汶川MS8.0地震前云南地区显著前兆观测异常分析

汶川M_S8.0地震前云南地区出现了显著的前兆观测异常. 该文从大地震的孕育范围出发分析认为这些地震前兆异常可能与汶川M_S8.0地震有关, 并认识到前兆观测出现的显著极值异常可能是M_S≥7.0大地震的前兆; 有学者认为大震震源区没有或较少出现前兆观测趋势异常是大地震的共性特征, 汶川M_S8.0地震的前兆观测异常也是相同的; 地震前兆观测异常开始和结束时间是多样的, 前兆异常的分布是复杂的, 因此利用震后总结的共性特征, 在震前对汶川M_S8.0地震作出预测是困难的.      

一株虹鳟源枯草芽孢杆菌的分离鉴定及生物学特性研究

为筛选对虹鳟(Oncorhynchus mykiss)有潜在益生效果的菌株,本研究从健康虹鳟幼鱼肠道中分离到1株潜在益生菌株RT-BS07,采用形态学观察和分子特征分析对该菌株进行了鉴定,并评价了该菌株的抑菌性、耐受性、黏附性和安全性。形态学观察显示,菌株RT-BS07为革兰氏阳性杆菌,有圆形或椭圆形芽孢。16S rRNA比对结果显示,该菌株与枯草芽孢杆菌(Bacillus subtilis)NCBI3610株的同源性为99.86%。结合16S rRNA基因序列分析和形态学观察结果,确定菌株RT-BS07为枯草芽孢杆菌。菌株RT-BS07具备产蛋白酶和纤维素酶能力,其酶活力分别为(0.039±0.002)和(0.393±0.002)U/mg;该菌株可有效抑制温和气单胞菌(Aeromonas sobria)、杀鲑气单胞菌(A.salmonicida)和鲁氏耶尔森氏菌(Yersinia ruckeri)等致病菌。菌株RT-BS07在pH为2~10 LB液体培养基中均可存活;在盐度为2%~8%条件下存活率为5.70%~93.28%,其存活率随盐度升高而降低。体外黏附试验结果表明,菌株RT-BS07可大量黏附在虹鳟前肠黏膜,不破坏肠道组织完整性,对左氟沙星、环丙沙星、氧氟沙星和链霉素等18种抗菌药物敏感。本研究分离筛选得到的枯草芽孢杆菌RT-BS07株具有产消化酶性能,其抗逆性能强,对虹鳟无毒害作用,可作为虹鳟健康养殖及益生菌制剂研发源益生菌候选株。     

A disk-corona model for the low/hard state of black hole X-ray binaries

A disk-corona model for fitting the low/hard（LH）state of the associated steady jet in black hole X-ray binaries（BHXBs）is proposed based on the large-scale magnetic field configuration that arises from the coexistence of the Blandford-Znajek（BZ）and Blandford-Payne（BP）processes,where the magnetic field configuration for the BP process is determined by the requirement of energy conversion from Poynting energy flux into kinetic energy flux in the jet.It is found that corona current is crucial to guarantee the consistency of the jet launching from the accretion disk.The relative importance of the BZ and BP processes in powering jets from black hole accretion disks is discussed,and the LH state of several BHXBs is fitted based on our model.In addition,we suggest that magnetic field configuration can be regarded as the second parameter for governing the state transition of BHXBs.     

Experimental study on static and impact strength of sintered agglomerates

Porous internal structure is common among small bodies in the planetary systems and possible range of porosity, strength, and scale of in-homogeneity is wide. Icy agglomerates, such as icy dust aggregates in the proto-planetary disks or icy re-accumulated bodies of fragments from impact disruption beyond snow-line would have stronger bulk strength once the component particles physically connect each other due to sintering.In this study, in order to get better understanding of impact disruption process of such bodies, we first investigated the critical tensile (normal) and bending (tangential) forces to break a single neck, the connected part of the sintered particles, using sintered dimer of macro glass particles of ∼5 mm in diameter. We found that the critical tensile force is proportional to the cross-section of the neck when the neck grows sufficiently larger than the surface roughness of the original particles. We also found that smaller force is required to break a neck when the force is applied tangentially to the neck than normally applied. Then we measured the bulk tensile strength of sintered glass agglomerates consisting of 90 particles and showed that the average tensile stress to break a neck of agglomerates in static loading is consistent with the measured value for dimers.Impact experiments with velocity from 40 to 280 m/s were performed for the sintered agglomerates with ∼40% porosity, of two different bulk tensile strengths. The size ratio of the beads to the target was 0.19. The energy density required to catastrophically break the agglomerate was shown to be much less than those required for previously investigated sintered glass beads targets with ∼40% porosity, of which the size of component bead is 10⁻² times smaller and the size ratio of the bead to target is also ∼10⁻² times smaller than the agglomerates in this study. This is probably due to much smaller number of necks for the stress wave to travel through the agglomerates and therefore the energy dissipation at the necks is minimal. Also, the much larger fraction of the surface particles enables the particles to move more freely and thus be broken more easily. The catastrophic disruption of the agglomerates is shown to occur when the projectile kinetic energy is a few times of the total energy to break all of the necks of the agglomerates. The result implies that finer fragments from sintered agglomerates may have smaller catastrophic disruption energy threshold for shattering than other larger fragments with similar porosity and bulk tensile strength but much larger number of constituent particles. If this is the case, size-dependence of (smaller is weaker) is opposite to those usually considered for the bodies in the strength regime.     

Families among high-inclination asteroids

We present a new classification of families identified among the population of high-inclination asteroids. We computed synthetic proper elements for a sample of 18,560 numbered and multi-opposition objects having sine of proper inclination greater than 0.295. We considered three zones at different heliocentric distances (inner, intermediate and outer region) and used the standard approach based on the Hierarchical Clustering Method (HCM) to identify families in each zone. In doing so, we used slightly different approach with respect to previously published methodologies, to achieve a more reliable and robust classification. We also used available SDSS color data to improve membership and identify likely family interlopers. We found a total of 38 families, as well as a significant number of clumps and clusters deserving further investigation.     

The role of flow geometry in influencing the stability criteria for low angular momentum axisymmetric black hole accretion

Using mathematical formalism borrowed from dynamical systems theory, a complete analytical investigation of the critical behaviour of stationary flows in low angular momentum axisymmetric black hole accretion, provides significant insight about the nature of the phase trajectories corresponding to transonic accretion in the steady state, without taking recourse to any explicit numerical method commonly reported in the literature on multi-transonic black hole accretion discs and related astrophysical phenomena. Investigation of an accretion process around a non-rotating black hole, forming different geometrical configurations of the flow structure under the influence of various pseudo-Schwarzschild potentials, reveals that the general profile of the parameter space divisions describing multi-critical accretion, is roughly equivalent for various flow geometries. However, a mere variation of the polytropic index of the flow cannot map a critical solution from one flow geometry to another, since the numerical domain of the parameter space responsible for producing multi-critical accretion does not undergo a continuous transformation in multi-dimensional parameter space. The stationary configuration used to demonstrate the aforementioned findings is shown to be stable under time-dependent linearised perturbations for all kinds of flow geometries, driven by any pseudo-Schwarzschild potential, and using a standard equation of state. Finally, the structure of the acoustic metric corresponding to the propagation of the linear perturbation is discussed for various flow geometries used.     

Hysteresis effects and diagnostics of the shock formation in low angular momentum axisymmetric accretion in the Kerr metric

The secular evolution of the purely general relativistic low angular momentum accretion flow around a spinning black hole is shown to exhibit hysteresis effects. This confirms that a stationary shock is an integral part of such an accretion disc in the Kerr metric. The equations describing the space gradient of the dynamical flow velocity of the accreting matter have been shown to be equivalent to a first order autonomous dynamical systems. Fixed point analysis ensures that such flow must be multi-transonic for certain astrophysically relevant initial boundary conditions. Contrary to the existing consensus in the literature, the critical points and the sonic points are proved not to be isomorphic in general, they can form in a completely different length scales. Physically acceptable global transonic solutions must produce odd number of critical points. Homoclinic orbits for the flow possessing multiple critical points select the critical point with the higher entropy accretion rate, confirming that the entropy accretion rate is the degeneracy removing agent in the system. However, heteroclinic orbits are also observed for some special situation, where both the saddle type critical points of the flow configuration possesses identical entropy accretion rate. Topologies with heteroclinic orbits are thus the only allowed non-removable degenerate solutions for accretion flow with multiple critical points, and are shown to be structurally unstable. Depending on suitable initial boundary conditions, a homoclinic trajectory can be combined with a standard non-homoclinic orbit through an energy preserving Rankine-Hugoniot type of stationary shock, and multi-critical accretion flow then becomes truly multi-transonic. An effective Lyapunov index has been proposed to analytically confirm why certain class of transonic flow cannot accommodate shock solutions even if it produces multiple critical points.     

STEREO卫星的CME观测研究进展

简要回顾利用"日地关系天文台"(Solar Terrestrial Relations Observatory,STEREO)卫星的立体观测资料在日冕物质抛射(Coronal Mass Ejection,CME)研究方面已取得的一些重要进展,主要包括(1)通过极紫外成像仪观测到的日冕极紫外暗化来更准确地估计CME质量,研究CME演化的结构特征;(2)利用STEREO卫星日冕仪的双角度观测,在CME立体传播特征方面取得的新进展;(3)STEREO卫星日球成像仪具有广阔的视场范围,可以跟踪研究CME从太阳表面爆发到形成行星际日冕物质抛射(Interplanetary CME,ICME),及其在内日球层和近地空间的演化特征以及运动特征等。同时,也介绍了利用三角测量技术测定CME特征物理量的新方法。     

Normal modes of black hole accretion disks

This article studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing Wentzel-Kramers-Brillouin (WKB) techniques, we obtain the eigenfrequencies and eigenfunctions of the modes for different values of the mass and angular momentum of the central black hole. We discuss the properties of the various types of modes and show for the first time that modes covering the whole extension of the disk (full-disk p-modes) can exist within the studied thin disk model. However, these modes have relatively short wavelengths.     

磁县断裂带的构造和地震活动特征

磁县断裂带是华北地震区中重要的断裂之一,1830年该断裂带发生了M7级地震.从分析该带的构造特征和地震活动特征出发,在结合历史地震活动和现今地震活动基础上,利用震级-时间模型对磁县断裂带未来强震活动进行预测,结果表明,未来该段中南的总体活动水平维持在5级左右.