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Found 6273 publications

Traffic-flow analysis for fast performance estimation of communication systems

Gábor Lencse

Publication Name: Journal of Computing and Information Technology

Publication Date: 2001-01-01

Volume: 9

Issue: 1

Page Range: 15-27

Description:

The traffic-flow analysis (TFA) is a promising method for the performance estimation of communication systems. TFA produces approximate results with much less computation (that is, much faster) than discrete-event simulation of the system. In the first step, TFA distributes the traffic in units of properly chosen size using the actual routing algorithm of the network. In the second step, TFA adjusts the time distribution of the traffic according to the finite capacities of the network. It was found that the results of TFA approximate the results of the analytical method well.

Open Access: Yes

DOI: 10.2498/cit.2001.01.02

A distance model for safety-critical systems

Miklós Szijártó Gabor Kallos Dietmár Gröger

Publication Name: Periodica Polytechnica Electrical Engineering

Publication Date: 2001-01-01

Volume: 45

Issue: 2

Page Range: 109-118

Description:

In this paper we introduce a new, theoretical model for safety-critical systems in which the distance from the dangerous conditions can be measured. To describe these systems we use besides the graph model Petri nets, too. We illustrate the theoretical discussion with some simple examples.

Open Access: Yes

DOI: DOI not available

On commutative asynchronous nondeterministic automata

A. Pukler M. Ito B. Imreh

Publication Name: Acta Cybernetica

Publication Date: 2000-01-01

Volume: 14

Issue: 4

Page Range: 607-617

Description:

In this paper, we deal with nondeterministic automata, in particular, commutative asynchronous ones. Our goal is to give their isomorphic representation under the serial product or equivalently, under the α0-product. It turns out that this class does not contain any finite isomorphically complete system with respect to the α0-product. On the other hand, we present an isomorphically complete system for this class which consists of one monotone nondeterministic automaton of three elements.

Open Access: Yes

DOI: DOI not available

The method of asymptotic expansion for plate problem in the linear theory of viscoelasticity

Lotfi Abdelhakim G. Y. Molnarka

Publication Name: ZAMM Zeitschrift Fur Angewandte Mathematik Und Mechanik

Publication Date: 2000-01-01

Volume: 80

Issue: 4 SUPPL. 2

Page Range: S391-S392

Description:

The method of asymptotic expansion originally developed for elasticity problems is generalized to linear viscoelastic problems. Three-dimensional, unsteady problems corresponding to a class of viscoelastic plates are considered. By employing the Laplace transform, the original problem is converted to an equivalent elastic problem, where the asymptotic expansion method is used. An application of this method to the Maxwell model is also presented.

Open Access: Yes

DOI: 10.1002/zamm.20000801467

Weed control with reduced herbicide applications in sugarbeets in Hungary

M. Lajos Katalin Lajos

Publication Name: Zeitschrift Fur Pflanzenkrankheiten Und Pflanzenschutz

Publication Date: 2000-01-01

Volume: 107

Issue: SPEC. ISS. 17

Page Range: 623-627

Description:

In a sugar beet trial in 1999 different herbicide applications were tested, to transfer the concept of reduced herbicide application rates to conditions of Hungaria. In every case the highest were below the registered application rate. We developed strategies with herbicides efficiencies of 90 to 100 %.

Open Access: Yes

DOI: DOI not available

On the negative weighting factors in the Muskingum-Cunge scheme

Sàndor Szél Csaba Gáspár

Publication Name: Journal of Hydraulic Research

Publication Date: 2000-01-01

Volume: 38

Issue: 4

Page Range: 299-306

Description:

The Muskingum-Cunge scheme applied to the one-dimensional unsteady advection-diffusion equation is investigated. To eliminate the numerical diffusion, the coefficients of the scheme are defined in such a way that the scheme does not contain the weighting parameters explicitly, but the Courant and Péclet numbers only. If one of the weighting factors is prescribed, the other should be necessarily negative in a lot of cases, which does not affect the applicability of the scheme. It is shown that the accuracy can be increased further, the numerical oscillations can also be eliminated by prescribing a simple relationship between the Courant and Péclet numbers. Sufficient conditions for strong stability are also presented.

Open Access: Yes

DOI: 10.1080/00221680009498329

Multi-level biharmonic and bi-Helmholtz interpolation with application to the boundary element method

Csaba Gáspár

Publication Name: Engineering Analysis with Boundary Elements

Publication Date: 2000-01-01

Volume: 24

Issue: 7-8

Page Range: 559-573

Description:

The scattered data interpolation problem is investigated. Instead of the direct use of radial basis functions, the interpolation function is sought as a solution of a higher order partial differential equation supplied with the interpolation equations as special boundary conditions. In this paper the methods based on the biharmonic and the bi-Helmholtz equations are analyzed. The interpolation problem is reformulated in variational forms. Existence and uniqueness theorems are proved in Sobolev spaces. The approximation properties of this interpolation are also investigated. A representation theorem is proved which shows the similarity to the method of radial basis functions based on the fundamental solution of the applied partial differential operator. To solve the appearing biharmonic/bi-Helmholtz equation, a multi-level method is presented which is based on a quadtree/octtree cell system generated by the interpolation points. It is shown that the overall computational cost of the presented method is much less than that of the traditional method of radial basis functions. The method makes it possible to avoid the solution of large, fully populated and often ill-conditioned systems of linear equations. Finally, some applications to solving partial differential equations are outlined. The biharmonic/bi-Helmholtz interpolation technique immediately defines a grid-free method, but can be combined with the boundary element method as well. A possible application in the dual reciprocity method is also presented.

Open Access: Yes

DOI: 10.1016/S0955-7997(00)00036-9

Weed control with reduced herbicide applications in sugarbeets in Hungary

No authors available

Publication Name: Zeitschrift fur Pflanzenkrankheiten und Pflanzenschutz

Publication Date: 2000-01-01

Volume: 107

Issue: SPEC. ISS. 17

Page Range: 623-627

Description:

In a sugar beet trial in 1999 different herbicide applications were tested, to transfer the concept of reduced herbicide application rates to conditions of Hungaria. In every case the highest were below the registered application rate. We developed strategies with herbicides efficiencies of 90 to 100 %.

Open Access: No

DOI: DOI not available

The influence of hydrogen molecules on shock-cloud collisions

U. Ziegler A. Horváth

Publication Name: Astronomy and Astrophysics

Publication Date: 1999-12-01

Volume: 349

Issue: 2

Page Range: 595-604

Description:

The interaction of shock fronts with molecular clouds is investigated. For this purpose, a two-fluid model describing an H-H2 gas mixture is applied. The resulting equations are solved with a 2D axial-symmetric, fully compressive hydrodynamics code. Radiative cooling and the thermodynamical properties of the H2 molecule, ie. rotational and vibrational degrees of freedom as well as thermal dissociation, are taken into account. The evolution of the shock/cloud system using this more sophisticated thermodynamical model is found to be very different from that involving a pure atomic H gas which obeys the ideal gas law. For example, the maximum density of the shocked cloud is about 5-10 times lower in the latter case. This significant result might become very important when estimating triggered star formation rates. Another difference is that in the case of H-H2 mixture, the shocked cloud gets a comet-like structure because of a smaller reexpansion. From the numerical experiments we conclude that the application of the ideal gas law is insufficient and gives only a crude approximation of the real dynamics of a shock/cloud collision.

Open Access: Yes

DOI: DOI not available