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Numerous Works (numerous + work)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Contextualizing Research on Social Capital in Regional Clusters

INTERNATIONAL JOURNAL OF URBAN AND REGIONAL RESEARCH, Issue 3 2007
UDO STABER
Abstract Numerous works in economic geography and regional studies have considered social capital a salient factor in the performance of regional business clusters. Theoretical arguments have focused on those structural, relational and cognitive features of social capital that are expected to facilitate cooperation and innovation as a basis for cluster success. However, the available empirical evidence on the performance implications of social capital is weak and largely inconsistent. I argue that one reason for the observed cross-study inconsistencies is the neglect of the situational context in which social capital evolves. I discuss how acontextual studies can lead to analytical error and flawed conclusions concerning the performance outcomes of social capital. I propose several approaches to contextualizing research and discuss how they would advance our understanding of the performance implications of social capital in a cluster setting. Résumé De nombreux travaux de géographie économique et études régionales voient dans le capital social un facteur fondamental de la réussite des pôles d'entreprises régionaux. Les discussions théoriques ont porté sur les caractéristiques structurelles, relationnelles et cognitives du capital social qui sont censées faciliter coopération et innovation, composantes de base de la réussite de ces pôles. Toutefois, les preuves empiriques disponibles des implications du capital social dans cette réussite sont fragiles et peu cohérentes. Cet article affirme que les incohérences des études croisées tiennent, pour une part, à l'ignorance du contexte situationnel dans lequel évolue le capital social. Il expose comment des études hors contexte peuvent conduire à une erreur analytique et à des conclusions incorrectes quant aux résultats générés par le capital social. Il propose plusieurs approches pour placer les recherches en contexte et analyse comment, grâce à elles, nous pourrions mieux comprendre la part de réussite propre au capital social dans le cadre d'un pôle donné. [source]

Chemical modification of chitosan: synthesis and biological activity of new heterocyclic chitosan derivatives

POLYMER INTERNATIONAL, Issue 2 2008
Mohamed EI Badawy
Abstract BACKGROUND: Numerous works have been published on the chemical modification of chitosan; this polymer is still being modified, leading to various derivatives with improved properties. In the present study, heterocyclic aldehydes including furan-2-carbaldehyde, 5-methylfuran-2-carbaldehyde, 3-pyridine carboxyaldehyde, benzo[d][1,3]dioxole-5-carbaldehyde and 4-oxo-4H -chromene-3-carbaldehyde were reacted with chitosan by a reductive alkylation reaction to produce for the first time five new N -heterocyclic chitosan derivatives to improve the biological activity of chitosan against the most important economic plant pests including fungi and insects, in particular the cotton leafworm Spodoptera littoralis. RESULTS: The chemical structures of the synthesized compounds were confirmed by 1H NMR spectroscopy and the degree of substitution ranged from 0.30 to 0.43. The fungicidal assessment was investigated in vitro using a mycelia radial growth inhibition technique against soil-borne pathogenic fungi Fusarium oxysporum and Pythium debaryanum and the rice leaf blast Pyricularia grisea. The results showed that N -[(5-methylfuran-2-yl)methyl] chitosan was the most active against P. grisea with an EC50 value of 0.919 mg mL,1 while N -(benzo[d][1,3]dioxol-5-ylmethyl) chitosan and N -(methyl-4H -chromen-4-one) chitosan exhibited the most potent fungicidal activity against P. debaryanum and F. oxysporum. An insecticidal bioassay against the larvae of S. littoralis showed that N -(methyl-4H -chromen-4-one) chitosan exhibited a significant growth inhibition and antifeedant activity among the synthesized compounds. CONCLUSION: The chemical modification of chitosan molecule with a heterocyclic moiety led to an enhancement in the biological activity against the plant pathogenic fungi F. oxysporum, P. debaryanum and P. grisea and the cotton leafworm insect S. littoralis. Copyright © 2007 Society of Chemical Industry [source]

Nanostructured Carbon and Carbon Nanocomposites for Electrochemical Energy Storage Applications

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 2 2010
Sheng Su
Abstract Electrochemical energy storage is one of the important technologies for a sustainable future of our society, in times of energy crisis. Lithium-ion batteries and supercapacitors with their high energy or power densities, portability, and promising cycling life are the cores of future technologies. This Review describes some materials science aspects on nanocarbon-based materials for these applications. Nanostructuring (decreasing dimensions) and nanoarchitecturing (combining or assembling several nanometer-scale building blocks) are landmarks in the development of high-performance electrodes for with long cycle lifes and high safety. Numerous works reviewed herein have shown higher performances for such electrodes, but mostly give diverse values that show no converging tendency towards future development. The lack of knowledge about interface processes and defect dynamics of electrodes, as well as the missing cooperation between material scientists, electrochemists, and battery engineers, are reasons for the currently widespread trial-and-error strategy of experiments. A concerted action between all of these disciplines is a prerequisite for the future development of electrochemical energy storage devices. [source]

Prediction of Water,s Mobility and Disorder in Protein Crystals Using Novel Local Hydrophobic Descriptors

MOLECULAR INFORMATICS, Issue 3 2010
Yuzhu Pan
Abstract The B-factors of crystal structures reflect the atomic fluctuations about their average positions and provide important information about molecular dynamics. Although numerous works have been addressed on theoretical and computational studies of B-factor profile of protein atoms, the methods used for predicting B-factor values of water molecules in protein crystals still remain unexploited. In this article, we describe a new approach that we named local hydrophobic descriptors (LHDs) to characterize the hydrophobic landscapes of protein hydration sites. Using this approach coupled with partial least squares (PLS) regression and least-squares squares support vector machine (LSSVM), we perform a systematic investigation on the linear and nonlinear relationships between the LHDs and water B-factors. Based upon an elaborately selected, large-scale dataset of crystal water molecules, our method predicts B-factor profile with coefficient of determination rpred of 0.554. We demonstrate that (i) the dynamics of water molecules is primarily governed by the local features of hydrophobic potential landscapes, and (ii) the accuracy of predicted B-factor values depends on water packing density. [source]