All articles. Vestnik MGTU

Analysis of Least Squares Method Efficiency with L-BFGS-B Optimization for Bilinear Autoregression Parameter Estimation Under Various Noise Distributions

Wed, 29 Jul 2026 00:00:00 +0400

Abstract

The article investigates the influence of various distributions of the updating process on the accuracy of parameter estimates for a bilinear autoregressive model, obtained using the least squares method with the L-BFGS-B optimization algorithm. The research examines the effectiveness of parameter estimation using the least squares method for normal, contaminated normal (Tukey distribution), Student’s t-distribution with various degrees of freedom, Laplace distribution, and uniform distribution. Special attention is given to analyzing the dependence of estimation accuracy on the degrees of freedom in the Student t-distribution and contamination parameters in the Tukey distribution. Calculations of errors and biases of the model parameters are conducted based on extensive computer modeling with the generation of stationary time series. The results show that the accuracy of estimates significantly depends on the type of distribution of the updating process, with the highest sensitivity observed for the parameter associated with the nonlinear term of the model. For the Student’s t-distribution, a nonlinear relationship between estimation errors and the number of degrees of freedom is established, while for the contaminated normal distribution, a critical influence of contamination parameters on the accuracy of estimates is revealed. The obtained results can be used in constructing bilinear time series models under conditions of non-standard residual distributions

Please cite this article in English as:

Goryainov V.B., Masyagin M.M., Semernya V.M. Analysis of least squares method efficiency with L-BFGS-B optimization for bilinear autoregression parameter estimation under various noise distributions. Herald of the Bauman Moscow State Technical University, Series Natural Sciences, 2026, no. 3 (126), pp. 4--23 (in Russ.). EDN: VVLPJN

Numerical Simulation of Laser Lap Welding--Brazing of Titanium and Aluminum Plates

Wed, 29 Jul 2026 00:00:00 +0400

Abstract

The developed mathematical model for the numerical study of laser welding thermophysical processes is applied to simulate the overlap welding of titanium and aluminum plates. The article investigates the influence of laser power and welding speed on the temperature distribution in the calculation area, and searches for optimal welding modes. To obtain quantitative process characteristics, a repeatedly tested numerical method of collocation and least squares for solving differential and integral equations is used, which is implemented in the Laser Welding3D software package. The problem is solved in a three-dimensional formulation, taking into account both heat exchange with the environment and the formation of a vapor-gas channel in the weld zone. The simulation is performed for various plate arrangements over a wide range of laser power values and plate speeds relative to the laser beam. It is shown that the choice of plate arrangement affects the characteristics of the resulting joint. A range of conditions has been determined that achieves the optimal welding-brazing mode for titanium and aluminum, when the temperature in the contact zone exceeds the melting point of aluminum, but is lower than the melting point of titanium. This mode produces a permanent joint that is free of brittle intermetallic phases that degrade joint quality. A comparison with the experimental results has been conducted. The results can be used to develop an effective technology for producing lap joints between titanium and aluminum plates using laser welding

The work was carried out as part of the State Assignment of the ITAM SB RAS (no. 124021400039-8)

Please cite this article in English as:

Shmagunov O.A., Shapeev V.P. Numerical simulation of laser lap welding-brazing of titanium and aluminum plates. Herald of the Bauman Moscow State Technical University, Series Natural Sciences, 2026, no. 3 (126), pp. 24--39 (in Russ.). EDN: VHPNNG

Two-Dimensional Janus Alloys for Spintronics on the Example of Fe₂I₃Br₃

Wed, 29 Jul 2026 00:00:00 +0400

Abstract

Two-dimensional (2D) Janus monolayers with mirror asymmetry have exceptional physical properties. This means that they can be used in next-generation optoelectronic, electronic, and electromechanical devices. Thе article presents a first-principles study of the electronic and magnetic properties of the 2D Janus monolayer Fe₂I₃Br₃ using density functional theory. A crystallographic model of the Fe₂I₃Br₃ Janus alloy has been created, its equilibrium structure has been calculated, and its electronic, magnetic, and mechanical properties have been determined. It is shown that the 2D Janus monolayers of Fe₂I₃Br₃ are dynamically and thermodynamically stable, as evidenced by the results of calculations of phonon spectra and formation energies, and also demonstrate a semiconductor nature. The band structure of Fe₂I₃Br₃ has a spin-polarized antiferromagnetic ordering with a band gap of about 1 eV. The Neel temperature was 75 K. In materials of this type, it is possible to realize states that are difficult or practically impossible to obtain in bulk magnetic samples. The results obtained can contribute to the development of science about two-dimensional functional materials, which will find application in various fields of the nanotechnology industry

The results were obtained using the equipment of Shared Resource Center "Far Eastern Computing Resource" IACP FEB RAS (https://www.cc.dvo.ru). The work was supported by the Russian Science Foundation (project no. 25-23-20239)

Please cite this article in English as:

Medintseva T.V., Kartsev A.I., Tarasov Yu.I. Two-dimensional Janus alloys for spintronics on the example of Fe₂I₃Br₃. Herald of the Bauman Moscow State Technical University, Series Natural Sciences, 2026, no. 3 (126), pp. 40--52 (in Russ.). EDN: LMUUFH

Investigation of Non-Isothermal Flow in a U-Shaped Tube in the Presence of Natural Convection

Thu, 30 Jul 2026 00:00:00 +0400

Abstract

The article examines the effect of the presence of natural convection on the formation of the thermoelectrokinetic effect in aqueous solutions of ionic compounds. The fields of temperatures and velocities of a liquid located in a U-shaped tube, which is heated from below in the presence of natural and forced convection, are calculated. The model is based on the unsteady Navier --- Stokes equations in the Boussinesq approximation, the thermal conductivity equation, and the continuity condition, supplemented by boundary conditions for forced and natural convection. The solution is obtained using a finite element method with a quadratic approximation of velocity and a linear approximation of pressure and temperature. A numerical analysis of the distribution of temperature and velocity fields at a fixed flow velocity is carried out. The structure of flows in the coils of a U-shaped tube, their spatial localization and quantitative characteristics are determined. The results demonstrate an asymmetric temperature distribution in the tube knees and localization of a sharp temperature gradient in the inlet knee due to the interaction of free and forced convection. The averaged and integral characteristics of the temperature field obtained by numerical calculation are consistent with the experimental results, which indicates the adequacy of the model used. The resulting model will be refined and generalized to simulate thermoelectromagnetic phenomena resulting from self-organization processes caused by natural convection in viscous electrically conductive media

Please cite this article in English as:

Sidorov A.V., Grabov V.M., Zaitsev A.A., et al. Investigation of non-isothermal flow in a U-shaped tube in the presence of natural convection. Herald of the Bauman Moscow State Technical University, Series Natural Sciences, 2026, no. 3 (126), pp. 53--72 (in Russ.). EDN: LDXYRF

All articles. Vestnik MGTU

Analysis of Least Squares Method Efficiency with L-BFGS-B Optimization for Bilinear Autoregression Parameter Estimation Under Various Noise Distributions

Numerical Simulation of Laser Lap Welding--Brazing of Titanium and Aluminum Plates

Two-Dimensional Janus Alloys for Spintronics on the Example of Fe2I3Br3

Investigation of Non-Isothermal Flow in a U-Shaped Tube in the Presence of Natural Convection

Two-Dimensional Janus Alloys for Spintronics on the Example of Fe₂I₃Br₃