VGTU Journals (Vilnius Gediminas Technical University - Vilnius Tech)
Not a member yet
12536 research outputs found
Sort by
A predation model considering a generalist predator and the Rosenzweig functional response
No full textThis work deals with the dynamics of an ordinary differential equation system describing a Leslie-Gower predator-prey model with a generalist predator and a non-differentiable functional response proposed by M. L. Rosenzweig, given by h(x) = qxα with 0 < α < 1. Two aspects have a significant impact on the model: (1) the predator’s carrying capacity depends on both the favorite prey population and an alternative food source, and (2) consumers have access to an alternative food source. Among the main results, a separatrix curve Σ arises dividing the phase plane into regions with different dynamic behaviors. Trajectories above the separatrix curve Σ reach the vertical axis in finite time, while those below Σ may converge to positive equilibrium points, limit cycles, or homoclinic connections. Furthermore, the system is non-Lipschitz, implying non-uniqueness of solutions at points of the vertical axis. Several bifurcations, including saddle-node, homoclinic, Hopf, generalized Hopf, and Bogdanov-Takens bifurcations, are identified through the use of computational techniques. The dynamics of the system are visualized by presenting a bifurcation diagram in a convenient parameter space
Global existence and uniqueness of mild solution for a fractional Keller-Segel system in Besov-Morrey spaces
No full textThis paper investigates the fractional Keller-Segel system involving both temporal and spatial variables. We examine fractional dissipation mechanisms for the physical variables, including chemotactic diffusion with fractional dissipation, and incorporate a time-fractional variation in the Caputo sense. Our analysis centers on the fractional heat semigroup, deriving time-decay and integral estimates for Mittag-Leffler operators in Besov-Morrey spaces. Furthermore, we establish a bilinear estimate arising from the nonlinearity of the Keller-Segel system, avoiding reliance on auxiliary norms. These results are then employed to demonstrate the existence and uniqueness of mild solution in Besov-Morrey spaces
The impact of the automatic terminal information service on airspace capacity and air traffic controllers workload
No full textThe Automatic Terminal Information Service (ATIS) is an important part of the organization of air traffic, which automatically provides pilots with important information about the status of the airport, runways in use, meteorological and other important data. In the absence of ATIS, air traffic controllers (ATC) must repeatedly relay this information, increasing communication demands and potentially contributing to ATC workload and operational inefficiencies. This study investigates the impact of ATIS implementation on sector capacity and controller workload. The research utilizes a year-long observational dataset from a regional airport operating without ATIS, where controller–pilot communication durations and frequencies were recorded under live operational conditions. Communication parameters, including the number of transmissions, mean message duration, and controller availability factor, were extracted and used to model sector capacity according to the Instruction of the Aeronautics Command (ICA) 100-30 methodology. The introduction of ATIS was then simulated by adjusting these parameters to reflect the automated transmission of routine information. Results show that ATIS significantly reduces the number and average duration of controller–pilot communications, leading to an increase in controller availability. Consequently, sector capacity rose by 36.03% for fixed-wing aircraft and 37.56% for rotorcraft. Statistical testing confirmed that these improvements were not attributable to random variation. The findings suggest that implementing ATIS can support more efficient communication, contribute to reducing controller workload, and may lead to a noticeable increase in sector capacity
Corrigendum: Exploring the social and economic consequences of the metaverse: a multi-criteria approach to the SDGs
No full textFatemeh Ghasemzadeh, Babak Ghahremannasab, Jurgita Antuchevičienė, Violeta Šniokienė, authors of the article “Exploring the social and economic consequences of the metaverse: a multi-criteria approach to the SDGs”, published in Technological and Economic Development of Economy, 31(5), 1619–1643, https://doi.org/10.3846/tede.2025.24858 inform that the first author\u27s last name is misspelt and we would like to make the following correction to the authorship:
Fatemeh GHASEMZADEH, Babak GHAHREMANNASAB, Jurgita ANTUCHEVIČIENĖ, Violeta ŠNIOKIENĖ
The authors regret the error
Review of the urbanism reader: design, technology, culture and the future of cities
No full textThe Urbanism Reader critiques postmodern urbanism as a reaction to modernist minimalism, focusing on diversity, responsiveness, and complexity in city design. Edited by Stefan Al and Tom Verebes, the anthology includes over 40 curated texts exploring urban theory since the 1960s. Topics range from spatial diversity, non-linear planning, density, public health, and informality to technology, AI, and environmental concerns. While the book includes minority and ecological perspectives, it lacks deeper political economy critiques. Ultimately, it offers a rich, if selective, overview of current urban discourse, highlighting the intersections of design, technology, and society as tools for navigating urban complexity
Barriers to blockchain implementation in supply chain finance – based on perspectives of grey transaction behaviour
No full textThe purpose of this study is to identify grey transaction behaviours that function as barriers to blockchain implementation in supply chain finance, explore which obstructions arise from these grey transaction behaviours and subsequently hinder blockchain implementation, and further measure the influence levels of the corresponding implementation barriers. The Delphi method and DANP are the main analysis methods used in this study. According to the analysis, three grey transaction behaviours that function as implementation barriers are identified, namely, kickbacks, internal and external accounting, and informal transaction relationships with banks. In addition, seven obstructions arise from these three barriers, and these obstructions can be adopted to explain why the three barriers hinder blockchain implementation. Finally, although internal and external accounting represents the main barrier, informal transaction relationships with banks may function as a critical underlying barrier that enhances the other two barriers. This study contributes in that it fills the gap of existing studies related to the intersection of supply chain finance and blockchain and provides a new perspective enabling practitioners to rethink how blockchain can be successfully implemented in the context of supply chain finance
Enhanced nitrogen removal and sludge characteristic in aerobic SBR by simultaneous nitrification and denitrification bacteria
No full textFour efficient heterotrophic nitrification and aerobic denitrification (HN-AD) strains were applied in sequencing batch reactors (SBRs) via two bioaugmentation strategies to enhance the nitrogen removal and sludge characteristic. Synthetic domestic wastewater with NH4-N concentrations of 30~50 mg L–1, was treated in three SBRs, with DO maintained at 4±0.5 mg L–1. Compared with the control (crude activated sludge), bioaugmentation improved TN removal by 7% averagely, increased nitration rate by 0.54 mg g–1 h–1, and reduced sludge volume index at 30 min (SVI30) by 3.5~14.7 mL g–1. The maximum TN removal efficiency reached 50.37% with effluent TN concentration of 14.64 mg L–1, meeting China’s Class 1A discharge standard (TN ≤ 15 mg L–1). SBR started by bacterial suspension without activated sludge exhibited high adaptability to low carbon/nitrogen ratio, achieving 35% TN removal at C/N = 3 (vs <10% in control), with <5% MLSS fluctuation versus 30% decline in control. Microbial community analysis revealed Saccharibacteria dominance (15.34% vs control’s 8.48%) coupled with 7.6% reduction in filamentous Saprospiraceae (12.78% to 5.18%), collectively explaining the enhanced nitrogen removal and sludge settleability. This study provides the first evidence of granular sludge formation via HN-AD bacterial coaggregation under low C/N conditions, offering a novel strategy for energy-efficient wastewater treatment
Statistical models for the utilization process of aviation radio equipment
No full textThe reliability of aviation equipment is a critical factor that directly influences the efficiency of tasks associated with flight operations. To assess reliability, various indicators are commonly employed, including mean time between failures, mean time between repairs, steady-state availability, availability function, downtime ratio, and utilization factor. However, in modern aviation, the operation of radio equipment often neglects considerations of economic impact, socio-political factors, and a comprehensive analysis of the efficiency of all components within the civil aviation infrastructure. Reliability indicators are typically stochastic in nature, necessitating the development of statistical models, the application of advanced statistical data processing methods, and the enhancement of decision-making technologies, including those leveraging artificial intelligence. External influences, operational conditions, degradation of electrical components, and instability in both autonomous and external power supplies often result in nonstationary trends across the range of parameters being monitored. These dynamic changes highlight the need for advancements in traditional data processing methods, particularly in areas such as dataset formation, classification, evaluation, and forecasting. This article focuses on the development of statistical models for the downtime ratio and utilization factor, specifically addressing scenarios characterized by nonstationary trends in diagnostic parameters
Modal and random vibration analysis for structural design of aircraft external stores
No full textThis study introduces a novel methodology for the structural design of aircraft external stores, focusing on the integration of modal and random vibration analysis through the Power Spectral Density (PSD) method. The primary goal is to develop a robust design approach that enhances structural reliability and avoids resonance, a critical challenge in aerospace applications. Unlike conventional methods, this research presents a convergent strategy combining Finite Element Analysis (FEA), Computational Fluid Dynamics (CFD), and fluid-structure interaction to accurately predict stress, displacement, and frequency responses under dynamic loading. The methodology is specifically applied to external stores mounted at the fuselage station of a subsonic turboprop aircraft. A key novelty of the work is the validation of structural response through PSD-based vibration analysis, offering a high-fidelity prediction of dynamic behavior. Results indicate a close correlation between FEA and vibration outcomes, with maximum stress and deformation well within material limits and outside the aircraft’s natural frequency range, thus avoiding resonance effects. The conclusions of this study provide a roadmap for the design of aircraft stores based on modal and random vibration analysis. The proposed methodology helps to understand aeroelastic behavior, avoid resonance, resist aerodynamic forces, and prevent structural damage to aircraft external stores
Fatigue indicators for metal structures: from aircraft to bridges
No full textThe papers focus on a fatigue monitoring method for two types of engineering structures: (a) aircraft and (b) steel bridges. However, the potential application of this new approach extends beyond these examples. It is demonstrated that, despite advancements in stress-strain analysis, improvements in fatigue life prediction methods, and progress in contemporary non-destructive inspection techniques, unexpected failures of metal structures still occur. This paper outlines the evolution of Fatigue Indicators for Metal Structures, progressing from conceptual development to a family of indicators capable of monitoring fatigue damage in key structural components. These include aircraft parts made of aluminum alloys and load-bearing elements of steel bridges. All the indicators discussed share a unifying concept: the metal surface subjected to cyclic loading reflects accumulated fatigue damage. The primary parameter used to assess this damage is the intensity of the surface deformation relief (extrusion/intrusion patterns), measured using a computer-aided optical method. The conceptual design of Fatigue Indicators for both uniaxial and biaxial fatigue is explored. The required sensitivity level of the indicators is achieved through the redistribution of the strains by geometric optimization, which is carried out using Finite Element Analysis.