Differential Development of Learning Strategies on a Pictorial Verbal Learning Test (PVLT) in Primary-School Children

The aim of this study was to test the hypothesis that developmental differences exist in the use of learning strategies in primary school children. Serial and subjective clustering in a multitrial Pictorial Verbal Learning Test (PVLT) were compared in 79 children aged 6–12. Correlation analyses indicated that serial clustering yielded better performance when information was presented on the initial trials of the test. Subjective clustering was superior when information was presented repeatedly, i.e., after three or more trials. Analyses of variance indicated that subjective clustering was used more often in older children with repeated presentations. On the other hand, there was no increase in the use of serial clustering with age and with repeated presentations. The findings imply that training in the use of proper strategies could have benefit for children who use an inefficient learning strategy and/or have a learning problem. In addition, they point to the importance of the factor “age” in relation to the way information is presented to children.     

Temperature-dependent crack surface tension

The fracture surface energy is calculated for a one-dimensional, exactly solvable model of a crack. The temperature dependence of the crack surface tension is determined on the basis of a self-consistent Einstein approach. It is found that lattice vibrations result in a strong reduction in the crack surface tension.     

Analysis of intrinsic diffusivities in multicomponent alloys

In this letter we consider the intrinsic diffusivities in a multicomponent random alloy in terms of the ratios of atom-vacancy exchange frequencies. Using the exact sum rule due to Moleko and Allnatt, which relates phenomenological coefficients in the multicomponent random alloy, we deduce an exact relationship between the intrinsic diffusivities and the ratios of the exchange frequencies. We exemplify the finding with a consideration of binary and ternary random alloys. We show that the new relationship should be robust enough for employment in multicomponent alloys showing non-ideality.     

Ferromagnetism in Kondo lattice models

We report the discovery of a new ferromagnetic phase in the one-dimensional Kondo lattice model for intermediate values of the coupling constant. This new ferromagnetic phase was observed using a non-Abelian density-matrix renormalization group algorithm, which allowed us to measure directly the magnetization of the ground state with high accuracy.     

Long-term natural ageing of a dissociated dislocation in a Cu-13.43 at.% Al alloy

The nature of impurity-dislocation interactions is one of the key questions governing the strength and plasticity of solid-solution materials. To investigate the influence of impurities on the mechanical properties of intermetallic NiAl, the electronic structure and energy of NiAl with a <100>{010} edge dislocation and transition-metal impurities was calculated using the real-space tight-binding linear muffin-tin orbital method. The localized electronic states, appearing in the core of the dislocation, are found to lead to strong impurity-dislocation interactions via two mechanisms: firstly, chemical locking, due to strong hybridization between impurity electronic states and dislocation localized states; secondly, electrostatic locking, due to long-range charge oscillations caused by the electron localization in the dislocation core. The results obtained explain qualitatively why the solid-solution hardening effect in NiAl correlates with the electronic structure of impurities rather than with size misfit, as expected according to traditional views.     

Diffusion kinetics for divacancies in the bcc lattice

In this letter we employ high-precision Monte Carlo simulations to investigate tracer diffusion kinetics for diffusion via divacancies in the bcc lattice. We utilize the mechanisms originally identified by Mehrer in which the divacancy can move by nearest-neighbour jumps with stable first-nearest-neighbour, second-nearest-neighbour and fourth-nearest-neighbour configurations of the divacancy. The tracer correlation factor and the 'impurity-form' correlation factor were found to be some 4-6% lower than those found by the matrix method. The tracer diffusion data and isotope effect for sodium were revisited in terms of monovacancy and divacancy contributions. The main change is a revision upwards from 0.55 to 0.61 of the j K kinetic factor for divacancies.     

Dislocations and cracks at Vickers indentations in (0 0 0 1) GaN single crystals

Single-crystal (0 0 0 1) GaN samples have been deformed with a Vickers indenter at room temperature using loads in the range from 0.02 to 4.90 N. Dislocations and cracks at the indentations were examined by means of scanning electron microscopy, cathodoluminescence, light microscopy and transmission electron microscopy. Geometrical relations could be found between the dislocation arrangement, cracks and the orientation of the indenter. The orientation of the indenter has only a slight effect on the dislocation pattern, but the crack system is predominantly determined by the symmetry and the orientation of the indenter.     

Indentation hardnesses of semiconductors and a scaling rule

The Vickers hardnesses of 15 semiconductors, namely Si, Ge, SiC, AlN, GaN, GaP, GaAs, GaSb, InP, InAs, InSb, ZnO, ZnSe, ZnTe and CdTe, have been investigated from room temperature to their melting points. The temperature dependences of the Vickers hardness H V of 11 of these semiconductors, namely those with a cubic structure, obey a universal relationship when H V and the temperature T are scaled respectively by the shear modulus G and by Gb 3 / k B, with b being the magnitude of the Burgers vector. The scaling rule is the same as that found for the temperature dependence of the critical shear stress c for the {111}<110> slip system, satisfying the relationship H V = (70-100) c .     

Locating dysprosium dopant atoms in the Bi2Sr2CaCu2Oy unit cell: Direct-space chemical crystallography

The position of Dy in the unit cell of Bi2Sr2CaCu2Oy has been determined by a real-space method. This is compared with the reciprocal-space atom location by channelling-enhanced microanalysis (ALCHEMI) method.     

Nanodefects in nanostructures

The notion of nanodefects (topological defects of nanoscale translational order) in nanostructures of various types is introduced. Experimental data reported in the literature are discussed giving direct evidence for the existence of nanodefects in self-assembled periodically ordered nanostructures such as arrays of quantum dots, self-assembled superlattice films of nanoparticles, and arrays of carbon nanotubes. Also, the specific geometric features of perfect and partial cellular dislocations (being a kind of nanodefect) and their role in superplastic deformation in nanocrystalline materials are considered.