General Momentum Research Articles

Angular momentum generation and control during a back handspring step out on the balance beam performed by female gymnasts

The back handspring step out (BHS) is a foundational skill in gymnastics balance beam routines that requires the generation of significant sagittal plane angular momentum while tightly regulating frontal plane momentum to control their balance. However, which body segments are critical for generating this momentum and successfully performing the BHS and whether skill level influences this generation remains unknown. Twenty-five gymnasts with a range of skill levels performed a BHS on a balance beam. The BHS was scored, and segmental contributions to whole-body angular momentum were analyzed during the take-off, flight, hand contact and landing phases. Angular momentum has previously been used to assess balance control, where higher ranges of frontal plane angular momentum are indicative of poorer balance control. There were no differences in segmental contributions to angular momentum during the take-off phase between high- and low-scoring groups. However, the low-scoring group had higher trunk contributions to frontal plane angular momentum after the take-off phase. The trailing leg was also found to be a large contributor to frontal plane angular momentum, and thus more likely than the leading leg to cause deviations in balance control. In the sagittal plane, momentum generation and skill level were weakly correlated, suggesting as gymnasts become more skilled, they produce larger sagittal plane motions and are more adept at generating angular momentum. Because the trunk and trailing leg had high contributions to frontal plane angular momentum, controlling the trunk and trailing leg should be a focus in training regimes to improve BHS performance.

Generation and Manipulation of High-Order Orbital Angular Momentum in Helically Twisted Dual-Core Photonic Crystal Fiber Based on Filling Polyglycerol

Generation and Manipulation of High-Order Orbital Angular Momentum in Helically Twisted Dual-Core Photonic Crystal Fiber Based on Filling Polyglycerol

Thermal radiation effect in electroosmosis regulated peristalsis transport of Williamson hybrid nanofluid via an asymmetric tapered channel

AbstractElectroosmosis effects in a peristaltic transport of nanofluids are significant for developing the biomimetic pumping structure at a microscopic extent in physiological medications, for instance, ocular drug delivery systems. The present article addresses the numerical assessment of a peristaltically driven electro‐osmotic flow of a Williamson hybrid nanofluid. The flow is intended to be two‐dimensional, incompressible, unsteady, and subjected to an asymmetric tapered micro‐channel. The characteristics of hybrid nanofluid, which consists of silver (Ag) and copper (Cu) as nanoparticles with base fluid‐blood, are explored in a relative manner with regular nanofluid Ag‐blood. Further, the study includes the impact of linear thermal radiation, energy dissipation through viscosity and resistance phenomena with an externally applied consistent magnetic field. The mathematical model is simplified using dimensionless similarity transformations and numerically solved via MATLAB software. Variations in momentum, thermal energy, and entropy generation against various emerging physical parameters are deliberated through graphical results. Longitudinal velocity towards the center line and heat transfer rate is also analyzed through numerical data illustrated in table form. This study introduces a novel mathematical model for the peristaltically driven electroosmosis flow of Ag‐Cu/blood hybrid nanofluid in a tapered asymmetric microchannel, incorporating external electric and magnetic field effects.

Healthy older adults generate transverse-plane momenta required for 90° turns while walking during the same phases of gait as used in straight-line gait

BackgroundGeneration and regulation (control) of linear and angular momentum is a challenge during turning while walking which may be exacerbated by age-related changes. In healthy older adults, little is known about how momentum is controlled during turns, especially within each phase of gait. Each phase of gait affords unique mechanical contexts to control momenta and regulate balance. In healthy young adults, we found that the transverse-plane linear and angular momenta generation strategies observed within specific phases of gait during straight-line gait were also used during turns. Therefore, in this study, we investigated whether healthy older adults shared similar momentum control strategies specific to each gait phase during straight-line gait and turns.MethodsNine healthy older adults completed straight-line gait and 90° leftward walking turns. We compared the change in transverse-plane whole-body linear and angular momentum across gait phases (left and right single and double support). We also compared the average leftward force and transverse-plane moment across gait phases.ResultsWe found that leftward linear momentum was generated most during right single support in straight-line gait and leftward turns. However, in contrast to straight-line gait, during leftward turns, average leftward force was applied across gait phases, with left single support generating significantly less leftward average force than other gait phases. Leftward angular momentum generation and average moment were greatest during left double support in both tasks. We observed some within-participant results that diverged from the group statistical findings, illustrating that although they are common, these momenta control strategies are not necessary.ConclusionsOlder adults generated transverse-plane linear and angular momentum during consistent phases of gait during straight-line gait and 90° turns, potentially indicating a shared control strategy. Understanding momentum control within each phase of gait can help design more specific targets in gait and balance training interventions.

How take-off technique affects muscle demand in the back handspring step out in female gymnasts.

When performing the back handspring step out (BHS) on the balance beam, most gymnasts use one of three take-off techniques: Simultaneous Flexion, Sequential Flexion or Double-Bounce. However, it remains unclear which technique results in the lowest muscle demand that could help reduce energy expenditure and fatigue and improve overall performance. The purpose of this study was to use musculoskeletal modelling and simulation to quantify the influence of take-off technique on muscle demand (integrated muscle power) and contributions to the critical biomechanical functions of whole-body angular momentum generation and control and trunk propulsion (mechanical power delivered to the trunk). Simulations of female gymnasts (n = 21; age: 15.3 ± 3.6) were generated using their self-selected BHS technique on a balance beam. Differences in muscle demand were small across the techniques. However, the vasti, ankle plantarflexors, gluteus maximus and hamstring muscle groups experienced large demand during the BHS take-off. The gluteus medius and ankle plantarflexors were crucial for maintaining balance. The hamstrings, ankle plantarflexors and vasti generated needed momentum and delivered power to the trunk. These results provide targets for muscle strengthening and conditioning to improve balance control and increase the height and distance of the BHS, which is needed before adding additional skills in combination.

N-point functions in conformal quantum mechanics: a momentum space odyssey

In this paper, we study the implications of conformal invariance in momentum space for correlation functions in quantum mechanics. We find that three point functions of arbitrary operators can be written in terms of the 2F1 hypergeometric function. We then show that generic four-point functions can be expressed in terms of Appell’s generalized hypergeometric function F2 with one undetermined parameter that plays the role of the conformal cross ratio in momentum space. We also construct momentum space conformal partial waves, which we compare with the Appell F2 representation. We test our expressions against free theory and DFF model correlators, finding an exact agreement. We then analyze five, six, and all higher point functions. We find, quite remarkably, that n-point functions can be expressed in terms of the Lauricella generalized hypergeometric function, EA, with n − 3 undetermined parameters, which is in one-to-one correspondence with the number of conformal cross ratios. This analysis provides the first instance of a closed form for generic momentum space conformal correlators in contrast to the situation in higher dimensions. Further, we show that the existence of multiple solutions to the momentum space Ward identities can be attributed to the Fourier transforms of the various possible time orderings. Finally, we extend our analysis to theories with N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 1, 2 supersymmetry, where we find that the constraints due to the superconformal ward identities are identical to identities involving hypergeometric functions.

Thinking big starting small: identifying considerations for small-scale tidal energy in southwest Nova Scotia

Nova Scotia’s marine renewable energy (MRE) sector can contribute to provincial goals for carbon neutrality. With this, tidal energy has been an interest to industry stakeholders for over two decades, yet general momentum for the industry has shifted. Previous tidal energy projects and recent studies suggest there needs to be a shift in focus towards scalable tidal energy (i.e., small-scale) development in the province. This research explores the considerations of developing tidal energy in Southwest Nova Scotia with an emphasis on small-scale tidal devices. Using a comprehensive literature review and in-depth semi-structured interviews with stakeholders from different sectors of Nova Scotia’s MRE energy industry, key issues and challenges were explored. Results underline four main themes that affect industry potential, which include cost and financing, technology, policy, and energy distribution. These results support a discussion around the value of small-scale technology, regulatory pathways, industry collaboration, and using global best practices to accelerate tidal energy industry goals in Nova Scotia.

Thermal performance analysis of oriented MHD convective flow and entropy production of hybrid nanofluids in a cavity induced by semicircles at different radii ratios

AbstractThe current study numerically treats the magnetic field impacts on the natural convection flow and entropy generation in a square cavity filled with hybrid nanofluid and induced by two isothermally heated semicircles at the bottom and left walls of the cavity. The cavity is filled by hybrid nanofluid (titanium oxide/silver‐water) and oriented under different inclination angles with the applied magnetic field. The simulations in this study were executed via a home‐made code written in the FORTRAN programing language. The numerical methodology considered to solve the coupled equations of continuity, momentum, energy, and entropy generation equations with the associated boundary conditions is the finite volume method and the full multigrid acceleration. Various wake parameters are considered in this research study, namely, the inclination angle of the cavity (α), the magnetic field inclination (γ), the Hartmann number (Ha), the Rayleigh number (Ra), the volume fraction of the hybrid nanofluid (ϕ) and the internal semicircles radii ratio (β). The major findings issued from the impact of these parameters on the fluid flow and heat transfer characteristics reveal that heat transfer and entropy generation are a decreasing function of the Hartmann parameter. Moreover, the total entropy generation is intensified by 85.23% from Ra = 103 to Ra = 106 for Ha = 10, by 85.818% for Ha = 50 and 83.813% for Ha = 100. Besides, the flow magnitude is found decreasing with increasing the radii ratio β of the semicircles. It is also found that optimal heat transfer rates deducted from the variation of average Nusselt number versus Ra for different volume fractions of the hybrid nanoparticles are obtained for the extreme values of the pertinent parameters (β = 1, ϕ = 8%, Ra = 106). Hence, the present work offers a useful tool and a parametric study for the research community and engineers on the design and optimization of thermal management systems used in a variety of industrial applications, such as heat exchangers, nuclear reactors, and energy systems.

Countermovement Jump and Momentum Generation Associations to Fastball Velocity Performance Among Division I Collegiate Pitchers.

Sakurai, M, Qiao, M, Szymanski, DJ, and Crotin, RL. Countermovement jump and momentum generation associations to fastball velocity performance among Division I collegiate pitchers. J Strength Cond Res 38(7): 1288-1294, 2024-The current study explored the relationships between countermovement jump (CMJ) profiles and baseball pitching performance. Nineteen Division I collegiate pitchers performed in-laboratory pitching and bilateral CMJs. Whole-body kinematics and ground reaction force were collected during both pitching and CMJ evaluations. Statistically significant correlations of concentric impulse and peak power in the CMJ test with fastball velocity were observed (r = 0.71 and 0.68). Concentric impulse in CMJ also showed a statistically significant correlation with linear momentum in the anterior-posterior direction during pitching (r = 0.68). Lean body mass and body mass showed statistically significant correlations with both of the 2 linear momentums during pitching (r = 0.71∼0.83), and concentric impulse in CMJ (r = 0.71 and 0.81). Pelvis and trunk pitching mechanics did not correlate with any of the CMJ variables at the statistically significant level, whereas the direction of the correlations varied (|r| < 0.45). Assessment of a baseball pitcher's CMJ should focus on concentric impulse and peak power because only these showed meaningful relationships with fastball velocity or momentum generation during pitching. An increase in lean body mass is also suggested to be able to generate more impulse and momentum. Baseball coaches, strength coaches, and clinicians are encouraged to include lower-body explosive training to enhance the force and power output capacity of baseball pitchers.

Optically reconfigurable multi-channel orbital angular momentum generator based on 3-bit coding metasurface

Optically reconfigurable multi-channel orbital angular momentum generator based on 3-bit coding metasurface

Peak angular momentum of pirouettes by a university-level contemporary dance cohort

Turning movements are an important movement to master in many dance styles. For advanced or professional dancers, the pirouette (completing one or more turns with a specific stylistic form) is difficult to master and increasing the revolutions heightens difficulty further. The purpose of this study was to investigate peak angular momentum generation (PAM) of completing single- and attempting triple-revolution pirouettes for contemporary dance students. Adaptations made by dancers whilst rotating and imbalances within the centre of mass over the base of support were identified. Ethical approval was received. Seven female university-level contemporary dance students completed five successful single-revolution pirouettes en dehors (PeDh) and attempting to complete five successful triple-revolution PeDh whilst being recorded using a three-dimensional VICON motion capture system. PAM and torso lean (TL) and a two-dimensional foot vector (FV) were then calculated using a six degree of freedom model (Visual3D). A one-way ANOVA (P &lt; 0.05) compared mean variance between single-, double-, and triple-revolution pirouettes. Significant effects were determined for all variables in each pirouette condition. A Tukey post-hoc test (P &lt; 0.05) determined overall significant differences between PAM (F2, 37 = 15.8, ⍵² = 0.426), TL (F2, 37 = 3.4, ⍵² = 0.108), and FV (F2, 30 = 4.9, ⍵² = 0.192) for the midpoint turn of each pirouette condition. Independent samples T-Tests (𝛼 &lt; 0.05) were conducted to compare PAM (t11 = 1.8, d = 1.026), TL (t11 = 0.1, d = 0.030), and FV (t6 = 0.6, d = 0.433) between successful and unsuccessful double pirouettes, with no differences reported. This test was repeated for successful and unsuccessful triple pirouettes. Again, no differences were observed for PAM (t15 = −2.2, d = −1.093), TL (t15 = −1.6, d = −0.802), and FV (t15 = −1.3, d = −0.648). This study concluded that PAM increased as the number of pirouette revolutions increased. Furthermore, a minimum threshold for PAM was calculated to produce successful double (0.597 kg·ms2⎺¹) and triple (0.637 kg·ms2⎺¹) pirouettes. Observations from the pirouette trials and FV data illustrated that dancers ‘hop’ when an imbalance is sensed, in an attempt to regain balance and continue pirouette revolutions. However, this method predominately produced unsuccessful pirouettes as the initial PAM was not achieved. This research can be applied to dance coaching as it provides an initial insight into mechanisms to support successful pirouette technique.

Exact Solution of the Riemann Problem for the One-Dimensional Blood Flow Equations with General Constant Momentum Correction Coefficient

Exact Solution of the Riemann Problem for the One-Dimensional Blood Flow Equations with General Constant Momentum Correction Coefficient

Orbital angular momentum modes in dielectrically chiral-core fibers

In this paper, we investigate a dielectrically chiral-core fiber for the generation of orbital angular momentum (OAM) modes. We observe that the presence of chirality induces a modal index split between the same order OAM modes with opposite topological charges and arbitrary phase front rotation directions, which are originally degenerate in achiral fibers. This split indicates the existence of circular birefringence (CB) associated with a dielectric chirality. The modal cutoff splitting results in a single polarization property without the possibility of coupling between the same order modes that correspond to a single +l or −l OAM mode guiding. However, neither of the two fundamental modes guided by the chiral fiber exhibits a cutoff, despite having different modal indices due to chirality. Upon fraction of modal power cutoff, the high-order modes in the core region display different cutoff fractions of modal power between the same order modes, while the fundamental mode has no cutoff fraction of modal power. Due to CB and different fractions of modal power in the core for different handed OAM modes, dielectrically chiral fibers have potential applications in chiral sensing, circular polarization-dependent OAM mode filters, and new kinds of OAM mode generators.

Single-frequency orbital angular momentum switchable modes from a microchip laser.

We demonstrate the direct generation of single-frequency switchable orbital angular momentum (OAM) modes in a 1 µm wavelength range using a Nd:YVO4 microchip laser. The 808 nm laser diode pump beam is shaped into annular through an axicon associated with a lens. By adjusting the diameter and power of the annular pump beam, various OAM modes with different mode volumes can oscillate inside the Nd:YVO4 microchip. Moreover, a single-frequency output is also available due to the short cavity of the microchip. In the proof-of-principle experiment, single-frequency twofold multiplexed OAM modes | ± 1> and | ± 2> are generated, with experimentally measured fidelity higher than 96%. This work presents a compact and versatile single-frequency OAM source and will inspire multiple advanced scenarios ranging from classical to quantum photonics.

Full-space energy-controlled multi-wavefront generators enabled by hybrid graphene-VO2 terahertz metasurfaces

In terahertz communication, multi-wavefront reconfigurable metasurfaces allowing for energy control are highly desirable for multiple channels and high capacity. However, existing metasurfaces can only produce limited wavefronts in either transmission or reflection space, severely hindering their practical application ranges. Herein, a dual-controlled reconfigurable metasurface integrated with graphene and VO2 is demonstrated for an energy-controlled multi-wavefront generator in full-space. By altering the geometry sizes and rotation angles of the meta-atoms as well as external excitations, the polarization independent phase responses are achieved to actively generate energy-controlled multiple wavefronts in full-space. As a proof-of-concept demonstration, three types of full-space metasurfaces are constructed to respectively realize various meta-deflectors, metalens/meta-deflector/orbital angular momentum (OAM) generator, and multimode OAM generator in full-space by utilizing the spin-decoupling method. Moreover, the intensities of these wavefronts can be actively modulated by adjusting the Fermi energy of graphene. Therefore, such diversified metasurface will possess a promising application prospect in terahertz multifunctional devices, and communication and imaging systems.

Generation of multiple orbital angular momentum and on-demand single photons by combining quantum dot to metalens

Generation of multiple orbital angular momentum and on-demand single photons by combining quantum dot to metalens

Метаповерхности Патчаратнама-Берри с генерацией углового орбитального момента и комбинированным фазовым кодированием для широкополосного широкоугольного снижения ЭПР

The phase mechanism of a broadband wide-angle radar cross-section (RCS) reduction is examined, based on the use of non-absorbing Patcharatnam-Berry (PB) metasurfaces (MSs) with the generation of orbital angular momentum (OAM) and a combination of different phase profiles. MS unit cells contain a thin shielded single-layer substrate and meta-particles in the form of perforated rectangular patches with a coded rotation angle. The purpose of the work is to compare the scattering characteristics and scattered field cancelation efficiency for structural elements (modules) of a MS, consisting of the same number of meta-particles, but having different PB-phase profiles. A profile with an azimuthal gradient, which forms broadband scattering of vortex waves with OAM, profiles with radial and linear gradients and anomalous scattering, parabolic profiles with wide-angle scattering, and various combined phase profiles are analyzed. The purpose of the work is comparing the scattering characteristics. The MS modules scattering characteristics are studied using the HFSS (finite element method) for co-polarization and cross-polarization in the case of irradiation with a normally incident plane circular polarized wave. The simulation showed that the scattering diagrams of the co-polarized MS field in these cases have a funnel-shaped vortex character with an intense OAM minus the first order (the order of the OAM remains the same as for an MS with an azimuthal phase gradient). OAM generation significantly suppresses backscattering by co-polarization. The far-field phase in the vortex region depends not only on the azimuthal, but also on the meridional observation angles. The combination of OAM and parabolic profile increases the diffusion of broadband scattering, realizes a wider-angle scattering of the resulting field with a vortex opening angle of about 100° (at an average frequency of 14 GHz), which is important for RCS reduction.

Controlled generation of OAM-switchable vortex beams at 639 nm from a Pr3+: YLF laser

In this paper, we reported and demonstrated a blue LD-pumped Pr3+: YLF laser for the controlled generation of orbital angular momentum (OAM) switchable vortex beams at 639 nm. To begin with, the quantitative tilt imbalance of the resonator was introduced to select the higher-order Hermite-Gaussian (HG) modes by utilizing the eigenvector method and introducing the concept of mode discriminant factor. Moreover, the mode converter, composed of two cylindrical mirrors, was applied to convert the Hermite- Gaussian (HG) modes into the Laguerre-Gaussian (LG) modes with the OAM. Then, the experiment setup was built to validate the correctness and effectiveness of the quantitative tilt imbalance. The results showed that the vortex beams with OAM of 0 to ±14 at 639 nm can be obtained by adjusting the tilted angle of the output mirror, which agreed well with the simulation results, and the slope efficiencies of the vortex beams with OAM = 1, 2, and 3 are 11.64%, 8.01%, and 6.05%, respectively. The method provided a viable solution for the generation of visible vortex beams with switchable OAM from the Pr3+: YLF laser.

Generation of OAM beams with quasi omnidirectional pattern using simple slotted waveguide array

Theory and design aspects of the Slotted Waveguide Antenna (SWA) array for the simultaneous generation of Orbital Angular Momentum (OAM) modes are proposed in this paper. The proposed method is a novel approach to OAM generation that uses a simple feeding scheme and has better performance, especially in terms of mode purity. Due to its all-metallic structure, the high-power OAM beams with first-order modes (+1&-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ +1 \\, \\& \\,-1$$\\end{document}) can be generated simultaneously along the propagation axis but in opposite directions, which improves the coverage and makes the proposed SWA be used in applications like radar target detection by mounting it on a mechanically rotating platform. The proposed theory is verified by the electromagnetic (EM) simulations, followed by the experimental verification done on the laboratory prototype. The near-field characteristics of the proposed antenna confirm the generation of first-order OAM beams with high mode purity. The far-field characteristics show the high gain and quasi-omnidirectional radiation pattern. Transmission of high-power OAM beams with good far-field characteristics makes the proposed antenna mitigate the issues of long-range OAM communication to a certain extent. However, the proposed antenna can be served well in strategic applications where the mostly high-power microwave is involved.

Soft Mesocrystal Enabled Multi‐Degree Light Modulation

AbstractMesocrystals introduce high‐level orders, such as chirality, topology, and hierarchy to the crystallography, and thus bring collective and emergent properties beyond traditional crystals. Orthogonally modulating the multiple degrees of light is highly pursued to fully explore the intrinsic multidimensional and large‐scale parallel processing capability of photon informatics. Unfortunately, it is unachievable with traditional light–matter interaction systems. Here, the multi‐degree light modulation is realized based on the hierarchical architecture of a soft mesocrystal. High‐quality monodomains of both blue phase I and blue phase II are formed via regulating the assembly of liquid crystals by photoalignment anchoring and electricity. The mapping relationship between optical freedoms (the spin, wavelength, and geometric phase of light) and hierarchical structures (the chirality of helix, lattice constant, and the azimuthal orientation of cubic lattices) is established. Omnidirectional spatial phase modulation with spin and full color selectivity is demonstrated. Based on the multi‐degree light modulation, 3D and wavelength‐selective orbital angular momentum generation as well as multichannel color holographic display are presented. This work extends the fundamental understanding of blue phase mesocrystals and provides a promising strategy for large‐scale parallel and multi‐degree light modulation that may be utilized in vital fields, such as supercomputing, optical communications, and virtual/augmented realities.