钨丝掩模大角度倾斜离子注入850nm垂直腔面发射激光器及其高频调制特性

采用钨丝掩模技术,通过调整制作过程中的工艺参数,研制出批量器件阈值在2 m A以内,最低阈值为1.2 5 m A的85 0 nm垂直腔面发射激光器.同时对TO封装的器件进行了高频特性测试,结果表明3d B带宽最高为4 .0 GHz,在应用于光通信收发模块的商品化同类器件中处于较好的水平,适合中、高速光通信应用     

Perspectives on allelopathy in mexican traditional agroecosystems: A case study in tlaxcala

Agroecosystems in Tlaxcala, Mexico, are surrounded by trees and water channels and have a great variety of cultivated and noncultivated plants. The main results of a study carried out on a traditional agroecosystem in Santa Inés, Tlaxcala are presented. Some ecological aspects of polycultures, plant covers (dry leaves of<i>Alnus firmifolia, Berula erecta</i>, and<i>Juncus</i> sp.), and the allelopathic potential of crops and noncultivated plants (fresh and dry material) were analyzed. The main plants (trees, shrubs, and herbs) present in the agroecosystem were identified. The total number of weeds in plots where plant covers were added was reduced. The number of nodules of<i>Rhizobium phaseoli</i> and the production of bean and squash increased with plant covers. Corn, beans, and squash showed a clear allelopathic effect, as well as<i>Chenopodium murale, Tradescantia crassifolia, Melilotus indicus</i>, and<i>Amaranthus hybridus</i>, among other weeds. The contribution of allelopathy in studies of traditional agroecosystems is of great importance for the management of species in space and time. Allelopathy can be the basis of biological control of pests and weeds and of the discovery of new useful substances.     

Wine phenolics—analysis of low molecular weight components by high performance liquid chromatography

Low molecular weight phenolic compounds were separated by high performance liquid chromatography on hydrocarbon-bonded reverse phase packings, with a water-methanol elution gradient. Phenolic compounds were extracted from wine with ethyl acetate. A first extraction at pH 7 enabled isolation of neutral molecules (catechins, procyanidins, flavonols, aromatic alcohols); a second extraction at pH 2 was performed to extract phenolic acids. Successive injections of these two extracts in the chromatograph gave the distribution of the different phenolic compounds in the wine under analysis. Analytical data are given for low molecular weight phenolic compounds present in young red Bordeaux wines from different vine cultivars.     

Estimation of compound classes in coal hydrogenation liquids by thin-layer chromatography

Compound classes in coal liquids were investigated by thin-layer chromatography coupled with a flame ionization detector (t.l.c.-f.i.d.). Individual t.l.c. peaks for coal liquids were identified as paraffins, aromatics, polar compounds and more strongly polar compounds or asphaltenes in order of increasing <em>R</em><sub><em>f</em></sub> values by comparison with specific compounds separated previously by conventional liquid chromatography. Concentrations of compound classes for a series of samples obtained by varying the hydrogenation time were estimated and good agreement was found with the results obtained by the USBM-API 60 liquid chromatography procedure. By using the t.l.c.-f.i.d. method, the relation of distribution of compound classes to the reaction conditions of coal hydrogenation could be derived quantitatively with relative ease.     

Gas phase hydroformylation of ethylene using organometalic Rh-complexes as heterogeneous catalysts

The heterogeneously catalysed gas phase hydroformylation of ethylene to propionaldehyde was studied over solid RhCl(PPh<sub>3</sub>)<sub>3</sub> and RhCl(CO)(PPh<sub>3</sub>)<sub>2</sub>. At 3 bar and 185 °C, an active phase formed from RhCl(PPh<sub>3</sub>)<sub>3</sub> which was different from RhCl(CO)(PPh<sub>3</sub>)<sub>2</sub> under the reaction conditions studied. The selectivity of RhCl(PPh<sub>3</sub>)<sub>3</sub> to propanal was much better than that of supported Rh-metal. Thus, solid metal-complexes operated in gas phase reactions clearly hold promise as a new class of heterogeneous catalysts.