Variation in 15N natural abundance of soil, humic fractions and plant materials in a disturbed and an undisturbed grassland

The natural abundance of δ¹⁵N in disturbed and undisturbed pasture soils was examined. From the disturbed soil, the top 10 cm of the profile was examined and the soil split into fractions based on particle size. Plant shoot and root material contained similar low enrichments in ¹⁵N, whereas recently deposited shoot residues were highly enriched. Differences between the soil fractions in observed total N did not reflect similar ¹⁵N variation. However, the enrichment of humic material extracted from the largest soil fraction was considerably lower in ¹⁵N relative to that from the smaller fractions. The complexity of the humic material from the larger fractions was less according to the E ₄ /E ₆ ratio. Analysis of the profile from the undisturbed soil showed increasing ¹⁵N enrichment with depth which corresponded well with visible soil horizons and showed an inverse relationship with total soil N. This ¹⁵N enrichment was mirrored by the enrichment in humic materials down the profile and also corresponded with an increasing chemical complexity as shown by the E ₄ /E ₆ ratio. Received: 15 March 1996     

丙烯酰胺/马来酸酐共聚高吸水树脂PAMMAH研究

以丙烯酰胺(AM)和马来酸酐(MAH)为单体M,N,N’-亚甲基双丙烯酰胺为交联剂C,过硫酸钾为引发剂I,在一定中和度下采用溶液聚合法,合成了丙烯酰胺／马来酸酐共聚高吸水树脂PAMMAH,并进行了吸液性能研究,得到最优合成条件为:R(n (AM):n(MAH))=5:1,WM=25％,WC=0．02％,WI=0．4％,N=130％,30℃(4 h)→60℃(4 h)→80℃(3 h)．最大吸液性能为:吸蒸馏水倍率Qw=3 193 g／s,吸0．9％NaCl盐水倍率Qs=213 g／g．PAMMAH树脂的吸蒸馏水倍率、吸0．9％NaCl盐水倍率与吸液时间的关系为:Qw=1 174．15 t0．2511和Qs=68．86 t0.2127．     

二氧化锰超细粉体的合成

以MnCl2和NaOH为原料，利用超临界流体干燥技术（SCFD）制备了MnO2超细粉体。研究和讨论了反应温度、反应物浓度、反应时间等对实验结果的影响，确定了最佳反应条件．XRD物相分析。产物为γ-MnO2，扫描电镜观察粒子基本为球形，平均粒径60nm，没有明显的团聚现象。     

利用粗老原料加工速溶红茶的品质改进

利用粗老原料加工速红茶可降低成本，充分利用茶叶资源，然而，其品质普遍存在茶叶香味淡薄、风味不显等缺陷。本文就红茶风味形成的物质基础，加工过程的物质转换，粗老原料的成分状况进行了讨论，并针对上述品质问题提出了一些具体的方法和思路，涉及风味成分的添加1乌龙茶原料和工艺的引入等。     

棉花倒四叶宽度变化规律及诊断指标

棉花主茎倒四叶宽度是看苗诊断的一项重要指标。本文应用沿江棉区海门县１９８３～１９９１年盐棉４８等５日定点生育调查资料，分析阑述了麦垄套栽、麦后移栽、地膜覆盖、露地直播４种茬口棉花的主茎倒四叶宽增长变化规律及其不同点，提出了不同茬口中熟陆地棉不同生育期的倒四叶宽诊断指标     

寒冷季节室外发酵料工艺探讨

在寒冷季节对培养料进行室外堆积发酵，采用不同覆盖物和翻堆时间的处理，观察培养料的发酵时间和发酵程度，得出结果为堆料第3天翻堆和覆盖草帘发酵质量好，时间短。     

Study on China’s Import Trade and Market in Main Forest Products

With the development for half a century in China, theproduction and utilization of forest products in Chinacannot be separated from the development ofeconomy and the civil life. Much greaterachievements have been made since China grantedaccess to WTO and became one of the biggestcountries in world trade in forest products from the1990s to nowadays. Along with the start of NaturalForest Protection Program at the time of crossingthe 21st century, importing more forest products willbe needed,…     

电力系统微机监控装置中图形编缉器的设计

设计开发了一种高速画面生成，并能进行实时不断电在线修改的图形编辑软件包．该系统以ＰＣ×ＴＡＴ计算机为核心，以８０８２６宏汇编语言为基本开发工具．实现对电力系统主接线图的在线编辑功能，并能实时反应电网断路器、隔离开关等遥信置的动态变化状态．     

纳米Fe3O4/PANI复合体系的微波电磁特性研究

用原位化学反应生成法制备了纳米Fe3O4/PANI复合材料,研究了样品在2~18 GHz范围的微波电磁特性与吸收性能以及复合材料组分对电导率、密度的影响.结果表明,Fe3O4颗粒尺寸约12.7 nm,Fe3O4在复合体系中的质量分数为35%左右时,电导率最大,密度相对较低,微波吸收率最高,吸收峰值为-21 dB,-10 dB频宽大于4 GHz,样品同时具有电损耗和磁损耗.可见,通过优化设计,纳米Fe3O4/PANI复合体系可以成为一种性能优良的微波吸收材料.     

DyFe11-xMnxTi赝三元化合物的结构和磁性

研究了Mn部分替代DyFe11Ti中的Fe对化合物结构和磁性的影响.利用真空电弧熔炼和真空热处理制备了DyFe11-xMnxTi(1.0≤x≤5.0)化合物样品.X-射线衍射和热磁曲线测量表明:用Mn部分取代DyFe11 Ti中的Fe仍保持ThMn12型结构,且具有较好的单相性;晶格常数a和单胞体积V随Mn含量的增加而增大;在DyFe7Mn4Ti化合物的热磁曲线上观察到了补偿点;随着Mn含量的增加,化合物在4.4 K温度下的饱和磁化强度逐渐减小,在某一成分点为零.而后随Mn含量的继续增加而增大.