共查询到20条相似文献,搜索用时 31 毫秒
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Optical tweezers have been successfully used in the study of colloid science. In most applications people are concerned with the behaviour of a single particle held in the optical tweezers. Recently, the ability of the optical tweezers to simultaneously hold two particles has been used to determine the stability ratio of colloidal dispersion. This new development stimulates the efforts to explore the characteristics of a two-particle system in the optical tweezers.An infinite spherical potential well has been used to estimate the collision frequency for two particles in the optical trap based on a Monte Carlo simulation. In this article, a more reasonable harmonic potential, commonly accepted for the optical tweezers, is adopted in a Monte Carlo simulation of the collision frequency. The effect of hydrodynamic interaction of particles in the trap is also considered. The simulation results based on this improved model show quantitatively that the collision frequency drops down sharply at first and then decreases slowly as the distance between the two particles increases. The simulation also shows how the collision frequency is related to the stiffness of the optical tweezers. 相似文献
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We consider the electric field of an induced dipole moment of a single small particle characterized by the absence of frequency dispersion of the permittivity and the field of a metal particle, which has frequency dispersion and is described in the free electron approximation taking into account the size effects of restriction of the electron free path. The influence of the induced field on the optical properties of a system of small particles is analyzed. It is shown that, for an ensemble of particles without frequency dispersion, the effective medium theory can be used up to concentrations corresponding to filling factors ? ≤ 0.52. In the case of metal particles, with frequency dispersion of dielectric functions and, especially, for the frequency range of the plasmon resonance, this theory can be used only for concentrations not exceeding the threshold ? ≈ 0.01. 相似文献
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B. A. Ivanov P. V. Bondarenko A. Yu. Galkin C. E. Zaspel D. D. Sheka 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(11):1494-1496
A low-frequency (the frequency ωVPM is in the sub-GHz range) mode exist for submicron magnetic particles in the vortex state. This mode corresponds to oscillations of the vortex center. The other modes form doublets with higher (several gigahertz) frequency and small (about ωVPM) splitting. Collective oscillations exist for lattices of such particles. The dependence of the frequency of these modes on the quasi-momentum can be nonanalytic. 相似文献
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《Physics letters. A》1998,239(6):378-384
The propagation of the dust ion acoustic and dust acoustic modes in a dusty plasma is studied. The effect of the coupling of the charge fluctuation on the dust particles to the modes is taken into account self-consistently. It is found that the charge fluctuation leads to frequency down shift as well as dissipation of the modes. For the dust ion acoustic modes, these are significant only when the frequency characterizing the rate of capture of electrons by the dust particles in the equilibrium state is of the order of the frequency of the mode, and the mode can propagate without significant dissipation only when its frequency is well above this characteristic frequency. For the dust acoustic modes, these are significant only when the frequency characterizing the rate of capture of ions by the dust particles in the equilibrium state is of the order of the frequency of the mode, and the mode can propagate without significant dissipation only when its frequency is well above this characteristic frequency. 相似文献
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二维频移激光多普勒测量油中悬浮粒子速度时,根据悬浮粒子通过针孔光阑时存在的四种不同情况,对原有激光多普勒测量悬浮粒子瞬时速度的方法进行了改进,提出一种悬浮粒子瞬时速度分析处理方法,利用该方法,对水平方管内的油中悬浮粒子的瞬时速度进行了测量分析。结果表明:改进方法获取的悬浮粒子瞬时速度的稳定性较好,能够表征在一组粒子通过激光多普勒的针孔光阑的时间段内粒子组随着时间的变化趋势,提高了频移激光多普勒采样数据的利用效率,有利于进一步准确表征悬浮粒子在油液中二维瞬时速度的分布特征和运动轨迹,为激光多普勒实验测量中悬浮粒子瞬时速度的表征提供理论支撑。 相似文献
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M. S. Veshchunov 《Journal of Engineering Thermophysics》2010,19(2):62-74
The traditional diffusion approach for calculation of the collision frequency function for coagulation of Brownian particles
is critically analyzed and shown to be valid only in the particular case of coalescence of small particles with large ones
and inapplicable to calculation of the coalescence rate for particles of comparable sizes. It is shown that coalescence of
Brownian particles generally occurs in the kinetic regime (realized under condition of homogeneous spatial distribution of
particles), however, the expression for the collision frequency function in the continuum mode of the kinetic regime formally
coincides with the standard expression derived in the diffusion regime for the particular case of large and small particles.
This explains the validity of the traditional form of the coagulation rate equation in a wide range of parameters, corresponding
to the continuum mode. Transition from the continuum to the free molecular mode can be described by the interpolation expression
derived within the new analytical approach with fitting parameters that can be specified numerically, avoiding semi-empirical
approach of existing models. 相似文献
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The possibility of the observation of Raman scattering resonances completely free from the influence of the Doppler effect has been examined for the first time. The phenomenon is based on the excitation of a Raman oscillation standing wave in a gas by two standing light waves, whose frequency difference is equal to half the Raman frequency. The complete compensation of Doppler shifts results from the simultaneous interactions between atomic particles and two pairs of counter-propagating waves. Doppler-free resonances of the second-order Raman light scattering appear in the number of particles excited to the upper Raman level and in the radiation at the Stokes and anti-Stokes frequencies. The amplitude estimate for the resonance in the number of particles is given for the example of neon. 相似文献
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In this Letter, the influence of dust particles on the plasma losses in a complex plasma afterglow is studied. It is shown that the dust particles can drastically shorten the plasma loss time by absorption-recombination onto their surfaces. The dust particle absorption frequency increases with the dust density but the dependence is not linear for high dust density. Finally, the possible use of dust absorption frequency measurements as a diagnostic for complex plasmas is mentioned and supported by comparison to existing experimental data. 相似文献
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G. S. Dragan 《Journal of Experimental and Theoretical Physics》2004,98(3):503-507
The frequencies of natural electroacoustic oscillations of aluminum oxide particles in a laminar disperse aluminum flame are determined experimentally using the capacitive method. A computational model is proposed for estimating the natural frequency of oscillations of charged particles in the smoky plasma taking into account the Doppler effect. It is shown that, for a natural frequency of oscillations of 51 kHz, two measured maxima at frequencies of 30 and 60 kHz in the oscillation spectrum correspond to the Doppler frequencies. 相似文献
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Possibilities to realize a negative refraction in chiral composites in dual-phase mixtures of chiral and dipole particles are studied. It is shown that because of a strong resonant interaction between chiral particles (helices) and dipoles, there is a stop band in the frequency area where the backward-wave regime is expected. The negative refraction can occur near the resonant frequency of chiral particles. Resonant chiral composites may offer a root to realization of negative-refraction effect and superlenses in the optical region. 相似文献
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Gomilšek M Seč D Skarabot M Ravnik M Zumer S Muševič I 《The European physical journal. E, Soft matter》2010,33(4):291-296
Laser tweezers have been used to drive the oscillations of a chain of entangled colloidal particles in the nematic liquid
crystal 5CB. The amplitude and phase of light-driven oscillations have been determined for the motion of individual colloidal
particles. The collective motion of 4.8μm silica particles is highly damped for a driving frequency above 0.5Hz. The results
were compared to an effective bead-spring model, where the motion of elastically coupled particles is hindered by viscous
damping and hydrodynamic coupling. Qualitative agreement between theory and experiment was obtained. 相似文献
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The radiation of a bunched beam of charged particles crossing the rectangular waveguide perpendicularly to its axis is considered. The emission spectrum is analyzed and it is shown that sharp peaks of quasicoherent radiation arise at the frequency of repetition of bunches and at its harmonics. It is shown that by measuring the center frequency of these peaks it is possible to determine the energy of charged particles in the bunches. 相似文献
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Experimental investigations of the average path length of oscillating dust particles inside a planar –type electric curtain (PTEC) are presented as a function of the frequency of the AC voltage. The frequency was adjusted within the range of 10–300 Hz. The oscillation paths of feldspar particles of diameter 40–60 μm inside a small cloud were recorded photographically. The main purpose of this investigation was to study the changes in average path length as a function of the supply voltage frequency. These results can be used to improve the precipitation and separation processes for charged dust particles inside a PTEC. 相似文献
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The fact that the concept of classical mass plays an important role in formulating relativistic theories of waves and particles is well-known. However, recent studies show that Galilean invariant theories of waves and particles can be formulated with the so-called ‘wave mass’, which replaces the classical mass and allows attaining higher accuracy of performing calculations [J.L. Fry and Z.E. Musielak, Ann. Phys. 325 (2010) 1194]. The main purpose of this paper is to generalize these results and formulate fundamental (Poincaré invariant) relativistic theories of waves and particles without the classical mass. In the presented approach, the classical mass is replaced by an invariant frequency that only involves units of time. The invariant frequencies for various elementary particles are deduced from experiments and their relationship to the corresponding classical and wave mass for each particle is described. It is shown that relativistic wave mechanics with the invariant frequency is independent of the Planck constant, and that such theory can attain higher accuracy of performing calculations. The choice of natural units resulting from the developed theories of waves and particles is also discussed. 相似文献
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Froth flotation for mineral beneficiation is one of the most important separation techniques; however, it has several challenges for processing fine and ultrafine particles. Attractive mineralization between particles and bubbles by ultrasonic standing wave (USW) is a novel and high-efficiency method that could assist fine particle flotation. Frequency is an important ultrasound parameter, whose effectiveness mechanisms on the attractive mineralization did not compressively address. This study explored the effect of the USW field with various frequencies on the fine coal flotation for filling this gap. Herein, a high-speed camera and a focused beam reflectance measurement (FBRM) were used to analyze three sub-processes of the attractive mineralization, including the microbubbles’ formation, the conventional flotation bubbles (CFBs)’ dispersion, and the particles’ movement. It was found that the maximum flotation metallurgical responses were obtained under the highest examined USW frequency (600 kHz). However, the flotation outcomes by a low USW frequency (50 kHz) were even lower than the conventional flotation tests. Observation and theoretical calculation results revealed these results were originated from the influence of frequency on the carrier bubbles’ formation and the action of the secondary acoustic force during USW-assisted flotation. These outcomes demonstrated that frequency is a key factor determining the success of attractive mineralization for fine particles’ flotation. 相似文献
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S. N. Starostenko K. N. Rozanov A. O. Shiryaev A. N. Lagar’kov A. N. Shalygin 《Physics of the Solid State》2017,59(11):2203-2210
The magnetic permeability of alsifer was restored from the frequency dependences of the dielectric and magnetic permeabilities of powder alsifer (AlSiFe alloy)–wax matrix composites. The permeabilities were measured using the coaxial line technique within a frequency range of 0.05–20 GHz. The effect of the concentration, shape, and size of powder particles on the microwave magnetic properties of composites was considered. A good agreement between the measurement results and the Maxwell–Garnett formula generalized with consideration for the particle shape, the percolation threshold, and the skin-effect was obtained. The found sizes of particles agreed with electron microscopy and granulometry data. Both the frequency and the ferromagnetic resonance line figure of merit (FOM) for lamellar particles proved to be higher than for spherical ones. Alsifer powders were shown to be promising fillers for radioabsorbing materials. 相似文献
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N. S. Ginzburg 《Optics Communications》1992,90(4-6):273-278
Superradiative instability developing in a cluster of electrons moving in an undulator field or in an electromagnetic pump wave field is considered. The instability is shown to have no threshold and the instability increment is estimated. The development of instability results in the bunching of particles in the cluster and their coherent radiation at frequencies nearly equal to the frequencies of individual radiation (scattering) of particles. When the translational velocity of the cluster is close to the velocity of light, the frequency of the high-frequency (HF) component of radiation (along the translational motion) may be much higher than the oscillation frequency of particles. 相似文献