a绝对=a相对＋a牵连在动力学中的运用

凡惯性定律成立的参照系，叫做惯性系；惯性定律不成立的参照系，叫做非惯性系．牛顿第一定律和第二定律在非惯性系中是不适用的．因此，在研究动力学问题时通常应选择惯性系做为参照系．为了在非惯性系中仍能应用牛顿运动定律，往往需引入惯性力的概念．但如果不是使用惯性力的概念，而是同时考虑非惯性系的变速运动以及质点相对非惯性系的相对运动，则在惯性系中使用牛顿运动定律依然方便．     

Radiation Rate of a Two-Level Atom in a Spacetime with a Reflecting Boundary

We study a two-level atom in interaction with a real massless scalar quantum field in a spacetime with a reflecting boundary. We calculate the rate of change of the atomic energy for the atom. The presence of the boundary modifies the quantum fluctuations of the scalar field, which in turn modifies the rate of change of the atomic energy. It is found that the modifications induced by the presence of a boundary make the spontaneous radiation rate of an excited atom to oscillate near the boundary and this oscillatory behaviour may offer a possible opportunity for experimental tests for geometrical （boundary） effects in flat spacetime.     

Random Motion of a Charged Test Particle with a Constant Classical Velocity in a Spacetime with a Plane Boundary

We study the random motion of a charged test particle coupled to electromagnetic vacuum fluctuations near a perfectly reflecting plane boundary with a nonzero classical constant velocity in a direction parallel to the plane. We calculate the mean squared fluctuations in the velocity and position of the test particle taking into account both fluctuating electric and magnetic forces. Our results show that the influence of fluctuating magnetic fields is, in general, of the higher order than that caused by fluctuating electric fields and is thus negligible.     

Wavelength switching in a mixed structure of a long-period and a Bragg fiber gratings

We built a numerical model for evaluating the coupling processes of a mixed structure of a Bragg fiber grat-ing and a long-period grating. From the numerical results, we not only confirmed the wavelength switchingphenomena observed in previously reported experiments, but also discovered a new coupling mechanism,which generated the reflection of a signal with its wavelength longer than the Bragg wavelength. Thedependencies of the wavelength switching behaviors on various parameters of the mixed grating structure     

Generation of a Dark Hollow Beam inside a Cavity

A new method is introduced to generate a hollow beam inside a cavity.Using a matrix eigenvalue method,the laser resonator with optical diffraction elements is theoretically analysed and simulated.The hollow beam can be obtained theoretically by controlling the parameters of the diffraction functions.After designed the diffraction components in the cavity,a hollow beam of good quality is realized experimentally using a YAG solid state laser.     

Tunneling through a time-dependent barrier — a numerical study

We present a numerical investigation of quantum mechanical tunneling process in a double well potential with fluctuating barrier. The tunneling probability and rate are calculated for two cases in which (i) the height of the barrier is undergoing harmonic oscillation with frequency θ and (ii) the height of the barrier is undergoing random fluctuation with frequency θ. It is observed that in both cases, the quantum mechanical tunneling probability and rate exhibit a maximum as a function of the fluctuation frequency. The optimal frequency i.e. the frequency at which rate exhibits a maximum shows a strong isotopic mass effect.     

Thickness Determination for a Two-Layered Composite of a Film and a Plate by Low-Frequency Ultrasound

We present an ultrasonic method for determining the thickness of a composite consisting of a soft thin film attached to a hard plate substrate, by resonance spectra in the low frequency region, The interrogating waves can be incident only to the two-layered composite from the substrate side. The reflection spectra are obtained by FFT analysis of the compressive pulsed echoes from the composite, and the thicknesses of the film and the substrate are simultaneously inversed by the simulated annealing method from the resonant frequencies knowing other acoustical parameters in prior. The sensitivity of the method to individual thickness, its convergence and stability against experimental noises are studied, Experiment with interrogating wavelength 4 times larger than the film thickness in a sample of a polymer film （0.054mm） on an aluminium plate （6.24mm） verifies the validity of the method. The average relative errors in the measurement of the thicknesses of the film and the substrate are found to be -4.1% and -0.62%, respectively.     

MHD Boundary Layer Flow of a Non-Newtonian Fluid on a Moving Surface with a Power-Law Velocity

A theoretical analysis for MHD boundary layer flow on a moving surface with the power-law velocity is presented. An accurate expression of the skin friction coefficient is derived. The analytical approximate solution is obtained by means of Adomian decomposition methods. The reliability and efficiency of the approximate solutions are verified by numerical ones in the literature.     

Primary information sensors for AFM based on quasiparticle flows

A new class of experimental techniques is presented which allows the behavior of elementary collective excitations (quasiparticles) in solids to be studied at the mesoscopic scale. New experimental equipment is being constructed in the classical scheme of an atomic force microscope in which the sensor of primary information is a cantilever. The defining feature of the proposed sensor based on a cantilever is the addition of a generator and detector of quasiparticles to its design. The generator is located either on the tip of the cantilever or in close proximity to the needle on the cantilever, so that the flow of quasiparticles emitted by the generator propagates along the needle of the cantilever to the point where the needle tip touches the surface. The detector is located in a similar way. The measured quantity is the reflection coefficient of the flux of quasiparticles from the interface between the cantilever needle tip and the surface being scanned.     

A spectroscopic study of water-soluble pyronin B and pyronin Y in Langmuir-Blodgett films mixed with stearic acid

Mono and multilayer of water-soluble pyronin B (PyB) and pyronin Y (PyY) mixed with stearic acid (SA) have been incorporated in Langmuir-Blodgett (LB) films. The surface pressure-area (π-A) isotherm studies pointed out that pure PyB and PyY are incapable of forming stable films at air-water interface and collapsed readily at low surface pressures. However, mixture of PyB or PyY with SA easily formed stable films at the air-water interface and they were easily transferred onto solid substrates. The average area per molecule of mixed films of PyB and PyY at the air-water interface was observed to decrease with increasing concentrations of PyB and PyY. The spectroscopic characteristics of PyB and PyY in chloroform, in SA containing chloroform and in LB films have also been investigated by using absorption and steady-state and time-resolved fluorescence spectroscopy techniques. The morphology of the LB film surfaces has been characterized by using atomic force microscopy (AFM).     

Capillary Interactions between a Probe Tip and a Nanoparticle

To understand capillary interactions between probe tips and nanoparticles under ambient conditions, a theoretical model of capillary forces between them is developed based on the geometric relations. It is found that the contribution of surface tension force to the total capillary force attains to similar order of magnitude as the capillary pressure force in many cases. It is also shown that the tip shape and the radial distance of the meniscus have great influence on the capillary force. The capillary force decreases with the increasing separation distances, and the variance of the contact angles may change the magnitudes of capillary forces several times at large radial distances. The applicability of the symmetric meniscus approximation is discussed.     

Silicon surface passivation by static charge

A properly passivated silicon surface is chemically stable, and all interface properties are constant. The silicon dioxide layers fulfil the chemical stability requirements; however, their surface and interface charges have effect on the silicon surface potential barrier. Positive charge is usually assumed at the oxide-silicon interface, thus depletion or inversion layer develops in the case of p and accumulation in the case of n-type silicon.The surface of silicon dioxide can be charged macroscopically by corona charger or by conductive rubber stamp, microscopically by a tip of some scanning probe microscope (STM or AFM). The oxide surface usually retains the charges for a long time, however in the case of ultra-thin or other leaky oxide continuous charging it is necessary to keep the constant surface potential.The main purpose of this work is to summarize the possibilities of charging up the surface, the effect of the surface and interface charge on the surface properties of the silicon. The rearrangement of the surface charges will also be discussed.     

Specific ion adsorption at hydrophobic solid surfaces

Molecular dynamics simulations of ions at a hydrophobic self-assembled monolayer with polarizable force fields for water and ions are used to extract potentials of mean force for Na+ and the halide ions Cl-, Br-, and I-. Similar to the air-water interface, the large halide ions are attracted to the surface, which is traced back to surface-modified ion hydration. The total effective interaction is parametrized and used within Poisson-Boltzmann theory to calculate surface potentials and interfacial tensions at finite ion concentration in qualitative agreement with experiments.     

Study of Probe-Surface Interaction in Shear-Force Microscopy: Effects of Humidity and Lateral Spring Constant

The shear force between a glass probe and a mica surface has been investigated as a function of the relative humidity, H, and the lateral spring constant of the probe, K. It was found that the interaction length D_o decreases with increasing H and exhibits a sharp drop around H=40%. With increase in K from 5 to 40 N/m, D_o gradually increases, although this feature was absent when a probe with a softer tip-end was used. The latter result indicates that the shear force in an atmospheric condition is not a remote force but results from some contact between the tip and the surface. Our results that D_o is independent of the oscillating amplitude and that the resonance curve of the probe is almost symmetric except in close vicinity to the surface are not in accord with the force model proposed recently, i.e., the knocking mechanism. It is proposed that the probe can vibrate even if the probe touches the surface, and that the resonance frequency increases steeply as the contact tightens. Theoretical estimation of the contribution of noncontact forces is also described.This paper was originally presented at the seventh Meeting on Near Field Optics, which was held on July 1, 1998 at Nagoya University, Nagoya, organized by Research Group on Near Field Optics, the Optical Society of Japan, an affiliate of the Japan Society of Applied Physics.     

Stability criterions of an oscillating tip-cantilever system in dynamic force microscopy

This work is a theoretical investigation of the stability of the non-linear behavior of an oscillating tip-cantilever system used in dynamic force microscopy. Stability criterions are derived that may help to a better understanding of the instabilities that may appear in the dynamic modes, Tapping and NC-AFM, when the tip is close to a surface. A variational principle allows to get the temporal dependence of the equations of motion of the oscillator as a function of the non-linear coupling term. These equations are the basis for the analysis of the stability. One find that the branch associated to frequencies larger than the resonance is always stable whereas the branch associated to frequencies smaller than the resonance exhibits two stable domains and one unstable. This feature allows to re-interpret the instabilities appearing in Tapping mode and may help to understand the reason why the NC-AFM mode is stable. Received 12 April 2001     

Analysis of the number of hydrogen bond groups of a multiwalled carbon nanotube probe tip for chemical force microscopy

In this paper, we describe a statistical method of quantification of the number of functional groups at the contact area of a probe tip for atomic force microscopy from the result of repetitive pull-off force measurements. We have investigated laboratory-made carbon nanotube (CNT) probe tips to apply them for chemical force microscopy because limited number of functional groups at the tip-end is expected. Using a CNT tip, we conducted repetitive pull-off force measurements against a self-assembled monolayer terminated with carboxyl group and analyzed them in terms of the number of hydrogen bond groups at the CNT tip. The elementary hydrogen bond rupture force quantum in n-decane medium was estimated to be 84.2 ± 0.5 pN in the present system. Thus it was revealed that only a couple of hydrogen bond groups of the CNT tip were participating in hydrogen bonding with the sample on an average in this experimental system.     

Probing viscosity of a polymer melt at the nanometre scale with an oscillating nanotip

The Navier-Stokes equation is used to analyze the additional phase delay when an oscillating nanotip touches intermittently an entangled polymer melt. Even when the tip oscillates at frequencies of several hundred kilohertz, it is shown that the inertial contributions are negligible as long as the indentation depth is no more than a few ten nanometers. Consequently, a stationary solution can be used leading to the simple Stokes formula. Two simple geometries of the tip are investigated. A smooth tip apex with a spherical shape and an elongated tip apex that aims at mimicking a single asperity. The tip shape has a drastic influence on the measured viscosity at the local scale. A simple calculation indicates that the viscous force acting against the tip motion may exhibit several different behaviors as a function of the indentation depth. Using the variational principle of least action, we derive the corresponding phase variation of the oscillator as a function of the indentation depth. It is shown that there exist situations for which an absolute value of the local viscosity could be measured. Received 13 April 2001 and Received in final form 1 August 2001     

A study on the emulsification of oil by power ultrasound

A commercial ultrasonic probe was used to study emulsification of an o/w system (5 wt% soybean oil stabilised with 1 wt% Tween 80 in water). Two different sets of experiments were performed.

Firstly, we investigated the effect of power, duty cycle and ultrasound time on the production of an oil-in-water emulsion from a coarse pre-emulsion mix. The droplets reached a stable size (0.7 μm) within 5 min independent of the power and duty cycle used.

Secondly, the mechanism of emulsification was studied by observing the emulsification process at an oil–water interface (no pre-mix) with a high-speed camera. Transient cavitation is thought to be responsible for acoustic emulsification; however there have been no measurements to relate the transient cavitation zone to the production of an emulsion. It has already been shown that the transient cavitation in probe systems is directly under the probe tip. High-speed observations showed that an emulsion could only be obtained if the interface was within a few millimetres of the probe tip. These results strongly suggest that the transient cavitation zone is responsible for the acoustic emulsification of oil.