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null (Ed.)Our group is developing a cyber-physical walking system (CPWS) for people paralyzed by spinal cord injuries (SCI). The current CPWS consists of a functional neuromuscular stimulation (FNS) system and a powered lower-limb exoskeleton for walking with leg movements in the sagittal plane. We are developing neural control systems that learn to assist the user of this CPWS to walk with stability. In a previous publication (Liu et al., Biomimetics, 2019, 4, 28), we showed a neural controller that stabilized a simulated biped in the sagittal plane. We are considering adding degrees of freedom to the CPWS to allow more natural walking movements and improved stability. Thus, in this paper, we present a new neural network enhanced control system that stabilizes a three-dimensional simulated biped model of a human wearing an exoskeleton. Results show that it stabilizes human/exoskeleton models and is robust to impact disturbances. The simulated biped walks at a steady pace in a range of typical human ambulatory speeds from 0.7 to 1.3 m/s, follows waypoints at a precision of 0.3 m, remains stable, and continues walking forward despite impact disturbances and adapts its speed to compensate for persistent external disturbances. Furthermore, the neural network controller stabilizes human models of different statures from 1.4 to 2.2 m tall without any changes to the control parameters. Please see videos at the following link: 3D biped walking control .more » « less
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null (Ed.)Estimating center of mass (COM) through sensor measurements is done to maintain walking and standing stability with exoskeletons. The authors present a method for estimating COM kinematics through an artificial neural network, which was trained by minimizing the mean squared error between COM displacements measured by a gold-standard motion capture system and recorded acceleration signals from body-mounted accelerometers. A total of 5 able-bodied participants were destabilized during standing through: (1) unexpected perturbations caused by 4 linear actuators pulling on the waist and (2) volitionally moving weighted jars on a shelf. Each movement type was averaged across all participants. The algorithm’s performance was quantified by the root mean square error and coefficient of determination ( R 2 ) calculated from both the entire trial and during each perturbation type. Throughout the trials and movement types, the average coefficient of determination was 0.83, with 89% of the movements with R 2 > .70, while the average root mean square error ranged between 7.3% and 22.0%, corresponding to 0.5- and 0.94-cm error in both the coronal and sagittal planes. COM can be estimated in real time for balance control of exoskeletons for individuals with a spinal cord injury, and the procedure can be generalized for other gait studies.more » « less
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A control system for simulated two-dimensional bipedal walking was developed. The biped model was built based on anthropometric data. At the core of the control is a Deep Deterministic Policy Gradients (DDPG) neural network that is trained in GAZEBO, a physics simulator, to predict the ideal foot location to maintain stable walking under external impulse load. Additional controllers for hip joint movement during stance phase, and ankle joint torque during toeoff, help to stabilize the robot during walking. The simulated robot can walk at a steady pace of approximately 1m/s, and during locomotion it can maintain stability with a 30N-s impulse applied at the torso. This work implement DDPG algorithm to solve biped walking control problem. The complexity of DDPG network is decreased through carefully selected state variables and distributed control system.more » « less
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Free, publicly-accessible full text available September 1, 2025
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The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high) charged hadron, inand central Pb-Pb collisions at center-of-mass energy per nucleon–nucleon collisionTeV. The large uncorrelated background in central Pb-Pb collisions is corrected using a data-driven statistical approach which enables precise measurement of recoil jet distributions over a broad range inand jet resolution parameter. Recoil jet yields are reported for, 0.4, and 0.5 in the rangeand, whereis the azimuthal angular separation between hadron trigger and recoil jet. The low-reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark–gluon plasma generated in high-energy nuclear collisions. Comparison ofdistributions fromand central Pb-Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.
©2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available July 1, 2025 -
The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high) hadron trigger in proton-proton and central Pb-Pb collisions at. A data-driven statistical method is used to mitigate the large uncorrelated background in central Pb-Pb collisions. Recoil jet distributions are reported for jet resolution parameter, 0.4, and 0.5 in the rangeand trigger-recoil jet azimuthal separation. The measurements exhibit a marked medium-induced jet yield enhancement at lowand at large azimuthal deviation from. The enhancement is characterized by its dependence on, which has a slope that differs from zero by. Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation.
© 2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available July 1, 2025 -
Free, publicly-accessible full text available June 1, 2025
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Measurements of the-dependent flow vector fluctuations in Pb–Pb collisions atusing azimuthal correlations with the ALICE experiment at the Large Hadron Collider are presented. A four-particle correlation approach [ALICE Collaboration, ] is used to quantify the effects of flow angle and magnitude fluctuations separately. This paper extends previous studies to additional centrality intervals and provides measurements of the-dependent flow vector fluctuations atwith two-particle correlations. Significant-dependent fluctuations of theflow vector in Pb–Pb collisions are found across different centrality ranges, with the largest fluctuations of up tobeing present in the 5% most central collisions. In parallel, no evidence of significant-dependent fluctuations oforis found. Additionally, evidence of flow angle and magnitude fluctuations is observed with more thansignificance in central collisions. These observations incollisions indicate where the classical picture of hydrodynamic modeling with a common symmetry plane breaks down. This has implications for hard probes at high, which might be biased by-dependent flow angle fluctuations of at least 23% in central collisions. Given the presented results, existing theoretical models should be reexamined to improve our understanding of initial conditions, quark–gluon plasma properties, and the dynamic evolution of the created system.
©2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available June 1, 2025 -
pairs may be produced in photonuclear collisions, either from the decays of photoproducedmesons or directly as nonresonantpairs. Measurements ofphotoproduction probe the couplings between theand charged kaons with photons and nuclear targets. The kaon-proton scattering occurs at energies far above those available elsewhere. We present the first measurement of coherent photoproduction ofpairs on lead ions in ultraperipheral collisions using the ALICE detector, including the first investigation of directproduction. There is significantproduction at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass rangeabove theresonance, for rapidityand, the measured coherent photoproduction cross section is. The center-of-mass energy per nucleon of the photon-nucleus (Pb) systemranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected forphotoproduction alone. The mass spectrum is fit to a cocktail consisting ofdecays, directphotoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for directphotoproduction are presented.
© 2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available May 1, 2025 -
A bstract Measurements of inclusive charged-particle jet production in pp and p-Pb collisions at center-of-mass energy per nucleon-nucleon collision
= 5$$ \sqrt{s_{\textrm{NN}}} $$ . 02 TeV and the corresponding nuclear modification factor are presented, using data collected with the ALICE detector at the LHC. Jets are reconstructed in the central rapidity region |$$ {R}_{\textrm{pPb}}^{\textrm{ch}\ \textrm{jet}} $$ η jet|< 0. 5 from charged particles using the anti-k Talgorithm with resolution parametersR = 0. 2, 0. 3, and 0. 4. Thep T-differential inclusive production cross section of charged-particle jets, as well as the corresponding cross section ratios, are reported for pp and p-Pb collisions in the transverse momentum range 10< $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 140 GeV/c and 10< $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 160 GeV/c , respectively, together with the nuclear modification factor in the range 10$$ {R}_{\textrm{pPb}}^{\textrm{ch}\ \textrm{jet}} $$ < $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 140 GeV/c . The analysis extends thep Trange of the previously-reported charged-particle jet measurements by the ALICE Collaboration. The nuclear modification factor is found to be consistent with one and independent of the jet resolution parameter with the improved precision of this study, indicating that the possible influence of cold nuclear matter effects on the production cross section of charged-particle jets in p-Pb collisions at = 5$$ \sqrt{s_{\textrm{NN}}} $$ . 02 TeV is smaller than the current precision. The obtained results are in agreement with other minimum bias jet measurements available for RHIC and LHC energies, and are well reproduced by the NLO perturbative QCD Powheg calculations with parton shower provided by Pythia 8 as well as by Jetscape simulations.Free, publicly-accessible full text available May 1, 2025