Showing papers by "University of Texas at Arlington published in 1987"

Coupled fixed points of nonlinear operators with applications

Abstract: A partir de quasi-solutions couplees des problemes aux valeurs initiales pour des equations differentielles ordinaires, on introuit le concept de points fixes couples abstraits pour certains operateurs. On donne des theoremes d'existence

Neural dynamics of attentionally modulated Pavlovian conditioning: blocking, interstimulus interval, and secondary reinforcement

Abstract: Selective information processing in neural networks is studied through computer simulations of Pavlovian conditioning data. The model reproduces properties of blocking, inverted-U in learning as a function of interstimulus interval, anticipatory conditioned responses, secondary reinforcement, attentional focusing by conditioned motivational feedback, and limited capacity short-term memory processing. Conditioning occurs from sensory to drive representations (conditioned reinforcer learning), from drive to sensory representations (incentive motivational learning), and from sensory to motor representations (habit learning).The conditionable pathwas contain long-term memory traces that obey a non-Hebbian associative law. The neural model embodies a solution to two key design problems of conditioning, the synchronization and persistence problems. This model of vertebrate learning is compared with data and models of invertebrate learning. Predictions derived from models of vertebrate learning are compared with data about invertebrate learning, including data from Aplysia about facilitator neurons and data from Hermissenda about voltage-dependent Ca(2+) currents. A prediction is stated about classical conditioning in all species, called the secondary conditioning alternative, and if confirmed would constitute an evolutionary invariant of learning.

A Profile of Browsers in Regional Shopping Malls

Abstract: Although undefined and ambiguous, the term “browsing” enjoys widespread usage among retailers. In this study, the concept is explored in terms of several different shopping behaviors. It is further demonstrated that these behaviors are associated with a variety of descriptive and attitudinal differences among retail mall patrons.

Does invasion sequence affect community structure.

Abstract: The effects of invasion sequence on community structure were evaluated using aquatic microcosms. Thirty 400—mL beakers were inoculated with replicated subsets of species from a species pool consisting of green, blue—green, and golden algae, ciliates, a rotifer, a dinoflagellate, and euglenoids. These species were added according to four distinct sequences and two different rates over a 23—wk period, resulting in four replicated sets of insular communities. Significant differences in community structure and species richness could be attributed to both sequence of invasion and distance effects. "Priority" effects were found to be important in some but not all instances. Communities could be divided into two primary types that are similar to the two community types previously reported to arise from the assembly of these same taxa according to different invasions schedules.

Existence and Lagrangian duality for maximizations of set-valued functions

Abstract: The maximization with respect to a cone of a set-valued function into possibly infinite dimensions is defined; some existence results are established; and a Lagrangian duality theory is developed

Employee Perspectives on Stock Ownership: Financial Investment or Mechanism of Control?

Abstract: This paper explores employee ownership as a financial investment rather than a mechanism of control. Viewed from such a perspective, relations among employee ownership, satisfaction, and desired influence are more complex than supposed. Employee owners' satisfaction with the firm and their jobs depends, in part, on their perceptions of the firm's financial performance and of the effectiveness of other employees. Dissatisfaction may increase efforts by employee owners to influence decision making.

Bond-centered hydrogen or muonium in diamond: The explanation for anomalous muonium and an example of metastability

Abstract: We present qualitative theoretical evidence that interstitial bond-centered hydrogen or muonium in diamond is stable as a result of unusually large lattice relaxation. The two geometrical configurations of neutral interstitial muonium explain the structures and properties of anomalous muonium (bond centered) and normal muonium (tetrahedral interstitial site), including the thermal conversion of normal to anomalous muonium and represent a well-defined example of interstitial metastability.

Antipredator mechanisms of larval anurans: protection of palatable individuals

Abstract: Newly-hatched and metamorphic climax stages of Bufo americanus are unpalatable to vertebrate and invertebrate predators but intermediate tadpole stages are palatable. Acquired avoidance by predators of newly-hatched toads confers a survival advantage on later developmental stages that are otherwise palatable.

Health Consequences of Stress

Abstract: Stress is the naturally occurring mind-body response to demanding and/or emergency situations, either of a chronic or episodic nature. Properly monitored and managed, the stress response contributes to a state of optimum health and well being. When improperly managed, the stress response may lead to a variety of medical, psychological and behavioral health problems. These problems range from cigarette smoking, alcohol and drug abuse, violence, and family conflict to insomnia, cardiovascular diseases, cancer, and ulcers. However, there are several stressful activities, including aerobic exercise, weight training, and flexibility training, which contribute to a number of health benefits. There are some individual differences in personality dimensions, sex, etc., which moderate the stress-health relationship.

Urban traffic network flow models

Abstract: Addressed in this paper are the development and comparative assessment of macroscopic network-level traffic flow models, which describe the behavior and interrelation between traffic variables defined at the network level. These variables include average speed, concentration, flow, the fraction of vehicles stopped in the network, and the two-fluid running time variables. Three alternative sets of interrelated models, each with a different starting postulate, are presented and tested in terms of their performance against a series of microscopic simulation runs corresponding to different concentration levels. In each model system, a different functional form is postulated for either the speed-concentration relation or the fraction of vehicles stopped versus concentration relation. The functional form for the other relation is then derived from the postulated model by invoking the two-fluid theory of town traffic. The models are calibrated and tested using the simulation results. The analysis indicates that the network-level traffic variables are interrelated in a manner similar to that captured by the traffic models established for individual road sections. In particular, a well-known linear speed-concentration model as well as a nonlinear alternative are found to be generally applicable at the network level.

A scattering model for perfectly conducting random surfaces. I - Model development. II - Range of validity

Abstract: The surface current on a perfectly conducting randomly rough surface is estimated by solving iteratively a standard integral equation, and the estimate is then used to compute the far-zone scattered fields and the backscattering coefficients for vertical, horizontal and cross polarizations. The model developed here yields a simple backscattering coefficient expression in terms of the surface parameters. The expression reduces analytically to the Kirchhoff and the first-order small-perturbation model in the high- and low-frequency regions, respectively. The range of validity of the model is determined.

Simplified Feeder Modeling for Loadflow Calculations

Abstract: Three models of a distribution system are developed in this paper. Included are descriptions of simulation models of the diverse components of a typical distribution system. The three system models are illustrated by examples. They are applied to an actual feeder and the results are analyzed to show the advantages and disadvantages of each model. A unique method is developed for combining the discrete distributed load voltage drop solution with the discrete distributed load losses solution. The development of this combined method is in the form of a tutorial , as are the developments of the components of this method. The conclusion is reached that it is possible to reduce many complex feeders to simple models in the study of feeder voltage profiles and losses with negligible error.

Calcium oxalate crystal morphology and development in agaricus bisporus

Abstract: Aerial hyphae of Agaricus bisporus grown in agar culture, or on natural substrates like rye grain, produce abundant calcium oxalate crystals associated with the hyphal wall. These deposits, when first formed, consist of acicular crystals that cover the surface of the hyphae, giving the elements of the aerial mycelium a bottle-brush appearance. SEM examination of the crystal-bearing hyphae reveals that the crystals are arranged more or less tangentially on the hyphal surface. The crystals appear to originate within the wall of the hyphae, and as they increase in length their distal ends protrude through the hyphal wall. While the crystalline deposits of hyphae grown on malt-extract agar or on rye grain are typically elongate crystals, calcium oxalate deposits of hyphae grown on enriched media consist of both elongate forms and large, plate-like crystals. Scanning and transmission electron micrographs, energydispersive x-ray elemental analysis, and x-ray powder diffraction analysis of these crystals are presented.

Electroactive copolymers of pyrrole containing covalently bound dopant ions: poly{pyrrole-co-[3-(pyrrol-1-yl)propanesulphonate]}

Abstract: A self-doped electroactive copolymer, poly{pyrrole-co-[3-(pyrrol-1-yl)propanesulphonate]}, in which the charge balancing counterion is covalently attached to the polymer chain, has been synthesized and cation controlled charge transport parameters have been evaluated.

Mutual Predation in Assembled Communities of Odonate Species

Abstract: Larval individuals from six anisopteran species were added to artificial ponds so that each pond contained an equal number and size distribution of each species. Half of these ponds were exposed to an additional anisopteran, Anax junius. Interodonate predation in Anax-free ponds was size dependent, with the smallest species, Perithemis tenera, experiencing the highest mortality. Predation in ponds containing Anax was not size dependent, but was species dependent. Plathemis lydia individuals were not signifi- cantly affected by Anax, probably due to the tendency of Plathemis to dig deeply into the sediment. Pe. tenera was shown to have a different allometric relationship between head width and body volume than the other six dragonfly species. We postulate that this is correlated with its small size and is an adaptation to increase the range of prey available to it.

Microhabitat selection as an antipredator strategy in the aquatic insect Pachydiplax longipennis Burmeister (Odonata: Libellulidae).

Abstract: An investigation of the larval dragonfly fauna associated with the plant, Sagittaria platyphylla, was conducted in a small pond. Despite the presence of several larval anisopteran species in the pond, only Pachydiplax longipennis larvae were found on Sagittaria plants. A study of the microspatial distribution of P. longipennis larvae on S. platyphylla indicated that larvae use the various regions of a plant in a highly non-random fashion. Larvae show a strong preference for the leaf axil area. A generalized predator, the bluegill sunfish (Lepomis macrochirus), was allowed to selectively eat either of two larvae placed in various plant regions. This experiment indicated that larvae in a leaf axil area were significantly less susceptible to bluegill predation than larvae positioned in other plant regions. The microspatial distribution of starved larvae revealed that larvae with high hunger levels occupied the leaf axil area significantly less than well fed larvae, suggesting 1) larvae do not use these regions as feeding sites, and 2) high hunger levels may induce a behavioral shift in habitat use, with starved larvae forced into areas of high predation risk by the need to fulfill nutritional requirements.

A simple proof of Kharitonov's theorem

Abstract: An alternative proof of Kharitonov's theorem on the stability of linear time-invariant continuous systems under parameter variations is presented.

Thermolytic Formation of Noble Metals and Their Oxides from Chloride Precursors A Thermal Analysis Study

Abstract: The thermolysis of two compound series, namely, and was studied by differential scanning calorimetry, differential thermal analysis, and thermogravimetry. Product identification and confirmation of thermolysis pathways were accomplished by x‐ray powder diffraction analyses, moisture evolution analyses, and IR spectroscopy. The thermolysis was carried out both in reactive (air) as well as in inert (argon) atmospheres. In the case of , oxide was obtained as the major thermolysis product in air. In argon, metal was the major thermolysis product—the degree of oxide formation being a sensitive function of the partial pressure (or argon flow rate). The thermal stability of the oxide as well as the parent chloride precursor showed significant differences in the series. New data are presented for and . In both cases, intermediate formation of the trichloride was accompanied by oxide and metal formation depending on the gaseous ambient. Unlike the case of the Ir compound, no evidence for was found for the thermolysis of . Similarities and differences in data trends are discussed with the aid of thermochemical calculations. The results of this study may have implications in the synthesis of noble metals and their oxides for catalytic and electronic device applications.