Spatial variation of optical and structural properties of ELO GaN directly grown on patterned sapphire by HVPE

A 275 mu m thick GaN layer was directly grown on the SiO2-prepatterned sapphire in a home-built vertical hydride vapour phase epitaxy (HVPE) reactor. The variation of optical and structure characteristics were microscopically identified using spatially resolved cathodeluminescence and micro-Raman spectroscopy in a cross section of the thick film. The D X-0(A) line with the FWHM of 5.1 meV and etch- pit density of 9 x 10(6) cm(-2) illustrated high crystalline quality of the thick GaN epitaxial layer. Optically active regions appeared above the SiO2 masks and disappeared abruptly due to the tapered inversion domains at 210 - 230 mu m thickness. The crystalline quality was improved by increasing the thickness of the GaN/sapphire interface, but the region with a distance of 2 mu m from the top surface revealed relatively low quality due to degenerate surface reconstruction by residual gas reaction. The x-ray rocking curve for the symmetric (0 0 2) and asymmetric (1 0 2) reflections also showed good quality and a small wing tilt of the epitaxial lateral overgrowth (ELO) GaN.

Spatial variation of suspended particulate matter in the Yellow Sea

A joint oceanographic cruise between the Institute of Oceanography, Chinese Academy of Science and the Department of Oceanography, Seoul National University was carried out in the Yellow Sea during the summer of 1996 to investigate the concentration and particle-size distribution of suspended particulate matter (SPM). The general trends in the surface and bottom waters show that SPM concentrations and particle sizes decreased seawards in both the western (Chinese) and eastern (Korean) coastal regions of the Yellow Sea. In the bottom waters, SPM concentrations were higher and particle sizes were larger along the eastern coast than along the western coast. We suggest this is due to the resuspension of bottom sediments by strong onshore summer typhoons in the southwestern coastal waters of Korea.

Seasonal and spatial variation in abundance and egg production of Paracalanus parvus (Copepoda: Calanoida) in/out Jiaozhou Bay, China

The spatial distribution of stage-specific abundance and reproduction of the copepod Paracalanus parvus were studied from October 2005 to September 2006 in the Jiaozhou Bay. This copepod occurred continuously in this bay throughout the year. The species reached the lowest abundance in April and peaked in June. From October to December, distribution center mainly occurred in offshore water and at the mouth of the bay. In winter, early copepodites and adults gradually decreased and till February, most of the population was only comprised of CIV-CV stages. Overwintering copepodites matured in March and males tended to mature before female. From May to September, each stage occurred in the population and gradually reached high abundance. Temperature and chlorophyll a (Chl-a) concentration in the three stations can't clearly explain the seasonal variation in stage-specific abundance, so we surmised the important effect of the Yellow Sea. Egg production rate (EPR) reached its lowest in winter and peaked in June at 60.8 eggs female(-1) day(-1) in nearshore water. In the warming period, EPR in nearshore water was statistically higher and EPR > 10 eggs female(-1) day(-1) lasted longer than that in offshore water, showing the importance of nearshore water for recruitment of R parvus. Our study showed that EPR was positively related to temperature and total chlorophyll a in offshore water and mouth of the bay. In nearshore water, the relationships between EPR and temperature and Chl-a in three size fractions were not the same as those in offshore water, suggesting complicated ecosystem in such a eutrophic area in warming period. (C) 2008 Elsevier Ltd. All rights reserved.

Small-scale species richness and its spatial variation in an alpine meadow on the Qinghai-Tibet Plateau

We investigated how the high small-scale species richness of an alpine meadow on the Qinghai-Tibet Plateau, China, is maintained. This area is characterized by strong wind and severe cold during long winters. In winter, most livestock is grazed on dead leaves in small pastures near farmers' residences, whereas in the short summer, livestock is grazed in mountainous areas far from farmers' residences. The number of plant species and the aboveground biomass were surveyed for three adjacent pastures differing in grazing management: a late-winter grazing pasture grazed moderately from 1 February to 30 April, an early-winter grazing pasture grazed lightly from 20 September to late October, and a whole-year grazing pasture grazed intensively throughout the entire year. In each pasture, we harvested the aboveground biomass from 80 or 100 quadrats of 0.01 m(2) along a transect and classified the contents by species. We observed 15.5-19.7 species per 0.01 m(2), which is high richness per 0.01 m(2) on a worldwide scale. The species richness in the two winter grazing pastures was higher than that in the whole-year grazing pasture. The spatial variation in species richness and species composition in the two winter grazing pastures in which species richness was high was greater than that in the whole-year grazing pasture in which species richness was lower. Most of the leaves that are preserved on the winter grazing pastures during summer are blown away by strong winds during winter, and the remaining leaves are completely exhausted in winter by livestock grazing. A pasture with a high richess is accompanied by a high spatial variation in species richness and species composition. There is a high possibility that the characteristic of spatial variation is also caused by traditional grazing practices in this area.

Effect of spatial variation on areal evapotranspiration simulation in Haibei, Tibet plateau, China

Quantification of areal evapotranspiration from remote sensing data requires the determination of surface energy balance components with support of field observations. Much attention should be given to spatial resolution sensitivity to the physics of surface heterogeneity. Using the Priestley-Taylor model, we generated evapotranspiration maps at several spatial resolutions for a heterogeneous area at Haibei, and validated the evapotranspiration maps with the flux tower data. The results suggested that the mean values for all evapotranspiration maps were quite similar but their standard deviations decreased with the coarsening of spatial resolution. When the resolution transcended about 480 m, the standard deviations drastically decreased, indicating a loss of spatial structure information of the original resolution evapotranspiration map. The absolute values of relative errors of the points for evapotranspiration maps showed a fluctuant trend as spatial resolution of input parameter data layers coarsening, and the absolute value of relative errors reached minimum when pixel size of map matched up to measuring scale of eddy covariance system. Finally, based on the analyses of the semi-variogram of the original resolution evapotranspiration map and the shapes of spatial autocorrelation indices of Moran and Geary for evapotranspiration maps at different resolutions, an appropriate resolution was suggested for the areal evapotranspiration simulation in this study area.

Variation of benthic diatoms in a shallow, eutrophic Chinese Lake, Lake Donghu

Benthic diatom communities were sampled monthly from May 2004 to May 2005 at four different sites in the littoral zone of Lake Donghu, a shallow eutrophic lake of China. The seasonal patterns of the total abundance, which were lowest in summer and highest in spring, were found at all sites. Total densities of diatom assemblages were significantly higher at hyper-eutrophic sites than at moderately eutrophic sites. Melosira varians was the most abundant species and dominant contributor to total abundance at all sites during spring, autumn and winter, whereas Achnanthes exigua dominated benthic diatom assemblages at the site with the highest nutrient concentrations during the summer. Achnanthes lanceolata var. dubia, Gomphonema parvulum, Navicula similis, Navicula verecunda and Nitzschia amphibia were generally observed at all sites throughout the year and were dominant at higher-nutrient sites. The abundance of ambient nutrients was probably responsible for the spatial variation in biomass, composition and diversity of benthic diatom assemblages, and lake water temperature was the major factor that controlled seasonal distribution.

NDVI spatial pattern and its differentiation on the Mongolian Plateau

GIMMS NDVI database and geo-statistics were used to depict the spatial distribution and temporal stability of NDVI on the Mongolian Plateau. The results demonstrated that: (1) Regions of interest with high NDVI indices were distributed primarily in forested mountainous regions of the east and the north, areas with low NDVI indices were primarily distributed in the Gobi desert regions of the west and the southwest, and areas with moderate NDVI values were mainly distributed in a middle steppe strap from northwest to southeast. (2) The maximum NDVI values maintained for the past 22 years showed little variation. The average NDVI variance coefficient for the 22-year period was 15.2%. (3) NDVI distribution and vegetation cover showed spatial autocorrelations on a global scale. NDVI patterns from the vegetation cover also demonstrated anisotropy; a higher positive spatial correlation was indicated in a NW-SE direction, which suggested that vegetation cover in a NW-SE direction maintained increased integrity, and vegetation assemblage was mainly distributed in the same specific direction. (4) The NDVI spatial distribution was mainly controlled by structural factors, 88.7% of the total spatial variation was influenced by structural and 11.3% by random factors. And the global autocorrelation distance was 1178 km, and the average vegetation patch length (NW-SE) to width (NE-SW) ratio was approximately 2.4:1.0.

Net primary productivity and spatial distribution of vegetation in an alpine wetland, Qinghai-Tibetan Plateau

To initially describe vegetation structure and spatial variation in plant biomass in a typical alpine wetland of the Qinghai-Tibetan Plateau, net primary productivity and vegetation in relationship to environmental factors were investigated. In 2002, the wetland remained flooded to an average water depth of 25 cm during the growing season, from July to mid-September. We mapped the floodline and vegetation distribution using GPS (global positioning system). Coverage of vegetation in the wetland was 100%, and the vegetation was zonally distributed along a water depth gradient, with three emergent plant zones (Hippuris vulgaris-dominated zone, Scirpus distigmaticus-dominated zone, and Carex allivescers-dominated zone) and one submerged plant zone (Potamogeton pectinatus-dominated zone). Both aboveground and belowground biomass varied temporally within and among the vegetation zones. Further, net primary productivity (NPP) as estimated by peak biomass also differed among the vegetation zones; aboveground NPP was highest in the Carex-dominated zone with shallowest water and lowest in the Potamogeton zone with deepest water. The area occupied by each zone was 73.5% for P. pectinatus, 2.6% for H. vulgaris, 20.5% for S. distigmaticus, and 3.4% for C. allivescers. Morphological features in relationship to gas-transport efficiency of the aerial part differed among the emergent plants. Of the three emergent plants, H. vulgaris, which dominated in the deeper water, showed greater morphological adaptability to deep water than the other two emergent plants.

The Pressure Transient Analysis Of Deformation Of Fractal Medium

The assumption of constant rock properties in pressure-transient analysis of stress-sensitive reservoirs can cause significant errors in the estimation of temporal and spatial variation of pressure. In this article, the pressure transient response of the fractal medium in stress-sensitive reservoirs was studied by using the self-similarity solution method and the regular perturbation method. The dependence of permeability on pore pressure makes the flow equation strongly nonlinear. The nonlinearities associated with the governing equation become weaker by using the logarithm transformation. The perturbation solutions for a constant pressure production and a constant rate production of a linear-source well were obtained by using the self-similarity solution method and the regular perturbation method in an infinitely large system, and inquire into the changing rule of pressure when the fractal and deformation parameters change. The plots of typical pressure curves were given in a few cases, and the results can be applied to well test analysis.

Influence Of Free Surface Curvature Of A Liquid Layer On The Critical Marangoni Convection

The Pearson instability was suggested to discuss the onset of Marangoni convection in a liquid layer of large Prandtl number under an applied temperature difference perpendicular to the free surface in the microgravity environment. In this case, the temperature distribution on the curved free surface is nonuniform, and the thermocapillary convection is induced and coupled with the Marangoni convection. In the present paper the effect of volume ratio of the liquid layer on the critical Marangoni convection and the corresponding spatial variation of the convection structure in zero-gravity condition were numerically investigated by two-dimensional model. (C) 2008 Elsevier Ltd. All rights reserved.

松嫩平原碱化草地景观空间格局及环境因子的综合分析

本文对松嫩平原羊草地的群落结构及空间格局进行了分析，主要内容包含以下三个方面： 1、本文第一部分是对碱化草地植物群落分布的空间、环境因子分离。决定碱化草地植物物种在空间分布的因素可以大致分解成4个部分：（1）通过物种的生态位起作用的环境因子;（2）决定物种、群落间竞争激烈程度的空间距离因子;（3）环境和空间因子的交叉或耦合作用;（4）其它未知因子（如生物和随机因子）。本研究在1996年野外实地采样的基础上，运用DCA消势对应分析（Detrended Correspondence Analysis）对群落主要变化趋势及其与土壤环境因子之间的关系进行了分析。运用DCCA消势典范对应分析（Detrended Canonical Correspondence Analysis）对影响松嫩平原碱化草地群落结构季节动态的空间和环境因素进行了定量的分解。结果表明： 在影响群落分布的各因子中，环境因子独立约占40％，而环境一空间耦合因子占35％，空间因子独立约占3％，其它因子约占20％。在诸多因子中，土壤的盐渍化程度在整个生长季起着决定性作用，但土壤水分和氮素的作用因季节而变化。在干旱季节，植物生长的主要制约因子表现为土壤碱化度和土壤水份，而土壤氮素的作用处于次要地位。但在降雨较多、土壤湿润度较大的季节，土壤氮素的影响明显增强，成为仅次于土经度的决定性因素。 2、第二部分对东北松嫩平原碱化草地植物群落空间格局的分形性质进行了分析，分别用边长－面积指数和Korcak指数估计了斑块边界复杂性和斑块面积分布的分形维数。结果表明： 随放牧强度增加，占优势的羊草斑块的相对斑块化加剧，而斑块的边界在中度放牧时最不规则： 在水淹地，占优势的羊草斑块和次优势的碱茅斑块、獐茅斑块的斑块边界复杂性和斑块化程度比未水淹地都低，说明水降低了群落复合体内的异质性： 水淹地优势植物斑块的边长－面积指数和Korcak指数均低于次优势种，但在重度放牧地结果好相反，说明两种样地处于不同的演替阶段; 斑块边界复杂性符合同一尺度规律，在现有的面积范围以内没有尺度转换，而斑块面积分布则存在尺度转换点。对重牧地和水淹地的尺度分析表明，较小尺度上， 群落空间格局的相对斑块化程度较低，说明较小尺度上的空间格局要相对稳定一些，而较大尺度上则相反。可能原因是放牧干扰对大尺度的斑块影响更大。 3、对1989年开始围栏封育的样地10年来的空间格局变化进行时间序列分析，研究恢复演替过程中各个主要斑块类型的分布特征及动态，以及整个样地总体格局在演替系列中的变化。得出如下结果： 羊草是该区植被的优势种，其格局动态为：1989－1993年，羊草斑块总面积增加，斑块数目减少，相对斑块化指数降低，1994年后羊草的空间格局基本稳定。 羊草的斑块面积分布曲线在20平方米左右发生转折，即空间格局在此尺度发生尺度转换。不同尺度上斑块的相对斑块化指数及其在恢复演替中的变化趋势不同：小斑块的相对斑块化指数低，在1989－1993年期间增加，而后降低;大斑块的情况正好相反。说明羊草空间格局的主要变化之一是中等大小斑块的合并和数目减少，羊草斑块生长对格局的影响比斑块合并的影响要小。 獐茅斑块的格局动态为：1989－1994，斑块总面积、斑块数目、最大斑块面积增大，1995年开始降低。相对斑块化程度则先降后增。碱蓬斑块在1989－1993年间的格局动态与羊草正好相反：总面积减少，斑块数目增加，斑块面积大小的变化范围变窄，说明1993年之前，控制碱蓬斑块的主要生态学过程是其他物种的侵入，隔离原来较大的斑块，同时占据某些小斑块。1994年之后，碱蓬斑块的变化比较随机，其格局变化受到其他物种如杂草对策种虎尾草等的影响很大。 样地总体格局的变化为：1991年前，斑块种类和总斑块数目增加，斑块化程度随着增大;1993年后，斑块种类基本稳定下来;1991－1995，斑块化指数降低。在此期间，斑块数目增加，所以斑块化程度降低意味着斑块大小频率分布趋于均匀，大斑块被分裂，小斑块在长大，群落总体空间格局逐渐稳定。总体格局在三个尺度上有不同的自相似规律，这三个尺度分别为：La(a)<=1; 15.5。小尺度上相对斑块化程度低，但年际间变化较中尺度剧烈;中尺度相对斑块化程度变化较为缓，大尺度上，斑块分布一直趋于减少最大的斑块数目。总的变化趋势为，随恢复演替的深入，最大和最小的斑块数目都减少，处于中间尺度的斑块最多。

内蒙古锡林河流域草原群落土壤呼吸的时空变异及其影响因子研究

　　土壤呼吸是全球碳循环中的一个重要环节，其对全球碳平衡的影响是近年来人们关注的焦点之一。探讨碳素的失汇(missing sink)问题，对陆地生态系统土壤呼吸的研究是必不可少的。环境因子与土壤呼吸之间的关系可以用于将土壤呼吸从“chamber”水平的测量放大到整个生态系统或更大尺度。而温度、水分和植被状况都是对土壤呼吸有重要影响的因子，随着全球气候的变化，这些因子也会发生相应的改变，在这种情况下，它们极有可能与土壤CO2排放之间形成正反馈。温带草原是主要的陆地生态系统类型之一，目前非常缺乏有关土壤呼吸的研究资料。因此，在2001年生长季，我们在内蒙古锡林河流域南部集水区设定了一条东西长约160km、南北宽约30km的样带，从中选择了11个不同的植物群落，采用碱液吸收法周期性地对这些群落的土壤呼吸速率进行同步测定，并对土壤呼吸的时空动态及其与温度、土壤水分和植被状况之间的关系进行了研究。现将主要研究结果概述如下： 　　①锡林河流域南部集水区的土壤呼吸表现出明显的季节变化和空间变异。温度是影响土壤呼吸季节变化的主要因子之一，指数模型能够较好地揭示各群落土壤呼吸对温度变化的响应，但低温时模型的拟合效果更好。各群落土壤呼吸的季节动态与温度变化不完全同步，表明温度并不是影响土壤呼吸的唯一因子 。 　　②土壤呼吸的温度敏感性在各群落之间存在着一定的差异。春小麦群落的Q10值高于草原群落，说明不同的土地利用方式会影响到土壤呼吸对温度变化的敏感程度。水分对土壤呼吸的温度敏感性有重要影响，秩相关分析的结果表明，土壤水分与Q10值之间存在着显著的正相关关系。此外，依据不同土壤层次的温度得出的Q10值各不相同，基于变化幅度大的浅层土壤温度和气温得出的Q10值较小，而根据变化幅度小的深层土壤温度得出的Q10值较大。 　　③水分对各群落的土壤呼吸也有较大影响，但其影响程度有一定的季节差异，生长旺季水分对土壤呼吸的影响显著高于其它季节。从各群落的具体情况来看，水分对土壤呼吸的影响明显受制于群落的水分供应状况。水分供应状况比较好的和水分变化幅度小的群落中，土壤呼吸与水分之间没有显著的函数关系，而水分相对欠缺的群落则存有显著的线性关系。消除温度的影响后，这种线性关系显著增强。土壤水分含量较低的芨芨草群落中，土壤呼吸与表层水分之间的关系也不明显，这与芨芨草根系分布较深，能够利用土壤中较深层次的水分有关。 　　④土壤呼吸季节变化与植被之间的关系与各群落内水分状况以及植被对水分的利用机制有关。所有群落土壤呼吸速率随着绿色活体生物量的增长有上升趋势，且在水分供应充足的群落和植被较为耐旱或能够利用深层土壤水的群落中，这二者之间呈显著或极显著的指数关系，其它群落中相关关系不够显著。由于植被立枯量大小反映了水热的综合状况，所以群落的土壤呼吸速率随立枯量的增长呈下降趋势，二者之间的关系也可以用指数方程来表示。 　　⑤土壤呼吸在锡林河流域南部的空间变异主要受水分和植被状况的影响。总体来看，土壤水分含量高、地上生物量（包括绿色活体生物量）大或地上净第一性生产力高的草地群落，其土壤呼吸速率也较高。基础呼吸速率对于改进土壤呼吸模型在时间和空间上的预测精度有重要意义。我们的研究结果表明，在平均温度低、水分状况好、地上和地下生物量大、地上净第一性生产力高的地方，基础土壤呼吸速率也相应较高。

玉米农田土壤呼吸作用动态与模拟研究

利用动态密闭气室法(Licor-6400-09)，对锦州玉米生长季(5～9月)农田土壤呼吸作用动态及其影响因子进行连续两年的野外动态观测，分析表明，在植株尺度上，玉米地土壤呼吸作用存在明显的空间异质性，较高的土壤呼吸速率通常出现在靠近玉米植株的地方。玉米地土壤呼吸作用的日变化为不对称的单峰型曲线，最小值和最大值分别出现在6:00～7:00和13:00左右。2005年玉米生长季土壤呼吸速率均值为3.16 µmol CO2 •m-2•s-1，最大值为4.77 µmol CO2 •m-2•s-1，出现在7月28日，最小值为1.31 µmol CO2 •m-2•s-1，出现在5月4日。 植物根系生物量的分布格局是影响土壤呼吸作用空间异质性的关键因素。土壤呼吸作用与根系生物量呈显著的线性关系，而土壤湿度、土壤有机质、全氮和碳氮比对土壤呼吸作用空间异质性的影响并不显著。在土壤呼吸作用日变化中，土壤呼吸速率(SR, µmol CO2 •m-2•s-1)与10 cm土壤温度(T, ℃)均呈显著的指数函数关系 。在季节尺度上，参数α和β是波动的，玉米净第一性生产力(NPP, g •m-2 •d-1)和生物量(B, g •m-2)分别为影响参数α和β季节性波动的主导因素。鉴于此，建立了方程 用以模拟土壤呼吸作用的季节变化。土壤温度、NPP和生物量共同影响着玉米生长季土壤呼吸作用的季节性变化，它们共同解释了土壤呼吸作用季节变化的93%。 小时尺度上，土环中的根系生物量是影响土壤呼吸速率空间变异的关键因子，土壤呼吸速率与根系生物量呈线性关系 ;日时间尺度上，土壤呼吸速率与根系生物量线性方程中的参数α和β是波动，土壤温度是影响α和β波动的主导因素，于是得到方程 。季节时间尺度上，土壤呼吸作用可表达为 ，土壤温度、土壤湿度和玉米NPP共同驱动着玉米生长季土壤呼吸作用的时间变化和空间变异，它们可以解释玉米生长季土壤呼吸作用时空变化的74%。 通过建立土壤呼吸作用与玉米根系生物量的回归方程，对根系呼吸作用占土壤呼吸作用的比例进行了间接估算。玉米生长季根系呼吸作用占土壤呼吸作用的比例在43.1～63.6%之间波动，均值为54.5%。假定玉米果实和秸杆中的碳在收获期间没有从农田中转移走，2005年整个生长季玉米生态系统的碳收支为–1127.0 gC•m-2，碳交换速率在 0.52～-18.05 g C•m-2 •d-1 之间波动。玉米生长初期，玉米生态系统表现为C的弱碳源;玉米播种后35天一直到收获，玉米生态系统表现为碳汇。