Tajik Technical University named after academic M.S.Osimi

Exergoeconomic analysis (EEA) offers a robust framework for optimizing heat transfer systems by merging thermodynamic and economic principles. This numerical study introduces a novel semi-elliptic enclosure design, featuring an inner semicircular wall under constant heat flux and an outer elliptical wall at a constant temperature, to analyze Magnetohydrodynamic (MHD) natural convection mechanism (NCM) of Al 2 O 3 /water nanofluid in the presence of a permanent magnetic field (PMF). The CFD based on the finite volume method (FVM) is employed to solve the governing equations and conduct a comprehensive parametric study of the Rayleigh number (Ra), Hartmann number (Ha), and inclination angle of PMF (θ). Results demonstrate that the applied PMF exerts significant control over heat transfer, with the Ha capable of reducing the heat transfer rate by 18.5% to 37.6%. The EEA reveals that this reduction, while decreasing thermal performance, can be optimized to minimize exergy destruction. The analysis confirms that the proposed system achieves a favorable balance between energy efficiency and economic viability, presenting a promising passive cooling solution for applications like advanced heat exchangers and electronic thermal management. The integration of EEA with CFD for this unique geometry provides a novel, state-of-the-art approach for designing thermally efficient and cost-effective systems.

Algorithms for the numerical solution of dynamic problems of building models with a seismic-isolating belts when the sliding plane is located at different levels have been developed. The algorithms take into account the nonlinear behavior of the structure associated with displacements in the area of the sliding layer, and allow for modeling taking into account various insulation parameters. A computer program implementing the proposed algorithms has been developed. It allows to calculate the dynamic response of buildings under various seismic effects, taking into account the geometrical and mechanical characteristics of the structure. The program implements numerical methods for integrating equations of motion, which ensures the accuracy and stability of calculations. Calculations of seismic-insulated building models with different system parameters, including the height of the sliding plane location, stiffness of the above-ground part and damping characteristics, have been carried out. The results showing the influence of these factors on the behavior of the structure under seismic loads have been obtained. The analysis of the results showed that the location of the sliding plane has a significant effect on the dynamic response of the building. In particular, the lower location of the sliding layer contributes to the reduction of accelerations transmitted to the above-ground part, which leads to a decrease in internal forces and an increase in the overall seismic resistance of the structure. The proposed algorithms and program can be used in the design of buildings with seismic insulation, as well as in the assessment of their reliability under various seismic effects

Molecular dynamics simulations (MDs) were conducted to investigate the alcohol dehydrogenase (ADH) enzyme and its cofactor, nicotinamide adenine dinucleotide (NAD), solvated in an aqueous system on a graphite-carbon surface. The study focuses on key structural aspects of ADH, particularly its conformational changes, including the rotation of the catalytic domain, the coenzyme binding domain, and the rearrangement of the active center required for catalytic activation. MDs were performed for 100 ns to track the conformational and rotational changes of the ADH+NAD complex in an aqueous environment. The diffusion process of ADH+NAD was observed for approximately 50–60 ns, after which the complex made contact with the graphite surface, leading to final relaxation. Upon adsorption of ADH onto the carbon surface, NAD exhibited fluctuations between 55 and 60 ns, coinciding with the opening of two catalytic loops associated with the NAD-binding region. Experimental and kinetic studies suggest that these structural changes may significantly impact the enzymatic activity of ADH in the presence of a carbon surface.

We consider the set L_2^((r)) 2π-periodic functions f∈L_2, whose (r-1)-th order derivative is absolutely continuous, and the r-th order derivative f^((r))∈L_2. We solve the extremal problem of finding an exact Jackson-Stechkin type constant that connects the best polynomial approximation of functions from L_2^((r)) with the average value of the generalized m-th order modulus of continuity of their derivative f^((r)) in the space L_2. We also consider the classes W_(m )^((r)) (u) and W_m^((r)) (u,Φ) of functions from L_2^((r)) such that the average value of the generalized m-th order modulus of continuity of their derivative f^((r)) is bounded from above by unity and, accordingly, by the value of some function Φ(u). We calculate the exact values of the known n-widths (according to Bernstein, to Gelfand, to Kolmogorov, linear, and projection) of the class W_(m )^((r) ) (u). Then we solve the extremal problem of finding the exact value of the best approximation for the class W_m^((r)) (u,Φ). The obtained results develop and complement some known results on the best approximation of various classes of functions in L_2. In the paper, we use methods for solving extremal problems in normed spaces, as well as the method developed by V.M. Tikhomirov for estimating from below the n-widths of functional classes in Banach spaces.

The assessment of the dynamics of spontaneous external respiration in children who passed without hardware respiratory support made it possible to identify a significantly significant increase in breathing in children of group 3 relative to the indicator in group 1 on the first day by 43%, 24%, 11% on days 1,3,4.All patients of the 2nd group needed respiratory prosthetics during the first 7 days.Despite the more pronounced severity of the condition in group 3, in the first week after SCTBI, an increase in respiratory rate of more than 35 per minute was not allowed, oxygen saturation at a level of 98.3 to 99.5% in all injured patients.A more stable level, the longest physiological position of the peak of the acrophase of the circadian rhythm of oxygen saturation was due to the respiratory support of lung ventilation.In group 1, hemodynamic restructuring was revealed according to the hyperdynamic type in conditions of a decrease in the oxygen saturation index.

The assessment of the dynamics of spontaneous external respiration in children who passed without hardware respiratory support made it possible to identify a significantly significant increase in breathing in children of group 3 relative to the indicator in group 1 on the first day by 43%, 24%, 11% on days 1,3,4.All patients of the 2nd group needed respiratory prosthetics during the first 7 days.Despite the more pronounced severity of the condition in group 3, in the first week after SCTBI, an increase in respiratory rate of more than 35 per minute was not allowed, oxygen saturation at a level of 98.3 to 99.5% in all injured patients.A more stable level, the longest physiological position of the peak of the acrophase of the circadian rhythm of oxygen saturation was due to the respiratory support of lung ventilation.In group 1, hemodynamic restructuring was revealed according to the hyperdynamic type in conditions of a decrease in the oxygen saturation index.

Analysis and modeling of an electrical power system with a distributed generation source in normal mode were carried out using the Matlab application program. The paper provides an analysis of the state of the electric power system, the main parameters of which change when an additional source of distributed generation based on a wind farm with a capacity of 9 MVA is introduced. A block diagram and, based on it, a simulation model of the power system have been compiled. Since the stability of the electric power system depends on the reliable operation of the emergency automatics, it is necessary to determine the values of the main parameters of the electric power system that characterize its stable operation: the change in the phase shift angle between the emf of the generator and the network voltage and the change in the main electrical quantities at the consumer source terminals.

The main purpose of the work is to propose and justify a new promising start-up of powerful high-voltage electric motors for pumping units of irrigation pumping stations. This method of starting electric motors helps to increase the technical life of electrical equipment of powerful irrigation pumping stations based on the use of soft start systems for high-voltage electric motors. In the process of research, methods of analysis of technological processes of pumping stations, methods of mathematical and computer modeling of AC electric drive systems were used in the work. As a result of the study, computer models have been developed to study the characteristics of asynchronous and synchronous electric drives of pumping stations with their direct and smooth start. A soft start system for high-voltage AC motors of irrigation pumping stations based on a current inverter is proposed and justified. The results of the study indicate an increase in the reliability and durability of the electrical equipment of the irrigation pumping station, which primarily depends on their technical resource. Factors affecting the technical life of electrical equipment of large irrigation pumping stations are considered to be starting transients that occur when large pumping units are started. The method proposed in this paper for starting high-voltage electric motors of irrigation pumping stations eliminates the negative effects of transient modes on the operation of electrical equipment. As a result, the technical resource and reliability of the power system of the irrigation pumping station as a whole increase.