Early solar system aqueous activity: K isotope evidence from Allende     

Yun Jiang  Piers Koefoed  Olga Pravdivtseva  Heng Chen  Chun‐Hui Li  Fang Huang  Li‐Ping Qin  Jia Liu  Kun Wang 《Meteoritics & planetary science》2021,56(1):61-76

The alkali element K is moderately volatile and fluid mobile; thus, it can be influenced by both primary processes (evaporation and recondensation) in the solar nebula and secondary processes (thermal and aqueous alteration) in the parent body. Since these primary and secondary processes would induce different isotopic fractionations, K isotopes could become a potential tracer to distinguish them. Using recently developed methods with improved precision (0.05‰, 95% confidence interval), we systematically measured the K isotopic compositions and major/trace elemental compositions of chondritic components (18 chondrules, 3 CAIs, 2 matrices, and 5 bulks) in the carbonaceous chondrite fall Allende. Among all the components analyzed in this study, CAIs, which formed initially under high‐temperature conditions in the solar nebula and were dominated by nominally K‐free refractory minerals, have the highest K₂O content (average 0.53 wt%) and have K isotope compositions most enriched in heavy isotopes (δ⁴¹K: ?0.30 to ?0.25‰). Such an observation is consistent with previous petrologic studies that show CAIs in Allende have undergone alkali enrichment during metasomatism. In contrast, chondrules contain lower K₂O content (0.003–0.17 wt%) and generally lighter K isotope compositions (δ⁴¹K: ?0.87‰ to ?0.24‰). The matrix and bulks are nearly identical in K₂O content and K isotope compositions (0.02–0.05 wt%; δ⁴¹K: ?0.62 to ? 0.46‰), which are, as expected, right in the middle of CAIs and chondrules. This strongly indicates that most of the chondritic components of Allende suffered aqueous alteration and their K isotopic compositions are the ramification of Allende parent‐body processing instead of primary nebular signatures. Nevertheless, we propose the small K isotope fractionations observed (< 1‰) among Allende components are likely similar to the overall range of K isotopic fractionation that occurred in nebular environment. Furthermore, the K isotope compositions seen in the components of Allende in this study are consistent with MC‐ICP‐MS analyses of the components in ordinary chondrites, which also show an absence of large (10‰) isotope fractionations. This is not expected as evaporation experiments in nebular conditions suggest there should be large K isotopic fractionations. Nevertheless, possible nebular processes such as chondrules back exchanging with ambient gas when they formed could explain this lack of large K isotopic variation.  相似文献   

平面不规则基础隔震结构抗扭设计研究   总被引：1，自引：0，他引：1       下载免费PDF全文

黄小宁  王威  王宁  杜永峰 《地震工程学报》2020,42(5):1283-1288

针对平面不规则结构在水平地震作用下的振动特性，通过调整隔震层隔震支座的布置，得到3种不同工况的隔震层刚心与上部结构质心、刚心相对位置关系，分别以楼层位移和层间位移为指标的扭转位移比，作为平面不规则基础隔震结构扭转响应指标，利用弹塑性时程分析方法，通过对3种不同工况的扭转指标对比分析研究，提出适用于平面不规则基础隔震结构的抗扭设计方法。结果表明：对于平面不规则结构，应在保证隔震层扭转位移比小于1.2的基础上，使隔震层的刚心和上部结构的刚心分别位于上部结构质心的两侧，可有效控制上部结构的扭转。  相似文献   

黑河中游夏季昼夜水汽同位素特征及水汽来源分析          下载免费PDF全文

孟鸿飞  张明军  王圣杰  邱雪  杜铭霞  张亚宁  余秀秀  周苏娥 《干旱区地理》2020,43(2):360-370

基于2012年6~8月的实测水汽同位素数据及相关气象数据，对黑河中游夏季昼夜的同位素基本特征、水汽来源方向及潜在蒸发源地进行了研究。结果表明：空气水汽线斜率白天大于夜晚和水汽过量氘值白天大于夜晚，综合说明白天局地蒸发较夜晚强烈；夏季受西风水汽影响显著。其中，6月主要受西风水汽和北冰洋水汽影响，7、8月主要受西风水汽和东南方向水汽影响，且8月受东南方向水汽影响最为明显；水汽运移路径上下垫面地形和气压带移动会影响水汽后向轨迹高度，西北方向上水汽输送通道较顺畅，风速较大，有利于水汽的输送；水汽蒸发源地主要集中在研究区周围及以东、以北部，其次是西北部。绿洲是主要的水汽蒸发源地，其次是城市和河流，白天较夜晚局地蒸发强烈且面积大。  相似文献   

游客-环境互动视角下旅游者目的地环境恢复性效应     

朱芳  苏勤  陶云  沈惊宏 《热带地理》2020,40(4):636-648

日常生活环境和旅游目的地环境都可以为个体提供恢复的机会，不同环境的属性特征导致不同程度的恢复。为了探究环境类型与恢复性效应之间的关系及停留时间的调节作用，文章采用问卷调查方式，利用配对样本t检验和混合设计方差分析相结合的方法，探讨游客在不同环境中的恢复性效应，并对这一现象提供心理上的解释。结果表明：1）恢复体验的4个维度（放松体验、心理脱离、掌握体验、控制体验）在旅游目的地环境中的得分均高于日常生活环境。2）掌握和控制体验维度在城市旅游目的地中的变化程度高于乡村旅游目的地，两种类型目的地的放松和心理脱离维度差异较小。3）随着在目的地停留时间的延长，乡村旅游目的地放松体验和心理脱离维度变化程度高于城市旅游目的地，两种类型目的地环境恢复性效应会相互靠近。因此，游客的环境恢复性效应不仅受到环境和目的地类型的影响，同时还与游客的适应程度有关，且受到其停留时间的调节作用。  相似文献   

Salinivibrio sp.YH4胞外丝氨酸蛋白酶EYHS耐盐性及生物信息学分析          下载免费PDF全文

武翠玲  宋英达  高慧芳  张廉芸  任晨霞 《盐湖研究》2020,28(1)

摘要：目的 探讨菌株Salinivibrio sp.YH4分泌的丝氨酸蛋白酶EYHS的耐盐性及结构特征。方法 明胶底物酶谱法分析EYHS的耐盐性。应用生物信息学手段对EYHS及6种耐盐的S8家族丝氨酸蛋白酶结构特征进行分析。结果 EYHS在4 mol/L的NaCl溶液中仍具有活性，属于耐盐蛋白酶。EYHS及6种S8家族丝氨酸蛋白酶分子表面的loop区等无规则卷曲所占比例较高，α-螺旋与β-片层则主要位于酶分子内部。EYHS分子表面酸性氨基酸含量较高，且具有弱疏水内核。多序列比对发现蛋白酶的催化三联体两侧存在高度保守的基序和保守的极性氨基酸及芳香族氨基酸，并存在多个保守的Gly与Ala。同源模建和表面电荷分布显示，α螺旋和β片层围成了蛋白酶的催化腔，EYHS活性中心包含由Asp32、His65与Ser215组成的催化三联体，且催化位点区域表面静电势为负。结论 上述结构特征可能有助于耐盐丝氨酸蛋白酶EYHS在高盐环境下维持其稳定性和适度柔性，并有助于其催化功能的发挥，为深入研究耐盐丝氨酸蛋白酶的高盐环境适应性提供了一定的理论依据。  相似文献   

Correspondence between the large volcanic eruptions and ENSO events over AD 1525–2000     

Fang  Xiuqi  Zheng  Xue  Zhang  Xing 《地理学报(英文版)》2020,30(1):103-118

ENSO is an interannual mode which may be affected by external forcing, such as volcanic eruptions. Based on the reconstructed volcanic eruptions chronology and ENSO sequences, both 195 large volcanic eruptions(VEI≥4) and 398 ENSO(El Ni?o and La Ni?a) events were extracted from 1525 to 2000. An analysis of the correspondence between the large volcanic eruptions and ENSO events was performed by matching the large volcanic eruptions with the types and magnitudes of ENSO events present in the 0–2 years after the eruptions. The results show the following:(1) The percentages of ENSO events within the 3 years after the large eruptions had increased to 68.3% from 31.7% compared with those with no-eruptions in the previous 0–2 years. In addition, the ratio of El Ni?o to La Ni?a events turned from 2:3 to 1:1, and more El Ni?o events occurred in the 0 year after eruptions in the low-latitudes of the Northern Hemisphere and in the tropics but more La Ni?a events occurred in the 0 year after in the high-latitudes of the Northern Hemisphere and the Southern Hemisphere.(2) After the eruptions, the weak(W) El Ni?o events had increased by 8 percentage points and the very strong(VS) El Ni?o events had decreased by 10 percentage points; conversely, there was a decrease by 15 percentage points of the weak La Ni?a events and an increase by 11.4 percentage points of the very strong La Ni?a events. Specifically, the percentages of strong La Ni?a events increased to a peak at 1(+1) year after the eruptions.(3) The percentage of eruptions followed by single-year ENSO was the greatest. The percentage of ENSO events that occurred in the consecutive 2 years following an eruption was approximately equal to the percentage of events that occurred consecutively 3 years following an eruption, and both sets of ENSO magnitudes showed a decreasing trend.  相似文献   

城镇化与生态环境耦合的动态模拟——研究进展与展望     

崔学刚  方创琳  刘海猛  刘晓菲  李咏红 《地理学报(英文版)》2020,30(2):333-352

Urbanization and eco-environment coupling is a research hotspot.Dynamic simulation of urbanization and eco-environment coupling needs to be improved because the processes of coupling are complex and statistical methods are limited.Systems science and cross-scale coupling allow us to define the coupled urbanization and eco-environment system as an open complex giant system with multiple feedback loops.We review the current state of dynamic simulation of urbanization and eco-environment coupling and find that:(1)The use of dynamic simulation is an increasing trend,the relevant theory is being developed,and modeling processes are being improved;(2)Dynamic simulation technology has become diversified,refined,intelligent and integrated;(3)Simulation is mainly performed for three aspects of the coupling,multiple regions and multiple elements,local coupling and telecoupling,and regional synergy.However,we also found some shortcomings:(1)Basic theories are inadequately developed and insufficiently integrated;(2)The methods of unifying systems and sharing data are behind the times;(3)Coupling relations and the dynamic characteristics of the main driving elements are not fully understood or completely identified.Additionally,simulation of telecoupling does not quantify parameters and is not systemically unified,and therefore cannot be used to represent spatial synergy.In the future,we must promote communication between research networks,technology integration and data sharing to identify the processes governing change in coupled relations and in the main driving elements in urban agglomerations.Finally,we must build decision support systems to plan and ensure regional sustainable urbanization.  相似文献   

Satellite-based Estimates of Canopy Photosynthetic Parameters for an Alpine Meadow in Northern     

NIU Ben  HE Yongtao  ZHANG Xianzhou  SHI Peili  DU Mingyuan 《资源与生态学报(英文版)》2020,11(3):253-262

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海域地质岩心钻探关键技术分析与应用          下载免费PDF全文

杨芳 《探矿工程》2020,47(7):23-29

海域固体矿产资源勘探、开发是海洋开发和利用的重要组成部分。本文主要从钻探设备、工艺、安全等方面对海域地质岩心钻探工程技术进行分析，总结了相关技术措施：一是除依据地质要求选择常规钻探设备外，要依据海域环境特点，选择安全可靠的钻探平台；二是钻孔结构设计、钻进方法、冲洗液等均应符合海域特点和要求；三是必须坚持安全第一原则，编制安全应急预案等。通过山东莱州三山岛北部海域金矿勘探项目应用实例，证实了海域地质钻探工程技术的适应性。  相似文献   

郯庐断裂带肥东北部文集地区构造岩类型与构造变形分析     

袁芳  宋传中  LIN ShouF  石永红  李加好  李振伟  王微  王阳阳 《岩石学报》2020,36(2):601-620

位于郯庐断裂带中南部的肥东地区是郯庐断裂带内韧性剪切带出露的主体区域之一。本文从肥东北部文集地区的构造岩组成及其变形入手,通过详细的野外观测、室内显微构造变形分析来确定该地区构造变形的几何学形态及其涡度、有限应变、分维度、差异应力、应变速率等参数。研究区主要出露角闪岩相肥东变质杂岩,构造岩以糜棱岩和糜棱岩化片麻岩为主,岩石变形强烈。根据极摩尔圆法得到的运动学涡度值为0.729~0.870,指示区域内的韧性剪切活动以简单剪切为主。几何学形态上,肥东北部文集地区构造整体呈一背形展出,其枢纽走向NE-SW,轴面倾向SE,物质及变形强度等方面均表现出一定的规律和对称性。研究区内动态重结晶石英颗粒边界具有统计学上的自相似性,其分维值D在1.143~1.208之间,且自背形核部向两翼,颗粒粒径增大,分维值减小。差异应力Δσ介于17.86~55.18MPa之间,应变速率ε值在1.960×10^-13~7.330×10^-12s^-1之间,且背形核部差异应力和应变速率较两翼大,呈近似对称性分布。通过对比以上构造参数可以发现,区内差异应力和应变速率表现出一定的正相关性,自核部向两翼二者均呈减小趋势;动态重结晶石英颗粒则与应变速率呈负相关性,即核部颗粒细小、两翼增大。本文从几何学、运动学以及显微构造变形分析等方面对该区构造变形展开精细化研究,借此来分析肥东北部地区郯庐断裂带的构造形态和运动学特征,这对进一步认识郯庐断裂带的演化过程及构造模型的建立有着重要的意义。  相似文献