Numerical nonlinear observers using pseudo‐Newton‐type solvers

In constructing a globally convergent numerical nonlinear observer of Newton‐type for a continuous‐time nonlinear system, a globally convergent nonlinear equation solver with a guaranteed rate of convergence is necessary. In particular, the solver should be Jacobian free, because an analytic form of the state transition map of the nonlinear system is generally unavailable. In this paper, two Jacobian‐free nonlinear equation solvers of pseudo‐Newton type that fulfill these requirements are proposed. One of them is based on the finite difference approximation of the Jacobian with variable step size together with the line search. The other uses a similar idea, but the estimate of the Jacobian is mostly updated through a BFGS‐type law. Then, by using these solvers, globally stable numerical nonlinear observers are constructed. Numerical results are included to illustrate the effectiveness of the proposed methods. Copyright © 2007 John Wiley & Sons, Ltd.     

含碳肥料与碳营养的探讨研究

碳是植物必需的营养元素,但土壤和部分肥料中有效碳含量很低,制约了作物高产和优质。介绍了碳元素的营养功能和碳营养现状,定义了含碳肥料的概念,分类讨论了有机含碳肥料、无机含碳肥料和含碳微生物肥料,并对碳营养的概念进行了探讨。     

Adaptive set‐point regulation of discrete‐time nonlinear systems

In this paper, adaptive set‐point regulation controllers for discrete‐time nonlinear systems are constructed. The system to be controlled is assumed to have a parametric uncertainty, and an excitation signal is used in order to obtain the parameter estimate. The proposed controller belongs to the category of indirect adaptive controllers, and its construction is based on the policy of calculating the control input rather than that of obtaining a control law. The proposed method solves the adaptive set‐point regulation problem under the assumption that the target state is reachable for each fixed parameter value. Additional feature of the proposed method is that Lyapunov‐like functions have not been used in the construction of the controllers. Copyright © 2015 John Wiley & Sons, Ltd.     

Hypergravity of 10<Emphasis Type="Italic">g</Emphasis> Changes Plant Growth,Anatomy, Chloroplast Size,and Photosynthesis in the Moss <Emphasis Type="Italic">Physcomitrella patens</Emphasis>

The photosynthetic and anatomical responses of bryophytes to changes in gravity will provide crucial information for estimating how these plant traits evolved to adapt to changes in gravity in land plant history. We performed long-term hypergravity experiments at 10g for 4 and 8 weeks using the moss Physcomitrella patens with two centrifuges equipped with lighting systems that enable long-term plant growth under hypergravity with irradiance. The aims of this study are (1) to quantify changes in the anatomy and morphology of P. patens, and (2) to analyze the post-effects of hypergravity on photosynthesis by P. patens in relation to these changes. We measured photosynthesis by P. patens for a population of gametophores (e.g., canopy) in Petri dishes and plant culture boxes. Gametophore numbers increased by 9% for a canopy of P. patens, with 24–27% increases in chloroplast sizes (diameter and thickness) in leaf cells. In a canopy of P. patens, the area-based photosynthesis rate (A _canopy) was increased by 57% at 10g. The increase observed in A _canopy was associated with greater plant numbers and chloroplast sizes, both of which involved enhanced CO₂ diffusion from the atmosphere to chloroplasts in the canopies of P. patens. These results suggest that changes in gravity are important environmental stimuli to induce changes in plant growth and photosynthesis by P. patens, in which an alteration in chloroplast size is one of the key traits. We are now planning an ISS experiment to investigate the responses of P. patens to microgravity.     

A method of damping transient rush voltage fluctuation of power systems due to a wind driven generator via nonlinear state feedback control

Squirrel-cage induction generators are widely used as generators for windmill power systems, because they are inexpensive, have high durability, and are capable of operating asynchronously with power systems. However, induction generators suffer the drawback that they cause transient rush currents that are several times larger than the rated value when connected to power systems. Also since wind energy is influenced by geographic and weather conditions, start/stop operations occur frequently for windmill power systems. Therefore, connecting induction generators to power systems causes undesirable voltage fluctuations in power systems, which is the major obstacle against the practical use of windmill generator systems. This motivates the study of transient rush current/voltage attenuation in windmill generator systems. In this paper, a nonlinear state-feedback controller for windmill power systems is proposed. The proposed controller globally asymptotically stabilizes the plant and effectively attenuates the transient current/voltage of these systems. Computer simulations using parameters for an actual windmill generator system also gave good results. © 1998 Scripta Technica, Electr Eng Jpn, 124(1):17–23, 1998     

Stabilization of continuous‐time homogeneous bilinear systems by constant inputs through nonlinear minimization with applications to the static output feedback stabilization problem

An algorithm to provide constant‐input stabilizing control inputs for multi‐input continuous‐time bilinear systems is proposed in this paper. The algorithm is based on the formal discrete‐time approximation of the system and the unconstrained nonlinear minimization. The key features of the new algorithm are as follows. First, the formal discrete‐time approximation makes the set of stabilizing control inputs star‐shaped centred at the origin, hence the minimization is to be performed only in a neighbourhood of the origin selected by the designer. Second, the algorithm is always capable of finding a solution if one exists, as long as the minimization inside the neighbourhood is successful. Third, by a slight modification, the algorithm permits us to place all the eigenvalues of the system inside a rectangular region in the complex plane, as long as it is feasible. The algorithm is also applicable to the static output feedback stabilization problem of linear time‐invariant systems. Copyright © 2007 John Wiley & Sons, Ltd.     

On the “Uniform” Observability of Discrete-Time Nonlinear Systems

In constructing an observer for a discrete-time nonlinear system, the system is commonly required to satisfy a certain kind of "uniform" observability condition, that is, the state should always be reconstructible from observation windows of a specific length, irrespective of the values of the state and inputs. In this technical note, it is proved that this "uniform" requirement is unnecessary in the sense that if the initial state and inputs are on a compact set, then the "uniform" observability is derived from its non-uniform counterpart.