Unraveling microplastic retention distribution in porous media: A unified framework coupling flow conditions and particle properties.

Gracilisuchus stipanicorum was a pseudosuchian archosaur from the Late Triassic period in Argentina. Because it was small-bodied with relatively long, slender limbs, traits that are potentially ancestral for archosaurs, such as its locomotor functions, are important to estimate. It has been illustrated as a quadruped with plantigrade autopodia, and probably with an 'erect' or 'semi-erect' stance, because it is a suchian archosaur, but there has been no deep analysis of these reconstructions. Here, we detail our reconstruction of a three-dimensional digital skeleton of Gracilisuchus from scans of the bones of four main specimens, including the holotype. In this procedure, we found hitherto unrecognised elements of the manus (metacarpals) and incorporated them in our model of the whole organism. We added estimated hindlimb musculature and body segment mass properties to form a musculoskeletal model. This model allowed us to address three key questions: Was it quadrupedal or bipedal; plantigrade or digitigrade; and more sprawling or more erect? Furthermore, we examine how its hindlimb muscle moment arms compare to those of three other small-bodied Triassic archosauriforms and an extant juvenile Nile crocodile in order to assess the diversity and potential evolutionary polarity of these traits. Our analyses of the model support the inferences that Gracilisuchus was quadrupedal (but facultative bipedalism cannot be ruled out) and plantigrade, and not strongly sprawling, but probably not strongly erect hindlimbs; although terming this posture 'semi-erect' would be an oversimplification. Gracilisuchus, as modelled here, seems to roughly be a reasonable approximation of the ancestral state of the archosaurian locomotor system. Our synthesis of numerous lines of evidence, from qualitative functional morphology to whole-body centre of mass and muscle moment arms, forms a new reconstruction of Gracilisuchus that future analyses can build on, both biomechanically and comparatively, in order to better understand archosauriform locomotor evolution.

Minor variations in radiographic measurements of variables underlying the coronal plane alignment of the knee (CPAK) classification can alter its categorisation. Accordingly, this study introduces a population-referenced framework for describing coronal knee alignment, based on the centre of mass (COM) of the arithmetic hip-knee-ankle angle (aHKA)-joint line obliquity (JLO) distribution. This study is presented as a descriptive and methodological contribution. It does not include clinical validation and does not propose an alternative alignment strategy for immediate clinical implementation. A geometric-statistical model was developed in which the COM of the aHKA-JLO distribution represents the population-referenced geometric reference point of central tendency. Each knee was characterised by its radial distance from the COM (magnitude of deviation, ) and its angular orientation relative to the COM (direction of deviation, ). Two concentric regions, encompassing 68% and 95% of the distribution, were defined based on radial distances for each value in the distribution. This model was subsequently applied to four previously published datasets comprising 2494 knees from Belgian, Spanish, Turkis, and Korean populations. The COM of the aHKA-JLO distribution and dispersion parameters differed across populations, indicating that neutral alignment is population-specific rather than universal. In the healthy reference cohort (500 knees), the COM was located at aHKA = -0.87° and JLO = 174.94°. The proposed framework allows each knee to be described according to its distance (magnitude of deviation) and orientation (direction of deviation) relative to this reference. Coronal knee alignment phenotypes may be described relative to the COM of a population-specific aHKA-JLO distribution, rather than by fixed angular thresholds. This population-referenced framework enables quantitative definition of both the magnitude and direction of alignment deviation, thereby preserving the geometric context of the distribution. The potential influence on classification stability, measurement-related variability and clinical applicability has yet to be determined and necessitates formal validation in future studies. N/A.

Effect of a virtual walking and therapeutic exercise-based intervention on gait and balance in people with incomplete spinal cord injury.

Sprinters need to generate horizontal impulse quickly in the first step out of the blocks to accelerate the body toward the finish line. The purpose of this study was to determine how body configuration at initial foot contact was correlated to ground reaction force measures and multijoint control during the first step out of the blocks by highly trained to world-class sprinters. Measurements of ground reaction forces and segment kinematics during sprint starts performed during a training session revealed that positioning the foot further behind the center of mass at initial contact significantly correlated with shorter contact times, greater average horizontal forces, and increased net joint moment impulse on the knee during the impact phase. Increases in average horizontal forces were significantly correlated with smaller magnitudes of shank angular velocity during the impact phase and shorter times to peak thigh angular velocity during the postimpact phase. We also used kinetic and kinematic data to provide feedback regarding an athlete's mechanics to coaches for use within a training session on the track.

Herein we analyze the dynamic behavior of a tethered space robot (TSR) for on-orbit capturing, considering large deformation of the tether. The robot is deployed from the mother satellite by using a long, flexible tether and moving along the target through the desired trajectory. The TSR is modeled as a flexible multibody system consisting of a point mass, a rigid body, and a flexible viscoelastic string. In this regard, the mother spacecraft is modeled as a point mass orbiting in a circular Keplerian orbit. The active robot, which is responsible for docking with the target, is modeled with a three-degree-of-freedom equation of motion that reflects its rigid body and free-floating characteristics. The flexible towing tether, which can experience large displacements and deformations, is modeled using an absolute nodal coordinate formulation (ANCF). The equations of motion of the whole system are derived by using Lagrange's equation. The overall equations of motion and parameters are described in the natural coordinate frame (NCF). Since the point where the tether is attached to the robot is displaced from its center of mass, there is highly nonlinear coupling between tether deformation/tension and robot motion. The robot's position and attitude are controlled actively to sync with the target based on relative pose motion equations, while the tether is dragged behind it. A numerical simulation based on the final approach scenario was conducted, and the results confirm the physical plausibility of the model.

Assessing inter-joint coordination during gait in hip osteoarthritis.

Background:Typically, 3 months is an early postoperative time point at which patients with femoroacetabular impingement syndrome (FAIS) demonstrate clinically meaningful improvement, while 6 months represents an important midterm stage for recovery and return to sport.Purpose:To assess continuous changes in the kinematics of the involved and uninvolved lower limbs in patients with FAIS at 3 and 6 months after hip arthroscopy as well as to examine their relationships with International Hip Outcome Tool–33 (iHOT-33) and Copenhagen Hip and Groin Outcome Score Sport subscale (HAGOS-Sport) scores.Study Design:Cohort study; Level of evidence, 2.Methods:The study included 15 patients who underwent hip arthroscopy between March 2024 and November 2024 as well as a healthy control group of 15 participants, matched to the patients by sex, age, and body mass index, recruited from the community. All participants performed the single-leg squat (SLS), and kinematic data were collected using an 8-camera motion capture system. One-way analysis of variance was used to compare baseline, 3-month postoperative, and 6-month postoperative kinematic data of the FAIS group with those of the healthy control group. Post hoc comparisons were conducted using the Tukey test to determine between-group differences. Correlation analysis was performed to assess the relationship between changes in the hip flexion angle and changes in iHOT-33 and HAGOS-Sport scores.Results:At 3 months postoperatively, the involved limb hip flexion angle (P = .021), hip adduction angle (P = .0011), knee flexion angle (P = .016), and change in the center of mass (P = .0034) were reduced compared with the healthy control group. At 6 months postoperatively, no significant kinematic differences were observed between the FAIS and healthy control groups. Correlations between changes in the iHOT-33 score at 3 months and changes in the hip flexion angle at 6 months were positive (r = 0.64; P = .0094), and changes in the iHOT-33 score at 6 months were also positively correlated with changes in the hip flexion angle at 6 months (r = 0.53; P = .041).Conclusion:Patients with FAIS exhibited abnormal kinematics during the SLS at 3 months postoperatively, which showed improvement by 6 months. Furthermore, improvement in sagittal-plane angles of the hip at 6 months postoperatively was correlated with the iHOT-33 score, supporting our hypothesis. Clinicians should not overlook functional recovery after hip arthroscopy for FAIS.

This paper presents a lightweight balloon‐dynamics method, built on the Position-Based Dynamics (PBD) framework, that reproduces real-time inflation–deflation–rotation as air is injected and released. Unlike volume/CFD approaches that require expensive fluid–structure coupling, our method avoids explicit fluid simulation by combining Bernoulli-derived reaction forces with PBD distance and volume constraints. Rotation is modeled as a global rigid-body motion (single rotation/quaternion update about the center of mass), while local shape changes are handled through constraint-based position correction—eschewing cluster-level or per-vertex local twisting. Geodesic-distance weighting of reaction forces and the separate treatment of translational and rotational components improve physical plausibility; minimal iterations and rigid-body rotation approximation preserve computational efficiency. Experiments on meshes with diverse geometries and mass distributions show consistent real-time performance on high-resolution models while capturing the characteristic balloon behaviors. The approach is well-suited for interactive applications such as games, VR/AR, and real-time physics-based content.

Traditional optofluidic droplet manipulation suffers from low transport efficiency due to the drag of surface tension. This study introduces laser-driven Leidenfrost droplets to achieve rapid, directional transport, with the total acceleration a up to ∼60mm/s2-approximately triple that of Leidenfrost droplets without a laser. Both higher laser energy and stronger light absorption by the droplet enhance the transport efficiency of Leidenfrost droplets. The kinetic model elucidates that the droplet's rapid motion driven by the laser is attributable to a shift in the droplet's center of mass, induced by the nucleation of plasmonic bubbles. The displacement of the droplet's center of mass generates a driving torque, enhancing droplet internal flow and the vapor film beneath the droplet asymmetry, thereby increasing motion propulsion. This study lays the foundation for efficient light-driven droplet transport, offering valuable insights for advancing the practical application and control of Leidenfrost droplets.

Marker-based motion capture is the gold standard for 3-dimensional gait analysis but is expensive and largely confined to specialized laboratories. Smartphone-based markerless tools such as OpenCap could scale gait assessment, yet their validity and repeatability during treadmill walking and running remain unclear. We evaluated agreement and within-session repeatability between OpenCap and motion capture during treadmill walking (4km·h-1) and running (8 and 14km·h-1) in 10 healthy adults, recorded simultaneously with both systems. We computed spatiotemporal variables, sagittal hip/knee/ankle angle waveforms and range of motion, and center-of-mass displacement waveforms and range of motion. Agreement was assessed with Bland-Altman, intraclass correlation coefficients, Pearson r, and root mean square error; repeatability with trial-to-trial SD, coefficient of variation, and waveform variability index (GaitSD). Spatiotemporal metrics showed bias close to 0 and very strong associations (r ≥ .96), with small minimum detectable changes (eg,≤0.01m for stride length and ≤0.03s for temporal variables). Sagittal range of motion showed good-to-excellent reliability (bias: ≈-4.5° to 2.9°, intraclass correlation coefficients = .76-.93). Waveform root mean square error was ≈1° to 4° for joint angles and ≈0.1 to 0.5cm for center of mass, and statistical parametric mapping indicated only localized differences. Repeatability and GaitSD were comparable between systems across variables and speeds. Under controlled treadmill conditions, OpenCap showed comparable performance and repeatability metrics to motion capture.

Older people often fall due to trips and slips in daily life. This study aimed to elucidate the mechanisms of trip- and slip-hazard avoidance while walking through an immersive virtual reality suburban footpath. Forty-six participants (71.8 ± 4.7 [65-84] years) wore an immersive head-mounted display (Oculus Rift S) and safety harness while walking on a split-belt treadmill (M-Gait). Participants walked on a virtual footpath while avoiding hazards including raised concrete slabs (trips) and puddles (slips) and as a secondary task collected apples. Foot-hazard contacts resulted in treadmill belt accelerations/decelerations to evoke balance loss. Hazard contact rates and gait kinematics were measured using Vicon motion capture. Participants contacted more trip-hazards (63.1%) than slip-hazards (22.2%; p <.001). Trip-hazards were more frequently collided with by the trailing foot (56.9%) compared to the leading foot (16.7%; p <.001). Trailing foot contact with both trip- and slip-hazards resulted in significant changes in extrapolated Centre of Mass (XCoM) and Margin of Stability (MoS) (p <.05). Following trailing foot contacting trip-hazards, participants compensated effectively by increasing MoS, whereas contacting slip-hazards reduced MoS, indicating a higher risk of losing balance. On a virtual suburban footpath, older adults often collided with trip-hazards with their trailing foot, which was typically beyond their visual field, while slip-hazards more commonly involved the leading foot. These insights can supportthe development of fall prevention programs that better mirroreveryday walking challenges.

Long-term balance impairments are prevalent after anterior cruciate ligament (ACL) injury and are possibly linked to an overreliance on visual information and related cortical processing. We therefore aimed to explore characteristics of functional brain networks related to postural control with and without vision following ACL reconstruction (ACLR). Twenty-seven individuals after ACLR and 24 non-injured controls performed single-leg balance tasks under eyes-open/eyes-closed conditions. Graph-theoretical measures of functional network segregation (clustering coefficient, CC) and integration (path length, PL) were derived from mobile electroencephalography. Sway characteristics were calculated based on centre of pressure (CoP; area and velocity) and the mean distance between CoP and centre of mass (CoM). Knee antero-posterior kinematics were also explored. Group effects were analysed using permutation-based ANCOVA. During eyes-open only, the ACLR group exhibited greater cortical network segregation (higher CC; p = 0.025) in the alpha-1 band (8-10Hz). While sway characteristics were similar between groups, the ACLR leg demonstrated greater knee flexion compared to their contralateral leg (p = 0.036). Individuals post-ACLR showed more efficient functional brain connectivity during eyes-open, combined with kinematic adaptations in their injured leg. These findings suggest post-ACLR neural adaptations of postural control mechanisms, particularly when visual information is available.

ABSTRACT SiO2 nanoparticles have great potential in enhancing oil recovery in low-permeability reservoirs due to their tunable wettability and interfacial activity. However, its oil displacement efficiency is influenced by surface modification, hydrophilic/hydrophobic ratio, and pore size, and the microscopic mechanism remains unclear. This study used MD simulations to systematically investigate the interfacial behaviour, wettability regulation and displacement efficiency of modified nanoparticles. The results indicate that when the ratio of hydrophilic to hydrophobic groups on the surface is 5:5(NM3), the nanoparticles form a stable adsorbed layer at the oil-water interface, significantly reducing interfacial tension; in 6nm pores, the displacement of the oil phase's centre of mass is maximised and the displacement efficiency is increased by 42% compared to the pure water system. Hydrophilic carboxyl-modified nanoparticles (NM5) increase the oil contact angle on rock from 28° to 72°, making the surface neutrally hydrophilic and reducing residual oil. In 2nm pores, C6COOH reduces capillary force by improving wettability, while C1OH particles show strong diffusion and fingering. Amphiphilic particles (such as C6OH) promote emulsification by splitting the oil phase into isolated domains. This study reveals the microscopic mechanism of modified SiO2 nanoparticles and provides a theoretical basis for efficient EOR in low-permeability reservoirs.

Motor sequence learning (MSL) involves transitioning from reactive, stimulus-led control to predictive, automated execution. While expertise is traditionally quantified by speed and accuracy, the underlying organizational shifts in fractal movement variability remain poorly understood. We propose the Readiness-Efficiency hypothesis: expertise emerges through a functional coupling of high preparatory complexity and reduced execution complexity. Participants (n = 22) performed a whole-body Dance Discrete Sequence Production task while Center of Mass (CoM) kinematics were recorded. Hurst exponents (H) quantified fractal complexity across ten blocks of practice and transfer. As learning progressed, preparatory dynamics shifted toward higher complexity (Hprep ↑), reflecting structured readiness, while execution dynamics shifted toward reduced complexity (Hexec ↓), reflecting automated efficiency. Crucially, a three-way interaction revealed that the fastest response times were achieved specifically when high preparatory readiness was coupled with reduced execution complexity. This coupling collapsed upon transfer to novel sequences, indicating task-specificity. State-space analysis confirmed the Readiness-Efficiency configuration acts as a functional attractor, with the probability of occupying this state increasing five-fold through practice. These findings demonstrate that expertise is characterized by dynamic flexibility – the capacity to dissociate and pair control regimes to meet phase-specific demands – providing a mechanistic framework for profiling skill acquisition.

The problem of transporting payloads suspended from a quadcopter is gradually acquiring not only theoretical but also practical importance. If the mass and size of the payload are large enough, control algorithms should take into account its motion relative to the copter and aerodynamic forces acting on the payload. Special attention should be paid to preventing large-amplitude payload oscillations, since such oscillations can lead to emergency situations. This paper considers a mechanical system consisting of a quadcopter and a spherical cargo suspended from its center of mass on a weightless rod using a spherical hinge. The system can perform spatial motion in a wind flow, the speed of which is assumed to be constant and directed horizontally. The drag force acting on the payload is taken into account. The controllability of the system in the vicinity of the uniform rectilinear flight is discussed. It is shown that the system is not completely controllable, with the uncontrolled variables corresponding to payload rotation about the axis coinciding with the rod. The remaining variables are completely controllable (at least if the aerodynamic force is small enough). To stabilize the uniform rectilinear flight, a control is constructed, optimal in the sense of the standard quadratic functional. The problem of the motion of the copter along a target sufficiently smooth trajectory with a given cruising speed, while preventing intense oscillations of the payload, is considered. An algorithm is constructed to control the forces generated by the copter’s rotors, which ensures the motion of the system along the target trajectory and prevents the occurrence of high-amplitude payload oscillations.

Background. Walking is a fundamental human activity, vital for daily living, social connection, employment, etc. Methods. In the current study, we present a mathematical model of it, based on the planar double pendulum system influenced by gravity. For parameters of the pendulum, i.e., the characteristic of the limbs (thigh + shank), we use realistic mass–inertial parameters. The model incorporates anthropometric and inertial data specific to the average Bulgarian, Russian, German, and American male, including segment masses, centres of mass, as well as densities of the segments taken from experimental studies. Results. We derive the corresponding nonlinear differential equations governing the model. We solve them analytically, when possible, and, in the general case, numerically. For moderate initial angles (from the frontal plane) and angular velocities of the thigh and shank, the pendulum exhibits motion closely resembling natural human gait. The results for all nationalities considered are very close to each other. For comparatively slow walking speeds, the model provides realistic results. Conclusions. Our approach highlights how a relatively simple biomechanical model can capture essential features of human locomotion and provides a foundation for further refinement and comparison with more complex gait modelling techniques. Such modifications are outlined.

Stabilizing bipedal gait is mechanically challenging. To analyze how gait is stabilized, previous studies have focused on the control of the body center of mass (CoM). These studies often linked deviations in linear momentum of the CoM to subsequent shifts in position of the center of pressure (CoP), or of the foot, relative to the COM, and interpreted these as stabilizing responses to correct linear CoM momentum. Mechanically, however, CoP shifts do not cause changes of linear CoM momentum, whereas they do cause changes in whole-body angular momentum. We hypothesized that experimentally observed correlations between CoP to CoM distance and horizontal ground reaction forces are related to the need to control both linear and whole-body angular momentum. We show that, in human walking, linear and angular momentum follow quasi-periodic functions with similar periodicity and phase. Combining the equations of linear and rotational motion for a system of linked rigid segments shows that, in this case, the horizontal distance between CoP and CoM should be correlated to horizontal force in the corresponding direction. This suggests that linear and angular momentum are simultaneously controlled and may explain the success of preceding studies that correlated CoM states to CoP or foot locations. Regression models fitted to experimental data of participants walking at normal and slow speeds showed that deviations in horizontal ground reaction forces and in moments of the ground reaction force about the sagittal and transverse axes could be predicted from deviations in the preceding linear and angular momentum respectively. Our analyses support that linear and angular momentum are indeed controlled simultaneously in human walking.

Sex differences in coordination of center of mass kinematics during table tennis footwork.

Vastus lateralis-gastrocnemius co-activation during gait is associated with reactive stability to slip-like perturbations in chronic stroke.