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排序方式: 共有123条查询结果,搜索用时 15 毫秒
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The main objective of this research was to develop an expected utility optimisation model to economically evaluate deficit irrigation within a multi-crop setting while taking into account the increasing production risk of deficit irrigation. The dynamic problem of optimising water use between multiple crops within a whole-farm setting when intraseasonal water supply may be limited was approximated by the inclusion of multiple irrigation schedules into the optimisation model. The SAPWAT model (South African Plant WATer) was further developed to quantify crop yield variability of deficit irrigation while taking the non-uniformity of irrigation applications into account. Stochastic budgeting procedures were used to generate appropriately correlated matrixes of gross margins necessary to incorporate risk into the water use optimisation model. Special care was taken to represent risk aversion consistently between the alternatives through the use of a new procedure to standardise values of absolute risk aversion. The model was applied to study the impact of increasing levels of risk aversion on the profitability of deficit irrigation under limited water supply conditions. The main conclusion from the analyses was that although deficit irrigation was stochastically more efficient than full irrigation under limited water supply conditions, irrigation farmers would not willingly choose to conserve water through deficit irrigation and would be expected to be compensated to do so. Deficit irrigation would not save water if the water that was saved through deficit irrigation were used to plant larger areas to increase the overall profitability of the strategy. Standard risk aversion was used to explain the simultaneous increasing and decreasing relationship between the utility weighted premiums and increasing levels of absolute risk aversion and was shown to be more consistent than when constant absolute risk aversion was assumed. 相似文献
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Shi T Simanova E Schönherr J Schreiber L 《Journal of agricultural and food chemistry》2005,53(6):2207-2212
Effects of diethyl suberate (DESU), diethyl sebacate (DES), dibutyl suberate (DBSU), dibutyl sebacate (DBS), and tributyl phosphate (TBP) on diffusion of 14C-2,4-dichlorophenoxy butyric acid (2,4-DB) across cuticular membranes (CM) was studied. Astomatous CM were isolated enzymatically from Stephanotis floribunda Brongn. leaves, and diffusion was measured at 20 degrees C. The alkyl-substituted dicarboxylic acids constitute a homologous series with carbon numbers increasing from C12 to C18. Molecular weights increased only moderately from 230.0 (DESU) to 314.5 (DBS), while partition coefficients varied over orders of magnitude from 92 (DESU), to 1213 (DES), to 15,988 (DBSU), to 210,762 (DBS). All the above compounds turned out to be accelerators as they increased 2,4-DB mobility by up to 40-fold with accelerator concentrations in the CM ranging from only 9.2 to 105 g kg(-1). Efficacy (2,4-DB mobility in the presence/mobility in the absence of accelerators) increased with increasing concentrations of accelerators in CM or in reconstituted cuticular waxes. Plotting efficacy vs accelerator concentration in the CM resulted in straight lines, and their slopes increased in the order DBS (0.14), DBSU (0.31), DES (0.51), and DESU (0.85). Hence, DESU was the most powerful accelerator in this series as it increased 2,4-DB mobility in the CM about 6 times more than DBSU. Waxes constitute the major barrier in plant cuticles, and plots of efficacy vs accelerator concentration in Stephanotis wax were also linear, but compared to CM slopes were steeper by factors of 3.20 (DBS), 2.97 (DBSU), 2.70 (DES), and 1.62 (DESU). TBP was similarly effective as DESU, but plots of efficacy vs concentration were not linear, and curves approached a plateau at 60-80 g kg(-1). These data are discussed with regard to suitability of these accelerators for formulating systemic pesticides. 相似文献
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This article investigates the role of local knowledge in the policy approach of neo-endogenous rural development, which may be held by local and regional actors such as municipal and county level politicians, local and regional level administration, entrepreneurs as well as local third sector representatives. The main question addressed is whether local knowledge under this approach is merely mobilised or if rural development processes are even based on such knowledge, placing it at the centre of such policy. The relevance of this approach to forestry is also explored. The types of forest owners for which the neo-endogenous rural development approach is appropriate and the types that may have difficulties in coping with this cross-sectoral and area-based approach are especially examined. Using a case study design on the German Active Regions funding program it is shown that the neo-endogenous approach is most relevant to large private forest owners and small-scale corporate enterprises, but also has potential for small- and medium-sized private owners. Concerning the role of knowledge held by local and regional actors, the approach is shown to largely build on the use of local expertise, and hence policy acceptance increases. However, scientific knowledge as well as politics are found to play a major role in the use, production and interpretation of local knowledge. 相似文献
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Li Jianwu Song Zhaoliang Ruan Li Yang Lihui Van Zwieten Lukas Hu Zhongchen He Shengjia Chenwu Wentao Wang Hailong 《Journal of Soils and Sediments》2019,19(1):232-240
Journal of Soils and Sediments - The present study was conducted to understand the pedogenesis of soils developed on basalts and reveal the impact of Asian dust on soils in subtropical China. Soils... 相似文献
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Yang Shilei Hao Qian Wang Hailong Van Zwieten Lukas Yu Changxun Liu Taoze Yang Xiaomin Zhang Xiaodong Song Zhaoliang 《Journal of Soils and Sediments》2020,20(4):1811-1823
Journal of Soils and Sediments - Phytolith-occluded carbon (PhytOC) is mainly derived from the products of photosynthesis, which can be preserved in soils and sediments for hundreds-to-thousands of... 相似文献
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Hellal F Hurtado A Ruschel J Flynn KC Laskowski CJ Umlauf M Kapitein LC Strikis D Lemmon V Bixby J Hoogenraad CC Bradke F 《Science (New York, N.Y.)》2011,331(6019):928-931
Hypertrophic scarring and poor intrinsic axon growth capacity constitute major obstacles for spinal cord repair. These processes are tightly regulated by microtubule dynamics. Here, moderate microtubule stabilization decreased scar formation after spinal cord injury in rodents through various cellular mechanisms, including dampening of transforming growth factor-β signaling. It prevented accumulation of chondroitin sulfate proteoglycans and rendered the lesion site permissive for axon regeneration of growth-competent sensory neurons. Microtubule stabilization also promoted growth of central nervous system axons of the Raphe-spinal tract and led to functional improvement. Thus, microtubule stabilization reduces fibrotic scarring and enhances the capacity of axons to grow. 相似文献
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MacArthur DG Balasubramanian S Frankish A Huang N Morris J Walter K Jostins L Habegger L Pickrell JK Montgomery SB Albers CA Zhang ZD Conrad DF Lunter G Zheng H Ayub Q DePristo MA Banks E Hu M Handsaker RE Rosenfeld JA Fromer M Jin M Mu XJ Khurana E Ye K Kay M Saunders GI Suner MM Hunt T Barnes IH Amid C Carvalho-Silva DR Bignell AH Snow C Yngvadottir B Bumpstead S Cooper DN Xue Y Romero IG; Genomes Project Consortium Wang J Li Y Gibbs RA McCarroll SA Dermitzakis ET Pritchard JK Barrett JC 《Science (New York, N.Y.)》2012,335(6070):823-828
Genome-sequencing studies indicate that all humans carry many genetic variants predicted to cause loss of function (LoF) of protein-coding genes, suggesting unexpected redundancy in the human genome. Here we apply stringent filters to 2951 putative LoF variants obtained from 185 human genomes to determine their true prevalence and properties. We estimate that human genomes typically contain ~100 genuine LoF variants with ~20 genes completely inactivated. We identify rare and likely deleterious LoF alleles, including 26 known and 21 predicted severe disease-causing variants, as well as common LoF variants in nonessential genes. We describe functional and evolutionary differences between LoF-tolerant and recessive disease genes and a method for using these differences to prioritize candidate genes found in clinical sequencing studies. 相似文献