The evolution of the viscoelastic retardation spectrum during the development of an epoxy resin network

The evolution of the viscoelastic behavior of an epoxy resin at various stages of curing has been followed with the changes in the retardation spectrum. The creep J(t) and recoverable creep compliance J_r(t) curves of the neat epoxy resin Epon l00lF (Shell) were determined at temperatures between 30 and 77°C. The viscosity decreased over 8 orders of magnitude as the temperature was increased. Specimens with eight stages of network development were prepared by reacting all of the epoxy resin's oxirane rings with amine hydrogens from varying ratios of a monofunctional amine (methyl aniline) and a tetrafunctional amine 4,4′-diamino diphenyl sulfone (DDS). Preparations in which 25, 35, and 40% DDS were used did not result in a molecular network, so they were viscoelastic liquids. With 45% DDS, the product had a nascent network and was judged to be just beyond the point of incipient gelation. The remaining preparations from 0.50, 0.60, 0.70, and 1.0 DDS yielded tighter less compliant molecular networks. The creep and recoverable compliance curves were measured over a range of temperatures above the glass transition temperature, T_g. They were reduced to T_g, and retardation spectra L(ln τ) were calculated.     

Chaos in a three-variable model of an excitable cell

We describe chaotic behavior in a model that consists of three first-order, non-linear differential equations, which represent ionic events in excitable membranes. For a certain range of conductances, the model generates chaotic action potentials, and the intracellular calcium concentration also varies chaotically. The chaos was characterized by constructing phase portraits and one-variable maps using the membrane potentials and calcium concentrations. This is the first, simple, biophysically realistic model for excitable cells that shows endogenous chaos.     

On counting theorems for self-avoiding walks

Certain differences are pointed out between two recently published counting theorems for self-avoiding walks on a lattice.     

Non-leptonic B decays into two light mesons in soft-collinear effective theory

We consider non-leptonic B decays into two light mesons at leading order in soft-collinear effective theory, and show that the decay amplitudes are factorized at next-to-leading order in _s. The operators for non-leptonic B decays in the full theory are first matched to the operators in SCET_I, which is the effective theory appropriate for with Λ0.5 GeV. We evolve the operators and the relevant time-ordered products in SCET_I to SCET_II, which is appropriate for . Using the gauge-invariant operators in SCET_II, we compute non-leptonic B decays in SCET, including the non-factorizable spectator contributions and spectator contributions to the heavy-to-light form factor. As an application, we present the decay amplitudes for in soft-collinear effective theory.     

Effect of NaOH on large-volume sample stacking of haloacetic acids in capillary zone electrophoresis with a low-pH buffer

Large-volume sample stacking (LVSS) is an effective on-capillary sample concentration method in capillary zone electrophoresis, which can be applied to the sample in a low-conductivity matrix. NaOH solution is commonly used to back-extract acidic compounds from organic solvent in sample pretreatment. The effect of NaOH as sample matrix on LVSS of haloacetic acids was investigated in this study. It was found that the presence of NaOH in sample did not compromise, but rather help the sample stacking performance if a low pH background electrolyte (BGE) was used. The sensitivity enhancement factor was higher than the case when sample was dissolved in pure water or diluted BGE. Compared with conventional injection (0.4% capillary volume), 97-120-fold sensitivity enhancement in terms of peak height was obtained without deterioration of separation with an injection amount equal to 20% of the capillary volume. This method was applied to determine haloacetic acids in tap water by combination with liquid-liquid extraction and back-extraction into NaOH solution. Limits of detection at sub-ppb levels were obtained for real samples with direct UV detection.     

Instanton contribution to 431-1431-1431-1decay

We study instanton effects on inclusive semileptonicb→u decay using the heavy quark effective field theory and the operator product expansion. The effect contributes not only to the hadronic matrix element but also to the coefficient functions in the operator product expansion. We find that the coefficient function is singular near the boundaries of the phase space. In order to use perturbative QCD reliably, it is necessary to introduce smearing near the boundary. However the instanton contribution tob→c decay seems negligibly small.     

Crisis transitions in excitable cell models

It is believed that sudden changes both in the size of chaotic attractor and in the number of unstable periodic orbits on chaotic attractor are sufficient for interior crisis. In this paper, some interior crisis phenomena were discovered in a class of physically realizable dissipative dynamical systems. These systems represent the oscillatory activity of membrane potentials observed in excitable cells such as neuronal cells, pancreatic β-cells, and cardiac cells. We examined the occurrence of interior crises in these systems by two means: (i) constructing bifurcation diagrams and (ii) calculating the number of unstable periodic orbits on chaotic attractor. Bifurcation diagrams were obtained by numerically integrating the simultaneous differential equations which simulate the activity of excitable membranes. These bifurcation diagrams have shown an apparent crisis activity. We also demonstrate in terms of the associated Poincaré maps that the number of unstable periodic orbits embedded in a chaotic attractor suddenly increases or decreases at the crisis.     

Instanton contribution toB→X s γ decay

We study instanton effects onBX _s decay using the heavy quark effective field theory and the operator product expansion. In the dilute gas approximation the effect is negligibly small. This is in contrast to the result of the instanton effect in inclusive semileptonicbu decay but similar to the inclusive hadronic decay. We discuss the similarities and differences of theBX _s decay compared to inclusive hadronic decay and semileptonicB decay.