Showing papers by "University of Houston published in 2000"

Linear Viscoelasticity of Disordered Polystyrene−Polyisoprene Block Copolymer Based Layered-Silicate Nanocomposites

Abstract: The melt-state linear viscoelastic properties for a series of intercalated nanocomposites are examined. The nanocomposites are based on a short disordered polystyrene−polyisoprene diblock copolymer and varying amounts of dimethyldioctadecylammonium modified montmorillonite. The linear dynamic oscillatory moduli and the stress relaxation moduli are in quantitative agreement and suggest that at short times the relaxation of the nanocomposites is essentially unaffected by the presence of the layered-silicate. However, at long times (or equivalently low frequency), the hybrids exhibit dramatically altered viscoelastic behavior. Hybrids with silicate loadings in excess of 6.7 wt % exhibit pseudo-solidlike behavior, similar to that observed in previous studies of exfoliated end-tethered nanocomposites. On the basis of simple phenomenological arguments, the long time behavior is attributed to the presence of anisotropic stacks of silicate sheets randomly oriented and forming a percolated network structure that i...

Recent models and findings in visual backward masking: A comparison, review, and update

Abstract: Visual backward masking not only is an empirically rich and theoretically interesting phenomenon but also has found increasing application as a powerful methodological tool in studies of visual information processing and as a useful instrument for investigating visual function in a variety of specific subject populations. Since the dual-channel, sustained-transient approach to visual masking was introduced about two decades ago, several new models of backward masking and metacontrast have been proposed as alternative approaches to visual masking. In this article, we outline, review, and evaluate three such approaches: an extension of the dual-channel approach as realized in the neural network model of retino-cortical dynamics (Ogmen, 1993), the perceptual retouch theory (Bachmann, 1984, 1994), and the boundary contour system (Francis, 1997; Grossberg & Mingolla, 1985b). Recent psychophysical and electrophysiological findings relevant to backward masking are reviewed and, whenever possible, are related to the aforementioned models. Besides noting the positive aspects of these models, we also list their problems and suggest changes that may improve them and experiments that can empirically test them.

Risk Sharing and Industrial Specialization: Regional and International Evidence

Abstract: We provide empirical evidence that risk sharing enhances specialization in production. First, we calculate an index of specialization for each of the European Community (EC) and non-EC OECD countries, U.S. states, Canadian provinces, Japanese prefectures, Latin American countries, and regions of Italy, Spain, and the United Kingdom. Then, we estimate the degree of capital market integration (risk sharing) within each of these groups of regions. Finally, we perform a regression of the specialization index on the degree of risk sharing, controlling for relevant economic variables and find a positive relation between the degree of specialization and the amount of risk sharing within a group. Instrumental variables regressions confirm that risk sharing is a causal determinant of specialization.

The myths and realities of information technology insourcing

Abstract: nformation technology outsourcing—the practice of transferring IT assets, leases, staff, and management responsibility for delivery of services from internal IT functions to third-party vendors—has become an undeniable trend ever since Kodak's 1989 landmark decision. In recent years, private and public sector organizations worldwide have outsourced significant portions of their IT functions,monwealth Bank of Australia. The IT outsourcing market, which was worth $76 billion in 1995, grew to over $120 billion in 1997 [5]. As the market evolves, a number of important aspects of these IT outsourcing decisions have been explored. These studies can be categorized as descriptive case studies and surveys of the current outsourcing practices, surveys of practitioners' perceptions of risks IT managers commiserate over the challenges of convincing senior executives that, contrary to popular belief, outsourcing isn't always a money-saving option.

Properties of ceramic foam catalyst supports: pressure drop

Abstract: Ceramic foams are prepared as positive images of corresponding plastic structures and exhibit bed porosities as high as 80–90%. This makes them attractive as catalyst supports in processes where high pressure drop in the reactor tube is a problem. In this research, pressure drop relationships were examined for 10, 30, 45 and 65 pores per inch (PPI) ceramic foam samples made from 92.0 and 99.5% α-Al2O3 and from ZrO2 stabilized with Mg, Ca, and La2O3. Pore distributions were determined with imaging analysis, using digital techniques. Pressure drop measurements confirmed that ceramic foams follow the Forscheimer relationship and may be interpreted with the Ergun model, in which the pressure drop is the sum of viscous and inertial terms. The Ergun parameters, α and β, are not constant, α decreases from 8.05 to 2.88 and β increases from 0.0338 to 0.111 as the pore density increases from 10 to 65 PPI. Empirical equations were developed for these parameters in terms of the mean pore size and the bed porosity, and these indicated a dependence on the media properties. Calculated pressure drop from these equations were within 15% of measured values. Up to 15 wt.% γ-Al2O3 washcoat was added to 30 PPI samples of α-Al2O3 foams. Nitrogen BET surface areas increased from about 2 m2 g−1 in the unwashcoated samples to almost 15 m2 g−1 at the highest loading. Both α and β increase linearly with the BET surface area, α by only about 50% but β by a factor of 8. This suggests that roughness introduced by the washcoat plays a dominant role in the turbulent resistance.

Bifurcation analysis of chen's equation

Abstract: Anticontrol of chaos by making a nonchaotic system chaotic has led to the discovery of some new chaotic systems, particularly the continuous-time three-dimensional autonomous Chen's equation with only two quadratic terms. This paper further investigates some basic dynamical properties and various bifurcations of Chen's equation, thereby revealing its different features from some other chaotic models such as its origin, the Lorenz system.

Synergy, Managerialism or Hubris? An Empirical Examination of Motives for Foreign Acquisitions of U.S. Firms

Abstract: This study examines the motives underlying foreign acquisitions of U.S. firms, estimates the extent of value creation associated with such acquisitions, and examines how total gains are shared between acquiring firms and targets. We show that the synergy hypothesis is the predominant explanation for our sample of foreign acquisitions of U.S. firms. However, the hubris hypothesis coexists with the synergy hypothesis in explaining the acquisitions in our sample that are characterized by positive total gains. The evidence is also consistent with the managerialism hypothesis for the acquisitions in our sample with negative total gains. We show that the incidence of competition is associated with higher total gains, as well as higher gains to targets.

Interparental conflict and child adjustment: testing the mediational role of appraisals in the cognitive-contextual framework.

Abstract: Children's appraisals of interparental conflict consistently have been associated with adjustment problems, but the processes that give rise to this association are not well understood. This paper proposes that appraisals of threat and self-blame mediate the association between children's reports of interparental conflict and internalizing problems, and tests this mediational hypothesis in two samples of children, one drawn from the community (317 ten- to fourteen-year-olds) and the other from battered women's shelters (145 ten- to twelve-year-olds). Results indicate that perceived threat mediates the association between interparental conflict and internalizing problems for boys and girls in both samples, and self-blame mediates this association for boys in both samples and girls in the shelter sample. Perceived threat and self-blame do not mediate links with externalizing problems, and there is no evidence of a moderating effect of appraisals on the association between conflict and child adjustment. Implications for understanding the mechanism by which exposure to interparental conflict could lead to child maladjustment are discussed.

Patterns of adjustment among children of battered women.

Abstract: Children exposed to interparental violence have been characterized by an array of psychological problems, but findings regarding the precise nature of these problems have been inconsistent. This study used cluster analysis to determine whether distinct patterns of adjustment could be identified in 228 8- to 14-year-old children residing in battered women's shelters. Five such patterns emerged: multiproblem-externalizing, multiproblem-internalizing, externalizing, mild distress, and no problems reported. This solution was cross-validated in independent halves of the sample and was similar for boys and girls. Differences among the clusters on relevant family and demographic variables were examined, and it was found that the clusters could be distinguished on the basis of the frequency of children's exposure to interparental violence, parent-child aggression, and children's appraisals of interparental conflict.

An Empirical Study of Bond Market Transactions

Abstract: Short histories of dealer-market and exchange-based bond transactions in machine-readable form have recently become available. They permitted us to provide for the first time direct estimation of the effective bid-ask spread for corporate bonds in the institutional and retail markets. Overall, we found effective spreads for NYSE-traded corporate bonds to be similar to effective spreads for dealer-market transactions. Evidence is that corporate bond spreads have declined over time and that dealers carry out U.S. government bond trades with major institutional clients as a nonprofit service, perhaps to support other (ostensibly) profitable activities. We demonstrate that bid-ask spreads and the magnitude of price discrepancies between data sources are reliably associated with proxies for risk and liquidity.

Early Maternal and Child Influences on Children's Later Independent Cognitive and Social Functioning

Abstract: The present study examined whether parenting and child characteristics of 2- and 3 Ω -year-old children had common paths of influence on their 4 Ω -year independent cognitive and social functioning. Structural equation modeling was guided by hypotheses that assumed children’s later independence is facilitated by specialized parental support in early social interactions. To address the importance of variability in early development for understanding children’s later independence, we included 104 term and 185 preterm children, as they are known to differ in early skills. As predicted, mothers’ maintaining of children’s interests indirectly supported 4 Ω -year cognitive and social independence through a direct, positive influence on 2- and 3 Ω -year skills. Directiveness positively supported children’s early cognitive and responsiveness skills but by 3 Ω years, high levels of this behavior had a direct, negative influence on their cognitive and social independence at 4 Ω years. Whereas high levels of maintaining interests across these ages support later independence, directiveness needs to decrease in relation to children’s increasing competencies. Results support a theoretical framework that emphasizes the importance of the social context for understanding the origins of children’s later independent functioning.

Bifurcation control: theories, methods, and applications

Abstract: Bifurcation control deals with modification of bifurcation characteristics of a parameterized nonlinear system by a designed control input. Typical bifurcation control objectives include delaying t...

Observation of five-fold local symmetry in liquid lead.

Abstract: The local point symmetry of the short-range order in simple monatomic liquids remains a fundamental open question in condensed-matter science. For more than 40 years it has been conjectured that liquids with centrosymmetric interactions may be composed of icosahedral building blocks. But these proposed mobile, randomly orientated structures have remained experimentally inaccessible owing to the unavoidable averaging involved in scattering experiments, which can therefore determine only the isotropic radial distribution function. Here we overcome this limitation by capturing liquid fragments at a solid-liquid interface, and observing the scattering of totally internally reflected (evanescent) X-rays, which are sensitive only to the liquid structure at the interface. Using this method, we observe five-fold local symmetry in liquid lead adjacent to a silicon wall, and obtain an experimental portrait of the icosahedral fragments that are predicted to occur in all close-packed monatomic liquids. By shedding new light on local bond order in disordered structures such as liquids and glasses, these results should lead to a better microscopic understanding of melting, freezing and supercooling.

Decadal Sea Surface Temperature Variability in the Subtropical South Pacific from 1726 to 1997 A.D.

Abstract: We present a 271-year record of Sr/Ca variability in a coral from Rarotonga in the South Pacific gyre. Calibration with monthly sea surface temperature (SST) from satellite and ship measurements made in a grid measuring 1 degrees by 1 degrees over the period from 1981 to 1997 indicates that this Sr/Ca record is an excellent proxy for SST. Comparison with SST from ship measurements made since 1950 in a grid measuring 5 degrees by 5 degrees also shows that the Sr/Ca data accurately record decadal changes in SST. The entire Sr/Ca record back to 1726 shows a distinct pattern of decadal variability, with repeated decadal and interdecadal SST regime shifts greater than 0. 75 degrees C. Comparison with decadal climate variability in the North Pacific, as represented by the Pacific Decadal Oscillation index (1900-1997), indicates that several of the largest decadal-scale SST variations at Rarotonga are coherent with SST regime shifts in the North Pacific. This hemispheric symmetry suggests that tropical forcing may be an important factor in at least some of the decadal variability observed in the Pacific Ocean.

Attachment, Emotional Regulation, and the Function of Marital Violence: Differences Between Secure, Preoccupied, and Dismissing Violent and Nonviolent Husbands

Abstract: The purpose of this study was to investigate behavioral differences among nonviolent, unhappily married husbands and violent husbands with different attachment classifications on the Adult Attachment Interview (AAI; Main and Goldwyn, 1994). Twenty-three Domestically Violent (DV) husbands and 13 maritally distressed but non-violent (DNV) husbands were interviewed using the AAI. Violent husbands (74%) were more likely than the distressed/nonviolent husbands (38%) to be classified into one of the insecure categories on the AAI. As predicted, during laboratory arguments with their wives, dismissing husbands were the most controlling and distancing, and preoccupied husbands the least distancing, during marital interactions. Secure husbands were significantly more defensive than the two insecure types. Sequential analyses of reports of violent arguments at home revealed different patterns among different types of batterers. For the preoccupied batterers only, wife withdrawal was a significant predictor of husband violence. For the dismissing batterer only, wife defensiveness was a significant precursor to husband violence. It is theorized that preoccupied batterers' violence and emotional abuse is related to expressive violence in response to abandonment fears; whereas dismissing batterers use instrumental violence to assert their authority and to control their wives. The overlap between this and other typologies of violent men is explored.

Coefficient alpha and related internal consistency reliability coefficients.

Abstract: The author studied the conditions under which coefficient alpha and 10 related internal consistency reliability coefficients underestimate the reliability of a measure. Simulated data showed that alpha, though reasonably robust when computed on n components in moderately heterogeneous data, can under certain conditions seriously underestimate the reliability of a measure. Consequently, alpha, when used in corrections for attenuation, can result in nontrivial overestimation of the corrected correlation. Most of the coefficients studied, including lambda 2, did not improve the estimate to any great extent when the data were heterogeneous. The exceptions were stratified alpha and maximal reliability, which performed well when the components were grouped into two subsets, each measuring a different factor, and maximized lambda 4, which provided the most consistently accurate estimate of the reliability in all simulations studied.

The Purchasing Power Parity Persistence Paradigm

Abstract: Rogoff (Journal of Economic Literature 1996;34:647–668) describes the ‘remarkable consensus’ of 3–5 year half-lives of purchasing power parity deviations among studies using long-horizon data. These studies, however, focus on rejections of unit roots in real exchange rates and do not use appropriate techniques to measure persistence. Our half-life estimates explicitly account for serial correlation, sampling uncertainty and, most importantly, small sample bias. Calculating confidence intervals as well as point estimates for long-horizon and post-1973 data, we find that, even though most of the point estimates lie within the 3–5 year range, univariate methods provide virtually no information regarding the size of the half-lives.

The uniform field and pattern ERG in macaques with experimental glaucoma: removal of spiking activity.

Abstract: Purpose To determine whether the uniform field and pattern ERGs that are reduced in macaque eyes with experimental glaucoma have the same inner-retinal origins. Methods ERGs were recorded from 14 anesthetized adult macaques using DTL electrodes. Six monkeys had laser-induced experimental glaucoma, and two others received intravitreal injections of tetrodotoxin (TTX, 6 microM) to block spiking activity of inner-retinal neurons. The remaining 6 animals were normal. Uniform fields and grating patterns (0.1-3 cpd) were square-wave modulated at 1.7 Hz (transient) and 8 Hz (steady state). The test field (42 degrees x 32 degrees) had a mean luminance of 44 cd/m2 and a contrast of 10% to 82%. Results In normal eyes transient ERGs to uniform fields contained photopic negative responses (PhNR) after the b-wave and after the d-wave. Transient pattern electroretinograms (PERGs) at each contrast reversal showed positive (P50) potentials followed by negative (N95) potentials of time course similar to that of the PhNR. The PhNR and N95 were greatly reduced or eliminated by experimental glaucoma and by TTX. Summing responses to luminance increments and decrements of the uniform field could simulate the PERG to low spatial frequency stimuli. Further, the PERG responses to high spatial frequencies were similar to the simulation in shape but slightly delayed in time. Experimental glaucoma and TTX had similar effects on the N95 of the simulated PERG as to those on the actual PERG. However, P50 was more reduced by experimental glaucoma than by TTX, indicating a nonspiking contribution to P50. For the steady state condition, the uniform field ERG, the simulated PERG, and the actual PERG all were affected by experimental glaucoma and TTX, indicating that they contained contributions from the spiking activity of ganglion cells. Conclusions The changes in the uniform field and PERG responses produced by experimental glaucoma are related and are largely a consequence of reduced spiking activity of ganglion cells and their axons. These findings raise the possibility that the uniform field ERG could serve as a useful alternative to the PERG in the assessment of clinical glaucomatous neuropathy.

The structure of unemployment

Abstract: We test for a unit root in postwar unemployment rates for sixteen OECD countries. When a one-time structural break is incorporated, the unit root hypothesis can be rejected for most of the countries and the measured persistence of unemployment falls dramatically. We then test for multiple structural changes and find evidence of one or two breaks for those countries for which the unit root hypothesis could be rejected. Almost all of the breaks are positive, reflecting the sustained rise in European unemployment. The major exception is the United States, where long-term unemployment rose in the 1970s and fell in the 1980s.

Vision-dependent changes in the choroidal thickness of macaque monkeys.

Abstract: PURPOSE. To determine whether changes in the eye’s effective refractive state produce changes in the thickness of the choroid in infant monkeys. METHODS. Normal developmental changes in choroidal thickness were studied in 10 normal rhesus monkeys. Hyperopia or myopia was induced by rearing 26 infant monkeys with either spectacle or diffuser lenses secured in front of one or both eyes. The treatment lenses were worn continuously beginning at approximately 3 weeks of age for an average of 120 days. Refractive status and ocular axial dimensions, including choroidal thickness, were measured by retinoscopy and high-frequency A-scan ultrasonography, respectively. RESULTS. Three lines of evidence indicate that the normal increase in choroidal thickness that occurs during early maturation can be altered by the eye’s refractive state. First, in monkeys experiencing form deprivation or those in the process of compensating for imposed optical errors, choroidal thickness and refractive error were significantly correlated with eyes developing myopia having thinner choroids than those developing hyperopia. Second, the choroids in eyes recovering from binocularly induced myopia increased in thickness at a faster rate than the choroids in recovering hyperopic eyes. Third, monkeys recovering from induced anisometropias showed interocular alterations in choroidal thickness that were always in the appropriate direction to compensate for the anisometropia. These changes in choroidal thickness, which were on the order of 50 mm, occurred quickly and preceded significant changes in overall eye size. CONCLUSIONS. Changes in the eye’s effective refractive state produce rapid compensating changes in choroidal thickness. Although these choroidal changes are small relative to the eye’s refractive error, they may play an important role in the visual regulation of axial growth associated with emmetropization. (Invest Ophthalmol Vis Sci. 2000;41:1259 ‐1269)

Fictive Kin as Social Capital in New Immigrant Communities

Abstract: Fictive kin, defined as family-type relationships, based not on blood or marriage but rather on religious rituals or close friendship ties, constitutes a type of social capital that many immigrant groups bring with them and that facilitates their incorporation into the host society. We describe three types of fictive kin systems in different immigrant populations and argue that their functions are similar across various ethnic groups and types of fictive kin relationships. Fictive kin systems expand the network of individuals who provide social and economic capital for one another and thereby constitute a resource to immigrants as they confront problems of settlement and incorporation. While anthropologists have long noted systems of fictive kin in premodern and modernizing societies, sociologists have paid little attention to fictive kin networks. We argue, however, that systems of fictive kin constitute an important part of the social networks that draw immigrants to a particular locale and provide them...

Joint Tests of Signaling and Income Smoothing Through Bank Loan Loss Provisions

Abstract: This study investigates the implications of bank managers' discretion over their loan loss provision. It empirically assesses whether discretionary loan loss provision contains both signaling and income smoothing components. To do so, the study identifies different environments in which either signaling or income smoothing or both motivations exist. The results indicate that relative undervaluation plays a critical role in motivating bank managers to use discretionary loan loss provision to signal their private information about future bank performance. The analysis also demonstrates that the level of current performance relative to the industry median is a key determinant of managers' decisions to smooth income.