All Articles

Summary: Nowadays, beams, boards and coatings with new complex properties are widely used in many branches of mechanical engineering and construction. The calculation and analysis of the amplitude characteristics of stability, strength and frequency of a structural element with these properties lead both to significant difficulties in mathematical terms and to the analysis of the results obtained, if ignored, serious errors may be made. Taking these into account, it becomes necessary to build mathematical models characterizing the real properties of the material when using a structural element made of new materials and establishing effective physical connections. There are materials in which the tensile strain diagrams characterizing their properties are diverse in tension-compression and torsion. Such materials include ceramics, some types of copper and cast iron, polymers, and composite materials. The mechanical and physical properties of these materials become strictly dependent on hydrostatic pressure. For materials with the above-mentioned specific property, classical elasticity and elastoplasticity cannot be considered under the conditions accepted by the theory of plasticity. In this paper, a problem of planar stability of an elastic, plastic plane differently resisting to tension and compression in pure bending is solved. It is assumed that the cross-section of the beam has one symmetry axis, under the action of concentrated moments applied at the ends of the bar is subjected to pure bending, and bending happens in the symmetry plane of the beam. Using the state of a neutral axis, absence of longitudinal force, continuity conditions for tension and compression, we determine the boundary of elastic and plastic domains. The equations of the loss of planar stability obtained for the classic case are reduced to the loss of planar stability for various modulus ideal elastic and plastic beams. The expressions of hardness for different modulus materials are obtained and are associated with critical moment and critical length. Expressions for calculating critical parameters for an ideally elastic, plastic beam with a rectangular cross section are obtained.

Summary: Increasing the properties of iron-based abrasive composition materials by volume and surface alloying is of scientific and technical importance. Since increasing the properties of composite materials by volume alloying causes a number of difficulties, surface alloying is often used to improve the properties of this type of materials. Therefore, in order to increase the properties, successive saturation processes of their surface layer with one or more carbide-forming elements are carried out. It was found that the properties enhancement with one-component coatings differs from the properties of multi-component coatings. It is clear that as a result of the saturation of the surface layer of the abrasive composition materials with certain elements, coatings with different composition are created in them. Carbide, nitride, boride and other coatings allow to obtain the necessary results. Therefore, the improvement of the structure and properties of iron-based abrasive composition materials directly depends on the coatings formed as a result of hammering the surface layer of construction materials with various elements. In the article, the effect of carbide, nitride and boride-containing coatings on the structure and properties of iron-based abrasive composition materials was considered. The distribution of chromium in the depth of the diffusion layer was studied by the method of micro-X-ray spectral analysis. The greatest concentration of chromium is observed on the surface, which increases as the degree of carbonization of the material increases. The change of the amount of chromium on the depth of the carbide zone obeys a linear law. At the boundary of the carbide zone, its concentration is approximately the same in the studied materials and is 58-61% In connection with the increase in the initial carbonization degree of the surface zone, the increase in the concentration of chromium is accompanied by the increase in the microhardness of the carbide coating. Based on the data of X-ray structural studies, the studied carbide coatings have the same phase composition (Cr, Fe) C 23 6, (Cr,Fe) C 7 3. The structure of the transition zone and its layers is determined by the degree of carbonization of the material during the initial processing. At relatively low temperatures (875 and 925 °C) in cementitized iron, as in the case of JQr 0.5 composition, a weakly tanned zone (20-25 μm thick) of an extremely saturated γ-solid solution with a microhardness H100 = 6100-7000 MPa, formed in the process of cooling from the air chroming temperature directly under the carbide layer is located. Behind it is a zone of high etching ability, which is caused by the eutectoid decomposition of the solid solution of chromium and carbon in γ-iron. The intermediate zone of annealed iron cementitized at 975-1025 °C undergoes eutectoid decomposition during cooling in air and metallographically is detected as a band with high etching ability.

Summary: This paper explores the effect of oil price, gross domestic product (GDP), and carbon dioxide (CO2) emissions on renewable energy consumption in China from 1990 to 2020, utilizing the canonical cointegrating regression (CCR) method. The findings indicate that the oil price, GDP and CO2 emissions positively and significantly affect renewable energy consumption over the examined time frame. Numerically, a 1% increase in oil prices, GDP, and CO2 emissions results in a 0.16%, 0.39%, and 1.70% increase in renewable energy consumption, respectively. The positive effect of oil prices on renewable energy consumption can be seen as the cost advantage of renewable energy, which may grow with rising oil prices, leading to a rise in its adoption. The study underscores the significance of promoting renewable energy usage, emphasizing the need for policies that aid energy security and environmental sustainability.

Summary: Exploring the relationship between international oil prices, income, and carbon dioxide (CO2) emissions in Saudi Arabia, this study examines if renewable energy consumption plays a lowering tool in international oil prices' impact on CO2 emissions, employing conventional econometric methods and the functional coefficient approach. The study reveals that the interaction between renewable energy consumption and international oil prices has a negative and statistically significant impact on CO2 emissions. This emphasizes the potential for Saudi Arabia to reduce carbon emissions by prioritizing renewable energy projects. In addition, a positive and statistically significant relationship between income and CO2 emissions is found, emphasizing the need to decouple economic growth from emissions growth. Furthermore, an interesting decoupling effect between oil price elasticity of CO2 emissions and per capita GDP is noted from the early 2000s–2015. This indicates that economic growth driven by rising oil prices can be managed to mitigate environmental impact, showcasing Saudi Arabia's commitment to sustainable development. Policy recommendations involve intensifying efforts to promote renewable energy implementation, lowering fossil fuel dependence in power generation, and incentivizing emissions reduction for a more sustainable energy future.

Summary: The article presents a theoretical and experimental assessment of noise levels during the analog-to-digital conversion of TV broadcast microwave signals. Mathematical expressions are derived to calculate the mean quantization noise power for different brightness distribution models on TV images, considering both linear and nonlinear characteristics of the “light-to-signal” converter. For the first time, the dependence of the average quantization noise power on the compression coefficient is obtained for an inversely proportional distribution of brightness on the television image. This is particularly relevant when the input unipolar positive TV broadcast luminance signal is small, i.e., when the signal level is below the first quantization level. Additionally, analytical expressions are provided to calculate the level of restriction noise and the ratio of restriction noise power to quantizing noise power, particularly when the brightness distribution on TV images follows an exponentially decreasing model or an inversely proportional model with a logarithmic quantization scale. The impact of quantization and restriction noise on image quality was experimentally tested in an Additive White Gaussian Noise (AWGN) channel.

Summary: In this work new pseudo-gemini type surfactants are constructed via a simple, energy and material efficient way, using piperazine, propylene oxide and seven different fatty acids: capric, lauric, myristic, stearic, oleic and linolenic. The compounds are characterized by 1H NMR, 13C NMR and FTIR studies. Micellization and adsorption properties of the novel pseudo-gemini surfactants are investigated via surface tension and conductivity measurements. Antimicrobial properties are evaluated using the simple disk diffusion test method. Dissipative Particle Dynamics (DPD) simulations are performed to model aggregation behavior of the new pseudo-gemini surfactants. Experimental studies revealed that Critical Micelle Concentration (CMC) of the obtained pseudo-gemini surfactants are lower than 1 mmol/L. Theoretically calculated CMC values are slightly higher than experimental CMC values. However, overall, very good agreement between theoretical and experimental CMC values is observed. Radial Distribution Function (RDF) and radius of gyration (Rg) plots are analyzed to gain further insight into aggregation of the surfactant molecules in aqueous environment. The DPD model of the pseudo-gemini amphiphiles successfully predicts the most important traits of the aggregation process.

Summary: The relevance of the problem under study lies in the growing threat of cyberattacks and unauthorized access to corporate data. The need for effective data management at the moment is due to the increased importance of securing corporate devices, which requires in-depth analysis and understanding of the role of data management in this context. The aim of the study is to comprehensively analyze the role of information governance in securing organizational technology. The used methods were: experiment, systematization, comparison, analysis, synthesis. The main findings of the study emphasize the importance of information management in securing enterprise technology. The study involves the development of a C++ program designed to simulate different scenarios of using data management strategies. This program is designed to demonstrate the effectiveness of different information security techniques in organizational technologies. In addition, a comparative analysis of data control techniques designed to protect organizational devices has been carried out. The results of this analysis are presented in the form of a table that discusses the various aspects of information management in this context. And the developed structural diagram of information management in organizations presents the main components and processes required to secure organizational technology. The paper also provides examples of practical applications of data control techniques in large corporations, emphasizing their importance in protecting sensitive information. This research makes a practical contribution by providing organizations not only with theoretical foundations but also with concrete data governance strategies to enhance the security of corporate devices, which is essential for today’s companies in the face of growing cyber threats. Limitations of the study include biases, simulated situations, and an inability to adequately address issues that arise in the actual world, such as organizational culture and cyber threats.

Summary: This work is dedicated to the modeling and solution of eigenvalue problems within shear deformation theory (SDT) of laminated cylindrical shells containing nanocomposite plies subjected to axial compressive load in thermal environments. In this study, the shear deformation theory for homogeneous laminated shells is extended to laminated shells consisting of functionally graded (FG) nanocomposite layers. The nanocomposite plies of laminated cylindrical shells (LCSs) are arranged in a piecewise FG distribution along the thickness direction. Temperature-dependent material properties of FG-nanocomposite plies are estimated through a micromechanical model, and CNT efficiency parameters are calibrated based on polymer material properties obtained from molecular dynamics simulations. After mathematical modeling, second-order time-dependent and fourth-order coordinate-dependent partial differential equations are derived within SDT, and a closed-form solution for the dimensionless frequency parameter and critical axial load is obtained for first time. After the accuracy of the applied methodology is confirmed by numerical comparisons, the unique influences of ply models, the number and sequence of plies and the temperature on the critical axial load and vibration frequency parameter within SDT and Kirchhoff–Love theory (KLT) are presented with numerical examples.

Summary: The study described in this paper develops a new technique which permits the execution of an open straddle strategy based on the superior volatility forecast for analyzing historical data. We extend the current litearure by measuring the volatility of an underlying asset in the last predefined period and comparing the actual volatility in currency with historical volatility in currency to make predictions of implied volatility. We calculated stock price volatility through an optimal holding period (OHP) and set up bars of volatility in currency. To obtain this, we solved optimization equations to find maximum and minimum movements in the volatility in currency within the defined range. We placed volatility in currency into percentile rankings and designed a straddle trading strategy based on the last OHP’s volatility in currency. The technique allows for an investor (or trader) to open either short or long positions based on calculations for a selected OHP’s volatility in currency. We applied this strategy to 130 stocks which are traded on CBOE. We developed a trading algorithm which can be used by institutional as well as individual investors. The algorithm is set to determine historical volatility in currency and forecast upcoming volatilities in currency through the understanding of the market sentiment. The empirical findings show that the stocks analyzed with the algorithm generate positive returns along a spectrum of changing volatilities of the underlying assets.

Summary: This is the PREFACE to the Special Issue “Queueing-inventory: analytical and simulation modeling and classical and retrial queues and inventory”. The year 2022 was the 30th anniversary of Queueing-inventory. It was in that connection that the guest editors requested Professor Endre Boros, the Editor-in-Chief of Annals of Operations Research, for permission to guest edit a special issue. This was granted by the Editorial Board of the journal.