Showing papers by "University of Delaware published in 2001"

Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

Abstract: Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

Affective commitment to the organization: the contribution of perceived organizational support.

Abstract: Three studies examined the interrelationships among work experiences, perceived organizational support (POS), affective commitment (AC), and employee turnover. Using a diverse sample of 367 employees drawn from a variety of organizations, Study 1 found that POS mediated positive associations of organizational rewards, procedural justice, and supervisor support with AC. Study 2 examined changes of POS and AC in retail employees over a 2-year span (N = 333) and a 3-year span (N = 226). POS was positively related to temporal changes in AC, suggesting that POS leads to AC. Study 3 found a negative relationship between POS and subsequent voluntary employee turnover that was mediated by AC in retail employees (N = 1,124) and in poultry- and feed-processing workers (N = 262). These results suggest that favorable work conditions operate via POS to increase AC, which, in turn, decreases employee withdrawal behavior.

Catalysis Research of Relevance to Carbon Management: Progress, Challenges, and Opportunities

Abstract: There is increased recognition by the world’s scientific, industrial, and political communities that the concentrations of greenhouse gases in the earth’s atmosphere, particularly CO_2, are increasing. For example, recent studies of Antarctic ice cores to depths of over 3600 m, spanning over 420 000 years, indicate an 80 ppm increase in atmospheric CO_2 in the past 200 years (with most of this increase occurring in the past 50 years) compared to the previous 80 ppm increase that required 10 000 years.2 The 160 nation Framework Convention for Climate Change (FCCC) in Kyoto focused world attention on possible links between CO2 and future climate change and active discussion of these issues continues.3 In the United States, the PCAST report4 “Federal Energy Research and Development for the Challenges of the Twenty First Century” focused attention on the growing worldwide demand for energy and the need to move away from current fossil fuel utilization. According to the U.S. DOE Energy Information Administration,5 carbon emission from the transportation (air, ground, sea), industrial (heavy manufacturing, agriculture, construction, mining, chemicals, petroleum), buildings (internal heating, cooling, lighting), and electrical (power generation) sectors of the World economy amounted to ca. 1823 million metric tons (MMT) in 1990, with an estimated increase to 2466 MMT in 2008-2012 (Table 1).

Biotic ligand model of the acute toxicity of metals. 1. Technical Basis

Abstract: The biotic ligand model (BLM) of acute metal toxicity to aquatic organisms is based on the idea that mortality occurs when the metal-biotic ligand complex reaches a critical concentration. For fish, the biotic ligand is either known or suspected to be the sodium or calcium channel proteins in the gill surface that regulate the ionic composition of the blood. For other organisms, it is hypothesized that a biotic ligand exists and that mortality can be modeled in a similar way. The biotic ligand interacts with the metal cations in solution. The amount of metal that binds is determined by a competition for metal ions between the biotic ligand and the other aqueous ligands, particularly dissolved organic matter (DOM), and the competition for the biotic ligand between the toxic metal ion and the other metal cations in solution, for example, calcium. The model is a generalization of the free ion activity model that relates toxicity to the concentration of the divalent metal cation. The difference is the presence of competitive binding at the biotic ligand, which models the protective effects of other metal cations, and the direct influence of pH. The model is implemented using the Windermere humic aqueous model (WHAM) model of metal-DOM complexation. It is applied to copper and silver using gill complexation constants reported by R. Playle and coworkers. Initial application is made to the fathead minnow data set reported by R. Erickson and a water effects ratio data set by J. Diamond. The use of the BLM for determining total maximum daily loadings (TMDLs) and for regional risk assessments is discussed within a probabilistic framework. At first glance, it appears that a large amount of data are required for a successful application. However, the use of lognormal probability distributions reduces the required data to a manageable amount.

In silico predictions of Escherichia coli metabolic capabilities are consistent with experimental data

Abstract: A significant goal in the post-genome era is to relate the annotated genome sequence to the physiological functions of a cell. Working from the annotated genome sequence, as well as biochemical and physiological information, it is possible to reconstruct complete metabolic networks. Furthermore, computational methods have been developed to interpret and predict the optimal performance of a metabolic network under a range of growth conditions. We have tested the hypothesis that Escherichia coli uses its metabolism to grow at a maximal rate using the E. coli MG1655 metabolic reconstruction. Based on this hypothesis, we formulated experiments that describe the quantitative relationship between a primary carbon source (acetate or succinate) uptake rate, oxygen uptake rate, and maximal cellular growth rate. We found that the experimental data were consistent with the stated hypothesis, namely that the E. coli metabolic network is optimized to maximize growth under the experimental conditions considered. This study thus demonstrates how the combination of in silico and experimental biology can be used to obtain a quantitative genotype-phenotype relationship for metabolism in bacterial cells.

Effects of age on validity of self-reported height, weight, and body mass index: findings from the Third National Health and Nutrition Examination Survey, 1988-1994.

Abstract: Objective To compare self-reported to measured heights and weights of adults examined in the Third National Health and Nutrition Examination Survey (NHANES III), and to determine to what extent body mass index (BMI) calculated from self-reported heights and weights affects estimates of overweight prevalence compared with BMI calculated from measured values. Design A complex sample design was used in NHANES III to obtain a nationally representative sample of the US civilian, noninstitutionalized population. During household interviews, survey respondents were asked their height and weight. Trained health technicians subsequently measured height and weight using standardized procedures and equipment. Subjects The analytical sample consisted of 7,772 men and 8,801 women 20 years old and older. Statistical analyses performed Only persons with measured and self-reported heights and weights were included in the analysis, and statistical sampling weights were applied, t Tests, Pearson product moment correlation coefficients, sensitivity, and specificity analyses were used to determine the validity of self-reported measurements and prevalence estimates of overweight, defined as BMI of 25 or greater. Results Age is an important factor in classifying weight, height, BMI, and overweight from self-reports. Statistically significant differences were found for the mean error (measured-self-reported values) for height and BMI that were notably larger for older age groups. For example, the mean error for height ranged from 2.92 to 4.50 cm for women and from 3.06 to 4.29 cm for men, 70 years and older. Despite the high correlation between measured and self-reported data, the prevalence of overweight calculated from measured values was higher than that calculated from self-reported values among older adults. When calculated with self-reported height, BMI was one unit lower than when calculated from measured height for persons >70 years. Specificity was high but sensitivity decreased with increasing age cohorts. Regression equations are provided to determine actual height from self-reported values for older adults. Conclusion/Applications Self-reported heights and weights can be used with younger adults, but they have limitations for older adults, ages >60 years. In research studies and in clinical settings involving older adults, failure to measure height and weight can result in subsequent misclassification of overweight status. Therefore, registered dietitians are encouraged to obtained a measured weight and height using a calibrated scale and stadiometer. J Am DietAssoc. 2001;101:28-34 .

An empirical investigation of the relationship between change in corporate social performance and financial performance: A stakeholder theory perspective

Abstract: Stakeholder theory provides a framework for investigating the relationship between corporate social performance (CSP) and corporate financial performance. This relationship is investigated by examining how change in CSP is related to change in financial accounting measures. The findings provide some support for a tenet in stakeholder theory which asserts that the dominant stakeholder group, shareholders, financially benefit when management meets the demands of multiple stakeholders. Specifically, change in CSP was positively associated with growth in sales for the current and subsequent year. This indicates that there are short-term benefits from improving CSP. Return on sales was significantly positively related to change in CSP for the third financial period, indicating that long-term financial benefits may exist when CSP is improved.

Emotion Knowledge as a Predictor of Social Behavior and Academic Competence in Children at Risk

Abstract: Following leads from differential emotions theory and empirical research, we evaluated an index of emotion knowledge as a long-term predictor of positive and negative social behavior and academic competence in a sample of children from economically disadvantaged families (N = 72). The index of emotion knowledge represents the child's ability to recognize and label emotion expressions. We administered control and predictor measures when the children were 5 years old and obtained criterion data at age 9. After controlling for verbal ability and temperament, our index of emotion knowledge predicted aggregate indices of positive and negative social behavior and academic competence. Path analysis showed that emotion knowledge mediated the effect of verbal ability on academic competence. We argue that the ability to detect and label emotion cues facilitates positive social interactions and that a deficit in this ability contributes to behavioral and learning problems. Our findings have implications for primary ...

Biotic ligand model of the acute toxicity of metals. 2. Application to acute copper toxicity in freshwater fish and Daphnia.

Abstract: The biotic ligand model (BLM) was developed to explain and predict the effects of water chemistry on the acute toxicity of metals to aquatic organisms. The biotic ligand is defined as a specific receptor within an organism where metal complexation leads to acute toxicity. The BLM is designed to predict metal interactions at the biotic ligand within the context of aqueous metal speciation and competitive binding of protective cations such as calcium. Toxicity is defined as accumulation of metal at the biotic ligand at or above a critical threshold concentration. This modeling framework provides mechanistic explanations for the observed effects of aqueous ligands, such as natural organic matter, and water hardness on metal toxicity. In this paper, the development of a copper version of the BLM is described. The calibrated model is then used to calculate LC50 (the lethal concentration for 50% of test organisms) and is evaluated by comparison with published toxicity data sets for freshwater fish (fathead minnow, Pimephales promelas) and Daphnia.

ATR-FTIR Spectroscopic Investigation on Phosphate Adsorption Mechanisms at the Ferrihydrite-Water Interface

Abstract: We investigated the phosphate(P) adsorption mechanisms at the ferrihydrite–water interface as a function of pH, ionic strength (I), and loading level, using a combination of adsorption envelopes, electrophoretic mobility (EM) measurements, and attenuated total reflectance Fourier transform infrared (ATR–FTIR) spectroscopy. The P adsorption envelopes show that: (1) adsorption decreases with increasing pH 3.5–9.5 and (2) adsorption is insensitive to changes in I at pH 4–7.5, but it slightly increases with increasing I from 0.01 to 0.8 at pH>7.5. The EM in 0.1 M NaCl decreases with increasing P concentration from 0 to 50 μmol L−1 at pH 3–9. The results of these macroscopic studies suggest the formation of inner-sphere complexes. The ATR–FTIR investigation shows that inner-sphere surface complexes are nonprotonated, bidentate binuclear species (≡Fe2PO4) at pH≥7.5 and could be associated with Na+ ions at P loading levels of 0.38 μmol m−2. At pH 4–6, protonated inner- sphere complexes are proposed at the loading levels between 0.38 and 2.69 μmol m−2.

Sensor information networking architecture and applications

Abstract: This article introduces a sensor information networking architecture, called SINA, that facilitates querying, monitoring, and tasking of sensor networks. SINA serves the role of middleware that abstracts a network of sensor nodes as a collection of massively distributed objects. SINA's execution environment provides a set of configuration and communication primitives that enable scalable and energy-efficient organization of and interactions among sensor objects. On top the execution environment is a programmable substrate that provides mechanisms to create associations and coordinate activities among sensor nodes. Users then access information within a sensor network using declarative queries, or perform tasks using programming script.

A Comparison of Mail, Fax and Web-Based Survey Methods:

Abstract: This study compares mail, fax and web-based surveys in a university setting for response speed, response rate and costs. The survey was distributed to 300 hospitality professors randomly chosen fro...

Development and application of triglyceride‐based polymers and composites

Abstract: Triglyceride oils derived from plants have been used to synthesize several different monomers for use in structural applications. These monomers have been found to form polymers with a wide range of physical properties. They exhibit tensile moduli in the 1–2 GPa range and glass transition temperatures in the range 70–120 °C, depending on the particular monomer and the resin composition. Composite materials were manufactured utilizing these resins and produced a variety of durable and strong materials. At low glass fiber content (35 wt %), composites produced from acrylated epoxidized soybean oil by resin transfer molding displayed a tensile modulus of 5.2 GPa, a flexural modulus of 9 GPa, a tensile strength of 129 MPa, and flexural strength of 206 MPa. At higher fiber contents (50 wt %) composites produced from acrylated epoxidized soybean oil displayed tensile and compression moduli of 24.8 GPa each, and tensile and compressive strengths of 463.2 and 302.6 MPa, respectively. In addition to glass fibers, natural fibers such as flax and hemp were used. Hemp composites of 20% fiber content displayed a tensile strength of 35 MPa and a tensile modulus of 4.4 GPa. The flexural modulus was ∼2.6 GPa and the flexural strength was in the range 35.7–51.3 MPa, depending on the test conditions. The flax composite materials had tensile and flexural strengths in the ranges 20–30 and 45–65 MPa, respectively. The properties exhibited by both the natural- and synthetic fiber-reinforced composites can be combined through the production of “hybrid” composites. These materials combine the low cost of natural fibers with the high performance of synthetic fibers. Their properties lie between those displayed by the all-glass and all-natural composites. Characterization of the polymer properties also presents opportunities for improvement through genetic engineering technology. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 703–723, 2001

Phosphorus limitation of nitrogen fixation by Trichodesmium in the central Atlantic Ocean

Abstract: Marine fixation of atmospheric nitrogen is believed to be an important source of biologically useful nitrogen to ocean surface waters1, stimulating productivity of phytoplankton and so influencing the global carbon cycle2. The majority of nitrogen fixation in tropical waters is carried out by the marine cyanobacterium Trichodesmium3, which supplies more than half of the new nitrogen used for primary production4. Although the factors controlling marine nitrogen fixation remain poorly understood, it has been thought that nitrogen fixation is limited by iron availability in the ocean2,5. This was inferred from the high iron requirement estimated for growth of nitrogen fixing organisms6 and the higher apparent densities of Trichodesmium where aeolian iron inputs are plentiful7. Here we report that nitrogen fixation rates in the central Atlantic appear to be independent of both dissolved iron levels in sea water and iron content in Trichodesmium colonies. Nitrogen fixation was, instead, highly correlated to the phosphorus content of Trichodesmium and was enhanced at higher irradiance. Furthermore, our calculations suggest that the structural iron requirement for the growth of nitrogen-fixing organisms is much lower than previously calculated6. Although iron deficiency could still potentially limit growth of nitrogen-fixing organisms in regions of low iron availability—for example, in the subtropical North Pacific Ocean—our observations suggest that marine nitrogen fixation is not solely regulated by iron supply.

How employees respond to personal offense: the effects of blame attribution, victim status, and offender status on revenge and reconciliation in the workplace

Abstract: This study investigated the relationships between blame, victim and offender status, and the pursuit of revenge or reconciliation after a personal offense. Results from a sample of 141 government agency employees showed that blame is positively related to revenge and negatively related to reconciliation. In addition, victim-offender relative status moderated the relation between blame and revenge such that victims who blamed sought revenge more often when the offender's status was lower than their own. The victims' own absolute hierarchical status also moderated this relation such that lower, not higher, status employees who blamed sought revenge more often.

Dielectrophoretic assembly of electrically functional microwires from nanoparticle suspensions.

Abstract: A new class of microwires can be assembled by dielectrophoresis from suspensions of metallic nanoparticles. The wires are formed in the gaps between planar electrodes and can grow faster than 50 micrometers per second to lengths exceeding 5 millimeters. They have good ohmic conductance and automatically form electrical connections to conductive islands or particles. The thickness and the fractal dimension of the wires can be controlled, and composite wires with a metallic core surrounded by a latex shell can be assembled. The simple assembly process and their high surface-to-volume ratio make these structures promising for wet electronic and bioelectronic circuits.

Coastal Processes with Engineering Applications

Abstract: Part I. Introduction to Coastal Processes: 1. Overview 2. Sediment characteristics 3. Long-term processes Part II. Hydrodynamics of the Coastal Zone: 4. Tides and storm surges 5. Waves and wave-induced hydrodynamics Part III. Coastal Response: 6. Field measurement techniques and analysis 7. Equilibrium beach profiles 8. Sediment transport 9. Miscellaneous coastal features 10. Modeling of beaches and shorelines Part IV. Shoreline Modification and Analysis: 11. Beach fill and soft engineering structures 12. Hard engineering structures 13. Tidal inlets 14. Shoreline management.

Glyphosate-resistant horseweed from Delaware

Abstract: No-tillage corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production has been widely accepted in the mid-Atlantic region, favoring establishment of horseweed [Conyza canadensis (L.) Cronq.]. Within 3 yr of using only glyphosate for weed control in continuous glyphosate-resistant soybeans, glyphosate failed to control horseweed in some fields. Seedlings originating from seed of one population collected in Delaware were grown in the greenhouse and exhibited 8- to 13-fold glyphosate resistance compared with a susceptible population. There were no differences between the isopropylamine or diammonium salts of glyphosate. Nomenclature: Corn; Zea mays L.; horseweed; Conyza canadensis (L.) Cronq. ERICA; soybean; Glycine max (L.) Merr.; glyphosate.

Attachment for Infants in Foster Care: The Role of Caregiver State of Mind

Abstract: The concordance between foster mothers' attachment state of mind and foster infants' attachment quality was examined for 50 foster mother-infant dyads. Babies had been placed into the care of their foster mothers between birth and 20 months of age. Attachment quality was assessed between 12 and 24 months of age, at least 3 months after the infants' placement into foster care. The two-way correspondence between maternal state of mind and infant attachment quality was 72%, kappa = .43, similar to the level seen among biologically intact mother-infant dyads. Contrary to expectations, age at placement was not related to attachment quality. Rather, concordance between maternal state of mind and infant attachment was seen for relatively late-placed babies, as well as early placed babies. These findings have two major implications. First, following a disruption in care during the first year and a half of life, babies appear capable of organizing their behavior around the availability of new caregivers. Second, these data argue for a nongenetic mechanism for the intergenerational transmission of attachment.

Highly Viscoelastic Wormlike Micellar Solutions Formed by Cationic Surfactants with Long Unsaturated Tails

Abstract: Cationic surfactants having long (C22) mono-unsaturated tails were studied in aqueous solutions containing salt using steady and dynamic rheology. The surfactant erucyl bis(hydroxyethyl)methylammonium chloride self-assembles into giant wormlike micelles, giving rise to unusually strong viscoelasticity. Under ambient conditions, the viscosity enhancement due to surfactant exceeds a factor of 107. Some samples behave as gel-like solids at low temperatures and revert to the viscoelastic (Maxwellian) response only at higher temperatures. These samples display appreciable viscosities (>10 Pa·s) up to very high temperatures (ca. 90 °C). Salts with counterions that penetrate into the hydrophobic interior of the micelles, such as sodium salicylate, are much more efficient at promoting self-assembly than salts with nonbinding counterions, such as sodium chloride. Changing the surfactant headgroup to the more conventional trimethylammonium group reduces the viscosity at high temperatures.

Compression of correlated binary sources using turbo codes

Abstract: We propose the use of punctured turbo codes for compression of correlated binary sources. Compression is achieved because of puncturing. The resulting performance is close to the theoretical limit provided by the Slepian-Wolf (1973) theorem. No information about the correlation between sources is required in the encoding process. The proposed source decoder utilizes iterative schemes, and performs well even when the correlation between the sources is not known in the decoder, since it can be estimated jointly with the iterative decoding process.

Neutrinos from propagation of ultrahigh energy protons

Abstract: We present a calculation of the production of neutrinos during propagation of ultrahigh energy cosmic rays, as may be produced in astrophysical sources. Photoproduction interactions are modeled with the event generator SOPHIA that represents very well the experimentally measured particle production cross sections at accelerator energies. We give the fluxes expected from different assumptions on cosmic ray source distributions, cosmic ray injection spectra, cosmological evolution of the sources and different cosmologies, and compare them to the Waxman-Bahcall limit on source neutrinos. We estimate rates for detection of neutrino induced showers in a ${\mathrm{km}}^{3}$ water detector. The ratio of the local high energy neutrino flux to the ultrahigh energy cosmic ray flux is a crucial parameter in distinguishing between astrophysical and cosmological (top-down) scenarios of the ultrahigh energy cosmic ray origin.

Dynamic stability in the anterior cruciate ligament deficient knee.

Abstract: Some individuals can stabilize their knees following anterior cruciate ligament rupture even during activities involving cutting and pivoting (copers), others have instability with daily activities (non-copers). Movement and muscle activation patterns of 11 copers, ten non-copers and ten uninjured subjects were studied during walking and jogging. Results indicate that distinct gait adaptations appeared primarily in the non-copers. Copers used joint ranges of motion, moments and muscle activation patterns similar to uninjured subjects. Non-copers reduced their knee motion, and external knee flexion moments that correlated well with quadriceps strength. Non-copers also achieved peak hamstring activity later in the weight acceptance phase and used a strategy involving more generalized co-contraction. Both copers and non-copers had high levels of quadriceps femoris muscle activity. The reduced knee moment in the involved limbs of the non-copers did not represent "quadriceps avoidance" but rather represented a strategy of general co-contraction with a greater relative contribution from the hamstring muscles.

Variability signatures distinguish verbal from nonverbal counting for both large and small numbers.

Abstract: Humans appear to share with animals a nonverbal counting process. In a nonverbal counting condition, subjects pressed a key a numeral-specified number of times, while saying “the” at every press. The mean number of presses increased as a power function of the target number, with a constant coefficient of variation (c.v.), both within and beyond the proposed subitizing range (1–4 or 5), suggesting small numbers are represented on the same continuum as larger numbers and subject to the same noise process (scalar variability). By contrast, when subjects counted their presses out loud as fast as they could, the c.v. decreased as the inverse square root of the target value (binomial variability instead of scalar variability). The unexpected power-law relation between target value and mean number of presses in nonverbal counting suggests a new hypothesis about the development of the function relating number symbols to mental magnitudes.