Messinian salinity crisis regulated by competing tectonics and erosion at the Gibraltar arc

The Messinian salinity crisis (5.96 to 5.33 million years ago) was caused by reduced water inflow from the Atlantic Ocean to the Mediterranean Sea resulting in widespread salt precipitation and a decrease in Mediterranean sea level of about 1.5 kilometres due to evaporation. The reduced connectivity between the Atlantic and the Mediterranean at the time of the salinity crisis is thought to have resulted from tectonic uplift of the Gibraltar arc seaway and global sea-level changes, both of which control the inflow of water required to compensate for the hydrological deficit of the Mediterranean. However, the different timescales on which tectonic uplift and changes in sea level occur are difficult to reconcile with the long duration of the shallow connection between the Mediterranean and the Atlantic needed to explain the large amount of salt precipitated. Here we use numerical modelling to show that seaway erosion caused by the Atlantic inflow could sustain such a shallow connection between the Atlantic and the Mediterranean by counteracting tectonic uplift. The erosion and uplift rates required are consistent with previous mountain erosion studies, with the present altitude of marine sediments in the Gibraltar arc and with geodynamic models suggesting a lithospheric slab tear underneath the region. The moderate Mediterranean sea-level drawdown during the early stages of the Messinian salinity crisis can be explained by an uplift of a few millimetres per year counteracted by similar rates of erosion due to Atlantic inflow. Our findings suggest that the competition between uplift and erosion can result in harmonic coupling between erosion and the Mediterranean sea level, providing an alternative mechanism for the cyclicity observed in early salt precipitation deposits and calling into question previous ideas regarding the timing of the events that occurred during the Messinian salinity crisis.     

盐和过氧化氢胁迫下交替氧化酶调节根生长和细胞死亡

用不同浓度的NaCl或外源过氧化氢(H_2O_2)溶液处理野生型(WT)拟南芥和交替氧化酶(alternative oxidase,AOX)基因反义抑制突变体(AS-12)拟南芥,发现随NaCl和过氧化氢浓度的增加,两种拟南芥幼根生长速率降低,且出现了明显的细胞死亡。在50和100 mM NaCl或在50 mM H_2O_2处理下,与WT植株相比,AS-12植株幼根的生长速率更低,且组织的细胞死亡程度也更加明显。150 mM NaCl或100及200 mM H_2O_2处理导致AS-12与WT幼根的生长停止和严重的细胞死亡,但两种植株幼根在生长速率和细胞死亡程度上无明显差别。以上实验结果说明交替氧化酶在一定水平的盐胁迫和氧化压力下能够影响幼根的生长和细胞死亡的发生。     

Confronting the coral reef crisis

The worldwide decline of coral reefs calls for an urgent reassessment of current management practices. Confronting large-scale crises requires a major scaling-up of management efforts based on an improved understanding of the ecological processes that underlie reef resilience. Managing for improved resilience, incorporating the role of human activity in shaping ecosystems, provides a basis for coping with uncertainty, future changes and ecological surprises. Here we review the ecological roles of critical functional groups (for both corals and reef fishes) that are fundamental to understanding resilience and avoiding phase shifts from coral dominance to less desirable, degraded ecosystems. We identify striking biogeographic differences in the species richness and composition of functional groups, which highlight the vulnerability of Caribbean reef ecosystems. These findings have profound implications for restoration of degraded reefs, management of fisheries, and the focus on marine protected areas and biodiversity hotspots as priorities for conservation.     

基于根系形态的根系固坡作用数值分析

将土体、根系作为一个复合的整体,选择典型护坡植物夹竹桃为对象,利用非线性有限元计算方法研究在雨水侵蚀力和坡面径流侵蚀力作用下,不同分布密度和不同侧根数量的根系对边坡表层土体稳定性的影响。结果表明,在降雨条件下,植物根系的存在能有效提高边坡表层土体整体刚度,随着根系的侧根数量和植株分布密度的增大,边坡表层位移量逐渐减小,雨水对边坡表层土体的侵蚀也逐渐减小,从而使边坡表层土体稳定性提高。     

陷入泥沼的第一步--"东京湾事件"始末

1964年,美国为了控制整个东南亚地区,派遣军舰到东京湾(即北部湾)地区执行所谓的水文地理研究任务。在与越南鱼雷艇遭遇时,率先开火发起攻击,然后又在第二天再次来到这一海域,并声称又一次遭到袭击。美国蓄意制造了“东京湾事件”,挑起战争,开始直接参与越南战争。但这处心积虑的第一步,却迈进了一个满是淤泥的沼泽。     

非负矩阵Perron根的计算

非负矩阵最大特征值即Perron根的计算是非负矩阵理论的重要课题.本文利用非负矩阵Perron余的有关性质,给出一种可以得到比较精确的Perron根的方法.并利用该方法给出MATLAB的算法及程序,实现了计算机编程求解非负矩阵的Perron根.最后,通过实例说明本文的方法是有效的.     

金融危机中企业受波及的数学模型

根据金融实际,对金融危机中企业受波及的数学模型进行了分析,建立了在金融危机中企业受到波及恢复正常后还有可能再次受到波及的一般情况的数学模型,即类似传染病中无免疫型的数学模型,并对模型进行了经济解释以及考虑金融危机中会有新的企业产生,企业由于其他的原因可引发破产倒闭的因素,对模型做了进一步的推广.     

危机营销及其对平顶山相关企业的启示

在竞争越来越激烈的今天,企业会遇到越来越多的难以防范的危机.危机的应对措施得当与否,直接影响着企业的生存.分析危机原因可以为平顶山相关企业提供防范危机的战略和解决方案.     

长江河口盐度监测布局研究

长江河口盐度监测是管理河口淡水资源与保障城市用水安全的重要基础工作之一,观测资料为水库取水调度、沿岸涉水工程的规划等提供依据.架设于河口区域的水文监测站及浮标是长江河口长时间序列盐度资料的主要来源,对研究长江河口整体上的盐度分布和输运过程、指导水库安全调度等具有重要的科学意义和应用价值.通过数值模拟结果和观测资料,分析了长江河口盐度分布的时空变化规律,并结合长江口盐度站网功能需求分析与监测要素,提出长江河口盐度监测站点布局的思路,对河口盐度监测的整体性、空间均衡性和对重点研究区域的站点架设进行科学合理的规划.     

深层搅拌桩在深基坑支护工程中的应用

介绍了搅拌桩在南京某复杂土层围护工程中的应用,探讨了质量控制和局部构造措施,指出搅拌桩支护的优势.     

关于根幂为根的多项式

设n次多项式f(x)的n个根为a1,a2…an,k为正整数,设φ（x）的n个根为a1^k,a2^k…,an^k,本文得到了φ（x）的两个表达式。     

关于模p原根的分布

设p为奇素数 ,k为整除p- 1的正整数 .研究了模p的k次剩余的分布性质 ,并给出一个有趣的渐近公式