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991.
992.
Four Decades of Plant Community Change in the Alpine Tundra of Southwest Yukon,Canada 总被引:1,自引:0,他引:1
Repeat measurements from long-term plots provide precise data for studying plant community change. In 2010, we visited a remote
location in Yukon, Canada, where a detailed survey of alpine tundra communities was conducted in 1968. Plant community composition
was resurveyed on the same four slopes using the same methods as the original study. Species richness and diversity increased
significantly over the 42 years and non-metric multidimensional scaling indicated that community composition had also changed
significantly. However, the direction and magnitude of change varied with aspect. Dominant species were not replaced or eliminated
but, instead, declined in relative importance. Fine-scale changes in vegetation were evident from repeat photography and dendro-ecological
analysis of erect shrubs, supporting the community-level analysis. The period of study corresponds to a mean annual temperature
increase of 2°C, suggesting that climate warming has influenced these changes. 相似文献
993.
Thyroid hormones, which influence body metabolism and development, could be affected by persistent organic pollutants. We sought to examine the relationship between polybrominated biphenyls (PBBs) and polychlorinated biphenyls (PCBs) and thyroid disease. We employed incidence density sampling to perform a nested case control analysis of the Michigan Long-Term PBB Cohort. Cohort members (n = 3333) were exposed to PBBs through contaminated cattle feed in 1973-1974 and to PCBs through daily life. Those with detectable serum PBB and PCB concentrations at enrollment were categorized into tertiles of PBB and PCB exposure. Case-patients were cohort members answering “Yes” to “Has a healthcare provider ever told you that you had a thyroid problem?” during follow-up interviews; control-patients were cohort members answering “No”. We used odds ratios (OR) with 95% confidence intervals (CI) to compare odds of thyroid disease by PBB and PCB exposure and by various risk factors. Total cumulative thyroid disease incidence after 33 years was 13.9% among women and 2.6% among men. After adjusting for body mass index, we found no statistically significant differences in odds of any type of thyroid disease among women or men with elevated PBB or PCB exposure. Compared to control-patients, women with thyroid disease had increased odds of being overweight/obese (OR = 2.82, 95% CI: 1.94-4.11) and developing infertility (OR = 1.71, 95% CI: 1.08-2.69), diabetes (OR = 1.61, 95% CI: 1.04-2.51), or arthritis (OR = 1.71, 95% CI: 1.18-2.50) during follow-up. Additional research should explore potential associations between PBBs/PCBs and thyroid disease among children exposed in utero. 相似文献
994.
The measurement of place attachment: Personal,community, and environmental connections 总被引:3,自引:0,他引:3
Place attachment has been researched extensively in the social and behavioural sciences over the past two decades. However, it is challenging for researchers to assimilate the mixed messages presented in the place attachment literature and to understand the multiple place attachment terms. In this study, a four-dimensional model of rural landholder attachments to their natural resource management region was conceptually and empirically developed with the aim of developing an integrated approach to the measurement of place attachment that clearly distinguishes between different elements of place scholarship. A 29-item place attachment scale with the dimensions of place identity, place dependence, nature bonding, and social bonding was tested on a random sample of rural landholders in the Adelaide and Mount Lofty Ranges in South Australia (N = 320). The majority of respondents were male (69.3%) and the average age was 59 years. The scale was reduced to 20-items and then administered simultaneously and in the same response format to rural landholders in two other areas of South Australia: the Northern and Yorke region (N = 664) and South Australian Murray-Darling Basin region (N = 659). In both studies, the majority of respondents were male (85%) and the average age was 55 years. Exploratory factor and reliability analyses of Adelaide and Mount Lofty Ranges and Northern and Yorke datasets produced a five-dimensional model of place attachment with high reliabilities. Social bonding divided into the constructs of family bonding and friend bonding. The refined five-dimensional model was then examined for convergent validity, with moderate but significant correlations found between individual attachment constructs and dependent variables expected to be related to the construct, such as place identity and length of residence, and nature bonding and time currently spent in nature. We used confirmatory factor analysis to test the goodness-of-fit of the South Australian Murray-Darling Basin (SAMDB) dataset to the proposed five-dimensional model and then compared its fit to the traditional two-dimensional model of place identity and place dependence. The five-dimensional model provided moderate fit for the SAMDB data. We conclude with a discussion of the validity and reliability of the five-dimensional model and its future role in place attachment research. 相似文献
995.
996.
本文结合湖北省自然科学基金项目"混凝土结构使役环境的智能模拟(2008CDB396)",在前期"211工程"项目"单轴约束可调式混凝土温度应力试验机"研究基础上,针对现有混凝土耐久性试验机在侵蚀溶液注入与氯离子浓度控制环境的空白,采用C51单片机为控制器,设计了一种混凝土结构使役环境中氯离子浓度控制系统,用于自动调节混凝土耐久性实验,模拟实验环境箱内的侵蚀溶液氯离子浓度,保证混凝土耐久性实验试件所处环境氯离子浓度稳定在设定的范围。系统采用溶液缓冲调节与循环注入方式,控制单元采用直读式离子浓度控制器,信号采集更方便。本系统不仅结构简洁,工作可靠性高,还能减少人力浪费,提高运行经济性。 相似文献
997.
章桂琴 《中国环境管理干部学院学报》2010,20(1):45-47,55
秦皇岛经济技术开发区经济迅猛发展,为避免走发达国家"先污染,后治理"的老路,必须以科学发展观为导向,优化产业结构,提高资源利用效率,节能减排,加强工业污染源的治理,完善基础设施建设,实现企业清洁生产,建立生态工业园区,以生态文明建设为引领,不断提升循环经济水平和持续发展能力,从而达到提高人民生活水平和改善人民生活环境的目的。 相似文献
998.
Emma M. Wilkie Anthony C. Roach Brendan P. Kelaher 《Environmental pollution (Barking, Essex : 1987)》2010,158(5):1261-1269
Benthic invertebrates can uptake metals through diffusion of free ion solutes, or ingestion of sediment-bound forms. This study investigated the efficacy of the metal chelating resin SIR 300™ in adsorbing porewater metals and isolating pathways of metal exposure. A field experiment (Botany Bay, Sydney, Australia) and a laboratory toxicity test each manipulated the availability of porewater metals within contaminated and uncontaminated sediments. It was predicted that within contaminated sediments, the resin would adsorb porewater metals and reduce toxicity to invertebrates, but in uncontaminated sediments, the resin would not significantly affect these variables. Whereas in the laboratory, the resin produced the predicted results, in the field the resin increased porewater metal concentrations of contaminated sediments for at least 34 days and decreased abundances of four macroinvertebrate groups, and richness in all sediments. These contrasting findings highlight the limits of extrapolating the results of laboratory experiments to the field environment. 相似文献
999.
1000.
粘滞阻尼支撑框架结构弹塑性时程分析 总被引:1,自引:0,他引:1
对阻尼支撑框架结构的弹塑性时程分析方法进行了探讨,给出了阻尼支撑的力学计算模型;对地震动的选用进行了分析,给出了地震动选取的初步建议。建立了两个三层的单榀粘滞阻尼支撑框架结构,利用IDARC 2D非线性分析软件进行了弹塑性时程分析,对框架弹塑性阶段的地震响应、塑性铰分布及结构损伤进行了对比研究,提出了阻尼支撑框架结构的设计要点,为实际工程提供设计依据。 相似文献