EUREKA: Physics and Engineering <p><strong>EUREKA: Physics and Engineering </strong>scientific journal whose main aim is to publish materials allowed to see&nbsp;<strong><em>new discoveries at the intersection of sciences.</em></strong></p> en-US <p style="text-align: justify;">Our journal abides by the <a href="" target="_blank" rel="noopener">Creative Commons CC BY</a> copyright rights and permissions for open access journals.</p> <p style="text-align: justify;">Authors, who are published in this journal, agree to the following conditions:</p> <p style="text-align: justify;">1. The authors reserve the right to authorship of the work and pass the first publication right of this work to the journal under the terms of a <a href="" target="_blank" rel="noopener">Creative Commons CC BY</a>, which allows others to freely distribute the published research with the obligatory reference to the authors of the original work and the first publication of the work in this journal.</p> <p style="text-align: justify;">&nbsp;2. The authors have the right to conclude separate supplement agreements that relate to non-exclusive work distribution in the form in which it has been published by the journal (for example, to upload the work to the online storage of the journal or publish it as part of a monograph), provided that the reference to the first publication of the work in this journal is included.</p> (Helen Klimashevska) (Helen Klimashevska) Sat, 30 Jul 2022 21:04:48 +0300 OJS 60 Theoretical approach for Fe(II/III) and its chlorophyll-related complexes as sensitizers in dye-sensitized solar cells <p>Dye is the key to the efficiency of harvesting solar energy in dye-sensitized solar cells (DSSCs). The dye performances such as light absorption, electron injection, and electron regeneration depend on the dye molecule structure. To predict it, one needs to compute the optimized molecule geometry, HOMO level, LUMO level, electron density distribution, energy gaps, and dipole moment in the ground and excited state. Chlorophyll-related chlorin and porphyrin, as well as their κ2O,O’ complexes with Fe(II/III), were investigated with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) computations using the B3LYP method and def2-TZVP basis set. NPA charges also were calculated to know the valence of the metal cations exactly. In general, the calculations show that the metal cations introduced occupied d orbitals with lower oxidation potentials than the chlorophyll ligand orbitals, which are responsible for the emergence of additional absorption bands. The states result in effective band broadening and the redshift of spectrum absorbance that is expected to improve DSSC performance.</p> <p>Another requirement that has to be possessed is the ability of electron regeneration, electron injection, and dipole moment. The Fe(II) complex has fulfilled these requirements, but not the Fe(III) complex due to having a low electron injection capability. However, this work has shown that Fe(III) complex exhibits a non-innocence ligand. It results in trivalent to divalent state change, in the appearance of a ligand radical cation, an extra hole, and a broader absorption spectrum. It also can affect its other electronic properties, such as electron injection capability. Thus, it can be considered an attractive candidate for the sensitizer in DSSCs</p> Mohamad Rodhi Faiz, Denny Widhiyanuriyawan, Eko Siswanto, Fazira Ilyana Abdul Razak, I Nyoman Gede Wardana Copyright (c) 2022 Mohamad Rodhi Faiz, Denny Widhiyanuriyawan, Eko Siswanto, Fazira Ilyana Abdul Razak, I Nyoman Gede Wardana Sat, 30 Jul 2022 20:02:58 +0300 Analysis of duck eggshells as hydroxyapatite with heat treatment method <p>Duck eggshell contains very high calcium, making it a raw material for hydroxyapatite (HA) biomedical applications. The aim of this study was to synthesize natural HA from duck eggshell waste using cleaning, drying, smoothing with a smoothness level of passing is 200&nbsp;meshes and heat treatment with temperature variations of 850&nbsp;ºC, 900&nbsp;ºC, and 950&nbsp;ºC for one hour. The resulting HA material was characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results of the physical characteristics of raw duck eggshells without heat treatment are white, slightly bluish in color, the smell and level of smoothness is smooth. However, heated powdered duck eggshells which are heated 950&nbsp;°C are whiter than the samples which are heated at 850&nbsp;ºC and 900&nbsp;ºC, they have no odor and their smoothness is the smoothest. The small peaks of HA from the non-heat duck eggshell powder were 64.89&nbsp;% with a CaCO<sub>3</sub> of 23.50&nbsp;%, then the peak of CaO increased along with the increasing of heat treatment temperature of 900&nbsp;°C that result HA in 69.31&nbsp;% and reduce CaCO<sub>3</sub> in 19.44&nbsp;%. Duck egg shell powder achieved the highest diffraction with the increasing formation of HA at a heat 950&nbsp;ºC by 91.87&nbsp;% with a very significant decrease of CaCO<sub>3</sub> in 2.25&nbsp;%. The XRF test results of duck eggshell powder showed that the chemical composition of CaO was 99.50&nbsp;%, with elemental calcium (Ca) of 99.71&nbsp;%. The FTIR test results on mesh 200 observed a reduction in the intensity of CaCO<sub>3</sub> absorption, while the intensity of CaO at 364.55 cm<sup>-1</sup> was getting stronger, which indicated the formation of CaO at 950&nbsp;°C. This showed that the CaO formation at a temperature of 950&nbsp;ºC was much more than the formation at a lower temperature. The deformation from the CaO to HA phase was close to perfect with 91.87&nbsp;% hydroxylapatite</p> Asmeati Sabir, Hammada Abbas, Ahmad Yusran Aminy, Sapta Asmal Copyright (c) 2022 Asmeati Sabir, Hammada Abbas, Ahmad Yusran Aminy, Sapta Asmal Sat, 30 Jul 2022 20:05:17 +0300 Experimental study of the correlation for turbulent burning velocity at subatmospheric pressure <p>Turbulent burning velocity is one of the most relevant parameters to characterize the premixed turbulent flames. Different correlation has been proposed to estimate this parameter. However, most of them have been obtained using experimental data at atmospheric pressure or higher. The present study is focused on obtaining a correlation for the turbulent burning velocity using data at sub-atmospheric pressure. The turbulent burning velocity was experimentally calculated using the burner method, where turbulent premix flames are generated in a Bunsen burner. Stoichiometric and lean conditions were evaluated at a pressure of 0.85&nbsp;atm and 0.98&nbsp;atm, whereas the turbulence intensity was varied for each condition. Perforated plates and a hot-wire anemometer were used to generate and measure the turbulence intensity. Schlieren images were used to obtain the average angle of the flame and calculate the turbulent burning velocity. Experiments and theory show that the turbulent deflagration rate decrease as pressure decrease. The turbulent deflagration speed decreased by up to 16&nbsp;% at 0.85&nbsp;atm concerning atmospheric conditions for the same turbulence intensity, discharge velocity, and ambient temperature, according to the experimental results. The comparison among the experimental results at sub-atmospheric conditions and the correlations reported in the literature exposes prediction issues because most of them are fitted using data at atmospheric conditions. A general correlation is raised between turbulent burning velocity (<em>S<sub>T</sub></em>), laminar burning velocity (<em>S<sub>L</sub></em>) and turbulence intensity (<em>u</em>’) proposed from the experimental data. This correlation has the form &nbsp;For sub-atmospheric and atmospheric conditions, the coefficients were determined</p> Arley Cardona Vargas, Hernando Alexander Yepes Tumay, Andrés Amell Copyright (c) 2022 Arley Cardona Vargas, Hernando Alexander Yepes Tumay, Andrés Amell Sat, 30 Jul 2022 20:07:25 +0300 Development of the project of modular prefabricated buildings <p>The issues of working design with the construction of modular prefabricated buildings, with the minimization of cold bridges are revealed. Cold bridges are typical for prefabricated buildings with inadequate attention to the design of both load-bearing metal and enclosing structures, as well as their connections. Connections should not pass through its cross section both zero and negative temperatures. As a result, an original project of two modular buildings was developed from easily prefabricated metal structures and wall structures with light mineral wool filling. This project is also intended for sharply continental regional natural and climatic conditions (regardless of the geographical location on the territory of Kazakhstan – south-eastern Kazakhstan, central, eastern or western Kazakhstan. In winter, natural and climatic conditions are similar in these areas). As a result of this study, it was found that the developed project meets the requirements of thermal insulation – at the interface of the supporting and enclosing structures. The thermal insulation requirements of the above structures are important to eliminate the dew point and consequently the formation of moisture and mold in all structures. In turn, mold and other microorganisms, as studies show, adversely affect the health and normal stay of people in the premises, both during the night and during the day. Many developers do not consider these factors in prefabricated buildings. These buildings are intended for various industries. For example, in healthcare, these are mobile hospitals. In military camps – buildings of temporary residence as barracks, etc.</p> Galym Issabayev, Aimash Slyambayeva, Alpysbay Kelemeshev, Dina Amandykova Copyright (c) 2022 Galym Issabayev, Aimash Slyambayeva, Alpysbay Kelemeshev, Dina Amandykova Sat, 30 Jul 2022 20:10:09 +0300 Quality comparison of Y-shape joints by tube hydroforming with and without counterforce <p>The design capability, strength, and structural rigidity provided by tube hydroforming (THF) are successfully used in many applications to produce high-strength parts and assemblies with improved mechanical properties, optimized service life, and weight features. In tubular metal forming, output parameters such as branch height, distribution of tube wall material thickness, distribution of damage factor, metal flow, effective stress, and effective strain significantly affect the quality of the product after the forming process. Therefore, this paper aims to evaluate the manufacturing quality of Y-shape joints from AISI304 material steel tube through output parameters of THF process with and without counter punch force on numerical simulation base. The Finite Element Method (FEM) has become an established feature of metal forming technology. The objective of FEM is to replace costly and elaborate experimental testing with fast, low-cost computer simulation. The simulation study uses finite element method-based virtual prototyping techniques to characterize output parameters, gain insight into strain mechanics, and predict mechanical properties of shaped components. The research results are presented clearly and unambiguously through the evaluation of 7&nbsp;criteria to compare the quality of the specimens hydroformed by two surveyed cases and optimize the crucial input process parameters. And these data can be applied in experiments, more efficient product and process design, calculation, and control of input parameters avoiding costly trial and error in industrial production. The findings can help technologists optimize process parameters in the hydroforming process of products with protrusion from a tubular blank</p> Quang Vu Duc, Duy Dinh Van, Trung Nguyen Dac, Quang Nguyen Huu Copyright (c) 2022 Quang Vu Duc, Duy Dinh Van, Trung Nguyen Dac, Quang Nguyen Huu Sat, 30 Jul 2022 20:12:37 +0300 Analysis of three-layer gasket performance affected by flange surface <p>Gaskets are components that play a very important role in piping connections to prevent leakage. Several factors affect the performance of the gasket, one of which is the contact surface of the flange. The quality of the contact surfaces in the connection also influences the leakage rate of each connection, therefore the gasket sealing performance is assessed by the rate of leakage that occurs. As a result, the surface roughness of the flange has an effect on sealing. This study examines the capability of a three-layer corrugated metal gasket to prevent leakage when the outside layer thickness and flange roughness are adjusted. The feature of three-layer corrugated metal gasket was elucidated using the finite element analysis (FEA) and experimental method. The leak rate was tested using a helium leak quantity test experimentally. The gasket was constructed with oxygen-free copper (C1020) as the outside layer and SUS304 as the base layer, and it was structured in a three-layer pattern with no bonding. A mold press was used to make the gasket. The simulation method applies finite element analysis software to investigate the correlation between contact stress, contact width, surface thickness and surface roughness. The projected results matched the experiment results fairly well. A three-layer corrugated metal gasket shows improvement capability to prevent leakage than a single gasket (standard). The gasket three-layer shows sealing performance improvement that leakage did not occur in low axial force 40&nbsp;kN for all surface roughness test. In terms of sealing, a three-layer gasket with a low thickness ratio works well. Surface roughness of the flange has no influence on the three-layer gasket</p> I Made Gatot Karohika, Shigeyuki Haruyama Copyright (c) 2022 I Made Gatot Karohika, Shigeyuki Haruyama Sat, 30 Jul 2022 20:15:21 +0300 Heat loads analysis and creation of a uniform model for commercial refrigeration equipment calculation <p>The global commercial refrigeration equipment market size was valued at USD 33.53&nbsp;billion in 2020. It is expected to expand at a compound annual growth rate (CAGR) of 4.2&nbsp;% from 2021 to 2028. Furthermore, factors such as regulatory pressures, shift to lower Global Warming Potential (GWP) refrigerants, technological breakthroughs, and the ability to cater to the ever-changing consumer behaviors are also anticipated to create promising growth opportunities for the market. Environmental issues related to high GWP refrigerants, including global warming and ozone depletion, are compelling commercial refrigeration equipment manufacturers to seek alternatives. The rising demand for advancements in technologies that can help reduce hazardous gas emissions has led to the market participants increasingly equipping their products with modern and magnetic refrigeration systems. Apart from this, these systems improve the energy efficiency of refrigeration equipment, bringing down the cost of operation.</p> <p>The analysis of the structure and heat loads of the commercial freezer with monitoring of temperature distribution on the body of heat-insulating fences and in the internal volume during operation of the system is carried out. The heat loads on the body depending on the structure of the freezer are substantiated on the example of the M400S commercial freezer model. The obtained results allow to significantly reduce the time of selection and calculation of the dimensions of a given model range of equipment for product storage, by developing a standard calculation taking into account the climatic class in which the equipment will be used, and taking into account experimental data obtained during the experiment</p> Ivan Konstantinov, Mykhailo Khmelniuk, Oleksii Ostapenko, Ruslan Talibli, Olga Yakovleva Copyright (c) 2022 Ivan Konstantinov, Mykhailo Khmelniuk, Oleksii Ostapenko, Ruslan Talibli, Olga Yakovleva Sat, 30 Jul 2022 20:17:53 +0300 Development of free water knock-out tank by using internal heat exchanger for heavy crude oil <p>Reactivation of an old oil well can be explicitly calculated to maximize crude oil production. The biggest challenge with the activation process is the crude oil content in old wells, which is not feasible to meet the specified minimum standards. In the case of the Bunian oil field, Indonesia, the crude oil produced has high water content. It causes a decrease in the quality of production and also hinders production capacity. The production scheme applied to the Bunian field has a storage tank that functions to reduce water content using the gravity method, but this is less effective. Let’s modify the storage tank into a heat exchanger tank through the engineering design process and labeled it as a free water knockout tank (FWKO). The FWKO is made of a multi-pass tube heat exchanger. The experiments are conducted through three phases’ tests before deciding the final design. From the test, the change in water content is varied with temperature differences of the working fluid and crude oil. The lowest water content is obtained at 0.5&nbsp;% at final tests. After analyzing the characteristic of each test result, the final design is taken by adjusting the suitable working fluid temperature and pressure. Finally, by using suitable parameters, the average water content of crude oil is decreased up to the minimum requirement (&lt;0.1&nbsp;%). The design of FWKO is considered simple with an excellent performance and can adapted easily. The FWKO able to process crude oil with water content <u>&lt;</u>20&nbsp;%, where it suitable for waxy oil well. The working fluid can be processed both in liquid and gas state. Furthermore, the heating source for the working fluid is gained from the gas flare by using thermic heater. Thus, it does not require an extra heating source for the heat exchanger</p> Ismail Ismail, Ambar Tri Mulyanto, Reza Abdu Rahman Copyright (c) 2022 Ismail Ismail, Ambar Tri Mulyanto, Reza Abdu Rahman Sat, 30 Jul 2022 20:22:35 +0300 Heat transfer analysis cabinet-type ERK solar dryer machine for drying agricultural products <p>The Cabinet-type ERK solar dryer is manufactured by a temperature distribution process so that the temperature inside the appliance is well distributed. The cabinet-type ERK solar dryer comprises several components to maintain the water content, including a drying oven, air blower, heat-resistant pipe, hot water pump, thermostat, heat exchanger, and heater. These tools are used to convert heat radiation into conduction or convection so that the dried agricultural products' water content is relatively low. The data needed to show the quality of the tool include temperature on temperature received by the wall (<em>T<sub>w</sub></em>), absorbent plate (<em>T<sub>p</sub></em>) and room temperature (<em>T<sub>r</sub></em>). And as for other supporting data including the environmental air/ ambient temperature (<em>T<sub>a</sub></em>) and solar irradiation (<em>I</em>) for optimal tool usage time.</p> <p>The experiment results for 5.5 hours, as many as 23 measurements with time interval 15 minutes, obtained a relatively unchanged temperature distribution. During that time, the average temperature received by the wall (<em>T<sub>w</sub></em>) was 41.26&nbsp;°C, while the middle plate temperature (<em>T<sub>p</sub></em>) was 40.65&nbsp;°C and room temperature (<em>T<sub>r</sub></em>) was 40.71&nbsp;°C. Thus, the temperature in the Cabinet-type ERK solar dryer is well distributed. The distribution percentage between wall temperature and plate temperature is 98.52&nbsp;%, while wall temperature and room temperature are 98.67&nbsp;%. The result indicates that the Cabinet-type ERK solar dryer is potential as a drying device for agricultural commodities. It is hoped that the Cabinet-type ERK solar dryer will be an alternative to a drying system that can improve the quality of agricultural commodities for farmers in Indonesia</p> Yayat Ruhiat, Yudi Guntara Copyright (c) 2022 Yayat Ruhiat, Yudi Guntara Sat, 30 Jul 2022 20:29:36 +0300 Analytical study of the velocity of the lubricating fluid in the hydrodynamic journal bearing with the effect of centrifugal force for short bearing type <p>The paper aims to obtain the expression of the velocity of lubricating fluid in the hydrodynamic journal bearings by analytical method. In the classical short-bearing theory, the fluid flow was studied by ignoring the effect of centrifugal force of the lubricating fluid film. However, the self-oscillation of the shaft of high-power motors does not follow the rules in classical hydrodynamic lubrication theory. To explain this phenomenon, a modified form of Reynolds equation, in which the influence of centrifugal force of the lubricant is not ignored, is established. The study aims to establish the modified Reynolds equation by including the effect of centrifugal forces for the case of the short bearing type. Integration of the Navier-Stokes equations, yield the expressions for the components of velocity of the lubricating fluid in the gap. The oil’s pressure in the hydrodynamic journal bearing is obtained by solving the modified Reynolds equation. The numerical results are considered in the case of the stable equilibrium position of the motion of the shaft, i.e. the symmetry axis of the shaft does not move. The plots of the velocity components in the tangential axial direction are displayed too. The theoretical results of a parabolic velocity distribution similar to that of a Newtonian fluid, derived from a Bingham plastic flow model. The flow in the gap, which are obtained by analytical method, are completely consistent with its boundary conditions and its physical properties. Further, with these results, the paper as a lemma to solve the dynamics problem in floating ring bearing with the influence of the centrifugal force of the lubricant</p> Nguyen Van Thang Copyright (c) 2022 Nguyen Van Thang Sat, 30 Jul 2022 00:00:00 +0300 Characterization of WO3 thin films deposited by spray pyrolysis technique and its role in gas sensing <p>The work investigated in this paper focused on the fabrication of WO<sub>3</sub> films by the spray pyrolysis technique, and different analyses were made to find optimized samples for studying properties suitable for the application of gas sensing. The substrate temperature is the most important parameter among other spray parameters for the synthesis of thin films hence WO<sub>3</sub> thin films were deposited on glass substrates by maintaining the substrate temperature at 350&nbsp;ºC, 450&nbsp;ºC, 550&nbsp;ºC, and 650&nbsp;°C using compressed air as a carrier gas. The influence of the substrate temperature on the structural, morphological, compositional, and optical properties of the WO<sub>3</sub> thin films has been justified using XRD data. Good and enhanced crystallinity is observed for the film deposited at a substrate temperature of 550&nbsp;ºC. The nonconventional properties were studied by different investigations and confirmed by past research work. The manipulation of surface morphology with the different deposition temperatures is monitored. Only the characteristic peaks of W and O are present in the fabricated WO<sub>3</sub> thin films. The optical activity of about 70 to 80&nbsp;% of the selected sample in the visible region (300 to 1200&nbsp;nm) is found. The selective absorption activity of light in the ultraviolet region and visible region is checked. The obtained IR bands confirmed the inter bridge stretching and bending modes of W-O and O-W-O. A high response towards ammonia compared to other test gases is exhibited. The repeatability of WO<sub>3</sub> towards NH<sub>3</sub> over three periodic sensing cycles, response, and recovery time has also been discussed. From all the characteristic studies, it has been suggested that the fabricated WO<sub>3</sub> thin films have been used in the health care field to detect the toxic NH<sub>3</sub> gas</p> Sivaraman Sethu Sivathas, Sambandam Murugan, Arthur Victor Babu, Singaravelu Ramalingam, Ramalingam Thirumurugan, Devanugraham Clement Easter Raj Bernice Victoria Copyright (c) 2022 Sivaraman Sethu Sivathas, Sambandam Murugan, Arthur Victor Babu, Singaravelu Ramalingam, Ramalingam Thirumurugan, Devanugraham Clement Easter Raj Bernice Victoria Sat, 30 Jul 2022 20:35:45 +0300 Detection of the synergetic influence of chemical and microbiological factors on the properties of concrete constructions at chemical plants during the long-term service <p>Long-term operation of reinforced concrete structures in the conditions of chemical enterprises has a powerful negative impact on the physical and chemical properties of concrete, which leads to its destruction. The aim of this research is to determine the effect of biological and chemical corrosion on concrete structures in the workshop for the production of titanium dioxide by the sulphate method and the storage of finished products. In particular, chemical production for the synthesis of titanium dioxide by the sulfate method causes the rapid course of chemical (acid and sulfate) and microbiological (thionic bacteria and microscopic fungi) corrosion processes. These corrosion processes reinforce each other according to a synergistic principle. As a result, temperature-programmed desorption mass spectrometry (TPD MS) and scanning electron microscopy have experimentally proven the presence and spatial localization of colonies of thionic bacteria and microscopic fungi in concrete structures. Correlations between the intensity of biochemical corrosion and the depth of damage to the microstructures of concrete structures have been established. Moreover, a change in the chemical composition of concrete in the workshop for the production of titanium dioxide (increased SO<sub>2</sub> content and reduced CO<sub>2</sub>) and the formation of gypsum crystals (CaSO<sub>4</sub> 2H<sub>2</sub>O) as a result of the dissimilation of microorganisms was established. Also, in the storage room for finished products, calcium citrate crystals and a violation of the formation of calcium carbonate are formed in the surface layers of concrete. In addition, the results of the study can be used to develop antimicrobial and anticorrosive protective agents to stop the biochemical corrosion of concrete in a chemical plant</p> Oksana Shkromada, Alina Pikhtirova, Vadym Chivanov, Viktoriia Ivchenko, Nataliia Sribniak, Olha Shvets, Yuliia Litsman Copyright (c) 2022 Oksana Shkromada, Alina Pikhtirova, Vadym Chivanov, Viktoriia Ivchenko, Nataliia Sribniak, Olha Shvets, Yuliia Litsman Sat, 30 Jul 2022 20:38:40 +0300 Geometric approach to the proof of Fermat’s last theorem <p>A geometric approach to the proof of Fermat’s last theorem is proposed. Instead of integers <em>a</em>, <em>b</em>, <em>c</em>, Fermat’s last theorem considers a triangle with side lengths <em>a</em>, <em>b</em>, <em>c</em>. It is proved that in the case of right-angled and obtuse-angled triangles Fermat's equation has no solutions. When considering the case when <em>a</em>, <em>b</em>, <em>c</em> are sides of an acute triangle, it is proved that Fermat's equation has no entire solutions for <em>p</em>&gt;2. The numbers <em>a</em>=<em>k</em>,<em> b</em>=<em>k</em>+<em>m</em>,<em> c</em>=<em>k</em>+<em>n</em>, where <em>k</em>, <em>m</em>, <em>n</em> are natural numbers satisfying the inequalities <em>n</em>&gt;<em>m</em>, <em>n</em>&lt;<em>k</em>+<em>m</em>, exhaust all possible variants of natural numbers <em>a</em>, <em>b</em>, <em>c</em> which are the sides of the triangle.</p> <p>The proof in this case is carried out by introducing a new auxiliary function <em>f</em>(<em>k</em>,<em>p</em>)=<em>k<sup>p</sup></em>+(<em>k</em>+<em>m</em>)<em><sup>p</sup></em>–(<em>k</em>+<em>n</em>)<em><sup>p</sup></em> of two variables, which is a polynomial of degree in the variable . The study of this function necessary for the proof of the theorem is carried out. A special case of Fermat’s last theorem is proved, when the variables <em>a</em>, <em>b</em>, <em>c</em> take consecutive integer values. The proof of Fermat’s last theorem was carried out in two stages. Namely, all possible values of natural numbers <em>k</em>, <em>m</em>, <em>n</em>, <em>p</em> were considered, satisfying the following conditions: firstly, the number (<em>n<sup>p</sup></em>–<em>m<sup>p</sup></em>) is odd, and secondly, this number is even, where the number (<em>n<sup>p</sup></em>–<em>m<sup>p</sup></em>) is a free member of the function <em>f</em>(<em>k</em>,&nbsp;<em>p</em>).</p> <p>Another proof of Fermat’s last theorem is proposed, in which all possible relationships between the supposed integer solution of the equation <em>f</em>(<em>k</em>,&nbsp;<em>p</em>)=0 and the number corresponding to this supposed solution &nbsp;are considered.</p> <p>The proof is carried out using the mathematical apparatus of the theory of integers, elements of higher algebra and the foundations of mathematical analysis. These studies are a continuation of the author's works, in which some special cases of Fermat’s last theorem are proved</p> Yuriy Gevorkyan Copyright (c) 2022 Yuriy Gevorkyan Sat, 30 Jul 2022 20:41:18 +0300 Study of the secondary characteristics of the bistatic scattering of a combined object in a covert radar surveillance system <p>The emergence of new means of attack, reconnaissance and methods of sabotage imposes special requirements on the technical means of protecting important state facilities (ISF). Modern trends in the construction of ISF physical protection systems are the integration of engineering barriers, perimeter signaling and detection tools. Detection tools should provide covert receipt of information about the approach of the intruder in "distant" intrigues. To do this, it is possible to use technical means built on the principle of semi-active bistatic radar with an external illumination source. However, in order to identify intruders in the ISF protection zone, it is necessary to have a priori information about the radar visibility of the combined location objects. The combined object is typically a complex object having both metallic and dielectric elements.</p> <p>To this end, a technique has been developed for estimating the radar cross-section (RCS) of combined objects in the field of external illumination. The electromagnetic field (EMF) scattered by a combined object in the meter and decimeter wavelength ranges is calculated as a coherent sum of fields, taking into account their phase, scattered by its metal and dielectric elements. This made it possible to take into account the electromagnetic interaction of the elements of the combined object. The method of integral equations (IE) was used to find the current density and magnetic field strength.</p> <p>The scatter diagrams of the person-intruder, the person-intruder in personal armor protection (PAP) under different conditions of irradiation and reception and illumination frequencies are obtained and analyzed. This made it possible to evaluate the effect of metallic elements on the scatter diagram of the combined object.</p> <p>The obtained a priori information is of significant practical importance at the stage of optimizing signal processing algorithms and designing new means of covert detection</p> Stanislav Horielyshev, Pavlo Volkov, Igor Boikov, Dmitro Baulin, Hryhorii Ivanets, Aleksandr Nakonechnyi, Svyatoslav Manzhura, Valentyn Yuriev, Natalia Gleizer Copyright (c) 2022 Stanislav Horielyshev, Pavlo Volkov, Igor Boikov, Dmitro Baulin, Hryhorii Ivanets, Aleksandr Nakonechnyi, Svyatoslav Manzhura, Valentyn Yuriev, Natalia Gleizer Sat, 30 Jul 2022 20:43:51 +0300 Analysis of GPON capacity by hybrid splitting-ratio base on customer segmentation for Indonesian market during the Covid-19 pandemic <p>During the Covid-19 pandemic, the impact on internet demand is very high throughout the world. In Indonesia, through a survey conducted, broadband users recorded 175 million people or equivalent to 64&nbsp;% of the population. Based on field observations, the Passive Optical Network (PON) port utility in the Optical Line Terminal (OLT) is presently below 75&nbsp;%, as opposed to the initial value, which was more than 95&nbsp;% [1]. Furthermore, it was also found that more than 80&nbsp;% of IndiHome customers use a maximum bandwidth of 20&nbsp;Mbps with majority using 10&nbsp;Mbps, which is very ineffective, especially related to network capacity. Generally, passive Optical Distribution Network (ODN) devices are not optimally used, therefore this research aims to determine the optimization level of the FTTH network by maximizing the available infrastructure capacity. This process was carried out by increasing the associate ratio of 1:32 to 1:64 while taking into account the Optical Line Terminal (OLT) capacity factor and the standard link budget with schemas A, B and C used to obtain adequate efficiency. Scheme A consists of a 1:2 passive splitter in the Optical Distribution Cabinet (ODC) &amp; 1:32 at the Optical Distribution Point (ODP). Scheme B consists of a 1:4 (ODC) &amp; 1:16 (ODP) passive splitter, while scheme C consists of a 1:8 (ODC) &amp; 1:8 (ODP) passive splitter intended for the use of different customer area types. The result showed an increase in network capacity from 32 to 64 per PON port while taking into account the technical quality of the Link Budget. In conclusion, to ensure this solution functions properly, both simulation and direct measurement tests are carried out using the existing network</p> Gunadi Dwi Hantoro, Purnomo S. Priambodo, Gunawan Wibisono Copyright (c) 2022 Gunadi Dwi Hantoro, Purnomo S. Priambodo, Gunawan Wibisono Sat, 30 Jul 2022 20:46:09 +0300 Development of a convolutional neural network joint detector for non-orthogonal multiple access uplink receivers <p>We present a novel approach to signal detection for Non-Orthogonal Multiple Access (NOMA) uplink receivers using Convolutional Neural Networks (CNNs) in a single-shot fashion. The defacto NOMA detection method is the so-called Successive Interference Cancellation which requires precise channel estimation and accurate successive detection of the user equipment with the higher powers. It is proposed converting incoming packets into 2D image-like streams. These images are fed to a CNN-based deep learning network commonly used in the image processing literature for image classification. The classification label for each packet converted to an image is the transmitted symbols by all user equipment joined together. CNN network is trained using uniformly distributed samples of incoming packets at different signals to noise ratios. Furthermore, let’s performed hyperparameter optimization using the exhaustive search method. Our approach is tested using a modeled system of two user equipment systems in a 64-subcarrier Orthogonal Frequency Division Multiplexing (OFDM) and Rayleigh channel. It is found that a three-layer CNN with 32&nbsp;filters of size 7×7 has registered the highest training and testing accuracy of about 81. In addition, our result showed significant improvement in Symbol Error Rate (SER) vs. Signal to Noise Ratio (SNR) compared to other state-of-the-art approaches such as least square, minimum mean square error, and maximum likelihood under various channel conditions. When the channel length is fixed at 20, our approach is at least one significant Figure&nbsp;better than the maximum likelihood method at (SNR) of 2&nbsp;dB. Finally, the channel length to 12 is varied and it is registered about the same performance. Hence, our approach is more robust to joint detection in NOMA receivers, particularly in low signal-to-noise environments</p> Raed S. H. AL-Musawi, Ali Hilal Ali, Kadhum Al-Majdi, Sarmad Al Gayar Copyright (c) 2022 Raed S. H. AL-Musawi, Ali Hilal Ali, Kadhum Al-Majdi, Sarmad Al Gayar Sat, 30 Jul 2022 20:49:05 +0300 Synthesis of decision making in a distributed intelligent personnel health management system on offshore oil platform <p>This paper proposes a methodological approach for the decision synthesis in a geographically distributed intelligent health management system for oil workers working in offshore industry. The decision-making methodology is based on the concept of a person-centered approach to managing the health and safety of personnel, which implies the inclusion of employees as the main component in the control loop. This paper develops a functional model of the health management system for workers employed on offshore oil platforms and implements it through three phased operations that is monitoring and assessing the health indicators and environmental parameters of each employee, and making decisions. These interacting operations combine the levels of a distributed intelligent health management system. The paper offers the general principles of functioning of a distributed intelligent system for managing the health of workers in the context of structural components and computing platforms. It presents appropriate approaches to the implementation of decision support processes and describes one of the possible methods for evaluating the generated data and making decisions using fuzzy pattern recognition. The models of a fuzzy ideal image and fuzzy real images of the health status of an employee are developed and an algorithm is described for assessing the deviation of generated medical parameters from the norm. The paper also compiles the rules to form the knowledge bases of a distributed intelligent system for remote continuous monitoring. It is assumed that embedding this base into the intelligent system architecture will objectively assess the trends in the health status of workers and make informed decisions to eliminate certain problems</p> Masuma Mammadova, Zarifa Jabrayilova Copyright (c) 2022 Masuma Mammadova, Zarifa Jabrayilova Sat, 30 Jul 2022 20:51:31 +0300