Spin Velocity Research Articles

A Novel Method to Constrain Tidal Quality Factor from A Nonsynchronized Exoplanetary System

We propose a novel method to constrain the tidal quality factor, Q′ , from an observed nonsynchronized star–planet system consisting of a slowly rotating low-mass star and a close-in Jovian planet, taking into account the coevolution of stellar spin and planetary orbit due to the tidal interaction and the magnetic braking. On the basis of dynamical system theory, the track of the coevolution of angular momentum from the fast-rotator regime for such a system exhibits the existence of a forbidden region in the Ωorb–Ωspin plane, where Ωspin and Ωorb denote the angular velocity of the stellar spin and planetary orbit, respectively. The forbidden region is determined primarily by the strength of the tidal interaction. By comparing the (Ωorb, Ωspin) of a single star–planet system to the forbidden region, we can constrain the tidal quality factor regardless of the evolutionary history of the system. The application of this method to the star–planet system NGTS-10–NGTS-10 b gives Q′≳108 , leading to a tight upper bound on the tidal torque. Since this cannot be explained by previous theoretical predictions for nonsynchronized star–planet systems, our result requires mechanisms that suppress the tidal interaction in such systems.

Non-Newtonian behaviors of ferrofluid Couette–Poiseuille flows in time-varying magnetic fields

We analyze the fully developed Couette–Poiseuille flows of ferrofluids between two parallel flat walls subject to three types of time-varying magnetic fields. In these scenarios, ferrofluids exhibit diverse non-Newtonian characteristics such as distinct flow velocity distribution, apparent viscosity and shear stress compared to ordinary Couette–Poiseuille flows. The influence of spin viscosity is explored first through the solution of the governing equations with zero and non-zero spin viscosities. It shows that although the value of the spin viscosity is very small, its inviscid limit would have great influence over the velocity and spin velocity distributions. The assumption of zero spin viscosity leads to an exaggerated non-Newtonian behavior induced by time-varying magnetic fields in the ferrofluid Couette–Poiseuille flows. Then the solutions of equations with non-zero spin viscosity are utilized to delve into non-Newtonian behaviors of ferrofluid Couette–Poiseuille flow under the application of the three time-varying magnetic fields. The results indicate that negative rotational viscosity will occur if the dimensionless frequency lies in the range 1–10, which is a distinguishing feature compared with Newtonian flows. At this point, non-Newtonian flow induced by magnetic field arises, although this effect is very tiny. Within the same frequency range, reversed tangential stress appears in strong uniform alternating magnetic fields. The minimum negative rotational viscosity may arrive at up to 20 % of the intrinsic viscosity in the rotating magnetic field when the magnetization relaxation time is 4 ms.

Time-periodic electrokinetic analysis of a micropolar fluid flow through hydrophobic microannulus

The oscillating aspects of pressure-driven micropolar fluid flow through a hydrophobic cylindrical microannulus under the influence of electroosmotic flow are analytically studied. The study is based on a linearized Poisson–Boltzmann equation and the micropolar model of Eringen for microstructure fluids. An analytical solution is obtained for the distributions of electroosmotic flow velocity and microrotation as functions of radial distance, periodic time, and relevant parameters. The findings of the present study demonstrate that, unlike the decrease in flow rate resulting from the micropolarity of fluid particles, velocity slip and spin velocity slip, when contrasted with Newtonian fluids, act as a counteractive mechanism that tends to enhance the flow rate. Additionally, the findings indicate that a square plug-like profile in electroosmotic velocity amplitude is observed when the electric oscillating parameter is low and the electrokinetic width is large, for both Newtonian and micropolar fluids. Moreover, in cases where there is a wide gap between the cylindrical walls and a high-frequency parameter, the electroosmotic velocity and microrotation amplitudes tend to approach zero at the center of the microannulus across all ranges of micropolarity and zeta potential parameters. Furthermore, it has been observed that the amplitude of microrotation strength rises as slip and spin slip parameters increase. Across the entire spectrum of micropolarity, the zeta potential ratio influences both the dimension and direction of the electroosmotic velocity profiles within the electric double layer near the two cylindrical walls of the microannulus. The study emphasizes the physical quantities by presenting graphs for various values of the pertinent parameters juxtaposing them with existing data in the literature and comparing them with the Newtonian fluids.Graphic abstract

Using a Sensor-Embedded Baseball to Identify Finger Characteristics Related to Spin Rate and Pitching Velocity in Pitchers.

Previous investigations have shown a positive relationship between baseball pitching velocity and the kinetic chain involved in pitching motion. However, no study has examined the influence of finger characteristics on pitching velocity and rate of spin via a sensor-embedded baseball. Twenty-one pitchers volunteered and were recruited for this study. An experimental baseball embedded with a force sensor and an inertial measurement unit was designed for pitching performance measurement. Finger length and strength were measured as dependent variables. Spin rate and velocity were independent variables. Pearson product-moment correlations (r) and intraclass correlation coefficients (ICCs) determined the relationship between finger characteristics and pitching performance. Finger length discrepancy, two-point pinch strength, index finger RFD (rate of force development), middle finger impulse, and force discrepancy had significant correlations with spin rate (r = 0.500~0.576, p ≤ 0.05). Finger length discrepancy, two-point pinch, three-point pinch strength, index and middle finger RFD, middle finger impulse, and force combination had significant correlations with fastball pitching velocity (r = 0.491~0.584, p ≤ 0.05). Finger length discrepancy, finger pinch strength, and pitching finger force including maximal force and RFD may be factors that impact fastball spin rate and fastball pitching velocity.

Impacts of activation energy and electroosmosis on peristaltic motion of micropolar Newtonian nanofluid inside a microchannel

This study investigates the impact of electroosmosis on the peristaltic flow of unsteady micropolar nanofluid with heat transfer. The findings could enhance the design of peristaltic pumps, potentially improving drug delivery systems, simulations of blood flow in medical devices, and cancer treatments. The fluid under investigation adheres to a micropolar model and flows through a microchannel that exhibits peristalsis along its walls. Moreover, the system is subjected to various external effects, including a uniform magnetic field, the electroosmotic phenomenon, heat absorption, and a chemical reaction with activation energy. Consequently, the problem is mathematically modulated by a system of nonlinear partial differential equations governing the velocity, temperature, and nanoparticle concentration. By employing wave transformation, these governing equations are reduced to ordinary differential equations (ODEs). The reduced equations were solved both analytically, using the homotopy perturbation method, and numerically, using the Runge–Kutta–Merson method. A comparison was made between the solutions, which were found to be closely aligned. Furthermore, a series of figures were employed to provide visual representation and discussion of the implications of the physical properties. The calculations reveal that the electroosmotic flow (EOF) enhances the axial flow of the micropolar fluid along the direction of the applied electric field. It is also observed that the increase in the activation energy (which indicates a low reaction rate) increases the concentration profile whereas the increase in the reaction rate parameter reduces the concentration profile. Additionally, the spin velocity of the particles is diminished by either an increase in the magnetic parameter or the coupling parameter.

Study on multifunctional resistive switching and UV light detection characteristics in p-PEDOT:PSS/i-BFO/n-ZnO hybrid structures

The present research work based on the newly prepared organic-inorganic hybrid heterostructure will be exploited to develop a multifunctional device including non-volatile resistance switching memory devices, and ultraviolet (UV) light detection behavior for the first time based on p-PEDOT:PSS/i-BFO/n-ZnO junctions. Using a spray pyrolysis technique, n-type zinc oxide (ZnO) and i-type bismuth ferrite (BiFeO3) thin film layers were prepared on the clean glass substrates at temperature 673 K. Using a spin coater method, the p-PEDOT:PSS were grown upon a bismuth ferrite (BiFeO3) thin film with a constant spin velocity of 2000 rpm and heated at 363 K. The current (I)–voltage (V), photoresponse characteristics and resistive switching (RS) behavior of the fabricated p-PEDOT:PSS/i-BFO/n-ZnO hybrid devices were carried out. The device shows high photoresponsivity (R) of 0.001 285 A W−1 and fast photoresponse switching speed with the measured rise and fall time of 493 and 970 ms respectively. Based on the electrical properties, a conductive filament formation/rupture mechanism is proposed to explain the observed RS characteristics.

Relaxation time for the alignment between quark spin and angular velocity in a rotating QCD medium

We compute the relaxation times for massive quarks and antiquarks to align their spins with the angular velocity in a rigidly rotating medium at finite temperature and baryon density. The rotation effects are implemented using a fermion propagator immersed in a cylindrical rotating environment. The relaxation time is computed as the inverse of the interaction rate to produce an asymmetry between the quark (antiquark) spin components along and opposite to the angular velocity. For conditions resembling heavy-ion collisions, the relaxation times for quarks are smaller than for antiquarks. For semicentral collisions, the relaxation time for quarks is within the possible lifetime of the QGP for all collision energies. However, for antiquarks, this happens only for collision energies sNN≳50 GeV. The results are quantified in terms of the intrinsic quark and antiquark polarizations, namely, the probability to build the spin asymmetry as a function of time. Our results show that these intrinsic polarizations tend to 1 with time at different rates given by the relaxation times with quarks reaching a sizable asymmetry at a faster pace. These are key results to further elucidate the mechanisms of hyperon polarization in relativistic heavy-ion collisions. Published by the American Physical Society 2024

Filamentary velocity scaling validation and spin dynamics in the DIII-D tokamak

Measured filament velocities in the DIII-D tokamak are compared against theoretical scalings, finding that the latter often represents an upper limit on experimental velocity distributions with most filaments possessing lower velocity. Filament spin from internal E × B drift is experimentally demonstrated to alter filament radial velocity. A critical spin velocity, where filament radial velocity peaks, is observed and corresponds to approximately 5 km/s. This transition is corroborated using a less direct measure of filament spin in the form of a temperature ratio. These techniques are combined to find that the critical spin velocity closely aligns with transport times along and across filaments becoming comparable. The normalized filament size distribution is consistent with the most stable size as dictated by Kelvin–Helmholtz and curvature-driven instabilities. Overall, the findings suggest filament stability and spin alter filamentary transport that may threaten the integrity of first walls in fusion devices.

Self-assembly of ferromagnetic particles into chains and spin under the control of traveling magnetic field

In this paper, the spin phenomenon of self-assembly of ferromagnetic particles to form particle chains under the action of a traveling magnetic field (TMF) is investigated, and a TMF generator is designed and fabricated to experimentally observe the self-assembly and spin phenomenon of ferromagnetic particles under the action of TMF. The TMF generator is capable of generating a TMF, which is an alternating motion magnetic field with sinusoidally varying and translating magnetic induction, under the action of which a chain of self-assembled ferromagnetic particles is subjected to an alternating magnetic force thereby generating a spin motion. By analyzing the spin mechanism of the self-assembled ferromagnetic particle chain, the relationship between the rotational velocity of the spin motion of the particle chain and the frequency of the three-phase AC power supply of the TMF generator was obtained. Adjusting the frequency of the three-phase AC power supply of the TMF generator can control the spin velocity of the particle chain. TMF generator enable ferromagnetic particles to self-assemble to form particle chains and drive the particle chains to spin controllably, which has a wide range of applications in micro-robotics, biomedicine, and microfluidics.

Neutron Star Kicks and Implications for Their Rotation at Birth

Neutron stars are born out of core-collapse supernovae, and they are imparted natal kicks at birth as a consequence of asymmetric ejection of matter and possibly neutrinos. Unless the force resulting from the kicks is exerted exactly at their center, it will also cause the neutron star to rotate. In this paper, we discuss the possibility that neutron stars may receive off-center natal kicks at birth, which imprint a natal rotation. In this scenario, the observed pulsar spin and transverse velocity in the Galaxy are expected to correlate. We develop a model of the natal rotation imparted to neutron stars and constrain it by the observed population of pulsars in our Galaxy. When considering a single-kick position parameter, we find that the location of the off-center kick is km at 90% confidence, and is robust when considering pulsars with different observed periods, transverse velocities, and ages. Nonetheless, the model encounters challenges in effectively fitting the data, particularly at small transverse velocities, prompting the exploration of alternative models that include more complex physics. Our framework could be used as a guide for core-collapse simulations of massive stars.

The role of thermal fluctuations in the motion of a free body

The motion of a rigid body is described in Classical Mechanics with the venerable Euler’s equations which are based on the assumption that the relative distances among the constituent particles are fixed in time. Real bodies, however, cannot satisfy this property, as a consequence of thermal fluctuations. We generalize Euler’s equations for a free body in order to describe dissipative and thermal fluctuation effects in a thermodynamically consistent way. The origin of these effects is internal, i.e. not due to an external thermal bath. The stochastic differential equations governing the orientation and central moments of the body are derived from first principles through the theory of coarse-graining. Within this theory, Euler’s equations emerge as the reversible part of the dynamics. For the irreversible part, we identify two distinct dissipative mechanisms; one associated with diffusion of the orientation, whose origin lies in the difference between the spin velocity and the angular velocity, and one associated with the damping of dilations, i.e. inelasticity. We show that a deformable body with zero angular momentum will explore uniformly, through thermal fluctuations, all possible orientations. When the body spins, the equations describe the evolution towards the alignment of the body’s major principal axis with the angular momentum vector. In this alignment process, the body increases its temperature. We demonstrate that the origin of the alignment process is not inelasticity but rather orientational diffusion. The theory also predicts the equilibrium shape of a spinning body.

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.

The electrokinetic flow of a micropolar fluid in a microtube with velocity and spin velocity slippage

This article examines a theoretical investigation of electrokinetic microstructure fluid flow in a circular microtube. It is based on a linearized Poisson–Boltzmann equation and a microstructure electrolyte of Eringen micropolar type. In our analysis, we assumed that the surface zeta potential was small due to the use of the Debye-Hückel approximation. The influences of velocity slip and spin velocity slip at the surface of the microtube, as well as overlapped electrical double layers are considered. The findings of the present study demonstrate that the micropolarity of fluid particles has a declining effect on volume transport, streaming potential, and energy transport efficiency, while velocity slip and spin velocity slip enhance these factors. It was found that when the ionic Péclet number decreases from 1 to 0.1, the volume transport decreases approximately 56%, the streaming potential decreases by around 334.6%, and the energy transport efficiency increases by approximately 88.2%. The physical quantities of this study are highlighted through graphs for different values of the relevant parameters and compared with the available data in the literature.

Spin Atomic Model: Role of Electron Spin in forming Atoms and Molecules

This paper recounts the history of atomic models and their limitations in brief. The role of spin motion of paired electrons in building the atoms is a subject of the discussion. The opposite spin velocity of paired electrons in an atom should reduce the repulsion between them. Hence, by adjusting their opposite spin velocity, the force of repulsion between the paired electrons and the force of attraction between the nucleus and the individual electrons in that pair can be balanced without revolving the electrons in orbits. In this way a pair of electrons can maintain their particular distance from the nucleus in atom with adjusting their spin motions. This arrangement easily supports the atoms to build the different molecules, compounds and solid materials. This atomic model may be referred as spin atomic model which should be the fact.

Effect of the Rotation and Inclined Magnetic Field on Peristaltic Slip Flow of a Bingham Fluid in Asymmetric Channel and Porous medium

This essay aims to describe the peristaltic behavior of Bingham's fluid in an asymmetric channel and porous material. The liquid is thought to flow in a porous media and be susceptible to a powerfully inclined magnetic field. The long wavelength dependency and low Reynolds number result in a major simplification of the nonlinear equations. The pressure gradient, pressure rise per wavelength, axial velocity, spin velocity, volume flow rate, and tilted magnetic number are all given specific attention. The findings reveal that rotation, density, permeability, coupling diversity, and non-dimensional wave amplitude all play significant roles in the phenomenon. With rising slip coefficient values and falling magnetic field strengths, permeability, and yield stress coefficients the trapped bolus grows in size

Optical and spin-selective time-of-flight measurement of light-induced desorption of Rb from Fe_3O_4 surfaces

Light-induced desorption of Rb atoms from a ferrimagnetic Fe_3O_4(001) surface was studied using a spin-selective optical method, which provides information on the spin polarization, velocity distribution, and amount of the desorbed atoms. The results showed that the intensity of the desorption of Rb from Fe_3O_4(001) induced by ultraviolet (UV) light irradiation was smaller than the detection limit at coverages lower than the threshold coverage at which the desorption rate began to increase. Moreover, the average magnetic quantum number of the desorbed atoms was smaller than that of electrons at the Fermi level of the Fe_3O_4(001) surface. These indicate that the light-induced desorption of Rb from an Fe_3O_4(001) surface occurs only in the high-coverage region in which the desorbing atoms are not in contact with the Fe_3O_4 surface, and that the desorption does not involve spin transfer.

Spin-velocity locking in a helical chain of atomic p± orbitals.

Observations of a high spin selectivity in various helical structures, which is called the chirality-induced spin selectivity, suggest a common mechanism originating from the helical geometry. In this paper, we consider a helical chain of atomic p± orbitals having the tangential angular momentum l = ±1. We show in this model that the coupling of l and the spin gives rise to spin-velocity locking, i.e., directions of spin and group velocity are parallel or antiparallel depending on the chirality of the helix, and consequently, an almost perfect spin selectivity in a specific energy region in a wide range of the curvature and the torsion of the helix. We find that the present spin-velocity locking originates from the helical symmetry in which the Hamiltonian is invariant with respect to a combined operation of the rotation around the helix axis and the translation along the helix axis. Therefore, we expect that spin-velocity locking occurs in a wide variety of helical structures.

Analysis of Joule Heating and Chemical Reaction Effects in Electroosmosis Peristaltic Transport of Couple-Stress, Micropolar and Nanofluids

Nanofluids have analysis of wide applications of energy technologies in recent times as the thermal amplification of several manufacturing industries. A mathematical model is developed to stimulate electrokinetic transfer through peristaltic pumping of couple-stress micropolar nanofluids in a microchannel. The effects of Joule heating and chemical reaction have been considered. The remarkable properties of nanofluid are demonstrated by thermophoresis and Brownian motion characteristics. Thermophoresis has relevance in mass transport processes in many higher temperature gradient operating systems. The highly non-linear partial differential equations into ordinary differential equations by using appropriate similarities transformations. The graphical estimates are presented for the axial velocity, spin velocity, temperature of nano fluid, concentration and pumping characteristics. The outcomes of this study reveal the activation of Joule heating and chemical reaction effects in electroosmosis peristaltic transport of couple-stress, micropolar and nanofluids. This model is applicable to the study of chemical fraternization/separation procedures and bio microfluidics devices for the resolution of diagnosis.

Pure spin current injection of single-layer monochalcogenides

We compute the spectrum of pure spin current injection in ferroelectric single-layer SnS, SnSe, GeS, and GeSe. The formalism takes into account the coherent spin dynamics of optically excited conduction states split in energy by spin–orbit coupling. The velocity of the electron’s spins is calculated as a function of incoming photon energy and angle of linearly polarized light within a full electronic band structure scheme using density functional theory. We find peak speeds of 520, 360, 270 and 370 Km s−1 for SnS, SnSe, GeS and GeSe, respectively which are an order of magnitude larger than those found in bulk semiconductors, e.g., GaAs and CdSe. Interestingly, the spin velocity is almost independent of the direction of polarization of light in a range of photon energies. Our results demonstrate that single-layer SnS, SnSe, GeS and GeSe are candidates to produce on demand spin-current in spintronics applications.

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.