Epibenthic megacrustaceans from the continental margin, slope and abyssal plain of the Southwestern Gulf of Mexico: Factors responsible for variability in species composition and diversity     

Elva G. Escobar-Briones  Adriana Gaytn-Caballero  Pierre Legendre 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2667

The community structure of megacrustaceans (orders Lophogastrida, Isopoda, and Decapoda) collected in trawls on the continental margin, upper slope and abyssal plain of the southern Gulf of Mexico was studied to determine to what extent broad-scale variation in community composition and diversity was influenced by geographic regions environmental variability and depth. Trawls were collected in the Mexican Ridges, the Campeche Bank, and the Sigsbee abyssal plain. There was variability in species composition, density and diversity among geographic regions and along the depth gradient. A total of 106 species were identified and grouped in three orders; five infraorders, 40 families, and 70 genera. This study extends the known geographic ranges of the species Homolodromia monstrosa and Ephyrina benedicti. The largest number of species was recorded in the Mexican Ridges and on the upper continental shelf; lower values were found on the continental margin and in the abyssal plain. The largest densities were recorded on the continental margin in the Mexican Ridges. Megacrustaceans show in general low frequencies and low abundances in trawls, characterizing them as rare components of benthic assemblages. Contrary to an accepted paradigm about deep-sea biodiversity, the highest H′ diversity values were recorded in the Sigsbee abyssal plain, followed by values from the upper continental slope; diversity values were correlated with evenness. Canonical Redundancy analysis results showed a significant affinity to regions for 18 crustacean species; 33 species showed a significant affinity to both regions and depth zones within regions.  相似文献   

Mismatch between biological,exploitation, and governance scales and ineffective management of sea urchin (Paracentrotus lividus) fisheries in Galicia     

《Marine Policy》2015

The spatial structure of fishery resources influences stock dynamics and finally the fishery. Therefore, this aspect should be included as a key topic in the assessment and management of fisheries. The fishery of the sea urchin Paracentrotus lividus in Galicia has been used as case study to demonstrate how the mismatch between biological, fishery and management scales causes failures in the governance, giving rise to over-exploitation. P. lividus is spatially distributed in nested biological units: patches, micro-stocks, local populations and metapopulations. Fishing operations are local exploiting micro-stocks; however management units in Galician comprise usually more than one local population. This pattern allows the depletion of several micro-stocks without any short-term signals in the exploitation rates over the complete managed territory. Management units should be redefined according to the boundaries of the local populations. In addition, the implementation of reserve networks or a rotation system could allow to effectively managing the resource at a fine-scale. Any of both regulations could also compensate the inverse density dependence that regulates recruitment and fecundity in this species.  相似文献   

273.15 到 308.15 K下二元体系（LiCl-H2O 和 MgCl2-H2O）和三元体系（LiCl-MgCl2-H2O）的体积性质研究          下载免费PDF全文

戈海文  杨红军  王敏 《盐湖研究》2022,30(4)

用高精度振动管在 273.15 至 308.15 K 的温度范围内以 5 K 的间隔对两个二元系统（LiCl-H2O 和 MgCl2-H2O）和三元系统（LiCl-MgCl2-H2O）的密度进行了实验测定密度计。基于 Vogel-Fulcher-Tamman (VFT) 方程,对 LiCl(aq) 和 MgCl2(aq) 密度与温度和摩尔浓度的相关方程的系数进行了参数化。 Young的理想混合规则被成功地应用于基于相关的二元解性质关联三元系统的密度。根据二元和三元体系的体积特性数据,根据 Pitzer 离子相互作用理论,得到 Pitzer 单盐参数和混合离子相互作用参数。在本工作中确定了三元体系在恒定离子强度下的混合体积 (ΔVm)。  相似文献   

NH₄Cl水溶液的微观结构和宏观物性研究          下载免费PDF全文

张宇  李非  费莉婷  纪志永  赵颖颖  郭小甫  刘杰  王士钊  汪婧  毕京涛  张盼盼  张丁予  袁俊生 《盐湖研究》2022,30(4)

通过拉曼光谱、同步辐射X射线散射和密度泛函理论(DFT)模拟,研究了质量分数为1.0 %-28.0 %的NH₄Cl水溶液的微观结构变化。同时在室温下测量了粘度、接触角和电导率。由拉曼光谱和密度泛函理论模拟结果可知,当溶质浓度升高至10.0 %时,在2900 cm_-1^和3100 cm_-1^{附近出现了明显的}N-H作用峰,且随着质量分数的升高,NH₄Cl水溶液中的氢键类型发生了转变。X射线散射结果表明,当NH₄Cl水溶液质量分数升高至10.0 %时,差值对分布函数G(r)在2.98 ?附近出现明显双峰,表明在该浓度下溶液中NH₄₊^-Cl_-^{接触离子对开始成为主要微观作用形式。对}NH₄Cl水溶液的宏观物性研究表明,粘度、接触角和电导率均随着NH₄Cl水溶液质量分数的增加而增大。作者推断,NH₄Cl水溶液中氢键类型的转变、O-H...N键占比增多以及逐渐增加的NH₄₊^-Cl_-^{接触离子对},是粘度和接触角随溶质浓度增加而增加的微观本质因素;电导率的增加与溶液中有效导电离子数量增加有关。  相似文献   

Putting accessibility in place: A relational reading of accessibility in policies for transit-oriented development     

《Geoforum》2015

In order to facilitate sustainable development, a shift from mobility-based to accessibility-based planning has been suggested. However, if we rely on the modern conceptualisation of accessibility, such a shift would have limited results. As an alternative, this paper proposes a relational reading of accessibility, which questions the divide between mobility and place upon which the modern definition is based. It argues that the accessibility of a place is characterised by a specific coordination of presences and absences that depends as much on boundaries and exclusions as on mobility. If accessibility changes, so does the place. This interpretation makes accessibility a matter of priorities and provides a critical perspective on arguments for time–space compressions and progress. This is illustrated here using the example of a regional strategy for transit-oriented development in Sweden (Region Scania). For that case, the discourse on accessibility revealed simplified arguments for densification, progress and metropolitan ideals, contradicting the initial inclusive intentions of the strategy. Thus, there is a need to put accessibility in place so that a shift to accessibility-based planning facilitates a move towards social and environmental sustainability.  相似文献   

Ab initio prediction of 29Si-NMR chemical shifts     

Chu Shidong  Li Yingxia  Song Ni  Guan Huashi 《中国海洋大学学报(英文版)》2002,1(1):63-65

The ability of several ab initio models to predict experimental ²⁹Si-NMR chemical shift is examined. The shielding values of trimethylsilyl chloride (A), t-butyldimethylsilyl chloride (B) and allytrimethylsilane (C) are calculated by GIAO, CSGT and IGAIM methods, using HF/6–31G^*, B3LYP/6-31G^*, HF/6–311+G^**, B3LYP/6–311+G^** and MPW1PW91/6–311+G^** models respectively. The ²⁹Si chemical shifts calculated by GIAO method using HF/6–311+G^** model are highly in agreement with those obtained experimentally. All of the models above reproduce the trends of chemical shifts in all cases studied, suggesting that the models are of practical value.  相似文献   

High-pressure isosymmetrical phase transition in calaverite     

R.?CaracasEmail author  X.?Gonze 《Physics and Chemistry of Minerals》2004,31(8):553-558

Using density functional theory, we perform ab initio calculations of the behaviour of calaverite, AuTe₂, at high pressures. Calaverite has a distorted CdI₂ structure, that presents a pronounced two-dimensional character and a rather anisotropic response to pressure. Increasing the pressure, we predict an isosymmetrical phase transition between 55 and 60 GPa, that is accompanied by an important distortion of the structure, observed in all its geometrical parameters, especially the c lattice parameter. Relaxing the pressure, the reverse phase transition is observed between 30 and 25 GPa.  相似文献   

偏硼酸锂溶液物种分布和物化性质          下载免费PDF全文

许沙  房艳  房春晖  周永全  朱发岩  陶松 《盐湖研究》2012,20(3):37-42

测量了不同浓度LiBO2溶液分别在298.15和323.15 K的密度、电导和pH,通过测得的pH和硼酸根离子化学平衡常数计算得到溶液中硼酸根离子的物种分布。根据获得的物种分布结果,推测溶液中各硼酸根离子之间的相互转化过程,并分别用偏摩尔体积公式和Onsager方程对溶液偏摩尔体积及摩尔电导率进行计算并拟合。对计算得到偏摩尔体积值和极限摩尔电导率值与文献报道的数据进行对比,计算结果与文献报道值吻合较好。  相似文献   

雷击地闪密度与雷暴日数的关系分析   总被引：13，自引：4，他引：9  

马金福  冯志伟 《气象科学》2009,29(5):674-678

根据美国卫星观测得到的我国各省区年平均总闪电资料并计算出各省区的年平均地闪密度(以下简称地闪密度);根据全国各省区220个站点的年平均雷暴日资料,按照<建筑物防雷设计规范>GB50057-94(2000年版)(以下简称<规范>)公式计算出全国各省区的地闪密度.比较两种方法得出的地闪密度,发现存在较大的差异,且不同区域差异变化很大.用单位雷暴日地闪密度概念,分析了我国各地单位雷暴日地闪密度的差异及其原因,指出单位雷暴日地闪密度能粗略反映与我国气候特征相适应的地闪密度的分布状况.进一步分析湖州市2007年人工观测和闪电定位仪观测的闪电资料,得到相同的结论.从而提出<规范>规定的地闪密度计算公式存在较大误差,应对其进行进一步的修订和完善.  相似文献   

时变重力场球面模型反演算法和模拟实验     

张贝  陈石  李红蕾  杨锦玲  韩建成  卢红艳 《地震》2021,41(1):13-24

时变重力场是研究地球内部介质物性变化的重要手段。本文提出了一种适用于地面流动重力测量获得的时变重力信号的场源反演方法,该方法采用球坐标系下的六面体单元来模拟场源介质,适合大尺度地震流动重力测量数据的等效源模型构建。通过引入重力时变信号的一阶光滑先验条件,压制了时变重力信号中的短周期高频分量,可用于提取与地震孕育相关的长周期信号。通过理论和模型实验证明了本文算法的可靠性和稳定性,并使用南北地震带南段2014—2017年的流动重力实测数据进行了反演解释,获得了地壳内部等效场源的视密度时变信号,变化量级在正常地壳密度的±0.7‰之间,其空间形态受川滇菱形块体边界控制。研究成果可用于时变重力场模型解释和深部场源特征提取,可为地震重力前兆信号分析和相关研究提供完备的方法保障。  相似文献