A two-dimensional hydrostatically equilibrium atmosphere of a neutron star with given differential rotation     

V. S. Imshennik  K. V. Manukovskii 《Astronomy Letters》2000,26(12):788-796

An analytic solution has been found in the Roche approximation for the axially symmetric structure of a hydrostatically equilibrium atmosphere of a neutron star produced by collapse. A hydrodynamic (quasione-dimensional) model for the collapse of a rotating iron core in a massive star gives rise to a heterogeneous rotating protoneutron star with an extended atmosphere composed of matter from the outer part of the iron core with differential rotation (Imshennik and Nadyozhin, 1992). The equation of state of a completely degenerate iron gas with an arbitrary degree of relativity is taken for the atmospheric matter. We construct a family of toroidal model atmospheres with total masses M≈ 0.1?2M _⊙ and total angular momenta J≈(1?5.5)×⁴⁹ erg s, which are acceptable for the outer part of the collapsed iron core, in accordance with the hydrodynamic model, as a function of constant parameters ω₀ and r ₀ of the specified differential rotation law Ω=ω₀exp[?(rsinθ)²/r ₀ ² ] in spherical coordinates. The assumed rotation law is also qualitatively consistent with the hydrodynamic model for the collapse of an iron core.  相似文献   

Nutrient fluxes induced by disturbance in Meiliang Bay of Lake Taihu   总被引：1，自引：0，他引：1  

LUO Liancong  QIN Boqiang  ZHU Guangwei  SUN Xiaojing  HONG Dalin  GAO Yajun  XIE Rui 《中国科学D辑(英文版)》2006,49(Z1)

A wave flume experiment was conducted to study nutrient fluxes at water-sediment interface of Meiliang Bay under different hydrodynamic conditions. The results reveal that hydrodynamics has remarkable effects on nutrient fluxes in this area. With a bottom wave stress of 0.019 N m-2 (equivalent to disturbance caused by wind SE 5-7 m s-1 at the sediment sample site of Meiliang Bay), the fluxes of TN, TDN and NH4+-N were separately 1.92× 10-3, -1.81 × 10-4 and 5.28× 10-4 mg m-2 s-1(positive for upward and negative for downward), but for TP, TDP and SRP, the fluxes were 5.69 × 10-4, 1.68 × 10-4 and -1.29 × 10-4 mgm-2 s-1. In order to calculate the released amount of nutrients based on these results, statistic analysis on the long-term meteorological data was conducted.The result shows that the maximum lasting time for wind SE 5-7 m s-1 in this area is about 15 h in summer. Further calculation shows that 111 t TN, 32 t NH4+-N, 34 t TP and 10 t TDP can be released into water (the sediment area was 47.45% of the whole surface area), resulting in concentration increase of 0.025, 0.007, 0.007 and 0.002 mg L-1 separately. With stronger disturbance (bottom wave stress is 0.217 N m-2 which is equivalent to disturbance caused by wind SE 10-11 m s-1 at the same site), there has been significant increase of nutrient fluxes (1.16× 10-2, 6.76×10-3, 1.14× 10-2 and 2.14× 10-3 mgm-2 s-1 for TN, DTN and NH4+-N and TP). The exceptions were TDP with flux having a decrease (measured to be 9.54× 10-5 mgm-2 s-1 ) and SRP with flux having a small increase (measured to be 5.42 × 10-5 mgm-2 s-1). The same statistic analysis on meteorological data reveal that the maximum lasting time for wind SE 10-11 m s-1 is no more than 5 h. Based on the nutrient fluxes and the wind lasting-time, similar calculations were also made suggesting that 232 t TN, 134.9 t TDN, 228 t NH4+-N, 42.7 t TP, 2.0 t TDP and 1.1 t SRP will be released from sediment at this hydrodynamic condition resulting in the concentration increases of 0.050, 0.029, 0.049, 0.009, 0.0004 and 0.0002 mg L-1. Therefore in shallow lakes, surface disturbance can lead to significant increase of nutrient concentrations although some components in water column had negative flux with weak disturbance (e.g. TDN and SRP in this experiment). In this case, sediment looks to be a source of nutrients. These nutrients deposited in sediment can be carried or released into water with sediment resuspension or changes of environmental conditions at water-sediment interface, which can have great effects on aquatic ecosystem and is also the characteristics of shallow lakes.  相似文献   

Evaluation of site effects using numerical and experimental analyses in Città di Castello (Italy)     

F. Pergalani  R. de Franco  M. Compagnoni  G. Caielli 《Soil Dynamics and Earthquake Engineering》2006,26(10):941-951

In the paper the results of the numerical and experimental analyses, at a site in the Umbria Region (Città di Castello—PG), are finalized and the evaluations of site effects are shown. The aim of the work was to compare the two types of analyses and give some methodologies that may be used at the level of urban planning. Therefore a series of geological, geomorphological (1:5.000 scale), geotechnical and seismic analyses have been carried out, to characterize the lithological units and to identify the areas affected by site effects. The expected seismic inputs were provided and two-dimensional numerical analyses have been done. An experimental analysis, using the registrations of small events, has been done. The results for the two approaches were performed in terms of elastic pseudo-acceleration spectra and amplification factors. The results are given as a ratio between spectral intensity, calculated using the pseudo-velocity spectra, in the periods of 0.1–0.5 s and 0.1–2.5 s of output and input. The results have been analyzed and compared, to provide a methodology that may be comprehensive and precise.  相似文献   

富铁橄榄石的高温变形实验研究   总被引：1，自引：3，他引：1  

赵永红  Zimmerman M Kohlstedt D L 《岩石学报》2005,21(3):999-1004

利用高精度Paterson气体介质变形装置对(Mg0.5,Fe0.5)2SiO4和(Mg0.7,Fe0.3)2SiO4橄榄石集合体进行了高温三轴压缩变形试验。首先用人工合成了纯铁橄榄石Fe2SiO4,然后用合成的纯铁橄榄石与天然圣卡罗橄榄石按一定比例混合烧结合成了含铁量分别为50％和30％的富铁橄榄石集合体Fo50和Fo70。三轴压缩蠕变变形试验在温度1223-1473 K和围压 300 MPa的条件下进行,差应力为10-300 MPa,应变率为10-7-10-4s-1,每个试件的最大变形量为20％．利用三维非线性方法对蠕变数据进行拟合,得出的流动律中,Fo50应力指数为4．1,活化能为499kJ／mol;Fo70应力指数为4．3,活化能为510kJ／ mol。将实验结果与Fo90圣卡罗橄榄石集合体的强度进行对比,发现含铁量的增加使橄榄石的强度明显下降,Fo50橄榄石集合体比Fo70的粘性低一个量级,Fo70比Fo90的粘性低一个量级。从而得到了含铁量对橄榄石的粘性(强度)影响的初步试验结果。  相似文献   

输水管道系统气体特性与水流冲击截留气团研究   总被引：1，自引：0，他引：1       下载免费PDF全文

郑源  索丽生  张健  刘德有 《水科学进展》2005,16(6):858-863

通过试验与理论相结合的方法,对输水管道系统气体特性与水流冲击截留气团进行了研究.研究表明,决定气团主要性质的气体多方指数n在输水管道系统发生水力过渡过程时存在较为显著的变化,并非单一常数,从而提出了相应的四过程:即压缩子过程1、膨胀子过程2、膨胀子过程3和压缩子过程4.在压缩子过程4与膨胀子过程2中,气体多方指数n取值为1.4~1.6;而在压缩子过程1与膨胀子过程3中,气体多方指数n取1.15.气体多方指数n的取值对压力水流冲击截留气团的结果有一定影响,n值越小,水流冲击截留气团的压力越大;反之越小.  相似文献   

Experimental validation of a numerical prediction model for free field traffic induced vibrations by in situ experiments     

G. Lombaert  G. Degrande 《Soil Dynamics and Earthquake Engineering》2001,21(6):692

This paper deals with the validation of a numerical model for traffic induced vibrations. Road unevenness subjects the vehicle to vertical oscillations that cause dynamic axle loads, which generate waves propagating in the subsoil. A 2D vehicle model is used for the calculation of the axle loads from the longitudinal road profile. The free field soil response is calculated with the dynamic Betti–Rayleigh reciprocity theorem, using a transfer function between the road and the receiver that accounts for dynamic road–soil interaction. The validation relies on the measured response of the vehicle's axles and the soil during the passage of a truck on an artificial unevenness with speeds varying from 30 to 70 km/h. The agreement between the numerical and the experimental results is good: the influence of the vehicle speed and the distance from the road is well predicted, while the ratio of the predicted and the measured PPV is less than two.  相似文献   

坡面水蚀过程水动力学研究进展   总被引：28，自引：1，他引：28       下载免费PDF全文

张光辉 《水科学进展》2001,12(3):395-402

径流分离上壤是侵蚀泥沙的主要来源,也是建立土壤侵蚀物理模型的控制参数之一。对国内外坡面径流分离土壤过程的研究方法、流速测定、控制方程、分离能力、挟沙力及存在的问题进行了系统深入的论述,旨在综合已有研究经验和成果,促进相关研究的发展。  相似文献   

地表通量研究进展   总被引：22，自引：4，他引：22  

黄妙芬 《干旱区地理》2003,26(2):159-165

通过对国内外地表通量中的显热和潜热通量的研究进展从试验仪器、计算模型和遥感反演三个方面分别进行综述。目前广泛应用于地表通量研究的仪器有波文比、涡度相关仪和闪烁通量仪。计算模型主要有涡度相关法，波文比法、空气动力学法，能量平衡一空气动力学阻抗法(即遥感法)、Penman—Monteith模型、互补相关模型和SR模型等。遥感反演主要立足于地表热量平衡方程，通过反演方程中的净辐射、土壤热流量和显热通量，进而推算出潜热通量。在最后还对目前地表通量研究中的热点问题进行了分析。  相似文献   

The charge-density distribution, its multipole refinement and the antiferromagnetic structure of dioptase, Cu6[Si6O18]·6H2O     

E. L. Belokoneva  Yu. K. Gubina  J. B. Forsyth  P. J. Brown 《Physics and Chemistry of Minerals》2002,29(6):430-438

 The chemical bonding in the ring silicate mineral dioptase is investigated on the basis of accurate single-crystal X-ray diffraction data. A multipole model is used in the refinements. Static deformation electron density is mapped for the silicon tetrahedron, Cu-octahedron and water molecule in different sections. The silicon tetrahedron exhibits peaks resulting from σ-bonds between Si–sp³ hybrid orbitals and O–p orbitals. The excess density is located on bonds between the Si atom and bridge (in ring) O(1)-, O(1′)-oxygens and across the interior of the Si–O–Si angle. In the Jahn-Teller distorted Cu octahedron, in addition to peaks which result from single Cu–O σ-bonds, there are peaks which are due to 3d electrons. The analysis of crystal-field influence on the Cu charge distribution is made using the tetragonal D _{4 d} approximation for the low-symmetry (C1) Cu octahedron. The calculation of the occupancies of the 3d atomic orbitals shows that the Cu non-bonding orbitals are most populated (˜20%) and the bonding orbitals least populated (14%), as is typical for the Jahn-Teller octahedron. The effective atomic charge on the Cu atom in dioptase determined from the multipoles is +1.23e: closer to the Cu⁺¹ than to the Cu⁺² state. The charge on the Si atom has a value +1.17e, which is in the range typical for Si atoms already determined by this method. The accumulation of density on bridge oxygens and across the interior of the Si–O–Si angle may be explained by additional strain in the bond with the decrease of the Si–O–Si angle in dioptase to 132°. The same effect was found earlier in coesite. A single-crystal neutron diffraction study shows that dioptase becomes antiferromagnetic below a Néel temperature of 15.9(1) K, in contrast to the previously reported specific heat anomaly at 21 K. The magnetic propagation vector is (0, 0, 3/2) on the hexagonal triple cell or (1/2, 1/2, 1/2) in rhombohedral indices. The relation between the antiferromagnetic and the charge-density models for dioptase is discussed. The less occupied Cu d _x2−y2 orbitals are responsible for the magnetic properties. These lie in the Cu–O squares, which are approximately perpendicular to c _hex, but which are alternately inclined to it by a small angle. The magnetic moments of 0.59(1)μ _B on the Cu ions in the same level are ordered ferromagnetically, but between ions in alternate levels the coupling is antiferromagnet. Within experimental error the magnetic moments are perpendicular to the square planes, which make an angle ±13(3)° to the triad axis. Received: 8 June 2001 / Accepted: 10 January 2002  相似文献   

A PRIMARY STUDY ON IONIC MATERIAL MOVEMENT WITH DIFFERENT VEGETATION─With an Example of Niujiatong Small Catchment,Guangdong Province     

YOU Lianyuan Professor  Institute of Geography  Chinese Academy of Sciences  Building  Datun Road  Beijing    China JIANG Lingse Engineer  Experimental Station of Water  Soil Conservation of Wuhua County  Huachen    Wuhua County  Gua 《国际泥沙研究》1997,(3)

MovementofsoilnutrientsappearedwithionicconditionSymbolizesecologicconditionOfaregionandrelatescloselytosoilerosionandtransportthere.ItisoneoltheimpoftalltelementsingeoecoSystem.TheymayeitherbedissolvedbywateranddischargedOutwithitorabsolbedbysacmentgrainandmovedoutwiththem.Thusitcanbeenseenthattheyshouldrelatetoraillfallandrunoff.InSOothChinachacterizedbyrichprecipitationandrunoff,backweather-layerOftheearthsurfaceaswell,thereisveryseriouslossofionicmaterial,andconsequently,declineinecoSy…  相似文献