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The dynamics of human gait
Matjaž Perc, 2005, izvirni znanstveni članek

Opis: We analyse the dynamics of human gait with simple nonlinear time series analysis methods that are appropriate for undergraduate courses. We show that short continuous recordings of the human locomotory apparatus possess properties typical of deterministic chaotic systems. To facilitate interest and enable the reproduction of presented results, as well as to promote applications of nonlinear time series analysis to other experimental systems, we provide user-friendly programs for each implemented method. Thus, we provide new insights into the dynamics of human locomotion, and make an effort to ease the inclusion of nonlinear time series analysis methods into the curriculum at an early stage of the educational process.
Ključne besede: dynamic systems, chaotic systems, nonlinear dynamics, human gait, human locomotion
Objavljeno: 01.06.2012; Ogledov: 1020; Prenosov: 19
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Evolutionary programming of CNC machines
Miha Kovačič, Miran Brezočnik, Ivo Pahole, Jože Balič, Borut Kecelj, 2005, izvirni znanstveni članek

Opis: The paper proposes a new concept for programming of CNC machines. The concept based on genetic algorithms assures evolutionary generation and optimization of NC programs on the basis of CAD models of manufacturing environment. The structure, undergoing simulated evolution, is the population of NC programs. The NC programs control the machine which performs simple elementary motions. During the evolution the machine movement becomes more and more complex and intelligent solutions emerge gradually as a result of the interaction between machine movements and manufacturing environment. The examples of evolutionary programming of CNC lathe and CNC milling machine tool for different complexities of the blanks and products are presented. The proposed concept showed a high degree of universality, efficiency, and reliability and it can be also simply adopted to other CNC machines.
Ključne besede: manufacturing systems, NC-programming, CNC lathes, simulated evolution, genetic algorithms
Objavljeno: 01.06.2012; Ogledov: 854; Prenosov: 38
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Encyclopedia of complexity and systems science
slovar, enciklopedija, leksikon, priročnik, atlas, zemljevid

Opis: Encyclopedia of Complexity and Systems Science provides an authoritative single source for understanding and applying the concepts of complexity theory together with the tools and measures for analyzing complex systems in all fields of science and engineering. The science and tools of complexity and systems science include theories of self-organization, complex systems, synergetics, dynamical systems, turbulence, catastrophes, instabilities, nonlinearity, stochastic processes, chaos, neural networks, cellular automata, adaptive systems, and genetic algorithms. Examples of near-term problems and major unknowns that can be approached through complexity and systems science include: The structure, history and future of the universe; the biological basis of consciousness; the integration of genomics, proteomics and bioinformatics as systems biology; human longevity limits; the limits of computing; sustainability of life on earth; predictability, dynamics and extent of earthquakes, hurricanes, tsunamis, and other natural disasters; the dynamics of turbulent flows; lasers or fluids in physics, microprocessor design; macromolecular assembly in chemistry and biophysics; brain functions in cognitive neuroscience; climate change; ecosystem management; traffic management; and business cycles. All these seemingly quite different kinds of structure formation have a number of important features and underlying structures in common. These deep structural similarities can be exploited to transfer analytical methods and understanding from one field to another. This unique work will extend the influence of complexity and system science to a much wider audience than has been possible to date.
Ključne besede: cellular automata, complex networks, computational nanoscience, ecological complexity, ergodic theory, fractals, game theory, granular computing, graph theory, intelligent systems, perturbation theory, quantum information science, system dynamics, traffic management, chaos, climate modelling, complex systems, dynamical sistems, fuzzy theory systems, nonlinear systems, soft computing, stochastic processes, synergetics, self-organization, systems biology, systems science
Objavljeno: 01.06.2012; Ogledov: 1414; Prenosov: 37
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MARS: A Metamodel Recovery System Using Grammar Inference
Faizan Javed, Marjan Mernik, Jeffrey G. Gray, Barrett Richard Bryant, 2008, izvirni znanstveni članek

Opis: Domain-specific modeling (DSM) assists subject matter experts in describing the essential characteristics of a problem in their domain. When a metamodel is lost, repositories of domain models can become orphaned from their defining metamodel. Within the purview of model-driven engineering, the ability to recover the design knowledge in a repository of legacy models is needed. In this paper we describe MARS, a semi-automatic grammar-centric system that leverages grammar inference techniques to solve the metamodel recovery problem. The paper also contains an applicative case study, as well as experimental results from the recovery of several metamodels in diverse domains.
Ključne besede: domain-specific languages, metamodeling, recovery systems, reverse engineering, re-ingineering
Objavljeno: 01.06.2012; Ogledov: 703; Prenosov: 33
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Basic solutions on shape complexity evaluation of STL data
Bogdan Valentan, Tomaž Brajlih, Igor Drstvenšek, Jože Balič, 2008, izvirni znanstveni članek

Opis: Purpose of this paper is to present basic solutions on shape complexity, based on basic information of the STL data. Design/methodology/approach: Paper presents a few methods of mathematically evaluating the complexity of the shape. Methods vary from very simple based on the number of triangles in STL file, STL file size and the parts volume, to the more complex mathematical evaluation based on the basic relations of the STL data. Findings: We discovered that evaluation of shape complexity based only on basic data of STL data gives us some basic results on part complexity and can be used for further researches. Research limitations/implications: For parts with large block volume/part volume ratio and thinner parts with free form surfaces only the first method is suitable and gives suitable results. Practical implications: In a rapidly developing field of manufacturing technologies choosing the optimal manufacturing procedure is a difficult and crucial decision. Usually the decision is based on experience evaluation that is fast and can be optimal. Usually, this method produces goods results, but in some cases this method can lead to cost increases and reduced economic efficiency without us even knowing that. Therefore, it is crucial, that a fast and simple solution is developed, by which the optimal way of manufacturing can be determined. Originality/value: Choosing maximum efficient manufacturing processes on base of part complexity is a new perspective in manufacturing, which, properly evolved and complied can cause revolution in manufacturing optimization, especially in hybrid manufacturing processes.
Ključne besede: manufacturing systems, shape complexity, complex shapes, manufacturing optimization, engineering design, STL files, STL file parameters
Objavljeno: 01.06.2012; Ogledov: 1142; Prenosov: 34
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Extended Lindstedt-Poincare method for non-stationary resonances of dynamical systems with cubic nonlinearit
Rudi Pušenjak, 2008, izvirni znanstveni članek

Opis: This paper presents the extended Lindstedt-Poincare (EL-P) method, which applies multiple time variables to treat non-stationary oscillations arising in dynamical systems with cubic nonlinearities due to the slowly varied excitation parameters. The method is applied extensively in research of non-stationary vibrations of clamped-hinged beams. Recognizing the aperiodic nature of non-stationary oscillations, the new formulation is presented by adding an additional, slow time scale beside time scales of the nonlinear system, which generally correspond to the incommensurate nonlinear frequencies of the response. Using this concept, a generalized approach of the study to the passage through fundamental, superharmonic and subharmonic resonances is presented in the paper. Effects of slowly varying excitation frequency and slowly varying excitation amplitude on the non-stationary oscillations are studied with the computation of deviations from the stationary response. Although the method is formulated for N-dof dynamical systems having weak cubic nonlinearities, it is applied for non-stationary vibrations, where two-mode shape approximation of damped and undamped clamped-hinged beam, respectively, is used and the simultaneous appearance of internal resonance is taken into account. Stability analysis of stationary solutions is performed and comparisons of stationary resonance curves by results obtained with the incremental harmonic balance (IHB) method show good agreement. The passage through the fundamental resonance of damped and undamped clamped-hinged beam, respectively, is investigated in detail.
Ključne besede: dynamical systems with cubic nonlinearities, nonlinear oscillations, nonstationary nonlinear oscillations, time scales, excitation frequency, resonance, Lindstedt-Poincare method
Objavljeno: 01.06.2012; Ogledov: 1058; Prenosov: 15
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Absorptive capacity in European manufacturing: a Delphi study
Petra Jung Erceg, Krsto Pandža, Heidi Armbruster, Carsten Dreher, 2007, izvirni znanstveni članek

Opis: This paper sets out to discuss the results of a specific part of a Europe-wide Delphi study that considers issues of absorptive capacity in European manufacturing. Owing to the importance to competitiveness of increasing innovative capabilities in manufacturing it is highly relevant to explore how a wide community of manufacturing experts experience the phenomenon of absorptive capacity and sense future developments. A two round Delphi method was designed in which more than 3,000 experts from 22 European countries assessed 101 statements. This paper discusses eight statements focused on the issue of absorptive capacity. The results show a general consensus about the influence of different inter-firm relationships in acquiring external knowledge and a diversified knowledge structure for assimilating the acquired knowledge. The study also indicates some potential challenges and contradictions in managing inter-firm relationships and knowledge diversity aswell as perceived barriers for future developments of absorptive capacity. Delphi survey is an empirical method subject to the limitation of testing or inductively building theoretical concepts. The results of the Delphi study arepredominantly centred on policy implication and on informing strategic decision-making at manufacturing firms. This paper discusses one of the biggest Delphi surveys ever conducted in Europe. Its comprehensiveness increases the value of the results.
Ključne besede: industry, manufacturing systems, knowledge capture, Delphi method, Europ
Objavljeno: 01.06.2012; Ogledov: 791; Prenosov: 29
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The wavelet transform for BEM computational fluid dynamics
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2004, izvirni znanstveni članek

Opis: A wavelet matrix compression technique was used to solve systems of linear equations resulting from BEM applied to fluid dynamics. The governing equations were written in velocity-vorticity formulation and solutions of the resulting systems of equations were obtained with and without wavelet matrix compression. A modification of the Haar wavelet transform, which can transformvectors of any size, is proposed. The threshold, used for making fully populated matrices sparse, was written as a product of a user defined factor and the average value of absolute matrix elements values. Numerical tests were performed to assert, that the error caused by wavelet compression depends linearly on the factor , while the dependence of the error on the share of thresholded elements in the system matrix is highly non-linear. The results also showed that the increasing non-linearity (higher Ra and Re numbervalues) limits the extent of compression. On the other hand, higher meshdensity enables higher compression ratios.
Ključne besede: fluid mechanics, computational fluid dynamics, boundary element method, wavelet transform, linear systems of equations, velocity vorticity formulation, driven cavity, natural convection, system matrix compression
Objavljeno: 01.06.2012; Ogledov: 1185; Prenosov: 31
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Designing the layout of single- and multiple-rows flexible manufacturing system by genetic algorithms
Mirko Ficko, Miran Brezočnik, Jože Balič, 2004, izvirni znanstveni članek

Opis: The paper presents a model of designing of the flexible manufacturing system (FMS) in one or multiple rows with genetic algorithms (GAs). First the reasons for studying the layout of devices in the FMS are discussed. After studying the properties of the FMS and perusing the methods of layout designing the genetic algorithms methods was selected as the most suitable method for designing the FMS. The genetic algorithm model, the most suitable way of coding the solutions into the organisms and the selected evolutionary and genetic operators are presented. In the model, the automated guided vehicles (AGVs) for transport between components of the FMS were used. In this connection, the most favourable number of rows and the sequence of devices in the individual row are established by means of genetic algorithms. In the end the test results of the application made and the analysis are discussed.
Ključne besede: flexible manufacturing systems, facility layout, optimization, genetic algorithms
Objavljeno: 01.06.2012; Ogledov: 919; Prenosov: 31
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