447 research outputs found
Biotransformation of explosives by the old yellow enzyme family of flavoproteins
Several independent studies of bacterial degradation of nitrate ester explosives have demonstrated the involvement of flavin-dependent oxidoreductases related to the old yellow enzyme (OYE) of yeast. Some of these enzymes also transform the nitroaromatic explosive 2,4,6-trinitrotoluene (TNT). In this work, catalytic capabilities of five members of the OYE family were compared, with a view to correlating structure and function. The activity profiles of the five enzymes differed substantially; no one compound proved to be a good substrate for all five enzymes. TNT is reduced, albeit slowly, by all five enzymes. The nature of the transformation products differed, with three of the five enzymes yielding products indicative of reduction of the aromatic ring. Our findings suggest two distinct pathways of TNT transformation, with the initial reduction of TNT being the key point of difference between the enzymes. Characterization of an active site mutant of one of the enzymes suggests a structural basis for this difference
A Redescription of Periclimenes yaldwyni Holthuis (Brachycarpus audouini Bate, 1888, Crustacea, Decapoda, Palaemonidae) and Its Occurrence in Australian Waters
The pontoniine shrimp Periclimenes yaldwyni Holthuis is
recorded for the first time from Australian waters and is redescribed and figured
in detail to augment the original description and illustration provided by Bate
(1888) as Brachycarpus audouini. The presently available data on carideans (eight
spp.) occurring in both Australian and New Zealand waters are summarized
Accurate simulation estimates of phase behaviour in ternary mixtures with prescribed composition
This paper describes an isobaric semi-grand canonical ensemble Monte Carlo
scheme for the accurate study of phase behaviour in ternary fluid mixtures
under the experimentally relevant conditions of prescribed pressure,
temperature and overall composition. It is shown how to tune the relative
chemical potentials of the individual components to target some requisite
overall composition and how, in regions of phase coexistence, to extract
accurate estimates for the compositions and phase fractions of individual
coexisting phases. The method is illustrated by tracking a path through the
composition space of a model ternary Lennard-Jones mixture.Comment: 6 pages, 3 figure
Nanostructuring of ÎČ-MnO<sub>2</sub>:The important role of surface to bulk ion migration
Manganese oxide materials are attracting considerable interest for clean energy storage applications such as rechargeable Li ion and Li-air batteries and electrochemical capacitors. The electrochemical behavior of nanostructured mesoporous beta-MnO, is in sharp constrast to the bulk crystalline system, which can intercalate little or no lithium; this is not fully understood on the atomic scale. Here, the electrochemical properties of beta-MnO2 are investigated using density functional theory with Hubbard U corrections (DFT+U). We find good agreement between the measured experimental voltage, 3.0 V, and our calculated value of 32 V. We consider the pathways for lithium migration and find a small barrier of 0.17 eV for bulk beta-MnO2, which is likely to contribute to its good performance as a lithium intercalation cathode in the mesoporous form. However, by explicit calculation of surface to bulk ion migration, we find a higher barrier of >0.6 eV for lithium insertion at the (101) surface that dominates the equilibrium morphology. This is likely to limit the practical use of bulk samples, and demonstrates the quantitative importance of surface to bulk ion migration in Li ion cathodes and supercapacitors. On the basis of the calculation of the electrostatic potential near the surface, we propose an efficient method to screen systems for the importance of surface migration effects. Such insight is valuable for the future optimization of manganese oxide nanomaterials for energy storage devices.</p
Understanding person acquisition using an interactive activation and competition network
Face perception is one of the most developed visual skills that humans display, and recent work has attempted to examine the mechanisms involved in face perception through noting how neural networks achieve the same performance. The purpose of the present paper is to extend this approach to look not just at human face recognition, but also at human face acquisition. Experiment 1 presents empirical data to describe the acquisition over time of appropriate representations for newly encountered faces. These results are compared with those of Simulation 1, in which a modified IAC network capable of modelling the acquisition process is generated. Experiment 2 and Simulation 2 explore the mechanisms of learning further, and it is demonstrated that the acquisition of a set of associated new facts is easier than the acquisition of individual facts in isolation of one another. This is explained in terms of the advantage gained from additional inputs and mutual reinforcement of developing links within an interactive neural network system. <br/
Lattice-switch Monte Carlo
We present a Monte Carlo method for the direct evaluation of the difference
between the free energies of two crystal structures. The method is built on a
lattice-switch transformation that maps a configuration of one structure onto a
candidate configuration of the other by `switching' one set of lattice vectors
for the other, while keeping the displacements with respect to the lattice
sites constant. The sampling of the displacement configurations is biased,
multicanonically, to favor paths leading to `gateway' arrangements for which
the Monte Carlo switch to the candidate configuration will be accepted. The
configurations of both structures can then be efficiently sampled in a single
process, and the difference between their free energies evaluated from their
measured probabilities. We explore and exploit the method in the context of
extensive studies of systems of hard spheres. We show that the efficiency of
the method is controlled by the extent to which the switch conserves correlated
microstructure. We also show how, microscopically, the procedure works: the
system finds gateway arrangements which fulfill the sampling bias
intelligently. We establish, with high precision, the differences between the
free energies of the two close packed structures (fcc and hcp) in both the
constant density and the constant pressure ensembles.Comment: 34 pages, 9 figures, RevTeX. To appear in Phys. Rev.
Molecular Characterization of a isoenzyme of the targeting peptide degrading protease, PreP2- catalysis, subcellular localization, expression and evolution
We have previously identified a zinc metalloprotease involved in the degradation of mitochondrial and chloroplast targeting peptides, the presequence protease (PreP). In the Arabidopsis thaliana genomic database, there are two genes that correspond to the protease, the zinc metalloprotease (AAL90904) and the putative zinc metalloprotease (AAG13049). We have named the corresponding proteins AtPreP1 and AtPreP2, respectively. AtPreP1 and AtPreP2 show significant differences in their targeting peptides and the proteins are predicted to be localized in different compartments. AtPreP1 was shown to degrade both mitochondrial and chloroplast targeting peptides and to be dual targeted to both organelles using an ambiguous targeting peptide. Here, we have overexpressed, purified and characterized proteolytic and targeting properties of AtPreP2. AtPreP2 exhibits different proteolytic subsite specificity from AtPreP1 when used for degradation of organellar targeting peptides and their mutants. Interestingly, AtPreP2 precursor protein was also found to be dual targeted to both mitochondria and chloroplasts in a single and dual in vitro import system. Furthermore, targeting peptide of the AtPreP2 dually targeted green fluorescent protein (GFP) to both mitochondria and chloroplasts in tobacco protoplasts and leaves using an in vivo transient expression system. The targeting of both AtPreP1 and AtPreP2 proteases to chloroplasts in A. thaliana in vivo was confirmed via a shotgun mass spectrometric analysis of highly purified chloroplasts. Reverse transcriptionâpolymerase chain reaction (RTâPCR) analysis revealed that AtPreP1 and AtPreP2 are differentially expressed in mature A. thaliana plants. Phylogenetic evidence indicated that AtPreP1 and AtPreP2 are recent gene duplicates that may have diverged through subfunctionalization
Dynamic renormalization group study of a generalized continuum model of crystalline surfaces
We apply the Nozieres-Gallet dynamic renormalization group (RG) scheme to a
continuum equilibrium model of a d-dimensional surface relaxing by linear
surface tension and linear surface diffusion, and which is subject to a lattice
potential favoring discrete values of the height variable. The model thus
interpolates between the overdamped sine-Gordon model and a related continuum
model of crystalline tensionless surfaces. The RG flow predicts the existence
of an equilibrium roughening transition only for d = 2 dimensional surfaces,
between a flat low-temperature phase and a rough high-temperature phase in the
Edwards-Wilkinson (EW) universality class. The surface is always in the flat
phase for any other substrate dimensions d > 2. For any value of d, the linear
surface diffusion mechanism is an irrelevant perturbation of the linear surface
tension mechanism, but may induce long crossovers within which the scaling
properties of the linear molecular-beam epitaxy equation are observed, thus
increasing the value of the sine-Gordon roughening temperature. This phenomenon
originates in the non-linear lattice potential, and is seen to occur even in
the absence of a bare surface tension term. An important consequence of this is
that a crystalline tensionless surface is asymptotically described at high
temperatures by the EW universality class.Comment: 22 pages, 5 figures. Accepted for publication in Physical Review
The purpose of mess in action research: building rigour though a messy turn
Mess and rigour might appear to be strange bedfellows. This paper argues that the purpose of mess is to facilitate a turn towards new constructions of knowing that lead to transformation in practice (an action turn). Engaging in action research - research that can disturb both individual and communally held notions of knowledge for practice - will be messy. Investigations into the 'messy area', the interface between the known and the nearly known, between knowledge in use and tacit knowledge as yet to be useful, reveal the 'messy area' as a vital element for seeing, disrupting, analysing, learning, knowing and changing. It is the place where long-held views shaped by professional knowledge, practical judgement, experience and intuition are seen through other lenses. It is here that reframing takes place and new knowing, which has both theoretical and practical significance, arises: a 'messy turn' takes place
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