Showing papers by "University of Houston published in 1990"
TL;DR: A hierarchical model which integrates the previously competing models provided the best fit to the data and serves to explain a large body of previous findings.
812 citations
TL;DR: In this paper, the AR concept is defined for efficiency analysis of the linear production possibility set and applied here to 83 farms, using only the special case of AR consisting of separate linear homogeneous restrictions on the input and output multipliers.
706 citations
TL;DR: The organization of the visual cortex has been considered to be highly stable in adult mammals, however, 5 degrees to 10 degrees lesions of the retina in the contralateral eye markedly altered the systematic representations in primary and secondary visual cortex when matched inputs from the ipsilateral eye were removed.
Abstract: The organization of the visual cortex has been considered to be highly stable in adult mammals. However, 5 degrees to 10 degrees lesions of the retina in the contralateral eye markedly altered the systematic representations of the retina in primary and secondary visual cortex when matched inputs from the ipsilateral eye were also removed. Cortical neurons that normally have receptive fields in the lesioned region of the retina acquired new receptive fields in portions of the retina surrounding the lesions. The capacity for such changes may be important for normal adjustments of sensory systems to environmental contingencies and for recoveries from brain damage.
696 citations
TL;DR: The effects of stress on the endocrine and central nervous Systems and the interactions between these systems and the immune response after exposure to stress signals are reviewed.
686 citations
TL;DR: These five groups of subjects demonstrated no differences on demographic characteristics but significantly differed on Alcohol Use Inventory subscales, a temptation to drink and abstinence self-efficacy measure as well as several outcome variables.
683 citations
TL;DR: La discussion porte sur le depot de couches de carbones type diamant mais on donne aussi des exemples pour d'autres systemes tels que Si, Ge and Ag.
Abstract: A model describing film growth from hyperthermal (\ensuremath{\sim}1--${10}^{3}$ eV) species impinging on substrates is presented. The model involves a shallow subsurface implantation process called ``subplantation,'' energy loss, preferential displacement of atoms with low displacement energy ${\mathit{E}}_{\mathit{d}}$, leaving the high-${\mathit{E}}_{\mathit{d}}$ atoms intact, sputtering of substrate material, and inclusion of a new phase due to incorporation of a high density of interstitials in a host matrix. Epitaxial or preferred orientation may result from the angular dependence of the ${\mathit{E}}_{\mathit{d}}$ and the boundary conditions imposed by the host matrix, i.e., the ``mold'' effect. The discussion focuses on deposition of carbon diamondlike films, but examples of other systems, such as Si, Ge, and Ag, are provided as well. The model is supported by classical-ion-trajectory calculations and experimental data. The calculations probe the role of ion range, local concentration, backscattering coefficient, sputtering yield, and ion-induced damage in film evolution. The experimental data emphasize in situ surface-analysis studies of film evolution. The physical parameters of the deposition process that are treated are as follows: (i) nature of bombarding species (${\mathrm{C}}^{+}$ versus ${\mathrm{C}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{C}}^{\mathrm{\ensuremath{-}}}$ versus ${\mathrm{C}}_{2}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{C}}_{\mathit{n}}$${\mathrm{H}}_{\mathit{m}}^{+}$, ${\mathrm{Ar}}^{+}$, and ${\mathrm{H}}^{+}$), (ii) ion energy, (iii) type of substrate, and (iv) substrate temperature during deposition.
517 citations
TL;DR: In this article, a model was constructed for conversion in a pellet by incorporating both the reverse reaction and the effect of external and internal diffusion, and the model was expanded to a large-scale packed bed with appropriate heat transfer parameters.
475 citations
TL;DR: In this paper, an empirically based taxonomy, developed through cluster analysis of consumer's perceptions of services, is presented, which offers several insights into strategic marketing for service marketers.
Abstract: A theme emerging in the services marketing literature indicates that services marketers should look beyond their own industry boundaries to gain marketing insight. A number of conceptual typologies for grouping services have been developed. However, none of these conceptualizations have been studied empirically. This article presents an empirically based taxonomy, developed through cluster analysis of consumer's perceptions of services. The results of the study offer several insights into strategic marketing for service marketers.
384 citations
TL;DR: The actin microfilaments were found to be the major cytoskeletal component determining the viscoelastic response of endothelial cells grown in static culture.
Abstract: The viscoelastic deformation of porcine aortic endothelial cells grown under static culture conditions was measured using the micropipette technique. Experiments were conducted both for control cells (mechanically or trypsin detached from the substrate) and for cells in which cytoskeletal elements were disrupted by cytochalasin B or colchicine. The time course of the aspirated length into the pipette was measured after applying a stepwise increase in aspiration pressure. To analyze the data, a standard linear viscoelastic half-space model of the endothelial cell was used. The aspirated length was expressed as an exponential function of time. The actin microfilaments were found to be the major cytoskeletal component determining the viscoelastic response of endothelial cells grown in static culture.
374 citations
TL;DR: Those who continued to work or retirees who elected to participate in regular activities sustained more constant CBF levels and scored better on cognitive testing after the fourth year of follow‐up compared to inactive retirees.
Abstract: Among neurologically normal volunteers approaching age 65 with an option for retirement, a four-year prospective longitudinal study was designed to examine effects of different levels of physical activity on cerebral perfusion by between-group comparisons. After the fourth year, cognitive performance was also tested. Three groups were compared, each composed of 30 elderly volunteers, assigned as follows: Group 1, who continued to work; Group 2, who retired but participated in regular physical activities; and Group 3, who retired but did not participate in regular, planned physical activities. Retirees who elected to become physically inactive exhibited significant declines in cerebral blood flow (CBF) throughout four years of follow-up. Those who continued to work or retirees who elected to participate in regular activities sustained more constant CBF levels. Active retirees and those who continued to work also scored better on cognitive testing after the fourth year of follow-up compared to inactive retirees.
368 citations
TL;DR: In this paper, the authors present a framework that may be used for viewing organizational stress interventions, briefly reviewing some of the stress management intervention literature in the context of this framework, and identify future needs that may also be particularly appropriate for organizational psychologists to address.
Abstract: Despite the general agreement that stress plays a role in everyday life, there continues to be substantial controversy about how stress can be managed at the worksite. During the last decade, our knowledge of stress management interventions has increased substantially. Despite this improvement, deficiencies in the literature exist. In this article, we offer a framework that may be used for viewing organizational stress interventions, briefly review some of the stress management intervention literature in the context of this framework, and identify future needs that may be particularly appropriate for organizational psychologists to address.
Journal Article•
TL;DR: Unlike Gaddum's M receptor, the putative 5-HT4 [corrected] receptor site exhibits a higher sensitivity to agonism by 5- HT and is resistant to antagonism by cocaine.
Abstract: Experiments were undertaken to characterize pharmacologically a neuronal receptor to 5-HT in guinea pig ileum. Segments of longitudinal muscle myenteric plexus preparations were treated with phenoxybenzamine and exposed to submaximal electrical field stimulation to evoke the cholinergically mediated "twitch" response. The ability of 5-HT to enhance the submaximal twitch response was investigated. Results using several antagonists (metergoline, spiperone, cyanopindolol, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide, N-hexanoyl-5-hydroxytryptophyl-5-hydroxytryptophan amide, ICS 205-930, GR 38032F, MDL 72222 and cocaine) indicate that 5-HT (3 X 10(-10) to 1 x 10(-7) M) agonizes a novel 5-HT receptor site distinct from the 5-HT1, 5-HT2, 5-HT3 and 5-HT1P subtypes as well as the M receptor. The receptor site is located neuronally and is characterized positively by a low affinity for ICS 205-930 (pA2 = 6.5 vs. 5-HT) and by the following order of agonist potency: 5-HT greater than 5-methoxytryptamine greater than BRL 24924 greater than alpha-methyl-5-hydroxytryptamine greater than zacopride = cisapride = 5-carboxamidotryptamine. Agonist-independent pA2 estimates for ICS 205-930 (6.3-6.6) suggest a single site of agonism. 2-Methyl-5-hydroxytryptamine and 5-hydroxyindalpine were inactive at 1 x 10(-5) M either as agonists or antagonists. Thus, the receptor site exhibits a pharmacological profile similar to that characterizing the recently described 5-HT4 [corrected] receptor. Unlike Gaddum's M receptor, which equates with the 5-HT3 [corrected] receptor, the putative 5-HT4 [corrected] receptor site exhibits a higher sensitivity to agonism by 5-HT and is resistant to antagonism by cocaine.
Journal Article•
TL;DR: It is concluded that, over a period of years, a shift of the oculomotor reference from the fovea to a nonfoveal locus is possible in patients with bilateral macular disease and the shift should facilitate the visual rehabilitation of such patients.
Abstract: Previous studies have shown that most patients with bilateral macular disease use a single retinal area during fixation which is typically located near the edge of the central scotoma. Through frame-by-frame playback of videorecordings showing the target's image on each patient's fundus, we evaluated the sequences of eye movements the patients make during fixation and refixation saccades. We show that although most of our patients with bilateral macular disease had a preferred fixation area, only one third exhibited additional oculomotor behaviors, indicating a complete rereferencing of their eye movements to the preferred area. Such behaviors include the maintenance of the target's image within a circumscribed retinal area during fixation; consistent imaging of the target at the same retinal area as a result of refixation saccades; and the complete absence of "foveating" saccades. Spatial precision of eye movements (fixation and the endpoints of saccades) of patients with a nonfoveal oculomotor reference tends to be scaled to the eccentricity of the preferred fixation area. Saccadic latencies were elevated in patients with bilateral macular disease; elevation was pronounced when the duration of disease was 2 yr or less, but was evident even in patients whose eye movement patterns were consistent with a single nonfoveal reference. We conclude that, over a period of years, a shift of the oculomotor reference from the fovea to a nonfoveal locus is possible in patients with bilateral macular disease. The shift should facilitate the visual rehabilitation of such patients.
TL;DR: The numerical implementation of a systematic method for the exact boundary controllability of the wave equation, concentrating on the particular case of Dirichlet controls, is discussed.
Abstract: In this paper we discuss the numerical implementation of a systematic method for the exact boundary controllability of the wave equation, concentrating on the particular case of Dirichlet controls. The numerical methods described here consist in a combination of: finite element approximations for the space discretization; explicit finite difference schemes for the time discretization; a preconditioned conjugate gradient algorithm for the solution of the discrete problems; a pre/post processing technique based on a biharmonic Tychonoff regularization. The efficiency of the computational methodology is illustrated by the results of numerical experiments.
TL;DR: In this paper, the authors give a characterization of unital operator algebras in terms of their matricial norm structure, and show that the quotient of an operator algebra by a closed two-sided ideal is again an unital algebra up to complete isometric isomorphism.
TL;DR: The results strongly suggest that cell damage can occur in the vicinity of the gas distributor and demonstrate that bubble size and gas flow rate are not the only important considerations of cell damage in sparged bioreactors.
Abstract: Pluronic F-68 is a widely used protective agent in sparged animal cell bioreactors. In this study, the attachment-independent Spodoptera frugiperda Sf9 insect cell line was used to explore the mechanism of this protective effect and the nature of cell damage in sparged bioreactors. First, bubble incorporation via cavitation or vortexing was induced by increasing the agitation rate in a surface-aerated bioreactor; insect cells were rapidly killed under these conditions of the absence of polyols. Supplementing the medium with 0.2% (w/v) Pluronic F-68, however, fully protected the cells. Next, cell growth was compared in two airlift bioreactors with similar geometry but different sparger design; one of these bioreactors consisted of a thin membrane distributor, while the other consisted of a porous stainless steel distributor. The flow rates and bubble sizes were comparable in the two bioreactors. Supplementing the medium with 0.2% (w/v) Pluronic F-68 provided full protection to cells growing in the bioreactor with the membrane distributor but provided essentially no protection in the bioreactor with the stainless steel distributor. These results strongly suggest that cell damage can occur in the vicinity of the gas distributor. In addition, these results demonstrate that bubble size and gas flow rate are not the only important considerations of cell damage in sparged bioreactors. A model of cell death in sparged bioreactors is presented.
05 Feb 1990
TL;DR: In this article, a temporal extension to an extended ER (entity-relationship) model is proposed, and the concept of life span for entities and relationships is incorporated in the ER model.
Abstract: A temporal extension to an extended ER (entity-relationship) model is proposed. The concept of life span for entities and relationships is incorporated in the ER model. Also specified is a temporal query and update language which is an extension of the GORDAS language. The concepts of temporal Boolean expressions, temporal selection, and temporal projection are introduced, and their use in the query language is illustrated. Temporal constraints are incorporated into the ER model, and the semantics of temporal update operations is defined. >
TL;DR: This finding shows that the more precise monocular signals are actively suppressed in fused or partially-fused stereoscopic images.
TL;DR: Laboratory crosses were carried out among three genetically differentiated Los Angeles populations and one San Diego population of the intertidal copepod Tigriopus californicus, finding that despite high levels of allozyme differentiation, all crosses produced viable F1 progeny.
Abstract: Laboratory crosses were carried out among three genetically differentiated Los Angeles populations (all located within approximately 15 km) and one San Diego population (approximately 150 km away) of the intertidal copepod Tigriopus californicus. Despite high levels of allozyme differentiation, all crosses produced viable F1 progeny. Most F1 progeny had shorter developmental times and reduced variance in developmental times compared to the parental populations. Only one pair of populations failed to produce viable F2 progeny; when the central Los Angeles population (AB) was crossed to the San Diego (SD) population, most larvae died during the late naupliar stages. Developmental times in the F2 generation of the other Los Angeles × San Diego crosses were typically 40% longer than developmental times of the parental populations. Among the Los Angeles populations, only one cross (and not its reciprocal) showed a similarly large increase in developmental time. Variance in F2 developmental times was greater than the parental variance in 5 of 10 crosses. These results are discussed with regard to the evolution of coadapted gene complexes and population differentiation in T. californicus.
TL;DR: In this article, the equivalence principle is used to predict the radiation pattern of a general class of leaky-wave antennas, consisting of a finite-size source which excites a radially propagating leaky wave on some planar surface.
Abstract: Formulas are derived for the far-infrared radiation pattern of cylindrical leaky waves propagating on a planar surface. The formulas can be used to predict the radiation pattern of a general class of leaky-wave antennas, consisting of a finite-size source which excites a radially propagating leaky wave on some planar surface. Leaky-wave antennas consisting of antenna elements embedded in dielectric layers (microstrip elements) fall into this category. Using the equivalence principle, formulas are derived for both transverse electric (TE) and transverse magnetic (TM) leaky waves with arbitrary propagation constants. The formulas allow for radiation from cylindrical apertures of arbitrary size, so that the effect of truncating the supporting planar surface with an absorbing material can be determined. Particular attention is devoted to the case of a leaky wave for which the real and imaginary parts of the complex propagation constant are equal, since this type of wave has been shown to be responsible for broadside radiation in certain leaky-wave antennas comprised of dielectric layers. >
TL;DR: In this paper, an extensive review of the research literature related to career counseling with Hispanics in the U.S. from 1970 to the present is presented, which is organized into four areas: occupational aspirations, vocational interests, on-the-job behavior, and educational attainment.
Abstract: This article presents an extensive review of the research literature related to career counseling with Hispanics in the U.S. from 1970 to the present. Most of the research reviewed dealt with Mexican-Americans, and only a few studies included Puerto Ricans in their sample. The article is organized into four areas: occupational aspirations, vocational interests, on-the-job behavior; and educational attainment. It was found that Hispanic students tend to have high occupational and educational aspirations, Holland 's hexagonal model of career interests seem to apply to Hispanics, middle-class and college-educated Hispanics and Anglos are similar in terms of work values and career progression behaviors, and educational attainment among Hispanics varies according to their national origin, generational status, and social class. It was concluded that, in general, the career counseling research related to Hispanics is very limited in terms of content, and for the most part lacks a theoretical base. The findings o...
TL;DR: In this paper, the authors obtained explicit equilibrium bidding functions for first-price and second-price auctions with uncertainty about the number of rivals, in a symmetric model with risk-neutral bidders holding independent information.
TL;DR: Some of the most important results that have provided insights into the cosmic and primitive Earth environments, particularly those environments in which life is thought to have originated are brought together.
Abstract: Results of the studies that have provided insights into the cosmic and primitive earth environments are reviewed with emphasis on those environments in which life is thought to have originated. The evidence bearing on the antiquity of life on the earth and the prebiotic significance of organic compounds found in interstellar clouds and in primitive solar-system bodies such as comets, dark asteroids, and carbonaceous chondrites are assessed. The environmental models of the Hadean and early Archean earth are discussed, as well as the prebiotic formation of organic monomers and polymers essential to life. The processes that may have led to the appearance in the Archean of the first cells are considered, and possible effects of these processes on the early steps of biological evolution are analyzed. The significance of these results to the study of the distribution of life in the universe is evaluated.
TL;DR: A user can formulate database queries and updates graphically, by manipulating schema diagrams, using an extended ER model incorporating various forms of generalization and specialization, including subset, union and partition relationships.
Abstract: A user can formulate database queries and updates graphically, by manipulating schema diagrams. The authors based the graphical data manipulation interface on the entity-relationship (ER) model because of its widespread use and increasing popularity. They use an extended ER model incorporating various forms of generalization and specialization, including subset, union and partition relationships. They call their model the extended conceptual entity-relationship or ECER model. A comparison with other graphical entity-relationship interfaces is included. >
TL;DR: The probabilistic model is expanded to include measured nonissue variables, thereby representing the general multivariate model of behavioral research and offering a general candidate equilibrium solution.
Abstract: Most applications of spatial modeling to the problem of electoral competition are pessimistic regarding the prospects for candidate equilibrium in more than one policy dimension. Probabilistic models of the vote, however, increase the likelihood of equilibrium. We expand the probabilistic model to include measured nonissue variables, thereby representing the general multivariate model of behavioral research. For this model we offer a general candidate equilibrium solution and illustrate with some simulations based on 1988 National Election Study data. The more complicated one's model of voters' motivations, the greater appears to be the chance of locating a candidate equilibrium position in policy space.
TL;DR: In this article, an effort has been made to expand upon the Demands and Capacities model and demonstrate how, through its use, it is possible to account for the substantial diversity observed in stutterers, both in the experimental laboratory and in the clinic.
TL;DR: The authors examined the effects of foreign aid on public sector budgets of developing countries and found that soft loan aid is quite stimulative, but that the IMF has the greatest impact on recipients.
TL;DR: In this article, a general method for the implementation of polarization in molecular dynamics simulations of small molecules is suggested, where the induction is treated explicitly, while the higher order contributions, the polarization due to induced dipoles, are taken into account in an average way by modification of potential parameters.
Abstract: A general method is suggested for the implementation of polarization in molecular dynamics simulations of small molecules. Induced dipole moments are evaluated on selected polarizability centers and represented by separation of charges. The positive polarization charges reside on the selected atoms. The negative polarization charges are treated as additional particles. The positions of these polarization charges are determined from the electrical fields due to the permanent charges of the system. Thus the induction is treated explicitly, while the higher order contributions, the polarization due to induced dipoles, are taken into account in an average way by modification of potential parameters. The forces can be evaluated for the new charge distribution in the conventional way. As an illustration of this approach initial results are reported for the development of a polarizable water model. The higher order polarization is treated in an average way by slight increase of the permanent charges as ...
TL;DR: In this paper, a projection operator approach was used to couple the inelastic and reactive portions of the total wave function and optical potentials to circumvent the necessity of using product arrangement coordinates.
Abstract: This paper describes a new approach to the study of atom–diatom reactive collisions in three dimensions employing wave packets and the time‐dependent Schrodinger equation. The method uses a projection operator approach to couple the inelastic and reactive portions of the total wave function and optical potentials to circumvent the necessity of using product arrangement coordinates. Reactive transition probabilities are calculated from the state resolved flux of the wave packet as it leaves the interaction region in the direction of the reactive arrangement channel. The wave packet does not need to be propagated into the asymptotic reactive region in order to determine accurate vibrationally resolved, but rotationally summed reaction probabilities. The present approach is used to obtain such vibrationally resolved reaction probabilities for the three‐dimensional H+H2 (J=0) hydrogen exchange reaction, using a body‐fixed system of coordinates.
TL;DR: The ability of these polyols to protect animal cells in sparged bioreactors was found to correlate well with the hydrophilic‐lipophilic balance (HLB).
Abstract: The nonionic surfactant Pluronic F-68 polyol is commonly used to protect cultured animal cells from the detrimental effects of sparging. In this study we investigated the structural features of the Pluronic F-68 molecule responsible for this protective behavior. Poly(oxyethylene)-poly(oxypropylene) block copolymer polyols of various molecular weights and percentages of hydrophobe (poly(oxypropylene)), including both Pluronic and reverse Pluronic polyols, were considered. The potential toxicity of these agents was examined in the absence of sparging (i.e., in spinner flasks) by using the attachment-independent Sf9 insect cell line as a model system. Each polyol resulted in one of three distinct types of behavior in these spinner flask experiments: (1) cells lysed at an exponential rate, (2) inhibition of cell growth (i.e., no net cell growth), or (3) uninhibited cell growth. It was then shown that all of the Pluronic and reverse Pluronic polyols that did not inhibit cell growth provided protection from sparging in the bioreactors used in this study; thus, finding a polyol that protected cells was synonymous with finding one that did not inhibit cell growth. The ability of these polyols to protect animal cells in sparged bioreactors was found to correlate well with the hydrophilic-lipophilic balance (HLB). Those polyols with the largest HLB values were found to be protective agents. These poly(oxyethylene)-poly(oxypropylene) polyols were also shown to be more effective protective agents than pure poly(oxyethylene); thus, the presence of the hydrophobe (poly(oxypropylene)) is important in their ability to serve as protective agents.