2—退化图的全色数

对任意简单图Ｇ，△（Ｇ）和ＸＴ（Ｇ）分别表示Ｇ的最大度和全色数。证明了当△（Ｇ）≥４时，２－退化图Ｇ的全色数ＸＴ（Ｇ）＝△（Ｇ）＋１。     

鲫鱼视网膜双极细胞在暗中的压抑

硬骨鱼的视网膜,视锥系统在长时间暗适应后受到强烈的压抑.Raynauld 等(1979)发现,金鱼视网膜中双拮抗型神经节细胞在暗适应2h 后,对光完全没有反应.杨雄里等报道,仅接受视锥输入的水平细胞(视锥水平细胞)的光反应性在长时间(>2h)暗适应后受到强烈的压抑.双极细胞处于自光感受器至神经节细胞的信息传递的直接通路上,长时间暗适应对双极细胞反应性的影响迄今未见报道.本工作应用完整的在位眼杯标本,发现接受视锥信号的超极化双极细胞,其感受野周围的对光去极化反应在长时间(>2h)暗适应后受到强烈压抑,连续闪光使之增大.     

Land degradation, government subsidy, and smallholders＇ conservation decision： the case of the loess plateau in China

Land degradation is one of the severe environmental problems in China. In order to combat land degradation, a soil conservation program was introduced since 2000 to reduce soil erosion by converting slope-cultivated land into forestry and pasture. This paper represents the first systematic attempt to investigate the impact of the soil conservation program on land degradation in the loess plateau. The results indicate that the soil conservation program to convert slope fields into forest or pasture is an effective way to combat soil erosion. However, a subsidy that is higher than profit of land use activity of slope fields before their conversion into forest and pasture is needed to encourage farmers to join the conservation program. A policy measure to encourage and assist farmers to develop sedentary livestock by using crops produced from fields as well as fodder and forage grass from the converted slope fields might contribute to combat soil erosion. Increase in off-farm job opportunities may encourage households to reduce cultivation in slope fields. That implies a policy measure to encourage rural urbanization might contribute to combat soil erosion.     

和田河流域生态脆弱性成因辨识

通过献资料和野外考察,认为和田河流域的脆弱生态环境是长期的自然作用过程及人类活动干预下形成的。自然地理要素有脆弱性的一面,不合理的人类活动加剧了生态环境退化的进程。和田河流域脆弱生态环境是水、植被环境恶化导致的生态平衡失调形成的。总体表现为以荒漠化为主体的环境问题日益加剧,并通过土地沙漠化、土壤盐渍化、草场退化、生物多样性丧失,以及干旱、风沙、盐碱、洪灾等表现出来。综合评价结果表明,和田河流域的生态环境质量属中等脆弱。     

Degradation of pyrene and characterization of<Emphasis Type="Italic">Saccharothrix</Emphasis> sp. PYX-6 from the oligotrophic Tianchi Lake in Xinjiang Uygur Autonomous Region,China

Bacterial strain PYX-6 that utilizes anthracene,phenanthrene, or pyrene for carbon and energy sources for growth was isolated from a non-polluted lake (Tianchi Lake) in Xinjiang Uygur Autonomous Region of China. Its morphology, physiological and biochemical properties, cell wall pattern and G C mol% content of DNA molecules were characterized. The 16S rRNA gene of strain PYX-6 was sequenced and analyzed for similarities to related bacterial species. Results indicated that strain PYX-6 is a member of the Genus Saccharothrix, and the strain was named Saccha-rothrix sp. PYX-6. When pyrene was the sole carbon source in cultural medium, the strain PYX-6 assimilated pyrene for growth and 0.005% of yeast extract stimulated pyrene degradation and assimilation. The optimal pH of cultural medium and the optimal shaking frequency during cultivation were 6-8 and 200 r/m, respectively. It was found that the disappearance of pyrene in medium occurred before significant growth of strain PYX-6 took place. Phthalic acid, benzylacetic acid, and benzylpropenoic acid were detected as catabolic intermediates during pyrene degradation with mass spectroscopy and this result indicated that Saccharothrix sp.PYX-6 adopted a pathway that is different from the pathway of the previously reported pyrene-degrading Mycobacterium sp. PYR-1.     

中国西北干旱区土地退化与生态建设问题

本文阐述了西北干旱区自然环境的基本特点，讨论了土地退化中土地沙漠化、土地盐渍化和草地退化问题。指出生态建设应当尊重自然,不宜大面积植树造林，采取生态修复措施和建立自然保护区有助于环境整治与生态建设。在区域发展中应当重视土地与水资源的合理开发利用以及区域间环境与发展协调等问题。     

球墨铸铁热浸镀铝的抗氧化性

为了延长铸铁工件的使用寿命,采用熔剂法将墨铸铁热浸镀铝,对镀层截面进行了形貌观察(SEM)、能谱分析(EDS)和衍射分析(XRD),测试了镀层的抗氧化性.结果表明,镀层由表面富铝层及扩散层构成,富铝层包含降温形成的针状FeAl3相,扩散层由FeAl3,Fe2Al5 物相组成,其形态呈舌状,并嵌入基体;氧化时镀层全部转变为扩散层,并能保持非常缓慢的退化速度,使球墨铸铁的抗氧化性显著提高.     

浅析陕北退化生态系统恢复与区域经济协调发展

文章分析了陕北生态系统退化的现状及原因,根据恢复生态学和区域经济可持续发展原理,提出了陕北地区恢复退化生态系统与区域经济协调发展的对策。     

二阶退化双曲型方程组的Darboux型问题

讨论了二阶退化双曲型方程组的Darboux型问题.文中先给出这个问题解的表示式,然后使用复分析方法,证明了此问题解的存在性和唯一性.