基于RS-485总线和MCU的频率合成器设计

本文主要介绍一款基于RS-485总线和MCU的频率合成器,重点介绍了频率合成器的总体结构,RS-485总线接口电路,高集成度频率合成芯片AD9850的外围硬件电路和控制软件。该合成器输出频率范围:5~40MHz,最小频率步进为≤20Hz,输出正弦波或方波幅度800mV。该频率合成器具有结构简单,精度高,控制灵活的特点。

双奇核~(142)Pm高自旋态能级纲图

利用能量为 75— 95MeV19F束流 ,通过反应12 8Te( 19F ,5nγ) 142 Pm研究了双奇核142 Pm的高自旋态能级结构 .实验中进行了γ射线的激发函数、γ射线单谱和γ γ符合测量 .建立了激发能达 70 3 0 .0keV的142 Pm的能级纲图 ,其中包括新发现的 2 5条γ射线和 1 3个新能级 .基于实验测量的γ跃迁各向异性度 ,建议了142 Pm能级的自旋值

Fischer-Tropsch reaction over cobalt catalysts supported on zirconia-modified activated carbon

An attractive Fischer-Tropsch catalyst was prepared using an activated carbon as carrier to support cobalt based catalysts. Zr promoted Co/AC catalysts remarkably enhanced the activity and the selectivity toward diesel distillates and lower the methane selectivity. This modification may be attributed to specific behavior of activated carbon with high surface area and the weak interaction between metallic cobalt active sites and activated carbon. It was emphasized that the pore size of activated carbon played a very important role in restricting the growth of carbon chain to wax.

北方稻田生态系统水量平衡及水分效率研究

１９９３～１９９５年研究了５种不同模式水稻田生态系统水量平衡及水分效率结果表明，不同水稻田模式其总耗水量之间有明显差异，其中节水模式和节水节肥模式较常规模式节省灌溉水达１５～２３％，水分生产效率增加３０％以上．各模式蒸发蒸腾耗水量在同一生长季内基本相同．田间结构及调控管理对其无明显影响实测水稻生育期田间蒸发蒸腾量与计算的可能蒸发蒸腾量相差不过５％。

Electrocatalytic properties of Cu-Zr amorphous alloy towards the electrochemical hydrogenation of nitrobenzene

The Cu-Zr amorphous alloy was studied as an electrocatalyst towards the electrochemical hydrogenation of nitrobenzene. The electrocatalyst was activated by chemical etching in HF solution. Resulted changes in the morphology, chemical composition and crystalline structure of the electrocatalyst surface were characterised by scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The electrocatalytic properties of the Cu-Zr amorphous alloy were assessed by voltammetric measurements. Due to the formation and aggregation of Zr residue modified Cu nanocrystals on the surface caused by the selective dissolution of Zr components in the chemical etching, the activated amorphous alloy is an effective electrocatalyst for the electrochemical reduction reaction of nitrobenzene with aniline as the main product. The positive shift of the peak potential and accompanying increase in the value of peak current in voltammograms with increasing Cu content and decreasing Zr content of the alloy surface in the chemical etching are indicative of improved electrocatalytic activity. (C) 2002 Elsevier Science B.V. All rights reserved.

黄土沟壑区小流域水土保持减水效益分析

在实测资料的基础上借助流域水沙耦合模型中的产流模式 ,将水土保持减水型措施和植被型措施在减流中的作用定量分割开来 ,为区域水土流失综合治理提供基础数据 .结果显示 ,高度综合治理的插财主沟和杨家沟小流域平均减水分别为 6 6 .2 %和 5 8.7% .其中减水型措施分别减水 42 .0 %和 19.8% ,植被型措施分别为 2 4.2 %和 38.9% .与未治理小流域相比 ,综合治理使小流域拦蓄水程度明显提高 ,减水型措施拦蓄径流作用显著高于植被型措施

辽西半干旱区春小麦氮磷水耦合产量效应研究

为了探讨春小麦水肥耦合作用,采用312-D最优饱和设计,于2000～2003年在辽西半干旱区开展了水肥耦合对春小麦产量效应的田间试验研究。结果表明:在该试验条件下水分对产量的作用最大,磷肥次之,氮肥最小;水肥耦合的产量效应是:中水中肥效应最高,高水高肥次之,低水低肥最低;水肥交互耦合效应大小顺序是:氮水耦合>氮磷耦合>磷水耦合。产量超过4000kg/hm2的水肥管理方案为:施氮量240.1～361.2kg/hm2,施磷量103.1～152.6kg/hm2,灌水量337.5～450.0mm。获得最高产量4610kg/hm2的施氮量为315.1kg/hm2、施磷量111.1kg/hm2、灌水量354.6mm。

农田和森林土壤中氧化亚氮的产生与还原(英文)

采用土壤淤浆方法对丹麦农田和山毛榉森林土壤反硝化过程中N2 O的产生与还原进行了研究 ,同时考察了硝酸根和铵离子对反硝化作用的影响 .结果表明 ,森林土壤反硝化活性大于农田土壤 ,但农田土壤中N2 O还原活性大于森林土壤 ,表现在农田和森林土壤中N2 O/N2 的产生比率分别为 0 .11和 3 .65 .硝酸根和铵离子能促进两种土壤中的N2 O产生 ,但可降低农田土壤中的N2 O还原速率 .与农田土壤相比 ,硝酸根可降低森林土壤N2 O的还原能力 ,而铵离子却表现出对N2 O还原的促进作用 .培养 1周内尽管农田土壤中硝酸根始终存在 ,但几乎所有产生的N2 O都被还原成N2 .然而 ,只有当硝酸根几乎耗尽 ,森林土壤中N2 O的还原才开始进行 .由于两种土壤 pH值的不同造成硝酸根对N2 O还原抑制作用的差异 ,因为酸性条件下硝酸根对N2O还原的抑制较强 .因此 ,土壤消耗大气N2 O的适宜条件为厌氧 ,pH中性和硝酸根含量低 .