In this paper, free surface problems of Stefan type for the parabolic heat equation are considered. The analytical solutions of the problems are based on the method of heat polynomials and integral error function in the form of series. Convergence of the series solution is considered and proved. Both one-and two-phase Stefan-type problems are investigated. Numerical results for one-phase inverse Stefan problem are presented and discussed. © 2024 Walter de Gruyter GmbH, Berlin/Boston.

In this study, we systematically study the efficient production method and electrochemical characteristics of activated carbons (AC) derived from rice husk (RH) and walnut shell (WS). In particular, the effectiveness of physical activation using carbon dioxide (CO2) was investigated and compared with the more common chemical activation method using potassium hydroxide (KOH). The results show that the KOH–activated samples have remarkable specific capacities, reaching 157.8 F g−1 for RH and 152 F g−1 for WS at 1 A g−1. However, the rate capability of AC obtained via KOH decreases significantly as the scanning rate increases, retaining only 51.5% and 68% of their original capacities for RH–KOH and WS–KOH, respectively, at 20 A g–1. In contrast, CO2–activated samples show a superior rate performance with a capacity retention of 75.6% for WS and 80% for RH at the same current density. In addition, electrochemical impedance spectroscopy (EIS) analysis shows that AC obtained via CO2 has a lower charge transfer resistance compared to its KOH counterparts. CO2–activated RH and WS electrodes show Rct values of 0.1 Ω and 0.24 Ω, respectively, indicating improved ion transport kinetics and surface area utilization. These results highlight the importance of activation techniques in tailoring the electrochemical behavior of biomass–derived carbon. This study not only expands the understanding of the interaction between activation, morphology, and performance but also indicates the potential of CO2 activation as an environmentally friendly and efficient alternative. As the field of sustainable energy storage advances, this work provides valuable guidance for the development of high–performance supercapacitor electrodes with less environmental impact. © 2023 by the authors.

В статье рассмотрены плотностные и магнитные характеристики горных пород восточной части Сарысу-Тенизского поднятия, расположенной на южной окраине Тенизской впадины в пределах рудной провинции Центрального Казахстана. На основе анализа геологических и петрофизических данных выполнено группирование пород по диапазонам плотности и магнитной восприимчивости. По плотностным характеристикам выделено шесть групп пород, а по магнитной восприимчивости - четыре группы от немагнитных до сильномагнитных. Полученные результаты позволяют оценивать геологическую природу источников гравитационных и магнитных аномалий и повышать информативность геофизических методов при прогнозировании рудоперспективных объектов.

В статье рассмотрена задача повышения информативности электрических методов каротажа при оценке фильтрационных свойств урановмещающих песков пластово-инфильтрационных месторождений. На основе статистической обработки данных кажущегося сопротивления, индукционного каротажа, керновых материалов и результатов опытных гидрогеологических откачек были установлены аналитические зависимости между электрическими параметрами пород, медианным диаметром зерен D50 и коэффициентом фильтрации Кф. Показано, что использование данных индукционного каротажа обеспечивает более высокую точность оценки фильтрационных свойств по сравнению с традиционным методом кажущегося сопротивления.

В статье рассмотрена научно-методическая проблема выбора и применения эффективных геофизических технологий на разных этапах геологоразведочных и горно-геологических работ на урановых месторождениях Казахстана. Основное внимание уделено систематизации физико-геологических и петрофизических характеристик пород и руд Шу-Сарысуской урановой провинции. На основе фондовых геологических материалов, опубликованных данных и статистической обработки были обобщены диапазоны физических свойств пород и скважинных геофизических полей. Полученные результаты показали необходимость более детального изучения проницаемых и непроницаемых пород по электрическим свойствам, плотности и скоростям сейсмических волн для повышения информативности геофизических методов и оптимизации технологий in-situ leaching.

В статье применены методы машинного обучения для выявления и классификации редких и аномальных минералов в крупной минералогической базе данных. С помощью Isolation Forest и One-Class SVM были определены минералы с нетипичными физико-химическими свойствами, после чего KMeans clustering был использован для группировки аномалий в три геологически интерпретируемые категории, связанные с эвапоритовыми, метаморфическими и магматическими условиями формирования. Полученные результаты показывают, что методы unsupervised learning могут повысить эффективность классификации минералов и прогнозирования редких минеральных месторождений.

Global energy and environmental issues are driving the development of modern advances in efficient and environmentally friendly energy storage systems. Such systems must meet a range of requirements, which include high energy and power density, long service life, flexibility, industrial scalability, security and reliability. Progressive achievements in the field of energy storage are associated with the development of various kinds of batteries and supercapacitors. Supercapacitors are state-of-the-art energy storage devices with high power density, long lifespan, and the ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. However, supercapacitors have limitations associated with low energy density, which can be solved by using various types of current collectors, since current collectors are one of the main massive components of supercapacitors. This review gives a complete understanding of the effect of current collectors on the actual performance and properties of supercapacitors. We reviewed current collectors based on carbon and metal-containing materials, and supercapacitor configurations to identify possible improvements in electrochemical performance in terms of specific capacitance, energy density, power density, service life and variability in their application. © 2022 The Author(s)

Short-term (daily) and long-term (seasonal) thermal energy storage allows efficient use of renewable thermal energy by replacing fossil fuel systems. In the present research, a three-dimensional numerical simulation of the thermal efficiency of a single-stage and three-stage cascaded shell-and-tube type latent heat thermal energy storage device is carried out using various phase change materials. The mathematical model is based on the fundamental conservation laws of mass, momentum, and energy. Numerical implementation was carried out using built-in solvers of COMSOL Multiphysics v.5.6 software. The numerical solver was verified by comparison with experimental data with acceptable agreement. A comparison of calculations between single and cascade configurations showed that the use of a multi-stage configuration allows for an increase in the temperature range of considered thermal energy storage devices. The use of the internal finned structure of containers almost halves the charging and discharging time. The developed numerical calculation tool can be used in the future to study the thermal efficiency of more complex thermal energy storage device configurations, considering three dimensions and phase transitions. © 2024 American Institute of Physics Inc.. All rights reserved.

The motion of planar hinge-lever mechanisms with flexible and elastic links in a closed pre-stressed contour is considered. Modeling of the mechanism motion is carried out on the basis of their kinetic-elastodynamic analysis, which takes into account the inertial relationship between the large-scale motion of mechanisms as a rigid body and nonlinear vibrations of the links as a result of their elastic deformation. This work pays attention to both longitudinal and lateral vibrations of elastic links. The equations of motion of the mechanisms are obtained by the use of Novozhilov’s nonlinear theory of elasticity, according to which the link deformations are assumed to be finite. Based on Biot’s theory of incremental deformations, the field of initial stresses in flexible elements is taken into account due to their preliminary tension, which determines the geometric nonlinearity of dynamic models. As an example, the dynamics of a planar five-link hinge-lever mechanism with closed pre-stressed contour is studied. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.

Hydrotechnical structures, being vital infrastructural objects, at the same time represent a great danger for human activity and the environment. The article discusses the results of geophysical studies of an earth dam in Kazakhstan. Despite its key role in agricultural water supply, the loam dam has not previously been subjected to a thorough geophysical evaluation. The study combines seismic refraction tomography using the correlation method of refracted waves with self-potential measurements to non-invasively detect internal heterogeneities and potential seepage pathways. Over one kilometre of seismic profiling has been performed with both P- and S-wave registrations by using standard geophones and pulse sources, allowing imaging to depths of up to 40 meters. Data processing included noise reduction, first arrival sampling, and velocity modelling with vertical gradients. The results show significant lithological and structural variability in the dam body. Subsidence anomalies with increasing permeable loams and low velocity zones have been identified, and soil loosening has been detected, indicating a possible seepage site. The comparison of seismic data and self-potential measurements has showed the highest correlation near the dam crest, with partial overlap elsewhere due to soil heterogeneity, metal structures, moisture changes, and complex topography. The combined interpretation has allowed identifying the main seepage zones in the dam body. The results of the study confirm the effectiveness of combining the correlation method of refracted waves and the self-potential method for detailed diagnostics of earth dams. The integrated approach allows for depth-resolved characterization and the development of a seepage regime model that identifies critical risk zones. Further detailed permeability testing, real-time seepage monitoring, and regular geophysical and hydrogeological surveys are recommended, especially near residential areas. The results of the surveys provide a solid foundation for engineering measures to enhance dam safety and mitigate the risk of failure. As part of the Geographic Information System platform, the data obtained are useful for monitoring the condition of dams, assessing their risks and impact on the environment, and for effective water resource management.