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1.
We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip.  相似文献   

2.
This paper addresses the problem of a robust UAV tracking, surveillance and landing of a mobile ground target. The translational and angular dynamics of the vehicle are affected by bounded uncertainties; a Quasi-Integral Sliding Mode control is designed to obtain robustness from nearly the initial time. The flying mission considers three different dynamics of movement: the take-off to the desired altitude, the relative circular surveillance motion around the mobile ground target and eventually precise landing over the ground vehicle. This paper introduces a novel dynamic motion planning generator to perform such tracking maneuvers. It is based on the solution of a second order nonlinear differential equation, whose solution is force to move in a set of new parameterized ‘Bifurcation Sliding Mode Surfaces’ that exploit the Hopf Bifurcation properties to change the dynamic around the equilibrium point. A temporal switching technique is introduced for changing between three different bifurcation sliding surfaces at different time intervals. To illustrate that the quadcopter effectively performs the desired maneuvers, a computer animation is provided at the end of the paper.  相似文献   

3.
We used two simple control laws based on linear velocity and cubic velocity feedback to suppress the high-amplitude vibrations of a structural dynamic model of the twin-tail assembly of an F-15 fighter when subjected to primary resonance excitations. We developed the nonlinear differential equations of motion and obtained an approximate solution using the method of multiple scales. Then, we conducted bifurcation analyses for the open- and closed-loop responses of the system and investigated theoretically the performance of the control strategies. The theoretical findings indicate that the control laws lead to effective vibration suppression and bifurcation control. Furthermore, we conducted experiments to verify the theoretical analysis. We built a digital control system that consists of a SIMULINK modeling software and a dSPACE controller installed in a personal computer. Actuators made of piezoelectric ceramic material were used. The results show that both laws are effective at suppressing the vibrations. To compare the performance of both techniques, we calculated the power requirements for a simple system.  相似文献   

4.
Bifurcation theory is commonly used to study the dynamical behavior of ecosystems. It involves the analysis of points in the parameter space where the stability of the system changes qualitatively. The type of bifurcation that associates equilibria with periodic solution is called Hopf bifurcation. In this paper, a life energy system dynamic model of two components with multiple delays is presented. It is shown that the interaction parameters of the delayed ecosystem play a fundamental role in classifying the rich dynamics and bifurcation phenomena. Regarding the combined interaction parameter as a bifurcation parameter, the bifurcation values in the parameter plane are displayed. The direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions are determined by applying the normal form theory and the center manifold theorem. Moreover, the amplitudes of oscillations always increase as the interaction parameters increase, while the robustness of periods occurs as the interaction parameters vary. From an ecological point of view, the existence of Hopf bifurcation expresses periodic oscillatory behavior of the life energy system.  相似文献   

5.
Dielectrophoresis (DEP), the phenomenon of directed motion of electrically polarizable particles in a nonuniform electric field, is promising for applications in biochemical separation and filtration. For colloidal particles in suspension, the relaxation of the ionic species in the shear layer gives rise to a frequency-dependent, bidirectional DEP force in the radio frequency range. However, quantification methods of the DEP force on individual particles with the pico-Newton resolution required for the development of theories and design of device applications are lacking. We report the use of optical tweezers as a force sensor and a lock-in phase-sensitive technique for analysis of the particle motion in an amplitude modulated DEP force. The coherent detection and sensing scheme yielded not only unprecedented sensitivity for DEP force measurements, but also provided a selectivity that clearly distinguishes the pure DEP force from all the other forces in the system, including electrophoresis, electro-osmosis, heat-induced convection, and Brownian forces, all of which can hamper accurate measurements through other existing methods. Using optical tweezers-based force transducers already developed in our laboratory, we have results that quantify the frequency-dependent DEP force and the crossover frequency of individual particles with this new experimental method.  相似文献   

6.
血滤器的中空纤维聚砜膜的形态学观察方法的探讨和评价   总被引：1，自引：0，他引：1  
提出了2种用于构建生物人工肾小管的中空纤维膜聚砜膜表面的观察的新方法.采用免疫荧光染色(immunofluorescence staining,IF)和原子力显微镜(atomic force microscopy,AFM)对中空纤维聚砜膜内和外壁进行观察研究.实验表明免疫荧光染色方法简便快捷,图象清晰,AFM的分辨率高,图象清晰,是除扫描电镜(scanning electronic micmscope,SEM)外的两种观察生物人工肾小管的简便可靠方法.普通显微镜观察不能观察到中空纤维聚砜膜形态,AFM简便,图象清晰,分辨率较高,并且可以观察立体三维形态,实验结果显示IF和AFM是观察生物人工肾小管的中空纤维膜聚砜膜表面的观察的新方法,并且简便使用,分辨率高,能观察三维结构.  相似文献   

7.
环境规制作为影响企业发展的一个全新变量,必然会对企业行为和绩效产生冲击。企业要实现经济绩效和环境保护的双赢,必须构建主动型的环境战略。基于动态能力视角,探讨环境规制下企业环境战略转型的过程机制。研究认为:环境规制在直接催化环境战略转型的同时也促使企业通过组织学习不断更新提升动态能力;企业动态能力则通过影响转型时机、构建转型支撑体系以及选择转型路径推进企业环境战略的转型。该研究对企业加强环境保护、促进环境战略转型具有重要意义。  相似文献   

8.
任立  吴萌  甘臣林  陈银蓉 《资源科学》2020,42(2):286-297
在农村土地制度改革和劳动力向城市转移的双重背景下,农户群体正经历由传统“农业生产劳动力”向新型“农业经营决策者”的转型。面对土地投入“高成本、高劳耗和低效益”的现实特征,小型农户是典型的“风险规避者”,其土地投入行为对风险因素更加敏感,但其背后的认知机理和决策逻辑尚未明确。本文基于分布式认知理论和感知价值理论,结合武汉城市圈近郊区483名小型农户的微观调查数据,采用结构方程模型和系统动力学模型的分析方法,对农户土地投入风险认知的影响因素和土地投入行为的发展趋势分别进行了静态分析和动态仿真。研究表明：①农户土地投入感知风险遵循分布式认知的基本框架,受到“个人力”“地域力”和“文化力”3个认知功能系统的影响,其效应排序为“地域力>个人力>文化力”,农户对土地投入的风险认知主要来源于土地投入行为本身,同时也是个体内部因素和外部环境因素综合作用的结果;②“高风险、低收益→弱化感知价值→降低投入意愿→减少投入行为→较高风险、更低收益”的“递弱回路”是制约农户土地投入的基本逻辑,在一定的政策引导和禀赋约束条件下,农户能够在短期内保持土地投入行为,但传统的低效土地利用方式终将难以持续,对于小型农户而言,土地资源作为生产资料的功能性衰退将不可逆转。助力培育新型农业经营主体、加快促进农业现代化转型是未来农村土地制度改革的发展目标。  相似文献   

9.
In this paper, a biological economic system which considers a prey-predator system with Holling type II functional response and harvest effort on prey is proposed. By using the differential-algebraic system theory and Hopf bifurcation theory, Hopf bifurcation of the proposed system is investigated. Different from previous researches on the dynamic behaviors of predator-prey systems, our model is described by differential-algebraic equations due to the economic factor. The economic profit is chosen as a positive bifurcation parameter here. It is found that a phenomenon of Hopf bifurcation occurs as the economic profit increases beyond a certain threshold. Lastly, with the help of Matlab software, numerical simulations are carried out to demonstrate the effectiveness of our results.  相似文献   

10.
This paper is a study of the bending-torsional flutter of a cantilevered wing subjected to a follower force, and containing a lumped mass, at the free end. In addition, a distributed aerodynamic loading is introduced along the wing. This results in a set of nonself-adjoint differential equations with variable, complex coefficients whose solutions are obtainable only in series form. Using the Frobenius method, a direct procedure is employed which retains the exact expression of the Theodorsen function and the unknown coefficients are evaluated on a computer which numerically converge to any prescribed accuracy. It is found that, as a result of the interaction of the two sources of non-conservative loadings, the follower force reduces considerably the critical speed of flows in all cases studied. An increase in the tip mass, however, has a stabilizing influence. The effect of structural damping is also examined and it is shown that internal damping forces may have pronounced influences on the flutter speed of the system.  相似文献   

11.
Having found hidden hyperchaos in a 5D self-exciting homopolar disc dynamo, we study the existence of a Hopf bifurcation, which leads to unstable limit cycles bifurcating from a stable equilibrium. Hidden chaos with only stable equilibria can be observed from the Hopf bifurcation: a typical way to enable hidden attractors to be located. We then provide a new fuzzy controller, and a fast fuzzy disturbance observer, based on terminal sliding mode control for synchronization of the hyperchaotic system. Fuzzy inference is considered to weaken the chattering phenomena. Using Lyapunov stability theory, the stability of the closed-loop system is proved. Finally, simulations of synchronization are illustrated to show the efficient performance of the designed control method via external disturbances and dynamic uncertainties.  相似文献   

12.
王兰 《中国科技信息》2011,(19):104-105
重视机械结构系统的动力学问题,研究机械系统在实际工作状态下的受力变化、运动情况及其动态行为,以满足机械结构静、动态特性及低振动、低噪声的要求。因此,有必要对所设计的减速器系统进行扭振动力学分析,找到影响动态特性的薄弱环节,从而为进一步动态结构优化设计、提高减速器的动态性能提供了理论依据。  相似文献   

13.
The effects of an added mass on the oscillations of a SDOF bluff body, elastically supported, exposed to a steady flow and undergoing galloping oscillations, are investigated. The stability boundaries of the trivial equilibrium position of the 2DOF system are determined in a four parameters space. The occurrence of different types of bifurcation on these boundaries is highlighted, namely, simple Hopf, non-resonant double Hopf and 1 : 1 resonant double Hopf. The perturbation multiple scale method is employed to analyze the system postcritical behavior around the codimension-1 and codimension-2 critical manifolds. The analytical results are compared with numerical solutions obtained through direct integration of the equations of motion. Finally, the effects of the closeness of the critical frequencies on the non-resonant double Hopf manifold, are discussed by using a quasi-resonant asymptotic solutions.  相似文献   

14.
The space debris removal system (SDRS) of tethered space tug is modelled as a cable dragged flexible spacecraft. The main goal of this paper is to develop a dynamic modeling approach for mode characteristics analysis and forced vibration analysis of the planar motion of a cable dragged flexible spacecraft. Solar arrays of the spacecraft are modelled as multi-beams connected by joints with additional rotating spring where the nonlinear stiffness, damping and friction are considered. Using the Global mode method (GMM), a novel analytical and low-dimensional nonlinear dynamic model is developed for vibration analysis of SDRS to enhance the design capacity for better fulfillment of space tasks. The linear and nonlinear partial differential equations that governing transverse vibration of solar arrays, transverse and longitudinal vibrations of cable are derived, along with the matching and boundary conditions. The natural frequencies and analytical global mode shapes of SDRS are determined, and orthogonality relations of the global mode shapes are established. Dynamical equations of the system are truncated to a set of ordinary differential equations with multiple-DOF. The validity of the method is verified by comparing the natural frequencies obtained from the characteristic equation with those obtained from FEM. Interesting mode localization and mode shift phenomena are observed in mode analysis. Dynamic responses of the system excitated by fluctuation of attitude control torque and short-time attitude control torque are worked out, respectively. Nonlinear behaviors are observed such as hardening, jump and super-harmonic resonances. Residual vibration of the overall system with considering the varous values of nonlinear stiffness, damping coefficient and friction coefficient has shown that the nonlinearity of joints has a great influence on the vibration of the overall system.  相似文献   

15.
Ever-increasing hardware capabilities and computation powers have enabled acquisition and analysis of big scientific data at the nanoscale routine, though much of the data acquired often turn out to be redundant, noisy and/or irrelevant to the problems of interest, and it remains nontrivial to draw clear mechanistic insights from pure data analytics. In this work, we use scanning probe microscopy (SPM) as an example to demonstrate deep data methodology for nanosciences, transitioning from brute-force analytics such as data mining, correlation analysis and unsupervised classification to informed and/or targeted causative data analytics built on sound physical understanding. Three key ingredients of such deep data analytics are presented. A sequential excitation scanning probe microscopy (SE-SPM) technique is first developed to acquire high-quality, efficient and physically relevant data, which can be easily implemented on any standard atomic force microscope (AFM). Brute-force physical analysis is then carried out using a simple harmonic oscillator (SHO) model, enabling us to derive intrinsic electromechanical coupling of interest. Finally, principal component analysis (PCA) is carried out, which not only speeds up the analysis by four orders of magnitude, but also allows a clear physical interpretation of its modes in combination with SHO analysis. A rough piezoelectric material has been probed using such a strategy, enabling us to map its intrinsic electromechanical properties at the nanoscale with high fidelity, where conventional methods fail. The SE in combination with deep data methodology can be easily adapted for other SPM techniques to probe a wide range of functional phenomena at the nanoscale.  相似文献   

16.
A three-degree-of-freedom vibro-impact system is considered. The nonlinear dynamical model and the six-dimensional Poincaré map are established and the dynamical behaviors of the system, including double Neimark–Sacker bifurcation, torus T2 and its routes to chaos, is investigated by numerical simulations. As the control parameters vary, the torus T2 changes into multi-circle torus T1 via one-frequency phase locking on its position, which are divided into longitude circles and latitude circles, and the system keeps quasi-periodic motion. Further the impact motion settles into periodic orbit via two-frequency phase locking, then the system leads eventually to chaos. The second route to chaos shows, by establishing the secondary Poincaré section, that the torus T2 leads to chaos via torus doubling bifurcation and there may exist torus doubling cascade.  相似文献   

17.
Dynamic systems containing particles and rigid bodies capable of movement in two- or three-dimensions may be represented by equations of motion in several basic forms. In all cases geometric nonlinearities are involved and terms arise in the equations which are difficult to understand and interpret. The equations often conceal the basic structure of the dynamic model of the system since only combinations of parameters and combined effects of various constraints finally appear.In this paper the basic relations for the dynamic elements as well as the transformations among internal forces and velocities are depicted using bond graphs. The energetic structure of the system is thus exhibited in multiport form. This aids in the exploration of alternative equation formulation and in understanding of the assumptions involved in any particular equation set. Further, a bond graph model is easily coupled with nonmechanical dynamic models through force or motion generators.  相似文献   

18.
The maximum principle developed by Sloss et al. [Optimal control of structural dynamic systems in one space dimension using a maximum principle, J. Vibr. Control 11 (2005) 245–261] is used to determine the optimal control functions for a class of one-dimensional distributed parameter structures. The distributed parameter structures are governed by systems of fourth order hyperbolic equations with constant coefficients. A quadratic performance index is formulated as the cost functional of the problem and can be used to represent the energy of the structure and the force spent in the control process. The developed maximum principle establishes a theoretical foundation for the solution of the optimal control problem and relates the optimal control vector to an adjoint variable vector. The method of solution is outlined which involves reducing the original problem to a system of ordinary differential equations. The solution of the general problem is given and a structural control problem is solved to illustrate the solution procedure. The effectiveness of the proposed control solution is shown by comparing the behavior of controlled and uncontrolled systems.  相似文献   

19.
This paper presents an effective approach for controlling chaos. First, a neural-network (NN) model is employed to approximate the chaotic system. Then, a linear differential inclusion (LDI) state-space representation is established for the dynamics of an NN model. Based on the LDI state-space representation, a fuzzy controller is proposed to tame the chaotic system. If the designed fuzzy controller cannot suppress the chaos, a high frequency signal, commonly called dithers, is simultaneously injected into the chaotic system. According to the relaxed method, an appropriate dither is introduced to steer the chaotic motion into a periodic orbit or a steady state. If the frequency of dither is high enough, the trajectory described by the dithered chaotic system and that of its corresponding mathematical model—the relaxed system can be made as close as desired. This phenomenon enables us to get a rigorous prediction of the dithered chaotic system’s behavior by obtaining the behavior of the relaxed system. Finally, a numerical example with simulations is given to illustrate the concepts discussed throughout this paper.  相似文献   

20.
In this paper, a delayed feedback controller with the delay-dependent coefficient is introduced into a multiple delay phytoplankton-zooplankton system. For uncontrolled system, choosing delays as the bifurcation parameters, we prove that Hopf bifurcation can occur when the delays change and cross some values. Then, the delays are still chosen as the bifurcation parameters to research the dynamic behaviors of the controlled system. Under this control mechanism, the onset of Hopf bifurcation can be delayed by selecting the appropriate control parameters and the stability domain can be extended as feedback gain (the decay rate) decreases (increases), and the influence of the decay rate cannot be ignored. Furthermore, using the crossing curve methods, the stable changes of equilibrium in two delay plane can be obtained. Some numerical simulations are given to verify the correctness and validity of the delayed feedback controller in the bifurcation control.  相似文献   

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