纳米TiO2粉晶的光学特性研究

用溶胶-凝胶方法(Sol-gel)制备了平均粒度为22nm的纳米TiO₂粉晶.用X射线衍射(XRD)分析了粉晶的结构变化,并用红外光谱法(IR)及紫外-可见光谱法(UV-VIS)对粒子的光学特性进行了分析.结果表明:经不同温度热处理的纳米TiO₂的光学性能随其晶型转变及粒子尺寸的变化而有着显著变化,与粗晶TiO₂相比,纳米TiO₂粒子在纳米尺度内,IR吸收边有明显红移和蓝移并存现象,而UV-VIS吸收边随粒子尺寸减小发生蓝移,表现出量子尺寸效应.     

Application of nonlinear fitting and selection of the most fitted equation by AIC in stability test of pharmaceutical ingredients

We proposed a method for objectively selecting the most fitted rate equation among candidate rate equations based on chemical kinetics by both nonlinear regression analysis and Akaike's information criterion (AIC), to express the decrease of pharmaceutical ingredient as an appropriate equation. Pseudo-zero, first, and second-order rate equations were prepared as candidates beforehand, and AIC was introduced for selecting the most fitted rate equation among the candidates. We compared the proposed method to the Weibull method that expressed any decrease patterns as a single equation.

We quantified the contents of thiamine nitrate (VB1) and taurine after storage for one, three, and six months under 40°C-75% relative humidity by high-pressure liquid chromatography. Decrease patterns of each sample were most fitted to one of the candidate rate equations, that is, pseudo-zero, first, and second-order rate equations, respectively, and the degree of fit in the most fitted equation was superior to that of the Weibull method, except for the pseudo-first-order rate equation.

Moreover, we confirmed that the proposed method was considerably precise for estimating the stability of pharmaceuticals by comparing estimated residual rates and confidence intervals to experimental data.     

Simulation of atmospheric phenomena

This paper presents a physically based simulation of atmospheric phenomena. It takes into account the physics of non-homogeneous media in which the index of refraction varies continuously, creating curved light paths. As opposed to previous research on this area, we solve the physically based differential equation that describes the trajectory of light. We develop an accurate expression of the index of refraction in the atmosphere as a function of wavelength, based on real measured data. We also describe our atmosphere profile manager, which lets us mimic the initial conditions of real-world scenes for our simulations. The method is validated both visually (by comparing the images with the real pictures) and numerically (with the extensive literature from other areas of research such as optics or meteorology). The phenomena simulated include the inferior and superior mirages, the Fata Morgana, the Novaya–Zemlya, the Viking's end of the world, the distortions caused by heat waves and the green flash.     

Trajectory tracking of leader–follower formations characterized by constant line-of-sight angles

A group of identical unicycles is controlled by means of local feedback laws that require measurements of the unicycles relative positions and speeds. Vehicle interconnections are considered unilateral and are modeled by means of a directed acyclic graph. Although not needed for the implementation of the controllers, the desired trajectory of each vehicle is derived from the requirement that the formation must rotate with the leader while ensuring that the relative positions and line-of-sight angles between unicycles are time-invariant. Exponential convergence of the actual trajectories to a ball centered on the desired trajectories is obtained by computing the Jacobian of the nonlinear dynamics and using results from contraction theory. Instrumental to this derivation is the subsystem feedback decomposition interpretation of the plant model. In this context, convergence depends on the uniform negative definiteness and strict positive realness of the forward and feedback subsystems. Such properties are obtained provided a set of linear and bilinear matrix inequalities as well as kinematic constraints are satisfied. A numerical example illustrates the convergence property of a leader–follower formation.     

Co-volume method for Riemannian mean curvature flow in subjective surfaces multiscale segmentation

We introduce semi-implicit complementary volume numerical scheme for solving the level setformulation of Riemannian mean curvature flow problem arising in image segmentation, edge detection, missing boundary completion and subjective contour extraction. The scheme is robust and efficient since it is linear, and it is stable in L_∞ and weighted W ^1,1 sense without any restriction on a time step. The computational results related to medical image segmentation with partly missing boundaries and subjective contours extraction are presented.     

Criteria for global minimum of sum of squares in nonlinear regression

Demidenko [2000. Is this the least squares estimate? Biometrika 87, 437-452] has established the relationship between the curvature of nonlinear regression and the local convexity of a sum of squares: the Hessian matrix is positive definite if the sum of squares is less than the minimum squared radius of the full curvature. In this paper, we continue developing the criteria for the global minimum of the sum of squares in nonlinear regression. In particular, the concept of the local unimodality is introduced; a function is called locally unimodal on a level set if it has a unique local minimum in each component of that level set. We show that the level of the local unimodality of the sum of squares is equal to the minimum squared radius of the intrinsic curvature of the nonlinear regression function. A new class of unidirected nonlinear regression models is introduced with an interpretation in terms of differential geometry. The criteria are illustrated by several popular nonlinear regression models.     

Robust adaptive fuzzy control scheme for nonlinear system with uncertainty

In this paper, a robust adaptive fuzzy control scheme for a class of nonlinear system with uncertainty is proposed. First, using prior knowledge about the plant we obtain a fuzzy model, which is called the generalized fuzzy hyperbolic model （GFHM）. Secondly, for the case that the states of the system are not available an observer is designed and a robust adaptive fuzzy output feedback control scheme is developed. The overall control system guarantees that the tracking error converges to a small neighborhood of origin and that all signals involved are uniformly bounded. The main advantages of the proposed control scheme are that the human knowledge about the plant under control can be used to design the controller and only one parameter in the adaptive mechanism needs to be on-line adjusted.     

On stabilization for a class of nonlinear stochastic time-delay systems： a matrix inequality approach

This paper treats the feedback stabilization of nonlinear stochastic time-delay systems with state and control-dependent noise. Some locally （globally） robustly stabilizable conditions are given in terms of matrix inequalities that are independent of the delay size. When it is applied to linear stochastic time-delay systems, sufficient conditions for the state-feedback stabilization are presented via linear matrix inequalities. Several previous results are extended to more general systems with both state and control-dependent noise, and easy computation algorithms are also given.     

A new nonlinear output tracking controller via output-feedback

1 Introduction Since the introduction of backstepping design [1], exten- sive research has been investigated on control design for the systems in the triangular structure [1～6], merged with non- linear damping [7], tuning functions [4], MT filters [5] and other techniques. Two classes of output-feedback nonlinear control sys- tems have been investigated intensely: the first is that non- linearities only depend on the measurable states. By output injection, a much simple but effectual observe…     

Optical nonlinearity of Cu:SrTiO3 composite fabricated by negative ion implantation

Optical nonlinearity and dispersion were studied for Cu nanoparticle composite. Negative Cu⁻ ions with 60 keV were applied for implanting into SrTiO₃ at a flux of 10 μA/cm² up to a total fluence of 1 × 10¹⁷ ions/cm². The steady-state optical spectrum of Cu-implanted SrTiO₃ showed a surface plasmon resonance resulting from the formation of nanoparticles. Transient transmission and reflection were measured by the pump–probe method with a femtosecond laser system. Optical nonlinearity originated from Cu:SrTiO₃ nanoparticle composite and from SrTiO₃ matrix overlap, in measured transient spectra. The nonlinear component of Cu:SrTiO₃ composite was extracted from the transient spectra with the difference of time response. Nonlinear dielectric coefficient and dispersion around the surface plasmon resonance were derived from extracted transient spectra. The dispersion was compared with a local electric field factor.