Time-Frequency Analysis of Nonlinear Systems: The Skeleton Linear Model and the Skeleton Curves

The joint time-frequency analysis method is adopted to study the nonlinear behavior varying with the instantaneous response for a class of S.D.O.F nonlinear system. A time-frequency masking operator, together with the conception of effective time-frequency region of the asymptotic signal are defined here. Based on these mathematical foundations, a so-called skeleton linear model (SLM) is constructed which has similar nonlinear characteristics with the nonlinear system. Two skeleton curves are deduced which can indicate the stiffness and damping in the nonlinear system. The relationship between the SLM and the nonlinear system, both parameters and solutions, is clarified. Based on this work a new identification technique of nonlinear systems using the nonstationary vibration data will be proposed through time-frequency filtering technique and wavelet transform in the following paper.

Finite-difference time-domain analysis of deformed square cavity filters with a traveling-wave-like filtering response by mode coupling

An add-drop filter based on a perfect square resonator can realize a maximum of only 25% power dropping because the confined modes are standing-wave modes. By means of mode coupling between two modes with inverse symmetry properties, a traveling-wave-like filtering response is obtained in a two-dimensional single square cavity filter with cut or circular corners by finite-difference time-domain simulation. The optimized deformation parameters for an add-drop filter can be accurately predicted as the overlapping point of the two coupling modes in an isolated deformed square cavity. More than 80% power dropping can be obtained in a deformed square cavity filter with a side length of 3.01 mu m. The free spectral region is decided by the mode spacing between modes, with the sum of the mode indices differing by 1. (c) 2007 Optical Society of America.

The motion and the core structure of a geostrophic vortex - one-time scale inner solution and the motion of the vortex

By means of the matched asymptotic expansion method with one-time scale analysis we have shown that the inviscid geostrophic vortex solution represents our leading solution away from the vortex. Near the vortex there is a viscous core structure, with the length scale O(a). In the core the viscous stresses (or turbulent stresses) are important, the variations of the velocity and the equivalent height are finite and dependent of time. It also has been shown that the leading inner solutions of the core structure are the same for two different time scales of S/(ghoo)1/2 and S/a (ghoo)1/2. Within the accuracy of O(a) the velocity of a geostrophic vortex center is equal to the velocity of the local background flow, where the vortex is located, in the absence of the vortex. Some numerical examples demonstrate the contributions of these results.

Identification of nonlinear dynamic systems: Time-frequency filtering and skeleton curves

The nonlinear behavior varying with the instantaneous response was analyzed through the joint time-frequency analysis method for a class of S. D. O. F nonlinear system. A masking operator an definite regions is defined and two theorems are presented. Based on these, the nonlinear system is modeled with a special time-varying linear one, called the generalized skeleton linear system (GSLS). The frequency skeleton curve and the damping skeleton curve are defined to describe the main feature of the non-linearity as well. Moreover, an identification method is proposed through the skeleton curves and the time-frequency filtering technique.

Identification of Nonlinear Systems Through Time-Frequency Filtering Technique

In the previous paper, a class of nonlinear system is mapped to a so-called skeleton linear model (SLM) based on the joint time-frequency analysis method. Behavior of the nonlinear system may be indicated quantitatively by the variance of the coefficients of SLM versus its response. Using this model we propose an identification method for nonlinear systems based on nonstationary vibration data in this paper. The key technique in the identification procedure is a time-frequency filtering method by which solution of the SLM is extracted from the response data of the corresponding nonlinear system. Two time-frequency filtering methods are discussed here. One is based on the quadratic time-frequency distribution and its inverse transform, the other is based on the quadratic time-frequency distribution and the wavelet transform. Both numerical examples and an experimental application are given to illustrate the validity of the technique.

Detection of Brillouin scattering temperature signal in Brillouin optical time-domain reflectometer sensing system based on instantaneous frequency measurement technology

abstract {We present a simple and practical method for the single-ended distributed fiber temperature measurements using microwave (11-GHz) coherent detection and the instantaneous frequency measurement (IFM) technique to detect spontaneous Brillouin backscattered signal in which a specially designed rf bandpass filter at 11 GHz is used as a frequency discriminator to transform frequency shift to intensity fluctuation. A Brillouin temperature signal can be obtained at 11 GHz over a sensing length of 10 km. The power sensitivity dependence on temperature induced by frequency shift is measured as 2.66%/K. © 2007 Society of Photo-Optical Instrumentation Engineers.}

水下滑翔机器人水动力研究与运动分析

水下滑翔机器人是一种无外挂推进系统,仅依靠内置执行机构调整重心位置和净浮力来控制其自身运动的新型水下机器人,主要用于长时间、大范围的海洋环境监测,因此要求其具有低阻性和高稳定性.文章主要从水动力特性出发对水下滑翔机器人进行优化设计,包括主载体线型、升降翼和稳定翼的优化等,并对水动力优化设计的结构进行了定常滑翔运动和空间螺旋回转运动分析,这将为后期的控制系统设计提供参考.

景物的三维信息获取及其运动分析

采用模糊熵函数对图象象素分类作出整体最优分类评价,实现了区域分割.利用矩及其函数做为各区域的特征表达,构成以区域为基元的符号特征集并描述图象内容。根据立体图象对间的几何关系,解出各区域(基元)的相对三维坐标。与象索匹配相比较,它可以获得较高精度的三维信息和可描述的景物信息.通过获取不同时空的各区域(基元)三维信息,确定了它们的空间运动状态。联系这些状态,构造出景物中物体间的空间关系和近似模型,实现了对景物的3-D识别和描述。

空间电动绳系推进的动力学建模与分析

为分析空间电动绳系的运动特性,从一般力学角度出发,结合电动力学知识,建立了近地轨道空间电动绳系推进飞行的动力学模型,得出了多种初始条件下的数值计算结果,并据此对电动绳系航天器的轨道机动过程进行了详尽的讨论,阐明了系统在轨道高度变化的同时,其轨道面也会发生变化,而且导电系绳还会旋转与弯曲变形等规律.此外,还对电动绳系推进系统的效率和地球自转的影响进行了估计.

Electron quantum path tuning and isolated attosecond pulse emission driven by a waveform-controlled multi-cycle laser field

We investigate high-order harmonic emission and isolated attosecond pulse (IAP) generation in atoms driven by a two-colour multi-cycle laser field consisting of an 800 nm pulse and an infrared laser pulse at an arbitrary wavelength. With moderate laser intensity, an IAP of similar to 220 as can be generated in helium atoms by using two-colour laser pulses of 35 fs/800 nm and 46 fs/1150 nm. The discussion based on the three-step semiclassical model, and time-frequency analysis shows a clear picture of the high-order harmonic generation in the waveform-controlled laser field which is of benefit to the generation of XUV IAP and attosecond electron pulses. When the propagation effect is included, the duration of the IAP can be shorter than 200 as, when the driving laser pulses are focused 1 mm before the gas medium with a length between 1.5 mm and 2 mm.

Inductive transcription and protective role of fish heme oxygenase-1 under hypoxic stress

Heme oxygenase-1 is the rate-limiting enzyme in the degradation of heme into biliverdin, carbon monoxide and free divalent iron. In this study, we cloned heme oxygenase isoform 1 (CaHO-1) from a hypoxia-tolerant teleost fish Carassius auratus. The full-length cDNA of CaHO-1 is 1247 bp and encodes a protein of 272 amino acids. RT-PCR and real-time PCR analysis indicated that CaHO-1 was predominantly transcribed in posterior kidney, head kidney, gill and intestine, and induction of gene transcription was observed predominantly in posterior kidney under hypoxic stress. Moreover, the hypoxia-induced transcription was confirmed in goldfish larvae and in in vitro cultured CAB cells. Fluorescence of the HO-1-GFP fusion protein revealed a cytoplasmic and plasma membrane localization, which was consistent with the putative transmembrane structure. Subsequently, we established a stably transfected CAB/pcDNA3.1-HO-1 cell line and a control CAB/pcDNA3.1 cell line, and found that the number of dead cells was obviously reduced in the pcDNA3.1-HO-1-transfected group following 4 days of hypoxic (1% O-2) treatment in comparison with numerous detached dead cells in the control pcDNA3.1-transfected cells. Furthermore, a significant cell viability difference between the two kinds of transfected cells during hypoxia-reoxygenation was revealed. Therefore, the data suggest that fish HO-1 might play a significant protective role in cells in response to hypoxic stress.

Identification of differentially expressed genes from the cross-subfamily cloned embryos derived from zebrafish nuclei and rare minnow enucleated eggs

Cross-species nuclear transfer (NT) has been used to retain the genetic viability of a species near extinction. However, unlike intra-species NT, most embryos produced by cross-species NT were unable to develop to later stages due to incompatible nucleocytoplasmic interactions between the donor nuclei and the recipient cytoplasm from different species. To study the early nucleocytoplasmic interaction in cross-species NT, two laboratory fish species (zebrafish and rare minnow) from different subfamilies were used to generate cross-subfamily NT embryos in the present study. Suppression subtractive hybridization (SSH) was performed to screen out differentially expressed genes from the forward and reverse subtractive cDNA libraries. After dot blot and real-time PCR analysis, 80 of 500 randomly selective sequences were proven to be differentially expressed in the cloned embryos. Among them, 45 sequences shared high homology with 28 zebrafish known genes, and 35 sequences were corresponding to 22 novel expressed sequence tags (ESTs). Based on functional clustering and literature mining analysis, up-and down-regulated genes in the cross-subfamily cloned embryos were mostly relevant to transcription and translation initiation, cell cycle regulation, protein binding, etc. To our knowledge, this is the first report on the determination of genes involved in the early development of cross-species NT embryos of fish. (C) 2007 Elsevier Inc. All rights reserved.

The first non-mammalian CXCR3 in a teleost fish: Gene and expression in blood cells and central nervous system in the grass carp (Ctenopharyngodon idella)

A novel fish chemokine receptor gene, chemokine (C-X-C motif) receptor 3 (CXCR3)-like was isolated from the grass carp Ctenopharyngodon idella , with its full-length genomic sequence. The cDNA of grass carp CXCR3-like (gcCXCR3-like) consists of 1261 bp with a 49bp 5'-UTR and a 189 bp 3'-UTR. An open reading frame of 1023 bp encodes a 341-amino acid peptide, with seven transmembrane helices. The deduced amino acid sequence showed the same sequence identities (37.8%) with its counterparts in goat and human. The gcCXCR3-like gene consists of two exons, with one intervening intron, spaced over approximately 2 kb of genomic sequence. Phylogenetic analyses clearly demonstrated that the gcCXCR3-like resembles the CXCR3s of other vertebrates. Real-time PCR analysis showed that gcCXCR3-like was expressed in all tested organs except heart and the expression level of gcCXCR3-like was highest in brain. Flow cytometric analyses showed the positive rate of labelled leukocytes from the healthy grass carp was 17.3%, and the labelled leukocytes were divided into three types by cell sorting. Immunohistochemical localization revealed that gcCXCR3-like expressed in whole brain regions including cerebel, diencephalon, medulla oblongata, optic lobe, and rhinencephalon, and that the labelled leukocytes are actually populations of monocyte and/or phagocyte, lymphocyte and the granulocyte. It is considered that fish CXCR expression and their function may need to be investigated in both nervous and immune systems. (c) 2006 Elsevier Ltd. All rights reserved.

Multimode resonances in metallically confined square-resonator microlasers

Directional emission InP/AlGaInAs square-resonator microlasers with a side length of 20 mu m are fabricated by standard photolithography and inductively coupled-plasma etching technique. Multimode resonances with about seven distinct mode peaks in a free-spectral range are observed from 1460 to 1560 nm with the free-spectral range of 12.1 nm near the wavelength of 1510 nm, and the mode refractive index versus the photon energy E (eV) as 3.07152+0.18304E are obtained by fitting the laser spectra with an analytical mode wavelength formula derived by light ray method. In addition, mode field pattern is simulated for cold cavity by two dimensional finite-difference time-domain technique.