Showing papers by "University of Delaware published in 1992"

Recovery of the Navier-Stokes equations using a lattice-gas Boltzmann method.

Abstract: It is known that the Frisch-Hasslacher-Pomeau lattice-gas automaton model and related models possess some rather unphysical effects. These are (1) a non-Galilean invariance caused by a density-dependent coefficient in the convection term, and (2) a velocity-dependent equation of state. In this paper, we show that both of these effects can be eliminated exactly in a lattice Boltzmann-equation model.

A theoretically correct mixing rule for cubic equations of state

Abstract: A new mixing rule developed for cubic equations of state equates the excess Helmholtz free energy at infinite pressure from an equation of state to that from an activity coefficient model. Use of the Helmholtz free energy insures that the second virial coefficient calculated from the equation of state has a quadratic composition dependence, as required by statistical mechanics. Consequently, this mixing rule produces the correct low- and high-density limits without being density-dependent. As a test, the mixing rule is used for ternary mixtures of cyclohexane + benzene + water, ethanol + benzene + water and carbon dioxide + n-propane + water, and all the constituent binaries. The new mixing rule and a simple cubic equation of state can be used for the accurate correlation of vapor-liquid and liquid-liquid equilibria for binary mixtures. Using the parameters obtained from binary systems, the phase behavior of ternary mixtures can be predicted. Also, unlike previous empirical mixing rules, this theoretically based mixing rule is equally applicable and accurate for simple mixtures containing hydrocarbons and inorganic gases and mixtures containing polar, aromatic and associating species over a wide range of pressures. This mixing rule makes it possible to use a single equation of state model with equal accuracy for mixtures usually described by equations of state and for those traditionally described by activity coefficient models. It is the correct bridge between these two classes of models.

Antibacterial action of chitosan

Abstract: The antibacterial action of chitosan hydroglutamate (CH), chitosan lactate (CL) and chitosan derived from fungal mycelia was examined against both gram‐negative and gram‐positive bacteria. Plate counts indicated inactivation rates of one‐ to five‐log‐cycles within one hour. Fungal chitosan had significantly less antibiotic effect than CH and CL. The antibacterial action of CH and CL was very similar and shown to be concentration dependent with 0.1 mg/mL more effective than 2.0 and 5.0 mg/mL. When CH (or CL) and polygalacturonate were added to cell suspensions, death was prevented, possibly indicating that chitosan complexed with polygalacturonate could not penetrate the cell or disrupt the membrane. Leakage of intracellular components caused by chitosan was determined by exposing lactose‐induced Escherichia coli to chitosan with assay for s‐galactosidase activity indicating that cell permeabilization occurred more extensively at the low chitosan concentrations. Microscopic examination showed that...

Basic emotions, relations among emotions, and emotion-cognition relations.

Abstract: From the cognitive theory perspective that emotions are cognition dependent and contain cognitive components, Ortony and Turner (1990) questioned the validity of the concept of basic emotions. They argued that the so-called basic emotions were neither psychologically or biologically "primitive" nor "irreducible building blocks" for generating the "great variety of emotional experiences." In the biosocial theory tradition, researchers have identified multiple noncognitive activators of emotion and demonstrated the usefulness of defining the essential components of emotion as phenomena that do not require cognitive mediators or constituents. In this framework, emotions are seen as basic because their biological and social functions are essential in evolution and adaptation. Particular emotions are called basic because they are assumed to have innate neural substrates, innate and universal expressions, and unique feeling-motivational states. The great variety of emotional experiences is explained as a function of emotion-cognition interactions that result in affective-cognitive structures.

A comparison of some methodologies for the factor analysis of non‐normal Likert variables: A note on the size of the model

Abstract: This paper expands on a recent study by Muthen & Kaplan (1985) by examining the impact of non-normal Likert variables on testing and estimation in factor analysis for models of various size. Normal theory GLS and the recently developed ADF estimator are compared for six cases of non-normality, two sample sizes, and four models of increasing size in a Monte Carlo framework with a large number of replications. Results show that GLS and ADF chi-square tests are increasingly sensitive to non-normality when the size of the model increases. No parameter estimate bias was observed for GLS and only slight parameter bias was found for ADF. A downward bias in estimated standard errors was found for GLS which remains constant across model size. For ADF, a downward bias in estimated standard errors was also found which became increasingly worse with the size of the model.

Process-Induced Stress and Deformation in Thick-Section Thermoset Composite Laminates:

Abstract: A study of process-induced stress and deformation in thick-section thermosetting composite laminates is presented. A methodology is proposed for predict ing the evolution of residual stress develop...

Phase behavior and structures of mixtures of anionic and cationic surfactants

Abstract: Spontaneous, single-walled, equilibrium vesicles of controlled size and surface charge can be prepared from aqueous mixtures of simple, commercially available, single-tailed cationic and anionic surfactants. We present detailed phase behavior and structural studies of one such mixture, sodium dodecylbenzenesulfonate (SDBS) and cetyl trimethylammonium tosylate (CTAT) in H 2 O, as well as results of less complete surveys of other mixtures

Microstructural design of fiber composites

Abstract: The optimum performance design of composite microstructures is discussed. The forces driving progress in fiber composites are examined, and recent developments in the mechanics of laminated composites are surveyed, emphasizing thick laminates, hygrothermal effects, and thermal transient effects. The strength of continuous-fiber composites is discussed, presenting analyses of local load redistribution due to fiber breakages and treatments of statistical tensile strength theories. Modes of failure of laminated composites are examined. Elastic, physical, and viscoelastic properties as well as the strength and fracture behavior of short-fiber composites are studied, and it is shown how the performance of composites can be controlled by selecting material systems and their geometric distributions. 2D textile structural composites based on woven, knitted, and braided preforms are considered, and techniques for analyzing and modeling the thermomechanical behavior of 2D textile composites are presented. Recent developments in the processing of 3D textile preforms are introduced and the processing-microstructure relationship is demonstrated. Finite elastic deformation of flexible composites is addressed.

Magnetic properties of ultrafine iron particles.

Abstract: The magnetic and morphological properties of fine Fe particles have been studied. Ultrafine particles of Fe were prepared using a vapor deposition technique under an argon atmosphere. The argon pressure was varied from 0.5 to 8 Torr during evaporation, and samples with a median diameter in the range 50--200 \AA{} were obtained having a log-normal distribution. The dependence of magnetic properties on particle size and temperature (10 KT300 K) were studied using superconducting-quantum-interference-device magnetometry and M\"ossbauer spectroscopy. Samples with particle diameter below 90 \AA{} showed a superparamagnetic behavior below room temperature. The saturation magnetization of the particles varied from 25 to 190 emu/g, with the higher values corresponding to larger particles. For these larger particles, a coercivity of 1.05 kOe was obtained at room temperature. The magnetic and structural data suggested a core-shell type of structure, where the core consists of metallic Fe and the shell is composed of Fe oxides.

Psychophysiology in Attachment Interviews: Converging Evidence for Deactivating Strategies

Abstract: By asking the subject to consider a host of potentially threatening attachment-related issues, the Adult Attachment Interview (AAI) allows an assessment of different strategies for regulating the attachment system. These strategies can be assessed along the 2 dimensions of security/anxiety and deactivation/hyperactivation. The greatest inferential leaps may be in characterizing strategies as deactivating. For example, individuals using deactivating strategies often report extremely positive relationships with parents, display restricted recall of attachment memories, and play down the significance of early attachment experiences. If these descriptive features are guided by a strategy that requires diverting attention from attachment information, subjects employing this strategy should experience conflict or inhibition during the Attachment Interview. In the present study, skin conductance levels were monitored for 50 college students during a baseline period and throughout the Attachment Interview. Subjects employing deactivating strategies showed marked increases in skin conductance levels from baseline to questions asking them to recall experiences of separation, rejection, and threat from parents. This finding supports the notion that individuals employing deactivating attachment strategies experience conflict or inhibition during the Attachment Interview.

A Conceptual Framework for Apparel Design

Abstract: To encourage students to think of designing garments for special needs as part of a general designframework, a problem-solving approach that does not distinguish between functional apparel design a...

Planck-scale corrections to axion models.

Abstract: It has been argued that quantum gravitational effects will violate all nonlocal symmetries. Peccei-Quinn symmetries must therefore be an accidental'' or automatic consequence of local gauge symmetry. Moreover, higher-dimensional operators suppressed by powers of {ital M}{sub Pl} are expected to explicitly violate the Peccei-Quinn symmetry. Unless these operators are of dimension {ital d}{ge}10, axion models do not solve the strong {ital CP} problem in a natural fashion. A small gravitationally induced contribution to the axion mass has little if any effect on the density of relic axions. If {ital d}=10, 11, or 12 these operators can solve the axion domain-wall problem, and we describe a simple class of Kim-Shifman-Vainshtein-Zakharov axion models where this occurs. We also study the astrophysics and cosmology of heavy axions'' in models where 5{le}{ital d}{le}10.

Problems with gait and posture in neuropathic patients with insulin-dependent diabetes mellitus.

Abstract: Peripheral neuropathy secondary to diabetes mellitus is believed to cause postural instability and uncoordinated gait, although this is not well documented. Two groups of patients from the Pittsburgh Epidemiology of Diabetes Complications Study, matched for age and duration of Type 1 diabetes, but with significantly different vibratory sensation thresholds as determined by Vibratron II testing, were therefore surveyed. The mean ages were 32.9 and 31.9 years and durations of diabetes were 22.0 and 18.8 years for the neuropathic and control groups, respectively. Patients provided details of fall injuries, and perception of safety during standing and walking. Multiple linear and logistic regression models were used to account for potentially associated variables such as gender, retinopathy, and duration of diabetes. The neuropathic group had adjusted odds ratios for reported injuries during gait of 15.0 relative to the control group (95% confidence intervals 1.04-216.59). The neuropathic group also reported significantly lower scores (less safe, p = 0.004) than the control group on perceived safety in unusual conditions. It is concluded that peripheral neuropathy has an effect on gait and posture which is clinically significant and that this effect merits further biomechanical study in neuropathic patients.

The beginning science teacher: Classroom narratives of convictions and constraints

Abstract: This article is a case study of a second-year middle school science teacher's beliefs about science and science teaching and how these beliefs influenced—or failed to influence—classroom instruction. It illustrates how beginning teachers struggle to reconcile (a) conflicting beliefs about what is desirable, and (b) conflicts between what they believe is desirable and what is possible within the constraints of their preparation and the institutions in which they work. This teacher, for example, struggled to reconcile his view of science as a creative endeavor with his belief that students need to be provided with a high degree of structure in order to learn within the context of formal schooling. He also had difficulty resolving the conflict between the informal (“messing about”) type of science learning that he believed was desirable and the personal and institutional constraints he faced in the classroom.

Temperature and Size Variabilities of the Western Pacific Warm Pool

Abstract: Variabilities in sea-surface temperature and size of the Western Pacific Warm Pool were tracked with 10 years of satellite multichannel sea-surface temperature observations from 1982 to 1991. The results show that both annual mean sea-surface temperature and the size of the warm pool increased from 1983 to 1987 and fluctuated after 1987. Possible causes of these variations include solar irradiance variabilities, El Nino-Southern Oscillaton events, volcanic activities, and global warming.

Lattice Boltzmann Computational Fluid Dynamics in Three Dimensions

Abstract: The recent development of the lattice gas method and its extension to the lattice Boltzmann method have provided new computational schemes for fluid dynamics. Both methods are fully paralleled and can easily model many different physical problems, including flows with complicated boundary conditions. In this paper, basic principles of a lattice Boltzmann computational method are described and applied to several three-dimensional benchmark problems. In most previous lattice gas and lattice Boltzmann methods, a face-centered-hyper-cubic lattice in four-dimensional space was used to obtain an isotropic stress tensor. To conserve computer memory, we develop a model which requires 14 moving directions instead of the usual 24 directions. Lattice Boltzmann models, describing two-phase fluid flows and magnetohydrodynamics, can be developed based on this simpler 14-directional lattice. Comparisons between three-dimensional spectral code results and results using our method are given for simple periodic geometries. An important property of the lattice Boltzmann method is that simulations for flow in simple and complex geometries have the same speed and efficiency, while all other methods, including the spectral method, are unable to model complicated geometries efficiently.

Electromagnetic pulses from high-energy showers: Implications for neutrino detection.

Abstract: We review the properties of electromagnetic showers in dense media and calculate in detail the associated electromagnetic pulses generated by shower electrons. We perform real-time simulations recording the charge, trajectory, and time of each cascade particle and compute the associated electromagnetic wave. Our results are relevant to experiments detecting radio pulses from showers initiated by cosmic particles interacting with the Earth.

The evolution of modern human childbirth

Abstract: Human birth follows a pattern which is unique among mammals. Distinctions include the orientation of the fetus as it passes through the birth canal, the way the fetus emerges from the birth canal, difficulty during labor, and behavior by the mother and/or other individuals around the time of birth. Birth has important implications for the morphology of the pelvis, for sex differences in the pelvis, for such aspects of human biology as size (and maturity) at birth, and for behavior (including cooperative behavior). This paper reviews the fossil and comparative evidence for when and how the modern pattern of birth evolved. The modern human pattern of birth evolved in a mosaic manner with some unique features appearing early in human evolution and others quite late. A human-like entry of the fetal head into the birth canal was already present among australopithecines as a result of their wide pelvic apertures. Other aspects of modern human birth such as the rotation of the head and body within the birth canal and the emergence of the fetal head in an occiput anterior position probably evolved later, when encephalization had placed increasing selection on both the form of the pelvis and the timing of birth. Cooperative behavior during and after birth accompanied the origin of the fully modern human mechanism of birth. The unique phenomenon of modern human birth did not evolve in response to a single “obstetrical dilemma” but as part of a complex interplay between changes in a number of aspects of human biology. © 1992 Wiley-Liss, Inc.

The Manufacture of `Public Opinion' by Reporters: Informal Cues for Public Perceptions of Protest Groups:

Abstract: This study examines how conceptions of `public opinion' are embedded within news-coverage of social protests at two levels: the micro-level in terms of informal characterizations of public opinion and the macro-level in terms of general conceptions of public opinion. At the micro-level, public opinion is brought into news stories in a variety of ways, including: statements about public opinion, depictions of compliance with or violation of social norms and laws, and portrayals of bystanders as symbols for public reaction. At the macro-level, coverage may have an underlying conception of public opinion as (1) aggregated individual opinion, (2) attempts of various groups to affect public policy and (3) a mechanism of social control. This case study of mainstream and alternative media coverage of three anarchist protests reveals differences at both the micro-descriptive and macro-conceptual levels.

Isotope fractionation associated with ammonium uptake by a marine bacterium

Abstract: Bacteria can account for a large fraction of total NH,’ uptake in both pelagic and benthic marine environments. 15N natural abundance was examined to understand the effect of NH,’ uptake by bacteria on nitrogen isotope biogeochemistry. Isotope fractionation (E) for NH,’ uptake by the marine bacterium Vibrio harveyi changed from -4 to -277~ when cells were grown on 23-l 82 PM NH,+ and then from -27 to - 14Ya when the NH;’ concentration increased to 23.3 mM. Changes in fractionation correlated with a switch in the pathway of NH,’ uptake from membrane diffusion of NH, and assimilation catalyzed by glutamate dehydrogcnase at millimolar NH,’ to active ammonium transport (Amt) and assimilation catalyzed by glutamine synthetase (GS) at micromolar NH,+. This transition occurred between 0.1 and I mM NH,+. Within this concentration range, cellular N demand was no longer supported by Fickian diffusion of NH:, and Amt activity increased. The isotope fractionation of whole cells with the highest GS activity (E = -4%) and that measured for the GS-catalyzed reaction in vitro (E = - 8%; pH = 7.1) differed by 5?&, which suggests that the GS reaction was not the rate-limiting step during NH,’ uptake. Isotope fractionation associated with NH,’ uptake by marine bacteria appears to depend on the membrane transport mechanism and the ammonium assimilation enzymes. Depending on NH, I- concentrations, marine bacteria using NH, + for growth may partly account for variation in the isotope composition of NH, k and particulate organic N in the water column and sediments of marine environments.

Seasonal iron cycling in the salt-marsh sedimentary environment : the importance of ligand complexes with Fe(II) and Fe(III) in the dissolution of Fe(III) minerals and pyrite, respectively

Abstract: A biogeochemical cycle is proposed for the reactivity of iron in salt-marsh sediments. The main reactions of the iron cycle are: (1) solubilization of Fe(III) by organic ligands; (2) reduction of soluble Fe(III) to Fe(II) by these ligands, soluble reduced sulfur or solid phase reduced sulfur, (3) the oxidation of the resulting Fe(II) (complexed to organic chelates) by Fe(III) minerals; (4) the formation of iron sulfide minerals when dissolved sulfide is in excess. The cycle of iron solubilization will continue as long as bacteria and/or plants produce organic ligands

CONSTRUCTING GENDER: An Exploration of Afro-American Men's Conceptualization of Manhood

Abstract: This article explores the meanings of manhood as articulated by Afro-American men (N = 32). Conceptualization and Q-sort methods are used to examine (1) men's construction of manhood and (2) men's ratings of the importance of selected attributes to being a man. Manhood emerged as a multidimensional construct with four major domains (self-determinism and accountability, family, pride, and spirituality and humanism) and 15 distinct clusters of ideas. The cluster of attributes rated as most important to being a man paralleled the conceptualization of manhood derived from the open-ended interviews for both professional and nonprofessional men. Men's ratings of attributes in the areas of ownership, manliness, spiritual and religious, and power varied by occupational status.

The equations of reduced magnetohydrodynamics

Abstract: The equations of high- and low-beta reduced magnetohydrodynamics (RMHD) are considered anew in order to elucidate the relationship between compressible MHD and RMHD and also to distinguish RMHD from recently developed models of nearly incompressible MHD. Our results, summarized in two theorems, provide the conditions under which RMHD represents a valid reduction of compressible MHD. The equations for low-beta RMHD and high-beta RMHD are shown to be identical. Furthermore, as a direct consequence of our analysis, the conditions under which both two-dimensional incompressible MHD (in terms of the spatial co-ordinates as well as the fluid variables) and 2½ dimensional incompressible MHD (i.e. only two-dimensional in the spatial co-ordinates) represent a valid reduction of three-dimensional compressible MHD are also formulated. It is found that the elimination of all high-frequency and long-wavelength modes from the magneto-fluid reduces the fully compressible MHD equations to either two-dimensional incompressible MHD in the plasma beta (β) limit β ≪ 1, or 2½-dimensional incompressible MHD for β ≈ 1. Our approach clarifies several inconsistencies to be found in previous investigations in that the reduction is exact. Our results and analysis are expected to be of interest for plasma fusion and space and solar physics.

Dynamic Pricing and Ordering Decisions by a Monopolist

Abstract: This paper considers the relationship between pricing and ordering decisions for a monopolistic retailer facing a known demand function where, over the inventory cycle, the product may exhibit: i physical decay or deterioration of inventory called wastage; and ii decrease in market value called value drop associated with each unit of inventory on hand. The retailer is allowed to continuously vary the selling price of the product over the cycle. We introduce a notion of instantaneous margin, and use it to derive profit maximizing conditions for the retailer. The model explains the markdown of retail goods subject to decay. It also provides guidance in determining when price changes during the cycle are worthwhile due to product aging, how often such changes should be made, and how such changes affect ordering intervals and quantities.

Support from Parents over the Life Course: The Adult Child's Perspective

Abstract: While previous research has established that parents in the contemporary U.S. often provide support to their adult children, little is known about how that support changes as both parents and children age over the life course. Using data from the National Survey of Families and Households, we examine how support received from parents changes as the child moves from young adulthood through middle age. Attention is given to several different dimensions of support and to life-course factors of the parent and the child that are related to receipt of support. In general, there is no change or a slight increase in support receivedfrom parents when children are in their 20s. Decline in all forms of support occurs after age 30. However, the pattern of decline varies by type of support, and in no case is the decline linear. We conclude by discussing the family roles played by parents in later life. Throughout childhood and adolescence, almost all children in the U.S. look to their parents for support. By the time individuals are old, e.g., age 70, few receive assistance from their parents. (This is true, of course, because few at this stage of life have living parents.) But, what is the trajectory of the flow of support from parents to children as children age from adolescence to old age? Does parental support only exhibit patterns of decline across the child's adulthood? Or, is the pattern of change bidirectional, for example increasing when a child marries and/or has children, and then declining gradually thereafter? Furthermore, does age-variation in receipt of parental support depend primarily on the child's life situation or that of the parents? Finally, does the age pattern of support differ for various types of assistance? Such questions about age patterns of parental support after childhood have received limited research attention.

N400 to semantically anomalous pictures and words

Abstract: The N400 component of the human event-related brain potential appears to be related to violations of semantic expectancy during language comprehension. The present experiment investigated whether the N400 is related specifically to activity in a language system or is an index of a conceptual system that is accessed by both pictures and words. Sentences were visually presented one word at a time with the last word being replaced in one condition by a line drawing representing the same concept (eg, the word “socks” was replaced by a picture of socks). The N400 recorded in the Pictures Condition was found to be identical to the N400 generated by words in terms of amplitude, scalp distribution, and latency. These results suggest that the N400 is an index of activity in a conceptual memory that is accessed by both pictures and words.