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    Tytuł:
    Obtaining ionic forces by the total-energy tight-binding method
    Autorzy:
    Dziedzic, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933173.pdf
    Data publikacji:
    2007
    Wydawca:
    Politechnika Gdańska
    Tematy:
    total-energy tight-binding
    TBMD
    Hellmann-Feynman
    ionic forces
    molecular dynamics
    Opis:
    Applying a non-orthogonal tight-binding method to calculate ionic forces in a molecular-dynamics simulation vastly improves the transferability the model's transferability to different environments, compared with the tradi-tional empirical potential-driven molecular-dynamics. In this paper we present the details of computing derivatives of Hamiltonian and overlap matrix elements appearing in the Hellmann-Feynman expression for ionic forces in the NRL-TB model of tight-binding. The presented expressions are validated with the results obtained using a tight-binding-driven molecular-dynamics program.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2007, 11, 3; 285-294
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Quantum-classical calculations of the nanomechanical properties of metals
    Autorzy:
    Dziedzic, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1964138.pdf
    Data publikacji:
    2009
    Wydawca:
    Politechnika Gdańska
    Tematy:
    hybric methods
    cross-scaling
    tight-binding
    learn-on-the-fly
    nanoscale
    metals
    nanoindentation
    molecular-dynamics
    Sutton-Chen potential
    Opis:
    Molecular-dynamics (MD) simulations constitute an important tool in the study of nanoscale metallic systems, especially so in the face of the difficulties plaguing their experimental analysis. Main limitations of the MD method stem from the empirical nature of the potentials employed, their functional form which is postulated ad hoc, and its classical nature. The neglect of electronic effects and the unjustified utilization of the potential for system configurations significantly different from those, for which the potential was parametrized makes the results of strictly classical calculations dubious, at least for a certain class of systems. On the other hand, high computational complexity of quantum-based methods, where atomic interactions are described ab initio, prohibits their direct use in the study of systems larger than several tens of atoms. In the last decade, a growing popularity of so-called hybrid (or cross-scaling) methods can be observed, that is, methods which treat the most interesting part of the system with a quantum-based approach, while the remainder is treated classically. Physically sound handshaking between the two methodologies (quantum and classical) within a single simulation constitutes a serious challenge, the majority of difficulties concentrating around the interface between the fragments of the system treated with the two methods. The aforementioned interface is most easily constructed for covalently bonded systems, where the bonds cut by the isolation of the quantum-based region can be saturated by the introduction of specially crafted link-atoms. In metallic systems, however, due to electronic delocalization, this traditional approach cannot be employed. This paper describes a physically sound and adequately efficient computational technique, which allows for the inclusion of results of locally employed quantum-based computations within a molecular-dynamics simulation, for systems described by the many-body Sutton-Chen (SC) potential, used in the study of fcc metals. The proposed technique was developed taking as a point of departure the Learn-on-the-Fly (LOTF) formalism, a recent development itself. The original LOTF approach is only suitable for two- or three-body potentials and is serial in nature, whereas the proposed technique can be used with many-body potentials and is parallel-ready. An implementation of the proposed approach in the form of computer code, which allows for parallel hybrid computations for metallic systems is also described. Finally, results from a set of hybrid simulations of nanoindentation of a copper workmaterial with a hard indenter utilizing the aforementoned technique and computer code is presented, as evidence of its viability.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2009, 13, 3; 207-310
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Voice command recognition using hybrid genetic algorithm
    Autorzy:
    Wroniszewska, M.
    Dziedzic, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1955309.pdf
    Data publikacji:
    2010
    Wydawca:
    Politechnika Gdańska
    Tematy:
    voice command recognition
    genetic algorithms
    K-nearest neighbour
    hybrid approach
    Opis:
    Speech recognition is a process of converting the acoustic signal into a set of words, whereas voice command recognition consists in the correct identification of voice commands, usually single words. Voice command recognition systems are widely used in the military, control systems, electronic devices, such as cellular phones, or by people with disabilities (e.g., for controlling a wheelchair or operating a computer system). This paper describes the construction of a model for a voice command recognition system based on the combination of genetic algorithms (GAs) and K-nearest neighbour classifier (KNN). The model consists of two parts. The first one concerns the creation of feature patterns from spoken words. This is done by means of the discrete Fourier transform and frequency analysis. The second part constitutes the essence of the model, namely the design of the supervised learning and classification system. The technique used for the classification task is based on the simplest classifier – K-nearest neighbour algorithm. GAs, which have been demonstrated as a good optimization and machine learning technique, are applied to the feature extraction process for the pattern vectors. The purpose and main interest of this work is to adapt such a hybrid approach to the task of voice command recognition, develop an implementation and to assess its performance. The complete model of the system was implemented in the C++ language, the implementation was subsequently used to determine the relevant parameters of the method and to improve the approach in order to obtain the desired accuracy. Different variants of GAs were surveyed in this project and the influence of particular operators was verified in terms of the classification success rate. The main finding from the performed numerical experiments indicates the necessity of using genetic algorithms for the learning process. In consequence, a highly accurate recognition system was obtained, providing 94.2% correctly classified patterns. The hybrid GA/KNN approach constituted a significant improvement over the simple KNN classifier. Moreover, the training time required for the GA to learn the given set of words was found to be on a level that is acceptable for the efficient functioning of the voice command recognition system.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2010, 14, 4; 377-396
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    MD simulations of ultraprecision machining of fcc monocrystals
    Autorzy:
    Rychcik-Leyk, M.
    Białoskorski, M.
    Dziedzic, J.
    Rybicki, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1943186.pdf
    Data publikacji:
    2010
    Wydawca:
    Politechnika Gdańska
    Tematy:
    nanomachining
    nanocutting
    nanomechanical properties
    nanoplasticity
    Opis:
    In technical sciences, the term "machining" refers to the process of forming an object into a desired shape and size, with a desired quality of surface, by removing layers of its material by means of a cutting tool. The paper describes research on ultra-precision machining (UPM), where the abovementioned process takes place on the atomic level and involves systems (a machined object and a tool) several dozen nanometers in size. Three-dimensional computer simulations (virtual experiments) of UPM of monocrystalline copper with an infinitely hard tool were performed utilizing the classical molecular dynamics (MD) method with a many-body potential to describe the interatomic interactions. Among the examined issues were: the effect of the tool shape, machining speed and depth on the obtained workmaterial surfaces, and on the stresses, slip patterns and local temperature increases generated during the process.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2010, 14, 1-2; 35-167
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Modeling the contact of stiff and soft bodies with a rigid support by short range force fields
    Autorzy:
    Contento, A.
    Di Egidio, A.
    Dziedzic, J.
    Tatone, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1943218.pdf
    Data publikacji:
    2009
    Wydawca:
    Politechnika Gdańska
    Tematy:
    impast
    contact
    short range interaction
    soft body dynamice
    Opis:
    Body impact-contact dynamics is a classical subject in mechanics. Most of the papers on the subject are based on a kinematical or impulse-exchange approach. In this paper a different approach has been adopted. It consists in assigning a constitutive description for the contact forces between the boundaries of bodies which get close to each other. In particular, a field of short range forces has been used to model the interaction between an affine body and the planar surface of a fixed rigid support. These forces are able to describe the impact, friction and adhesion allowing the body to have complex motions which look rather realistic. By an affine body we mean a body which undergoes affine, or homogeneous, deformations. Depending on the material, such a body can show very different behavior, from a quite rigid motion to a motion characterized by very large deformations. A soft body is assumed to be made of a viscous incompressible Mooney-Rivlin material. Though a microscopic model of surface interaction could be used in a multiscale approach, the description provided here is macroscopic only.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2009, 13, 1-2; 155-181
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-5 z 5

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