Cooling flows in clusters of galaxies

Summary X-ray images and spectra of clusters of galaxies show strong evidence for cooling flows. In many clusters, the hot gas in the core is cooling at rates of 100Myr^–1 and greater. Few traces of the cooled gas have been observed, but it probably forms into low-mass stars (perhaps brown dwarf or even Jupiter-mass objects). X-ray surface-brightness profiles show that the cooling gas is highly inhomogeneous. Overdense gas cools rapidly to form cooled clumps distributed throughout the flow, with little of the gas ever reaching the cluster centre. Cooled and cooling clumps are disrupted because of their motion relative to the remainder of the gas, tending to produce small cooled fragments and, ultimately, low-mass stars. Large molecular clouds, which are the sites of massive star formation in our galaxy, do not occur in the outer parts of cooling flows. There is evidence of larger gas clumps and the formation of more massive stars in the central few kpc of some cooling flows. It is argued that cooling flows efficiently form dark matter. This has wider implications for the formation of dark matter in massive galaxies.     

滨州市海岸带工程地质特征分析

根据该次工程地质调查和钻探工作取得的大量数据,结合收集的钻孔资料,对研究区土体工程地质层进行了系统研究,并依据地层沉积年代、成因类型、地层结构、工程力学性质,对研究区陆域地表以下,海底以下50m深度范围内的土层进行分层研究,并对各层工程地质特征进行了分析,对区内软土分布范围、饱和砂土液化进行了综合研究,为滨州海岸带港口及重大工程规划建设提供系统的基础地质资料和决策依据。     

Displacement ring load Green's functions for saturated porous transversely isotropic tri‐material full‐space

Based on the Biot's poroelastic theory and using scalar potential functions both the ring load and point load displacement Green's functions for a transversely isotropic saturated porous full‐space composed of an upper half‐space, a finite thickness middle layer and a lower half‐space is analytically presented for the first time. It is assumed that each region consists of a different transversely isotropic material. The equations of poroelastodymanics in terms of the solid displacements and the pore fluid pressure are uncoupled with the help of two scalar potential functions, so that the governing equations for the potential functions are either a second order wave equation or a repeated wave‐heat transfer equation of sixth order. With the aid of Fourier expansion with respect to circumferential direction and Hankel integral transforms with respect to the radial direction in cylindrical coordinate system, the response is determined in the form of line integrals in the real space, followed by theorem of inverse Hankel integral transforms. The solutions degenerate to a single phase elastic material, and the results are compared with previous studies, where an excellent agreement may be observed with the results provided in the literature. Some examples of displacement Green's functions are finally given to illustrate the solution. Copyright © 2016 John Wiley & Sons, Ltd.     

A stabilized assumed deformation gradient finite element formulation for strongly coupled poromechanical simulations at finite strain

An adaptively stabilized finite element scheme is proposed for a strongly coupled hydro‐mechanical problem in fluid‐infiltrating porous solids at finite strain. We first present the derivation of the poromechanics model via mixture theory in large deformation. By exploiting assumed deformation gradient techniques, we develop a numerical procedure capable of simultaneously curing the multiple‐locking phenomena related to shear failure, incompressibility imposed by pore fluid, and/or incompressible solid skeleton and produce solutions that satisfy the inf‐sup condition. The template‐based generic programming and automatic differentiation (AD) techniques used to implement the stabilized model are also highlighted. Finally, numerical examples are given to show the versatility and efficiency of this model. Copyright © 2013 John Wiley & Sons, Ltd.     

Steady flow to a partially penetrating blind‐wall well in a confined aquifer

Wells in aquifers of loose collapsible sediment are cased so that they have a blind wall and gain water only from the bottom. The hydraulic gradient established at the bottom of these wells during pumping brings the aquifer materials in a quicksand state, which may cause abrasion of pipes and pumps and even the destruction of well structure. To examine the quicksand occurrence, an analytical solution for the steady flow to a partially penetrating blind‐wall well in a confined aquifer is developed. The validity of the proposed solution is evaluated numerically. The sensitivity of maximum vertical gradient along the well bottom in response to aquifer and well parameters is examined. The solution is presented in the form of dimensionless‐type curves and equations that can be easily used to design the safe pumping rate and optimum well geometry to protect the well against sand production. The solution incorporates the anisotropy of aquifer materials and can also be used to determine the hydraulic conductivity of the aquifer. Copyright © 2012 John Wiley & Sons, Ltd.     

Transport and retention of Escherichia coli in a mixture of quartz,Al‐coated and Fe‐coated sands

Transport and retention of Escherichia coli through the mixture of quartz, Al‐coated and Fe‐coated sands was examined using column experiments to investigate the effect of geochemical heterogeneity on bacteria transport. The first set of the experiments was performed in quartz, Al‐coated and Fe‐coated sand mixtures (coated sand: 0, 5, 10, 25, 50, 100%) to examine the influence of positively‐charged sand grains on bacteria transport. The second experiments were carried out to observe the impact of pH (range 6·74–8·21) on bacteria transport in the mixture of quartz 50% and Fe‐coated sand 50%. The third experiments were conducted to analyse the effect of ionic strength (0, 50, 100, 200 mM) on bacteria transport in the mixture of quartz 50% and Al‐coated sand 50%. The first experiments show that bacterial mass recoveries were in the range of 3·6–43·4%, decreasing nonlinearly as the content of Al‐ and Fe‐coated sands increased. In the second experiments, the bacterial mass recoveries were in the range of 35·5–79·2%, increasing linearly as the solution pH increased. In the third experiments, the mass recovery was 3·4% at 0 mM. As the ionic strength increased to 50mM, the mass recovery decreased to 0%. When the ionic strength increased further to 100 and 200 mM, no bacterial mass was recovered as in the case of 50 mM. It indicates that in the mixed medium of quartz 50% and Al‐coated sand 50% both positive (increment of bacterial adhesion) and negative (decrement) effects of ionic strength may be counterbalanced, minimizing the impact of ionic strength on the bacterial adhesion. This study helps to understand the role of metal oxides and solution chemistry in the transport of bacteria in geochemically heterogeneous media Copyright © 2008 John Wiley & Sons, Ltd.     

The Sun – Earth Workshop: A Summary of the Outcome

This special issue includes a set of papers that deal with extended solar activity, the launching of CMEs at the Sun, their propagation through interplanetary space, and the detection and study of the ejecta near Earth and of their interaction with the Earth’s magnetic environment. In particular solar events that occurred on 28 October 2003, 6 and 7 November 2004, and 20 January 2005, for which the related shocks arrived at Earth about two days later, are considered. The summary paper extracts the principal outcomes that were arrived at in the areas treated during the workshop and seeks to draw conclusions both on the progress made and on possible directions for future work in these areas.