883 research outputs found
A bilateral shear layer between two parallel Couette flows
We consider a shear layer of a kind not previously studied to our knowledge.
Contrary to the classical free shear layer, the width of the shear zone does
not vary in the streamwise direction but rather exhibits a lateral variation.
Based on some simplifying assumptions, an analytic solution has been derived
for the new shear layer. These assumptions have been justified by a comparison
with numerical solutions of the full Navier-Stokes equations, which accord with
the analytical solution to better than 1% in the entire domain. An explicit
formula is found for the width of the shear zone as a function of wall-normal
coordinate. This width is independent of wall velocities in the laminar regime.
Preliminary results for a co-current laminar-turbulent shear layer in the same
geometry are also presented. Shear-layer instabilities were then developed and
resulted in an unsteady mixing zone at the interface between the two co-current
streams.Comment: 6 pages, 7 figures. Accepted for publication in Phys. Rev.
Cellulose production is coupled to sensing of the pyrimidine biosynthetic pathway via c-di-GMP production by the DgcQ protein of Escherichia coli
Production of cellulose, a stress response-mediated process in enterobacteria, is modulated in Escherichia coli by the activity of the two pyrimidine nucleotide biosynthetic pathways, namely, the de novo biosynthetic pathway and the salvage pathway, which relies on the environmental availability of pyrimidine nitrogenous bases. We had previously reported that prevalence of the salvage over the de novo pathway triggers cellulose production via synthesis of the second messenger c-di-GMP by the DgcQ (YedQ) diguanylate cyclase. In this work, we show that DgcQ enzymatic activity is enhanced by UTP, whilst being inhibited by N-carbamoyl-aspartate, an intermediate of the de novo pathway. Thus, direct allosteric control by these ligands allows full DgcQ activity exclusively in cells actively synthesizing pyrimidine nucleotides via the salvage pathway. Inhibition of DgcQ activity by N-carbamoyl-aspartate appears to be favoured by protein-protein interaction between DgcQ and PyrB, a subunit of aspartate transcarbamylase, which synthesizes N-carbamoyl-aspartate. Our results suggest that availability of pyrimidine bases might be sensed, somehow paradoxically, as an environmental stress by E. coli. We hypothesize that this link might have evolved since stress events, leading to extensive DNA/RNA degradation or lysis of neighbouring cells, can result in increased pyrimidine concentrations and activation of the salvage pathway
Interventions to Reduce Adult Nursing Turnover: A Systematic Review of Systematic Reviews.
Background: Nurse turnover is an issue of concern in health care systems internationally. Understanding which interventions are effective to reduce turnover rates is important to managers and health care organisations. Despite a plethora of reviews of such interventions, strength of evidence is hard to determine. Objective: We aimed to review literature on interventions to reduce turnover in nurses working in the adult health care services in developed economies. Method: We conducted an overview (systematic review of systematic reviews) using the Cochrane Database of Systematic Reviews, MEDLINE, EMBASE, Applied Social Sciences Index and Abstracts, CINAHL plus and SCOPUS and forward searching. We included reviews published between 1990 and January 2015 in English. We carried out parallel blinded selection, extraction of data and assessment of bias, using the Assessment of Multiple Systematic Reviews. We carried out a narrative synthesis. Results: Despite the large body of published reviews, only seven reviews met the inclusion criteria. These provide moderate quality review evidence, albeit from poorly controlled primary studies. They provide evidence of effect of a small number of interventions which decrease turnover or increase retention of nurses, these being preceptorship of new graduates and leadership for group cohesion. Conclusion: We highlight that a large body of reviews does not equate with a large body of high quality evidence. Agreement as to the measures and terminology to be used together with well-designed, funded primary research to provide robust evidence for nurse and human resource managers to base their nurse retention strategies on is urgently required
Dynamical effects induced by long range activation in a nonequilibrium reaction-diffusion system
We both show experimentally and numerically that the time scales separation
introduced by long range activation can induce oscillations and excitability in
nonequilibrium reaction-diffusion systems that would otherwise only exhibit
bistability. Namely, we show that the Chlorite-Tetrathionate reaction, where
autocatalytic species diffuses faster than the substrates, the spatial
bistability domain in the nonequilibrium phase diagram is extended with
oscillatory and excitability domains. A simple model and a more realistic model
qualitatively account for the observed behavior. The latter model provides
quantitative agreement with the experiments.Comment: 19 pages + 9 figure
A structure-based approach for novel immunodiagnostics targeting Trypanosoma cruzi and Schistosoma spp.
The tropical diseases Chagas Disease and Schistosomiasis, caused by the parasites Trypanosoma cruzi and Schistosoma spp, respectively, are often misdiagnosed and if untreated can be fatal. Indeed, their diagnosis presents a current challenge, due to difficulties in recognizing clinical symptoms and the lack of specific and reliable diagnostic tools.
Highest prevalence is respectively in Latin America and Central Africa. However, massive human migration from endemic areas and travelling to tropical regions, contribute to the diffusion of these diseases in non-endemic areas, increasing the need of rapid diagnostic tools and prevention strategies.
The aim of this project is to develop rapid, peptide-based microarrays that present multiple immunoreactive epitopes predicted from 3D protein structures of antigens from several pathogens, to be applied in point-of-care diagnostic kits for use in the Lombardy area of Italy. This approach showed promising results when applied to antigens from bacterial pathogens, in particular Burkholderia pseudomallei that led to the identification of epitopes with both diagnostic and therapeutic potential.
Putative antigens selected from both parasites will be overexpressed, purified and crystallized for 3D structure studies. Based on the determined 3D protein structures, Molecular Dynamics (MD) analyses will be carried out and epitope predictions will be made on output MD structures using the Matrix of Local Coupling Energies method that detects residues located in conformationally dynamic regions of the protein surface. Predicted reactive epitopes will be synthetized as peptides, tested for immunoreactivity against immune sera from infected patients and used for antibody production. Selected immunoreactive synthetic peptides will be immobilised in specific orientations, using click chemistry, on a polymeric coated microarray chip. Sensitivity and specificity of the chip will be evaluated with sera of infected patients
Widely applicable background depletion step enables transaminase evolution through solid-phase screening
Directed evolution of transaminases is a widespread technique in the development of highly sought-after biocatalysts for industrial applications. This process, however, is challenged by the limited availability of effective high-throughput protocols to evaluate mutant libraries. Here we report a rapid, reliable, and widely applicable background depletion method for solid-phase screening of transaminase variants, which was successfully applied to a transaminase from Halomonas elongata (HEWT), evolved through rounds of random mutagenesis towards a series of diverse prochiral ketones. This approach enabled the identification of transaminase variants in viable cells with significantly improved activity towards parasubstituted acetophenones (up to 60-fold), as well as tetrahydrothiophen-3-one and related substrates. Rationalisation of the mutants was assisted by determination of the high-resolution wild-type HEWT crystal structure presented herein
Continuous twin screw rheo-extrusion of an AZ91D magnesium alloy
© The Minerals, Metals & Materials Society and ASM International 2012The twin screw rheo-extrusion (TSRE) is designed to take advantage of the nondendritc microstructure and thixotropic characterization of semisolid-metal slurries and produce simple metal profiles directly from melts. The extrusion equipment consists of a rotor-stator high shear slurry maker, a twin screw extruder, and a die assembly. The process is continuous and has a potential for significantly saving energy, manufacturing cost, and enhancing efficiency. The present investigation was carried out to study the process performance for processing rods of an AZ91D magnesium alloy and the microstructure evolution during processing. The semisolid slurry prepared by the process was characterized by uniformly distributed nondendritic granular primary phase particles. AZ91D rods with uniform and fine microstructures and moderate mechanical properties were produced. For the given slurry making parameters, decreasing extrusion temperature was found to improve microstructures and properties. The mechanisms of particle granulation and refinement and the effect of processing parameters on process performance and thermal management are discussed. © 2012 The Minerals, Metals & Materials Society and ASM International.EPSRC (UK) and Rautomead Lt
Grain Boundary Motion Exhibits the Dynamics of Glass-Forming Liquids
Polycrystalline materials can be viewed as composites of crystalline
particles or grains separated from one another by thin amorphous grain boundary
(GB) regions. While GB have been exhaustively investigated at low temperatures,
where these regions resolve into complex ordered structures accessible to
measurement, much less is known about them at higher temperatures where the GB
can exhibit significant mobility, structural disorder, and where experimental
characterization methods are limited. The time and spatial scales accessible to
molecular dynamics (MD) simulation make this method appropriate for
investigating both the dynamical and structural properties of grain boundaries
at elevated temperatures. In the present study, we use MD simulations to
determine how the GB dynamics changes with temperature and applied stress. It
has long been hypothesized that GB have features in common with glass-forming
liquids based on the processing characteristics of polycrystalline materials.
We find remarkable support for this suggestion, as evidenced by string-like
collective motion, transient caging of atom motion, and non-Arrhenius
(Vogel-Fulcher) temperature dependence of GB mobility. Evidently, the
frustration caused by the inability of atoms in GB region to simultaneously
order with respect to competing grains is responsible for this striking
similarity. The paradigm that grains in a polycrystalline material are
encapsulated by a frustrated fluid provides a powerful conceptual model of
polycrystalline materials, pointing the way to improved control over their
material properties.Comment: Plan to submit paper to Proceedings of the National Academy of
Science (USA
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Synchrotron radiography studies of shear-induced dilation in semi-solid Al alloys and steels
An improved understanding of the response of solidifying microstructures to load is required to further minimize casting defects and optimize casting processes. This article overviews synchrotron radiography studies that directly measure the micromechanics of semisolid alloy deformation in a thin sample direct-shear cell. It is shown that shear-induced dilation (also known as Reynoldsâ dilatancy) occurs in semisolid alloys with morphologies ranging from equiaxed-dendritic to globular, at solid fractions from the dendrite coherency point to ~90% solid, and it occurs in both Al alloys and carbon steels. Discrete-element method simulations that treat solidifying microstructures as granular materials are then used to explore the origins of dilatancy in semisolid alloys
Crystal structure of Y10F mutant of Sh28GST: insight into GSH activation mechanism and isomerisation of prostaglandin H2 to prostaglandin D2
Suite Ă notre confĂ©rence du 20 septembre, un sĂ©minaire de travail sur les recherches collaboratives sâest dĂ©roulĂ© hier aprĂšs-midi Ă la facultĂ© des sciences de lâĂ©ducation de lâUniversitĂ© Saint Joseph. Lâobjectif Ă©tait dâidentifier les thĂ©matiques de recherches prioritaires pour les quarante participants, et de travailler collectivement sur les modalitĂ©s possibles de mise en Ćuvre de ce type de recherche au Liban. AprĂšs une introduction prĂ©sentant lâexemple des trois LĂ©A CollĂšge Garcia Lorca, ..
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