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1

Vehicular flow simulators based on complex queuing systems

Pasini L., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2013

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Vol. 17, No 3-4

155--180

EN

The crux of this paper is to demonstrate how it is possible to model systems of vehicular trafic by means of complex queuing network models. The objects comprising the library that we define in this work all follow the approach whereby they are composed of one or more queuing networks of service systems that are traversed by customers (vehicles).

2

Graphical Application for the Construction of a Simulator of Urban Vehicular Traffic Flows

Pasini L., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2010

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Vol. 14, No 4

405-430

EN

One of the most fundamental problems encountered during the construction of a simulator of urban vehicular traffic flows concerns the method of gathering the data describing the real system. In this paper, we present a graphical application developed for AutoCAD. This application allows to process the images of a vehicular traffic system in AutoCAD. During the graphical processing performed by means of our application, a file describing the system is generated. This file is subsequently read by a procedure which generates the simulator of the system. The images of the traffic system can be acquired by means of several applications available on the Internet, such as Google Maps, Google Earth, Bing, etc. Performing image processing in the context of AutoCAD allows to consistently handle distance measurements in the system, and, in general, to address the problems related to the scale ratios of an image.

3

Simulators of VOIP Traffic in P2P Networks

Pasini L., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2009

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Vol. 13, No 4

315-345

EN

This study is included in a research programme developed by the authors at the University of Studies in Camerino for the construction of traffic flow simulators in computer and telecommunication networks [1–4]. The article contains the definition of a library of object types whose architecture is based on the queue networks, for a simulation of the VOIP traffic in P2P networks. Basing on this library, we simulate the traffic in a P2P network that is locally implemented with three different technology types: 1. Fast Ethernet, 2. Wireless, 3. ADSL2+. In this context, we simulate traffic flows due to file-sharing applications in the network and due to voice communications through the VOIP technology. Thus, we evaluate the impact of the VOIP traffic for procedures of file-sharing in a P2P network.

4

Queue-based simulators of P2P networks

Pasini L., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2007

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Vol. 11, No 3

203-235

EN

A technique is introduced for the construction of simulators of telecommunication networks based on the P2P protocol with a decentralized directory. The context of the application concerns P2P networks used both by sharing software and by telecommunication applications, as in VoIP applications. P2P systems have the advantages of boundless scalability and the break-up insensibility of devices, but suffer from heavy traffic of signals and network delays. Therefore, simulation of signal traffic in P2P networks is an important issue. The technique we have developed enables individuation of a generic P2P network's components and their functional characterization. We have worked at this level of description in order to determine the architecture of every component as a model of queues' networks. We have therefore defined a library of new types of objects for the construction of P2P network simulators with the Qnap2.V9 programming language. In this context, we have defined a procedure automatically generating the simulator of an any P2P network. During its execution, the procedure reads data from a file containing a description of the structure of the considered P2P network and values of the characteristic parameters of its components. Results related to the simulation of three configurations of a P2P network are introduced in Section 5 below. They differ according to the technology used to realize the local interconnection networks. The context of the present paper is a research program developed at the University of Camerino in defining specific computer procedures aimed at construction of simulators of telecommunication and computing networks. This technique also enables simulation of the software elaboration phases on computer networks and evaluation of the impact of specific choices concerning the structure of transmission protocols and operation paradigms of software applications [1, 2].

5

Model angular distribution functions in CA3, CA4 and CA6 structural units of glassy systems

Bergmański G., Feliziani S., Rybicki J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2007

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Vol. 11, No 3

185-195

EN

We have calculated model partial angular distribution functions (pADFs) in CA3, CA4 and CA6 structural units, i. e. an equilateral triangle with three vertical anions, A, and a central cation, C, a regular tetrahedron with four vertical anions, A, and a central cation, C and a square bipyramid with six vertical anions, A, and a central cation, C. The model pADFs were calculated employing a simple Monte Carlo procedure: the ions were being shifted at random within 3D spheres of radius r with uniform probability density and the AAA, ACA and CAA angles were calculated for each random configuration. Repeating the calculation 10(8) - 10(9) times produced smooth probability densities for the angles' values. Conventional reference data so obtained can be applied to estimate the overall degree of deformation of the considered structural units in numerically simulated materials.

6

Simulation of road systems and queuing network models

Pasini L., Feliziani S., Giorgi M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2005

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Vol. 9, No 4

397-408

EN

The purpose of this paper is to describe the versatility of queuing network systems for modelling vehicular traffic flows in road systems. These techniques are applicable in a simulation context because of the complexity of the resulting models, which can not be solved by mathematical analytical solvers. Moreover, these techniques can be used to model and simulate the behaviour of an automatic control system of vehicular flow in the same frame.

7

Construction of queue-based simulators for web applications distributed on computer networks

Pasini L., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2005

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Vol. 9, No 4

373-396

EN

Modern Internet and web applications involve interactions among remote host computers connected by communication networks. Simulation modelling is an important technique to evaluate performance in the implementation of a web-distributed application over given networks formed by computer hosts connected by heterogeneous networks. In this paper we extend a previous work concerning the construction of a queue-based simulator of communication networks. We define a set of new queue-based object types which permit us to specify the behaviour of a web-distributed application whose software components run over different hosts in a given communication network. We apply this technique to show how to build a simulator to evaluate the performance of various software architectures for a web-distributed application run over a given computer network.

8

The structure of rarefied and densified PbSiO3 glass: a molecular dynamics study

Bergmański G., Białoskórski M., Rychcik-Leyk M., Witkowska A., Rybicki J., Mancini G., Frigio S., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2004

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Vol. 8, No 3

393-412

EN

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).

9

Networks of queues for the simulation of urban flow systems: an intermodal traffic system

Pasini L., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2004

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Vol. 8, No 1

121-130

EN

In this paper we introduce a queueing network model, which can be used to simulate the behaviour of specific traffic systems in an urban context. The frame of the work is that of road automation and traffic system control by queue based models simulation.

10

A method to build network-of-queues-based simulators for communication systems

Pasini L., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2004

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Vol. 8, No 3

333-358

EN

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.

11

The structure of porous and spontaneously densified amorphous PbSiO3 : a molecular dynamics study

Chomenko K., Bergmański G., Białoskórski M., Rychcik-Leyk M., Feliziani S., Frigio S., Witkowska A., Rybicki J.

Computational Methods in Science and Technology

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2004

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Vol. 10, nr 1

21-38

EN

In the paper we propose and test a "gel-drying" method of obtaining porous oxide glasses in Molecular Dynamics (MD) simulations. The simulation is started with low (screened) values of ionic charges. Then, the charges are gradually increased (to mimic the gradual elimination of a polar solvent) up to full ionic charges (a completely dry gel). This computational trick is applied to produce a porous PbSiO3 system. The structure of the resulting low-density samples is analysed in detail. Then, the porous structures are submitted to spontaneous densification, and the structure of the obtained dense bulk glasses is analysed. Finally, the structures of bulk glass obtained via spontaneous densification (density p - 8250 kg/m3) and bulk glass of the same density obtained via isotropic compression are compared.

12

Molecular dynamics study of short and medium range order in modified BGO glasses

Walentynowicz A., Witkowska A., Białoskórski M., Rybicki J., Feliziani S., Frigio S., Cosimi G.

Computational Methods in Science and Technology

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2004

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Vol. 10, nr 2

203-218

EN

In the paper we present our recent Molecular Dynamics (MD) simulations of the structure of bismuth-germanate (BGO) glasses of x[pBi2 (1-p)Bi2O3](1-x)GeO2 composition, where x denotes the content of the bismuth oxide in unmodified glasses, and p - the fraction of neutral bismuth that can appear in the surface modification process (e.g, annealing in hydrogen atmosphere). We consider glasses of compositions x = 0.1, 0.2, 0.3 and reduction degrees = O, 0.25, 0.5, 0.75, 1. The simulation results are analysed in detail and compared with the structural data provided by other authors.

13

The structure of Pb-PbO-SiO2 glass via molecular dynamics simulation

Rybicki J., Witkowska A., Bergmański G., Mancini G., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2003

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Vol. 7, No 2

243-256

EN

The paper is dedicated to a molecular dynamics (MD) study of the structure of partially reduced lead-silicate glass of composition 1Pb 1PbO 1SiO2. The simulations have been performed in the constant volume regime, using a two-body potential (Born-Mayer repulsive forces, and Coulomb forces due to full ionic charges). The system was initially prepared as a well equilibrated hot melt, and then slowly cooled down to 300K. The information on short-range correlations were obtained in a conventional way (from pair and angular distribution functions), while the medium-range order was studied via cation-anion ring analysis. In the paper, the short- and medium-range order in the simulated system is discussed and compared with the structure of a glassy completely reduced system, i.e. 2Pb 1SiO2 and unreduced one, i.e. 2PbO 1SiO2 glass.

14

The structure of rarefied and densified PbGeO3 and PbGeO2 glasses : a molecular dynamics study

Rybicki J., Witkowska A., Bergmański G., Bośko J., Mancini G., Feliziani S.

Computational Methods in Science and Technology

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2001

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Vol. 7, nr 1

91--112

EN

The paper is dedicated to a molecular dynamics (MD) study of the structure of rarefied and densified lead-germanate glasses, of compositions PbGeO3 and PbGeO2. The simulations have been performed at constant volume for systems with densities of 3000, 4000, 5000, 6285 (normal density), 7000, and 8000 kg/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 300 K. 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. In the paper, the short- and medium-range order in the rarefied and densified glasses is discussed and compared with the structure of the PbGeO3 and PbGeO2 glasses at normal conditions.

15

Structure of rarefied PbGeO/sub 3/ glass: a molecular dynamics study.

Rybicki J., Witkowska A., Bośko J., Mancini G., Feliziani S.

Optica Applicata

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2000

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Vol. 30, nr 4

709-717

EN

The present contribution is dedicated to a molecular dynamics (MD) study of the structure of rarefied lead-germanate glasses of composition PbGeO/sub 3/. The simulations have been performed in the constant volume regime for systems with densities of 3000, 4000, 5000 and 6285 kg/m/sup 3/, using a two-body potential (Born-Mayer repulsive forces, and Coulomb forces due to full ionic charges). 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. In the paper the short and medium range order in the rarefied glasses is discussed and compared with the structure of the PbGeO/sub 3/ glass in normal conditions.

16

Metal atom clustering in reduced lead-, bismuth- and antimony-silicate glasses: a comparative molecular dynamics study.

Witkowska A., Rybicki J., Bośko J., Feliziani S.

Optica Applicata

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2000

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Vol. 30, nr 4

685-689

EN

We report on the results of molecular dynamics (MD) simulations of the formation of metallic granules in totally reduced lead-, bismuth- and antimony-silicate glasses of composition xMe(1-x)SiO/sub 2/, Me=Pb, Pi Sb, x=0.25, 0.5. The simulations were performed in the NVE ensemble, with two-body Born-Mayer-Huggins interaction potential. For all the glasses considered a strong tendency of heavy metal atoms to agglomerate was observed. In this contribution we compare the distributions of the sizes of Pb, Bi and Sb granules and their packing.

17

Short- and medium-range order in bismuth-silicate glasses: a solecular dynamics study

Witkowska A., Rybicki J., Laskowski R., Mancini G., Feliziani S., Alda W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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1999

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Vol. 3, No 2

239-254

EN

We report on the results of classical molecular dynamics (MD) simulations of str ucture of amorphous 15 Bi2O3 85 SiO2 [% mol] and 40 Bi2O3 60 SiO2 [% mol], and their totally reduced forms, 15 Bi2 85 SiO2 [% mol], and 40 Bi2 60 SiO2 [% mol], respectively. The simulations have been perfo rmed in the isobaric-isoenthalpic ensemble, using a two-body interaction potential. The set of the potential parameters was constructed as a suitable com bination of the parameters which were previously proposed for pure Bi2O3, and SiO2. Both unreduced, and reduced sy stems were initially prepared as well equilibrated hot melts, and then slowly co oled down to 300K. The structural information from the MD simulations was obtained from radial and angular distribution functions, static structural factors, Voronoi polyhedra sta tistics, and ring analysis. The simulation results can be summarised as follows. In unreduced glass with 15% [mol] Bi2O3 contents, the silicon structural units (mainly regular tetrahedra) form continuous network, whereas in 40% [mol] Bi2O3 glass these units are disconnected. In both unreduced systems Bi ions have mainly six-fold oxygen co-ordination, and no dominating structural unit can be individuated. However, the distorted bismu th units form a continuous network. In both totally reduced glasses (15% Bi2 85% SiO2, and 40% Bi2 60% SiO2 [% mol]), the silica network is built entirely from corner shari ng SiO4 tetrahedra. The structure of the silica subsystem is similar to that of pure *-SiO2. After the reduction, the Bi-Bi co-ordination significantly increases, whereas the first neighbour distance decreases. Moreover, partial static structural fact ors for Bi-Bi pairs indicate that the medium-range order in reduced glasses exhi bits greater periodicity than in unreduced glasses. Neutral Bi atoms form small clusters within the silica matrix.

18

The structure of the first co-ordination shell of Pb atoms in lead - silicate glasses : a molecular dynamics study

Rybicka A., Rybicki J., Witkowska A., Feliziani S., Mancini G.

Computational Methods in Science and Technology

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1999

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Vol. 5

67-74

EN

The structure of lead-silicate glasses, although being investigated for over sixty years, rema ins still controversial. One of the open questions is the structure of the lead subsystem: what are the basic structural units like, and how are they interconnected. In the literature the appearance of [PbO4]n, or [PbO3]n chains is reported even in the glasses of the same stoichiometry. In order to elucidate the problem of contradicting experimental findings, extensive molecular dynamics (MD) simulations in the isobaric-isoenthalpic (NpH) ensemble of the structure of lead-silicate glasses have been performed in the whole range of glassformation. The atoms were assumed to interact by a two-body Born-Mayer-Huggins interaction potential with full ionic charges. The potential parametrization was taken from Damodaran et al. [Phys. Chem. Glasses, 31, 212 (1990)]. The simulation box contained about 3000 atoms. For each composition an equilibrated melt at 10000 K was prepared, and then slowly (6 ź 1013 K/s) cooled down to 300 K, passing several equilibrium states at intermediate temperatures. The simulation results can be summarised as follows. For 0.1 = x = 0.33, about ? of all Pb atoms is either placed in the front of the faces of the SiO 4 tetrahedra, forming PbO3 pyramids with the Pb atom in the vertices or in the middle of an almost flat triangle formed from apical oxygens of three different SiO 4 tetrahedra. Another ? of all Pb atoms can be qualified as vertices of rather distorted square pyramids. The remaining ? o f lead atoms have neighbourhoods difficult to classify. For x = 0.67 only a few Pb atoms were identified as remaining in the front of a face of a SiO 4 tetrahedron. Most of the Pb atoms are placed in the vertices of edge sharing square PbO4 pyramids. Our MD results are compared with available experimental data.