Vilnius Gediminas Technical University
Recent publications
Sandwich panels (SP) are very promising components for structures as they ally high levels of specific stiffness and strength. Civil, marine and automotive industries are some examples of the sectors that use SPs frequently. This work demonstrates the potential of manufacturing Z-pin-reinforced foam core SPs, using a design strategy that indicated optimal values for both pin position and angle, keeping the same pin diameter as determined in a previous study. A simple search algorithm was applied to optimize each design, ensuring maximum flexural stiffness. Designs using optimal pin position, optimal pin angle and optimal values for both parameters are herein investigated using numerical and experimental approaches. The optimal pin position yielded an increase in flexural stiffness of around 8.0% when compared to the non-optimized design. In this same comparison, the optimal pin angle by itself increased the flexural stiffness by about 63.0%. Besides, the highest increase in the maximum load was found for those composites, molded with optimized levels of pin position and pin angle, which synergistically contributed to this result. All results were demonstrated with numerical and experimental results and there was a good agreement between them.
Studying women’s entrepreneurial intentions is critical not only for encouraging women’s entrepreneurship but also for developing their entrepreneurial competencies. However, in the case of Lebanon, there is still a gap in the scientific studies related to identifying factors influencing women’s entrepreneurial intentions. In order to fulfill this gap, this research analyzes the main factors influencing Lebanese women’s entrepreneurial intentions: dominance, innovativeness, independence, and social encouragement. A scientific literature review was conducted to develop the research model and propose the research hypotheses. A survey questionnaire was prepared and distributed online to collect data from 620 Lebanese women. Then, the collected data was analyzed and presented employing descriptive statistics, inferential statistics, PLS structural equation modeling techniques, and importance-performance map analysis. The findings revealed significant relationships between the research variables except for women’s independence. Also, the findings showed that social encouragement for women partially mediates the relationship between innovativeness and women’s entrepreneurial intentions.
Public real estate is considered an integral part of national wealth. It generates a wide range of economic activities that contribute to creating and providing common public goods. This study examines the efficiency of public real estate management in Lithuania. Our findings show that public property use, disposal, and management strongly depend on the managerial approach. We apply data envelopment analysis (DEA) in addition to the income value, regression, and correlation methods. We find that there are certain biases present due to the exclusion of some state-owned properties from the public register. Furthermore, we identify the need for greater precision in the indicators used for financial reporting of state-owned assets. The excessive number of vacant asset units poses a challenge, as it requires substantial maintenance expenditures. Moreover, the appraisal of alternative use of these assets is lacking, thereby limiting the potential for maximizing public benefits. Our analysis reveals that the rental price per 1 m2 and the residual value of the leased premises are the most critical determinants influencing the management efficiency of publicly owned property. Furthermore, it is evident that the residential property is the only type of state-owned property managed efficiently within the Lithuanian public sector. These findings underscore the importance of formation of robust public real estate policies.
The Authors investigated the Aviation English proficiency levels of Vilnius Tech Aircraft Piloting and Air Traffic Control (ATC) students by considering general English examination scores, marks for Aviation English modules and proficiency levels of a specialised speaking task. The aim was to assess how well students acquire the skills and abilities not only to pass an Aviation English proficiency examination (level 4), but also to obtain a higher level 5 necessary for a longer endorsement of their language certificate. Finally, it was determined which areas of language are the easiest and most difficult to master with regards to either a level 4 or 5 according to the ICAO (International Civil Aviation Organisation) Rating scale. It was found that four out of five students have the background skills to reach at least an ICAO level 4 upon graduating, however only a fifth are able to achieve a higher level 5. The proportion of level 5 students does not match the proportion of students with good initial general English results, so there should be a greater focus on improving the language training programme by making it more challenging and broadening its scope in terms of vocabulary and grammar in particular.
Drug delivery using nanosecond pulsed electric fields is a new branch of electroporation-based treatments, which potentially can substitute European standard operating procedures for electrochemotherapy. In this work, for the first time, we characterize the effects of ultra-fast repetition frequency (1–2.5 MHz) nanosecond pulses (5–9 kV/ cm, 200 and 400 ns) in the context of nano-electrochemotherapy with calcium. Additionally, we investigate the feasibility of bipolar symmetric (↑200 ns + ↓200 ns) and asymmetric (↑200 ns + ↓400 ns) nanosecond protocols for calcium delivery. The effects of bipolar cancellation and the influence of interphase delay (200 ns) are overviewed. Human lung cancer cell lines A549 and H69AR were used as a model. It was shown that unipolar pulses delivered at high frequency are effective for electrochemotherapy with a significant improvement in ef- ficiency when the delay between separate pulses is reduced. Bipolar symmetric pulses trigger the cancellation phenomenon limiting applications for drug delivery and can be compensated by the asymmetry of the pulse (↑200 ns + ↓400 ns or ↑400 ns + ↓200 ns). The results of this study can be successfully used to derive a new generation of nsPEF protocols for successful electrochemotherapy treatments.
Computer-Aided Civil and Infrastructure Engineering (CACAIE) provides innovators a growing discussion and opinion exchange platform. It stands out from the other specialized journals by focusing on the real-world application of modern theories, placing it at the forefront of knowledge transfer from research to engineering practice. The founder and Editor-in-Chief, Professor Hojjat Adeli, described the CACAIE essence as a rigorously peer-reviewed journal publishing original computational contributions and outstanding discoveries. The shear resistance analysis of deep beams by Pak et al. (2023) motivated this discussion, digressing the central principle of the Journal, which requires a clear definition of the research problem.
In this paper, attention was focused on identifying the components of the amplitude-frequency spectrum of pressure pulsations in a hydraulic system in which an external low-frequency mechanical vibration was subjected to a proportional hydraulic directional control valve. It was observed that an operating machine or device equipped with hydraulic valves is a source of mechanical vibrations with a wide frequency spectrum. The influence of these vibrations on the pressure pulsation spectrum was analyzed, identifying the components resulting from the forcing of the directional control valve spool. In addition, it was noted that the pressure pulsation spectrum includes components resulting from the pulsation of the displacement pump output feeding the hydraulic system. A description of these spectrum components was also made and, using the solution superposition method, the components of the pressure pulsation spectrum over a wide frequency range were identified.
This study examines the impact of the morphological characteristics of plots in the Helsinki Metropolitan Area (HMA) on the retail landscape, with a focus on understanding the ways in which the morphological characteristics potentially influence the distribution, agglomeration and diversity of retail businesses. Although frequently underestimated in contemporary placemaking practices, this research emphasizes the role of the dual nature of plots as an element of urban form and an element of control over the retail landscape of the city. In this sense, the role of the morphological characteristics of plots in shaping the retail landscape of the city was investigated. The compositional (size, frontage ratio) and configurational (integration, betweenness, frequency) features of the plot in the HMA ( n = 77,736) were measured. Thereafter an unsupervised two-step clustering method was applied to reveal the subtle morphological regions through plot patterns. Computational plot characterization with open data sets yielded six plot types having different morphological characteristics and geographic distribution patterns. The spatial capacities of each plot type for retail distribution, agglomeration and diversity were then analysed and compared. This research argues that the interrelationship of the dual nature of plot plays an important role in placemaking processes. The results suggest that the spatial capacity of plots to accommodate street-based retail clusters is improved with spatially integrated, fine-grained urban fabric with independent micro-businesses involving a diversity of uses and actors. The study argues that these spatial conditions might also increase retail resilience and contribute to the vitality and viability of the retail landscape.
One of the ways to modify selected parameters of lime mortars is the use of biopolymers of animal origin, such as bone glue, skin glue, bovine blood, eggs, and casein. These are protein-based biopolymers. Casein is an example of an organic polymer produced from cow’s milk. The aim of the work was to investigate the possibilities of improving selected properties of mortars based on hydrated lime and metakaolin. The mixture was modified with powdered technical casein in amounts of 0.5%, 1.5%, 1%, 1.5%, and 2% as a partial mass replacement for the binding mixture. Additionally, the influence of increasing the amount of water on the properties of the mortar with a casein admixture of 2% was checked. This study examined consistency, shrinkage, water absorption, capillary action, porosity, flexural, compressive strength, and Young’s modulus. The admixture of casein influenced the properties of the mortar, but not in all cases, and it was possible to determine a clear trend related to the variable amount of casein. Strength properties deteriorated as the amount of casein increased. When air bubbles were introduced into the mortar after the casein was dissolved, the porosity increased as the amount of admixture increased. The moisture properties improved; namely, casein led to a reduction in water absorption and water absorption caused by capillary action. No relationship was observed between the amount of casein and the drying shrinkage. Increasing the amount of water in the mixture led to the expected effects, i.e., an increase in porosity, shrinkage, and water absorption, and a decrease in mechanical strength.
The Internet of Things has emerged as one of the most important components for fault diagnostics in industrial applications. The emergence of the digital twin has further enhanced the capability to develop and implement industrial applications more easily to simulate industrial environments. This article describes an alternate method to generate data using a digital twin of the wind generator, which can be utilized for data collection and fault diagnostics using trained predictive models. The model of the wind turbine can provide valuable information for monitoring, controlling, and predicting the wind generator’s behavior. This also helps to reduce costs for shutdowns and scheduled maintenance as the maintenance can be moved to on-demand. It also provides a platform to optimize and test out new models for wind generators before implementing them in the field. The test bench presented in the article enables implementation of different design curves for wind generators to generate data for different faults and scenarios using a servomotor. This can help in optimizing the design for wind farms that can support wind energy generation efficiently.
Choosing the pricing of a construction project and the type of construction contract from the perspective of customers is a responsible and complex process. The success of a construction project depends on the correct decisions taken in the preparation of tender documents. This process is complex, and the most mistakes are made in this phase. Disputes between customers and contractors arise during the implementation of a contract, which can have a significant impact on the success of the project. There have been a number of studies on the choice of construction project costs from the point of view of contractors when submitting commercial bids. The main objective of this study is to propose a mathematical model from the point of view of customer, and an online tool for the pricing of a construction project and for the selection of the type of construction contract. The paper analyses scientific sources, presents the algorithm of the mathematical model, the application of the mathematical model in a real construction project, draws conclusions and makes recommendations on the appropriate pricing and type of construction contract.
Construction uses different innovative solutions and advanced technologies to increase effectiveness, safety assessment, site preparation, logistic, save resources, reduce waste and reworks. One of the ways to find the best solution is introducing specific problem-based evaluation criteria and applying complex multi-criteria evaluation systems. The aim of the current research is to develop a multifaceted criteria system for evaluation of suspended veneer façade installation solutions by increasing effectiveness according to sustainability at the construction stage, including expert survey and determining relative significance (weights) of criteria. The authors suggested three groups of criteria, evaluating preparation for construction, installation and the result, each group consisting of eight criteria. Some criteria were analyzed together with the future application of decision system tools and building information modelling (BIM) for information management and data analysis. The determined criteria weights will be applied in ranking of alternative suspended veneer façade solutions by using multiple criteria decision-making methods.
Citation: Fiodorov, V.; Trusovas, R.; Mockus, Z.; Ratautas, K.; Račiukaitis, G. Laser-Induced Graphene Formation on Polyimide Using UV to Mid-Infrared Laser Radiation. Polymers 2023, 15, 4229. https:// Abstract: Our study presents laser-assisted methods to produce conductive graphene layers on the polymer surface. Specimens were treated using two different lasers at ambient and nitrogen atmospheres. A solid-state picosecond laser generating 355 nm, 532 nm, or 1064 nm wavelengths and a CO 2 laser generating mid-infrared 10.6 µm wavelength radiation operating in a pulsed regime were used in experiments. Sheet resistance measurements and microscopic analysis of treated sample surfaces were made. The chemical structure of laser-treated surfaces was investigated using Raman spectroscopy, and it showed the formation of high-quality few-layer graphene structures on the PI surface. The intensity ratios I(2D)/I(G) and I(D)/I(G) of samples treated with 1064 nm wavelength in nitrogen atmosphere were 0.81 and 0.46, respectively. After laser treatment, a conductive laser-induced graphene layer with a sheet resistance as low as 5 Ω was formed. Further, copper layers with a thickness of 3-10 µm were deposited on laser-formed graphene using a galvanic plating. The techniques of forming a conductive graphene layer on a polymer surface have a great perspective in many fields, especially in advanced electronic applications to fabricate copper tracks on 3D materials.
BACKGROUND: Healthy children’s gait support patterns play a critical role in their development and overall well-being. Therefore, in order to develop a correct gait, it is necessary to constantly update knowledge. OBJECTIVE: To identify differences in gait support among children in neighbouring countries. METHODS: 44 healthy children from Poland and Lithuania (4–11 years old) participated in the study. The spatiotemporal and plantar pressure parameters of 88 neutrally aligned feet were analysed and compared. RESULTS: Statistically significant differences between stance, single-limb support, double support, swing duration, cadence, and velocity, max. force and pressure in the forefoot, as well as in the times of occurrence of max. forces in all three zones. Defined that age is related (p< 0.05) to cadence (R= 0.32), swing phase (R= 0.53), max. force under the midfoot (R= 0.35) and the heel (R= 0.47), max. pressure under the forefoot (R=-0.52), midfoot (R=-0.63) and heel (R=-0.47). CONCLUSION: The results can help caregivers, as well as clinicians and researchers, understand how gait mechanics change with development and the growth course of the children of that country. Also, the results are important for the analysis and comparison of children’s gait, as control reference data from the same country.
BACKGROUND: Understanding the mechanical properties of aortic tissue is essential for developing numerical computation tools and assessing the risk of aortic aneurysm fractures. Tensile tests using aortic wall specimens allow for the determination of stress and strain depending on the location and direction of the sample. OBJECTIVE: The aim of this study was to perform a mechanical tensile test using canine aorta samples and create a numerical model of aortic tissue tension from the processed data. METHODS: Dogbone-shaped samples were dissected from canine aortic segments. The initial measurements were made at zero tension and the tensile tests were conducted at 10 mm/min until rupture. Force and stretch data were used to obtain engineering and true stress-strain curves. The true stress-strain curves were taken until the maximum strength was obtained, after which they were smoothed and fitted using a logistic function with three coefficients. These curves were then used as material mechanical properties for a numerical model of the aortic tissue tension. A simplified rectangle form was used to mimic the middle of the dogbone-shaped portion of the tissue specimen. Experimental displacement data were collected for the boundary conditions of the finite element 3D model. RESULTS: The experimental data processing revealed that the logistic function described the nonlinear behaviour of the aorta soft tissue with an accuracy of 95% from the start of the tension to the media layer rupture. By applying numerical simulations, we obtained a correspondence of the load curve with an RMSE = 0.069 for the theoretical and experimental external tension data. CONCLUSION: The numerical investigation confirmed that the non-linear soft tissue was validated by applying a logistic function approach to the mechanical properties of the aortic wall.
Waste Tyre Textile Fibres (WTTF) are one of the main components of end-of-life tyres. During the recycling process, it is been separated from the rubber and the metal parts. According to the EU Directive on Landfills 1999/31/EC end-of-life tyres may not be accepted by the facility, and it is encouraged to recycle them. Rubber has been successfully recycled and reused for asphalt and playground surfaces production, while metals could be remelted and used again. However, there is a lack of knowledge how to use WTTF. In this research we are proposing WTTF composite material for sound absorption applications. To bind the fibres, polyurethane resin was used. Different percentage by weight of binder was used to determine its’ effect on sound absorption coefficient. The sound absorption coefficient determination method is based on the experimental data based on the ISO 10534-2 standard, and Delany-BazleyMiki (DBM) acoustic prediction model of fibrous materials, using non-acoustic parameters of the material. The results showed that DBM model accuracy rate varied from 4.9 to 12.7%. Such result indicated that DBM acoustic model has errors in prediction. The aim of this study is to predict the sound absorption coefficient using Delany-Bazley-Miki acoustic model and compare to the experimental study using impedance tube.
Metakaolin (MK), which is of higher fineness than cement, is an emerging supplementary cementitious material for the production of high performance concrete. Silica fume (SF), which is of even higher fineness, has been used widely for the production of high strength concrete or ultra-high strength concrete. Very often, either MK or SF is being added to the concrete mix alone. Theoretically, they can also be added together but there are relatively few trials. In this study, the possible synergistic effect of MK and SF on strength of mortar phase of concrete was evaluated. For this purpose, mortar mixes containing varying MK and SF contents at four different water/cementitious materials (W/CM) ratios were prepared and tested. Experimental results show that both MK and SF can improve strength; moreover, the co-addition of MK and SF has synergistic effect in increasing strength over the sole addition of MK or SF at the same cement replacement ratio.
Layered concrete structures provide many benefits in construction of a new project and repair, strengthening of already existing structures. However, this type of structural member has a vulnerable point, which is the interface between the layers. If the stiffness of the interface between the layers is not sufficient, the structure might fail at the interface and the layers might slip relative to each other. Interface behaviour is a complex process, which is yet to be fully understood. This article presents a theoretical method for analysing the behaviour of the interface. Using this method, an analysis of experimentally tested specimens, which were tested by other authors, was conducted. After the results of the analysis, it was confirmed that the proposed theoretic method is an appropriate tool for analysing the interface. Additionally, a parametric analysis was carried out by changing the values of concrete strength and connector ratio. Lastly, using the determined values of shear stress and slippage, a shear stress modulus for experimental specimens was calculated.
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4,494 members
Vasarevicius Saulius
  • Department of Environmental Protection and Water Engineering
Stanislav Dadelo
  • Faculty of Creative Industries
Jolanta Sereikaite
  • Department of Chemistry and Bioengineering
Eugenijus Kurilovas
  • Department of Information Technologies
Romualdas Bausys
  • Department of Graphical Systems
Saulėtekio al. 11, LT–10223, Vilnius, Lithuania
Head of institution
Rector Alfonsas Daniūnas
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