VGTU Journals (Vilnius Gediminas Technical University - Vilnius Tech)
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Toward a lightweight high-speed fin: structural and flutter analysis for thickness reduction
No full textReducing the mass of supersonic aerodynamic surfaces is a critical challenge in the development of high-speed rockets to further their potential range. This study presents the redesign of a supersonic fin with the primary objective of reducing its thickness from 25 mm. Two designs are investigated, with thicknesses of 10 and 12 mm, respectively, to ensure structural integrity under extreme flight conditions. A comprehensive computational approach is employed, combining static structural analysis, modal analysis, and aeroelastic analysis. Modal analysis is validated through an experimental method using a hammer impulse test for modal frequencies. The 10 mm rocket fin cannot withstand the static load simulated under the flight condition of 15-degree angle of attack, maximum operational flight speed of Mach 3.27, and air density at sea level. The 12 mm thick fin meets the requirements and demonstrates a flutter speed of Mach 11, significantly exceeding the required flutter speed of Mach 3.99. This research highlights the feasibility of substantial weight reduction in supersonic fins without compromising stability, offering a pathway for future advancements in lightweight, high-speed control surfaces
The impact of industrialization and self-renewing energy utilization on carbon discharges in the country economics
No full textIndustrialization has been pivotal in driving economic development. The research problem is the negative impact of industrialization to global warming and climate change. The relevance – enabling the use of renewable energy and green solutions to decrease CO₂ emissions. This research aims to evaluate the impact of short and long-term of industrialization, consumption of renewable energy, trade openness and economic growth on carbon emissions per capita in Indonesia. This research analyses [2000–2023] data, applying econometric ARDL approach and diagnostic tools. The Breusch-Godfrey Serial Correlation (BGSC) results revealed no consistent correlations, when Breusch-Pagan-Godfrey (BPG) test heteroscedasticity was confirmed. Ramsey RESET test (RRT) showed that the model is perfectly specified and significant; CUSUMSQ and CUSUM tools proved the stability of the model, when the VIF multicollinearity results indicated that no multicollinearity exists between the variables. Research findings show: trade openness and the consumption of renewable energy demonstrate a favourable effect for carbon output per capita in Indonesia as outcomes of economic progress, while industrialization has an adverse relationship with emissions of carbon per capita. The research originality – complex evaluation of the relationship between mentioned variables interplay. This publication provides recommendations for policymakers to improve the quality of environment
Creating a new brand name: a research with the case study method
No full textWith the rapid growth of the fast-food restaurant sector in Azerbaijan, the number of domestic and international enterprises is increasing. With this, the brand name becomes very important. Based on this, the purpose of the study is to create brand names for new fast-food restaurants. The study is qualitative research and was analysed by case method. As a result of the study, brand names were suggested by participants, and these brand names were analysed. Suggested brand names were classified before being analysed. Brand names classified in 7 groups as creative, national, fast, delicious, local, global, and competitive were then analysed. Among the brand names suggested by the participants, the most suitable were for the creative concept. Brand names with the meaning national suggested by the participants in both cases are among the most recommended. When evaluated in general, a total of 118 brand names have been suggested, and among these names, more suggested names are suitable for the words national, creative, local, delicious, global, food, and fast. The rapid development of the fast-food sector in Azerbaijan and the interest of both local and global companies in this sector create a need for new brand names. In this respect, it is thought that the article will contribute to the academic literature and practitioners
Using RS and AI GIS in land management and urban planning in Mosul, Iraq for sustainable development
No full textThe importance of Remote Sensing (RS) and Geographic Information Systems (GIS) comes from the fact that they are means that have been proven effective in supporting and developing the decision-making process in the field of urban control. The city of Mosul in Iraq has been subjected to a tremendous change in the dynamics of land use due to the wars. This study aims to use RS techniques and Artificial Intelligence Geographic Information Systems (AI GIS), as the study relies on Sentinel-2 images and online data sources to evaluate the changes that occurred in the natural environment by comparing the years during and after the destruction. Four classification methods were used in this study; Support Vector Machine (SVM) learning, Scene Classification technique (SC), Normalized Difference Vegetation Index (NDVI), and Normalized Difference Water Index (NDWI). High classifications accuracies were obtained ranging between (92%–97%). The residential area had decreased, followed by vegetation, which was converted to bare land by 64% in the year 2017 due to the war effect. In 2023 some recovery of settlement and increasing in other sectors was observed. The approach highlights the capability of spatial technologies and the role of RS and GIS in sustainable development
Are renewable energy stocks, investor sentiment, and the cryptocurrency market-related?
No full textThis paper applies wavelet quantile correlation to research on the relationship among renewable energy stocks, investor sentiment, and the cryptocurrency market. The empirical results indicated that under extremely negative conditions, in both the short and medium run, renewable energy stocks and cryptocurrencies are negatively correlated, implying that during such periods, renewable energy stocks can be used as a safe haven for cryptocurrencies. The opposite happens when the market is average or booming. This indicates that investors tend to invest simultaneously in these two promising asset classes when the market performs well. Under varied market conditions, FGI correlates positively with cryptocurrency, demonstrating sentiment influences price patterns. Moreover, the correlation between FGI and renewable energy stocks further validates the relationship between cryptocurrencies and renewable energy stocks. These findings can be used to improve the prediction of market trends by investors using sentiment indices and to devise more effective portfolio diversification strategies that minimize risk amid an evolving market
From farm to fork: determinants of supplier-retailer relation in organic agri-food supply chain on EU Eastern – Western approach
No full textThe European Union’s Farm to Fork Strategy, embedded within the Green Deal, aims to create equitable and sustainable food systems, fostering environmentally responsible practices and addressing challenges comprehensively throughout the agri-food supply chain. Organic farming plays an important role in this transition, particularly in the context of the circular economy. This study explores the key determinants influencing supplier-retailer relationships in the organic agri-food supply chain, focusing on the interaction between Romanian suppliers and retailers from Germany, Austria, and Switzerland. Using a mixed-methods approach that combines quantitative and qualitative analysis, the research identifies price, quality, and trust as essential factors shaping demand. Given Romania’s growing organic agriculture sector and the increasing consumption of organic products in German-speaking markets, this study highlights both challenges and opportunities for enhancing trade relations. As one of the first investigations into the East-West dynamics of the EU organic agri-food supply chain, the findings provide valuable insights for strengthening sustainable agriculture and market integration in Romania. It is also relevant for other Eastern European countries emphasizing the importance of a strong green agri-food sector throughout the European Union, as well as coordinated efforts along the supply chain
What causes the return and volatility spillover in Chinese green finance markets? A time-frequency perspective
No full textThis paper analyzes both return and volatility spillovers between green bonds, green stocks, clean energy, and carbon markets from April 28, 2014, to May 31, 2024, using the time-frequency connectedness methodology. Further, determinants of these spillovers are examined from perspectives of economic fundamentals (macroeconomics, inflation, and rate), market contagion (market volatility and investor sentiment), and uncertainties (EPU, CPU, GPR, and the COVID-19 pandemic) with the linear regression and quantile regression methods. Our investigation demonstrates that return and volatility spillovers exhibit significant crisis jumps during periods of financial turmoil. During most periods, both return and volatility spillovers occur predominantly in the short run. Second, green bonds and carbon markets show safe-haven characteristics as net risk recipients. Furthermore, economic fundamentals, market contagion, and uncertainty factors exhibit obvious impacts on both green finance market spillovers, albeit in differing magnitudes and directions. Notably, both return and volatility spillovers in the short and long run are determined by economic fundamentals, market contagion, and uncertainty variables. What’s more, these factors exhibit stronger interpretations of extreme return spillovers. These findings pose significant ramifications for risk mitigation and portfolio diversification for investors and authorities throughout Chinese green finance markets
Spatial pattern and its driving forces analysis of soil available nitrogen, phosphorus, and potassium in semi-arid grassland surface coal mining areas
No full textMining activities not only provide a large amount of material basis for socio-economic development but also cause great damage to the environment. It is of great significance to study the spatial variation characteristics of soil Available Nitrogen (AN), Available Phosphorus (AP), and Available potassium (AK) in mining areas for land reclamation and ecological protection. Currently, research on soil AN, AP, and AK in mining areas is lacking in large-scale survey, sampling, spatial pattern, and driving force research for surface coal mines in semi-arid grassland areas, and it is not possible to comprehensively grasp the distribution characteristics and driving forces of soil AN, AP, and AK in surface coal mines. Given this, this study took the Shengli Coal Field in Xilinhot City, the hinterland of Xilingol Grassland, as an example to study the spatial pattern and driving forces of soil AN, AP, and AK in the semi-arid grassland surface coal mining areas. The results showed that: (1) There was no strong spatial correlation among AN, AP, and AK in the soil of the study area, and the spatial pattern heterogeneity was strong. The content of AN, AP, and AK in southeast soil was relatively low. (2) The influence degree of each factor on the spatial pattern of AN was ranked as follows: NDVI > Agriculture > Water > Town > Mining > Industry; (3) The influence degree of each factor on the spatial pattern of soil AP was ranked as follows: NDVI > Mining > Water > Industry > Town > Agriculture; (4) The influence degree of each factor on the spatial pattern of soil AK was ranked as follows: NDVI > Town > Agriculture > Water > Mining > Industry; (5) The interaction between two factors presented two relationships: nonlinear enhancement and dual-factor enhancement. The interaction between various factors was higher than that of a single factor
Numerical differentiation of fractional order derivatives based on inverse source problems of hyperbolic equations
No full textIn this paper, we mainly study the numerical differentiation problem of computing the fractional order derivatives from noise data of a single variable function. Firstly, the numerical differentiation problem is reformulated into an inverse source problem of first order hyperbolic equation, and the corresponding solvability and the conditional stability are provided under suitable conditions. Then, four regularization methods are proposed to reconstruct the unknown source of hyperbolic equation which is the numerical derivative, and they are implemented by utilizing the finite dimensional expansion of source function and the superposition principle of hyperbolic equation. Finally, Numerical experiments are presented to show effectiveness of the proposed methods. It can be conclude that the proposed methods are very effective for small noise levels, and they are simpler and easier to be implemented than the previous PDEs-based numerical differentiation method based on direct and inverse problems of parabolic equations
Boundary feedback stabilization of quasilinear hyperbolic systems with zero characteristic speed
No full textIn this paper, we investigate the boundary feedback stabilization of a quasilinear hyperbolic system with zero characteristic speed and a partially dissipative structure. This structure enables us to construct a Lyapunov function that guarantees exponential stability for the H2 solution. We also introduce another set of stability conditions by restricting terms corresponding to zero eigenvalues to the dissipative part, which still ensures exponential stability. As an application, we achieve feedback stabilization for the modified model of neurofilament transport in axons