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11.
12.
Jørgen Lauritzen Jensen 《Journal of Wood Science》2005,51(6):577-582
A quasi-non-linear fracture mechanics model based on beam on elastic foundation theory is applied for analysis of the splitting
failure of dowel joints loaded perpendicular to grain. Simply supported beams symmetrically loaded by two dowels are considered,
and the effects of edge distance, dowel spacing, and distance between dowels and supports are accounted for. The foundation
modulus used in the beam on elastic foundation model is chosen so that the perpendicular-to-grain tensile strength and fracture
energy properties of the wood are correctly represented. This ensures that a conventional stress analysis and failure criterion
lead to the same solution as the compliance method of fracture mechanics. A semiempirical efficiency factor is proposed to
account for the influence of the total beam depth, which does not enter the beam on elastic foundation model, but the effect
of which is evident from tests. It is shown that the so-called Van der Put/Leijten model, which recently has been adopted
in Eurocode 5, appears as a special case of the model presented. Tests on simply supported beams with a single dowel joint
at midspan are compared with the theoretical predictions. Various edge distances, beam depths, and spans were tested. 相似文献
13.
G. J. Glova 《Ecology of Freshwater Fish》2003,12(4):247-253
Abstract – The interaction between brown trout ( Salmo trutta ; fork length (FL) range 255–390 mm) and inanga ( Galaxias maculatus ; FL range 55–115 mm) was tested during summer through autumn in an artificial stream consisting of a single run-riffle-pool sequence with a natural food supply. Each experimental trial lasted for 15 days, and consisted of two brown trout and 50 inanga collected fresh from a nearby stream, with each species given prior residence in four replicate tests, totalling eight trials in all. In addition, two control trials (each 10 days), with 50 inanga in each, were run. Brown trout almost exclusively occupied the pool, whereas inanga occupied all habitat types, although in different proportions, when tested with and without brown trout. The proportion of inanga in the pool was appreciably lower in the experimental trials with brown trout than in the control trials with no brown trout; prior residence had no significant effect on inanga habitat use. Mortality of inanga attributable to predation by brown trout ranged from 0 to 40% with a mean of 14.5 ± 4.7%. The results suggest that habitat use and survival of inanga populations in small streams can be adversely affected by brown trout. 相似文献
14.
XIAOLi 《东北农业大学学报(英文版)》2001,8(2):139-151
This article analyzes the importance of non-use values in the management of natural resources with a model of imperfect competition.By constucting a framework of duopolistic exploiters.the incorporation of non-use values based on self-interest and altruistic motives appears to be significant for determining the degree of inefficiency caused by the problem of common property at the non-cooperative Nash equilibrium.It is found that when the non-use value placed by the altruist exploiter is bounded by that placed by the pure selfinterest exploiter,the effect of market power is dominated by the effect of common exploitation.In this case,the exploiters‘ harvesting strategy will response in the same direction to the change of each other‘s harvesting at the non-cooperative Nash equilibrium.In contrast,when the non-use value placed by the altruist is substantially larger or smaller than that placed by the self-interest exploiter,one exploiter‘s increase in harvesting will lead to a decrease in harvesting of the other exploiter at the non-cooperative Nash equilibrium. 相似文献
15.
保护地甜椒新品种海丰26号选育初报 总被引:4,自引:0,他引:4
引进国外优良的甜椒杂交种,进行花药培养,获得大量花培当代单株。再选留优良花培品系,配制杂交组合,并选择优良的杂交组合进行品比试验和区域试验。并在各地的保护地内进行试种。 相似文献
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18.
刘晓燕 《安徽农业大学学报》2004,(1):90-92
1996年《刑事诉讼法》的修改,产生了律师阅卷难问题。为解决这一问题,真正实现控辩双方公平对抗,我国应设立刑事证据开示制度。文章对刑事证据开示制度的内涵、设立的必要性、设立的原则以及具体建议进行法律思考。 相似文献
19.
According to the requirements of the conversion of farmland to forests project (CFFP), we investigated the vegetation factors
and environmental factors from more than 6,105 sub-compartments in Liangcheng County, Inner Mongolia by using the Matlab,
analytic hierarchy process (AHP), and the hierarchical cluster method (HCM). The site conditions were classified quantitatively.
The results show that CFFP at this site comprises five site-type groups and 19 site types. A quantitative site classification
system method has been established in this paper.
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Translated from Journal of Beijing Forestry University, 2005, 27(6) [译自: 北京林业大学学报, 2005, 27(6)] 相似文献
20.
通过对贵州省贞丰、桐梓、锦屏等若干县市林业生态建设监理、检查、造林实绩核查等工作的实践和研究,认为退耕还林工程与农村经济发展相结合,目前应加强以下工作:选择林业主导产业;林产业时间、空间的合理布局;树种、林种的结构优化;林业体制创新;实施相关配套工程。 相似文献