George E. Chatzarakis

Estimation of wind turbines optimal number and produced power in a wind farm using an artificial neural network model

One of the most significant issues in the design of a new wind farm is the estimation of optimal number of wind turbines that has to be installed in it. The goal of every wind farm designer is the production of the maximum possible power, minimizing the installation cost. The cost can be significantly reduced using the minimum required number of wind turbines for specific power production, occupying at the same time the least possible acreage of land. In this work an artificial neural network (ANN) model is developed which has the ability to estimate the optimal number of wind turbines and the total produced power in a wind farm. The ANN model’s results are compared with those of earlier studies that have followed other approaches, proving that the ANN model is well working and has an acceptable accuracy. The proposed model can be useful in the studies of wind farm designers as a supportive tool for the estimation of the optimal number of wind turbines in a wind farm.

LMDS diversity systems: a new performance model incorporating stratified rain

Cell-site diversity may prove an efficient fade mitigation technique to increase the availability of local multipoint distribution service systems, in this Letter, a recently suggested physical model for the prediction of cell-site diversity performance is properly modified to include stratified rain. The model-obtained is satisfactorily verified using radar derived data from UK and Canada. Simulated BEP results concerning LMDS diversity systems are also presented.

Outage Performance of Single/dual Polarized Fixed Wireless Access Links in Heavy Rain Climatic Regions

The outage performance of line-of-sight fixed wireless access channels operating above 10 GHz is predominantly controlled by rain attenuation. In this paper, a prediction model, appropriate for heavy rain climatic regions based on gamma distribution assumption for the rainfall rate and the rain attenuation is being reviewed to incorporate the recently released ITU-R rainmaps. The model exhibits a very good performance, as validated by tests against the ITU-R databank Moreover, the above model is extended to evaluate the outage performance of a dual-polarized mm-wave fixed wireless access link located in heavy rain climatic regions. The obtained numerical results focus on the investigation of the effects of various operational parameters upon the outage performance of the microwave communication link.

Iterative oscillation tests for differential equations with several non-monotone arguments

Sufficient oscillation conditions involving lim sup and lim inf for first-order differential equations with several non-monotone deviating arguments and nonnegative coefficients are obtained. The results are based on the iterative application of the Grönwall inequality. Examples illustrating the significance of the results are also given.

Channel Model for Satellite Communication Links Above 10GHz Based on Weibull Distribution

Modern satellite communication networks will employ frequencies above 10GHz. At these frequency bands, rain attenuation is the dominant fading mechanism. In this paper, a novel channel model, a synthesizer for generating rain attenuation time series for satellite links operating at 10GHz and above is presented. The proposed channel model modifies Maseng-Bakken (M-B) model since it generates rain attenuation time series that follow the Weibull distribution. The new stochastic dynamic model is based on the first-order Stochastic Differential Equations (SDEs) and considers rain attenuation induced on a slant path as a Weibull-based stochastic process. Moreover, the theoretical expressions for the computation of the exceedance probability of hitting time random variable are presented. The hitting time statistics may be employed for the optimum design of Fade Mitigation Techniques (FMTs). The synthesizer is verified in terms of the exceedance probability and the theoretical CCDF of hitting time comparing to these derived from the simulations in the numerical results section.

Oscillations of difference equations with general advanced argument

AbstractConsider the first order linear difference equation with general advanced argument and variable coefficients of the form

Oscillation Criteria for Delay and Advanced Differential Equations with Nonmonotone Arguments

\nabla x(n) - p(n)x(\tau (n)) = 0, n \geqslant 1,

Iterative oscillation tests for difference equations with several non-monotone arguments

where {p(n)} is a sequence of nonnegative real numbers, {τ(n)} is a sequence of positive integers such that