Vilnius Gediminas Technical University
Vilniaus Gedimino Technikos Universitetas: VGTU Talpykla / Vilnius Gediminas Technical University: VGTU RepositoryNot a member yet
4122 research outputs found
Sort by
A New Hybrid MCDM Model: Sustainable Supplier Selection in a Construction Company
No full textSustainable development is one of the most important preconditions for preserving resources and balanced functioning of a complete supply chain in different areas. Taking into account the complexity of sustainable development and a supply chain, different decisions have to be made day-to-day, requiring the consideration of different parameters. One of the most important decisions in a sustainable supply chain is the selection of a sustainable supplier and, often the applied methodology is multi-criteria decision-making (MCDM). In this paper, a new hybrid MCDM model for evaluating and selecting suppliers in a sustainable supply chain for a construction company has been developed. The evaluation and selection of suppliers have been carried out on the basis of 21 criteria that belong to all aspects of sustainability. The determination of the weight values of criteria has been performed applying the full consistency method (FUCOM), while a new rough complex proportional assessment (COPRAS) method has been developed to evaluate the alternatives. The rough Dombi aggregator has been used for averaging in group decision-making while evaluating the significance of criteria and assessing the alternatives. The obtained results have been checked and confirmed using a sensitivity analysis that implies a four-phase procedure. In the first phase, the change of criteria weight was performed, while, in the second phase, rough additive ratio assessment (ARAS), rough weighted aggregated sum product assessment (WASPAS), rough simple additive weighting (SAW), and rough multi-attributive border approximation area comparison (MABAC) have been applied. The third phase involves changing the parameter ρ in the modeling of rough Dombi aggregator, and the fourth phase includes the calculation of Spearman’s correlation coefficient (SCC) that shows a high correlation of ranks.This article belongs to the Special Issue Multi-Criteria Decision-Making Techniques for Improvement Sustainability Engineering Processe
Estimating Conditional Value at Risk in the Tehran Stock Exchange Based on the Extreme Value Theory Using GARCH Models
No full textThis paper attempted to calculate the market risk in the Tehran Stock Exchange by estimating the Conditional Value at Risk. Since the Conditional Value at Risk is a tail-related measure, Extreme Value Theory has been utilized to estimate the risk more accurately. Generalized Autoregressive Conditional Heteroscedasticity (GARCH) models were used to model the volatility-clustering feature, and to estimate the parameters of the model, the Maximum Likelihood method was applied. The results of the study showed that in the estimation of model parameters, assuming T-student distribution function gave better results than the Normal distribution function. The Monte Carlo simulation method was used for backtesting the Conditional Value at Risk model, and in the end, the performance of different models, in the estimation of this measure, was compared.This article belongs to the Special Issue Rational Decision Making in Risk Managemen
Sustainable Business Models: A Review
No full textDuring the past two decades of e-commerce growth, the concept of a business model has become increasingly popular. More recently, the research on this realm has grown rapidly, with diverse research activity covering a wide range of application areas. Considering the sustainable development goals, the innovative business models have brought a competitive advantage to improve the sustainability performance of organizations. The concept of the sustainable business model describes the rationale of how an organization creates, delivers, and captures value, in economic, social, cultural, or other contexts, in a sustainable way. The process of sustainable business model construction forms an innovative part of a business strategy. Different industries and businesses have utilized sustainable business models’ concept to satisfy their economic, environmental, and social goals simultaneously. However, the success, popularity, and progress of sustainable business models in different application domains are not clear. To explore this issue, this research provides a comprehensive review of sustainable business models literature in various application areas. Notable sustainable business models are identified and further classified in fourteen unique categories, and in every category, the progress -either failure or success- has been reviewed, and the research gaps are discussed. Taxonomy of the applications includes innovation, management and marketing, entrepreneurship, energy, fashion, healthcare, agri-food, supply chain management, circular economy, developing countries, engineering, construction and real estate, mobility and transportation, and hospitality. The key contribution of this study is that it provides an insight into the state of the art of sustainable business models in various application areas and future research directions. This paper concludes that popularity and the success rate of sustainable business models in all application domains have been increased along with the increasing use of advanced technologies
Predicting the Frequency Characteristics of Hybrid Meander Systems Using a Feed-Forward Backpropagation Network
No full textThe process of designing microwave devices is difficult and time-consuming because the analytical and numerical methods used in the design process are complex. Therefore, it is necessary to search for new methods that will allow for an acceleration of synthesis and analytic procedures. This is especially important in cases where the procedures of synthesis and analysis have to be repeated many times, until the correct device configuration is found. Artificial neural networks are one of the possible alternatives for the acceleration of the design process. In this paper we present a procedure for analyzing a hybrid meander system (HMS) using the feed-forward backpropagation network (FFBN). We compared the prediction results of the transmission factor S21(f) and the reflection factor S11(f) , obtained using the FFBN, with results obtained using traditional analytical and numerical methods, as well as with experimental results. The comparisons show that prediction results significantly depend on the FFBN structure. In terms of the lowest difference between the characteristics calculated using the method of moments (MoM) and characteristics predicted using the FFBN, the best prediction was achieved using the FFBN with three hidden layers, which included 18 neurons in the first hidden layer, 14 neurons in the second hidden layer, and 2 neurons in the third hidden layer. Differences between the predicted and calculated results did not exceed 7% for the S11(f) parameter and 5% for the S21(f) parameter. The prediction of parameters using the FFBN allowed the analysis procedure to be sped up from hours to minutes. The experimental results correlated with the predicted characteristics.This article belongs to the Section Microwave and Wireless Communication
Transapikalinės mitralinio vožtuvo korekcijos skaitinis modeliavimas
Get PDFThis dissertation presents the numerical modeling approach for the simulation of transapical mitral valve (MV) repair procedure. The main object of the research is the development of the finite element (FE) model of the MV with ruptured chordae tendineae and its application for modeling of MV repair with neochordae implantation through the transapical approach. The dissertation aims to develop and implement a numerical model of the MV for quantitative evaluation of transapical MV repair surgical procedure and its effect on post-operative MV function. The work presents five tasks. Firstly, studies describing computational models used for investigation of MV biomechanical functions and evaluation of novel MV repair surgical techniques are reviewed. Next, the modeling strategy for the numerical simulation of virtual transapical MV repair procedure is developed. Patient-specific echocardiographic image data are obtained for the reconstruction of MV geometry and creation of structural FE model with MV prolapse. Virtual repair using different neochordal lengths is performed and the systolic function of the MV model is simulated. Finally, the outcomes of virtual transapical MV repair are evaluated and the eligibility of numerical modeling strategy is considered. The present thesis consists of an introduction, three main chapters, general conclusions, references, a list of publications by the author on the topic of the dissertation and a summary in Lithuanian. The introduction presents the research problem, the relevance of the thesis, the object of the research, formulates the aim and the tasks of the work, describes the research methodology and scientific novelty, considers the practical significance of the results and the defensive statements. Chapter 1 discusses the problem of MV prolapse from both medical and mechanical point of view. In the medical part, the anatomy and physiology of the human heart are described and thorough analysis of the MV structure is presented. In the mechanical part, an overview of studies describing computational MV models is provided and the models analyzing different MV repair techniques are distinguished. Chapter 2 introduces the modeling strategy applied for virtual transapical MV repair and its mathematical formulation. Chapter 3 presents the systolic function simulations of virtual repair procedures using two sets of patient-specific data and evaluates the parameters calculated during these simulations before and after virtual repair. The results of this dissertation were published in 4 scientific papers: two articles in journals with impact factor indexed in Clarivate Analytics Web of Science database, one article in a journal indexed in other international databases and one paper in international conference proceedings. These results were presented at 7 international conferences.Dissertatio
Control of piezomechanical microrobots moving in trajectories
Get PDFPlokštumoje judantys pjezomechaniniai mikrorobotai – tai įrenginiai, kurių judesys formuojamas atvirkštiniu pjezoefektu veikiančiais ir mechaninį judesį generuojančiais pjezomechaniniais keitikliais. Disertacijoje tiriamieji pjezorobotai neturi papildomų judesį generuojančių mechanizmų, tokių kaip ratai kojos ar panašius įtaisai, o tik tiesioginius kontakto su statine plokštuma taškus. Tokiems pjezomechaniniams mikrorobotams judesiui formuoti klasikiniai judėjimo trajektorija formavimo metodai netinka. Tokiam judėjimui reikalingas sudėtinis atskirų pjezoelektrinių keitiklių ak-tyvių segmentų valdymas siekiant nukreipti pjezoroboto judėjimą reikiama trajektorija.
Mokslinių tyrimų tikslas – sukurti ir ištirti naujus trajektorijomis ju-dančių pjezorobotų valdymo metodus ir algoritmus.
Darbe sprendžiami šie pagrindiniai uždaviniai: pjezoroboto konstrukci-jos parinkimas, pjezorobotų judesio generavimo metodų analizė, pje-zorobotų valdymo algoritmų sudarymas, aparatinės įrangos pjezorobotų valdymui parinkimas ir sistemos sudarymas, programinės įrangos, skirtos plokštumoje judantiems pjezorobotams, sukūrimas, judančių pjezorobotų trajektorijų atkartojimo tikslumo ir greičio matavimai, analizė ir valdymo metodų parinkimas konkrečioms judėjimo užduotims.
Įvadiniame skyriuje formuluojama problema, aptariamas darbo ak-tualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas ir uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, formuluojami ginamieji teiginiai. Pirmajame skyriuje analizuojama literatūra, pateikti judesio generavimo ir judėjimo tra-jektorijomis formavimo metodai. Antrajame skyriuje formuluojami pje-zoroboto judesio trajektorijos formavimo uždaviniai, nagrinėjami detalūs trajektorijų formavimo algoritmai. Trečiajame skyriuje aprašomas pje-zorobotų valdymo sistemos sukūrimas. Pateikiama sukurta valdymui skirta programinė įranga. Ketvirtame skyriuje aprašomi autoriaus atlikti praktiniai eksperimentai. Atlikta pjezorobotų trajektorijos atkartojamumo ir greičio parametrų analizė pjezorobotą valdant trimis skirtingais metodais. Pateikiamos išvados apie valdymo metodų tinkamumą pjezorobotų judėjimui trajektorijomis realizuoti. Disertacijos tema paskelbti 8 straipsniai, perskaityti 5 pranešimai Lietuvos bei tarptautinėse konferencijose.
Didžioji dalis mokslinių tyrimų buvo finansuojama LMA projektų MIP – 075/2012 ir MIP-084/2015
Didysis išgamų kraustymasis. Liūdna komedija kiaurą parą: dviejų dalių pjesė
Get PDFMikalai Rudkouski pjesėje „Didysis išgamų kraustymasis“ per ironijos prizmę bandomą pažvelgti į migracijos fenomeną globalizacijos laikais. Kūrinyje keletą istorijų vienija ta pati tema – laimės kitur paieškų kartėlis
Iš anksto įtemptais bazalto pluošto strypais armuotų lenkiamųjų betoninių elementų įlinkių analizė veikiant ciklinei apkrovai
Get PDFThe behaviour of prestressed concrete beams reinforced with non-metallic reinforcement under cyclic loading is analysed in this doctoral thesis. Review on the advantages and disadvantages of non-metallic reinforcement is provided, strength properties and the most crucial parameter values, necessary for the development of the topic of this thesis, are investigated and determined. Arguments on why and at which certain situations the use of this reinforcement can be superior compared to steel are provided. A separate experimental program is developed to determine the behaviour of non-metallic reinforcement undergoing repetitive or cyclic loading. The effect of initial prestressing level and stress range caused by the cyclic load to the final number of load cycles endured is also analysed. Moreover, the influence of cyclic loading on the mechanical properties of concrete is being investigated in this study.
The dissertation consists of introduction, three main chapters, general conclusions, the lists of references and author’s publications on the topic of the dissertation.
The introductory chapter presents the problem formulation, the relevance of the thesis and research object, formulates the aim of the study, describes research methodology, scientific novelty and practical significance of the obtained results.
Chapter 1 describes the fatigue phenomena and the main reasons causing fatigue to concrete and composite reinforcement. Besides, attention to static, cyclic creep of concrete and recommendations of the evaluation of these effects in design codes are reviewed.
Chapter 2 is dedicated generally for the description of the proposed deflection calculation method based on the principles of structural dynamics concerning cyclic creep of concrete and a possible decrease in mechanical properties of composite reinforcement due to cyclic loading. A detailed calculation algorithm of the proposed method and general assumptions are provided.
The 3rd and final Chapter describes in detail the experimental study performed investigating basalt fibre reinforced polymer bars and tests of BFRP prestressed concrete beam deflection estimation results which are compared to the proposed and other authors methods. The adequacy of proposed method is evaluated thru statistical analysis.
The topic of the thesis has been published in 7 articles: 5 – in the jour-nals with an Impact Factor, 1 – in scientific journals of other international databases and 1 in the conference proceedings referred by the Clarivate Analytics Web of Science.Dissertatio
Validation of a SPICE Model for High Frequency Electroporation Systems
No full textIn this paper, we present an analysis and a validation of a simulation program with integrated circuit emphasis (SPICE) model for a pulse forming circuit of a high frequency electroporation system, which can deliver square-wave sub-microsecond (100–900 ns) electric field pulses. The developed SPICE model is suggested for use in evaluation of transient processes that occur due to high frequency operations in prototype systems. A controlled crowbar circuit was implemented to support a variety of biological loads and to ensure a constant electric pulse rise and fall time during electroporation to be independent of the applied buffer bioimpedance. The SPICE model was validated via a comparison of the simulation and experimental results obtained from the already existing prototype system. The SPICE model results were in good agreement with the experimental results, and the model complexity was found to be sufficient for analysis of transient processes. As result, the proposed SPICE model can be useful for evaluation and compensation of transient processes in sub-microsecond pulsed power set-ups during the development of new prototypes.This article belongs to the Section Circuit and Signal Processin
Contractor Selection for Sgraffito Decoration of Cultural Heritage Buildings Using the WASPAS-SVNS Method
No full textSgraffito is an ancient decorative technique applied in walls, produced by using layers of cement plaster tinted in contrasting colours to a moistened surface. This decoration originated in Italy and has been expanded in different European cities or villages. Nowadays, this decoration technique has almost disappeared because of decomposition, inexperience, or lack of knowledge. The preservation and restoration of the sgraffito technique is the most challenging and vital task of cultural heritage buildings’ preservation. Consequently, the conservation of sgraffito depends not only on the historical and architectural knowledge, studies, and conservation projects of the cultural heritage buildings, but also demands the experience, proper qualification, and knowledge of the contractor. This paper presents six principal criteria. Three possible variants for contractor selection for sgraffito decoration of cultural heritage buildings are proposed, and six principal criteria for their evaluation are suggested. The research employs the Analytic Hierarchy Process (AHP), SWARA (Step-Wise Weights Assessment Ratio Analysis), and WASPAS-SVNS (Weight Aggregated Sum Product Assessment-Single- Valued Neutrosophic Set) methods