Modelling of Dynamic Strain Aging with a Dislocation-Based Isotropic Hardening Model and Investigation of Orthogonal Loading

Based on experimental results, a dislocation material model describing the dynamic strain aging\ud effect at different temperatures is presented. One and two stage loading tests were performed in\ud order to investigate the influence of the loading direction as well as the temperature influence due\ud to the hardening mechanism. Bergström’s theory of work hardening was used as a basis for the\ud model development regarding the thermal isotropic behavior as well as the Chaboche model to\ud describe the kinematic hardening. Both models were implemented in an in-house FE-Code in\ud order to simulate the real processes. The present paper discusses two hardening mechanisms,\ud where the first part deals with the pure isotropic hardening including dynamic strain aging and the\ud second part involves the influence of the loading direction regarding combined (isotropic and\ud kinematic) hardening behavior

Substrate binding tunes the reactivity of hispidin 3-hydroxylase, a flavoprotein monooxygenase involved in fungal bioluminescence

Fungal bioluminescence was recently shown to depend on a unique oxygen-dependent system of several enzymes. However, the identities of the enzymes did not reveal the full biochemical details of this process, as the enzymes do not bear resemblance to those of other luminescence systems, and thus the properties of the enzymes involved in this fascinating process are still unknown. Here, we describe the characterization of the penultimate enzyme in the pathway, hispidin 3-hydroxylase, from the luminescent fungus Mycena chlorophos (McH3H), which catalyzes the conversion of hispidin to 3-hydroxyhispidin. 3-Hydroxyhispidin acts as a luciferin substrate in luminescent fungi. McH3H was heterologously expressed in Escherichia coli and purified by affinity chromatography with a yield of 100 mg/liter. McH3H was found to be a single component monomeric NAD(P)H-dependent FAD-containing monooxygenase having a preference for NADPH. Through site-directed mutagenesis, based on a modeled structure, mutant enzymes were created that are more efficient with NADH. Except for identifying the residues that tune cofactor specificity, these engineered variants may also help in developing new hispidin-based bioluminescence applications. We confirmed that addition of hispidin to McH3H led to the formation of 3-hydroxyhispidin as sole aromatic product. Rapid kinetic analysis revealed that reduction of the flavin cofactor by NADPH is boosted by hispidin binding by nearly 100-fold. Similar to other class A flavoprotein hydroxylases, McH3H did not form a stable hydroperoxyflavin intermediate. These data suggest a mechanism by which the hydroxylase is tuned for converting hispidin into the fungal luciferin.</p

Hominin paleoenvironment in East Asia: the Middle Paleolithic Xuchang-Lingjing (China) mammalian evidence

Bioarchaeolog

Relocation of active site carboxylates in major facilitator superfamily multidrug transporter LmrP reveals plasticity in proton interactions

The expression of polyspecific membrane transporters is one important mechanism by which cells can obtain resistance to structurally different antibiotics and cytotoxic agents. These transporters reduce intracellular drug concentrations to subtoxic levels by mediating drug efflux across the cell envelope. The major facilitator superfamily multidrug transporter LmrP from $\textit{Lactococcus}$ lactis catalyses drug efflux in a membrane potential and chemical proton gradient-dependent fashion. To enable the interaction with protons and cationic substrates, LmrP contains catalytic carboxyl residues on the surface of a large interior chamber that is formed by transmembrane helices. These residues co-localise together with polar and aromatic residues, and are predicted to be present in two clusters. To investigate the functional role of the catalytic carboxylates, we generated mutant proteins catalysing membrane potential-independent dye efflux by removing one of the carboxyl residues in Cluster 1. We then relocated this carboxyl residue to six positions on the surface of the interior chamber, and tested for restoration of wildtype energetics. The reinsertion at positions towards Cluster 2 reinstated the membrane potential dependence of dye efflux. Our data uncover a remarkable plasticity in proton interactions in LmrP, which is a consequence of the flexibility in the location of key residues that are responsible for proton/multidrug antiport.A.V.N. is a research associate funded by the Biotechnology and Biological Sciences Research Council (BBSRC). H.S., S.R. and Z.T. received scholarships from the Cambridge Commonwealth, European and International Trust. A.N. is the recipient of a Herchel-Smith Scholarship. K.A. is funded through a programme grant from the Human Frontier Science Program

Stabilizing forces acting on ZnO polar surfaces: STM, LEED, and DFT

published_or_final_versio

Low-energy peak structure in strong-field ionization by mid-infrared laser-pulses: two-dimensional focusing by the atomic potential

We analyze the formation of the low-energy structure (LES) in above-threshold ionization spectra first observed by Quan et al.\ \cite{quan09} and Blaga et al.\ \cite{blaga09} using both quasi-classical and quantum approaches. We show this structure to be largely classical in origin resulting from a two-dimensional focusing in the energy-angular momentum plane of the strong-field dynamics in the presence of the atomic potential. The peak at low energy is strongly correlated with high angular momenta of the photoelectrons. Quantum simulations confirm this scenario. Resulting parameter dependences agree with experimental findings \cite{quan09,blaga09} and, in part, with other simulations \cite{liu10,yan10,kast11}.Comment: 12 pages, 6 figure

Fully Automatic Expression-Invariant Face Correspondence

We consider the problem of computing accurate point-to-point correspondences among a set of human face scans with varying expressions. Our fully automatic approach does not require any manually placed markers on the scan. Instead, the approach learns the locations of a set of landmarks present in a database and uses this knowledge to automatically predict the locations of these landmarks on a newly available scan. The predicted landmarks are then used to compute point-to-point correspondences between a template model and the newly available scan. To accurately fit the expression of the template to the expression of the scan, we use as template a blendshape model. Our algorithm was tested on a database of human faces of different ethnic groups with strongly varying expressions. Experimental results show that the obtained point-to-point correspondence is both highly accurate and consistent for most of the tested 3D face models

On the Assumption of Initial Factorization in the Master Equation for Weakly Coupled Systems II: Solvable Models

We analyze some solvable models of a quantum mechanical system in interaction with a reservoir when the initial state is not factorized. We apply Nakajima-Zwanzig's projection method by choosing a reference state of the reservoir endowed with the mixing property. In van Hove's limit, the dynamics is described in terms of a master equation. We observe that Markovianity becomes a valid approximation for timescales that depend both on the form factors of the interaction and on the observables of the reservoir that can be measured.Comment: 25 page