ISSN 1312-2622

YEAR X No. 2 / 2012

CONTENTS

Periodic Solidification in a Rectangular Duct Due to Velocity Modulation; One-dimensional Analysis
Computational Aspects of In-silico Experiments for Investigating the Impact of the Host Genome on the Influenza Virus A Variability
Modelling Control of a Wind Turbine
Open Problems in High-Performance Molecular-Dynamics Simulations
Bi-level Optimization for Portfolio Modelling
Impact of Volume of Information on Human Behavior

 

Periodic Solidification in a Rectangular Duct Due to Velocity Modulation; One-dimensional Analysis
S. Kimura, H. Yamamoto, K. Kanev
Key Words:
Phase change; dynamic solidification; perturbation solution; convection heat transfer; duct flows, e-learning.
Abstract:
In the present study, we report on the solid phase dynamic response due to time-varying duct flows when a portion of a duct wall is cooled to below the liquidus temperature, along which unidirectional solidification from the cooling duct wall, perpendicular to the flow direction, is assumed. A one-dimensional numerical model for the average solid phase thickness has been formulated employing the boundary tracking method. It is shown that a quasi-steady state temperature in the solid layer allows us to develop an analytical solution, making use of perturbation technique. The afore-mentioned perturbation analysis identifies important three nondimensional parameters, i.e. the Biot number based on the temperature difference between the cooling wall and the liquidus temperatures, and the Stefan number based on the liquidus and the flowing liquid temperatures. results obtained by both approaches agree well in general, and the time-variation trends of solid phase thickness and its phase delay have been obtained as a function if the non-dimensional angular frequency of the modulating dict flow velocity, with the above three non-dimensional parameters. Various applications in practical engineering and in engineering education have been identified and are being addressed by the developed Graphical Interface Framework for Educational and Engineering Support (GIFEES).

Computational Aspects of In-silico Experiments for Investigating the Impact of the Host Genome on the Influenza Virus A Variability
P. Borovska, V. Gancheva, E. Asenov, I. Georgiev
Key Words:
Bioinformatics; high performance computing; influenza virus; multiple sequence alignment; sequence alignment.
Abstract:
Nowadays the study of the variability of influenza virus is a problem of very great importance. Influenza type A viruses cause epidemics and pandemics. The problem of restricting the spreading of pandemics and the treatment of the people infected by the influenza virus is widely based on the latest achievements of molecular biology, bioinformatics and biocomputing, as well as many other advanced areas of science. In silico biological sequence processing is a key for molecular biology. This scientific area requires powerful computing resources for exploring large sets of biological data. The paper presents parallel computational simulations for the case study of investigating the role of the host genome in the evolution and the fast changeability of the influenza virus A on supercomputer BlueGene/P. The experimental framework is based on all available existing influenza virus A nucleotide sequences, the clustalw algorithm for multiple sequence alignment, the blast algorithm for sequence searching, the Philip software for philogenetic tree reconstruction and the recombination analysis tool for finding hot-spots of mutation/recombination in influenza A virus genomes.

Modelling Control of a Wind Turbine
J. Genov, G. Venkov, B. Gilev
Key Words:
Wind turbine model; control system.
Abstract:
A mathematical method of the system consisting of wind turbine, gear box and asynchronous generator is presented. The oscillation of tower tip is modelling. The behavior of the system for two different wind speeds was studied. One controller, which provides a mode of frequency stabilization in over-nominal wind speed is developed. Then other controller, which provides a mode of maximum power genaration in under-nominal wind speed, is developed. Provided is switching between two controllers without adverse transients responds.

Open Problems in High-Performance Molecular-Dynamics Simulations
D. Grancharov, E. Lilkova, N. Ilieva, P. Petkov, L. Litov
Key Words:
Molecular-dynamics simulations; symplectic algorithms; scalability; large atomic systems; work-load distribution; GROMACS; NAMD; SCALASCA.
Abstract:
Molecular-dynamics simulations provide reliable information about the microscopic behavior of the investigated systems by numerical solution of the equations of motion. The constantly growing computer performance (in particular, the number of computing cores) makes wider the range of research topics - and systems - accessible by these means. However, simulation continuance increases drastically with the size of the systems and the scalability of the most popular simulation packages worsens. We aim at the development of a multiple step-size symplectic integrator adapted to the large biomolecular systems particular features, such as multiple frequency modes, interaction hierarchy and strong inhomogeneity. To this end, we analyze the scalability and the work-load increase and distribution among the computing cores in the packages GROMACS and NAMD on the example of three test systems with increasing size, by means of the GROMACS in-built tool g_tune_pme and of the dedicated package SCALASCA.

Bi-level Optimization for Portfolio Modelling
K. Stoilova
Key Words:
Financial portfolio; bi-level optimization; hierarchical theory.
Abstract:
The optimal resource allocation of sets of securities, available in the financial market can be done by solving a multicriterion optimization task, aimed at maximization of portfolio return and minimization of portfolio risk. Here is proposed the utilization of hierarchical coordination for solving the bi-level optimization problem, which formalizes the investment process. A two-level hierarchical approach for solving the portfolio optimization problem is applied where the optimal Sharp ratio of risk versus return is solved at the upper level and as a result is determined by the investor's preferences for taking risk on the basis of objective considerations. The optimal portfolio is evaluated at the lower level.

Impact of Volume of Information on Human Behavior
K. Boyanov
Key Words:
Human behavior, information processing; brain-computer; digital society; volume of information.
Abstract:
The paper is dedicated to problems, emerging with human behavior in digital society and the ever increasing volume of information, which he has to perceive. An attempt has been made to draw an analogy human mind-computer on the basis of information processing. Some issues concerning educational features and the link human - environment in the digital society are discussed.

The John Atanasoff Society of Automatics and Informatics

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