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951.
本文通过对福建及其周边地区地震活动人工神经网络模型的构建,研究了人工神经网络方法在基于该区域地震活动性指标的地震分析预报中的应用。选用含一个中章层的前向神经网络模型,并采用与之相适应的BP算法,以该地区1971~1997年的地震活动性资料为基础,用神经网络进行实际计算、分析和检验。结果表明:神经网络模型对福建及其周边地区地震震级的预测检验效果较好的,可以在一定精度范围内使震级预测的内符率达100% 相似文献
952.
953.
L. C. Watson J. B. Hearnshaw K. R. Pollard P. M. Kilmartin A. C. Gilmore 《Monthly notices of the Royal Astronomical Society》2000,315(1):69-76
The star HD 6628, heretofore classified as a G5 subgiant, is shown to be a chromospherically active single-lined spectroscopic binary with a period of 27.332±0.008 d. From high-resolution spectra, the system is found to consist of a late F-type dwarf and an active G8–K1 bright subgiant, the latter having a rotation period of not more than 14.8±3.8 d derived from the width of metal lines. Further stellar and orbital parameters are derived and presented. 相似文献
954.
955.
江淮流域大洪水的发生规律探讨 总被引:7,自引:3,他引:4
对江淮流域的大洪水进行分析 ,得出如下三点新的认识 :(1)在太阳黑子活动的峰谷年前后 ,江淮流域一般容易出现大洪水 ;(2 )在太阳黑子活动的磁周期转变年前后 ,江淮流域容易出现大洪水 ,甚至是特大洪水 ;(3)在太阳黑子活动磁周期转变年前后的厄尔尼诺同年或次年 ,江淮流域更容易出现大洪水 ,甚至是特大洪水。这些认识可以为长期及超长期的洪水预报提供一定的理论依据。 相似文献
956.
957.
Lake Rotoiti in Taupo Volcanic Zone was formed by damming of the drainage system through the floor of Okataina Caldera. Basin sediments are predominantly silt or sand, with mineralogy consistent with derivation from local silicic rocks and airfall tephras. Sandy lithofacies around the shoreline are wave worked deposits. Sand and gravel lithofacies in deeper water and on steep slopes are largely relict or airfall tephras, or both. Profundal sediments are diatomaceous silts. Organic-rich diatomaceous silts also accumulate in near-shore wave-damped zones under weed beds.Short cores penetrated the Tarawera (1886 AD) and Kaharoa (1180 AD) Tephras, identified by their stratigraphic position, geochemistry and mineralogy. Localised slumping is evidenced from secondary tephras interbedded and redeposited within the basin silts. Sedimentation rates in the basins, estimated from the age of bounding tephras, are 0.9 to 4.0 mm y-1, and are highest under the influence of inflowing water from adjacent Lake Rotorua. For several hundred years prior to the Tarawera eruption sediment accumulation rates and the sediment geochemistry remained unchanged; deposition was predominantly biogenic opaline silica with a small terrestrial component. The Tarawera eruption deposited a terrestrial-silica, aluminum-rich primary tephra across the lake, which was followed by reworked tephra from within the catchment, the effects of which were progressively diluted by biogenic opaline silica as conditions stabilised. While the major effects of the eruption have been rapidly absorbed the lake has not returned to pre-eruption background conditions. A new equilibrium has been attained in which Tarawera Tephra continues to be eroded into the lake and is the principal source for a doubling of sedimentation rates following the eruption. High arsenic levels in some diatomaceous silts are attributed to episodic venting of hydrothermal fluids or gases into the water column. 相似文献
958.
本文对太阳活动第21周、22周(1976年—1992年间)97个质子活动区进行统计分析,包括活动区的面积、型别、磁结构、半影纤维等,结果表明:75%的质子耀斑产生于面积为500≤Sp≤3000单位的黑子群中;耀斑爆发前一天及后一天活动区面积有显著减少;质子活动区含δ复杂磁结构的占70%;具有半影旋涡形态的质子活动区中,约77%的耀斑发生在旋涡黑子出现以后。 相似文献
959.
本文讨论了第22太阳活动周的下列重要特点:1.呈现双峰,并在双峰期的槽中又突起孤立的单峰。2.黑子面积峰值滞后相对数峰值的仅占16.67%;黑子面积与相对数同步占58.33%;二者峰值不能对应占25%。3.1986年10月以后,纬度≥30°的有半影的黑子群共出现87群;延迟在峰年期间出现的有53群,占60.92%;对应有M级以上X射线爆发的活动区18个,占20.69%。这一现象与“蝴蝶图”规律不符。 相似文献
960.
K. Urushibara-Yoshino 《Environmental Geology》1996,28(3):154-160
The properties of soils on previously dated sand dunes from Robe to Naracoorte in South Australia were examined. In these
areas younger sand dunes are composed of fresh sand, but older sand dunes are composed of calcarenited sand. The soils on
the sand dunes developed successionally by the age of sand dunes. The soil properties of these sand dunes differ depending
on the ages of the sand dunes. The properties of sand particles in soils are as follows:
(1) On the sand dunes of 4300 years B.P., A/C profile developed (Rendzina). On the sand dunes older than 125 000 years B.P.
and on the plateau of Tertiary limestone, soil profiles of A1/AB/B/C on the sand dunes of 83 000 years B.P. and A1/A3/B1/B2/C (Terra rossa) are well developed.
(2) Within the sand of A/C horizons of the sand dunes with the age of 4300 year B.P., the calcite grain content is about 64%,
and the quartz content is about 35%. Within the B horizons of soils on the dunes from 83 000 years B.P. to 347 000 years B.P.,
the calcite grain content is only 1–2%; however, the quartz grain content is about 92%. In the B2 horizons of soils on the dune of 690 000 years B.P. and on the Tertiary plateau, there are some calcite grains but the quartz
grain content is about 96%.
(3) The average size of quartz grains in the soils on the sand dunes from 4300 B.P. to 347 000 years B.P. is generally smaller,
but the average size of quartz on the sand dunes of 690 000 year B.P. becomes larger and the grains are well rounded. On the
Tertiary limestone plateau, the average quartz size becomes again smaller, and the grains are more rounded.
(4) Fet in B2 horizon of the soil profiles increases clearly corresponding to the age. Iron activity expressed by Feo/Fed also shows a close relation to the chronological sequence. The B horizon of the soil profiles shows a drastic decrease of
Feo/Fed according to the age. Iron crystalinity, (Fed-Feo)/Fet, has a tendency for a positive relation with increasing age.
Received: 1 June 1995 · Accepted: 4 December 1995 相似文献