Development of algorithms and software for forecasting, nowcasting and variability of TEC

Total Electron Content (TEC) is an important characteristic of the ionosphere relevant to communications. Unpredictable variability of the ionospheric parameters due to various disturbances limits the efficiencies of communications, radar and navigation systems. Therefore forecasting and nowcasting of TEC are important in the planning and operation of Earth-space and satellite-to-satellite communication systems. Near-Earth space processes are complex being highly nonlinear and time varying with random variations in parameters where mathematical modeling is extremely difficult if not impossible. Therefore data driven models such as Neural Network (NN) based models are considered and found promising in modeling such processes. In this paper the NN based METU-NN model is introduced to forecast TEC values for the intervals ranging from 1 to 24 h in advance. Forecast and nowcast of TEC values are also considered based on TEC database. Day-to-day and hour to-hour variability of TEC are also estimated using statistical methods. Another statistical approach based on the clustering technique is developed and a preprocessing approach is demonstrated for the forecast of ionospheric critical frequency foF2

Karl Rawer’s interest and encouragement regarding new approaches to ionospheric modeling

Professor Karl Rawer encourages, stimulates researchers. He takes initiative and supports researchers in producing papers about new techniques and methods. As a typical case the authors here report their experience with Professor Rawer during the publication of their papers about a Neural Network approach to model near Earth space processes

A case study on the ELF characterization of the Earth-ionosphere cavity: Forecasting the Schumann resonance intensities

Schumann Resonances (SR) are the electromagnetic (EM) phenomena which occur in the cavity formed by the conducting Earth and the ionosphere, with peak mode frequencies close to 8, 14, 20, 26, 32 Hz, etc. [Price, C., Melnikov, A., 2004. Diurnal, seasonal and inter-annual variations in the Schumann resonance parameters. Journal of Atmospheric and Solar-Terrestrial Physics 66, 1179-1185]. The spectral characteristics of the SR modes are defined by their resonant mode amplitudes, center frequencies and half-widths [Price, C., Melnikov, A., 2004. Diurnal, seasonal and inter-annual variations in the Schumann resonance parameters. Journal of Atmospheric and Solar-Terrestrial Physics 66, 1179-1185]. The objective of this work is two fold: (i) to investigate the characteristics of SR parameters obtained at Sarkoy in Turkey and (ii) to model the dynamical characteristics of the SR processes by forecasting the first SR mode power values using a neural network (NN) model. The NN model is revised version of the METUNN [Tulunay, Y., Tulunay, E., Senalp, E.T., 2004a. The neural network technique-1: a general exposition. Advances in Space Research 33, 983-987]

Development of algorithms and software for forecasting, nowcasting and variability of TEC

Total Electron Content (TEC) is an important characteristic of the ionosphere relevant to communications. Unpredictable variability of the ionospheric parameters due to various disturbances limits the efficiencies of communications, radar and navigation systems. Therefore forecasting and nowcasting of TEC are important in the planning and operation of Earth-space and satellite-to-satellite communication systems. Near-Earth space processes are complex being highly nonlinear and time varying with random variations in parameters where mathematical modeling is extremely difficult if not impossible. Therefore data driven models such as Neural Network (NN) based models are considered and found promising in modeling such processes. In this paper the NN based METU-NN model is introduced to forecast TEC values for the intervals ranging from 1 to 24 h in advance. Forecast and nowcast of TEC values are also considered based on TEC database. Day-to-day and hour to-hour variability of TEC are also estimated using statistical methods. Another statistical approach based on the clustering technique is developed and a preprocessing approach is demonstrated for the forecast of ionospheric critical frequency foF2

Aspects of HF radio propagation

<p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">radio systems. From the point of view Working Group 2 of the COST 296 Action, interest lies with effects associated</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">with propagation via the ionosphere of signals within the HF band. Several aspects are covered in this paper:</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">a) The directions of arrival and times of flight of signals received over a path oriented along the trough have</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">been examined and several types of propagation effects identified. Of particular note, combining the HF observations</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">with satellite measurements has identified the presence of irregularities within the floor of the trough that</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">result in propagation displaced from the great circle direction. An understanding of the propagation effects that</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">result in deviations of the signal path from the great circle direction are of particular relevance to the operation</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">of HF radiolocation systems.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">b) Inclusion of the results from the above mentioned measurements into a propagation model of the northerly</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">ionosphere (<em>i.e. </em>those regions of the ionosphere located poleward of, and including, the mid-latitude trough)</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">and the use of this model to predict the coverage expected from transmitters where the signals impinge on the</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">northerly ionosphere.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">c) Development of inversion techniques enabling backscatter ionograms obtained by an HF radar to be used</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">to estimate the ionospheric electron density profile. This development facilitates the operation of over the horizon</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">HF radars by enhancing the frequency management aspects of the systems.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">d) Various propagation prediction techniques have been tested against measurements made over the trough</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">path mentioned above, and also over a long-range path between Cyprus and the UK.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">e) The effect of changes in the levels of ionospheric disturbances on the operational availability at various</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">data throughput rates has been examined for the trough path mentioned earlier.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">The topics covered in this paper are necessarily brief, and the reader is referred to full papers referenced</p> <br /&gt

Application of Numerical Methods in Design and Analysis of Orthopedic Implant Integrity

In this paper a numerical analysis of hip implant model and hip implant model with a crack in a biomaterial is presented. Hip implants still exhibit problem of premature failure, promoting their integrity and life at the top of the list of problems to be solved in near future. Any damage due to wear or corrosion is ideal location for crack initiation and further fatigue growth. Therefore, this paper is focused on integrity of hip implants with an aim to improve their performance and reliability. Numerical models are based on the finite element method (FEM), including the extended FEM (X-FEM). FEM became a powerful and reliable numerical tool for analysis of structures subjected to different types of load in cases where solving of these problems was too complex for exclusively analytical methods. FEM is a method based on discretization of complex geometrical domains into much smaller and simpler ones, wherein field variables can be interpolated using shape functions. Numerical analysis was performed on three-dimensional models, to investigate mechanical behaviour of a hip implant at acting forces from 3.5 to 6.0 kN. Short theoretical background on the stress intensity factors computation is presented. Results presented in this paper indicate that acting forces can lead to implant failure due to stress field changes. For the simulation of crack propagation extended finite element method (XFEM) was used as one of the most advanced modelling techniques for this type of problem