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201.
在野外试验基地进行了沙棘柔性坝拦沙效应试验。基于试验数据,分析了不同含沙水流条件下沙棘柔性坝对沿程含沙量及出入口悬沙粒径分布的影响,并探讨了沙棘柔性坝的阻力特性。结果表明,沙棘柔性坝对不同含沙水流的拦沙效果显著不同,对原型沙B的拦截效果最好,其次为原型沙A,最后为模型沙。对250~1 000μm粒径范围内的原型沙拦截效果最佳,且原型沙含沙量与中值粒径之间呈现正相关关系,对100~1 000μm粒径范围内的模型沙的拦截效果较好。各不同含沙水流条件下的沿程含沙量主要受沙棘柔性坝阻力的影响。本研究有助于深入理解沙棘柔性坝的拦沙效应,并对沙棘植物柔性坝这一生态工程在砒砂岩区沟道的推广应用提供理论依据。 相似文献
202.
Riitta Kettunen Sanna Saarnio Pertti J. Martikainen Jouko Silvola 《Nutrient Cycling in Agroecosystems》2006,74(2):175-189
The effects of elevated atmospheric CO2 concentration on soil moisture, N2O fluxes, and biomass production of Phleum pratense were studied in the laboratory. Farmed peat and sandy soil mesocosms sown with P. pratense were fertilized with a commercial fertilizer. In peat soil 10 g N m−2 of commercial fertilizer were added and in sandy soil 15 g N m−2. In both experiments, soil moisture was regulated with deionized water; 18 mesocosms were tended to keep equally moist, and
the other 18 were watered with equal amounts of water. Nine mesocosms from both watering treatments were grown under ambient
(360 μmol mol−1) CO2 concentration and the remaining nine under doubled (720 μmol mol−1) CO2. N2O efflux was monitored using a closed chamber technique and a gas chromatograph. The elevated supply of CO2 increased production of above- and belowground biomass, soil moisture and N2O fluxes, but decreased the total N content in the aboveground biomass, especially for the sandy soil. In similar water levels,
N2O efflux from the sandy soil was the same magnitude as that from the peat soil. In addition to moisture, N availability was
the main limiting factor for N2O production, but C availability also seemed to regulate the denitrification activity. In addition to an increase in C availability
the increase in the N2O efflux under the raised CO2 concentration also required a simultaneous increase in soil moisture. 相似文献
203.
Abstract. This paper deals with the third-order asymptotic theory for Gaussian autoregressive moving-average (ARMA) processes with unknown mean μ. We are interested in the estimation of ρ = ( α1 …, αp , β1 …, βq ), where α 1 …, αρ and β 1 …, βq are the coefficients of the autoregressive part and the moving-average part, respectively. First, we investigate the third-order asymptotic optimality of the bias adjusted maximum likelihood estimator (MLE) of ρ in the presence of the nuisance parameters μ and 2 (innovation variance). Next, for a Gaussian AR(1μ μ, 2 ), we propose a mean corrected estimator αc1c2 of the autoregressive coefficient. We make a comparison between the bias adjusted estimator αc1c2 * and the bias adjusted MLE, in terms of their probabilities of concentration around the true value, or equivalently, in terms of their mean squared errors. Finally some numerical studies are provided in order to verify the third-order asymptotic theory. 相似文献
204.
Hydraulic resistance of rigid polyurethane foams to penetration by water at high pressures is studied in this work in the context of buoyancy applications. Micron sized silica particles are used as nucleating agents. The effect of the variation of the concentrations of the surfactant, water, and nucleating agent on cell structure, closed cell content, and compressive modulus, is examined. Foams have densities in the range of 145 to 165 kg/m3. At a particular water concentration, with increase in the concentration of the surfactant, the window area of the cells becomes smaller and the hydraulic resistance of the foam increases. A cell window is the lamella of the foam material that separates two adjacent cells. With increase in the concentration of water keeping surfactant concentration constant, the average window area remains almost the same but the cell window area distribution becomes wider and the hydraulic resistance of the foams decreases. Foams made with silica have smaller cell windows but lower hydraulic resistance than that of the foams made without silica. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2830–2837, 2004 相似文献
205.
The preparation of dibasic acid-containing soy phospholipid was made by transesterification reaction with alkyl ester of diabasic acid with both lipase and alkoxide as a catalyst. The extent of incorporation of a dibasic acid varied with the molecular size of the dibasic acid. The extent of incorporation in soy phospholipids was 4–13% in the case of adipic acid and 9–20% in the case of sebacic acid. The surface-active properties of these modified soy phospholipids were examined and were found to be different from those of the original (unmodified) soy phospholipid. The interfacial properties such as critical micelle concentration (CMC), γCMC, surface excess concentration Γmax, and minimum area per molecule (Å), and thermodynamic parameters such as standard free energy of micellization, were found to depend on the hydrophobic part of the dibasic acids. 相似文献
206.
207.
Seung-Min Oh Mark. Cappelli Dong-Wha Park 《Korean Journal of Chemical Engineering》2002,19(5):903-907
Nano-sized silicon carbide (SiC) powder was prepared by thermal plasma process using silicon tetrachloride (SiCl4) and methane (CH4). The synthesized powder was characterized by X-ray diffraction pattern, scanning electron microscopy, transmission electron
microscopy, FT-IR spectroscopy and particle size analyzer. The powder was dominated by β-SiC including some of α-SiC and free
carbon species. The quality of the powder was varied with process conditions such as the molar ratio of H/Si and C/Si, and
collecting positions. It was known that the conversion to SiC was mainly affected by the addition of hydrogen gas because
it promoted the decomposition and reduction of SiCL. CH4 was easily decomposed to carbon species for the formation of SiC as well as removal of impure oxygen, but excessive carbon
suppressed the formation of crystalline SiC and resulted in the solid carbon contamination. The optimum ratio of H/Si was
approx. 26 and that of C/Si was 1.1. For collecting positions, the powder collected at the vessel and filter was preferable
to that at the reaction tube. The average size of the powder synthesized was estimated to be below 100 nm and uniform in distribution. 相似文献
208.
断续流对旋流器油水分离效率影响的实验研究 总被引:2,自引:0,他引:2
目前,大部分井下油水分离的旋流器由地面游梁式抽油机通过抽油杆柱提供能量,这样进入旋流器流量产生断续现象。通过实验证明断续流流量的不连续性使旋流器油水分离效率下降5%以内,存在一定负影响;溢流含油浓度越高,断续流对旋流分离效率的负影响也越大,所以井下油水分离过程中,不能偏面追求过高的溢流口含油浓度,提高分流比F与入口含油浓度C_i比值,减小断续流对分离效率的影响。 相似文献
209.
The recoverable shear strain (SR) for the liquid crystal‐forming hydroxypropyl cellulose solutions was determined by means of a concentric cylinder rotational apparatus as functions of shear stress prior to recovery and concentration of the solutions at 30°C. SR greatly depended on shear stress and concentration; the phase of the solution (the single phase or biphase) governed the dependences of SR on stress and concentration. SR increased with increasing stress for the single phase and decreased for the biphase. SR seemed to be related to the die swell (B): SR ∝ Bn. SR exhibited a maximum and a minimum with respect to concentration. SR for the cellulosic cholesteric liquid crystalline solutions was greater than that for the isotropic solutions. A model was proposed for explaining the greater SR. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 865–872, 2002 相似文献
210.