Does a representative volume element exist for fatigue life prediction? The case of aggregate composites     

Adel Lachihab  Karam Sab 《国际地质力学数值与分析法杂志》2008,32(9):1005-1021

In a previous work, discrete modeling and a statistical approach were used to quantify the minimal representative volume element (RVE) size for aggregate composites, such as bituminous materials in the linear elastic regime (Comput. Mater. Sci. 2005; 33 :467–490). In this paper, the discrete model is extended to strain‐softening behavior under cyclic loading. The existence of a RVE for fatigue life prediction is numerically proved and its minimal size is determined. It is found that it is much larger than the minimal RVE size in the elastic regime. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Atmospheric Eclipses in Wr+o Binaries: From Kopal and Shapley to Present Days     

A. M. Cherepashchuk 《Astrophysics and Space Science》2005,296(1-4):55-65

Kopal and Shapley (1946) were the first to suggest to solve an integral equation for interpretation of atmospheric eclipses in WR+O binary systems. In our studies, this idea was developed in two ways: solution of two integral equations; development of efficient methods of solution of ill-posed problems. Application of the new method to the interpretation of the light curve of the WN5+O6 eclipsing binary V444 Cyg allowed us to determine the radius and the temperature of the WN5 star core. Some astrophysical applications of these results are presented.  相似文献   

Energization of interstellar media and cosmic ray production by jets from X-ray binaries     

R. P. Fender  T. J. Maccarone  Z. van Kesteren 《Monthly notices of the Royal Astronomical Society》2005,360(3):1085-1090

Drawing on recent estimates of the power of jets from X-ray binary systems as a function of X-ray luminosity, combined with improved estimates of the relevant  log( N )–log( L _X)  luminosity functions, we calculate the total energy input to the interstellar medium (ISM) from these objects. The input of kinetic energy to the ISM via jets is dominated by those of the black hole systems, in contrast to the radiative input, which is dominated by accreting neutron stars. Summing the energy input from black hole jets L _J in the Milky Way, we find that it is likely to correspond to ≥1 per cent of L _SNe, the time-averaged kinetic luminosity of supernovae, and ≥5 per cent of L _CR, the cosmic ray luminosity. Given uncertainties in jet power estimates, significantly larger contributions are possible. Furthermore, in elliptical galaxies with comparable distributions of low mass X-ray binaries, but far fewer supernovae, the ratio   L _J/ L _SNe  is likely to be larger by a factor of ∼5. We conclude that jets from X-ray binaries may be an important, distributed, source of kinetic energy for the ISM in the form of relativistic shocks, and as a result are likely to be a major source of cosmic rays.  相似文献   

wham: a WENO-based general relativistic numerical scheme – I. Hydrodynamics     

Alexander Tchekhovskoy  Jonathan C. McKinney  Ramesh Narayan 《Monthly notices of the Royal Astronomical Society》2007,379(2):469-497

Active galactic nuclei, X-ray binaries, pulsars and gamma-ray bursts are all believed to be powered by compact objects surrounded by relativistic plasma flows driving phenomena such as accretion, winds and jets. These flows are often accurately modelled by the relativistic magnetohydrodynamic (MHD) approximation. Time-dependent numerical MHD simulations have proven to be especially insightful, but one regime that remains difficult to simulate is when the energy scales (kinetic, thermal, magnetic) within the plasma become disparate. We develop a numerical scheme that significantly improves the accuracy and robustness of the solution in this regime. We use a modified form of the weighted essentially non-oscillatory (WENO) method to construct a finite-volume general relativistic hydrodynamics code called wham that converges at fifth order. We avoid (1) field-by-field decomposition by adaptively reducing down to two-point stencils near discontinuities for a more accurate treatment of shocks and (2) excessive reduction to low-order stencils, as in the standard WENO formalism, by maintaining high-order accuracy in smooth monotonic flows. Our scheme performs the proper surface integral of the fluxes, converts cell-averaged conserved quantities to point-conserved quantities before performing the reconstruction step, and correctly averages all source terms. We demonstrate that the scheme is robust in strong shocks, very accurate in smooth flows and maintains accuracy even when the energy scales in the flow are highly disparate.  相似文献   

Quantum tunneling makes a Reissner–Nordstrom black hole turn into a Kerr–Newman black hole under angular momentum conservation     

Wenbiao Liu 《Astrophysics and Space Science》2007,310(1-2):81-84

Hawking radiation can be viewed as a process of particle quantum tunneling near a black hole horizon. When a particle with angular momentum tunnels across the event horizon of a Reissner–Nordstrom black hole, the black hole will change into a Kerr–Newman one. In previous papers, axisymmetric black hole has been studied only when a keeps constant. Changing from Reissner–Nordstrom to Kerr–Newman should be a simple case when a varies. After this, more general radiation including changed a in Kerr or Kerr–Newman spacetimes can be studied in the future. The emission rate of the massless particles with angular momentum is calculated, and the result is consistent with an underlying unitary theory.   相似文献   

Jet disc coupling in black hole binaries     

Julien Malzac 《Astrophysics and Space Science》2007,311(1-3):149-159

In the last decade multi-wavelength observations have demonstrated the importance of jets in the energy output of accreting black hole binaries. The observed correlations between the presence of a jet and the state of the accretion flow provide important information on the coupling between accretion and ejection processes. After a brief review of the properties of black hole binaries, I illustrate the connection between accretion and ejection through two particularly interesting examples. First, an INTEGRAL observation of Cygnus X-1 during a ‘mini-’ state transition reveals disc jet coupling on time scales of orders of hours. Second, the black hole XTEJ1118+480 shows complex correlations between the X-ray and optical emission. Those correlations are interpreted in terms of coupling between disc and jet on time scales of seconds or less. Those observations are discussed in the framework of current models.  相似文献   

Probable intermediate-mass black holes in NGC 4559: XMM–Newton spectral and timing constraints     

Mark Cropper  Roberto Soria  Richard F. Mushotzky  Kinwah Wu  Craig B. Markwardt  Manfred Pakull 《Monthly notices of the Royal Astronomical Society》2004,349(1):39-51

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中国大陆科学钻探工程卫星孔CCSDPP6钻孔橄榄岩岩石学研究   总被引：1，自引：0，他引：1       下载免费PDF全文

任玉峰杨经绥  张仲明李天福 《地质学报》2007,81(7):1004-1016

中国大陆科学钻探工程卫星孔PP6钻孔位于苏鲁超高压变质带的山东荣成滕家集马草夼橄榄岩体中。该橄榄岩出露于元古代花岗闪长片麻岩中,面积为300m×130m。地表岩石风化强烈,钻孔内岩石新鲜,劈理发育。孔深196m,橄榄岩厚度约110m,下部为花岗闪长片麻岩。橄榄岩主体呈块状构造,边缘呈条带状构造,靠近片麻岩的橄榄岩蛇纹石化强烈。除了10cm厚的岩脉原岩为岩浆分异的产物外,岩石主元素、微量和稀土元素地球化学显示,原岩为极亏损的地幔方辉橄榄岩。岩石主要矿物组成为橄榄石(85%~95%) 斜方辉石(3%~5%) 角闪石(3%~5%) 尖晶石(约0.5%) 镍硫化物(<0.1%),个别部位含有石榴石、单斜辉石和白云石。根据矿物的结构和成分,大体分为三个期次的组合。早期残余地幔矿物组合,由镁橄榄石、富铝顽火辉石、铬尖晶石和透辉石组成,具残余斑状结构,常含有包体,为高温低压组合;超高压变质期矿物组合,由镁橄榄石、镁铝榴石(Pyr=62~66)、低铝顽火辉石、铬尖晶石组成,具细粒变晶结构,无包体,变质温压为840~940°C、3.0~4.1GPa;麻粒岩相─角闪岩相变质期矿物组合,包括韭闪石、镁铝尖晶石、铬尖晶石、白云石、透闪石、蛇纹石,变质温度和压力为650~780℃、<1.8GPa。马草夼橄榄岩作为地幔楔,在印支期发生了超高压变质作用,并在折返过程中叠加了麻粒岩相-角闪岩相的变质作用。  相似文献   

岩溶地区冲孔灌注桩的施工方法     

吴辰光 《中国煤田地质》2007,19(A01):63-64,73

以龙岩地区岩溶地带某一项目施工为例，分析冲孔灌注桩孔内漏浆、塌孔的原因，探讨在岩溶地区预防和处理塌孔的方法：改善泥浆品质，安放钢护筒，挤压黄土入裂隙，减小泥浆渗透，以及分层加入一定量水泥，使其形成水泥土护壁层。实践证明，诸类方法的使用可有效遏制孔内漏浆和塌孔，提高施工效率。  相似文献   

影响钻孔波速测试质量的因素分析          下载免费PDF全文

陈坤 《甘肃地质》2007,16(1):90-92

钻孔波速测试是对地基土力学性质进行原位测试方法中的一种，目前广泛应用于岩土工程勘察中，本文主要叙述了在进行钻孔波速测试时现场应注意的一些问题。  相似文献