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A novel high-precision model of a custom-made coaxial chamber used for broadband measurement of the relative complex permittivity at microwave frequencies is presented. The model is based on a surface integral-equation formulation of the method of moments tailored for bodies of revolution. All singular integrals encountered in the numerical analysis are calculated in a unified way with a novel integral transformation, which enables the precision of up to 12 significant digits using the 64-bit representation of real numbers. The dielectric parameters are estimated from the reflection-coefficient measurement of the chamber with a disk-shaped dielectric sample by comparison of the measured data with the high-precision numerical analysis of the chamber. The complete measurement procedure is illustrated and verified using samples of known dielectric properties. This is the peer-reviewed version of the paper: Petrović, J.G., Olćan, D.I., Obradović, N.N., Djordjević, A.R., 2022. High-Precision Method of Moments Applied to Measurement of Dielectric Parameters at Microwave Frequencies. IEEE Transactions on Microwave Theory and Techniques, 70, 2, 970-979. [https://doi.org/10.1109/TMTT.2021.3136294]

An approach to singularity cancelation by a variable transformation of Green’s function in 2-D case, having log( $R$ ) singularity, is outlined. It is intended for the method of moments analysis of 2-D structures of both curvilinear and flat cross sections. If the transformation is used with Legendre or Chebyshev polynomials as entire-domain basis functions, all involved integrals can be calculated with high precision using Gauss–Legendre quadrature. The optimal parameter of the transformation, having the minimal number of integration samples needed to reach 14-digit precision, is provided. Error estimations are presented for calculated current distributions on strips up to 400 wavelengths wide, analyzed with up to 1500 entire-domain basis functions.

Nonuniform helical antennas have many degrees of freedom, which makes the search space for the optimal design very challenging. The objective of this paper is to systematically analyze nonuniform helical antennas with linearly varying geometrical parameters and to provide analytical equations that approximate the optimal design and the gain of the designed antennas. Using various optimization algorithms, we made a large database of the optimal nonuniform helical antennas with linearly varying geometrical parameters. Based on these results, we made analytical equations that approximate the optimal design and the gain of the designed antennas. These equations allow for a fast design procedure yielding all necessary parameters needed for the design and fabrication of nonuniform helical antennas that meet specified characteristics. Special attention is devoted to antenna losses. Antennas designed following the presented procedure achieve around 2.5 dB higher gain than uniform helical antennas of the same axial length, while maintaining the bandwidth and axial ratio. As a verification of the proposed design procedure, a helical antenna with the central operating frequency of 1 GHz was designed, simulated, fabricated, and measured. The comparison between measured and simulated results confirms the validity of the presented design procedure.

The aim of the research is to assess the influence of pszchosocial factors of the working environment on the working capacitz index of health workers in clinical and hospital activities. ...

Solid-state reaction between BaTiO3and Fe2O3was used to produce a multiferroic heterostructure composite. Commercial BaTiO3and Fe(NO3)3•9H2O were suspended in ethanol for 30 minutes in an ultrasound bath. The prepared mixture was thermally processed at 300°C for 6 h. Sintering at 1300 °C for 1 h resulted in a mixture of different phases, BaTiO3, BaFe12O19and Ba12Ti28Fe15O84, which were confirmed by x-ray powder diffraction. A dense microstructure with a small volume fraction of closed porosity was indicated by the scanning electron microscopy, while a homogeneous distribution of Fe ions over BaTiO3phase was visible from energy dispersive spectroscopy mapping. Doping of BaTiO3with Fe2O3resulted in formation of magnetic hexaferrite phases, as confirmed by dielectric measurements that showed a broadened maximum of the permittivity measured as a function of temperature. © 2021 Authors. Published by association for ETRAN Society.

We propose a design approach for band-pass microwave filters based on optimization of discrete-valued parameters of filters using an implementation of (1 + (l, l)) genetic algorithm. If the filter is made of SMD components then only discrete values are allowed. The proposed design approach yields a solution with feasible components values in the end, without further need for tuning and adjustments of component values that is needed in the case when real numbers are used during optimization. The optimization setup is run for 20 times and obtained (suboptimal) solutions are presented. One of the best optimized solutions of a band-pass filter is chosen for further analysis. The found filter design is verified using a circuit solver including the yield analysis, 3D electromagnetic simulations and by measurements of the manufactured prototype. The presented results as well as the optimization run-time show that the proposed approach based on discrete optimization can be used to design microwave filters.

Sintering of pure cordierite 2MgO:2Al2O3:5SiO2, and cordierite with the addition of 5 mass % TeO2 was studied. Green bodies were prepared from powder mixtures mechanically activated in a high-energy planetary mill, shaped by uniaxial (20 MPa) and cold isostatic pressing (1000 MPa). The pressure-less sintering of these specimens was performed at 1350°C for 1 h. High relative density over 95% of the theoretical value was obtained through solid-state reaction and pressure-less sintering of powder activated for 40 min, and for the first time reported in the literature. Phase composition and microstructures of sintered samples were determined by XRD and SEM, coupled with EDS mapping. The real part of the complex relative permittivity of the samples was measured at 200 MHz. The loss tangent of all samples was below the resolution of the measurement setup. A strong correlation between the relative permittivity and the density agrees with previously published data. This is the peer-reviewed version of the article: Obradović, N., Pavlović, Vera, Kachlik, M., Maca, K., Olćan, D., Đorđević, A., Tshantshapanyan, A., Vlahović, B., Pavlović, Vladimir, 2018. Processing and properties of dense cordierite ceramics obtained through solid-state reaction and pressure-less sintering. Advances in Applied Ceramics. [https://doi.org/10.1080/17436753.2018.1548150]

На сьогодні бухгалтерська звітність є одним з найбільш динамічних елементів методу обліку. Перш за все, це пов’язано з відповідністю його предметa вимогам різних користувачів, які бажають дізнатися, що економічні умови в реальності швидко змінюються. Тому, застосовуючи методи економічного аналізу на основі даних бухгалтерського обліку, можна розрахувати діапазон цифр, що дають можливість оцінити як фінансовий стан, так і економічний потенціал підприємства в майбутньому і минулому. Тому для обчислення таких цифр у справах бухгалтерського обліку повинна бути інформація про надзвичайні наслідки, що впливають на виробничі процеси, вартість продукції і фінансові результати підприємства. Ця умова дозволить оцінити їхній вплив на фінансові показники та економічний потенціал підприємства. Сформульовано напрями розширення фінансової звітності за змістом і формою. Фінансова звітність удосконалюється з метою відображення інформації про надзвичайні наслідки за рахунок розширення факторів у наявних главах (як частина інших витрат) і формування нової глави V «Зовнішні та внутрішні ризики впливу на навколишнє середовище», що містить інформацію про відокремлення надзвичайних наслідків від витрати на діяльність. Фрагменти приміток до річної фінансової звітності розроблено, що дає можливість оцінити вплив надзвичайних наслідків на необоротні та оборотні активи і виробничий процес. Побудова конкретної інформації для внутрішнього використання про надзвичайні наслідки здійснюється на основі обґрунтованих напрямів формування внутрішньої звітності та розроблення шляхів і механізмів формування їхніх факторів. Це дозволило підвищити якість інформаційного простору управління діловою діяльністю в надзвичайних умовах. Використання пропозицій на практиці сприяло підвищенню якості інформаційного простору при ухваленні рішень користувачами і розробленні комплексу заходів щодо запобігання надзвичайним наслідкам та їх ліквідації . У свою чергу, аналітичні заходи, розраховані на основі їхніх фактів, ураховуватимуть низку факторів, що дозволяють повністю оцінити фінансовий стан та економічний потенціал., На сегодня бухгалтерская отчетность является одним из наиболее динамичных элементов бухгалтерского учета. Прежде всего, это связано с соответствием его предмета требованиям различных пользователей, желающих узнать, что экономические условия в реальности быстро меняются.Поэтому, применяя методы экономического анализа на основе данных бухгалтерского учета, можно рассчитать диапазон цифр, которые дают возможность оценить как финансовое состояние, так и экономический потенциал предприятия в будущем и прошлом. Построение конкретной информации для внутреннего использования о чрезвычайных последствия осуществляется на основе обоснованных направлений формирования внутренней отчетности и разработки путей и механизмов формирования их факторов. Использование предложений на практике способствовало повышению качества информационного пространства при принятии решений пользователями и разработке комплекса мероприятий по предотвращению и ликвидации чрезвычайных последствий., Nowadays accounting statements is one of the most dynamic accounting method elements. First and foremost it is related to the correspondence of its subject-matter to the demands of different users willing to know economic conditions in reality changing rapidly. Thus, applying methods of economic analysis on the basis of accounting data it is possible to calculate a range of figures giving an opportunity to estimate both financial condition and economic potential of the enterprise in the future and the past. That is why to calculate such figures in the copes of accounting there should be information about emergency consequences cases affecting the production processes, product cost and further the enterprise’s financial results. This condition will allow estimate their influence on the financial figures and economic potential of the enterprise. The directions of financial statement’s expanding in content and form are articulated. Financial statement is improved in order to reflect information about emergency consequences through expanding factors in already existing chapters (as a part of other costs) and formation of the new chapter V «External and internal risks environmental impact» containing information about separation of emergency consequences from activity costs. Fragments of notes to the annual financial statement are developed giving an opportunity to estimate the impact of emergency consequences on noncurrent and current assets and the production process. Building specific information for internal use about emergency consequences is performed on the basis of justified directions of internal reporting formation and development of ways and mechanisms of their factors formation. It allowed to increase quality of information space of business activity management in emergency conditions. The use of suggestions in practice contributed to increasing the information space quality in users’ decision-making and developing a complex of measures to prevent and address the emergency consequences. In its turn analytical measures calculated on the basis of their facts will take into account a number of factors allowing to fully estimate the financial condition and economic potential.

This paper proposes a method for efficient identification of instruction-dependent sources on a printed circuit board (PCB) by localizing magnetic field sources from a limited number of measurements around the PCB. We first excite the processor by generating an artificial leakage signal at a specific frequency that is directly related to processor instructions. Then, we collect all three components of the magnetic field, but only at locations around the edge of the board. Furthermore, we model these magnetic field sources and then solve a forward–backward optimization problem using the model and measured data to identify the locations of the magnetic field sources, the magnitudes of the moments, and their orientations. The localization results are first verified using simulations, then tested when noise is added to the simulation results, and finally verified against measurements on field-programmable gate array (FPGA) and internet of things (IoT) development boards. The results show that the number of strong magnetic field sources on a board depends on the instructions used to excite the board. Furthermore, the results show that the proposed localization algorithm can accurately identify those sources, regardless of the frequency at which the measurements are conducted and the instruction pairs that are executed. Finally, the proposed method can significantly reduce the number of measurement points and the time needed to identify magnetic field sources on a PCB.

The aim of this paper is to research the processes and relationships between urban network and administrative divisions in the Republic of Serbia. The hierarchy of urban centers is established on the basis of two indicators of European Spatial Planning Observation Network (ESPON) methodology: the population morphological urban area (minimum of 15,000 inhabitants or close to this number in specific cases) and percentage of functional urban areas above 0.5 percent of the national population. On the basis of relevant data comparison is conducted of functional urban areas and the status of cities in the new territorial organization of local government in the Republic of Serbia.

Excess attenuation of electric field of an electromagnetic wave propagating through deciduous forest is approximated with two novel analytical formulas. The coefficients of those formulas were obtained through a computationally intensive optimization process by fitting the simulation results obtained from stochastic 3D and 2D models of forests. The electric field was either vertically or horizontally polarized, at frequencies 30 MHz, 60 MHz and 100 MHz. According to numerical experiments, these formulas predicted the excess attenuation within several decibels, up to at least 100 MHz. Nevertheless, the proposed formulas matched very well the measured data from literature below 1 GHz, and neatly followed the measurements even up to 10 GHz. Therefore, the frequency range considered in the numerical experiments can be extrapolated at least tenfold.

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The problem of study of the influence of information and communication technologies (ICT) on the change of indicators of export and import of goods, which forms the basis for calculation and forecasting of changes in indicators of foreign trade security of the state, is considered. It is established that the influence of this factor on the foreign trade security of the state in any country is dual: as an opportunity to strengthen it and as a threat to its stability. It is determined that the search for an acceptable balance between the possibilities of strengthening the foreign trade security of the state in the conditions of rapid growth of ICT (digitalization), on the one hand, and the risks arising from the inadequate level of development of different types of ICT infrastructure of the country on the other hand, is becoming a relevant research problem. The most significant economic researches in the field of theoretical foundations of the theory of gravitational modeling and the main stages of its evolution are analyzed. The basic gravity model of trade has been improved due to the additional inclusion of indicators of the state of development of ICT as institutional factors and indicators of foreign trade security of the country in terms of country and time effects (on the example of the main export commodity group of Ukraine — steel and its products). Parameters of the gravity model were estimated on the basis of retrospective data using econometric methods using software packages of Stata or R. The results of the simulation of the estimation of the influence of factors of development of ICT of the country on volumes of foreign trade in steel and steel products are analyzed. The results indicate a positive impact of the use of the Internet and mobile phones on increasing exports of steel and products from it. This gives grounds for confirming the theoretical assumptions about the large volumes of steel products traded between countries with high demand and supply, and also points to the importance of reducing costs and time for the transport of these goods, in the case of countries not neighboring. At the same time, the use of modern ICT tools will have a positive effect on the volumes of metallurgical products sales, both in the domestic and foreign markets, by gaining competitive advantages in relation to other players in the market., Рассмотрена проблема изучения влияния информационно-коммуникационных технологий (ИКТ) на изменение показателей экспорта и импорта товаров, составляющих основу для расчета и прогнозирования изменения индикаторов внешнеторговой безопасности государства. Проанализированы наиболее значимые экономические исследования в сфере теоретических основ теории гравитационного моделирования и основные этапы ее эволюции. Усовершенствована базовую гравитационную модель торговли за счет дополнительного включения показателей состояния развития ИКТ в качестве институциональных факторов и индикаторы внешнеторговой безопасности государства в качестве фиксированных по странам и время эффектов (на примере основной экспортной товарной группы Украина — стали и изделий из нее). Проанализированы результаты моделирования оценки воздействия факторов развития ИКТ страны на объемы внешней торговли сталью и стальными изделиями., Розглянуто проблему вивчення впливу інформаційно-комунікаційних технологій (ІКТ) на зміну показників експорту та імпорту товарів, що є основою для розрахунку та прогнозування змін показників зовнішньоторговельної безпеки держави. Установлено, що вплив цього фактору на зовнішньоторговельну безпеку держави в будь-якій країні є подвійним: як можливість зміцнити її і як загрозу її стабільності. Визначено, що пошук прийнятного балансу між можливостями зміцнення зовнішньоторговельної безпеки держави в умовах стрімкого зростання ІКТ (оцифрування), з одного боку, та ризиків, що виникають з неадекватного рівня розвитку, — з другого, різні види ІКТ-інфраструктури країни стають актуальною дослідницькою проблемою. Проаналізовано найбільш значні економічні дослідження в області теоретичних основ теорії гравітаційного моделювання та основні етапи її еволюції. Удосконалено базову гравітаційну модель торгівлі завдяки додатковому включенню показників стану розвитку ІКТ як інституційних чинників і показників зовнішньоторговельної безпеки країни в умовах країни та часових ефектів (на прикладі основної експортної товарної групи Україна — сталь та її продукція). Параметри гравітаційної моделі оцінювали на основі ретроспективних даних з використанням економетричних методів та програмних пакетів Stata або R за результатами моделювання оцінки впливу факторів розвитку ІКТ країни на обсяги зовнішньої торгівлі. Проаналізовано сталь і сталеву продукцію. Результати вказують на позитивний вплив використання Інтернету та мобільних телефонів на збільшення експорту сталі та виробів з неї. Це дає підстави для підтвердження теоретичних припущень про великі обсяги торгівлі виробами зі сталі між країнами з високим попитом і пропозицією, а також вказує на важливість зниження витрат і часу на перевезення цих товарів у країнах, які не є сусідніми. Водночас використання сучасних засобів ІКТ позитивно вплине на обсяги реалізації металургійної продукції як на внутрішньому, так і на зовнішньому ринках, за рахунок отримання конкурентних переваг щодо інших гравців на ринку.

We present a design of a high-gain quad array of nonuniform helical antennas. The design is obtained by optimization of a 3-D numerical model of four nonuniform helical antennas placed above a ground plane, including a model of a feeding network, utilizing the method of moments with higher-order basis functions. The gain of one optimal nonuniform helical antenna can be about 2.5 dB higher than the gain of a uniform helical antenna of the same axial length. Creating a 2×2 array further increases the gain up to about 6 dB. The resulting quad array fits into a box whose dimensions are 2.5×3.3×3.3 wavelengths, and the gain in the main radiating direction is about 20.5 dBi in the frequency range from 0.9 GHz to 1.1 GHz. The design is verified by measurements of a prototype of the quad array.

A novel diakoptic method based on volume integral equation (VIE) modeling of subsystems is proposed for 3-D electromagnetic analysis. The theoretical foundation of the method is the surface and volume equivalence principles, as it combines the VIE and surface integral equation (SIE) formulations, in conjunction with the method of moments (MoM). The method breaks the original structure into a number of nonoverlapping closed-region subsystems that contain inhomogeneous dielectric materials and an open-region subsystem. Each subsystem is analyzed completely independently applying the double higher order large-domain Galerkin generalized MoM-VIE-SIE (VSIE) or MoM-SIE solvers. The final solution is obtained from diakoptic matrices expressing linear relations between the electric and magnetic equivalent surface current coefficients on diakoptic surfaces. The proposed VSIE-diakoptic method is validated, evaluated, and discussed in several characteristic examples. The examples demonstrate that the diakoptic method substantially increases the efficiency of the conventional MoM-VIE approach. When compared with the pure MoM-VIE double higher order technique, the diakoptic approach enables very considerable accelerations and memory savings, while fully preserving the accuracy of the analysis.

The mechanical activation can help reduce production costs and modify cordierite-based materials. In this study, the structure and electrical properties of the mechanically activated MgO-Al2O3-SiO2 system have been analyzed. The mixtures of MgO-Al2O3-SiO2 powders were mechanically activated in a planetary ball mill for time periods ranging from 0 to 160 min. Structural investigations were performed on the obtained powders. The effects of activation and a two-step sintering process on the microstructure and crystal structure were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The thermal stability was analyzed using DTA. Electrical measurements showed variations of the dielectric constant (epsilon(r)) and loss tangent (tan delta) as a function of the time of mechanical treatment.

Cordierite-based ceramic materials are attracting much interest for their various applications in industry, for manufacturing multilayer circuit boards, catalytic converters, filters, thermal insulation, kiln furniture, components of portable electronic devices, etc. In order to reduce production costs and modify cordierite-based materials, mechanical activation can be used. In this study, microstructural and electrical properties of mechanically activated MgO-Al2O3-SiO2 system have been analyzed. The mixtures of MgO-Al2O3-SiO2 powders were mechanically activated in a planetary ball mill for the time periods from 0 to 160 min. Morphological investigations have been performed on the obtained powders. The effects of activation and two-step sintering process on microstructure were investigated by scanning electron microscopy (SEM). Electrical measurements showed variations of the dielectric constant (er) and loss tangent (tan δ) as a function of time of mechanical treatment.