Mass Current at a Domain Wall in Superfluid 3He A-Phase

In the superfluid ³He A-phase, the amplitude and direction of angular momentum by topological edge mass current coincide with the expected amplitude and direction of ground-state angular momentum by Cooper pairs. The topological mass current also flows at a domain wall in the A-phase, namely, an interface between the A-phases with the opposite direction of l-vector. We show that the amplitude of the topological mass current at the energetically favorable domain wall is almost equal to that at the specular edge; however, the topological mass current flows toward the opposite direction expected from angular momentum of Cooper pairs. Thus, the direction of topological mass current cannot be fixed only by the topological nature which is related to angular momentum of Cooper pairs.     

On the magnetic field acting upon moving domain walls in (Bi,Yb)3(Fe,Ga)5O12 garnet ferrite films

The dependence of the domain wall velocity V on the magnetic field strength H in (111)-oriented (Bi, Yb)₃(Fe,Ga)₅O₁₂ single crystal garnet ferrite films is studied by the method of pulsed remagnetization at the point of angular momentum compensation. It is established that the acting field strength H is decreased by an effective internal magnetic field existing in the films studied.     

Equivalent geometric transformations for spin and orbital angular momentum of light

We consider the analogous geometric transformations for spin and orbital angular momentum states of light. Spin angular momentum is manifested as polarization and its possible transformations are typified by those introduced by waveplates and the rotation associated with optical activity. Orbital angular momentum is associated with the mode structure of the beam and, while the action of a waveplate is similar to that of a mode converter, the equivalent analogue of optical activity is not obvious. We reason that the equivalent is a rotation of the transmitted image. We consider the extent to which an image orientation of this type might be achieved by a coherent fibre bundle, twisted around its central axis. The possibility of equivalents to the Kerr, Pockels and Faraday electro-optic effects for orbital angular momentum is raised.     

基于柔性补偿的带柔性铰空间机器人鲁棒控制

研究了载体位姿均不受控制的漂浮基带柔性铰空间机器人工作空间轨迹跟踪的鲁棒控制问题。利用系统动量、动量矩守恒关系及拉格朗日方法,导出了系统的动力学方程。考虑到空间机器人各关节铰往往具有较强的柔性,引入了一种关节柔性补偿控制器,以较好地补偿关节柔性对系统控制精度所带来的影响。之后结合奇异摄动技术,针对系统惯性参数存在不确定的复杂情况,提出了一种空间机器人工作空间期望运动轨迹跟踪的鲁棒控制方案。通过对一个平面带柔性铰空间机器人系统的数值仿真运算,证实了上述方法的有效性。     

Spin-to-orbit conversion at acousto-optic diffraction of light: conservation of optical angular momentum

Acousto-optic diffraction of light in optically active cubic crystals is analyzed from the viewpoint of conservation of optical angular momentum. It is shown that the availability of angular momentum in the diffracted optical beam can be necessarily inferred from the requirements of angular momentum conservation law. As follows from our analysis, a circularly polarized diffracted wave should bear an orbital angular momentum. The efficiency of the spin-to-orbit momentum conversion is governed by the efficiency of acousto-optic diffraction.     

Application of orbital angular momentum to simultaneous determination of tilt and lateral displacement of a misaligned laser beam

We present an analysis of the combined effects of tilt and lateral displacement on the orbital angular momentum spectrum of a laser beam. Our theory explains the symmetries and properties of the spectrum under the influence of misalignments. We apply the theory to establish a reliable and efficient method for determining and subsequently eliminating tilt and lateral displacement. An improved technique for obtaining the orbital angular momentum spectrum employing Laguerre-Gaussian modes is proposed. Finally, a numerical experiment is carried out to verify the method.     

Effects of free convection on the oscillatory flow of a polar fluid through a porous medium in the presence of variable wall heat flux

The purpose of this work is to study a laminar two-dimensional free convective oscillatory flow of an incompressible polar fluid through a saturated porous medium occupying a semi-infinite region of the space which is bounded by an infinite vertical permeable plate in the presence of oscillating suction and variable wall heat flux. The governing equations are based on the local volume averaging technique. The generalized Darcy equation accounting for polar effects is employed. Analytical expressions for the linear momentum, angular momentum, and energy fields are obtained by using the two-term perturbation technique. The numerically computed results are shown graphically and compared with the corresponding ones for a viscous (Newtonian) fluid. Distribution of the mean velocity of a polar fluid is found to increase as compared to the Newtonian fluid. The analysis reveals multiple boundary-layer structure for velocity. Published in Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 868–884, September–October, 2008.     

Quantisation of the free electromagnetic field implies quantisation of its angular momentum

It is shown that when the gauge-invariant Bohr–Rosenfeld commutators of the free electromagnetic field are applied to the expressions for the linear and angular momentum of the electromagnetic field interpreted as operators then, in the absence of electric and magnetic charge densities, these operators satisfy the canonical commutation relations for momentum and angular momentum. This confirms their validity as operators that can be used in quantum mechanical calculations of angular momentum.     

Implementing torsional-mode Doppler ladar

Laguerre-Gaussian laser modes carry orbital angular momentum as a consequence of their helical-phase front screw dislocation. This torsional beam structure interacts with rotating targets, changing the orbital angular momentum (azimuthal Doppler) of the scattered beam because angular momentum is a conserved quantity. I show how to measure this change independently from the usual longitudinal momentum (normal Doppler shift) and derive the apropos coherent mixing efficiencies for monostatic, truncated Laguerre and Gaussian-mode ladar antenna patterns.     

Derivation of the paraxial form of the angular momentum of the electromagnetic field from the general form

It is shown how the standard forms for the spin and orbital components of the angular momentum of a paraxial wave of electromagnetic radiation are obtained from general expressions for the angular momentum that have been derived recently. This result will enable general expressions for angular momentum to be applied with confidence to the many configurations of electromagnetic fields that are more complicated than plane or paraxial waves.     

Unconditionally stable algorithms for rigid body dynamics that exactly preserve energy and momentum

We show that, for rigid body dynamics, the mid-point rule formulated in body co-ordinates exactly conserves energy and the norm of the angular momentum for incremental force-free motions, but fails to conserve the direction of the angular momentum vector. Further, we show that the mid-point rule formulated in the spatial representation is, in general, physically and geometrically meaningless. An alternative algorithm is developed which exactly preserves energy, and the total spatial angular momentum in incremental force-free motions. The implicit version of this algorithm is unconditionally stable and second order accurate. The explicit version conserves exactly angular momentum in incremental force-free motions. Numerical simulations are presented which illustrate the excellent performance of the proposed procedure, even for incremental rotations over 65 degrees. The procedure is directly applicable to transient dynamic calculations of geometrically exact rods and shells.     

Magnetic and Electric Control of Circularly Polarized Emission through Tuning Chirality‐Generated Orbital Angular Momentum in Organic Helical Polymeric Nanofibers

Circularly polarized light emission promotes the development of smart photonic materials for advanced applications in chiral sensing and information storage. The orbital angular momentum is a unique property for organic chiral helical materials. In this work, a type of organic chiral polymeric nanowires is designed with strong chirality induced orbital angular momentum. Under the stimulus of an external magnetic field of 600 mT, circularly polarized emission from the chiral polymeric nanowire becomes more pronounced, where the g factor increases from 0.21 to 0.3. The observed phenomena mainly originate from the chirality‐dependent orbital angular momentum. Moreover, the orbital angular momentum in helical chiral nanowire structures can be suppressed by inhibiting electron transport in a helical way to diminish circularly polarized light emission at room temperature.     

Similarity solutions to rotating Couette flow with power law fluids

Summary The nonlinear rheological effects of a power law fluid in rotating Couette flow are addressed. The governing equations are derived and exact similarity solutions to the Cauchy problem for the angular velocity and shear stress distributions are shown and discussed. The case when the flow is generated by a line impulse of angular momentum is considered. The existence of a travelling wave solution for a shear thickening fluid is shown.     

An analysis of the angular momentum of a light field in terms of angular harmonics

Abstract

This paper proposes an optical interpretation for the Lie algebra's symmetry operators of the paraxial wave equation. In particular, the angular momentum operator is used to derive a relation for the expression of the angular momentum of an arbitrary light field in terms of angular harmonics. Furthermore, experimental results are presented demonstrating a filter that extracts angular harmonics from different Gauss-Laguerre modes.     

Transfer of orbital angular momentum from a stressed fiber-optic waveguide to a light beam

A stressed fiber-optic waveguide is used to impart orbital angular momentum to a Hermite-Gaussian (HG(10)) laser mode. The transmitted beam has an annular intensity profile and a well-defined azimuthal phase dependence. We confirm the phase structure of the beam by observing the interference pattern produced between it and a plane wave. The transfer of the angular momentum to the light occurs because of a difference in phase velocity within the fiber for two orthogonal modes that comprise the input beam. This represents a mechanism for the transfer of orbital angular momentum to a light beam that has not hitherto been identified.     

Stability of the entry flow rate of pulsating liquid in a tapered leaking elastic tube

Summary The two gas-kinetical simulation methods, the molecular dynamics method and the direct simulation Monte Carlo method, are used to calculate the Oseen vortex decay. The simulation solutions are compared with the analytical solution of the Navier-Stokes equation, this allowing examination of the influence of method-specific parameters on the simulation solution, particularly in relation to the conservation of angular momentum.The results obtained with the molecular dynamics method near the limit of the continuum-mechanical regime correlate very well with the analytical solution, the angular momentum being conserved exactly, due to the nature of the method. The direct simulation Monte Carlo method can also be used to simulate the vortex decay, provided that suitable parameters are selected. In this case, however, the angular momentum is not conserved exactly, due to the statistical assumptions. One of the objectives of this work is to optimize the Monte Carlo simulation method in relation to the conservation of angular momentum.With 10 Figures     

Controlled enhancement of spin-current emission by three-magnon splitting

Spin currents--the flow of angular momentum without the simultaneous transfer of electrical charge--play an enabling role in the field of spintronics. Unlike the charge current, the spin current is not a conservative quantity within the conduction carrier system. This is due to the presence of the spin-orbit interaction that couples the spin of the carriers to angular momentum in the lattice. This spin-lattice coupling acts also as the source of damping in magnetic materials, where the precessing magnetic moment experiences a torque towards its equilibrium orientation; the excess angular momentum in the magnetic subsystem flows into the lattice. Here we show that this flow can be reversed by the three-magnon splitting process and experimentally achieve the enhancement of the spin current emitted by the interacting spin waves. This mechanism triggers angular momentum transfer from the lattice to the magnetic subsystem and modifies the spin-current emission. The finding illustrates the importance of magnon-magnon interactions for developing spin-current based electronics.     

Quasi-Hermitian Hamiltonians,minimum-uncertainty (MU) angular momentum states and interferometers

Minimum-uncertainty (MU) angular momentum states which are eigenstates of a nonunitary angular momentum displacement operator are found also to be eigenstates of a quasi-Hermitian Hamiltonian which has a certain metric with real eigenvalues. Various properties of these states are discussed. The relations between electromagnetic (EM) MU angular momentum states which have been proposed for improving the resolution in interferometers and the present theory are discussed.     

Mixed convection boundary layer flow of a micropolar fluid along vertical cylinders and needles

An analysis is presented to investigate the effects of buoyancy and curvature on convection along vertical cylinders and needles placed in a micropolar fluid. The governing equations for momentum, angular momentum and energy are solved numerically by finite difference scheme. The heat transfer results are presented for a range of values of the buoyancy parameters, the curvature parameter and the material parameters of the fluid. The effect of the microrotation boundary conditions on heat transfer is discussed.     

Geometric phase in optics and angular momentum of light

Abstract

The Physical mechanism of the geometric phase in terms of angular momentum exchange is elucidated. It is argued that the geometric phase arising out of the cyclic changes in the transverse mode space of Gaussian light beams is a manifestation of the cycles in the momentum space of the light. The apparent non-conservation of orbital angular momentum in the spontaneous parametric down conversion for the classical light beams is proposed to be related to the geometric phase.