TASK Quarterly
Scientific Bulletin of the Academic Computer Centre in Gdansk
ISSN 1428-6394
The current issue: 4/2017

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From the History of Science in Gdansk
  • A.Januszajtis, Stroke of Fate


  • K.Murawski and A.Zawada, The Influence of Wave-noise on Wave Speeds and Amplitudes of Surface-gravity Waves

    We have analytically examined surface-gravity waves which propagate in space- and time-dependent random velocity fields. Using a perturbative method, we have derived a dispersion relation which is solved for the case of wave-noise whose spectrum E(k,ω) ∼ E(k)δ(ω-crk), where δ is Dirac's delta-function and cr is the random phase speed. We have found that for a dispersionless noise resonance occurs when cr is equal to the group velocity cg of the surface-gravity wave. In this resonance the real part of the wave frequency is finite, but its imaginary part exhibits the characteristic 1/x singularity. The wave-noise interacts with a packet of the surface-gravity waves in such a way that the waves are attenuated for cr < cg and are amplified for cr > cg. As the real part is positive for high values of k, the surface-gravity waves are accelerated by the wave-noise.

  • R.Ogrodowczyk and K.Murawski, Parallel Computing in a Network of Workstations

    In this paper we describe a few architectures and software for parallel-processing computers. We have tested a cluster constructed with the use of MPI. All tests have been performed for one- and two-dimensional magneto-hydrodynamic plasma. We have concluded from the results of these tests that a simple problem should be run in a sequential node, as its execution time does not essentially decrease with the number of processors used. At the same time, the execution time of a complex problem decreases significantly with the number of processors. In the case of two-dimensional plasma the acceleration factor has reached the value of 3.7 with the use of 10 processors.

  • L.Pasini and S.Feliziani, A Method to Build Network-of-Queues-Based Simulators for Communication Systems

    In this study we build a library of new object types whose architecture is based on models of networks-of-queues to simulate communication networks. We also define a class of procedures to automatically generate a simulator of a generic communication network described by the library's objects.

  • E.Frulloni and S.Fiori, Quality Enhancement of Eddy-Current-Based Non-Destructive Evaluation Data through Independent Component Analysis

    The aim of this paper is to examine the performance of an independent component analysis algorithm based on neural networks applied to the solution of an electrical engineering problem related to non-destructive evaluation of conductive objects. The proposed application is assessed through computer experiments carried out on real-world data, which prove the usefulness of this non-destructive evaluation technique.

  • M.Kekana and J.Badur, An Analysis of a Piezo-elastic Restrictor Using a Capacitive Shunt

    The study investigates the control of structural response using collocated piezoelectric elements mounted on both sides of beam. A capacitive shunt is introduced into the circuitry to provide passive control of the beam's configuration. The energy method is used to develop the structure's governing equations. In order to select the appropriate electrostatic relations for the material, i.e. conductor or insulator material, the free charge rearrangement time is used. The effects of the capacitive shunt are introduced into the electrostatic relations using additive decomposition of capacitance. As an application of the model, a piezo-elastic beam restrictor using a capacitive shunt is investigated. Numerical results show that the capacitive shunt can effect passive control of the configuration of the beam.

  • E.A.Anagnostakis, Finite Difference Method Determination of the Nano-hetero-interface Wave-function Engineering of Inter-subband LASER Functionality

    A novel LASER action nano-hetero-structure of the inter-subband, mid-infrared functionality type is designed on the basis of optically pumped dual resonant tunnelling of conductivity electrons within an appropriately energetically determined scheme of five subbands hosted by two communicating asymmetric, approximately rectangular quantum wells (QWs). The upper LASER action level employed is the second excited subband of the nanostructure's back, wider QW and is provided with electrons via resonant tunnelling from the first excited subband of the nanostructure's front QW populated through remotely ignited optical pumping out of the local fundamental subband. The first excited back QW subband functions as the lower LASER action level, directly delivering the received electrons to the local fundamental subband - via fast vertical longitudinal optical phonon scattering - wherefrom they are being recycled back to the nanostructure's front QW fundamental subband by virtue of a second-reverse sense-resonant tunnelling-mediated normal charge transport mechanism. The handling of the de Broglie wave-function problem evolves into a numerical calculation of a Sturm-Liouville eigensystem solved by means of a finite difference method employing an appropriate tridiagonal coefficient matrix.

  • G.Bergmanski, M.Bialoskorski, M.Rychcik-Leyk, A.Witkowska, J.Rybicki, S.Frigio and S.Feliziani, The Structure of Rarefied and Densified PbSiO3 Glass: a Molecular Dynamics Study

    The paper is a molecular dynamics (MD) study of the structure of rarefied and densified lead-silicate glass of the PbSiO3 composition. Simulations have been performed in the constant volume regime for systems with densities of 3000, 4000, 5000, 5970 (normal density), 7000 and 8000kg/m3, using a two-body potential (Born-Mayer repulsive forces and Coulomb forces due to full ionic charges). All the systems were initially prepared as well equilibrated hot melts, and then slowly cooled down to 300K. The information on short-range correlations was obtained in a conventional way (from radial and angular distribution functions), while the middle-range order was studied via cation-anion ring analysis, using our new programme for basal ring determination. The structure of rarefied and densified glasses is compared with the structure of the same glasses under normal conditions. Moreover, the present results on PbSiO3 glass are compared with the corresponding data previously obtained for rarefied and densified PbGeO3 glass (Rybicki et al. 2001 Comput. Met. Sci. Technol. 7 91-112).

  • M.Brylinski, W.Jurkowski, L.Konieczny and I.Roterman, Limitation of Conformational Space for Proteins -- Early Stage Folding Simulation of Human α and β Hemoglobin Chains

    The starting structure of ab initio protein structure prediction methods is problematic as the energy minimization procedure stops searching for an optimal structure of the function's local minimum. The method presented in the paper helps to find the starting structure. Although it is based on the known native protein structure, it seems to deliver a key to the formation of a common universal starting structure. The limited conformational sub-space, defined on the basis of a geometrical model of the polypeptide backbone with the side chain-side chain interaction excluded, seems to deliver the original structure of the polypeptide, which is modified step by step as the role of the side chain interactions increases during the energy minimization procedure. Here, the method is applied to human hemoglobin chains α and β to test the applicability of the method to proteins with a high content of helical forms and lacking disulphide bonds.

  • K.Grzeda, A.Nowakowski and P.Czarnul, Analysis of Non-linear Properties of Cardiomyocyte Cellular Membranes

    Non-linear properties of cardiomyocyte membranes are poorly understood. We model a cell membrane using the Beeler-Reuter model with the Drouhard-Roberge modification (the BRDR model). Simulations are performed using AC voltage test excitation of 1 or 100kHz frequency and 1 or 10mV RMS. Values of currents flowing through the cell membrane are considered to be the response. The BRDR response is presented at the fundamental frequency and at its second and third harmonics. The response is mainly contributed to by the time-independent potassium current (iK1) during resting membrane potential. The level of currents varies strongly during the period of action potential. However, the linear response from the membrane capacitance is relatively high. The second and third harmonics of the 1kHz/10mV probing voltage carry some information about the action potential. In particular, it may be used to investigate the process of repolarization and its disorders.

  • B.G.Trzeciak, M.Jaskiewicz and J.Siebert, Using the Internet to Determine Fatal Cardiovascular Risk in the Polish Population

    We present the first program in Poland to determine the cardiovascular disease (CVD) risk of individuals, called Ryzyko. The program is freely available at www.ryzyko.amg.gda.pl. Our program, partially based on the European SCORECARD program, takes into account parameters such as age, sex, systolic blood pressure, total cholesterol concentration and cigarette smoking, and enables internet users to observe themselves to determine the degree of their CVD risk.

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