A brief discussion: Thermodynamic and dynamic fragilities,non-divergent dynamics and the Prigogine–Defay ratio

This article brings together some of the work performed by the present author and collaborators that is related to the glass transition event and to some of its entropy aspects. The purpose of the work and discussion was motivated by a view that some of the frameworks in which we currently look at glassy behavior, while potentially useful, may also have limitations that we often do not fully consider. Discussion focuses on isochoric glass formation paths, thermodynamic and dynamic fragilities and how dynamic fragility in many systems (especially polymers, metals, ionic liquids and hydrogen bonding systems) seems to vary primarily with the glass transition temperature itself. This leads to the conclusion that such systems have an apparent activation energy that varies as the square of the glass temperature. The work then discusses evidence for a non-diverging relaxation time or viscosity as the glass temperature is approached and ends with a discussion of the Prigogine–Defay ratio.     

A dielectric study of poly(vinyl acetate) using a pulse-probe technique

There is considerable literature available that describes our understanding of the viscoelastic properties of polymers subjected to mechanical stresses or deformations. What we refer to here as a pulse-probe technique is one method that is commonly used to study the time-dependent behavior of materials in histories, e.g., temperature-jump or step-deformations, that exhibit fading memory responses. In the linear case the behavior is well understood in the context of Boltzmann superposition ideas. However, there is only limited work available that investigates the dielectric response of materials within this same context. In the present study, we present an investigation of the dielectric behavior of poly(vinyl acetate) (PVAc) using a two-step pulse-probe technique. Time domain dielectric experiments were performed in the vicinity of the glass transition temperature. After establishing the linear response function in single-step experiments, two types of pulse-probe experiments were performed. In one, the time duration t ₁ of the first step in the probe was varied. In the second case, the magnitude of the field E ₁ applied to the sample for the first step was varied. We not only demonstrate the existence of the memory effect in the dielectric response, but also find that the responses are consistent with the linear Boltzmann superposition principle. Evidence of deviations from linear superposition at the highest electric fields is also presented.     

Computational Analysis of Mixing and Scale-Up in Emulsion Polymerization Reactors

Summary: A hybrid multi-zonal/computational fluid dynamics (CFD) framework is currently being developed to aid in the scale-up of high solid content latex production and processing. Poly3D, a commercial laminar CFD code tailored to modelling the mixing of non-Newtonian fluids, has been coupled to a population balance model via a customized interface. CFD is used to generate flow fields inside a series of reactors; this information is then transferred to a multi-zone population balance model to assess the impact of non-homogenous mixing on the evolution of the latex particle size distribution (PSD) when concentrated latex suspension is altered via the addition of a coagulant. The rheological properties of high solid content latexes are sensitive to changes in the PSD, so the flow field is periodically updated if significant changes in the rheological properties of the latex are detected in any of the zones. The details of the models comprising the framework are presented and the utility of the framework is demonstrated.     

High frequency shaking induced by low frequency forcing: Periodic oscillations in a spring–cable system

We investigate the response of a piecewise linear spring to very low frequency forcing. It has been observed that the bifurcation picture is very complicated with many multiple periodic responses with a high frequency component. We show many new aspects of this phenomenon, including what happens if the nonlinearity is smoothed out. Methods used include Newton’s method, in combination with continuation algorithms, and a steepest descent method for finding new isolated branches of solutions.     

Synthesis of Polyacrylic/Silica Nanocomposite Latexes using Static Mixer

Summary: Static mixers (Sulzer Chemtech; SMX) were used to prepare silica/ MMA-co-BA miniemulsions that were polymerized to produce nanocomposite latexes. Acceptable conditions for the formulation of polymerizable nanodroplets were found and subsequently used to produce silica/poly(MMA-co-BA) nanocomposites. The droplet size distribution of the resulting miniemulsions was narrow enough that it could be successfully polymerized. It was found that the droplet size depends on the silica content and increases with increasing the silica concentration. It was also shown that there is a relationship between the droplet size and the viscosity of the dispersed phase. The majority of droplets were nucleated upon polymerization when less than 15% silica was used. However, when the silica content exceeded 15%, the ratio of the number of particles in the final latex to the number of droplets (Np/Nd) increased to value much higher than 1 indicating the occurrence of homogeneous nucleation.     

Selective hydrophobic pocket binding observed within the carbonic anhydrase II active site accommodate different 4-substituted-ureido-benzenesulfonamides and correlate to inhibitor potency

4-Substituted-ureido benzenesulfonamides showing inhibitory activity against carbonic anhydrase (CA, EC 4.2.1.1) II between 3.3-226 nM were crystallized in complex with the enzyme. Hydrophobic interactions between the scaffold of the inhibitors in different hydrophobic pockets of the enzyme were observed, explaining the diverse inhibitory range of these derivatives.     

High-spin structure of yrast-band in 78Kr

Lifetime of levels up to 22⁺, have been measured in ⁷⁸Kr and an oblate shape is assigned to the ground state using the CSM and the configuration dependent shell correction calculations. Calculations further show that ⁷⁸Kr is highly γ-soft nucleus. The experimental Q _t values coupled with theoretical calculations indicate an oblate shape for ⁷⁸Kr at low spins and triaxial shape at higher spins     

Uncertainty and value of information when allocating resources within and between healthcare programmes

A two-stage stochastic mathematical programming formulation has been developed to optimally allocate resources within and between healthcare programmes when there is an exogenous budget and the parameters of the healthcare models are variable and uncertain. This formulation solves the optimal resource allocation problem and calculates the expected value of acquiring additional information to resolve the uncertainties within the allocation. It is shown that the proposed formulation has several advantages over the chance constrained and robust mathematical programming methods.