Volume 62 (2011): Issue 6 (November 2011)

A universal filter with dual-output current follower (DO-CF), two transconductance amplifiers (OTAs) and two passive elements is presented in this paper. The filter is tunable, of the single-input multiple-output (SIMO) type, and operates in the current mode. Our solution utilizes a low-impedance input node and high-impedance outputs. All types of the active elements used can be realized using our UCC-N1B 0520 integrated circuit and therefore the paper contains not only simulation results that were obtained with the help of behavioral model of the UCC-N1B 0520 element, but also the characteristics that were gained by measurement with the mentioned circuit. The presented simulation and measurement results prove the quality of designed filter. Similar multi-loop structures are very-well known, but there are some drawbacks that are not discussed in similar papers. This paper also contains detailed study of parasitic influences on the filter performance.

Recently, the Lambert W function has arisen in the analysis of many systems including a restricted class of time-delay systems. An alternative approach to this analysis, based on the well-established root locus method, is shown here to contain the Lambert W function as a special case.

As a purely illustrative example of the equivalence between the Lambert W function and analytic root locus a system comprising a Proportional controller with a time-delay process is analysed. Controller designs based on rightmost eigenvalue location and the dominant eigenvalue method are described.

Voltage sags can cause interruptions of industrial processes, which could result as a malfunction of equipment and considerable economic losses. Thus, it is very useful to see certain rules of voltage sags occurrence due to duration and depth.

This paper presents statistical analyses of voltage sags in several domestic and industrial transformer stations. Voltage sag probability functions are calculated from actual measurement data, by means of a hill climbing algorithm. Lognormal and Weibull frequency distribution functions are used to describe distribution of measured voltage dips.

Modern electric power systems are large-scale systems with a complex structure comprised of interconnected networks. The balance between the generation and consumption of electricity has to be maintained at any moment. Transmission System Operator (TSO) uses ancillary services for keeping the domestic power balance. Selection of the services can be viewed as an optimization problem. In this contribution the optimization problem is solved via the Self-Organizing Migration Algorithm which belongs to the class of evolutionary algorithms. The comparison with historical activations of ancillary services showed the improved performance in terms of reduced cost for ancillary services.

Within only the last decade, usage of mobile phones and many other electronic devices with high speed wireless RF connection is rapidly increasing. Modern life requires reliable, quick and high-quality information connections, which explains the widely spreading craze for electronic mobile devices of various types. The vast technological advances we are witnessing in electronics, electro-optics, and computer science have profoundly affected our everyday lives.

Meanwhile, safety concerns regarding the biological effects of electromagnetic (EM) radiation have been raised, in particular at a low level of exposure which we everyday experience. A variety of waves and signals have to be considered such as different sine waves, digital signals used in radio, television, mobile phone systems and other information transfer systems. The field around us has become rather complicated and the "air space is getting more and more dense with RF. The establishing of safety recommendations, law norms and rules augmented by adequate measurements is very important and requires quite an expertise.

But as many scientific researches suggest, what we are currently witnessing is very likely to generate a great public danger and a bad influence over the human body. There are many health organisations warning the public for possible development of cancer, mental and physical disorders etc [7, 8]. These suggestions are quite serious and should not be neglected by the official bodies and the test laboratories.

In the following work, the effects of electromagnetic field over a virtual model of a human head have been simulated in the frequency range from 900 MHz to 1800 MHz (commonly created in the real life by mobile GSM system) with the help of the program MEFiSTo 2D Classic [1]. The created virtual models using the 2D simulation & computation software proved that the use of new high tech nanotextile materials for shielding layers around the human body can reduce the effects of EM fields dramatically if chosen properly according to the area of application.

The well known Shockley-Read-Hall (SRH) model considers emission and capture processes at defects exhibiting a single level or multiple non-coupled levels in the band gap of the semiconductor. The present paper generalizes the model to the case of two mutually coupled defect levels acting as trapping centres. If the intercenter transition is not considered, the model reduces to the case of two non-coupled levels treated by the SRH model.

Oscillation-based test (OBT) is one of the approaches for measuring static ADC parameters such as differential nonlinearity (DNL) and integral nonlinearity (INL) that can be implemented in a built-in self-test arrangement. When applying the OBT approach in practice we noticed an inherent measurement uncertainty related to the slope of the ADC input signal in OBT test mode. Experimental environment in Matlab has been set up to study the phenomenon. Experiments with varying values of slope were performed to demonstrate the margins of DNL measurement uncertainty.

Titanium oxide thin films were deposited at room temperature by reactive magnetron sputtering in a mixture of oxygen and argon on oxidized silicon substrates. The optimal etching characteristics of TiO₂ films by reactive ion etching (RIE) and RIE with inductively coupled plasma source (ICP) were investigated. Patterning of TiO₂ tip arrays by electron beam lithography and dry etching were developed. Different spot sizes 200 and 500 nm in diameter and with spacing 500 and 1000 nm were investigated with regards to the minimal size and the pyramidal shape. Experimental results have shown that the exposure dose optimization wa a significant parameter for controlling the tip size and its shape. We successfully fabricated the pyramidal TiO₂ tip arrays over an 1 × 1 mm² area. The TiO₂ tip array can be expected to have an important application in gas microsensors.

In this work, the quantities have been determined experimentally that are needed for reliable and precise quantitative interpretation of Auger spectra of nitrides AlN, GaN and of their ternary alloys Al_xGa_{1 - x}N. Measurements of reference samples AlN and GaN under various parameters of the primary electron beam (energy 3 and 5 keV, beam incidence angle with respect to the surface normal 12.5° and 45°) and of the ion beam (energy 0.5 and 1.0 keV, beam incidence angle with respect to the surface normal 67.5° and 35°) allowed to find the elemental sensitivity factors for these nitrides, and measurements on reference samples of ternary alloys Al_xGa_{1 - x}N allowed to find the component sputtering yields Y_Ga/Y_Al. To the best of our knowledge there is a lack of such data for those materials in the literature.

The development of stereophonic sound in Slovakia in the late sixties had a profound impact on the quality of recorded music in all areas of artificial and non-artificial music and it also played an important role in composing music for radio plays. However, the Czechoslovak Radio in Bratislava was at that time the only technically equipped institute in Slovakia where a stereophonic record could be created. Therefore our research studies have particularly been concerned with examining the archives of this institution as well as the valuable information on implementation of the recordings we have collected through interviews with the former staff of the broadcasting organization. Our research focuses for the first time on the period of the beginnings of stereophonic sound in Slovakia, hence the purpose of this article is to summarize the research results.