应试作文的困惑

在中学语文诸多能力的培养中,写作能力的培养是至关重要的一个方面,然而,写什么,怎样写,如何解决自己贫乏的语言仓库表达绚丽多彩的大千世界的矛盾,又让莘莘学子谈文色变,提笔沉重.为此,从1993年开始,结合自己多年作文教学的体会,汲取其它同行的一些成功经验,我选择议论文教学为突破口,尝试通过切实可行的方法,激发同学的写作兴趣,提高写作水平.

Fixed Ammonium Contents and NH Fixation Capaci-ties of Some Cnltivated Soils in China

Fixed ammonium contents and fixation capacities of some representative cultivated soils collectedfrom 16 provinces of China were studied. Results showed that the contents of fixed ammonium in soilsranged from 35 to 573 mg N kg￣(-1), with an average of 198 mg N kg￣(-1). The content of fixed ammoniumcorrelated very significantly with mica content for tropical and subtropical soils, whereas this was not thecase for soils in the temperate zone. At the end of K-exhansting experiment the fixed ammonium contentincreased in most soils studied. However, it decreased in some temperate soils. Generally, fixation of addedNH could not be found either before or after K-exhausting experiment for highly weathered soils, includingtropical soils and soils derived from granite-gneiss or Quaternary red clays in the subtropic zonet while formost soils in the Yangtze River dalta the NH fixation capacity was rather high and increased siguificantlyin the K-exhausted soils.

Optimum line reclosing time for the enhancement of interconnected power system stability

Automatic line reclosing schemes used in an extra-high-voltage power system is an economical and effective means to maintain transient stability. A novel method is proposed in the paper to adaptively optimize the automatic line reclosing time after a transient fault for enhancement of interconnected power system transient stability. Both the study on the transient energy over network and the structure-preserving multi-machines power system model illustrate that the excessive convergence of potential energy on the lines with a certain cutset deteriorate power system stability, and therefore, an optimum line reclosing strategy can be established by minimizing the change in transient potential energy distribution across a cutset lines in the vicinity of the faulty line as an optimization target, and the optimal reclosure time is set to the time of minimum line phase angle difference. Without any pre-determined knowledge, the method is adaptive to various power system operation modes and fault conditions, and easy to implement because only a limited number of data measured at one location on a tie-line linking sub-networks are required. Simulations have been performed with the OMIB(One Machine and Infinite Bus System) and a real inter-connected power system to verify the applicability of the method proposed.

Isolation and Identification of Phosphobacteria in PoplarRhizosphere from Different Regions of China

A few soil microorganisms can convert insoluble forms of phosphorus （P） to an accessible form to increase plant yields The objectives of this study were to isolate, screen and identify the phosphobacteria, i.e., phosphate-solubilizing bacteria （PSB） and phosphate-mineralizing bacteria （PMB）, in some poplar plantations and to select potential microbial inoculants that could increase the P uptake by plants. Seventy four PSB strains and 138 PMB strains were preliminarily screened from 797＂colonies isolated from the rhizosphere soil of poplar by the visible decolorization in the National Botanical Research Institute＇s phosphate growth medium （NBRIP） containing a pH indicator of bromophenol and by the clear/halo zone on yeast malt agar plate, respectively. Then, based on the solubilization of Ca3（PO4）2 in liquid NBRIP medium and the mineralization of lecithin in liquid Menkina medium, 15 PS1R strains and 7 PMB strains were further determined for their abilities to solubilize Ca3（PO4）2 and to mineralize lecithin. The results showed that the 15 PSB strains exhibited inorganic P-solubilizing abilities ranging between 376.62 and 669.56 mg L-1 and the 7 PMB strains exhibited organic P-mineralizing abilities vaxying from 0.32 to 1.56 mg L-1 three days after incubation. Three of PSB strains with the highest P-solubilizing ability, named JW-JS1, JW-JS2 and JW-SX2, were all preliminarily identified as Pseudomonas ftuorescens, while two of PMB strains with the highest P-mineralizing ability, named JYZ-SD1 and JYT-JS2, were preliminarily identified as Bacillus cereus and Bacillus subtilis, respectively. All the efficient PSB and PMB strains should be further studied under both pot culture and field conditions to test their beneficial effects on poplar.

Constructing hydrophobic protection for ionic interactions toward water,acid,and base-resistant self-healing elastomers and electronic devices

Dynamically crosslinked materials generally lose their self-healing ability and mechanical robustness in aqueous,acidic,and basic environments due to disruption of their dynamic interactions and bonds.Herein,a micelle-like structure with a hydrophobic outer layer is used to protect ionic interactions.This structure ensures the self-healing and long-term stability of the ionically crosslinked elastomers in aqueous,acidic,and basic environments.The elastomer possesses a tensile strength of 6.7 MPa and a strain at break of 1400%,which is superior to the existing waterproof selfhealing elastomers.The strain sensors and dielectric actuators based on the elastomer are highly stable and self-healable,even in extremely harsh environments.This design strategy of hydrophobic protection for dynamic interactions is quite general,allowing it to be extended to other self-healing materials.