Observations of Rapid Velocity Variations in the Slow Solar Wind     

S. A. Hardwick  M. M. Bisi  J. A. Davies  A. R. Breen  R. A. Fallows  R. A. Harrison  C. J. Davis 《Solar physics》2013,285(1-2):111-126

The technique of interplanetary scintillation (IPS) is the observation of rapid fluctuations of the radio signal from an astronomical compact source as the signal passes through the ever-changing density of the solar wind. Cross-correlation of simultaneous observations of IPS from a single radio source, received at multiple sites of the European Incoherent SCATter (EISCAT) radio antenna network, is used to determine the velocity of the solar wind material passing over the lines of sight of the antennas. Calculated velocities reveal the slow solar wind to contain rapid velocity variations when viewed on a time-scale of several minutes. Solar TErrestrial RElations Observatory (STEREO) Heliospheric Imager (HI) observations of white-light intensity have been compared with EISCAT observations of IPS to identify common density structures that may relate to the rapid velocity variations in the slow solar wind. We have surveyed a one-year period, starting in April 2007, of the EISCAT IPS observing campaigns beginning shortly after the commencement of full science operations of the STEREO mission in a bid to identify common density structures in both EISCAT and STEREO HI datasets. We provide a detailed investigation and presentation of joint IPS/HI observations from two specific intervals on 23 April 2007 and 19 May 2007 for which the IPS P-Point (point of closest approach of the line of sight to the Sun) was between 72 and 87 solar radii out from the Sun’s centre. During the 23 April interval, a meso-scale (of the order of 10⁵ km or larger) transient structure was observed by HI-1A to pass over the IPS ray path near the P-Point; the observations of IPS showed a micro-scale structure (of the order of 10² km) within the meso-scale transient. Observations of IPS from the second interval, on 19 May, revealed similar micro-scale velocity changes, however, no transient structures were detected by the HIs during that period. We also pose some fundamental thoughts on the slow solar wind structure itself.  相似文献   

Origin of the structure and planform of small impact craters in fractured targets: Endurance Crater at Meridiani Planum, Mars     

Wesley A. Watters  John P. Grotzinger  John Grant  Rongxing Li  Maria T. Zuber 《Icarus》2011,211(1):472-497

We present observations and models that together explain many hallmarks of the structure and growth of small impact craters forming in targets with aligned fractures. Endurance Crater at Meridiani Planum on Mars (diameter ≈ 150 m) formed in horizontally-layered aeolian sandstones with a prominent set of wide, orthogonal joints. A structural model of Endurance Crater is assembled and used to estimate the transient crater planform. The model is based on observations from the Mars Exploration Rover Opportunity: (a) bedding plane orientations and layer thicknesses measured from stereo image pairs; (b) a digital elevation model of the whole crater at 0.3 m resolution; and (c) color image panoramas of the upper crater walls. This model implies that the crater’s current shape was mostly determined by highly asymmetric excavation rather than long-term wind-mediated erosion. We show that modal azimuths of conjugate fractures in the surrounding rocks are aligned with the square component of the present-day crater planform, suggesting excavation was carried farther in the direction of fracture alignments. This was previously observed at Barringer Crater in Arizona and we show the same relationship also holds for Tswaing Crater in South Africa. We present models of crater growth in which excavation creates a “stellate” transient cavity that is concave-cuspate in planform. These models reproduce the “lenticular-crescentic” layering pattern in the walls of some polygonal impact craters such as Endurance and Barringer Craters, and suggest a common origin for tear faults and some crater rays. We also demonstrate a method for detailed error analysis of stereogrammetric measurements of bedding plane orientations.  相似文献   

Incorporating Parameter Variability in Rock Mechanics Analyses: Fuzzy Mathematics Applied to Underground Rock Spalling     

John P. Harrison  John A. Hudson 《Rock Mechanics and Rock Engineering》2010,43(2):219-224

Although fuzzy analysis has been widely developed, its use in rock mechanics and rock engineering is limited. Here, it has been used to evaluate the potential for underground rock spalling at the boundary of a circular excavation in terms of rock strength and in situ rock stress, given the uncertainty in both of these input parameters. Using standard techniques from fuzzy mathematics, we develop an expression for the fuzzy factor of safety, and extend this to form the crisp parameters Safety Certainty Value and its complement, the Failure Certainty Value. Plots of the Failure Certainty Value in terms of the in situ stress ratio and rock strength/stress ratio show the effect of uncertainty on the assessment of stability. From these plots, we illustrate how the relative importance of uncertainty in the input parameters can be assessed, with the associated ramifications for site investigation and subsequent engineering design.  相似文献   

IUGS Commission on Geoscience Edoucation, Training and Technology Transfer （COGE） http ：//www.geoed.com.au/IUGSeducation/indexcomm.html     

Gary Lewis Wesley Hill 《《幕》》2006,29(4):310-311

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