Atomistic theory and simulation of the morphology and structure of ionic nanoparticles

Computational techniques are widely used to explore the structure and properties of nanomaterials. This review surveys the application of both quantum mechanical and force field based atomistic simulation methods to nanoparticles, with a particular focus on the methodologies available and the ways in which they can be utilised to study structure, phase stability and morphology. The main focus of this article is on partially ionic materials, from binary semiconductors through to mineral nanoparticles, with more detailed considered of three examples, namely titania, zinc sulphide and calcium carbonate.     

Electron and photon beams interacting with plasma

A comparison is made between the interaction of electron bunches and intense laser pulses with plasma. The laser pulse is modelled with photon kinetic theory, i.e. a representation of the electromagnetic field in terms of classical quasi-particles with space and wave number coordinates, which enables a direct comparison with the phase space evolution of the electron bunch. Analytical results are presented of the plasma waves excited by a propagating electron bunch or laser pulse, the motion of electrons or photons in these plasma waves and collective effects, which result from the self-consistent coupling of the particle and plasma wave dynamics.     

Working memory and the control of action: Evidence from task switching.

A series of 7 experiments used dual-task methodology to investigate the role of working memory in the operation of a simple action-control plan or program involving regular switching between addition and subtraction. Lists requiring switching were slower than blocked lists and showed 2 concurrent task effects. Demanding executive tasks impaired performance on both blocked and switched lists, whereas articulatory suppression impaired principally the switched condition. Implications for models of task switching and working memory and for the Vygotskian concept of verbal control of action are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dealing with Zero-Time Transitions in Axiom Systems

In the modalization of time-dependent systems it is often useful to use the abstraction ofzero-time transitions, i.e., changes of system state that occur in a time that can be neglected with respect to the whole dynamics of system evolution. Such an abstraction, however, sometimes generates critical situations in the formal system analysis. This may lead to limitations or unnatural use of such formal analysis. In this paper we present an approach that keeps the intuitive appeal of the zero-time transition abstraction, yet maintains simplicity and generality in its use. The approach is based on considering zero-time transitions as occurring in an infinitesimal, yet nonnull time. The adopted notation is borrowed from nonstandard analysis. The approach is illustrated through Petri nets as a case of state machines and TRIO as a case of logic-based assertion language, but it can be easily applied to any formal system dealing with states, time, and transitions.     

Citric acid as a green additive to retard calcium carbonate scales on process equipment

In this paper, the retarding effect of a green additive, citric acid, towards calcium carbonate scale deposition is studied. Scale formation is one of the most common causes of malfunctions in process equipment. This is the reason it is crucial to retard scale precipitation, that is, in order to reduce economic damages. With this additive in the solution, experimental runs have been carried out in supersaturation conditions in terms of concentration of calcium carbonate at equilibrium, with a supersaturation ratio ranging from 16 to 280, at 25°C. Three different concentrations of citric acid have been investigated (0.520 × 10⁻³, 1.041 × 10⁻³ and 1.561 × 10⁻³ M) in a laboratory scale plant. Comparing results obtained in terms of induction time with previous experimental runs, performed without additives, citric acid has shown its significant capacity to retard calcium carbonate precipitation, by increasing induction time values. This behaviour is enhanced by raising the additive concentration in solution up to a specific threshold value, beyond which no benefit in terms of calcium scale inhibition is gained. Furthermore, interfacial tension has been computed without and with citric acid at 0.520 × 10⁻³ and 1.041 × 10⁻³ M, as a function of the different concentration amounts investigated. The values obtained are in good agreement with data reported in the literature.