Search Results (569)

Deep-water gravity flow deposits constitute a critical frontier in global hydrocarbon exploration, and characterizing flows controlled by complex topography remains a significant challenge. Focusing on the Cretaceous Pointe Indienne Formation in the Lower Congo Basin, West Africa, this study systematically investigates the depositional characteristics, flow types, vertical sedimentary sequences, and depositional models of lacustrine gravity flows, based on newly acquired drill core data, analytical test results, and three-dimensional seismic interpretation from the study area. Three major gravity flow types are identified in this study: sandy debris flows, muddy debris flows and turbidity currents. Meanwhile, we highlight the critical roles of slide–slump deposits and contour currents in deep-water depositional evolution, which further clarifies the sedimentary characteristics, vertical facies association patterns and spatial distribution of the Pointe Indienne Formation. Based on these results, we construct a stepped-slope depositional model for lacustrine rift basins. This “stepped-slope-controlled gravity flow” model describes the evolution of sediment transport from high-density, block-based processes (slides/debris flows) to low-density turbulent processes (turbidity currents). Beyond explaining the geological features of sub-salt gravity flow deposits in the Lower Congo Basin, this model improves the accuracy of predicting deep-water gravity flow sand body distribution in lacustrine basins with analogous structural and topographic settings, providing robust geological and theoretical support for hydrocarbon exploration in similar regions. Full article

Pulse wave propagation through blood vessels is affected by many biophysical parameters that change with aging. The aim of this study was to investigate both theoretically and experimentally how the pulse wave velocity changes in the vertical position and to introduce a new parameter in biophysics: pulse wave acceleration (PWA). Using a biophysical model of the cardiovascular system, placed in horizontal and vertical positions, pressure waveforms were measured along the arterial tree at several sites at different diastolic pressures and pump frequencies. Blood flow waveforms on the carotid and femoral arteries in the supine and standing positions were measured on the subjects. The results showed that the pulse pressure wave accelerates in the direction of gravity and decelerates in the opposite direction both in the model and in humans. A new biophysical parameter, PWA, was defined, and the experimental results are in agreement with the mathematical model. Due to the acceleration of the pulse wave, the reflected wave in the standing position arrives earlier in systole and contributes to the increase in pressure. This emerging biophysical parameter may contribute to a better understanding of the phenomenon of wave propagation of blood through blood vessels. Full article

Analysis of freely moving Drosophila captures complex movement behaviors. However, previous experiments have been limited by the inability to distinguish between falls and downward jumps (downjumps). Here, individual flies moving freely in a culture vial were recorded using a single 58 fps video camera. Upward jumps were readily identified by positive movement in the vertical direction. Several statistical and machine learning methods were used to distinguish between falls and downjumps, including Principal Component Analysis (PCA), K-Means Clustering, Uniform Manifold Approximation and Projection (UMAP), Hierarchical Density-Based Spatial Clustering with Applications to Noise (HDBSCAN) and Shapley Additive Explanations (SHAP). Falls were abundant and characterized by an initial velocity consistent with simple acceleration due to gravity. Downjumps were more rare, and were characterized by a greater initial velocity, indicating active propulsion by the fly. Aged flies took longer to resume movement after a fall, suggesting possible negative effects of falls. Falls in young w[1118]-strain flies exhibited mid-event velocities that were lower than expected, indicating some compensatory behavior that was reduced in aged flies. These methods should facilitate future studies of the effects of aging and neurodegenerative disease models on locomotor behaviors and falls, including the testing of potential interventions. Full article

Natural weak discontinuities, such as natural fractures, bedding planes, and coal–rock interfaces, are widely developed in deep coal reservoirs. During hydraulic fracture propagation, induced fractures readily interact with these weak planes through crossing, deflection, and combined activation, thereby forming complex fracture geometries and significantly affecting proppant transport and placement. To clarify the transport behavior of proppant under different fracture geometries, four representative tortuous wedge-shaped fractures were constructed to characterize typical fracture propagation patterns in deep coal reservoirs, namely a vertical straight fracture (“|”), a horizontal straight fracture (“—”), a T-shaped fracture, and a cross-shaped fracture (“+”). On this basis, a two-way coupled fluid–particle model was established using the CFD–DEM method to systematically investigate proppant migration, settling, and placement in different fractures, as well as the effects of injection velocity, particle size, and fluid viscosity. The results show that fracture geometry exerts a significant influence on proppant transport patterns and placement performance. Specifically, proppant transport in the “|”-shaped, T-shaped, and “+”-shaped fractures can be divided into three distinct stages: rapid start-up, stratified transport, and front advancement. In contrast, particles in the “—”-shaped fracture are only weakly affected by gravity and remain almost entirely in an orderly front-advancement regime, exhibiting the most stable and continuous placement behavior. Increasing injection velocity and fluid viscosity both improve proppant placement uniformity and markedly promote branch entry in the T-shaped fracture, whereas their improvement in the “+”-shaped fracture is relatively limited. When the fluid viscosity increases from 1 mPa·s to 5 mPa·s, the placement uniformity coefficient (PUC) of the “—”-shaped, “|”-shaped, T-shaped, and “+”-shaped fractures increases by approximately 3.2%, 5.6%, 6.3%, and 7.1%, respectively. These findings provide mechanistic insight into geometry-dependent proppant transport and placement in complex fractures of deep coal seams, and offer theoretical support for hydraulic fracturing design and parameter optimization. Full article

A generalized mathematical model is constructed to describe the isothermal two-phase flow of a three-component system and to investigate light non-aqueous phase liquid (LNAPL) displacement during surfactant-enhanced remediation in vertical porous media. The model integrates the dominant physical mechanisms governing immiscible fluid redistribution, including gravitational and capillary forces under different wettability conditions. The hyperbolic part of the system is analyzed within the framework of a Riemann problem, allowing for the characterization of shock and rarefaction wave formation in saturation and concentration profiles. Numerical simulations performed using a first-order upwind (FOU) scheme reveal pronounced artificial dissipation, as confirmed by von Neumann stability analysis. To overcome this limitation, a high-order non-oscillatory scheme based on nonlinear flux limiters and polynomial reconstruction is developed, enabling accurate resolution of sharp displacement fronts. A comparative analysis of limiter functions reveals that their suitability depends on the degree of nonlinearity in relative phase permeabilities, highlighting the necessity for careful selection in multiphase flow modeling. Parametric investigations quantify the effects of gravity, capillary parameters, Peclet number, and wettability alteration on displacement efficiency in homogeneous porous media. The proposed framework is validated against experimental MRI data, demonstrating its reliability for describing two-phase displacement in porous media. Overall, the developed numerical model provides a predictive framework for resolving nonlinear front dynamics and optimizing surfactant-enhanced remediation strategies in contaminated subsurface reservoirs. Full article

Summertime westward-to-eastward zonal wind reversal near the mesopause is a key manifestation of wave–mean flow interaction in the mesosphere and lower thermosphere. We examined this zonal wind reversal over Langfang, China, during May–July 2024 using co-located MF and meteor–radar winds together with SD-WACCM output. The reversal height and vertical shear near the reversal height were obtained from a linear fitting. Both radars showed pronounced temporal dependence for the zonal wind-reversal height, with a higher height at the beginning of summer, which decreased from May to July. The MF radar placed the transition slightly higher than meteor radar, both of which are confined to the mesopause region. The SD-WACCM output showed clear zonal wind reversal, but the reversal heights were between MF and meteor observations. Moreover, the decreasing trend of the zonal wind-reversal height in the SD-WACCM output was less evident than in radar observations. Nevertheless, the zonal wind reversal exhibited clear diurnal variations. The total zonal wind tendency due to gravity wave-breaking in the SD-WACCM output was utilized to diagnostically analyze the reasons, wherein diurnal variations in the wind-reversal height corresponded well to the diurnal variations in gravity wave-dragging. Monthly model diagnostics further showed the positive strengthening of gravity wave drag near 80–90 km from May to July. Our analysis showed that the temporal variation in the background flow and the reversal layers during 2024 were intimately related to gravity wave momentum deposition locally and globally. Full article

Accurate measurements of wind fields in the troposphere and stratosphere are essential for advancing atmospheric dynamics research, improving weather prediction, and supporting aerospace operations. However, a single Doppler lidar technique usually has limited capability to provide vertically extended wind profiles across both aerosol-rich lower altitudes and molecular-dominated higher altitudes. In this paper, we present a hybrid Doppler lidar system that combines a 355 nm scanning incoherent Rayleigh Doppler lidar with a 1550 nm coherent aerosol Doppler lidar for multi-scale wind field detection. The coherent Doppler lidar is used for boundary-layer wind retrievals, while the Rayleigh Doppler lidar, based on the double-edge technique, extends wind profiling from the upper boundary layer to approximately 40 km. Field deployments demonstrate continuous wind profiling from 50 m to 40 km, extending from the boundary layer to the stratosphere. Comparisons with radiosonde measurements show good agreement during the field campaigns, supporting the feasibility of this hybrid configuration for vertically extended wind profiling. The resulting high-resolution wind measurements across multiple atmospheric regions provide valuable data sources for studies of multi-scale circulation research, gravity wave dynamics, and climate-related atmospheric processes. Full article

To investigate the dynamic characteristics of key parameters in a piston gravity energy-storage system, an experimental system for novel piston gravity energy storage is designed and developed. Firstly, the structure and working principle of the piston gravity energy-storage system are analyzed. Adopting a modular modeling approach, the system is divided into four core modules, and the piston motion, vertical cylinder chamber pressure, hydraulic actuator, and turbine power models are established. Subsequently, a case study simulation is conducted on the piston gravity energy-storage system to model its dynamic characteristics during discharge conditions, analyzing the variation patterns of key parameters such as the chamber pressure, flow rate, and output power within the system. Finally, the experimental system integrates a digital controller with proportional–integral power regulation and an automatic mode switching logic to enable the constant power closed-loop control, with real-time acquisition of the chamber height, pressure, flow rate, and electrical parameters. The dynamic responses of various system parameters are analyzed. Experimental results indicate that under constant power charging and discharging conditions, the height of the upper chamber exhibits a linear trend, the pressure in the lower chamber is inversely proportional to the height of the upper chamber, and the flow rate remains stable with charging and discharging power. Neglecting energy losses of the pump and hydraulic turbine and only considering friction and hydraulic losses, the charge–discharge efficiency of the energy-storage experimental system is 65%. Full article

A time-dependent nonlinear model is presented to describe internal gravity waves propagating upwards in the F-region of the Earth’s ionosphere. The model is based on a configuration where the background neutral velocity is constant, the geomagnetic field is approximately constant, and the angular gyrofrequency of the ions is much larger than the ion-neutral collision frequency, which is in turn larger than the angular frequency of the gravity waves. For small-amplitude waves the equations are linearized, and a time-dependent analytical solution is obtained for the special case corresponding to the limit of zero vertical-to-horizontal aspect ratio. This analytical solution and the linear numerical results for general aspect ratio show that in the limit of infinite time the linear solution approaches a steady state in which the ion damps the wave amplitude in the vertical direction. For the more general configuration that includes larger amplitude waves, time-dependent nonlinear numerical simulations show that, in the presence of the ion drag, there are wave mean-flow interactions even in the absence of vertical shear in the background neutral flow. With time, the perturbation develops a zero-wavenumber component corresponding to a wave-induced mean flow acceleration, which depends on the dip angle of the geomagnetic field and on the aspect ratio. Full article

Coal mine underground reservoirs are increasingly used for mine-water storage and reuse in ecologically fragile mining regions, but the dynamic response of artificial dam structures under coupled water-pressure and seismic loading remains insufficiently understood. This study develops a simplified two-dimensional frame-based dynamic model to compare flat slab, gravity, and arch-equivalent artificial dams. Two water pressure levels, 0.1 and 1.0 MPa, and two seismic intensities, PGA = 0.1 g and 0.5 g, were considered using four representative acceleration histories. The arch dam was represented by a vertical rectangular section with equivalent arch-action lateral restraint. Results show that water pressure primarily controls peak total displacement, whereas PGA mainly governs the dynamic displacement increment and absolute acceleration. Increasing water pressure from 0.1 to 1.0 MPa markedly amplified total displacement and tensile stress demand, while increasing PGA from 0.1 g to 0.5 g produced a clearer effect on dynamic increments than on total displacement. The arch-equivalent dam consistently showed the smallest displacement response, while the gravity-type dam developed higher tensile stress demand under high water pressure in the simplified model. Effective modal frequencies were relatively high, explaining the coexistence of small displacement demand and noticeable acceleration response. The results provide a mechanistic basis for artificial dam-type comparison and preliminary safety assessment in underground reservoirs. Full article

The problem of constructing consistent interactions between a Weyl graviton—with its free limit expressed by the linearized Weyl action—and a photon—with its free dynamics generated from the standard Maxwell action—is analyzed as a deformation problem for the antifield-BRST generator associated with the non-interacting free model. By relaxing the standard working hypotheses to allow at most four spacetime derivatives in the interaction vertices, while not restricting the number of derivatives on the photon potentials, the most general cross-couplings are derived. This proves the uniqueness of the previously geometrically prescribed, overall fourth-order Lagrangian dynamics of the electromagnetic field in the presence of dynamical-type full Weyl gravity. Full article

Fighting against gravity is a common challenge for all terrestrial animals, including most mammals. It means, in particular, avoiding falls to the ground while performing daily tasks, such as standing up, locomotion, or foraging for food. This means that balance control in humans involves a wide variety of contexts and balance paradigms, such as upright standing, hand standing, tightrope walking, ice-skater spinning, bicycling, whole-body gesturing, and fingertip stick balancing, among others. From the cybernetic point of view, the underlying control problem is to keep the CoP (Center of Pressure) and the CoM (Center of Mass) aligned dynamically on the common vertical axis, and this means that the variety of balance strategies can be reduced to two basic paradigms: the CoP strategy (the CoP is the control variable and the CoM is the controlled variable) and the CoM strategy (the CoM is simultaneously the control and the controlled variable). It is suggested that the two balance strategies are implemented by combining four basic control paradigms, as a function of the task and environmental conditions: • Opportunistic control: exploitation of a physical phenomenon as the gyroscopic effect. • Stiffness control: exploitation of the elastic properties of skeletal muscles. • Feedback control: measuring an incipient fall index and closing the loop in real time. In particular, it is shown that a phase-space-based formulation of intermittent feedback control can compensate for the destabilization effect of conventional continuous control due to the large feedback delay. • Feedforward control: exploitation of an internal body model to generate stable whole-body synergies in an anticipatory manner. Such control paradigms are illustrated by summarizing the results of experimental and simulated data. Full article

Background/Objectives: In a recent article we outlined how the vestibular efferent system connects the stereo/kinociliary complex at the apex of the macular vestibular hair cells of the inner ear and coordinates movement so that planned body movements are precisely timed to coordinate with the expected otoconial movement that the body movement induces. Methods: Our present article proposes an extension of this concept with details about how a sailor develops “sea legs.” The rocking motion of a boat in rough seas requires sailors to sway in order to remain vertical. This causes fluctuation in the gravity-referenced otoconial signal. Results: As a sailor develops sea legs, it is necessary that the routine vestibular efferent system activity (based on gravity-referenced orientation on land) is disrupted as the otoconia move with this rocking process in order to re-coordinate with the new otoconial movement. As a result, the cerebral cortex must reconfigure vestibular efferent activity so that the stereo/kinociliary complex moves in conjunction with the otoconial movement. This process is carried out via the striated organelle (STO) and is one that takes several days. Those who are unfortunate and have severe motion sickness, become extremely unwell with nausea, vomiting, severe unsteadiness, and anorexia during this time. Conclusions: The present article describes how “sea legs” develop and discusses why an unpleasant symptom set can accompany it. We will also outline how a new medication, a calcitonin gene-related peptide (CGRP) inhibitor, which is presently used for the treatment of vestibular dysfunction, has been shown to suppress vestibular efferent activity and may be an effective therapy for these overly symptomatic individuals. Full article

Background: Ancient depictions of Pankration techniques have traditionally been interpreted through qualitative comparison with modern combat sports, without systematic biomechanical evaluation. The present study examines whether postural configurations derived from archeological artifacts are geometrically compatible with a continuous sagittal-plane trajectory under constrained inverse kinematics. Methods: A reduced planar humanoid model with three active rotational degrees of freedom was implemented in MATLAB Simulink(2024b), and artifact-derived initial and terminal postures were treated as boundary conditions. An analytical inverse kinematics solution was used to generate a continuous end-effector trajectory, from which joint kinematics and center-of-gravity displacement were computed. Motion capture data from ten participants were used solely to assess whether the generated trajectory is physically executable within human joint limits. Results: The results demonstrated strong agreement in selected local horizontal joint trajectories, while larger discrepancies were observed in vertical motion and global center-of-gravity behavior, reflecting the limitations of the reduced model. Conclusions: The study provides a reproducible framework for evaluating the kinematic feasibility of artifact-derived movements under explicitly defined constraints, limited to the assessment of geometric compatibility and physical executability. Full article

We present and discuss time-lapse gravity variations recorded by a large-scale absolute gravity network operating in Central Italy. The network comprises four stations distributed across the Lazio, Umbria, and Abruzzo regions, areas affected by the significant seismic activity of 2009 and 2016–2017. From 2018 to 2023, six campaigns were carefully conducted using an FG5 absolute gravimeter. We detected significant gravity decreases around 2020 reaching between −15 and −20 μGal in three sites and approximately −37 μGal at the fourth. The Sentinel-1 time series of permanent scatterers (PS) allowed us to exclude significant contribution from vertical deformations to the observed gravity changes. We analyzed both ground-based data (rainfall gauges and well water levels) and satellite-based observations (the Gravity Recovery and Climate Experiment-Follow-On, GRACE-FO, mission) together with the Global Land Data Assimilation System (GLDAS) and precipitation models. The results reveal a significant decrease in the regional groundwater content from 2018 to the end of 2020, which coincides temporally with the observed gravity decrease. We show that the absolute gravity variation trends observed at all stations are consistent with regional-scale hydrological processes, pointing to a significant decrease in terrestrial water storage (TWS) during the same time interval. At L’Aquila (AQUI), the gravity anomaly is larger than expected from regional hydrological products alone, suggesting an additional local component possibly related to the hydrogeological response of the fractured karst system undergoing significant post-seismic activity. Full article