土地利用系统健康评价的框架与指标选择

随着社会经济的发展，人类行为对生态系统产生越来越大的影响，生态系统的健康状况也引起了国内外学者的普遍关注，作为一个以土地利用为基础的自然、经济、社会复合的土地利用系统。它既具有生态系统的一般特征。又具有其本身的特殊性，集中体现了人口增长、经济发展与资源短缺的矛盾。因此，为了人类可持续发展。必须关注土地利用系统的健康状态。本文在对土地利用系统的分析基础上，提出土地利用系统健康的概念，土地利用系统健康评价的本质、目的，并初步建立了土地利用系统健康评价框架体系。     

First trimester screening for Down syndrome and assisted reproduction: no basis for concern

In pregnancies obtained after assisted reproduction the false-positive rate of second trimester Down syndrome (DS) screening is increased by 1.5–3-fold. This may cause an increase in the number of amniocenteses and the fetal loss rate. The present study for the first time examined whether assisted reproductive technologies affect the results of first trimester screening. The markers PAPP-A, free β-hCG and the nuchal translucency (NT) thickness were examined at 12–14 weeks' gestation. Screening markers in 47 in vitro fertilisation (IVF), 63 ovulation induction (OI) and 3026 spontaneously conceived singleton pregnancies were compared. The MoM (multiples of the median) value in the IVF pregnancies was 1.02 (95% CI: 0.85–1.22) for PAPP-A, 1.14 (95% CI: 0.95–1.37) for β-hCG and 0.97 (95% CI: 0.89–1.05) for NT; the MoM value in the OI pregnancies was 0.89 (95% CI: 0.76–1.05) for PAPP-A, 1.08 (95% CI: 0.93–1.25) for β-hCG and 1.02 (95% CI: 0.95–1.11) for NT. The first trimester marker values in assisted reproductive pregnancies and spontaneously conceived pregnancies were not significantly different. Estimated false-positive rates for a risk cut-off of 1:400 varied from 4.7% in IVF pregnancies to 5.1% in OI pregnancies. Therefore the false-positive rate in Down syndrome screening should be independent of the method of conception. Copyright © 2001 John Wiley & Sons, Ltd.     

TiO2/Ti光电极电助光催化降解甲草胺的研究

采用阳极氧化法制备了TiO₂/Ti光电极,并通过电助光催化的方法研究了恒电流法和恒电压法对甲草胺的降解效率.实验证实了在光催化和电催化之间存在协同效应,反应溶液中加入Na₂SO₄电解质后,SO₄^2-可以被价带空穴氧化成强氧化性的S₂O₈^2-,继而可以氧化处理物质,提高甲草胺的降解效率.实验结果表明：甲草胺在羟基自由基的作用下通过羟基化作用和脱烷作用,发生断键、开环等一系列的氧化还原反应,最终生成CO₂和H₂O等无机小分子物质.     

西北地区石油,煤炭资源可持续利用战略构想

西北地区石油、煤炭资源丰富,是西北地区经济发展的一大优势。持续开发西北地区石油、煤炭资源,对促进西北乃至全国的经济发展具有重大意义。文章从当前西北地区开发石油、煤炭资源的现状和条件入手,提出这些资源开发和利用的战略构想,并指出保证战略构想实现所应采取的相应措施。     

The Value of Species and the Ethical Foundations of Assisted Colonization

Abstract: Discourse around assisted colonization focuses on the ecological risks, costs, and uncertainties associated with the practice, as well as on its technical feasibility and alternative approaches to it. Nevertheless, the ethical underpinnings of the case for assisted colonization are claims about the value of species. A complete discussion of assisted colonization needs to include assessment of these claims. For each type of value that species are thought to possess it is necessary to determine whether it is plausible that species possess the type of value and, if so, to what extent their possessing it justifies assisted colonization. I conducted such an assessment for each of the predominant types of value ascribed to species: ecological, instrumental (including option value), existence, and intrinsic value (including interest‐based, objective, and valuer‐dependent intrinsic value). The vast majority of species, including several that have been proposed as candidates for assisted colonization, have much less value than is often presumed. Moreover, with respect to some types of value, assisted colonization would not fully preserve the value of the target species even if it were to keep the target species in existence. Therefore, the case for assisted colonization is significantly weaker and more qualified than its advocates often suppose. There may be exceptional species for which assisted colonization is well justified—and for this reason, case‐by‐case assessment is necessary—but in general the burden of justification generated by the ecological risks associated with assisted colonization is not met by the value potentially preserved by assisted colonization. This suggests that assisted colonization ought to have, at most, a very minor role in the portfolio of ecosystem management practices, even as it pertains to species conservation under conditions of rapid climate change.     

Securing the Demographic and Genetic Future of Tuatara through Assisted Colonization

Abstract: Climate change poses a particular threat to species with fragmented distributions and little or no capacity to migrate. Assisted colonization, moving species into regions where they have not previously occurred, aims to establish populations where they are expected to survive as climatic envelopes shift. However, adaptation to the source environment may affect whether species successfully establish in new regions. Assisted colonization has spurred debate among conservation biologists and ecologists over whether the potential benefits to the threatened species outweigh the potential disruption to recipient communities. In our opinion, the debate has been distracted by controversial examples, rather than cases where assisted colonization may be a viable strategy. We present a strategic plan for the assisted migration of tuatara (Sphenodon punctatus), an endemic New Zealand reptile. The plan includes use of extant populations as reference points for comparisons with assisted‐colonization populations with respect to demography, phenotypic plasticity, and phenology; optimization of genetic variation; research to fill knowledge gaps; consideration of host and recipient communities; and inclusion of stakeholders in the planning stage. When strategically planned and monitored, assisted colonization could meet conservation and research goals and ultimately result in the establishment of long‐term sustainable populations capable of persisting during rapid changes in climate.