Volume 47 (2010): Issue 5 (January 2010)

A new approach to FTTx solutions is proposed, in the framework of which a hybrid TDM/WDM system using cascaded FWM-generated optical signals is evaluated by calculating the BER parameter and the optical power budget. Computer simulation is employed as the main method of calculations, with the results presented both in numerical and graphical forms. The results show that the use of a forward error correction allows the power margin of 4 dB to be achieved for the system to work reliably. The system can provide the total number of users up to 128 (8γx16 TDM users) with a bandwidth of multiple hundreds of Mbit/s p.u. by means of the existing passive optical networking infrastructure, with only minor improvements needed.

Possibilities of increasing the distance protection (DP) sensitivity are considered for a double-circuit transmission line connected to a substation busbar only with one circuit-breaker in each phase. The DP sensitivity can be increased on such a line using mutual connections of the phase wires along its whole length. The minimal (optimal) number of the connections is found by the proposed calculation method.

In the reported study of growth-rates of grey alder (Alnus incana) stands at different quality sites the authors, as a continuation of an earlier study, propose and use analytical models to approximate experimental data of mean annual increments of standing stock. The model equations of growth-rate functions are further used to optimise the cutting age by minimising the total area of stands for sustainable annual supply of biomass. The growth-rate behaviour with the age of natural grey alder stands is described by an exponential function of three parameters defining the initial and the maximum growth-rates, and the age at which the growth-rate maximum is reached. None of the parameters is known from experiment, and they are found by least-square fit of the available experimental mean values appraised at the chosen time intervals into the model. A high correlation between the experimental data and the model function is found. The optimum cutting age of 18 years determined in the earlier study is confirmed. In farmed stands the growth-rate is made to continue increasing at a lower speed, and is well approximated by a linear function, in which case it is shown that the cutting age cannot be optimised with respect to the area minimum existing under the condition of a decreasing growth-rate after passing a maximum. In the case of a constant or slowly growing annual increment the authors suggest considering the ratio between the increment of stock per unit of the total area to the increase in the area. The overall efficiency of using the product of photosynthesis for a 20-year-old grey alder stand is roughly estimated to be 0.3%.

The article considers the possibilities of saving the regenerative braking energy in Škoda 24Tr type trolleybuses by installing the onboard supercapacitor energy storage system (ESS) and improving its performance with automated switching to the autonomous traction mode. Proposed is an ESS control system with constant DC bus voltage in the supercapacitor charging mode and supercapacitor current proportional to the AC drive current in the discharging mode. The authors investigate stability of the trolleybus ESS control system operating together with AC traction drive in various overhead voltage failure modes. The co-simulation of ESS operation was done by Matlab/Simulink AC drive and PSIM ESS continuous models.

Cathodoluminescence (CL) spectra and decay times have been studied for oxyfluoride glasses and glass ceramics of the system: SiO₂ - Al₂0₃ - Na₂O - LaF₃ - NaF, activated by terbium and ytterbium.

The CL spectra of the glasses and glass ceramics show characteristic Tb³⁺ luminescence bands: blue (⁵D₃ → ⁷F_J) and green (⁵D₄ → ⁷F_J) groups. With increasing terbium concentration the blue- to green-group ratio decreases.

The CL decay curves can be sufficiently well approximated by two exponents - fast and slow. Decay times for the blue-group CL bands are faster than for those of green group.

As the terbium concentration increases, the lifetimes for the lines of the blue group shorten, while for the green group they remain unchanged. This could be explained by the cross-relaxation between the transitions ⁵D₃ → ⁵D₄ and ⁷F₆ → ⁷F₀ of two terbium ions.

A human eye suffers from optical distortions or aberrations classified into lower-order aberrations and higher-order aberrations. The influence of higher-order aberrations on the visual perception has been much investigated. In our study, we paid attention to the influence of interocular differences between the degrees of different type aberrations on the ability to resolve dichoptic images. We investigated four types of aberrations - astigmatism, coma, trefoil, and spherical aberration. The lowest threshold was observed for the trefoil aberration, whereas the highest - for spherical aberration. Thus we have concluded that the thresholds of interocular differences between the degrees of higher-order aberrations needed to resolve dichoptic images strongly depend on the symmetry and orientation of the wavefront map and also on the aberrations to which the observer has adapted throughout the life.

The aim of this research was to study the influence of magnetic field on the growth of microorganisms. In our experiments this influence was tested using Escherichia coli strain BT21. The experiments were carried out in a shaker flask at different intensities of magnetic field. The application of magnetic drives and joints in the bioreactors imposes strong requirements on the hermetic sealing of the testing vessels, which is utterly important from the sterility point of view. Our experiments have convincingly shown that the magnetic influence results in higher growth rate of biomass. In addition, some indications have been obtained that as the magnetic strength exceeds a definite level its positive influence on the bacterial growth decreases.