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排序方式: 共有432条查询结果,搜索用时 15 毫秒
161.
Delay-dependent stability and added damping of SDOF real-time dynamic hybrid testing 总被引:1,自引:1,他引:0
It is well-recognized that a transfer system response delay that reduces the test stability inevitably exists in real-time dynamic hybrid testing (RTDHT).This paper focuses on the delay-dependent stability and added damping of SDOF systems in RTDHT.The exponential delay term is transferred into a rational fraction by the Padé approximation, and the delay-dependent stability conditions and instability mechanism of SDOF RTDHT systems are investigated by the root locus technique.First, the stability conditions are discussed separately for the cases of stiffness, mass, and damping experimental substructure.The use of root locus plots shows that the added damping effect and instability mechanism for mass are different from those for stiffness.For the stiffness experimental substructure case, the instability results from the inherent mode because of an obvious negative damping effect of the delay.For the mass case, the delay introduces an equivalent positive damping into the inherent mode, and instability occurs at an added high frequency mode.Then, the compound stability condition is investigated for a general case and the results show that the mass ratio may have both upper and lower limits to remain stable.Finally, a high-emulational virtual shaking table model is built to validate the stability conclusions. 相似文献
162.
Debasish Sarkar Sudip Kumar Das Paramartha Mukherjee Amitava Bandyopadhyay 《洁净——土壤、空气、水》2010,38(8):764-770
Experiments have been carried out to characterize the adsorption of chromium(VI) in the aqueous phase onto dried roots of water hyacinth. Results revealed a very high degree of removal efficiency (∼100%). Theoretical analyzes are also made for describing the sorption and diffusion processes. The effective pore diffusivity of chromium(VI) in the water hyacinth roots is determined by a suitable global optimization technique. The depth of penetration, on the other hand, has been estimated for various initial concentrations of chromium(VI). Theoretically predicted concentration profiles are in excellent agreement with the experimental values. 相似文献
163.
多效唑对多年生黑麦草扩展性和根系特性的影响 总被引:2,自引:0,他引:2
在盆栽条件下研究了多效唑对多年生黑麦草(Lolium perenne.L)单株扩展性和根系特性的影响,以期为多效唑在多年生黑麦草草坪的养护管理中提供依据。结果表明,在100~1 900 mg·L-1质量浓度范围内,多效唑能有效抑制多年生黑麦草植株的生长、地上枝叶的水平扩展、地上植物量的积累和根系的垂直生长,促进分蘖。质量浓度大于400 mg·L-1时对地上植物量积累的抑制趋缓,大于700 mg·L-1时对最大扩展距离和根系生长的抑制作用减缓,大于1 000 mg·L-1时对株高的抑制趋缓,大于1 300 mg·L-1时覆盖面积的减小趋缓。分蘖数、根系表面积和体积、地下植物量随多效唑质量浓度的增加呈先增加后减小的趋势,1 300 mg·L-1质量浓度处理均达最大值。从扩展性评价结果看,地上枝叶扩展性随多效唑质量浓度的增加而减弱,但质量浓度大于700 mg·L-1时减弱趋缓;地下根系扩展性随多效唑质量浓度的增加呈先增强后减弱的趋势,1 300 mg·L-1质量浓度对地下扩展最为有利;综合扩展性总体呈随多效唑质量浓度的增加而减弱的趋势。 相似文献
164.
165.
极端干旱环境下的胡杨细根分布与土壤特征 总被引:5,自引:2,他引:3
以塔里木河下游的中龄胡杨为研究对象,采用开挖剖面分层取样法,对胡杨细根(D≤2 mm)的空间分布以及与土壤特征因子之间的关系进行了分析。结果表明:①在长期干旱胁迫下,胡杨细根(D≤2 mm)根长密度(RLD)、根表面积密度(SAD)从表层到地下100 cm土层内,呈逐渐增加趋势,100~140 cm土层内表现为减少的波动分布趋势;细根RLD、SAD集中分布在60~120 cm土层内,约占0~140 cm土层总细根RLD和SAD的74%以上;在水平方向上,距树干0.75~2.5 m范围内,呈逐渐减少趋势,而在3.5~5.5 m范围内呈波动的增加趋势。②胡杨细根(D≤2 mm)RLD和SAD与土壤总盐、土壤有效养分含量之间呈显著负相关关系,适合乘幂模型,与土壤含水率之间呈一定程度的正相关关系,适合三次曲线模型。 相似文献
166.
探地雷达技术在植物根系探测研究中的应用 总被引:5,自引:0,他引:5
植物根系传统研究方法的局限性迫切需要寻求一种无损性的根系探测技术.基于无损性探测的特点,探地雷达已被证明是一种能够应用于根系探测的潜在工具.对探地雷达探测原理及其在植物根系形态绘图、根径大小和生物量测量等几个方面中的应用研究进行了综述,阐述了该方法的优势和应该注意的问题.根系形态分布探测需要提高雷达的发射频率和保持足够小的扫描间距;在估计植物根系大小和生物量方面主要依赖于有效的、能够反映相关特征的雷达探测信息参数的提取,同时还需要高级的数值分析和数据处理技术的支持. 相似文献
167.
168.
The recently discovered Nikos kimberlite on Somerset Island, in the Canadian Arctic, hosts an unusually well preserved suite of mantle xenoliths dominated by garnet–peridotite (lherzolite, harzburgite, dunite) showing coarse and porphyroclastic textures, with minor garnet–pyroxenite. The whole rock and mineral data for 54 Nikos xenoliths indicate a highly refractory underlying mantle with high olivine forsterite contents (ave. Fo=92.3) and moderate to high olivine abundances (ave. 80 wt.%). These characteristics are similar to those reported for peridotites from the Archean Kaapvaal and Siberian cratons (ave. olivine Fo=92.5), but are clearly distinct from the trend defined by oceanic peridotites and mantle xenoliths in alkaline basalts and kimberlites from post-Archean continental terranes (ave. olivine Fo=91.0). The Nikos xenoliths yield pressures and temperatures of last equilibration between 20 and 55 kb and 650 and 1300°C, and a number of the peridotite nodules appear to have equilibrated in the diamond stability field. The pressure and temperature data define a conductive paleogeotherm corresponding to a surface heat flow of 44 mW/m2. Paleogeotherms based on xenolith data from the central Slave province of the Canadian craton require a lower surface heat flow (40 mW/m2) indicating a cooler geothermal regime than that beneath the Canadian Arctic. A large number of kimberlite-hosted peridotites from the Kaapvaal craton in South Africa and parts of the Siberian craton are characterized by high orthopyroxene contents (ave. Kaapvaal 32 wt.%, Siberia 20 wt.%). The calculated modal mineral assemblages for the Nikos peridotites show moderate to low contents of orthopyroxene (ave. 12 wt.%), indicating that the orthopyroxene-rich mineralogy characteristic of the Kaapvaal and Siberian cratons is not a feature of the cratonic upper mantle beneath Somerset Island. 相似文献
169.
Incorporating upper mantle differentiation through decompression melting in a numerical mantle convection model, we demonstrate that a compositionally distinct root consisting of depleted peridotite can grow and remain stable during a long period of secular cooling. Our modeling results show that in a hot convecting mantle partial melting will produce a compositional layering in a relatively short time of about 50 Ma. Due to secular cooling mantle differentiation finally stops before 1 Ga. The resulting continental root remains stable on a billion year time scale due to the combined effects of its intrinsically lower density and temperature-dependent rheology. Two different parameterizations of the melting phase-diagram are used in the models. The results indicate that during the Archaean melting occurred on a significant scale in the deep regions of the upper mantle, at pressures in excess of 15 GPa. The compositional depths of continental roots extend to 400 km depending on the potential temperature and the type of phase-diagram parameterization used in the model. The results reveal a strong correlation between lateral variations of temperature and the thickness of the continental root. This shows that cold regions in cratons are stabilized by a thick depleted root. 相似文献
170.