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71.
72.
Dust is a major environmental factor on the surface and in the atmosphere of Mars. Knowing the electrical charge state of this dust would be of both scientific interest and important for the safety of instruments on the Martian surface. In this study the first measurements have been performed of dust electrification using suspended Mars analogue material. This has been achieved by attracting suspended dust onto electrodes placed inside a Mars simulation wind tunnel. The Mars analogue used was from Salten Skov in Denmark, this contained a high concentration of ferric oxide precipitate. Once suspended, this dust was found to consist of almost equal quantities of negatively (46±6%) and positively (44±15%) charged grains.These grains were estimated to typically carry a net charge of around 105e, this is sufficient to dominate the processes of adhesion and cohesion of this suspended dust. Evidence is presented for electrostatic aggregation of the dust while in suspension. Development of a simple instrument for measuring electrical charging of the suspended dust on Mars will be discussed. 相似文献
73.
基于IDA方法的地震易损性分析是目前一种较为常用的建筑结构抗震性能评价方法。选取15条地震动,三向作用于结构,对影响最大的两类支座分别施加200mm沉降量后的模型和未沉降模型基于IDA方法进行地震易损性分析。结果表明:在地震动强度较小时,短柱端支座沉降模型由于预应力增加会使结构相比与未沉降模型更加趋于稳定;当地震动强度较大时,短柱端支座沉降模型的破坏概率随着地震动强度的增加而迅速增加,此时未沉降模型的破坏概率将大幅低于另外两类模型。 相似文献
74.
笏山金矿发生事故后,我单位按应急救援指挥部的要求施工了6号救援钻孔。针对该矿区花岗岩硬度高,地层岩石破碎,以及地层含水丰富等特点,从设备安装到施工工艺及操作流程,制定了一套完整的施工技术方案。从而避免了误工误时,避免了救援过程中次生事故的发生。全孔采用气动潜孔锤钻进,合理调整钻进参数,不但解决了花岗岩地层进尺慢、钻效低的问题,还确保了钻孔一次性进入预定靶区,施工中做到了“稳、准、快”,最终圆满完成了救援孔的施工任务。 相似文献
75.
Learning to combine multiple string similarity metrics for effective toponym matching 总被引:1,自引:0,他引:1
Rui Santos Patricia Murrieta-Flores Bruno Martins 《International Journal of Digital Earth》2018,11(9):913-938
Several tasks related to geographical information retrieval and to the geographical information sciences involve toponym matching, that is, the problem of matching place names that share a common referent. In this article, we present the results of a wide-ranging evaluation on the performance of different string similarity metrics over the toponym matching task. We also report on experiments involving the usage of supervised machine learning for combining multiple similarity metrics, which has the natural advantage of avoiding the manual tuning of similarity thresholds. Experiments with a very large dataset show that the performance differences for the individual similarity metrics are relatively small, and that carefully tuning the similarity threshold is important for achieving good results. The methods based on supervised machine learning, particularly when considering ensembles of decision trees, can achieve good results on this task, significantly outperforming the individual similarity metrics. 相似文献
76.
77.
Mahesh Kumar Yadav Anirudh Pradhan Sheel Kumar Singh 《Astrophysics and Space Science》2007,311(4):423-429
Some Bianchi type-I viscous fluid string cosmological models with magnetic field are investigated. The viscosity coefficient
of bulk viscous fluid is assumed to be a power function of mass density ξ(t)=ξ
0
ρ
m
, where ξ
0 and m are constants. To get a determinate model, we assume conditions ρ=(1+ω)λ, where ρ is rest energy density, ω a positive constant and λ the string tension density and expansion θ is proportional to eigen value σ
11 of the shear tensor σ
j
i
. The behaviour of the models from physical and geometrical aspects in presence and absence of magnetic field is discussed.
相似文献
78.
D. R. K. Reddy R. L. Naidu S. Atchuta Rao K. N. Devi 《Astrophysics and Space Science》2007,310(3-4):177-180
Field equations in the presence of cosmic string source are obtained in a scalar tensor theory of gravitation proposed by
Brans and Dicke (Phys. Rev. 124, 925 (1961)) with the aid of a five-dimensional Kaluza–Klein metric. An exact string cosmological model is presented which represents
a five-dimensional Reddy string (Astrophys. Space Sci. 286, 2003b) in Brans–Dicke theory. Some physical properties of the model are also discussed 相似文献
79.
We revisit the equations governing the bending motions in thin rods and analyse the filtration of flexural waves in vertical drill strings pre‐stressed by gravity. The aim is to study transverse drill‐string vibrations at seismic frequencies for acoustic communication purposes and provide an algorithm for processing reflected and transmitted bending motions generated by downhole lateral vibrations. We obtain the dispersion equation, including attenuation due to a gravity pre‐stress gradient and frequency‐dependent reflection and transmission coefficients at the interface between subsequent tube intervals. We then develop a propagation‐matrix algorithm to simulate flexural waves in a drill string consisting in an assembly of multiple tube sections of different dimensions. The deflection vibrations are obtained at any arbitrary recording point in the drill string. The modelling is cross‐checked with a full‐wave grid algorithm. The analysis shows that the waves produced by a concentrated force are partitioned in standing and propagating modes, which are calculated by using the flexural impedance of the drill string. Moreover, the reflection coefficients weakly depend on the pre‐stress conditions and pre‐stress has important effects for far‐field signal transmission with variable weight on bit (WOB). We discuss the approximations and limits of the method with respect to realistic drilling conditions. 相似文献
80.
钢筋混凝土框架结构在地震作用下应满足强柱弱梁等抗震设计理念,但由于设计和施工各种综合原因所致,在历次地震中,规范要求的"强柱弱梁"理想破环机制始终没有出现,竖向承重构件遭受了不同程度的损伤和破坏,不满足现有规范的相关规定,为了保证钢筋混凝土竖向承重构件不先于水平构件破坏,对于一些重要位置的钢筋混凝土构件进行修复加固显得十分重要。本文以加大截面加固法、外贴碳纤维加固法、喷射混凝土技术加固法、外包钢加固法、外包粘钢加固法等加固处理方式为例,对钢筋混凝土构件的修复加固方法及其抗震性能进行对比分析。研究对于钢筋混凝土构件的修复加固工程具有一定的参考价值。 相似文献