Showing papers by "University of Arkansas published in 2001"

Formation of high-quality CdTe, CdSe, and CdS nanocrystals using CdO as precursor.

Abstract: High-quality colloidal semiconductor nanocrystals are nanometer-sized, single crystalline fragments of the corresponding bulk crystals, which have well-controlled size and size distribution and are dispersible in desired solvents/media. Recently, semiconductor nanocrystals are of great interest for both fundamental research and technical applications, 1-8 due to their strong size dependent properties and excellent chemical processibility. Synthesis of highquality semiconductor nanocrystals has been playing a critical role in this very active field. 1,9-15 As the most developed system in terms of synthesis, 1,9,10,15high-quality CdSe nanocrystals with nearly monodisperse size and shape are in active industrial development for biological labeling reagents. 5,6 Since Murray et al. 15 reported the synthesis of high quality cadmium chalcogenides nanocrystals using dimethyl cadmium (Cd(CH 3)2) as the cadmium precursor, the synthesis of CdSe nanocrystals using this precursor has been well developed. 1,9,10In comparison, the synthesis of CdTe and CdS15,16are not as advanced. For instance, there is no method to controllably vary the shape of CdTe and CdS nanocrystals. Cd(CH3)2 is extremely toxic, pyrophoric, expensive, unstable at room temperature, and explosive at elevated temperatures by releasing large amount of gas. Due to these reasons, the Cd(CH 3)2related schemes require very restricted equipments and conditions and are not suited for large-scale synthesis. In this paper, we will prove that Cd(CH3)2 can be replaced by CdO. Surprisingly, this new synthetic scheme works significantly better than the Cd(CH3)2-related ones. Without any size-sorting, the quality of quantum-confined dots and rods (quantum dots and quantum rods) of all cadmium chalcognides formed by the new method is comparable to that of the best CdSe nanocrystals reported in the literature. The new scheme is reproducible and simple and thus can be readily scaled up for industrial production. Recently, we identified that Cd(CH 3)2 decomposes in hot trioctylphosphine oxide (TOPO) and generates insoluble metallic precipitate. 9 With a strong ligand, either hexylphosphonic acid (HPA) or tetradecylphosphonic acid (TDPA), Cd(CH 3)2 is immediately converted into cadmium HPA/TDPA complex (Cd HPA/Cd-TDPA) if the cadmium to HPA/TDPA ratio is lower than 1. After the formation of the complex, an injection of Se dissolved in tributylphosphine (TBP) generates high-quality CdSe nanocrystals. This result implies that Cd(CH 3)2 may not be necessary, if we can generate the complex by other means. We first synthesized and purified Cd -HPA from CdCl 2 or Cd(CH3)2. High-quality CdSe nanocrystals were indeed yielded from this complex. This success encouraged us to develop a one-pot synthesis which does not require separated preparation of cadmium complex. We failed to make high-quality CdSe nanocrystals using CdCl2 by the one-pot approach although CdCl 2 can be dissolved in the reaction mixture at elevated temperatures. In contrast, CdO works very well for the one-pot approach. We think this is due to the low stability of CdO relative to phosphonic acids, compared to that of CdCl 2. Experimentally, CdO, TOPO, and HPA/TDPA were loaded in a three-neck flask. At about 300 °C, reddish CdO powder was dissolved and generated a colorless homogeneous solution. Introducing tellurium, selenium, and sulfur stock solutions yields high quality nanocrystals. 17 The samples for all of the measurements shown in this paper are directly from synthesis without any size separation. The growth kinetics of nanocrystals grown by the new approach possesses a pattern similar to that of the best CdSe nanocrystals formed by the Cd(CH3)2 approach (Figure 1). 10 Figure 1 and Figure 2 further reveal that the size of all three kinds of nanocrystals can be close to monodisperse, represented by the sharp absorption peaks if the growth stops in the “focusing of size distribution” regime. 10 Transmission electron microscopy (TEM) measurements indicate that these nanocrystals have very narrow distribution. The relative standard deviation of the size of the nanocrystals shown in Figure 3 (top) is about 10%. The high crystallinity of these wurtzite nanocrystals was confirmed by X-ray powder diffraction. For this CdO approach, the size of relatively monodisperse CdSe nanocrystals can be continuously tuned down to the sizes with the first absorption peak at 440 nm (see the first absorption spectrum in Figure 1). Relatively monodisperse CdSe nanocrystals with the first exciton absorption peak below 480 nm are difficult to synthesize directly with the existing Cd(CH 3)2-related approach. 10,18 (1) Peng, X. G.; Manna, L.; Yang, W. D.; Wickham, J.; Scher, E.; Kadavanich, A.; Alivisatos, A. P. Nature2000, 404, 59-61. (2) Heath, J. R. (editor). Acc.f Chem. Res. 1999. (3) Alivisatos, A. P.Science1996, 271, 933-937. (4) Huynh, W.; Peng, X.; Alivisatos, A. P. AdV. Mater. 1999, 11, 923927. (5) Bruchez, M.; Moronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P. Science 1998, 281, 2013-2016. (6) Chan, W. C. W.; Nie, S. M. Science1998, 281, 2016-2018. (7) Schlamp, M. C.; Peng, X. G.; Alivisatos, A. P. J. Appl. Phys.1997, 82, 5837-5842. (8) Mattoussi, H.; Radzilowski, L. H.; Dabbousi, B. O.; Thomas, E. L.; Bawendi, M. G.; Rubner, M. F. J. Appl. Phys.1998, 83, 7965-7974. (9) Peng, Z. A.; Peng, X. G. J. Am. Chem. Soc. , in revision. (10) Peng, X. G.; Wickham, J.; Alivisatos, A. P. J. Am. Chem. Soc. 1998, 120, 5343-5344. (11) Murray, C. B.; Norris, D. J.; Bawendi, M. G. J Am. Chem. Soc. 1993, 115, 8706-8715. (12) Nozik, A. J.; Micic, O. I.MRS Bull.1998, 23, 24-30. (13) Peng, X. G.; Schlamp, M. C.; Kadavanich, A. V.; Alivisatos, A. P. J. Am. Chem. Soc. 1997, 119, 7019-7029. (14) Dabbousi, B. O.; RodriguezViejo, J.; Mikulec, F. V.; Heine, J. R.; Mattoussi, H.; Ober, R.; Jensen, K. F.; Bawendi, M. G. J. Phys. Chem. B 1997, 101, 9463-9475. (15) Vossmeyer, T.; Katsikas, L.; Giersig, M.; Popovic, I. G.; Diesner, K.; Chemseddine, A.; Eychmuller, A.; Weller, H. J. Phys. Chem. 1994, 98, 76657673. (16) Mikulee, F.; Ph.D. Thesis, MIT, Boston, 1998. (17) A typical synthesis for CdTe nanocrystals: 0.0514 g of CdO, 0.2232 g of TDPA and 3.7768 g of TOPO were loaded into a 25 mL flask. The mixture was heated to 300 -320 °C under Ar flow, and CdO was dissolved in TDPA and TOPO. The temperature of the solution was cooled to 270 °C, tellurium stock solution (0.0664 g of tellurium powder dissolved i n 2 g of TOP) was injected. After injection, nanocrystals grew at 250 °C to reach desired size. (18) Bawendi, M. G. Private communication. Figure 1. Temporal evolution of size and size distribution of CdTe, CdSe, and CdS nanocrystals studied by UV -vis. 183 J. Am. Chem. Soc. 2001,123,183-184

Mechanisms of the Shape Evolution of CdSe Nanocrystals

Abstract: The temporal shape evolution of CdSe quantum confined nanorods (quantum rods) in nonaqueous solvents with organometallic precursors was studied quantitatively and systematically. The experimental results revealed three distinguishable stages in the shape evolution. At high monomer concentrations, nanocrystals grow exclusively along the c-axis of the wurtzite structure, making this axis the long axis of the rods. At intermediate concentrations, nanocrystals grow simultaneously in three dimensions. At low monomer concentrations, the aspect ratio decreases in a process controlled by intraparticle diffusion on the surface of the nanocrystals. This intraparticle ripening stage is different from normal Ostwald ripening, which occurs at lower monomer concentrations and is by monomer migration from small to larger ones. Addition of hexylphosphonic acid or tetradecylphosphonic acid, strong cadmium ligands, is important mainly because it enables the high monomer concentrations needed for the growth of quantum rods....

Photochemical instability of CdSe nanocrystals coated by hydrophilic thiols.

Abstract: The photochemical instability of CdSe nanocrystals coated by hydrophilic thiols was studied nondestructively and systematically in water. The results revealed that the photochemical instability of the nanocrystals actually included three distinguishable processes, namely the photocatalytic oxidation of the thiol ligands on the surface of nanocrystals, the photooxidation of the nanocrystals, and the precipitation of the nanocrystals. At first, the thiol ligands on the surface of a nanocrystal were gradually photocatalytically oxidized using the CdSe nanocrystal core as the photocatalyst. This photocatalytic oxidation process was observed as a zero-order reaction in terms of the concentration of the free thiols in the solution. The photogenerated holes in a nanocrystal were trapped onto the thiol ligands bound on the surface of the nanocrystal, which initiated the photooxidation of the ligands and protected the nanocrystal from any photooxidation. After nearly all of the thiol ligands on the surface of the ...

Alternative Routes toward High Quality CdSe Nanocrystals

Abstract: Different kinds of safe, common, and low-cost compounds were proven to be good solvents/precursors for the synthesis of high quality CdSe nanocrystals. The size, shape, and crystal structure of CdSe nanocrystals synthesized by these alternative routes can be varied in a controllable manner in a very broad size range, from about 1.5 nm to above 25 nm. Without any size sorting, the size distribution of the wurtzite nanocrystals in the size range smaller than about 15 nm can be readily controlled as narrow as with 5−10% relative standard deviation. The highest photoluminescence quantum efficiency of the nanocrystals was up to 20−30%. Cd(Ac)2 and fatty acids were found to be the most versatile cadmium precursor and solvent/ligand, respectively. The synthesis of high quality CdSe nanocrystals in the current systems is not feasible when the system contains any anions from a strong acid, either in the form of a cadmium precursor or as an added cadmium ligand. The experimental results indicate that the synthesis ...

The development of self-regulation in the first four years of life.

Abstract: This study examined longitudinally the development of self-regulation in 108 young children during the first 4 years of life. Children's committed compliance (when they eagerly embraced maternal agenda) and situational compliance (when they cooperated, but without a sincere commitment) were studied. Both forms of compliance were observed in "Do" contexts, in which the mothers requested that the children sustain unpleasant, tedious behavior, and in "Don't" contexts, in which they requested that the children suppress pleasant, attractive behavior. Children's internalization while alone in the similar contexts was also studied. Parallel assessments were conducted when the children were 14, 22, 33, and 45 months of age. At all ages, the Do context was much more challenging for children than the Don't context. Girls surpassed boys in committed compliance. Both forms of compliance were longitudinally stable, but only within a given context. Children's fearfulness and effortful control, observed and mother reported, correlated positively with committed compliance, but mostly in the Don't context. Committed, but not situational, compliance was linked to children's internalization of maternal rules, observed when the children were alone in the Do and Don't contexts. These links were both concurrent and longitudinal, context specific, and significant even after controlling for maternal power assertion. There was modest preliminary evidence that committed compliance may generalize to interactions with adults other than the mother.

The strategic management of people in work organizations: Review, synthesis, and extension

Abstract: The strategic management of human resources (HR) has been one of the most rapidly growing areas of research within human resources. In the last decade, there have been numerous empirical examinations and theoretical treatments of the link between HR and firm performance. In this paper, we review this empirical and conceptual literature and highlight areas of agreement and those that need further development. We then begin the process of building a conceptual framework based on this review and the extensive employment systems literature. Using our framework, we then discuss several methodological concerns that must be addressed for continued substantive research to proceed. We conclude with our suggestions for future empirical and conceptual work.

Quantifying Turfgrass Cover Using Digital Image Analysis

Abstract: Accurate cover estimates in turfgrass research plots are often difficult to obtain because of the time involved with traditional sampling and evaluation techniques. Subjective ratings are commonly used to estimate turfgrass cover, but the data can be quite variable and difficult to reproduce. New technologies and software related to digital image analysis (DIA) may provide an alternative method to measure turfgrass parameters more accurately and efficiently than current techniques. A series of studies was conducted to determine the applicability of DIA for turfgrass cover estimates. In the first study, plots containing a range (1-16) of bermudagrass [Cynodon dactylon (L.) Pers.] plugs of specific diameter (15.0 cm) were established to represent values of turfgrass cover from 0.75 to 12%, by 0.75% increments. Digital images (1280 by 960 pixels) were taken with a digital camera and processed for percent green color to a software package. Estimates of green turfgrass cover by DIA were highly correlated (r 2 > 0.99) to the calculated values of turfgrass cover. In a second study, DIA of turfgrass cover was compared by subjective analysis (SA) and line-intersect analysis (LIA) methods for estimating cover in eight plots of zoysiagrass (Zoysia japonica Steudel). The mean variance of percent cover determined by DIA (0.65) was significantly lower than SA (99.12) or LIA (13.18). Digital image analysis proved to be an effective means of determining turfgrass cover, producing both accurate and reproducible data. In addition, the technique effectively removes the inherent error and evaluator bias commonly associated with subjective ratings.

Exotic plant invasion alters nitrogen dynamics in an arid grassland

Abstract: The introduction of nonnative plant species may decrease ecosystem stability by altering the availability of nitrogen (N) for plant growth. Invasive species can impact N availability by changing litter quantity and quality, rates of N 2-fixation, or rates of N loss. We quantified the effects of invasion by the annual grass Bromus tectorum on N cycling in an arid grassland on the Colorado Plateau (USA). The invasion occurred in 1994 in two community types in an undisturbed grassland. This natural experiment allowed us to measure the immediate responses following invasion without the confounding effects of previous disturbance. Litter biomass and the C:N and lignin:N ratios were measured to determine the effects on litter dynamics. Long-term soil incubations (415 d) were used to measure potential microbial respiration and net N mineralization. Plant-available N was quantified for two years in situ with ion-exchange resin bags, and potential changes in rates of gaseous N loss were estimated by measuring denitrification enzyme activity. Bromus invasion significantly increased litter biomass, and Bromus litter had significantly greater C:N and lignin:N ratios than did native species. The change in litter quantity and chemistry decreased potential rates of net N mineralization in sites with Bromusby decreasing nitrogen available for microbial activity. Inorganic N was 50% lower on Hilaria sites with Bromus during the spring of 1997, but no differences were observed during 1998. The contrasting differences between years are likely due to moisture availability; spring precipitation was 15% greater than average during 1997, but 52% below average during spring of 1998. Bromus may cause a short-term decrease in N loss by decreasing substrate availability and denitrification enzyme activity, but N loss is likely to be greater in invaded sites in the long term because of increased fire frequency and greater N volatilization during fire. We hypothesize that the introduction of Bromus in conjunction with land-use change has es- tablished a series of positive feedbacks that will decrease N availability and alter species composition.

Enhanced Kerr nonlinearity via atomic coherence in a three-level atomic system.

Abstract: We measure the Kerr-nonlinear index of refraction of a three-level Lambda-type atomic system inside an optical ring cavity. The Kerr nonlinearity is modified and greatly enhanced near atomic resonant conditions for both probe and coupling beams. The Kerr nonlinear coefficient n(2) changes sign when the coupling beam frequency detuning switches sign, which can lead to interesting applications in optical devices such as all-optical switches.

Sexual dimorphism in primate evolution.

Abstract: Sexual dimorphism is a pervasive phenomenon among anthropoid primates. Comparative analyses over the past 30 years have greatly expanded our understanding of both variation in the expression of dimorphism among primates, and the underlying causes of sexual dimorphism. Dimorphism in body mass and canine tooth size is familiar, as is pelage and “sex skin” dimorphism. More recent analyses are documenting subtle differences in the pattern of skeletal dimorphism among primates. Comparative analyses have corroborated the sexual selection hypotheses, and have provided a more detailed understanding of the relationship between sexual selection, natural selection, and mating systems in primates. A clearer picture is emerging of the relative contribution of various selective and nonselective mechanisms in the evolution and expression of dimorphism. Most importantly, recent studies have shown that dimorphism is the product of changes in both male and female traits. Developmental studies demonstrate the variety of ontogenetic pathways that can lead to dimorphism, and provide additional insight into the selective mechanisms that influence dimorphism throughout the lifetime of an animal. Evidence from the fossil record suggests that dimorphism probably evolved in parallel twice, and the dimorphism in some extinct hominoids probably exceeded that of any living primate. Our advances in understanding the behavioral/ecological correlates of dimorphism in living primates have not improved our ability to reconstruct social systems in extinct species on the basis of dimorphism alone, beyond the inference of polygyny or intense male-male competition. However, our understanding of the behavioral/ecological correlates of growth and development, and of the expression of dimorphism as a function of separate changes in male and female traits, offers great potential for inferring evolutionary changes in behavior over time. Yrbk Phys Anthropol 44:25–53, 2001. © 2001 Wiley-Liss, Inc.

Returns on Investments in Information Technology: A Research Synthesis

Abstract: Understanding the return on investments in information technology is the focus of a large and growing body of research. The objective of this paper is to synthesize this research and develop a model to guide future research in the evaluation of information technology investments. We focus on archival studies that use accounting or market measures of firm performance. We emphasize those studies where accounting researchers with interest in market-level analyses of systems and technology issues may hold a competitive advantage over traditional IS researchers. We propose numerous opportunities for future research. These include examining the relation between IT and business processes, and business processes and overall firm performance, understanding the effect of contextual factors on the IT-performance relation, examining the IT-performance relation in an international context, and examining the interactive affects of IT spending and IT management on firm performance.

Influence of Potassium Deficiency on Photosynthesis, Chlorophyll Content, and Chloroplast Ultrastructure of Cotton Plants

Abstract: In cotton (Gossypium hirsutum L) grown in controlled-environment growth chamber the effects of K deficiency during floral bud development on leaf photosynthesis, contents of chlorophyll (Chl) and nonstructural saccharides, leaf anatomy, chloroplast ultrastructure, and plant dry matter accumulation were studied After cotton plants received 35-d K-free nutrient solution at the early square stage, net photosynthetic rate (PN) of the uppermost fully expanded main-stem leaves was only 23 % of the control plants receiving a full K supply Decreased leaf PN of K-deficient cotton was mainly associated with dramatically low Chl content, poor chloroplast ultrastructure, and restricted saccharide translocation, rather than limited stomata conductance in K-deficient leaves Accumulation of sucrose in leaves of K-deficient plants might be associated with reduced entry of sucrose into the transport pool or decreased phloem loading K deficiency during squaring also dramatically reduced leaf area and dry matter accumulation, and affected assimilate partitioning among plant tissues

A Partition-Limited Model for the Plant Uptake of Organic Contaminants from Soil and Water

Abstract: In dealing with the passive transport of organic contaminants from soils to plants (including crops), a partition-limited model is proposed in which (i) the maximum (equilibrium) concentration of a contaminant in any location in the plant is determined by partition equilibrium with its concentration in the soil interstitial water, which in turn is determined essentially by the concentration in the soil organic matter (SOM) and (ii) the extent of approach to partition equilibrium, as measured by the ratio of the contaminant concentrations in plant water and soil interstitial water, αpt (≤ 1), depends on the transport rate of the contaminant in soil water into the plant and the volume of soil water solution that is required for the plant contaminant level to reach equilibrium with the external soil-water phase. Through reasonable estimates of plant organic-water compositions and of contaminant partition coefficients with various plant components, the model accounts for calculated values of αpt in several pu...

Characterization of Different Starches Oxidized by Hypochlorite

Abstract: The effects of starch origin (potato, corn, and rice starches) and hypochlorite level (NaOCl, 0.8% and 2% w/w) on the structures and physicochemical properties of oxidized starches were investigated. Carboxyl and carbonyl group contents of oxidized starches increased with increasing NaOCl level, with potato starch having the highest and corn starch having the lowest carboxyl groups content at both NaOCl levels. Oxidation generally reduced the pasting temperature and viscosity of native starches as demonstrated by using a Rapid Visco Analyser. The peak viscosities of oxidized rice and corn starches were higher than those of their native counterparts at 0.8% NaOCl. The morphology of starches was not altered and X-ray diffraction patterns of all the starches remained unchanged after oxidation. Oxidized starch batters exhibited greater adhesions than did native starch batters, with rice starch batter exhibiting the greatest adhesion. Carbohydrate profiles by high-performance size-exclusion chromatography indicated that both amylopectin and amylose were degraded during oxidation. The level of oxidation was largely dependent on the degree of crystallinity of starch and the degree of polymerization of amylose, whereas the adhesion property of oxidized starch was mainly attributed to its granular size and shape.

Extraction, denaturation and hydrophobic properties of rice flour proteins

Abstract: Rice proteins were extracted from defatted rice flour. Turbidity measurement of supernatants revealed isoelectric points of albumin (pH 4.1), globulin (pH 4.3 and pH 7.9), and glutelin (pH 4.8), at which they were precipitated with 82.3 to 93.2% recovery efficiency. Prolamin did not aggregate and precipitate upon pH adjustment, but was precipitated by acetone. Denaturation temperatures (73.3, 78.9, and 82.2 °C) as well as enthalpy values (2.88, 3.14, and 3.79 J/g), of albumin, globulin, and glutelin were different. Prolamin did not show any thermographic denaturation peak. Heat-denaturation of globulin and glutelin resulted in progressive increases in their surface hydrophobicities. Measurement of surface hydrophobicity would be an effective parameter to evaluate rice protein denaturation.

Mechanisms for the adsorption of substituted nitrobenzenes by smectite clays.

Abstract: To more fully understand the potential for transport of nitroaromatic compounds in soils and subsoils, the adsorption of a series of para- and meta-substituted nitrobenzenes (SNBs) by K-smectite clay was measured. Adsorption isotherms were fit to the Freundlich equation, and the resultant Freundlich adsorption coefficients (log(Kf)) were positively correlated with the Hammett substituent constant (r2 = 0.80). This relationship and a positive reaction constant (ρ = 1.15) indicate that the adsorption reaction is favored by electron-withdrawing substituents. These results are consistent with an electron donor (smectite)−acceptor (substituted nitrobenzene) mechanism offered previously. However, quantum calculations did not reveal any systematic relationship between the Hammett constant and the electron density on the aromatic ring, which would explain a donor−acceptor relationship. Rather, electron density donated by a second substituent on nitrobenzene appears to be appropriated by the nitro group leaving ri...

Measurement Error in Research on Human Resources and Firm Performance: Additional Data and Suggestions for Future Research

Abstract: Gerhart and colleagues (2000) and Huselid and Becker (2000) recently debated the presence and implications of measurement error in measures of human resource practices. This paper presents data from 3 more studies, 1 of large organizations from different industries at the corporate level, 1 from commercial banks, and the other of autonomous business units at the level of the job. Results of all 3 studies provide additional evidence that single respondent measures of HR practices contain large amounts of measurement error. Implications for future research into the HR firm performance relationship are discussed.

Sacramento river flow reconstructed to a.d. 869 from tree rings1

Abstract: A time series of annual flow of the Sacramento River, California, is reconstructed to A.D. 869 from tree rings for a long-term perspective on hydrologic drought. Reconstructions derived by principal components regression of flow on time-varying subsets of tree-ring chronologies account for 64 to 81 percent of the flow variance in the 1906 to 1977 calibration period. A Monte Carlo analysis of reconstructed n-year running means indicates that the gaged record contains examples of drought extremes for averaging periods of perhaps = 6 to 10 years, but not for longer and shorter averaging periods. For example, the estimated probability approaches 1.0 that the flow in A.D. 1580 was lower than the lowest single-year gaged flow. The tree-ring record also suggests that persistently high or low flows over 50-year periods characterize some parts of the long-term flow history. The results should contribute to sensible water resources planning for the Sacramento Basin and to the methodology of incorporating tree-ring data in the assessment of the probability of hydrologic drought.

Determinants of Market Reactions to Restatement Announcements

Abstract: We examine the market reaction to a sample of 403 restatement announcements made from 1995 to 1999. We find significantly negative average abnormal returns of about 9 percent over a two-day announcement window. We also document substantial variance in the abnormal returns. Our analysis indicates that more severe reactions are related to indications of management fraud, more material dollar effects and restatements that are attributed to auditors. We hypothesize that the negative signal associated with fraud and auditor-initiated restatements is associated with an increase in investors' expected monitoring costs, while higher materiality is associated with greater revisions of future performance expectations.

Potential contributions of smectite clays and organic matter to pesticide retention in soils.

Abstract: Soil organic matter (SOM) is often considered the dominant sorptive phase for organic contaminants and pesticides in soil-water systems. This is evidenced by the widespread use of organic-matter-normalized sorption coefficients (K(OM)) to predict soil-water distribution of pesticides, an approach that ignores the potential contribution of soil minerals to sorption. To gain additional perspective on the potential contributions of clays and SOM to pesticide retention in soils, we measured sorption of seven pesticides by a K-saturated reference smectite clay (SWy-2) and SOM (represented by a muck soil). In addition, we measured the adsorption of atrazine by five different K-saturated smectites and Ca-saturated SWy-2. On a unit mass basis, the K-SWy-2 clay was a more effective sorbent than SOM for 4,6-dinitro-o-cresol (DNOC), dichlobenil, and carbaryl of the seven pesticides evaluated, of which, DNOC was sorbed to the greatest extent. Atrazine was sorbed to a similar extent by K-SWy-2 and SOM. Parathion, diuron, and biphenyl were sorbed to a greater extent by SOM than by K-SWy-2. Atrazine was adsorbed by Ca-SWy-2 to a much lesser extent than by K-SWy-2. This appears to be related to the larger hydration sphere of Ca(2+) (compared to that of K(+)) which shrinks the effective size of the adsorption domains between exchangeable cations, and which expands the clay layers beyond the apparently optimal spacing of approximately 12.2 A for sorption of aromatic pesticide structures. Although a simple relation between atrazine adsorption by different K-smectites and charge properties of clay was not observed, the highest charge clay was the least effective sorbent; a higher charge density would result in a loss of adsorption domains. These results indicate that for certain pesticides, expandable soil clays have the potential to be an equal or dominant sorptive phase when compared to SOM for pesticide retention in soil.

Market Incentives for Safe Foods: An Examination of Shareholder Losses from Meat and Poultry Recalls

Abstract: Meat and poultry recalls, while voluntary, are carried out under governmental oversight If firms have financial incentives to avoid being implicated in a recall situation, governmental involvement in recalls may cause firms to internalize social costs when making investment decisions concerning food safety controls To examine these incentives, we analyze federally supervised meat and poultry recalls from 1982 to 1998 within an event study Results show significant shareholder losses when publicly traded food companies are implicated in a recall involving serious food safety hazards We find no evidence that the stock market reacts negatively when recalls involve less severe hazards Each year unsafe foods sicken millions and lead to losses in terms of life and productivity Mead et al estimate that foodborne pathogens account for 76 million illnesses and 5,000 deaths in the United States Given human error and the limitations of food safety technology, food items that pose undue risks to the public will be distributed from time to time When this occurs, the firms involved stand to incur expenses related to recovering, disposing of, or reconditioning potentially contaminated products already placed on the market In addition, negative publicity can lead to reductions in product demand and may erode prior investments in reputation and brand capital These firms may also face costs from liability claims associated with an outbreak of food-related illnesses or injury Our main objective in this paper is to examine reductions in food company valuations that result from food contamination incidents We focus specifically on meat and poultry firms that have shipped products that were later recalled for food safety reasons Because preventative actions taken by firms can affect the probability of being implicated in a product recall situation, the wealth that is lost when companies are required to recall

A novel jasmonic acid-inducible rice myb gene associates with fungal infection and host cell death.

Abstract: Endogenous signal molecules such as jasmonic acid (JA) and salicylic acid (SA) play an important role in induced resistance against pathogen infection and insect herbivory. In rice seedlings, JA is an effective inducer of systemic acquired resistance (SAR) against infection of blast fungus (Pyricularia grisea). To gain further insights into JA-mediated defense signaling pathways, we isolated and characterized a pathogen- and JA-induced rice gene (JAmyb) that encodes a Myb transcription factor. The JAmyb gene was induced within 1 day after fungal infection in resistant and susceptible interactions prior to lesion formation. Unlike most defense-related genes that are activated faster and stronger in resistant interactions, JAmyb induction by blast fungus is much higher in susceptible interactions, accompanied by large lesions and extensive tissue damage. Significant induction of JAmyb also was observed during cell death and lesion formation in certain lesion mimic mutants. Interestingly, JAmyb was activated rapidly by JA or wounding, independent of de novo protein synthesis, but not by other endogenous signal molecules such as SA and abscisic acid or SAR inducers such as benzothiadiazole and probenazole. We used SA-deficient transgenic plants to further demonstrate that depletion of SA in rice did not abolish but rather enhanced blast-induced JAmyb expression. These results suggest that JAmyb is related closely to host cell death and is involved in the JA-mediated, SA-independent signaling pathways in rice.

Structures and Physicochemical Properties of Acid‐Thinned Corn, Potato and Rice Starches

Abstract: The structures and physicochemical properties of acid-thinned corn, potato, and rice starches were investigated. Corn, potato, and rice starches were hydrolyzed with 0.14 N hydrochloric acid at 50 °C until reaching a target pasting peak of 200—300 Brabender Units (BU) at 10% solids in the Brabender Visco Amylograph. After acid modification the amylose content decreased slightly and all starches retained their native crystallinity pattern. Acid primarily attacked the amorphous regions within the starch granule and both amylose and amylopectin were hydrolyzed simultaneously by acid. Acid modification decreased the longer chain fraction and increased the shorter chain fraction of corn and rice starches but increased the longer chain fraction and decreased the shorter chain fraction of potato starch, as measured by high-performance size-exclusion chromatography. Acid-thinned potato starches produced much firmer gels than did acid-thinned corn and rice starches, possibly due to potato starch's relatively higher percentage of long branch chains (degree of polymerization 13—24) in amylopectin. The short-term development of gel structure by acid-thinned starches was dependent on amylose content, whereas the long-term gel strength appeared dependend on the long branch chains in amylopectin.

Structures of Gramicidins A, B, and C Incorporated Into Sodium Dodecyl Sulfate Micelles.

Abstract: Gramicidins A, B, and C are the three most abundant, naturally occurring analogues of this family of channel-forming antibiotic. GB and GC differ from the parent pentadecapeptide, GA, by single residue mutations, W11F and W11Y, respectively. Although these mutations occur in the cation binding region of the channel, they do not affect monovalent cation specificity, but are known to alter cation-binding affinities, thermodynamic parameters of cation binding, conductance and the activation energy for ion transport. The structures of all three analogues incorporated into deuterated sodium dodecyl sulfate micelles have been obtained using solution state 2D-NMR spectroscopy and molecular modeling. For the first time, a rigorous comparison of the 3D structures of these analogues reveals that the amino acid substitutions do not have a significant effect on backbone conformation, thus eliminating channel differences as the cause of variations in transport properties. Variable positions of methyl groups in valine and leucine residues have been linked to molecular motions and are not likely to affect ion flow through the channel. Thus, it is concluded that changes in the magnitude and orientation of the dipole moment at residue 11 are responsible for altering monovalent cation transport.

Explaining employees' health care costs: a prospective examination of stressful job demands, personal control, and physiological reactivity.

Abstract: The authors tested the ability of stressful demands and personal control in the workplace to predict employees' subsequent health care costs in a sample of 105 full-time nurses. Both subjective and objective measures of workload demands interacted with personal control perceptions in predicting the cumulative health care costs over the ensuing 5-year period. Tonic elevations in salivary cortisol, moreover, mediated the effects of demands and control on health care costs. Neither the job demands variables nor physiological reactivity measures, however, explained subsequent mental health. The results support findings from the epidemiological literature that demonstrate an important role for employees' control in explaining occupational inequalities in coronary heart disease and mortality. The authors argue that the results also encourage control-enhancing job design interventions by suggesting that their outcomes can benefit both organizations and their members.

Intraocular lens power calculation after laser in situ keratomileusis for myopia and hyperopia: a standardized approach.

Abstract: Purpose.(1) To determine the effect of myopic and hyperopic laser in situ keratomileusis (LASIK) on calculation of intraocular lens (IOL) power. (2) To determine a standard way to approach the IOL power determination after LASIK, and (3) To compare different suggested methods.Methods.Biometric analy

Intimacy dysfunction and trauma symptomatology: Long‐term correlates of different types of child abuse

Abstract: The relationships among interpersonal functioning, symptomatology, and childhood abuse were examined in 315 university women. Women reporting childhood abuse had lower quality of past interpersonal relationships, greater fear of intimacy, and greater trauma symptomatology than nonabused women had. Regression analyses indicated that experiencing both sexual and physical abuse, more extensive psychological abuse, and current sexual concerns, defensive avoidance, dissociation, and intrusive experiences were significant predictors of fear of intimacy. Dysfunctional sexual behaviors, impaired self-reference, and depression were significant predictors of the quality of current interpersonal relationships, whereas sexual abuse or multiple abuse experiences in childhood and anger/irritability were predictors of the quality of prior interpersonal relationships. Implications for future research and treatment are discussed.

Selective maintenance modeling for industrial systems

Abstract: In many industrial environments, systems are required to perform a sequence of operations (or missions) with finite breaks between each operation. During these breaks, it may be advantageous to perform repair on some of the system’s components. However, it may be impossible to perform all desirable maintenance activities prior to the beginning of the next mission due to limitations on maintenance resources. In this paper, a mathematical programming framework is established for assisting decision‐makers in determining the optimal subset of maintenance activities to perform prior to beginning the next mission. This decision‐making process is referred to as selective maintenance. The selective maintenance models presented allow the decision‐maker to consider limitations on maintenance time and budget, as well as the reliability of the system. Selective maintenance is an open research area that is consistent with the modern industrial objective of performing more intelligent and efficient maintenance.