Kutta-Joukowski force expression for viscous flow

The Kutta Joukowski(KJ) theorem, relating the lift of an airfoil to circulation, was widely accepted for predicting the lift of viscous high Reynolds number flow without separation. However, this theorem was only proved for inviscid flow and it is thus of academic importance to see whether there is a viscous equivalent of this theorem. For lower Reynolds number flow around objects of small size, it is difficult to measure the lift force directly and it is thus convenient to measure the velocity flow field solely and then, if possible, relate the lift to the circulation in a similar way as for the inviscid KJ theorem. The purpose of this paper is to discuss the relevant conditions under which a viscous equivalent of the KJ theorem exists that reduces to the inviscid KJ theorem for high Reynolds number viscous flow and remains correct for low Reynolds number steady flow. It has been shown that if the lift is expressed as a linear function of the circulation as in the classical KJ theorem, then the freestream velocity must be corrected by a component called mean deficit velocity resulting from the wake. This correction is small only when the Reynolds number is relatively large. Moreover, the circulation, defined along a loop containing the boundary layer and a part of the wake, is generally smaller than that based on inviscid flow assumption. For unsteady viscous flow, there is an inevitable additional correction due to unsteadiness.     

Influence of ultrasonic vibration on friction force

1IntroductionTheinIluenceofultrasonicvibrationonfrictionforceekistswidelyinmanyfields,includingultrasonicprocessing,ultrasonicweldingandultrasonicmotor.Accordingtotheclassicalslidingfrictiontheoryfrictionforceonlydependsonloadandmaterialproperty-IthasbeenprovdexperimeDtallythatabovetheorycanonlybeusedforaPpr~ation.UndermaDyconditions,especiallyunderultrasonicvibration,colitactarea,vibrationamplitude,slldingvelocity)etc.,alsoinIluencethefrictionforce.Moreandmorescholarspayattelltiontotheindu…     

Δ contribution to the parity-violating nucleon-nucleon force

Because the nucleon may be excited and transformed into a virtual Δ resonance easily, we consider the decuplet contribution to the parity-violating (PV) nucleon-nucleon interaction in the chiral effective field theory. The effective PV nucleon-nucleon potential is derived without introducing any unknown coupling constants.     

Scanned-cantilever atomic force microscope with large scanning range

A scanned-cantilever atomic force microscope (AFM) with large scanning range is proposed, which adopts a new design named laser spot tracking. The scanned-cantilever AFM uses the separate flexure x-y scanner and z scanner instead of the conventional piezoelectric tube scanner. The closed-loop control and integrated capacitive sensors of these scanners can insure that the images of samples have excellent linearity and stability. According to the experimental results, the scanned-cantilever AFM can realize maximal 100×100 (μm) scanning range, and 1-nm resolution in z direction, which can meet the requirements of large scale sample testing.     

Optomechanical force gradient sensing with levitated nanosphere pair

Guided by recent progress in ground state cooling and ultraweak force sensing in the optomechanical systems with optically levitated particles,we propose a novel quantum sensing protocol that can detect the gradient of a force field directly with extremely high sensitivity.The system consists of a pair of nanospheres levitated in the high vacuum environment with optical tweezers and an optical resonator.By positioning the two spheres suitably relative to the cavity,only the collective breathing mode of the sphere pair couples to the cavity field.This optomechanical coupling will transfer the information of force difference acting on the two sensors to cavity photons,which can then be detected directly at the output of the cavity.Given the optimal control of various technical noise sources,the sensitivity could reach 10^-15N m^-1/√HZ with a high spatial resolution of micron scale on a state-of-the-art experimental setup.The potential application of this protocol in searching for short range“new force”is analyzed.Compared with conventional searching protocols with a single levitated sphere,the method proposed here can increase the signal-to-noise ratio by more than one magnitude in a large searching parameter space.     

Oscillatory disturbance in force calibration of optical tweezers

In the calibration of the optical trap stiffness, it is found that there appears an attenuating oscillation as an oscillatory disturbance added to the trapped bead movement, when the scanner is driven by a triangular wave input.An equivalent oscillator model is put forward to explain the mechanism of the oscillatory disturbance. Both the measurements and calculations show that the attenuating oscillation comes from the oscillation of the scanner and the triangular wave drive causes this additional oscillation of the scanner. Furthermore, the analysis indicates that the oscillatory disturbance will become stronger, when the stiffness of the trap increases or the natural frequency of the scanner decreases. We adopt another driving way, i.e. a sinusoidal wave input is used instead of the triangular wave input. Our experiment has verified that in this case the oscillatory disturbance is eliminated completely.     

Chirality-asymmetry force between ɑ-quartz and copper block

The chirality-asymmetry macroscopic force mediated by light pseudoscalar particles between α -quartz and some achiral matter is studied. If this force between achiral source mass and α -quartz with some chirality is attractive, it will become repulsive when the chirality of the α -quartz crystal is changed. According to the tested limits of the coupling constant g_s g_p /\hbar c< 1.5× 10^-24 at the Compton wavelength λ = 10^-3 m, the force (F) between a 0.08× 0.08× 0.002 m³ block of α -quartz and a 0.08× 0.08× 0.01 m³ copper block with a separation being 0.5× 10^-3 \mbox{m} in between, is estimated from the published data at less than 4.64× 10^-24 N, i.e. F < 4.64× 10^-24 N.     

Correlated Lvy flight in external force fields

The correlated Lvy flight is studied analytically in terms of the fractional Fokker-Planck equation and simulated numerically by using the Langevin equation,where the usual white Lvy noise is generalized to an Ornstein-Uhlenbeck Lvy process(OULP)with a correlation timeτc.We analyze firstly the stable behavior of OULP.The probability density function of Lvy flight particle driven by the OULP in a harmonic potential is exactly obtained,which is also a Lvy-type one withτc-dependence width;when the particle is bounded by a quartic potential,its stationary distribution has a bimodality shape and becomes noticeable with the increase of τc.     

Resonant gradient force on atom interacting with laser field

The gradient force, as a function of position and velocity, is derived for a two-level atom interacting with a standing-wave laser field. Basing on optical Bloch equations, the numerical solutions for the gradient force f⊥,n (n = 0,1, 2,3,4, …) pointing in the direction of the transverse of the laser beam are given. It is shown the higher order gradient force plays important role at strong intensity (G = 64), the contribution of them can not be neglected.     

Weak gravity-like force detector by “Atom interferometers”

We study nonlinear interaction of counter-propagating plane light waves in a semi-infinite isotropic lossless nonlinear Kerr medium and report existence of several regions of optical-polarization-multistability. The counter-propagating waves may be produced by normal reflection of an incident beam by a mirror in the nonlinear Kerr medium. We obtain nonlinear coupled differential equations for Stokes parameters of the two beams and solve them following the method of Prakash et al. [Mod. Phys. Lett. B 14, 47 (2000)] and the boundary conditions at the mirror. We find that, for the same incident intensity and for the same polarization state of the incident beam, output beam may exist in several stable polarization states.     

Methods of calibration to optical trapping force upon non-spherical cells

The dynamical equation of a trapping cell is solved to find calibration methods for the trapping force, and two methods are compared by synthetic experiment data. Results indicate that: Boltzmann distribution method (BDM) is available for the force calibration of non-spherical or anisotropic cells in arbitrary trap potential; the mean square displacement method (MSDM) is available only for a symmetric harmonic optical trap. The spatial resolution requirement of the calibration system is about a nanometer. The results agree with the reported experiments.     

A study of nanostructure magnetosolid Nd–Ho–Fe–Co–B materials via atomic force microscopy and magnetic force microscopy

Nanostructure Nd–Ho–Fe–Co–B alloys have been probed via atomic force microscopy and magnetic force microscopy (AFM and MFM, respectively). The ribbon samples with a thickness of ~30 μm are prepared via the rapid solidification on a rotating copper barrel. A part of samples has been subjected to hydration, whereas another one has undergone severe plastic deformation. AFM was mainly used to study the contact and free surface of ribbon samples. This has enabled us to establish the topography, structure, defects of both sides, morphology of magnetic inclusions of the initial quenched samples and the materials subjected to the subsequent external effects. The AFM and MFM data allowed the magnetic hysteresis properties of the bulk samples with the identical composition to be interpreted.     

S-ware πN scattering effects in the nuclear three-body force

We examine the contributions of the off-mass-shell,s-wave N scattering amplitude terms in the Tucson-Melbourne two-pion-exchange three-body force to the trion binding energy. While thea andc terms are not as important as thep-wave terms, they comprise a nonnegligible part of the three-nucleon force which produces nonperturbative effects in the triton wave function.     

Radiation force on a two-level atom with modulated excited state

The radiation force on a two-level atom with modulated excited state, interacting with a travelling wave, is calculated. The result shows that under appropriate conditions, the radiation force is much larger than spontaneous emission force and then it can be used in laser cooling with high efficiency.     

Padé approximation methods applied to the intermolecular force series

The H(1s)-H⁺, He-He, H(1s)-H(1s) and H(1s)-H(2s) interactions are considered as model systems for investigating the use of the Padé approximation method in summing the R ^-1 intermolecular force series. Various Padé approximants and partial sums of the R ^-1 expansions of the second-order Coulomb interaction energies are compared with the corresponding non-expanded results for each interaction. The computations are based on Unsöld's average energy approximation and on exact results for the H(1s)-H interaction. The results indicate that the Padé approximation method is a simple, useful way to remove some of the difficulties associated with the slow rate of convergence of the R ^-1 force series but that it does not alleviate the problems associated with the asymptotic divergent nature of the series. The results for the H(1s)-H⁺ interaction illustrate a possible difficulty in using Unsöld's method in the calculation of interaction energies.     

Evaluation and analysis of the radiation force in laser trap

Forces exerted on a small transparent dielectric sphere in a Gaussian beam is an-alyzed.The stable position of the sphere in the Gaussian beam was calculated.The effects ofthe sphere size,the beam radius etc.on the exerted forces,on the equilibrium positions aswell as on other parameters of the sphere are discussed.     

Radiative force on atoms from the view of photon emission

In this Letter, we present a possible methodology to directly “read” the force on an atom via the photons emitted from the atom. In this methodology, the mean radiative force on an atom exerted by external fields can be expressed as a function of the average number of emitted photons h N i and its derivatives via the generating function approach developed by us recently.