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821.
US regional and state migration data from the 1940s–80s, when members of the baby boom generation aged into their years of peak labor force mobility, suggest ways in which changing age composition regulates geographical mobility and interregional migration. Labor supply pressure plays a key role in the dynamics of the national migration system. A “delayed mobility” effect in the 1980s similar to the delayed fertility of the baby boom cohorts appears to be a result of the depressed rates of mobility experienced by members of this generation when they flooded regional labor markets with record numbers of entrants in the 1970s. Recent temporal shifts in age-specific volumes of interregional migration help predict the future pace of migration based upon the projected age distribution of the nation. 相似文献
822.
M. Matsumoto S. Wallis M. Aoya M. Enami J. Kawano Y. Seto N. Shimobayashi 《Journal of Metamorphic Geology》2003,21(4):363-376
A largely undocumented region of eclogite associated with a thick blueschist unit occurs in the Kotsu area of the Sanbagawa belt. The composition of coexisting garnet and omphacite suggests that the Kotsu eclogite formed at peak temperatures of around 600 °C synchronous with a penetrative deformation (D1). There are local significant differences in oxygen fugacity of the eclogite reflected in mineral chemistries. The peak pressure is constrained to lie between 14 and 25 kbar by microstructural evidence for the stability of paragonite throughout the history recorded by the eclogite, and the composition of omphacite in associated eclogite facies pelitic schist. Application of garnet‐phengite‐omphacite geobarometry gives metamorphic pressures around 20 kbar. Retrograde metamorphism associated with penetrative deformation (D2) is in the greenschist facies. The composition of syn‐D2 amphibole in hematite‐bearing basic schist and the nature of the calcium carbonate phase suggest that the retrograde P–T path was not associated with a significant increase or decrease in the ratio of P–T conditions following the peak of metamorphism. This P–T path contrasts with the open clockwise path derived from eclogite of the Besshi area. The development of distinct P–T paths in different parts of the Sanbagawa belt shows the shape of the P–T path is not primarily controlled by tectonic setting, but by internal factors such as geometry of metamorphic units and exhumation rates. 相似文献
823.
利用已知的统计结果对高红移类星体光谱进行MonteCarlo模拟,得到了UBVRI五色测光的色指数,并利用模拟的选择判据计算了选择效应函数,当2.4<z<3.0时,选择效应来自于与主序星的混淆;当z>3.0时,则是由于较暗的类星体与晚型矮星同时从U.B等颜色的图象上消失,导致可利用色指数的减少。 相似文献
824.
GPS是现代高科技,它采用微型接收机,可以实现快速定位并取得测量点的3维座标。这种新技术在数字化地质、提高找矿效果等方面,应用前景广阔,侧重介绍了ASHTECH GPS接收机在区域重力调查中,怎样建立基准站与流动观测站、数据的传输与预处理和测量点3维座标的换算,以及应用数据自动生成布格异常等值线图。这项新技术的使用完全可以满足1:20万区域重力调查的精度要求。 相似文献
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Laser ablation multi-collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) has become a valuable tool for the in situ measurement of the boron isotope composition of geological samples at high (tens to hundreds of μm) spatial resolution. That said, this application suffers from significant analytical challenges. We focus in this study on the underlying processes of two of the main causes for inaccuracies using this technique. We provide empirical evidence that not only Ca ions (Sadekov et al. 2019, Standish et al. 2019, Evans et al. 2021) but also Ar ions, that are reflected within the flight tube of the mass spectrometer, are the source for previously reported issues with spectral baselines. We also address the impact of plasma conditions on the instrumental mass fractionation as a source for matrix- and mass-load-related analytical biases. Comparing experimental data with the results of a dedicated release and diffusion model (RDM) we estimate that a close to complete (~ 97%) release of boron from the sample aerosol is needed to allow for consistently accurate LA boron isotope measurement results without the need for corrections. 相似文献
829.
HU Zhikai LI Yi LI Qi DIAO Yujie MA Xin LIU Hejuan FENG Guanhong WANG Fugang YU Qingchun 《《地质学报》英文版》2023,97(3):911-924
Gas breakthrough pressure is a key parameter to evaluate the sealing capacity of caprock, and it also plays important roles in safety and capacity of CO2 geological storage. Based on the published experimental results, we present numerical simulations on CO2 breakthrough pressure in unsaturated low-permeability rock under 9 multiple P-T conditions (which can keep CO2 in gaseous, liquid and supercritical states) and thus, a numerical method which can be used to accurately predict CO2 breakthrough pressure on rock-core scale is proposed. The simulation results show that CO2 breakthrough pressure and breakthrough time are exponential correlated with P-T conditions. Meanwhile, pressure has stronger effects on experimental results than that of temperature. Moreover, we performed sensitivity studies on the pore distribution index λ (0.6, 0.7, 0.8, and 0.9) in van Genuchten-Muale model. Results show that with the increase of λ, CO2 breakthrough pressure and breakthrough time both show decreasing trends. In other words, the larger the value of λ is, the better the permeability of the caprock is, and the worse the CO2 sealing capacity is. The numerical method established in this study can provide an important reference for the prediction of gas breakthrough pressure on rock-core scale and for related numerical studies. 相似文献
830.
我国相继在多个盆地陆相页岩油勘探中获得突破,展示了良好的发展前景。基于现阶段勘探认识,本文认为陆相页岩油富集主要条件是:(1)稳定且有规模和适宜热成熟度的富有机质页岩是重要物质基础,以TOC含量>2%,最佳为3%~4%、母质类型Ⅰ和Ⅱ1型为主,Ro>0.9%或更高(咸化环境0.8%);(2)有一定容积规模的微纳米孔隙且具脆性的多类储层是重要条件,页岩储层有效孔隙度宜>3%~6%;成岩阶段偏低时,纯页岩段不是中高熟页岩油富集段,致密砂岩和混积岩黏土含量宜<20%;成岩阶段高时,页岩黏土含量可高至40%左右;(3)滞留烃数量大且品质好是重要保证,以S1>2 mg/g为门限,最佳>4~6 mg/g;气油比>80 m3/m3,最佳150~300 m3/m3;(4)顶底板具封闭性保持超压且滞留足够多轻-中组分烃类。陆相页岩油分布特征是:(1)有外物质注入的深-半深湖相是页岩油主要富集区;(2)具备“四高... 相似文献