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1.
几种一维原子链晶格振动特性比较研究 总被引：2，自引：0，他引：2
本文从结构、态密度和本征波函数三个方面系统研究了单原子周期链、双原子周期链、无序链、纳米链、Ｆｉｂｏｎａｃｃｉ准晶链和Ｔｈｕｅ－Ｍｏｒｓｅ链六种一维体系的晶格振动特性，给出并讨论了他们的区别和联系。 相似文献
2.
Nanostructure-based surface-enhanced infrared absorption (SEIRA) spectroscopy has attracted tremendous interest as an ultrasensitive detection tool that supplies chemical-fingerprint information. The interactions between molecular vibrations and plasmons lead to not only the enhancement of spectral intensity, but also the distortion of spectral Lorentzian lineshapes into asymmetric Fano-type or more complicated lineshapes in the SEIRA spectra; this effect hampers the correct readout of vibrational frequencies and intensities for an accurate interpretation of the measured spectra and quantitative analysis. In this work, we investigate the Fano interference between molecular vibrations and plasmons based on exact electrodynamic simulations and theoretical models. We report that, even if the molecular vibrational energy is equal to the plasmon resonant energy, the molecule–nanostructure distance-dependent dipole–dipole interactions, the plasmon-mediated coherent intermolecular interactions and the decay rates of plasmons have a significant impact on the SEIRA lineshapes. This study paves the way for controllable Fano interference at the nanoscale and more studies on plasmon-dressed molecular electronic or vibrational excited states. 相似文献
3.
The atomic force microscope system (AFM) has become a popular and useful instrument to measure the intermolecular forces with atomic resolution that can be applied in electronics, biological analysis, materials, semiconductors, etc. This paper studies the bifurcation phenomenon and complex nonlinear dynamic behavior of the probe tip between the sample and microcantilever of an atomic force microscope using the differential transformation method. The dynamic behavior of the probe tip is characterized with reference to bifurcation diagrams, phase portraits, power spectra, Poincaré maps, and maximum Lyapunov exponent plots produced using the time-series data obtained from differential transformation method. The results indicate that the probe tip behavior is significantly dependent on the magnitude of the vibrational amplitude. Specifically, the probe tip motion changes from T-periodic to 3T-periodic, then from 6T-periodic to multi-periodic, and finally to chaotic motion with windows of periodic motion as the vibrational amplitude is increased from 0 to 5.0. Furthermore, it is demonstrated that the differential transformation method is in good agreement for the considered system. 相似文献
4.
张立敏 《中国科学院研究生院学报》2010,27(3):289-305
综述了近几年来关于三原子分子离子(CS+2, SO+2, CO+2)的光激发和光解离动力学研究结果.实验是在射流气束条件下进行的.首先利用一束电离激光使中性三原子分子通过共振增强多光子电离制备出振动态选择的三原子分子离子,再用一束或两束解离激光激发获得母体分子离子的光解离谱(母体离子的凹陷谱和碎片离子的增强谱).由此研究了三原子分子离子(CS+2, SO+2, CO+2)电子态的光激发和光解离动力学. 相似文献
5.
Yao Zhang Ben Yang Atif Ghafoor Yang Zhang Yu-Fan Zhang Rui-Pu Wang Jin-Long Yang Yi Luo Zhen-Chao Dong J G Hou 《国家科学评论(英文版)》2019,6(6):1169
The strong spatial confinement of a nanocavity plasmonic field has made it possible to visualize the inner structure of a single molecule and even to distinguish its vibrational modes in real space. With such ever-improved spatial resolution, it is anticipated that full vibrational imaging of a molecule could be achieved to reveal molecular structural details. Here we demonstrate full Raman images of individual vibrational modes at the ångström level for a single Mg-porphine molecule, revealing distinct characteristics of each vibrational mode in real space. Furthermore, by exploiting the underlying interference effect and Raman fingerprint database, we propose a new methodology for structural determination, which we have called ‘scanning Raman picoscopy’, to show how such ultrahigh-resolution spectromicroscopic vibrational images can be used to visually assemble the chemical structure of a single molecule through a simple Lego-like building process. 相似文献
6.
In this paper, we first develop an adaptive shifted Legendre–Gauss (ShLG) pseudospectral method for solving constrained linear time-delay optimal control problems. The delays in the problems are on the state and/or on the control input. By dividing the domain of the problem into a uniform mesh based on the delay terms, the constrained linear time-delay optimal control problem is reduced to a quadratic programming problem. Next, we extend the application of the adaptive ShLG pseudospectral method to nonlinear problems through quasilinearization. Using this scheme, the constrained nonlinear time-delay optimal control problem is replaced with a sequence of constrained linear-quadratic sub-problems whose solutions converge to the solution of the original nonlinear problem. The method is called the iterative-adaptive ShLG pseudospectral method. One of the most important advantages of the proposed method lies in the case with which nonsmooth optimal controls can be computed when inequality constraints and terminal constraints on the state vector are imposed. Moreover, a comparison is made with optimal solutions obtained analytically and/or other numerical methods in the literature to demonstrate the applicability and accuracy of the proposed methods. 相似文献
7.
简单阐述了压缩机旋转失速和喘振的关系,着重分析压缩机旋转失速和喘振的产生机理.由于离心武压缩机发生故障的主要特征是机器伴有异常的振动和噪声.振动信号是周期性信号,利用频域分析的方法对离心式压缩机故障进行诊断.取得了很好的效果. 相似文献
8.
《Journal of The Franklin Institute》2019,356(14):7785-7809
Distributed multi-actuator systems can provide effective solutions for mitigating the vibrational response of large structures. In this paper, we present a computational strategy to design inerter-based multi-actuation systems for the seismic protection of adjacent structures. The proposed approach allows considering both interstory and interbuilding Tuned Mass-Inerter Damper (TMID) actuators, and aims at simultaneously reducing the vibrational response of the individual buildings and avoiding the interbuilding impacts. The tuning procedure is based on an H∞ cost-function and uses a constrained global-optimization solver to compute parameter configurations with high-performance characteristics. To illustrate the main features of this work, two different Tuned Inerter Damper (TID) multi-actuator schemes are considered for the seismic protection of a particular multi-story two-building system. A multi-actuator Tuned Mass Damper (TMD) system is also designed and is taken as a reference in the performance assessment. The obtained results demonstrate the flexibility and effectiveness of the proposed design methodology, and clearly show the superior performance and robustness of the TID actuation systems. 相似文献
9.
A novel control scheme combining disturbance observer technique and back-stepping method is proposed for a class of nonlinear system with multiple mismatched disturbances. The uncertain multiple mismatched disturbances contain not only single harmonic or constant disturbances but also another unexpected nonlinear signal presented as a nonlinear function. The composite adaptive disturbance observers are designed to estimate the disturbances with partial known information. By integrating disturbance observer based control with back-stepping method, a composite controller is designed. Here, the disturbance estimations are introduced into the design of virtual control laws in each step to compensate the mismatched disturbances. Rigorous stability analysis for the closed-loop system is established by direct Lyapunov function method. It is shown that the system output asymptotically converges to zero in spite of existing multiple mismatched disturbances. Finally, a simulation example is applied to demonstrate the effectiveness of the proposed method. 相似文献
10.
《Journal of The Franklin Institute》2021,358(13):6385-6407
Most extant control designs for uncertain pure-feedback systems are based on backstepping procedure or dynamic surface control, requiring repeated calculation or approximation of the derivatives of the virtual control action. The fuzzy logic systems or neural networks used to cope with unknown dynamics also inherently introduce excess computation burden and sluggish convergence. In view of these, this paper provides a novel backstepping approach by combining extended state observers with dynamic inversion controllers. With high gain properties both on the observers and controllers, the resulting closed-loop system presents relatively fast convergence. By using dynamic inversion backstepping, the explosion of complexity problem that restricts the applicability of backstepping-like control methods, which are representatively employed to the control of pure-feedback systems, is entirely surmounted without resorting to filtering. The theoretical analysis of stability shows the closed-loop system has adjustable tracking performance. Finally, the efficiency of the proposed method is illustrated by comparative simulations. 相似文献
11.
《Journal of The Franklin Institute》2022,359(10):4699-4726
The vibration of a railway car body is a superposition of the vibrations of its various modes. It is typically easy to obtain the physical vibration of the car body using sensors in an in situ or a simulated test vehicle. However, it is difficult to determine the modal vibration of the body and its contribution. There are no effective multi-mode vibration control methods for the car bodies. This study proposes a modal vibration decomposition method (MVDM) based on singular value decomposition (SVD) and least squares fitting (LSF). Accordingly, the physical vibration of a railway car body is decomposed into modal vibrations. A method for calculating the modal contribution factor (MCF) is presented, and the dominant flexible modes of the car body are determined and considered the target for the vibration control method. Several pieces of equipment are considered as dynamic vibration absorbers (DVAs) to control the multi-mode vibration of the car body using the dynamic vibration absorption theory and determine the installation parameters of the individual equipment. Finally, the effectiveness of vibration control is verified through dynamic simulations. The results demonstrate the effective decomposition of the physical vibration of the car body into various modal vibrations using the MVDM. This provides accurate data for the MCF calculation and determination of the flexible modes of the car body. The proposed method reduces the vibration of the target modes and improves the ride quality of the railway vehicle. At the optimal damping ratio, the vibration of the DVA-based equipment itself is acceptable. This allows for multi-mode vibration control without requiring extensive modification to the car body structure or suspension system parameters of the vehicle. 相似文献
12.
《Journal of The Franklin Institute》2023,360(10):6994-7020
This paper investigates the event-based consensus problems for linear multi-agent systems under directed network topology. First, a new event-triggered control method is proposed for the leader-following consensus problem of agents under directed graphs. Then this new method is applied to the cluster control problem under special topological conditions. The new event-based control scheme is better than some existing literature in the following aspects. 1) The graph only needs to contain a spanning tree instead of being required to be strongly connected graph or undirected, and the triggering function is state-dependent rather than time-dependent. 2) Some parameters are designable for the trade-off between the event interval and the performance of the controlled system. Besides, the optimization of some parameters is studied to reduce the trigger frequency. All the agents can achieve consensus with an exponential speed when communications among follower agents are intermittent, and Zeno behavior is excluded under the proposed method. 3) When applying this method to the cluster control problem, agents in the same cluster share the same form of triggering function. Cluster consensus can be achieved regardless of intra- and inter-cluster relative coupling strength under the event-triggered control framework. 相似文献
13.
It is advantageous to use the substructural and/or decentralized techniques in structural control to save on computations and time. In this paper, a generalized substructural approach is presented in the control of fuzzy nonlinear flexible structures with discrete sensors/actuators. The substructural control scheme is developed using the static condensation technique together with the LQG control method. The subcontrollers and subobservers designed at substructure levels are used to assemble the global controller and observer for the whole structure. Nonlinear effects are included in the structural formulations and a fuzzy methodology is adopted for handling the imprecision present in the structure modeling. The nonlinear and fuzzy schemes are applied to one structural control problem to illustrate the accuracy and capability of the substructural control technique. 相似文献
14.
Data-driven fault diagnosis of closed loop processes has been a challenge in the process control community. The issue of the interaction between the process model and the controller model exists in models directly identified from closed loop data, because for all the measured process outputs, no matter whether they are normal or faulty, they are fed back into the controllers so that the reconstruction-based contribution (RBC) as the fault diagnosis method has a severe fault smearing effect. This article proposes a novel sampling scheme which can significantly eliminate the adverse effect of modeling issues in feedback control. The identifiability condition of model parameters is satisfied in the new sampling framework so that the RBC recovers its efficiency even though the process runs under feedback control. Two benchmarks, a continuous stirred-tank heater process and the Tennessee Eastman challenge problem, are used to test the efficiency of the proposed method. 相似文献
15.
It is well known that sliding mode control is based on the definition of an invariant manifold, where the system dynamics are forced to in a finite time. Such a manifold is somewhat arbitrarily defined, as long as the system dynamics are stable on it. Computational and control effort may vary depending on selected manifold. Obviously, if a system has naturally acceptable stable dynamics around a desired equilibrium point, no control is needed unless uncertainties or disturbances are present. It would be desirable that if such a system had uncertainties or disturbances, the control effort be designed only to overcome the effect of such factors. For a system with first order dynamics and affine control input, designing a sliding mode control overcoming only such uncertainties or disturbances is a trivial task. When a higher order dynamics system is involved, unit control may be used, where the input control signals are not discontinuous, but when only discontinuous control inputs are available, a design approach is not readily available. In this paper, taking advantage of the natural stable dynamics of a system, a sliding mode control approach is introduced for designing multiple discontinuous control inputs, where the control effort overcomes only uncertainties, disturbances or unstable dynamics. Two illustrative examples are given in order to show the feasibility of the method. 相似文献
16.
金融投资的操作风险是与金融投资业务相联系的风险,它包括因内部风险因素导致的操作失败风险和因对外部环境因素做出反应时选择不恰当战略所致的操作战略风险。其度量方法以分析或评价方法为主。对操作风险进行管理首先应制定明确的操作风险控制政策,包括为交易员或业务设定合适的操作风险限额以及建立完善的内部控制制度等;其次,要对每一项业务设置规范化的操作流程和投资决策流程;另外,还要对职员进行相关的培训和风险教育。 相似文献
17.
信息化背景下以抖音和快手为代表的短视频APP（手机应用软件）快速普及应用为数字农技推广提供新途径。以湖北省和河南省770份水稻和小麦种植户样本数据,运用内生转换概率模型验证了短视频APP使用对农户绿色防控技术采纳的影响。研究发现：①37.78%的样本农户使用抖音、快手和西瓜等自媒体短视频APP查询浏览过绿色防控技术信息。影响农户使用短视频APP的因素主要有受访者年龄、教育年限、兼业状态、家庭收入和公职身份。②农户使用短视频APP可以显著提升绿色防控技术采纳概率9.0%~10.4%。且运用倾向得分匹配法、样本调整检验法和安慰剂检验法等进行了稳定性检验,结论依然成立。③研究进一步发现,短视频APP使用主要通过提升农户绿色防控技术易用性感知,进而促进绿色防控技术采纳。因此,在数字经济发展背景下,要善于利用抖音和快手等短视频APP搭建数字农技推广服务平台,要鼓励新型农业经营主体和种植能手参与绿色防控技术的分享与传播。并通过绿色农产品优质优价的市场力量来助力绿色防控技术的推广应用。 相似文献
18.
《Journal of The Franklin Institute》2023,360(7):4947-4972
Attitude takeover control of failed spacecraft, which is a key technology in on-orbit service, has received extensive attention in recent years. In the attitude takeover control mission, inertial parameters of the failed spacecraft are unknown or inaccurate. In the meantime, actuator consumption must be considered owing to the limited fuel or energy of the service spacecraft. Using a failed spacecraft takeover control mission executed by multiple nanosatellites as an example, an optimal attitude takeover control method is proposed in this paper to optimize actuator consumption while addressing model uncertainties. Firstly, an auxiliary nonlinear system is constructed and then a radial basis function neural network is employed to estimate the unknown nonlinear dynamics model. Secondly, an optimal control law is designed by combining the inverse optimal principle, adaptive technique, and backstepping theory. Finally, the Harris Hawks optimization (HHO) is adopted for the control allocation problem of multiple nanosatellites. Simulation results demonstrate the feasibility and effectiveness of the proposed method. 相似文献
19.
The present paper proposes a numerical approach to a linear optimal control problem with a quadratic performance index. In this technique, the time interval is divided into a number of time segments and all of the unknown functions which appear in the performance index are either interpolated linearly with respect to time or assumed to be constant in each time segment. The augmented performance index is discretized within each time element through the ordinary finite element technique.The main advantage of the present method is as follows: all of the necessary conditions for the performance index to be stationary can be expressed in the form of algebraic equations and the performance sequence of the state variables can be eliminated. As a result, the optimal control problem is reduced to the simple one of finding the sequence of control variables alone, which minimizes the quadratic performance index.A general formulation of the method is given and simple numerical examples are shown to demonstrate the effectiveness of the technique. 相似文献
20.
《Journal of The Franklin Institute》2021,358(16):8443-8469
Rejection of periodic disturbance and/or tracking of periodic reference is of importance in high-precision control systems. Conventional repetitive control is often used to solve the problem, but it cannot precisely set effective frequency points and adversely amplify the non-periodic component disturbance. Therefore, it is not applicable in actual systems where external disturbances exist in the whole frequency domain. In this paper, we propose an improved discrete-time repetitive control method based on the disturbance observer to correct the undesired deviation at repetitive frequencies and mitigate the amplification of the non-components. Moreover, in the observer structure, an intuitive and flexible Q-filter design is presented to suppress low-frequency broadband and intermediate-frequency narrowband disturbances. The conditions of closed-loop stability, performance analysis, and the implementation of the proposed scheme are provided in detail. Finally, the effectiveness of the method is verified by simulation and experimentation on an optoelectronic precision positioning system under the condition of disturbances, and the disturbance suppression and tracking error attenuation are improved. 相似文献