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The scope of the Nordtest method is to evaluate the moisture buffer value (MBV) of materials exposed to indoor air. The test is intended to simulate daily variations with relative humidity (RH) between 75 % during 8 hours and 33 % during 16 hours. The specimens follow a recipe that consists of waste paper, glue and water. Specimens made of paper plaster were covered with different colours. The results of the experiment showed that the type of paint used and the number of layers applied affected the MBV. Natural colours have a better moisture permeability than chemical paints, but the number of natural colour layers affects the MBV. The higher the number of layers, the lower the MBV. [ABSTRACT FROM AUTHOR]

The paper proposes a method of simultaneous reconstruction of the electrical conductivity and magnetic permeability profiles of planar metal research objects based on the results of single measurements by eddy current probes using surrogate optimization techniques in a reduced compact subspace design and accumulating the full amount of the most important a priori information about the modes of electromagnetic objects. In addition to the information on the response of probe signals to changes in electrophysical parameters, a priori information includes the data on multifrequency sensing and changes in the lift-off between metal research objects and eddy current probes. All the main stages for the implementation of the method of solving the inverse problem are demonstrated, namely, creating a uniform computer quasi-design of the experiment with improved 2D-projections based on LPτ-Sobol's sequences; creating surrogate models on fully connected deep neural networks; reducing the dimensionality of the full design space using the principal components method of PCA; reconstructing profiles as a result of surrogate optimisation in a compact subspace. Numerical examples of the method are also presented in the paper. [ABSTRACT FROM AUTHOR]

Standards are critically important for smartening the grid because they affect the interoper-ability, compatibility, efficiency, and realisation of new technologies and services. In this paper we assess the contribution of EU funded Horizon 2020 projects to adapting or initiating new Smart Grid standards. We provide a comprehensive overview of the Smart Grid standardisation ecosystem and identify opportunities for researchers and innovators to participate in stan-dardisation activities. We identify 225 Horizon 2020 Smart Grid projects and explore which have contributed to the creation or revision of Smart Grid standards. We identify the type of standardisation activities undertaken and explore the factors that influence engagement. We have found that 21 % of EU Horizon 2020 Smart Grid projects engage in some level of standardisation activities. Of these projects the majority (60 %) are involved in understanding standards, 31 % actively engage in influencing standards, while 8 % successfully participate in elaborating new standards. Our study demonstrates that despite the complexity of the Smart Grid Standardisation ecosystem, EU funded researchers and innovators play an important role in the standardisation process. [ABSTRACT FROM AUTHOR]

The paper demonstrates a spectrum slicing technique applied to PAM-4 modulated signal spectrum at 40 Gbaud baudrate for optical access networks. The spectrum slicing is shown in VPIphotonics simulation environment, where characteristics of key components are measured in the laboratory and loaded into the corresponding elements of the simulation setup. The spectrum of electrical baseband signal is sliced in four slices introducing an additional degree of freedom – higher data rate signals can be transmitted by re-using already-existing lower bandwidth transceiver components in an optical access network. This tackles the electronic bottleneck enabling the on-demand variable bandwidth allocation and extends the life span of opto-electrical components during network upgrades. Furthermore, the use of the proposed spectrum slicing technique has a positive side-effect when it comes to security concerns, as the signal spectrum is divided into slices. All slices are necessary to obtain the reconstructed signal and even if an eavesdropper gets most of the slices it is still not enough. The simulation results show that the proposed spectrum slicing and stitching approach is a viable solution to overcome the problem of limited frequency bandwidth of electrical components. [ABSTRACT FROM AUTHOR]

The paper investigates the process of phase separation and morphology of organic-inorganic interpenetrating polymer networks (OI IPNs) based on the cross-linked polyurethane (PU), poly(hydroxyethyl methacrylate) (PHEMA) and poly(titanium oxide) (–TiO2–)n obtained by solgel method in the presence of poly(oxypropylene glycol) (POPG) at various molar ratio of titanium (IV) isopropoxide (Ti(OPri)4) and water. It has been established that the phase separation in OI IPNs depends on the kinetics of PHEMA-component formation and it occurs through the mechanism of the spinodal decomposition. It has been shown that by varying the ratio of IPNs components, content of inorganic component and Ti(OPri)4/H2O molar ratio it is possible to control the phase separation process and obtain OI IPNs with a different phase structure. [ABSTRACT FROM AUTHOR]

Hydrogen has been widely recognised as a versatile and environmentally-friendly energy carrier, with a broad range of potential applications across various sectors. The abundance of hydrogen in the universe and its high energy content makes it an attractive alternative to conventional fossil fuels. Moreover, the utilization of hydrogen does not produce greenhouse gases or other pollutants that contribute to air pollution and climate change. In recent years, there has been a growing interest in developing and deploying hydrogen technologies for a sustainable energy future. This paper provides an in-depth exploration of the potential of hydrogen as a clean energy source in different sectors, such as transportation, energy storage, power generation, industry, buildings, maritime transport, and aviation. The aim of the paper is to provide an overview of the current state of hydrogen applications in Europe and the Baltic States, including examples of ongoing projects and initiatives, and to assess the advantages and disadvantages of hydrogen technologies in different sectors. The main results of the paper highlight that hydrogen has the potential to significantly reduce greenhouse gas emissions and achieve carbon neutrality targets. However, the deployment of hydrogen technologies also faces various challenges such as high production costs, lack of infrastructure, and safety concerns. The tasks of the paper are to provide an insight into the potential of hydrogen, identify the challenges and limitations, and highlight ongoing research and development efforts in this field. The paper concludes that the widespread adoption of hydrogen technologies is a long-term goal that requires the cooperation of various stakeholders and the development of innovative and cost-effective solutions. Despite the challenges, the current state of hydrogen applications and ongoing projects in Europe and the Baltic States demonstrate that hydrogen has the potential to play a significant role in the transition to a sustainable and low-carbon future. [ABSTRACT FROM AUTHOR]

The introduction of hydrogen and natural gas blends in existing gas transportation and distribution networks would ensure faster and more efficient decarbonization of energy sector, but, at the same time, this process would request solution of many practical and technical problems. This paper explores thermodynamics of hydrogen and natural gas blend combustion products and estimates the amount of condensate and latent energy recovery from flue gas as a function of condensing temperature. The efficient energy recovery depends on network return temperature, and it is possible to overcome this limitation by implementation of heat pump for extraction of low temperature heat from flue gases. The case study considers operation of heat only boiler and flue gas condenser with integrated cascade of heat pumps, which consist of absorption lithium bromide-water chiller (in heat pump mode) and vapour compression unit. Presented results of energy recovery hence are limited by data collected from the natural gas combustion for district heating network energy supply. However, previous thermodynamic consideration allows extending the obtained results for case of hydrogen and natural gas blend combustion. A proof of concept of heat recovery by combination of flue gas condenser supported by a cascade of heat pumps demonstrates the efficiency in case of hydrogen and natural gas blend combustion. [ABSTRACT FROM AUTHOR]

Meeting the challenges of the energy sector relies on data – in particular sharing it internally and externally with a wide range of partners. Unfortunately, this valuable data often cannot be obtained from real objects due to location specifics or privacy concerns, although accurate, open-source data are a priority to provide researchers and energy experts with the information needed to accelerate the energy transition. In recent years, many studies have focused on the development of energy communities, using different methods to create data for case studies; however, these methods are often too broad and do not correlate with conditions in real locations. This work aims to identify the challenges associated with creating realistic datasets for energy community studies, as well as highlight the methods of defining input data, considering the factors that make energy community studies a very complex task, and discuss the flaws of commonly used methods. [ABSTRACT FROM AUTHOR]

The paper presents the results of standard specimen fracture made of anisotropic carbon fiber plastic with an epoxy matrix. Static stepwise loading of the specimen was carried out on an Instron 8801 testing machine to determine the characteristics of ductile fracture G1C in the first mode in accordance with ASTM D5528. During loading, the parameters of acoustic emission (AE) signals, such as AE impulse amplitudes and their energy were synchronously recorded. At the same time, the magnitude of the opening and the growth of the crack initiated by the artificial cut at the end of the specimen were recorded. According to the analysis of the acoustic emission signals, three zones with different G1C behaviour were identified: initial crack propagation, its stationary growth and accelerated fracture of the specimen. The zonal character of the change in the acoustic emission signals made it possible to determine the energy of the acoustic emission signals as diagnostic evidence for the onset of rapid destruction of the specimen. The amplitude of the AE-signals in the zones, however, remained constant. Online monitoring of changes in the energy of acoustic emission signals will prevent the onset of rapid destruction of an object in places of its deformations. The paper does not aim at defining G1C as usual. It presents the investigation of the fracture stages for a composite material using an acoustic emission method. [ABSTRACT FROM AUTHOR]

The paper focuses on the numerical analysis of the mass transfer of impurities from the wavy surface of molten silicon to the gas phase. The mathematical model is described herein, with the modelling of a wavy silicon melt surface being done with the moving mesh technique. The model employs assumptions about the mass transfer process on the surface, namely, that it can be modelled with effective diffusion across the interface. The assumption is verified against limited experimental data for a stationary melt surface, and reasonable agreement is obtained. Thereafter, numerical studies are undertaken for a wavy melt surface. The dependence of impurity removal rate on the wave amplitude, wavelength and frequency is analysed. It is shown that the waves on the surface of the liquid increase the mass transfer rate in a certain parameter range. Finally, results are analysed to find an explanation for this increase and to determine technological factors that impact it. Surface enlargement due to waves and altered flow patterns near the silicon melt are determined as potential reasons for the improved impurity removal rate. A dimensionless criterion for the minimal wave amplitude required to obtain improved impurity removal is found and discussed. [ABSTRACT FROM AUTHOR]

It is almost impossible to name a field of human activity where porous materials are not used. Filters, membranes, thermal insulators, fuel cells, catalysts, wicks of heat transfer devices, sorbents, textiles, and other examples of porous materials explain such an increased interest in the study of their properties, design of new materials, and development of technologies for their manufacture. The recent need for in-orbit spacecraft refuelling has led to the development of gas thermal compression technology based on the use of porous material as both a fuel retention mechanism and thermal interface. The present paper reveals the thermal aspects of porous material design for a device intended for pumping xenon, fuel for ion thrusters, in zero-gravity conditions – Xenon Refuelling Compressor. [ABSTRACT FROM AUTHOR]

This study analyses a turbine flow meter in the context of a hydrogen compressor system. Basic concepts of turbine flow meter, accuracy and linearity, as well as calibration are described. Physical experimental testing scheme is presented in the paper. The viscosity of the fluid is one of the major factors that affects the performance of turbine flow meters. Numerical modelling experiments for different fluids with different viscosities are performed. Performed numerical modelling experiments give a possibility to continue research into the hydrogen compression system. [ABSTRACT FROM AUTHOR]

A partial solar eclipse occurred on 25 October 2022, in the central and northern parts of Europe. The partial solar eclipse was observed at Aalto University Metsähovi Radio Observatory, Finland at the radio wavelength of 8 mm (37 GHz). In Finland, the magnitude of the partial solar eclipse was 62.7 %. Solar radio maps at the time cadence of about 9 minutes were observed over the whole eclipse. The solar eclipse observations could be used for instrument calibration purposes. This paper investigates the solar brightness temperature, the limb brightening effect, the height of the chromosphere and the location of radio brightening using the aforementioned partial solar eclipse observations. We got the confirmation that our earlier results are consistent, e.g., the solar brightness temperature matches with 8100 K ± 300 K. It was also possible to detect limb brightening effect. However, the prevailing solar activity might have distorted the final conclusions. The Moon should operate as a focusing element and the location of radio brightenings could be defined more carefully than in the normal conditions. We investigated this feature. Our results are in some parts unexpected and need further investigations. [ABSTRACT FROM AUTHOR]

The article is devoted to the study of the mechanism of nanopore formation in the junctions of polycrystal grains under the plastic deformation of a polycrystal due to the conservative sliding of lattice dislocations. A mechanism for the formation of a stress concentrator at the junction of the polycrystal grain boundaries is proposed. The possibility of relaxation of the stress state due to the formation of a junction nanopore is considered in the paper. [ABSTRACT FROM AUTHOR]

Near–dry machining and dry machining lead to increased temperature of the cutting tools. To reduce tool wear and extend the tool lifetime, and, eventually, to keep the accuracy of manufactured parts within acceptable limits as long as possible, a sustainable cooling technique is required. The technology of internal cooling of the cutting tool appears to be the most promising, because it allows eliminating the presence of the coolant on the manufacturing part and delivers the heat–transferring fluid to the very cutting area of the tool. This paper provides a literature review on the closed–loop internally cooled cutting tools (CLICCT) for turning. The current level of knowledge and experimental machining with prototypes has proven that CLICCT can utilize the benefits of dry cooling, having a longer tool life. [ABSTRACT FROM AUTHOR]

A simplified life cycle of any product or service consists of three main stages – manufacturing, including obtaining, transformation, combination of raw materials; transportation, as well as packaging; consumption from purchase up to actual use. Energy is not an exception, it is also an item offered by the market in different forms, and everyone in need of it has the right to buy it in case the price is acceptable. Heat power is one of the energy types required by households and important for proper maintenance. Without heating, as well as electricity, modern houses cannot function appropriately, are not attractive to their inhabitants, do not provide comfort and safety. Nevertheless, heat power often is considered as a by-product of electricity production, nowadays a swift price increase for both types of energy is inevitable. Energy efficiency is the level of appropriate usage of energy resources, which can be determined as the relation between final product type, quality, quantity and consumption of energy necessary to create this product [1]. Indirectly energy efficiency impacts health of the society in general and each individual in particular. Renovated energy efficient apartment buildings have a better ventilation system and microclimate. The problem of moisture and mold is at least partly solved, comfort is reached by consuming less energy, especially, heat power [2]. The aim of the paper is to research the impact of different energy efficiency increasing measures on heat consumption in multi-apartment buildings. [ABSTRACT FROM AUTHOR]

The paper presents a lifetime consumption estimation model of 6 degrees of freedom industrial robot arm. The primary goal of the research is to provide estimated lifetime data of semiconductor power modules of robot axis power supply circuit, providing new opportunities for cost-saving, predictive maintenance, with highly customized input for different manufacturing applications. Evaluation of thermal stress and estimation of isolated gate bipolar transistor current are completed, based on MATLAB model translating KUKA robot program code to electrical energy consumption, which is a novel approach. Energy losses are considered in the model to provide accuracy of the inverter load current. The simulation results prove that lifetime consumption depends on a robot application type, for more agile movement programs with large power amplitudes, such as handling, the degradation in power modules is significant compared to slower applications, such as gluing or welding. Various options for future development are suggested and considered in the paper. [ABSTRACT FROM AUTHOR]

With an emphasis on the visual appearance of buildings, surface and internal gas pipelines are being built into structures and walls, which can affect system serviceability and occupant safety. When placing gas pipelines in a closed room (shafts, ducts, facade structures, etc.) there is a risk that in case of leakage, natural gas will accumulate in the room, which together with the ambient air, within the specified concentration limits, forms an explosive mixture. The present paper analyses the built-in internal gas pipeline systems, their installation norms, operation and maintenance problems in different types of buildings. It is shown that requirements do not cover all possible gas pipeline installation options. The analysis of the gas supply system operator shows that non-compliance with the applicable norms has been identified in every third of the 400,000 gas consumers in Latvia in the surface and internal gas pipeline system. To improve and develop safety requirements, it is planned to perform an experiment that is described in detail in this paper. Pre-experimental calculations are made to set reference points in the study and find the main influencing parameters on gas leakage process. [ABSTRACT FROM AUTHOR]

The study focuses on the development and evaluation of a motion control system for the Large Range Robotic Motion Simulator (LaRRMoS), which is based on a serial manipulator with 6 degrees-of-freedom. Two motion cueing algorithms (MCAs) – Classical Washout Filter (CWF) and Classical Washout Filter with Cylindrical coordinates (CYL) – are implemented and tested for simulation fidelity and LaRRMoS workspace utilization. CWF and CYL motion cueing performance gets assessed in two use cases: car simulation and luge sports simulation. The car case is a typical driving simulator application. The luge sports case is chosen for its high dynamics to assess the limits of the robot and motion cueing. Though this study uses a pre-recorded set of motion data and runs simulations in non-interactive mode, it aims for real-time interactive simulation for LaRRMoS in the future, so only MCAs capable of real-time operation are inspected. Conducted tests show that the CYL algorithm provides superior performance in highly dynamic motion replication, particularly in lateral accelerations. [ABSTRACT FROM AUTHOR]

An approximate method for analysis and synthesis of moving rigid bodies (prisms) in the airflow without using numerical methods of space-time programming techniques is described by applying a fluid (air)–rigid solid body interaction concept for engineering applications through a straightforward mathematical model. The interaction of rigid body (prism) and air is encountered in different cases: moving body (prism) in the air; stationary bodies (prism) in the airflow; moving body (prism) in the airflow. The complicated task of rigid body (prism) and air interaction is simplified by using superposition principles, i.e., by taking into account the upstream and downstream rigid body (prism) and air interaction phenomenon, which has been found to be different under varying speeds. Numerical results obtained for various forms of prisms are shown for constant air–speed, where the steady state Reynolds-averaged Navier–Stokes (RANS) equation is solved by using k-ε realizable turbulence model. A detailed explanation to support the proposed approximate method is given by using numerical results obtained in ANSYS computations. All equations are formed based on laws of classical mechanics; the interaction of viscous forces is neglected in forming the mathematical model. Numerical results for different model prisms are compared and the theoretical results discussed in detail. The mathematical model in the present paper is applicable only to bodies that undergo a rectilinear translation motion. In the final part of the present paper, the proposed method is used in the synthesis and optimization task of energy extraction by considering the motion of a variable parameter prism in the airflow. [ABSTRACT FROM AUTHOR]

The paper covers the main aspects and restrictions on siting small-scale wind farms in Latvia and benefits of using energy storage systems with small-scale wind farms. The restrictions of siting have been analysed. Grid connection restrictions are addressed as the main issues for small-scale wind farm development in Latvia. Two small-scale wind farm models with similar properties have been made and analysed within the framework of the research. The paper proposes the idea for maximising the production of small-scale wind farm in a small area site with high wind potential. [ABSTRACT FROM AUTHOR]

The paper describes the design and control method of the synchronous reluctance machine with improved efficiency compared to traction induction motor for electric vehicle application. Magnetic field finite element modelling is used in the design process. The paper presents load characteristics calculation method for the design process, considering the cross magnetic saturation effect. Control algorithm with constant d-axis current control method is developed in the research. The prototype of the machine is constructed and tested. [ABSTRACT FROM AUTHOR]

The paper covers the main aspects of designing a low voltage three-phase PWM rectifier for bidirectional AC/DC power flow with unity power factor. A model in Matlab/Simulink environment has been built for a 10kW active rectifier with an LCL filter connected to grid side of the rectifier. The primary goal of the model is to achieve low grid current harmonic content for frequency ranges described in worldwide applicable standards and above. LCL filter parameter design procedure is described in the paper and implemented in the rectifier model to achieve a better power quality with limitations in passive element size. A simple "p-q" theory-based voltage oriented control algorithm is used in the model and described in the present paper. Model performance is characterised by dynamic response, stability and grid parameters during simulation. The simulation results demonstrate that the modelled rectifier system is stable and the grid current harmonic content is low both in the low-and high-frequency ranges. [ABSTRACT FROM AUTHOR]

Four-wave mixing optical frequency comb fibre-based setups (FWM-OFCs) have the potential to improve the combined dense wavelength division multiplexed passive optical network (DWDM-PON) and fibre Bragg grating (FBG) temperature sensors network providing easier application, broader technological opportunities for network development, and energy efficiency by substituting a power-demanding laser array. In this research, OFCs are generated for the purpose of combined network application of DWDM-PON and FBG optical sensors. The paper also investigates compatibility scenarios with OFCs in such systems. The mathematical simulation model has been developed and the performance of FWM-OFC based 8-channel 50 GHz spaced non-return-to-zero on-off keying (NRZ-OOK) modulated DWDM-PON transmission system, operating at 50 km single-mode fibre (SMF) with a bit rate of at least 10 Gbps embedded with 7 FBG optical temperature sensors, has been studied. As it is shown, FWM application results in OFC source that has fluctuations of the individual comb tones of less than 3 dB in power, and with an extinction ratio of about 33 dB for operation range of 192.9–193.25 THz, acting as a unified light source for all the data transmission channels. Embedded FBG optical sensors network causes negligible 0.3 dB power penalty. [ABSTRACT FROM AUTHOR]

The present paper provides the dependence of the temperature change on time and the depth of the soil massif based on numerical calculations. Mathematical modelling of the one-dimensional soil temperature field via an algorithm and a PC program is carried out without taking into account the influence of the phase transition of moisture in the soil pores during seasonal freezing and thawing using the finite difference method. The amplitude of fluctuations in the temperature regime is obtained as that decreases with depth from the soil surface. It is established that over time heat spreads from the pipeline to the surface of the soil, and over time more intense heating occurs both near the pipeline and in the body of the soil massif. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive transmission line fault location method, which incorporates fault location devices at both line ends and utilises data import from a supervisory control and data acquisition system without strictly requiring data synchronisation. The developed method aims at achieving a higher degree of robustness, adaptiveness and accuracy. The adaptiveness is achieved by dynamic updating of mathematical models used on the basis of network-wide information, such as data on the state of circuit-breakers and apparent power at load and generation nodes. The robustness and accuracy are enhanced by incorporating two stages of identification of model parameters with the goal of reducing the decision variable space for the stage identifying fault parameters. Furthermore, in addition to utilisation of all measurements available at a particular substation, the developed method partially employs the measurements from the other end of the line by means of result cross-checks, but does not require a full data set, unlike deterministic-model-based methods. An optimisation-based approach, redundancy on the basis of extended measurement set, and cross-checks reduce the risk of fault location errors due to measurement errors or "voids" in the data available. Testing of the developed method demonstrates its accuracy and robustness in a wide range of pre-fault and fault regime scenarios, even when considering various pre-fault contingencies. [ABSTRACT FROM AUTHOR]

Artificial intelligence is widely spreading in all modern technologies. Such a very powerful methodology can have important applications in radio astronomy technology, for instance, in the new DBBC4 VLBI backend development project and in the low frequency array AntArr under development on the Etna slopes in Italy. In the present paper, we describe the method currently adopted for those projects and some possible applications, which could provide substantial new features in this decade to the radio astronomy science and technology. [ABSTRACT FROM AUTHOR]

The aim of our paper is to evaluate the maximum Shannon (syntactic) information carried through a video lecture. To achieve the aim, we have considered a natural lecture delivered by a lecturer as a signal transmitted over the physical communication channel consisting of a sound sub-channel and light sub-channel. Receivers are eyes and ears of listeners whose physical characteristics are taken into account. The physiological, neurological and cognitive aspects of the problem are neglected in calculations. The method has been developed to calculate the absolute maximum values of Shannon information characteristics of a natural lecture basing on the capacity formula of continuous communication channel and physical considerations taken into account for the first time, to our knowledge. Maximum Shannon information characteristics (entropies of sound and light frames, amounts of total acoustical and optical information, capacities of sound and light sub-channels, total amount of information and total capacity) of a natural lecture perceived by the audience have been calculated. These values are the upper bounds of a video lecture. The obtained results are discussed in the paper. After some modification, the proposed method can be practically applied for the optimization of both natural and video lectures because there is some correlation between syntactic and semantic information characteristics. [ABSTRACT FROM AUTHOR]

The 694–790 MHz band (700 MHz) known also as the second digital dividend was allocated to the mobile radiocommunication service on a primary basis in Region 1 and identified to International Mobile Telecommunications by the World Radiocommunication Conference 2012 (WRC-12). The designation of mobile service in Europe and other countries of Region 1 in 700 MHz band was obtained after the World Radiocommunication Conference 2015 (WRC-15). Administrations of Region 1 will be able to plan and use these frequencies for mobile networks, including IMT. The goal of this study is to estimate the electromagnetic compatibility of Digital Video Broadcasting – Terrestrial (DVB-T/DVB-T2) and LTE (Long Term Evolution) technology operating both in 700 MHz band. The study assumes frequency division duplex (FDD) channel arrangement of 703–733 MHz (for uplink) and of 758–788 MHz (for downlink). The model contains two parts: a DVB-T/DVB-T2 system and LTE mobile broadband network. Co-channel scenario is considered in this paper, and possible impact of DVB-T/DVB-T2 on LTE base stations (receivers) is also investigated. The Monte Carlo simulations within SEAMCAT software and the Minimum Coupling Loss (MCL) method are used for interference investigation. The coordination trigger field strength value predetermined by GE06 Agreement is also used in this study. The Monte Carlo method presents more relaxed electromagnetic compatibility scenario in comparison with the MCL method. For SEAMCAT simulations, ITU-R P.1546-5 radio propagation model is used. The obtained results present the required minimum separation distance between DVB-T/DVB-T2 and LTE networks in the 694–790 MHz in order to provide the necessary performance of LTE mobile network. [ABSTRACT FROM AUTHOR]

In this paper, we study by numerical simulation, the cooling of a solar photovoltaic panel using a nanofluid as a cooler. The solar panel is subjected to a hot temperature that character-ises the climate of the city of Bechar located in southwestern Algeria. The nanofluid (Al2O3-water) is introduced in the cavity with a constant horizontal speed and subjected to the ambient (cold) temperature. The equations governing the hydrodynamics of the flow and the heat transfer are described by the Navier-Stockes and energy equations. The finite element method is used to solve the system of partial differential equations (PDEs) based on the Galerkin method. We consider the effect of solid volume fraction and form factor for different values of Reynolds number on the results in the form of isotherms, streamlines, temperature, velocity, average Nusselt numbers and solar panel efficiency. [ABSTRACT FROM AUTHOR]

Autonomous off-grid systems might be seen as a favourable option when it comes to high grid connection fees and for a sustainable electric system in transition to a low-carbon, renewable-based decentralized system. To ensure such a system, accurate analysis of different scenarios is required to determine the optimal energy source mix and sizing of the off-grid system. Software computing techniques or mathematical models can help solve this task, but, unfortunately, it is unpredictable how actually such systems will perform in real life. There are not so many publications, where the real data and off-grid systems are analysed and compared to simulation results. Thus, this paper examines an experimental stand-alone electrical off-grid solution in Latvia. The operational data of real autonomous off-grid system are obtained for the off-grid system performance and control strategy analysis, which is highly relevant for the planning and dimensioning of affordable renewable off-grid systems. [ABSTRACT FROM AUTHOR]

In this paper a ventilation element is designed with the constant cross-sectional area of 3.14 mm2 with the outer ring, to study the efficiency of ventilation at three different inlet air velocities (2, 5 and 8 m/s). There are five different cases analysed in the study, in which four cases are with different coordinate values of outer ring and core while the fifth case is studied with ventilation element without outer ring. The results of all five cases are analysed and compared to see the efficiency of ventilation element design. These ventilation elements are attached at ventilation hole at the inner part of the protective jacket. The attached ventilation element increases mechanical strength of the clothing by covering ventilation hole and restricting direct access of insects to the body. Moreover, ventilation elements permit smooth flow of air inside jacket. The objective is to determine which element's geometrical configuration results in the minimum flow energy losses in the cell flow channel from the inlet to the outlet, which are represented by the pressure difference. Flow energy losses increase with increasing pressure difference (ΔP), and the body cooling reduces if the flow is weakened or there is of lost energy. SolidWorks Flow Simulation is used to calculate the pressure, temperature, and heat flux for the simplified elliptical model of the human body with a protective jacket. The obtained results are compared and analysed to study the concept of constant cross-sectional area in the design of ventilation elements with and without outer ring. The pressure and temperature difference for each case are calculated for the comparison and the obtained results show that the element design without outer ring provides better overall results and less flow energy loss in the cell flow channel than that of element design with outer ring. [ABSTRACT FROM AUTHOR]

Green and sustainable hydrogen has a major role in moving towards decarbonization of energy, providing viable solutions in all most challenging sectors of the national economies. It would penetrate practically all sectors of economic activity, such as long-haul transport, steel and chemical industries, power generation and energy storage. Green and sustainable hydrogen cost competitiveness is also closely linked to developments of large-scale renewable energy sources (in case of green hydrogen; hereinafter – RES) and further commercialization of carbon dioxide (in case of sustainable hydrogen produced from natural gas; hereinafter – CO2) capture and storage (hereinafter – CCS) technologies. In the European Union (hereinafter – EU), sustainable and especially green hydrogen is gaining strong political and business momentum, emerging as one of major components in governments' net zero plans within the European Green Deal and beyond. Being extremely versatile both in production and consumption sides, it is light, storable, has high energy content per unit mass and can be readily produced at an industrial scale. The key challenge comes from the fact that hydrogen is the lightest known chemical element and so has a low energy density per unit of volume, making some forms of long-distance transportation and storage complex and costly. In this paper, green and sustainable hydrogen is reviewed as a vital part of emerging European smart energy framework, which could contribute significantly to economy decarbonization agenda of the EU and Latvia in both in short- and mid-term perspective. [ABSTRACT FROM AUTHOR]

The paper discusses issues related to the optimisation of magnetic couplings used in bioreactors (manufactured by JSC "Biotehniskais Centrs"). The purpose of optimisation was to preserve the maximum breakaway torque of the magnetic coupling while reducing the mass of rare earth elements used in its structure. The paper presents the rationale for the selected optimisation option taking into account the economic aspect. To solve the optimisation problem, the factors affecting the maximum torque of the magnetic coupling, such as the shape and height of the internal and external magnets, the angle of the external and internal magnets, as well as the height of the internal and external yoke, were determined. The design of the existing magnetic coupling was optimised and its prototype was made based on the results of optimisation. The results obtained by means of optimisation were compared with the results obtained experimentally by testing the manufactured prototype. [ABSTRACT FROM AUTHOR]

The paper presents the use of phase change material (PCM) in window application that was studied in the framework of the ERA-NET-LAC Project "Solar Hybrid Translucent Component for Thermal Energy Storage in Buildings" (SOLTREN). Increase of energy savings in buildings is the main aim of this study. To achieve the aim, it has been decided to create a theoretical model of the impact of the PCM on the characteristics of the window and, at the next stage, to experimentally test the model. Paraffin has been chosen as the most suitable and available material as PCM. Pure paraffin has high transparency in liquid phase, and dull white colour in solid phase. The paper shows results of total transmittance and absorption spectra for different thicknesses of paraffin with a melting temperature of 35°C, as well as absorption of the glass sample with PCM at different angles of incidence of light. [ABSTRACT FROM AUTHOR]

The paper analyses the possibilities to form a coalition of several heat energy providers in order to participate in the district heating market considering the open electricity market. Cooperation would allow the participants to better dispatch the existing energy sources and would ensure higher total profit for the participants. The objective function for such a cooperation is provided. To optimise the operation of the coalition, mixed integer linear programming is used, considering constraints of different heating energy market participants and the need to fulfil heating energy balance. If any additional profit is made, it is shared between coalition participants according to the Shapley value, which grants interest for market participants to form the coalition. Case study based on historical hourly data is provided and numerical results are presented in the paper. [ABSTRACT FROM AUTHOR]

Energy poverty is a growing concern in the European Union. Following energy market liberalization, the problem of energy affordability has entered the political discussion, making it necessary to estimate its dimensions, develop and implement a policy and means for its mitigation. To evaluate the situation in Latvia, the paper reviews the way energy poverty is currently defined and measured, investigating the advantages and shortcomings of various definitions and approaches. It then provides a brief analysis of energy poverty in three char-acterising dimensions: low income, high costs of energy services and unsatisfactory housing conditions (primarily related to energy efficiency aspects), using available statistical data. The characterising indicators of energy poverty are compared with the EU average values. Finally, this paper highlights individual policy measures for diminishing energy poverty. [ABSTRACT FROM AUTHOR]

To develop an advanced control of thermal energy supply for domestic heating, a number of new challenges need to be solved, such as the emerging need to plan operation in accordance with an energy market-based environment. However, to move towards this goal, it is necessary to develop forecasting tools for short- and long-term planning, taking into account data about the operation of existing heating systems. The paper considers the real operational parameters of five different heating networks in Latvia over a period of five years. The application of regression analysis for heating load dependency on ambient temperature results in the formulation of normalized slope for the regression curves of the studied systems. The value of this parameter, the normalized slope, allows describing the performance of particular heating systems. Moreover, a heat load forecasting approach is presented by an application of multiple regression methods. This short-term (day-ahead) forecasting tool is tested on data from a relatively small district heating system with an average load of 20 MW at ambient temperature of 0 °C. The deviations of the actual heat load demand from the one forecasted with various training data set sizes and polynomial orders are evaluated for two testing periods in January of 2018. Forecast accuracy is assessed by two parameters – mean absolute percentage error and normalized mean bias error. [ABSTRACT FROM AUTHOR]

The paper assesses the integration of solar photovoltaic technology in the industrial and residential sectors under energy market conditions. The aim is to determine and compare the payback period for the use of solar photovoltaic technology between the industrial and residential sectors, taking into account the application of optimal load scheduling and level of direct consumption. The industrial sector is represented by a glassware company. Installing PV technologies for a larger area and power is cheaper than installing low-power solar photovoltaic technologies. In addition, direct consumption has significant benefit due to high network service tariffs. [ABSTRACT FROM AUTHOR]

Improved end-user engagement is considered to be a key factor in decarbonization efforts towards climate neutral energy systems. While first adopters are already actively seeking ways how to optimize their energy consumption, a true shift in consumer behaviour can only be achieved if the financial benefits are well established and presented. The study aims at estimating the economic performance of end-user engagement in provision of demand response services using air-to-air heat pumps as the underlying technology. The results of the paper help evaluate in a real data setting whether the existing market framework provides sufficient incentives to facilitate end-user participation in the demand response service. [ABSTRACT FROM AUTHOR]

The paper presents a new approach to energy indicator determination, such as specific fuel consumption and energy efficiency of the power plant. The essence of the new method is to determine the instantaneous power of the installation with subsequent data processing. The use of this method allows establishing the dependence of specific energy indicators on the generating unit load levels. The established distribution allows defining optimum parameters of experimental setup and consumption at various loading levels. The highest specific energy consumption of fuel is observed (1189–1297 g /(kW·h) and 962–1147 g / / kW·h)) at the lowest and the highest load for different fuels. Experimental data show that fuel without ethanol impurities can generate more electricity, which should be used at higher demand. [ABSTRACT FROM AUTHOR]

On 4 July 2022, a complex low-frequency solar radio burst was observed in Metsähovi Radio Observatory of Aalto University. The radio burst was observed at a frequency range between 20 and 80 MHz. In GOES (Geostationary Operational Environmental Satellite) class, the event was classified as C5.1. However, coronal mass ejection (CME) was not associated to this event. The observed radio burst was a long-lasting (~10 minutes) event, and it could be mainly classified as type II solar radio event. Also type III solar events were observed before long-lasting type II event. The event includes common frequency drifting emission structures, both fundamental and harmonic structures, but also rarely observed continuum-like or stationary structure. It is assumed that the continuum-like radio emission structure is originated from the stationary flare (coronal) loop, which was visible over the whole event. The drifting emission structure means accelerated electrons, which are produced by the shock related phenomena. The paper provides the observations from this event on radio wavelength, and also soft-X-ray regime and optical wavelength (AIA 171). In addition, a possible, simplified scenario is presented for forming the drifting and continuum solar radio emissions in type II solar burst. [ABSTRACT FROM AUTHOR]

Surface potential decay (SPD) of a corona charged polymeric material is a powerful tool to characterise electrical properties such as charge transport, trapping/detrapping and recombination. Over the years, various predictive simulation techniques have been proposed to describe charge transport within the material. Despite recent progress, it appears that there have been a few attempts to theoretically interpret the nature of the charge migration on the insulation surface. The aim of the present paper is to introduce a new technique with differential evolution algorithm (DEA) to reveal the steady state surface potential decay experimental results. Experimental measurement was carried on a thin film of polyethylene terephthalate (thickness: 0.5 mm; surface: 50 mm × 50 mm). The domains of variation of the factors used were respectively: 1000 V to 1800 V; 25 to 55 °C; 50 % to 80 %. The simulation results show that computational modelling and optimization approaches may improve the effectiveness to characterise electrical properties of polymers. More importantly, these studies demonstrate that DEA is effective and performs better than the experimental design method. [ABSTRACT FROM AUTHOR]

The paper analyses the constraints related to optical tracking of an HMD with a single commercial binocular stereoscopic optical tracking system and offers an overview of different factors affecting the best active fiducial set-up and marker geometries for reliable tracking with a focus on the rotational accuracy of a marker. Two IR diode models with different emission characteristics were tested as active fiducials and the results were compared to localization accuracy of passive fiducials. In terms of preferable marker geometry, it was found that the area enclosed by the fiducials should be maximized. Thus, due to geometrical constraints, very small marker geometries may not be stable or feasible entirely. Rotational accuracy was analysed for cases when the marker was not directly facing the tracking device and it was found that rotation about one axis introduced errors to the determined orientation in space related to the other axes as well. [ABSTRACT FROM AUTHOR]

The paper presents a simulation model developed for a special optical coupler intended for coupling radiation from signal and pump sources used for the realization of cladding-pumped doped fibre amplifiers. The model is developed in COMSOL Multiphysics and used to assess the pumping efficiency for different side pumping angles and different numbers of electromagnetic modes. The obtained results show that the highest pumping efficiency, above 75 %, is achieved for 5–14 modes when two fibres representing the pump source and the signal source form a 10-degree angle between their central axes. The search for the optimal number of modes corresponds to the development trend in optical coupler technology where the multimode pumping by light-emitting diode (LED) replaces the classical scheme with a single-mode pumping by a laser diode (LD). [ABSTRACT FROM AUTHOR]

Copyright of Latvian Journal of Physics & Technical Sciences is the property of Sciendo and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Latvian Journal of Physics & Technical Sciences is the property of Sciendo and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Latvian Journal of Physics & Technical Sciences is the property of Sciendo and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Operational monitoring of large sea aquatorium areas with the aim of detecting and controlling oil pollution is now carried out using various technological systems, such as satellite remote sensing, sea-going vessels, various aircraft and remotely piloted aircraft (RPA). Currently, the use of RPA for the fulfilment of monitoring tasks in the aquatorium is being intensively developed and can eliminate problems of remote sensing performed by satellites and piloted aircraft, such as short presence in the monitoring area, very long delay of information (up to 48 hours) and low quality of imagery. This paper presents mathematical modelling of RPA multi-sensor pay-loads for oil spill detection, monitoring and control. Information obtained from payload sensors is critical for increasing effectiveness of detection and monitoring of oil spills. Nowadays, many types of sensors are used for oil spill detection and monitoring. The most common sensors for detection of oil pollution are optical, multispectral, hyperspectral, thermal and laser fluorometers. Some oil pollution detection sensors have limitations, such as false alarm, only daytime operation, weather restrictions. Airborne remote sensors cannot provide all information required for detection of and response to oil spills, and water quality monitoring in the spill area. A model for selecting sensors for multi sensor payload that will make it possible to optimize the application of RPA for oil spill detection was developed. The RPA payload can be increased/reduced to the greatest possible extent with the help of different types of equipment at various parameters. The mathematical model of the integrated payload considers detection capability of sensors, weather conditions, sensor characteristics, and false alarm rate. The optimal multi-sensor payload will optimize the application of RPA for oil spill detection and monitoring. [ABSTRACT FROM AUTHOR]

The paper presents the results of the research, which was initiated in our previous publication. The main goal of the research is to develop and validate our own multi-objective simulation tool for determination of optimal mix and sizing of off-grid and grid-connected microgrid systems. The first version of the developed model was tailored specifically for simulation of household off-grid system, which consisted of solar photovoltaics (PV), micro wind turbine, electric batteries, and backup power generator. Proposed algorithms are based on simulation of mentioned resources and hourly electric loads of off-grid system with the objective to reduce unsupplied energy volumes and total system costs. Several alternatives were considered with different configurations of the off-grid system and dispatching strategies of available resources. The developed model was validated with calculations of real off-grid system and results were compared to those, which were made in the previous publication, using Homer Pro software. [ABSTRACT FROM AUTHOR]