Showing papers by "University of Texas at Austin published in 1995"

Patterns in Hydrogen Bonding: Functionality and Graph Set Analysis in Crystals

Abstract: Whereas much of organic chemistry has classically dealt with the preparation and study of the properties of individual molecules, an increasingly significant portion of the activity in chemical research involves understanding and utilizing the nature of the interactions between molecules. Two representative areas of this evolution are supramolecular chemistry and molecular recognition. The interactions between molecules are governed by intermolecular forces whose energetic and geometric properties are much less well understood than those of classical chemical bonds between atoms. Among the strongest of these interactions, however, are hydrogen bonds, whose directional properties are better understood on the local level (that is, for a single hydrogen bond) than many other types of non-bonded interactions. Nevertheless, the means by which to characterize, understand, and predict the consequences of many hydrogen bonds among molecules, and the resulting formation of molecular aggregates (on the microscopic scale) or crystals (on the macroscopic scale) has remained largely enigmatic. One of the most promising systematic approaches to resolving this enigma was initially developed by the late M. C. Etter, who applied graph theory to recognize, and then utilize, patterns of hydrogen bonding for the understanding and design of molecular crystals. In working with Etter's original ideas the power and potential utility of this approach on one hand, and on the other, the need to develop and extend the initial Etter formalism was generally recognized. It with that latter purpose that we originally undertook the present review.

The quantum theory of fields

Abstract: In this third volume of The Quantum Theory of Fields, available for the first time in paperback, Nobel Laureate Steven Weinberg continues his masterly exposition of quantum field theory. This volume presents a self-contained, up-to-date and comprehensive introduction to supersymmetry, a highly active area of theoretical physics. The text introduces and explains a broad range of topics, including supersymmetric algebras, supersymmetric field theories, extended supersymmetry, supergraphs, non-perturbative results, theories of supersymmetry in higher dimensions, and supergravity. A thorough review is given of the phenomenological implications of supersymmetry, including theories of both gauge and gravitationally-mediated supersymmetry breaking. Also provided is an introduction to mathematical techniques, based on holomorphy and duality, that have proved so fruitful in recent developments. This book contains much material not found in other books on supersymmetry, including previously unpublished results. Exercises are included.

Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen

Abstract: The maintenance of life on earth, our food, oxygen, and fossil fuels depend upon the conversion of solar energy into chemical energy by biological photosynthesis carried out by green plants and photosynthetic bacteria. In this process sunlight and available abundant raw materials (water, carbon dioxide) are converted to oxygen and the reduced organic species that serve as food and fuel. A long-standing challenge has been the development of a practical artificial photosynthetic system that can roughly mimic the biological one, not by duplicating the self-organization and reproduction of the biological system nor the aesthetic beauty of trees and plants, but rather by being able to use sunlight to drive a thermodynamically uphill reaction of an abundant materials to produce a fuel. In this Account we focus on “water splitting”, the photodriven conversion of liquid water to gaseous hydrogen and oxygen:

Greedy Randomized Adaptive Search Procedures

Abstract: Today, a variety of heuristic approaches are available to the operations research practitioner. One methodology that has a strong intuitive appeal, a prominent empirical track record, and is trivial to efficiently implement on parallel processors is GRASP (Greedy Randomized Adaptive Search Procedures). GRASP is an iterative randomized sampling technique in which each iteration provides a solution to the problem at hand. The incumbent solution over all GRASP iterations is kept as the final result. There are two phases within each GRASP iteration: the first intelligently constructs an initial solution via an adaptive randomized greedy function; the second applies a local search procedure to the constructed solution in hope of finding an improvement. In this paper, we define the various components comprising a GRASP and demonstrate, step by step, how to develop such heuristics for combinatorial optimization problems. Intuitive justifications for the observed empirical behavior of the methodology are discussed. The paper concludes with a brief literature review of GRASP implementations and mentions two industrial applications.

The prevalence and characteristics of fibromyalgia in the general population

Abstract: Objective. To determine the prevalence and characteristics of fibromyalgia in the general population. Methods. A random sample of 3,006 persons in Wichita, KS, were characterized according to the presence of no pain, non-widespread pain, and widespread pain. A subsample of 391 persons, including 193 with widespread pain, were examined and interviewed in detail. Results. The prevalence of fibromyalgia was 2.0% (95% confidence interval [95% CI] 1.4, 2.7) for both sexes, 3.4% (95% CI 2.3, 4.6) for women, and 0.5% (95% CI 0.0, 1.0) for men. The prevalence of the syndrome increased with age, with highest values attained between 60 and 79 years (>7.0% in women). Demographic, psychological, dolorimetry, and symptom factors were associated with fibromyalgia. Conclusion. Fibromyalgia is common in the population, and occurs often in older persons. Characteristic features of fibromyalgia–pain threshold and symptoms–are similar in community and clinic populations, but overall severity, pain, and functional disability are more severe in the clinic population.

Information Technologies and Business Value: An Analytic and Empirical Investigation

Abstract: An important management question today is whether the anticipated economic benefits of Information Technology IT are being realized. In this paper, we consider this problem to be measurement related, and propose and test a new process-oriented methodology for ex post measurement to audit IT impacts on a strategic business unit SBU or profit center's performance. The IT impacts on a given SBU are measured relative to a group of SBUs in the industry. The methodology involves a two-stage analysis of intermediate and higher level output variables that also accounts for industry and economy wide exogenous variables for tracing and measuring IT contributions. The data for testing the proposed model were obtained from SBUs in the manufacturing sector. Our results show significant positive impacts of IT at the intermediate level. The theoretical contribution of the study is a methodology that attempts to circumvent some of the measurement problems in this domain. It also provides a practical management tool to address the question of why or why not certain IT impacts occur. Additionally, through its process orientation, the suggested approach highlights key variables that may require managerial attention and subsequent action.

Sex differences in the functional organization of the brain for language

Abstract: A MUCH debated question is whether sex differences exist in the functional organization of the brain for language1–4. A long-held hypothesis posits that language functions are more likely to be highly lateralized in males and to be represented in both cerebral hemispheres in females5,6, but attempts to demonstrate this have been inconclusive7–17. Here we use echo-planar functional magnetic resonance imaging18–21 to study 38 right-handed subjects (19 males and 19 females) during orthographic (letter recognition), phonological (rhyme) and semantic (semantic category) tasks. During phonological tasks, brain activation in males is lateralized to the left inferior frontal gyrus regions; in females the pattern of activation is very different, engaging more diffuse neural systems that involve both the left and right inferior frontal gyrus. Our data provide clear evidence for a sex difference in the functional organization of the brain for language and indicate that these variations exist at the level of phonological processing.

A Meta-Analysis of Country-of-Origin Effects

Abstract: This note reports a quantitative analysis of the country-of-origin (COO) effect. Based on fifty-two articles or papers containing sixty-nine independent studies and 1,520 effect sizes, an analysis of fifteen study characteristics revealed that country-of-origin effects are only somewhat generalizable. Using omega-squared as the measure of effect size, verbal product descriptions produced larger COO effect sizes than did the presence of an actual product. Likewise, single-cue studies produced larger COO effect sizes than did multiple-cue studies, and larger samples produced effect sizes that on average were greater than those produced by smaller samples. The size of an observed COO effect was a function of whether the dependent variables was a quality/reliability perception or a purchase intention; the average effect size of quality/reliability perceptions was .30, whereas the average effect size for purchase intentions was .19. Purchase intentions were most susceptible to methodological artifacts than were quality/reliability perceptions. Study findings selectively confirm and refute common beliefs regarding the impact of a country-of-origin cue on product perceptions and purchase intentions.

Thermomechanical aspects of NiTi

Abstract: The uniaxial behavior of a nearly equiatomic NiTi alloy is studied experimentally. Experiments are conducted in a temperature and deformation regime in which the alloy exhibits the shape memory effect and pseudoelasticity. These characteristics are due to the displacive nature of transformation between the two major phases of the material, austenite and martensite, and to the fact that in this alloy martensite accommodates deformation by twinning. A series of uniaxial experiments is conducted on NiTi wire at temperatures in the range of approximately −20 to 100 °C where the fundamental material response changes drastically. In addition, the loading rate and the choice of ambient medium were found to have a significant influence on the recorded stress-strain responses due to a complex interaction between the inherent mechanical properties of the material and the prevailing heat transfer conditions of the experiment. It is demonstrated that local measurements of strain and temperature can help clarify events that take place at different stages of a typical loading-unloading history. These local measurements are used to track the movement of the interfaces between phases during stress-induced phase transformations at different loading rates.

Resistance of candida species to fluconazole

Abstract: JOHN H. REX,* M. G. RINALDI, AND M. A. PFALLER Center for Infectious Diseases, Department of Internal Medicine, University of Texas Medical School, and Department of Medical Specialties, M. D. Anderson Cancer Center, Houston, Texas; Department of Pathology, University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pathology, University of Iowa College of Medicine, Iowa City, Iowa

Modes of immigration politics in liberal democratic states.

Abstract: "The politics of immigration in liberal democracies exhibits strong similarities that are, contrary to the scholarly consensus, broadly expansionist and inclusive. Nevertheless, three groups of states display distinct modes of immigration politics. Divergent immigration histories mold popular attitudes toward migration and ethnic heterogeneity and affect the institutionalization of migration policy and politics....I begin by discussing those characteristics of immigration politics found in all liberal democracies. I then investigate the distinctive modes of immigration politics in the three subsets of Western democratic states with distinctive immigration histories. I conclude by considering whether these three patterns will persist or how they might change as a result of future migration pressures and the further institutionalization of immigration politics and policies in Europe." Comments by Rogers Brubaker (pp. 903-8) and a rejoinder by the author (pp. 909-13) are included.

Stomatal responses to increased CO2: implications from the plant to the global scale

Abstract: Increased atmospheric CO 2 often but not always leads to large decreases in leaf conductance. Decreased leaf conductance has important implications for a number of components of CO 2 responses, from the plant to the global scale. All of the factors that are sensitive to a change in soil moisture, either amount or timing, may be affected by increased CO 2 . The list of potentially sensitive processes includes soil evaporation, run-off, decomposition, and physiological adjustments of plants, as well as factors such as canopy development and the composition of the plant and microbial communities. Experimental evidence concerning ecosystem-scale consequences of the effects of CO 2 on water use is only beginning to accumulate, but the initial indication is that, in water-limited areas, the effects of CO 2 -induced changes in leaf conductance are comparable in importance to those of CO 2 -induced changes in photosynthesis. Above the leaf scale, a number of processes interact to modulate the response of canopy or regional evapotranspiration to increased CO 2 . While some components of these processes tend to amplify the sensitivity of evapotranspiration to altered leaf conductance, the most likely overall pattern is one in which the responses of canopy and regional evapotranspiration are substantially smaller than the responses of canopy conductance. The effects of increased CO 2 on canopy evapotranspiration are likely to be smallest in aerodynamically smooth canopies with high leaf conductances. Under these circumstances, which are largely restricted to agriculture, decreases in evapotranspiration may be only one-fourth as large as decreases in canopy conductance. Decreased canopy conductances over large regions may lead to altered climate, including increased temperature and decreased precipitation. The simulation experiments to date predict small effects globally, but these could be important regionally, especially in combination with radiative (greenhouse) effects of increased CO 2 .

Global Optimization Methods in Geophysical Inversion

Abstract: Part 1 Preliminary statistics: random variables random nunmbers probability probability distribution, distribution function and density function joint and marginal probability distributions mathematical expectation, moments, variances and covariances conditional probability Monte Carlo integration importance sampling stochastic processes Markov chains homogeneous, inhomogeneous, irreducible and aperiodic Markov chains the limiting probability. Part 2 Direct, linear and iterative-linear inverse methods: direct inversion methods model based inversion methods linear/linearized inverse methods iterative linear methods for quasi-linear problems Bayesian formulation solution using probabilistic formulation. Part 3 Monte Carlo methods: enumerative or grid search techniques Monte Carlo inversion hybrid Monte Carlo-linear inversion directed Monte Carlo methods. Part 4 Simulated annealing methods: metropolis algorithm heat bath algorithm simulated annealing without rejected moves fast simulated annealing very fast simulated reannealing mean field annealing using SA in geophysical inversion. Part 5 Genetic algorithms: a classical GA schemata and the fundamental theorem of genetic algorithms problems combining elements of SA into a new GA a mathematical model of a GA multimodal fitness functions, genetic drift, GA with sharing, and repeat (parallel) GA uncertainty estimates evolutionary programming - a variant of GA. Part 6 Geophysical applications of SA and GA: 1-D seismic waveform inversion pre-stack migration velocity estimation inversion of resistivity sounding data for 1-D earth models inversion of resistivity profiling data for 2-D earth models inversion of magnetotelluric sounding data for 1-D earth models stochastic reservoir modelling seismic deconvolution by mean field annealing and Hopfield network. Part 7 Uncertainty estimation: methods of numerical integration simulated annealing - the Gibbs' sampler genetic algorithm - the parallel Gibbs' sampler numerical examples.

Why do Banks Disappear? The Determinants of U.S. Bank Failures and Acquisitions

Abstract: This paper seeks to identify the characteristics that make individual U.S. banks more likely to fail or be acquired. We use bank-specific information to estimate competing-risks hazard models with time-varying covariates. We use alternative measures of productive efficiency to proxy management quality, and find that inefficiency increases the risk of failure while reducing the probability of a bank's being acquired. Finally, we show that the closer to insolvency a bank is (as reflected by a low equity-to-assets ratio) the more likely is its acquisition.

Dynamic Storage Allocation: A Survey and Critical Review

Abstract: Dynamic memory allocation has been a fundamental part of most computer systems since roughly 1960, and memory allocation is widely considered to be either a solved problem or an insoluble one. In this survey, we describe a variety of memory allocator designs and point out issues relevant to their design and evaluation. We then chronologically survey most of the literature on allocators between 1961 and 1995. (Scores of papers are discussed, in varying detail, and over 150 references are given.)

Use of implicit motor imagery for visual shape discrimination as revealed by PET

Abstract: Positron emission tomography (PET) can be used to map brain regions that are active when a visual object (for example, a hand) is discriminated from its mirror form. Chronometric studies suggest that viewers 'solve' this visual shape task by mentally modelling it as a reaching task, implicitly moving their left hand into the orientation of any left-hand stimulus (and conversely for a right-hand stimulus). Here we describe an experiment in which visual and somatic processing are dissociated by presenting right hands to the left visual field and vice versa. Frontal (motor), parietal (somatosensory) and cerebellar (sensorimotor) regions similar to those activated by actual and imagined movement are strongly activated, whereas primary somatosensory and motor cortices are not. We conclude that mental imagery is realized at intermediate-to-high order, modality-specific cortical systems, but does not require primary cortex and is not constrained to the perceptual systems of the presented stimuli.

1/f noise in human cognition

Abstract: When a person attempts to produce from memory a given spatial or temporal interval, there is inevitably some error associated with the estimate. The time course of this error was measured in a series of experiments where subjects repeatedly attempted to replicate given target intervals. Sequences of the errors in both spatial and temporal replications were found to fluctuate as 1/f noises. 1/f noise is encountered in a wide variety of physical systems and is theorized to be a characteristic signature of complexity.

Timing of Hot Spot—Related Volcanism and the Breakup of Madagascar and India

Abstract: Widespread basalts and rhyolites were erupted in Madagascar during the Late Cretaceous. These are considered to be related to the Marion hot spot and the breakup of Madagascar and Greater India. Seventeen argon-40/argon-39 age determinations reveal that volcanic rocks and dikes from the 1500-kilometer-long rifted eastern margin of Madagascar were emplaced rapidly (mean age = 87.6 ± 0.6 million years ago) and that the entire duration of Cretaceous volcanism on the island was no more than 6 million years. The evidence suggests that the thick lava pile at Volcan de l'Androy in the south of the island marks the focal point of the Marion hot spot at 88 million years ago and that this mantle plume was instrumental in causing continental breakup.

Maximum likelihood estimation of the heterogeneity of substitution rate among nucleotide sites.

Abstract: This paper presents a maximum likelihood approach to estimating the variation of substitution rate among nucleotide sites. We assume that the rate varies among sites according to an invariant+gamma distribution, which has two parameters: the gamma parameter alpha and the proportion of invariable sites theta. Theoretical treatments on three, four, and five sequences have been conducted, and computer program have been developed. It is shown that rho = (1 + theta alpha)/(1 + alpha) is a good measure for the rate heterogeneity among sites. Extensive simulations show that (1) if the proportion of invariable sites is negligible, i.e., theta = 0, the gamma parameter alpha can be satisfactorily estimated, even with three sequences; (2) if the proportion of invariable sites is not negligible, the heterogeneity rho can still be suitably estimated with four or more sequences; and (3) the distances estimated by the proposed method are almost unbiased and are robust against violation of the assumption of the invariant + gamma distribution.

Testosterone administration to elderly men increases skeletal muscle strength and protein synthesis.

Abstract: Aging men develop a significant loss of muscle strength that occurs in conjunction with a decline in serum testosterone concentrations. We investigated the effects of testosterone administration to six healthy men [67 +/- 2 (SE) yr] on skeletal muscle protein synthesis, strength, and the intramuscular insulin-like growth factor I (IGF-I) system. Elderly men with serum testosterone concentrations of 480 ng/dl or less were given testosterone injections for 4 wk to produce serum concentrations equal to those of younger men. During testosterone administration muscle strength (isokinetic dynamometer) increased in both right and left hamstring and quadricep muscles as did the fractional synthetic rate of muscle protein (stable-isotope infusion). Ribonuclease protection assays done on total RNA from muscle showed that testosterone administration increased mRNA concentrations of IGF-I and decreased mRNA concentrations of insulin-like growth factor binding protein-4. We conclude that increasing testosterone concentrations in elderly men increases skeletal muscle protein synthesis and strength. This increase may be mediated by stimulation of the intramuscular IGF-I system.

The War of Desire and Technology at the Close of the Mechanical Age

Abstract: From the Publisher: Allucquere Rosanne Stone examines the interface of technology and desire: from busy cyberlabs to the electronic solitude of the Internet, from "virtual cross-dressers" to the trial of a man having raped a woman by seducing one of her multiple personalities. Writing eloquently of creating a "text that breaks rules," Stone employs elements from a wide range of disciplines and genres, including cultural and critical theory, social sciences, pulp journalism, science fiction, and personal memoir.