Predictions and detection of the “accommodation” forces on Janus particles subjected to directed radiation in a rarefied gas

The results of theoretical and experimental study of so-called “accommodation” forces acting on particles with artificial asymmetry of surface properties in rarefied gas in the directed radiation field are presented. The gas-kinetic theory of phenomenon in the free-molecular regime for some different types of boundary conditions of gas-surface interactions is developed. The theory predicts appearance of the unusual force caused by the difference of the normal momentum accommodation coefficients on hemispheres of considered model Janus particle. The measurements conducted by the experimental technique with macroparticles have confirmed the existence of the accommodation forces affecting a particle together with the forces of radiometric photophoresis. The experimental results for the system “steel particle-helium” are in good agreement with theoretical predictions, and the ratio of the “accommodation” forces to the photophoretic force does not exceed 3%. The estimations show that the “accommodation” forces can be comparable in some cases with the radiometric photophoretic forces for micron-sized particles in stratosphere, but do not exceed the gravity force. The action of “accommodation” forces, in our opinion, is not capable to provide effective vertical transport of aerosol particles against gravity at stratospheric altitudes.     

Study on cathode spot motion and macroparticles reduction in axisymmetric magnetic field-enhanced vacuum arc deposition

Cathode spot motion and macroparticles (MPs) reduction on related films are the two main issues in the application of the vacuum arc deposition (VAD). In the present work, an axisymmetric magnetic field (AMF) was applied to the cathode surface to investigate the influence of the AMF on the cathode spot motion and the MPs reduction on TiN films. The results show that the AMF affected the cathode spot motion by redistributing the dense plasma connected with the initiation of the new spot. With increasing AMF, there is an increasing tendency for the cathode spot to rotate and drift toward the cathode target edge. Based on the results of FEM simulation and the physical mechanism of the cathode spot discharge, the mechanism of the cathode spot motion in the AMF was discussed. The morphology, detailed size distribution, and roughness of the resultant TiN films were systematically investigated. Fewer and smaller MPs ejection is observed with an increase in the transverse component of AMF. The effect of the AMF on the MPs reduction on TiN films was discussed, and the results were compared with the theoretical predictions.     

Preparation and characterization of luminescent PbWO4 nano- and macrostructure

The PbWO₄ nano- and macroparticles with uniform size and shape have been synthesized via a wet chemical process in the presence of surfactant. The products were characterized by the techniques of X-ray diffraction (XRD) and transmission electron microscopy (TEM). Experiment results indicated that the surfactant poly(vinylpyrrolidone K30) (PVP) played a key role in the formation of the rhombic-shaped PbWO₄ macroparticles. A growth mechanism contributed to the formation of the well-fined PbWO₄ macroparticles was proposed. The luminescence properties of PbWO₄ nano- and macrostructure were investigated.     

Preparation and characterization of luminescent PbWO4 nano- and macrostructure

The PbWO₄ nano- and macroparticles with uniform size and shape have been synthesized via a wet chemical process in the presence of surfactant. The products were characterized by the techniques of X-ray diffraction (XRD) and transmission electron microscopy (TEM). Experiment results indicated that the surfactant poly(vinylpyrrolidone K30) (PVP) played a key role in the formation of the rhombic-shaped PbWO₄ macroparticles. A growth mechanism contributed to the formation of the well-fined PbWO₄ macroparticles was proposed. The luminescence properties of PbWO₄ nano- and macrostructure were investigated.     

Macroparticles monitoring for biocontamination prevention

This study investigated a potential correlation between deposited macroparticles?>5µm and bioaerosols. Bioaerosols were detected using both passive (culture plates) and dynamic sampling (biocollectors). Bioaerosols were then revealed visually on culture plates after incubation and counted in colony forming unit (CFU)/cm². Macroparticles were counted on line by CLEAPART-100 (patent CEA – Aix Marseille University – Winlight System). It enables continuous monitoring of the deposit of macroparticles on surfaces. We have shown that those macroparticles could be strongly correlated to viable particle measurements (bacteria and mould) after dynamic sampling by biocollectors. As viable particle measurements require an incubation period of at least 48 hours, it is easy to understand the advantage in continuous macroparticle done by CLEAPART-100. CLEAPART-100 is therefore an instrument which enables the alert to be raised in relation to any contamination or biocontamination events.     

非线性"转子-轴承-密封"系统动力分析

将非线性油膜力模型与密封流体Muszynska密封力模型相结合，建立了具有非线性转子-轴承-密封系统的动力学模型。针对转速等因素对耦合系统动态响应的影响进行了仿真计算，给出了系统响应随转子转速变化、压差变化和密封间隙变化的分叉图和最大Lyapunov指数曲线图，以及一些典型的Poincare截面图、轴心轨迹图和频谱图。数值仿真表明，非线性密封力抑制了系统出现倍周期分叉，并且该耦合系统呈现出复杂的动力学行为，产生了包括周期、倍周期和拟周期等丰富的振动现象。     

Wave radiation by a submerged source undergoing large amplitude periodic motion

Equations are derived to calculate the water waves radiation at infinity bya submerged source undergoing large amplitude motion. These equations do not require the full solution of the velocity potential itself, as demonstrated by a number of two- and three-dimensional examples. The results obtained are used to derive a far field equation for calculating the steady force (the drift force) on a submerged body undergoing large amplitude motion. It is concluded that the equations derived are useful to cases such as a deeply submerged body for which the source distribution may be taken as those obtained in an unbounded fluid domain.     

Aerodynamic forces and flow structures of an airfoil in some unsteady motions at small Reynolds number

Summary The aerodynamic forces and flow structures of a NACA 0012 airfoil in some unsteady motions at small Reynolds number (Re=100) are studied by numerically solving the Navier-Stokes equations. These motions include airfoil acceleration and deceleration from one translational speed to another and rapidly pitching up in constant freestream (equivalent to pitching up during translational motion at constant speed). It is shown that at small Reynolds number (Re=100), when the airfoil is performing fast acceleration or deceleration from one speed to another, a large aerodynamic force can be generated during and for a time period after the acceleration or deceleration; a large aerodynamic force can also be generated when the airfoil is performing a fast pitching motion in a constant freestream. In these fast unsteady motions, an airfoil in low Re flow can produce a large aerodynamic force as effective as in large Re flow, or the effect of unsteady motion dominates the Reynolds number effect. During the fast unsteady motion of the airfoil, new layers of strong vorticity are formed near the upper and lower surfaces of the airfoil under the previously existing thick vorticity layers, and it is the generation and motion of the new vorticity layers that is mainly responsible for the generation of the large aerodynamic force; the large-scale structure and movement of the newly produced vorticity layers are similar to that of high Re flow.     

Quantitative force and dissipation measurements in liquids using piezo-excited atomic force microscopy: a unifying theory

The use of a piezoelectric element (acoustic excitation) to vibrate the base of microcantilevers is a popular method for dynamic atomic force microscopy. In air or vacuum, the base motion is so small (relative to tip motion) that it can be neglected. However, in liquid environments the base motion can be large and cannot be neglected. Yet it cannot be directly observed in most AFMs. Therefore, in liquids, quantitative force and energy dissipation spectroscopy with acoustic AFM relies on theoretical formulae and models to estimate the magnitude of the base motion. However, such formulae can be inaccurate due to several effects. For example, a significant component of the piezo excitation does not mechanically excite the cantilever but rather transmits acoustic waves through the surrounding liquid, which in turn indirectly excites the cantilever. Moreover, resonances of the piezo, chip and holder can obscure the true cantilever dynamics even in well-designed liquid cells. Although some groups have tried to overcome these limitations (either by theory modification or better design of piezos and liquid cells), it is generally accepted that acoustic excitation is unsuitable for quantitative force and dissipation spectroscopy in liquids. In this paper the authors present a careful study of the base motion and excitation forces and propose a method by which quantitative analysis is in fact possible, thus opening this popular method for quantitative force and dissipation spectroscopy using dynamic AFM in liquids. This method is validated by experiments in water on mica using a scanning laser Doppler vibrometer, which can measure the actual base motion. Finally, the method is demonstrated by using small-amplitude dynamic AFM to extract the force gradients and dissipation on solvation shells of octamethylcyclotetrasiloxane (OMCTS) molecules on mica.     

地下管线在空间随机分布的地震作用下的反应

强震作用下地下管线地震反应计算以往多采用波动法求解。这种方法假定地震波为一行进波,沿管线的轴向或成某一角度传播,它只能求得地面运动的相位差引起的管线的变形和内力。有些文献将地震地面运动假定为空间变化的平稳随机过程,用随机振动理论求得管线的地震反应,但不能反映地面运动的非平稳性对管线地震反应的影响。而地面运动的非平稳性,特别是时域非平稳性很可能是产生地下管线变形和内力的最重要原因。根据地面运动的统计模型生成管线轴线上各点的地面运动时程,用级数解法求管道的地震反应。由于这种方法能较好地反映地面运动的时域非平稳性,所以得到的计算结果更真实。     

The shock wave structure in a dense electronegative gas containing conductive particles

The structure of a flat shock wave in an electronegative gas containing a rarified suspension of small metallic particles (macroparticles) is considered. When heated due to thermal electron emission, the particles are ionized in the shock compression that occurs in the carrying gas. The emitted electrons adhere to the electronegative neutral molecules, which gives rise to the formation of a multicomponent gas mixture composed of ions, electrons, neutrals, and positively charged macroparticles. The profiles of the corresponding variables are calculated within the Navier-Stokes approximation. The reaction of sticking is analyzed with the use of chemical kinetics equations. The calculations were performed for the case of air, which assumed by binary mixture of molecules O₂ and N₂. The initial temperature and the Mach number of the oncoming flow are T = 500 K and M = 3.     

有限长轴承非稳态油膜力建模在线性油膜失稳

根据文献[1]提出的非稳态非线性油膜力基本表达式导出了有限长轴承非稳态油膜力近似公式,应用该公式,采用数值模拟,对有限长油膜轴承支撑的刚性Jeffcott转子进行了不平衡力下油膜振荡的非线性分析,得出与文献[13]的结论相类似的分岔和混沌特性。     

The theory of quasistatic nanomachines

The motion of a system of several bodies linked by bonds of variable length in a spatially periodic potential is studied. It is shown that quasistatic periodic variations of the system parameters in time can induce translational motion of the system in the absence of directed external forces, or motion in the direction opposite to that of an external force. To provide for the possibility of the induced translational motion, the system parameters (e.g., bond lengths) must vary in the space of these parameters according to closed trajectories containing one or several closed bifurcation sets of the given system. The bifurcation sets for some model systems are found. It is demonstrated that the proposed mechanism of the translational motion induction can be realized, in particular, by applying an alternating elliptically polarized electric field to particles of nanometer dimensions occurring on a chemically inert crystal (e.g., graphite) surface.     

Design optimization of machinery mounting systems with an elastic support structure

An elastic support-based optimization model is developed for a machinery mounting system comprising a vibrating machine supported on an elastic structure by multiple resilient mounts. This model is used to investigate the design optimization of an X?Y motion stage mounting system used in microelectronics wire-bonding equipment. By varying the stiffness coefficients of the resilient mounts while constraining the dynamic displacement amplitudes of the X?Y motion stage, the total force transmitted from the X?Y motion stage (the vibrating machine) to the equipment table (the elastic support structure) is minimized at each frequency interval in the frequency range of interest for different stiffnesses of the equipment table. The results show that, when the equipment table is relatively flexible, the total transmitted force minimized by the model developed is significantly lower than that minimized using a conventional rigid support-based optimization model at some critical frequency. When the equipment table is sufficiently rigid, both models provide almost the same predictions of the total transmitted force.     

Trapping of water waves by moored bodies

Certain types of floating bodies are known to support trapped modes, with oscillatory fluid motion near the body and no energy radiation in the far field. Previous work has considered either fixed bodies, where the boundary conditions are homogeneous, or bodies which are freely floating and moving without any exciting force. For a fixed body the existence of a trapped mode implies that there is no unique solution of the boundary-value problem for the velocity potential with a prescribed body motion. For a free body which supports a trapped mode, the solution of the coupled problem for the motions of the fluid and body does not have a unique solution. A more general case is considered here, of a body with a linear restoring force such as an elastic mooring. The limiting cases of a fixed and free body correspond to infinite or zero values of the corresponding spring constant. A variety of body shapes are found including cylinders in two dimensions and axisymmetric bodies in three dimensions, which illustrate this more general case of trapping and provide a connection between the fixed and free cases.     

Harmonic motion detection in a vibrating scattering medium

Elasticity imaging is an emerging medical imaging modality that seeks to map the spatial distribution of tissue stiffness. Ultrasound radiation force excitation and motion tracking using pulse-echo ultrasound have been used in numerous methods. Dynamic radiation force is used in vibrometry to cause an object or tissue to vibrate, and the vibration amplitude and phase can be measured with exceptional accuracy. This paper presents a model that simulates harmonic motion detection in a vibrating scattering medium incorporating 3-D beam shapes for radiation force excitation and motion tracking. A parameterized analysis using this model provides a platform to optimize motion detection for vibrometry applications in tissue. An experimental method that produces a multifrequency radiation force is also presented. Experimental harmonic motion detection of simultaneous multifrequency vibration is demonstrated using a single transducer. This method can accurately detect motion with displacement amplitude as low as 100 to 200 nm in bovine muscle. Vibration phase can be measured within 10° or less. The experimental results validate the conclusions observed from the model and show multifrequency vibration induction and measurements can be performed simultaneously.     

Effect of sloshing on the mechanics of dewar systems in low-gravity

The mechanics of a spacecraft or space module, that contains a dewar system, is affected by sloshing of the cryogen. When a spacecraft is in orbit the acceleration level is very low and sloshing differs in several ways from that on Earth. Surface tension replaces gravity as the restraining force. The liquid–gas interface is curved and the depth is variable. Cryogens have low surface tension and this causes the resonant frequencies of sloshing to be very low. Programs were developed to calculate sloshing in low-g in dewars with annular and circular cross sections and with segmented and ring baffles. The programs correct for surface curvature and variable depth. The driving force for sloshing is the motion of the wall of the dewar. Dewar motion is an unknown because the sloshing force contributes to the motion of the support structure. Programs were also written for the dynamics of the system treating the motion of the dewar as an unknown. The combined program for sloshing and dynamics is called LOWGSLOSH. The calculations are carried out in the frequency domain so that both coherent and random driving forces can be used as input. The output is the motion of the spacecraft if the dewar is firmly attached to the vehicle. For modules suspended by a vibration-isolation interface, the output is the acceleration spectrum of the module. The calculations show the conditions when sloshing has an appreciable effect on the spacecraft or module. The timeline of spacecraft maneuvers is very important in determining the sloshing amplitude. In many cases, it is possible to reduce sloshing drastically by timing a maneuver properly. The results are illustrated using calculations on two NASA projects: the Space Infrared Telescope Facility spacecraft (SIRTF) and the Low Temperature Microgravity Physics Facility (LTMPF), a module for the International Space Station.     

Macroparticle Acceleration in a Carbon Arc

Consideration is given to the mechanisms of acceleration of carbon macroparticles forming a cathode coating in a carbon arc under the conditions of fullerene formation. Based on experimental data and theoretical estimates, the macroparticle velocity is determined. It is shown that on collision of particles with the cathode surface the conditions are realized in the zone of contact where graphite fusion can occur.     

Rocking instability of a pulled suitcase with two wheels

Summary Rocking motions of a two-wheeled suitcase are considered. The suitcase is pulled on a horizontal ground and may rock back and forth, first with one wheel in contact with the ground, then the other, and so on. When a wheel impacts the ground, some energy is lost. It is assumed that the puller's walking motion induces a periodic force or moment on the handle of the suitcase. In addition, the puller may apply an additional restoring moment in an attempt to suppress the rocking motion. Under certain conditions, the motion may grow until the suitcase overturns. The effects of the excitation frequency and the coefficient of the restoring moment on the critical excitation amplitude are examined for the special case in which yaw and pitch motions are neglected and the suitcase is pulled in a straight line. Due to the nonlinearities of the problem, the results exhibit some irregular behavior.     

多节伸缩装车机相关计算理论研究

目的 对多节伸缩装车机的输送运动和伸缩运动进行相关计算理论的研究,方便进行关键部件的选型,保证选型的正确性。方法 以伸缩装车机的结构为基础,结合现有的相关研究理论,分析多节伸缩装车机输送带驱动辊筒圆周力的组成部分,得出输送带驱动辊筒圆周力的计算方法;以机架伸缩运动原理为基础,对伸缩装车机各级伸缩部分进行受力分析,得出伸缩驱动力的计算方法;以某伸缩装车机产品为例,结合SolidWorks motion模块仿真结果,对计算方法进行验证。结果 验证结果表明,通过输送带驱动辊筒圆周力和伸缩驱动力计算所得的驱动电机功率与产品一致。结论 伸缩装车机输送运动和伸缩运动相关参数计算方法可行,结果正确,在伸缩装车机的研究中有一定的参考价值。