Search Results (201)

In order to mitigate the effects of micro-vibrations due to control moment gyroscopes (CMGs) on spacecraft attitude control system, they are often mounted on isolation platforms. However, the flexible deformation of isolators may cause certain disturbances in CMG gimbal servo systems. In addition, gimbal servo systems also suffer from intrinsic disturbances due to rotor imbalance and gimbal components. Since these disturbances are distributed over a wide frequency range, they are difficult to suppress and may seriously deteriorate gimbal control performance. To suppress multiple disturbances and improve gimbal speed accuracy, a composite anti-disturbance control method is proposed. The proposed method consists of two components. The first component adopts an adaptive proportional-integral-resonant controller with phase compensation to suppress disturbance due to isolator and rotor imbalance disturbance with improved transient performance. The second component adopts an adaptive extended state observer to estimate and then compensate slowly varying disturbances with improved dynamic performance and steady-state accuracy. By integrating these two components, the proposed method can effectively suppress multiple disturbances in CMG gimbal servo systems. Simulation and experimental results demonstrate the superior performance of the proposed method. Full article

The gimbal servo system in a control moment gyroscope (CMG) is critical for high-precision spacecraft attitude control, where comprehensive performance testing and evaluation are essential for ensuring spacecraft reliability and service life. Traditional motor testbenches exhibit limitations, whereas the electric motor emulator (EME) based on power electronic converters is a promising alternative for testing extreme operating conditions, such as ultra-low speed operation and fault scenarios. However, existing EME control methods suffer from limited system bandwidth and insufficient emulation accuracy, which limits their applicability. To address these issues, this paper proposes an improved current control strategy for the ultra-low speed permanent magnet synchronous motor (PMSM) emulator. First, a mathematical model of the EME based on the topology of the voltage source converter is established. Then, based on the deadbeat control concept, a deadbeat predictive current control (DPCC) strategy is developed to enhance the dynamic performance. Furthermore, to suppress the parameter mismatch disturbance, an optimization scheme based on a cascaded extended state observer (CESO) is introduced. The first-stage ESO is applied to estimate and compensate for total disturbances, while the second-stage ESO is a supplement to suppress the remaining disturbances in the EME system, which improves the robustness of the DPCC controller. Finally, the effectiveness of the improved emulation accuracy of the proposed method is verified through experiments. Full article

Given the extremely low proven rate of coal-measure gas (CMG) in China, this review treats CMG as an integrated whole to analyze its co-accumulation dynamics, building upon its fundamental differences from conventional oil and gas accumulation. It systematically evaluates the geological controls, dynamic mechanisms, and qualitative and quantitative research methods of CMG co-accumulation reservoirs. Based on superimposition characteristics, CMG reservoirs are classified into three types. Relevant studies highlight that the CMG co-accumulation process is profoundly governed by extreme reservoir heterogeneity, leading to the formation of distinct diffusion and seepage pore systems within the porous media. Currently, although traditional qualitative analysis methods for CMG accumulation are relatively mature, quantitative research still holds significant room for advancement. In light of this, key future research directions are proposed, aiming to provide a theoretical foundation for the efficient co-exploration and co-exploitation of CMG. Full article

This paper proposes a momentum envelope design strategy for a satellite equipped with control moment gyroscopes (CMGs). The objective is to improve spacecraft maneuverability while preserving singularity-free operation of a roof-array CMG assembly. To this end, the three-axis angular momentum components are optimally redistributed according to a prescribed eigen-axis maneuver condition so that the achievable rotational speed is maximized within the feasible angular momentum region. The optimization problem is formulated analytically and solved with a low-complexity numerical procedure. Numerical examples show that the proposed method improves the achievable rotational speed compared with the previous fixed-envelope design approach, while additional attitude control simulations confirm that the designed envelope avoids near-singular operation. The proposed method therefore provides a maneuver-dependent extension of the previous singularity-free momentum envelope design framework. Full article

Dahua in Guangxi is an important soft jade mining area in southern China. Despite this, research on the nephrite from this region, particularly on the coloring mechanism of black nephrite, remains limited. This study systematically investigates the gemological, mineralogical, and geochemical properties of black nephrite from Dahua. Petrographic analysis reveals that tremolite is the primary mineral, with clinochlore and apatite as associated minerals. Tremolite (SiO₂: 58.00 wt%; MgO: 24.75 wt%; CaO: 12.46 wt%) in Dahua nephrite is close to the theoretical values of tremolite. Chlorite thermometry indicates formation temperatures of 240 °C and 328 °C. Geochemical analysis of the samples shows enrichment in light rare earth elements (LREEs), flat heavy rare earth element (HREEs) patterns, and Ce and Eu anomalies. The Mg²⁺/(Mg²⁺ + Fe²⁺) ratio was below 0.06. In the c(Ca²⁺), c(Mg²⁺), and c(Fe²⁺ + Fe³⁺) ternary diagram, the amphibole plots close to the Dahua green nephrite, suggesting a similar genetic environment and supporting a contact metasomatic origin for the amphibole. Combined with the geological setting, mineralization was driven by hydrothermal fluids from diabase magma, which introduced Si and heat, with Ca and Mg being mobilized from the dolomitic limestone host rocks. These findings contribute to the understanding of nephrite formation in Dahua, distinguishing it from nephrite from other regions and providing a foundation for future studies on the geochemical and mineralogical characteristics of nephrite. Full article

Gas condensate banking can significantly reduce near-well gas productivity by as much as ~60% in tight gas reservoirs. Existing treatment techniques are resource demanding and could alter the reservoir structure permanently. This study investigates the effectiveness of enhanced electrokinetic oil recovery (EK-EOR) as a low-impact alternative for treating condensate banks. Using compositional reservoir simulation (CMG GEM), the influence of key reservoir and operational parameters—porosity, permeability, producer well location (i, j), injection rate, and injection pressure—on cumulative gas production (CGP) was examined. A Box–Behnken design of experiments was employed to generate 62 simulation runs, and a proxy model was developed to approximate full-field responses. Statistical validation showed strong model fidelity (R² = 0.99, AAPE = 2.2%). The proxy was then optimized using a genetic algorithm (GA) to identify conditions that maximize gas recovery. Results indicate that lower injection rates and lower injection pressures maximize CGP through enhanced electro-osmotic flow and reduced water blocking, achieving a peak cumulative gas of 4.06 × 10⁸ ft³. A secondary optimum at high injection pressure could be attributed to re-pressurization and partial re-vaporization of condensate near the wellbore. Reservoir quality also exerted a strong control: higher permeability and moderate porosity favoured gas yield, while optimal producer placement near the reservoir boundary increased drainage efficiency. This study demonstrates a systematic optimization framework combining design of experiments, proxy modelling, and evolutionary algorithms to evaluate EK-EOR performance. Full article

Background/Objectives: Multimodal neuroimaging, particularly the integration of electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS), has emerged as a key methodology for investigating brain function and classifying neural activity. However, the efficient fusion of these two signals remains a formidable challenge due to their significant spatio-temporal heterogeneity. This paper presents the BiSTF-Net, which integrates decoupled and bi-directional spatio-temporal fusion mechanisms to enhance the performance of cognitive task recognition. Methods: In BiSTF-Net, the spatial features of EEG and fNIRS are mutually guided and enhanced through an efficient bi-directional cross modal guidance (Bi-CMG). Then, the temporal latencies of fNIRS signals are aligned in a data-driven manner using adaptive temporal alignment (ATA). Subsequently, the aligned features are deeply fused into a modality-invariant, discriminative representation via a symmetric cross-attention fusion (SCAF) module. Results: Evaluated on the mental arithmetic (MA), motor imagery (MI), and word generation (WG) tasks, the BiSTF-Net achieves average accuracies of 83.33%, 82.09%, and 84.99% respectively. Conclusions: The BiSTF-Net exhibits superior performance compared to the existing methods, offers a robust and interpretable solution for multimodal EEG-fNIRS cognitive task classification, and provides a methodological foundation for future extensions to other multimodal data and broader real-world clinical applications. Full article

Drought is a slow-onset hazard whose economic impacts can propagate across sectors with multi-year delays. This study develops a non-linear autoregressive model with exogenous drought inputs (ARX) to assess whether U.S. drought severity, measured by the Drought Severity and Coverage Index (DSCI), contains incremental predictive information for monthly stock returns. Using weekly DSCI and stock price data from 2013 to 2023, we constructed monthly compound returns and multi-year drought lags spanning 1–5 years for four sector-representative firms: a water utility (American Water Works, AWK), two food service firms (Chipotle Mexican Grill, CMG; Starbucks, SBUX), and an industrial manufacturer (Tesla, TSLA). We compared regularized linear ARX baselines (Elastic Net, Ridge) with a non-linear Histogram Gradient Boosting Regressor (HGB) ARX model and used permutation importance to diagnose drought-relevant lag horizons. Results showed a clear, delayed drought signal for the water utility, with a dominant ~48-month drought lag, consistent with multi-year transmission through operations, regulation, and investment cycles. In contrast, drought lags added limited or unstable information for the food service firms and negligible information for TSLA, whose dynamics were dominated by non-drought drivers. Overall, the findings indicate that drought–return relationships are sector-specific and can emerge at multi-year lags, and that non-linear ARX models provide a flexible tool for detecting these delayed climate-risk signals. Full article

The high-speed rotor electric drive system in control moment gyroscopes (CMGs) is essential for precise spacecraft attitude control. Rigorous testing of this system is critical for ensuring reliability and longevity throughout orbital missions. However, conventional test bench methods exhibit numerous limitations. In contrast, the electric motor emulator (EME) provides a flexible and efficient alternative for power-level testing of the CMG high-speed rotor brushless DC motor drive system. To address the challenges of trapezoidal back-electromotive force (back-EMF) emulation and insufficient square-wave current tracking accuracy in existing brushless DC motor emulator (BLDCME) implementations, this paper proposes a sliding time window-based dynamic current compensation control (STW-DCCC) strategy for the CMG high-speed rotor BLDCME. First, based on the VSC single-conversion-circuit topology, the BLDCME basic control strategy based on the motor port current and the current change rate is implemented to achieve a tracking control of the square-wave current and emulation of the trapezoidal back-EMF. Building upon this foundation, a sliding time window-based RMS current compensation optimization strategy for the BLDCME is designed to provide dynamic compensation for system disturbances and thereby enhance the tracking accuracy of the square-wave current. Furthermore, by incorporating fault information, the proposed STW-DCCC strategy can also emulate the resistance unbalance fault of the brushless DC motor. Finally, through experiments, a comparative analysis is conducted between the basic control strategy and the proposed STW-DCCC strategy under normal operating conditions, parameter mismatch operating conditions, and resistance unbalance fault conditions, thereby validating the effectiveness of the proposed method. Full article

This study presents an optimal design combined with comprehensive multiphysics validation to enhance the torque density of a coaxial magnetic gear (CMG) incorporating an overhang structure. Four high non-integer gear-ratio CMG configurations exceeding 1:10 were designed using different pole-pair combinations, and three-dimensional finite element method (3D FEM) was employed to accurately capture axial leakage flux and overhang-induced three-dimensional effects. Eight key geometric design variables were selected within non-saturating limits, and 150 sampling points were generated using an Optimal Latin Hypercube Design (OLHD). Multiple surrogate models were constructed and evaluated using the root-mean-square error (RMSE), and the Kriging model was selected for multi-objective optimization using a genetic algorithm. The optimized CMG with a 1:10.66 gear ratio achieved a 130.76% increase in average torque (65.75 Nm) and a 162.51% improvement in torque density (117.14 Nm/L) compared with the initial design. Harmonic analysis revealed a strengthened fundamental component and a reduction in total harmonic distortion, indicating improved waveform quality. To ensure the feasibility of the optimized design, comprehensive multiphysics analyses—including electromagnetic–thermal coupled simulation, high-temperature demagnetization analysis, and structural stress evaluation—were conducted. The results confirm that the proposed CMG design maintains adequate thermal stability, magnetic integrity, and mechanical robustness under rated operating conditions. These findings demonstrate that the proposed optimal design approach provides a reliable and effective means of enhancing the torque density of high gear-ratio CMGs, offering practical design guidance for electric mobility, robotics, and renewable energy applications. Full article

It is a challenge in experimental studies today to accurately predict the trapping mechanisms in saline aquifers that influence the long-term CO₂ storage capacities. The inability in current experimental studies to quantify the effects of combined processes of solubility, hysteresis, and mineralization as a means of affecting saline aquifer properties that influence CO₂ trapping mechanisms makes this topic interesting. A systematic framework in CMG-GEM compositional simulation studies is proposed in this article to assess the effects of gradually modelled trapping mechanisms on CO₂ storage performance. Simulation studies are conducted under identical constraints, trapping mechanisms, as well as operational factors in a sequential process that activates (i) solubility, (ii) solubility + hysteresis, and (iii) solubility + hysteresis + mineralization. The findings demonstrate distinct differences in trapping process behaviors as well as simulation stability under various modes: hysteresis effects largely improve immobile reserves as well as decrease plume migration, and, on the other hand, mineralization adds long-term dynamics of capacity increase as well as porosity-permeability alterations, especially in carbonate reservoirs. Through long-term post-injection simulations (up to 1000 years), the findings demonstrate that various trapping processes trigger over distinct time periods—years for immobile reserves, decades for dissolution, and centuries in the case of mineralization. This contribution is able to point out the computational efficiency as well as defective model behavior of concern to various physics levels, providing a practical guide to modelers in making a well-informed decision on what constitutes a minimum set of physics in long-term trustworthy CO₂ storage. Full article

Utilizing saline aquifers for carbon mineralization has proven to be a reliable approach for CO₂ storage. However, less attention has been given to CO₂ mineralization and geomechanical response at engineering durations and spatial scales. The objective of the study is to evaluate the feasibility of a potential CO₂ sequestration site in the Ordos Basin, located at a depth of approximately 1100 m, using the CMG-GEM numerical simulator. A coupled hydraulic–mechanical–chemical model was formulated, accounting for multiphase fluid flow, geochemical reactions, and geomechanical response. The simulation results indicated the following: (1) When CO₂ is injected into a saline formation, it can react with minerals. These chemical reactions may lead to the precipitation of certain minerals (e.g., calcite, kaolinite) and the dissolution of others (e.g., anorthite), potentially affecting the porosity and permeability of the storage formation; however, the study found that the effect on porosity is negligible, with only a 1.2% reduction observed. (2) The extent of ground uplift caused by CO₂ injection is strongly influenced by the injection rate. The maximum vertical ground displacements after 25 years is 6.1 cm at an injection rate of 16,000 kg/day; when the rate is increased to 24,000 kg/day, the maximum displacement rises to 9.4 cm, indicating a 54% increase. Full article

Currently, the use of scintillation crystals connected via optical fiber to a luminescence spectrometer (so-called fiber-optic dosimeters) offers a promising approach for real-time dosimetric measurements during brachytherapy treatments with γ-ray sources. This study aims to evaluate the applicability of fiber-optic dosimeters for in situ dose measurements during brachytherapy procedures, using Al₂O₃:C and Al₂O₃:C,Mg crystals, which have near-tissue density and effective atomic number (ρ = 3.99 g/cm³, Z_eff = 10.8), as well as heavy GAGG:Ce scintillation crystals (ρ = 6.63 g/cm³, Z_eff = 54.4). Radiation dose delivery was assessed through measurements of the resulting radioluminescence of the aforementioned scintillation crystals, connected via long optical fibers and recorded with highly sensitive, compact luminescence spectrometers. Measurements were performed in a dedicated phantom under clinical conditions at the Oncology Center in Bydgoszcz, Poland. The dosimeters were evaluated for in situ dose monitoring within the 0.5–8 Gy range during brachytherapy procedures using a ¹⁹²Ir (392 keV) source. The results showed a clear linear relationship between the delivered radiation dose and the scintillation output measured by the fiber-optic detector. The Gd₃Al_2.5Ga_2.5O₁₂:Ce crystal detector exhibited excellent linearity, while the Al₂O₃:C and Al₂O₃:C,Mg crystal detectors also showed a nearly linear dose–response relationship. Full article

The past decade has seen significant advancement in our understanding of DNA replication-coupled chromatin assembly, especially parental histone recycling that is essential for epigenetic inheritance. Leading strand-specific and lagging strand-specific pathways have been found to promote the transfer of parental histones H3-H4 to nascent DNA. It is now clear that the replisome initially characterized as the machinery that carries out the duplication of genomic DNA is also responsible for parental histone recycling. A series of replisome components including CMG (Cdc45-MCM-GINS) replicative helicase, DNA polymerases Polε, Polδ, Polα-primase, and FPC (Fork Protection Complex) that promote parental histone recycling exhibit histone-binding activities. Structural analyses of native and reconstituted replisomes, together with AlphaFold modeling of histone (H3-H4)₂ tetramer binding by replisome components, provided a framework for understanding the molecular mechanisms of parental histone recycling. A working model has emerged in which the mobile histone chaperone FACT (Facilitates Chromatin Transcription) binds parental histone (H3-H4)₂ tetramer or (H3-H4)₂-(H2A-H2B) hexamer on the front of the replication fork, and escorts it across the replisome to the daughter strands in the wake of the replication fork. In this model, parental histones transiently associate with the histone-binding modules in the replisome as steppingstones during their movement. Future studies are needed to elucidate the spatiotemporal coordination of the functions of replisome factors in parental histone transfer. Full article

In recent years, the production of tight reservoirs with waterflooding in China has entered a progressively declining phase with unstable oil rate and higher water cut, rising challenges to any further enhancement of oil recovery. Targeting the high water cut and complex pore structure characteristics typical of these reservoirs, this work evaluates the reservoir compatibility of a microspheres-alternating-nanoemulsion flooding process and optimizes its injection strategy. Representative reservoir scenarios were first established; laser-particle-size analyzers and other laboratory instruments were then employed to quantify formulation-reservoir compatibility. A multiscale numerical study has been performed with CMG-STARS v.2022. The core-scale simulations systematically examined the influence of key factors on displacement efficiency improvement and water cut reduction, matched with the experimental results of core flooding tests. The combined experimental/numerical workflow furnishes a theoretical framework for optimizing the injection scheme. Beyond assessing formulation compatibility, the study delivers optimized injection parameters and strategies for microspheres-alternating-nanoemulsion flooding, providing both theoretical analysis and practical technology reference for improving oil recovery in tight reservoirs with higher water cut. Specifically, when the microsphere concentration increased from 0.1% to 0.3%, the minimum water cut was reduced by approximately 5%, while further concentration increases showed no significant additional impact on water content. Compared with water flooding, the relative permeability curve of the microspheres-alternating-nanoemulsion flooding system shifted entirely to the right. Numerical simulation of representative well groups revealed that a slug design with a microsphere-to-nanoemulsion ratio of 1:3 yielded the optimal enhanced oil recovery effect, and after ten years of production, the recovery factor increased by 0.46%. Full article