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Spreadsheets in function of optimisation of logistics network
Mimo Drašković, Drago Pupavac, 2016, independent scientific component part or a chapter in a monograph

Abstract: This scientific paper discusses how estimated spreadsheets functions in logistics networks optimisation. The suggested working hypothesis for efficacy of estimated spreadsheets in designing logistics networks is proved and a practical example. In this way the given model can be applied to all logistics networks of similar problem capacity. Logistics network model confronting estimated spreadsheets present a real world at a level needed for understanding the problem of optimisation of logistic networks. Applied scientific research for recognition of the set hypothesis is based on analysis and synthesis method, mathematical method and information modelling method.
Keywords: spreadsheets, estimation, logistics network design, optimization
Published: 09.05.2018; Views: 379; Downloads: 44
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Organization in finance prepared by stohastic differential equations with additive and nonlinear models and continuous optimization
Pakize Taylan, Gerhard-Wilhelm Weber, 2008, original scientific article

Abstract: A central element in organization of financal means by a person, a company or societal group consists in the constitution, analysis and optimization of portfolios. This requests the time-depending modeling of processes. Likewise many processes in nature, technology and economy, financial processes suffer from stochastic fluctuations. Therefore, we consider stochastic differential equations (Kloeden, Platen and Schurz, 1994) since in reality, especially, in the financial sector, many processes are affected with noise. As a drawback, these equations are hard to represent by a computer and hard to resolve. In our paper, we express them in simplified manner of approximation by both a discretization and additive models based on splines. Our parameter estimation refers to the linearly involved spline coefficients as prepared in (Taylan and Weber, 2007) and the partially nonlinearly involved probabilistic parameters. We construct a penalized residual sum of square for this model and face occuring nonlinearities by Gauss-Newton's and Levenberg-Marquardt's method on determining the iteration step. We also investigate when the related minimization program can be written as a Tikhonov regularization problem (sometimes called ridge regression), and we treat it using continuous optimization techniques. In particular, we prepare access to the elegant framework of conic quadratic programming. These convex optimation problems are very well-structured, herewith resembling linear programs and, hence, permitting the use of interior point methods (Nesterov and Nemirovskii, 1993).
Keywords: stochastic differential equations, regression, statistical learning, parameter estimation, splines, Gauss-Newton method, Levenberg-Marquardt's method, smoothing, stability, penalty methods, Tikhonov regularization, continuous optimization, conic quadratic programming
Published: 10.01.2018; Views: 550; Downloads: 59
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Tourism sector, travel agencies, and transport suppliers
Nataša Kovačić, Darja Topolšek, Dejan Dragan, 2015, original scientific article

Abstract: The paper addresses the effect of external integration (EI) with transport suppliers on the efficiency of travel agencies in the tourism sector supply chains. The main aim is the comparison of different estimation methods used in the structural equation modeling (SEM), applied to discover possible relationships between EIs and efficiencies. The latter are calculated by the means of data envelopment analysis (DEA). While designing the structural equation model, the exploratory and confirmatory factor analyses are also used as preliminary statistical procedures. For the estimation of parameters of SEM model, three different methods are explained, analyzed and compared: maximum likelihood (ML) method, Bayesian Markov Chain Monte Carlo (BMCMC) method, and unweighted least squares (ULS) method. The study reveals that all estimation methods calculate comparable estimated parameters. The results also give an evidence of good model fit performance. Besides, the research confirms that the amplified external integration with transport providers leads to increased efficiency of travel agencies, which might be a very interesting finding for the operational management.
Keywords: tourism sector, structural equation modeling, estimation methods, external integration, efficiency, travel agencies, logistics
Published: 03.04.2017; Views: 644; Downloads: 130
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Real-time cutting tool condition monitoring in milling
Franc Čuš, Uroš Župerl, 2011, original scientific article

Abstract: Reliable tool wear monitoring system is one of the important aspects for achieving a self-adjusting manufacturing system. The original contribution of the research is the developed monitoring system that can detect tool breakage in real time by using a combination of neural decision system and ANFIS tool wear estimator. The principal presumption was that force signals contain the most useful information for determining the tool condition. Therefore, the ANFIS method is used to extract the features of tool states from cutting force signals. ANFIS method seeks to provide a linguistic model for the estimation of tool wear from the knowledge embedded in the artificial neural network. The ANFIS method uses the relationship between flank wear and the resultant cutting force to estimate tool wear. A series of experiments were conducted to determine the relationship between flank wear and cutting force as well as cutting parameters. Speed, feed, depth of cutting, time and cuttingforces were used as input parameters and flank wear width and tool state were output parameters. The forces were measured using a piezoelectric dynamometer and data acquisition system. Simultaneously flank wear at the cutting edge was monitored by using a tool maker's microscope. The experimental force and wear data were utilized to train the developed simulation environment based on ANFIS modelling. The artificial neural network, was also used to discriminate different malfunction states from measured signals. By developed tool monitoring system (TCM) the machining process can be on-line monitored and stopped for tool change based on a pre-set tool-wear limit. The fundamental limitation of research was to develop a single sensor monitoring system, reliable as commercially available system, but 80% cheaper than multisensor approach.
Keywords: end-milling, tool condition monitoring, wear estimation, ANFIS
Published: 10.07.2015; Views: 1163; Downloads: 100
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Improved frequency characteristics of the randomized PWM boost rectifier
Franc Mihalič, Miro Milanovič, Carlos Cuoto, 2003, original scientific article

Abstract: A randomized pulse width modulation (RPWM) algorithm is applied in the control unit of the boost rectifier to achieve improved frequency characteristics in the wide band. First, the introduction of the RPWM switching is reflected in a smaller increase of the total harmonic distortion (THD) factor in the input current. Nevertheless, decrease of the power factor is negligibly small. Second, the power spectrum density (PSD) of the input current is estimated and measured to evaluate the influence of randomization in the high-frequency range. This approach offers an effective and credible prediction method for reduction of conductive electromagnetic interference (EMI) by using the RPWM switching.
Keywords: rectifiers, boost rectifiers, randomized pulse width modulation, estimation methods, total harmonic distortion, power factor, conductive electromagnetic interference
Published: 01.06.2012; Views: 1613; Downloads: 65
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Assessment of the consequences of accident scenarios involving dangerous substances
Zorka Novak-Pintarič, 2007, original scientific article

Abstract: This paper highlights the major steps in the procedure for evaluating the consequences of accidents involving dangerous substances, especially during storage, loading and unloading activities. The procedure relies on identifying accident scenarios that could be encountered in particular plants, followed by modelling of these scenarios by means of available modelling systems. Finally, the resultant outcomes are identified, together with their effects on both people and property. The resources needed to perform this proceedure are discussed, in order to clarify the roles of operators, external experts and other institutions when evaluating any accident conesquences. Four examples, all relevant in industrial practice, are given in order to illustrate the procedure: the releasing of liquefied petroleum gas, flammable organic solvents, toxic chlorine, and fuel oil. The results of these studies may be used for a quick order-of-magnitude estimation of accidents consequences.
Keywords: chemical industries, dangerous substances, transportation, storage, risk, accidents, consequences estimation, Seveso II, loading, unloading, safety report
Published: 01.06.2012; Views: 1709; Downloads: 85
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Use of genetic algorithm for fitting Sovova's mass transfer model
Dejan Hrnčič, Marjan Mernik, Maša Knez Hrnčič, 2010, original scientific article

Abstract: A genetic algorithm with resizable population has been applied to the estimation of parameters for Sovovaćs mass transfer model. The comparison of results between a genetic algorithm and a global optimizer from the literatureshows that a genetic algorithm performs as good as or better than a global optimizer on a given set of problems. Other benefits of the genetic algorithm, for mass transfer modeling, are simplicity, robustness and efficiency.
Keywords: Sovova's mass transfer model, genetic algorithm, parameter estimation
Published: 31.05.2012; Views: 1330; Downloads: 44
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Parameter identification of the Jiles-Atherton hysteresis model using differental evolution
Matej Toman, Gorazd Štumberger, Drago Dolinar, 2008, original scientific article

Abstract: In this paper, parameters of the Jiles-Atherton (J-A) hysteresis model are identified using a stochastic search algorithm called differential evolution (DE). The J-A hysteresis model's parameters are identified by DE in such a way, that best possible agreement is obtained between the measured and model calculated hysteresis loops. This agreement is furthermore increased by improving the J-A hysteresis model. The improvement is achieved by replacing a constant pinning parameter in the J-A hysteresis model with a variable one. Here, the variable pinning parameter is written as a function of a magnetic field. Bz DE identified parameters are used in the J-A hysteresis model, which is included in the dynamic model of a single-phase transformer. The effectiveness of the improved J-A hysteresis model and parameters identification approach is verified with experiments and simulations.
Keywords: Jiles-Atherton model, J-A hysteresis model, magnetic hysteresis, optimization methods, parameters estimation, single-phase transformer
Published: 31.05.2012; Views: 1565; Downloads: 38
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Cost estimation, optimization and competitiveness of different composite floor systems
Uroš Klanšek, Stojan Kravanja, 2006, original scientific article

Abstract: This paper presents self-manufacturing cost estimation, cost optimization and competitiveness of different composite floor systems: composite I beams, composite trusses produced from rolled channel sections and composite trusses made from cold formed hollow sections. Part 1 of this two-part series of papers presents the estimation of the self-manufacturing (direct production) costs for composite and steel structures. The self-manufacturing costs are proposed to be defined as the sum of the material, the power consumption and the labour costs. The material costs of the structural steel, concrete, reinforcement, the shear connectors, electrodes, the anti-corrosion, fire protection and top coat painting, the formwork floor-slab panels and gas consumption are presented in detail. The power consumption costs comprise costs of sawing the steel sections, edge grinding, drilling, welding, stud welding and vibrating the concrete. The labour costs (times) presented define the costs of metal cutting, edge grinding, preparation, assembling and tacking, welding, welding of shear connectors, steel surface preparation and protection, drilling, cutting, placing and connecting the reinforcement, concreting, consolidating and curing the concrete. New approximation functions are proposed for the calculation of some manufacturing times and material consumptions. As the discussed costs vary significantly around the world, the proposed cost expressions are given in the open form to be used for cost estimation in different economic conditions. A numerical example of the estimation of the self-manufacturing costs for a composite I beam floor system shows the suitability of the proposed approach. On the basis of the defined self-manufacturing costs, introduced in Part 1, the cost optimization and the competitiveness of different composite floor systems are discussed in Part 2.
Keywords: cost estimation, self-manufacturing costs, material costs, power consumption costs, labour costs, steel structures, composite structures, welded structures
Published: 30.05.2012; Views: 1651; Downloads: 23
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