Showing papers by "University of Houston published in 1993"

In Search of How People Change: Applications to Addictive Behaviors

Abstract: How people intentionally change addictive behaviors with and without treatment is not well understood by behavioral scientists. This article summarizes research on self-initiated and professionally...

Equalizing Exchange: Trade Liberalization and Income Convergence

Abstract: How does movement toward freer trade affect income disparity among countries? This paper attempts to shed some light on the issue by examining episodes of major postwar trade hberalization within specified groups of countries. The findings suggest a strong link between the timing of trade reform and income convergence among countries.

Independent Private Value Auctions: Bidder Behaviour in First-, Second- and Third-Price Auctions with Varying Numbers of Bidders

Abstract: The symmetric equilibrium of third-price auctions is characterized. It makes a number of contrasting predictions relative to firms and second-price auctions: bids exceed private values, the marginal effects on bids of an increase in private values is greater than one, increasing numbers of bidders reduces bids, and risk aversion requires bidding below the risk neutral Nash equilibrium. In the experiment, bidders do not always satisfy the point predictions of the theory. However, the game theoretic models correctly anticipate, at least directionally, the important effects of the price rule changes. Copyright 1993 by Royal Economic Society.

On feedback control of chaotic continuous-time systems

Abstract: Extends the ideas and techniques developed previously by the present authors for controlling discrete-time chaotic dynamic systems using traditional feedback control strategies to continuous-time chaotic systems. The authors study how the conventional engineering approach using canonical feedback controllers can control the chaotic trajectory of a continuous-time nonlinear system to converge to its equilibrium points and, more significantly, to its multiperiodic orbits including unstable limit cycles. They describe an approach via a detailed investigation of the chaotic Duffing equation, with special emphasis on the control of its chaotic trajectory to one of its multiperiodic orbits. Finally, the authors provide a rigorous mathematical theory and some computer simulations to support and visualize such controllability of the Duffing equation. >

Ultraviolet radiation and coral bleaching

Abstract: EPISODES of coral bleaching resulting from dissociation of endosymbiotic algae (zooxanthellae) from host coral tissues have occurred with increasing frequency over the past decade on reefs throughout the tropics1,2. These episodes have usually been attributed to increases in sea water temperatures3–10, but the mass bleaching events that occurred throughout the Caribbean during 1987 and 1990 were not readily explained by temperature alone11,12. An additional factor that may have contributed to these bleaching episodes is ultraviolet radiation in the 280–400-nm band. At many localities where bleaching occurred in 1987 and 1990, sea conditions were described as extremely calm with exceptionally clear water13. In the absence of suspended organic and inorganic matter in the water column, higher than average intensities of ultraviolet radiation probably reached all depths within the photic zone for several consecutive months. Evidence for a possible link between ultraviolet radiation and coral bleaching has not been forthcoming2. Here we report results of a field experiment showing that, irrespective of high water temperatures, short-term (three weeks) increases in ultraviolet radiation of a magnitude possible under calm, clear water column conditions can readily induce bleaching in reef-building corals.

From Chaos to Order - Perspectives and Methodologies in Controlling Chaotic Nonlinear Dynamical Systems

Abstract: Controlling (or ordering) chaos is a new concept, which has recently drawn much attention from the communities of engineering, physics, chemistry, biomedical sciences and mathematics. This paper offers an overview of the different interpretations and approaches in the investigation of controlling chaos for various nonlinear dynamical systems. Relevant historical background is provided, several successful techniques are described and analyzed with necessary verifications, and some realistic yet instructive examples are included. The paper also aims at promoting more efforts to be devoted to this challenging and promising new direction of research, as well as its potential applications in nonlinear systems science and engineering.

Microstrip patch designs that do not excite surface waves

Abstract: Two variations of a circular microstrip patch design are presented which excite very little surface wave power. Both of the designs are based on the principle that a ring of magnetic current in a substrate (which models the patches) will not excite the dominant TM/sub 0/ surface wave if the radius of the ring is a particular critical value. Numerical results for radiation efficiency and radiated field strength from a ring of magnetic current are shown to verify this basic design principle. The proposed patch designs are chosen to have a radius equal to this critical value, while maintaining resonance at the design frequency. The designs excite very little surface-wave power, and thus have smoother radiation patterns when mounted on finite-size ground planes, due to reduced surface-wave diffraction. They also have reduced mutual coupling, due to the reduced surface-wave excitation. Measured results for radiation patterns and field strength within the substrate are presented to verify the theoretical concepts. >

Multiple-site titration and molecular modeling: two rapid methods for computing energies and forces for ionizable groups in proteins.

Abstract: Computer models of proteins frequently treat the energies and forces associated with ionizable groups as if they were purely electrostatic. This paper examines the validity of the purely electrostatic approach, and concludes that significant errors in energies can result from the neglect of ionization changes. However, a complete treatment of ionizable groups presents substantial computational obstacles, because of the large number of ionization states which must be examined in systems having multiple interacting titratable groups. In order to address this problem, two novel methods for treating the energetics and forces associated with ionizable groups with a minimum of computer time have been developed. The most rapid method yields approximate energies by computing the free energy of a single highly occupied ionization state. The second method separates ionizable groups into clusters, and treats intracluster interactions exactly, but intercluster interactions approximately. This method yields both accurate energies and fractional charges. Good results are obtained in tests of both methods on proteins having has many as 123 ionizable groups. The more rapid method requires computer times of 0.01 to 0.34 sec, while the more accurate method requires 0.7 to 15 sec. These methods may be fast enough to permit the incorporation of ionization effects in iterative computations, such as energy minimizations and conformational searches. © 1993 Wiley-Liss, Inc.

Irish setter dogs affected with rod/cone dysplasia contain a nonsense mutation in the rod cGMP phosphodiesterase beta-subunit gene.

Abstract: Irish setter dogs affected with a rod/cone dysplasia (locus designation, rcd1) display markedly elevated levels of retinal cGMP during postnatal development. The photoreceptor degeneration commences approximately 25 days after birth and culminates at about 1 year when the population of rods and cones is depleted. A histone-sensitive retinal cGMP phosphodiesterase (PDE; EC 3.1.4.35) activity, a marker for photoreceptor PDEs, was shown previously to be present in retinal homogenates of immature, affected Irish setters. Here we report that, as judged by HPLC separation, this activity originates exclusively from cone photoreceptors, whereas rod PDE activity is absent. An immunoreactive product the size of the PDE alpha subunit, but none the size of the beta subunit, can be detected on immunoblots of retinal extracts of affected dogs, suggesting a null mutation in the PDE beta-subunit gene. Using PCR amplification of Irish setter retinal cDNA, we determined the complete coding sequence of the PDE beta subunit in heterozygous and affected animals. The affected PDE beta-subunit mRNA contained a nonsense amber mutation at codon 807 (a G-->A transition converting TGG to TAG), which was confirmed to be present in putative exon 21 of the affected beta-subunit gene. The premature stop codon truncates the beta subunit by 49 residues, thus removing the C-terminal domain that is required for posttranslational processing and membrane association. These results suggest that the rcd1 gene encodes the rod photoreceptor PDE beta subunit and that a nonsense mutation in this gene is responsible for the production of a nonfunctional rod PDE and the photoreceptor degeneration in the rcd1/rcd1 Irish setter dogs.

Institutional Variables Affecting Female Representation in National Legislatures: The Case of Norway

Abstract: A controversy exists over whether district magnitude, the number of seats per district, has a positive effect on female representation. This study considers district magnitude's effect on female representation in Norway over a 40-year period. The data analysis finds that party magnitude, the size of a party's district delegation, is a more powerful explanatory factor than district magnitude. Party magnitude's effect appears to follow a cycle. Prior to demands for representation being raised, party magnitude has little effect. As women mobilize and representation demands are raised party magnitude plays a significant role, but once women are firmly entrenched as powerful players in party politics, party magnitude's effect decreases. This formulation is consistent with the Norwegian findings and also explains why previous cross-sectional research has produced inconsistent findings. In addition, the crucial role that candidate nomination processes play in explaining the high levels of representation found in...

A neurophysiologically-based mathematical model of flash visual evoked potentials

Abstract: Evidence is presented that a neurophysiologically-inspired mathematical model, originally developed for the generation of spontaneous EEG (electroencephalogram) activity, can produce VEP (visual evoked potential)-like waveforms when pulse-like signals serve as input. It was found that the simulated VEP activity was mainly due to intracortical excitatory connections rather than direct thalamic input. Also, the model-generated VEPs exhibited similar relationships between prestimulus EEG characteristics and subsequent VEP morphology, as seen in human data. Specifically, the large correlation between the N1 amplitude and the prestimulus alpha phase angle, and the insensitivity of P2 to the latter feature, as observed in actual VEPs to low intensity flashes, was also found in the model-generated data. These findings provide support for the hypothesis that the spontaneous EEG and the VEP are generated by some of the same neural structures and that the VEP is due to distributed activity, rather than dipolar sources.

Lottery choice: incentives, complexity and decision time

Abstract: This paper reports the results of an experiment on lottery choice in which decision cost is measured as decision making time. A simple decision cost model motivates this measurement and the experiment, and predicts relationships between incentive mechanism manipulations and decision making time which are borne out in the experiment. The decision cost model also suggests that decisions will change in the face of the incentive manipulations in the experiment. This suggestion is borne out in a complex decision-making environment, but not in a simple one. Specification tests demonstrate that observed changes in subjects' behavior are not merely due to changes in subject-specific error variance. One may conclude from this that the 'payoff dominance'problem is a real issue in complex decision making experiments. Copyright 1993 by Royal Economic Society.

Chicxulub multiring impact basin - Size and other characteristics derived from gravity analysis

Abstract: The buried Chicxulub impact structure in Mexico, which is linked to the Cretaceous- Tertiary (K-T) boundary layer, may be significantly larger than previously suspected. Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets. The outer ring, probably corresponding to the basin's topographic rim, is almost 300 kilometers in diameter, indicating that Chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago.

Chaos, dynamics, and fractals : an algorithmic approach to deterministic chaos

Abstract: This book develops deterministic chaos and fractals from the standpoint of iterated maps, but the emphasis makes it very different from all other books in the field. It provides the reader with an introduction to more recent developments, such as weak universality, multifractals, and shadowing, as well as to older subjects like universal critical exponents, devil's staircases and the Farey tree. The author uses a fully discrete method, a 'theoretical computer arithmetic', because finite (but not fixed) precision cannot be avoided in computation or experiment. This leads to a more general formulation in terms of symbolic dynamics and to the idea of weak universality. The connection is made with Turing's ideas of computable numbers and it is explained why the continuum approach leads to predictions that are not necessarily realized in computation or in nature, whereas the discrete approach yields all possible histograms that can be observed or computed.

Genetic heterogeneity in families with hereditary multiple exostoses.

Abstract: The authors have carried out a linkage analysis on 11 families segregating gene(s) for hereditary multiple exostoses (EXT). Four highly informative, short tandem-repeat (STR) markers that have been physically mapped to an interval surrounding the Langer-Giedion chromosomal region (8q24.11-q24.13) were used in a multipoint linkage analysis. Significant evidence for linkage of EXT with genetic heterogeneity was found. A model of heterogeneity with linkage of the disease gene to the STR markers in 70% of the families (with a 95% confidence interval of 26%-96%) produced a maximum LOD score of 8.11, with the most likely position of EXT between D8S85 and D8S199. Thus there are at least two genes that are capable of causing hereditary multiple exostoses, one in the Langer-Giedion region and one at another, unlinked location. 20 refs., 3 figs., 2 tabs.

Examining the Relation of Parenting to Children's Coping with Everyday Stress

Abstract: The relation between parenting and the coping styles of children in response to everyday stress was investigated. 60 children, 9-10 years old, and their mothers participated. Children and mothers described how they responded to stressful episodes the child had experienced within the past 2 months. Mothers completed questionnaires that assessed a variety of parenting dimensions (e.g., nurturance, directiveness, organization). Results indicated that (a) the aspects of child coping studied (e.g., perceived effectiveness, variety of coping strategies) were relatively independent, (b) children from families with high levels of maternal support and relatively low levels of family structure used the greatest variety of coping strategies, (c) children of supportive mothers used the greatest number of avoidant strategies (but only in uncontrollable situations), and (d) children from families with high levels of parental structure used fewer aggressive coping strategies.

Synthesis of the high-temperature superconductors HgBa2CaCu2O6+δ and HgBa2Ca2Cu3O8+δ

Abstract: The newly-discovered homologous series HgBa 2 Ca n −1 Cu n O 2 n +2+δ [Hg-12 ( n -1) n ] with n = 1, 2, 3,… possesses the highest superconducting transition-temperature ( T c ) to date. Unfortunately, because of the complexity of its compound chemistry, it remains a challenge to prepare samples with pure or nearly-pure Hg-12 ( n -1) n for both scientific and applied studies. In the present investigation, we report the successful development of a controlled vapor/solid reaction process for the synthesis of samples with up to 75 to 90% Hg-1212 and 65 to 75% Hg-1223 by volume, which display sharp superconducting transitions up to 135 K. Detailed steps of the process are presented and discussed.

Leaky-wave propagation and radiation for a narrow-beam multiple-layer dielectric structure

Abstract: Previous work has demonstrated that very narrow beam radiation patterns can be obtained from a simple source embedded within multiple dielectric layers of appropriate thicknesses above a ground plane. The configuration consists of dielectric layers having permittivities epsilon /sub 1/ and epsilon /sub 2/ stacked in an alternating arrangement, with epsilon /sub 2/> epsilon /sub 1/. This narrow-beam effect can be attributed to weakly attenuated leaky waves that exist on the structure. Simple asymptotic formulas for the propagation and attenuation constants are derived. The formulas show how the beamwidth varies with the number of layers and the material constants. The exact radiation pattern is compared with the leaky-wave pattern for a specific case to demonstrate the role of the leaky waves in determining the total pattern. >

The Effects of Psychological Trauma on Children and Adolescents

Abstract: In this review the authors examine the cognitive, affective, behavioral, and somatic-physiological effects documented in the literature as sequelae of overwhelming life events in children and adolescents. Findings from the literature are compared with the current formulations of Post-traumatic Stress Disorder (PTSD) in the Diagnostic and Statistical Manual of Mental Disorders, third edition, revised (DSM-III-R, American Psychiatric Association, 1987) as this diagnostic category applies to children. Responses likely to be observed in children and adolescents who have been exposed to traumatic events are discussed. Suggestions for future research and counseling practice are presented

Toward an integrated theory of gender stratification

Abstract: Determinants of gender stratification range through eveny institutional sphere and every leel of sociological analysis. An integrated theory is presented which charts the connections and feedbacks among three main blocks of causal factors and two blocks of outcomes. The GENDER ORGANIZATION OF PRODUCTION block includes the degree of

Tolerating Economic Reform: Popular Support for Transition to a Free Market in the Former Soviet Union.

Abstract: The mass public in the Soviet Union is not enthusiastic about free-market reform How, then, do citizens in a former communist regime develop an appreciation for free-market reforms? Different explanations for attitudes toward free market reforms are tested using data from a survey of the European USSR conducted in May 1990 First, negative assessments of recent economic performance is a catalyst for popular support for the market economy Although very underdeveloped, there is a nascent free-market culture in the Soviet Union that makes a modest contribution to support for free-market reforms The free-market culture that is developing in the former Soviet Union resembles that of social democracy, rather than laissez-faire capitalism Democratic values and support for free markets are mutually reinforcing, suggesting that support for democracy makes a very important contribution to support for free-market reform

Broadside radiation from periodic leaky-wave antennas

Abstract: A double-strip grating leaky-wave antenna consisting of two strips per unit cell is analyzed. The stopband behavior exhibited at broadside scan in the single-strip grating antenna is characteristic of all periodic leaky-wave antennas having a single strip per unit cell, and results in a drastic increase in the attenuation rate of the leaky wave as the beam is scanned to broadside. By nearly eliminating this stopband behavior, the double-strip leaky-wave antenna can scan from backward end fire to forward end fire without any large frequency regions of high attenuation. An approximate design rule for the double-strip antenna is discussed, and results are presented to show how the antenna may be further optimized to achieve the minimum possible variation in attenuation as the beam is scanned through broadside. Although the stopband behavior is never completely eliminated with the addition of the extra strip, the optimum design shows an almost negligible region of rapidly varying attenuation near broadside. >

Differential effects of ultraviolet radiation on green and brown morphs of the Caribbean coral Porites astreoides

Abstract: In waters 5 2 m deep, green colonies of reef-building Porites astreoides Lamarck are significantly more abundant than their brown counterparts To determine whether this distributional pattern reflects differences in the ability of green and brown colonies to tolerate high intensities of ultraviolet-A (320-400 nm) and -B (280-320 nm) radiation, I enhanced UV intensities by transplanting colonies of each color from 6 to 1 m deep After 104 d, brown P astreoides exposed to UV radiation at 1 m exhibited algal mitotic indices and linear skeletal extensions that were significantly lower than brown conspecifics shielded from UV light In contrast, green P astreoides were unaffected by UV radiation incident at 1 m These morphspecific differences in UV tolerance corresponded with variation in the quantities of UV light-absorbing mycosporinelike amino acids (MAAs) present in the corals Both morphs had mycosporine-glycine (A,,, = 3 10 nm), palythine (X,,, = 320 nm), asterina-330 (X,,, = 330 nm), and shinorine (X,,, = 334 nm), but green P astreoides had significantly greater concentrations of aster-ma-330 than brown colonies both before and after transplantation Increasing the concentration of a single MAA with a broad absorbance range may represent an effective means of countering high UV intensities, and UV light may be an important abiotic factor structuring the shallow-water distribution of P astreoides

Structural similarities among oxygen-deficient perovskites

Abstract: A general review and description is given of vacancy patterns in oxygen-deficient perovskites A[sub m]B[sub m]O[sub 3m[minus]x]. Thirteen compounds that contain unique oxygen vacancy patterns and that adopt structures related to cubic closet packing are examined in detail: m = 2, x = 1, Ca[sub 2]Mn[sub 2]O[sub 5], LaSrCuGaO[sub 5], La[sub 2]Ni[sub 2]O[sub 5], LaSrCuAlO[sub 5], YBaCuFeO[sub 5], Ca[sub 2]Co[sub 2]O[sub 5]; m = 3, x = 1, 2, or 3, LaBa[sub 2]Cu[sub 2]TaO[sub 8], LaSr[sub 2]Fe[sub 3]O[sub 8], YBa[sub 2]Cu[sub 3]O[sub 7], LnSr[sub 2]Cu[sub 2]GaO[sub 7], YBa[sub 2]Cu[sub 3]O[sub 6]; m = 4, x = 1, Ba[sub 2]La[sub 2]Cu[sub 2]Sn[sub 2]O[sub 11] and Ca[sub 4]Ti[sub 2]Fe[sub 2]O[sub 11]. The structural similarity among the compounds is stressed by the presentation and examination of AO[sub 3[minus]x] slices. The influence of the A and B cations on the manner in which successive AO[sub 3[minus]x] layers are stacked is presented and discussed. 73 refs., 17 figs.

Naloxone precipitates nicotine abstinence syndrome in the rat.

Abstract: Recently, a rodent model of nicotine abstinence syndrome has been developed based on continuous subcutaneous infusion of nicotine tartrate and observing the frequency of spontaneous behavioral signs following termination of infusion. The observed signs closely resemble those commonly seen in rat opiate abstinence syndrome, raising the possibility that there is an endogenous opioid component in nicotine dependence. The present study demonstrates that the opiate antagonist naloxone can precipitate an abstinence syndrome in nicotine-dependent rats. Fourteen rats were infused for 7 days with 9 mg/kg/day nicotine tartrate in saline via an Alzet osmotic minipump. Fourteen rats were sham-operated and remained nicotine-naive. Half of each group received 4.5 mg/kg naloxone SC immediately before a “blind” 15-min observation, while the other half received saline alone. ANOVA revealed significant nicotine infusion, naloxone injection and interaction effects. Post-hoc analysis showed that the nicotine-infused rats injected with naloxone had significantly more signs than all other groups (P<0.01). In a second experiment, 2 mg/kg morphine sulfate SC produced a significant (P<0.01) 91.2% reduction of spontaneous abstinence signs observed 21 h after termination of nicotine infusion. These results are consistent with the hypothesized endogenous opioid component in nicotine dependence and abstinence syndrome.

Acetylcholinesterase: electrostatic steering increases the rate of ligand binding.

Abstract: Brownian dynamics simulations have been used to calculate the diffusion-controlled rate constants for the binding of a positively charged ligand to several models of acetylcholinesterase (AChE). The crystal structure was used to define the detailed topography and the active sites of the dimeric enzyme. The electric field around AChE was then computed by solving the Poisson equation for different charge distributions in the enzyme at zero ionic strength. These fields were used in turn to calculate the forces on the diffusing ligand. Significant increases in the rate constant resulted in going from a model with no charges to one with the net charges concentrated at the centers of the monomers and then to a model with a realistic distribution of charges throughout the enzyme. The results show that electrostatic steering of ligands contributes to the high rate constants that are observed experimentally for AChE.