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Archive for June, 2012

Preparation of co3o4 nanowires grown on nickel foam with superior electrochemical capacitance

Abstract: Co3O4 nanowires have been successfully synthesized on nickel foam by a hydrothermal method. The morphology of Co3O4 is examined by scanning and transmission electron microscopy and the phase structure of Co3O4 nanowires is confirmed by X-ray diffraction. The electrochemical capacitance behavior of the Co3O4 nanowires electrode is investigated by cyclic voltammetry, galvanostatic charge/discharge test and electrochemical impedance spectroscopy in 6moldm−3 KOH solution. The results show that the Co3O4 nanowires have diameters of around 100nm and the lengths up to 1–2μm. The specific capacitance of Co3O4 nanowires is 1019.58Fg−1 at 3.38Ag−1 and 466.06Fg−1 at 33.80Ag−1. The capacitance loss is less than 5% after 1000 charge/discharge cycles at 3.38Ag−1 and with columbic efficiency higher than 98%. The enhancement of pseudocapacitive properties at a higher charging/discharging rate is due to the porous nanostructure and the high utilization of active material. [Copyright &y& Elsevier]

June 25, 2012 Tags: COBALT compounds, ELECTROCHEMICAL analysis, METAL foams, NANOSTRUCTURES, NANOWIRES -- Synthesis, NICKEL, X-rays -- Diffraction
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Precipitation of amorphous colloidal silica from aqueous solutions—aggregation problem

Abstract: Batch process of silica precipitation was investigated experimentally and interpreted based on available theories and models. Silica was manufactured by neutralization of dilute sodium silicate solution with sulphuric acid in a baffled stirred tank reactor of diameter D T =145mm. Effects of pH, temperature, silica and electrolyte (NaCl) concentration were investigated. Particle size measurements were performed using a Malvern Zetasizer ZS ZEN 3500. Effects of process conditions on agglomeration of silica particles and stabilization of the silica nano-particle suspensions were interpreted using the DLVO based theories and models of surface composition. The stability ratio and surface composition were expressed in terms of the properties of the solution. Results of theoretical investigations together with experimental data show that effects resulting from colloidal forces including repulsion and attraction are not enough to explain aggregation phenomena and thus effects resulting from surface reactions should be considered in modeling as well. [Copyright &y& Elsevier]

June 25, 2012 Category: Articles No Comments

Potentiostatic intermittent titration technique (pitt) for spherical particles with finite interfacial kinetics

Abstract: The potentiostatic intermittent titration technique (PITT) is an electroanalytical method that has been widely used to study diffusion of solutes (such as lithium) in electrode materials. Here, we extend the conventional PITT method to account for finite interfacial reaction kinetics and derive analytic equations for electric current under PITT operations. Using the modified PITT, the lithium diffusion coefficient in host materials and the interfacial reaction kinetics can be determined simultaneously. We demonstrate this modified PITT by an example of lithium diffusion in graphite (mesocarbon microbeads, MCMB) and show the improvements of the modified PITT theory over the conventional PITT for investigating the kinetics of electrodes comprising spherical particles. [Copyright &y& Elsevier]

June 25, 2012 Tags: CHEMICAL equations, CHEMICAL kinetics, CHEMICAL reactions, DIFFUSION, ELECTRIC currents, ELECTROCHEMICAL analysis, POTENTIOSTAT
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Possible mechanisms involved in chemokine synergy fine tuning the inflammatory response

Abstract: The arrest and directed migration of leukocytes during homeostasis, tumour development and inflammation is orchestrated by a multitude of chemokines, which govern leukocyte migratory activities. Immune cells are particularly adept at adjusting rapidly to changes within the environment by migration in response to chemokines. The confrontation of leukocytes with different combination of chemokines that are concomitantly produced under physiological or pathological conditions in vivo is complex. There are different ways to enhance or reduce leukocyte migration mediated by chemokines such as posttranslational modifications. Here, we described a positive regulatory mechanism in leukocyte trafficking, by the synergism between chemokines to rapidly augment the local leukocyte influx, thereby enhancing the outcome of an inflammatory response in vivo. The cellular mechanisms involved in chemokine synergy are still debated, but probably include chemokine and/or receptor heterodimerization and subsequent cooperation in signal transduction. [Copyright &y& Elsevier]

June 25, 2012 Tags: CELL migration, CHEMOKINES, HOMEOSTASIS, INFLAMMATION, LEUCOCYTES, TUMORS -- Growth
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Plant and bacterial systems biology as platform for plant synthetic bio(techno)logy

Abstract: The recent implementation of various high-throughput biochemical and bioanalytical platforms for the study of biological systems has resulted in a wealth of experimental information that systems biology integrates into models and functional descriptions of organisms. The fast tempo of systems biology development is currently bringing in a revolution in the understanding of cell networks by providing with a holistic comprehension of cellular components and their interaction dynamics. This thorough description of biological systems has laid the grounds for the development of synthetic biology, a discipline applying basic principles of engineering for the rational assembly of biological modules into higher order complex biological systems with desired properties. Despite the success of this new field for the generation of biotechnological tools, it has not been yet widely applied to plant systems. This review aims at describing the current status of systems biology, its contribution to our understanding of plant metabolism, expression and regulatory networks and how synthetic biology approaches could benefit utilising plant and bacterial ‘omics’ as a source for the design and development of biological modules for the improvement of plant stress tolerance and crop production, among other applications. The article further describes synthetic biology strategies currently being applied to plant metabolic engineering, development of signalling pathways and synthetic organelles, and the potential of this new field for the understanding of plant cellular functioning and the generation of plant biotechnological tools. [Copyright &y& Elsevier]

June 25, 2012 Tags: ACTIVE oxygen, BIOENGINEERING, BIOLOGICAL systems, BOTANICAL chemistry, NUCLEAR magnetic resonance, PLANT biotechnology, SYNTHETIC biology, SYSTEMS biology
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Phosphorus dynamics in an ephemeral wetland ecosystem after re-flooding

Abstract: To test whether large amounts of phosphorus (P) are accumulated in the floodplain during dry antecedent conditions, and whether they would be released as the predominant source of P in the overlaying floodwater, in accord with the Flood Pulse Concept, we calculated the mass balance of P in an intermittent floodplain wetland after environmental water application. The P mass balance was calculated by combining a wetland water balance model and P releasing dynamics that were estimated from glasshouse sediment inundation experiments. Upon receiving environmental water, which inundated 412 ha of swamps and river red gum (Eucalyptus camaldulensis) woodlands, our results showed that 394.5 kg of P was mobilised in the system (342.0 kg from 368.4 ha of woodland and 52.5 kg from 43.6 ha of swamp and channels). In addition, the mass of P in incoming water was 74.0 kg, giving a peak in situ mass of 468.5 kg P in the water column. The estimation was verified using the water column P calculated from field samples. Our results indicated that the majority of P (84.2%) was internal loading, and the floodplain may be a source of P enrichment for adjacent water bodies or groundwater if floodwater is discharged rapidly. However, our modelling results also suggested that the high concentration of P in the water column was not sustained most probably because soils re-adsorbed the dissolved P. Approximately 110 days for the woodland and 39 days for the swamp were needed to reduce the P levels to 20% of their peak values respectively. Environmental water managers must decide how to manage P-enriched floodwater; retaining floodwater in the floodplain for a long time could reduce the risk of P enrichment downstream receiving water bodies; or, keeping internal P loading in the wetland could cause eutrophication in the system that was initially targeted for restoration. Best management practices, such as staged flooding and flooding timing are discussed. [Copyright &y& Elsevier]

June 24, 2012 Tags: BIOTIC communities, ENVIRONMENTAL impact analysis, FLOODPLAIN ecology, MASS budget (Geophysics), MATHEMATICAL models, PHOSPHORUS, VERNAL pools
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Parameters influencing calcium phosphate precipitation in granular sludge sequencing batch reactor

Abstract: Calcium phosphate precipitation inside microbial granules cultivated in a granular sequenced batch reactor (GSBR) has been demonstrated to contribute to phosphorus removal during wastewater treatment. Whereas hydroxyapatite (HAP) is proven to accumulate in the granule, the main calcium phosphate precursors that form prior to HAP are here investigated. A separate batch reactor was used to distinguish reactions involving biological phosphate removal from physicochemical reactions involving phosphate precipitation in order to establish the kinetics and stoichiometry of calcium phosphate formation. Experiments and simulations with PHREEQC and AQUASIM software support the assumption that amorphous calcium phosphate (ACP) is the intermediary in HAP crystallization. The results provide the kinetic rate constants and thermodynamic constants of ACP. The formation of bioliths inside biological aggregates as well as the main parameters that drive their formations are discussed here. Finally, the influence of pH and calcium and phosphate concentrations in the influent was also assessed, in order to determine the contribution of precipitation in the different operating conditions. [Copyright &y& Elsevier]

June 24, 2012 Category: Articles No Comments

Overview of the mechanisms regulating chemokine activity and availability

Abstract: Physiological leukocyte homing and extravasation of leukocytes during inflammatory processes is directed by a number of proteins including adhesion molecules, proteases, cytokines and chemokines. Tight regulation of leukocyte migration is essential to ensure appropriate migration. A number of mechanisms exist that regulate leukocyte migration including up- or down-regulation of chemokine or chemokine receptor gene expression. However, chemokine availability in vivo also depends on the interaction of chemokines with specific glycosaminoglycans such as heparan sulfate on the surface of endothelial layers. Modification of the interaction of chemokines with these glycosaminoglycans alters the presentation of chemokines to chemokine receptors on circulating leukocytes. On top, binding of chemokines to atypical chemokine receptors that do not signal through G proteins affects chemokine availability on the endothelial layers. In addition to mechanisms that modulate chemokine availability, this review summarizes mechanisms that fine-tune chemokine function. These include synergy or antagonism between chemokines and alternative splicing of chemokine genes. Moreover, chemokines may be posttranslationally modified leading to molecules with enhanced or reduced potency to bind to G protein-coupled receptors or GAGs or generating chemokines with altered receptor specificity. Cross-talk between these different mechanisms generates a complex regulatory network that allows the organism to modulate leukocyte migration in a highly specific manner. [Copyright &y& Elsevier]

June 24, 2012 Tags: CELL adhesion molecules, CHEMOKINES, EXTRAVASATION, INFLAMMATION, LEUCOCYTES, PHYSIOLOGY, PROTEINS, PROTEOLYTIC enzymes
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Optimisation of the quantification of glutamine synthetase and myelin basic protein in cerebrospinal fluid by a combined acidification and neutralisation protocol

Abstract: The measurement of proteins in cerebrospinal fluid (CSF) by enzyme-linked immunosorbent assays (ELISAs) is becoming increasingly important in the diagnosis of many neurodegenerative diseases such as Alzheimer”s Disease. However, detection of proteins in these immunoassays can be hampered by confounding factors either present in the sample matrix or inherent to the protein of interest. These confounding factors may, for example, include protein aggregation or binding to other proteins resulting in epitope masking. Furthermore, the pH of CSF may vary considerably amongst different samples which may limit standardisation of CSF analysis. Pre-treatment of CSF to liberate epitopes or optimise conditions for antibody binding may enhance protein detection. In the current study we investigated whether CSF acidification followed by neutralisation (in short: AFBN) or neutralisation alone prior to measurement might improve the detection of a panel of brain-specific proteins. We demonstrate that the AFBN pre-treatment protocol for CSF significantly enhances the measurement of glutamine synthetase (GS) and myelin basic protein (MBP) in CSF but does not affect detection of glial fibrillary protein (GFAP), amyloid β 42 (Aβ42), total tau (t-tau) or phosphorylated tau (p-tau). Neutralisation alone did not improve detection of any of the proteins tested. Based on our results, we suggest including the AFBN protocol in the evaluation of new biomarker development protocols to avoid confounders such as CSF pH or epitope-masking of the target protein. [Copyright &y& Elsevier]

June 24, 2012 Tags: ACIDIFICATION, Analytic -- QuantitativeEXAMINATION, CEREBROSPINAL fluid, CHEMISTRY, GLUTAMINE synthetase, MYELIN, NEUTRALIZATION (Chemistry)
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On calibration data selection: the case of stormwater quality regression models

Abstract: A stormwater quality model should be calibrated and verified against available data before it can be confidently used. This paper mainly examines two questions: how do the size and selection of calibration data sets affect model performances and how should the calibration data sets be selected. Regression models are used to simulate stormwater quality (TSS and COD) with variables characterizing rainfall and flow characteristics. Based on large databases of three catchments in France, several models are calibrated and verified with different data subsets. It is confirmed that the selection of calibration data sets leads to significant uncertainty in model performance. The information content in the calibration data sets is also important in addition to their size. Generally model performances can be improved by using a large size of calibration data sets and by selecting calibration data that are representative of all data. Three methods endeavoring to improve model performance by selecting calibration data either according to model outputs or model inputs are developed based on the principle of choosing calibration data that are representative of the whole data set. The effectiveness of the three selection methods is demonstrated by their application on databases of the three catchments. Model performances can be generally improved by selection methods. The selection methods based on model inputs that consider multi-dimension information perform better than the method with one-dimension information consideration. [Copyright &y& Elsevier]

June 24, 2012 Tags: CALIBRATION, DATABASE selection, MATHEMATICAL models, PERFORMANCE evaluation, RAIN & rainfall, RAINWATER -- Analysis, WATER quality, WATERSHEDS
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