Volume 48 (2011): Issue 2 (April 2011)

The dynamic optimization process is analyzed from the viewpoint of simplifying the power flow calculations. The aim of the work was to reduce the calculation time using all admissible algorithms. Although the conventional iteration methods are simple and fast enough, the use of the so-called relaxation principle leads to increased calculation time. The paper exemplifies the power flow calculation based on the iteration method using acceleration factor. Proposals concerning the modelling of a power system are put forward in the aspect of its future development.

A great diversity of the nominal voltages in power networks can be explained based on the sizes and shape of the fed zone. To find the reason of such diversity, some assumptions should be made: the variation in parameters is continuous, the voltage is constant, the electricity consumers are spread uniformly, etc. To pass from continuous load to its discrete location, a discreteness factor is calculated for various shapes of the fed zone. The expression obtained for specific costs of the network shows that they decrease in the following cases: with voltage increasing as far as the costs of line construction are not rising too rapidly; with the load density and specific conductance of phase conductor increasing; when the consumers are located more sparsely. To reduce specific costs, an appropriate current density in phase conductors should be chosen. In the work it is shown that the choice of optimal sizes for the fed zone should be made with due consideration for the step-down transformer.

To prepare cathode material for lithium batteries, LiFePO₄ powder was sputtered using an RF magnetron. Thin LiFePO₄ films were obtained on different ~1000 nm thick substrates. The compositional and morphological examination of these films by SEM has shown that on a silicon substrate the annealed nano-crystalline thin film of LiFePO₄ material condenses in larger monocrystals (with thin film disappearance), while such a film on the stainless steel substrate coalesces in a uniform nano-structured layer after annealing. As shown by the energy-dispersive X-ray analysis, the annealed film consists of phosphorus, iron, and oxygen in the ratio corresponding to the stoichiometric LiFePO₄. Cyclic voltammograms of the LiFePO₄ thin layer were obtained with typical red-ox reaction peaks characterizing the electrochemical lithium insertion/extraction reactions in LiFePO₄. The obtained thin films have a relatively high charge capacity of 127 mAh g^-1.

A multi-photon polymerization system has been designed based on a pulsed irradiation light source (diode-pumped solid state femtosecond laser Yb:KGW, 300 fs, 1030 nm, 1-200 kHz) in combination with large working area and high precision linear motor driven stages (100×100×50 mm³). The system is intended for high resolution and throughput 3D micro- and nanofabrication and enables manufacturing the polymeric templates up to 1 cm² areas with sub-micrometer resolution. These can be used for producing 3D artificial polymeric scaffolds to be applied for growing cells, specifically, in the tissue engineering. The bio-compatibility of different acrylate, hybrid organic-inorganic and biodegradable polymeric materials is evaluated experimentally in vitro. Variously sized and shaped polymeric scaffolds of biocompatible photopolymers with intricate 3D geometry were successfully fabricated. Proliferation tests for adult rabbit myogenic stem cells have shown the applicability of artificial scaffolds in biomedicine practice.

The reported ultrasonic velocity measurements have been performed using a device in which the transmitter and the detector of sound vibrations are rigidly mounted at a constant distance from each other to avoid statistical errors at measuring the distance travelled by acoustic waves. The accuracy of measurements was thus dependent only on the resolution of the device determined by the frequency of time reference signals, its stability, the travelled distance, and the sound velocity.

The velocities measured in six objects exhibit a common behaviour with time, reaching a maximum between the 9-th and 33-rd hour after complete disruption in the blood supply and remaining higher compared with the initial value at least for 80 h after disruption. The obtained values of sound velocity are consistent with the results found by other authors, while the rise after disruption in the blood supply - with the increase in elasticity of the bone tissue.

For mapping the bilirubin distribution in bruised skin the multi-spectral imaging technique was employed, which made it possible to observe temporal changes of the bilirubin content in skin photo-types II and III. The obtained results confirm the clinical potential of this technique for skin bilirubin diagnostics.

In the work, interpretation is given for a microwave source associated with a stable isolated sunspot as a sample to study the sharp changes in ordinary mode microwave emission. The appropriate microwave source of the solar active region NOAA 10325 was observed with the radio telescope RATAN-600 and the Nobeyama Radio Heliograph during March 30 - April 4, 2003. The radio emission brightness in ordinary mode is shown to be depressed below the brightness of the quiet Sun when the sunspot was near the solar disk centre (April 2-3) but sharply increased in the wavelength range 1.76-2.67 cm at the longitudes |θ| > 50°.

Microwave radiation by gyroresonance mechanism is analysed in relation to the particular features of the images taken in He I 10830 Å chromospheric line (Chromospheric Helium-I Imaging Photometer) and EUV emission lines (Coronal Diagnostic Spectrometer). We have constructed a new model according to which above the sunspot's surroundings at the levels of gyroresonance emission the atmosphere is as cold as a "sunspot plume" (T ~ 10⁵-10⁶ K, N ~ 10⁹ cm^-3). As could be supposed from the He I line intensity, the central part of the sunspot atmosphere contains open magnetic field and rarefied plasma (N ~ 10⁸ cm^-3, T ~ 10^5.5-10⁶ K).