Gravitational collapse and equilibrium conditions of a toroidal vortex with thermal pressure     

K. Yu. Bliokh  V. M. Kontorovich 《Astronomy Letters》2003,29(11):724-730

We found the equilibrium conditions for a self-gravitating toroidal vortex by taking thermal pressure into account. These conditions are shown to significantly differ from those for a disk or a sphere. The evolution of a thin vortex turns it into a compact vortex that loses mechanical stability for low masses at a polytropic index γ<4/3 but retains stability for sufficiently high masses and densities determined by the velocity circulation in the vortex.  相似文献   

Geobarometry for Peridotites: Experiments in Simple and Natural Systems from 6 to 10 GPa   总被引：3，自引：0，他引：3  

Brey  Gerhard P.; Bulatov  Vadim K.; Girnis  Andrei V. 《Journal of Petrology》2008,49(1):3-24

Experiments with peridotite minerals in simple (MgO–Al₂O₃–SiO₂,CaO–MgO–SiO₂ and CaO–MgO–Al₂O₃–SiO₂)and natural systems were conducted at 1300–1500°Cand 6–10 GPa using a multi-anvil apparatus. The experimentsin simple systems demonstrated consistency with previous lowerpressure experiments in belt and piston–cylinder set-ups.The analysis of spatial variations in pyroxene compositionswithin experimental samples was used to demonstrate that pressureand temperature variations within the samples were less than0·4 GPa and 50°C. Olivine capsules were used in natural-systemexperiments with two mineral mixtures: SC1 (olivine + high-Alorthopyroxene + high-Al clinopyroxene + spinel) and J4 (olivine+ low-Al orthopyroxene + low-Al clinopyroxene + garnet). Theexperiments produced olivine + orthopyroxene + garnet ±clinopyroxene assemblages, occasionally with magnesite and carbonate-richmelt. Equilibrium compositions were derived by the analysisof grain rims and evaluation of mineral zoning. They were comparedwith our previous experiments with the same starting mixturesat 2·8–6·0 GPa and the results from simplesystems. The compositions of minerals from experiments withnatural mixtures show smooth pressure and temperature dependencesup to a pressure of 8 GPa. The experiments at 9 and 10 GPa producedandradite-rich garnets and pyroxene compositions deviating fromthe trends defined by the lower pressure experiments (e.g. higherAl in orthopyroxene and Ca in clinopyroxene). This discrepancyis attributed to a higher degree of oxidation in the high-pressureexperiments and an orthopyroxene–high-P clinopyroxenephase transition at 9 GPa. Based on new and previous resultsin simple and natural systems, a new version of the Al-in-orthopyroxenebarometer is presented. The new barometer adequately reproducesexperimental pressures up to 8 GPa. KEY WORDS: garnet; mineral equilibrium; multi-anvil apparatus; orthopyroxene; geobarometry  相似文献   

On the Assessment of Failure in Slope Stability Analysis by the Finite Element Method   总被引：3，自引：0，他引：3  

H. Zheng  D. F. Liu  C. G. Li 《Rock Mechanics and Rock Engineering》2008,41(4):629-639

  相似文献   

Formation of Equilibrium Beach Profile of the Abandoned Yellow River Delta Coast in North Jiangsu     

XU  Min 《中国海洋工程》2001,(1):139-146

The abandoned Yellow River Delta coast is a typical erodible silty and muddy coast in China. The paper analyses the marine dynamic characteristics and the mechanism of beach erosion of this area. Analysis and calculation show that in this sea area wave and tidal current action should be considered. Based on the above analysis, an equilibrium beach profile calculation model is developed, in which the wave-current interaction is considered while sediment supply and sediment re-deposition are neglected. The model consists of four parts: (1) calculation of wave parameters, (2) calculation of velocity due to wave-current interaction at different water depth, (3) calculation of friction velocity and shear stress at different water depths, and (4) calculation of the amount of sediment erosion, erosion intensity and variation of beach profile. Calculated results are in good agreement with observed data. Finally, the evolution tendency is discussed and the equilibrium beach profile of this coast is calculated. B  相似文献   

波浪作用下岸坡和海底平衡条件的研究     

沈剑平  范德江 《中国海洋大学学报(自然科学版)》1993,(4)

提出波浪作用下岸坡和海底动态和静态平衡条件的数学模型。在已建立的推移质泥沙体积输沙率基本关系式的基础上,根据连续方程,计算出底坡、泥沙、波浪三要素在动态和静态平衡情况下的关系式,得出反映这种关系的底坡平衡函数曲线图。用实际资料对这一函数曲线进行了验证,并对实际资料相对模型的某些差异作出解释。  相似文献   

闽南近海常见鲨鳐类肝油的四种理化常数和角鲨烯含量   总被引：8，自引：0，他引：8  

刘晓春  丘书院 《台湾海峡》1997,16(4):468-472

本文分析测定了闽南近海常见鲨鳐类肝油的理化常数和角鲨烯含量。尖头斜齿鲨肝油的碘值特别高，说明其中脂肪酸的不饱和程度很高；非皂化物含量很低，约占肝油重的38×10－3（m／m）；角鲨烯含量极微，在肝油中仅占84×10－5（m／m）。闽南近海常见鲨鳐类肝油的角鲨烯含量均很低，变化在（31～116）×10－5（m／m）之间。在相同的气相色谱条件下，小孔沙条鲨和狭纹虎鲨肝油中没有检测到角鲨烯。  相似文献   

Complexation of mercury by dissolved organic matter in surface waters of Galveston Bay, Texas   总被引：3，自引：0，他引：3  

Seunghee Han  Gary A. Gill  Ronald D. Lehman  Key-Young Choe 《Marine Chemistry》2006,98(2-4):156-166

The chemical speciation of dissolved mercury in surface waters of Galveston Bay was determined using the concentrations of mercury-complexing ligands and conditional stability constants of mercury-ligand complexes. Two classes of natural ligands associated with dissolved organic matter were determined by a competitive ligand exchange-solvent solvent extraction (CLE-SSE) method: a strong class (L_s), ranging from 19 to 93 pM with an average conditional stability constant (K_HgLs) of 10²⁸, and a weak class (L_w) ranging from 1.4 to 9.8 nM with an average K_HgLs of 10²³. The range of conditional stability constants between mercury and natural ligands suggested that sulfides and thiolates are important binding sites for dissolved mercury in estuarine waters. A positive correlation between the estuarine distribution of dissolved glutathione and that of mercury-complexing ligands supported this suggestion. Thermodynamic equilibrium modeling using stability constants for HgL, HgCl_x, Hg(OH)_x, and HgCl(OH) and concentrations of each ligand demonstrated that almost all of the dissolved mercury (> 99%) in Galveston Bay was complexed by natural ligands associated with dissolved organic matter. The importance of low concentrations of high-affinity ligands that may originate in the biological system (i.e., glutathione and phytochelatin) suggests that the greater portion of bulk dissolved organic matter may not be important for mercury complexation in estuarine surface waters.  相似文献   

岬间海湾岸线平衡形态神经网络模型   总被引：1，自引：0，他引：1  

李志龙  陈子燊 《海洋通报》2007,26(3):19-25

讨论了目前海湾岸线平衡形态经验模型存在的不足之处。从沿岸输沙公式入手,阐述了平衡岸线的机理模式,重新定义了平衡海湾的“下岬角”,给出了模型参数与主波向的具体计算方法,并以华南典型海湾为学习样本,建立了岸线平衡形态的神经网络模型。通过模拟海湾与实际稳定海湾——乌场湾间的对比分析,表明所建神经网络模型是较抛物模型更为理想的平衡岸线模型。  相似文献   

Equilibrium constants of triethanolamine in major seawater salts     

I. Brandariz  P. Castro  M. Montes  F. Penedo  M.E. Sastre de Vicente 《Marine Chemistry》2006,102(3-4):291-299

Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl₂ or CaCl₂), with binary mixtures of MgCl₂ and CaCl₂, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl₂, while it is increased by the other electrolytes used in this work.  相似文献   

一类全局最优化问题的动态隧道方法     

李博  曹圣山 《中国海洋大学学报(自然科学版)》2003,33(1):160-164

研究了连续变量函数的全局最优化问题 ,给出了动态隧道方法。该动态隧道方法由局部搜索和动态隧道 2个阶段构成。在局部搜索阶段用了动态系统方法。对全局最优化问题的实例进行了数值实验 ,数值结果表明了该方法的稳健性和有效性。  相似文献