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Sofia, Bulgaria

The Technical University , based in Sofia, is the largest technical university in Bulgaria. Founded on 15 October 1945 as part of the Higher Technical School , it is an independent institution since 1953, when the Polytechnic was divided into four separate technical institutes. It has had its present name and university status since 21 July 1995 and has 14 main faculties based in Sofia, Plovdiv and Sliven, as well as 3 additional ones with education only in foreign languages — German, English and French. Wikipedia.

Uzunov I.M.,Technical University of Sofia
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

A perturbation study of the suppression of the soliton self-frequency shift by the bandwidth-limited optical amplification is proposed. The stability of the equilibrium point for the soliton amplitude and velocity identified by the adiabatic approximation of the soliton perturbation theory (SPT) is analyzed by a numerical solution of a linearized system in the neighborhood of the equilibrium point. The obtained analytical expressions for the eigenvalues of the linearized system allow the determination of the values of pulse and material parameters for which the equilibrium point is stable. A perturbation approach that leads to the research of the equation of strongly nonlinear Duffing-Van der Pol oscillator is suggested. The last equation is explored by two different methods. First, the recently obtained results for this equation by the hyperbolic perturbation method are used. Next, the hyperbolic Lindstedt-Poincare perturbation method is applied to the exploration of this equation. The equilibrium velocity of the perturbed stationary solution was calculated as a critical value of the control parameter in both methods. It turned out that the coupling of the equilibrium velocity and the amplitude of the perturbed stationary solution in both methods is similar to the relation between the soliton amplitude and velocity derived by the adiabatic approximation of SPT. The change in the form of the perturbed stationary solution has also been identified by means of the hyperbolic Lindstedt-Poincare perturbation method. © 2010 The American Physical Society. Source

Gyulchev G.N.,Sofia University | Stefanov I.Z.,Technical University of Sofia
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

In some models dark energy is described by phantom scalar fields (scalar fields with the "wrong" sign of the kinetic term in the Lagrangian). In the current paper we study the effect of phantom scalar field and/or phantom electromagnetic field on gravitational lensing by black holes in the strong deflection regime. The black-hole solutions that we have studied have been obtained in the frame of the Einstein-(anti-)Maxwell-(anti)dilaton theory. The numerical analysis shows a considerable effect of the phantom scalar and electromagnetic fields on the angular position, brightness, and separation of the relativistic images. © 2013 American Physical Society. Source

Kolev L.,Technical University of Sofia
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2011

The paper considers the following worst-case steady-state tolerance analysis problem: given a linear dc circuit whose resistors and sources have preset tolerances, determine the range of the electrical power consumed in the circuit. It is shown that the power range sought can be computed as the range of an associated interval linear programming problem. A method for solving the latter problem is suggested whose numerical complexity is not a priori exponential. A numerical example illustrating the new method is provided. © 2011 IEEE. Source

Popov D.,Technical University of Sofia
Applied Thermal Engineering | Year: 2014

The objective of this paper is to offer a concept for innovative hybridization of gas turbine combined cycle plant and solar power system. This conceptual plant is named as Solar Assisted Combined Cycle, as the solar energy is indirectly involved in power generation. The proposed solar hybridization can be accomplished in two ways. The first solar assisted option introduces mechanical chiller for a complete cooling of gas turbine inlet air. Such of cooling is commonly used to increase the power output of gas turbines during hot days of the year. This mechanical chiller is powered with electricity generated by a dedicated photovoltaic plant. The next solar assisted option does the same but with an absorption chiller. The steam for this chiller is generated in a solar field equipped with Linear Fresnel Reflectors. The efficiency and the total additional costs for development of these two configurations are estimated with relevant software packages. Similar power augmentation can be achieved with traditional Integrated Solar Combined Cycle plant. All main additional costs for construction of this alternative plant are also estimated. As a result, the specific costs for solar augmentation of a basic GTCC plant are obtained and compared. The configuration with an absorption chiller has lower specific incremental plant capital costs and requires smaller land area than the others. The proposed solar assisted plant concept offers an effective way for further implementation of compact linear Fresnel reflector technology. © 2013 Elsevier Ltd. All rights reserved. Source

Mihov Y.Y.,Technical University of Sofia
IEEE Communications Letters | Year: 2012

This letter investigates the quality of service provisioning in infrastructure-based secondary cognitive radio networks operating in compliance with the hierarchical spectrum overlay approach for dynamic spectrum access. A cross-layer analytical model is developed and a novel cross-layer approach for quality of service provisioning of the secondary users is proposed and validated by extensive simulation experiments. © 2012 IEEE. Source

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