Search Results (101)

With the continuous advancement of deep and ultra-deep well drilling technologies, formations with complex pressure windows are becoming increasingly common. During casing running operations, it is necessary to ensure both leak prevention in loss-prone formations and pressure stabilization in high-pressure formations, demanding increasingly higher accuracy in wellbore pressure calculation. This study establishes a wellbore pressure calculation model for managed pressure casing (MPC) running in deep wells, specifically addressing the scenario where a multi-density gradient drilling fluid column exists in the annulus after tripping out. The model’s novelty lies in integrating transient surge pressure calculation with a dynamic fluid column structure model that tracks the displacement of multi-density drilling fluid layers during casing running. The governing equations based on one-dimensional unsteady flow theory are solved using the method of characteristics with adaptive time stepping and a grid independence study confirming the discretization scheme. Quantitative analysis reveals that casing running speed is the dominant factor affecting surge pressure; when the speed increases from 0.5 m/s to 1.5 m/s, the surge pressure increases from approximately 1.2 MPa to 3.5 MPa at a 2000 m depth. Drilling fluid properties also significantly influence surge pressure: increasing the density from 2.0 g/cm³ to 2.22 g/cm³ results in a surge pressure increase of approximately 0.6 MPa; increasing the yield value from 2.85 Pa to 15 Pa leads to an increase of about 1.1 MPa; the surge pressure shows a clear increasing trend with both the consistency coefficient and flow behavior index. Casing running depth affects the buffering effect of the bottomhole flow channel; when the casing is run to 7000 m, the surge pressure is approximately 0.5 MPa higher than at 2000 m. Taking a typical deep well (8578 m) with a negative pressure window of −0.008 g/cm³ as an example, three casing running speed plans were designed and evaluated. Plan 1 was selected with running speeds ranging from 0.16 m/s in the upper section to 0.115 m/s in the lower section, maintaining the equivalent circulating density (ECD) within the safe density window throughout the entire operation. Field application of this plan proceeded smoothly without any occurrences of lost circulation or overflow. This provides a practical basis for MPC running technology in deep wells with narrow or negative pressure windows. Full article

This study investigates the dominant mechanisms governing transient-voltage evolution in hydro–wind–solar hybrid systems to address practical engineering requirements. A quantitative index system is constructed to evaluate the factors affecting system transient voltage, and the impacts of key factors are quantified. Specifically, the voltage drop during system faults is mainly affected by fault location and network structure, whereas post-fault recovery depends more on the collaborative process of dynamic reactive power balance and multi-time-scale control. A multi-level transient voltage quantification method is proposed to identify system influencing factors and weak points. The evaluation system comprises maximum voltage drop depth, voltage recovery time, transient voltage severity index (TVSI), hierarchical aggregation indicators, and system-level SSI indicators. The ability of these indicators to characterize systemic risks and disturbance propagation effects is enhanced by introducing fault-point extreme-value correction. The key mechanisms affecting transient voltage stability of hydro–wind–solar hybrid systems are clarified. Multi-scenario analysis shows that transient voltage risks are mainly concentrated in the 220 kV and 110 kV collection layers and are most sensitive during the recovery stage after fault clearing. Detailed quantitative analyses are conducted on four influencing factors: fault location, wind and solar power output, wind-to-solar ratio, and renewable energy penetration rate. Full article

This paper presents a numerical method for solving transient one-dimensional heat conduction problems in multilayer slabs with temperature-dependent thermal conductivities. The governing nonlinear partial differential equations are formulated separately in each layer, allowing for distinct material properties. Perfect thermal contact at internal interfaces is enforced through continuity of temperature and heat flux, while general boundary conditions are imposed at the external boundaries, including prescribed temperature, specified heat flux, and convective exchange. A key feature of the proposed approach is to discretize the partial differential equations first in time using the implicit Euler method, thereby reducing the original problem to a sequence of nonlinear two-point boundary value problems with interface (transmission) conditions. A second-order finite difference scheme is employed for spatial discretization, and the resulting system is expressed in global form using a unified indexing strategy. The system is solved at each time step by Newton linearization, yielding a sparse Jacobian matrix that is tridiagonal in the interior and locally extended at the interfaces. Efficient banded solvers lead to O(N) cost per time step, where N is the number of spatial nodes. Numerical experiments confirm the expected accuracy, unconditional stability, and computational complexity of the method. Full article

Hydropower units operating in isolated grids are characterized by low rotational inertia and weak damping, making it difficult to balance rapid frequency regulation and overshoot suppression. To address this issue, this paper proposes a GA–SQP hybrid optimization control strategy for multiple operating conditions based on a high-fidelity nonlinear dynamic model. Deep feedforward neural networks are first employed to reconstruct the nonlinear torque and discharge characteristics of the hydro-turbine, providing smooth and continuously differentiable mappings for subsequent gradient-based optimization. An improved performance index combining the Integral of Time-Cubed Absolute Error (ITCAE) with a transient overshoot penalty is then formulated to suppress long-tail errors and prioritize smooth responses with reduced transient overshoot. A two-stage optimization framework is further developed, in which the Genetic Algorithm (GA) performs global exploration to identify a promising parameter region, followed by Sequential Quadratic Programming (SQP) for high-precision local refinement. Comparative simulations under low-, rated-, and high-head high-load conditions show that the proposed strategy achieves higher optimization accuracy with fewer iterative resources. Within the investigated operating range, the optimized controller maintains a very low overshoot level while preserving satisfactory response speed, effectively improving the balance between rapidity and stability in isolated-grid frequency regulation. Full article

Standard ISO testing of cosmetic emulsions offers limited insight into the microstructural mechanisms governing long-term stability. We hypothesize that a single weight-percent increase in emulsifier concentration is sufficient to determine, through its effect on inter-bilayer junction connectivity, whether the lamellar gel network consolidates or fails. To test this, we apply a two-tier strategy combining ISO/TR 18811 testing and Turbiscan turbidimetry with rheology, laser diffraction, and AI-assisted polarized light microscopy, on two oil-in-water emulsions structured by a lamellar gel network and stabilized by Cetearyl Alcohol/Cetearyl Glucoside at 2 wt% (Emulsion A) and 3 wt% (Emulsion B) over 30 days of storage. First-tier testing distinguished formulations only at Day 30; Turbiscan index values (2.64, 1.78) stayed below threshold throughout. The second-tier protocol resolved structural divergence from Day 8 to 15, two to three weeks earlier. In Emulsion A, a transient birefringent fraction (51.5% at Day 8) preceded network disruption, droplet coalescence, and a drift of the loss tangent toward more liquid-like values. In Emulsion B, birefringence expanded to 98.4% by Day 30 and the loss tangent declined to 0.325. These results indicate that a 1 wt% difference in emulsifier concentration, within a range of industrial use, is sufficient to determine whether the lamellar gel network consolidates or fails, and that combining rheology, laser diffraction and AI-assisted microscopy resolves this divergence two to three weeks before conventional ISO criteria are met. Full article

The conventional fault-control strategy for fiber-optic communication failures in modular multilevel converters (MMCs) directly bypasses faulty submodules (SMs). However, once communication is restored, the bypassed SMs cannot be reintegrated, and the converter must shut down when redundancy is exhausted. This paper establishes a fault-propagation model and proposes a long-timescale non-bypass fault-tolerant control strategy that avoids unnecessary SM bypassing and improves system reliability. First, a mathematical fault-propagation model is developed for downlink command loss and uplink status-feedback interruption. The model reveals a positive correlation between modulation-index deviation and current fluctuation during downlink faults and derives the coupling mechanism between switching states and DC-voltage fluctuation during uplink faults. On this basis, a non-bypass fault-tolerant control method is developed in which a faulty SM switches to a local constant-voltage closed-loop mode. This mode preserves the SM’s electrical connection and voltage stability while enabling rapid resynchronization and recommissioning after fiber-optic communication is restored. Hardware-in-the-loop (HIL) results show that the proposed strategy limits current fluctuations to within 0.1% under transient faults and DC-voltage fluctuations to within ±1% under permanent faults while substantially improving system availability compared with the conventional bypass scheme. The proposed method provides a cost-effective and practically implementable approach to maintaining uninterrupted operation of VSC-HVDC MMCs under communication-link failures. Full article

Red blood cell (RBC) aggregation and viscosity-related flow resistance are important hemorheological parameters for assessing blood flow abnormalities, but their simultaneous measurement often requires multiple pumps or intermittent flow stoppage. In this study, we propose a single syringe pump microfluidic sensing method for simultaneous evaluation of RBC aggregation and transient flow response under continuous pulsatile blood delivery. The device consists of a single inlet, a main straight channel, a bifurcated test channel, and a big outlet. An optimized pulsatile-flow profile was applied by periodically switching the flow rate between high flow rate (Q_h = 6 mL/h for 2 min) and low flow rate (Q_l = 1 mL/h for 4 min), and the transient velocity response was analyzed to extract the time constant (λ₁) as a viscosity-related indicator. After optimization, the selected flow profile provides stable and reproducible measurements of both λ₁ and the RBC aggregation index (AI) while reducing unnecessary blood consumption. The λ₁ shows a strong correlation with viscosity and is significantly affected by syringe air compliance. The proposed AI exhibits consistent trends when compared with conventional aggregation indices. Furthermore, it exhibits temporal stability under continuous blood flow. Finally, the method is adopted to detect time-dependent changes in blood during continuous blood infusion, which demonstrates its potential as a simple, sensitive, and practical microfluidic sensor for real-time hemorheological monitoring. Full article

Biomass torrefaction represents a highly promising thermochemical pathway for upgrading low-density agricultural residues into high-value solid biofuels. However, optimizing reactor operations requires resolving the conflict between product energy enrichment and mass loss under transient heat transfer limitations. In this work, a transient kinetics-coupled Pareto optimization and techno-economic framework is developed for the torrefaction of rice husk residues (Oryza sativa), with pine wood (Pinus sp.) as a validation reference. The framework connects a transient 1D radial finite-difference heat transfer model in a cylindrical particle to a two-stage sequential chemical kinetics scheme, which was successfully calibrated against experimental thermogravimetric analysis (TGA) data. The physical model outputs (instantaneous species concentrations, temperature profiles, and process thermal demand) are dynamically coupled to an economic module to calculate the Levelized Cost of Torrefaction (LCOT). A grid sweep with Pareto non-dominance filtering is conducted on the active torrefaction design space (using a product quality constraint $Y_{BT}\le 0.96$ to avoid degenerate zero-conversion limits) to identify the Pareto frontier that minimizes LCOT while maximizing the efficiency index ($\eta$). To evaluate the financial and technical stability of the Pareto operating point for rice husk (523 K, 30 min), a global sensitivity and uncertainty analysis (GSA) is executed using 250 Latin Hypercube Sampling (LHS) Monte Carlo simulations coupled with Standardized Regression Coefficients (SRCs). The results show a baseline LCOT of 6.49 USD/GJ for rice husk at its 1 dry t/h pilot Pareto knee point (523 K, 30 min), which is projected to decrease to 4.12 USD/GJ under an industrial-scale techno-economic scenario (50 dry t/h). Under uncertainty, LCOT displays a mean value of $6.486\pm 0.565$ USD/GJ (95% CI: $5.517$–$7.644$ USD/GJ), which is heavily dominated by the raw feedstock acquisition cost ($\beta =0.7430$, $p<0.001$) and CAPEX contingency multiplier ($\beta =0.6129$). The efficiency index exhibited limited variability (mean $91.40\%\pm 0.96\%$, 95% CI: $89.80\%$–$93.26\%$), governed primarily by the particle diameter $d_p$ ($\beta =0.7828$) and secondary convective heat transfer coefficient h ($\beta =-0.5929$, $p<0.001$). This work successfully demonstrates that coupling transient transport phenomena to a techno-economic cash-flow layer provides a physics-informed framework for techno-economic evaluation and scale-up of thermochemical bioreactors. Full article

Background & Aims: Accurate assessment of liver fibrosis is important for the management of pediatric chronic liver disease (CLD). Transient Elastography (TE) has emerged as a validated non-invasive method for accurately assessing hepatic fibrosis, yet it remains available only in specialized centers and requires specialized equipment. We aimed to develop and internally validate a novel, simple, blood-based scoring system—the pediatric-adapted liver score (PAL score)—to predict advanced fibrosis as defined by liver stiffness, measured using TE across diverse etiologies. Methods: A retrospective study was conducted on 107 pediatric patients with CLD who underwent liver stiffness measurement through TE. Advanced fibrosis was defined as a liver stiffness measurement corresponding to the F3 METAVIR stage or above. Independent predictors of advanced fibrosis were identified using multivariable logistic regression with manual backward elimination. To facilitate bedside utility, the regression model was simplified into a ratio-based index. Performance was assessed via the area under the receiver operating characteristic curve (AUROC) and validated using bootstrap resampling (10,000 iterations). Results: Gamma-glutamyl transferase (GGT), platelets, and albumin were identified as independent predictors of fibrosis. The simplified PAL score demonstrated good discrimination with an AUROC of 0.901 (95% CI: 0.84–0.95). While statistically equivalent to the adult-derived GGT-to-platelet ratio (GPR) and S-Index, the PAL score incorporates parameters of hepatic synthesis and portal hypertension that are absent from other ratios and is easier to calculate at the patient’s bedside. At a clinically practical integer cut-off of 5.0, the score achieved a sensitivity of 95.5% and a negative likelihood ratio of 0.06, effectively ruling out advanced fibrosis. Bootstrap validation confirmed the stability of the model (bootstrap-corrected AUC 0.901). Conclusions: The PAL score is the first simple fibrosis index derived for a diverse pediatric population. Highlighting its primary strength as a highly effective screening tool, the score achieves a sensitivity of 95.5% and a negative likelihood ratio of 0.06 at a user-friendly cut-off of 5. These robust metrics allow clinicians to confidently rule out advanced fibrosis, offering an accessible triage alternative in primary care settings where transient elastography is unavailable. Full article

In transient stability preventive control of power systems, time-domain simulation is computationally intensive. In addition, the initial operating feature data often contain abundant redundant and irrelevant information. These factors may adversely affect the assessment performance of machine learning models. To address these issues, a transient stability preventive control method based on the sample convolution and interaction network (SCINet) is proposed. First, a feature selection algorithm based on the orthogonal maximal information coefficient and information gain (OMICIG) is developed to extract the key operating features of the system. Second, the SCINet model is employed to learn the nonlinear mapping relationship between the selected key operating features and the transient stability index (TSI). Then, the trained SCINet model is embedded into the transient stability constrained optimal power flow (TSCOPF) model as a surrogate transient stability constraint. In this way, the complicated computation associated with nonlinear differential-algebraic equations (DAE) in the conventional TSCOPF model is avoided. Furthermore, an improved dung beetle optimizer (IDBO) algorithm is used to iteratively solve the resulting model, thereby deriving a preventive control strategy that ensures transient stability while maintaining system operating economy. Finally, simulation studies on the New England 10-machine 39-bus and the IEEE 118-bus system demonstrate the effectiveness of the proposed method. Full article

The influence of internal substrate geometry on thermal stability during Laser Directed Energy Deposition Repair (DED-R) remains insufficiently understood, particularly for components containing internal cavities and cooling channels. This study investigates the thermal response of solid (Alpha), blind-hole (Bravo), and channeled (Charlie) AISI 316L substrates using dual infrared thermography, transient finite element modeling, and Short-Time Fourier Transform (STFT)-frequency-domain analysis. Despite substantial differences in internal heat-dissipation pathways, all substrate configurations exhibited similar peak surface temperatures (~1700–2100 °C), indicating that conventional temperature monitoring alone is insufficient to distinguish geometry-dependent melt-pool behavior. To address this limitation, a Spectral Entropy Index (SEI) derived from STFT analysis was proposed to quantify thermal stability. The channeled substrate exhibited the lowest entropy value (H_s = 0.172), compared with the solid (H_s = 0.181) and blind-hole (H_s = 0.183) configurations, indicating a more ordered and predictable thermal response. Furthermore, distinct variations in the spectral stability shadow revealed geometry-dependent oscillatory behavior that was not observable from thermal histories. Finite element simulations showed good agreement with experimental measurements in conduction-dominated regions (RMSE ≈ 46 °C), whereas deviations were observed within the melt-pool region (~250–310 °C), highlighting the increasing influence of fluid-flow phenomena not captured by the conduction-based model. The results demonstrate that internal substrate architecture primarily influences melt-pool stability through frequency-domain thermodynamics rather than significant changes in peak temperature. The proposed STFT method provides a quantitative approach for monitoring thermal stability and assessing the feasibility of L-DED repair over complex internal geometries. Full article

This paper addresses a specific dynamic limitation in conventional adaptive super-twisting sliding mode control (ASTSMC) for permanent-magnet synchronous motor (PMSM) speed regulation: the reactive lag of gain adaptation. In standard ASTSMC, controller gains are adjusted based solely on the sliding variable, which grows only after a disturbance has already induced a tracking error. This reactive behavior may produce a non-negligible transient speed droop during abrupt load variations. To alleviate this limitation, a proactive gain-scheduled ASTSMC (PDG-ASTSMC) strategy is proposed. A second-order nonlinear extended state observer (NESO) is employed to estimate the lumped disturbance and to extract its time derivative ${\dot{\widehat{d}}}_l$. This disturbance-derivative signal is incorporated into the gain adaptation law to increase the controller gains during the incipient phase of a load change, before significant speed error accumulates. Stability analysis based on a composite Lyapunov function establishes uniformly ultimately bounded convergence of the closed-loop system, and a quantitative relationship between the proactive index and transient droop reduction is derived. Experimental validation on a 1.42 kW PMSM platform shows that, compared with conventional reactive ASTSMC, the proposed PDG-ASTSMC reduces transient speed droop by over 17% (from 10.5 rpm to 8.7 rpm) and shortens load recovery time by approximately 69% (from 140 ms to 44 ms), without increasing steady-state chattering or current ripple. Full article

Climate change threatens ecosystem stability in arid Central Asia, yet regional vegetation responses remain poorly resolved at the operational scale of land-use policy. We integrated long-term meteorological records (2000–2024) from Kazhydromet with Landsat surface-reflectance imagery for four epochs (2010, 2015, 2020, 2025) across the five administrative regions of Southern Kazakhstan (≈710,000 km²). After cross-sensor harmonization of Landsat 5 TM and Landsat 8 OLI, dense vegetation cover (NDVI > 0.4) increased modestly across all regions, with the cumulative area growing from 9.09 to 9.60 million hectares (+5.6%) and a transient 2020 minimum linked to the 2018–2020 drought. Per-region OLS trend slopes were not statistically significant at p < 0.05, given the four-epoch sampling (n = 4). A composite Biodiversity–Climate Sensitivity Index (BCSI), constructed from four normalized components (temperature trend, precipitation deficit, NDVI trend, and the coefficient of variation of dense-vegetation cover as a biodiversity–vulnerability proxy), identifies the lower Syr Darya floodplain and former Aral Sea margins as the most sensitive territories and the Northern Tien Shan as the most resilient. The framework provides an operational evidence base for climate-adaptive conservation aligned with SDG 13 and SDG 15. Full article

Major depressive disorder remains a leading cause of disability, and decades of monoamine-centered pharmacology have yielded delayed and often incomplete relief. Rapid-acting antidepressants reshaped the field by linking swift symptom improvement to glutamatergic plasticity, yet durable benefit depends on how newly reconfigured circuits are stabilized and tuned. This review synthesizes evidence that antidepressant efficacy arises from the coordinated engagement of synaptic plasticity, spanning induction and consolidation, and intrinsic excitability, which provides gain control, and proposes an integrated framework to guide future discovery. It first outlines induction through N-methyl-D-aspartate receptors (NMDARs) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), exemplified by ketamine and esketamine, followed by consolidation mediated by tropomyosin receptor kinase B (TrkB) signaling, translational disinhibition via eukaryotic elongation factor 2 kinase (eEF2K), and presynaptic stabilization indexed by synaptic vesicle glycoprotein 2A (SV2A); together, these processes transform transient potentiation into persistent network change. It then highlights intrinsic excitability, emphasizing voltage-gated potassium channel subfamily Q (Kv7), hyperpolarization-activated cyclic nucleotide-gated (HCN), and G protein-gated inwardly rectifying potassium (GIRK) channels as circuit-level governors that normalize firing and limit relapse-prone hyperexcitability. Finally, it presents the Induction–Consolidation–Maintenance (ICM) framework as a hypothesis-generating roadmap for future studies, with SV2A positron emission tomography (PET), electroencephalography (EEG), and functional magnetic resonance imaging (fMRI) biomarkers discussed as candidate tools rather than validated guides for treatment timing or patient selection. The proposed contribution is not another list of plasticity pathways, but a phase-specific model that links synaptic induction, consolidation, and excitability-based maintenance to distinct therapeutic windows, biomarkers, and relapse-prevention strategies. Full article

The tension of a marine winch rope depends on the hydraulic pressure supplied to its input hydraulic motor. Traditionally, winches employ a relief valve to control the oil pressure of hydraulic motors. Owing to the inherent control characteristics of the relief valve, this control mode leads to continuous fluctuations in the system oil pressure, causing severe variations in the rope tension during operation. In this study, a direct-acting three-way proportional pressure-reducing valve was used to control the oil pressure of the winch, ensuring that the input pressure to the hydraulic motor was maintained at a set value, thereby mitigating the risk of drastic fluctuations in rope tension during vessel mooring. However, proportional pressure-reducing valve control exhibits shortcomings, such as static nonlinearities, insufficient dynamic response, and poor anti-interference stability, leading to oscillations in the outlet oil pressure and resulting in rope tension fluctuations in the winch. Based on the force and flow balance equations of the proportional pressure-reducing valve and in conjunction with the load characteristics of the winch, a mathematical model of the winch control system was established. An operating point for the pressure-reducing valve was determined, and the control system model was linearized. According to the Bode plot and frequency-domain index analysis, four key parameters affecting the outlet pressure fluctuation of the pressure-reducing valve were identified (valve port flow gain coefficient, viscous damping coefficient, transient hydraulic damping coefficient, and hydraulic spring stiffness). From the perspective of winch operation management, the working parameters of the hydraulic system were adjusted accordingly, and their effects on the four key parameters were analyzed. The results, in combination with model linearization and Bode plot analysis, indicate that appropriately lowering the operating temperature of the hydraulic oil can effectively improve the frequency-domain indices and stability margin of the control system, significantly enhancing the relative stability of the marine winch rope tension. Full article