Structural,elastic, electronic,phonon and thermal properties of Ir3Ta and Rh3Ta alloys

We have studied the structural, elastic, electronic, phonon and thermodynamic properties of Ir₃Ta and Rh₃Ta alloys, using ab initio calculations. For the L1₂ phase, we report the calculated lattice constants, bulk modulus and elastic constants, and these values are compared with previously published values. We also derive the elastic constants from the values of the slopes of the acoustic branches in the phonon dispersion curves. The band structures show that both materials are metallic. The phonon dispersion curves, and their corresponding total and projected densities of states, are obtained using a linear response in the framework of the density functional perturbation theory. The specific heat capacity at constant volume and different temperatures is calculated, and this aspect is discussed using the quasi-harmonic approximation.     

Analysis of the relation between structure and the superconducting transition in YBa2 Cu3 O∼7

Abstract

It is shown that in the high-T_c YBa₂ Cu₃ O_～7 superconductor the critical temperature is a function of the orthorhombic distortion (b–a)/a of the unit cell. From the extrapolation of the (b - a)/a ratio against T_c , a maximum critical temperature of 66 K for the tetragonal phase of YBa₂ Cu₃ O_～7 was predicted. From the correlation between the transition width δT_c and the orthorhombic distortion there was deduced an upper limit for T_c , in the orthorhombic phase of YBa₂ Cu₃ O_～7 of 94·5K.     

Correlation between ductility and work function in NiAl–Ce–Cr alloys

In spite of many superior high-temperature properties of intermetallics, it has been difficult to understand their intrinsic brittleness. To eliminate or improve the embrittlement, the conventional alloying technique based on the trial-and-error method is still the most effective and practical. However, it remains a main challenge for both physicists and materials scientists to provide either an alloying principle or a deep insight into its toughening mechanism at an atomic or electronic level. This letter reports a simple experimental approach that uses work function (WF) as a sensitive indicator of the role of alloying in changing mechanical behavior. NiAl is chosen as a typical example. It is found that with the addition of Cr and Ce, the ductility of NiAl increases significantly. Such an increase in ductility corresponds to a concomitant decrease in the WF, which is attributed to a change in the nature of the atomic bonding or in the electronic structure induced by the alloying. This fundamental understanding on the embrittlement nature of NiAl could provide some alloying guidelines or principles for other intermetallics.     

On the possibility of tuning the energy separation between space-quantized levels in a quantum well

The idea about change of energy distances between space-quantized energy levels by ionization of an impurity delta layer situated within a quantum well (QW) is put forward and justified. The self-consistent solutions of Schrödinger, Poisson, and electroneutrality equations made for n-type SiGe/Si/SiGe rectangular QW show that the effect really exists and the most dramatic changes can be observed for an edge-delta-doped QW structure.     

Pressure-induced changes in electronic and vibrational properties of LaS

The high-pressure induced phase transition in LaS has been investigated by means of first-principles calculations, and density-functional linear-response theory. A pressure-induced soft-acoustic phonon mode is identified at 30?GPa, which is in favourable agreement with the measured pressure-induced phase transition in LaS from the rocksalt to the CsCl structure. Phonon calculations reveal that pressure-induced instabilities of the transverse acoustic modes at the [?00] and [??0] directions are responsible for the phase transition. Furthermore, it is found that a decrease of bonding for S-p bonds and an increase of anti-bonding for La-d bonds significantly weakens the stability of the rocksalt phase of LaS under pressure, and hence inducing the structural phase transformation.     

Site preference of refractory elements in γ′-Ni3Al alloyed with Ru

The influence of ruthenium (Ru) on the partitioning behavior of W, Re and Cr in γ′-Ni₃Al has been studied using the Dmol3 method based on the density functional theory. The calculated results show that W, Re and Cr have a preference for the Ni site in γ′-Ni₃Al alloyed with Ru. When Ru substitutes the central Ni atom, the site preference for W, Re and Cr varies. Furthermore, an electronic structure analysis of the alloy in terms of the Mulliken population and partial density of states was performed to elucidate the alloying mechanism of Ru in γ′-Ni₃Al. The results show that the strengthening effect of Ru in the alloy arises from a reduction in the binding energy of Ru as well as p-orbital hybridization between Ru and the host atoms.     

The Effects of Library User-Education Programmes on the Information-Seeking Behaviour of Brisbane College of Theology Students

ABSTRACT

An increasing proportion of students entering the Brisbane College of Theology (BCT) are adult learners and engaged in theological education for general academic purposes or personal enrichment. In meeting the needs of these students, the user-education programmes conducted by the BCT Libraries endeavour to address the Australian Information Literacy Standards.¹ The literature reveals that information literacy is learned through experience primarily shaped by both librarians and faculty. This case study, which uses an adaptation of Biggs' model of presage, process, and product, looks at the information search process from the perspective of one theological library. As a phenomenographic study, it examines the interconnected theories of students' experience, perception, approach, and learning outcomes in the information search process. It will be shown here that user-education programmes and mediation with the librarian significantly influence the information-seeking behaviour of students.     

Ab-initio study of the structural,electronic, elastic and vibrational properties of HfX (X = Rh,Ru and Tc)

The structural, elastic, electronic and phonon properties of HfX (X = Rh, Ru and Tc) in the caesium-chloride phase have been investigated using the density functional theory within the generalized gradient approximation. The optimized lattice constant (a₀), bulk modulus (B) and the elastic constants (C_ij) are evaluated. The results are in a good agreement with the available experimental and theoretical data in the literature. Electronic band structures and densities of states have been derived for these compounds. The present band structure calculations indicate that the phases of caesium-chloride HfX (X = Rh, Ru and Tc) compounds are metals. Phonon dispersion curves and their corresponding total and projected density of states have been obtained using the direct method. The phonon spectra suggest that these compounds are dynamically stable in the caesium-chloride phase.     

A feedback intervention to increase digital and paper checklist performance in technically advanced aircraft simulation

This study examined whether pilots operating a flight simulator completed digital or paper flight checklists more accurately after receiving postflight graphic and verbal feedback. The dependent variable was the number of checklist items completed correctly per flight. Following treatment, checklist completion with paper and digital checklists increased from 38% and 39%, respectively, to nearly 100% and remained close to 100% after feedback and praise for improvement were withdrawn. Performance was maintained at or near 100% during follow-up probes.