Search Results (269)

This study investigates why single planetary gravity assists fail to provide competitive impulsive architectures for rendezvous with the metallic main-belt asteroid (16) Psyche. A decade-long Lambert-based trajectory survey (2028–2037) is performed using a patched-conic model with powered gravity assists to compare direct Earth–Psyche, Earth–Mars–Psyche, and Earth–Venus–Psyche transfer architectures. The optimal direct transfer requires 9.65 km s⁻¹, whereas Venus-assisted trajectories demand 15.3–15.7 km s⁻¹. For Mars, the survey shows that no feasible near-ballistic solution exists within the entire decade: the low-energy Earth–Mars legs arrive at Mars with the hyperbolic excess velocity directed against the planet’s motion, so that redirecting it towards the asteroid belt requires turn angles of approximately 115–120°, far exceeding the ≈65° that Mars can deliver at its minimum allowable flyby periapsis, defined as the planetary mean radius plus a 250 km altitude margin. Two complementary analytical results explain this behaviour. A Tisserand-based reachability criterion shows that reaching Psyche requires a minimum hyperbolic excess speed of approximately 9.8 km s⁻¹ at Venus but only 4.1 km s⁻¹ at Mars, an energetic penalty that is fixed before the encounter because an unpowered flyby preserves the magnitude of the excess velocity. A directional feasibility condition then shows that satisfying the scalar criterion is necessary but not sufficient: the excess-velocity vector delivered by the inbound leg must also lie within the attainable deflection cone of the assisting planet, a condition that Venus fails energetically and Mars fails geometrically. Together, the two conditions form a predictive analytical framework for screening gravity-assist planets prior to computationally intensive optimisation, and they explain why low-thrust propulsion—rather than any single impulsive flyby—underpins the trajectory of NASA’s Psyche mission. Full article

Low-pressure gas wells treated by foam-assisted deliquification often suffer from poor temporal coordination between foamer and defoamer injection, excessive defoamer consumption under continuous dosing, and foam carryover into surface facilities. This study proposes a coordinated intermittent strategy based on the complete foam-transport timeline. A visual vertical-pipe facility quantified the effects of chemical concentration on foam generation, liquid holdup, frictional pressure loss, and foam collapse. A gravity-driven annular falling-film model predicted the time required for the foamer to reach the bottomhole. The wellbore was then discretized, and local liquid holdup was coupled with actual liquid velocity to predict foam return from the bottomhole to the wellhead. Together, the models determine the defoamer start time, injection duration, and dose. Increasing foamer concentration reduced liquid holdup but increased flow resistance above an effective range; excess defoamer likewise produced little additional collapse. In a tight-gas well, the optimized schedule maintained liquid unloading and stable surface operation while reducing daily defoamer consumption from 36 to 6 L and chemical cost by more than 80%. The method provides a quantitative basis for digitally controlled chemical dosing in foam-assisted gas-well deliquification. Full article

Seafloor topography (ST) has important significance for earth science research, marine resource exploration and underwater navigation. The conventional ST inversion methods are limited by linear approximation and poor small-scale topographic feature prediction. This study proposes a novel Wavelet-Assisted and High-Frequency Enhancement Neural Network (WAHFENN), an architecture integrating discrete wavelet transform (DWT), low-frequency retainment module (LFRM) and high-frequency enhancement module (HFEM) to enhance bathymetry prediction accuracy and capture small-scale topographic features. We apply the WAHFENN to predict the ST in a local area of the South China Sea (SCS). The results demonstrate that the WAHFENN model achieves a standard deviation (STD) of 50.66 m against shipborne single-beam check points, outperforming the topo_27.1 and SDUST2023BCO models by 31.46% and 28.49%, and surpassing the conventional Smith and Sandwell (SAS) method, gravity-geological method (GGM), and convolutional neural network (CNN) method by 78.23 m, 65.18 m, and 4.4 m, respectively. The WAHFENN model achieves a STD of 103.80 m against shipborne multibeam bathymetry data, representing improvements of 38.75%, 25.16%, and 15.58% over the SAS, GGM, and CNN models, respectively. The topographic detail comparisons and power spectral density analysis demonstrate that the WAHFENN model has the potential to outperform conventional methods in identifying small-scale topographic features. Full article

High arch dams are structurally efficient hydraulic structures for demanding loading conditions, including extreme loading, and are widely recognized for the transfer mechanism of such loads acting on them. The distinctive performance of these thin concrete structures during their service life is often intriguing and worth investigating. Unlike in the case of concrete gravity dams, in arch dams—especially, thin arch dams—the impact of temperature loads assumes significance due to the geometry and load-transfer mechanism. In this paper, an existing high double-curvature thin concrete arch dam experiencing fluctuations in reservoir levels is analyzed regarding the combined effect of thermal loads and the deflections and stresses caused. Thermal loads arising from continuous exposure of intrados and extrados faces contribute to critical loading scenarios. The FEM-based simulations assisted with field monitoring data and were used to study the structural response under the influence of temperature in steady-state conditions. The study found that the increase in body temperature is a cause of undesirable tensile stresses in the upper parts of the dam body, close to 2.0 MPa, which may cause the development of horizontal cracks. Small areas of upstream heel portion also develop higher tensile stresses due to temperature loads. The dam in its 50-year service life showed apparently aberrant behavior in deflections. The seasonal temperature variation—an increase—can be a cause of the atypical response of the dam. The anomalous nature of the behavior cannot be considered unusual, but the study also found that mitigation measures are effective, suggesting that continuous monitoring is required for sustained healthy functioning. Full article

Reliable short-term position forecasting may provide anticipatory state information for collision-risk assessment, communication management, and prediction-assisted control in Internet of Things (IoT)-enabled unmanned aerial vehicles (UAVs); these downstream functions are not evaluated directly here. This study reformulates UAV position prediction as a flight-wise, multi-horizon, three-dimensional forecasting problem and tests whether position, velocity, gravity-resolved acceleration, and quaternion-orientation histories improve predictive accuracy while measuring model-level edge-inference cost rather than end-to-end system latency. The dataset contains 3100 AirSim flights with high-rate kinematic, inertial, attitude, pressure, and magnetic-field measurements under variable horizontal wind. The reported generalization is flight-disjoint within one AirSim domain; route/scenario disjointness and transfer to physical UAVs are not established. Signals are converted to a common navigation frame, gravity-resolved, low-pass filtered, resampled to 50 Hz, and partitioned by flight identifier before normalization and window construction. Each learned model receives 2 s of history and predicts the complete next 1 s trajectory, with errors evaluated at 0.1, 0.5, and 1.0 s. The sensor-enriched LSTM (LSTM-PVAQ) is compared under matched conditions with persistence, constant-velocity, constant-acceleration, extended Kalman filter, reduced-feature LSTM, GRU, temporal convolutional network (TCN), and compact Transformer baselines. LSTM-PVAQ achieved 3D RMSE values of 0.043, 0.168, and 0.371 m at 0.1, 0.5, and 1.0 s, respectively. At 1 s, its RMSE was 21.7% lower than LSTM-PV, 13.1% lower than GRU-PVAQ, 9.3% lower than TCN-PVAQ, and 16.8% lower than Transformer-PVAQ. Its one-second ADE and FDE were 0.216 and 0.339 m. On a Raspberry Pi 5 CPU using one FP32 thread and batch size one, median neural forward-pass latency was 0.88 ms, well below the 20 ms model-update interval. The results show that gravity-resolved inertial and orientation histories improve multi-horizon prediction, while TCN-PVAQ remains an attractive lower-latency alternative. Full article

Transforming agricultural residues into functional porous materials provides a sustainable strategy for wastewater remediation. Herein, cellulose was separated from cotton stalks via formic acid-assisted hemicellulose extraction and sodium chlorite delignification, and then sulfuric acid hydrolysis. Chitosan-assisted hydrothermally treated cellulose (CC) was prepared via hydrothermal treatment in the presence of chitosan. Anisotropic CC/chitosan composite aerogels were prepared via glutaraldehyde crosslinking and unidirectional freeze-drying. The hydrophilic CC/CS aerogel exhibited an oriented porous structure, a low density of 0.03 g cm⁻³, and a porosity of 85.33%. For Congo red (CR) adsorption, the equilibrium data were described well by the pseudo-second-order kinetic and Langmuir isotherm models, with a calculated maximum adsorption capacity of 483.09 mg g⁻¹. Electrostatic attraction, hydrogen bonding, and pore-mediated retention jointly contributed to CR uptake. To realize oil–water separation, methyltrimethoxysilane (MTMS) vapor modification was applied to prepare hydrophobic aerogel (M-CC/CS). M-CC/CS presented an initial water contact angle (WCA) of around 134°, and the WCA remained above 115° after 600 s of water droplet exposure. The aerogel showed absorption capacities of 16.22–40.13 g g⁻¹ toward various oils and organic solvents. Under gravity, M-CC/CS separated immiscible oil/water mixtures at a flux of 565.47 L m⁻² h⁻¹ and several water-in-oil (W/O) emulsions with efficiencies above 99.9% while maintaining high separation efficiency over 10 cycles. This work demonstrates a cotton-stalk-derived aerogel platform whose hydrophilic and hydrophobically modified forms can be used for dye adsorption and oily water treatment, respectively. Full article

On-body robots that travel around a human limb must keep a firm enough grip to avoid slipping or detaching, while never pressing hard enough to hurt—a balance that is hardest to strike precisely when the robot is orbiting the limb and gravity continually redistributes the contact loads. This paper presents an open, non-anthropomorphic robot that wraps around a compliant cylindrical surface with a three-contact grasp: a central traction module with two in-line driven wheels, and two lateral spring-loaded arms with distal wheels. Its central contribution is an actuation-space decomposition in which the two lateral wheel torques, expressed in a common-mode/differential basis, simultaneously drive the orbital motion and regulate the central normal force. We show that this basis diagonalises both the rolling kinematics and the static force balance, so the differential (grip-regulating) channel is provably orthogonal to the common-mode (propulsion) channel: a single pair of actuators perform both tasks without mutual interference and without a dedicated force mechanism. A model-based feedforward law derived from the static contact model, corrected by a PI term fed back from the compliant arms—which double as the force sensor—keeps the central force within a safe band; in a full-revolution simulation the differential command reverses sign to counteract the gravitational load swing while leaving the orbit undisturbed. The same compliant arms yield a closed-form estimate of the cylinder radius and contact geometry, accurate to below one millimetre across a 45–87 mm diameter range, from proprioception alone. Preliminary prototype tests reproduce the predicted behaviour, supporting the approach for future wearable and assistive applications. Full article

Soft exoskeletons have attracted increasing attention as wearable robotic devices for lower limb rehabilitation and assistive mobility. This study presents an integrated modelling, control, and mechanical design framework for a cable-driven soft exoskeleton operating in the sagittal plane, targeting elderly users with reduced mobility. Lower limb swing-phase dynamics were derived using the Euler–Lagrange formulation and subsequently recast via a Legendre transformation into a Hamiltonian representation of the coupled hip–knee system under tendon-driven actuation. Building upon this model, a hierarchical control architecture combining Quasi-Sliding Mode Control (QSMC) for angular regulation with Sliding Mode Control (SMC) for conjugate-momentum dynamics is developed. A Lyapunov-based stability analysis formally establishes the asymptotic stability of the closed-loop system and derives explicit gain conditions for robust tracking in the presence of bounded disturbance. In parallel, a compact winch-based actuation module was designed and geometrically optimized using a genetic algorithm to minimize the distal mass while preserving mechanical robustness and ergonomic wearability. The framework was validated through numerical simulations in MATLAB–Simulink^® and physics-based simulations in a MuJoCo–ROS2 environment, in which gravity, contact interactions, and cable compliance were considered. A modular mechanical prototype was developed and worn by users with different anthropometric characteristics for a static qualitative assessment of its fit and structural feasibility. These results establish a rigorous foundation for the future integration of embedded sensing and actuation hardware into experimental rehabilitation assessment. Full article

Deep-seated gravitational slope deformations (DGSDs) are large, slow-moving landslides that strongly influence mountain landscape evolution and slope stability. Despite their geomorphological importance, no standardized regional geospatial dataset describing DGSDs and their associated gravity-induced landforms has been available for the Friuli Venezia Giulia Region (NE Italy). In this study, a dataset including DGSDs and their gravity-induced landforms that affect the mountainous sector of the above-mentioned region is presented. The dataset was produced through the integrated interpretation of high-resolution LiDAR-derived digital elevation models, orthophotos, European Ground Motion Service (EGMS) InSAR data, landslide inventories, and uncrewed aerial vehicle (UAV)-assisted field surveys. It is distributed as a GeoPackage containing DGSD boundaries together with point, line, and polygon layers representing gravity-induced landforms, as well as an attribute table describing the geometry, morphometry, geology, auxiliary data, metadata, and associated landforms of each mapped DGSD. Its standardized and interoperable structure facilitates visualization, querying, comparison, and integration with other geospatial datasets, providing a reproducible resource for future geomorphological investigations and database updates. Full article

Background and Objectives: Unilateral biportal endoscopic (UBE) decompression has become an increasingly popular minimally invasive technique for the treatment of lumbar spinal stenosis. Although irrigation management is a critical component of this procedure that may influence operative efficiency and irrigation-related complications, comparative evidence regarding irrigation systems remains limited. Therefore, this study aimed to compare gravity-based and pump-assisted irrigation systems in patients undergoing UBE decompression for lumbar spinal stenosis with respect to clinical and functional outcomes, operative efficiency, and complication rates. Materials and Methods: This retrospective study included 107 patients who underwent single-level UBE decompression for lumbar spinal stenosis between 1 June 2023 and 1 January 2026. Patients were allocated to either the gravity-based (n = 51) or pump-assisted (n = 56) irrigation group according to the availability of the pump-assisted irrigation device at the time of surgery. Pain and functional outcomes were evaluated using the Numeric Rating Scale (NRS) and Oswestry Disability Index (ODI). Operative time, bleeding control time, and perioperative complications were compared between the groups. A mixed-design ANCOVA was used to analyze the changes in clinical outcomes over time. Multivariable linear and logistic regression analyses were performed to identify the independent factors associated with operative time and complications. Results: Significant improvements in the NRS and ODI scores were observed in both groups during follow-up (time effect, p < 0.001 for both), with no significant differences between the irrigation methods (group effect, p > 0.05). Operative and bleeding control times were significantly shorter in the pump-assisted irrigation group (both p < 0.001). Multivariable linear regression analysis demonstrated that pump-assisted irrigation independently reduced operative time by approximately 8 min (p < 0.001), whereas bilateral decompression independently increased operative time by approximately 24.5 min (p < 0.001). Although the overall complication rate was lower in the pump-assisted irrigation group (12.5% vs. 27.5%), the difference was not statistically significant (p = 0.052). Multivariable logistic regression analysis also demonstrated a trend toward a lower risk of complications with pump-assisted irrigation (OR = 0.408, p = 0.096). Conclusions: Pump-assisted irrigation improved operative efficiency by reducing operative and bleeding control times while providing clinical and functional outcomes comparable to those of gravity-based irrigations. Although the reduction in complication rates did not reach statistical significance, pump-assisted irrigation may represent an effective irrigation strategy that improves operative efficiency and may contribute to surgical safety in UBE decompression surgery. Full article

This study presents a short-term outdoor comparison of mirror-glass and AISI 304 stainless-steel reflectors in parabolic trough collectors equipped with identical helical copper absorbers. Both configurations were operated simultaneously using the same collector geometry, fixed inclination angle, water-supply arrangement, measurement schedule, and instrumentation. Solar irradiance, inlet and outlet water temperatures, absorber temperature, and reflector temperature were recorded over three consecutive experimental days, namely 24–26 October 2025. The results were evaluated using temperature rise and time-dependent temperature output because the gravity-assisted system was not equipped with a flow meter or active flow-control device, preventing reliable calculation of useful heat gain and thermal efficiency. The descriptive results showed that the mirror-glass configuration produced a modestly higher overall temperature response and lower variation among the three daily mean values, although it did not outperform stainless steel at every measurement time or in every daily average. The observed difference is interpreted primarily in terms of the expected higher specular reflectivity and lower optical scattering of mirror glass, which can increase the solar radiation intercepted by the absorber. However, the conclusions are limited by the three-day testing period, absence of verified mass-flow data, lack of direct reflectivity measurements, and unquantified cosine losses associated with fixed operation without automatic tracking. The findings therefore provide configuration-specific guidance for reflector selection rather than a generalized ranking of collector performance. Full article

This study investigates the mechanisms and performance of oxygen-reduced air flooding (ORAF) and oxygen-reduced air gravity drainage (ORAGF) through laboratory experiments on crude oil and cores from the Kunbei Oilfield. PVT experiments show that injecting N₂ or oxygen-reduced air (5% and 10% O₂) increases saturation pressure and reduces oil viscosity comparably. Low-temperature oxidation (LTO) tests reveal that oxygen consumption rate declines exponentially with decreasing initial O₂ concentration; at 5% O₂, oxidation products are nearly indistinguishable from the original crude oil. Long-core displacement experiments demonstrate that vertical (gravity-assisted) injection significantly outperforms horizontal injection, with oil recovery reaching 39.8% (10% O₂) versus 26.2% horizontally, owing to gravity segregation suppressing gas fingering and enhancing oil–gas contact. Among injection strategies, gas-assisted gravity drainage (GAGD) and water-alternating-gas (WAG) improve recovery by 7.7% and 7.2% over continuous waterflooding, respectively, with GAGD being more suitable for high water cut reservoirs. Reservoir rhythm and permeability contrast affect performance and gravity-driven injection mobilizes low-permeability layers more effectively than horizontal injection, exhibiting good adaptability to heterogeneous reservoirs. Fracture orientation relative to injection direction plays a critical role—horizontal fractures achieve the highest recovery (~50%), whereas through-going fractures impair performance. These findings provide experimental guidance for optimizing oxygen-reduced air gravity flooding in tight and heterogeneous oil reservoirs. Full article

Steam-assisted gravity drainage (SAGD) makes a significant contribution to Canada’s heavy oil production. Yet, it faces notable efficiency challenges during late-life stages, characterized by increased Steam–Oil Ratios and environmental concerns. Non-condensable gas (NCG) injection has emerged as a promising strategy to address these issues, particularly in late-life and post-steam SAGD phases. This review systematically examines the mechanisms, phase behavior, thermochemical interactions, field applications, and operational impacts of injecting NCGs such as methane, nitrogen, and carbon dioxide. This work exclusively synthesizes the application of NCG injections in mature SAGD reservoirs while outlining existing challenges. It delivers a unified perspective on this domain, introducing practical insights to improve NCG injection efficiency. Critical analysis of the existing literature reveals key benefits, including reservoir pressure maintenance, steam chamber stabilization, and viscosity reduction. However, literature gaps persist regarding long-term field-scale validation, complex drive mechanisms at the steam chamber flanks, thermochemical reactions, interactions with geological heterogeneity, and detailed thermodynamic modeling under non-equilibrium conditions. Emphasizing these gaps underscores the importance of further research and integrated modeling to optimize NCG utilization, thus enhancing recovery efficiency, reducing environmental footprints, and extending reservoir life. Full article

In heterogeneous edge-water carbonate gas reservoirs during the middle-to-late development stage, edge-water invasion and pressure depletion significantly compromise production stability and gas recovery. To investigate water invasion behavior under permeability heterogeneity and evaluate the effectiveness of CO₂ injection for water control and enhanced gas recovery, a series of long-core depletion experiments and three-dimensional vertically heterogeneous physical-model experiments were conducted based on representative reservoir conditions. The results show that permeability contrast plays a key role in governing water breakthrough timing and gas production performance. High-permeability cores experience earlier water breakthrough but contribute higher overall recovery, whereas low-permeability cores exhibit delayed depletion and pronounced production decline after breakthrough due to large pressure differentials. In multilayer commingled production, interlayer pressure imbalance drives fluid crossflow from low- and medium-permeability zones toward high-permeability zones, leading to premature water breakthrough, delayed layer activation, and the development of water-blocked gas zones, thereby intensifying interlayer heterogeneity. After depletion, CO₂ injection effectively modifies fluid flow pathways and improves reservoir connectivity. Through gravity-assisted displacement and energy replenishment, CO₂ mitigates water invasion, reconnects previously isolated gas zones, and enhances overall reservoir utilization. The findings demonstrate that CO₂ injection provides a dual benefit in both water control and production enhancement, offering valuable insights for improving recovery strategies in heterogeneous edge-water gas reservoirs. Full article

The discrepancy between observed galaxy rotation curves and predictions based on visible baryonic matter remains a central challenge in astrophysics. Within the standard ΛCDM framework, these observations are explained through extended halos of non-baryonic dark matter, while alternative approaches such as Modified Newtonian Dynamics reproduce many galactic scaling relations through empirical modifications of low-acceleration dynamics. Recent advances in symbolic machine learning provide a complementary route for investigating whether stable empirical relations can be discovered directly from observational data without imposing strong theoretical priors. In this work, we present the Phenomenological Dark Matter Nonlinear Pipeline, an AI-assisted symbolic discovery framework designed to identify mathematical relationships linking baryonic and observed gravitational accelerations. The analysis was performed using 3175 radial measurements from 175 galaxies derived from SPARC-based rotation-curve catalogs. Symbolic regression was conducted across 173 independent leave-one-galaxy-out validation folds, followed by bootstrap analysis, residual diagnostics, and regime-specific testing. The symbolic search repeatedly converged toward a stable family of non-linear logarithmic acceleration relations exhibiting strong recurrence across independent discovery folds. The resulting empirical relation successfully reproduces the observed Radial Acceleration Relation, naturally generates Baryonic Tully–Fisher Relation like scaling without explicit enforcement during training, and consistently outperforms classical Newtonian gravity while remaining competitive with a MOND-like reference model. Global validation yielded a coefficient of determination of R² = 0.9026 compared with R² = 0.8934 for the MOND-like model and R² = −0.0485 for the Newtonian baseline. Additional analyses demonstrate stable performance across low-acceleration systems, low-surface-brightness galaxies, and other galactic environments. The recovered relation should be interpreted as an empirically discovered scaling law rather than a replacement for General Relativity, ΛCDM, or existing modified-gravity theories. Nevertheless, the repeated emergence of a common symbolic structure across independent validation folds highlights the potential of AI-assisted symbolic discovery as a tool for uncovering interpretable empirical regularities in complex astrophysical datasets. Full article