Spin Velocities Research Articles

Exploring microrotational effects and temperature variations in electroosmotic peristalsis in tapered microchannel

AbstractThe current study is based on the effects of microrotational dynamics, microinertial effects, and temperature changes on electroosmotic peristalsis in a tapered microchannel. This has been addressed by an analytical study of heat transfer in the setting of electroosmotic peristaltic flow involving a micropolar fluid, specifically considering a symmetrically tapered channel. The Navier–Stokes equation, the Poisson–Boltzmann equation, the energy equation, and the micropolar fluid model are all included in the mathematical model. On the flow and temperature fields, a thorough parametric analysis is carried out, investigating the impacts of numerous variables, including the micropolar parameter, Prandtl number, Brinkman number, Grashof number, thermal conductivity ratio, and channel aspect ratio. The findings show that peristalsis and electroosmosis both contribute to higher heat transfer rates. Notably, the electroosmotic parameter and Brinkman number have a substantial impact on the distribution of temperature. The micropolar parameter and Brinkman number have a significant effect on the flow and temperature fields. Furthermore, electrokinetic phenomena are crucial in controlling the axial and spin velocities of the micropolar fluid. These findings have significant ramifications for the design and optimization of microfluidic devices in engineering and biomedical applications that employ the electroosmotic peristaltic flow of micropolar fluids.

Irreversibility of heat transfer with the curvature effect on peristaltic thrusting of micropolar fluid in a resilient channel in the presence of heat generation: nonlinear analysis

In this work, we perform an investigation of the peristaltic thrusting of an incompressible viscous micropolar fluid in a symmetric resilient channel with consideration of streamline curvature effects and inertia forces. We obtained the partial differential equations for fluid flow in two dimensions for micropolar fluids in addition to the heat equation. These equations have been transformed to another domain by using a transformation between the fixed and wave frames. Asymptotic solutions of have been obtained by using the compatible boundary conditions using the perturbation technique of arbitrary Reynolds number and long-drawn wavelength. The solutions for longitudinal, normal and spin velocities, stream function, heat transfer and rate of working walls have been obtained. The several of biophysical parameters influence has been demonstrated through the graphs. Both time flow rate and pressure gradient relations are obtained. Different characteristics for fluid flow, temperature profile, normal force, microrotation (spin) velocity and Nusslet number are greatly influenced at the channel walls by the presence of micropolar fluid. Trapping and pumping phenomena are further discussed. It is found that the maximum value for the Bejan number occurs near the centre of the channel, i.e. the heat transfer irreversibility dominates around the centre of the channel.

On the Rotation Properties of a Post-explosion Helium-star Companion in Type Iax Supernovae

Recent studies have suggested that type Iax supernovae (SNe Iax) are likely to result from a weak deflagration explosion of a Chandrasekhar-mass white dwarf in a binary system with a helium (He)-star companion. Assuming that most SNe Iax are produced from this scenario, in this work we extend our previous work on the three-dimensional hydrodynamical simulation of ejecta-companion interaction by taking the orbital and spin velocities of the progenitor system into account. We then follow the post-impact evolution of a surviving He-star companion by using the one-dimensional stellar evolution code MESA. We aim to investigate the post-explosion rotation properties of a He-star companion in SNe Iax. We find that the He-star companion spins down after the impact due to the angular-momentum loss and expansion caused by the mass-stripping and shock heating during the interaction. This leads to the situation where the surface rotational speed of the surviving companion can drop to one-third of its pre-explosion value when it expands to a maximum radius a few years after the impact. Subsequently, the star shrinks and spins up again once the deposited energy is released. This spin-switching feature of the surviving He-star companions of SNe Iax may be useful for the identification of such objects in future observations.

Topological phases and collective modes in U(1) and SU(2) sectors of spin-orbit-coupled two-dimensional superfluid Fermi gases

We study the emergence of finite-temperature topological phase transitions of the Berezinskii-Kosterlitz-Thouless type and the collective mode spectrum of two-dimensional Fermi gases in the presence of attractive $s$-wave interactions, spin-orbit coupling, and Zeeman fields. We show that neglecting the spin-dependent phase shift on the fermionic wave function misses an important point. Including this spin-dependent shift, we derive the effective low-energy and long-wavelength quantum action for independent (unlocked) phase fluctuations in the U(1) (charge) and SU(2) (spin) sectors and show that at least two phase transitions occur because charge and spin degrees of freedom are coupled due to the presence of spin-orbit and Zeeman fields. Furthermore, we demonstrate that vortex and antivortex excitations are characterized by two topological quantum numbers, corresponding to the quantized circulation of charge and spin velocities. Finally, we show that there are two collective modes in the superfluid phase at low temperatures which arise due to the coupling between sound and transverse-spin waves.

Spin acceleration mechanism for wave energy converter using gyroscopic effect and geared feedback

To realize a small-sized floating-type wave energy converter, a vibrational power generator that uses the gyroscopic effect and a geared acceleration mechanism is presented. First, equations of motion for the spin acceleration mechanism are derived. Next, numerical analyses are presented to show that the spin velocity of the gyro-flywheel is accelerated or decelerated by the rotating vibration, and the convergent power generations at various vibration frequencies are calculated. In addition, a simple equation that expresses the relationship between the vibration and equipment parameters and the convergent power generation is derived. The result shows that the generated power is 10W when the flywheel diameter is 600mm, the weight is 20kg, the input frequency is 0.2Hz, and the amplitude is 10°. Finally, an experimental apparatus with a spin acceleration mechanism containing a flywheel 300mm in diameter is fabricated to show that the experimental and calculated steady-state spin and precession velocities agree when the vibration period is 1.5 and 2.0s

Nonlocal vibration analysis of spinning nanotubes conveying fluid in complex environments

In the current paper, hygro-thermo-magnetically induced vibrations of small-scale viscoelastic tubes containing flow with a spin motion under gravity and tangential loads are analyzed by including surface effects. The dynamic equations are derived in the framework of the modified nonlocal elasticity theory (NET) and Rayleigh beam model. The Galerkin method and Laplace transformation are implemented to solve model equations. Vibration frequencies, stability boundaries, and Campbell diagrams of the system are acquired. Impacts of influential parameters such as scale rotary inertia factor, scale parameter, viscoelastic materials, gravity and tangential loads, flow and spin velocities, geometrical properties, and environmental conditions on the stability of the structure are examined. Also, the obtained results are compared for the Rayleigh and Euler-Bernoulli (EB) beam models. The golden results of this work are that by fine-adjusting the scale parameter and magnetic intensity in the system, destructive effects of hygro-thermal loads can be dampened. Besides, the increment of the rotary inertia factor and nanotube thickness induces destabilizing effect on the system.

Contribution of the spin velocity to a case of magnetic levitation

The concept of induced spin velocity is used to study a case of magnetic levitation in a device containing spinning and rotating magnets. Its background theory belongs to the geometry of curves in 3-dimensional Euclidean space and it is expressed in terms of the curvature and torsion of the trajectory. In the mechanical applications, spin velocity concept is useful, since spin velocities are induced in non-inertial frames and they transform using Galilean instead of Lorentz transformations. We describe a configuration of spinning and orbiting magnets similar to rolling bearings, and give conclusions about the electromotive force and the angular velocity, of the magnetized levitating parts.

Study on Gear-Driven Gyroscopic Power Generator

To realize a small-sized floating-type wave energy converter, a vibrational power generator that utilizes the gyroscopic effect and a geared acceleration is presented. First, equations of motions of the spin accelerating mechanism are derived. Next, it is shown by the numerical analyses that the spinning velocity of the gyro-flywheel is accelerated by the rotating vibration, a steady-state small vibration with the frequency twice the input frequency exists in the flywheel spin, and the generated power is 10 W at the conditions that the flywheel diameter is 600 mm, the weight is 20 kg, the input frequency is 0.2 Hz and the amplitude is ±10 deg. Finally, an experimental apparatus of the spin accelerating mechanism with a flywheel of φ300 mm is developed to show that the experimental and calculated spin and precession velocities agree well.

Investigating friction spin welding of thermoplastics in shear joint configuration

The welding of thermoplastic pipes under a shear joint configuration using friction spin welding is investigated. The shear joint configuration consists of two cylindrical and concentric polypropylene plastic parts joined with each other at their interfacing cylindrical surfaces through frictional heat generation. The effects of welding pressure and rotational velocity on the joint overlap distance and joint strength between the parts of polypropylene plastic are evaluated. The study is of a specific application in making plastic pressure vessels and joining of pipes. The joint strength is tested by conducting the hydraulic pressure burst test. The burst test is conducted for welded specimens manufactured using different values of rotational velocity and welding pressure. It is observed that at the constant spin velocities, the welding pressure in the range 64.8 to 65.2 kPa produced better joint strength than the other values of welding pressure in the overall range 64–76 kPa. It is concluded that the suitable welding pressure range to manufacture polypropylene plastic pressure vessels in the shear joint configuration using friction spin welding is 64.5 to 65.2 kPa. Further, it is established that the user can control the joint overlap distance at 64.8 kPa welding pressure by selectively controlling the rotational velocity in the range of 700 to 2500 rpm.

Hygro–thermo–magnetically induced vibration of nanobeams with simultaneous axial and spinning motions based on nonlocal strain gradient theory

In this paper, based on the nonlocal strain gradient theory (NSGT), the coupled vibrations of nanobeams with axial and spinning motions under complex environmental changes are modeled. A detailed parametric investigation is also performed to determine the effect of size-dependent parameters, boundary conditions, hygro–thermo–magnetic loads, axial and spin velocities on the dynamical behavior and stability regions of the system. Adopting the Galerkin discretization technique, the eigenvalue problem is solved, and natural frequencies, divergence and flutter instability thresholds of the system are extracted accordingly. The acquired outcomes are compared with the reported results in the literature. Besides, the accuracy of the numerical method is compared with analytical approaches and a good agreement is observed. The obtained results demonstrate that considering the nonlocal and hygro–thermal effects in modeling has destabilizing impacts on the dynamical response of the system. While imposing the strain gradient term and magnetic field leads to the enhancement of vibrational frequencies and enlargement of stability areas. In addition, it is concluded that in hygro–thermal environments, by ascending the spin velocity, instead of the occurrence of divergence instability, the system experiences the flutter conditions. Meanwhile, the attained outcomes indicated that the variation of spin velocity does not affect the flutter instability threshold of the system.

As the Worlds Turn: Constraining Spin Evolution in the Planetary-mass Regime

Abstract To understand how planetary spin evolves and traces planet formation processes, we measure rotational line broadening in eight planetary-mass objects (PMOs) of various ages (1–800 Myr) using near-infrared high-resolution spectra from NIRSPEC/Keck. Combining these with published rotation rates, we compile 27 PMO spin velocities, 16 of which derive from our NIRSPEC/Keck program. Our data are consistent with spin velocities v scaling with planetary radius R as v ∝ 1/R. We conclude that spin angular momentum is conserved as objects cool and contract over the sampled age range. The PMOs in our sample spin at rates that are approximately an order of magnitude below their break-up values, consistent with the hypothesis that they were spun down by magnetized circum-PMO disks (CPDs) during the formation era at ages ≲a few Myr. There is a factor of 4–5 variation in spin velocity that has yet to be understood theoretically. It also remains to be seen whether spin evolves on timescales ≳1 Gyr for PMOs, as it does for stars and high-mass brown dwarfs emitting magnetized winds.

Dynamical stability of embedded spinning axially graded micro and nanotubes conveying fluid

ABSTRACT In this study, the dynamical stability of spinning axially graded micro and nanotubes transporting fluid rested on the Kerr foundation is analyzed. A detailed parametric study is performed to clarify the effect of various factors such as axial material gradation and size-dependent parameters on the divergence and flutter instability thresholds of the system. To model the micro and nanofluidic systems, modified couple stress theory (MCST) and nonlocal strain gradient theory (NSGT) are implemented, respectively. The backward and forward vibrational frequencies, as well as critical divergence spin and fluid velocities of the system, are obtained. It is concluded that the stability evolution of spinning micro and nanostructures containing fluid can be altered by fine-adjustment of axial material gradation. Besides, it is found that the enhancement of elastic modulus gradient, strain gradient, material length scale, and foundation parameters improve the dynamical stability of the small-scale structures.

Vibration of viscoelastic axially graded beams with simultaneous axial and spinning motions under an axial load

For the first time, the structural dynamics and vibrational stability of a viscoelastic axially functionally graded (AFG) beam with both spinning and axial motions subjected to an axial load are analyzed, with the aim to enhance the performance of bi-gyroscopic systems. A detailed parametric study is also performed to emphasize the influence of various key factors such as material distribution type, viscosity coefficient, and coupled rotation and axial translation on the dynamical characteristics of the system. The material properties of the system are assumed to vary linearly or exponentially in the longitudinal direction with viscoelastic effects. Adopting the Laplace transform and a Galerkin discretization scheme, the critical axial and spin velocities of the system are obtained. An analytical approach is applied to identify the instability thresholds. Stability maps are examined, and for the first time in this paper, it is demonstrated that the stability evolution of the system can be altered by fine-tuning of axial grading or viscosity of the material. The variation of density and elastic modulus gradient parameters are found to have opposite effects on the divergence and flutter boundaries of the system. Furthermore, the results indicate that the destabilizing effect of the axial compressive load can be significantly alleviated by the simultaneous determination of density and elastic modulus gradation in the axial direction of the system.

Vibration of spinning functionally graded nanotubes conveying fluid

As a first attempt, the vibration and stability analysis of magnetically embedded spinning axially functionally graded (AFG) nanotubes conveying fluid under axial loads is performed based on the nonlocal strain gradient theory (NSGT). A detailed parametric investigation is conducted to elucidate the influence of key factors such as material distribution type and size-dependent parameters on the divergence and flutter instability borders. Also, a comparative study is conducted to evaluate the available theories in the modeling of nanofluidic systems. The material characteristics of the system are graded along the longitudinal direction based on the power-law and exponential distribution functions. To accurate model and formulate the system, the no-slip boundary condition is considered. Adopting the Laplace transform and Galerkin discretization technique, the governing size-dependent dynamical equations of the system are solved. The backward and forward natural frequencies, as well as critical fluid and spin velocities of the system, are extracted. Besides, an analytical approach is applied to identify the instability thresholds of the system. Dynamical configurations, Campbell diagrams, and stability maps are analyzed. Meanwhile, it is concluded that, in contrast to the influence of nonlocal and density gradient parameters, the increment of strain gradient and elastic modulus gradient parameters expands the stability regions and alleviate the destabilizing effect of the axial compressive load.

Numerical simulation of ball-pitch impact in cricket

Pitch conditions provide very important inputs that determine the flight and spin of the cricket ball before it reaches the batsman in the game of cricket. Due to insufficient understanding of the factors that influence the playing quality of the pitch, dependence upon experience or using some thumb rule remains the only option. This study uses numerical tools to understand the different parameters influencing the impact between cricket ball and pitch. Pitch is modelled as two-layer composite of top clay-soil foundation. Numerical simulation is used in the present work to study the variation of ball flight parameters such as rebound velocities, exit spin velocities, rebound angle on different surface conditions of the pitch.

Experimental analysis of the spin–orbit coupling dependence on the drift velocity of a spin packet

Spin transport was studied in a two-dimensional electron gas hosted in a wide GaAs quantum well occupying two subbands. Using space and time Kerr rotation microscopy to image drifting spin packets under an in-plane accelerating electric field, optical injection and detection of spin polarization were achieved in a pump–probe configuration. The experimental data exhibited high spin mobility and long spin lifetimes allowing us to obtain the spin–orbit fields as a function of the spin velocities. Surprisingly, above moderate electric fields of 0.4 V/cm with velocities higher than 2 µm/ns, we observed a dependence of both bulk and structure-related spin–orbit interactions on the velocity magnitude. A remarkable feature is the increase in the cubic Dresselhaus term to approximately half of the linear coupling when the velocity is raised to 10 µm/ns. In contrast, the Rashba coupling for both subbands decreases to about half of its value in the same range. These results yield new information on the application of drift models in spin–orbit fields and about limitations for the operation of spin transistors.

Steady flow in a rapidly rotating spheroid with weak precession: I

The celebrated Poincaré (1910) steady solution, the uniform vorticity flow in a precessing spheroid, which is realized in the inviscid interior region outside the boundary layer in the strong spin and weak precession limit, is derived, as a unique solution analytically without any prior assumption on the spatial structure, and its singular behavior for a sphere is resolved. Assuming that the spin and precession axes are respectively parallel and perpendicular to the symmetry axis of the spheroid, we denote the spin and precession angular velocities by and respectively, and define the Reynolds number Re = and the Poincaré number , where a is the equatorial radius and ν is the kinematic viscosity of fluid. An ellipsoidal coordinate system is introduced, which makes it possible to express the solution explicitly in a separable form. It is shown that only the uniform vorticity flow can develop as a steady flow in the inviscid limit. The vorticity, relative to the spinning spheroid, is in magnitude and points to or against the z-axis for an oblate (c < 1) or a prolate (c > 1) spheroid. This expression of vorticity magnitude diverges to infinity for a sphere (c = 1), where the inviscid solution is degenerate. This apparent singular behavior of the vorticity is resolved by introducing viscosity and analyzing the flow by invoking the torque balance equation for a spheroid close to a sphere in the limit , where . It is found that the vorticity vector changes the orientation smoothly by 180° over and that the parallel and the perpendicular (to the spin axis) components of vorticity is expressed, up to the nontrivial leading order, as the twice of −0.7876Po2/[(2.620δ)2 + (0.2585δ + 1 − c)2] and , respectively. The latter is included in Busse ()'s formula, whereas the former is new. An analysis of the same flow as the present paper from a different approach was performed recently by Zhang et al (). Unfortunately, however, an inconsistency is found in their results.

Modeling the Formation of the Family of the Dwarf Planet Haumea

Abstract The dwarf planet (136108) Haumea has an intriguing combination of unique physical properties: near-breakup spin, two regular satellites, and an unexpectedly compact family. While these properties point toward formation by a collision, there is no self-consistent and reasonably probable formation hypothesis that can connect the unusually rapid spin and low relative velocities of Haumea family members (“Haumeans”). We explore and test the proposed formation hypotheses (catastrophic collision, graze-and-merge, and satellite collision) in detail. We flexibly parameterize the properties of the collision (e.g., the collision location) and use simple models for the unique three-dimensional velocity ejection field expected from each model to generate simulated families. These are then compared to the observed Kuiper Belt objects using Bayesian parameter inference, including a mixture model that robustly allows for interlopers from the background population. After testing our methodology, we find that the best match to the observed Haumeans is an essentially isotropic ejection field with a typical velocity of 150 m s−1. The graze-and-merge formation hypothesis—in which Haumeans are shed due to excess angular momentum—is clearly disfavored because the observed Haumeans are not oriented in a plane. The satellite collision model is also disfavored. Including these new constraints, we present a detailed discussion of the formation hypotheses, including variations, some of which are tested. Some new hypotheses are proposed (a cratering collision and a collision where Haumea’s upper layers are “missing”) and scrutinized. We do not identify a satisfactory formation hypothesis, but we do propose several avenues of additional investigation. In the process of these analyses, we identify many new candidate Haumeans and dynamically confirm seven of them as consistent with the observed family. We also confirm that Haumeans have a shallow size distribution and discuss implications for the discovery and identification of new Haumeans.

Application of the geometry of curves in Euclidean space

In this article the so called induced spin velocities are studied, and it is an improvement of the paper [13] using the geometry of curves in 3-dimensional Euclidean space. Some essential properties of them are given, and they are rather different than the ordinary velocities. Indeed, the induced spin velocities are non-inertial and instead of the Lorentz transformations for them the Galilean transformations should be used. The induced spin velocity is derived in terms of the curvature and torsion of the trajectory. Two applications of the induced spin velocities are studied.

Physical process of tidal synchronization and orbital circularization in rotating binaries

The tide is a very important physical factor which can significantly affect the structure and evolution of stars. The physical factors which can affect tidal synchronization and orbital circularization are explored in this paper. For stars with radiative envelopes, radiative damping mechanism is required to explain the observed synchronization and circularization of close binaries. A star can experience a range of oscillations that arise from, and are driven by, the tidal field:the dynamical tides. The dynamical tide is the dynamical response to the tidal force exerted by the companion; it takes into account the elastic properties of the star, and the possibilities of resonances with its free modes of oscillation. The dissipation mechanism acting on this kind of tide is the deviation from adiabaticity of the forced oscillation, due to the radiative damping. Several physical factors can have an influence on the process of radiative damping which is scaled with thermal timescale. These physical factors include stellar mass, initial velocity, orbital period, metallicity, overshooting, etc. According to the equations for angular momentum transfer and chemical elements diffusion, we can obtain how these physical factors affect the evolution of rotating binaries and the mixing of chemical elements in two rotating components. The results indicates that the binaries with massive stars, smaller initial spin velocities, smaller overshooting parameters, and shorter orbital periods can attain the equilibrium speed and orbital circularization early. At synchronous states, the tidal torque is zero and stellar winds continue to brake the star. Therefore, two components cannot keep the synchronous state for a long time. At the equilibrium state, the tidal torque is counteracted by wind torques. Therefore, the equilibrium speed is less than the synchronous one. The system with smaller initial spin velocities reaches the equilibrium speed and orbital circularization early because angular momentum transformation between spin and the orbit can shorten the orbital distance and increase the tidal torques. Nitrogen enrichment in binaries is weaker than the one in single stars due to tidal braking. The results reveal that the system with massive components, higher metallicities, larger overshooting parameters, and shorter orbital periods can display high nitrogen enrichment. Stellar radius is small in the star with lower mass, lower metallicities, slower spin speeds and larger overshooting parameters whereas the star with lower metallicities have higher surface effective temperature. Rapid rotating stars evolve towards low temperature and luminosity in the HR diagram.