非豆科固氮树木色赤杨联合共生体的研究

非豆科树木共生固氮体系抗逆性强，具有耐干旱、耐盐碱、耐低PH、耐水湿等特点，且分布广泛，资源丰富，因此开展Frankia-非豆科树木联合共生体系的理论与应用研究，不仅对丰富和发展联合共生理论具有重要意义，而且在加速树木生长、解决农村资源短缺、减少水土流失、改良土壤和改善生态环境等方面将产生重大的经济和生态环境效益.该文通过对非豆科固氮树木色赤杨的菌根、根瘤联合共生体人工构建技术以及赤杨联合共生增效作用的研究，选择出色赤杨的最适共生菌根菌、弗兰克氏菌，为联合共生体接种技术在造林生产实践尤其是在逆境条件下的应用提供理论依据.

The Relationship between Decision Trees and the Scale of Train Data Set

Decision Trees need train samples in the train data set to get classification rules. If the number of train data was too small, the important information might be missed and thus the model could not explain the classification rules of data. While it is not affirmative that large scale of train data set can get well model. This Paper analysis the relationship between decision trees and the train data scale. We use nine decision tree algorithms to experiment the accuracy, complexity and robustness of decision tree algorithms. Some results are demonstrated.

Local thermal fixing of a photorefractive LiNbO3 hologram by use of a CO2 laser

A real-time, in situ fixing method by use of heating with a CO2 laser beam is suggested for thermal fixing of a small local hologram in the bulk of a Fe:LiNbO3 photorefractive crystal. For heating up to 100 degrees C-200 degrees C a volume with a shape similar to that of the laser beam a heat-guiding technique is developed. On the basis of the heat-transfer equations, different heating modes with or without metal absorbers for heat guiding-obtained by use of a continuous or pulsed laser beam are analyzed. The optimal mode may be pulsed heating with absorbers. On this basis experiments have been designed and demonstrated. It is seen that the fixing process with CO2 laser beam is short compared with the process by use of an oven, and the fixing efficiency is quite high. (C) 1998 Optical Society of America.

Characteristics of recording and thermal fixing in lithium niobate

We present a theoretical model in which the band-transport equations and the coupled-wave equations are considered to study the two thermal-fixing methods (simultaneous fixing and postfixing) in Fe:LiNbO3. We found that, in simultaneous fixing, the existing ionic-grating affects the writing of the electronic grating by reduction of the coupling gain, and the grating envelope of the fixed-index grating is quite uniform inside the photorefractive crystal in comparison with the method of postfixing. The resulting diffraction efficiency of the fixed-volume grating is dependent mainly on the initial intensity modulation of the two writing beams. A set of experiments is also presented. (C) 1998 Optical Society of America.