The erosion of CVD diamond by diamond particles

This paper describes the damage features generated by the high-velocity impact of diamond particles on diamond produced by chemical vapour deposition (CVD). Two types of diamond grit - angular and cubo-octahedral - were used to impact the surface of the diamond target at a mean impact velocity of 268?m?s^?1. The main damage features were elastic-plastic radial and lateral cracks. Distorted Hertzian ring cracks were also seen on samples impacted with cubo-octahedral diamond grit. This indicates that, in contrast to previous experiments by the authors using silica sand erodent, Hertzian damage can be generated at this velocity when the mechanical properties of the erodent and target are comparable. Fragmentation of the diamond grit occurred on impact; however, the extent of the degradation was much reduced compared with the silica sand erodent.     

High-resolution imaging of n-alkane crystals by atomic force microscopy

X-ray and electron crystallography of polymethylene chain compounds are known to be hindered by the very strong scattering from a dominant sublattice, and the use of high-resolution electron microscopy is severely limited by radiation damage. This study shows that these problems may be overcome by using highresolution atomic force microscopy (AFM) imaging. The work was performed on four types of linear alkane crystal, namely n-C26H54, n-C30H62, n-C36H74 and n-C44H90, of different molecular lengths. They were prepared by vapour deposition and from solution and deposited on mica and on highly oriented pyrolytic graphite. The results show that firstly AFM may complement, at a molecular and a submolecular level, the data provided by X-ray and electron crystallography, secondly alkane crystals may be prepared with different orientations and the type of substrate has no influence, and thirdly AFM may be used to induce orientational and conformational changes.     

Characterization of platelet-related infrared luminescence in diamond

Characterization of the platelet-related infrared emission in diamond using photoluminescence (PL) and PL excitation techniques is reported. It is suggested that the emission originates from the radiative recombination of electrons and holes at platelet-induced bands of electron states separated by a gap of about 1.7eV.     

Mechanical properties of nanocrystalline deformed layers induced by nanogrinding of CdZnTe single crystals

Nanocrystalline deformed layers were generated in cadmium zinc telluride (CZT) single crystals by nanogrinding using three different grit sizes. The mechanical properties of the deformed layers were measured using nanoindentation. The hardness of the deformed nanocrystalline layers in the soft-brittle CZT semiconductor was higher than that of the perfect single crystal. This result is different from those found for deformed layers of hard-brittle silicon semiconductors, where the hardness of the deformed layers is lower than those of the perfect single crystal.     

Orientation of the diamond and the square revisited

Below the age of 7 or 8, children find it very difficult to reproduce a diamond compared with a square. They are also highly sensitive to contextual alignment cues from the age of three years. It is shown here that over the brief age-span of 4-6 years (inclusive), children come to control the weight they give to contextual cues. It is argued that this is a more likely precursor of the older child's ability to cope with obliques, than is the converse process of learning to specify targets and thence to prevent themselves from responding inappropriately to the context. Of course, both target-specification and contextual-responsiveness are manifest at all the ages, but the latter seems to have the leading edge in early development.     

Creep behaviour of ice single crystals loaded in torsion explained by dislocation cross-slip

Torsion creep experiments are carried out in order to understand the physics of ice plasticity. A dislocation spreading mechanism based on double cross-slip of basal dislocations is proposed to explain the strong plastic anisotropy and the power law relationship between stress and strain rates. The scenario is tested using three-dimensional dislocation dynamics simulations. Numerical investigations give a stress exponent n?=?2.3 in agreement with experimental measurements. This dislocation spreading mechanism sheds a new light on the interpretation of former experimental observations.     

Growth orientation of one-dimensional silicon nanowires prepared by thermal evaporation

One-dimensional silicon nanowires have been grown by thermal evaporation and their growth orientations determined by transmission electron microscopy studies. The nanowires, which are often highly curved in morphology and heavily twinned in microstructure, are crystallographically separated into several sections, each with a characteristic crystallographic orientation along the wire axis. Straight nanowires, or straight sections in a curved nanowire, are found to have non-unique crystallographic orientations when {111} twinning occurs.     

Impact resistance performance of diamond film on a curved molybdenum substrate

Diamond films with different thicknesses were deposited on flat and curved molybdenum substrate by the microwave plasma chemical vapour deposition (MPCVD) method. Scanning electronic microscopy, atomic force microscopy and Raman spectroscopy were employed to characterise the morphology, the surface roughness and the composition of the films, respectively. A NanoTest system was used for hardness, elastic modulus and nanoimpact tests. The curved surface and ductility of the molybdenum substrate allow large deformation for the thinner films. The substrate has less effect on impact for the thicker film, the deformation of which is mainly determined by the film composition. Under a load of 50 mN and 75 cycles, less deformation occurred for the 22 μm thick film on the curved molybdenum substrate.     

BDNF reverses the CTA memory deficits produced by inhibition of protein synthesis

Brain-derived neurotrophic factor (BDNF) is an essential protein synthesis product that has emerged as one of the most potent molecular mediators of not only central synaptic plasticity, but also behavioral interactions between an organism and its environment. Our previous studies on the insular cortex (IC), a region of the temporal cortex implicated in the acquisition and storage of conditioned taste aversion (CTA), have demonstrated that intracortical microinfusion of BDNF induces a lasting potentiation of synaptic efficacy in the projection from the basolateral nucleus of the amygdala (Bla) to the IC of adult rats in vivo. Recently, we found that intracortical microinfusion of BDNF previous to CTA training enhances the retention of this task. In this work, we present experimental data showing that acute intracortical delivery of BDNF (2 microg/2 microl per side) reverses the deficit in CTA memory caused by inhibition of insular cortex protein synthesis due to anisomycin administration (100 microg/microl per side) in male adult Wistar rats. These findings suggest that BDNF is a protein synthesis product essential for neocortical long-term memory storage.     

The diamond ratio: A visual indicator of the extent of heterogeneity in meta-analysis

The result of a meta-analysis is conventionally pictured in the forest plot as a diamond, whose length is the 95% confidence interval (CI) for the summary measure of interest. The Diamond Ratio (DR) is the ratio of the length of the diamond given by a random effects meta-analysis to that given by a fixed effect meta-analysis. The DR is a simple visual indicator of the amount of change caused by moving from a fixed-effect to a random-effects meta-analysis. Increasing values of DR greater than 1.0 indicate increasing heterogeneity relative to the effect variances. We investigate the properties of the DR, and its relationship to four conventional but more complex measures of heterogeneity. We propose for the first time a CI on the DR, and show that it performs well in terms of coverage. We provide example code to calculate the DR and its CI, and to show these in a forest plot. We conclude that the DR is a useful indicator that can assist students and researchers to understand heterogeneity, and to appreciate its extent in particular cases.     

The rhythm of melatonin synthesis in the epiphysis and its control by light

The paper deals with the central regulation of the circadian rhythm of the melatonin in the pineal gland by light according to the literature. Examples of the effects of melatonin and their inclusion in the total endocrine complexity are pointed out. Possibilities for a therapy of chronobiological diseases with bright light resulting from animal experiments are discussed in connection with requirements for a future application to the therapy of human beings.     

Homogeneous nucleation of dislocation loops under stress in perfect crystals

We present an analysis and results on the homogeneous nucleation of a dislocation loop under stress in a perfect crystal. By using a variational boundary integral method in the Peierls-Nabarro framework, we have determined the saddle-point configurations of embryonic dislocation loops and their associated activation energies under stress levels up to the ideal shear strength. The high-energy barriers under the usual levels of applied shear stresses, differing markedly from the ideal shear strength, confirm the widely held view that thermal motion should play no role in such nucleation. The result provides means for more definitive solutions of fundamental problems involving homogeneous nucleation of dislocation loops and has significant implications for models based on the mechanism of nucleation of dislocations from a perfect crystal.     

Estimation of a Latent Variable Regression Growth Curve Model for Individuals Cross-Classified by Clusters

The cross-classified multiple membership latent variable regression (CCMM-LVR) model is a recent extension to the three-level latent variable regression (HM3-LVR) model which can be utilized for longitudinal data that contains individuals who changed clusters over time (for instance, student mobility across schools). The HM3-LVR model can include the initial status on growth effect as varying across those clusters and allows testing of more flexible hypotheses about the influence of initial status on growth and of factors that might impact that relationship, but only in the presence of pure clustering of participants within higher-level units. This Monte Carlo study was conducted to evaluate model estimation under a variety of conditions and to measure the impact of ignoring cross-classified data when estimating the incorrectly specified HM3-LVR model in a scenario in which true values for parameters are known. Furthermore, results from a real-data analysis were used to inform the design of the simulation. Overall, it would be recommended for researchers to utilize the CCMM-LVR model over the HM3-LVR model when individuals are cross-classified, and to use a bare minimum of more than 100 clustering units in order to avoid overestimation of the level-3 variance component estimates.     

Perceptual depth synthesis in the visual system as revealed by selective adaptation

Selective adaptations was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients.     

Mathematical modelling of nucleation and growth of crystals with buoyancy effects

A complete analytical solution of the integro-differential model describing the nucleation of crystals and their subsequent growth in a binary system with allowance for buoyancy forces is constructed. An exact analytical solution of the Fokker-Planck-type equation for the three-parameter density distribution function is found for arbitrary nucleation kinetics. Two important cases of the Weber–Volmer–Frenkel–Zel’dovich and Meirs kinetics are considered in some detail. It is shown that the solute concentration decreases and the distribution function increases with increasing the melt supercooling (with increasing the depth of a metastable system). It is demonstrated that the distribution function attains its minimum at a certain size of crystals owing to buoyancy forces.