Tomas Bata University in Zlín
Institutional repository of Tomas Bata University LibraryNot a member yet
10673 research outputs found
Sort by
Study of injection molding process to improve geometrical quality of thick-walled polycarbonate optical lenses by reducing sink marks
Get PDFThis study investigates the challenges and potential of conventional injection molding for producing thick-walled optical components. The research primarily focuses on optimizing process parameters and mold design to enhance product quality. The methods include software simulations and experimental validation using polycarbonate test samples (optical lenses). Significant parameters such as melt temperature, mold temperature, injection pressure, and packing pressure were varied to assess their impact on geometric accuracy and visual properties. The results show that lower melt temperatures and higher mold temperatures significantly reduce the occurrence of dimensional defects. Additionally, the design of the gate system was found to be crucial in minimizing defects and ensuring uniform material flow. Effective packing pressure was essential in reducing volumetric shrinkage and sink marks. Furthermore, we monitored the deviation between the predicted and actual defects relative to the thickness of the sample wall. After optimization, the occurrence of obvious defects was eliminated across all sample thicknesses (lenses), and the impact of the critical defect, the sink mark on the planar side of the lens, was minimized. These findings demonstrate the substantial potential of conventional injection molding to produce high-quality thick-walled parts when these parameters are precisely controlled. This study provides valuable insights for the efficient design and manufacturing of optical components, addressing the growing demand for high-performance thick-walled plastic products.Internal Grant Agency of Tomas Bata University in Zlin; [IGA/FT/2024/003]Internal Grant Agency of Tomas Bata University in Zlin, (IGA/FT/2024/003
The "dark side" and negative consequences of cryptocurrencies usage for unethical purposes as barriers to invest in Middle East and African (MEA) countries
No full textPurpose: This paper aims to unveil the darker side of cryptocurrencies by delving into its role as an obstacle to investments in Middle East and African (MEAs) countries, unravelling the challenges involved. Indeed, despite the rise of blockchain-related technologies, specifically cryptocurrencies, having undeniably unlocked new avenues for business and society, crypto for venture funding purposes may exhibit a "dark side" due to their use for unethical purposes, for example, money laundering or terrorism financing, largely diffused in certain areas of MEA countries.
Design/methodology/approach: Through an explorative research design, using a mix of techniques based on both qualitative and interpretive methods, we conducted in-depth interviews among 33 European managers of companies engaged in MEA markets or aspiring to invest in such foreign markets, to analyse their thoughts, perceptions and possible strategies concerning the management of the "dark side" of cryptocurrencies in MEAs.FindingsOur investigation unearthed seven pivotal issues, which manifest as significant barriers related to the ambivalent use of crypto for funding projects, encompassing seven important consequential elements: (1) lack of knowledge about the technology's potentialities; (2) perceptions of crypto technology's ambivalence; (3) reputation and image consequences; (4) uncertainty about the destination of the invested funds; (5) decreased attractiveness of MEAs; (6) competition and market; and (7) lack of control and regulation. We grouped these into technology-related, business-related and legal- and policy-related barriers. Such findings underline the probable decrease in attractiveness of MEAs in terms of investments, together with the triggering factors and potential strategic solutions to mitigate such circumstances.
Research limitations/implications: Future studies could explore a broader sample of managers since we only considered the perception of European managers operating in companies that invest (or are intending to invest) in MEAs. Moreover, future research may extend the analysis to MEA-native companies or those engaging in reciprocal exchanges with Western countries.
Practical implications: Practically, our findings suggest several elements in which to intervene to mitigate managers' negative perception of the unethical use of cryptocurrencies in MEAs and to support CEOs' and CFOs' strategies, together with requirements to ensure the unaltered attractiveness of investments in an otherwise thriving region of the world, without overlooking the protection and safeguarding of investments and the health of the market and competition. Furthermore, a call for future research in this domain, along with at least minimal regulatory mechanisms, clearly emerges.
Social implications: Our findings underline the social challenges associated with the perception and acceptance of cryptocurrencies in these contexts, influencing cultural and social dynamics. Moreover, the identification of these barriers could underscore the significance of awareness of and education on blockchain technology and cryptocurrencies within society, including implications for policymakers.
Originality/value: Despite prior investigations into the negative effects of cryptocurrencies as a form of venture funding, no studies to date have examined managers' perceptions by focusing on possible barriers to investment in MEA countries due to the unethical usage of crypto. Importantly, this paper unravels the unexplored complexities of crypto's impact on ethical investments in MEAs, showcasing an original perspective
Photocatalytically active layered double hydroxide-PVDF composite membranes for effective remediation of dyes contaminated water
No full textIn this work, polyvinylidene fluoride (PVDF) intercalated CuFe layered double hydroxides (LDH) membranes were fabricated and investigated for UV-LED/persulfate degradation of methylene blue (MB), crystal violet (CV), methyl orange (MO), and Eriochrome black T (EBT) dyes from water. The PVDF-CuFe membrane exhibited improved heterogeneity, surface functionality (CuO, Fe–O, Cu–O–Fe), surface roughness, and hydrophilicity. The process parameters were optimized by response surface methodology, and maximum MB removal (100%) was achieved within 45.22–178.5 min at MB concentration (29.45–101.93 mg/L), PP concentration (0.5–2.41 g/L) and catalyst dosage (1.84–1.95 g/L). The degradation kinetics was well described by a pseudo-first-order model (R2 = 0.982) and fast reaction rate (0.029–0.089/min). The MB dye degradation mechanism is associated with HO·/SO4•− reactive species generated by Fe3+/Fe2+ or Cu2+/Cu+ in PVDF-CuFe membrane and PP dissociation. The PVDF-CuFe membrane demonstrated excellent recyclability performance with a 12% reduction after five consecutive cycles. The catalytic membrane showed excellent photocatalytic degradation of crystal violet (100%), methyl orange (79%), and Eriochrome black T (60%). The results showed that UV-LED/persulfate-assisted PVDF-CuFe membranes can be used as a recyclable catalyst for the effective degradation of dye-contaminated water streams.Qatar University, QU; National Capacity Building Program; NCBP, (QUCP-CAM23/24-153
Detektory pozarowe i ich podłączenie przeznaczone do stosowania w budynkach mieszkalnych, komercyjnych i przemysłowych
No full textSafety and security are currently highly resolved issues. One type of security is fire protection, which is solved in one of the options by applying fire detectors, which are part of the fire detection and alarm system. Fire detectors' main task is protecting people's lives and health and the safety of various assets through timely detection of fire threats with the subsequent performance of given measures. In addition to the types of fire detectors, the article also deals with the principle of their connection to the system.Department of Security Engineering, Faculty of Applied Informatics, Tomas Bata University in Zlí
Properties of quaternized and cross-linked hydroxyethylcellulose composite films
Get PDFAlthough trimetylammonium-2-hydroxypropyl-hydroxyethylcellulose (QHEC) is a well-known polysaccharide material, some of its properties have not been previously studied in detail. Therefore, we applied a combination of multidimensional nuclear magnetic resonance (NMR) in D2O on hydroxyethylcellulose (HEC) and HEC derivatives, and size-exclusion chromatography with multi-angle laser light scattering (SEC-MALS) in carbonate buffer at pH 10; while Fourier-transform infrared spectroscopy (FTIR), the X-ray diffraction (XRD), the thermogravimetry/differential/differential thermogravimetry (TG/DTG/DTA) and atomic force microscopy (AFM) in film form. SEC-MALS revealed various water-solubility of prepared derivatives: HEC (98%) > CHEC (72%) > QHEC (26%) > QCHEC (14%). Due to its substituents, the HEC macromolecule forms coil structures with varying gyration radii: QHEC (38–260 nm) > QCHEC (10–230 nm) > CHEC (21–100 nm) > HEC (23–50 nm). FTIR analysis of all prepared films confirmed their identical structure compared to that observed in liquid form in D2O. Onset temperatures (OT) of films degradation decreased in order: HEC (222 °C) > QCHEC (162 °C) > CHEC (142 °C) > QHEC (141 °C). The X-ray diffraction confirmed residual crystallinity of cellulose II (CII) in all four types of prepared films and was linked to ~ 2% water-insolubility of HEC derivatives revealed by SEC-MALS. Atomic force microscopy (AFM) showed significant differences in surface morphology among the four prepared films with surface roughness of: HEC (25 nm) > QCHEC (5.8 nm) > QHEC (4.2 nm) > CHEC (2.8 nm). Various spherical particles were found in case of HEC, circular depressions/holes approximately 4 μm in diameter were observed in case of QHEC. Except for the HEC, all other films showed granular surface probably due to insoluble components. Based on the mechanisms of quaternization and crosslinking and the results of analysis on water-soluble part and films we could assume that there are similarities in structures between the soluble and insoluble products of the reactions.Ministry of Education, Science, Research and Sport, (2/0071/22)Ministry of Education, Science, Research and Sport of the Slovak Republic; Centre for Scientific and Technical Information of the Slovak Republic; Vedecka Grantova Agentura MSVVaS SR a SAV [2/0071/22
The release of organic acids and low molecular weight carbohydrates from matcha tea after in vitro digestion
Get PDFBackground/Objectives: This study tested the influence of in vitro digestion on the release of organic acids and low molecular weight saccharides of matcha.
Methods: The concentrations of analytes in the raw and undigested portion of matcha were measured using HPLC with spectrometric and refractometric detection to establish their residual values after a two-step enzymatic digestion that was finally presented as a retention factor.
Results: It was established that dry matter digestibility values after simulated gastric and both gastric and intestinal phases were 67.3 and 85.9%, respectively. Native matcha, citric acid (44.8 mg/g), malic acid (32.2 mg/g), trehalose (36.1 mg/g), and L-arabinose (8.20 mg/g) reached the highest values and were predominant, whereas D-fructose, xylose, maltose, and saccharose were not detected. Regarding gastric phase digestion, succinic and malic acids, trehalose and D-glucose were the worst-releasing compounds and their remaining factors reached 34, 19, 18, and 50%, respectively, whereas L-arabinose was completely released. Focusing on gastric and small intestinal digestion, the least-releasing compounds of matcha tea leaves were succinic acid and trehalose, with their retention factors at 7 and 13%, which can proceed with the leaf matrix to the large intestine.
Conclusions: Malic, oxalic, and citric acids, the carbohydrates D-glucose, L-arabinose, and L-rhamnose, are almost entirely released from matcha tea during digestion in the stomach and small intestine and can be available for absorption in the small intestine. In the measurement of oxalic acid, considering that the process of shading tea leaves increases the concentration of this acid and its retention factor value is too small, it would be appropriate in the future to evaluate the recommended maximum daily intake of matcha tea for people sensitive to the formation of urinal stones.Univerzita Tomáše Bati ve Zlíně, UTB, (IGA/FT/2024/006); Univerzita Tomáše Bati ve Zlíně, UTBTomas Bata University in Zlin [IGA/FT/2024/006
The effect of moisture on laser beam wood machining
Get PDFWood moisture can affect various parameters of the engraving process, such as the depth of engraving, the structure and surface of the wood, and thus the overall quality of the created image. The investigation of the influence of moisture contained in different types of wood on their machining was carried out on samples of oak, beech, pine, spruce, alder, ash and cherry produced using the laser device ILS 3NM, CO2, with a wavelength of 10.6 μm and a maximum power 100 W, with a maximum feed speed of 1524 mm·s"1. The depth of ablation and the surface of the machined surface were studied for selected samples with the moisture of the wood plants in the laboratory room, the outdoor and with the moisture created by immersion in the water bath
Dealing with student mistakes in mathematics at primary school
Get PDFThe article focuses on how teachers deal with student mistakes during mathematics instruction at primary school. The theoretical framework encompasses a constructivist culture of teaching and learning and dialogic teaching. Two general strategies are distinguished: avoiding mistakes and using mistakes as opportunities to learn. The presented qualitative study is based on 24 audio recordings of mathematics instruction, supplemented by interviews with six teachers. Through axial coding, we arrived at seven categories that describe specific ways of dealing with mistakes: not responding; making students aware of a mistake; encouraging students to present proofs; leading students to a level where they do not fail; expanding the student network of mathematical knowledge; creating opportunities for presenting content to clarify mistakes; and providing opportunities for students to find the cause of their mistakes. The findings are discussed in the context of the constructivist approach to instruction
Tailoring end-use properties of polypropylene through a combination of specific nucleation and long-chain branching
No full textThe present study presents an assessment of the interrelations between long-chain branching, specific nucleation, and end-use properties of polypropylene blends: blends of linear polypropylene (L-PP) and long-chain branched polypropylene (LCB-PP) modified by a specific β-nucleating agent (NA). Specimens with various LCB-PP compositions with and without NA were prepared under complex flow fields by injection molding. Wide-angle X-ray scattering was employed to capture the X-ray patterns of both the skin and core of the specimens, determining the overall crystallinity and amounts of individual polymorphs. The increasing content of LCB-PP and γ-phase, at the same time, in the blends is reflected in both increasing crystallinity and improved mechanical properties, namely, yield stress and Young’s modulus. On the other hand, the composition of the blends had no significant effect on the impact strength, except for nucleated L-PP. It has been demonstrated that adding a relatively small amount of LCB-PP is sufficient to modify the mechanical properties of linear polypropylene. Even a very small amount of LCB-PP in the L-PP suppressed the effectiveness of NA
Innovation activity of Slovak SMEs operating in the ICT sector
Get PDFThe objective of this study was to analyse contemporary trends in innovation among small and medium-sized enterprises in Slovakia's ICT sector. The study explored different types of innovations, the factors that either promote or hinder innovation, and the innovative practices of small and medium-sized enterprises within this sector. To achieve this goal, a questionnaire survey was conducted between September 2021 and February 2022. The research sample consisted of 1,000 randomly selected small and medium-sized enterprises operating in the ICT sector, drawn from a total of 8,416 eligible companies. Ultimately, 124 respondents completed the questionnaire, including 73 microenterprises and 51 small and medium-sized enterprises. The research hypotheses were evaluated via descriptive statistical analysis and the Z score methodology. The findings revealed that the most prominent form of innovation in Slovakia's ICT sector was service innovation, followed by product innovation and the adoption of new production processes. The primary motivational factor driving innovation is the desire to achieve high customer satisfaction by meeting customer needs and enhancing service quality. Conversely, the most significant barrier to innovation was identified as a lack of time. The study indicated that approximately 75% of small and medium- sized enterprises intend to pursue innovation within the next few years. Moreover, innovation plans were more pronounced among small and medium- sized enterprises than among microenterprises. The primary areas of interest for future innovations included enhancing existing products and services, developing new products or services, and implementing new technologies or production processes. With respect to the research hypotheses, no statistically significant differences were observed between the innovation activities of microenterprises and those of small and medium-sized enterprises