Oriented polycrystalline α-HgI2 thick films grown by physical vapor deposition

This work investigates the growth of polycrystalline α-HgI₂ thick films from physical vapor deposition. By varying the growth conditions, the as-deposited thick films are characterized by scanning electron microscopy, X-ray diffraction, current–voltage and photoconductivity measurements. The growth mechanism and its effects to the properties of these polycrystalline α-HgI₂ thick films are then discussed. Finally, the best deposition conditions for polycrystalline α-HgI₂ thick films compactly formed by separated columnar monocrystallines with uniform orientation along c-direction and with good crystallinity are reported.     

Kinetics of dopant incorporation in GaAs grown by organometallic vapor-phase epitaxy

A diffusive capture reaction of dopant atoms by relevant host atoms, via the Rideal–Eley mechanism, in GaAs grown by organometallic vapor-phase epitaxy is shown to result in the dopant concentration in the crystal acquiring a dependence on p_Ga (which is proportional to the growth rate) in agreement with data on S_As, Zn_Ga, and Si_Ga where p_Ga is the partial pressure of trimethylgallium in the input gas stream.     

Surface chemistry and transport effects in GaN hydride vapor phase epitaxy

A simple quasi-thermodynamic model of surface chemistry in GaN hydride vapor phase epitaxy (HVPE) is presented. The model is coupled with the detailed 3D simulations of species transport in a horizontal-tube reactor and validated by the comparison with the data on the GaN growth rate obtained by laser reflectometry. Parametric study of the growth rate as a function of temperature and species flow rates has been performed over a wide range of growth conditions. The important role of species transport in an HVPE reactor is demonstrated. In particular, a strong effect of the natural concentration convection resulting in the formation of recirculation zones and in a non-uniform vapor composition is revealed by modeling. The impact of these effects on the GaN growth rate and V/III ratio on the growth surface is discussed in detail.     

Dynamic process of crystallization of Sb2Se3 from Sb50Se50 amorphous film

Dynamics of crystallization of amorphous antimony-selenium film deposited on carbon substrate have been studied by the high-resolution transmission electron microscopy. The amorphous film was suddenly crystallized at 200°C by heating in vacuum. By the electron beam irradiation crystallization occurred at the focused electron beam region in the amorphous film. The growth process of crystallization by electron beam irradiation was recorded on a video image at the atomic resolution mode. The growth front of crystallization showed nano-concave and -convex shapes. The recrystallization with the different orientation at the first grown crystal have been found, and discussed as the influence of remaining antimony crystallites at the first crystallized film region.     

Q-Dock: Low-resolution flexible ligand docking with pocket-specific threading restraints

The rapidly growing number of theoretically predicted protein structures requires robust methods that can utilize low-quality receptor structures as targets for ligand docking. Typically, docking accuracy falls off dramatically when apo or modeled receptors are used in docking experiments. Low-resolution ligand docking techniques have been developed to deal with structural inaccuracies in predicted receptor models. In this spirit, we describe the development and optimization of a knowledge-based potential implemented in Q-Dock, a low-resolution flexible ligand docking approach. Self-docking experiments using crystal structures reveals satisfactory accuracy, comparable with all-atom docking. All-atom models reconstructed from Q-Dock's low-resolution models can be further refined by even a simple all-atom energy minimization. In decoy-docking against distorted receptor models with a root-mean-square deviation, RMSD, from native of approximately 3 A, Q-Dock recovers on average 15-20% more specific contacts and 25-35% more binding residues than all-atom methods. To further improve docking accuracy against low-quality protein models, we propose a pocket-specific protein-ligand interaction potential derived from weakly homologous threading holo-templates. The success rate of Q-Dock employing a pocket-specific potential is 6.3 times higher than that previously reported for the Dolores method, another low-resolution docking approach.     

Application of receptor models to airborne particulate matter

The human activities in their various aspects cause a change in the natural air quality. This change results more marked in very populated and in high industrialized areas. Some pollutants emitted are typical of a particular activity. Each source of pollution is identified by its profile in the composition of the emissions in the environment. Multivariate receptor models can be used in order to apportion pollutants to the different sources assessing the contribution of each source to the total pollution.This paper deals with the application of Absolute Principal Component Scores (APCS) receptor model to data obtained from the automatic network of air quality monitoring in the city of Bari (South Italy). The parameters monitored by automatic networks, as bihourly values, are PM₁₀, NO_x, CO, Benzene, Toluene, Xilene. The data shown in this paper concerning 1 month almost of sampling in different monitoring stations of Bari Municipality during the period of time from January 2005 to April 2006. Moreover preliminary results obtained applying the APCS model to daily PM_2.5 samples collected during SITECOS PRIN project are shown. The results concerning data collected in corso Cavour (Bari) during the month of October 2005.The results obtained by APCS receptor model seem to suggest a poor contribution of the “vehicular traffic source” and a relevant contribution of the “secondary particulate source” to particulate matter concentrations.     

On some problems of weak consistency of quasi-maximum likelihood estimates in generalized linear models

In this paper,we explore some weakly consistent properties of quasi-maximum likelihood estimates(QMLE) concerning the quasi-likelihood equation in=1 Xi(yi-μ(Xiβ)) = 0 for univariate generalized linear model E(y |X) = μ(X'β).Given uncorrelated residuals {ei = Yi-μ(Xiβ0),1 i n} and other conditions,we prove that βn-β0 = Op(λn-1/2) holds,where βn is a root of the above equation,β0 is the true value of parameter β and λn denotes the smallest eigenvalue of the matrix Sn = ni=1 XiXi.We also show that the convergence rate above is sharp,provided independent non-asymptotically degenerate residual sequence and other conditions.Moreover,paralleling to the elegant result of Drygas(1976) for classical linear regression models,we point out that the necessary condition guaranteeing the weak consistency of QMLE is Sn-1→ 0,as the sample size n →∞.     

Quasi-Monte Carlo for Highly Structured Generalised Response Models

Highly structured generalised response models, such as generalised linear mixed models and generalised linear models for time series regression, have become an indispensable vehicle for data analysis and inference in many areas of application. However, their use in practice is hindered by high-dimensional intractable integrals. Quasi-Monte Carlo (QMC) is a dynamic research area in the general problem of high-dimensional numerical integration, although its potential for statistical applications is yet to be fully explored. We survey recent research in QMC, particularly lattice rules, and report on its application to highly structured generalised response models. New challenges for QMC are identified and new methodologies are developed. QMC methods are seen to provide significant improvements compared with ordinary Monte Carlo methods.      

A (computational) social science perspective on societal transitions

This paper aims to illustrate how social sciences, sociology in particular, have theorized on societal transitions. The first section introduces some preliminary definitions. The assumption is that a societal transition is more than a social, economic or technological change. It is a large-scale and long-term macro process through which a given social system radically changes its structural basis, in terms of new socio-technical practices, governance rules, social and economic institutions, cultural frames, and patterns of social life. The second section provides an excursus on social science accounts on transitions. In particular, the attention has been given to Norbert Elias’ famous study on the rise and fall of the court society in France, between 17th and 18th century and to Manuel Castells’ recent analysis of the emergence of the network society. The third section discusses problems and challenges of standard approaches and suggests some building blocks of societal transition models, taken from complexity and social simulation literature. The concluding section suggests some way-forward measures towards a computational social science approach to societal transitions.