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291.
292.
Strength equilibrium slopes are rock slopes whose gradient θ and rock mass strength (RMS) are in adjustment. The identification of such slopes depends on the accurate specification of the strength equilibrium envelope. Previous attempts to delimit the envelope are reviewed and modifications are proposed that permit its more rigorous statistical definition. Because θ can be measured much more reliably than RMS, the structural relation between these variables is estimated by regressing RMS on θ, and the strength equilibrium envelope is defined by the 95 per cent confidence limits. The analysis is performed on a data set of 268 rock slopes, representing all the data on RMS and θ hitherto employed in published studies of strength equilibrium slopes. 相似文献
293.
Focal mechanisms for 116 acoustic emission events associated with uniaxial cyclic loading of Westerly granite have been investigated using P-wave first-motions. Polarities were observed at eight transducers positioned on the sample to provide good azimuthal coverage. The P-wave radiation patterns can be fit by a quadrupole source but not by a simple pure tensional source. The predominant orientations of the two nodal planes for the quadrupole fit were subparallel to and perpendicular to the 1 direction. Events with close hypocenters, i.e., within a radius of 3 mm, display a remarkable similarity in focal mechanisms irrespective of the cycle or time within a cycle at which they occur. The polarity observations of 48 of 116 acoustic emission events could be fit with the simple quadrupole indicating that the microfracturing processes even in uniaxial compression often simplistically portrayed as propagating axial cracks are indeed quite complex. 相似文献
294.
Wind-tunnel experiments were carried out to measure the shear stressduring snow saltation. Shear stress acting on the snow surface, measured directly with a newly developed drag meter system, revealedthat the shear stress increased with the development ofsaltation. This result supports Owen's hypothesis that the saltationlayer acts as an increased roughness to the flow above the saltationlayer, leading to an increase in surface shear stress. To investigate the contribution of the grain borne shear stressg and the fluid shear stress f to the increment of the total shear stress total, g was calculated from the loss of horizontal momentum of saltating snowparticles. Since g is the largest contribution to theincrement of total, the collision of thesaltating particles is dominant for the shear stressmodification. The results qualitatively support the numericalsimulation reported by McEwan and Willetts. 相似文献
295.
Low frequency electrostatic waves are studied in magnetized plasmas with an electron temperature which varies with position in a direction perpendicular to the magnetic field. For wave frequencies below the ion cyclotron frequency, the waves need not follow any definite dispersion relation. Instead a band of phase velocities is allowed, with a range of variation depending on the maximum and minimum values of the electron temperature. Simple model equations are obtained for the general case which can be solved to give the spatial variation of a harmonically time varying potential. A simple analytical model for the phenomenon is presented and the results are supported by numerical simulations carried out in a 2.5-dimensional particle-in-cell numerical simulation. We find that when the electron temperature is striated along B0 and low frequency waves (ci) are excited in this environment, then the intensity of these low frequency waves will be striated in a manner following the electron temperature striations. High frequency ion acoustic waves (ci) will on the other hand have a spatially more uniform intensity distribution. 相似文献
296.
Previous work has shown that ionospheric HF radar backscatter in the noon sector can be used to locate the footprint of the magnetospheric cusp particle precipitation. This has enabled the radar data to be used as a proxy for the location of the polar cap boundary, and hence measure the flow of plasma across it to derive the reconnection electric field in the ionosphere. This work used only single radar data sets with a field of view limited to 2 h of local time. In this case study using four of the SuperDARN radars, we examine the boundary determined over 6 h of magnetic local time around the noon sector and its relationship to the convection pattern. The variation with longitude of the latitude of the radar scatter with cusp characteristics shows a bay-like feature. It is shown that this feature is shaped by the variation with longitude of the poleward flow component of the ionospheric plasma and may be understood in terms of cusp ion time-of-flight effects. Using this interpretation, we derive the time-of-flight of the cusp ions and find that it is consistent with approximately 1 keV ions injected from a subsolar reconnection site. A method for deriving a more accurate estimate of the location of the open-closed field line boundary from HF radar data is described. 相似文献
297.
Ionosphere-magnetosphere disturbances at high latitudes, e.g. magnetic substorms, are accompanied by energetic particle precipitation and strong variations of the ionospheric electric fields and currents. These might reasonably be expected to modify the local atmospheric electric circuit. We have analysed air-earth vertical currents (AECs) measured by a long wire antenna at Esrange, northern Sweden during 35 geomagnetic substorms. Using superposed epoch analysis we compare the air-earth current variations during the 3 h before and after the time of the magnetic X-component minimum with those for corresponding local times on 35 days without substorms. After elimination of the average daily variation we can conclude that the effect of substorms on AEC is small but distinguishable. It is speculated that the AEC increases observed during about 2 h prior to the geomagnetic X-component minimum, are due to enhancement of the ionospheric electric field. During the subsequent 2 h of the substorm recovery phase, the difference between substorm and quiet atmospheric currents decreases. The amplitude of this substorm variation of AEC is estimated to be less than 50% of the amplitude of the diurnal variation in AEC during the same time interval. The statistical significance of this result was confirmed using the Van der Waerden X-test. This method was further used to show that the average air-earth current and its fluctuations increase during late expansion and early recovery phases of substorms. 相似文献
298.
石英裂变径迹蚀刻条件的对比实验研究 总被引:5,自引:0,他引:5
通过 40%的 HF溶液、KOH饱和溶液和 19 mol/L的 NaOH溶液这三种常用方法对大、小颗粒石英进行裂变径迹蚀刻实验的对比发现,用环氧树脂固定的小颗粒石英样品,不宜用 KOH饱和溶液(150 ℃)和 19 mol/L的 NaOH溶液(沸点,约 120 ℃)作为裂变径迹的蚀刻剂,宜用 40%的 HF溶液;三种方法均适宜于大颗粒石英,但不同的蚀刻方法蚀刻效率不同, 40%的 HF溶液(29 ℃)的蚀刻效率最高,且操作简单、安全性高.40%的 HF溶液最佳蚀刻时间为: 温度在 4 ℃左右(冬季)时为 40 min,温度在 29 ℃左右(夏季)时为 30 min,可在全年室内常温条件下操作. 相似文献
299.
Centrifuge Modeling of Rock Slopes Susceptible to Block Toppling 总被引:2,自引:0,他引:2
Summary This paper presents the results of centrifuge tests that were aimed at validating the Goodman-Bray method for rock slope toppling
analysis. The Goodman-Bray method was extended by the authors to accommodate non-persistent basal planes of rock columns.
Two gypsum column models, with and without anchors were used to represent the failure modes. Measured critical centrifuge
accelerations were in agreement with the results obtained from numerical modeling. A background of the toppling slope failures
associated with a large hydropower project in China instigated the need for the centrifuge study. The centrifuge model tests
used an artificial rock. The observed failure mode did not follow a straight failure plane as proposed by Goodman and Bray.
The failures revealed a bi-planar slip surface with a deep-seated portion near the toe of the slope. The outcomes of the centrifuge
tests illustrated the need to search for the critical failure surface when performing a toppling analysis. The search technique
is similar to that usually performed in a conventional sliding analysis. 相似文献
300.
使用氢化物发生—原子荧光光谱法测定锑精矿中的微量砷在国内外报道较少。文章在锑干扰状况试验、高锰酸钾溶液消除干扰的最佳条件选择试验、锑精矿中共存元素的干扰和消除试验的基础上,对样品进行了实测,并就其灵敏度、准确度和精密度进行了讨论。研究表明,该方法是测定锑精矿中微量砷的有效方法。 相似文献