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541.
Latex was purified from Parthenium argentatum Gray (guayule), Hevea brasiliensis Müll. Arg. (the Brazilian or para rubber tree), and Ficus elastica Roxb. (the Indian rubber tree) in ammonium alginate at pH 10. The rheological properties of the different latices (rubber particle suspensions) were determined and compared using flow temperature ramps. Latex from all three species became more viscous with increasing rubber particle concentration and decreasing temperature. At any particular temperature and concentration, latex from F. elastica was by far the most viscous, whereas the H. brasiliensis latex was the least viscous. In addition, the tendency for the latex to coagulate increased with increasing temperature and increasing particle concentration. F. elastica latex was highly sensitive to temperature, H. brasiliensis latex was the least sensitive, and P. argentatum latex demonstrated intermediate properties. The underlying causes of these differences in latex rheology are not clear but may partially relate to the particle size (largest in F. elastica and smallest in H. brasiliensis), the particle size distribution, and/or to the considerable differences in the biochemical components of the monolayer biomembrane that surrounds the various rubber particles. Differences in the molecular weight of the rubber contained within the rubber particles seem less likely to play a role because the particles remain intact in this study. 相似文献
542.
在概述了自然资源和自然资源系统含义的基础上,分析了自然资源系统在人类发展的不同阶段(采集狩猎社会、原始农业社会、传统农业社会、工业社会、后工业社会、知识经济社会)的演化过程及其主要特征,并从自然界和人类活动两个方面探讨了自然资源系统演化的动力机制。 相似文献
543.
544.
攀枝花市资源开发与经济持续发展研究 总被引:1,自引:0,他引:1
攀枝花市是我国西部重要的能源、原材料生产基地和资源开发型城市,矿产、水能和农业自然资源是其最具开发优势的资源。从20世纪60年代中期以来大规模的资源开发促进了现代钢铁工业基地和城市社会经济的快速发展,但同时也带来了严重的生态环境问题:地质灾害、环境污染与生态破坏。针对攀枝花市资源开发利用中存在的资源开发结构单一、资源综合利用程度低、生态环境问题突出等问题,作者提出了实现资源合理开发与经济持续发展的相应措施。 相似文献
545.
粘土对水中氟离子吸附去除机理的研究 总被引:9,自引:0,他引:9
研究了用粘土和天然絮凝剂MR去除水中氟离子的机理,探讨了吸附时间、溶液温度及pH对吸附的影响。结果证明,吸附过程属一级反应,在不同温度下吸附平衡遵循Langmuir等温式。同时也计算了热力学参数。 相似文献
546.
547.
Donald D. Adelman 《Journal of the American Water Resources Association》2003,39(5):1079-1092
ABSTRACT: Ground water irrigation pumpage of the High Plains Aquifer is controlled at the state level in Texas and Oklahoma but at the regional level in Kansas and Nebraska. Critical declines in the aquifer that threatened the reliability of local public water supply wells prompted Nebraska's Upper Republican Natural Resources District (URNRD) to mandate water restrictions in 1978. Under current regulations, irrigators may not extract more than 1,842 millimeters of water per certified hectare (ha) in any five‐year period. Meter monitoring ensures that irrigators comply with restrictions. Farmers now incorporate irrigation scheduling into their cropping practices in order to meet URNRD controls. This study examines whether irrigators are using ground water efficiently while complying with pumpage limits. Crop irrigation requirements (CIR) from 1986 to 1999 were derived from a water balance approach incorporating Penman‐Monteith evapotranspira‐tion (ET) calculations from weather data supplied by the High Plains Climate Center automated weather station network. A ratio of average water pumped per well to the CIR was developed to verify irrigation efficiency. Results indicate that irrigation applications were less than CIR during most irrigation seasons. Irrigation efficiency increases can be attributed to crop rotations, favorable growing season precipitation, use of ET estimates to schedule irrigation, and water allocations limited to less than all certified hectares. 相似文献
548.
对自制天然有机高分子絮凝剂DXSL-I实际应用和环境生物效应进行初步的实验研究。实验结果表明,DXSL-I对高浓度油污水具有较高的处理效率;当油份浓度大于2000×10-6g/L时,只需要处理10h,处理效率就能达到60%以上,可用于高浓度油污水的快速预处理。通过生物实验可以明显的观察到,孔雀鱼的LD50约为416×10-6g/L,泥鳅的LD50约为870×10-6g/L,因而可以推定其具有相对较高的环境安全性;而且经过DXSL-I常规浓度处理的养殖用水对某些水产养殖生物的生长具有改善促进作用。表明,DXSL-I在水处理中具有较理想的实际应用前景。 相似文献
549.
Non‐governmental organisations (NGOs) are widely believed to raise their flag in humanitarian hotspots with a strong media presence in order to attract higher private donations. We assess this hypothesis by comparing the changes in donations between US‐based NGOs with and without aid operations in the four countries most affected by the tsunami in the Indian Ocean in 2004. Simple before‐after comparisons tend to support the hypothesis that ‘flying the flag’ helps attract higher private donations. However, performing a difference‐in‐difference‐in‐differences (DDD) approach, we find only weak indications that private donors systematically and strongly preferred NGOs with operations in the region. Extended specifications of the baseline regressions reveal that our major findings are robust. NGO heterogeneity matters in some respects, but the DDD results hold when accounting for proxies of the NGOs’ reputation and experience. 相似文献
550.
目的 掌握东南亚地区环境特征,提出产品环境适应性工作对策。方法 采用主成分分析法开展东南亚地区环境精细化分类,依据分类结果,开展环境特征分析和规律研究,并在产品环境适应性问题原因分析的基础上,提出东南亚地区使用产品环境适应性工作对策。结果 东南亚地区具有年温度较高、相对湿度高、雨量充沛、太阳辐射较强等特征,但不同类别之间具有一定的差异性,D1、D2类环境呈现一定的季节性特征,D3、D4类全年环境较为稳定,温度、平均湿度、太阳辐射和降雨量均稳定地保持在较高量值范围内,温度常年保持在20~30℃,平均相对湿度在70%以上。结论 东南亚地区环境整体较为严酷,在产品环境适应性论证、设计和使用维护等阶段应采取针对性措施,以保证东南亚地区使用产品的环境适应性。 相似文献