The Condition for Lifting Flax Retted Straw Ribbons by the Pickup Drum

In musculoskeletal simulation, individualized joint axes enhance the accuracy and reliability of kinematic and kinetic simulation results. We investigated the correctness and performance of an analytical method for identifying the instantaneous axis of rotation between two bodies based on motion data in OpenSim. The instantaneous center of rotation is the point at which two bodies have the same velocity. The relative linear and angular velocity between the two bodies, as well as their relative position to each another, are required as inputs to calculate it. Using the instantaneous center of rotation, fixed or moving joint centers of rotation can be identified. To prove the general applicability of the method, the instantaneous centers of rotation of a revolute joint of a simple double pendulum model and the hip and knee joint of a more complex musculoskeletal model were investigated. The hip joint is defined as a ball joint. The knee joint is defined as an OpenSim custom joint which describes the motion of the child segment in relation to the parent segment as a function of generalized coordinates. To verify the correctness of the approach in OpenSim, the moving centers of rotation were calculated using synthetic noisefree data. The results were compared to the implementation of the respective joints in the model which act as the ground truth. White Gaussian noise was added to the synthetic data to analyze its effect on the quality of the calculated centers of rotation. We were able to correctly identify the center of rotation of each joint using noisefree data. In the case of noisy data, joint centers of rotation can be determined by applying additional filtering or optimization methods to the calculated instantaneous centers of rotation. Consequently, we are able to determine the center of rotation for arbitrary joints based on noisy synthetic data. This approach is applicable for both fixed and moving centers of rotation which distinguishes it from commonly used methods in the field of biomechanical simulation.Supplementary InformationThe online version contains supplementary material available at 10.1186/s42490-025-00102-7.

Bone loss in patients undergoing revision THA poses a considerable challenge for orthopaedic surgeons. Often, to achieve better fixation in remaining bone, larger diameter acetabular components and reaming superiorly may be necessary. However, this is likely to raise the hip center of rotation, which may lead to altered biomechanics, specifically, insufficiency of the abductor muscles, altered gait, and increased risk of dislocation from impingement. More recently, a newer acetabular shell has been designed to more closely replicate the native hip center of rotation in these circumstances while maintaining adequate fixation. The purpose of this study was to compare the radiographic parameters of this newer design with conventional hemispheric cups in revision THA. Specifically, we assessed the differences in (1) vertical center of rotation (COR) displacement and (2) horizontal COR displacement. Between January 2016 and April 2016, five reconstructive surgeons at five institutions utilized a newer highly porous acetabular shell designed with peripheral screw holes and vertically eccentric COR to allow for restoration of center of hip rotation in revision THA. We included all patients who received this device. During this time, the general indications at these sites for using the new device included Paprosky Stage IIA, IIB, IIC, or IIIA acetabular defects. This yielded 29 patients who were subsequently matched (one to two) by cup size and sex to a cohort who underwent revision THA with conventional hemispheric cups between January 2015 and May 2016. To determine hip COR, radiographic measurements were performed. A circle contiguous to the acetabulum was drawn and the center was determined as the hip COR. All measurements were made from the interteardrop line for both the revised and native hips. A line through the teardrops was used for all horizontal measurements. Center position adjustments were made based on the manufacturer-specified values. Comparisons were performed using chi-square tests for categorical and t-tests for continuous variables. There was no difference in the severity of bone loss before the revision in the groups, as evidenced by Paprosky staging of preoperative radiographs. The mean vertical COR displacement was smaller in patients who had the novel cup (3.5 mm; range, -12 to 15 mm; mean difference, -7.3 mm; 95% confidence interval [CI], -13.2 to -1.5) as compared with those who had the conventional cup (10.5 mm; range, -4 to 50 mm; mean difference, 7.3 mm; 95% CI, -12.5 to -2.2; p = 0.003). There was no difference in mean horizontal displacement between the two groups (-0.06 ± 6.1 versus 1.7 ± 7.1; mean difference, -1.8; p = 0.903). Although hip COR was improved based on radiographic measurements with the use of this novel acetabular design, and although this may improve hip biomechanics, more studies are required before its widespread adoption for revision cases of this nature can be recommended. Both implant costs and the risks associated with using a new design in practice will have to be justified by studies that evaluate fixation, clinical function and implant survival, and patient-reported outcome scores, all of which were beyond the scope of this preliminary report. Level III, therapeutic study.

Estimation of the center of rotation using wearable magneto-inertial sensors

Particle swarm optimization coupled with exhaustive search method (PSO-ESM) is proposed for inverse synthetic aperture radar (ISAR) cross-range scaling (CRS). Robust scatterers against angular scintillation are extracted using scale-invariant feature transform, and locations of the extracted scatterers are applied to PSO-ESM that estimate not only the rotation center (RC), but also rotation velocity (RV). In simulations, it was observed that PSO-ESM can perform robust CRS owing to the joint estimation of RC and RV.

In many stroke patients, a motor cortex lesion alters motor control. Initially, paresis is most prominent, but then over time, joint stiffening and hyperreflexia may occur. How these different disorders develop over time is still unknown due to high system complexity. Secondary changes in the corticospinal tract, peripheral biomechanics and spinal reflexive system, may also occur. This thesis is part of the EXPLICIT-Stroke study (see Chapters 1, 2 and 3), a randomized, controlled trial that researches the effect of early therapy on post stroke recovery of the upper limb. Amongst other measurements, the EXPLICIT-Stroke study investigates post-stroke changes of brain function and corticospinal tract with fMRI and TMS, respectively. The work in this thesis aims to identify post stroke changes in peripheral biomechanics and the spinal reflexes of the wrist: wrist joint neuromechanics. Neuromechanics play an important role in the functioning of a joint. Inputs to the neuromechanical system are: neural input originating from supraspinal regions and externally applied rotation/torque. Neuromechanics therefore represent the translation from supraspinal input to muscle contraction and resultant joint rotation, torque and/or stiffness, and also describe the relationship between external perturbation and joint response. Joint impedance, the dynamic relationship between joint angle and resultant joint torque, was used to investigate joint neuromechanics. Neuromechanics can be split into: dynamics of passive soft tissues, voluntary muscle contraction and reflexive muscle contraction. Knowledge of changes in the underlying properties yields insight into the complex development of movement disorders and can eventually lead to targeted therapy. Measurement of impedance is achieved by external (motorised) angular perturbation of the joint whilst measuring the joint torque response. This is commonly supported by measurement of muscle activation: Electromyography (EMG). Joint neuromechanics are highly nonlinear. Although many nonlinear neuromechanical properties are known from literature, the effects of these nonlinear properties on joint impedance, and thus their functional and clinical relevance, have generally not been quantified. Commonly known examples of nonlinearity are increased resistance against movement in extreme angles of the range of motion and increased joint stiffness with muscle contraction. Due to nonlinearity, linearly observed neuromechanics depend on input, i.e., depend on measurement conditions. In line with the previous examples, joint stiffness depends on muscle contraction and joint angle. Therefore, understanding nonlinearity is essential for interpretation of joint impedance. Linear modelling and system identification methods allow for estimation of neuromechanical parameters. Use of these linear methods restricts measurement to small deviations in joint angle, angular velocity and muscle contraction. As normal movement often includes large deviations in angle, angular velocity and muscle contraction, such measurements do not describe the full range of interest in joint neuromechanics. Furthermore, comparison of subjects requires that they are measured in the same angles, angular velocities and contraction levels, such that observed differences between subjects are due to differences in neuromechanical properties, and not due to nonlinearity. For example, high joint stiffness in Chapter 9, was hypothesized to be caused by co-activation of the antagonistic muscle pair, i.e., the nonlinear system under a different contraction level (active state), and not caused by different peripheral neuromechanical properties.

<p>Inspection of large space structures is imperative for long term mission success. One solution is to utilize a second free flying spacecraft capable of performing inspection in orbit. An Extended Kalman Filter (EKF) is used to perform estimations on the relative position, velocity, angular velocity, and attitude through the use of navigation markers. Simulation takes place using MATLAB to compare the true values with the estimated values using the EKF. The initial covariance (P), process noise covariance (Q), and measurement noise covariance (R) matrices were tuned for a space structure with three navigation points. The largest recorded errors over 100 iterations occurred during the initial estimation yielding 26.78 centimeters in relative position, 1.80 centimeters per second in relative velocity, 0.0444 radians per second in relative angular velocity, and a difference of 0.0172 in the unit vector of relative attitude. After allowing 20 seconds of settling time the maximum errors were reduced to 5.0 centimeters in relative position, 0.40 centimeters per second in relative velocity, 0.0046 radians per second in relative angular velocity, and a difference of 0.0020 in the unit vector of relative attitude. The paper also discusses the application of training algorithms to tune the EKF parameters for future consideration.</p>

This study aims to develop a Lagrangian stochastic model for simulating suspended sediment transport in open channel flows. The model focuses on a pair of particles, describing the trajectories of paired particles, which are dependent on the Reynolds number. It uses relative particle velocity as a foundation for tracking sediment motion, with key factors such as separation distance and relative velocity being critical in defining particle interactions and their role in separation processes. This model captures non-Gaussian turbulence features in Eulerian statistics to construct a relative velocity probability density function. A structure-function approach is employed to derive Eulerian velocity moments from velocity increments, ensuring stable dispersion by considering relevant scale properties. The model incorporates the Langevin equation for relative velocity, consisting a drift term defined by conditional acceleration and a Eulerian probability density function, and a random term defined by a scale-dependent diffusion coefficient influenced by viscous effects, exhibiting Brownian motion properties.The model extends the fluid particle framework to sediment particles through the principles of force balance and accounts for the resuspension mechanism for sediment particles. In sediment transport, the influence of the resuspension mechanism on the two particles must be considered. This mechanism is different from those in fluid particle models and single-particle sediment models. Additionally, the relative velocity model is transformed into an absolute velocity model, and two-particle coefficients are introduced to determine particle motion. The Ornstein-Uhlenbeck (OU) process is employed to simulate velocity fluctuations for individual particles.Compared to single-particle models, this two-particle stochastic model investigates turbulent sediment transport in terms of relative velocity and separation distance variations. We analyze the variation of the diffusion coefficient across scales by tuning specific parameters. Results are compared with direct numerical simulation (DNS) data across different Reynolds numbers to calibrate the model coefficients effectively. The initial findings provide valuable insights into the influence of turbulence characteristics on sediment behavior, particularly in relation to relative velocity and separation distance variations. This work contributes to a deeper understanding of the complex interactions governing sediment transport in turbulent open channel flows.

In this work, a single tablet model and a discrete element method (DEM) computer simulation are developed to obtain the angular circulation speed of tablets in a vibratory tablet coating pan for range of vibration frequencies and amplitudes. The models identify three important dimensionless parameters that influence the speed of the tablets: the dimensionless amplitude ratio (a/R), the Froude number (aω2/g), and the tablet-wall friction coefficient, where a is the peak vibration amplitude at the drum center, ω is the vibration angular frequency, R is the drum radius, and g is the acceleration due to gravity. The models predict that the angular circulation speed of tablets increases with an increase in each of these parameters. The rate of increase in the angular circulation speed is observed to decrease for larger values of a/R. The angular circulation speed reaches an asymptote beyond a tablet-wall friction coefficient value of about 0.4. Furthermore, it is found that the Froude number should be greater than one for the tablets to start circulating. The angular circulation speed increases as Froude number increases but then does not change significantly at larger values of the Froude number. Period doubling, where the motion of the bed is repeated every two cycles, occurs at a Froude number larger than five. The single tablet model, although much simpler than the DEM model, is able to predict the maximum circulation speed (the limiting case for a large value of tablet-wall friction coefficient) as well as the transition to period doubling.

Particle swarm optimization coupled with exhaustive search method (PSO-ESM) is proposed for inverse synthetic aperture radar cross-range scaling (CRS). Robust scatterers against angular scintillation are extracted using scale-invariant feature transform, and locations of the extracted scatterers are applied to PSO-ESM that estimate not only rotation center (RC), but also rotation velocity (RV). In simulations, it was observed that PSO-ESM can perform robust CRS owing to the joint estimation of RC and RV.

In this paper, a novel algorithm estimating not only target's rotation velocity (RV) but also rotation center (RC) is proposed for inverse synthetic aperture radar (ISAR) image cross-range scaling. Scale invariant feature transform (SIFT) is applied to two different ISAR images formed at different aspect angles for extracting non-fluctuating scattering points. Then, a criterion based on the distance between RC and locations of extracted features is optimized through the proposed algorithm based on particle swarm optimization (PSO) combined with exhaustive search method. Simulation results show that the proposed method can accurately estimate both RV and RC of a target.

As an object rotates, each location on the object moves with an instantaneous linear velocity, dependent upon its distance from the center of rotation, whereas the object as a whole rotates with a fixed angular velocity. Does the perceived rotational speed of an object correspond to its angular velocity, linear velocities, or some combination of the two? We had observers perform relative speed judgments of different-sized objects, as changing the size of an object changes the linear velocity of each location on the object's surface, while maintaining the object's angular velocity. We found that the larger a given object is, the faster it is perceived to rotate. However, the observed relationships between size and perceived speed cannot be accounted for simply by size-related changes in linear velocity. Further, the degree to which size influences perceived rotational speed depends on the shape of the object. Specifically, perceived rotational speeds of objects with corners or regions of high-contour curvature were less affected by size. The results suggest distinct contour features, such as corners or regions of high or discontinuous contour curvature, provide cues to the angular velocity of a rotating object.

Using space geodetic observations from four techniques (GPS, VLBI, SLR and DORIS), we simultaneously estimate the angular velocities of 11 major plates and the velocity of Earth's centre. We call this set of relative plate angular velocities GEODVEL (for GEODesy VELocity). Plate angular velocities depend on the estimate of the velocity of Earth's centre and on the assignment of sites to plates. Most geodetic estimates of the angular velocities of the plates are determined assuming that Earth's centre is fixed in an International Terrestrial Reference Frame (ITRF), and are therefore subject to errors in the estimate of the velocity of Earth's centre. In ITRF2005 and ITRF2000, Earth's centre is the centre of mass of Earth, oceans and atmosphere (CM); the velocity of CM is estimated by SLR observation of LAGEOS's orbit. Herein we define Earth's centre to be the centre of mass of solid Earth (CE); we determine the velocity of CE by assuming that the portions of plate interiors not near the late Pleistocene ice sheets move laterally as if they were part of a rigid spherical cap. The GEODVEL estimate of the velocity of CE is likely nearer the true velocity of CM than are the ITRF2005 and ITRF2000 estimates because (1) no phenomena can sustain a significant velocity between CM and CE, (2) the plates are indeed nearly rigid (aside from vertical motion) and (3) the velocity of CM differs between ITRF2005 and ITRF2000 by an unacceptably large speed of 1.8 mm yr−1. The velocity of Earth's centre in GEODVEL lies between that of ITRF2000 and that of ITRF2005, with the distance from ITRF2005 being about twice that from ITRF2000. Because the GEODVEL estimates of uncertainties in plate angular velocities account for uncertainty in the velocity of Earth's centre, they are more realistic than prior estimates of uncertainties. GEODVEL differs significantly from all prior global sets of relative plate angular velocities determined from space geodesy. For example, the 95 per cent confidence limits for the angular velocities of GEODVEL exclude those of REVEL (Sella et al.) for 34 of the 36 plate pairs that can be formed between any two of the nine plates with the best-constrained motion. The median angular velocity vector difference between GEODVEL and REVEL is 0.028° Myr−1, which is up to 3.1 mm yr−1 on Earth's surface. GEODVEL differs the least from the geodetic angular velocities that Altamimi et al. determine from ITRF2005. GEODVEL's 95 per cent confidence limits exclude 11 of 36 angular velocities of Altamimi et al., and the median difference is 0.015° Myr−1. GEODVEL differs significantly from nearly all relative plate angular velocities averaged over the past few million years, including those of NUVEL-1A. The difference of GEODVEL from updated 3.2 Myr angular velocities is statistically significant for all but two of 36 angular velocities with a median difference of 0.063° Myr−1. Across spreading centres, eight have slowed down while only two have sped up. We conclude that plate angular velocities over the past few decades differ significantly from the corresponding angular velocity averaged over the past 3.2 Myr.

Objectives: Traditionally, the hip has been thought of as a particularly stable ball and socket joint with a fixed center of rotation and no translation. This view has been the basis for several simulation platforms studying hip impingement and instability for treatment planning and outcome analyses. More recently, in vivo imaging and cadaveric studies have suggested that, in addition to rotation, the femoral head and center of rotation (COR) translate within the joint throughout physiologic range of motion. A recent MRI study has shown an average translation of 2 mm, with up to 7 mm translations in certain positions, among subjects with asymptomatic hips. Importantly, substantial magnitudes of translation can alter hip contact and impingement patterns with downstream effects on the treatment planning and patient outcomes. However, there is a paucity of literature regarding how hip translation may influence hip impingement. Therefore, the purpose of this study was to use a validated simulation platform, capable of simulating hip translation during impingement analysis, to map the trajectory of the hip COR and its effects on impingement-free hip range of motion (ROM). Methods: Following institutional review board approval, the New Mexico Decedent Image Database (NMDID) was queried to identify computed tomography scans with full coverage of the hip and femur from subjects with no documented bone and joint pathology (n = 1222 hips, 611 patients, age: 30.4 ± 8.8; 67% male patients). A custom-developed and validated program (VirtualHip, Boston Children’s Hospital) was used to automatically segment the bones, identify landmarks (Dice 0.94 – 0.99), and define an anatomical coordinate system based on International Society of Biomechanics (ISB) recommendations. The pelvis was then fixed in 3D and the femur was moved to simulate uniplanar rotations (ie, flexion: 0° to 150°, extension: 0° to 50°, abduction/adduction: 0° to 75°, internal /external rotations: 0° to 75°). The simulations were first done assuming a fixed hip COR (no translation) and then repeated by incrementally allowing the hip COR to translate by up to 5 mm with increments of 1 mm, avoiding bone-to-bone penetration or hip dislocation (distance between the femoral head and acetabulum exceeding the joint space width measured at neutral). Mixed linear models were used to evaluate the relationships between COR translation and impingement-free rotation (maximum rotation prior to impingement). The effect of translation on ROM was characterized by calculating the proportion of hips able to achieve each ROM. Finally, the path of the hip COR was mapped throughout the tested ranges of motion. Results: The effect of COR translation on achieved impingement-free range of motion along with COR trajectories are shown in Figure 1. Hip flexion was associated with COR posterior (by 4.0 ± 0.9 mm), lateral (only after 100°, by 3.6 ± 1.4 mm), and superior (only after 100°, by 2.0 ± 1.8 mm) translations (P < 0.001). Hip extension was only associated with anterior COR translation (by 0.8 ± 0.7 mm, P < 0.001). Hip adduction was associated with anterior (by 2.9 ± 1.3 mm), lateral (by 4.0 ± 1.3 mm), and superior (by 4.4 ± 0.6 mm) translations (P<0.01). Hip abduction was only associated with medial (by 2.6 ± 1.5 mm) and inferior (by 2.9 ± 1.7 mm) translations (P < 0.02). There were minimal COR translations during hip internal rotation (P > 0.05). Hip external rotation was associated with anterior (by 3.7 ± 1.4 mm) and inferior (by 1.2 ± 1.3 mm) translations (P < 0.05). Conclusions: This is the first study to map the hip COR trajectory under common movements in a large cohort of patients. The current findings highlight the importance of hip translation (nonfixed COR) on physiologic hip range of motion. As the hip is not a perfect ball and socket joint, with an aspherical femoral head, translation is required to accommodate physiologic rotation (ie, glide mechanism) without bony impingement between the femur and pelvis. These preliminary observations highlight the need for a comprehensive assessment of normal and pathologic hip translation along with their role in biomechanics, injury risk, and response to treatment. A clear understanding of the role of hip translation in hip function and health will improve clinical care through better diagnosis and personalized treatment planning, which can ultimately lead to improved treatment outcomes, particularly lower risk of osteoarthritis. [Figure: see text]

In the winches of cable-driven parallel robots (CDPRs), the transmission ratio between motor torque and cable force is determined by the drum radius. 3D printing allows the design of variable radius drums (VRDs), where the local drum radius can be individually adjusted for each cable length. Within a desired workspace, the maximum load profile is determined. Based on this, a winding path is calculated so that a specific maximum torque is reached, for each cable length. A drum shape is created such that a groove guides the cable on the winding path. For a purely translational 2T demonstration robot, the design steps are performed and a corresponding VRD is manufactured. This is compared with a conventional constant radius drum (CRD).

We investigated an image reconstruction algorithm to reduce cone-beam artifacts in cone-beam CT. To examine the factors involved in the occurrence of cone-beam artifacts, micro-spheres phantom were arranged longitudinally at different positions and a computer simulation was performed. Due to differences in projection angle, data projected onto the detector surface were projected along trajectories shown as different periodic functions depending on the distance and position from the center of rotation. Therefore, projection along several detector channels based on different projection data resulting from different periodic functions is considered responsible for the increase in cone-beam artifacts associated with an increase in the distance of reconstruction planes from the center of rotation. Our new algorithm to reduce such artifacts features: 1) A change in weighting with respect to projection data obtained at different projection angles. 2) Distribution of correction coefficients so that they are larger near the center of the detector, while taking individual channel data for the detector into account, and smaller near the edges. 3) Three-dimensional back-projection of corrected projection data. The effect of the reduction in cone-beam artifacts of an object located at the edges markedly enhanced reconstruction planes at positions further from the center of rotation.