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451.
Meteoroids that orbit the Sun encounter the Earth with speeds between 11 and 74 km/sec. However, the distribution of the velocities of meteoroids between these limits is not well known. The uncertainty is caused by the difficulty in measuring the true flux of meteors at the extrema of the velocity distribution. Whilst the most comprehensive measurements of meteor flux are those obtained using radio techniques, meteors with speeds > 50 km/sec occur at heights where the effects of initial radius of the trail and diffusion significantly reduce the radio reflection from the trails; on the other hand the high dependence of the collisional ionization probability on velocity (to the power 3.5) significantly inhibits the detection of meteors with speeds < 20 km/sec. Recent developments in meteor radar systems are now making it possible to measure the velocity of meteors at the extrema of the distribution. For meteoroids ablating at heights between 100 and 120 km the speed of entry can be measured at 2 and 6 MHz using a radar with a 1 km diameter array located near Adelaide; these observations will commence early in 1995. In the meantime a 54 MHz MST radar is being operated at a pulse repetition frequency of 1024 Hz to search for the presence of interstellar (speed > 74 km/sec) meteors. Both these radars exploit the phase information available prior to the closest-approach (to) point. 相似文献
452.
We have calculated the response functions for the Springhill (Ottawa) and Christchurch (New Zealand) radars. Using the sizes and locations of each of the six sporadic radio-meteor sources found in our previous study (Jones and Brown, 1993), we have determined the response of each radar to each of the sources. Then, using least-squares fit to data collected over several years, we have determined the strength of each source. Excellent agreement with the non-radar data is obtained for the total flux after application of a correction for the initial train radius. The results from the two radars show good consistency for the sources which are visible to both of them. For individual years the fits are good to between 5 and 10% but there does appear to be some variability from year to year which may be due to atmospheric effects.
Presented at theInternational Conference on Meteoroids 28–31 August 1994 in Bratislava.Submited to Earth, Moon and Planets 相似文献
453.
The wave height distribution with Edgeworth’s form of a cumulative expansion of probability density function (PDF) of surface elevation are investigated. The results show that a non-Gaussian model of wave height distribution reasonably agrees with experimental data. It is discussed that the fourth order moment (kurtosis) of water surface elevation corresponds to the first order nonlinear correction of wave heights and is related with wave grouping. 相似文献
454.
月相对江南春雨年际变率的可能影响 总被引:1,自引:0,他引:1
验证华南气候谚语“六月逢双暑,有米无柴煮”的符号正确率达到90%,其内部隐含的物理本质可能反映的是月球相对于地球的位相(月相)的年际变化对华南前汛期降水的影响。将其推广到一般情况,求得月相与华南前汛期降水以及江南春雨的相关分布图,表明相关显著,特别是与江南春雨的关系更为密切。计算了月相与江南春雨的30年滑动相关,发现该相关具有很高的稳定性。小波分析表明两者具有相同的2~3年显著周期,说明它们之间内部可能存在物理联系。因此,月相可以作为江南(华南)预测春季(前汛期)降水的一个重要的预报参考判据。月相对降水影响的内部物理机制目前尚不清楚,可能是日月的引潮力的年际变化引起的。 相似文献
455.
针对近年来煤田地质单位设备管理的状况,阐述设备管理工作在经济建设中的重要地位,提出了强化设备管理的思路。 相似文献
456.
457.
Alain Plouffe 《Environmental Geology》1998,33(2-3):183-196
Abundant cinnabar (HgS) mineralization is associated with the Pinchi Fault in central British Columbia. Two formerly producing
mercury mines have been developed on this fault: Pinchi and Bralorne Takla. The mercury content of till (a sediment type directly
deposited by glaciers) in the area of this fault is primarily controlled by the occurrence of cinnabar mineralization in bedrock
and the direction of ice flow. Cinnabar-bearing bedrock was eroded by glaciers, transported in the direction of ice flow,
and deposited "down-ice" from its source. An example of such a dispersal train is documented for the Pinchi Mine area where
mercury ore was transported over a distance of 12 km, as measured in the clay-sized fraction (< 0.002 mm) of till, and could
have been transported over 24 km according to heavy mineral concentrates (specific gravity >3.3) of this same sediment. Antimony,
chromium, and nickel dispersal trains were also detected in the region. These data indicate that natural glacial processes
can result in the "mobilization" of metals in the surficial environment, a factor which has to be considered at mine sites
in glaciated terrain, where mine reclamation and remediation measures are now required.
Received: 31 October 1996 · Accepted: 27 May 1997 相似文献
458.
459.
Introduction To the impact pattern, the dynamic test with high strain is generally grouped into two kinds.One is stricken by hammer and another is by rocket. The former is widely used and the latter isused widely abroad and seldom used at home. To the analyzing method, it is also divided into twokinds. One is the method of wave equation and another is the method of experimental formula.The methods of Smith, Case and Capwap and other improved methods belong to the former, andthe methods … 相似文献
460.
运用台风移动涡旋影响域统计分析动态区域序列概念,采用 3个目标台风卫星TBB资料 ,对台风螺旋云带波列结构特征进行了功率谱合成分析。研究结果揭示出台风涡旋中心与周 边区域对流云的相关场呈螺旋带波状特征;台风影响域螺旋波亦表现出显著次天气、中尺度 波动特征,其波动周期尺度及其传播相速可类似重力内波与涡旋Rossby波,即周期呈双峰特 征,为大于6h与24h左右时间尺度;螺旋波高、低空流型特征与台风的维持、发展结构特征 相关;扰动TBB场时间偏差分布呈类似涡旋Rossby波螺旋波列,其波列路径与涡 旋Rossby波传播特征相似,并提出了台风涡旋螺旋波结构模型。 相似文献