Showing papers by "University of Delaware published in 1996"

Assessment and Prediction of Stress-Related Growth

Abstract: This article reports the development of the Stress-Related Growth Scale (SRGS) and its use in a study examining determinants of stress-related positive outcomes for college students. Study 1 analyses showed that the SRGS has acceptable internal and test-retest reliability and that scores are not influenced by social desirability. Study 2 analyses showed that college students' SRGS responses were significantly related to those provided by friends and relatives on their behalf. Study 3 analyses tested the determinants of stress-related growth longitudinally. Significant predictors of the SRGS were (a) intrinsic religiousness; (b) social support satisfaction; (c) stressfulness of the negative event; (d) positive reinterpretation and acceptance coping; and (e) number of recent positive life events. The SRGS was also positively related to residual change in optimism, positive affectivity, number of socially supportive others, and social support satisfaction, lending further support to the validity of this new scale. Results have implications for current theory on stress-related positive outcomes.

Microphytobenthos: The ecological role of the “secret garden” of unvegetated, shallow-water marine habitats. I. Distribution, abundance and primary production

Abstract: The microphytobenthos consists of unicellular eukaryotic algae and cyanobacteria that grow within the upper several millimeters of illuminated sediments, typically appearing only as a subtle brownish or greenish shading. The surficial layer of the sediment is a zone of intense microbial and geochemical activity and of considerable physical reworking. In many shallow ecosystems, the biomass of benthic microalgae often exceeds that of the phytoplankton in the overlying waters. Direct comparison of the abundance of benthic and suspended microalgae is complicated by the means used to measure biomass and by the vertical and horizontal distribution of the microphytobenthos in the sediment. Where biomass has been estimated as chlorophyll a, there may be negligible to large (40%) error due to interference by degradation products, except where chlorophyll is measured by high-performance liquid chromatography. The vertical distribution of microphytobenthos, aside from mat-forming species, is determined by the opposing effects of their vertical migration, which tends to concentrate them near the surface, and physical mixing by overlying currents, which tends to cause an even vertical distribution through the mixed layer of sediment. Uncertainties in vertical distribution are compounded by frequently patchy horizontal distribution. Under-sampling on small (<1 m) scales can lead to errors in the estimate that are comparable to the ranges of seasonal and geographic variation. These uncertainties are compounded by biases in the techniques used to estimate production by the microphytobenthos. In most environments studied, biomass (as chlorophyll a) and light availability appear to be the principal determinants of benthic primary production. The effect of variable light intensities on integral production can be described by a functional response curve. When normalized to the chlorophyll content of the surficial sediment, the residual variation in the data described by the functional response curve is due to changes in the chlorophyll-specific response to irradiance. Production by the benthos is often a significant fraction of production in the water column and microphytobenthos may contribute directly to water column production when they are resuspended. Thus on both the basis of biomass and biogeochemical reactivity, benthic microalgae play significant roles in system productivity and trophic dynamics, as well as such habitat characteristics as sediment stability. *** DIRECT SUPPORT *** A01BY074 00003

Foci And Bases Of Employee Commitment: Implications For Job Performance

Abstract: Previous research has found that employee commitment and job performance are largely unrelated. However, prior work has not distinguished among individual foci (targets) and bases (motives) of commitment. We found, as expected, that commitment to supervisors was positively related to performance and was more strongly associated with performance than was commitment to organizations. Further, internalization of supervisors' and organizations' values was associated with performance but identification with these foci was not.

The fate of nitrogen and phosphorus at the land-sea margin of the North Atlantic Ocean

Abstract: Five large rivers that discharge on the western North Atlantic continental shelf carry about 45% of the nitrogen (N) and 70% of the phosphorus (P) that others estimate to be the total flux of these elements from the entire North Atlantic watershed, including North, Central and South America, Europe, and Northwest Africa. We estimate that 61 · 109 moles y-1 of N and 20 · 109 moles y-1 of P from the large rivers are buried with sediments in their deltas, and that an equal amount of N and P from the large rivers is lost to the shelf through burial of river sediments that are deposited directly on the continental slope. The effective transport of active N and P from land to the shelf through the very large rivers is thus reduced to 292 · 109 moles y-1 of N and 13 · 109 moles y-1 of P.

A simple method for solving inverse scattering problems in the resonance region

Abstract: This paper is concerned with the development of an inversion scheme for two-dimensional inverse scattering problems in the resonance region which does not use nonlinear optimization methods and is relatively independent of the geometry and physical properties of the scatterer It is assumed that the far field pattern corresponding to observation angle and plane waves incident at angle is known for all From this information, the support of the scattering obstacle is obtained by solving the integral equation where k is the wavenumber and is on a rectangular grid containing the scatterer The support is found by noting that is unbounded as approaches the boundary of the scattering object from inside the scatterer Numerical examples are given showing the practicality of this method

Distributed intelligent agents

Abstract: In Retsina, the authors have developed a distributed collection of software agents that cooperate asynchronously to perform goal-directed information retrieval and integration for supporting a variety of decision-making tasks. Examples for everyday organizational decision making and financial portfolio management demonstrate its effectiveness.

Problem Solving as a Basis for Reform in Curriculum and Instruction: The Case of Mathematics

Abstract: We argue that reform in curriculum and instruction should be based on allowing students to problematize the subject. Rather than mastering skills and applying them, students should be engaged in resolving problems. In mathematics, this principle fits under the umbrella of problem solving, but our interpretation is different from many problem-solving approaches. We first note that the history of problem solving in the curriculum has been infused with a distinction between acquiring knowledge and applying it. We then propose our alternative principle by building on John Dewey’s idea of “reflective inquiry,” argue that such an approach would facilitate students’ understanding, and compare our proposal with other views on the role of problem solving in the curriculum. We close by considering several common dichotomies that take on a different meaning from this perspective

The power of problem‐based learning in teaching introductory science courses

Abstract: In its use of complex, real-world problems to introduce concepts and motivate learning in an active and cooperative learning environment, problem-based learning provides a powerful alternative to the passive lecture tradition in introductory science courses in biology, physics, and chemistry.

Size-dependent magnetic properties of MnFe 2 O 4 fine particles synthesized by coprecipitation

Abstract: Manganese ferrite, ${\mathrm{MnFe}}_{2}$${\mathrm{O}}_{4}$, fine particles in the size range 5--15 nm have been prepared by an aqueous phase coprecipitation method. The freshly prepared particles are in a metastable state with regard to the cation distribution between the A and B sites of the spinel lattice. Thermomagnetic, differential scanning calorimetry and M\"ossbauer spectroscopy show that heat treatment under inert gas to 670 K irreversibly changes the cation distribution to a stable state. Heat treatment of freshly prepared samples in air to 470 K both changes the cation site distribution somewhat and, most importantly, oxidizes the ${\mathrm{Mn}}^{2+}$ to ${\mathrm{Mn}}^{3+}$. The Curie temperature is modified in association with these changes. With this knowledge, we create a series of samples with various sizes but the same microstructure. We find the following. (1) The Curie temperature decreases relative to the bulk as size decreases. The decrease is consistent with finite size scaling. (2) The fit of the spontaneous magnetization to the Bloch ${\mathit{T}}^{3/2}$ law yields a Bloch constant larger than the bulk increasing with decreasing size in proportion to the specific surface area of the particles. We find a better fit is obtained if the exponent of the temperature is increased to be in the range 1.6 to 1.8. (3) The saturation magnetization decreases with decreasing size also in proportion to the specific surface area of the particles. \textcopyright{} 1996 The American Physical Society.

An Analysis of Arithmetic Problem Posing by Middle School Students.

Abstract: The mathematical problems generated by 509 middle school students, who were given a brief written "story-problem" description and asked to pose questions that could be answered using the information, were examined for solvability, linguistic and mathematical complexity, and relationships within the sets of posed problems. It was found that students generated a large number of solvable mathematical problems, many of which were syntactically and semantically complex, and that nearly half the students generated sets of related problems. Subjects also solved eight fairly complex problems, and the relationship between their problem-solving performance and their problem posing was examined to reveal that "good" problem solvers generated more mathematical problems and more complex problems than "poor" problem solvers did. The multiple-step data analysis scheme developed and used herein should be useful to teachers and other researchers interested in evaluating students' posing of arithmetic story problems.

Atmospheric deposition of nutrients to the North Atlantic Basin.

Abstract: Atmospheric chemical models are used to estimate the deposition rate of various inorganic oxides of nitrogen (NOy), reduced nitrogen species (NHx) and mineral dust to the North Atlantic Ocean (NAO). The estimated deposition of NOy to the NAO (excluding the coastal ocean) and the Caribbean is 360 × 109 Moles-N m-2 yr-1 (5.0 Tg N); this is equivalent to about 13% of the estimated global emission rate (natural and anthropogenic) and a quarter of the emission rate from sources in North America and Europe. In the case of NHx, 258 Moles-N m-2 yr-1 (3.6 Tg N) are deposited to the NAO and the Caribbean; this is about 6% of the global continental emissions. There is relatively little data on the deposition rate of organic nitrogen species; nonetheless, this evidence suggests that concentrations and deposition rates are comparable to those for inorganic nitrogen.

Customer Perceptions of Corporate Responses to Product Complaints: The Role of Explanations

Abstract: Using the justice and impression management literatures as a guide, we examined company responses to customer complaints in a field study. Explanations in which a company accepted responsibility fo...

A dynamic model of photoadaptation in phytoplankton

Abstract: We present a new dynamic model that uses a small number of prescribed parameters to predict the chlorophyll a:carbon ratio and growth rate of phytoplankton in both constant and varying irradiance. The model provides a self-contained description of energy and mass fluxes and regulation of partitioning of photosynthate during phytoplankton adaptation to irradiance. The kinetics and steady-state outcomes of photoadaptation are described in terms of changes in the rates of synthesis of three intracellular carbon pools. These pools account for the distribution of cell material between light-harvesting components, the biosynthetic apparatus, and energy storage compounds. Regulation of the flow of recent photosynthate to these pools is controlled by the ratio of realized to potential photosynthetic electron flow at a given instant. The responses of growth rate and Chl a:C to static and dynamic irradiance regimes can be adequately described by specifying four parameters: the initial slope of the photosynthesis-irradiance curve, the maximum growth rate, the maximum Chl a:C observed under light limitation, and the maintenance metabolic rate. The model predictions compared favorably with observations of the diatoms Thalassiosira pseudonana and Phaedactylum tricornutum.

Microphytobenthos : The ecological role of the "Secret Garden" of unvegetated, shallow-water marine habitats. II. Role in sediment stability and shallow-water food webs

Abstract: The microphytobenthos form an important component of all shallow-water ecosystems where enough light reaches the sediment surface to support appreciable primary production. Although less conspicuous than macroalgae or vascular plants, the microphytobenthos can contribute significantly to primary production and can modify habitat characteristics. The microphytobenthos alter sediment properties (e.g., erodibility) both directly, in the extreme forming a mat or scum on the sediment surface, and indirectly by modifying the activities of benthic infauna (e.g., pelletization, burrowing, tube building, and sediment tracking). Carbon dioxide fixed by the microphytobenthos supports higher, grazing trophic levels. These include deposit-feeding and suspension-feeding macrofauna as well as meiofauna and microfauna. Quantitative relations between the feeding and growth rates of macrofauna and the abundance of microphytobenthos and suspended organic matter (i.e., functional responses) are reviewed. Given the current state of knowledge of the direct and indirect interactions involving trophic dynamics, sediment properties, and benthic microalgae, we argue for reductionist studies of particular interactions as distinct entities. This is a prerequisite for the emergence of a comprehensive picture of unvegetated ecosystems and the ability to predict their responses to man’s activities. *** DIRECT SUPPORT *** A01BY074 00005

Photonic band structure of fcc colloidal crystals.

Abstract: Polystyrene colloidal crystals form three dimensional periodic dielectric structures which can be used for photonic band structure measurements in the visible regime. From transmission measurements the photonic band structure of an fcc crystal has been obtained along the directions between the $L$ point and the $W$ point. Kossel line patterns were used for locating the symmetry points of the lattice for exact positioning and orientation of the crystals. In addition, these patterns reveal the underlying photonic band structure of the crystals in a qualitative way.

A high-silica zeolite with a 14-tetrahedral-atom pore opening

Abstract: Zeolites (microporous aluminosilicates) and related molecular sieves have found wide application as catalysts, sorbents and ion-exchange materials. New zeolites with large pores are much in demand, and have been sought for several decades. All known zeolites, both natural and synthetic, contain pores comprised of 12 or fewer tetrahedrally coordinated silicon or aluminium atoms (T-atoms), but several microporous aluminophosphates with wider pores are now known. The practical value of these large-pore phosphate-based materials is limited, however, by their poor thermal and hydrothermal stability. Here we report the synthesis of a high-silica zeolite with pores comprised of 14 T-atoms. Preliminary data indicate that this thermally stable large-pore material exhibits the kind of strong acidity that makes other zeolites useful catalysts.

Attachment processes in eating disorder and depression.

Abstract: This study examines the relationship between attachment strategies and symptom reporting among college women. Sixty-one college women were selected who reported high or low levels of depressive and eating disorder symptoms. The Adult Attachment Interview (AAI) was administered, and interview transcripts were rated with the Attachment Interview Q-Sort. The results indicated that women with hyperactivating AAI strategies were prone to reporting elevated levels of depressive symptoms, whereas women with deactivating strategies were prone to reporting elevated levels of eating-disorder symptoms, when depression was statistically controlled. These findings support the hypothesis that secondary or defensive attachment strategies predispose individuals toward different forms of symptom expression.

Recovery of blocky images from noisy and blurred data

Abstract: The purpose of this investigation is to understand situations under which an enhancement method succeeds in recovering an image from data which are noisy and blurred. The method in question is due to Rudin and Osher. The method selects, from a class of feasible images, one that has the least total variation.Our investigation is limited to images which have small total variation. We call such images “blocky” as they are commonly piecewise constant (or nearly so) in grey-level values. The image enhancement is applied to three types of problems, each one leading to an optimization problem. The optimization problems are analyzed in order to understand the conditions under which they can be expected to succeed in reconstructing the desired blocky images. We illustrate the main findings of our work in numerical examples.

Flavodoxin as an in situ marker for iron stress in phytoplankton

Abstract: A fundamental issue in marine science is the identification of the factors controlling biological uptake of CO2, in high-nitrate, low-chlorophyll regions. A recent in situ iron fertilization experiment demonstrated that iron limitation is responsible for low phytoplankton stocks in the equatorial Pacific4. Here we show that flavodoxin, a biochemical marker of iron limitation, can be used to map the degree of iron stress in natural populations. Flavodoxin assays along a 900-km east-west transect in the northeastern subarctic Pacific revealed a pronounced increase in iron stress in the region west of the 135° W meridian. Addition of dissolved iron alleviated this stress. Immunostaining of single cells from the most western station showed that flavodoxin is present specifically within the chloroplasts of diatoms. Our approach provides a rapid means of defining the extent of iron stress in the ocean5 and supports the hypothesis that diatoms are iron stressed in the northeast Pacific.

Active cycling of organic carbon in the central Arctic Ocean

Abstract: THE notion of a barren central Arctic Ocean has been accepted since English's pioneering work1 on drifting ice-islands. The year-round presence of ice, a short photosynthetic season and low temperatures were thought to severely limit biological production1,2, although the paucity of data was often noted. Because primary production appeared to be low1,2, subsequent studies assumed that most organic carbon was either derived from river inputs or imported from adjacent continental-shelf regions3,4. Here we present shipboard measurements of biological produc-tion, biomass and organic carbon standing-stocks made during a cruise through the ice covering the central Arctic Ocean. Our results indicate that the central Arctic region is not a biological desert. Although it is less productive than oligotrophic ocean regions not covered by ice, it supports an active biological community which contributes to the cycling of organic carbon through dissolved and particulate pools.

Origin of Entropy Convergence in Hydrophobic Hydration and Protein Folding.

Abstract: An information theory model is used to construct a molecular explanation why hydrophobic solvation entropies measured in calorimetry of protein unfolding converge at a common temperature. The entropy convergence follows from the weak temperature dependence of occupancy fluctuations for molecular-scale volumes in water. The macroscopic expression of the contrasting entropic behavior between water and common organic solvents is the relative temperature insensitivity of the water isothermal compressibility. The information theory model provides a quantitative description of small molecule hydration and predicts a negative entropy at convergence. Interpretations of entropic contributions to protein folding should account for this result.

An underground route for the water cycle

Abstract: Water flows from the land to the sea in rivers - that is the classroom picture that seems too self–evident to question. But there is evidence that a comparable amount may flow underground directly into coastal waters.

Atmospheric neutrino flux above 1 GeV

Abstract: In this paper we extend an earlier calculation of the flux of atmospheric neutrinos to higher energy. The earlier calculation of the neutrino flux below 3 GeV has been used for calculation of the rate of contained neutrino interactions in deep underground detectors. The fluxes are needed up to neutrino energies of 10 TeV to calculate the expected rate of neutrino-induced muons passing into and through large, deep detectors. We compare our results with several other calculations, and we evaluate the uncertainty in the rate of neutrino-induced muons due to uncertainties in the neutrino flux. \textcopyright{} 1996 The American Physical Society.