Formalization of Fixed-Point Arithmetic in HOL

This paper addresses the formalization in higher-order logic of fixed-point arithmetic. We encoded the fixed-point number system and specified the different quantization modes in fixed-point arithmetic such as the directed and even quantization modes. We also considered the formalization of exceptions detection and their handling like overflow and invalid operation. An error analysis is then performed to check the correctness of the quantized result after carrying out basic arithmetic operations, such as addition, subtraction, multiplication and division against their mathematical counterparts. Finally, we showed by an example how this formalization can be used to enable the verification of the transition from floating-point to fixed-point algorithmic level in the signal processing design flow.     

Optimal Prediction with Conditionally Heteroskedastic Factor Analysed Hidden Markov Models

The deficiencies of stationary models applied to financial time series are well documented. A special form of non-stationarity, where the underlying generator switches between (approximately) stationary regimes, seems particularly appropriate for financial markets. We use a dynamic switching (modelled by a hidden Markov model) combined with a linear conditionally heteroskedastic latent factor model in a hybrid conditionally heteroskedastic factor analysed hidden Markov model (CHFAHMM) and discuss the practical details of training such models with a new approximated version of the Viterbi algorithm in conjunction with the expectation-maximization algorithm to iteratively estimate the model parameters in a maximum-likelihood sense. The performance of the CHFAHMM is evaluated on both simulated and financial data sets. On the basis of out-of-sample forecast encompassing tests as well as other measures for forecasting accuracy, our results indicate that the use of this new method yields overall better forecasts than those generated by competing models.     

Comparison of semi-elliptical cracks in cylinders with a thickness transition and in a straight cylinders - Elastic-plastic behaviour

This paper presents a study of a circumferential external semi-elliptical crack in a cylinder with a thickness transition. Crack harmfulness is compared to the harmfulness of a similar crack in a straight cylinder, on the basis of J-integral calculations. Loads considered are pure tensile stress and bending moment. A numerical analysis is performed considering elastic plastic behaviour of material. A crack mesh was designed for 3D models. The results show that the cylinder with a thickness transition is more vulnerable to the defect. A simple method for J calculation at the deepest point of the crack in the transition zone is also proposed.     

Influence of vertical vibrations on the separation of a binary mixture in a horizontal porous layer heated from below

We study the influence of vertical high-frequency and small-amplitude vibrations on the separation of a binary mixture saturating a shallow horizontal porous layer heated from below. The monocellular flow obtained for a separation ratio ψ > ψ_mono > 0 leads to a migration of the species towards the two vertical boundaries of the cell. The 2D direct numerical simulations and the linear stability analysis of the averaged governing equations show that the vertical vibrations delay the transition from monocellular flow to multicellular flow. The vibrations also decrease the value of ψ_mono, which allows species separation for a wide variety of binary mixtures.     

Effects of processing method and fiber size on the structure and properties of wood–plastic composites

The aim of this study was to understand the roles of processing method and fiber size on the properties of wood–plastic composites (WPC). Composites were manufactured using extrusion or injection molding (IM) and fibers of different fiber length-to-diameter (L/D) ratio. IM resulted in better mechanical properties and lower water absorption and swelling than extrusion. These differences can be explained by the structure and surface quality of the composites. Fiber L/D ratio had a beneficial effect on mechanical properties but resulted in decreased water absorption characteristics. These results allow identifying a suitable forming process and/or fiber size according to application needs. This study provides a better understanding of the relationships between processing method, fiber characteristics, and composite behavior.     

Preparation of functionalized lignin beads from oak wood alkaline lignin

Alkaline lignin extracted from oak wood cooperage wastes was chemically modified to prepare beads by suspension polymerization on water without the use of organic solvents. These beads were macroporous and swelled in hydrophilic solvents. They were functionalized under microwaves to be used as scavenging agents in winery applications. The beads prepared by this approach have the advantage of being more acceptable by winemakers than synthetic polymer supports previously reported. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

The Effect of Defects on the Mobility of HEMT Transistors Based on AIGaN/GaN

A phenomenological low-filed mobility model is developed to describe the dependence ot the carrier molgmty on me gate to source bias applied for AIGaN/GaN high electron mobility transistor. The results show excellent agreement with experimental data, when compared thereby proving the validity of the model. In the proposed work the temporal evolution of the mobility degradation shows a sharp decline in emission rates below 456 s-1. We also note a sharp decline for large defects densities.     

Optimization of Laminates for Maximum Buckling Load

Journal of Failure Analysis and Prevention - Objective of this work is to optimize the structural configuration of laminates in terms of design for the maximization of buckling resistance of...