rss_2.0Latvian Journal of Physics and Technical Sciences FeedSciendo RSS Feed for Latvian Journal of Physics and Technical Sciences Journal of Physics and Technical Sciences Feed Concept of Energy Communities in the European Union<abstract> <title style='display:none'>Abstract</title> <p>In accordance with the goal approved by the Council of the European Union, a European climate-neutrality must be achieved by 2050. Namely, the European Union must significantly reduce greenhouse gas emissions and find ways to compensate for the remaining and unavoidable ones. Within the framework of the European Green Deal, which is a set of policy initiatives to achieve climate neutrality goals, energy communities are considered in the context of two initiatives: a just transition and clean and safe energy at an affordable price. Within the latter, energy community is seen as citizen-led actions in the energy sector that will help pave the way for the transition to clean energy.</p> </abstract>ARTICLEtrue of Phase Separation and Morphology of Organic-Inorganic Interpenetrating Polymer Networks<abstract> <title style='display:none'>Abstract</title> <p>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) (–TiO<sub>2</sub>–)<sub>n</sub> obtained by solgel method in the presence of poly(oxypropylene glycol) (POPG) at various molar ratio of titanium (IV) isopropoxide (Ti(OPr<sup>i</sup>)<sub>4</sub>) 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(OPr<sup>i</sup>)<sub>4</sub>/H<sub>2</sub>O molar ratio it is possible to control the phase separation process and obtain OI IPNs with a different phase structure.</p> </abstract>ARTICLEtrue Polarization Gratings in an Azobenzene-Based Molecular Glassy Film<abstract> <title style='display:none'>Abstract</title> <p>Holograms recorded by focused light beams have several advantages over usual plane wave holograms such as reduced size, white light readout possibility and others. Focused polarization grating recording in an azobenzene-based molecular glasy film 5,5,5-triphenylpentyl 4-((4-(2-(4-bis(2-hydroxyethyl)amino)phenyl)-1-cyanovinyl)phenyl)dyazenyl)benzoate (which we shortly denoted as B11) is experimentally studied and compared with such grating recording in other materials. It has been determined that focusing manifests itself differently than in other materials, e.g., as in a-As<sub>2</sub>S<sub>3</sub> and a-As-S-Se chalcogenide films. Thus, it reduces the holographic grating recording efficiency independently of recording and readout beam polarizations. It has also been found that recording efficiency with circularly and orthogonally <italic>L-R</italic> polarized beams is higher than with linearly polarized <italic>p-p</italic> beams. The highest diffraction eficiency of 26% is achieved with <italic>L-R</italic> polarized unfocused beams.</p> <p>Recording efficiency grating period dependences for unfocused beams at 200 J/cm<sup>2</sup> exposure and at 1000 J/cm<sup>2</sup> exposure are different with a maxima at 2 μm and 6 μm, respectively. In contrast, recording efficiency grating period dependences for focused beams at 200 J/cm<sup>2</sup> exposure and at 1000 J/cm<sup>2</sup> exposure are the same with the maximum at 6 μm.</p> <p>The obtained results are discussed in terms of <italic>trans-cis-trans</italic> photoisomerization followed by mass transfer and their light intensity dependence, light electric field gradient force, the photoinduced light scattering and photoelastic forces.</p> </abstract>ARTICLEtrue Investigation on Thorium Mox Fuel in Vver-1000 Reactor Assembly<abstract> <title style='display:none'>Abstract</title> <p>The accumulation of plutonium produced by LWR operations causes public concern related to its radiotoxicity and proliferation issue. Therefore, there is some interest in developing various methods for consuming plutonium through plutonium incineration i.e., by utilising thorium-based nuclear fuel. Thorium-plutonium mixed oxide fuel (Thorium MOX) is an attractive option considered for plutonium incineration. The aim of the study is to investigate the neutronic characteristics of Thorium MOX fuel in VVER-1000 nuclear reactor fuel assemblies. The VVER-1000 Benchmark model was utilised in the present study. A series of calculations were performed with the MCNP6 code and the ENDF/B-VII library. The calculation results show that a proper increase in Pu content could increase <italic>k</italic><sub>inf</sub> of ThMOX fuel, so it could have almost the same <italic>k</italic><sub>inf</sub> with MOX fuel or increase Pu content when needed. It was also shown that Thorium MOX fuel assembly had more negative Doppler reactivity due to neutron capture by thorium (<sup>232</sup>Th). The moderator temperature coefficient was found to be more negative than the Doppler coefficient, and it could be concluded that replacing uranium with thorium could reduce the amount of plutonium produced while increasing plutonium consumption.</p> </abstract>ARTICLEtrue of Electrophysical Parameter Distribution During Eddy Current Measurements of Structural Features of Planar Metal Objects<abstract> <title style='display:none'>Abstract</title> <p>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 LP<sub>τ</sub>-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.</p> </abstract>ARTICLEtrue of Alternative Energy Sources and Equipment in Residential Buildings in Latvia<abstract> <title style='display:none'>Abstract</title> <p>At the end of 2019, the EC presented the European Green Deal – a set of policy initiatives with the ultimate goal of making Europe climate-neutral by 2050. This means that all EU member states must reach climate neutrality. Emissions in all sectors shall be substantially reduced to achieve this goal. Most of the energy is produced using fossil fuels, which contributes to climate change, water and air pollution, as well as the depletion of natural resources. Individual and district heating systems, which supply residential buildings with heat and hot water, are responsible for a part of global emissions.</p> <p>Electricity generation also produces emissions. The EU recognises the mitigation of climate change as one of the main challenges that must be overcome to ensure sustainable development of the European Union, which is why it has defined ambitious goals to promote decarbonisation and is deliberately moving towards the implementation of renewable energy.</p> <p>This article aims at analysing the opportunity of using renewable energy resources in multi-apartment residential buildings in the context of sustainability.</p> </abstract>ARTICLEtrue of Various Factors Affecting Economic Indicators in Prosumer and Consumer Energy Communities: A Case Study of Latvia<abstract> <title style='display:none'>Abstract</title> <p>This study explores the recent legislative changes allowing prosumers and consumers in Latvia to form energy communities (EnCs). In spite of legal advancements, the absence of supporting regulations and potential barriers, such as the lack of tailored support schemes and forecasting tools, pose challenges. International experiences highlight additional hurdles, including weak stakeholder dialogue and limited EnC modelling tools. To address these issues, the study proposes a prosumer and consumer EnC business model aligned with Latvia’s legislation, emphasising a peer-to-peer (P2P) trading approach. The model incorporates state aid, electricity trader responsibilities, and reinvestment of EnC profits, eliminating the need for a dedicated trading platform. The study introduces a user-friendly planning tool in MS Excel, evaluating economic viability through case studies and scenarios. Findings emphasise the optimisation of EnC effectiveness by adjusting tariffs, minimising initial investment costs, securing external funding, and managing loan durations. The planning tool serves as a universal instrument, offering insights into individual EnC economic indicators based on their unique characteristics. The research provides valuable guidance to stakeholders and policymakers in Latvia’s evolving energy landscape.</p> </abstract>ARTICLEtrue Transceiver Capacity with a Scalable Spectrum Slicing Technique for Optical Access Networks<abstract> <title style='display:none'>Abstract</title> <p>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.</p> </abstract>ARTICLEtrue First Application of Laser-Induced Breakdown Spectroscopy: A Fast-Analytical Technique in Targeted Search for Elements in Geological Samples from Deep Boreholes in Latvia<abstract><title style='display:none'>Abstract</title> <p>Laser-induced breakdown spectroscopy (LIBS) provides a rapid, cost-effective, and extra-sensitive analysis of geological samples to make preliminary conclusions about the presence of valuable elements up to the trace levels in the ore. We present the first results of a highly sensitive qualitative analysis of the core samples of geological ore from two boreholes in Latvia (Staicele 1, from a depth range of 794–802 m, and Garsene (Subate) 2A, from a depth range of 1102–1103 m) using LIBS. Our measurements using this technique confirmed the high iron content and indicated traces of rare and high in-demand metals (such as Ti, V, Co, Sm, etc.) in the sample from Staicele, renewing interest in studying boreholes across Latvia. The presented pilot studies demonstrated effectiveness and unique possibility in performing a very sensitive and time-saving qualitative analysis of the composition of samples of ores from the old but still valuable borehole cores by using the LIBS method. We compare these measurements with other methods of sample analysis.</p> </abstract>ARTICLEtrue of the Energy Consumption for Heating in Schools<abstract><title style='display:none'>Abstract</title> <p>The aim of the study is to analyse energy consumption for heating in set of the school buildings. Data analysis includes three data sets – predictions from energy performance certificates (EPC), measured data from heat meters and measured climate corrected data. Data sets were statistically checked and processed and represented graphically. The actual energy consumption differs from the one stated in the EPCs in all cases, which means that schools consume on average 15 % more energy than it is stated in the EPC. Overall, the data reveal that the actual energy consumption differs from the theoretical consumption, with all schools having higher actual consumption than the theoretical values. The differences in the data sets are discussed, and possible improvements are suggested taking into account strong relation between energy consumption and indoor air quality.</p> </abstract>ARTICLEtrue Performance of Higher Education Institutions Buildings Operating During Quarantine Restrictions and/or Martial Law in Ukraine<abstract><title style='display:none'>Abstract</title> <p>During the pandemic and periods of martial law, educational institutions in Ukraine implemented various forms of organising the educational process, combining in-person and remote classes. As a result, there has been a decrease in the level of use of building premises. The analysis of the characteristics of energy consumption in these conditions requires additional attention. In this study, a dynamic energy model of the building was created using the educational building of Igor Sikorsky Kyiv Polytechnic Institute as an example. Energy consumption for heating needs was determined for normal operating conditions and quarantine conditions in Ukraine (only a specific part of the premises is being operated, ensuring that the standard temperature value is maintained while people are present). Based on the results of the study, the features of the energy consumption of the building during quarantine/martial law restrictions, subject to the partial use of the building, were analysed, and the main disadvantages of such a mode were identified. For the educational building of the university, the total energy consumption for heating needs depends on the number of rooms that are actively used, and the modes of regulation of heating and ventilation; the consumption can decrease depending on the chosen scenario by 61 %, 56 %, and 34 % in quarantine mode. The findings indicate that the efficiency of regulation modes can decrease by more than four times when compared to normal mode due to internal heat exchange with unoccupied rooms.</p> </abstract>ARTICLEtrue Scalable Synthesis of TiSe and VSe Thin Films<abstract><title style='display:none'>Abstract</title> <p>Transition metal dichalcogenides (TMDs), specifically those involving V and Ti, possess fascinating material properties, making them interesting candidates for scientific studies. The existing growth methods of these materials are typically limited by scalability – either low yield or high cost. Here, we propose an alternative 2-step method valid for scalable production. In the first step, precursor films of Ti / V are deposited using magnetron sputtering, followed by the second step of selenization of these samples using elemental Se in a vacuum-sealed quartz ampoule for conversion to their respective diselenide material. Synthesized films are char-acterised using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron (XPS). The method demonstrated here can be used to increase the active surface area of TiSe<sub>2</sub> and VSe2 for their potential catalytic and HER applications using nanostructured substrates, while also providing an opportunity for scalable synthesis of films that can be extended to synthesize other TMDs as well.</p> </abstract>ARTICLEtrue High-Precision Quadrotor Trajectory Following Capabilities: Modelling, Parameter Estimation, and LQR Control<abstract><title style='display:none'>Abstract</title> <p>Quadrotor unmanned aerial vehicles (UAVs) are small, agile four-rotor systems suitable for various applications, from surveillance to disaster support missions. Hence, achieving high-precision trajectory tracking is crucial for their successful deployment. This research focuses on modelling, parameter identification, and Linear Quadratic Regulator (LQR) control design for quadrotors, aiming to enhance their trajectory following capabilities. The quadrotor dynamics are a sixth degree-of-freedom (6DOF) equation of motion derived from Newton’s second law, encompassing moment of inertia, centre of gravity, weight, and thrust of propeller parameters. Experimental measurements are conducted to accurately determine these parameters, ensuring a realistic representation of the quadrotor system. Subsequently, a linearized model is constructed to provide a suitable plant for control system development. The LQR control design is intended to improve the trajectory tracking performance. This control strategy is validated through simulation and practical experiments, demonstrating its effectiveness in achieving high-precision trajectory following capabilites. The proposed approach demonstrates that LQR control effectively guides the quadrotor to resemble a predefined trajectory, experiencing only 3 % overshoot observed during the initial phase of flight.</p> </abstract>ARTICLEtrue of Renewables Gases Into the Existing Gas Distribution Grids and Employment of Reverse Gas Flow Technique<abstract><title style='display:none'>Abstract</title> <p>Sustainability and longevity of existing gas grid exploitation perspective are closely related to two fundamental issues: their ability to adopt to changing gas fuel production and supply landscape in the context of methane-based fuels, mostly, biomethane, and in the context of non-methane-based fuels, mostly, low carbon and green hydrogen. Renewable gases and their ever-growing presence in gas transmission and distribution systems open up a discussion about the necessity to revise and restructure the original – vertically integrated layout of the gas systems, where gas supply is only technically possible from the transmission system towards distribution one, and not vice versa. Development of numerous decentralized biomethane production facilities connected to the gas distribution system causes a necessity to ensure the possibility to pass biomethane surplus of a certain production area into the gas transmission grid, thus avoiding necessity to install biomethane storage capacities locally and granting other regions an opportunity to use said surplus in their gas consumption immediately. The article addresses biomethane production trends and actions taken towards the development of reverse flow gas stations in France – one of biggest biomethane producers in Europe to date, and opportunities and challenges, which this technique might face in smaller and less active renewable gas markets as the one of Latvia.</p> </abstract>ARTICLEtrue Persistent Luminescence and Trap Properties of MgSiO: Mn, M (M = B; Al; Ga; In) Material<abstract><title style='display:none'>Abstract</title> <p>Persistent luminescence (PersL), also called long-lasting phosphorescence or simply afterglow, is a luminescence characterised by the emission of radiation from a few seconds to several days after the excitation source has been switched off. Over the past two decades, research on PersL materials, both in fundamental and applied physics, has developed rapidly; however, the explanation for the physical processes that cause afterglow still needs to be clarified. Today, PersL materials are used mainly for luminescent paints, safety signs and decorations. At the same time, research into using such materials in medicine, information storage, anti-counterfeiting technology, etc., is underway.</p> <p>Currently, information on the long persistent luminescence materials with emission in the blue and green spectral range is widely available. In contrast, the number of publications on the afterglow in the red and near-infrared spectral range is considerably lower.</p> <p>Within the framework of this research, Mg<sub>2</sub>SiO<sub>4</sub>: Mn<sup>2+</sup>; M<sup>3+</sup> (M<sup>3+</sup> = B3+; Al<sup>3+</sup>; Ga<sup>3+</sup>; In<sup>3+</sup>) materials were synthesised using solid state reaction synthesis. When excited with X-rays, the materials exhibited a broad Mn<sup>2+</sup> PersL band with two maxima at approximately 625 nm and 730 nm. After cessation of irradiation, an afterglow of at least 6 hours could be observed.</p> <p>The research focuses on the trap properties of the materials. It was concluded that at least three discrete trap levels with activation energies approximately between 0.4–1.6 eV were present in the samples. Additionally, co-doping with Al<sup>3+</sup>; Ga<sup>3+</sup>; In<sup>3+</sup> ions improved PersL longevity of the Mg<sub>2</sub>SiO<sub>4</sub>: Mn<sup>2+</sup> material.</p> </abstract>ARTICLEtrue Polarization Optical Time-Domain Reflectometry Technique for Fibre Optical Infrastructure Monitoring<abstract><title style='display:none'>Abstract</title> <p>This interdisciplinary research is focused on constructing and demonstrating enhanced-reach polarization optical time-domain reflectometer (POTDR) for monitoring single-mode fibre optical communication lines. An optical signal state of polarization measurements enables several new possibilities for real-time monitoring solutions in fibre optics. However, there is no commercial equipment available to determine the location in fibre optical cable where the light polarization state changes. The authors present a monitoring technique of an optical signal state of polarization based on reflected signal time-amplitude analysis with improved operation parameters, namely, timing resolution (2 to 3 ps RMS) and amplitude measurement resolution of nanosecond scale pulses (8 to 10 bits) for monitoring of fibre optical communication lines. Additionally, the demonstrated POTDR provides a considerable optical fibre line measurement reach of up to 40 km.</p> </abstract>ARTICLEtrue Citrate and Polyvinylpyrrolidone Captured Silver Nanoparticles Transfer to Organic Solvents<abstract> <title style='display:none'>Abstract</title> <p>Silver nanoparticles (NPs) have gathered extensive attention due to their properties – chemical stability, good conductivity, catalytic activity, and antimicrobial activity. This makes NPs suitable for potential applications in the development of new technologies in the field of photonics, electronics, medicine, biochemical sensing, and imaging. Nanoprisms have local surface plasmon resonance starting from visible to near infra-red spectrum, broadening the possibilities of their applications. Ag NPs typically are synthesized in aqueous solution but the handling of NPs often requires their dispersion into nonpolar solvents and their mixing with organic compounds. Thus, nanoparticle transfer to organic media is essential for application in the field of emission enhancement due to NPs – organic semiconductor interaction. A shell changing method for NP tranfer was successfully used with a high transfer rate, but rather low stability. The previously proposed sonochemical method for NP transfer from aqueous to organic polymeric media is extended to different organic solvents. The ultrasonic method is suitable to obtain stable NPs in both organic solvent and organic solvent/organic compound solutions, and it can be stored at ambient conditions for at least several months. Transfer efficiency is suficient and NPs remain stable in an organic solvent like chlorobenzene, anisole, dichloromethane. The method has potential in NPs containing thin film preparation because sonication prevents the agglomeration of clusters.</p> </abstract>ARTICLEtrue Resolution Quadrupole Mass Spectrometer for Ion Beam Processing<abstract> <title style='display:none'>Abstract</title> <p>The mass filtering equipment in the ion beam processing industry plays a vital role. Mass filtering is usually achieved through classic magnetic mass selector techniques. The drawbacks of these techniques are the dimensions, weight, price, and power consumption. We suggest mitigating it by using the electrostatic RF mass selector instead of the magnetic one. We discuss the development of a novel ion beam processing apparatus that employs a QMS filter in a vacuum of superior purity. We describe the experimental setup in terms of part design. The article presents the successful test results of that parts. The article also explains in detail the basic principles and the technical realization of the whole apparatus and presents experimental data showing its high capabilities.</p> </abstract>ARTICLEtrue Assessment for Nitrate-Based Salt as a Phase Change Material for a Medium-Temperature Latent Storage Tank<abstract> <title style='display:none'>Abstract</title> <p>The present study assesses the heat characteristic of the nitrate-salt mixture as a phase change material (PCM) for a medium-temperature latent storage system (LSS). Two binary and ternary mixtures are evaluated, which demonstrate different thermal behaviour. The highest melting and latent heat capacity is obtained by KNO<sub>3</sub>(0.4)/NaNO<sub>3</sub>(0.6) at 223.8 °C and 161.5 J/g. However, it has a higher supercooling degree with a partial phase transition between 217.6 °C and 251.5 °C, making it unfeasible for a medium-temperature LSS tank. The ternary mixture (TM) with NaNO<sub>2</sub>(0.4)/KNO<sub>2</sub>(0.53)/NaNO<sub>3</sub>(0.7) demonstrates a stable phase transition with minimum partial phase transition (22.1 °C) and suitable heat of fusion (98.1 J/g). Further evaluation through static thermal profiling demonstrates that the TM has a notable performance during solid-sensible charge with a charge level indicator (CLI) around 45.3 %–49.1 %. The TM can be charged up to 85.7 % until the end stage of the phase transition. It promotes a better storage capacity with suitable performance since the system can be charged effectively at a suitable temperature range (&lt; 160 °C) for various applications. The micrograph observation indicates some dispersed particles and local agglomeration, which makes phase stabilization as an advantageous method to promote a stable phase change process. The TM can be considered a suitable PCM for a medium-temperature LSS tank that allows for a better solar thermal renewable system operation.</p> </abstract>ARTICLEtrue of Accuracy Error for Time Interval Measurements<abstract> <title style='display:none'>Abstract</title> <p>A method of accuracy error compensation for the time interval is examined, allowing to decrease the dependence of accuracy error on the duration of measured intervals and minimising the influence of destabilising factors – ambient temperature changes and the initial deviation of the meter clock generator frequency from the nominal value. The compensation method is based on a calibration procedure that measures precise time intervals under conditions of changing ambient temperature. Then the dependence of the accuracy error on temperature for a particular meter is recorded. Based on these data, a correction table is compiled containing correction factors and temperature values at which these factors were determined. Under real measurement conditions, the correction factor corresponding to the current temperature is determined from the table for measured result correction. The table with correction factor values could be stored in the memory of the meter or processing computer. Experimental verification of the method showed that applying a correction for a meter with a standard XO class clock generator (certificated instability of ±50 ppm) could obtain an equivalent clock generator instability of ±0.15 ppm. The application of the method is efficient in cases where the use of high-end clocking to ensure the required measurement accuracy is not economically feasible.</p> </abstract>ARTICLEtrue