Spin Rate Research Articles

Non‐Synchronous Rotation on Europa Driven by Ocean Currents

AbstractIt has been suggested that the ice shell of Jupiter's moon Europa may drift non‐synchronously due to tidal torques. Here we argue that torques applied by the underlying ocean are also important and can result in non‐synchronous rotation. The resulting spin rate can be slightly slower than the synchronous angular rate that would have kept the same point of the ice shell facing Jupiter. We develop an ice shell rotation model, driven by ocean stress calculated using a high‐resolution state‐of‐the‐art ocean general circulation model, and take into account the viscoelastic deformation of the ice shell. We use the ice shell model results together with observed limits on the ice shell drift speed to constrain ice shell parameters such as effective viscosity, which is currently uncertain by at least four orders of magnitude. Our results suggest, at best, sluggish ice shell convection. Depending on the relaxation time scale of the ice shell and on the ocean currents, the ice shell may exhibit negligible drift, constant drift, or oscillatory drift superimposed on random fluctuations. The expected rotation rate exceeds ∼30 m/yr; future spacecraft observations can be used to test these predictions and yield insight into the properties of the ice shell and underlying ocean.

Mechanism for control of ball spin rate by the upper limb in baseball pitching based on singular value decomposition

This study aims to examine the mechanism by which the ball spin rate during fastball pitching is controlled by synergistic joint torque. The participants were seven baseball players. The kinematics and kinetics of the fingers, wrist, elbow, and shoulder were calculated using the inverse dynamics method. The synergistic relationship between the joint torques was calculated using singular value decomposition. The similarity of the spatial pattern of the joint torque in each participant was evaluated using cosine similarity. The results indicated that there were three types of synergistic torque control: (1) two pitchers had a synergistic torque control that was primarily based on shoulder internal rotation torque, (2) two pitchers had a synergistic torque control that was primarily based on elbow extension torque, and (3) three pitchers had a synergistic torque control that was primarily based on shoulder horizontal adduction torque. In particular, pitchers with a high spin rate relative to the ball velocity (SPV) had a torque control of the shoulder internal rotation type. In contrast, pitchers with a low SPV had a torque control of the shoulder horizontal adduction type. It is considered that pitchers with a high SPV execute shoulder internal rotation torque, which has the same direction as that of ball spin, based on hierarchical control to increase the ball spin rate. These results suggest that pitchers with high and low SPVs exhibit different motor patterns. Pitchers and coach need to focus on the shoulder joint as well as the fingers when they throw fastball.

Effect of PTAA and PCBM concentrations on the electrical response of bilayer heterojunction PTAA/PCBM Diode

Poly[bis(4-phenyl) (2,4,6-trimethylphenylamine] (PTAA) is a new promising hole transport material, and [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) is a suitable electron acceptor material. This study deposited thin-film PTAA and PCBM at different spin coatings ranging from 1000 rpm to 5000 rpm. Ultraviolet–visible (UV–vis) spectrometer, X-ray diffraction (XRD) machine, and scanning electron microscope (SEM) techniques were used to determine the optical properties and structural properties, respectively. Thermal annealing with temperatures of 80 °C, 100 °C, 120 °C, and 150 °C was introduced to improve the properties of the PTAA and PCBM thin film. The results of SEM images for PTAA annealed at 150 °C appeared to darken and melt, whereas PCBM annealed at 120 °C and 150 °C had granule properties. The ideality factors for bilayer heterojunction diodes and bulk heterojunction PTAA/PCBM diodes with increased layers were 5.8–60.2 and 30.8–77.2, respectively. The optimum spin rate for the bilayer heterojunction PTAA/PCBM was 5000 rpm. The most appropriate diode behavior of the bilayer was at 5.0/1.0 wt%, 1.0/5.0 wt%, and 3.0/3.0 wt% of PTAA/PCBM, with the calculated ideality factors of 5.8, 6.2, and 15.45 with turn-on voltage of 1.57 V, 1.70 V, and 1.82 V, respectively.

The relationship between pitching parameters and release points of different pitch types in major league baseball players.

The purpose of this study was to deepen our understanding of pitches and to obtain basic knowledge about pitches by comparing 4-seam and other pitches in Major League Baseball (MLB). We analyzed big data for 1,820 professional baseball pitchers of MLB on release speed, spin rate, release point 3D coordinates (X, Y, and Z axes), amount of change for 4-seam, and seven changing ball types (sinker, slider, changeup, cutter, curve, split finger, and knuckle curve), using PITCHf/x and TrackMan. We also evaluated three relationships: (1) between the release points and the ball types of pitch; (2) between the amount of change in the ball and the release speed; and (3) between the release speed and the spin rate. The release speed was significantly slower in seven changing ball types than in the 4-seam (p < 0.01, respectively). The spin rate and the amount of change (ΔX and ΔZ) were significantly different between 4-seam and seven changing ball types (p < 0.01, respectively). Release point 3D coordinates (X, Y, and Z axes) were significantly different between 4-seam and slider, cutter, and curve (p < 0.01, respectively). Based on these findings, the eight pitch types were mainly divided into three groups: 4-seam, curve, and off-speed pitch types. Seven changing ball types included specific characteristics for each parameter. The correspondence among the release speed, ΔX, and ΔZ at the 3D coordinates is an arch with 4-seam as the apex. Our results suggest an effective strategy for changing the release point and displacement of a ball's trajectory to improve the performance of baseball pitchers.

Orbital precession in short-period hot Jupiter exoplanet systems

ABSTRACT In several exoplanet systems the stellar rotation axis is not aligned with the normal to the orbital plane. For the class of ‘hot Jupiters’, a significant fraction of total angular momentum resides in the orbit. Orbit precessional motion has been observed in several such systems. We expect the tides raised by the orbiting exoplanet to induce normal mode oscillations in the host star, with the possibility of normal mode-orbit resonance. Gravity modes possess frequencies in the range of typical orbital Keplerian frequencies and their overtones. These resonances, confined to very narrow ranges of frequency space, would be highly improbable unless ‘resonance locking’ occurs, driven, for example, by structural and spin rate changes of the host star, operating on nuclear evolutionary time-scales. Resonance locking amplifies the amplitude of tidally driven oscillations, possibly by orders of magnitude, compared to the equilibrium tide displacements. We address the problem of precession and nutation in a system with a single exoplanet, with non-aligned spin and orbit axes, coupling the gravitational perturbations of normal mode distortions with orbital motion. Resonant modes are expected to have large amplitudes, contributing significantly to the gravitational perturbation already present due to rotational distortion of the star that gives rise to uniform orbital precession. The relative magnitude of rotational distortion and normal-mode perturbations is estimated. For Kepler-13Ab, estimates of their influence on transit time variations are given, and suggest they may be discernible with modern space telescope missions.

Laminar separation bubble on a rotating cylinder in uniform flow

We study the effect of spin ( 0 ≤ α ≤ 2) of a cylinder, placed in uniform flow, on the transition of the boundary layer. Large Eddy Simulation, with the Sigma turbulence model to account for the sub-grid scales, is carried out using a stabilized finite element formulation. The Reynolds numbers ( R e = 0.6 × 10 5 and 1.0 × 10 5) lie in the high-subcritical regime for a non-rotating cylinder where the boundary layer separates in a laminar state and does not reattach. Magnus effect is observed at low α wherein separation is delayed on the retreating side and preponed on the advancing side, resulting in a lift force that increases with increase in α. At a certain critical α, the boundary layer on the advancing side transitions to a turbulent state, causing it to reattach. A laminar separation bubble (LSB) forms, significantly delaying the final separation and increasing suction. At R e = 1.0 × 10 5, this suction overcomes that on the retreating side, leading to a reversal in the direction of lift force, referred to as the inverse Magnus effect. The LSB is accompanied by weakened vortex shedding at increased frequency. The spatial extent of the LSB and the magnitude of reverse lift, at a given Re, decreases with increase in α. The lift force changes direction yet again at a certain α marking the end of the inverse Magnus effect regime and beginning of the second Magnus effect regime. The LSB vanishes beyond a certain spin rate, and the boundary layer directly transitions to a turbulent state.

Satellite Attitude Control Using Double-Gimbal Variable-Speed Control Moment Gyroscope: Single-Loop Control Formulation

A single-loop control architecture is proposed to achieve singularity-free attitude control of satellites actuated using a double-gimbal variable-speed control moment gyroscope (DGVSCMG). Satellite and DGVSCMG combined rotational dynamics is modeled in the framework of geometric mechanics. It is shown that the combined attitude dynamics is in control-affine form when the motor torques of the DGVSCMG are taken as control inputs. A single-loop hybrid robust nonsingular fast finite-time sliding mode control (NFFTSMC) is designed to ensure an unwinding-free attitude maneuver. In the proposed single-loop formulation, the respective motor torques of the DGVSCMG are computed directly using only one NFFTSMC without requiring the steering law, resulting in mathematical singularity-free attitude control. A novel sliding surface is also proposed to ensure that the rotor angular speed converges to its nominal value after the maneuver. This eliminates the need of repeated desaturation of the rotor spin rate, unlike all the steering-law-based control architecture. Unwinding-free global stability of the system using the proposed hybrid NFFTSMC is proved for the sliding and reaching phases. Simulation results are presented to substantiate the claim made, assuming the rigid satellite to be equipped with only one DGVSCMG.

Lifted particles from the fast spinning primary of the Near-Earth Asteroid (65803) Didymos

An increasing number of Near Earth Asteroids (NEAs) in the range of a few hundred metres to a few kilometres in size have relatively high spin rates, from less than 4 h, down to ∼2.2 h, depending on spectral type. For some of these bodies, local acceleration near the equator may be directed outwards so that lift off of near-equatorial material is possible. In particular, this may be the case for asteroid Didymos, the primary of the (65803) Didymos binary system, which is the target of the DART (NASA) and Hera (ESA) space missions. The study of the dynamics of particles in such an environment has been carried out – in the frame of the Hera mission and the EC-H2020 NEO-MAPP project – according to the available shape model, known physical parameters and orbital information available before the DART impact. The presence of orbiting particles in the system is likely for most of the estimated range of values for mass and volume. The spatial mass density of ejected material is calculated for different particle sizes and at different heliocentric orbit epochs, revealing that large particles dominate the mass density distribution and that small particle abundance depends on observation epoch. Estimates of take off and landing areas on Didymos are also reported. Available estimates of the system mass and primary extents, after the DART mission, confirm that the main conclusions of this study are valid in the context of current knowledge.

Technical skills in complex tennis situations: Dutch talented players U15 compared to players U17.

Technical skills in complex situations appear crucial for progress towards elite tennis performance. However, it is unknown how these skills develop in different age categories in a group of talented youth players. The aim of this study is to evaluate possible differences in technical skills among Dutch talented youth tennis players U15 compared to U17. A total of 19 players (12 males, 7 females; age 14.6 ± 1.4 years) were tested on ball speed, accuracy, percentage errors and spin rate using the on-court Dutch Technical-Tactical Tennis Test. With a ball machine, four games were simulated which were either fixed (game 1 and game 2) or variable (game 3 and game 4), depending on the complexity of the task. Each game consisted of two offensive, two neutral and two defensive rallies, representing different tactical situations. A two-way ANOVA revealed a statistically significant interaction between the effects of age category and sex for ball speed (F(1,15) = 5.472, p = 0.034, η 2 = 0.267), indicating that males U17 produced higher ball speed compared to males U15, whereas no differences were found between females U15 and U17. A one-way ANCOVA showed that, regardless of sex, players U17 scored significantly higher on accuracy than players U15 (F(1,16) = 5.021, p = 0.040, η 2 = 0.239). No differences were found between players U15 and U17 for spin rate and percentage errors (p > .05), although there was a medium to large effect size for males U17 to produce higher spin rates compared to males U15. A closer examination of accuracy revealed that players U17 scored significantly higher compared to players U15 in game 4 (F(1,17) = 6.358, p = .022, η 2 = .272) and in defensive situations (F(1,17) = 9.602, p = .007, η 2 = .361). In conclusion, the results of the current study suggest that technical skills, especially ball speed for males and accuracy in complex situations for both males and females, continue to develop in adolescence in talented tennis players. There is an increased understanding about underlying technical skills that contribute to progress towards elite tennis performance. To effectively develop technical skills, coaches are encouraged to design specific practices where these skills are performed in complex situations under high cognitive and temporal pressure.

Boundary Layers of Circumplanetary Disks around Spinning Planets. I. Effects of Rossby Waves

Gas giant planets are believed to accrete from their circumplanetary disks (CPDs). The CPDs usually involve accretion through the boundary layer (BL) in the vicinity of planets. Prior studies have concentrated on the BL of nonspinning planets. We investigate the influence of planetary spin on the wave behaviors within the BL. The rotation profile in such BLs would show a sharp transition from the rigid rotation to the Keplerian rotation. We examine the angular momentum transport in these BLs in terms of linear perturbation analysis. We find that the global inertia-acoustic mode associated with spinning planets would give rise to the inflow of angular momentum and the accretion of gas. In this work, we identify a new kind of global mode, namely the Rossby mode. The Rossby mode can lead to the outflow of angular momentum and the decretion of gas from a spinning planet. The Rossby mode provides a negative feedback that regulates the planetary spin and mass. We compare the growth rate of the two modes as a function of the width of BL, the Mach number, and the spin rate of planets. Our results reveal the underlying hydrodynamic mechanism of terminal spins and asymptotic mass of the giant planets.

Attitude control experiment of a spinning spacecraft using only magnetic torquers

Magnetic torquers are attitude control devices used in spacecraft systems, and extensive research has been conducted on the attitude control of such spacecraft systems equipped with magnetic torquers. In this paper, a control law for spin spacecraft systems is proposed. Unlike existing control laws that switch between the spin rate and spin axis orientation control, the proposed angular momentum control law (AMCL) simultaneously provides feedback control for the spin rate and spin axis orientation based on the angular momentum error from the target. The steady-state and asymptotic behaviors of the angular momentum error are analyzed. In the analysis, both the saturated and unsaturated magnetic moments are considered. A testbed with magnetic torquers and a geomagnetic field simulator are developed to experimentally evaluate the performance of the AMCL. The geomagnetic field simulator is constructed using three Helmholtz coils to generate a time-variant magnetic field similar to that in orbit. The AMCL is used to conduct two ground experiments on the spin rate and spin axis orientation control. The effectiveness of the AMCL and behavior of the testbed are experimentally evaluated by comparing and analyzing the experimental and numerical simulation results. Consequently, the AMCL is found to achieve the required states in the experiments, and the asymptotic and steady-state behaviors appear to be consistent with the estimations made by numerical simulations. In conclusion, the proposed AMCL can appropriately control the spin motion of a spacecraft.

Elbow Ulnar Collateral Ligament Tears: A Modified Consensus Statement

To establish consensus statements on the treatment of ulnar collateral ligament (UCL) injuries and to investigate whether consensus on these distinct topics could be reached. A modified consensus technique was conducted among 26 elbow surgeons and 3 physical therapists/athletic trainers. Strong consensus was defined as 90% to 99% agreement. Of the 19 total questions and consensus statements 4 achieved unanimous consensus, 13 achieved strong consensus, and 2 did not achieve consensus. There was unanimous agreement that the risk factors include overuse, high velocity, poor mechanics, and previous injury. There was unanimous agreement that advanced imaging in the form of either magnetic resonance imaging or magnetic resonance arthroscopy should be performed in a patient presenting with suspected/known UCL tear that plans to continue to play an overhead sport, or if the imaging study could change the management of the patient. There was unanimous agreement regarding lack of evidence for the use of orthobiologics in the treatment of UCL tears as well as the areas pitchers should focus on when attempting a course of nonoperative management. The statements that reached unanimous agreement for operative management were regarding operative indications and contraindications for UCL tears, prognostic factors that should be taken into consideration in when performing UCL surgery, how to deal with the flexor-pronator mass during UCL surgery, and use of an internal brace with UCL repairs. Statements that reached unanimous agreement for return to sport (RTS) were regarding portions of the physical examination should be considered when determining whether to allow a player to RTS; unclear how velocity, accuracy, and spin rate should be factored into the decision of when players can RTS and sports psychology testing should be used to determine whether a player is ready to RTS. V, expert opinion.

Numerical Analysis of the Magnus Effect on the Forces Past an Axisymmetric Body at High Incidence

Rolling motion is the motion where a body flies at a constant pitch angle α with respect to the freestream velocity vector, while undergoing a constant angular rotation p about its longitudinal axis. An effect of this motion is the appearance of a Magnus force and moment, which add to the static forces and moments. One problem that arises at high angles of attack is that the flow is not symmetric in these conditions, leading to a non-zero side force at a zero spin rate. Additionally, the roughness induces a roll angle effect on the side and normal forces, and therefore on the moments. Then, at low roll rates, the prediction is difficult to assess due to the complex interactions due to the moving walls, roughness and shedding vortices that appear at the leeside. Computational fluid dynamics (CFD) is an appropriate tool for investigating these non-linear effects, particularly at high angles of attack. It can help provide a more accurate model of the forces and moments and provide insight into the complex flow field. It is necessary to use high-level turbulence models, transient calculations and fine grids in order to capture the flow field and obtain accurate forces, moments and their derivatives. The calculations have shown that the flow is not symmetrical with the roll rate. There are differences depending on the sign of the spin velocity. The Magnus forces are difficult to determine from the total forces, as there are significant non-linear effects.

Spectra of puffy accretion discs: the kynbb fit

AbstractPuffy disc is a numerical model, expected to capture the properties of the accretion flow in X‐ray black hole (BH) binaries in the luminous, mildly sub‐Eddington state. We fit the kerrbb and kynbb spectral models in XSPEC to synthetic spectra of puffy accretion discs, obtained in general relativistic radiative magnetohydrodynamic simulations, to see if they correctly recover the BH spin and mass accretion rate assumed in the numerical simulation. We conclude that neither of the two models is capable of correctly recovering the puffy disc parameters, which highlights a necessity to develop new, more accurate spectral models for the luminous regime of accretion in X‐ray BH binaries. We propose that such spectral models should be based on the results of numerical simulations of accretion.

Photometric Observations of Nine High Mass X-Ray Binaries and Analysis of Potential Periodicities and Variations

Beginning with American Association of Variable Star Observers Alert Notice 348 (2007 April 6) and being continually extended and updated through 2020 April 17 with Alert Notice 377, Dr. Gordon Sarty requested continuing assistance with his ongoing radial velocity observations of High Mass X-Ray Binaries. As of Alert Notice 377, nine targets were identified. These are: 1H 1936+541, RX J2030.5+4751, V2175 Cyg, V1008 Cep, V831 Cas, RX J0440.9+4431/LS V+44 17, V420 Aur, HD 249179, and SAX J0635+0533. While these Alert Notices prioritized radial velocity observations with the objective of determining orbital periods of these binary systems, optical photometry can also reveal other periods and variations due to mass transfer, pulsations, rotations, spin rates, and other effects. This Research Note will address in more detail the observation and analysis of one of these nine High Mass X-Ray Binaries, specifically 1H 1936+541.

The Orbital Architecture of Qatar-6: A Fully Aligned Three-body System?

The evolutionary history of an extrasolar system is, in part, fossilized through its planets’ orbital orientations relative to the host star’s spin axis. However, spin–orbit constraints for warm Jupiters—particularly in binary star systems, which are amenable to a wide range of dynamical processes—are relatively scarce. We report a measurement of the Rossiter–McLaughlin effect, observed with the Keck/HIRES spectrograph, across the transit of Qatar-6 A b—a warm Jupiter orbiting one star within a binary system. From this measurement, we obtain a sky-projected spin–orbit angle λ = 0.°1 ± 2.°6. Combining this new constraint with the stellar rotational velocity of Qatar-6 A that we measure from TESS photometry, we derive a true obliquity —consistent with near-exact alignment. We also leverage astrometric data from Gaia DR3 to show that the Qatar-6 binary star system is edge-on (), such that the stellar binary and the transiting exoplanet orbit exhibit line-of-sight orbit–orbit alignment. Ultimately, we demonstrate that all current constraints for the three-body Qatar-6 system are consistent with both spin–orbit and orbit–orbit alignment. High-precision measurements of the projected stellar spin rate of the host star and the sky-plane geometry of the transit relative to the binary plane are required to conclusively verify the full 3D configuration of the system.

Is a baseball like knuckleball possible in cricket?

The knuckleball is considered to be one of the hardest pitches to hit in baseball due to its seemingly unpredictable motion. It has gained popularity in cricket in recent times. It is shown that the delivery referred to as knuckleball in cricket, at present, does not exhibit a zigzag motion and is, therefore, a misnomer. We propose a delivery in cricket that is associated with an erratic trajectory similar to the knuckleball pitch in baseball. Force measurement experiments in a wind tunnel on a new cricket ball in various orientations of the seam to the incoming flow and at different Reynolds number are carried out. The results are utilized to estimate the trajectory of knuckleball deliveries. The key parameters are the seam angle, speed and spin rate of the ball at the time of its release. Their effect on the trajectory is studied in detail. The optimal combination of these parameters that result in a knuckleball, which is likely hard for the batter to play, is identified.

The comparison of a top-level Japanese tennis player's serve-performance evolution between two seasons

This study sought to determine the impact of changes in serve performance (relationship between speed, spin rate, reproducibility, and impact height) on world rankings for one top-level Japanese tennis player in 2017, when he became the All Japan Student Champion, and in 2022, when he represented Japan in the Davis Cup and won the ITF tournament (M25 Monastir: 10 Jan - 16 Jan 2022). This study clarifies the impact of changes in serve performance on world rankings in 2022. The results showed that, among the three types of serves (flat, slice, and kick), there were higher values for slice and kick in 2022 compared to 2017. Higher ball speed values were found for flat in 2022 and lower values for slice and kick in 2017. In 2022, all serve heights were higher, resulting in an increase in the flat success rate, which had the lowest reproducibility. These results suggest that longitudinal measurement and evaluation of the relationship between speed, spin rate, reproducibility, and impact height when serving is important for improving competitive performance.

Increased Caribbean seismicity and volcanism during minima in Earth’s rotation rate: Search for a physical mechanism and a 2030 forecast

Three quarters of all Mw ≥ 6.6 earthquakes and volcanic eruptions surrounding the Caribbean plate occur preferentially during periods of decadal minima in Earth’s angular spin velocity. This correlation is revealed most clearly as a 4–6 years phase lag following the first derivative of the length of the day (LOD), Earth’s angular deceleration. We show that local strains and displacements resulting from oblateness changes, or plate boundary stresses associated with changes in tropical rotation rates are orders of magnitude lower than those typically associated with earthquake or volcano triggering. Notwithstanding the absence of a satisfactory causal physical mechanism, the relationship permits decadal trends in Caribbean tectonic hazards to be anticipated many years before their occurrence. The next period of increased tectonic activity in the Caribbean, corresponding to a probable slowing in Earth’s spin rate, will occur in the decade starting on or about 2030.

A topspin rate exceeding 110 rps reduces the ball time of arrival to the opponent: a table tennis rally study

ABSTRACT This study experimentally investigated the factors affecting the time a table tennis ball with topspin takes to reach the opponent. Six skilled young players and one coach performed topspin forehand strokes under the observation of three high-speed cameras. As the distribution of the participants’ measurements was uneven, additional data were collected using a launching machine that could control the ball speed and spin. To verify the effect of the spin rate on speed decay by drag, the translational speed was measured at 0.15 s after passing the baseline (23 m/s); the balls with topspin ≥110 rps, close to participants’ average (117 ± 29 rps) were 1.4 m/s faster than those with topspin ≤80 rps. The horizontal ball speed changed in the range of −3.1 to 2.6 m/s owing to table bounce. At topspins ≥110 rps the ball reached a point 1 m past the end line (estimated receiving position) 27 ± 5 ms faster than at topspins ≤80 rps, for the same initial speed. The relationship between spin rate and travel time was non-linear with boundaries at 80 and 110 rps. Therefore, maintaining a spin rate of ≥ 110 rps along with a high initial speed is an effective strategy for reducing the opponent’s preparation time.