All Articles

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.

Summary: Most countries have tried to decline fossil fuels dependency by supporting clean energy transition. In light of this, this study investigates the impact of energy security risk (ESR) and geopolitical risk (GPR) on the load capacity factor (LCF) in four fragile countries (Brazil-BRA; India-IND; South Africa-ZAF, Türkiye-TUR). The study applies quantile approaches for the period between 1985/m2 and 2018/m12, which represents the largest amount of accessible data. The results show that (i) at higher quantiles, ESR declines the LCF in IND and ZAF, while it has an increasing impact in BRA and a mixed impact in TUR; (ii) GPR increases the LCF in BRA, ZAF, and TUR at lower and middle quantiles, while GPR decreases ecological quality at higher quantiles in all countries; (iii) ESR and GPR have a causal effect on the LCF across various quantiles; (iv) ESR and GPR are strong predictors of the LCF, but their predictive power varies by quantile and becomes significantly weaker with increasing lags. With these fresh outcomes, the study underlines the significant influence of ESR and GPR in ensuring ecological sustainability across all quantiles and countries. The overall findings of the study emphasize that risks and uncertainties degrade the ecological quality of four fragile countries and that policymakers should turn to clean energy sources in case of an increase in geopolitical and energy risks.

Summary: On the one hand, economies, particularly developing ones, need to grow. On the other hand, climate change is the most pressing issue globally, and nations should take the necessary measures. Such a complex task requires new theoretical and empirical models to capture this complexity and provide new insights. Our study uses a newly developed theoretical framework that involves renewable energy consumption (REC) and total factor productivity (TFP) alongside traditional factors of CO2 emissions. It provides policymakers with border information compared to traditional models, such as the Environmental Kuznets Curve (EKC), being limited to income and population. Advanced panel time series methods are also employed, addressing panel data issues while producing not only pooled but also country-specific results. 20 Renewable Energy Country Attractiveness Index (RECAI) nations are considered in this study. The results show that REC, TFP, and exports reduce CO2 emissions with elasticities of 0.3, 0.4, and 0.3, respectively. Oppositely, income and imports increase emissions with elasticities of 0.8 and 0.3. Additionally, we show that RECAI countries are commonly affected by global and regional factors. Moreover, we find that shocks can create permanent changes in the levels of the factors but only temporary changes in their growth rates. The main policy implication of the findings is that authorities should implement measures boosting TFP and REC. These factors are driven mainly by technological progress, innovation, and efficiency gains. Thus, they can simultaneously reduce emissions while promoting long-run green economic growth, which addresses the complexity mentioned above to some extent.

Summary: Doping effects on the electronic and magnetic properties of Zn1−x(Co,Cr)xO systems are investigated within Local Spin Density Approximation and Hubbard U methods. Based on Density Functional Theory the spin-polarization band structures, density of states for investigated systems are calculated. Systematic analysis of the electronic properties shows that TM-doped ZnO has generated new energy levels in the vicinity of Fermi energy level. From first-principle calculations we obtained Cr-ZnO and Co-ZnO systems are metallic and half-metallic ferromagnetic materials, respectively. The obtained results for Cr-doped ZnO 128- and 192-atom supercell systems show magnetic properties with higher Curie temperature than room temperature. There are large local moments, ∼2.9 and ∼4.2 for Co and Cr dopants, respectively. Magnetic moments are related with two electron defects in the supercell structure and unpaired electrons of transition metal. The ferromagnetic and antiferromagnetic phases and the total energy are obtained for x = 2.08%, 3.125%, 4.16%, 6.25%, 8.3%, 12.5%, and 25% impurity concentrations for doped ZnO.