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1.
STICTION AND ANTI—STICTION IN MEMS AND NEMS 总被引:6,自引:1,他引:6
赵亚溥 《Acta Mechanica Sinica》2003,19(1):1-10
Stiction in microelectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining
in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when solutions to this problem are emerging,
such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in
MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS).
First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers
are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary,
electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions
(relative humidity and temperature) on stiction are also discussed. As hydrophobic films, the self-assembled monolayers (SAMs)
turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part.
The project supported by the Distinguished Young Scholar Fund of NSFC (10225209), key project from the Chinese Academy of
Sciences (KJCX2-SW-L2) and National “973” Project (G1999033103) 相似文献
2.
Francisco J. Montáns Francisco Chinesta Rafael Gómez-Bombarelli J. Nathan Kutz 《Comptes Rendus Mecanique》2019,347(11):845-855
In the past, data in which science and engineering is based, was scarce and frequently obtained by experiments proposed to verify a given hypothesis. Each experiment was able to yield only very limited data. Today, data is abundant and abundantly collected in each single experiment at a very small cost. Data-driven modeling and scientific discovery is a change of paradigm on how many problems, both in science and engineering, are addressed. Some scientific fields have been using artificial intelligence for some time due to the inherent difficulty in obtaining laws and equations to describe some phenomena. However, today data-driven approaches are also flooding fields like mechanics and materials science, where the traditional approach seemed to be highly satisfactory. In this paper we review the application of data-driven modeling and model learning procedures to different fields in science and engineering. 相似文献
3.
Flows around two airfoils performing fling and subsequent translation and translation and subsequent clap 总被引:1,自引:0,他引:1
The aerodynamic forces and flow structures of two airfoils performing “fling and subsequent translation“ and “translation and subsequent clap“ are studied by numerically solving the Navier-Stokes equations in moving overset grids. These motions are relevant to the flight of very small insects. The Reynolds number, based on the airfoil chord length c and the translation velocity U, is 17. It is shown that: (1) For two airfoils performing fling and subsequent translation, a large lift is generated both in the fling phase and in the early part of the translation phase. During the fling phase,a pair of leading edge vortices of large strength is generated; the generation of the vortex pair in a short period results in a large time rate of change of fluid impulse, which explains the large lift in this period. During the early part of the translation, the two leading edge vortices move with the airfoils;the relative movement of the vortices also results in a large time rate of change of fluid impulse, which explains the large lift in this part of motion. (In the later part of the translation, the vorticity in the vortices is diffused and convected into the wake.) The time averaged lift coefficient is approximately 2.4 times as large as that of a single airfoil performing a similar motion. (2) For two airfoils performing translation and subsequent clap, a large lift is generated in the clap phase. During the clap, a pair of trailing edge vortices of large strength are generated; again, the generation of the vortex pair in a short period (which results in a large time rate of change of fluid impulse) is responsible for the large lift in this period. The time averaged lift coefficient is approximately 1.6 times as large as that of a single airfoil performing a similar motion. (3) When the initial distance between the airfoils (in the case of clap, the final distance between the airfoils) varies from 0.1 to 0.2c, the lift on an airfoil decreases only slightly but the torque decreases greatly. When the distance is about lc, the interference effects between the two airfoils become very small. 相似文献
4.
McGleenan T 《Community genetics》2000,3(2):45-49
Genetic screening and testing techniques provide a powerful diagnostic tool for the acquisition of predictive information. The potential value of such diagnostic techniques cannot be overstated. However, commercial organisations such as insurance companies and employers are also highly interested in the acquisition and use of genetic information. Concerns about the potential abuse of genetic information have stimulated a counter-current of public pressure for restrictions on the use which can be made of genetic diagnostic information. In a number of countries this pressure has generated enough concern to stimulate legislatures to enact laws which curtail the use and acquisition of genetic information. This pattern has clearly emerged in the United States of America and there are indications that similar trends are developing in Europe. This paper examines the law and policy issues arising from the interface between genetics and insurance. 相似文献
5.
Fernando Stassi D'Alia 《Meccanica》1969,4(1):67-77
Summary The problem of drawing of wires and of strips has been treated in several studies; among these the studies of Sachs seem essential. However, the results deduced according to similar theories are not always in accordance with the experimental results: reduction of area or of thickness are in fact usually smaller than those resulting from the theory. This is in dependance of the fact that Sachs has adopted the Limiting Condition of Yielding by v. Mises, according to which the limit values of stress in traction and compression are equal. More recently other AA. (Alberti, Noto La Diega, Bugini), admitting the Limiting Condition of Yielding by A. (or of the Paraboloid of Revolution) of which we have treated in one of our previous works, attain results tallying with the experience. In the present study the above said subjects are treated as to evidence their unitarian signifiance and clarify their several aspects. The approximate formulas proposed by A. result of easy and quick application. In the same manner are treated other problems, among which the problem of the extrusion (Bagarello, Ammendola).
Sommario Il problema della trafilatura dei fili metallici e delle strisce di lamiera è stato trattato in diverse Memorie, fra le quali fondamentali sono quelle del Sachs. I risultati dedotti in base a tali studi non sempre però concordano con le risultanze sperimentali: i rapporti di riduzione delle aree o degli spessori sono infatti di norma inferiori a quelli che risultano da tali teorie. Ciò dipende dal fatto che il Sachs ha posto a base dei suoi studi la Condizione di Plastificazione del v. Mises secondo la quale i limiti di resistenza del materiale che si considera alla trazione e alla compressione semplice sono uguali. Più recentemente altri AA. (Alberti, Noto La Diega, Bugini), adottando la Condizione di Plastificazione dell' A. (o del Paraboloide di Rivoluzione), del quale abbiamo trattato in un precedente lavoro, pervengono a risultati più attinenti alla practica. Col presente studio gli argomenti vengono trattati mettendone in evidenza il significato unitario e chiarendone i vari aspetti. Le formule approssimate proposte dall' A. risultano di facile e immediata applicazione. In maniera analoga vengono trattati altri problemi, fra i quali quello dell'estrusione (Bagarello, Ammendola).相似文献
6.
V. S. Nagornyi 《Journal of Applied Mechanics and Technical Physics》2000,41(2):225-230
The physical and mathematical principles of the method of electrogas-and electrohydrodynamic conversion of electrical signals
to pneumatic (hydraulic) signals and vice versa for control of gas and liquid jets and flows in electropneumohydraulic systems
are considered.
St. Petersburg State Technical University, St. Petersburg 195251. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika,
Vol. 41, No. 2, pp. 25–31, March–April, 2000. 相似文献
7.
Yan-Ming Cen 《Acta Mechanica Solida Sinica》1988,1(1):1-13
Based on the assumption that the yield criterionF(,)=0 is a differentiable surface in stress space and by starting from a specially defined real Euclidean space, the fundamental properties of the elasto-plastic matrix in the incremental theory of plasticity is discussed in detail. By using these results, a convex analysis is made to prove the existence and uniqueness of 1) the distribution of incremental elasto-plastic stress for work-hardening materrials; 2) the displacement distribution for work-hardening materials. Material isotropy is assumed in all discussions of relevant problems. 相似文献
8.
Amit Acharya 《Journal of Elasticity》2011,104(1-2):23-44
A methodology is devised to utilize the statistical mechanical entropy of an isolated, constrained atomistic system to define constitutive response functions for the dissipative driving-force and energetic fields in continuum thermomechanics. A thermodynamic model of dislocation mechanics is discussed as an example. Primary outcomes are constitutive relations for the back-stress tensor and the Cauchy stress tensor in terms of the elastic distortion, mass density, polar dislocation density, and the scalar statistical density. 相似文献
9.
Derivatives and Rates of the Stretch and Rotation Tensors 总被引:2,自引:0,他引:2
Luciano Rosati 《Journal of Elasticity》1999,56(3):213-230
General expressions for the derivatives and rates of the stretch and rotation tensors with respect to the deformation gradient
are derived. They are both specialized to some of the formulas already available in the literature and used to derive some
new ones, in three and two dimensions. Essential ingredients of the treatment are basic elements of differential calculus
for tensor valued functions of tensors and recently derived results on the solution of the tensor equation A X + XA= H in the unknown X.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
《International Journal of Solids and Structures》2007,44(24):7891-7905
The material and spatial settings of the nonlinear coupling problem of electro- and magneto-elastostatics are discussed in this paper. The governing equations and variational formulations of the problem derived in these two settings using basic equations of electricity, magnetism and elasticity allow the consideration of material defects by the material force method. 相似文献
11.
The flow and heat transfer in cylindrical and conical annular flow-passages with through flow and inner-wall rotation have been numerically simulated by using the large eddy simulation with a Lagrangian dynamic subgrid-scale model. Inlet through-flow Reynolds number was 1000 and the Taylor number was set at 0, 1000, 2000, and 4000. In the conical flow passage, when the inner-wall rotation speed was increased, at first spiral vortices in the downstream region and then much more complicated vortices appeared. The vortices for Ta = 4000 changed the structure in both through-flow and wall-normal directions in the downstream half of the passage. The flow structure and heat transfer of the conical case were completely different from those of the cylindrical case. It was because of the three factors: the expansion of the flow passage, the rotation radius change in the through-flow direction, and the centrifugally driven through-flow. The last factor is due to the acute angle between the centrifugal and through-flow directions. 相似文献
12.
Direct numerical simulations were made to examine the local structure of the reaction zone for a moderately fast reaction between unmixed species in decaying, homogeneous turbulence and in a homogeneous turbulent shear flow. Pseudospectral techniques were used in domains of 643 and higher wavenumbers. A finite-rate, single step reaction between non-premixed reactants was considered, and in one case temperature-dependent Arrhenius kinetics was assumed. Locally intense reaction rates that tend to persist throughout the simulations occur in locations where the reactant concentration gradients are large and are amplified by the local rate of strain. The reaction zones are more organized in the case of a uniform mean shear than in isotropic turbulence, and regions of intense reaction rate appear to be associated with vortex structures such as horseshoe vortices and fingers seen in mixing layers. Concentration gradients tend to align with the direction of the most compressive principal strain rate, more so in the isotropic case. 相似文献
13.
14.
Jean-François Pinton Guillaume Brillant 《Theoretical and Computational Fluid Dynamics》2005,18(6):413-433
We review several aspects of the propagation of sound in vortical flows. We restrict ourselves to isothermal, humidity-free flows at low Mach number M. Since vorticity plays a major role in vortex-flow interactions we focus on vortical flows. We consider two main canonical situations. The first concerns the transmission of sound. We analyze the evolution of acoustic wavefronts as they propagate across a single vortex. The second situation addresses the scattering of sound waves by nonstationary vortices. We study the evolution of the acoustic pressure emitted in the far field, at an angle with the initial direction of propagation. In this geometry one performs direct spectroscopy of the flow vorticity field. In each case, we review theoretical results and compare with experimental measurements and numerical simulations when available. We also briefly report how the following new acoustic techniques have recently been used to study complex or turbulent flows: time-resolved acoustic spectroscopy, speckle interferometry and Lagrangian particle tracking. PACS 43.25, 43.28, 47.32, 67.40 相似文献
15.
In this paper, we use the asymptotic perturbation method to investigate nonlinear oscillations and chaotic dynamics in a rotor-active magnetic bearings (AMB) system with 8-pole legs and the time-varying stiffness. The stiffness in the AMB is considered as the time varying in a periodic form. Because of considering the weight of the rotor, the formulation on the electromagnetic force resultants includes the quadratic and cubic nonlinearities. The resulting dimensionless equations of motion for the rotor-AMB system with the time-varying stiffness in the horizontal and vertical directions are a two-degree-of-freedom nonlinear system with quadratic and cubic nonlinearities and parametric excitation. The asymptotic perturbation method is used to obtain the averaged equations in the case of primary parametric resonance and 1/2 subharmonic resonance. It is found that there exist period-3, period-4, period-6, period-7, period-8, quasiperiodic and chaotic modulated amplitude oscillations in the rotor-AMB system with the time-varying stiffness. It is seen from the numerical results that there are the phenomena of the multiple solutions and the soft-spring type and the hardening-spring type in nonlinear frequency-response curves for the rotor-AMB system. The parametric excitation, or the time-varying stiffness produced by the PD controller is considered to be a controlling force which can control the chaotic response in the rotor-AMB system to a period n motion. 相似文献
16.
E.C. Aifantis 《International Journal of Non》1996,31(6):797-809
The role and implications of microstructure heterogeneity and non-linearity in interpreting a variety of experimental observations during plastic flow and fracture are outlined. Traditionally, these observations were not related to theoretical modelling efforts as recent techniques in non-linear dynamics were not available and usual applications were limited to standard materials and processes where micro- and macroscales do not interact and can be treated independently. Advanced technology has imposed the need for the development of models accounting for scale coupling effects. One class of such models, the so-called gradient models, will be described in the paper in connection with the phenomena of dislocation and strain patterning, as well as with existing observations on oscillatory fracture. 相似文献
17.
Adsorption Characteristics and Thermodynamic Analysis of CH4 and CO2 on Continental and Marine Shale
Yang Kang Zhou Junping Xian Xuefu Zhang Chengpeng Tian Shifeng Dong Zhiqiang Fan Maolin Cai Jianchao 《Transport in Porous Media》2021,140(3):763-788
Transport in Porous Media - To better understand the CO2 sequestration and enhanced shale gas recovery, it is of great significance to study the adsorption characteristics of CO2 and CH4 in... 相似文献
18.
V. Ilic D. Tullock N. Phan-Thien A.L. Graham 《International Journal of Multiphase Flow》1992,18(6):1061-1075
The terminal settling velocities and rotation rates of spherical particles settling in circular and square conduits were investigated experimentally and numerically with the aim to benchmark the numerical predictions using the boundary element method. Spheres were allowed to settle in viscous Newtonian fluid under conditions such that only hydrodynamic forces exerted an appreciable effect. The terminal settling velocities and the rotation rates were measured as a function of the size and density of the falling sphere, the drop position of the sphere in the conduit and the dimensions and geometry of the containing vessel or conduit. The experimental measurements were subjected to an exacting error analysis and compared with fully three-dimensional boundary element calculations. We found that the results of the experiments and numerical simulations showed remarkable agreement within the bounds of experimental error. 相似文献
19.
颜心力 《应用数学和力学(英文版)》1988,9(10):953-958
In this paper, we obtain the sufficient conditions under which there exists the fixed point of sum and product about concave and – convex operators in the positive cone of linear semi-order space, and the iterative procedure and error estimate can be given. The relation between eigenvalue and eigenelement will also be studied in this paper. 相似文献
20.
The stream function and the velocity potential can be easily computed by solving the Poisson equations in a unique way for the global domain.Because of the various assumptions for handling the boundary conditions,the solution is not unique when a limited domain is concerned.Therefore,it is very important to reduce or eliminate the effects caused by the uncertain boundary condition.In this paper,an iterative and adjusting method based on the Endlich iteration method is presented to compute the stream function and the velocity potential in limited domains.This method does not need an explicitly specifying boundary condition when used to obtain the effective solution,and it is proved to be successful in decomposing and reconstructing the horizontal wind field with very small errors.The convergence of the method depends on the relative value for the distances of grids in two different directions and the value of the adjusting factor.It is shown that applying the method in Arakawa grids and irregular domains can obtain the accurate vorticity and divergence and accurately decompose and reconstruct the original wind field.Hence,the iterative and adjusting method is accurate and reliable. 相似文献