Silver Nanoparticles Stabilised by Cationic Gemini Surfactants with Variable Spacer Length

The present study is focused on the synthesis and investigation of the physicochemical and biological properties of silver nanoparticles stabilized with a series of cationic gemini surfactants having a polymethylene spacer of variable length. UV-VIS spectroscopy, dynamic light scattering, scanning electron microscopy and zeta potential measurements were applied to provide physicochemical characterization of the silver nanoparticles. The mean size values of the nanoparticles were found to be in the 50 to 115 nm range. From the nanoparticle size distributions and scanning electron microscopy images it results that a population of small nanoparticles with the size of several nanometers was confirmed if the nanoparticles were stabilized with gemini molecules with either a short methylene spacer (two or four CH2 groups) or a long spacer (12 CH2 groups). The average zeta potential value for silver nanoparticles stabilized with gemini molecules is roughly independent of gemini surfactant spacer length and is approx. +58 mV. An interaction model between silver nanoparticles and gemini molecules which reflects the gained experimental data, is suggested. Microbicidal activity determinations revealed that the silver nanoparticles stabilized with gemini surfactants are more efficient against Gram-negative bacteria and yeasts, which has a direct relation to the interaction mechanism of nanoparticles with the bacterial cell membrane and its structural composition

Application of RFID technology in logistics

Práce se zaměřuje na technologii RFID a popisuje její historii. Také popisuje současné využití v oboru logistiky v ČR a zahraničí. Obsahuje popis fungování RFID systému a porovnává ho s čárovými kódy. Práce dále popisuje návrh konfigurace RFID systému pro využití v logistice.The work focuses on RFID technology and describes history. The work also describes current use in logistics in Czech Republic and abroad. It contains a description of the RFID system and compares it with barcodes. The work also describes the configuration of the RFID system for use in logistics.Dopravní fakulta Jana PerneraStudent přednesl ucelenou a logicky uspořádanou obhajobu své bakalářské práce. V ní dokázal přesvědčivým způsobem obhájit závěry svých řešení. U doplňkových otázek prokázal schopnost logického myšlení, pohotové reakce, jasného a srozumitelného vysvětlení

Financial analysis of selected rail passenger transport operators

Práce je zaměřena finanční analýzu vybraných provozovatelů osobní železniční dopravy. V rámci práce je pozornost věnována dvěma vybraným společnostem - provozovatelům osobní železniční dopravy v České republice (České dráhy, a.s. a RegioJet a.s.). Je provedena externí finanční analýza vybraných společností s cílem identifikovat slabé a silné stránky finančního zdraví. Na základě výsledků finanční analýzy jsou navržena opatření pro zlepšení finanční situace a tato opatření jsou zhodnocena.The work is focused on financial analysis of selected passenger railway operators. In the thesis, attention is spend to two selected companies - passenger rail transport operators in the Czech Republic (České dráhy, a.s. and RegioJet a.s.). An external financial analysis of selected companies is carried out to identify the weaknesses and strengths of financial health. Based on the results of the financial analysis, measures are proposed to improve the financial situation and these measures are evaluated.Dopravní fakulta Jana PerneraDiplomant přednesl ucelenou a logicky uspořádanou obhajobu své diplomové práce. V ní dokázal přesvědčivým způsobem obhájit závěry svých řešení. Na poznámky, resp. připomínky oponenta reagoval správně a v plném rozsahu je zodpověděl. U doplňkových otázek prokázal schopnost logického myšlení, pohotové reakce, jasného a srozumitelného vysvětlení

Recent State Policy and Its Impact on Geopark Establishment and Operation in Slovakia

The geological evolution and structure of the territory of Slovakia plays a key role in the current geodiversity of the country. The importance of this key element of the environment is widely and most effectively represented in geoparks. This paper is devoted to the state policy of geopark establishment and operation in Slovakia. Despite the relatively well-established concept of geoparks in the world, its position is not entirely clear in Slovak legislation. So, both bottom-up initiatives and top-down strategies are not quite successful in geopark operations, especially when considering the sustainability of Slovak geoparks. The possible future position of geoparks in Slovakia, in terms of state policies, may be found (as discussed in this paper) in adopting specific legislation which will effectively support the development of these potential (geo)tourist areas, contributing to both sustainable tourism development and nature protection

Active Learning in STEM Education with Regard to the Development of Inquiry Skills

Active learning, represented by inquiry-based science education (IBSE) strategies, is considered essential for students to develop skills and knowledge to prepare for the challenges of the 21st century world. The success of IBSE, and the resulting development of inquiry skills in particular, can be enhanced by various factors. This study is focused on the synergetic effect of the implementation of IBSE through well-designed inquiry activities across STEM-related disciplines, enhanced by digital technologies and formative assessment tools, delivered by teachers educated in this field. The corresponding research based on a quasi-experimental design evaluated the effect on the development of inquiry skills that were identified before and after a period of consistent implementation of IBSE, using a written test of inquiry skills as the main research instrument. The research findings on the sample of 2307 upper secondary school students confirmed a low initial level of inquiry skills, however a statistically significant improvement in students’ inquiry skills with medium size effect was identified. The detailed analysis shows the largest impact in the skill of determination of accuracy and statistically significant differences between genders without practical importance, however no difference was identified with regard to the number of inquiry activities undertaken

Diagnostics of Hydrogen-Containing Mixture Compression by a Two-Stage Piston Compressor with Cooling Demand Prediction

The present article describes the diagnostics of a compressor that is compressing a mixture of H2 and N2 on the basis of the results that were obtained by operational measurements of the flow rates and temperatures at selected compressor sites, as well as of the acoustic pressure levels during the full loading thereof. The obtained data were subsequently used to determine the limit conditions of the compressor operations in terms of the cooling capacity. A thermodynamic analysis of the compression of the H2/N2 gas mixture was carried out with subsequent heat and energy flow calculation and the determination of the minimum cooling water flow rate that is required to ensure the continuous compressor operations

An Investigation of the Techno-Economic and Environmental Aspects of Process Heat Source Change in a Refinery

This study of process heat source change in industrial conditions has been developed to aid engineers and energy managers with working towards sustainable production. It allows for an objective assessment from energetic, environmental, and economic points of view, thereby filling the gap in the systematic approach to this problem. This novel site-wide approach substantially broadens the traditional approach, which is based mostly on “cheaper” and “cleaner” process heat sources’ application and only takes into account local changes, while neglecting the synergic effect on the whole facility’s operations. The mathematical model employed assesses the performance change of all the affected refinery parts. The four proposed aromatic splitting process layouts, serving as a case study, indicate feasible heat and condensate conservation possibilities. Although the estimated investment needed for the most viable layout is over €4.5 million, its implementation could generate benefits of €0.5–1.5 million/year, depending on the fuel and energy prices as well as on the carbon dioxide emissions cost. Its economics is most sensitive to the steam to refinery fuel gas cost ratio, as a 10% change alters the resulting benefit by more than €0.5 million. The pollutant emissions generated in the external power production process contribute significantly to the total emissions balance

The Synthesis, Self-Assembled Structures, and Microbicidal Activity of Cationic Gemini Surfactants with Branched Tridecyl Chains

Cationic gemini surfactants with polymethylene spacer and linear alkyl chains containing an even number of carbon atoms have been extensively studied in the recent past, with the emphasis put on the determination of their aggregation behaviour in aqueous solution and their biological properties. However, the information on the aggregation of branched gemini surfactants with an odd number of carbon atoms in their alkyl chains is only sparsely reported in the literature. To help cover this gap in the research of cationic gemini surfactants, a series of branched bisammonium cationic gemini surfactants with an odd number of carbon atoms in alkyl chains (tridecane-2-yl chains) and a polymethylene spacer with a variable length ranging from 3 to 12 carbon atoms have been synthesized and investigated. Critical micelle concentration, which was determined by three methods, was found to be in the order 10−4 mol/L. A comparison of the obtained data of the novel series of tridecyl chain geminis with those of gemini surfactants with dodecyl chains and an identical spacer structure revealed that structural differences between both series of gemini surfactants result in different aggregation and surface properties for surfactants with 6 and 8 methylene groups in the spacer (N,N’-bis(tridecane-2-yl)-N,N,N’,N’-tetramethylhexane-1,6-diaminium dibromide and N,N’-bis(tridecane-2-yl)-N,N,N’,N’-tetramethyloctane-1,8-diaminium dibromide) with the cmc values 8.2 × 10−4 mol/L and 6.5 × 10−4 mol/L, respectively, as determined by surface tension measurements. Particle size analysis showed the formation of small stable spherical micelles in the interval between 2.8 and 5 nm and with zeta potential around +50 mV, which are independent of surfactant concentration and increase with the increasing spacer length. Microbicidal activity of 13-s-13 gemini surfactants was found to be efficient against Gram-positive, Gram-negative bacteria and yeast