A stochastic differential equation for local times of super-Brownian motion

We show that local times of super-Brownian motion, or of Brownian motion indexed by the Brownian tree, satisfy an explicit stochastic differential equation. Our proofs rely on both excursion theory for the Brownian snake and tools from the theory of superprocesses.Comment: 32 page

Excluded volume effects on the structure of a linear polymer under shear flow

The effect of excluded volume interactions on the structure of a polymer in shear flow is investigated by Brownian Dynamics simulations for chains with size $30\leq N\leq 300$. The main results concern the structure factor $S({\bf q})$ of chains of N=300 Kuhn segments, observed at a reduced shear rate $\beta=\dot{\gamma}\tau=3.2$, where $\dot{\gamma}$ is the bare shear rate and $\tau$ is the longest relaxation time of the chain. At low q, where anisotropic global deformation is probed, the chain form factor is shown to match the form factor of the continuous Rouse model under shear at the same reduced shear rate, computed here for the first time in a wide range of wave vectors. At high q, the chain structure factor evolves towards the isotropic equilibrium power law $q^{-1/\nu}$ typical of self-avoiding walk statistics. The matching between excluded volume and ideal chains at small q, and the excluded volume power law behavior at large q are observed for ${\bf q}$ orthogonal to the main elongation axis but not yet for ${\bf q}$ along the elongation direction itself, as a result of interferences with finite extensibility effects. Our simulations support the existence of anisotropic shear blobs for polymers in good solvent under shear flow for $\beta>1$ provided chains are sufficiently long.Comment: 36 pages, 11 figures, submitted to J. Chem. Phy

Peptide inhibitors of Streptomyces DD-carboxypeptidases

1. Peptides that inhibit the dd-carboxypeptidases from Streptomyces strains albus G and R61 were synthesized. They are close analogues of the substrates of these enzymes. The enzymes from albus G and R61 strains are in general inhibited by the same peptides, but the enzyme from strain R39 differs considerably. 2. The two C-terminal residues of the peptide substrates and inhibitors appear to be mainly responsible for the initial binding of the substrate to the enzymes from albus G and R61 strains. The side chain in the third residue from the C-terminus seems critical in inducing catalytic activity. 3. Experimental evidence is presented suggesting that the amide bond linking the two C-terminal residues has a cis configuration when bound to the enzymes from strains albus G and R61. 4. The peptide inhibitors are not antibiotics against the same micro-organisms

Binding of beta-lactam antibiotics to the exocellular DD-carboxypeptidase-transpeptidase of Streptomyces R39

Benzylpenicillin and cephaloridine reacted with the exocellular dd-carboxypeptidase-transpeptidase from Streptomyces R39 to form equimolar and inactive antibiotic-enzyme complexes. At saturation, the molar ratio of chromogenic cephalosporin 87-312 to enzyme was 1.3:1, but this discrepancy might be due to a lack of accuracy in the measurement of the antibiotic. Spectrophotometric studies showed that binding of cephaloridine and cephalosporin 87-312 to the enzyme caused opening of their beta-lactam rings. Benzylpenicillin and cephalosporin 87-312 competed for the same site on the free enzyme, suggesting that binding of benzylpenicillin also resulted in the opening of its beta-lactam ring. In Tris-NaCl-MgCl(2) buffer at pH7.7 and 37 degrees C, the rate constants for the dissociation of the antibiotic-enzyme complexes were 2.8x10(-6), 1.5x10(-6) and 0.63x10(-6)s(-1) (half-lives 70, 130 and 300h) for benzylpenicillin, cephalosporin 87-312 and cephaloridine respectively. During the process, the protein underwent reactivation. The enzyme that was regenerated from its complex with benzylpenicillin was as sensitive to fresh benzylpenicillin as the native enzyme. With [(14)C]benzylpenicillin, the released radioactive compound was neither benzylpenicillin nor benzylpenicilloic acid. The Streptomyces R39 enzyme thus behaved as a beta-lactam-antibiotic-destroying enzyme but did not function as a beta-lactamase. Incubation at 37 degrees C in 0.01m-phosphate buffer, pH7.0, and in the same buffer supplemented with sodium dodecyl sulphate caused a more rapid reversion of the [(14)C]benzylpenicillin-enzyme complex. The rate constants were 1.6x10(-5)s(-1) and 0.8x10(-4)s(-1) respectively. Under these conditions, however, there was no concomitant reactivation of the enzyme and the released radioactive compound(s) appeared not to be the same as before. The Streptomyces R39 enzyme and the exocellular dd-carboxypeptidase-transpeptidase from Streptomyces R61 appeared to differ from each other with regard to the topography of their penicillin-binding site

Reflection symmetry breaking scenarios with minimal gauge form coupling in brane world cosmology

This article synthesises and extends recent work on the cosmological consequences of dropping the usual Z_2 reflection symmetry postulate in brane world scenarios. It is observed that for a cosmological model of homogeneous isotropic type, the relevant generalised Birkhoff theorem establishing staticity of the external vacuum in the maximally symmetric ``bulk'' outside a freely moving world brane will remain valid for the case of motion that is forced by minimal (generalised Wess Zumino type) coupling to an external antisymmetric gauge field provided its kinetic action contribution has the usual homogeneous quadratic form. This means that the geometry on each side of the brane worldsheet will still be of the generalised Schwarzschild anti de Sitter type. The usual first integrated Friedmann equation for the Hubble expansion rate can thereby be straightforwardly generalised by inclusion of new terms involving 2 extra parameters respectively measuring the strength of the gauge coupling and the degree of deviation from reflection symmetry. Some conceivable phenomenological implications are briefly outlined, and corresponding limitations are derived for possible values of relevant parameters.Comment: 13 pages latex (revised to rectify a couple of sign transcription errors

Urban aerosols survey LIDAR and numerical model

In this paper, we present a new methodology for urban aerosol survey, coupling Lidar measurements and numerical models. The aim of this study is build a continuous survey of aerosol impact on the local and regional scale

The Role of Cognition and Social Functioning as Predictors in the Transition to Psychosis for Youth With Attenuated Psychotic Symptoms

In the literature, there have been several attempts to develop prediction models for youth who are at clinical high risk (CHR) of developing psychosis. Although there are no specific clinical or demographic variables that seem to consistently predict the later transition to psychosis in those CHR youth, in addition to attenuated psychotic symptoms, the most commonly occuring predictors tend to be poor social functioning and certain cognitive tasks. Unfortunately, there has been little attempt to replicate alogorithms. A recently published article by Cornblatt et al suggested that, for individuals with attentuated psychotic symptoms (APS), disorganized communication, suspiciousness, verbal memory, and a decline in social functioning were the best predictors of later transition to psychosis (the RAP model). The purpose of this article was to first test the prediction model of Cornblatt et al with a new sample of individuals with APS from the PREDICT study. The RAP model was not the best fit for the PREDICT data. However, using other variables from PREDICT, it was demonstrated that unusual thought content, disorganized communication, baseline social functioning, verbal fluency, and memory, processing speed and age were predictors of later transition to psychosis in the PREDICT sample. Although the predictors were different in these 2 models, both supported that disorganized communication, poor social functioning, and verbal memory, were good candidates as predictors for later conversion to psychosis

Coupled structural and magnetic properties of ferric fluoride nanostructures: part II, a Monte-Carlo Heisenberg study

We present a numerical study of the magnetic structure of nanostructured iron fluoride, using the Monte-Carlo-Metropolis simulated annealing technique and a classical Heisenberg Hamiltonian with a superexchange angle dependence. The parameters are adjusted on experimental results, and the atomic structure and topology taken from a previous atomistic model of grain boundaries in the same system. We find perfect antiferromagnetic crystalline grains and a disordered magnetic configuration (speromagnetic like) at the grain boundary, in agreement with experimental findings. Both the lowest magnetic energy and the rate of magnetic frustration are found to be dependent on the relative disorientation of crystalline grains, i.e. on the cationic topology. By simulating hysteresis loops, we find that the magnetization rotation is not spatially uniform. We conclude on possible extensions of the model.Comment: submitted to JMM