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The paper aims to present a learning environment for optimal synthesis of voltage regulator circuits (LEOS‐VRC) using PSPICE simulator.

LEOS‐VRC supports a database with voltage regulator circuits edited as projects in PSPICE compatible format and a methodology for optimal synthesis. The methodology is based on the estimation of multiple voltage regulator circuits' realizations over a given specification, through comparative study in PSPICE, using a set of predefined specific electrical characteristics, which values are determined from simulation waveforms. LEOS‐VRC allows integrating the voltage regulator circuit in a power supply system through adding transformer, rectifier and control stages. Both linear and switch‐mode power supplies are considered.

The methodology and examples proposed illustrate the efficiency of LEOS‐VRC for teaching and self‐education in the area of power supply circuit design.

In future LEOS‐VRC database will be enlarged with new voltage regulator circuit topologies and new controller circuits.

LEOS‐VRC is suitable for students in electronics and designers of power supply circuits.

With LEOS‐VRC students become familiar with multisolution synthesis. By analyzing the complex behaviour of the power supply system and applying comparative study and optimization criteria, they can make a motivated selection of an optimal voltage regulator design solution for a concrete application.

The period of transition to democracy in which Generation Z members in Bulgaria grew up was characterised by profound changes in the economic and social system of the country, with frequent episodes of chaos and instability resulting in a long-term demographic decline. At the same time, the years of their adolescence have been marked by globalisation processes and the rapid development of digital technologies opening countless opportunities for work, study and travel to this group of young people.

Although research on Generation Z in Bulgaria is scarce, in this chapter, we have attempted to draw a portrait of the typical representative of the young generation based on the results of a couple of empirical surveys. Decreasing social orientation, less focus on sustaining interpersonal relationships and lower self-confidence and initiative are among our most remarkable observations making this generation of young people rather different than previous ones. Furthermore, Generation Z members were found to be quite demanding at work requiring stress-free working conditions, good work–life balance, opportunities for competency development and adequate pay from employers. This certainly creates a serious challenge for Bulgarian employers who might have to change their standard human resource practices in order to attract and retain the potential of this new group of employees. Generation Z members could be a source of innovation, meaningfulness and flexibility for the Bulgarian labour market and because of that they certainly need to be studied in more detail.

Two perspectives provide alternative insights into household composition in contemporary Eastern Europe. The first stresses that individuals have relatively fixed preferences about living arrangements and diverge from them only when they cannot attain their ideal. The second major approach, the adaptive strategies perspective, predicts that individuals have few preferences. Instead, they use household composition to cope with economic hardship, deploy labor, or care for children or the elderly. This article evaluates these approaches in five post‐socialist East‐European countries, Bulgaria, Hungary, Poland, Romania, and Russia, using descriptive statistics and logistic regression. The results suggest that household extension is common in these countries and provide the most evidence for the adaptive strategies perspective. In particular, the results show that variables operationalizing the adaptive strategies perspective, including measures of single motherhood, retirement status, agricultural cultivation, and poverty, increase the odds of household extension.

The purpose of this paper is to determine and compare the tribological characteristics (weight wear and friction moment) of a friction couple C45/C330 at running‐in with motor oil SAE 30 and different friction modifiers of copper oleate and zinc oleate.

Friction couples are tested using the model “roller‐sector” and they are lubricated with oil SAE 30 and two other samples of SAE 30 containing 0.6 per cent copper oleate and 0.6 per cent zinc oleate, respectively. Graphic dependencies are drawn for the weight wear of the sectors, rollers and couples; as well as for the running‐in moment, the friction moments at the end of the loading and at the end of the test.

The weight wear, running‐in moment and friction moments are evaluated for friction with SAE 30 as reference and oils containing copper oleate and zinc oleate as friction modifiers. The best performing material is the oil with zinc oleate.

From a practical point of view this paper offers a new idea about a friction modifier – zinc oleate. Data for tribological characteristics and suitable concentration in the oil composition are given in the paper.

The paper aims to present a new friction modifier (mixture of zinc and copper oleates) proper for industrial running-in of repaired engines.

The method of comparison was used for testing the offered friction modifier, a market product “Renom Engine” and a blank sample of motor oil as an etalon. Running-in time has been established. The mechanical losses change and the relevant coefficients have been determined. Data of the bearings wear have been included.

The benefit of the metal oleates and Renom Engine usage as friction modifiers has been proved. Time for industrial cold running-in of repaired engines decreases by around 20 per cent when friction modifiers are used in comparison with the etalon oil. The coefficient of the mechanical losses reduction at running-in with friction modifiers is higher than the coefficient for the etalon oil. The higher coefficient values indicate that the running-in of the working surfaces occurs more intensively and for a shorter period of time. Lower wear of the bearings is combined with smaller roughness of the friction surface, which secures higher quality of the surfaces run-in with the friction modifiers and greater capacity by around 30 per cent.

This study introduces a new friction modifier for industrial running-in of repaired engines. It would be of interest to the customers and manufacturers of oil additives.