Th microanalysis using fission tracks

External uniaxial stress effects on the radiation damage dynamics in a a-Fe b.c.c. structure are studied by means of the computer simulation method. Focused collision chains, defocused ones, and atom-atom collision cascades were simulated. The external uniaxial stresses affect the intervals between a vacancy and an interstitial atom produced due to a collision chain, i.e. changes a dynamical crowdion path. The external stresses change the number of stable point defects and their arrangement in the cascade development region if an atom-atom collision cascade develops in a stressed crystal. The studies of focused collision chains of energies close to the atom displacement threshold energies show that the latter can either increase or decrease due to the external stresses depending on the direction of the effect.     

The Low Temperature Polarised Electronic Spectra of Some Tetragonal Nickel(II) Haloacetate Complexes

We have recently reported the single crystal electronic spectra of some substituted ethylenediamine complexes of nickel(II), discussing both cis (1) and trans (2) examples. We have also reported data for their cobalt(II) analogs (3). These were analysed using the Normalised Spherical Harmonic Hamiltonian (NSH) (4) and the Orbital Angular Overlap Model (OAM) (5) approaches. We have     

Label Switching in Bayesian Mixture Models: Deterministic Relabeling Strategies

Label switching is a well-known problem in the Bayesian analysis of mixture models. On the one hand, it complicates inference, and on the other hand, it has been perceived as a prerequisite to justify Markov chain Monte Carlo (MCMC) convergence. As a result, nonstandard MCMC algorithms that traverse the symmetric copies of the posterior distribution, and possibly genuine modes, have been proposed. To perform component-specific inference, methods to undo the label switching and to recover the interpretation of the components need to be applied. If latent allocations for the design of the MCMC strategy are included, and the sampler has converged, then labels assigned to each component may change from iteration to iteration. However, observations being allocated together must remain similar, and we use this fundamental fact to derive an easy and efficient solution to the label switching problem. We compare our strategy with other relabeling algorithms on univariate and multivariate data examples and demonstrate improvements over alternative strategies. Supplementary materials for this article are available online.     

Complex Region Spatial Smoother (CReSS)

Conventional smoothing over complicated coastal and island regions may result in errors across boundaries, due to the use of Euclidean distances to measure interpoint similarity. The new Complex Region Spatial Smoother (CReSS) method presented here uses estimated geodesic distances, model averaging, and a local radial basis function to provide improved smoothing over complex domains. CReSS is compared, via simulation, with recent related smoothing techniques, Thin Plate Splines (TPS), geodesic low rank TPS (GLTPS), and the Soap film smoother (SOAP). The GLTPS method cannot be used in areas with islands and SOAP can be hard to parameterize. CReSS is comparable with, if not better than, all considered methods on a range of simulations. Supplementary materials for this article are available online.     

The reliability of routine clinical post-processing software in assessing potential diffusion-weighted MRI “biomarkers” in brain metastases

Background and Purpose

Diffusion MRI characteristics have been used as biomarkers to guide prognosis in cerebral pathologies including brain metastases. The measurement of ADC is often described poorly in clinical and research studies with little detail given to the practical considerations of where to place ROIs, which post processing software package to use and how reproducible the resulting metrics will be.

Method

We investigated a series of 12 patients with brain metastases and preoperative DWI. Three post processing platforms were used. ROI were placed over the tumour, peritumoural region and across the brain-tumour interface. These recordings were made by a neurosurgeon and a neuroradiologist. Inter-intra-observer variability was assessed using Bland-Altman analysis. An exploratory analysis of DWI with overall survival and tumour type was made.

Results

There was excellent correlation between the software packages used for all measures including assessing the whole tumour, selective regions with lowest ADC, the change of ADC across the brain-tumour interface and the relation of the tumour ADC to peritumoural regions and the normal white matter. There was no significant inter- or intra-observer variability for repeated readings. There were significant differences in the mean values obtained using different methodologies and different metrics had differing relationships to overall survival and primary tumour of origin.

Conclusion

Diffusion weighted MRI metrics offer promise as potential non-invasive biomarkers in brain metastases and a variety of metrics have been shown to be reliably measured using differing platforms and observers.     

Bayesian Nonparametric Inference for a Multivariate Copula Function

The paper presents a general Bayesian nonparametric approach for estimating a high dimensional copula. We first introduce the skew–normal copula, which we then extend to an infinite mixture model. The skew–normal copula fixes some limitations in the Gaussian copula. An MCMC algorithm is developed to draw samples from the correct posterior distribution and the model is investigated using both simulated and real applications.     

Dispersion stability of nanoparticles in ecotoxicological investigations: the need for adequate measurement tools

One of the main challenges in nanoecotoxicological investigations is in the selection of the most suitable measurement methods and protocols for nanoparticle characterisation. Several parameters have been identified as being important as they govern nanotoxicological activity, with some parameters being better defined than others. For example, as a parameter, there is some ambiguity as to how to measure dispersion stability in the context of ecotoxicological investigations; indeed, there is disagreement over which are the best methods to measure nanoparticle dispersion stability. The purpose of this article is to use various commercially available tools to measure dispersion stability and to understand the information given by each tool. In this study, CeO₂ was dispersed in two different types of media: de-ionised water and electrolyte-containing fish medium. The DLS mean particle size of freshly dispersed sample in DI water was ~200 nm in diameter. A visual sedimentation experiment showed that nanoparticle dispersion made in the fish medium was less stable compared to corresponding dispersion in de-ionised water. Stability of these dispersions was monitored using various techniques, for a period of 3 days. Our findings have shown that dispersion stability can be suitably assessed by monitoring: (a) surface charge, (b) sedimentation events and (c) presence of agglomerates, through time. The majority of techniques employed here (zeta potential, particle size via DLS, fluorescence and UV–Vis spectroscopy and SEM) were shown to provide useful, complementary information on dispersion stability. Nanoparticle Tracking Analysis (NTA) provides useful, quantitative information on the concentration of nanoparticles in suspension, but is limited by its inability to accurately track the motion of large agglomerates found in the fish medium.     

Insertion devices–recent developments and future trends

The first Ultrafast X-ray Summer School, organized and chaired by Nora Berrah (WMU), was held June 18–22, 2007, at the Stanford University's PULSE Center, located at the Stanford Linear Accelerator Center (SLAC). With the advent of 4^th generation X-ray light sources, and in particular, the Linac Coherent Light Source (LCLS) under construction at SLAC, it was timely to begin the process of building a competitive community of scientists. It was also primordial to communicate to everyone the excitement many of us have about these new tools and to help raise awareness of the opportunities in ultrafast X-ray research.     

Real time spectroscopic ellipsometry of CuInSe2: Growth dynamics,dielectric function,and its dependence on temperature

This Letter reports real time spectroscopic ellipsometry studies of copper indium diselenide (CuInSe₂; CIS). A Volmer‐Weber nucleation process was identified from the measured thickness dynamics, and accurate dielectric functions were obtained in‐situ, avoiding oxidation while correcting for surface roughness. The energy and broadening parameters of the critical points in the dielectric functions obtained versus measurement temperature (including three previously unreported ones) yield a database that is valuable for on‐line materials analysis. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)