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941.
Time discounting and the decision to protect areas that are near and threatened or remote and cheap to acquire 下载免费PDF全文
Paul R. Armsworth 《Conservation biology》2018,32(5):1063-1073
Should conservation organizations focus on protecting habitats that are at imminent risk of being converted but are expensive or more remote areas that are less immediately threatened but where a large amount of land can be set aside? Variants of this trade‐off commonly arise in spatial planning. I used models of land‐use change near a deforestation frontier to examine this trade‐off. The optimal choice of where to protect was determined by how decisions taken today accounted for ecological benefits and economic costs of conservation actions that would occur sometime in the future. I used an ecological and economic discount rate to weight these benefits and costs. A large economic discount rate favored protecting more remote areas, whereas a large, positive ecological discount rate favored protecting habitat near the current deforestation frontier. The decision over where to protect was also affected by the influence economic factors had on landowners' decisions, the rate of technological change, and ecological heterogeneity of the landscape. How benefits and costs through time are accounted for warrants careful consideration when specifying conservation objectives. It may provide a niche axis along which conservation organizations differentiate themselves when competing for donor funding or other support. 相似文献
942.
Parameters of the production and destruction processes in different types of tundras are compared. It is shown that there is a fairly high degree of correspondence between the structure of tundra communities and the ecotopes occupied by them. On the other hand, typologically similar lowland and mountain tundras markedly differ in the functional respect. The rate of decomposition processes is higher under environmental conditions of the mountain tundra belt. 相似文献
943.
František Vožeh Antonín Doněk Jan Cendelín Ivana Korelusová Jan Vrba 《The Environmentalist》2007,27(4):501-504
The effect of long-term exposure to high frequency electromagnetic field (HF EMF) on some somatic and neural characteristics
was studied in neurodefective Lurcher mutant (+/Lc) and normal wild type mice (+/+). Both newborn and young adult (3 months)
animals derived from two strains (C3H, B6CBA) were exposed to HF EMF (870 MHz) from 1st to 21st day or from 91st to 120th
day respectively. In animals of both groups and controls we observed the development of body weight. Moreover, in the HF EMF
exposed adult B6CBA animals we studied spatial learning ability, motor functions and the CNS excitability. To investigate
specific energy absorption rate (SAR) in experimental animals we have done the basic 3D calculations of the electromagnetic
energy distribution in the simplified model of the mouse. The HF EMF exposed animals exhibited mild differences of body weight
between them and unexposed controls. The long-term exposure to HF EMF did not significantly influence the ability to learn
in the Morris water maze. However, significant lower swimming speed was found in the irradiated +/Lc as well as lower motor
activity of +/+ in the open field when compared to controls. No significant differences were found between HF EMF irradiated
animals and controls in examination of the CNS excitability and motor functions. 相似文献
944.
The complexity of the evacuation process is associated with the flow of occupants through various egresses available inside the building. Several methods and algorithms are now available to analyse the problem related to evacuation. In the present paper an algorithm, evacuation discrete time model (EDTM) has been presented to analyse the building egress evacuation time problem with previous works. The algorithm is based on the crowd flow theory and uses discrete computational approach to identify various widths of egresses available for movement of the people, which is more accurate and practicable because the crowd flow rate is variable. The developed model has been compared with an existing model to show the capabilities of the developed algorithm. A case of stadium stand egress is chose for the validity of EDTM, and a comparison of EDTM, previous model and computer simulation indicates that both the EDTM and the simulation curves were found to give better predictions than the previous model. Based upon the comparison analysis with stranded crowd and evacuation crowd at a certain time, EDTM shows great value in explaining the cause of stampede-trampling and crushing incident of egress or narrow passage zone. 相似文献
945.
Guangshan Liu Sumei Liu Jing Zhang Yipu Huang Min Chen 《Water, Air, & Soil Pollution: Focus》2007,7(6):693-701
Sediment cores were collected from two sites (A2 and ZQ) in the Qingdao sea area of the Yellow Sea. Radionuclides 40K, 137Cs, 210Pb, 226Ra, 228Ra, 228Th, 234Th, and 238U in the cores were measured using HPGe γ spectrometry. The sedimentation rate of the A2 Core using 210Pbex and 137Cs was 0.665 cm yr−1, therefore this 32 cm long core represents a 48 year timespan leading to the sampling date in 2001. The mixing layer was
restricted to the upper 5 cm as determined from the profile of 234Th. The uniformity of the activity distributions of 40K and 238U throughout the A2 Core and the activity distributions of 226Ra, 228Ra and 228Th below the mixing layer suggested that no significant oceanographic event or change in sediment material source had occurred
during this timespan. The 210 Pb was in excess relative to 226Ra, but 226Ra was deficient with respect to 238U in the entire A2 Core, while excess 234Th and 228Th were apparent only in the surface 5 cm. Total organic matter (TOM) in Core A2 decreases with depth. The second core, taken
to a depth of 14 cm, was from Site ZQ, which is located near Zhanqiao, Qingdao. The variations of the nuclide activity ratios
in this core were similar to those in the A2 Core, i.e., the excess 210 Pb and 226Ra deficiency were consistent throughout the core but excess 228Th was only in the surface to a depth of 2 cm. The 40K activity in the ZQ Core fluctuated and showed no real trend with depth. The activities of 137Cs, 210Pb, 226Ra and 238U in the entire length of Core ZQ, and 228Ra and 228Th from 2 cm to the bottom, were comparable within the uncertainty of measured activity. 相似文献
946.
J. Bai K. R. Li D. Y. Liu J. Zhang H. F. Zhang G. S. Liu J. L. Li Z. Y. Li D. M. Gao 《Water, Air, & Soil Pollution: Focus》2007,7(6):673-681
The distribution patterns and factors affecting uptake rates and turnover times of dissolved inorganic nutrients by heterotrophic
bacterioplankton (HB) in Jiaozhou Bay were studied based on in situ surveys and laboratory culturing. The uptake rates of
dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN) by HB are limited by the temperature of the water
and the concentration of dissolved organic carbon. The turnover times of DIP and DIN by HB are regulated by the concentrations
of the nutrients and the numbers of HB, which show significant spatiotemporal variability in Jiaozhou Bay. HB may aggravate
the P-limitation of phytoplankton by competing for phosphorus in summer in Jiaozhou Bay. HB play an important role in the
biogeochemical cycling of nutrients and may increase the N:P ratio and the accumulation of DIN, thereby accelerating the imbalance
of the N:P ratio in Jiaozhou Bay. 相似文献
947.
煤气管道的震害率分析 总被引:2,自引:0,他引:2
埋地管道的地震危险性分析方法可以分为理论分析法和经验统计法。震害率是经验统计法中常用的一个概念。埋地管道在地震中破坏的主要原因是地面运动和场地土液化等引起的场地土失效,另外管线的接口类型、管材、管径等也是决定其震害的因素。在查阅相关文献的基础上,对埋地管道的震害率分析方法进行了综述,并运用经验统计法提出了便于使用的煤气管道震害率估算表达式。 相似文献
948.
二次过街路口行人违反交通法规规律的研究 总被引:1,自引:0,他引:1
为了解在不同类型二次过街路口行人违反交通法规闯红灯的违法率,找出二次过街路口不同参数对行人违法率的影响,从而找出降低路口行人违法率的对策,保障路口行人交通安全和人车流畅通,本文选取上海市5种类型的二次过街路口调查行人在路口的违法率.通过分析调查数据,行人在路口一次穿越车道数为2~7,两次穿越车道总数为6~12,违法率随车道数的增加而降低.在红灯等待时间90 s之内,行人违法率随等待时间的升高呈一定的下降趋势.红灯等待时间在90~150 s之间,行人违法率没有确定的规律.安全岛、引导护栏、中继信号灯等设施具有明显降低行人违法率的作用.根据二次过街路口设置安全岛、引导护栏、中继信号灯、车道数以及是否从路边穿越5个影响因素的安全评价系数之和建立综合安全评价系数,得到行人在二次过街路口违法率随综合安全评价系数的增大而降低.研究表明,完善和优化二次过街路口的设施参数可以降低路口行人违法率. 相似文献
949.
950.