Mass Kinematics Research Articles

Probing CPT Invariance with Top Quarks at the LHC

The first model-independent sensitivity to CPT violation in the top-quark sector is extracted from ATLAS and CMS measurements of the top and antitop kinematical mass difference. We find that the temporal component of a CPT-violating background field interacting with the top-quark vector current is restricted within the interval [−0.13,0.29] GeV at 95% confidence level. Published by the American Physical Society 2024

Center of mass kinematic reconstruction during steady-state walking using optimized template models.

Template models, such as the Bipedal Spring-Loaded Inverted Pendulum and the Virtual Pivot Point, have been widely used as low-dimensional representations of the complex dynamics in legged locomotion. Despite their ability to qualitatively match human walking characteristics like M-shaped ground reaction force (GRF) profiles, they often exhibit discrepancies when compared to experimental data, notably in overestimating vertical center of mass (CoM) displacement and underestimating gait event timings (touchdown/ liftoff). This paper hypothesizes that the constant leg stiffness of these models explains the majority of these discrepancies. The study systematically investigates the impact of stiffness variations on the fidelity of model fittings to human data, where an optimization framework is employed to identify optimal leg stiffness trajectories. The study also quantifies the effects of stiffness variations on salient characteristics of human walking (GRF profiles and gait event timing). The optimization framework was applied to 24 subjects walking at 40% to 145% preferred walking speed (PWS). The findings reveal that despite only modifying ground forces in one direction, variable leg stiffness models exhibited a >80% reduction in CoM error across both the B-SLIP and VPP models, while also improving prediction of human GRF profiles. However, the accuracy of gait event timing did not consistently show improvement across all conditions. The resulting stiffness profiles mimic walking characteristics of ankle push-off during double support and reduced CoM vaulting during single support.

Effects of final state interactions on Landau singularities

In certain kinematic and particle mass configurations, triangle singularities may lead to line-shapes which mimic the effects of resonances. This well-known effect is scrutinized here in the presence of final-state rescattering. The goal is achieved first by utilizing general arguments provided by Landau equations, and second by applying a modern scattering formalism with explicit two- and three-body unitarity.

Violation of weak cosmic censorship in de Sitter space

Inspired by the recent discovery of a violation of strong cosmic censorship (SCC) for the near-extremal Reissner-Nordström black holes in de Sitter space (RN-dS), we investigate if the weak cosmic censorship conjecture (WCCC) can also be violated in RN-dS with a fixed cosmological constant. Our method is based on the recent formulation of examining WCCC by the constraint of the second law, which in this case requires the sum of areas of the event and cosmic horizons cannot decrease during the infall process of Wald’s gedanken experiment. We find that the WCCC can be violated for the near-extremal RN-dS in some regimes of second-order perturbation of field configurations. Given the charge parameter of RN-dS, we can find the lowest value of the subextremality parameter, beyond which the WCCC holds. Our results imply that there might be possible correlations between the violation of SCC and WCC. Because of a lack of an unambiguous relation between the gravitational mass and matter’s kinematic mass in asymptotically de Sitter space, we cannot compare the corresponding regimes of parameter space for the violations of SCC and WCCC. We also discuss the subtlety in formulating the first- and second-law approaches to examine WCCC. Published by the American Physical Society 2024

Center of mass states render multi-joint torques throughout standing balance recovery.

Reactive balance control requires coordination of neurally-mediated feedforward and feedback pathways to generate stabilizing joint torques at the hip, knee, and ankle. Using a sensorimotor response model, we decomposed reactive joint torques into feedforward and feedback contributions based on delays relative to center of mass kinematics. Responses across joints were driven by the same signals, but contributions from feedforward versus feedback pathways differed, likely due to differences in musculotendon properties between proximal and distal muscles.

Discovery of a Barium Blue Straggler Star in M67 and “Sighting” of Its White Dwarf Companion* * This is paper XV of the UVIT Open Cluster Study (UOCS).

We report the discovery of a barium blue straggler star (BSS) in M67, exhibiting enhancements in slow neutron-capture (s-)process elements. Spectroscopic analysis of two BSSs (WOCS 9005 & WOCS 1020) and four stars located near the main-sequence turn-off using GALAH spectra, showed that WOCS 9005 has a significantly high abundance of the s-process elements ([Ba/Fe] = 0.75 ± 0.08, [Y/Fe] = 1.09 ± 0.07, and [La/Fe] = 0.65 ± 0.06). The BSS (WOCS 9005) is a spectroscopic binary with a known period, eccentricity, and a suspected white dwarf (WD) companion with a kinematic mass of 0.5 M ⊙. The first “sighting” of the WD in this barium BSS is achieved through multiwavelength spectral energy distribution (SED) with the crucial far-UV data from the UVIT/AstroSat. The parameters of the hot and cool companions are derived using binary fits of the SED using two combinations of models, yielding a WD with T eff in the range 9750–15,250 K. Considering the kinematic mass limit, the cooling age of the WD is estimated as ∼60 Myr. The observed enhancements are attributed to a mass transfer (MT) from a companion asymptotic giant branch star, now a WD. We estimate the accreted mass to be 0.15 M ⊙, through wind accretion, which increased the envelope mass from 0.45 M ⊙. The detection of chemical enhancement, as well as the sighting of WD in this system, have been possible due to the recent MT in this binary, as suggested by the young WD.

MHD-driven thermal dynamics of bionanofluid flow on stretching porous media and the critical impact of multiple slip effects

Incorporating slip conditions into computational fluid dynamics (CFD) simulations and experiments helps engineers predict and improve the effectiveness of superhydrophobic surfaces in reducing drag. This optimization approach leads to significant enhancements in fuel efficiency and performance across a range of fluid-flow systems, including marine vessels and aircraft. This study models the phenomena of velocity and temperature slip, coupled with MHD, within the context of nanofluid flow undergoing bioconvection over a stretching sheet. Subsequently, the study seeks to analyze the resulting effects on heat and mass kinematics. The bvp4c solver effectively calculates analytical solutions for the reduced problem obtained through similarity transformation from the underlying partial differential equations. Velocity and temperature slip both impact temperature, with velocity slip increasing heat transfer rates and temperature slip decreasing them. The thermal radiation parameter enhances nanoparticle concentration, although it’s offset by an increased Lewis number. Brownian motion amplifies mass transfer, but the thermal radiation parameter hampers it. The escalation in the microorganism density profile correlates with the increase in both the Bioconvection Lewis number and the Peclet number. Likewise, as thermophoresis parameters and the bioconvection constant increase, the microorganism density along the profile also rises.

Combined translational and rotational perturbations of standing balance reveal contributions of reduced reciprocal inhibition to balance impairments in children with cerebral palsy.

Balance impairments are common in cerebral palsy. When balance is perturbed by backward support surface translations, children with cerebral palsy have increased co-activation of the plantar flexors and tibialis anterior muscle as compared to typically developing children. However, it is unclear whether increased muscle co-activation is a compensation strategy to improve balance control or is a consequence of reduced reciprocal inhibition. During translational perturbations, increased joint stiffness due to co-activation might aid balance control by resisting movement of the body with respect to the feet. In contrast, during rotational perturbations, increased joint stiffness will hinder balance control as it couples body to platform rotation. Therefore, we expect increased muscle co-activation in response to rotational perturbations if co-activation is caused by reduced reciprocal inhibition but not if it is merely a compensation strategy. We perturbed standing balance by combined backward translational and toe-up rotational perturbations in 20 children with cerebral palsy and 20 typically developing children. Perturbations induced forward followed by backward movement of the center of mass. We evaluated reactive muscle activity and the relation between center of mass movement and reactive muscle activity using a linear feedback model based on center of mass kinematics. In typically developing children, perturbations induced plantar flexor balance correcting muscle activity followed by tibialis anterior balance correcting muscle activity, which was driven by center of mass movement. In children with cerebral palsy, the switch from plantar flexor to tibialis anterior activity was less pronounced than in typically developing children due to increased muscle co-activation of the plantar flexors and tibialis anterior throughout the response. Our results thus suggest that a reduction in reciprocal inhibition causes muscle co-activation in reactive standing balance in children with cerebral palsy.

Investigation on transient response of gas face seals based on a double mass kinematic model considering Coulomb friction

Investigation on transient response of gas face seals based on a double mass kinematic model considering Coulomb friction

ANALYSIS OF ROCK QUALITY AND LANDSLIDE POTENTIAL IN NORTH JERING HILLS, SLEMAN, YOGYAKARTA

The study was to identify the direction and type of potential landslides, as well as assess the rock quality on the slopes of North Jering Hills. The scanline method, consisting of stretching the meter, was employed to collect data on the plane of failure. The information gathered encompassed the direction, slope level, and condition of the unsuccessful plane, aligned with the parameters in the RMR table of Bieniawski from 1989. Following the collation of data, kinematic and rock mass quality analysis was undertaken using stereographic projection and RMR parameter weighting respectively. The kinematic analysis revealed a planar avalanche type on the slope. The RMR value of the research location's slope was 80, classifying it as good rock.

Center of Mass Estimation for Impaired Gait Assessment Using Inertial Measurement Units.

Injury or disease often compromise walking dynamics and negatively impact quality of life and independence. Assessing methods to restore or improve pathological gait can be expedited by examining a global parameter that reflects overall musculoskeletal control. Center of mass (CoM) kinematics follow well-defined trajectories during unimpaired gait, and change predictably with various gait pathologies. We propose a method to estimate CoM trajectories from inertial measurement units (IMUs) using a bidirectional Long Short-Term Memory neural network to evaluate rehabilitation interventions and outcomes. Five non-disabled volunteers participated in a single session of various dynamic walking trials with IMUs mounted on various body segments. A neural network trained with data from four of the five volunteers through a leave-one-subject out cross validation estimated the CoM with average root mean square errors (RMSEs) of 1.44cm, 1.15cm, and 0.40cm in the mediolateral (ML), anteroposterior (AP), and inferior/superior (IS) directions respectively. The impact of number and location of IMUs on network prediction accuracy was determined via principal component analysis. Comparing across all configurations, three to five IMUs located on the legs and medial trunk were the most promising reduced sensor sets for achieving CoM estimates suitable for outcome assessment. Lastly, the networks were tested on data from an individual with hemiparesis with the greatest error increase in the ML direction, which could stem from asymmetric gait. These results provide a framework for assessing gait deviations after disease or injury and evaluating rehabilitation interventions intended to normalize gait pathologies.

Connection between gravitational and inertial masses of compound objects and the weak equivalence principle

The connection between gravitational and inertial masses of compound objects (e.g. nucleons, nuclei, atoms, and molecules) in the presence of rapid internal motions of their constituent parts is considered. The equality of gravitational and inertial masses of such objects confirming the weak equivalence principle is proven provided that their moving constituent parts are confined. The result is very nontrivial because of a substantial difference between particle dynamics in noninertial frames and gravitational fields. Paradoxically, gravitational effects are different for the same particles moving in the closed box and in the free space. The gravitational and inertial masses are equal to the corresponding kinematic masses. In contrast, gravitational masses of ensembles of noninteracting moving particles cannot be introduced because the total gravitational forces acting on these ensembles do not correspond to their kinematic masses.

Experience influences kinematic motor synergies: an Uncontrolled manifold approach to simulated Nordic skiing

ABSTRACT Motor synergies are defined as central nervous system mechanisms which adjust participating degrees of freedom to ensure dynamic stability (control) of certain performance variables and have been identified during many motor tasks. The potential for synergistic control of individual segments during full-body tasks is often overlooked. Thus, this study compared individual differences in the potential stabilization of multiple performance variables on the basis of experience during a full-body sport activity. Normalized time series of synergy indices from Uncontrolled Manifold analyses on experienced (n = 9) and inexperienced (n = 19) participants were analysed using statistical parametric mapping during simulated Nordic skiing. Regardless of experience, hand, upper arm, and whole-body centre of mass (COM) kinematics were found to be stabilized by kinematic motor synergies. Only experienced Nordic skiers stabilized trunk COM position at all, while trunk COM velocity was stabilized for a longer duration than inexperienced participants. However, inexperienced participants stabilized hand velocity for a greater duration overall and to a greater magnitude during early pull phase than the experienced skiers. That motor synergies for hand and trunk COM velocity differed between experience groups suggests potential utility for these performance variables as indicators of motor skill development for full-body tasks such as Nordic skiing.

Simulating the effect of ankle plantarflexion and inversion-eversion exoskeleton torques on center of mass kinematics during walking.

Walking balance is central to independent mobility, and falls due to loss of balance are a leading cause of death for people 65 years of age and older. Bipedal gait is typically unstable, but healthy humans use corrective torques to counteract perturbations and stabilize gait. Exoskeleton assistance could benefit people with neuromuscular deficits by providing stabilizing torques at lower-limb joints to replace lost muscle strength and sensorimotor control. However, it is unclear how applied exoskeleton torques translate to changes in walking kinematics. This study used musculoskeletal simulation to investigate how exoskeleton torques applied to the ankle and subtalar joints alter center of mass kinematics during walking. We first created muscle-driven walking simulations using OpenSim Moco by tracking experimental kinematics and ground reaction forces recorded from five healthy adults. We then used forward integration to simulate the effect of exoskeleton torques applied to the ankle and subtalar joints while keeping muscle excitations fixed based on our previous tracking simulation results. Exoskeleton torque lasted for 15% of the gait cycle and was applied between foot-flat and toe-off during the stance phase, and changes in center of mass kinematics were recorded when the torque application ended. We found that changes in center of mass kinematics were dependent on both the type and timing of exoskeleton torques. Plantarflexion torques produced upward and backward changes in velocity of the center of mass in mid-stance and upward and smaller forward velocity changes near toe-off. Eversion and inversion torques primarily produced lateral and medial changes in velocity in mid-stance, respectively. Intrinsic muscle properties reduced kinematic changes from exoskeleton torques. Our results provide mappings between ankle plantarflexion and inversion-eversion torques and changes in center of mass kinematics which can inform designers building exoskeletons aimed at stabilizing balance during walking. Our simulations and software are freely available and allow researchers to explore the effects of applied torques on balance and gait.

High-resolution APEX/LAsMA 12CO and 13CO (3–2) observation of the G333 giant molecular cloud complex

Context. Hub-filament systems are suggested to be the birth cradles of high-mass stars and clusters. Aims. We investigate the gas kinematics of hub-filament structures in the G333 giant molecular cloud complex using 13CO (3–2) observed with the APEX/LAsMA heterodyne camera. Methods. We applied the FILFINDER algorithm to the integrated intensity maps of the 13CO J = 3–2 line to identify filaments in the G333 complex, and we extracted the velocity and intensity along the filament skeleton from moment maps. Clear velocity and density fluctuations are seen along the filaments, allowing us to fit velocity gradients around the intensity peaks. Results. The velocity gradients we fit to the LAsMA and ALMA data agree with each other over the scales covered by ALMA observations in the ATOMS survey (<5 pc). Changes in velocity gradient with scale indicate a funnel structure of the velocity field in position-position-velocity (PPV) space. This is indicative of a smooth, continuously increasing velocity gradient from large to small scales, and thus is consistent with gravitational acceleration. The typical velocity gradient corresponding to a 1 pc scale is ~1.6 km s−1 pc−1. Assuming freefall, we estimate a kinematic mass within 1 pc of ~1190 M⊙, which is consistent with typical masses of clumps in the ATLASGAL survey of massive clumps in the inner Galaxy. We find direct evidence for gravitational acceleration from a comparison of the observed accelerations to those predicted by freefall onto dense hubs with masses from millimeter continuum observations. On large scales, we find that the inflow may be driven by the larger-scale structure, consistent with the hierarchical structure in the molecular cloud and gas inflow from large to small scales. The hub-filament structures at different scales may be organized into a hierarchical system extending up to the largest scales probed through the coupling of gravitational centers at different scales. Conclusions. We argue that the funnel structure in PPV space can be an effective probe for the gravitational collapse motions in molecular clouds. The large-scale gas inflow is driven by gravity, implying that the molecular clouds in the G333 complex may be in a state of global gravitational collapse.

Assisting walking balance using a bio-inspired exoskeleton controller

BackgroundBalance control is important for mobility, yet exoskeleton research has mainly focused on improving metabolic energy efficiency. Here we present a biomimetic exoskeleton controller that supports walking balance and reduces muscle activity.MethodsHumans restore balance after a perturbation by adjusting activity of the muscles actuating the ankle in proportion to deviations from steady-state center of mass kinematics. We designed a controller that mimics the neural control of steady-state walking and the balance recovery responses to perturbations. This controller uses both feedback from ankle kinematics in accordance with an existing model and feedback from the center of mass velocity. Control parameters were estimated by fitting the experimental relation between kinematics and ankle moments observed in humans that were walking while being perturbed by push and pull perturbations. This identified model was implemented on a bilateral ankle exoskeleton.ResultsAcross twelve subjects, exoskeleton support reduced calf muscle activity in steady-state walking by 19% with respect to a minimal impedance controller (p < 0.001). Proportional feedback of the center of mass velocity improved balance support after perturbation. Muscle activity is reduced in response to push and pull perturbations by 10% (p = 0.006) and 16% (p < 0.001) and center of mass deviations by 9% (p = 0.026) and 18% (p = 0.002) with respect to the same controller without center of mass feedback.ConclusionOur control approach implemented on bilateral ankle exoskeletons can thus effectively support steady-state walking and balance control and therefore has the potential to improve mobility in balance-impaired individuals.

The influence of athletic background, lower limb dominance and cutting angle on the center of mass kinematics during a sidestep cutting task

BACKGROUND: Successful performance in futsal depends on athletes' ability to change direction efficiently. AIM: To investigate the effect of athletic background on COM kinematics during sidestep cutting maneuver performed at different cutting angles towards both sides. METHOD: Eighteen futsal athletes participated, comprised of nine high-level training (Group high-level) and nine recreational (Group Control, GC). Twenty reflective markers were placed on the participant's trunk and upper and lower limbs. Participants performed acceleration at maximum speed and in a straight line for 10 meters, followed by a change of direction (30º, 60º, and 90º). The whole body's COM trajectory was identified using a body model for each trial. Differences in angular error and COM speed were evaluated with a three-way analysis of variance [Group (GH vs. GC) X Cutting angle (30º vs. 60º vs. 90º) X Side (dominant and non-dominant), with repeated measures for the last two factors]. RESULTS: The main results indicated that the angular error increased as the cutting angle increased. The high-level futsal athletes performed a cutting task for the dominant side with greater speed and higher angular errors than the control group. These findings provided important information for understanding the trajectory of the center of mass at different angles and velocities and the possible repercussions on body dynamics. CONCLUSION: Athletic background affected the kinematic patterns of the center of mass during sidestep cutting maneuvers; when sidestep is performed with the dominant side, high-level futsal athletes changed direction faster with more significant angular error than recreational athletes.

Digital Rock Mass Analysis for the Evaluation of Rockfall Magnitude at Poorly Accessible Cliffs

The analysis of a digital rock cliff model, built by airborne photogrammetric data and infrared thermal images, is herein presented as an alternative tool for rock mass study in restricted and poorly accessible areas. Photogrammetric and infrared thermography techniques were combined for the geostructural and morphological characterization of an unstable cliff located in a nature reserve, where the rock mass extension and the environmental preservation rules required the use of minimally invasive surveying solutions. This methodological approach provided quantitative and qualitative data on both the spatial orientation of discontinuities and the location of major structural features, jutting blocks and past rockfall source areas. The digitally derived spatial data were used to carry out a rock mass kinematic analysis, highlighting the most recurring unstable failure patterns. Thermal images were overlapped to the photogrammetric cliff model to exploit the data combination and to analyze the presence of protruding rock mass volumes to be referred to as potential unstable volumes. Based on this activity, rock volumes were quantified on the digital model and the results were used to provide a zonation map of the potential magnitude of future rockfalls threatening the reserve. Digital data were validated by a field surveying campaign, which returned a satisfactory match, proving the usefulness and suitability of the approach, as well as allowing the quick and reliable rock mass characterization in the frame of practical use and risk management purposes.

On soft gluon resummation for associated single top production with a Higgs boson at the LHC

We investigate threshold resummation of soft gluon corrections for the s-channel process of a single top quark production in association with a Higgs boson in the Standard Model. We choose to work in the three-particle invariant mass kinematics in direct QCD, i.e. in the space of Mellin moments. Our results take into account terms of up to next-to-leading logarithmic (NLL) precision, as well as {mathcal {O}} (alpha _{textrm{s}}) non-logarithmic terms which do not vanish at threshold. After presenting analytical expressions, we discuss the corresponding numerical results for the total cross section and the invariant mass distribution at the LHC.

Balance improvements in healthy subjects are independent to postural strategies involved in the training

BackgroundAdequate postural strategies have a pivotal role in ensuring balance during the performance of daily or sport activities. These strategies are responsible for the management of center of mass kinematics and depend on the magnitude of perturbations and posture assumed by a subject. Research questionAre there differences in postural performance after a standardized balance training performed in sitting versus standing posture in healthy subjects? Does a standardized unilateral balance training with the dominant or non-dominant limb improve balance on trained and untrained limbs in healthy subjects? MethodsSeventy-five healthy subjects reporting a right-leg dominance were randomized into a Sitting, Standing, Dominant, Non-dominant or Control groups. In the Experiment 1, Sitting group performed a 3-week balance training in seated posture, whereas Standing group performed the same training in bipedal stance. In the Experiment 2, Dominant and Non-dominant groups underwent a 3-week standardized unilateral balance training on the dominant and non-dominant limbs, respectively. Control group underwent no intervention and was included in both experiments. Dynamic (Lower Quarter Y-Balance Test with the dominant and non-dominant limbs and trunk and lower limb 3D kinematics) and static (center of pressure kinematics in bipedal and bilateral single-limb stance) balance were assessed before and after the training, and at 4 weeks follow-up. ResultsA standardized balance training in sitting or standing posture improved balance without between-group differences, while a unilateral balance training with the dominant or non-dominant limb improved postural stability on the trained and untrained limbs. Trunk and lower limb joints range of motion increased independently to their involvement in the training. SignificanceThese results may allow clinicians to plan effective balance interventions even when a training in standing posture is not possible or in subjects with restricted limb weight-bearing.