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991.
The results of a study on morphophysiological variation in fish inhabiting a subarctic lake exposed to chronic industrial pollution are described using an example of cisco, Coregonus lavaretus. It is shown that indices of the heart, liver, kidneys, gills, and fatness in these fish are increased significantly and have retained increased values for the past 20 years. The observed changes are analyzed on the basis of biochemical data. The results of studies on the dynamics of hematological parameters in fish are used for characterizing the development of toxicosis. Adaptive rearrangements associated with an increase in the metabolic rate and the activation of protective systems in the fish are explained in the context of S.S. Schvarts' concept. The idea is proposed that the additional energy cost of detoxification may be responsible for morphophysiological variation in fish under conditions of water pollution. 相似文献
992.
木本植物休眠的诱导因子及其细胞内Ca2+水平的调节作用 总被引:9,自引:0,他引:9
本研究揭示 ,越冬木本植物在夏秋转变过程中对光周期变化十分敏感 .在北纬 4 5°的明尼苏达州圣保罗地区 ,当日照变短 72min时 (2 0 0 0年 8月 8日 ) ,桑树顶芽细胞质浆和细胞核内即出现Ca2 流入 ,而在夏天长日照时期 (7月上、中旬 )很少有Ca2 存在的细胞质和细胞核 .12d后 (8月 2 0日 ) ,观测到桑树和杨树芽已经开始进入生理休眠 .从 9月上旬到 11月中旬 ,细胞质和细胞核内的Ca2 浓度显著升高 ,11月中旬达到高峰 .与此同时 ,芽的生理休眠深度也迅速增加 ,并于 11月达到高峰 ,4 2d培养也不见萌芽迹象 .到 12月中旬 (12月 2 0日 ) ,细胞核和细胞质中的Ca2 浓度又恢复到夏季观察到的低水平 ,显示早先进入细胞质和细胞核中的Ca2 已经被排出 .此后 ,在 12月下旬 (2 5日 ) ,检测到生理休眠的终结 .室外补充光照实验进一步证明 ,只有日照缩短才会引发植物进入自然生理休眠 ;保持日照长度不变 ,晚夏时期的自然温度降低 ,不能诱导植株停止生长和进入休眠 .这些结果表明 ,越冬木本植物在晚夏到冬季的生理休眠发展过程中 ,日照缩短引起的核和质内Ca2 的流入不仅起着传递日照变短信号的作用 ,导致生理休眠的起始 ;而且 ,高水平的核 /质Ca2 浓度还起着发展和保持深度生理休眠的作用 .图版 1图 1表 2参 相似文献
993.
994.
995.
Brian L. Altland Danielle Cox Robert M. Enick Eric J. Beckman 《Resources, Conservation and Recycling》1995,15(3-4)
High-pressure, near-critical liquids were used as float-sink separation media for the microsortation of polyolefin mixtures and PET/PVC mixtures. Near-critical carbon dioxide was used for the refinement of the polyolefins, and sulfur hexafluoride was used to separate post-consumer PVC from PET. Preliminary experiments indicated that there was no overlap in the density ranges of post-consumer HDPE, LDPE and PP containers. There was no overlap in the PET and PVC densities, with the exception of a single PVC packaging material with a density in the PET range. These initial results indicated that a float-sink separation was a viable means of microsortation. Separations of 91% LDPE (1/8′ beads)/9% PP (1/8′ chopped strands) resin mixtures and mixed post-consumer polyolefin flakes were then conducted in a laboratory-scale, 1-I batch apparatus. This apparatus not only permitted the observation of the separation, but also enabled the separated fractions to be removed from the high-pressure environment. The results indicated that LDPE purity of greater than 98.9% was obtained in 3 min or less if (a) the fluid density was 0.018 g/cm3 greater than the PP density and only 0.002 g/cm3 less than the LDPE density, thereby providing the greatest buoyancy force for the removal of the PP, (b) the fluid was recirculated upward through the bed of mixed plastics, facilitating the upward movement of the PP, and (c) the loading was kept at levels below 40% by volume. HDPE purity of 99% was also attained with clean, dry, post-consumer mixed plastic flakes. The loadings for these separations were very low, however, due to the difficulty in agitating the mixed bed of plastics using fluid recirculation. An economic analysis of these microsortation processes indicated that the value of the sorted plastics relative to the mixed feed must increase by approx. $0.08/lb for the CO2-based separation and approx. $0.27/lb for the SF6-based separation to justify the implementation of these high-pressure processes. 相似文献
996.
997.
This paper analyzes the energy price-employment nexus and contributes to the literature by showing that it is important to decompose the regulatory effect into demand, cost, and factor-shift effects. This is done by means of a cross-country multi-sectoral dataset. The results show that both rising energy prices and shadow prices of energy have no significant effect on net employment when the manufacturing sectors only are analyzed. While finding significant variations across countries, the average employment effects become significantly positive once jobs in the economy as a whole are considered. This change is driven mainly by larger positive cost effects, which more than offset the negative demand effects and reductions in the positive factor-shift effects. Moreover, the paper reveals that the often implemented approach of using a simple regulation regressor, instead of decomposing the employment effect, can result in biased estimates. 相似文献
998.
Background, Aim and Scope
Due to their large potential for manifold applications, the use of nanoparticles is of increasing importance. As large amounts
of nanoparticles may reach the environment voluntarily or by accident, attention should be paid on the potential impacts on
the environment. First studies on potential environmental effects of photocatalytic TiO2 nanoparticles have been performed
on the basis of widely accepted, standardized test systems which originally had been developed for the characterization of
chemicals. The methods were adapted to the special requirements of testing photocatalytic nanoparticles.
Materials and Methods:
Suspensions of two different nanoparticles were illuminated to induce their photocatalytic activity. For testing, the growth
inhibition test with the green alga Desmodesmus subspicatus and the immobilization test with the daphnid Daphnia magna were
selected and performed following the relevant guidelines (algae: ISO 8692, OECD 201, DIN 38412-33; daphnids: ISO 6341, OECD
202, DIN 38412-30). The guidelines were adapted to meet the special requirements for testing photocatalytic nanoparticles.
Results:
The results indicate that it is principally possible to determine the ecotoxicity of nanoparticles. It was shown that nanoparticles
may have ecotoxicological effects which depend on the nature of the particles. Both products tested differ in their toxicity.
Product 1 shows a clear concentration-effect curve in the test with algae (EC50: 44 mg/L). It could be proven that the observed
toxicity was not caused by accompanying contaminants, since the toxic effect was comparable for the cleaned and the commercially
available product. For product 2, no toxic effects were determined (maximum concentration: 50 mg/L). In the tests with daphnids,
toxicity was observed for both products, although the concentration effect-curves were less pronounced. The two products differed
in their toxicity; moreover, there was a difference in the toxicity of illuminated and non-illuminated products.
Discussion:
Both products differ in size and crystalline form, so that these parameters are assumed to contribute to the different toxicities.
The concentration-effect curves for daphnids, which are less-pronounced than the curves obtained for algae, may be due to
the different test organisms and/or the differing test designs. The increased toxicity of pre-illuminated particles in the
tests with daphnids demonstrates that the photocatalytic activity of nanoparticles lasts for a period of time.
Conclusions:
The following conclusions can be drawn from the test results: (I) It is principally possible to determine the ecotoxicity
of (photocatalytic) nanoparticles. Therefore, they can be assessed using methods comparable to the procedures applied for
assessing soluble chemicals. - (II) Nanoparticles may exert ecotoxicological effects, which depend on the specific nanoparticle.
- (III) Comparable to traditional chemicals, the ecotoxicity depends on the test organisms and their physiology. - (IV) The
photocatalytic activity of nanoparticles lasts for a relevant period of time. Therefore, pre-illumination may be sufficient
to detect a photocatalytic activity even by using test organisms which are not suitable for application in the pre-illumination-phase.
Recommendations and Perspectives:
First results are presented which indicate that the topic 'ecotoxicity and environmental effects of nanoparticles' should
not be neglected. In testing photocatalytic nanoparticles, there are still many topics that need clarification or improvement,
such as the cause for an observed toxicity, the improvement of the test design, the elaboration of a test battery and an assessment
strategy.
On the basis of optimized test systems, it will be possible to test nanoparticles systematically. If a potential risk by specific
photocatalytic particles is known, a risk-benefit analysis can be performed and, if required, risk reducing measures can be
taken. 相似文献
999.
贵州喀斯特地区旅游资源的变异与可持续利用 总被引:6,自引:0,他引:6
殷红梅 《中国人口.资源与环境》1999,9(2):68-72
喀斯特景观与民族文化是不可再生的旅游资源,其开发在促进喀斯特地区经济、文化发展的同时,也加剧了环境的损耗和地方特色的消失,旅游资源变异现象普遍发生。文中分析了资源变异的几种情况,并指出控制资源变异,实现可持续利用的途径 相似文献
1000.
重庆金佛山岩溶区不同植被条件下土壤-植被系统CO2浓度日变化 总被引:1,自引:0,他引:1
对重庆金佛山典型岩溶区林地、裸地表层岩溶生态系统CO2浓度进行短时间尺度变化的野外观测结果表明,林地与裸地不同深处土温变化幅度由地表向土壤深部逐步降低,裸地地表温度和不同深度土温波动幅度均较林地大.林地与裸地各层次土壤CO2浓度变化与土温呈较好的相关关系.林地各层土壤CO2浓度波动微弱,变幅小于裸地.林地与裸地土层中CO2浓度随土层深度增加而增高.植被各层的温度和温度变化幅度从大到小依次为林层、灌层和草层.林层温度最大值滞后于气温约3 h. 相似文献