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Optimization methods for solving transportation problems on networks
Katja Prnaver, 2011, dissertation

Abstract: In this thesis we study problems from real situations, which can be applied to network graphs and solved using mathematical graph theory. We start with the problem of oriented network design. The problem originates from networks, where the flow over the arcs is important and many times limited with the capacity of the networks. There are several techniques and results on the problem of assigning the flow through the network channels. In our problem, we try to find the optimal network structure, which could be used in the design phase of the network. With metaheuristics, we search for optimal network structures for a given number of nodes. We define triangle neighborhood and compare the results of the algorithm with the conjecture by Choplin et al. [8]. Further, we study the problem of order picking and order batching in block structured warehouses. For order picking problem, we present the extension of a dynamic programming algorithm by Ratliff and Rosenthal [42], which enables the development of an algorithm for an unlimited number of blocks. In order to achieve this, a new presentation of states and transitions of dynamic programming algorithm is given. We prove that the resulting path is optimal for the given structure. We compare the optimal path lengths to the results found in literature and also investigate the impact of warehouse layout parameters onto the routing. Closely related to the problem of order picking, we investigate the order batching problem. We discuss the variation of the order batching problem with time windows and present the algorithmic approach to solving the problem. The previously presented optimal path algorithm is applied in the algorithm to ensure even better quality of results. We introduce the evaluation function of a batch and compare the results of the algorithm with the test data from the literature as well as with data from the real warehouse. We conclude by summarizing the results and stating some possible extensions and further work.
Keywords: graph theory, networks, optimization, shortest path problem, traveling salesman problem, algorithms, metaheuristics, order batching
Published: 03.06.2011; Views: 3735; Downloads: 146
.pdf Full text (925,86 KB)

Using neural networks in the process of calibrating the microsimulation models in the analysis and design of roundabouts in urban areas
Irena Ištoka Otković, 2011, dissertation

Abstract: The thesis researches the application of neural networks in computer program calibration of traffic micro-simulation models. The calibration process is designed on the basis of the VISSIM micro-simulation model of local urban roundabouts. From the five analyzed methods of computer program calibration, Methods I, II and V were selected for a more detailed research. The three chosen calibration methods varied the number of outgoing traffic indicators predicted by neural networks and a number of neural networks in the computer program calibration procedure. Within the calibration program, the task of neural networks was to predict the output of VISSIM simulations for selected functional traffic parameters - traveling time between the measurement points and queue parameters (maximum queue and number of stopping at the roundabout entrance). The Databases for neural network training consisted of 1379 combinations of input parameters whereas the number of output indicators of VISSIM simulations was varied. The neural networks (176 of them) were trained and compared for the calibration process according to training and generalization criteria. The best neural network for each calibration method was chosen by using the two-phase validation of neural networks. The Method I is the calibration method based on calibration of a traffic indicator -traveling time and it enables validation related to the second observed indicator – queue parameters. Methods II and V connect the previously described calibration and validation procedures in one calibration process which calibrates input parameters according to two traffic indicators. Validation of the analyzed calibration methods was performed on three new sets of measured data - two sets at the same roundabout and one set on another location. The best results in validation of computer program calibration were achieved by the Method I which is the recommended method for computer program calibration. The modeling results of selected traffic parameters obtained by calibrated VISSIM traffic model were compared with: values obtained by measurements in the field, the existing analysis methods of operational roundabouts characteristics (Lausanne method, Kimber-Hollis, HCM) and modeling by the uncalibrated VISSIM model. The calibrated model shows good correspondence with measured values in real traffic conditions. The efficiency of the calibration process was confirmed by comparing the measured and modeled values of delays, of an independent traffic indicator that was not used in the process of calibration and validation of traffic micro-simulation models. There is also an example of using the calibrated model in the impact analysis of pedestrian flows on conflicting input and output flows of vehicles in the roundabout. Different traffic scenarios were analyzed in the real and anticipated traffic conditions.
Keywords: traffic models, traffic micro-simulation, calibration of the VISSIM model, computer program calibration method, neural networks in the calibration process, micro-simulation of roundabouts, traffic modeling parameters, driving time, queue parameters, delay
Published: 02.06.2011; Views: 3572; Downloads: 245
.pdf Full text (13,21 MB)

Stochastic resonance on excitable small-world networks via a pacemaker
Matjaž Perc, 2007, original scientific article

Abstract: We show that the correlation between the frequency of subthreshold pacemaker activity and the response of an excitable array is resonantly dependent on the intensity of additive spatiotemporal noise. Thereby, the effect of the underlying network, defining the interactions among excitable units, largely depends on the coupling strength. Only for intermediate coupling strengths is the small world property able to enhance the stochastic resonance, whereas for smaller and larger couplings the impact of the transition from diffusive to random networks is less profound. Thus, the optimal interplay between a localized source of weak rhythmic activity and the response of the whole array demands a delicate balance between the strength of excitation transfer and the effectiveness of the network structure to support it.
Keywords: stochastic resonance, small-world networks, cardiology, neurophysiology, nonlinear dynamical systems, spatiotemporal phenomena
Published: 31.05.2012; Views: 961; Downloads: 44
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Improvement of the Peyravian-Jeffries`s user authentication protocol and password change protocol
Marko Hölbl, Tatjana Welzer-Družovec, Boštjan Brumen, 2008, original scientific article

Abstract: Remote authentication of users supported by passwords is a broadly adopted method of authentication within insecure network environments. Such protocols typically rely on pre-established secure cryptographic keys or public key infrastructure. Recently, Peyravian and Jeffries [M. Peyravian, C. Jeffries, Secure remote user access over insecure networks, Computer Communications 29 (5-6) (2006) 660-667] proposed a protocol for secure remote user access over insecure networks. Shortly after the protocol was published Shim [K.A. Shim, Security flaws of remote user access over insecure networks, Computer Communications 30 (1) (2006) 117-121] and Munilla et al. [J. Munilla, A. Peinado, Off-line password-guessing attack to Peyravian-Jeffries`s remote user authentication protocol, Computer Communications 30 (1) (2006) 52-54] independently presented an off-line guessing attack on the protocol. Based on their findings we present an improved secure password-based protocol for remote user authentication, password change, and session key establishment over insecure networks, which is immune against the attack.
Keywords: networks, user authentication, remote user access, password-based protocol, security
Published: 31.05.2012; Views: 992; Downloads: 35
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The use of artificial neural networks for colour prediction in textile printing
Darko Golob, Jure Zupan, Đurđica Parac-Osterman, 2008, published scientific conference contribution

Abstract: An attempt of using artificial neural networks for the prediction of dzes in textile printing paste preparation is presented. An existing collection of printed samples served as the basis for neural network training. It consists of 1340 samples printed using either a single dze or a combination of two dzes. First the proper combination of dzes was determined, because in most cases onlz two dzes are combined in the printing paste. Then the necessarz concentration of each dze was predicted. The reflectance value, and the colourvalues L*, a*, b* serve as input data and the known combination and concentrations of dzes for each sample were the targets. Some variations of neural network were tested, as well as various numbers of neurons in the hidden lazer. In addition, the influence of the training set organisation was examined, together with the number of learning epochs on the learning success.
Keywords: artificial neural networks, textile printing, colour recipe prediction
Published: 31.05.2012; Views: 1024; Downloads: 30
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Synthesis of non-isothermal heat integrated water networks in chemical processes
Miloš Bogataj, Miguel J. Bagajewicz, 2008, original scientific article

Abstract: This paper presents a new approach for the simultaneous synthesis and optimization of heat integrated water networks. A new superstructure for heat exchanger network (HEN) synthesis is proposed. The procedure is based on mixed integer non-linear mathematical programming (MINLP). Four relevant examples are presented to illustrate various aspects of the proposed approach.
Keywords: chemical processing, chemical process design, process water networks, water networks, wastewater minimization, heat integration, MINLP, HEN synthesis, superstructures, process synthesis
Published: 31.05.2012; Views: 1203; Downloads: 44
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Advanced modelling and simulation methods for communication networks
Jože Mohorko, Matjaž Fras, Saša Klampfer, 2008, original scientific article

Abstract: This paper contains a brief overview of suitable simulation tools available for education and research on network technologies and protocols. Among the mentioned tools we present advanced methods for network simulations using the OPNET modeler simulation tool. This is one of the most widespread simulation tools for network simulations, appropriate for both for teaching and also for the researching procedures of new internet devices and protocols. The basic package is intended for simulating communication networks and for protocols and devices development. There are also additional specific modules, such as a module assigned to the simulation of wireless networks, an ACE module for application analyzing, 3DNV module for visualizing networks on virtual terrain and the "System in the loop" module for simulating networks with real communication equipment in the loop, in real-time.
Keywords: network simulation, simulation tools, modelling, communication networks, OPNET
Published: 31.05.2012; Views: 998; Downloads: 25
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Spatial network representation of complex living tissues
Dean Korošak, Marjan Rupnik, 2008, published scientific conference contribution

Abstract: Networks were widely used to describe organizational and functional principles of living organisms across various scales. The topology of such biological complex networks often turned out to be "scale-free", with the power-law distribution of number of links per node, robust and modular with underlying self-similar structure. However, the topology of cytoarchitecture in living tissues has not yet received wide attention from the network perspective. Here we discuss the spatial complex network model of coupled clusters of beta cells in pancreatic islets. Networks of cells in pancreatic islets were constructed from the 2D section images presenting fluorescently labelled intercellular spaces obtained by two-photon laser scanning microscopy of whole pancreas tissue slices, and cells conductances measured electrophysiologically using whole-cell patch-clamp. We find that the heterogeneity of beta cells in intact living islets induces scale-free topology of the tissue network. Furthermore, we show that the islet-like structures visually similar to 2D section images can be obtained using Voronoi diagrams of random points.
Keywords: pancreatic islets, betta cells, complex networks, cytoarchitecture
Published: 31.05.2012; Views: 1138; Downloads: 37
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Combined feedforward and feedback control of end milling system
Franc Čuš, Uroš Župerl, Jože Balič, 2011, original scientific article

Keywords: machining, force control, neural networks
Published: 01.06.2012; Views: 719; Downloads: 14
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