共查询到20条相似文献,搜索用时 31 毫秒
1.
We extend the study of velocity quantization phenomena recently found in the classical motion of an idealized 1D model solid lubricant - consisting of a harmonic chain interposed between two periodic sliding potentials [A. Vanossi, M. Manini, G. Divitini, G.E. Santoro, E. Tosatti, Phys. Rev. Lett. 97 (2006) 056101]. This quantization is due to one slider rigidly dragging the commensurate lattice of kinks that the chain forms with the other slider. In this follow-up work we consider finite-size chains rather than infinite chains. The finite-size (i) permits the development of robust velocity plateaus as a function of the lubricant stiffness, and (ii) allows an overall chain length re-adjustment which spontaneously promotes single-particle periodic oscillations. These periodic oscillations replace the quasi-periodic motion produced by general incommensurate periods of the sliders and the lubricant in the infinite-size model. Possible consequences of these results for some real systems are discussed. 相似文献
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This paper reports the successful operation of a 70 MHz driving surface acoustic wave (SAW) linear motor with a miniaturized stator transducer. This paper also deals with an investigation into an optimized slider design for the miniaturized SAW linear motor. The performance of three silicon type sliders, with different projection size, was compared. Output forces of the three sliders were measured with change of pre-load. It was found that the slider with smaller projection tended to produce greater output force. 相似文献
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The disk clamping distortion and slider crown sensitivity induced flying height (FH) variation is investigated. The experimental results which were measured with in situ method were compared with simulated numerical results. Both results indicate that the disk clamping distortion has significant influence on the FH variation. Crown sensitivity of the sliders is one of the factors that determine the amplitude of the FH variation. Higher crown sensitivity sliders exhibit greater FH variation. 相似文献
4.
Least-squares finite difference (LSFD) method, one of mesh-free methods, is used to solve slider air bearings problem through discritizing the generalized Reynolds equation into nonlinear systems of algebraic equations. Two approximation schemes for the linearization of these equations are presented and compared. And, some new techniques to search supporting points for the reference node in the mesh-free method were proposed and explored. Therefore, these improvements eliminate some potential limitation of the LSFD method previously published and further facilitate its employment in complex slider models. Advanced step slider as an example of negative pressure sliders is simulated and verified using the improved LSFD mesh-free method in head disk systems. 相似文献
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Yan Liu & Hejun Du 《advances in applied mathematics and mechanics.》2011,3(6):716-728
Ramp load/unload (L/UL) mechanisms are widely used to rest sliders in hard disk drives (HDDs).
Loading/unloading a slider swiftly and smoothly is crucial in a HDD design. A novel, efficient
simulation scheme is proposed to investigate the behaviors of a head disk interface (HDI) in
ramp unloading processes. A dual scale model is enabled by decoupling the nano-meter scale change
of an air bearing and the micro- or milli-meter scale deformation of a suspension. A modified
Reynolds equation governing the air bearing was solved numerically. The slider design was
characterized with performance functions. Three stages in an unloading process were analyzed
with a lumped parameter suspension model. Key parameters for the model were estimated with a
comprehensive finite element suspension model. Finally, simulation results are presented for
a commercial HDI design. 相似文献
6.
Zhi-Min Yuan Siang Huei LeongSumitro Joyo Taslim Ka Wei NgBo Liu 《Journal of magnetism and magnetic materials》2008
The flying dynamics and flying stability of a slider are the key issues at sub-5 nm flying height (FH) under thermal FH control. The resonant frequencies of current sliders are at 100 kHz level. At present linear disk velocities, the disk waviness at sub-mm level and 10 micron level can excite the resonant modes of the slider and induce FH modulation. This work uses the triple-harmonic method to monitor the dynamic FH signal during the process of thermal FH control. As the FH reduces, the same disk waviness characteristics excite larger dynamic FH modulation. 相似文献
7.
Dr. Werner A. Schlup 《Zeitschrift für Physik B Condensed Matter》1971,13(4):307-324
A diffusion constant for electrons in a current-carrying semiconductor can be unambiguously defined in nearly uniform systems. For frequency-dependent density gradients it is $$D_{\alpha \beta } (\omega ) \equiv \int\limits_0^\infty {dt e^{i\omega t} \overline {\Delta \upsilon _\alpha (t)\Delta \upsilon _\beta (0),} } $$ where \(\overline {\Delta \upsilon _\alpha (t)\Delta \upsilon _\beta (0)} \) is the velocity correlation function with respect to the steady state in a bias field. This result has been elucidated in the relaxation approximation by different approaches to the diffusion problem. Essential for its derivation is a statistical independence assumption of space and velocities, and in order to get a classical diffusion law of Fick's type certain velocities have to be distributed according to the steady state in a bias field. Diffusion constant and noise temperature are discussed for a few band structures in the relaxation approximation. 相似文献
8.
Dynamic fracture in a wide class of materials reveals a "fracture energy" Gamma much larger than the expected nominal surface energy due to the formation of two fresh surfaces. Moreover, the fracture energy depends on the crack velocity, Gamma=Gamma(upsilon). We show that a simple dynamical theory of viscoplasticity coupled to asymptotic pure linear elasticity provides a possible explanation to the above phenomena. The theory predicts tip blunting characterized by a dynamically determined crack tip radius of curvature. In addition, we demonstrate velocity selection for cracks in fixed-grip strip geometry accompanied by the identification of Gamma and its velocity dependence. 相似文献
9.
Wu Z Hoyt K Rubens DJ Parker KJ 《The Journal of the Acoustical Society of America》2006,120(1):535-545
The authors have recently demonstrated the shear wave interference patterns created by two coherent vibration sources imaged with the vibration sonoelastography technique. If the two sources vibrate at slightly different frequencies omega and omega+deltaomega, respectively, the interference patterns move at an apparent velocity of (deltaomega/2omega)upsilon(shear), where upsilon(shear) is the shear wave speed. We name the moving interference patterns "crawling waves." In this paper, we extend the techniques to inspect biomaterials with nonuniform stiffness distributions. A relationship between the local crawling wave speed and the local shear wave velocity is derived. In addition, a modified technique is proposed whereby only one shear wave source propagates shear waves into the medium at the frequency omega. The ultrasound probe is externally vibrated at the frequency omega-deltaomega. The resulting field estimated by the ultrasound (US) scanner is proven to be an exact representation of the propagating shear wave field. The authors name the apparent wave motion "holography waves." Real-time video sequences of both types of waves are acquired on various inhomogeneous elastic media. The distribution of the crawling/holographic wave speeds are estimated. The estimated wave speeds correlate with the stiffness distributions. 相似文献
10.
Kohlstedt K Snezhko A Sapozhnikov MV Aranson IS Olafsen JS Ben-Naim E 《Physical review letters》2005,95(6):068001
We study velocity statistics of electrostatically driven granular gases. For two different experiments, (i) nonmagnetic particles in a viscous fluid and (ii) magnetic particles in air, the velocity distribution is non-Maxwellian, and its high-energy tail is exponential, P(upsilon) approximately exp(-/upsilon/). This behavior is consistent with the kinetic theory of driven dissipative particles. For particles immersed in a fluid, viscous damping is responsible for the exponential tail, while for magnetic particles, long-range interactions cause the exponential tail. We conclude that velocity statistics of dissipative gases are sensitive to the fluid environment and to the form of the particle interaction. 相似文献
11.
将二维三角晶格光子晶体波导和微腔结构结合,优化设计了一种二维三角晶格光子晶体共振耦合腔波导,运用时域有限差分法(FDTD)模拟共振耦合腔波导TE偏振光的透射谱,通过透射谱得到传输光的透射率和群速度。结果表明,合适参数的二维三角晶格共振耦合腔波导在波长1.551μm处的群速度为c/130、透射率为20.1%,在波长1.502μm处的群速度为c/50、透射率为29.2%。运用平面波展开法(PWE)计算的该波导的能带结构对慢光特性进行了分析。这种慢光特性的光子晶体波导将在光存储、光延迟及光子集成等方面有潜在的应用价值。 相似文献
12.
Elastic friction drive of surface acoustic wave motor 总被引:2,自引:0,他引:2
Importance of elastic deformation control to obtain large output force with a surface acoustic wave (SAW) motor is discussed in this paper. By adding pre-load to slider, stator and slider surfaces are deformed in a few tens nanometer. Appropriate deformation in normal direction against normal vibration displacement amplitude of SAW existed. By moderate deformation, the output force of the SAW motor was enlarged up to about 10 N and no-load speed was 0.7 m/s. To produce this performance, the transducer weight and slider size were only 4.2 g and 4 x 4 mm(2).By traveling wave propagation, surface particles of the SAW device move in elliptical motion. Due to the amplitude of the elliptical motion is 10 or 20 nm order, the contact condition of the slider is very critical. To control the contact condition, namely, the elastic deformation of the slider and stator surface in nanometer order, a lot of projections were fabricated on the slider surface. The projection diameter was 20 micro m. In static condition, the elastic deformation and stress were evaluated with the FEM analysis. From this calculation and the simulation result, it is consider that the wave crest is distorted, hence the elasticity has influence on the friction drive condition.Elastic deformation of the stator surface beneath the projection from the initial position were evaluated. In 4 x 4 mm(2) square area, the sliders had from 1089 to 23,409 projections. Depression was independent to the contact pressure. However, the output force depended on the depression although the projection density were different. From the view point of the output power of the motor, the proper depression was independent to the projection density. Around 25 nm depression, the output force and output power were maximized. This depression value was almost same as the vibration displacement amplitude of the stator transducer. 相似文献
13.
We probe possible new physics (NP) effects beyond the standard model (SM) in the decays \({\overline B ^0} \to \pi \tau \overline \upsilon ,{\overline B ^0} \to \rho \tau \overline \upsilon ,and{\overline B ^0} \to \tau \overline \upsilon \), based on an effective Hamiltonian including non-SM operators. Experimental constraints on different NP scenarios are provided by recent measurements of the ratios \({{R\left( {{D^{\left( * \right)}}} \right) \equiv B\left( {{{\overline B }^0} \to {D^{\left( * \right)}}\tau \overline \upsilon } \right)} \mathord{\left/ {\vphantom {{R\left( {{D^{\left( * \right)}}} \right) \equiv B\left( {{{\overline B }^0} \to {D^{\left( * \right)}}\tau \overline \upsilon } \right)} {B\left( {{{\overline B }^0} \to {D^{\left( * \right)}}\mu \overline \upsilon } \right)}}} \right. \kern-\nulldelimiterspace} {B\left( {{{\overline B }^0} \to {D^{\left( * \right)}}\mu \overline \upsilon } \right)}}\), as well as the branching \(B\left( {{B^ - } \to \tau \overline \upsilon } \right)\). The corresponding hadronic form factors and leptonic decay constants are calculated in the covariant confined quark model developed by us. 相似文献
14.
考古发掘表明,我国新石器晚期已经大量使用"白灰面"建筑涂料,这种建筑涂料,不仅坚固、美观、卫生,而且有一定的防潮作用,考古学家推测,这种建筑涂料很可能就是我国早期人工烧制的石灰.为此,本工作采用红外光谱分析方法,对取自陶寺遗址的"白灰面"、"白条石"做了红外光谱的对比研究.结果表明,"白灰面"与"白条石"红外光谱的v2/v4比值明显不同,反应了二者碳酸钙晶体的无序度有较大区别,从而说明经过煅烧而得到的白灰面,即人工烧制的石灰是町以通过红外光谱方法鉴定的,这为我国行灰起源研究提供了一种简单易行的判别方法.此外,本工作还借助显微镜与红外光谱分析方法研究了白灰面中掺和料,结果表明白灰面中的掺和料为纤维素类物质. 相似文献
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H. G. Bennewitz R. Haerten O. Klais G. Müller 《Zeitschrift für Physik A Hadrons and Nuclei》1971,249(2):168-184
Radio frequency spectra of CsF in the rotational stateJ=1 have been measured for the vibrational statesv=0, 1,..., 8 using the molecular beam electric resonance method. The analysis of the spectra yields the electric dipole moment μv and the quadrupole coupling constanteq v Q connected with the quadrupole moment of the Cs nucleus. The results are: $$\begin{gathered} \mu _\upsilon = 7.8478 + 0.07026(\upsilon + 1/2) + 0.000195(\upsilon + 1/2)^2 debye \hfill \\ eq_\upsilon Q/h = 1245.2 - 16.2(\upsilon + 1/2) + 0.31(\upsilon + 1/2)^2 kHz. \hfill \\ \end{gathered} $$ 相似文献
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A hybrid simulation method is used to study the transition from stick-slip motion to steady sliding as the sliding velocity increases above a critical value v(c). The effects of the geometry, elasticity, and mass M of the sliding object are varied to test competing theories. When the slider has a tapered geometry, v(c) scales as M(-1/2), and the elasticity of the slider is irrelevant. When the slider has a constant columnar cross section, elasticity dominates, and v(c) is independent of mass as M--> infinity. The tapered geometry is more typical of existing measurements, but the columnar geometry could be realized using a nanotube. 相似文献