[Book review] Psicologia Della Prova [Psychology of Proof]

Review of: Psicologia Della Prova [Psychology of Proof] edited by C. Cabras, Giuffré, Milano. 1996.

Zinc polycarboxylate dental cement for the controlled release of an active organic substance: proof of concept

The potential of employing zinc polycarboxylate dental cement as a controlled release material has been studied. Benzalkonium chloride was used as the active ingredient, and incorporated at concentrations of 1, 2 and 3% by mass within the cement. At these levels, there was no observable effect on the speed of setting. Release was followed using an ion-selective electrode to determine changes in chloride ion concentration with time. This technique showed that the additive was released when the cured cement was placed in water, with release occurring by a diffusion mechanism for the first 3 h, but continuing beyond that for up to 1 week. Diffusion coefficients were in the range 5.62 × 10(−6) cm(2) s(−1) (for 1% concentration) to 10.90 × 10(−6) cm(2) s(−1) (for 3% concentration). Up to 3% of the total loading of benzalkonium chloride was released from the zinc polycarboxylate after a week, which is similar to that found in previous studies with glass-ionomer cement. It is concluded that zinc polycarboxylate cement is capable of acting as a useful material for the controlled release of active organic compounds.

Applications of Feller-Reuter-Riley transition functions

A Feller–Reuter–Riley function is a Markov transition function whose corresponding semigroup maps the set of the real-valued continuous functions vanishing at infinity into itself. The aim of this paper is to investigate applications of such functions in the dual problem, Markov branching processes, and the Williams-matrix. The remarkable property of a Feller–Reuter–Riley function is that it is a Feller minimal transition function with a stable q-matrix. By using this property we are able to prove that, in the theory of branching processes, the branching property is equivalent to the requirement that the corresponding transition function satisfies the Kolmogorov forward equations associated with a stable q-matrix. It follows that the probabilistic definition and the analytic definition for Markov branching processes are actually equivalent. Also, by using this property, together with the Resolvent Decomposition Theorem, a simple analytical proof of the Williams' existence theorem with respect to the Williams-matrix is obtained. The close link between the dual problem and the Feller–Reuter–Riley transition functions is revealed. It enables us to prove that a dual transition function must satisfy the Kolmogorov forward equations. A necessary and sufficient condition for a dual transition function satisfying the Kolmogorov backward equations is also provided.

Uniqueness criteria for continuous-time Markov chains with general transition structures

We derive necessary and sufficient conditions for the existence of bounded or summable solutions to systems of linear equations associated with Markov chains. This substantially extends a famous result of G. E. H. Reuter, which provides a convenient means of checking various uniqueness criteria for birth-death processes. Our result allows chains with much more general transition structures to be accommodated. One application is to give a new proof of an important result of M. F. Chen concerning upwardly skip-free processes. We then use our generalization of Reuter's lemma to prove new results for downwardly skip-free chains, such as the Markov branching process and several of its many generalizations. This permits us to establish uniqueness criteria for several models, including the general birth, death, and catastrophe process, extended branching processes, and asymptotic birth-death processes, the latter being neither upwardly skip-free nor downwardly skip-free.

A study of modelling approaches for rail vehicle collision behaviour

A rigid wall model has been used widely in the numerical simulation of rail vehicle impacts. Finite element impact modelling of rail vehicles is generally based on a half-width and full-length or half-length structure, depending on the symmetry. The structure and components of rail vehicles are normally designed to cope with proof loading to ensure adequate ride performance. In this paper, the authors present a study of a rail vehicle with driving cab focused on improving the modelling approach and exploring the intrinsic structural weaknesses to enhance its crashworthiness. The underpinning research used finite element analysis and compared the behaviour of the rail vehicle in different impact scenarios. It was found that the simulation of a rigid wall impact can mask structural weaknesses; that even a completely symmetrical impact may lead to an asymmetrical result; that downward bending is an intrinsic weakness of conventional rail vehicles and that a rigid part of the vehicle structure, such as the body bolster, may cause uncoordinated deformation and shear fracture between the vehicle sections. These findings have significance for impact simulation, the full-scale testing of rail vehicles and rail vehicle design in general.

Can Pickering emulsion formation aid the removal of creosote DNAPL from porous media?

The purpose of this investigation was to examine the proposition that creosote, emplaced in an initially water saturated porous system, can be removed from the system through Pickering emulsion formation. Pickering emulsions are dispersions of two immiscible fluids in which coalescence of the dispersed phase droplets is hindered by the presence of colloidal particles adsorbed at the interface between the two immiscible fluid phases. Particle trapping is strongly favoured when the wetting properties of the particles are intermediate between strong water wetting and strong oil wetting. In this investigation the necessary chemical conditions for the formation of physically stable creosote-in-water emulsions protected against coalescence by bentonite particles were examined. It was established that physically stable emulsions could be formed through the judicious addition of small amounts of sodium chloride and the surfactant cetyl-trimethylammonium bromide. The stability of the emulsions was initially established by visual inspection. However, experimental determinations of emulsion stability were also undertaken by use of oscillatory rheology. Measurements of the elastic and viscous responses to shear indicated that physically stable emulsions were obtained when the viscoelastic systems showed a predominantly elastic response to shearing. Once the conditions were established for the formation of physically stable emulsions a "proof-of-concept" chromatographic experiment was carried out which showed that creosote could be successfully removed from a saturated model porous system. (C) 2007 Elsevier Ltd. All rights reserved.

Polyunsaturated fatty acids in the pathogenesis and treatment of multiple sclerosis

Epidemiological, biochemical, animal model and clinical trial data described in this overview strongly suggest that polyunsaturated fatty acids, particularly n-6 fatty acids, have a role in the pathogenesis and treatment of multiple sclerosis (MS). Data presented provides further evidence for a disturbance in n-6 fatty acid metabolism in MS. Disturbance of n-6 fatty acid metabolism and dysregulation of cytokines are shown to be linked and a "proof of concept clinical trial" further supports such a hypothesis. In a randomised double-blind, placebo controlled trial of a high dose and low dose selected GLA (18:3n-6)-rich oil and placebo control, the high dose had a marked clinical effect in relapsing-remitting MS, significantly decreasing the relapse rate and the progression of disease. Laboratory findings paralleled clinical changes in the placebo group in that production of mononuclear cell pro-inflammatory cytokines (TNF-alpha, IL-1 beta) was increased and anti-inflammatory TGF-beta markedly decreased with loss of membrane n-6 fatty acids linoleic (18:2n-6) and arachidonic acids (20:4n-6). In contrast there were no such changes in the high dose group. The improvement in disability (Expanded Disability Status Scale) in the high dose suggests there maybe a beneficial effect on neuronal lipids and neural function in MS. Thus disturbed n-6 fatty acid metabolism in MS gives rise to loss of membrane long chain n-6 fatty acids and loss of the anti-inflammatory regulatory cytokine TGF-beta, particularly during the relapse phase, as well as loss of these important neural fatty acids for CNS structure and function and consequent long term neurological deficit in MS.