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Volume 8, August
Mathematical and Computational Applications is published by MDPI from Volume 21 Issue 1 (2016). Previous articles were published by another publisher in Open Access under a CC-BY (or CC-BY-NC-ND) licence, and they are hosted by MDPI on mdpi.com as a courtesy and upon agreement with the previous journal publisher.

Math. Comput. Appl., Volume 8, Issue 3 (December 2003) – 15 articles , Pages 263-384

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Article
Sliding Mode Speed Control for DC Drive Systems
Math. Comput. Appl. 2003, 8(3), 377-384; https://doi.org/10.3390/mca8030377 - 01 Dec 2003
Cited by 4 | Viewed by 763
Abstract
In this study, the Sliding Mode Control theory of the Variable Structure System has been applied to the speed control of a de motor. The dynamic performance of the sliding mode speed control system has been studied against system parameter variations and external [...] Read more.
In this study, the Sliding Mode Control theory of the Variable Structure System has been applied to the speed control of a de motor. The dynamic performance of the sliding mode speed control system has been studied against system parameter variations and external load disturbance and the simulation results are given. The application of the sliding mode control theory to controller design for DC drive control system shows a robust system performance. Full article
Article
Evaluation of Control Methods on a Structural System
Math. Comput. Appl. 2003, 8(3), 369-376; https://doi.org/10.3390/mca8030369 - 01 Dec 2003
Cited by 2 | Viewed by 695
Abstract
In this study, PID, LQR and sliding mode controllers are designed as active seismic isolation devices on a multi degrees of freedom structure. At first PID control is applied as a conventional method. Since this control method can be applied easily and well [...] Read more.
In this study, PID, LQR and sliding mode controllers are designed as active seismic isolation devices on a multi degrees of freedom structure. At first PID control is applied as a conventional method. Since this control method can be applied easily and well known widely, it has an important role in control applications. Secondly, a LQR is designed to suppress the vibrations of the structural system. But these methods are not insensitive to parameter changes. Since the model might have uncertainties and/or parameter changes. sliding mode control has been introduced because of its well-known robust character and superior performance. Additionally, this control method can easily be applied to non-linear systems. The simulated system has four stories. A disturbance input representing earthquake is applied to the base. At the end of the study, the Lime history of the storey displacements, control voltage and frequency responsc of the both uncontrolled, PID, LQR and sliding mode controlled structures have been presented and results have been compared. Full article
Article
Simulation of Swarm Intelligence and Possible Applications in Engineering
Math. Comput. Appl. 2003, 8(3), 361-368; https://doi.org/10.3390/mca8030361 - 01 Dec 2003
Viewed by 800
Abstract
Modeling biological and natural systems in order to solve complex problems have become popular. Traditional techniques fail at solving some types of problems. On the other hand, it is seen that these kind of problems are solved in nature without help of human. [...] Read more.
Modeling biological and natural systems in order to solve complex problems have become popular. Traditional techniques fail at solving some types of problems. On the other hand, it is seen that these kind of problems are solved in nature without help of human. Swarm intelligence(SI) as a research field, proposes such solutions. SI models the collective behavior of the social insects like ants, bees or termites and their coordination without communication. The emerged intelligence has some special characteristics and it can be applied to some areas. Some of the application fields are robotics, networking, finance and entertainment. In this paper, principles of SI systems, original simulations of some SI techniques, and new approaches are presented. Full article
Article
A Dynamic Load Balancing Model for a Distributed System
Math. Comput. Appl. 2003, 8(3), 353-360; https://doi.org/10.3390/mca8030353 - 01 Dec 2003
Cited by 6 | Viewed by 697
Abstract
A communication protocol designed for fault tolerance in distributed real time systems is implemented and a dynamic load balancing model is designed and implemented over this protocol. The protocol consists of cluster based, hierarchical rings which use synchronous communication. The rings are synchronous. [...] Read more.
A communication protocol designed for fault tolerance in distributed real time systems is implemented and a dynamic load balancing model is designed and implemented over this protocol. The protocol consists of cluster based, hierarchical rings which use synchronous communication. The rings are synchronous. At the lowest level in the hierarchy, there are clusters that consist of computing processors, called nodes. The higher level consists of the cluster representatives that manage the clusters of the lower level. There can be two or more levels in the hierarchy. Ring protocols in each cluster can work in parallel. Also, a fault tolerance mechanism is integrated to the protocol. The dynamic distributed load balancing module designed over the protocol aims to maximize the overall performance of the whole system by distributing the load submitted to the system efficiently and transparently among the nodes. While performing operations to achieve this goal, the module also considers the real-time constraints of the system Full article
Article
A Comparison on the Commutative Neutrix Products of Distributions
Math. Comput. Appl. 2003, 8(3), 343-351; https://doi.org/10.3390/mca8030343 - 01 Dec 2003
Cited by 1 | Viewed by 654
Abstract
In this work, we define a new commutative neutrix product of distribution and than we make a comparison with present commutative product of distributions by providing a counterexample that two commutative neutrix products of the distributions differ. Full article
Article
The Resonance Analysis Caused by Harmonics in Power Systems Including Thyristor Controlled Reactor
Math. Comput. Appl. 2003, 8(3), 335-341; https://doi.org/10.3390/mca8030335 - 01 Dec 2003
Cited by 1 | Viewed by 800
Abstract
The static VAR compensators having fixed capacitor thyristor controlled reactor (FC-TCR) used to improve voltage stability in power systems are nonlinear elements. The fixed capacitor group will produce reactive power while the thyristor controlled reactor will consume reactive power in compensators having FC-TCR. [...] Read more.
The static VAR compensators having fixed capacitor thyristor controlled reactor (FC-TCR) used to improve voltage stability in power systems are nonlinear elements. The fixed capacitor group will produce reactive power while the thyristor controlled reactor will consume reactive power in compensators having FC-TCR. Changing the firing angles of TCR provides the reactive power variation of the system since the reactive power production of capacitors is fixed at a determined voltage level. In some cases, the variation of these firing angles will cause the harmonics in the system. In this study, TCR's are discussed to be harmonic sources and the resonance case caused by harmonics has been investigated with Fourier Matrix Model and MATLAB Software. Full article
Article
Aspects of the Gurson Model and Its Applications
Math. Comput. Appl. 2003, 8(3), 327-334; https://doi.org/10.3390/mca8030327 - 01 Dec 2003
Cited by 1 | Viewed by 884
Abstract
Ductile fracture in metals can involve the generation of considerable porosity caused by nucleation, growth and coalescence of microvoids. This process takes place on micro-level and can not describe by traditional constitutive laws such as von Mises theory. Hence, A. L. Gurson developed [...] Read more.
Ductile fracture in metals can involve the generation of considerable porosity caused by nucleation, growth and coalescence of microvoids. This process takes place on micro-level and can not describe by traditional constitutive laws such as von Mises theory. Hence, A. L. Gurson developed a theory which takes account of void growth and showed the role of hydrostatic stress in plastic yield and void growth. In this model the void volume fraction f (the portion of void in the material) is the single damage parameter; its evolution is defined by the incompressibility of the matrix material. (For Lameitre's model the damage variable D is relevant.) To model the material damage by using the Gurson damage approach a series of single elements including different types of loading are used. In the single element cases the results of the Gurson model and von Mises are also compared. In calculations the MARC finite elements software is used to calculate stress, strains and f the void volume fraction. Full article
Article
Determination of Complex Dielectric Permittivity of Loss Materials at Microwave Frequencies
Math. Comput. Appl. 2003, 8(3), 319-326; https://doi.org/10.3390/mca8030319 - 01 Dec 2003
Cited by 2 | Viewed by 797
Abstract
The method of determination of complex dielectric permIttIvIty of loss materials at microwave frequencies (X-band) using measured amplitudes of reflection and transmission coefficients and numerical calculations is developed. Different numerical methods namely graphical, bisection (halving), newton, and secant, are applied in order to [...] Read more.
The method of determination of complex dielectric permIttIvIty of loss materials at microwave frequencies (X-band) using measured amplitudes of reflection and transmission coefficients and numerical calculations is developed. Different numerical methods namely graphical, bisection (halving), newton, and secant, are applied in order to determine the permittivity of cement-based materials. Simulation time and errors of these methods are compared. It is shown that the fastest and most accurate method is the bisection (halving) method because it is a global method. Full article
Article
Application of FFT and Arma Spectral Analysis to Arterial Doppler Signals
Math. Comput. Appl. 2003, 8(3), 311-318; https://doi.org/10.3390/mca8030311 - 01 Dec 2003
Cited by 2 | Viewed by 795
Abstract
In this study, Doppler signals recorded from arteries of 105 subjects were processed by PC-computer using fast Fourier transform, and least squares modified Yule-Walker autoregressive moving average methods. By using these spectrum analysis techniques, the variations in the shape of the Doppler spectrums [...] Read more.
In this study, Doppler signals recorded from arteries of 105 subjects were processed by PC-computer using fast Fourier transform, and least squares modified Yule-Walker autoregressive moving average methods. By using these spectrum analysis techniques, the variations in the shape of the Doppler spectrums as a function of time were presented in the form of sonograms in order to obtain medical information. These sonograms were then used to compare the applied methods in terms of their frequency resolution and the effects in determination of stenosis and occlusion in arteries. Reliable information on hemodynamic alterations in arteries can be obtained by evaluation of these sonograms. Full article
Article
A Different Method Determining Dielectric Constant of Soil and Its FDTD Simulation
Math. Comput. Appl. 2003, 8(3), 303-310; https://doi.org/10.3390/mca8030303 - 01 Dec 2003
Cited by 3 | Viewed by 673
Abstract
In this study, a different method determining the dielectric constant of soil via probes is presented. The method is based on the principle of measuring pulse delay in a given matter. The experimental study, which was carried out basically using an HP8753A vector [...] Read more.
In this study, a different method determining the dielectric constant of soil via probes is presented. The method is based on the principle of measuring pulse delay in a given matter. The experimental study, which was carried out basically using an HP8753A vector network analyser, was repeated for various soil mixtures having different values of wetness. The results obtained from the measurements have clearly shown that the dielectric constant of the soil was increasing almost proportionally with that of the moisture content in the soil. The suitability of the measuring method was also checked with a number of simulation results obtained directly using the finite difference time domain method (FDTD). Full article
Article
Mechanical Stability and Elastic Properties of Some FCC Metals: A Many- Body Potential Applications
Math. Comput. Appl. 2003, 8(3), 295-302; https://doi.org/10.3390/mca8030295 - 01 Dec 2003
Viewed by 666
Abstract
To represent the total energy of fcc metals(Cu. Ag, Al. Ca, Sr) the potential functions are assumed to be composed of the two-body pairwise Rydberg potential and volume dependent energy (P1V) which represent many body interactions. Energy, stress and [...] Read more.
To represent the total energy of fcc metals(Cu. Ag, Al. Ca, Sr) the potential functions are assumed to be composed of the two-body pairwise Rydberg potential and volume dependent energy (P1V) which represent many body interactions. Energy, stress and elastic moduli calculations are performed on the basis of Rydberg and Rydberg plus P1V potentials to locate the stress-free bcc phase on the fcc metals. The studied crystals are subjected to unconstrained (100) uniaxial tension and compression for all computations. Also, these potentials are used to calculate the second- and third-order elastic constants, Cij and Cijk, The obtained results are compared with the available experimental data and the agreement is good. Full article
Article
A Windows-Based Digital Filter Design
Math. Comput. Appl. 2003, 8(3), 287-294; https://doi.org/10.3390/mca8030287 - 01 Dec 2003
Cited by 5 | Viewed by 700
Abstract
This study aims to describe a general digital filter, practically for Windows’ users. For this purpose. an I/O interfacing circuits base on PIC16F877 was designed to receive analog signal into the PC and return filtered signals. This I/O module was then communicated with [...] Read more.
This study aims to describe a general digital filter, practically for Windows’ users. For this purpose. an I/O interfacing circuits base on PIC16F877 was designed to receive analog signal into the PC and return filtered signals. This I/O module was then communicated with PC using parallel port protocol with EPP mode, and a digital filter program was introduced using C++. Various filters; such as LPF, HPF, BPF, and BSF were designed using the method of frequency transformation on normalized Butterworth and Chebyshev analog filters. The grades of the designed filters range from n=1 to n=8. Using this application the proposed windows-based digital filter design worked better and faster. Full article
Article
The Monitoring Simulation of a Lathe
Math. Comput. Appl. 2003, 8(3), 279-286; https://doi.org/10.3390/mca8030279 - 01 Dec 2003
Cited by 3 | Viewed by 725
Abstract
The study of machine-tool dynamic is realised here as “monitoring”, meaning checking and improving the functioning of the machine. The state of processing is followed with certain sensors which signs are processed inside the computer, then it takes the decision of monitoring, meaning [...] Read more.
The study of machine-tool dynamic is realised here as “monitoring”, meaning checking and improving the functioning of the machine. The state of processing is followed with certain sensors which signs are processed inside the computer, then it takes the decision of monitoring, meaning the identification of a class from the set of classes (process conditions). For monitoring in turning, it is shown the classes (tool conditions). The vibrograms that represent: - the components variations of the cutting force; - the relative displacement between tool and piece, on the repelling direction; - the power furnished by the electric engine, are realised with the functions RANDN and RAND (from MATLAB). Based on them it is calculating 11 monitoring indices. The class resulted at the experiment (simulate) i, which corresponds to the monitoring indices, we establish with the function REM. The ANN with 11 inputs (the number of monitoring indices) and 8 outputs (the number of classes) is realised with 3 layers. The network is made with the function newff, trained with the function train and simulated with the function sim. Full article
Article
Boolean Functions Simplification Algorithm of O(n) Complexity
Math. Comput. Appl. 2003, 8(3), 271-278; https://doi.org/10.3390/mca8030271 - 01 Dec 2003
Cited by 10 | Viewed by 1009
Abstract
The minimization of Boolean functions allows designers to make use of fewer components, thus reducing the cost of particular system. All procedures for reducing either two-level or multilevel Boolean networks into prime and irredundant form have O(2n) complexity. Prime [...] Read more.
The minimization of Boolean functions allows designers to make use of fewer components, thus reducing the cost of particular system. All procedures for reducing either two-level or multilevel Boolean networks into prime and irredundant form have O(2n) complexity. Prime Implicants identification step can be computational impractical as n increases. Thus it is possible to get method in order to find the minimal set of Prime Implicants of O(n) complexity instead of O(2n). Full article
Article
Multilevel Architecture for Multidimensional Data Base
Math. Comput. Appl. 2003, 8(3), 263-269; https://doi.org/10.3390/mca8030263 - 01 Dec 2003
Viewed by 665
Abstract
A Multidimensional Data Base is an essential element of decision support, which allows to process complex queries. In this paper, a multilevel distributed Data Model for MDDB is presented. Metadata for MDDB on relations is introduced. To improve efficiency of query processing, fuzzy [...] Read more.
A Multidimensional Data Base is an essential element of decision support, which allows to process complex queries. In this paper, a multilevel distributed Data Model for MDDB is presented. Metadata for MDDB on relations is introduced. To improve efficiency of query processing, fuzzy cache fact table is proposed. Full article
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