拆坝对河流生态系统的影响及评估方法综述

为研究拆坝对河流生态系统造成的影响,从短期和长期两个时间尺度综合分析了河流水文情势、地形地貌、岸边带植物、鱼类和底栖动物等关键生态因子对拆坝的响应,并总结了目前拆坝对生态系统影响的两种主要评估方法。认为根据实际拆坝情况进行评估和基于数值模型进行预测两种评估方法中,实地观测是最直接、最有说服力的研究方法,但受成本和一些不可控因素限制;数值模拟具有速度快、费用低、无比尺影响等优点,可对拆坝影响进行预测,为管理者提供参考,但精度和准确性有待提高。指出后续研究中应综合考虑拆坝过程中各生态因子间的耦合效应,需对不同拆坝时机和分阶段拆坝方式对河流生态系统的影响进行深入研究。     

2005年我国氯碱生产能力超高速增长

对截止2005年7月末我国氯碱装置的生产能力、2005年投产的装置、目前在建装置进行了介绍.国内大型氯碱生产装置、离子膜法装置在增多,但存在企业多、局部地区企业密集、产能增长过速的问题.     

玻璃钢件固化成型中变形现象的剖析

结合实例剖析由产品结构、成型工艺和工艺装备等主要因素影响的复合夹层结构玻璃钢件和实体玻璃钢件在固化成型中的变形现象，并指出了预防变形的各相应有效措施。     

混合遗传算法求解应急抢修点选址问题

考虑设备应急抢修的时限要求和整个应急抢修系统的服务质量要求,采用0-1整数规划模型描述了应急抢修点选址问题,并针对该问题设计了一种混合遗传算法。在算法中使用启发式算法对种群中的不可行解进行修复,以保持种群在可行域内搜索,并采用近邻搜索算法改善种群中的最佳个体。算例计算的结果表明,该算法求得的结果要优于基于罚函数的遗传算法和采用简单修复算法的遗传算法。     

The allelopathic mechanisms of dominance in bracken (Pteridium aquilinum) in Southern California

Bracken,Pteridium aquilinum, exerts a strong dominance over associated plants throughout much of its worldwide range. Associated plants are often severely inhibited or even excluded from dense stands of the fern. This study investigated the various aspects of herb suppression in bracken stands and assessed the contribution of the various forms of interference between plants to the establishment and maintenance of bracken dominance. It was shown that competition for soil moisture, light, and nutrients could not account for the lack of herbs in bracken stands. Further, uniformity of soil pH, texture, water-holding capacity, and organic matter content ruled out variability in physical factors as a cause. Baiting and trapping experiments showed that the higher concentration of animal activity inside the bracken stands contributed significantly to the pattern of herb suppression, but only against select species. The maintenance of this pattern in the animal-free Santa Cruz Island stands indicates the importance of another factor, allelopathy. It was found that phytotoxins leached from the dead, standing bracken fronds with the first few rains of the wet season were largely responsible for herb suppression. These toxins were isolated in raindrip and from soil inside the fern stands. Removal of the fronds from the stand before the rains could leach them resulted in reinvasion by the herbs after several seasons, and, conversely, placing fronds over the herbs in the grassland brought about herb inhibition. A number of known allelopathic chemicals were tentatively identified from bracken leachates. The importance of the interaction of allelopathy with other factors of plant interference is illustrated by bracken.     

Evaluation of methods of measurement of nitrogen in poultry and animal manures

Kjeldahl nitrogen (N), total N and forms of inorganic N (ammoniacal (NH₄)-N, nitrate (NO₃)-N and nitrite (NO₂)-N) were measured in a range of animal manures. The manures include fresh samples of poultry manure, sheep manure, horse manure, dairy slurry and pig slurry and composted poultry manure. Kjeldahl N was measured by standard micro-Kjeldahl digestion. For total N measurements, NO₃-N and NO₂-N were recovered during Kjeldahl digestion by pretreatments with various oxidizing and reducing agents. Inorganic forms of N were measured by extraction with 2M KCl solution.Kjeldahl digestion alone allowed measurement only of organic N and NH₄-N. Amongst various modifications to the Kjeldahl, pretreatment with either acidified (H₂SO₄) Zn-CrK(SO₄)₂ or acidified (H₂SO₄) reduced Fe achieved complete recovery of NO₃-N. Nitrite N was only recovered by first oxidising the NO ₂ ^- to NO ₃ ^- with KMnO₄ followed by reduction to NH₄-N with acidified (H₂SO₄) reduced Fe.More than 95% of the total N in fresh animal manure was present as organic N and NH₄-N which were recovered by the standard Kjeldahl digestion. In the case of fresh manures there was no difference between the amount of total N measured by the Kjeldahl digestion and its modified methods. However composting of poultry manure or drying of poultry manure, pig slurry and dairy slurry resulted in an increase in NO₃-N which was not recovered during Kjeldahl digestion alone. Under these conditions the total N could be measured by pretreating the samples with KMnO₄ and reduced Fe prior to Kjeldahl digestion.Drying of animal manures caused a decrease in organic N and NH₄-N, especially in poultry, pig and dairy manures. There was a slight increase in NO₃-N; but most of the decrease in N content with drying was attributed to the volatilization loss of ammonia (NH₃). Amongst various drying methods examined air drying caused maximum loss of N as NH₃ whereas freeze drying caused minimum loss of N. This suggests that fresh animal manures can be freeze dried for analysis of N which causes minimum loss of N.     

数字电子技术实验教学的改革初探

数字电子技术实验是《数字电子技术基础》课程的重要组成部分,也是理论和实践相结合,培养学生实践动手能力的主要途径。本文为适应高职教育改革的新特点,对实验教学进行了改革,以课题"简易秒表计时器"为例,着重培养学生的基本操作技能,从而激发学生学习专业课程的激情。     

肽类消化吸收方式与机制研究进展

最新研究表明,寡肽可以被小肠直接吸收,但其吸收方式是与氨基酸不同的、相互独立的转运机制。寡肽的特殊载体,通过氢离子和钙离子浓度电导的消耗能量的主动转运系统、具pH依赖性的非耗能性钠离子和氢离子交换系统和谷胱甘肽（GSH）等三种系统进行转运。食物蛋白质的品质、肽链长度与肽的氨基酸组成、生理状况等因素都会影响寡肽的消化吸收。     

高校体育产业的发展现状及其发展策略探讨

分析并探索了高校体育产业的发展现状、存在问题及解决思路,指出当前高校在体育产业发展中存在经营理念落后、产权模糊、管理混乱等问题,为此急需开拓思路,采取顺应市场经济运作规律的改革举措,在保障高校基本教学训练的前提下扩大和提高高校体育设施的利用途径与效率,通过互利和双赢较好的解决目前社会上体育设施和场地不足以及高校体育场地部分闲置、设备经费投入不足的矛盾．     

The replacement of animal testing: ethical issues and practical realities

Increasing expectation that products and materials of many kinds should be 'safe' is leading to demands for more toxicity testing. At the same time, there is mounting pressure to reduce, refine and replace laboratory animal experimentation. The testing of cosmetics is particularly controversial. The only way out of this dilemma is the development, validation, acceptance and use of non-animal test procedures, i.e. replacement alternative methods. Given realism and determination, more funding, better science and good strategic planning, the future for replacement alternatives, and thus for human and animal welfare, could be a very bright one.