All Articles

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.

Summary: A set of self-consistent thermodynamic parameters of the GeTe-rich germanium-bismuth tellurides were determined using an electromotive force (EMF) method with a glycerol electrolyte in a temperature range from 300 to 450 K. The solid-phase equilibrium diagram of the GeTe-Bi2Te3-Te system at 400 K was constructed using X-ray diffraction (XRD) and scanning electron miscroscope (SEM) techniques of synthesized electrode alloys, as well as available literature data. It is found that all telluride phases in GeTe-Bi2Te3 pseudo-binary section have a tie-line connection with elemental tellurium. The relative partial thermodynamic functions of GeTe in alloys were calculated using data from EMF measurements of concentration cells relative to the GeTe electrode. These findings together with the corresponding thermodynamic functions of GeTe and Bi2Te3 were used to calculate the relative partial molar functions of germanium in alloys, and also the standard thermodynamic functions of formation and standard entropies of the ternary compounds, namely Ge2Bi2Te5, Ge3Bi2Te6 and Ge4Bi2Te7.

Summary: The present study aimed to investigate the presence of asymmetric stochastic volatility and leverage effects within the Nasdaq-100 index. This index is widely regarded as an important indicator for investors. We focused on the nine leading stocks within the index, which are highly popular and hold significant weight in the investment world. These stocks are Netflix, PayPal, Google, Intel, Microsoft, Amazon, Tesla, Apple, and Meta. The study covered the period between 3 January 2017 and 30 January 2023, and we employed the EViews and WinBUGS applications to conduct the analysis. We began by calculating the logarithmic difference to obtain the return series. We then performed a sample test with 100,000 iterations, excluding the first 10,000 samples to eliminate the initial bias of the coefficients. This left us with 90,000 samples for analysis. Using the results of the asymmetric stochastic volatility model, we evaluated both the Nasdaq-100 index as a whole and the volatility persistence, predictability, and correlation levels of individual stocks. This allowed us to evaluate the ability of individual stocks to represent the characteristics of the Nasdaq-100 index. Our findings revealed a dense clustering of volatility, both for the Nasdaq-100 index and the nine individual stocks. We observed that this volatility is continuous but has a predictable impact on variability. Moreover, apart from Intel, all the stocks in the model exhibited both leverage effects and the presence of asymmetric relationships, as did the Nasdaq-100 index. Overall, our results show that the characteristics of stocks in the model are like the volatility characteristic of the Nasdaq-100 index and can represent it.

Summary: Utilizing ligands based on pyrazole synthesized some transition metal complexes. Selected salts such as Co(CH3COO)2·4H2O, Ni(CH3COO)2·4H2O (in the presence of triethylamine), Cu(CH3COO)2·H2O (in the presence of triethylamine) and CuCl2·2H2O reacted with the ligand (E)-1-(amino(1H-pyrazol-1-yl) methylene) guanidinium chloride in methanol as a solvent. Obtained novel metal complexes characterized using different analyses such as infrared spectroscopy, electrospray ionization mass spectrometry, single-crystal X-ray diffraction, and elemental analysis. Additionally, a novel series of complexes (2a-d) were investigated for their ability to inhibit enzymes. They exhibited highly potent inhibition effect on human carbonic anhydrase I and II (hCA I and II) and α-glycosidase (Ki values are in the range of 7.14 ± 1.97 to 29.34 ± 3.18 µM, 9.86 ± 2.46 to 32.47 ± 4.82 µM, and 2.08 ± 0.11 to 4.03 ± 0.30 µM for hCA I, hCA II, and α-glycosidase, respectively). Indeed, insulin and oral antidiabetic medications are the two mainstays of clinical diabetes treatment. To learn more about the potential of pyrazole-based metal complexes of Cu, Ni, and Co and how successfully they can inhibit hCA I, hCA II, and α-Gly enzymes, molecular docking applications were performed.