Showing papers by "University of Houston published in 1987"
TL;DR: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure.
Abstract: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.
5,965 citations
TL;DR: An apparent superconducting transition with an onset temperature above 40 K has been detected under pressures in the La-Ba-Cu-O compound system synthesized directly from a solid-state reaction of La/sub 2/O/ sub 3/, CuO, and BaCO/sub 3/ followed by a decomposition of the mixture in a reduced atmosphere.
Abstract: An apparent superconducting transition with an onset temperature above 40 K has been detected under pressure in the La-Ba-Cu-O compound system synthesized directly from a solid-state reaction of La2O3, CuO, and BaCO3 followed by a decomposition of the mixture in a reduced atmosphere. The experiment is described and the results of effects of magnetic field and pressure are discussed.
1,128 citations
TL;DR: The results suggest that the unique square planar Cu atoms, each surrounded by four or six oxygen atoms, are crucial to the superconductivity of oxides in general.
Abstract: Superconductivity has been found in the 90-K range in ABa2Cu3O(6 + x) with A = La, Nd, Sm, Eu, Gd, Ho, Er, and Lu in addition to Y. The results suggest that the unique square-planar Cu atoms, each surrounded by four or six oxygen atoms, are crucial to the superconductivity of oxides in general. In particular, the high Tc of ABa2Cu3O(6 + x) is attributed mainly to the quasi-two-dimensional assembly of the CuO2-Ba-CuO(2 + x)Ba-CuO2 layers sandwiched between two A layers, with particular emphasis in the CuO(2 + x) layers. Higher-Tc oxides are predicted for compounds with bigger assemblies of CuO2 layers coupled by Ba layers.
719 citations
TL;DR: The three-dimensional stability of two-dimensional vortical states of planar mixing layers is studied by direct numerical integration of the Navier-Stokes equations in this article.
Abstract: The three-dimensional stability of two-dimensional vortical states of planar mixing layers is studied by direct numerical integration of the Navier-Stokes equations. Small-scale instabilities are shown to exist for spanwise scales at which classical linear modes are stable. These modes grow on convective timescales, extract their energy from the mean flow and exist at moderately low Reynolds numbers. Their growth rates are comparable with the most rapidly growing inviscid instability and with the growth rates of two-dimensional subharmonic (pairing) modes. At high amplitudes, they can evolve into pairs of counter-rotating, streamwise vortices, connecting the primary spanwise vortices, which are very similar to the structures observed in laboratory experiments. The three-dimensional modes do not appear to saturate in quasi-steady states as do the purely two-dimensional fundamental and subharmonic modes in the absence of pairing. The subsequent evolution of the flow depends on the relative amplitudes of the pairing modes. Persistent pairings can inhibit threedimensional instability and, hence, keep the flow predominantly two-dimensional. Conversely, suppression of the pairing process can drive the three-dimensional modes to more chaotic, turbulent-like states. An analysis of high-resolution simulations of fully turbulent mixing layers confirms the existence of rib-like structures and that their coherence depends strongly on the presence of the two-dimensional pairing modes.
376 citations
TL;DR: In this paper, a conceptual model of how training can impact the acceptance of information systems within the organization is presented and empirically evaluated via an extensive field study of 100 middle-and upper-level managers from 20 companies.
Abstract: This article presents and empirically evaluates a conceptual model of how training can impact the acceptance of information systems within the organization. Specifically, the training of end users is explored via an extensive field study of 100 middle- and upper-level managers from 20 companies. The results indicate that (1) a positive relationship exists between the computer-related training an individual receives and his/her computer-related ability, and (2) a positive relationship exists between the computer-related ability of an end user and his/her acceptance of information systems products and technologies.
356 citations
TL;DR: This paper found that respondents use a variety of processes in answering behavioral frequency questions in a field setting and that task conditions impact response formulation processes, indicating that new models are needed for complete understanding of response errors in frequency data for a varietyof behaviors of interest to consumer researchers.
Abstract: Behavioral frequency questions are a common and important part of consumer surveys. The conventional model of how people answer such questions and how response errors occur has presumed that respondents recall and enumerate specific behavioral episodes. Recent laboratory research, however, has shown that respondents use a variety of processes in answering such questions. Results of this study confirm this finding in a field setting and show that task conditions impact response formulation processes. These results indicate that new models are needed for complete understanding of response errors in frequency data for a variety of behaviors of interest to consumer researchers.
346 citations
TL;DR: In this paper, a modified version of Tinto's student attrition model on a Chicano student population in two-year colleges was tested and the results indicated that the hypothesized relationship between measures of social integration could not be substantiated.
Abstract: This study tested a modified version of Tinto's student attrition model on a Chicano student population in two-year colleges. Structural equation modeling and LISREL VI were used to examine the parameter estimates of the structural and measurement models of the hypothesized causal model. Measures of goodness of fit were examined to provide indices for the overall fit of the causal model in the study. The measurement and structural models were found to represent a plausible causal model of student retention among Chicano students. Although the measures used in assessing the fit of the model reflected the overall strength of the hypothesized model, the present study was not entirely supportive of Tinto's model. The findings were only minimally supportive of the hypothesized relationship between measures of academic integration and retention. The results indicated that the hypothesized relationship between measures of social integration could not be substantiated. Moreover, measures of initial commitments were found to have a significantly large direct effect on the dependent variable, retention.
345 citations
TL;DR: Kilbler-Ross's five-stage model and the concept of loss of attachment served as the theoretical underpinnings for an examination of the psychological and behavioral responses of employees of acquired firms as discussed by the authors.
Abstract: Whenever a young child who is attached to her mother is separated from her, she shows distress-and should the child be placed in a new environment, the distress is likely to intensify. The way the child behaves in this situation will follow a distinct pattern: At first she protests vigorously and tries by all possible means to recover her mother. Later, she seems to despair of getting her mother back, but nevertheless remains preoccupied with her. Finally, the child seems to lose interest and becomes emotionally detached from the mother.'2 What is happening to thousands of employees in acquired firms is similar to the loss of attachment experienced by the child. Employees attach themselves to organizations, jobs, coworkers, work routines, the application of personal skills, and performance and career goals. Like the child, many employees involved in acquisitions experience a powerful sense of loss when strong attachments are destroyed or changed.3 Loss is a common life process. Some losses are more permanent than others; for example, the loss that one experiences when a son leaves for college is more temporary than that experienced when losing a job. Each loss, however, involves a period of immediate grief, a period of adjustment to the loss, and a period that heralds the beginning of the next cycle in life.4 Elisabeth Kiubler-Ross defines death or loss in terms of stages: denial, anger, bargaining, depression, and acceptance." Kilbler-Ross's five-stage model and the concept of loss of attachment served as the theoretical underpinnings for our examination of the psychological and behavioral responses of employees of acquired firms. The loss of an organization, a job, a coworker, or a work routine, like the loss of a mother figure, a friend, or relative, can be disruptive and painful. Executives and consultants responsible for structuring acquisitions have shown creative expertise in putting together the legal and financial aspects of deals." Unfortunately, they have not exhibited corresponding creativity and expertise in understanding and dealing with the psychological trauma that these forms of corporate growth create for employees; continued failure to do so will likely undermine the success of an acquisition venture. Can managers in acquired firms be better prepared to deal with the loss of attachment that many employees experience in anticipation and after a deal is consummated? We believe that once managers become aware of the power of loss of attachment, they will want to help employees avoid many of the negative consequences of that loss. In this article we will discuss the implications of the loss of attachment that is experienced by many employees in acquired firms. We studied individuals who remained with the acquired firm and those who lost their jobs. The research findings point to specific steps that managers can take to ease the loss of attachment and minimize the negative effects.
310 citations
TL;DR: X-ray powder-diffraction studies show that the high-temperature superconductivity in Y-Ba-Cu-O can only be attributed to one or more phases with structures different from the cubic perovskite or tetragonal layered ones.
Abstract: The pressure effect on the superconducting state above 77 K in the new Y-Ba-Cu-O compound system has been determined In strong contrast to what is observed in the La-Ba-Cu-O and La-Sr-Cu-O systems, pressure has only a slight effect on the superconducting transition temperature
306 citations
TL;DR: Two types of calculations that show special promise as design tools, the thermodynamic cycle-perturbation method and the Brownian reactive dynamics method, can be applied to calculate equilibrium and rate constants that describe many aspects of molecular recognition, stability, and reactivity.
Abstract: Theoretical chemistry, as implemented on fast computers, is beginning to yield accurate predictions of the thermodynamic and kinetic properties of large molecular assemblies. In addition to providing detailed insights into the origins of molecular activity, theoretical calculations can be used to design new molecules with specific properties. This article describes two types of calculations that show special promise as design tools, the thermodynamic cycle-perturbation method and the Brownian reactive dynamics method. These methods can be applied to calculate equilibrium and rate constants that describe many aspects of molecular recognition, stability, and reactivity.
302 citations
TL;DR: In this paper, the authors investigate the style and magnitude of seafloor spreading along the axis of the Mid-Atlantic Ridge and demonstrate dramatic changes in the style of tectonic extension, development of the neovolcanic zone, expression of hydrothermal venting, types oflithologic exposures and morphology of the median valley.
Abstract: Recent investigations with the manned submersible Alvin and the Angus deep-towed camera sled greatly extended the known range of variations in the style of seafloor spreading along the axis of the Mid-Atlantic Ridge. Five transects of the spreading centre at intervals of10–20 km south of the Kane Fracture Zone at 24° N latitude demonstrate dramatic changes in the style and magnitude of tectonic extension, development of the neovolcanic zone, expression of hydrothermal venting, types oflithologic exposures and morphology of the median valley.
TL;DR: An effective intramolecular potential is presented for use in conjunction with existing three-site models of water by including a Urey-Bradley-like term in an otherwise standard molecular mechanics form it was found that the experimental transition frequencies of water monomer can be reproduced accurately.
Abstract: An effective intramolecular potential is presented for use in conjunction with existing three-site models of water. Two commonly used internal geometries were fit to the same form yielding slightly different parametrizations. By including a Urey-Bradley-like term in an otherwise standard molecular mechanics form it was found that the experimental transition frequencies of water monomer can be reproduced accurately. Good qualitative agreements for spectral shifts were subsequently found for the models in condensed-phase applications. Harmonic analysis of clusters indicates good qualitative agreement with experimental environmental shifts in frequencies at low temperatures for these models. This model should be useful for a wide variety of applications including simulations of biopolymers and ionic solutions.
TL;DR: Single-crystal x-ray techniques were used to determine two structures that comprise the Y-Ba-Cu-O superconductor, related to a 1:1:3 AB perovskite: Ba and Y order in A sites and Cu is in B sites.
Abstract: Single-crystal x-ray techniques were used to determine two structures that comprise the Y-Ba-Cu-O superconductor. A green phase has the orthorhombic ${\mathrm{Y}}_{2}$${\mathrm{BaCuO}}_{5}$ structure. An opaque phase (${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathrm{x}}$, 0\ensuremath{\le}x\ensuremath{\le}1.0) is tetragonal (a=3.859 A\r{}, c=11.71 A\r{}; space group P4\ifmmode\bar\else\textasciimacron\fi{}m2;Z=1). The structure is related to a 1:1:3 AB${\mathrm{O}}_{3}$ perovskite: Ba and Y order in A sites and Cu is in B sites. Systematic oxygen vacancies between adjacent copper atoms lead to a fivefold-coordinate Cu in proximity to Y and a twofold-coordinate Cu in the vicinity of the Ba site.
TL;DR: R Rationale is developed for why process tracing methods are an important addition to the inventory of methodologies available to researchers, stressing the need to explore the "black box" of decision processes.
Abstract: An overview is provided of the appficability to DSS research of process tracing methodologies in general and verbal protocol analysis in particular. Rationale is developed for why process tracing methods are an important addition to the inventory of methodologies available to researchers, stressing the need to explore the "black box" of decision processes. A variety of process tracing methods are presented, along with their relative strengths and weaknesses. Verbal protocol analysis is discussed as a particularly promising method for use in DSS research. The nature of verbal protocols is outlined and methods for analysis are reviewed. The criticisms of this method and the controversy surrounding its use are discussed, and an assessment of the validity of these criticisms is provided. Finally, areas of DSS research in which protocols may prove valuable are identified and relevant studies are examined.
TL;DR: In this article, large-scale organized structures in the turbulent plane wake of a circular cylinder are investigated in air up to a downstream distance of 40d at a Reynolds number of Red = 1.3 × 104; d is the cylinder diameter.
Abstract: Large-scale organized structures in the turbulent plane wake of a circular cylinder are investigated in air up to a downstream distance of 40d at a Reynolds number of Red = 1.3 × 104; d is the cylinder diameter. Velocity signals from a linear transverse rake of 8 X-wires are sampled simultaneously to calculate the instantaneous span wise vorticity. We have appropriately smoothed the temporal traces of vorticity to obtain time evolutions (including the transverse displacement, sign, strength and size distributions) of organized structures identified by vorticity contour maps. The periodicity of the initial structures is rapidly lost: dispersion in streamwise spacing, transverse displacement, strength and size of structures increases with increasing downstream distance.Particular emphasis is placed on examining alternative general schemes for educing coherent structures in natural or unexcited turbulent shear flows, especially in their fully developed states. The optimal eduction scheme employed involves centring the rake at the most probable transverse location of centres of advected structures and accepting those structures that: (i) are centred at the midpoint of the rake, (ii) have a peak value of (smoothed) vorticity of a given sign above a specified level, and (iii) have streamwise and transverse extents of the (smoothed) vorticity contours above a specified size. From successive accepted structure signatures the instants of occurrence of structure centres (i.e. smoothed vorticity peaks) are identified. Un-smoothed signals are then time-aligned with respect to these instants and ensemble averaged to educe coherent structure and incoherent turbulence characteristics. Further enhancement is achieved by iteratively improving the time-alignment by maximizing the cross-correlation of individual structure vorticity with the ensemble-averaged vorticity and by discarding structures that require excessive time shifts or that produce significantly weak peak correlation values.Following this optimal scheme, large-scale coherent structures have been educed in the fully turbulent wake. The average structure centre is found to be closer to the wake centreline than the half-width location, and the structure size does not increase in proportion to the wake width, suggesting that transverse wandering of structures (including their three-dimensionality) increases significantly with increasing downstream distance. The various flow properties associated with coherent and incoherent turbulence, and the coherent structure dynamics, in particular the role of vortex stretching (at the saddle) in turbulence production and mixing, are discussed.
TL;DR: In this paper, the equivalence of the Euler and the Lagrangian equations of gas dynamics in one space dimension for weak solutions which are bounded and measurable in Eulerian coordinates is demonstrated.
TL;DR: In this article, the authors examined research perspectives from role theory with a large sample of purchasing professionals in an effort to increase understanding of industrial buyer behavior and the buying environment, and the role of role theory in the buying process.
Abstract: Research perspectives from role theory are examined with a large sample of purchasing professionals in an effort to increase understanding of industrial buyer behavior and the buying environment. A...
01 Jan 1987
TL;DR: In this article, the authors explore the patterns which exist under conditions of microgravity when these body forces are suppressed and propose a flow pattern map for air-water flow in tubes during drop tower experiments.
Abstract: The prediction of flow patterns during gas-liquid flow in conduits is central to the modern approach for modeling two phase flow and heat transfer. The mechanisms of transition are reasonably well understood for flow in pipes on earth where it has been shown that body forces largely control the behavior observed. This work explores the patterns which exist under conditions of microgravity when these body forces are suppressed. Data are presented which were obtained for air-water flow in tubes during drop tower experiments and Learjet trajectories. Preliminary models to explain the observed flow pattern map are evolved.
TL;DR: A superconducting transition with an onset temperature of 52.5 K has been observed under hydrostatic pressure in compounds with nominal compositions given by (La0.9Ba0.1)2 CuO4-Y.
Abstract: The electrical properties of the (La/0/9/Ba/0.1/)CuO/4-y/ system are examined under ambient and hydrostatic pressures. The resistance, ac magnetic susceptibility, and superconductivity onset, midpoint, and intercept temperatures are measured. It is observed that at ambient pressure the resistance decreases with temperature decreases, and the ac susceptibility shows diamagnetic shifts starting at about 32 K. Under hydrostatic pressure a superconducting transition with an onset temperature of 52.5 K is observed, and the resistance increases at lower temperatures. The data reveal that the electrical properties of the La-Ba-Cu-O system are dependent on samples and preparation conditions. Various causes for the high temperature superconductivity of the system are proposed.
TL;DR: The results showed that normal foveal vision and the vision of anisometropic amblyopes show little benefit from adding discrete samples to the stimulus, and the data of the normal periphery and of the central field of strabismic Amblyopes suggest that the cortical sampling grain imposes a fundamental limit upon their positional acuity.
TL;DR: Language performance was assessed using the Neurosensory Center Comprehensive Examination for Aphasia during the subacute stage of recovery and acquired aphasia in children and posttraumatic linguistic deficits in adults were discussed.
Abstract: Fifty-six children and adolescents who sustained a closed-head injury were divided into two groups based on neurological criteria. Language performance was assessed using the Neurosensory Center Comprehensive Examination for Aphasia during the subacute stage of recovery. Naming, expressive, and written language were more impaired than receptive-language functions. At least 20% of the sample exhibited deficits on measures of describing the function of objects, sentence repetition, verbal associative fluency, writing to dictation, and copying sentences. No sparing of function was observed in children relative to adolescents. Moreover, written-language performance was more depressed in children than adolescents. Results were discussed in terms of acquired aphasia in children and posttraumatic linguistic deficits in adults.
TL;DR: In this article, sound generation by vortex pairing in circular and elliptic cold-air jets at Mach 015-035 is investigated experimentally, with a focus on the effects of initial conditions.
TL;DR: Finite-difference versions of some recently developed Krylov subspace projection methods are presented and analyzed in the context of solving systems of nonlinear equations using Inexact-Newton Met... as discussed by the authors.
Abstract: Finite-difference versions of some recently developed Krylov subspace projection methods are presented and analysed in the context of solving systems of nonlinear equations using Inexact-Newton Met...
01 Dec 1987
TL;DR: In this paper, the authors discuss eduction of coherent structures, measurement of propagation velocities of perturbation in turbulent flows, and direct evaluation of the Taylor hypothesis in turbulent flow.
Abstract: Activities are summarized for each of the three topics discussed: eduction of coherent structures; measurement of propagation velocities of perturbation in turbulent flows; and direct evaluation of the Taylor hypothesis.
TL;DR: The results indicate higher density values for wavelengths on the long wavelength side of the absorption maximum, compared to the standard absorbance curve (Wyszecki and Stiles, 1967), and the mean density is higher than that previously reported.
TL;DR: The results imply that three-dot vernier thresholds are set by a single orientation mechanism at all eccentricities and that two-dot bisection thresholds areset by a pair of mechanisms.
Abstract: Position acuity was measured over a wide range of eccentricities, from 3 min to 10 deg in the horizontal meridian, by using both a three-dot bisection task and a three-dot vernier task. A foveal fixation dot appeared for 1 sec before an outer pair of test dots was flashed for 200 msec. Bisection and vernier tasks were used to measure position acuity in the radial and tangential directions, respectively. The vernier data were well fitted by a straight line on linear axes of offset threshold versus eccentricity. The bisection data, on the other hand, were poorly fitted by a single straight line. However, a double-line fit worked very well. The line segment at large eccentricities (>0.5 deg) had an x intercept of about 0.6 deg, in good agreement with previous estimates based on cortical magnification and on hyperacuity in the presence of flanks. These results imply that three-dot vernier thresholds are set by a single orientation mechanism at all eccentricities and that three-dot bisection thresholds are set by a pair of mechanisms. For eccentricities less than 15 min, thresholds are in good agreement with calculations based on spatial-frequency filters. For larger eccentricities, the bisection thresholds agree with scaled anatomical modules that are presumed to exist in the human visual cortex. The thresholds for position acuity in the tangential direction are as low as 0.005 times the eccentricity. In the radial direction, thresholds are poorer, implying that additional cortical factors may further constrain performance.
TL;DR: This paper found that the state of residence is an important predictor of partisan and ideological identification, independent of their demographic characteristics, and that state culture dominates state demography as a source of state-to-state differences in opinion.
Abstract: Do the states of the United States matter (or are they of no political consequence)? Using a data set with over 50 thousand respondents, we demonstrate the influence of state political culture on partisanship and ideology. For individuals, we find that the state of residence is an important predictor of partisan and ideological identification, independent of their demographic characteristics. At the aggregate level, state culture dominates state demography as a source of state-to-state differences in opinion. In general, geographic location may be a more important source of opinion than previously thought. One indication of the importance of state culture is that state effects on partisanship and ideology account for about half of the variance in state voting in recent presidential elections.
TL;DR: A primary prevention program, the Houston Parent-Child Development Center, directed towards infants and their parents, has effectively reduced the frequency of behavior problems for these children 5 to 8 years after the program's completion.
Abstract: A primary prevention program, the Houston Parent-Child Development Center, directed towards infants and their parents, has effectively reduced the frequency of behavior problems for these children 5 to 8 years after the program's completion. Teacher ratings showed significantly fewer acting-out, aggressive behaviors for program children. Ratings of classroom behaviors found program children significantly less hostile and more considerate than control boys. This appears to be the first primary prevention program to have demonstrated effectiveness in reducing behavior problems over such a long time.