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.

Thermal fatigue on pistons induced by shaped high power laser. Part II: Design of spatial intensity distribution via numerical simulation

In the laser induced thermal fatigue simulation test on pistons, the high power laser was transformed from the incident Gaussian beam into a concentric multi-circular pattern with specific intensity ratio. The spatial intensity distribution of the shaped beam, which determines the temperature field in the piston, must be designed before a diffractive optical element (DOE) can be manufactured. In this paper, a reverse method based on finite element model (FEM) was proposed to design the intensity distribution in order to simulate the thermal loadings on pistons. Temperature fields were obtained by solving a transient three-dimensional heat conduction equation with convective boundary conditions at the surfaces of the piston workpiece. The numerical model then was validated by approaching the computational results to the experimental data. During the process, some important parameters including laser absorptivity, convective heat transfer coefficient, thermal conductivity and Biot number were also validated. Then, optimization procedure was processed to find favorable spatial intensity distribution for the shaped beam, with the aid of the validated FEM. The analysis shows that the reverse method incorporated with numerical simulation can reduce design cycle and design expense efficiently. This method can serve as a kind of virtual experimental vehicle as well, which makes the thermal fatigue simulation test more controllable and predictable. (C) 2007 Elsevier Ltd. All rights reserved.

Coherent population accumulations of multiphoton transitions induced by an ultrashort pulse train in polar molecules

Coherent population accumulations of multiphoton transitions induced by an ultrashort pulse train in a two-level polar molecule are investigated theoretically by solving the density-matrix equations without invoking any of the standard approximations. It is shown due to the effects of permanent dipole moments, that the population accumulation of multiphoton transitions can be obtained in the polar molecule. Moreover, the population accumulations depend crucially on the relative phase between two sequential pulses, and the period in which the maximum population accumulation occurs is 2 pi/N in N-photon transitions.

用于蓝光可录存储的无机材料研究进展

蓝光存储是信息存储领域发展的一个重要方向。用于蓝光存储的可录型光盘，由于其巨大的商业价值，将是今后研究的热点。本文总结了近几年来国内外文献报道的适用于蓝光可录存储的无机材料的最新研究成果，详细阐述了用于蓝光可录存储的无机薄膜的制备方法、无机记录材料的种类及存储原理。最后，对用于蓝光可录存储的无机材料今后的发展前景进行了展望。

鉴别用变方位角导模共振滤光片的设计

设计了在0°和90°方位角下都具有低旁带的鉴别用导模共振滤光片。利用严格的耦合波理论，分析了这种器件在不同入射角、不同光栅槽深和覆盖不同厚度SiO2层情况下的衍射特性。得到了满足鉴别要求的导模共振滤光片结构。在30°入射角情况下，对于TE模式偏振光，设计的滤光片在0°和90°方位角下都有形状对称的反射光谱、低的旁带、两个位置分开的共振峰和适当的半宽度。

苋属入侵种的可能分布区预测及相关环境因子分析

苋属（Amaranthus）约40种，世界均有分布。我国有20种，分布很广，其中外来种为17种(11种为入侵种)，危害旱田作物、果树、茶树和蔬菜。反枝苋（Amaranthus retroflexus L.）是苋属入侵种中发生频率最多、分布最广、危害最严重的杂草。本文首先基于反枝苋在世界范围内4207个实际分布点及其对应的气候、地形和土壤三类要素28个环境因子的定量关系，利用主成分分析确定了影响其分布的主要环境因子，据此估测其中心可能分布区和最大可能分布区，并与实际分布点进行比较;然后利用GARP生态位模型和地理信息系统(GIS)对影响苋属8个入侵种地理分布的环境因子进行分析并对其全球可能分布区进行预测，并根据苋属入侵种与环境因子的关系对8个苋属入侵种进行聚类分析;最后基于Receiver Operating Characteristics(ROC)分析对GARP模型及GIS模型对反枝苋全球可能分布区的预测结果进行精度检验和比较，结果表明： (1) GIS模型预测显示14个环境因子在决定反枝苋全球分布格局中起着重要作用。反枝苋中心可能分布区位于新西兰南部、澳大利亚东南部、南美洲北部少数地区、北美洲西北部及东南部部分地区、欧洲大部分地区和中国东南部。最大可能分布区位于南美洲中南部、北美洲大部分、非洲北部小部分、澳大利亚南部及北部少数区域、欧洲大部分地区和亚洲大部分地区及中国除西藏、青海、新疆、四川西部以外的地区。中心可能分布区的预测结果与实际分布点吻合较好，而最大可能分布区则过于广阔。 (2) GARP模型预测显示14个环境因子中雨日频率，极端低温，海拔这三个环境因子的影响较为重要，是苋属8个入侵种分布的主要限制因子。聚类分析表明8种苋属入侵种按欧式距离的长度可分为三类：第一类：反枝苋、凹头苋;第二类：刺苋、皱果苋、尾穗苋;第三类：绿穗苋、白苋、北美苋。 ROC分析结果显示GARP模型对反枝苋的可能分布区模拟效果（AUCGARP=0.857）好于GIS模型，其中GIS模型对反枝苋中心可能分布区的模拟效果(AUCGIS-CENTER=0.832)好于最大可能分布区(AUCGIS-MAX=0.778)。 苋属8个入侵种均有分布的地区为澳大利亚沿海地区，新西兰，中国东南沿海，欧洲西部，南美洲部分国家，美国，非洲中部。 (3)两种模型所预测的反枝苋的可能分布区有很大程度的重合性，GARP模型预测的可能分布区大于GIS模型预测出的中心可能分布区，但小于GIS模型预测出的最大可能分布区，且和实际分布点拟合程度较好。

一种以浒苔为原料制取生物乙醇的方法

本发明公开一种以浒苔为原料制取生物乙醇的方法，包括以下步骤：（1）对浒苔进行漂洗；（2）对浒苔粉碎至粒径为0.5～2mm；（3）将步骤（2）所得的浒苔投入到酸解装置中，料液比为1：20-1：5，加入酸，至酸浓度为0.5%-2.5%(w/w)。反应釜中110℃-150℃水解；（4）将步骤（3）所得的浒苔水解液中加入氢氧化钙中和至中性，室温静置；压滤除去固形物，得富含葡萄糖和木糖的水解液；（5）将步骤（4）所得的水解液，接入5%的休哈塔假丝酵母30℃发酵1~5天；（6）发酵液蒸馏得到生物乙醇。本发明利用浒苔作为乙醇发酵的原料，结合浒苔的特点，不需经过酶解，水解液可直接用于生物乙醇发酵。

大蹼铃蟾蛋白提取物对膀胱癌细胞株的抑制作用及对端粒酶的影响

目的探讨大蹼铃蟾蛋白提取物对膀胱癌细胞株的 抑制作用及对端粒酶的影响。方法采用肿瘤细胞培养方 法，检测大蹼铃蟾蛋白提取物对膀胱癌细胞株."%、/01’)+、 234/56的抑制作用；以.&-7’78&’9:02-方法检测大蹼铃 蟾蛋白提取物对膀胱癌细胞株端粒酶表达的影响。结果 大蹼铃蟾蛋白提取物表现出对膀胱癌细胞株有较强的抑制 作用；对膀胱癌细胞株端粒酶表达则无影响。结论大蹼铃 蟾蛋白提取物对多个膀胱癌细胞株具有直接细胞杀伤作用， 其作用机制不通过抑制端粒酶活性。

滇金丝猴下颌的生物力学研究

滇金丝猴雄性比雌性具有相对更长的下颌, 这就导致了整个下颌结构在两性 间的差异。在分析的8个变量中, 4个被选为性别鉴别的重要特征, 判别式为: D=-27.65-0.729 CONM1+0.596MANDL+1.024 MANDSYM-1.778 MANCORPW。与猕猴和 长鼻猴相比, 滇金丝猴具有相对短的下颌骨, 较宽的下颌髁和较高的下颌体。 图4表4参17

长江中游典型鱼塘植莲的环境与经济效益分析

长江中游湿地区域的池塘经过连续多年的化肥养鱼导致了大量的氮、磷沉积在鱼塘底泥中。分析了鱼塘植莲对养殖后沉积的氮、磷的重新利用及植莲的经济效益。实验于2004年在位于长江中游的武汉市涨渡湖渔场进行。根据收支平衡计算了实验池氮、磷的转移量,根据投入产出计算了实验池的经济收入。逐月分析了池塘中水质理化指标和底泥中总凯氏氮(TKN)和总磷(TP)的含量。方差分析表明:总凯氏氮、总磷在池塘底泥表层(0～5 cm)、中层(5～10 cm)和底层(10～50 cm)当中的含量都出现显著性降低(P<0.05)。养鱼池塘通

江豚

<正> 江豚(Neophocaena ariaeorientalis)俗称江猪.隶属于鲸目,齿鲸亚目,鼠海豚科.全身铅黑色,无喙无背鳍.在印度、巴基斯坦、日本和中国沿海及内河、通江湖泊均有分布.最大体长达1.9米,重220公斤,而在长江中常见个体一般为1～1.5米,30～80公斤.我国江豚的背部中线还有一条皮肤隆起,上有3～4排颗粒状突起. 江豚一般为3～5头一群,亦常见一头单独活动的.我们还见过20多头一群扶老携幼,成群结队地游弋于江边.江豚个性活拨,属近岸型豚类,经常在江边浅水区戏水和追捕鱼类,有时跃

Low threshold current density, low resistance oxide-confined VCSEL fabricated by a dielectric-free approach

We present the fabrication process and experimental results of 850-nm oxide-confined vertical cavity surface emitting lasers (VCSELs) fabricated by using dielectric-free approach. The threshold current of 0.4 mA, which corresponds to the threshold current density of 0.5 kA/cm(2), differential resistance of 76 Omega, and maximum output power of more than 5 mW are achieved for the dielectric-free VCSEL with a square oxide aperture size of 9 mu m at room temperature (RT). L-I-V characteristics of the dielectric-free VCSEL are compared with those of conventional VCSEL with the similar aperture size, which indicates the way to realize low-cost, low-power consumption VCSELs with extremely simple process. Preliminary study of the temperature-dependent L-I characteristics and modulation response of the dielectric-free VCSEL are also presented.