An approach to understanding avalanche statistics in mean‐field driven threshold systems

Driven threshold models that produce complex histories of avalanches are used to simulate the dynamics of many complex interacting systems, such as earthquake generating faults and neural networks. A mean‐field model may be formulated in a way that makes avalanches Abelian, so the final size of the avalanche depends only on the initial conditions, not the algorithm. If the initial stress distribution is statistically stationary, the avalanche size distribution is generated by the first intersection of a random process with a curvilinear boundary. Solutions show that such mean‐field models are never truly critical, but always exhibit dissipation or finite‐size effects. © 2005 Wiley Periodicals, Inc. Complexity 10:68–72, 2005     

The strangeness-conserving effective weak interaction in the quark basis

Strong interaction corrections to the Glashow-Salam-Weinberg model of electroweak interaction are studied, for the up and down quarks only, to all orders of leading logarithms using renormalization-group techniques. The resulting quark effective weak hamiltonian is explicitly written out in a form convenient for obtaining matrix elements. The accuracy of this result is estimated by a comparison with finite, one-loop calculations of parity-violating parts of the interaction.     

A quark model calculation of the weak parity violating asymmetry in high-energy proton-nucleon scattering

We perform a quark-model calculation of the parity-violating asymmetry in high-energy polarized proton-unpolarized nucleon scattering. Strong interaction enhancement has been taken into account using both renormalization group techniques and precise one-loop calculations. Essential high-twist (bound state) contributions to the asymmetry have been included. Our results indicate large (～10^?6) positive values for the parity-violating asymmetry at high energy, in agreement with the experimental results of Lockyer et al.     

Nematogenic aromatic block copolymers of rigid and flexible units. II. Phase equilibria

The solubility and mesophase behavior are investigated for block copolymers of poly(p-benzamide) (PBA), the polyterephthalamide of p-aminobenzhydrazide (PABH-T), and PBA and poly(m-phenylene isophthalamide) (MPD-I) dissolved in N,N-dimethylacetamide (DMAc) containing 3% LiCl. The block copolymers, whose synthesis and characterization were described in the previous paper in this series, included samples prepared by the two-step and multistep copolycondensations. The first of these methods yields a considerable amount of the flexible homopolymer (PABH-T) and also some of the rigid homopolymer. The flexible homopolymer can be removed from the block copolymer by extraction with dimethyl sulfoxide (DMSO), whereas precipitation may offer a way to remove the rigid homopolymer. The results observed for the block copolymers are compared with those for the homopolymers and mixtures of homopolymers. The apparent solubility of the PBA/PABH-T block copolymers obtained by the two-step method is unusually large but decreases toward the value observed for mixtures after the flexible homopolymer had been extracted with DMSO. Labile adducts involving PABH-T and/or the block copolymer appear to be capable of forming a single mesophase. This offers a most interesting approach to the preparation of composite materials involving rigid and flexible polymers.     

Optimal Control of Some Simple Deterministic Epidemic Models

Using control variables such as the level of medicare programme effort and the level of inoculation programme effort, three simple mathematical models of epidemics are transformed into optimal control problems. These are multi-state problems with the state variables as numbers of infectives and susceptibles and with the objective function being minimization of the total present value of the social or economic costs of infectives and medical controls. The problems are analysed with the framework of the maximum principle to obtain or, at least, partially characterize the optimal policies over time.     

The EPR spectra of irradiated KHCO3 crystals

The EPR spectra of γ-irradiated KHCO₃ and KDCO₃ crystals were re-examined in the hope of identifying in them the species HOCO. This proved unsuccessful, but some anomalies in the results and conclusions of earlier workers concerning trapped CO^?₂ and CO^?₂ radicals are re-interpreted in the light of improved data.     

Development of a high-throughput enzyme-linked immunosorbent assay for the routine detection of the carcinogen acrylamide in food, via rapid derivatisation pre-analysis

The spontaneous formation of the neurotoxic carcinogen acrylamide in a wide range of cooked foods has recently been discovered. These foods include bread and other bakery products, crisps, chips, breakfast cereals, and coffee. To date, the diminutive size of acrylamide (71.08 Da) has prevented the development of screening immunoassays for this chemical. In this study, a polyclonal antibody capable of binding the carcinogen was produced by the synthesis of an immunogen comprising acrylamide derivatised with 3-mercaptobenzoic acid (3-MBA), and its conjugation to the carrier protein bovine thyroglobulin. Antiserum from the immunised rabbit was harvested and fully characterised. It displayed no binding affinity for acrylamide or 3-MBA but had a high affinity for 3-MBA-derivitised acrylamide. The antisera produced was utilised in the development of an ELISA based detection system for acrylamide. Spiked water samples were assayed for acrylamide content using a previously published extraction method validated for coffee, crispbread, potato, milk chocolate and potato crisp matrices. Extracted acrylamide was then subjected to a rapid 1-h derivatisation with 3-MBA, pre-analysis. The ELISA was shown to have a high specificity for acrylamide, with a limit of detection in water samples of 65.7 μg kg⁻¹, i.e. potentially suitable for acrylamide detection in a wide range of food commodities. Future development of this assay will increase sensitivity further. This is the first report of an immunoassay capable of detecting the carcinogen, as its small size has necessitated current analytical detection via expensive, slower, physico-chemical techniques such as Gas or Liquid Chromatography coupled to Mass Spectrometry.