1,721,035 research outputs found
Novel approach to study diffusion of hydrogen bearing species in silicate glasses at low temperatures
No full textDetection of Covalent and Noncovalent Intermediates in the Polymerization Reaction Catalyzed by a C149S Class III Polyhydroxybutyrate Synthase
No full textPolyhydroxybutyrate (PHB) synthases catalyze the conversion of 3-hydroxybutyryl coenzyme A (HBCoA) to PHB with a molecular mass of 1.5 MDa. The class III synthase from Allochromatium vinosum is a tetramer of PhaEPhaC (each 40 kDa). The polymerization involves covalent catalysis using C149 of PhaC with one PHB chain per PhaEC dimer. Two mechanisms for elongation have been proposed. The first involves an active site composed of two monomers in which the growing hydroxybutyrate (HB) chain alternates between C149 on each monomer. The second involves C149 and covalent and noncovalent (HB)[subscript n]CoA intermediates. Two approaches were investigated to distinguish between these models. The first involved the wild-type (wt) PhaEC primed with sTCoA [a CoA ester of (HB)[subscript 3] in which the terminal HO group is replaced with an H] which uniformly loads the enzyme. The primed synthase was reacted with [1-[superscript 14]C]HBCoA by a rapid chemical quench method and analyzed for covalent and noncovalent intermediates. Radiolabel was found only with the protein. The second approach used C149S-PhaEC which catalyzes polymer formation at 1/2200 of the rate of wt-PhaEC (1.79 min[superscript −1] vs 3900 min[superscript −1]). C149S-PhaEC was incubated with [1-[superscript 14]C]HBCoA and chemically quenched on the minute time scale to reveal noncovalently bound [1-[superscript 14]C](HB)[subscript 2]CoA and (HB)[subscript 3]CoA as well as covalently labeled protein. Synthesized (HB)[subscript n]CoA (n = 2 or 3) was shown to acylate PhaEC with rate constants of 1−2 min[superscript −1], and these species were converted into polymer. Thus, the (HB)[subscript n]CoA analogues function as kinetically and chemically competent intermediates. These results support the mechanism involving covalently and noncovalently bound intermediates.National Institutes of Health (U.S.) (Grant GM49171)National Institutes of Health (U.S.). Ruth L. Kirschstein National Research Service Award (Postdoctoral Fellowship F32GM082067
Evaluation of smart eco-friendly public transport options in coastal cities: towards a green future for the city of Southampton
No full textCoastal regions are of economic importance to global economies and host a disproportionate amount of global population. Coastal zones account for only 2% of the world’s total land area but approximately 13% of the world’s urban population lives in these zones. The continuous growth of population and associated climate change can adversely affect these regions in every aspect. Necessary action needs to be taken to protect coastal zones and coastal cities and make them sustainable.Transport is one of the important sectors in a coastal city that can be seriously affected by climate change and ever increasing load from urban growth. Though development of sustainable/eco-friendly transport for cities is challenging but new innovative ideas are emerging. Use of renewable energy sources in transport is gaining popularity both in public and government sectors. Although the current scenario for use of renewables in transport is challenging, the analysis in this report highlights the outlook for the future. The study proposes an integrated transport system supported by a hybrid hydrogen plant from renewable energy (wind and solar). The work provides new perspective regarding implementation of sustainable transport in the city of Southampton, UK. The main contributions of this work are assessment of the availability of renewable energy (wind and solar), annual energy requirements and cost analysis. The findings of this study show that for a conceptual network of public transport it is economically feasible to produce and use hydrogen as an alternative to diesel. One of the important highlight of this work has been that the energy generated from solar photovoltaic could alone support the entire hydrogen demand for the conceptual transport system
Diffusion across the glass transition in silicate melts: Systematic correlations, new experimental data for Sr and Ba in calcium-aluminosilicate glasses and general mechanisms of ionic transport
No full textViscosity and diffusivity of silicate melts and glasses are related to each other through relaxation timescales. The systematic is explored based on published data. Diffusion coefficients for Sr and Ba were measured in calcium aluminosilicate glasses at conditions near the glass/supercooled liquid boundary in temperature - time space making use of thin film technology and Rutherford Backscattering Spectroscopy (RBS) to measure concentration profiles on nanoscales. These data extend the range of published diffusion coefficients and combined with the systematic noted above allow the nature of change of diffusion coefficients across the glass transition region to be studied. Activation energies for diffusion in the glassy state (similar to 360 kJ/mol) are higher than in the molten liquid (similar to 213 kJ/mol). A defect based model of glass transition derived by Ojovan and coworkers, where attainment of a percolation threshold of configuron-type defects accounts for the glass - liquid transition, can explain the observed diffusion behaviour. Data treatment using this model yields a defect formation enthalpy of similar to 146 kJ/mol and a migration enthalpy of similar to 213 kJ/mol. The results of this study provide generalized expressions for the prediction of diffusion coefficients of cations in silicate melts for any composition at any temperature. (C) 2016 Published by Elsevier B.V
Well-Defined Iron Catalysts for the Acceptor less Reversible Dehydrogenation-Hydrogenation of Alcohols and Ketones
No full textAcceptorless dehydrogenation of alcohols, an important organic transformation, was accomplished with well-defined and inexpensive iron-based catalysts supported by a cooperating PNP pincer ligand. Benzylic and aliphatic secondary alcohols were dehydrogenated to the corresponding ketones in good isolated yields upon release of dihydrogen. Primary alcohols were dehydrogenated to esters and lactones, respectively. Mixed primary/secondary diols were oxidized at the secondary alcohol moiety with good chemoselectivity. The mechanism of the reaction was investigated using both experiment and DFT calculations, and the crucial role of metalligand cooperativity in the reaction was elucidated. The iron complexes are also excellent catalysts for the hydrogenation of challenging ketone substrates at ambient temperature under mild H-2 pressure, the reverse of secondary alcohol dehydrogenation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A mild alkali treated jute fibre controlling the hydration behaviour of greener cement paste
Get PDFTo reduce the antagonistic effect of jute fibre on the setting and hydration of jute reinforced cement, modified jute fibre reinforcement would be a unique approach. The present investigation deals with the effectiveness of mild alkali treated (0.5%) jute fibre on the setting and hydration behaviour of cement. Setting time measurement, hydration test and analytical characterizations of the hardened samples (viz., FTIR, XRD, DSC, TGA, and free lime estimation) were used to evaluate the effect of alkali treated jute fibre. From the hydration test, the time (t) required to reach maximum temperature for the hydration of control cement sample is estimated to be 860 min, whilst the time (t) is measured to be 1040 min for the hydration of a raw jute reinforced cement sample. However, the time (t) is estimated to be 1020 min for the hydration of an alkali treated jute reinforced cement sample. Additionally, from the analytical characterizations, it is determined that fibre-cement compatibility is increased and hydration delaying effect is minimized by using alkali treated jute fibre as fibre reinforcement. Based on the analyses, a model has been proposed to explain the setting and hydration behaviour of alkali treated jute fibre reinforced cement composite.The authors would like to acknowledge the BK21, Government of Korea (republic of) for their funding to pursue this research program. Additionally, the authors would like to acknowledge the Indian Institute of Technology, Kharagpur, India for their technical support
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