Nikola Petrović

Nonautonomous vector matter waves in two-component Bose-Einstein condensates with combined time-dependent harmonic-lattice potential

We construct exact self-similar soliton solutions of three-dimensional coupled Gross–Pitaevskii equations for two-species Bose–Einstein condensates (BECs) in a combined time-dependent harmonic-lattice potential. Based on these solutions, we investigate the control and manipulation of solitary waves for three kinds of BECs with changing diffraction and nonlinearity coefficients; the solutions include Ma breathers and Peregrine and Akhmediev soliton solutions. Our results indicate that matter waves readily propagate in this system. It is shown that diffraction and lattice potential factors play important roles in the beam evolution characteristics, such as the peak, the phase offset, the linear phase, and the chirp.

Vortex solitons in the (2 + 1)-dimensional nonlinear Schrödinger equation with variable diffraction and nonlinearity coefficients

Using Hirotas bilinear method, we determine approximate analytical localized solutions of the (2 + 1)-dimensional nonlinear Schrodinger equation with variable diffraction and nonlinearity coefficients. Our results indicate that a new family of vortices can be formed in the Kerr nonlinear media in the cylindrical geometry. Variable diffraction and nonlinearity coefficients allow utilization of the soliton management method. We present solitary solutions for two types of distributed coefficients: trigonometric and exponential. It is demonstrated that the soliton profiles found are structurally stable, but slowly expanding with propagation.

Modulation stability analysis of exact multidimensional solutions to the generalized nonlinear Schrödinger equation and the Gross-Pitaevskii equation using a variational approach

We analyze the modulation stability of spatiotemporal solitary and traveling wave solutions to the multidimensional nonlinear Schrödinger equation and the Gross-Pitaevskii equation with variable coefficients that were obtained using Jacobi elliptic functions. For all the solutions we obtain either unconditional stability, or a conditional stability that can be furnished through the use of dispersion management.

Spatiotemporal soliton supported by parity-time symmetric potential with competing nonlinearities

We construct explicit spatiotemporal or light bullet (LB) solutions to the (3 + 1)-dimensional nonlinear Schrodinger equation (NLSE) with inhomogeneous diffraction/dispersion and nonlinearity in the presence of parity-time (PT) symmetric potential with competing nonlinearities. The solution is based on the similarity transformation, by which the initial inhomogeneous problem is reduced to the standard NLSE with constant coefficients but with redefined variables and potential. Transmission characteristics of LB solutions, such as the phase change, half width and chirp, are studied in the media with exponentially decreasing diffraction/dispersion and with periodic modulation. Our outcomes demonstrate that diffraction/dispersion and nonlinearity management can prolong the stability of LBs in a PT potential.

Exact traveling wave solutions to coupled generalized nonlinear Schrödinger equations

Exact extended traveling wave solutions are found for the system of generalized nonlinear Schrodinger equations for co- and counterpropagating beams with self-phase and cross-phase modulation. A number of stable periodic solutions are obtained whose signal does not decrease in time in the absence of externally induced loss.

Controlling the Ćuk Converter Using Polytopic Lyapunov Functions

In this brief, the Ćuk dc/dc converter is controlled by a switching sequence based on the values of a polytopic Lyapunov function. In particular, the switching control signal is computed using a Lyapunov function which has polytopic level sets and it is not everywhere differentiable. The problem of not everywhere differentiability is handled using the Filippov’s approach for discontinuous differential equations. The main advantage of the presented control design approach is that it provides exact computation of the state variables’ ripple values which could not be obtained with previously used quadratic Lyapunov functions. The implementation particularities of the approach are illustrated and verified using a number of simulations.

Analyses of decimation filter stopband attenuation influence on subjective quality of audio signals

Decimation is a frequently used technique in audio signal processing. This paper investigates the influence of the values of stopband attenuation of decimation filters on subjective perception of resulting audio signals. In practice, the demands for stopband attenuation of these filters are quite rigorous. The paper examines how justified these demands are from the psychoacoustic point of view. Basic procedure within such a research is a subjective test. Aside from objective parameters, subjective evaluation is a method that can give insight into characteristics of audio signal processing under testing. Results of subjective testing of the influence of different values of stopband attenuation on the perceptibility of interfering signal are presented for various audio signals. To increase the validity of psychoacoustic test, the probability of false detection of differences is measured by presenting subjects with equivalent signals. The results of subjective testing can prove to be useful in the design process of decimation filters for audio system applications.

LTE performance in a hybrid indoor DAS (Active vs. Passive)

This paper analyses LTE performance of active and passive sections in a medium-size hybrid Distributed Antenna System (DAS), in real indoor conditions. Overall, the measurements have shown similar results at both sections, in terms of latency and throughput. The passive portion outperforms the active in average FTP DL throughput by 7.3%, while FTP UL throughputs are nearly the same, differing by less than 0.3%. The results indicate that the utilization of expensive active elements in small to medium-size In-Building Solutions (IBS) is reasonable for overcoming large cable lengths, but does not necessarily imply better LTE performance.