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831.
1 IntroductionOpenclustersareidealtargetswithwhichtoinvestigatethestructureandevolutionoftheGalacticdiskaswellastheformationandevolutionofstarsandstellarclusters.Thereareabout1 ,2 0 0knownopenclustersintheCatalogueofOpenClusterData (Lynga 1 987) .Inspiteofmany… 相似文献
832.
Clockwise rotations recorded in Early Cretaceous rocks of South Korea: implications for tectonic affinity between the Korean Peninsula and North China 总被引:12,自引:0,他引:12
Xixi Zhao Robert S. Coe Ki-Hong Chang Soon-Ok Park Sheraz K. Omarzai Rixiang Zhu Yaoxiu Zhou Stuart Gilder & Zhong Zheng 《Geophysical Journal International》1999,139(2):447-463
Recent interest has focused on whether South Korea may have undergone variable tectonic rotations since the Cretaceous. In an effort to contribute to the answer to this question, we have completed a palaeomagnetic reconnaissance study of Early Cretaceous sedimentary and igneous rocks from the Kyongsang basin in southeast Korea. Stepwise thermal demagnetization isolated well-defined characteristic magnetization in all samples. The palaeomagnetic directions reveal patterns of increasing amounts of clockwise (CW) rotation with increasing age for Aptian rock units. Palaeomagnetic declinations indicate clockwise vertical-axis rotations of R = 34.3° ± 6.9° for the early Aptian rock unit, R = 24.9° ± 10.6° for the middle Aptian, and R = −0.9° ± 11.8° for the late Aptian relative to eastern Asia. The new Cretaceous palaeomagnetic data from this study are consistent with the hypothesis that Korea and other major parts of eastern Asia occupied the same relative positions in terms of palaeolatitudes in the Cretaceous. An analysis of and comparison with previously reported palaeomagnetic data corroborates this hypothesis and suggests that much of Korea may have been connected to the North China Block since the early Palaeozoic. A plausible cause of the rotation is the westward subduction of the Kula plate underneath the Asian continent, which is inferred to have occurred during the Cretaceous according to several geological and tectonic analyses. 相似文献
833.
This paper briefly examines the current position in absolute and exterior orientation and highlights some of the limitations of existing techniques. An alternative system for performing absolute orientation and, potentially, exterior orientation is introduced. Some preliminary tests have given encouraging results. 相似文献
834.
A brief error analysis associated with the use of the new method to determine the zero-plane displacement proposed by De Bruin and Verhoef has been performed. It is shown that use of temperature fluctuation data is more suited to determining the zero-plane displacement data over a heterogeneous surface. 相似文献
835.
The rate of Ostwald ripening of forsterite is experimentally measured in a haplobasaltic melt (SiO2–Al2O3–CaO–MgO). The goal of the experiments is to determine if the rate of Ostwald ripening is sufficient to affect textural development in crystallizing magmas of a basaltic composition. With preequilibrated charges, experiments were run isothermally so that all textural changes could be ascribed to Ostwald ripening. An increase of crystal size from 3.5 μm to 14 μm (in average) has been observed during 10 days. Glass compositions were identical in all charges, indicating that the observed increase in average crystal size is not the results of chemical disequilibrium but the results of Ostwald ripening. Due to the constraints on experimental duration, the rate-limiting process (i.e., diffusion control or reaction control) could not be determined. Our experimental results, however, demonstrate that the rate of Ostwald ripening in basaltic rocks is sufficient to be of fundamental importance in the development of textures in igneous rocks. These results strongly suggest that Ostwald ripening, as well as nucleation and crystal growth, should be considered in analyses of textures in igneous rocks. 相似文献
836.
837.
In order to identify the distribution of aluminium (Al) within an acid hillslope and its release to a stream, the spatial distribution of acid ammonium oxalate extractable Al (Alo) and exchangeable Al3+ have been investigated on a podzolized hillslope in Bicknoller Combe, Somerset, UK. The eluviated Al from topsoils is mainly deposited in the lower soil horizons forming podzolic B horizons, but some Al flows downslope carried by lateral throughflow. Al oxides may provide the main source of exchangeable Al3+ on the study slope due to high soil acidity. Examination of the spatial distribution of exchangeable Al3+ suggests that the slope hollow, where active convergent throughflow occurs, and the saturation wedge at the base of the slope are the main delivery routes of dissolved Al3+ to the stream. Divalent base cations (Ca2+ and Mg2+), supplied from atmospheric input and organic decomposition and carried by throughflow, exchange Al3+ via cation exchange reactions under high water content. Laterally illuviated Al oxides in the lower hollow adjacent to the saturation wedge probably provide a pool for continuous delivery of Al either as soluble or complexed forms to the stream via the saturated wedge. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
838.
Park Heon-Joon Ko Kil-Wan Song Young-Hun Song Myung-Jun Jin Seokwoo Ha Jeong-Gon Kim Dong-Soo 《Acta Geotechnica》2020,15(9):2637-2648
Acta Geotechnica - A disconnected piled raft (DPR) foundation has been introduced as an effective pile design to reduce the vertical loading experienced by the pile. The characterization of DPRs... 相似文献
839.
Young-Gyu Park Kyung-Hee Seol Kyung-On Boo Johan Lee Chunho Cho Young-Hwa Byun Seongbong Seo 《Ocean Science Journal》2018,53(3):437-448
This modeling study investigates the impacts of increasing atmospheric CO2 concentration on acidification in the East Sea. A historical simulation for the past three decades (1980 to 2010) was performed using the Hadley Centre Global Environmental Model (version 2), a coupled climate model with atmospheric, terrestrial and ocean cycles. As the atmospheric CO2 concentration increased, acidification progressed in the surface waters of the marginal sea. The acidification was similar in magnitude to observations and models of acidification in the global ocean. However, in the global ocean, the acidification appears to be due to increased in-situ oceanic CO2 uptake, whereas local processes had stronger effects in the East Sea. pH was lowered by surface warming and by the influx of water with higher dissolved inorganic carbon (DIC) from the northwestern Pacific. Due to the enhanced advection of DIC, the partial pressure of CO2 increased faster than in the overlying air; consequently, the in-situ oceanic uptake of CO2 decreased. 相似文献
840.
Sangil Kim Suk Hyun Youn Hyun-Ju Oh Sun Kyeong Choi Yun Hee Kang Tae-Hoon Kim Hyuk Je Lee Kwang-Sik Choi Sang Rul Park 《Ocean Science Journal》2018,53(3):595-600
We conducted testing to determine whether stipe length is a useful indicator of reproductive maturity in the kelp Ecklonia cava, a species that plays a pivotal role in ecosystem functioning and services in subtidal areas. Approximately 100 sporophytes with stipes of various lengths were collected during the fertile period (July–November, 2013). We investigated the relationships between stipe length and other morphological characteristics to determine whether stipe length could indicate the age of reproductive maturity. Primary blade length, longest blade length, thallus height, and total length showed significant relationships with stipe length. The length of the primary and longest blades gradually declined as stipe length increased above 125 mm. Zoosporangial sori were found on the blades of more than 70% of individuals with stipes longer than 125 mm, but on only 8% of individuals with stipes less than 125 mm long. Stipe length therefore seems to be an acceptable proxy for reproductive maturity. Another factor to consider, however, is that all specimens with zoosporangial sori, regardless of stipe length, had a dry weight of 80 g or more; thus, individual biomass may also be an important parameter influencing the initiation of reproduction. 相似文献