Showing papers by "University of Delaware published in 1982"

Some Comments on the Evaluation of Model Performance

Abstract: Quantitative approaches to the evaluation of model performance were recently examined by Fox (1981). His recommendations are briefly reviewed and a revised set of performance statistics is proposed. It is suggested that the correlation between model-predicted and observed data, commonly described by Pearson's product-moment correlation coefficient, is an insufficient and often misleading measure of accuracy. A complement of difference and summary univariate indices is presented as the nucleus of a more informative, albeit fundamentally descriptive, approach to model evaluation. Two models that estimate monthly evapotranspiration are comparatively evaluated in order to illustrate how the recommended method(s) can be applied.

Cosmic rays and particle physics.

Abstract: Preface 1. Cosmic rays 2. Particle physics 3. Cascade equations 4. Hadrons and photons 5. Accelerator data 6. Muons 7. Neutrinos 8. Neutrino-induced muons 9. Propagation 10. Gamma rays and antiprotons 11. Acceleration 12. Acceleration to >100 TeV 13. Astrophysical beam dumps 14. Air showers 15. Electromagnetic cascades 16. Cosmic ray showers 17. Simulation techniques References Index.

Stiffness and strength behaviour of woven fabric composites

Abstract: This paper presents three analytical models for the investigation of the stiffness and strength of woven fabric composites. The “mosaic model” is effective in predicting the elastic properties of fabric composites. The “fibre undulation model” takes into account fibre continuity and undulation and has been adopted for modelling the “knee behaviour” of plain weave fabric composites. The “bridging model” is developed to simulate the load transfer among the interlaced regions in satin composites. The theoretical predictions coincide extremely well with experimental measurements. The elastic stiffness and knee stress in satin composites are higher than those in plain weave composites due to the presence of the bridging regions in the weaving pattern.

Sulfur Poisoning of Metals

Abstract: Publisher Summary This chapter provides an overview of the sulfur poisoning of metals. Sulfur apparently bonds so strongly to metal surfaces that marked activity reduction occurs at extremely low gas-phase concentrations of sulfur-containing compounds. In commercial practice, the life of supported metal catalysts may be reduced to only a few months or weeks in the presence of only ppm quantities of sulfur contaminants in the feed. Because of the essentially irreversible adsorption of sulfur compounds on metals, regeneration is usually impossible or impractical. This chapter integrates available information on the interaction of sulfur with metal surfaces with that of poisoning studies to provide a more complete picture of sulfur poisoning and of the mechanism. The chapter stresses the importance of experimental techniques that provide definitive, fundamental information regarding sulfur adsorption and poisoning.

Elastic Behavior of Woven Hybrid Composites

Abstract: Basic geometrical and material parameters are identified to characterize the structure of hybrid fabrics Analysis of the elastic behavior is made based upon a mosaic model and the fabric composite

Diel and depth variations in dissolved free amino acids and ammonium in the Baltic Sea determined by shipboard HPLC analysis1

Abstract: A precolumn fluorimetric labeling method was tested for shipboard HPLC analysis of dissolved free amino acids (DFAA) in natural waters. No sample preparation is required and all naturally occurring amino acids plus ammonium are sufficiently separated within 30 min. Striking diel trends were observed to a depth of at least 60 m, with maximal DFAA concentrations (200–400 nM) in the late evening and minimal concentrations (30–40 nM) in the early day. Concurrent with the evening concentration maxima were elevated relative abundances of basic amino acids (especially ornithine and lysine) and ammonium. During the day very low levels of amino acids were found in the upper water. The magnitude of the night-to-day drop in total DFAA suggests a net heterotrophic uptake rate of up to 6 µg AA·liter−1 h−1. A pronounced amino acid maximum at the O2−HS− interface in the water column was presumably derived from microbial populations inhabiting this region. Pronounced, coincidental minima in amino acid and ammonium concentrations just above this interface may be related either to scavaging by precipitating metal oxyhydroxides or to enhanced heterotrophic utilization.

Television's influence on social reality

Abstract: The value of “cultivation analysis” as both a theoretical and analytic framework for the investigation of the effects of television viewing has been questioned. Using commonality analysis as its framework, this study suggests that perceived program realism is a key predictor variable which has been excluded from prior cultivation research.

Species-specific defense reactions and avoidance learning

Abstract: Bolles (1970) proposed a theory of avoidance learning, the species-specific defense reaction (SSDR) hypothesis, which emphasized innate constraints on the response repertoire of rats in aversive situations and minimized the role of reinforcement in avoidance learning. The present paper describes Bolles’ (1970, 1971, 1972, 1975, 1978) development of SSDR theory and reviews the empirical tests of its assumptions and predictions. It is concluded that the SSDRs described by Bolles, along with some others, are highly probable in aversive situations but that the response repertoire is not limited to them. Further, there is strong evidence for reinforcement effects in the establishment and maintenance of at least some avoidance responses.

A probabilistic theory of the strength of short-fibre composites with variable fibre length and orientation

Abstract: This paper adopts a probabilistic approach to examine the effects of fibre length and orientation distribution on the strength of short fibre composites. A general theory has been formulated in terms of fibre length and orientation distribution function as well as the composite geometrical and physical properties. The final result is presented in the form of a modified “rule of mixtures”. The result has been applied to discuss several special cases of fibre arrangements. They are (a) unidirectional short fibre composites with uniform fibre length, (b) unidirectional short fibre composites with fibre length distribution, (c) random short fibre composites with uniform fibre length and (d) partially-aligned short fibre composites with uniform fibre length. Comparisons of the present results with previous work are also discussed.

Functional Properties of Chitin and Chitosan

Abstract: Chitin (poly-β (1⇒4)-N-acetyl-D-glucosamine), chitosan (deacetylated chitin) and microcrystalline chitin (redispersible chitin powder) were compared with microcrystalline cellulose to examine the use of those cellulose-like biopolymers as functional additives for potential application in food formulations. Water binding, fat binding and emulsifying properties were studied. Baking tests were performed with 0.5–2.0% (flour basis) of microcrystalline chitin added to wheat flour bread or to potato protein fortified (8% potato protein concentrate) white bread. Water-binding capacity and fat binding capacity of chitin, chitosan and microcrystalline chitin ranged from 230–440s (w/w) and from 170–315% (w/w). Chitosan and chitin did not produce emulsions but microcrystalline chitin showed good emulsifying properties and was superior to microcrystalline cellulose. Increasing concentration of microcrystalline chitin (0.12–0.8 g/100 ml water) had a positive effect on emulsion stability. Addition of microcrystalline chitin increased specific loaf volume of white bread and protein fortified breads. Water addition of 65% (flour basis) was found to be optimum for “chitin breads.”

Interlaminar Fracture of Composite Materials

Abstract: Interlaminar fracture characteristics of a graphite/epoxy composite material (AS1/3501-6) are investigated under the opening, shearing and mix ed mode conditions. The Arcan test fixture was modified to accomodate the composite specimen containing an embedded interlaminar crack. Both critical stress intensity factor and strain energy release rate data were deter mined and the quadratic interaction for mixed mode behavior was compared to experimental data. Results of over sixty tests showed that the test fixture yielded results which compare favorably with results from contemporary test fixtures. Critical fracture parameters for the opening and shearing modes were shown to differ by a factor of 9.1. Further, the test results showed general agreement with the quadratic interaction relation.

The defense motivation system: A theory of avoidance behavior

Abstract: A motivational system approach to avoidance behavior is presented. According to this approach, a motivational state increases the probability of relevant response patterns and establishes the appropriate or “ideal” consummatory stimuli as positive reinforcers. In the case of feeding motivation, for example, hungry rats are likely to explore and gnaw, and to learn to persist in activities correlated with the reception of consummatory stimuli produced by ingestion of palatable substances. In the case of defense motivation, fearful rats are likely to flee or freeze, and to learn to persist in activities correlated with consummatory stimuli produced by flight from a dangerous place. Defense system activation is distinct from alarm reactions. The latter prepare the animal for probable noxious events, involve relatively intense negative affect and extinguish rapidly in situations where the noxious event no longer occurs. In contrast, defense system activation potentiates innate and modified defense reactions, thus preparing the animal for possible, but not necessarily probable, noxious events; it involves little or no negative affect and extinguishes very slowly when the noxious event no longer occurs. With these assumptions and the resulting model we attempt to resolve several long-standing problems in avoidance learning, including the low correlation between negative affect and avoidance performance, differential rates of extinction for avoidance performance and conditioned emotional responses, and evidence that some avoidance responses are much more easily learned than others. In addition, the model has implications for the study of parallels between appetitive and aversive motivation, sign tracking in aversive conditioning, and orientation of flight responses. Historical antecedents and alternative approaches are discussed.

The microstructure of injection-molded semicrystalline polymers: A review

Abstract: The microstructure of semicrystalline polymers solidified with and without concurrent applied strain is reviewed. Fluid flow in the filling and packing stages of injection-molding are discussed. Observations of the microstructures of a number of polymers under various conditions are described. In general, the microstructure is extremely inhomogeneous and anisotropic; a skin layer is highly oriented (or, in some cases, finely granular), whereas the core is composed of larger, isotropic spherulites. The principles governing the formation of such microstructures are given. Relations between microstructure and macroscopic properties are briefly described.

Seasonal abundance and vertical distribution of crab larvae in Delaware Bay

Abstract: Larvae of 15 species or genera of crabs were collected and identified during a six month (May 26 to October 28, 1978) study in the mouth of Delaware Bay. Seasonal abundance and vertical distribution of each species were investigated. Most species studied had peak abundance in July and August except forCancer irroratus andOvalipes ocellatus which showed peak occurrence in May and June, respectively. Larvae of species strongly dependent on estuarine habitats, such asUca spp.,Pinnixa chaetopterana, andP. sayana, showed a tendency to congregate in near-bottom waters where net flow of water is landward, thus favoring retention within the estuary. Larvae ofOvalipes ocellatus, Cancer irroratus, andCallinectes sapidus were more common at the surface. This vertical distribution suggests that these larvae are flushed out of the estuary. The mechanisms of recruitment and replenishment of adult populations within the estuary would therefore depend on migration of megalopa and juveniles. *** DIRECT SUPPORT *** A01BY019 00006

The importance of an infrequently flooded intertidal marsh surface as an energy source for the mummichog Fundulus heteroclitus: An experimental approach

Abstract: Fundulus heteroclitus is known to ascend onto the marsh surface to feed. Our study investigated whether the marsh surface food items are a necessary source of caloric intake for the Canary Creek, Delaware, USA population of this species. Enclosure techniques were used to restrict mummichogs from the marsh surface and the growth rates of these fish were compared to those having access to the marsh surface. Growth rates were significantly higher for mummichogs allowed access to the marsh surface. Food addition and density reduction experiments showed that food availability per fish, rather than behavioral responses due to fish crowding, was responsible for the increased growth. Although food was available in the subtidal portion of the habitat, it was of insufficient quantity for fish at natural density to grow at a normal rate, and mummichogs must utilize the marsh surface for at least a portion of their energy intake.

A thin film photovoltaic solar cell and method of making the same

Abstract: A thin film photovoltaic solar cell having an opaque electrical contact which consists of a low-cost substrate, such as a metal alloy or a metallurgical grade crystalline silicon and a barrier layer which is optically reflective, a first semiconductor layer, a second semiconductor layer, a transparent electrical contact and an encapsulant.

Decision support systems: issues and perspectives

Abstract: Information Systems Working Papers Series

Acid rain on Bermuda

Abstract: Increased acidity of precipitation due to combustion of fossil fuels has been well documented for both the eastern USA1 and Canada2 The SO2 and NOxemitted by the burning of coal, natural gas, fuel oil and petrol are oxidized in the atmosphere to sulphuric and nitric acids which subsequently give rise to acid precipitation1 However, the SO2 and NOx emitted, and their oxidation products, are not all removed by atmospheric deposition over the North American continent; a large fraction is advected east out of North America3 In a study between 1 May 1980 and 30 April 1981, we have detected acid precipitation (pH<56) on the island of Bermuda, which is ∼1,000 km east of the Atlantic seaboard of the USA We report here that the acidity of such precipitation is eight times greater on a volume-weighted annual average than rainwater in natural atmospheric equilibrium, and that the acids present are almost wholly sulphuric with a small nitric acid contribution There is a strong correlation between the presence of these strong acids and the meteorological back trajectory of Bermuda storm systems to the North American continent, which suggests long-range atmospheric transport of acid rain precursors to Bermuda, these having similar anthropogenic origins (that is, from remote fossil fuel combustion) to acid rain precursors on the continent