Vilnius Gediminas Technical University
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Influence of Hot Carrier and Thermal Components on Photovoltage Formation across the p–n Junction
No full textIn the present work we reveal the existence of the hot carrier photovoltage induced across a p–n junction in addition to the classical carrier generation-induced and thermalization-caused photovoltages. On the basis of the solution of the differential equation of the first-order linear time-invariant system, we propose a model enabling to disclose the pure value of each photovoltage component. The hot carrier photovoltage is fast since it is determined by the free carrier energy relaxation time (which is of the order of 10−12 s), while the thermal one, being conditioned by the junction temperature change, is relatively slow; and both of them have a sign opposite to that of the electron-hole pair generation-induced component. Simultaneous coexistence of the components is evidenced experimentally in GaAs p–n junction exposed to pulsed 1.06 μm laser light. The work is remarkable in two ways: first, it shows that creation of conditions unfavorable for the rise of hot carrier photovoltage might improve the efficiency of a single junction solar cell, and second, it should inspire the photovoltaic society to revise the Shockley–Queisser limit by taking into account the damaging impact of the hot carrier photovoltage.This article belongs to the Section Applied PhysicsThis work was in part supported by the Research Council of Lithuania (grant No. 01.2.2-LMT-K-718-01-0050)
Investigation and Improvement of Bond Performance of Synthetic Macro-Fibres in Concrete
No full textStrength and stiffness are the key parameters characterising the bond performance of fibres in concrete. However, a straightforward procedure for estimating the bond parameters of a synthetic macro-fibre does not exist. This study employs pull-out tests to investigate the bond behaviour of synthetic macro-fibres. Two types of macro-fibres available in the market were investigated. A gripping system was developed to protect the fibres from local damage. The experimental campaign consisted of two stages. At the first stage, 32 concrete specimens were manufactured for performing 96 pull-out tests (three fibre samples were embedded in each cube perpendicular to the top surface and two sides). Two types of macro-fibres with either 10 or 20 mm embedment length were tested. The obtained load–displacement diagrams from pull-out tests demonstrate that the bond performance (characterised by the strength and deformation modulus) of the “top” fibres is almost 20% weaker than fibres positioned to the side surfaces. At the second stage, one type of macro-fibre was chosen for further experimentation of the feasibility of improving the bond performance through the use of colloidal silica or steel micro-fibres. This investigation stage employed an additional 36 concrete specimens. The use of steel micro-fibres was found to be an efficient alternative. The success of this solution requires a suitable proportioning of the concrete.This article belongs to the Special Issue Advanced Composites: From Materials Characterization to Structural Application (Second Volume)This project has received funding from the European Regional Development Fund (Project
No. 01.2.2-LMT-K-718-03-0010) under grant agreement with the Research Council of Lithuania (LMTLT). The APC
was funded by Vilnius Tech
Development of energy efficient photovoltaic microinverter
No full textDarbe siūlomi sprendimai ir atliekami tyrimai skirti fotovoltinio mikroinverterio naudingumo koeficiento didinimui bei jo tiekiamos srovės į elektros tinklą netiesinių iškraipymų mažinimui. Sukurtas ir eksperimentiškai ištirtas energetiškai efektyvus vienos pakopos fotovoltinis tinklo mikroinverteris. Sukurtas valdymo algoritmas ir jį įgyvendinantis valdiklis tiekiamos į elektros tinklą mikroinverterio srovės valdymui.
Disertaciją sudaro įvadas, trys skyriai, bendrosios išvados, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai.
Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimai konferencijose bei disertacijos struktūra.
Pirmajame skyriuje atlikta fotovoltinių inverterių savybių mokslinių tyrimų analizė. Išanalizuoti fotovoltinių mikroinverterių veikimo principai, aptarti jų privalumai ir trūkumai, išanalizuotos mikroinverterio išėjimo srovės valdymo sistemos. Apžvelgti mikroinverteriuse naudojami nuolatinės įtampos keitikliai. Suformuluoti disertacijoje uždaviniai.
Antrajame skyriuje pateikti sukurtų nuolatinės įtampos grįžtamojo (angl. Flyback) keitiklio su alternatyvia aktyviąja viršįtampio gesinimo grandine ir dviejų raktų grįžtamojo keitiklio eksperimentiniai naudingumo koeficiento tyrimų rezultatai. Jie palyginti su klasikinio nuolatinės įtampos grįžtamojo keitiklio tyrimų rezultatais. Pasiūlytas naujas vienos pakopos fotovoltinis mikroinverteris, sukurtas naudojant du dviejų raktų grįžtamuosius nuolatinės įtampos keitiklius. Atlikti mikroinverterio naudingumo koeficiento ir išėjimo įtampos bei srovės tyrimai.
Trečiajame skyriuje pasiūlytas naujas proporcinis integralinis (PI) valdiklis su keičiamu laike proporciniu koeficientu, ištirta mikroinverterio srovės valdymo sistema su sukurtu valdikliu. Gauti mikroinverterio išėjimo srovės spektrai, įvertinti ir palyginti srovės netiesiniai iškraipymai. Ištirta mikroinverterio elementų parametrų įtaka naudingumo koeficientui. Tyrimai atlikti eksperimentiškai bei modeliuojant. Sukurto mikroinverterio naudingumo koeficiento padidinimui, patobulintas jame naudojamas grįžtamasis transformatorius.
Pagrindiniai disertacijos rezultatai paskelbti 7 mokslinėse publikacijose – 5 iš jų atspausdinti recenzuojamuose mokslo žurnaluose, 2 konferencijų leidiniuose. Rezultatai viešinti 10 mokslinių konferencijų.Daktaro disertacij
The Efficiency of Utilisation of High-strength Steel in Tubular Profiles
No full textThe use of high-strength steel (HSS) is a current trend of the construction industry. Tubular profiles are widely used in various structural applications because of their high stiffness-to-weight ratio, exceptional resistance to torsion, and aesthetic appearance. However, the increase of the strength for the same elastic modulus of the material and geometry of tubular profiles is often not proportional to the rise of the load-bearing capacity of the structural element. The obtained experimental results support the above inference. The study was based on the flexural test results of two groups of HSS and normal-strength steel (NSS) tubular specimens with a 100 × 100 × 4 mm (height × width × thickness) cross-section. Numerical (finite element) simulation results demonstrated that the shape of the cross-section influenced the efficiency of utilisation of HSS. The relationship between the relative increase of the load-bearing capacity of the beam specimen and the corresponding change of the steel strength determined the utilisation efficiency.This article belongs to the Special Issue Advanced Composites: From Materials Characterization to Structural ApplicationThe European Social Fund provided a financial support for this research within the framework of the project “Development of Competences of Scientists, other Researchers and Students through Practical Research Activities” (project no. 09.3.3-LMT-K-712)
The First Application of Nanoelectrochemotherapy in Feline Oral Malignant Melanoma Treatment—Case Study
No full textThe aim of this study was to present the first domestic animal trial of nanosecond electroporation with chemotherapy and CO2 laser surgery. Methods: sixteen-year-old domestic cat with diagnosed melanoma on oral cavity was the case used in the study. Firstly, CO2 laser surgery was used for the removal of most of tumor mass. Then nanoelectrochemotherapy with bleomycin was applied including appropriate margin of healthy tissue. A 15 ± 4 kV/cm × 15 ns pulsing protocol was employed with a total of 800 ± 100 pulses. Only one session of nanoelectrochemotherapy (nanoECT) was performed. Results and conclusions: during the next two weeks areas of focal necrosis were replaced by the granulation tissue. Complete wound healing was observed four weeks after initial treatment. After 15 weeks post treatment, no local recurrence was apparent.This article belongs to the Special Issue Spontaneous Neoplasms in AnimalsThe research was supported by National Science Centre (Poland) within a framework of SONATA BIS 6
2016/22/E/NZ5/00671; PI: J. Kulback
Pinpointing the Barriers to Recycling at Destination
No full textThis paper aims to gain further understanding of the barriers that prevent tourists at tourist destinations from recycling. Methodologically, a survey was carried out with a questionnaire, reaching 371 units through a convenience sampling procedure on the island of Gran Canaria. The measuring instruments consisted of a Likert ‘beliefs’ scale, comprising statements related to a wide range of recycling barriers, as well as both sociodemographic and situational information. Firstly, we performed an exploratory factor analysis on the barriers scale, and several obstacles to recycling were identified, such as a lack of knowledge and familiarity, blaming of the system of collection, assumed incompatibility with a relaxing holiday, erroneous beliefs about environmental usefulness, disregard towards the place being visited and a certain sense of detachment, the non-existence of incentives, and an unwillingness to comply with perceived demands. Secondly, by means of ANOVA tests, we measured the causal relationship between these barriers to recycling and the tourists’ sociodemographic and situational profiles. The practical implications shed light on how to overcome the difficulties that occur for the tourist at the destination with regards to recycling, by considering the tourists’ beliefs and their sociodemographic and situational background.This article belongs to the Special Issue Optimal Tourism DevelopmentThis research received no external funding, but the principal author is involved in the Soclimpact project.
This project subject matter consists of fighting against Climate Change in the Islands and has received funding
from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 776661
Improving Safety of Transportation of Dangerous Goods by Railway Transport
No full textThe transport of dangerous goods by rail carries a high risk of accident and every effort should be made to ensure that such transport is carried out under the best possible safety conditions. The research objective was to analyze and identify the main risks associated with the transport of dangerous goods by rail as well as to identify and assess the main factors of safe transport in order to reduce the risk of accident. For this purpose, analysis of the literature, systematization, generalization, and evaluation by experts was applied. The article states that in order to ensure the safe transport of dangerous goods by rail, it is necessary to comply with the rules for loading and unloading dangerous goods, the established requirements and instructions, and technical conditions of wagons and their labelling as well as preventive measures to reduce the risk. Recommendations are provided on how to reduce accidents and incidents in the transport of dangerous goods by rail
Analyzing the Status of Sustainable Development in the Manufacturing Sector Using Multi-Expert Multi-Criteria Fuzzy Decision-Making and Integrated Triple Bottom Lines
No full textA sustainable manufacturing company depends on the developments in three aspects in order to minimize harmful impacts on the environment, improve the social relations, and simultaneously maximize the economic benefits. Despite the increasing types of investigations that researchers have carried out in environmental and economic aspects, the minimum attention has been paid to social relations. In response to this deficiency, this paper proposes a new framework to obtain the overall sustainability index in manufacturing companies by encapsulating the sustainability criteria/sub-criteria. This article collected 33 sub-criteria for five pillars of sustainability as social, environment, economic, technological advancement, and performance management. The key contributions of this paper are highlighted as the hierarchical method that obtains the status of sustainability in uncertain conditions, the ability to identify the weak points, and a new framework for gathering the data about sustainability performance in manufacturing companies. The findings of this paper will aid both policymakers and decision-makers to assess the sustainability status of manufacturing systems and improve the performances of them.This article belongs to the Special Issue Health Environment and Sustainable DevelopmentThe work was supported by the European Union’s Horizon 2020 project H2020-MSCA-RISE-2014 CLUSDEVMED Grant No. 64573073
Reduced-Reflection Multilayer PCB Microstrip with Discontinuity Characterization
No full textIn the era of technology and communication, printed circuit boards (PCBs) can be found in a myriad of devices—from ordinary household items, to state of the art custom metrology equipment. Different types of component for wireless communications are available and come in various packages, supplied by multiple manufacturers. The signal landpads for some high-frequency connectors and components, encapsulated in larger packages, are usually wider than the controlled impedance trace, thereby introducing unwanted impedance mismatch and resulting in signal reflections. The component land pad and microstrip width a discrepancy issue can be found in both complex high-density industrial devices and system-level academic research papers. This paper addresses the topic of compensating discontinuities, introduced by signal pads, which are wider than the target impedance microstrip, characterizes the difference between the compensated and uncompensated microstrip with discontinuity, and proposes a generalized guideline on compensating for the introduced impedance change in multilayer PCBs. The compensation method is based upon carefully designing the stackup of the PCB allowing for a reference plane cutout under the discontinuity to even out the impedance mismatch. A 6-layer PCB with IT180A dielectric material containing three structures has been manufactured and characterized using an Agilent E8363B vector network analyzer (VNA). A 4–12 dB improvement in S11 response in the whole frequency range up to 10 GHz, compared to that when no compensation has been applied, was observedThis article belongs to the Section Circuit and Signal Processin
Improvement of Diagnostic Parameters of a Rolling Wheel with Flat Spot and Experimental Test on Lithuanian Railways
No full textThe JSC (Joint-Stock Company) “Railway Products Conformity Assessment Center”, under a contract with JSC “Lithuanian Railways”, carried out a rolling stock geometry and rolling surface defect risk assessment study which analyzed the principles and algorithm of the ATLAS-LG system used by JSC “Lithuanian Railways” and the system’s advantages and similarities with other systems used for rolling surface defect prediction worldwide. According to the results of this study, JSC “Voestalpine VAE Legetecha” made changes to the algorithms of its ATLAS-LG computing system and changed the parameter used to determine the damage to wheelsets. The goal of this work was to review the automatic systems of rolling stock used to evaluate the state of the rolling stock, compare the criteria for culling, describe the methodology for setting a new parameter for detecting wheel damage Pderivative instead of the previous parameter Kdm, and upgrade operational algorithms of ATLAS. This paper describes the algorithm and methodology for setting a new parameter, evaluating the construction of rolling stock and movement speed. To develop a replacement algorithm for the ATLAS-LG system, a new parameter verification methodology using the inverse Laplace transform for the mathematical model was used.The research was funded by the Vilnius Gediminas Technical University (VGTU)