A vacuum tube amplifier for small direct voltages

A simple means for combining a small direct voltage with an alternating carrier is described. This consists of connecting the direct voltage in series with an alternating voltage of the same order of magnitude. The two are then passed through a copper oxide rectifier which suppresses one part of the cycle. The degree of suppression depends upon the magnitude of the direct voltage. The resulting fluctuating voltage can be amplified to any desired degree in a conventional amplifier.The theory for the simple case of pure resistance is worked out, with an example. The solution of the more general case with inductances is indicated.The practical circuit which has been used for the amplification of thermo-couple currents, and as a galvanometer power multiplier, is shown.     

Local exponential stabilization via boundary feedback controllers for a class of unstable semi-linear parabolic distributed parameter processes

This paper addresses the problem of local exponential stabilization via boundary feedback controllers for a class of nonlinear distributed parameter processes described by a scalar semi-linear parabolic partial differential equation (PDE). Both the domain-averaged measurement form and the boundary measurement form are considered. For the boundary measurement form, the collocated boundary measurement case and the non-collocated boundary measurement case are studied, respectively. For both domain-averaged measurement case and collocated boundary measurement case, a static output feedback controller is constructed. An observer-based output feedback controller is constructed for the non-collocated boundary measurement case. It is shown by the contraction semigroup theory and the Lyapunov’s direct method that the resulting closed-loop system has a unique classical solution and is locally exponentially stable under sufficient conditions given in term of linear matrix inequalities (LMIs). The estimation of domain of attraction is also discussed for the resulting closed-loop system in this paper. Finally, the effectiveness of the proposed control methods is illustrated by a numerical example.     

Control of PDE-ODE cascades with Neumann interconnections

We extend several recent results on full-state feedback stabilization and state estimation of PDE-ODE cascades, where the PDEs are either of heat type or of wave type, from the previously considered cases where the interconnections are of Dirichlet type, to interconnections of Neumann type. The Neumann type interconnections constrain the PDE state to be subject to a Dirichlet boundary condition at the PDE-ODE interface, and employ the boundary value of the first spatial derivative of the PDE state to be the input to the ODE. In addition to considering heat-ODE and wave-ODE cascades, we also consider a cascade of a diffusion-convection PDE with an ODE, where the convection direction is “away” from the ODE. We refer to this case as a PDE-ODE cascade with “counter-convection.” This case is not only interesting because the PDE subsystem is unstable, but because the control signal is subject to competing effects of diffusion, which is in both directions in the one-dimensional domain, and counter-convection, which is in the direction that is opposite from the propagation direction of the standard delay (transport PDE) process. We rely on the diffusion process to propagate the control signal through the PDE towards the ODE, to stabilize the ODE.     

Output feedback adaptive robust control of hydraulic actuator with friction and model uncertainty compensation

This paper studies output feedback control of hydraulic actuators with modified continuous LuGre model based friction compensation and model uncertainty compensation. An output feedback adaptive robust controller is constructed which combines the adaptive control part and the robust control part seamlessly. The adaptive part is constructed to handle the parametric uncertainties existed in the model. The residuals coming from parameter adaption and the unmodeled dynamics are taken into consideration by the robust part. Since only the position signal is available, the velocity, pressure, and internal friction states are obtained by observation or estimation. The errors coming from observation and estimation are also dealt with the robust part. Furthermore, the convergence of the closed-loop controller–observer scheme is achieved by the Lyapunov method in the presence of parametric uncertainties only. Extensive comparative experiments performed on a hydraulic actuator demonstrate the effectiveness of the proposed controller–observer scheme.     

Stabilization for a coupled PDE–ODE control system

A control system of an ODE and a diffusion PDE is discussed in this paper. The novelty lies in that the system is coupled. The method of PDE backstepping as well as some special skills is resorted in stabilizing the coupled PDE–ODE control system, which is transformed into an exponentially stable PDE–ODE cascade with an invertible integral transformation. And a state feedback boundary controller is designed. Moreover, an exponentially convergent observer for anti-collocated setup is proposed, and the output feedback boundary control problem is solved. For both the state and output feedback boundary controllers, exponential stability analyses in the sense of the corresponding norms for the resulting closed-loop systems are given through rigid proofs.     

Pertubation in the I/O Map of a Non-linear Feedback System Caused by Large Plant Perturbation

This paper studies the perturbation in the input-output (I/O) map of a multi-input multi-output non-linear feedback system caused by large plant perturbations. It compares the effect of these perturbations on the given feedback system and on the nominally equivalent open-loop system. First the unity feedback system is considered, then a more general configuration—which includes the usual summing node as a special case—is analyzed. In both cases it is shown that the degree of desensitization provided by feedback is controlled by the linearized return difference operator.     

Optimal time-delayed open/closed-loop control of a damped beam

Vibration suppression of a structurally damped beam via open and closed-loop controls is investigated. In doing so, minimization of a weighted, energy-based performance measure leads to closed-form expressions for optimal open-loop parameters in terms of feedback gains. The control problem is then completed by optimizing these feedback parameters numerically. Methods to determine optimal terminal time of control are also presented. Furthermore, techniques are established to optimize the response and performance of a system experiencing a known feedback time delay. Different types of optimization are proposed and, for each one, the trade-off between performance and computational efficiency is fully discussed.     

The role of feedback in changing organizational routine: A case study of Haier,China

The ability to change organizational routines according to the need of organizational transformation is difficult to achieve, but increasingly vital for an organization to survive in a highly turbulent business environment. However, despite fruitful research on organizational routines, how routines evolve through feedback remains unclear. This study aims to investigate the role of feedback in routine changes by examining a case study of Haier, the largest home appliance manufacturer in the world. The findings of this case show that feedback of a routine plays a critical role in routine changes. It highlights that feedback helps an organization to make sense of its behavior patterns and evaluate these patterns properly, which enable the organizations to better initiate and advocate routine changes that are necessary for a successful organizational transformation. Further, this case shows the importance of leveraging IT in managing routine changes.     

Finite-time lag synchronization of master-slave complex dynamical networks with unknown signal propagation delays

This paper studies the finite-time lag synchronization issue of master-slave complex networks with unknown signal propagation delays by the linear and adaptive error state feedback approaches. The unknown signal propagation delays are fully considered and estimated by adaptive laws. By designing new Lyapunov functional and discontinuous feedback controllers, which involves the estimated error rather than the general synchronization error, sufficient conditions are derived to ensure lag synchronization of the networks within a setting time. It is interesting to discover that the setting time is related to initial values of both the estimated error and the estimated unknown signal propagation delays. Finally, two numerical examples are given to illustrate the effectiveness and correctness of the proposed finite-time lag synchronization criteria.     

On the dynamics of a quantum coherent feedback network of cavity-mediated double quantum dot qubits

The purpose of this paper is to present a comprehensive study of a coherent feedback network where the main component consists of two distant double quantum dot (DQD) qubits which are directly coupled to a cavity. This main component has recently been physically realized (van Woerkom et al., Microwave photon-mediated interactions between semiconductor qubits, Physical Review X, 8(4):041018, 2018). The feedback loop is closed by cascading this main component with a beamsplitter. The dynamics of this coherent feedback network is studied from three perspectives. First, an analytic form of the output single-photon state of the network driven by a single-photon state is derived. In contrast to the experimental observations made in the above paper where a laser is used as input, new interesting physical phenomena are revealed by means of single-photon input. Second, excitation probabilities of DQD qubits are computed when the network is driven by a single-photon input state. Finally, if the input is vacuum but one of the two DQD qubits is initialized in its excited state, the explicit expression of the steady-state joint system-field state is derived, which shows that the output single-photon field and the two DQD qubits can form an entangled state if the transition frequencies of two DQD qubits are equal. This analytical expression can be used to interpret experimental results in the existing literature.     

Bifurcation and control of a planktonic ecological system with double delays by delayed feedback control

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.     

Verbosity normalized pseudo-relevance feedback in information retrieval

Document length normalization is one of the fundamental components in a retrieval model because term frequencies can readily be increased in long documents. The key hypotheses in literature regarding document length normalization are the verbosity and scope hypotheses, which imply that document length normalization should consider the distinguishing effects of verbosity and scope on term frequencies. In this article, we extend these hypotheses in a pseudo-relevance feedback setting by assuming the verbosity hypothesis on the feedback query model, which states that the verbosity of an expanded query should not be high. Furthermore, we postulate the following two effects of document verbosity on a feedback query model that easily and typically holds in modern pseudo-relevance feedback methods: 1) the verbosity-preserving effect: the query verbosity of a feedback query model is determined by feedback document verbosities; 2) the verbosity-sensitive effect: highly verbose documents more significantly and unfairly affect the resulting query model than normal documents do. By considering these effects, we propose verbosity normalized pseudo-relevance feedback, which is straightforwardly obtained by replacing original term frequencies with their verbosity-normalized term frequencies in the pseudo-relevance feedback method. The results of the experiments performed on three standard TREC collections show that the proposed verbosity normalized pseudo-relevance feedback consistently provides statistically significant improvements over conventional methods, under the settings of the relevance model and latent concept expansion.     

Optimum tearing in large scale systems and minimum feedback cutsets of a digraph

In this paper we consider the problem of finding a minimum number of nonzero elements of a given nxn matrix on removal of which the resulting matrix can be permuted to an nxn lower triangular matrix using summetric permutations on the rows and columns of the matrix. The problem is related to finding a minimum feedback cutset for the digraph of the matrix. A topological method for finding a minimum feedback cutset for a given digraph is presented. Possible extensions to our work are indicated.     

排列组合解题的常用策略

排列组合是数学比较独特的一部分，是进一步学习概率的基础，同时这个知识模块也是考试必考的环节之一，知识虽然比较容易掌握，也比较有趣，但是题型非常多，本文主要根据自己的教学经验，总结排列组合解题的常用策略，希望能为教育工作者带来一些帮助。     

Lyapunov-based design of locally collocated controllers for semi-linear parabolic PDE systems

The design problem of collocated feedback controllers is addressed in this paper for a class of semi-linear distributed parameter systems described by parabolic partial differential equation (PDE), where a finite number of local actuators and sensors are intermittently distributed in space. A Lyapunov direct method for the exponential stability analysis of the resulting closed-loop system is first presented for the system, in which the first mean value theorem for integration and the Wirtinger's inequality are employed. The corresponding stabilization condition is then derived through the analysis result. Finally, the proposed design method is implemented on the feedback control of a fisher equation and its effectiveness is evaluated through simulation results.     

Immunomodulation of excretory secretory materials from the filarial parasite<Emphasis Type="Italic">Setaria digitata</Emphasis>

ES materials released along with the release of mf showed immunosuppression as evidenced by a decrease in T lymphocyte levels in the immunised animals. Lipid fractions of the mf associated ES materials and protein fractions of the detergent soluble materials were found to cause suppression of immune response in the host. Further study revealed that the suppression associated with the lipid fractions is actually the end result and that mf associated ES materials is actually a mixture of immunosuppressive and immunopotentiating components and the release of the components is most likely regulated.     

反馈寻求行为对制造业服务化的跨层次影响机制

基于制造业企业301份调查问卷数据提出并验证反馈寻求、双元创新、组织整合惯性、组织结构特性、组织公平感和制造业服务化的跨层次有中介的调节模型。实证结果表明反馈寻求行为正向影响制造业服务化,并以组织双元创新为中介;此外,组织整合惯性,组织结构特性和组织公平感在其中产生正向和负向的调节作用。研究结论对我国整体制造业企业如何有效的利用反馈寻求行为和双元创新促进制造业服务化具有现实借鉴意义。     

神经网络的特点及改进方法综述

本文在对前馈神经网络训练算法分析的基础上,阐述了标准BP算法的特点,并分析了在实际应用中存在的不足,指出了产生不足的原因,最后介绍了一些常见的改进算法,说明了进一步研究的方向。     

Anti-disturbance stabilization for a hybrid system of non-uniform elastic string

This paper is concerned with the anti-disturbance boundary feedback stabilization for a hybrid system coupling a non-uniform elastic string with a rigid body at one end by the active disturbance rejection control technology. An infinite-dimensional disturbance estimator and a Luenberger state observer are designed to estimate the disturbance and state of the system, respectively, based on which, a boundary output feedback control is further proposed to stabilize the system. The control consists of two parts: one part is for the stabilization of system without external disturbance, and the other part is for the rejection of the disturbance by virtue of the disturbance estimator. The well-posedness and exponential stability of the closed-loop system are proved by employing the semigroup theories and frequency domain method. Besides, all the signals of the closed-loop system are shown to be uniformly bounded. Finally, some numerical simulations are presented to validate the effectiveness of the proposed control strategy.     

Stabilization of periodic oscillations with transient delayed feedback control

Transient delayed feedback control is proposed by applying the transient control technique to the original delayed feedback control, with the aim of enlarging the stable region of the stabilized periodic oscillation, where the stable region is a subset of the parameter space of feedback gains for which the periodic oscillation is stabilized. The control signal is activated when the system is in a certain subset (the controlling area) of the state space, and inactivated otherwise, which is different from the standard control signal of the original delayed feedback control. The specific control performances of the transient delayed feedback control are investigated through case studies. The relationship between the stable region of the stabilized periodic oscillation and the controlling area is obtained by calculating the maximum Lyapunov exponent, which is a function of the feedback gain. It is shown that the stable region varies non-smoothly with the change of the controlling area. When the controlling area is properly chosen, the stable region with transient delayed feedback control is much larger than the stable region with original delayed feedback control.