Showing papers by "University of Texas at Arlington published in 1992"
TL;DR: In this paper, a theoretical characterization of the guided-mode resonance properties of planar dielectric waveguide gratings is presented, and the linewidths of the resonances can be controlled by the grating modulation amplitude.
Abstract: A theoretical characterization of the guided‐mode resonance properties of planar dielectric waveguide gratings is presented. Efficient exchange of energy between forward and backward propagating diffracted waves is shown to be possible with smooth line shapes. The linewidths of the resonances can be controlled by the grating modulation amplitude. Due to the inherent separation between the TE and TM modes associated with the waveguide grating, these elements can provide polarization separation. Applications to polarization sensitive filtering and to electro‐optic switching are suggested. The guided‐mode resonance filter represents a basic new optical element.
904 citations
TL;DR: It is shown that the Nitrogen:Phosphorus ratio within zooplankton herbivores varies substantially intraspecifically but not intraspectively, and it is demonstrated that N:P stoichiometry can successfully account for shifts in N- and P-limitation previously observed in whole-lake experiments.
Abstract: Most ecosystem models consolidate members of food-webs, e.g. species, into a small number of functional components. Each of these is then described by a single state variable such as biomass. When a multivariate approach incorporating multiple substances within components is substituted for this univariate one, a ‘stoichiometric’ model is formed. Here we show that the Nitrogen:Phosphorus ratio within zooplankton herbivores varies substantially intraspecifically but not intraspecifically. By using stoichiometric theory and recent measurements of the N:P ratio within different zooplankton taxa, we calculate large differences in ratios of nutrients recycled by different zooplankton species. Finally, we demonstrate that N:P stoichiometry can successfully account for shifts in N- and P-limitation previously observed in whole-lake experiments. Species stoichiometry merges food-web dynamics with biogeochemical cycles to yield new insights.
299 citations
TL;DR: In the early Cambrian, there was a northward migration of Laurentia towards the Equator as its separation from Baltica and Siberia increased, and a southward movement of Gondwana as discussed by the authors.
Abstract: Climatically-related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early Cambrian world. Laurentia, Baltica and Siberia appear to have formed a continental group which rifted apart from each other prior to 600 Ma. The consolidation of much of Gondwana probably occurred (in the Pan-African orogeny) well before the Cambrian, though the assembly of several east Asian terranes is still speculative. The archaeocyathan reefs of Siberia, southern Europe and Morocco, with their bigotinid trilobite fauna, suggest that these areas were adjacent to each other and at low latitudes. Avalonia had close faunal links with western Gondwana, but lacked bigotinids and archaeocyathans and may have been situated off west Africa and Florida. During the early Cambrian, there was a northward migration of Laurentia towards the Equator as its separation from Baltica and Siberia increased, and a southward movement of Gondwana.
284 citations
TL;DR: Size-selective grazing of three heterotrophic nanoflagellates isolated from Lake Arlington, Texas was examined, indicating preferential flagellate grazing on the larger size classes within the lake bacterioplankton.
Abstract: Size-selective grazing of three heterotrophic nanoflagellates (with cell sizes of 21, 44, and 66 mum) isolated from Lake Arlington, Texas was examined by using a natural mixture of fluorescence labelled lake bacteria. Sizes of ingested bacteria in food vacuoles were directly measured. Larger bacterial cells were ingested at a frequency much higher than that at which they occurred in the assemblage, indicating preferential flagellate grazing on the larger size classes within the lake bacterioplankton. Water samples were collected biweekly from June through September, 1989, fractionated by filtration, and incubated for 40 h at in situ temperatures. The average bacterial size was always larger in water which was passed through 1-mum-pore-size filters (1-mum-filtered water) (which was predator free) than in 5-mum-filtered water (which contained flagellates only) or in unfiltered water (in which all bacterivores were present). The increase of bacterial-cell size in 1-mum-filtered water was caused by a shift in the size structure of the bacterioplankton population. Larger cells became more abundant in the absence of flagellate grazing.
204 citations
TL;DR: In this paper, the sensitivity of the additive model's classifications in data envelopment analysis (DEA) is investigated by means of new DEA formulations focusing on the stability (sensitivity) of an organization's classification (whether efficient or inefficient).
Abstract: In contrast to existing sufficient conditions for preservation of efficiency under special perturbations and matrix structural assumptions, sensitivity of the additive model's classifications in data envelopment analysis (DEA) is investigated by means of new DEA formulations focusing on the stability (sensitivity) of an organization's classification (whether efficient or inefficient). The formulations for the additive model are linear programming problems whose solutions yield a particular region of stability, a ‘cell’, in which an organization's classification remains unchanged. The largest such cell can always be easily computed for each organization and additionally theoretically characterized simply as optimal solutions of particular linear programming problems.
192 citations
TL;DR: In this article, the antecedents of personal goal level, and antecedent and consequences of goal commitment based on 78 goal-setting studies were examined. And the results of the meta-analyses on the consequences of personal commitment showed goal commitment to significantly affect goal achievement.
159 citations
TL;DR: In this paper, the authors report the results of a study of the intentions of male and female executives, managers and professionals to leave their organizations and highlight the importance of two components of job satisfaction, meaningful work and opportunities for promotion.
Abstract: The anticipated labor shortages of the 1990's will intensify organizational needs to retain their existing employees. Women represent an increasingly important segment of the labor force and their turnover rates are thought to exceed men's. Earlier studies of turnover and its psychological antecedent, the behavioral intention to leave, suggest that work-related factors may contribute to women's relatively higher turnover rates. The current paper reports the results of a study of the intentions of male and female executives, managers and professionals to leave their organizations. The results support the pattern of findings in earlier studies that gender differences disappear when job satisfaction is controlled in the analysis. Further analysis highlights the importance of two components of job satisfaction — meaningful work and opportunities for promotion. The authors conclude that organizations might improve their retention rates of female managers through job enrichment and by enhancing their advancement opportunities.
156 citations
149 citations
TL;DR: The output-nulling, unknown-input and composite subspaces are defined for singular systems, with recursions given for their computation, and the notions of composite preimage and composite image are introduced.
144 citations
TL;DR: The pattern of correlations that emerged between certainty and other constructs suggested that uncertainty reflects the phenomenal experience of a tenuous self-view, and stability of self-esteem appears to reflect the extent to which one's self- view is malleable, which may not be completely available to conscious awareness.
Abstract: We examined stability and level of self-esteem as predictors of excuse making; the extent to which self-ratings of stability are related to a statistical index of self-esteem stability; and the relations between stability and certainty of self-esteem and a variety of other psychological constructs. Regarding excuse making, our findings indicated that for high self-esteem individuals, instability was related to greater excuse making following success, but not following failure. However, for low self-esteem individuals, instability was related to greater excuse making following failure, but not following success. Other findings indicated that self-ratings of stability were only minimally related to a statistical measure of stability based on repeated assessments of self-esteem obtained in naturalistic contexts. Finally, stability of self-esteem was not significantly correlated with certainty of self-esteem. In addition, the pattern of correlations that emerged between certainty and other constructs suggested that uncertainty reflects the phenomenal experience of a tenuous self-view. On the other hand, stability of self-esteem appears to reflect the extent to which one's self-view is malleable, which may not be completely available to conscious awareness. Our discussion focuses on the nature of self-esteem stability and the roles of stability and level of self-esteem in reactions to evaluative events.
144 citations
TL;DR: In this article, polypyrrole films containing nanometer-sized platinum particles (ppy/Pt) were electrosynthesized at glassy carbon and gold electrode surfaces.
TL;DR: In this article, the authors suggest the following criteria, ordered in decreasing ease of identification, to distinguish strongly rheomorphic tuffs from extensive silicic lavas: (1) the character of basal deposits; (2) the nature of distal parts of flows; (3) the relationship of units to pre-existing topography; and (4) the type of source.
Abstract: High-temperature silicic volcanic rocks, including strongly rheomorphic tuffs and extensive silicic lavas, have recently been recognized to be abundant in the geologic record. However, their mechanisms of eruption and emplacement are still controversial, and traditional criteria used to distinguish conventional ash-flow tuffs from silicic lavas largely fail to distinguish the high-temperature versions. We suggest the following criteria, ordered in decreasing ease of identification, to distinguish strongly rheomorphic tuffs from extensive silicic lavas: (1) the character of basal deposits; (2) the nature of distal parts of flows; (3) the relationship of units to pre-existing topography; and (4) the type of source. As a result of quenching against the ground, basal deposits best preserve primary features, can be observed in single outcrops, and do not require knowing the full extent of a unit. Lavas commonly develop basal breccias composed of a variety of textural types of the flow in a finer clastic matrix; such deposits are unique to lavas. Because the chilled base of an ashflow tuff generally does not participate in secondary flow, primary pyroclastic features are best preserved there. Massive, flow-banded bases are more consistent with a lava than a pyroclastic origin. Lavas are thick to their margins and have steep, abrupt flow fronts. Ashflow tuffs thin to no more than a few meters at their distal ends, where they generally do not show any secondary flow features. Lavas are stopped by topographic barriers unless the flow is much thicker than the barrier. Ash-flow tuffs moving at even relatively slow velocities can climb over barriers much higher than the resulting deposit. Lavas dominantly erupt from fissures and maintain fairly uniform thicknesses throughout their extents. Tuffs commonly erupt from calderas where they can pond to thicknesses many times those of their outflow deposits. These criteria may also prove effective in distinguishing extensive silicic lavas from a postulated rock type termed lava-like ignimbrite. The latter have characteristics of lavas except for great areal extents, up to many tens of kilometers. These rocks have been interpreted as ash-flow tuffs that formed from low, boiling-over eruption columns, based almost entirely on their great extents and the belief that silicic lavas could not flow such distances. However, we interpret the best known examples of lava-like ignimbrites to be lavas. This interpretation should be tested through additional documentation of their characteristics and research on the boiling-over eruption mechanism and the kinds of deposits it can produce. Flow bands, flow folds, ramps, elongate vesicles, and probably upper breccias occur in both lavas and strongly rheomorphic tuffs and are therefore not diagnostic. Pumice and shards also occur in both tuffs and lavas, although they occur throughout ash-flow tuffs and generally only in marginal breccias of lavas. Dense welding, secondary flow, and intense alteration accompanying crystallization at high temperature commonly obliterate primary textures in both thick, rheomorphic tuffs and thick lavas. High-temperature silicic volcanic rocks are dominantly associated with tholeiitic flood basalts. Extensive silicic lavas could be appropriately termed flood rhyolites.
TL;DR: Findings show that the pMMO is capable of TCE oxidation; although the rates are lower than those observed for the sMMO.
Abstract: Trichloroethylene (TCE) oxidation was examined in 9 different methanotrophs grown under conditions favoring expression of the membrane associated methane monooxygenase. Depending on the strain, TCE oxidation rates varied from 1 to 677 pmol/min/mg cell protein. Levels of TCE in the reaction mixture were reduced to below 40 nmolar in some strains. Cells incubated in the presence of acetylene, a selective methane monooxygenase inhibitor, did not oxidize TCE.
TL;DR: In this article, the effects of water content, temperature, and the presence of CaCl 2 on aggregation number, surfactant monomer concentration, and size of aggregates were investigated by controlled partial pressure-vapor pressure osmometry and quasi-elastic light scattering.
Abstract: In reverse micelles of Triton X-100 in cyclohexane, the effects of water content, temperature, and the presence of CaCl 2 on aggregation number, surfactant monomer concentration, and size of aggregates were investigated by controlled partial pressure-vapor pressure osmometry and quasi-elastic light scattering. The monomer concentration is reduced by the addition of water but is increased by raising the temperature
TL;DR: The afferent inputs associated with cardioventilatory control in fish are described and direct and indirect evidence indicates that some fishes may possess intracardiac receptors homologous to mammalian atrial and ventricular stretch receptors.
Abstract: Publisher Summary This chapter describes the afferent inputs associated with cardioventilatory control in fish. The basic respiratory rhythm and rhythmic contractions of the heart result from the actions of endogenous rhythm generators and do not require afferent feedback for their initiation or maintenance in fish. Mechanoreceptors sensitive to displacement of the pharynx, pharyngeal pads, gill arches, gill rakers and filaments, and air-breathing organs have been identified in fishes. As in other vertebrates, these mechanoreceptors appear to be simple free nerve endings located in connective tissue or muscle. There is direct and indirect evidence that indicates that some fishes may possess intracardiac receptors homologous to mammalian atrial and ventricular stretch receptors. The internally oriented chemoreceptors respond to the mixed venous blood somewhere between the ventral aorta and the afferent filamental artery. Nociceptors with characteristics similar to juxtapulmonary receptors in mammalian lungs have been demonstrated in the gills of dogfish.
01 Dec 1992
TL;DR: The biaxial mechanical properties of right ventricular free wall (RVFW) myocardium was found to be consistently anisotropic, with a greater stiffness along the preferred (or averaged) fiber direction.
Abstract: The biaxial mechanical properties of right ventricular free wall (RVFW) myocardium were studied. Tissue specimens were obtained from the sub-epicardium of potassium-arrested hearts and different stretch protocols were used to characterize the myocardium's mechanical response. To assess regional differences, we excised tissue specimens from the conus and sinus regions. The RVFW myocardium was found to be consistently anisotropic, with a greater stiffness along the preferred (or averaged) fiber direction. The anisotropy in the conus region was more pronounced than in the sinus region. A comparison with studies of left ventricle (LV) midwall myocardium revealed that, 1) the fiber direction stiffnesses are greater in the RVFW than in the LV, 2) the degree of anisotropy is greater in the RVFW than in the LV.
TL;DR: The results contradict the invertebrate predation hypothesis (Dodson, 1974) in that D. lumholtzi's head and tail spines continue to grow during adulthood instead of stopping after the juvenile instars.
Abstract: SUMMARY
1. Daphnia lumholtzi, not previously reported in North America, was found in a small reservoir in East Texas in January, 1991, This species possesses extremely long spines and large fornices; an allometric study was performed to detect any temporal differences in specific growth rates of the spines relative to the body.
2. In nature, mature females attained 1.8mm body length, excluding spines, but when the head and tail spines are included, the total length reached a maximum of 5.6mm.
3. Differences in the growth patterns of the head spine and the tail spine relative to the body existed for D. lumholtzi from January to March 1991. Both the head and the tail spines grew at a faster rate than the body during all 3 months although the rates varied between them. The results contradict the invertebrate predation hypothesis (Dodson, 1974) in that D. lumholtzi's head and tail spines continue to grow during adulthood instead of stopping after the juvenile instars.
4. The head spines grew at a constant allometric rate over time while the tail spine grew faster as the temperature increased. Both varied significantly in length over the 3 months, with animals having the shortest spines in February and the longest in March.
TL;DR: This paper provides a brief summary of the current state of the theory of 2-D implicit systems and suggests that the implicit models are more suited to the description of naturally occurring two-dimensional systems, such as are described by the hyperbolic equation and the heat equation.
TL;DR: In this article, a low band-gap poly(2,3-dihexylthieno[3,4-b]pyrazine)2b has been proposed, which is dark blue-black in the neutral state and becomes transparent light yellow when doped.
Abstract: A new soluble, low band-gap polymer, poly(2,3-dihexylthieno[3,4-b]pyrazine)2b, which is dark blue–black in the neutral state and which becomes transparent light yellow when doped has been prepared; it has a doped film conductivity of 3.6 × 10–2 S cm–1 and a band-gap (film) of ca. 0.95 eV making it one of the lowest band-gap polymers prepared to date.
05 Feb 1992
TL;DR: Particle layering is introduced as an effective and convenient technique for enhancing boiling nucleation on a surface as discussed by the authors, which can be applied without stress or damage to a surface, it can be implemented in immersion cooling, with boiling, of electronic equipment components.
Abstract: Particle layering is introduced as an effective and convenient technique for enhancing boiling nucleation on a surface. Because it can be applied without stress or damage to a surface, it can be implemented in immersion cooling, with boiling, of electronic equipment components. Such an enhanced surface, which has an increased number of nucleation sites, shows a decreased level of wall superheat under boiling and an increased critical heat flux relative to superheat and critical heat flux values for an untreated surface. Application of this technique results in a decrease of heated surface temperature and a more uniform temperature of the heated surface; both effects are important in immersion cooling of electronic equipment. >
TL;DR: In this article, the micropolarities in Triton X-100 reverse micelles were invetigated in the mixed solvent of 30% (v/v) benzene and 70% n-hexane, by the use of methyl orange (MO) and 1-methyl-8-oxyquinolinium betaine (QB) as absorption probes, information about the distribution of the probe, water, and solvent molecule in aggregates was obtained.
Abstract: The micropolarities in Triton X-100 reverse micelles were invetigated in the mixed solvent of 30% (v/v) benzene and 70% (v/v) n-hexane, by the use of methyl orange (MO) and 1-methyl-8-oxyquinolinium betaine (QB) as absorption probes, Information about the distribution of the probe, water, and solvent molecule in the aggregates was obtained. MO is located in the polar core of the reverse micelles, but is not solubilized in the water pools, whereas QB transfers from the polar cores into the water pools when the latter are formed. In dry solutions, solubilized MO exists in two spectrophotomctrically distinguishable states
TL;DR: In this article, the deformation method is used to move an existing grid to a new position according to a system of n ordinary differential equations (n=spacial dimension), and the resulting grid has prescribed mesh sizes.
Abstract: An entirely new approach to numerical grid generation, the deformation method, is presented. Each point of an existing grid is moved, in an inter-related manner, to a new position according to a system of n ordinary differential equations (n=spacial dimension). The resulting grid has prescribed mesh sizes.
TL;DR: This research note suggests metric conjoint analysis (Louviere, 1988) as a tool for evaluating the decision policies employed by top managers in making strategic decisions.
Abstract: This research note suggests metric conjoint analysis (Louviere, 1988) as a tool for evaluating the decision policies employed by top managers in making strategic decisions. As an example of the technique, a descriptive field study is presented wherein the decision rules for stategy-structure-environment alignment used by the chief executives of 33 autonomous, nondiverstfied manufacturing firms are examined. Implications for future strategy research on managerial cognitions are discussed.
TL;DR: In this article, the surface backscattering coefficient as a function of roughness, incidence angle, frequency and polarization state was analyzed and the transition from the standard small perturbation scattering model into the Kirchhoff scattering model as frequency increases.
Abstract: This paper summarizes the properties of the surface backscattering coefficient as a function of roughness, incidence angle, frequency and polarization state. Results are presented in the form of like- and cross-polarized backscattering coefficient curves versus the incidence angle and the polarization state for different values of the surface roughness parameters and frequency. It is seen that there is a gradual transition from the standard small perturbation scattering model into the Kirchhoff scattering model as frequency increases. It is also shown that in the intermediate frequency region neither the small perturbation nor the Kirchhoff model is applicable. The maximum value of the polarized backscattering coefficient occurs at VV polarization and its two minimum values occur at zero ellipticity and orientation angles between 0 deg and 45 deg and between 135 deg and 180 deg. The cross-polarized scattering coefficient has two maximum values which occur in the same polarization state regions as the minima of the polarized coefficients.
TL;DR: In this article, an electrochemically initiated chain polymerization, featuring a high polymerization rate and involving little charge transport, was found under specific conditions in the presence of ClO−4, BF−4 and PF−6 electrolytes.
Abstract: The electrochemical quartz crystal microbalance has been employed to investigate the electropolymerization of pyrrole in a variety of aqueous electrolytes. In contrast to the generally accepted cation–radical coupling process for the electropolymerization of pyrrole, an electrochemically initiated chain polymerization, featuring a high polymerization rate and involving little charge transport, was found under specific conditions in the presence of ClO−4, BF−4, and PF−6 electrolytes. The more typical cation-radical coupling mechanism, characterized by a constant polymerization charge to mass deposited ratio, is observed in the presence of Cl−, NO−3, dodecyl sulfate, copper phthalocyanine tetrasulfonate, β-cyclodextrin tetradecasulfate, and poly(styrene sulfonate). Electrochemical characterizations of polypyrrole films prepared in aqueous ClO−4 electrolytes reveal that the polymer formed via chain polymerization exhibits the ability to transport both cations and anions during electrochemical switching between redox states, while the polymer synthesized through cation-radical coupling is only capable of transporting a single ionic species.
TL;DR: The equilibrium geometries, total energies, binding energies, and fragmentation energies for the clusters B n, with n=2-8, in both the neutral and cationic states are calculated by means of ab initio techniques.
Abstract: We have calculated, by means of ab initio techniques, the equilibrium geometries, total energies, binding energies, and fragmentation energies for the clusters B n , with n=2-8, inboth the neutral and cationic states. The ionization potentials for the neutral clusters have also been calculated. Electron correlation has been included through a perturbative approach. The results have beencompared with previ ously available theoretical and experimental work
TL;DR: In this article, the authors highlight some of the problems inherent in traditional screening measures for giftedness and suggest the student portfolio as a promising alternative for the identification of gifted children, especially those from special populations.
Abstract: Research has documented the underrepresentation of minority children in gifted programs. This article highlights some of the problems inherent in traditional screening measures for giftedness and suggests the student portfolio as a promising alternative for the identification of gifted children, especially those from special populations.
TL;DR: In this paper, the thermodynamics for the cathodic electrosynthesis of and were analyzed with the aid of Pourbaix diagrams, and strategies for modulating the Cd content and thus the photoresponse of alloy thin films were developed.
Abstract: This paper concerns electrodeposition chemistry in the Cd‐Zn‐Se system. First, the thermodynamics for the cathodic electrosynthesis of and were analyzed with the aid of Pourbaix diagrams. Strategies for modulating the Cd content and thus the photoresponse of alloy thin films were developed. These thin films were analyzed by cyclic photovoltammetry and photocurrent spectroscopy. X‐ray photoelectron spectroscopy provided further confirmation of the alloy composition. Finally a ramp‐hold method was developed for modulating the composition of these thin films to generate superstructures. These experiments demonstrate the feasibility of securing modulation lengths spanning the submicron regime.
TL;DR: In this article, the authors present a measurement of the inclusive jet cross section in {ital {bar p}p} collisions at {radical}{ital s} = 1.8 TeV at the Fermilab Tevatron using the Collider Detector.
Abstract: We present a measurement of the inclusive jet cross section in {ital {bar p}p} collisions at {radical}{ital s} =1.8 TeV at the Fermilab Tevatron using the Collider Detector at Fermilab. Good agreement is seen with the predictions of recent next-to-leading-order ({ital O}({alpha}{sub {ital s}}{sup 3})) QCD predictions. The dependence of the cross section on clustering cone size is reported for the first time. An improved limit on {Lambda}{sub {ital c}}, a term characterizing possible quark substructure, is set at 1.4 TeV (95% C.L.).