Dynamics of a nonmagnetic drop suspended in a magnetic fluid in a rotating magnetic field

The behavior of a nonmagnetic drop suspended in a magnetic fluid and subjected to the action of a rotating magnetic field is studied experimentally. The configurations of the drop in the form of prolate and oblate ellipsoids of revolution in the rotating field are investigated, and disintegration of the drop in the rotating field and the development of comb instability of its surface under certain conditions are observed.     

Capillary oscillations and stability of a charged drop rotating about the axis of symmetry

The stability of a charged conductive liquid drop rotating about the axis of symmetry against the pressure of the self-charge electric field and inertial force pressure is investigated in an approximation linear in oscillation amplitude and square of the spheroidal drop deformation eccentricity. It is found that the axisymmetric modes of the rotating drop are stable. Only nonaxisymmetric modes with azimuthal numbers maximal for a given mode may be unstable. The Coriolis force plays a stabilizing role.     

Nonlinear analysis of the equilibrium shape of a charged conducting drop in an electrostatic suspension

An analytical asymptotic expression is derived that describes the equilibrium shape of a charged drop of an ideal incompressible conducting liquid suspended in superposed collinear uniform electrostatic and gravitational fields. The expression is obtained in an approximation quadratic in the small amplitude of deviation of the equilibrium drop from a sphere, with the electrostatic field dimensionless strength taken as a measure of the deviation amplitude. With allowance for the gravitational and electrostatic fields and interaction between the drop self-charge and external electrostatic field, the equilibrium shape of the drop is found to be very close to a spheroid when the charge and the electrostatic field strength are far from their critical values. The analysis is carried out with a refined procedure of calculation of the equilibrium shape of drops placed in external force fields.     

Nonlinear analytical calculation of the equilibrium shape of a charged drop uniformly accelerated in an electrostatic field

An analytical asymptotic expression for the equilibrium shape of a charged drop of an ideal incompressible conducting liquid uniformly accelerated in collinear electrostatic and gravitational fields is derived in an approximation quadratic with respect to the deviation of the equilibrium shape of the drop from a sphere. It is found that the equilibrium shape of the drop is close to a prolate spheroid when its self-charge and the external electric field strength are far from their values critical in terms of instability against the self-charge and induced charge. This spheroid experiences an insignificant pear-shaped distortion even when the charge of the drop and the electrostatic field strength are high.     

Spin-flip shot noise in a quantum dot coupled to carbon nanotube terminals responded by a rotating magnetic field

We have investigated the spectral density of shot noise of the system with a quantum dot (QD) coupled to two single-wall carbon nanotube terminals, where a rotating magnetic field is applied to the QD. The carbon nanotube (CN) terminals act as quantum wires which open quantum channels for electrons to transport through. The shot noise and differential shot noise exhibit novel behaviors originated from the quantum nature of CNs. The shot noise is sensitively dependent on the rotating magnetic field, and the differential shot noise exhibits asymmetric behavior versus source-drain bias and gate voltage. The Fano factor of the system exhibits the deviation of shot noise from the Schottky formula. The super-Poissonian and sub-Poissonian shot noise can be achieved in different regime of source-drain bias.     

The shape of a drop in a constant electric field

The variation of the shape of a drop immersed in an immiscible liquid under the action of an electric field is calculated. The charge is transferred both by ohmic current through the interface and by the convective component over the interface. A solution quadratic in the parameter that is the ratio of the electric pressure to the capillary pressure is analyzed. Conditions where the drop transforms into a spheroid that is prolate or oblate along the electric field vector are found. An experimental study of the drop deformation by electric forces is carried out.     

Three-lobed shape bifurcation of rotating liquid drops

The evolution of axisymmetric equilibrium shapes of a rigidly rotating liquid drop can be extended beyond the 2-lobed shape bifurcation point if the rotating drop is driven in the n = 2 axisymmetric shape oscillation (perturbation), where n is the mode of oscillation. A reason for the extended stability of the perturbed rotating drop is that the inertia of the driven axisymmetric shape oscillation suppresses growth of a natural nonaxisymmetric shape fluctuation which leads to the 2-lobed shape bifurcation. The axisymmetric shape of the drop eventually bifurcates into either a 2- or a 3-lobed shape at a higher bifurcation point which is asserted to be the 3-lobed shape bifurcation point.     

水平管内二氟乙烷两相流动摩擦压降实验研究

对制冷剂二氟乙烷(HFC-152a)在内径为8mm的水平管内进行了两相流动沸腾摩擦压降的实验测量.实验测量的压力范围为0.19—0.41MPa,热流密度范围为14—62kW/m2,流量范围为128—200kg/m2s.实验测量表明:HFC-152a的两相摩擦压降随质量流量、质量含气率的增大而增大;热流密度则对摩擦压降的直接影响很小,但通过影响两相流流型间接影响了摩擦压降;当流型由分层流动转变为半环状流或环状流时,总压降中加速压降所占比例有所减小,而摩擦压降所占比例则有所增大;摩擦压降随饱和压力的增大而减小.使用两个应用广泛的压降计算式进行了计算.实验测试结果与计算结果对比后发现,Friedel模型与实验结果偏差较大,而Müller-Steinhagen-Heck模型则与实验结果符合较好.     

Experimental study of the dynamic Newtonian field with a cryogenic gravitational wave antenna

We present an experiment performed to study the behaviour of the dynamic gravitational interaction at laboratory scale. We used as field generator a mass quadrupole rotating in the range of 460 Hz and we detected the acceleration field with the cryogenic gravitational wave antenna Explorer of the Rome group. We report the measurements of this interaction as a function of the distance between the field source and the detector. An upper limit on the parameters of a Yukawa-like potential, modeling an hypotetic deviation from the Newtonian law of gravity, is derived. Received: 14 June 1998 / Published online: 16 September 1998     

Magnetic fluid behavior in uniform DC,AC, and rotating magnetic fields

New flows and instabilities are demonstrated for magnetic fluids and by dual analogy to dielectric fluids. If a fluid drop is contained in a thin gap between two glass plates (Hele–Shaw cell) with a simultaneously applied in-plane rotating field and a DC axial field, smooth spirals or an abrupt transformation to many small droplets can occur. A preliminary minimum magnetization and surface energy analysis is presented to model the abrupt transformation in ferrofluids. An analysis of effective DC magnetoviscosity is also presented for planar Couette flow with an applied uniform DC field transverse to a duct axis with the effective magnetoviscosity and flow spin velocity calculated as a function of field strength. Related Couette viscometer measurements of ferrofluid viscosity show zero and negative magnetoviscosity values for rotating magnetic fields.     

Critical equilibrium spheroidal deformation of a drop of dielectric liquid in a uniform electrostatic field

The stability of a dielectric drop, which in an external electrostatic field takes on the equilibrium shape of a prolate spheroid, is analyzed using the principle of minimum total potential energy of an isolated system. The values of the Taylor parameter and degree of spheroidal deformation at which the drop loses stability are determined for a wide range of dielectric constants of the substance of the drop. Zh. Tekh. Fiz. 69, 23–28 (July 1999)     

非旋波近似中两能级原子与热库相互作用时原子的消相干特性

两能级原子与外部环境（热库）相互作用时,采用非旋波近似,研究原子与热辐射场单光子和双光子作用过程,利用小系统与库耦合行为的量子理论,计算原子约化密度矩阵非对角元,分析原子状态的消相干特性。     

Nonlinear analysis of the equilibrium shape of a charged drop rotating around its symmetry axis

From the condition of pressure balance on the free surface of a charged rotating conducting-liquid drop, an analytical expression for the equilibrium shape of the drop is derived in the second-order approximation in a small parameter, the ratio of the deformation amplitude to the radius of the initial spherical shape. It is found that, in the linear approximation in the small parameter, the drop takes the form of an oblate spheroid, while in the quadratic approximation, the equilibrium shape of the drop differs from the spheroidal one.     

Some laws of polarization and dispersion of a drop in an electrostatic field

The laws of distribution among contributions in various interactions to the total polarization energy of a conductor in a uniform electrostatic field was analyzed. It is shown that in a closed system, spontaneous shape variations of a liquid conductor with a free surface in an external magnetic field are possible only if they are accompanied by an increase in the conductor dipole moment. Variations of the intrinsic energy of a conductor are studied by the example of a conductive liquid drop in the case where a drop affected by a polarization charge becomes unstable. Analytical expressions defining the sizes and charges of the droplets ejected out of the initial drop under the conditions of instability are derived.     

Equilibrium shape and stability of a charged drop in an air flow under an electric field

The pressure balance on the surface of a charged liquid drop moving along a uniform electrostatic field is analyzed. The liquid is assumed to be nonviscous and incompressible. In the approximation linear in deformation amplitude, the equilibrium shape of the drop as a function of the charge, field strength, and velocity of travel can be both a prolate and an oblate spheroid. Critical conditions for the surface instability of such a drop are obtained analytically in the form of a relationship between the charge, field strength, and velocity of travel. An instability criterion is found by extrapolating to large Reynolds numbers. This makes it possible to fit the earlier model of a corona-initiated lightning in the vicinity of large charged water drops or hailstones to the charges of the drops, field strengths, and velocities of travel (relative to the medium) typical of thunderclouds.     

Near field acoustic solution of a rotating point source in frequency domain

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Calculation of the problem on a rotating flexible thread

A solution to the problem of a flexible thread rotating around a horizontal axis is presented. Dependences calculated in elementary functions with graphic applications are obtained for determining the parameters of the rotating thread, such as the thread-shape outline, the largest deviation from the axis, the values of curvature angles, and the thread tension, among others.     

Capillary disintegration of a suspended filamentary drop of a viscous magnetic fluid in a longitudinal magnetic field

A differential equation that describes the axisymmetric motion of two immiscible magnetic fluids of the same density and viscosity is derived. It includes in explicit form the contribution of capillary forces localized at the interface between the fluids, which has the form of a weakly distorted cylindrical surface. With this equation, a dispersion relation for the problem of capillary instability of an extended axisymmetric drop placed in a uniform longitudinal magnetic field is obtained. The effect of magnetic forces on the capillary disintegration of the drop for the extreme cases (large and small Ohnesorge numbers) is analyzed.     

Investigation of the shape and stability of a liquid drop on a rotating substrate

The shape and stability of a capillary-sized water drop sitting on a rotating substrate are studied both theoretically and experimentally. The theoretical and experimental data are found to be in good agreement. The results of the study may be used in fabricating self-assembled thin films by means of spin coating technology.