: We present a computational method for prediction of the conformation of a ligand when bound to a macromolecular receptor. The method is intended for use in systems in which the approximate location of the binding site is known and no large-scale rearrangements of the receptor are expected upon formation of the complex. The ligand is initially placed in the vicinity of the binding site and the atomic motions of the ligand and binding site are explicitly simulated, with solvent represented by an implicit solvation model and using a grid representation for the bulk of the receptor protein. These two approximations make the method computationally efficient and yet maintain accuracy close to that of an all-atom calculation. For the benzamidine/trypsin system, we ran 100 independent simulations, in many of which the ligand settled into the low-energy conformation observed in the crystal structure of the complex. The energy of these conformations was lower than and well-separated from that of others sampled. Extensions of this method are also discussed. © 1995 by John Wiley & Sons, Inc.

Race and Ideology: African-American Images in Television Advertising:

Abstract: Although the numerical representation of African-Americans in contemporary television advertising has improved in recent years, the authors’ analysis illustrates how the potentially positive effect...

Chapter 16 Immunofluorescence Microscopy

Abstract: Publisher Summary This chapter provides a practical guide to immunofluorescence microscopy of Caenorhabditis elegans. In this method, fixed tissue is stained with a fluorescently labeled antibody, and visualized with the light microscope. The antibody ensures that staining is limited to the location of the antigen, and the microscope provides a magnified image of the fluorescent area. Immunofluorescence microscopy is an especially powerful tool for studies of C. elegans. Immunofluorescence staining can provide essential information for the analysis of mutant phenotypes. Mutations that alter developmental programs or the expression of particular proteins can be examined in situ and described at the level of individual cells or cell lineages. Immunofluorescence microscopy can be used to detect the expression of transgenes in C. elegans. Specific epitope tags can be incorporated into a transgene, such that the epitope-tagged protein can be detected with a specific antibody that does not react with the endogenous protein. Epitope tagging is particularly useful for cases in which a null mutation in the endogenous gene is either not available or desirable in the transgenic animal.

A Markov Model for the Term Structure of Credit Risk Spreads

Abstract: This paper provides a Markov model for the term structure of credit risk spreads. The model is based on Jarrow and Turnbull (1995) with the bankruptcy process following a discrete state space Markov chain in credit ratings. The parameters of this process are easily estimated using observable data. This model is useful for pricing and hedging corporate debt with imbedded options, for pricing and hedging OTC derivatives with counterparty risk, for pricing and hedging (foreign) government bonds subject to default risk (e.g., municipal bonds), for pricing and hedging credit derivatives, and for risk management.

Assembly of VP26 in herpes simplex virus-1 inferred from structures of wild-type and recombinant capsids

Abstract: The 1250 A diameter herpes simplex virus-1 (HSV-1) capsid shell consists of four major structural proteins, of which VP26 (approximately 12,000 M(r)) is the smallest. Using 400 kV electron cryomicroscopy and computer reconstruction, we have determined the three-dimensional structures of the wild-type capsid and a recombinant baculovirus-generated HSV-1 capsid which lacks VP26. Their difference map demonstrates the presence of VP26 hexamers attached to all the hexons in the wild-type capsid, and reveals that the VP26 molecule consists of a large and a small domain. Although both hexons and pentons are predominantly composed of VP5, VP26 is not present on the penton. Based on the interactions involving VP26 and the hexon subunits, we propose a mechanism for VP26 assembly which would account for its distribution. Possible roles of VP26 in capsid stability and DNA packaging are discussed.