Bio-composites of kenaf fibers in polylactide: Role of improved interfacial adhesion in the carding process

Bio-composites comprised of kenaf fiber reinforced polylactide are fabricated by carding followed by treatment with a 3-glycidoxypropyl trimethoxy silane and hot-pressing. The effects of the silane coupling agent on composite properties was highly beneficial leading to increased moduli and heat deflection temperatures as well as reduced water swelling. Swelling is found to increase with increasing kenaf loading levels but to decrease with increasing coupling agent concentrations. Mechanical properties of the bio-composites at tempertaures above the glass transition are vastly improved in comparison to the base PLA polymer. As little as 10 wt.% kenaf fiber in PLA provides a heat distortion temperature in excess of 140 °C when combined with the coupling agent. The thermal stability towards degradation is slightly decreased relative to the base PLA and the ash content is increased. Thermal properties such as the glass transition, melting temperature, and percent crystallinity of the matrix PLA are largely unaffected by incorporation into the composites. Evidence of successful reaction of the silane with the kenaf fibers is provided by FTIR and implied by decreased swelling in water. A prototypical automotive headliner is fabricated as a means of demonstrating the viability of the present bio-composites in real manufacturing processes.     

Synthesis and characterization of biocomposites with different hydroxyapatite–collagen ratios

Hydroxyapatite (HA)-type I collagen (Col) composite is a tissue-engineered bone graft which can act as a carrier or a template structure for cells or any other agents. In this paper, the effect of Col ratio on the scaffold structure and composition was analyzed. Scaffolds composed by HA/Col with different weight ratios (80:20; 50:50; 20:80, and 10:90) were produced by the precipitation method at pH 8–9, 37°C and 6 h of ripening. Using X-ray diffraction data, the Rietveld structure refinement showed that the size of HA crystals along the c-axis direction (002) decreases significantly in the presence of Col. Thus, the HA crystal shape turned from needle-like in pure HA, into spherical, in the 10:90 composite due to Col fibrillogenesis. The homogeneity of the composite was significantly dependent on the amount of Col in it. HA/Col 20/80 composite presented HA particles in a more homogenous way. Such a biocomposite was successfully produced in a rapid way and it is potentially useful for both small tissue repairs and engineering.     

Thin film graphite electrodes with low stress generation during Li-intercalation

We report here the development of thin film ‘graphite’ electrodes for Li-ion batteries, with near theoretical Li-intercalation/de-intercalation capacity (∼372 mAh/g). These films, synthesized by chemical vapor deposition at a relatively low temperature of 1000 °C, exhibit strong graphitic order with the basal planes oriented parallel to the Ni current collector. During galvanostatic cycling, in-situ stress measurements show that full lithiation corresponds to the development of only modest in-plane compressive stresses of ∼ −250 MPa. These stresses are more than an order of magnitude lower than expected, which should promote long cycle life.     

Formalization of Workflows and Correctness Issues in the Presence of Concurrency

In this paper, main components of a workflow system that are relevant to the correctness in the presence of concurrency are formalized based on set theory and graph theory. The formalization which constitutes the theoretical basis of the correctness criterion provided can be summarized as follows:-Activities of a workflow are represented through a notation based on set theory to make it possible to formalize the conceptual grouping of activities.-Control-flow is represented as a special graph based on this set definition, and it includes serial composition, parallel composition, conditional branching, and nesting of individual activities and conceptual activities themselves.-Data-flow is represented as a directed acyclic graph in conformance with the control-flow graph.The formalization of correctness of concurrently executing workflow instances is based on this framework by defining two categories of constraints on the workflow environment with which the workflow instances and their activities interact. These categories are:-Basic constraints that specify the correct states of a workflow environment.-Inter-activity constraints that define the semantic dependencies among activities such as an activity requiring the validity of a constraint that is set or verified by a preceding activity.Basic constraints graph and inter-activity constraints graph which are in conformance with the control-flow and data-flow graphs are then defined to represent these constraints. These graphs are used in formalizing the intervals among activities where an inter-activity constraint should be maintained and the intervals where a basic constraint remains invalid.A correctness criterion is defined for an interleaved execution of workflow instances using the constraints graphs. A concurrency control mechanism, namely Constraint Based Concurrency Control technique is developed based on the correctness criterion. The performance analysis shows the superiority of the proposed technique. Other possible approaches to the problem are also presented.     

An Empirical Assessment of On-Farm Water Productivity using Groundwater in a Semi-Arid Indian Watershed

Realistic estimation of irrigation volume applied to any crop at farm level generally requires information on event based discharge rates and corresponding periods of irrigation application. Use of mean seasonal discharge rates leads to erroneous estimation of volume due to unaccounted seasonal fluctuations in the water table, upon which the discharge rate of tube well is dependent. In the absence of such information, an alternative approach of estimating farm level water application based upon water table fluctuation data has been adopted in this study. The total actual water extracted during each irrigation event from the watershed was distributed among the farms irrigating crops in proportion to the product of irrigation time and the pump capacity (h_p). Volume of water withdrawal concurrent to an irrigation event was computed based on the water level fluctuations in the wells in conjunction with potential recharge contribution from the surface storage structures to the groundwater aquifer. A production function approach was used to estimate the marginal productivity of water for selected crops at various stages of plant growth. Water, as an input in the production function, encompassed either in-situ soil moisture storage from rainfall or irrigation from groundwater or both. The inter-season as well as intra-season groundwater use, and the consequent groundwater withdrawals were analyzed based on the marginal value and output elasticity of water at different crop growth stages during the season. The cotton crop realized marginal value product of water, ranging from Rs. 1.03/m³ to Rs. 10.43/m³ at different crop growth stages in cotton. Castor crop had the marginal value product ranging from Rs. 2.89/m³ to Rs. 6.81/m³. The availability and use of water, including soil moisture, in the two seasons, coupled with the local harvest prices received, yielded the differential marginal values of water.     

Evaluation of Vulnerability to Extreme Climatic Events in the Brazilian Amazonia: Methodological Proposal to the Rio Acre Basin

The southern border of the Brazilian Amazon is one of the most sensitive areas to deforestation in Brazil. In addition to problems related to changes in land use, new issues are emerging, including climate change and its negative effects on the regional hydrological cycle. In recent years considerable research has been undertaken focusing on climate change and its effects on Amazon Biodiversity, carbon cycle, fire incidence and even on regional water resources, but there is very little research linking territorial planning and public policies to prospective planning scenarios and climate change and the necessary adaptation or mitigation actions to address climate vulnerability. This study examines issues pertaining to social, economic and environmental vulnerability, including new challenges posed by climate change. Examples of environmental problems related to climate dynamics of the Rio Acre Basin are floods and dry periods such as the major drought of 2005 and the 2009 flood. The use of methodology for integrated assessment of vulnerability to river basins in Amazon Region constitutes a valuable instrument for territorial planning, since it takes into account both the challenges of poverty and the environmental fragility, as well the possible aggravations of extreme climatic events in the future.     

Lithium naphthalenides in non-polar or in low-polarity media: some insights regarding their use as initiators in anionic polymerizations

The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) and naphthalene (Naph), under mild conditions, in non-polar (benzene) or low-polarity media (benzene/THF mixtures) is reported. The efficiency of these initiators to provide macromolecules with well-defined structures was demonstrated. Model linear homopolymers from styrene (S) or hexamethyl(ciclotrisiloxane) (D₃) monomers were synthesized using classical anionic polymerization (high-vacuum techniques). The model polymers obtained were analyzed using the conventional analytical techniques, and showed narrow molar mass distributions, a broad range of molar masses (from 3000 to 1,000,000 g/mol) and polydispersity indexes (M _w/M _n) lower than 1.1. High molar mass polymers were obtained using pure benzene as solvent, whereas lower molar masses were obtained in benzene/THF mixtures in which the concentration of THF was lower than 10 % v/v. The ratio [Li]/[Naph] and the nature of the reaction medium are the experimental parameters to be controlled to obtain the desired lithium naphthalenides.     

Thermally stable conducting composites based on a carbon black‐filled polyoxadiazole matrix

New thermally stable conducting materials can be obtained by dispersing conducting carbon black into poly(4,4′‐diphenylether‐1,3,4‐oxadiazole) (POD–DPE) solution in NMP. The blend preparation process resulted in quite good dispersed composite and a relatively low percolation threshold (around 5 wt % of CB). The effect of the compressive stress on the resistivity of composite has been evaluated. The resistivity decreases continuously as the applied pressure is increased. In addition to the electrical conductivity, the presence of carbon black resulted in higher thermally stable materials. The thermal stability, electrical conductivity, and pressure‐sensible characteristics make this conducting material a good candidate for application in manufacture of pressure sensors for high temperature ambient. This material shows a typical semiconductor behavior, characterized by an increase of conductivity with the temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1631–1637, 2004