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模拟酸雨对黑麦草种子萌发及生理特性的影响 总被引：1，自引：0，他引：1
以一年生黑麦草(Annual Ryegrass Lolium multifolorum)种子为材料,研究不同pH值的模拟硫酸型酸雨作用下,种子的萌发及幼苗生理特性发生的变化.实验分别测定了种子发芽率、发芽势、发芽指数及幼苗鲜重、叶片导电率等指标.结果表明,一年生黑麦草种子的发芽势、发芽率、发芽指数整体变化趋势比较一致,随着模拟酸雨pH值的增大而减小.幼苗叶片的生长量变化差异比较大,单株幼苗的平均鲜重随模拟酸雨酸性的减弱而增大,所测幼苗叶片的相对电导率值随模拟酸雨pH值的升高而减小,与对照相比差异显著,表明幼苗叶片受到了酸雨的破坏.试验表明,一年生黑麦草种子在pH≥3.09的弱酸条件下能够正常萌发和生长,具有一定的耐酸性,但是在pH≤2.03的强酸条件下,种子的萌发和幼苗的生长受到了显著的抑制. 相似文献
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基于隔离布防护的水稻冠层上方风速分布特征 总被引：1，自引：1，他引：0
为了确定隔离布防护转基因水稻基因漂流效果,设计了隔离布防护措施的田间试验,研究防护区内、外水稻冠层上方的风速分布特征。结果表明,背风面不同风向角的1 m高度风速变化规律基本相同,1~2.5 H（H为隔离布高度,2 m）区域内风速降低幅度最大;其次是2.5~5 H区域内,而在5~10 H区域内风速降低幅度相对较小;随着风向角的增大,风速降低幅度有所减小。迎风面不同风向角的1 m高度风速在2.5 H处风速降低幅度最大,为60%~70%。隔离区内1 m高度风速整体减小,越靠近隔离布,风速减小越明显。因此,隔离布防护风障降低隔离区内外风速明显,可有效缩短转基因水稻花粉扩散距离。 相似文献
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模拟酸雨对紫花苜蓿种子萌发及幼苗生理特性的影响 总被引：14，自引：0，他引：14
以紫花苜蓿的种子为研究材料，研究种子在不同pH值的模拟硫酸型酸雨作用下，种子的萌发和幼苗生理特性发生的变化。实验分别测定了种子的发芽势、发芽率、发芽指数、活力指数、幼苗的鲜重、根长、芽长、叶片叶绿素含量、叶片电导率等指标。结果表明，紫花苜蓿种子的发芽势、发芽率、发芽指数、活力指数的整体变化趋势比较一致，随着模拟酸雨浓度的增大而减小。幼苗叶片的生长量的变化差异比较大，单株幼苗的平均鲜重和根长随模拟酸雨酸性的减弱而增大，单株幼苗的平均芽长则随pH值的增大而减小，幼苗芽的生长受到酸雨的抑制主要是由根的生长受到抑制引起的。幼苗叶片叶绿素含量的整体变化趋势是随着模拟酸雨pH值的升高而增大。所测幼苗叶片的相对电导率值随模拟酸雨pH值的升高而减小，与对照相比差异显著，表明幼苗叶片受到了酸雨的破坏。试验表明，紫花苜蓿种子在pH≥4．0的弱酸条件下能够正常萌发和生长，具有一定的耐酸性，但是在pH≤3．0的强酸条件下，种子的萌发和幼苗的生长受到了显著的抑制。 相似文献
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小麦堆体变模量的测定与实验研究 总被引：2，自引：0，他引：2
利用应变控制式三轴仪对小麦的体积压缩和体变模量进行了实验测定,并探讨了围压和水分对体变模量的影响。结果表明:小麦堆的体积随着围压的增大而减小;小麦堆(水分为13.7%、16.4%、18%)的体变模量随着围压(5 kPa～30 kPa)的增大而增大,它们的体变模量的范围分别为173.5 kPa～259.3 kPa、164 kPa～240 kPa、151 kPa～229.4kPa;小麦堆体变模量随着水分的增大而减小,当小麦堆围压为30 kPa,水分为13.7%～18%时,它的体变模量变化范围为223.5 kPa～270 kPa。 相似文献
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采用棱柱体试件,通过快速冻融试验方法,对冻融损伤后同配合比普通混凝土、喷射混凝土及钢纤维喷射混凝土单轴受压应力应变全曲线进行研究。对应力应变关系中相关参数进行回归分析,得出冻融循环后试件应力应变全曲线方程。结果表明：随着冻融循环次数增加,受压应力应变曲线趋于扁平;峰值应力降低,峰值应变增大,分别与冻融循环次数呈线性和指数变化。与普通混凝土相比,喷射混凝土峰值应力下降速率小,而钢纤维喷射混凝土的下降速率进一步减小。而后,采用扫描电子显微镜及压汞法,对损伤后试件微观结构和孔结构进行观察分析,发现随着冻融循环次数增加,在渗透压和冻胀压力综合作用下,试件内部微裂纹及气孔增多,孔径增大,试件密实度显著降低;而钢纤维喷射混凝土中仅出现少量连通毛细孔,这与宏观力学性能变化呈现一致性。 相似文献
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考虑堆场上覆堆积体自重引起的土体固结与溶质运移的耦合效应已成为环境土工领域中的热点问题。在Biot固结理论和溶质运移理论相结合的基础上,以孔隙率作为耦合参量,将固结方程与运移方程相联系,考虑土体固结对溶质运移模型参数的影响,建立了溶质在固结变形土体中运移的三维耦合模型。采用多场耦合有限元软件COMSOL Multiphysics对模型进行了数值求解。数值模拟结果表明,土体固结变形对溶质运移过程具有较强和持久的阻滞作用,导致溶质运移深度以及污染羽范围的减小,在模拟运移20 a时,运移距离减小率已高达27.75%,且随着时间的增加而逐渐增大;溶质在水平方向的迁移距离不可忽略,随着横向水力梯度的增大而增大。 相似文献
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在高层建筑结构设计中,由于上部荷载较大或梁的跨度较大,使得梁的截面高度较高,通常会影响建筑的有效层高和建筑的总体高度。为了减小各层梁板结构高度,有效增大各层净高,提出了一种钢箱梁嵌入现浇板的新型组合梁板连接方式。针对这种新型连接方式,对6个钢箱梁混凝土板组合连接区域进行了板承受支座负弯矩的单调加载试验,对比分析了采用钢箱梁嵌入混凝土板组合楼盖与传统栓钉连接组合楼盖中板抵抗支座负弯矩的性能差异;并利用ABAQUS对试件进行了有限元分析。试验与有限元分析结果表明：采用钢箱梁嵌入板连接组合方式,其混凝土板抵抗支座负弯矩的能力与传统连接方式板抵抗支座负弯矩能力没有明显差异。 相似文献
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春玉米叶面积系数动态特征的密度效应 总被引：17，自引：0，他引：17
为进一步明确春玉米不同密度群体叶面积系数(LAI)特征参数的密度效应,以吉单209和郑单958为材料,于2005年和2006年在东北春玉米区(吉林)分别设置4.5~10.5万株 hm-2 5个密度和3.0~12.0万株 hm-2 7个密度处理试验,应用作物高产群体相对LAI动态普适模型方程y= (a+bx)/(1+cx+dx2)模拟分析不同密度对LAI动态特征参数的影响。结果表明,春玉米群体最大LAI在3.0~12.0万株hm-2范围内随密度增加呈近似直线增大趋势,而最大LAI出现的时间随密度增加而提早;将LAI数据相对化处理后,不同密度群体的LAI差异在最大LAI之后较之前表现明显,高密度群体较低密群体LAI衰减迅速。全生育期平均LAI随密度增加呈显著线性增大趋势,而平均LAI与最大LAI的比率则随密度增加呈显著线性减小趋势。密度对模拟方程各参数均有不同程度的影响,相邻密度差异不明显,间隔3.0万株 hm-2的差异显著;不同参数变化趋势不同,其中参数a接近“0”,受密度影响不大;b、c均随密度的增加而减小,d随密度的增加而增大。全生育期群体LAI变化速率呈“N”形变化趋势,且与群体LAI变化及生育期对应,高密度群体LAI增加及衰减的速率均大于低密度群体,拔节期和大喇叭口期为密度响应敏感期。由此可见,密度对春玉米全生育群体LAI动态具有调节作用,尤其群体LAI变化速率、最大LAI及其到达的时间、平均LAI及其与最大LAI的比率等重要特征参数对密度响应较为敏感,可作为对春玉米群体密度调控的参考指标。 相似文献
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Wind induced vibration is one of the main control factors in the Long span bridge structure design. The wind tunnel tests for measuring the static wind forces on the bridge girder and the section model wind tunnel dynamic testing for Caiyuanba Yangtze River Bridge in Chongqing are introduced in this paper. The wind tunnel testing for measuring static wind forces and vortex- induced vibration test on the arch are introduced taking account of the influence between two arches. The main contents and outcomes of testing are presented. It is indicated that the bridge girder has excellent wind stability and the arch mechanical characters are rather complicated. The drag force on the hind arch varied a lot because of the font arch interference on the wind flow. The drag force on the hind arch will be negative when two arches are close to each other. It increases with the space of two arches. The results of testing will give the data of buffeting and vortex - induced vibration and flutter analysis of the bridge. 相似文献
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The main arch of a long-span arch bridge is a compression member. The static wind loads on the bridge not only causes changes of dynamic characters, but also leads the structure to collapse or buckling. Especially, when the arch bridge has longer span and less lateral braces,its stability is much different from the long span cable-stayed bridges and suspension bridges. This paper takes Chongqing Caiyuanba Yangzi River Bridge as a typical example and conducted the wind section tunnel tests. The displacement response of the bridge is obtained and its yield and static stability mechanism under static wind is analyzed. The results show that those factors, such as initial attack angle of the static wind, material yield strength and the static forces coefficients, have great effects on the aerostatics stability of a long span half-through arch bridge. 相似文献
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Under the dynamic load of vehicle, the bridge will vibrate and radiate low frequency noise which is harmful to human health. A method for predicting the low frequency noise is proposed based on the analysis of vibration of bridge deck. The prediction includes the analysis of vehicle bridge coupling vibration considering the bridge deck and the analysis of sound radiation and propagation in the air. By taking a bridge with low frequency noise as example, the vibration and sound radiation of the bridge are analyzed respectively by the current method and the previous method based on the grillage model. The results show that the prediction based on the vibration of bridge deck is more accurate. Furthermore, the measures to reduce the noise of bridge are explored, and the results indicate that a smoother road surface leads to lower noise. But when the condition of road surface is up to the extremely good standard defined by ISO, the effect of reducing the roughness of surface is not significant. Also, strengthening the crossbeam in the bridgehead is a simple and effective way to reduce the low frequency noise of bridge. 相似文献
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The experimental task was very large for solving fremitus derivative of bridge by free vibration method proposed by R.H.Scanlan.And in the process of extracting cross derivative, it was difficult that the frequency ratio and damping ratio under vertical motion and torsional motion were kept the same in all wind speed.Besides, the discriminating error of uncoupled derivative would be coupled in derivative.Considering these, an improved method based on Modified Ibrahim Time domain Method was proposed.With the application, it was found that this method was better than least square method. 相似文献
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The cable's motion was modeled by a spring-mass-damper system. The flow field was calculated by RSM combined with the enhanced wall function model and the vibration equation of the cable was solved by the Four Step Runge-Kutta Algorithm, which was written into FLUENT software to be analyzed. It was adopted to analyse the factors influencing vortex-induced vibration of submerged floating tunnel cable, such as mass ratio, damping ratio of the cable and whether to consider streamline movement. The main conclusion included: mass ratio has little influence on the transverse vortex induced vibration amplitude of the cable, but has a big influence on the region of the reduced velocity; damping ratio almost has little influence on the region of the reduced velocity of cable's viv, but has an influence on the cable's vibration amplitude significantly; In the case of low-mass ratio, considered the impact of the cable streamline movement, the transverse vortex-induced vibration amplitude is bigger than not considered the case. 相似文献
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Drag coefficients of quad-bundled conductor under different wind speeds and attack angles are firstly determined by means of wind tunnel test. Meanwhile, the drag coefficients are obtained by numerical simulation method and the results are consistent with those by the wind tunnel test. Furthermore, cross flows around six-bundled and eight-bundled conductors are numerically investigated, and the drag coefficients are then determined. Compared with the determination method of wind load on conductor in current Chinese code and the IEC code for the design of transmission line, the drag coefficients defined in the Chinese code may be too large for bundled conductors, and may need to be adjusted based on further theoretical and wind tunnel test investigation. 相似文献
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Zhang LiangLiang Song XiaoBin Wu YunFang Zhu ZhengGang Xiao KeJian Lin GuanMing Lin RongSheng 《保鲜与加工》2005,(4):52
Considering the complication of the coefficient of wind-induced vibration for tall buildings,the scale 1:300 model test of Ying Li Building is completed in the second wind tunnel of Beijing University.Based on the calculation and analysis of the test results,the static and dynamic wind pressure acting on the building can be obtained and the value of the coefficient of wind-induced vibration for this tall building can be solved directly,thus a new way is laid for the research of complicated tall buildings. 相似文献
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An improved computational method for buffeting forces of long span bridges, which substitutes the traditional wind tunnel test with the bridge segment model for CFD method, is proposed. In the case study of Tsing Ma Bridge, the pressure distribution induced by the wind field of the bridge decks was simulated. The nodal buffeting forces were computed and the local stress responses were obtained according to the CFD simulation and the refined finite element model. Preparation for buffeting induced fatigue analysis of bridges and structural health monitoring are provided. 相似文献
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With the development of modern construction technique and the application of new material,arch bridges which progress towards small rigidity,long span and light weight,what's more is that long span bridge's rigidity under construction is much less than that in use stage.So it is very necessary to study the aerodynamic characteristics of long span bridge.The regularity of the three dimensional static component forces coefficient varying with attack angle and the girder's flutter properties of Caiyuanbai Bridge over Yangtse River are investigated with segmental molding's static wind-tunnel test and segmental molding's dynamic wind-tunnel test.Eight derivatives of the girder are also identified from the segmental molding's dynamic wind-tunnel test.Finally the assessment to wind resistant properties of the bridge is given based on detailed analysis of the test results.The conclusion which gets from analysis can provide an suggestion to design and construction this kind bridge. 相似文献
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Considering the complicated distribution of wind load on the surface of the tall building, the 1:300 scale model test of YingLi building is completed in the No.2 environment wind tunnel, which belongs to the State Key Lab of Environmental Engineering College, Beijing University. Based on the calculation and analysis of the test results, this paper discusses the coefficient of wind-induced vibration and shape coefficient of wind load , gives the maximum and minimum value of surface wind load, which can be used for the wind resistant design and insure the security of the building under 100 years return period wind load. 相似文献