垄上线源滴灌湿润体特性研究

在米脂县孟岔试验基地进行大田试验,研究了同一灌水量、不同流量条件下,垄上线源滴灌湿润体特征值的变化规律及滴灌结束后的水分再分布规律。试验结果表明:在线源交汇入渗情况下,滴头处和交汇面处垂直入渗距离与入渗时间均满足良好的幂函数关系。在灌水量为9L的情况下,湿润体沿滴灌管布置方向剖面上的土壤含水率等值线大致以15cm深度为分界线,上层呈现以滴头为中心的椭圆状,而下层则相对平缓。滴灌停止后24h时的湿润体较为稳定,其特征值可以作为线源滴灌灌水量设计的依据,同一灌水量条件下,滴头流量对滴灌停止后24h的湿润体特征值影响并不大。

黄土丘陵区县南沟流域生态恢复的生态经济耦合评价

探索一套简单、易于操作的小尺度生态经济耦合效应指标体系及其评价方法模型。【方法】基于生态经济协调理论,在继承传统指标的基础上,引用了2个创新性指标——能值可持续性指数(ESI)和生态压力指数(EFPI),应用模糊综合评价方法对县南沟流域生态恢复的生态经济耦合进行评价。【结果】县南沟"农-经济林果型"生态恢复模式的生态经济处于基本协调状态。【结论】"农-经济林果型"模式有效地改善了流域生态条件,促进了经济发展,产生了生态经济耦合效应。

微灌技术在陕北山地红枣生产中的应用示范研究

干旱缺水与水土流失并存是制约黄土高原地区生态环境建设和经济可持续发展的二大瓶颈因子,也是导致该区生态脆弱的根本原因。这一问题不仅是国家关注的重点,也是科学界关注的热点和难点。长期以来,由于水土流失与干旱缺水互为矛盾,甚至互为因果,很难同时实现这二大问题的同步解决。我们在20世纪末曾提出“以降雨径流调控与利用”为主要手段,通过山地降雨径流的调控消除水土流失动力,通过现代农业节水技术实现有限径流的高效利用,从而同步解决上述二大难题的构想,并进行了多年探索与实践,系统地研究了人工汇集雨水利用技术及雨水高效集蓄利用技术,并在生产中得到了较为广泛的应用,并取得了一定的效果。滴灌是一种资金和技术需要较高的灌溉技术,其一次性投资较大,必须在经济价值较高的作物上实施才能产生较好的经济效益,也才能体现技术自身的优势。同时,实施滴灌技术在现有的土地联产承包机制下,也给该技术的应用和工程设计带来了一定困难。由于土地种植的不连续性,土地经营与管理的个体性,很难发挥技术本身的优势,不仅增加了工程设计的难度和建设成本,也给工程管理与运行带来了一定困难。所以,尽管我们在2005年就基本完成了这项成果的理论研究,但一直没有在生产中进行应用、...

A linkage map of common carp (Cyprinus carpio) based on AFLP and microsatellite markers

P>Common carp (Cyprinus carpio) is an important fish for aquaculture, but genomics of this species is still in its infancy. In this study, a linkage map of common carp based on Amplified Fragment Length Polymorphism (AFLP) and microsatellite (SSR) markers has been generated using gynogenetic haploids. Of 926 markers genotyped, 151 (149 AFLPs, two SSRs) were distorted and eliminated from the linkage analyses. A total of 699 AFLP and 20 microsatellite (SSR) markers were assigned to the map, which comprised 64 linkage groups and covered 5506.9 cM Kosambi, with an average interval distance of 7.66 cM Kosambi. The normality tests on interval map distances showed a non-normal marker distribution. Visual inspection of the map distance distribution histogram showed a cluster of interval map distances on the left side of the chart, which suggested the occurrence of AFLP marker clusters. On the other hand, the lack of an obvious cluster on the right side showed that there were a few big gaps which need more markers to bridge. The correlation analysis showed a highly significant relatedness between the length of linkage group and the number of markers, indicating that the AFLP markers in this map were randomly distributed among different linkage groups. This study is helpful for research into the common carp genome and for further studies of genetics and marker-assisted breeding in this species.

AN ALUMINUM OXYNITRIDE FILM

We report on an aluminum oxynitride (AlON) film which was successfully made using the reactiver r.f. sputtering method in an N2-O2 mixture. The fabrication process, atomic components, breakdown field and refractive index of the AlON film are shown in detail. The AlON film is a new polyfilm combining the good properties of Al2O3 and AlN, and it is very interesting with regard to optoelectronic devices and integrated optic circuits.

An investigation of the formation mechanisms of electric field domains in GaAs/AlAs superlattices

We have studied the vertical transport and formation mechanisms of electric field domains in doped weakly-coupled GaAs/AlAs superlattices. Under hydrostatic pressure two kinds of sequential resonant tunneling are observed within the pressure range from 0 to 4.5 kbar. A transition from Gamma-Gamma to Gamma-X sequential resonant tunneling occurs at P-t approximate to 1.6 kbar. For P < P-t, the high electric field domain is formed by the Gamma-Gamma process, while for P > P-t it is preferentially formed by the Gamma-X process.

Pressure dependence of the electronic subband structure of strained In0.2Ga0.8As/GaAs MQWs

We have measured low-temperature photoluminescence (PL) and optical absorption spectra of an In0.2Ga0.8As/GaAs multiple quantum well (MQW) structure at pressures up to 8 GPa. Below 4.9 GPa, PL shows only the emission of the n = 1 heavy-hole (HH) exciton. Three new X-related PL bands appear at higher pressures. They are assigned to spatially indirect (type-II) and direct (type-I) transitions from X(Z) states in GaAs and X(XY) valleys of InGaAs, respectively, to the HH subband of the wells. From the PL data we obtain a valence band offset of 80 meV for the strained In0.2Ga0.8As/GaAs MQW system. Absorption spectra show three features corresponding to direct exciton transitions in the quantum wells. In the pressure range of 4.5 to 5.5 GPa an additional pronounced feature is apparent in absorption, which is attributed to the pseudo-direct transition between a HH subband and the folded X(Z) states of the wells. This gives the first clear evidence for an enhanced strength of indirect optical transitions due to the breakdown of translational invariance at the heterointerfaces in MQWs.

The plasmon resonance absorption of Ag/SiO2 nanocomposite films

The plasmon resonance absorption of the Ag/SiO2 nanocomposite film is investigated. The measured absorption spectra are compared with those calculated by the Mie theory. The results indicate that the Mie theory on the basis of classical electrodynamics can only partially explain the optical absorption spectra of the Ag/SiO2 nanocomposite film. We believe that the plasmon resonance absorption is mainly an intrinsic quality of the metal particle, and can be explained only with the electronic structure of the metal particle. In the latter, surface resonance state is introduced to systematically discuss the optical absorption spectra of the Ag/SiO2 nanocomposite film. (C) 2003 Elsevier Science B.V. All rights reserved.

水土保持林土壤改良效应及其效益评价

土壤侵蚀是土地退化的一种重要表现形式，是当今世界重大环境问题之一。水土保持林正是针对这一环境问题而采取的一项生态林业工程措施，对于防止土壤侵蚀，控制水土流失具有极其重要的作用。论文以大量的文献为基础，对土壤侵蚀的定义、成因、规律和研究进展，以及水土保持林的功能进行了分析研究，发现有关土壤侵蚀规律和水土保持林水文效应方面的研究较多，可是关于土壤侵蚀内在机制和水土保持林土壤改良效应方面的研究较少。而事实上，水土保持林防止土壤侵蚀和改善区域水文状况的作用，与其改良土壤的作用有着密切的关系。水土保持林对生态环境的改善，正是以改良土壤的作用为前提的基础的。通常认为，森林改良土壤就是改善土壤的理化性状，提高土壤的肥力水平。论文通过对国内外有关文献的分析和朝阳地区的区域性考察，首次提出水土保持林作为保持水土、防止土壤侵蚀的特有林种，它的土壤改良效应不仅体现在土壤肥力水平的提高，更重要地表现为土壤抗蚀性能和抗冲性能的增强。这恰恰体现了水土保持林保持水土、防止土壤侵蚀的功能所在。因此对水土保持林土壤改良效应内容的拓展，有利于进一步认识土壤改良效应与水土保持林功能之间的关系，为高效、多功能水土保持林体系的建设提供了理论依据。水土保持林土壤改良效应是通过林冠截留、枯枝落叶层的作用以及根系的活动来实现的。论文通过对不同类型水土保持林林冠层的厚度和面积、枯枝落叶层的现存量和分解状况、以及根系分布特点的分析，阐明针阔叶混交林与针叶纯林相比，其水土保持性能更有利于土壤改良。随着林龄的增长，林分的水土保持性能增强，土壤改良效果更好。论文还着重对水土保持林土壤改良效应进行了研究，明确指出水土保持林土壤改效应包括土壤肥力提高、土壤抗蚀性能增强和土壤抗冲性能增强三个方面的内容。并根据其各自的性质和特点，分别选择土壤酶活性、土壤有机质含量、有机－无机复合体和微团聚体等作为土壤肥力的评价指标：水稳性团聚体含量及其平均重量直径、团聚度、分散率等作为土壤抗蚀性能的指标：土壤硬度、渗透系数等作为土壤抗冲性能的指标。用这些指标对不同类型水土保持林土壤肥力、土壤抗蚀性能和抗冲性能进行评价，得出的结论是一致的，即：针阔叶混交林土壤肥力、土壤抗蚀性能和抗冲性能均高于针叶纯林：同一树种林龄越大的林分，土壤肥力越高，土壤抗蚀、抗冲性能越强。例如，以土壤中脲酶、磷酸酶和蔗糖酶活性对土壤肥力进行评价时得出：与纯林相比，混交林土壤中脲酶活性提高了6.4 ～ 142.36%，磷酸酶活性提高了20.55 ～ 99.04%，蔗糖酶活性提高了4.23 ～ 198.96%。以水稳性团聚体含量对土壤抗蚀性能进行评价时，混交林土壤中水稳性团粒含量比纯林增加了1.71 ～ 38.53%，48年生和28年生油松林比15年生油松林增加了89.94 ～ 149.27%，等等。因此论文指出，与针叶纯林相比，针阔叶混交林改良土壤的效果更好。林龄越大的林分，土壤改良效果越佳。森林效益评价是目前林业研究的热点，也是难点。论文在掌握足够文献的基础上，对水土保持林综合效益评价做了较为系统、全面的分析和论述，提出了一套比较完整的效益评价方法和步骤。水土保持林土壤改良效益是其综合效益的一个非常重要的方面，也是水土保持林最直接、最基本的一项效益。论文在水土保持林土壤改良效应研究的基础上，明确提出了效益评价的方法和思路，这在目前还是不多见的。在所取和参与专家意见的基础上，筛选出了水土保持林土壤改良效益的评价指标，建立了由指标维、时间维和地类维构成的三维效益评价指标体系，确定了由总目标层、准则层和指标层构成的指标维的结构图，指出总目标层为水土保持林土壤改良效益评价综合指标：准则层包括土壤肥力、土壤抗蚀性能和土壤抗冲性能；指标层有土壤酶活性、土壤有机质含量、水稳性团粒平均重理直径、分散率、团聚度、土壤硬度、土壤渗透系数和pH值等。进而用层次分析法确定了指标体系中各项指标的权重，用于的评价计算。论文按照效益结构图中的层次，分步求算得到了水土保持林土壤改良效益评价综合指数。并尝试用消除立地因子影响的方法，对效益评价综合指数进行了校正。文中还分别以林地枯落物生物量(x_1)、林分平均胸径（地径）生长量(x_2)、林分平均树高生长量(x_3)以及平均胸径（地径）平方和树高乘积(x_4)为自变量，以效益评价综合指数为因变量进行模拟运算，得到了水土保持林土壤改良效益的评价模型，模拟结果较好的模型有：y = 0.7 + 0.2208x_1 - 0.0053x_1~2 R~2 = 0.5396 y = 0.5815x_2~(0.4885) R~2 = 0.4827 y = 0.8529 + 0.1869x_3 - 0.004x_3~2 R~2 = 0.3391 y = 2.7695x_4~(0.1533) R~2 = 0.4410生产实践中，可根据实际情况选择适当的模型加以应用。论文根据计算得到的效益评价综合指数的相对值，将朝阳地区水土保持林土壤改良效益划分为四个等级，即相对值>3为好；2.5 ～ 3为较好；2 ～ 2.5为中等；<2为较差。最后，还通过实例说明了效益评估模型和评价标准在当地生产实践中的应用。