Self-diffusion in a triple-defect A-B binary system : Monte Carlo simulation

In this comprehensive and detailed study, vacancy-mediated self-diffusion of A- and B-elements in triple-defect B2-ordered ASB1-S binaries is simulated by means of a kinetic Monte Carlo (KMC) algorithm involving atomic jumps to nearest-neighbour (nn) and next-nearest-neighbour (nnn) vacancies. The systems are modelled with an Ising-type Hamiltonian with nn and nnn pair interactions completed with migration barriers dependent on local configurations. Self-diffusion is simulated at equilibrium and temperature-dependent vacancy concentrations are generated by means of a Semi Grand Canonical MC (SGCMC) code. The KMC simulations reproduced the phenomena observed experimentally in Ni-Al intermetallics being typical representatives of the 'triple-defect' binaries. In particular, they yielded the characteristic ‘V’-shapes of the isothermal concentration dependencies of A- and B-atom diffusivities, as well as the strong enhancement of the B-atom diffusivity in B-rich systems. The atomistic origins of the phenomenon, as well as other features of the simulated self-diffusion such as temperature and composition dependences of tracer correlation factors and activation energies are analyzed in depth in terms of a number of nanoscopic parameters that are able to be tuned and monitored exclusively with atomistic simulations. The roles of equilibrium and kinetic factors in the generation of the observed features are clearly distinguished and elucidated

Producing and using community health education films in low- and middle-income countries

Objective: To analyse the production and use of health education films in Kenya, Tanzania and Zambia. // Design: Review of community health education films and their use by three partner organisations. // Methods: A focused content analysis of 18 community health education films was conducted, and three exemplar films were selected for more detailed review. Interviews were carried out with four film production personnel and seven project workers using the films in health education projects in Kenya, Tanzania and Zambia. Concepts drawn from the Ottawa Charter for Health Promotion and Anchored Instruction informed the study. // Findings: The films, produced primarily for use across sub-Saharan Africa, mostly conveyed biological information and addressed behavioural issues related to maternal and child health topics. The predominantly low-literacy audiences reached by the projects may further benefit from localised content highlighting the social determinants of health through engaging narrative formats. While the health education projects provided some opportunities to discuss the films after screening, linked problem-solving activities could raise awareness of the multiple factors influencing health and help community members formulate holistic action plans. // Conclusion: The film production company responded to emerging findings, noting that more context-specific films should be produced, with community members being more fully involved in planning, production and evaluation. Such an approach could generate more relevant content and engage audiences more effectively in problem-solving related to health and wellbeing

INFLUENCE OF DOUBLE SOLUTION TREATMENT ON HARDNESS IN 17-4 PH STEEL

The investigated material is a corrosion-resistant, Cu precipitation hardened steel 17-4PH, which undergoes a macroscopic contraction, as a result of applying the following heat treatment: double solution treatment at 1028°C for 1 h (condition A), ageing at 540°C for 4 h (condition H1025). The second solution treatment at 1028°C was found to eliminate the retained austenite, being the evidence of a completely finished martensitic transformation.Indeed, the only phase identified in all samples was fcc lath martensite exhibiting a parallel striped structure. Unfortunately, this additional heat-treatment operation leads likewise to significant and irregular grain growth, which consequently causes a drop in material hardness. Moreover, the second solution annealing, caused a shift in the XRD peaks to higher 2θ angles, resulting from a lattice parameter decrease by0,25%. The two subsequent heat-treatment procedures bring the lattice parameter back to its initial value. This seemingly reversible process of decrease and increase of the lattice parameter was observed for samples subjected to all the heat treatment operations, strongly suggesting the existence of a relation between the microstructural changes and the macroscopic contraction of the steel material. In addition to the martensitic phase, in the unaged samples, a δ- ferrite phase could be identified by TEM and electron diffraction, which is favorable for ductility and toughness of the material. In all samples, non-coherent fcc-NbC precipitates identified by electron diffraction and EDX mapping having sizes up to 70 nm were found

Requirements modelling and formal analysis using graph operations

The increasing complexity of enterprise systems requires a more advanced analysis of the representation of services expected than is currently possible. Consequently, the specification stage, which could be facilitated by formal verification, becomes very important to the system life-cycle. This paper presents a formal modelling approach, which may be used in order to better represent the reality of the system and to verify the awaited or existing system’s properties, taking into account the environmental characteristics. For that, we firstly propose a formalization process based upon properties specification, and secondly we use Conceptual Graphs operations to develop reasoning mechanisms of verifying requirements statements. The graphic visualization of these reasoning enables us to correctly capture the system specifications by making it easier to determine if desired properties hold. It is applied to the field of Enterprise modelling

Investigation of the Jahn-Teller Transition in TiF3 using Density Functional Theory

We use first principles density functional theory to calculate electronic and magnetic properties of TiF3 using the full potential linearized augmented plane wave method. The LDA approximation predicts a fully saturated ferromagnetic metal and finds degenerate energy minima for high and low symmetry structures. The experimentally observed Jahn-Teller phase transition at Tc=370K can not be driven by the electron-phonon interaction alone, which is usually described accurately by LDA. Electron correlations beyond LDA are essential to lift the degeneracy of the singly occupied Ti t2g orbital. Although the on-site Coulomb correlations are important, the direction of the t2g-level splitting is determined by the dipole-dipole interactions. The LDA+U functional predicts an aniferromagnetic insulator with an orbitally ordered ground state. The input parameters U=8.1 eV and J=0.9 eV for the Ti 3d orbital were found by varying the total charge on the TiF$_6^{2-}$ ion using the molecular NRLMOL code. We estimate the Heisenberg exchange constant for spin-1/2 on a cubic lattice to be approximately 24 K. The symmetry lowering energy in LDA+U is about 900 K per TiF3 formula unit.Comment: 7 pages, 9 figures, to appear in Phys. Rev.

INFLUENCE OF DOUBLE SOLUTION TREATMENT ON HARDNESS IN 17-4 PH STEEL

The investigated material is a corrosion-resistant, Cu precipitation hardened steel 17-4PH, which undergoes a macroscopic contraction, as a result of applying the following heat treatment: double solution treatment at 1028°C for 1 h (condition A), ageing at 540°C for 4 h (condition H1025). The second solution treatment at 1028°C was found to eliminate the retained austenite, being the evidence of a completely finished martensitic transformation.Indeed, the only phase identified in all samples was fcc lath martensite exhibiting a parallel striped structure. Unfortunately, this additional heat-treatment operation leads likewise to significant and irregular grain growth, which consequently causes a drop in material hardness. Moreover, the second solution annealing, caused a shift in the XRD peaks to higher 2θ angles, resulting from a lattice parameter decrease by0,25%. The two subsequent heat-treatment procedures bring the lattice parameter back to its initial value. This seemingly reversible process of decrease and increase of the lattice parameter was observed for samples subjected to all the heat treatment operations, strongly suggesting the existence of a relation between the microstructural changes and the macroscopic contraction of the steel material. In addition to the martensitic phase, in the unaged samples, a δ- ferrite phase could be identified by TEM and electron diffraction, which is favorable for ductility and toughness of the material. In all samples, non-coherent fcc-NbC precipitates identified by electron diffraction and EDX mapping having sizes up to 70 nm were found

A Minimal Model of Metabolism Based Chemotaxis

Since the pioneering work by Julius Adler in the 1960's, bacterial chemotaxis has been predominantly studied as metabolism-independent. All available simulation models of bacterial chemotaxis endorse this assumption. Recent studies have shown, however, that many metabolism-dependent chemotactic patterns occur in bacteria. We hereby present the simplest artificial protocell model capable of performing metabolism-based chemotaxis. The model serves as a proof of concept to show how even the simplest metabolism can sustain chemotactic patterns of varying sophistication. It also reproduces a set of phenomena that have recently attracted attention on bacterial chemotaxis and provides insights about alternative mechanisms that could instantiate them. We conclude that relaxing the metabolism-independent assumption provides important theoretical advances, forces us to rethink some established pre-conceptions and may help us better understand unexplored and poorly understood aspects of bacterial chemotaxis