Characterization of seasonal variation of forest canopy in a temperate deciduous broadleaf forest, using daily MODIS data

In this paper, we present an improved procedure for collecting no or little atmosphere- and snow-contaminated observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. The resultant time series of daily MODIS data of a temperate deciduous broadleaf forest (the Bartlett Experimental Forest) in 2004 show strong seasonal dynamics of surface reflectance of green, near infrared and shortwave infrared bands, and clearly delineate leaf phenology and length of plant growing season. We also estimate the fractions of photosynthetically active radiation (PAR) absorbed by vegetation canopy (FAPAR_canopy), leaf (FAPAR_leaf), and chlorophyll (FAPAR_chl), respectively, using a coupled leaf-canopy radiative transfer model (PROSAIL-2) and daily MODIS data. The Markov Chain Monte Carlo (MCMC) method (the Metropolis algorithm) is used for model inversion, which provides probability distributions of the retrieved variables. A two-step procedure is used to estimate the fractions of absorbed PAR: (1) to retrieve biophysical and biochemical variables from MODIS images using the PROSAIL-2 model; and (2) to calculate the fractions with the estimated model variables from the first step. Inversion and forward simulations of the PROSAIL-2 model are carried out for the temperate deciduous broadleaf forest during day of year (DOY) 184 to 201 in 2005. The reproduced reflectance values from the PROSAIL-2 model agree well with the observed MODIS reflectance for the five spectral bands (green, red, NIR₁, NIR₂, and SWIR₁). The estimated leaf area index, leaf dry matter, leaf chlorophyll content and FAPAR_canopy values are close to field measurements at the site. The results also showed significant differences between FAPAR_canopy and FAPAR_chl at the site. Our results show that MODIS imagery provides important information on biophysical and biochemical variables at both leaf and canopy levels.     

Upsetting Tests of Fresh Cementitious Composites for Extrusion

Upsetting tests were conducted on cylindrical specimens made of a typical fresh short fiber-reinforced cementitious composite (SFRCC) paste for extrusion at various boundary conditions to derive the paste’s constitutive behavior. Due to friction present at the specimen and the equipment platens interfaces, stress was not uniformly distributed in the specimen and had to be corrected. In this study, two analytical methods were utilized to derive the true flow stress of the fresh SFRCC paste through correcting the nominal yield stress obtained from the upsetting test. One of them was the stress extrapolation method, which required a large number of experimental data and predetermined boundary friction. It was found that the results corrected by this method from experiments at the lubricated boundary were more reliable than those at the dry boundary and this method could also give an approximate estimation of the boundary friction coefficient. As comparison, the flow stress correction method required only a small amount of experimental data and no predetermined boundary friction. It was found that this method provided better results at the dry boundary than at the lubricated boundary. The fresh SFRCC paste exhibited both strain and strain rate hardening characteristics whereas strain rate hardening effect was more significant and dominated.     

我国企业经营管理的变革与IE应用探讨

分析并讨论了建立现代企业制度过程中企业经营管理变革的基本特征，提出了工业工程（ＩＥ）应用是实现企业经营变革的重要管理技术，并且论述了我国推广与应用ＩＥ的有效途径     

大时间常数开关电容积分器的实现与推广

本文提出了一种新型的大时间常数开关电容积分器(SCI),并且形成一系簇。这种新型积分器具有对寄生电容不敏感的特点,且不需要复杂的时钟电路。积分器系蔟通过二阶节的级联,可用来实现高阶滤波器函数。     

采用Lynch-Davisson编码方法压缩多元信源序列

为了利用Ｌｙｎｃｈ－Ｄａｖｉｓｓｏｎ编码压缩多进制序列,提出了一种推广方法,该方法不再将信源序列划分成多个序列分别进行压缩,而是采用一种统一的算法直接对信源进行压缩处理,并证明了这种方法在渐进意义上可达到熵界。     

线性拟合解谱时σ的选取及其对峰位漂移所造成误差的补偿作用

用线性拟合法分析核素能谱时,标准偏差σ是一个重要的参数。本文介绍了如何选取σ的方法,说明了它对峰位漂移所造成误差的补偿作用。     

探析城市精神与城市行为识别的互动性

城市精神反映了城市共同的理想目标、精神信念、文化底蕴、行为准则和生活方式的价值观念体系和群体意识,城市精神通过城市行为识别并表现出来。城市精神识别与政府行为、企业行为、公众行为、窗口行业行为、市民个体行为、行为环境改善、经济健康发展等城市行为具有互动性。城市精神的行为识别表现将促进城市形象的建设,增进城市个性繁荣与城市可持续发展,塑造完美的城市文化,延续历史文脉,促进社会文明。     

45CrNiMoVA高速切削条件下本构关系建模技术研究

为建立连续介质材料高速切削的材料本构关系模型,以45Cr Ni Mo VA材料为研究对象,通过准静态扭转试验和直角自由切削试验相结合的方法,建立了满足高速切削仿真要求的45Cr Ni Mo VA材料的Johnson-Cook本构模型.采用建立的Johnson-Cook本构模型参数,利用ABAQUS有限元分析软件建立了直角自由切削的有限元模型,对切削过程中的切屑厚度、主切削力、进给抗力进行了仿真,并将仿真预测值同试验测量值进行了对比.结果表明:由于切削仿真过程中刀具不存在磨损,进给抗力的仿真误差较大;主切削力和切屑厚度的仿真预测值与试验测量值的误差在10%之内,模型的准确度较好.最后,利用VB和C语言,开发了Johnson-Cook材料本构集成建模系统,并验证了其使用效果的实用性.     

Assessing the potential of VEGETATION sensor data for mapping snow and ice cover: A Normalized Difference Snow and Ice Index

The VEGETATION (VGT) sensor in SPOT 4 has four spectral bands that are equivalent to Landsat Thematic Mapper (TM) bands (blue, red, near-infrared and mid-infrared spectral bands) and provides daily images of the global land surface at a 1-km spatial resolution. We propose a new index for identifying and mapping of snow/ice cover, namely the Normalized Difference Snow/Ice Index (NDSII), which uses reflectance values of red and mid-infrared spectral bands of Landsat TM and VGT. For Landsat TM data, NDSII is calculated as NDSII_TM=(TM3-TM5)/(TM3+TM5); for VGT data, NDSII is calculated as NDSII_VGT=(B2-MIR)/(B2+MIR). As a case study we used a Landsat TM image that covers the eastern part of the Qilian mountain range in the Qinghai-Xizang (Tibetan) plateau of China. NDSIITM gave similar estimates of the area and spatial distribution of snow/ice cover to the Normalized Difference Snow Index (NDSI=(TM2-TM5)/(TM2+TM5)) which has been proposed by Hall et al. The results indicated that the VGT sensor might have the potential for operational monitoring and mapping of snow/ice cover from regional to global scales, when using NDSII_VGT.     

β21S钛合金工艺塑性图

主要研究了β21S钛合金的工艺塑性图，制定了该合金的锻造工艺参数。通过该合金的工艺塑性图，确定变形温度为750-1050℃，最大变形量为75％－80％，终缎温度为700℃。从合金的工艺塑性角度来看，以上 数据是合理的。