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 's Cover Optical Coupler Simulation by Comsol Multiphysics Software<abstract> <title style='display:none'>Abstract</title> <p>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).</p> </abstract>ARTICLE2022-10-13T00:00:00.000+00:00Sphere and Random Flat Surface Contact<abstract> <title style='display:none'>Abstract</title> <p>The research is devoted to the elaboration of the wear part contact estimation using 3D surface texture parameters defined in the standard ISO 25178-2:2012 for contact (it is known that elastic contact gives less wear rate) area, friction, and wear rate determination. In our research, the sphere and random flat surface model was used, where the height of surface asperities h(x, y) had a normal probability distribution. As a result of research, the equations for estimation of the elastic contact area were derived and, we obtained conditions at which it was possible to use equations for flat random surfaces. The results of this study could have wide practical application, for example, in design, choosing the geometrical and physical-mechanical parameters of the parts, calculation of real stresses, wear rate and life time of contact parts, etc.</p> </abstract>ARTICLE2022-10-13T00:00:00.000+00:00Potential Decay Simulation on Insulating Films<abstract> <title style='display:none'>Abstract</title> <p>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.</p> </abstract>ARTICLE2022-10-13T00:00:00.000+00:00Influence of Internal Gas Pipelines Built into the Structure on the Safety of Residents and Energy Eficiency Factors of the Building<abstract> <title style='display:none'>Abstract</title> <p>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.</p> </abstract>ARTICLE2022-10-13T00:00:00.000+00:00Comparison of Passive and Active Fiducials for Optical Tracking<abstract> <title style='display:none'>Abstract</title> <p>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.</p> <p>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.</p> </abstract>ARTICLE2022-10-13T00:00:00.000+00:00Oxygen Mass Transfer Coefficient Application in Characterisation of Bioreactors and Fermentation Processes<abstract> <title style='display:none'>Abstract</title> <p>This review article covers the topics of evaluation and experimental determination of oxygen mass transfer coefficients (<italic>k<sub>L</sub>a</italic>) for their application in characterising bioreactors and fermentations processes. The article provides a comparison of different experimental approaches for determining <italic>k<sub>L</sub>a</italic> in bioreactors. Additionally, the influence of bioreactor design and fermentation parameters on <italic>k<sub>L</sub>a</italic> is discussed. The aim of the article is to provide useful information regarding the approaches for selecting bioreactors and their working regimes to achieve optimal fermentation results.</p> </abstract>ARTICLE2022-10-13T00:00:00.000+00:00Development of Liquid Crystal Layer Thickness and Refractive Index Measurement Methods for Scattering Type Liquid Crystal Displays<abstract> <title style='display:none'>Abstract</title> <p>We report the measuring method of scattering type display liquid crystal layer thickness based on capacitance values suitable for inline production process control. The method is selected for its effectiveness and simplicity over spectroscopic methods as conventional methods for scattering type displays are not applicable. During the method approbation process, a novel diffuser liquid crystal mixture refractive index was determined based on liquid crystal layer thickness measurement data.</p> </abstract>ARTICLE2022-08-17T00:00:00.000+00:00Development Solutions of Riga City Local Geodetic Network<abstract> <title style='display:none'>Abstract</title> <p>Throughout the centuries, Riga has been the city with dynamic development. Its territory has unceasingly expanded, whereby previously unused territories have been urbanized. Managers of the city understood already at the end of 19th century that unified geodetic network had great importance in the development of the city. Since then, Riga’s local geodetic network has evolved with the city, several coordinate and height systems have been replaced, but the task has remained the same – to provide a flawless, homogeneous geodetic foundation for various surveying activities. In 2018, the development of the local geodetic network in several parts of the city was completed, whereby the problem arose – altitude values of surveyed terrain points determined by using the improved geodetic network did not coincide with altitude values determined using the GNSS method. Considering the above-mentioned problem, the objectives of this study were set: to plan and carry out control measurements of the improved local geodetic network in the vicinity of Grizinkalns, to provide analysis of the obtained results and recommendations for further development of a local geodetic network. The difference between the heights determined by the geometric levelling method and the heights determined by the GNSS method shall not exceed 2 mm. According to the GNSS method, using the quasi-geoid model LV’14 v2, the determined heights of the geodetic grid points differ from the given ones by 0.062 m on average. The differences are systematic. To overcome these differences, the quasi-geoid model needs to be refined.</p> </abstract>ARTICLE2022-08-17T00:00:00.000+00:00Analysis of Test Results of the Developed Synchronous Reluctance Motor for Public Transport Application<abstract> <title style='display:none'>Abstract</title> <p>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.</p> <p>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.</p> </abstract>ARTICLE2022-08-17T00:00:00.000+00:00Analysis of Remotely Piloted Aircraft Payload for Oil Spill Detection<abstract> <title style='display:none'>Abstract</title> <p>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.</p> </abstract>ARTICLE2022-08-17T00:00:00.000+00:00The Green Hydrogen and the EU Gaseous Fuel Diversification Risks<abstract> <title style='display:none'>Abstract</title> <p>Hydrogen is the most abundant chemical element on the Earth, and it has really a wide variety of applications, starting from use in refining, petrochemical industry, steel manufacturing, and ending with use in energy production and renewable gas (<italic>hereinafter</italic> – RG) blending for gradual replacement of natural gas in all sectors of the national economy. Being practically emission-free, if produced in sustainable way or from renewable energy sources (<italic>hereinafter –</italic> RES), hydrogen is regarded as one of the most promising energy sources for decarbonisation of practically the entire segment of industrial and energy production. Growing pressure of the European climate neutrality targets has triggered special interest in production, use, storage and transportation of hydrogen – especially the green one, which can be used in at least four fundamental ways: as a basic material, a fuel, an energy carrier and an energy storage medium. In the context of sector coupling, however, hydrogen facilitates decarbonisation of those industrial processes and economic sectors in which carbon dioxide (<italic>hereinafter</italic> – CO<sub>2</sub>) emissions can either not be reduced by electrification or this reduction would be minimal and linked to very high implementation costs. At the same time, development of an extensive hydrogen economy is the key to the achievement of the European climate protection targets, with the European Commission’s (<italic>hereinafter –</italic> EC) Hydrogen Strategy, a framework created in 2020 to develop and promote sustainable hydrogen economy in the European Union (<italic>hereinafter –</italic> EU), in its centre.</p> <p>Green hydrogen also will take its legitimate place in the gaseous fuel diversification risk management strategy, as this gaseous fuel is not only one of the most perspective future energy sources, but also one of the most volatile and demanding sources. In the process of gaseous fuel diversification in the EU and worldwide, new logistical chains and supply – demand networks of green hydrogen will emerge. Therefore, adequate addressing of potential challenges of this new regional and global production, delivery and consumption framework will be of utmost importance for secure, safe and predictable functioning of future energy systems.</p> </abstract>ARTICLE2022-08-17T00:00:00.000+00:00Energy Transport in SiO Crystals: Luminescence Excitation Spectra of Stishovite and α-Quartz<abstract> <title style='display:none'>Abstract</title> <p>The migration of elementary electronic excitations was studied in a single crystal of stishovite and compared with migration in a crystal of α-quartz and polycrystalline stishovite powder. The research method is based on comparing the transfer of absorbed energy to luminescence centers, used as detectors of quasiparticles, and the near-surface nonradiative annihilation of electronic excitations. A sign of migration is the appearance of some minima in the photoluminescence (PLE) excitation spectrum in the region of maxima in the intrinsic absorption spectrum. The PLE spectrum of stishovite contains the first minimum at 9.8 eV, indicating the migration of electronic excitations and the existence of an intrinsic absorption band in stishovite at 9.8 eV. In α-quartz, the first minimum in the PLE spectrum is located at 10.5 eV and corresponds well to the intrinsic absorption band of the exciton.</p> </abstract>ARTICLE2022-08-17T00:00:00.000+00:00Mathematical Model for Household Off-Grid Simulation (Off-Grid System Sizing)<abstract> <title style='display:none'>Abstract</title> <p>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.</p> </abstract>ARTICLE2022-08-17T00:00:00.000+00:00Radar Observations of Old Centaur Rocket from 1966<abstract> <title style='display:none'>Abstract</title> <p>We report the results of radar observations of a near-Earth object discovered on 17 September 2020, with the Pan-STARRS 1 telescope at the Haleakala Observatory in Hawaii. Initially, this object was considered an asteroid and even received the standard provisional designation 2020 SO by the Minor Planet Center. However, its Earth-like orbit and low relative velocity suggested that the object may be of artificial origin, being the Centaur rocket booster from the Surveyor 2 mission that was launched to the Moon on 20 September 1966. In the period from November 2020 to March 2021, this object approached the Earth twice within one lunar distance of the Earth. Radar observations were conducted on 30 November in bistatic mode with the 70-m Goldstone Solar System Radar DSS-14 and 32-m radio telescope RT-32 at the Svetloe Observatory, while the object was in the visibility window of two antennas at about 200 thousand km from the Earth. The main goal of the study was to determine the physical properties of this object using radar astronomy to clarify its origin.</p> </abstract>ARTICLE2022-06-23T00:00:00.000+00:00Magnetic Flux Switching Type Permanent Magnet Generator for Bicycles: Modelling and an Experimental Study<abstract> <title style='display:none'>Abstract</title> <p>The article introduces two new designs of flux switching permanent magnet alternators with a radial and an axial arrangement of the inductor relative to the magnetic flux switch. The study presents the results of 3D magnetic flux modelling along with the outcomes of physical experiments. In the course of laboratory experiments, the results of theoretical estimations are compared with actual physical performance parameters. The results are presented in the form of power and output voltage curves in relation to the frequency and load current. The study proposes the practical application of the alternators based on the magnetic flux switching principle in the development of a bicycle generator. Laboratory test models are made of a laminated steel using a waste-free technology.</p> </abstract>ARTICLE2022-06-23T00:00:00.000+00:00Importance of Spectrum Management in Radio Astronomy<abstract> <title style='display:none'>Abstract</title> <p>The increasing terrestrial and space-borne communications are causing major problems to the radio astronomy observations. Only a minor part of the frequencies is allocated to the passive services, such as Radio Astronomy Services (RAS). There are only a few, relatively narrow frequency bands below 20 GHz, which are still suitable for the radio astronomical observations. In addition, Out-of-Band (OoB) emissions will be a real threat to the observations on these bands. On behalf of all European radio astronomers, the Committee on Radio Astronomy Frequencies (CRAF) of the European Science Foundation (ESF) coordinates activities to keep the frequency bands used by radio astronomy and space sciences free of interference. Along with interference caused by active radio communication services, the local electronic device selection should be considered in the observatories. For instance, more common LED based lamps could cause harmful interference for the observations. Thus, it is very important to perform continuous radio frequency interference (RFI) monitoring locally, in each radio observatory.</p> </abstract>ARTICLE2022-06-23T00:00:00.000+00:00Relationship Between Solar Millimeter and Soft X-Ray Emissions<abstract> <title style='display:none'>Abstract</title> <p>The connection between solar radio and soft X-ray emission has earlier been studied at various radio frequencies. For instance, the intensity peak times during solar flares have been compared between these two wavelength regimes. It has been reported that solar radio emission peaks before soft X-ray emission during a flare. However, opposite results have also been presented. In this study, we compare millimetre (8 mm) solar and soft X-ray emissions (0.5–4 Å and 1–8 Å). The radio observations were made at Metsähovi Radio Observatory of Aalto University in Finland between 2015 and 2019. The soft X-ray data were observed with GOES-15 (Geostationary Operational Environmental Satellite). The data show that the solar millimetre emission can peak either before or after soft X-ray peak emission. In this study, we present two different scenarios, which could explain the peaking time differences and behaviour. The first scenario proposes a tight connection between the millimetre (8 mm) and soft X-ray emissions, the second one is for cases where the emission mechanisms are more separate.</p> </abstract>ARTICLE2022-06-23T00:00:00.000+00:00Microwave Observations of the Sun with Virac RT-32 Radio Telescope: The Expansion of Possibilities<abstract> <title style='display:none'>Abstract</title> <p>Nowadays there is increasing interest in narrowing coronal areas with reduced brightness temperatures (LTR – Low Temperature Regions) associated with local open magnetic fields (S-web, “coronal partings”, “dark coronal corridors”) as one of the eventual sources of slow solar wind. Ventspils International Radio Astronomy Centre (VIRAC) performs routine spectral polarimetric observations of the Sun with RT-32 radio telescope equipped with the multi-channel (16 frequency channels) spectral polarimeter for the wave length range of 3.2–4.7 cm (6.3–9.3 GHz) and both circular polarizations simultaneously. The analysis of relevant tasks of clear and reliable observations and detections of LTR shows the necessity to improve noise parameters, dynamic range and stability of the actual solar spectral polarimeter and to expand its wavelength range. Taking into account these requirements, the low noise and thermally stabilized solar spectral polarimeter was developed. The new multi-channel spectral polarimeter is expected to observe right and left circular polarization of the solar emission in the wavelength range of 2.1–7.5 cm (4.1–14.3 GHz) divided into 12 frequency bands. The dynamic range was expanded to &gt;36 db and the signal/noise ratio (referred to as quiet Sun brightness temperatures) was enhanced to &gt; 22–24 db.</p> <p>The paper deals with some test observations of the newly developed solar spectral polar-imeter and its feature analysis. Some eventual problems of solar physics which could be solved with the spectral polarimeter are also discussed.</p> </abstract>ARTICLE2022-06-23T00:00:00.000+00:00Observations of Weak Galactic OH Masers in 1.6 GHz Frequency Band Using Irbene RT-32 Radio Telescope<abstract> <title style='display:none'>Abstract</title> <p>Ventspils International Radio Astronomy Centre (Ventspils University of Applied Sciences) is implementing the scientific project “Complex Investigations of the Small Bodies in the Solar System” (lzp-2018/1-0401) related to the research of the small bodies in the Solar system (mainly, focusing on asteroids and comets) using methods of radio astronomy and signal processing. One of the research activities is weak hydroxyl (OH) radical observation in the radio range – single antenna observations using Irbene RT-32 radio telescope. To detect weak (0.1 Jy) OH masers of astronomical objects using radio methods, a research group in Ventspils adapted the Irbene RT-32 radio telescope working at 1665.402 and 1667.359 MHz frequencies. Spectral analysis using Fourier transform and continuous wavelet transform was applied to radio astronomical data from multiple observations related to weak OH maser detection. Multiple observation sessions of OH maser objects (R LMi, RU Ari, V524 Cas, OH 138.0+7.2, U Aur, etc) were carried out in 2020–2021.</p> </abstract>ARTICLE2022-06-23T00:00:00.000+00:00Artificial Intelligence Meets Radio Astronomy<abstract> <title style='display:none'>Abstract</title> <p>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.</p> <p>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.</p> </abstract>ARTICLE2022-06-23T00:00:00.000+00:00en-us-1