The change in the concept of urban agriculture has been driven by social, political and economic factors, changing the role of agriculture in the urban environment. From the second half of 20th century topicality and practices of urban agriculture are growing widely not only in social initiatives but also in scientific research (the number of articles in scientific databases has increased 18-30 times since 2000). Growing interest has identified various variations and tendencies in the interpretation of the concept of urban agriculture, having regard to the current United Nations definition that is broad, but in research works and case studies researchers adapt the definitions to the local characteristics and aim of the study, thus creating a number of risks in the interpretation of the concept, including limited possibilities for quantitative comparisons between studies. The aim of the article is to identify the historical development stages of the concept of urban agriculture and to determine the main research tendencies in its application. To achieve this aim, the method of monographic and descriptive analysis was used for theoretical discussion, analysis, synthesis and deduction - for information gathering, logical systematization and classification. As a result of the study, it was identified that the concept of urban agriculture is developed in three different stages - originally associated with the technical solutions of urban planning for providing food for city dwellers, it is currently developing in tendencies of different directions: analysis of agriculture’s role in urban areas (including mitigating climate change risks), classification of types of urban agriculture, opportunities for adapting innovations and technological solutions to urban agriculture, the place and context of urban agriculture for sustainable development in the circumstances of urbanization. Such in-depth research of the experience and impact of urban agriculture on sustainable development could increase dynamically due to environmental considerations, aspect of the circular economy, and new paradigms in planning urban and peri-urban areas.

This paper investigates the effect of separated exhaust expansion chamber parameters on pressure oscillations in spark-ignited internal combustion (IC) gasoline engines. It is known that exhaust expansion chambers are becoming increasingly more popular among both – original equipment (OE) and aftermarket equipment (AE) exhaust system manufacturers for performance-oriented motorcycles equipped with mainly single cylinder engines, but the companies are reluctant to reveal any detailed principles of operation of the mentioned expansion chambers. The subject of this research is the type of expansion chamber (separate) as used on performance-oriented motorcycles, particularly its’ effect on exhaust pressure pulsations as different chamber volumes, locations and passage sizes are tested. Time-dependent computational fluid dynamics (CFD) analysis was carried out in Solidworks Flow Simulation environment on a simplified exhaust header pipe model imitating engine operation at full load and steady speed. Honda CRF450R motorcycle engine was used as the example and fully defined using a 1D engine performance calculator software to determine the combustion chamber pressure and exhaust valve lift at any given crankshaft position. Volume flow rate of exhaust gasses at the header pipe inlet was calculated based on engine parameters and operating speed. The average pressure values with respect to physical time were measured and graphed across the header pipe inlet cross-section. Eight different header pipe and exhaust expansion chamber combinations were modelled, tested, and results compared at low, medium and high engine speeds. It was found that the presence of exhaust expansion chamber tends to dampen the amplitude and decrease the frequency of pressure oscillations generated at the opening of the exhaust valve(s). Observations show that the addition of an expansion chamber as per design of performance-oriented motorcycles helps to decrease the negative effect of engine tuning while also dampening the positive effect.

The experiment was conducted to analyse the effect of fermented acid whey permeate on milk yield and composition in the lactating cows. Propionic acid bacteria and their metabolites have been used in the lactating cows feeding over decades, primarily to improve growth performance, feed conversation and milk production efficiency. Two groups of the lactating cows were arranged in the study: control group (n=50) and experimental group (n=50). Experimental group’s animals received 0.5 L of fermented whey permeate daily. Acid whey permeate was inoculated with the freeze-dried PS-4 (Propionibacterium freudenreichii subsp. shermanii, Chr.Hansen, Denmark) starter and fermented anaerobically for 48 hours at 20±2 ᵒC. Fat, protein, lactose and total solids concentration in acid whey permeate and fermented acid whey permeate was analysed by the standard methods, but propionic acid was detected by HPLC. Milk composition and quality indices were determined at the beginning of the study and each month during 6 months period. At the end of the study the feeding of fermented acid whey permeate was stopped, but milk composition and quality data were monitored additionally after one month. Milk fat, protein, lactose, total solids, urea concentration and somatic cell count were analysed by a near infrared spectroscopy. The variability in milk composition and quality data across trial was greater in the experiment group than in the control. Milk fat and somatic cell count were significantly different (p<0.05) than other studied parameters in the experimental group cows’ milk. Milk yield and lactose concentration were tended to increase during feeding of fermented acid whey permeate in the lactating cows without significant differences between control and experimental groups. Fermented acid whey permeate as feed supplement improves energy metabolism for dairy cows which results in the higher milk yield and fat concentration.