Vilnius Gediminas Technical University
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The Impact of the Amount of Water Used in Activation Solution and the Initial Temperature of Paste on the Rheological Behaviour and Structural Evolution of Metakaolin-Based Geopolymer Pastes
No full textThis study aimed to determine the impact of the initial temperature of the paste (from 5 °C to 35 °C) and the addition of water, which reflects a decrease in the molarity of activation solutions (AS) by diluting 10 M NaOH with distillate water, on the rheological properties of geopolymer pastes. Additionally, this resulted in changes to the physical–mechanical properties of geopolymers after curing. A higher amount of water in the AS composition and higher initial paste temperature led to an increase in the spread values up to 28% and decreases viscosity. A smaller amount of water in the AS composition and a higher initial paste temperature accelerated the speed of the geopolymer structure formation up to 1.5 times during the curing period, increased compressive strength and reduced apparent porosity and pore size. X-ray diffraction confirmed the compressive strength test results and revealed that the lower amount of water in the AS and the higher initial paste temperature for the geopolymer preparation significantly affected the mineral formation and physical and mechanical properties of the samples.This article belongs to the Special Issue Advanced Construction and Architecture 2020This research was funded by the European Regional Development Fund project, “A New Concept for Low-Energy Eco-Friendly House”, Grant Agreement No. 1.1.1.1/19/A/017
Asymmetric Compensation of Reactive Power Using Thyristor-Controlled Reactors
No full textThe thyristor-controlled reactor (TCR) compensator for smooth asymmetric compensation of reactive power in a low-voltage utility grid is proposed in this work. Two different topologies of compensator were investigated: topology based on a single-cored three-phase reactor and topology with separate reactors for every phase. The investigation of the proposed TCR compensator was performed experimentally using a developed experimental test bench for 12 kVAr total reactive power. The obtained results show that employment of separate reactors for every phase allows us to control the reactive power in every phase independently, and that the TCR compensator with three single-phase reactors is suitable for smooth and asymmetric compensation of reactive power in a low-voltage utility grid.This article belongs to the Special Issue Symmetry in Renewable Energy and Power SystemsThe paper is funded by UAB Lietpak and UAB Navitus under Grant No. 3400-S510
Rigid Polyurethane Foams Reinforced with POSS-Impregnated Sugar Beet Pulp Filler
No full textRigid polyurethane (PUR) foams were reinforced with sugar beet pulp (BP) impregnated with Aminopropylisobutyl-polyhedral oligomeric silsesquioxanes (APIB-POSS). BP filler was incorporated into PUR at different percentages—1, 2, and 5 wt.%. The impact of BP filler on morphology features, mechanical performances, and thermal stability of PUR was examined. The results revealed that the greatest improvement in physico-mechanical properties was observed at lower concentrations (1 and 2 wt.%) of BP filler. For example, when compared with neat PUR foams, the addition of 2 wt.% of BP resulted in the formation of PUR composite foams with increased compressive strength (~12%), greater flexural strength (~12%), and better impact strength (~6%). The results of thermogravimetric analysis (TGA) revealed that, due to the good thermal stability of POSS-impregnated BP filler, the reinforced PUR composite foams were characterized by better thermal stability—for example, by increasing the content of BP filler up to 5 wt.%, the mass residue measured at 600 °C increased from 29.0 to 31.9%. Moreover, the addition of each amount of filler resulted in the improvement of fire resistance of PUR composite foams, which was determined by measuring the value of heat peak release (pHRR), total heat release (THR), total smoke release (TSR), limiting oxygen index (LOI), and the amount of carbon monoxide (CO) and carbon dioxide (CO2) released during the combustion. The greatest improvement was observed for PUR composite foams with 2 wt.% of BP filler. The results presented in the current study indicate that the addition of a proper amount of POSS-impregnated BP filler may be an effective approach to the synthesis of PUR composites with improved physico-mechanical properties. Due to the outstanding properties of PUR composite foams reinforced with POSS-impregnated BP, such developed materials may be successfully used as thermal insulation materials in the building and construction industry.This article belongs to the Special Issue Environmentally Friendly Polymeric Blends from Renewable Source
Research of heat storage tank operation modes in cogeneration plant
No full textDisertacijoje nagrinėjami būdingi šilumos akumuliacinės talpos veikimo režimai, susiformuojantys nedidelės galios kogeneracinėje jėgainėje, tiriamas šiluminės stratifikacijos susidarymas tokioje talpoje ir atliekamas jos modeliavimas. Pagrindinis disertacijos tikslas – ištirti nedidelės galios kogeneracinės jėgainės šilumos akumuliacinės talpos veikimo režimų ypatumus, sudaryti algoritmą, padedantį parinkti tokios talpos tūrį ir pateikti modelį, leidžiantį nustatyti šiluminę stratifikaciją akumuliacinėje talpoje bet kuriuo jos veikimo metu.
Disertaciją sudaro įvadas, keturi skyriai, bendrosios išvados, naudotos literatūros ir autorės publikacijų disertacijos tema sąrašai bei du priedai.
Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė ir pateikiami ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema paskelbtos autorės publikacijos ir pranešimai konferencijose bei disertacijos struktūra.
Pirmajame skyriuje pateikiama literatūros apžvalga, susijusi su šilumines stratifikacijos, susidarančios akumuliacinėse talpose, veikimu ir principais, stratifikuotų akumuliacinių talpų taikymu, tūrio nustatymu ir optimizavimo metodais kogeneracinėse jėgainėse. Aptariami šių šilumos akumuliacinių talpų modeliavimo metodai. Atlikta tyrimų apžvalga leidžia nustatyti trūkstamų tyrimų sritį ir suformuoti darbo uždavinius.
Antrajame skyriuje aprašoma taikoma akumuliacinės talpos tūrio parinkimo metodika nedidelės galios kogeneracinėms jėgainėms ir pristatomas realios jėgainės modelis. Pateikiamos pusiau analitinio ir skaitinio tyrimo metodikos, skirtos temperatūros pasiskirstymo akumuliacinėje talpoje nustatymui.
Trečiajame skyriuje pristatomi šilumos akumuliacinės talpos ekonominio tūrio paieškos ir analizės rezultatai. Pateikiami susiformuojantys būdingi talpos veikimo režimai.
Ketvirtajame skyriuje aprašomas šiluminės stratifikacijos modeliavimas, naudojant skaitinį ir pusiau analitinius modelius. Atliekamas modeliavimo rezultatų palyginimas su realios kogeneracinės jėgainės šilumos akumuliacinės talpos duomenimis.
Disertacijos tema paskelbti 9 straipsniai: vienas – ISI Web of Science ir du – Inspec duomenų bazėse referuojamuose žurnaluose bei 6 straipsniai (vienas iš jų priimtas spaudai) tarptautinių ir respublikinių konferencijų medžiagose.Daktaro disertacij
Research and development of a three-stage biogas production reactor with a modified mixer
No full textDisertacijoje nagrinėjamas biodujų gamybos ir valymo nuo CO2 ir H2S procesas, naudojant biodujų gamybos reaktorius. Pagrindinis disertacijos tikslas – ištyrus vienos ir dviejų pakopų biodujų gamybos reaktorius ir pritaikius mechaninės maišyklės konstrukcijos modifikacijas, atsižvelgiant į teorinius, skaitinio modeliavimo bei eksperimentinius tyrimus, sukurti trijų pakopų biodujų gamybos reaktorių. Darbe sprendžiami keli uždaviniai. Pirmasis skirtas temperatūros nusistovėjimo anaerobinėje kameroje teoriniams tyrimams, siekiant ištirti šilumos mainų procesą. Antrasis – skirtas eksperimentiniams tyrimams, apimantiems bioįkrovos bioanglies priedų įtakos biodujų kokybei bei išeigai nustatymui. Trečiasis – skirtas trijų pakopų biodujų gamybos reaktoriaus tarpinės kameros bei modifikuotos mechaninės maišyklės eksperimentiniams tyrimams, siekiant nustatyti jų įtaką biodujų kokybei bei išeigai. Ketvirtasis uždavinys skirtas biodujų valymo sistemos eksperimentiniams tyrimams, siekiant įvertinti biodujų valymo nuo H2S ir CO2 efektyvumą. Penktasis – skirtas skaitinio modeliavimo tyrimui atlikti, norint įvertinti temperatūros pasiskirstymą biodujų gamybos reaktoriaus anaerobinėje kameroje. Šeštasis – skirtas trijų pakopų biodujų gamybos reaktoriaus kūrimui ir testavimui.
Disertaciją sudaro įvadas, trys skyriai, bendrosios išvados, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Įvadiniame skyriuje aptariamas problemos formulavimas, pristatomas darbo aktualumas, tyrimų objektas, darbo tikslas bei uždaviniai, tyrimų metodika, mokslinis darbo naujumas, praktinė darbo rezultatų reikšmė ir ginamieji teiginiai. Įvado pabaigoje pateiktos disertacijos tema paskelbtos autoriaus publikacijos bei disertacijos struktūra. Pirmajame skyriuje pateikta biologiškai skylančių atliekų susidarymo apžvalga, biodujų energinis potencialas, mikrobiologiniai anaerobinio skaidymo procesai, šilumos mainų dėsniai, biodujų valymo būdai ir reaktorių konstrukcijos. Antrajame skyriuje pateiktos biodujų gamybos proceso teorinių, eksperimentinių ir modeliavimo tyrimų metodikos. Trečiajame skyriuje pateikti tyrimų rezultatai ir jų analizė, skirti biodujų gamybos ir valymo nuo CO2 ir H2S efektyvumui įvertinti. Suformuluotos trečiojo skyriaus išvados, bendrosios darbo išvados ir pateikta rekomendacija.
Disertacijos tema yra publikuoti 8 moksliniai straipsniai: penki – mokslo žurnaluose, įtrauktuose į Clarivate Analytics Web of Science sąrašą, vienas – recenzuojamame mokslo žurnale, referuojamame kitose duomenų bazėse, du – konferencijų pranešimų leidiniuose. Gauti du Lietuvos Respublikos patentai ir paduota paraiška Europos patentui gauti. Disertacijoje aprašytų atliktų tyrimų rezultatai buvo paskelbti dešimtyje mokslinių renginių Lietuvoje ir kitose šalyse.Daktaro disertacij
Assessment of Sustainable Socioeconomic Development in European Union Countries
No full textThere are still debates in the scientific literature about the factors influencing countries’ sustainable socioeconomic development. Therefore, the current article aims at determining the factors of sustainable socioeconomic development and assessing its level in the EU countries. The following methods were employed for the research: an evaluation based on distance from average solution (EDAS) and hierarchical cluster analysis (HCA). EDAS was used to reveal which countries have the highest level of sustainable socioeconomic development, and which have the lowest. The ranking was done based on the appraisal score, which is an outcome of EDAS. Hierarchical cluster analysis (HCA) was used for clustering the countries based on the appraisal scores in order to distinguish groups of countries having a similar level of sustainable socioeconomic development. The results revealed that the highest level of sustainable socioeconomic development is in Germany, and the lowest in Portugal. Based on HCA, the countries were divided into three groups. The first cluster’s countries have the weakest sustainable socioeconomic development, and countries assigned to the third cluster have the best. In the current research, the third cluster consists of one country, Germany, which supports the results obtained with the EDAS method, i.e., Germany is the country with the highest level of sustainable socioeconomic development in the EU.This article belongs to the Section Economic and Business Aspects of Sustainabilit
Current Research Trends on Interrelationships of Eco-Innovation and Internationalisation: A Bibliometric Analysis
No full textIn this paper, bibliometric analysis is conducted on eco-innovation and internationalisation, since in the scientific literature, both research fields have been considered as being interrelated. Although the adoption of eco-innovation and internationalisation are risky processes, they reduce competitive risk and increase performance in a highly competitive business environment. The main objective of this study is to identify current research trends on the interrelationships of eco-innovations and internationalisation as well as the main areas of knowledge and to provide a general overview of research streams that can be classified using by papers, authors and journals found in the Web of Science database. In total, 1677 publications published between 1991 and 2020 related to eco-innovations and internationalisation were taken into consideration. For the visualisation of bibliographic material, VOSviewer software was used. These findings provide valuable insights by revealing the trends and highlighting the possible research streams for future investigations in the field of eco-innovations and internationalisation research.This article belongs to the Special Issue Innovation, Internationalization and Entrepreneurshi
Application of Walnut Shells-Derived Biopolyol in the Synthesis of Rigid Polyurethane Foams
No full textThis study aimed to examine rigid polyurethane (PUR) foam properties that were synthesized from walnut shells (WS)-based polyol. The Fourier Transform Infrared Spectroscopy (FTIR) results revealed that the liquefaction of walnut shells was successfully performed. The three types of polyurethane (PUR) foams were synthesized by replacement of 10, 20, and 30 wt% of a petrochemical polyol with WS-based polyol. The impact of WS-based polyol on the cellular morphology, mechanical, thermal, and insulating characteristics of PUR foams was examined. The produced PUR foams had apparent densities from 37 to 39 kg m−3, depending on the weight ratio of WS-based polyol. PUR foams that were obtained from WS-based polyol exhibited improved mechanical characteristics when compared with PUR foams that were derived from the petrochemical polyol. PUR foams produced from WS-based polyol showed compressive strength from 255 to 310 kPa, flexural strength from 420 to 458 kPa, and impact strength from 340 to 368 kPa. The foams that were produced from WS-based polyol exhibited less uniform cell structure than foams derived from the petrochemical polyol. The thermal conductivity of the PUR foams ranged between 0.026 and 0.032 W m−1K−1, depending on the concentration of WS-based polyol. The addition of WS-based polyol had no significant influence on the thermal degradation characteristics of PUR foams. The maximum temperature of thermal decomposition was observed for PUR foams with the highest loading of WS-based polyol.This article belongs to the Special Issue Performance Research of Polyurethane Foams and Composite
Enhancement of the Purcell Effect by the Wire Metamaterials Formed by the Hexagonal Unit Cells
No full textThe dependence of the Purcell factor on nanowire metamaterial geometry was analyzed. Calculations made about the Purcell factor in realistic composites, operating at an optical spectral range, are provided. We applied a metamaterial, aiming to mitigate the negative effects of absorption in metals on the Purcell effect in nanowire structures. A nanowire metamaterial was treated as an anisotropic composite in the long-wavelength limit. We investigated the mode patterns of the surface waves, propagating at the boundary separating such a structure and a dielectric material, along with the position of the peak in the local density of states, for the various filling factors of the periodic structure. By calculating the frequency dependence of the Purcell factor, we showed an increase in the peak value in comparison with the conventional plasmonic structure in the (1–100 THz) frequency range. Moreover, an optimal set of the parameters, needed to obtain the two topological transitions in the frequency range under investigation, is proposed.This article belongs to the Section Applied PhysicsThis project has received funding from the European Union’s Horizon 2020 research and innovation programme, under the Marie Sklodowska Curie grant agreement No 713694, and from the Engineering and Physical Sciences Research Council (EPSRC) (Grant No. EP/R024898/1). E.U.R. also acknowledges the partial support from the Academic Excellence Project 5-100, as proposed by Peter the Great St. Petersburg Polytechnic Universit
mNet2FPGA: A Design Flow for Mapping a Fixed-Point CNN to Zynq SoC FPGA
No full textThe convolutional neural networks (CNNs) are a computation and memory demanding class of deep neural networks. The field-programmable gate arrays (FPGAs) are often used to accelerate the networks deployed in embedded platforms due to the high computational complexity of CNNs. In most cases, the CNNs are trained with existing deep learning frameworks and then mapped to FPGAs with specialized toolflows. In this paper, we propose a CNN core architecture called mNet2FPGA that places a trained CNN on a SoC FPGA. The processing system (PS) is responsible for convolution and fully connected core configuration according to the list of prescheduled instructions. The programmable logic holds cores of convolution and fully connected layers. The hardware architecture is based on the advanced extensible interface (AXI) stream processing with simultaneous bidirectional transfers between RAM and the CNN core. The core was tested on a cost-optimized Z-7020 FPGA with 16-bit fixed-point VGG networks. The kernel binarization and merging with the batch normalization layer were applied to reduce the number of DSPs in the multi-channel convolutional core. The convolutional core processes eight input feature maps at once and generates eight output channels of the same size and composition at 50 MHz. The core of the fully connected (FC) layer works at 100 MHz with up to 4096 neurons per layer. In a current version of the CNN core, the size of the convolutional kernel is fixed to 3×3. The estimated average performance is 8.6 GOPS for VGG13 and near 8.4 GOPS for VGG16/19 networks.This article belongs to the Section Artificial Intelligence Circuits and Systems (AICAS)This research is supported by Central Project Management Agency (Vilnius, Lithuania), project
number 01.2.2-CPVA-K-703-02-0017