All Articles

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.

Summary: The study investigates the inverse scattering problem for the Schrodinger operator with complex potentials, considering indefinite discontinuous coefficients on the axis. Using the integral representation of the Jost solutions on the real and imaginary axes, solved the direct scattering problem. An additional study of the operator's spectrum was conducted, scattering data was introduced, and the eigenfunction expansion was obtained. Integral equations derived play a crucial role in solving the inverse problem and finally prove the uniqueness theorem for the solution. © 2024

Summary: Green function of a 2n-th order differential equation with normal coefficients on the half-axis is studied. We first consider the Green function of our equation with “frozen” coefficients. Using Levi’s method, we obtain a Fredholm-type integral equation for the Green function of our problem, whose kernel is a Green function of a problem with constant coefficients. We prove an existence and uniqueness theorem for this integral equation in some Banach spaces of operator-valued functions. The main result of this paper is a theorem stating that the solution of the obtained integral equation is a Green function of our problem.

Summary: The article discusses issues of improving the operational properties of pressure and drilling compressor pipes. For oil and gas production, three main types of pipes are used: drill casing and tubing. Taking into account production requirements and the importance of this element in the chain of work carried out, the service life of oil country pipes is complex and varied. In oil-producing and exporting countries, the requirements for the main technical parameters of pipes used in the oil industry differ from the requirements in other areas, the pipes and pipe fittings used. Taking into account the above, pipes intended for the production and transportation of oil and gas must have the necessary performance properties in terms of performance, reliability and safety. At the same time, taking into account operating pressures and other environmental factors, the issue of improving the properties (strength and stability) of the material from which pipes are made, while maintaining mechanical characteristics, is relevant. Improving the properties of pipes, especially the mechanical properties, is an important and important issue. Therefore, you should first be careful when choosing the material from which the pipe is made. Because the material from which the pipe is made must be of high quality in terms of mechanical properties. Considering that pipes, especially those used for oil and gas transportation, carry material for large kilometers. That is, the pipes pass through deserted and empty areas. In other words, if there is a malfunction in them, it can result in the loss of the transported material, which is considered undesirable for the economy. In this regard, their properties, especially mechanical properties, should be high. Corrosion can occur in the part where liquid flows through the pipes, which can also be cavitation corrosion. Cavitation corrosion is also considered a defect for pipes.

Summary: The lack of information about the chemical composition and structure of asphaltenes in crude oil, which has a sufficient share in the economy of Azerbaijan, complicates its processing and use. As a first attempt, this research is devoted to the detailed analysis of the average molecular structure and properties of asphaltenes isolated from crude oil samples collected from the Zaglı oil field using the integrated application of high-sensitivity devices such as Nuclear Magnetic Resonance (NMR), Ultraviolet–Visible (UV–Vis), Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction analysis, Elemental analysis, Scanning Electron Microscope (SEM), Differential Thermal Analysis (DTA), Dynamic Light Scattering (DLS). The average molecular formula of asphaltene monomer was determined to be C49.5H55O3.04N0.95S2. An island architecture with one polycyclic aromatic hydrocarbon (PAH) in each molecule of this compound is predominant. Amorphous asphaltene molecule contains vanadium-based porphyrins, –COOH group, disulfide (−S-S-) linkage. It was found that asphaltene of crude oil is stable up to 406 °C. The three-stage pyrolysis process in the temperature range of 406–818 °C resulted in the formation of 12.58 % coke. Due to the absence of free radicals in the range of 25–100 ℃, the asphaltene sample is dielectric. The decrease of monodispersity with particle growth in asphaltene compound in different solvents was analyzed by dynamic and static light scattering. The HOMO-LUMO energy gap of the asphaltene molecule was 2.666 eV, indicating high stability. The knowledge gained about the chemical composition and molecular structure of asphaltenes can help prevent problems arising in oil production and refining processes.