The Mechanism of the Amorphous-to-Crystalline Transition in Ge2Sb2Te5 Ternary Alloys1

The kinetics of the amorphous-to-crystalline phase transformation in alloys with compositions around Ge₂Sb₂Te₅, used as erasable optical memories, was investigated by electric impedance, Raman spectroscopy, and optical and transmission electron microscopy. To induce the transformation, isothermal and isokinetic experiments were carried out at various temperatures and various heating rates. The results obtained agree with the Johnson–Mehl–Avrami model and show that the overall activation energy for the transition is about 8 eV, which exceeds previous estimations. The nucleation process changes during the transition and depends on both temperature and heating rate. The available data indicate that nuclei are formed both in the bulk and at the surface of crystallites, and that the structural details of the material (the crystallite size, in particular) depend greatly on the transformation conditions. Intercrystalline inclusions, which appear after the transition, contain Te precipitates within a structurally disordered phase. These inclusions have electrical and optical properties essentially different as compared to the rest of the sample; they could be residual phases formed due to the nonstoichiometric nature of the samples.     

Estimating quantiles under sampling on two occasions with arbitrary sample designs

A practical problem related to the estimation of quantiles in double sampling with arbitrary sampling designs in each of the two phases is investigated. In practice, this scheme is commonly used for official surveys, in which quantile estimation is often required when the investigation deals with variables such as income or expenditure. A class of estimators for quantiles is proposed and some important properties, such as asymptotic unbiasedness and asymptotic variance, are established. The optimal estimator, in the sense of minimizing the asymptotic variance, is also presented. The proposed class contains several known types of estimators, such as ratio and regression estimators, which are of practical application and are therefore derived. Assuming several populations, the proposed estimators are compared with the direct estimator via an empirical study. Results show that a gain in efficiency can be obtained.     

New technologies for relaxation: The role of presence.

In recent years, several publications have appeared on virtual reality (VR) therapy in the treatment of anxiety disorders. However, a limited number of these studies targeted stress management and relaxation. To evaluate the efficacy of VR as a support tool in the relaxation process, this study compared its efficacy with two other media (DVD and audiotape). The goals of the experiment were to test the efficacy of each condition in increasing relaxation and reducing anxiety, and whether the sense of presence-the feeling of being inside the media content-correlated with the efficacy of the treatment. Results suggested the importance of the sense of presence as a mediating variable between the media experience and the efficacy of the protocol. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An analysis of the determinants in Economics and Business publications by Spanish universities between 1994 and 2004

The objective of this study consists, firstly, of quantifying differences between Spanish universities’ output (in terms of publications and citations), and secondly, analysing its determinants. The results obtained show that there are factors which have a positive influence on these indicators, such as having a third-cycle programme, with public financing obtained in competitive selection procedures, having a large number of full-time researchers or involvement in collaborations with international institutions. However, other factors which appear to have the opposite effect were also noted. These include a higher number of students per lecturer or a lower proportion of lecturers with recognised six-year periods.     

The Transtheoretical Model and obesity: A bibliometric study

The Transtheoretical Model of behaviour change is currently one of the most promising models in terms of understanding and promoting behaviour change related to the acquisition of healthy living habits. By means of a bibliographic search of papers adopting a TTM approach to obesity, the present bibliometric study enables the scientific output in this field to be evaluated. The results obtained reveal a growing interest in applying this model to both the treatment of obesity and its prevention. Otherwise, author and journal outputs fit the models proposed by Lotka and Bradford, respectively.     

Evolution of nanoparticles in gold-implanted glass

The interest in metal nanocrystals is focused on their nonlinear optical properties, as they are expected to have a large third-order nonlinear susceptibility. In order to explore the possibility of tuning the size and shape of metal nanocrystals, we implanted gold into fused silica substrate. The implantation energy was 1.1 MeV and doses were of 1, 3, and 6×10¹⁶ ions/cm². All samples were subsequently annealed in air at 1000 and 1100 °C. Grazing incidence small-angle X-ray scattering was used to study the morphology and the distribution of gold nanoparticles formed in the substrate. The clustering process is evident already during the implantation itself. Upon annealing, the number of clusters, as well as their size is increased. The clusters are smaller in the vicinity of the surface, where the effective implant concentration is lower, regardless of the annealing temperature. At the highest annealing temperature the clustering diverges into two distinct size distributions.     

Bayesian parametric inference in a nonparametric framework

This paper considers the problem of reporting a “posterior distribution” using a parametric family of distributions while working in a nonparametric framework. This “posterior” is obtained as the solution to a decision problem and can be found via a well-known optimization algorithm.      

Quantifying the exploration performed by metaheuristics

In this article we propose a formalisation of the concept of exploration performed by metaheuristics. In particular, we define and test a method for studying this aspect regardless of the specific approach implemented. Understanding the behaviour of metaheuristics is important for being able to boost their results. Measuring the exploration performed may help increase this understanding. We propose an experimental analysis to show how the measure of exploration defined may be used to this aim. We quantify the different level of exploration implied by different parameter settings in an ant colony optimisation and in a genetic algorithm for the travelling salesman problem. The results suggest that it may be possible to establish a relation between exploration and performance of the algorithm.