Simulation of less‐mobile porosity dynamics in contrasting sediment water interface porous media

Considering heterogeneity in porous media pore size and connectivity is essential to predicting reactive solute transport across interfaces. However, exchange with less‐mobile porosity is rarely considered in surface water/groundwater recharge studies. Previous research indicates that a combination of pore‐fluid sampling and geoelectrical measurements can be used to quantify less‐mobile porosity exchange dynamics using the time‐varying relation between fluid and bulk electrical conductivity. For this study, we use macro‐scale (10 s of cm) advection–dispersion solute transport models linked with electrical conduction in COMSOL Multiphysics to explore less‐mobile porosity dynamics in two different types of observed sediment water interface porous media. Modeled sediment textures contrast from strongly layered streambed deposits to poorly sorted lakebed sands and cobbles. During simulated ionic tracer perturbations, a lag between fluid and bulk electrical conductivity, and the resultant hysteresis, is observed for all simulations indicating differential loading of pore spaces with tracer. Less‐mobile exchange parameters are determined graphically from these tracer time series data without the need for inverse numerical model simulation. In both sediment types, effective less‐mobile porosity exchange parameters are variable in response to changes in flow direction and fluid flux. These observed flow‐dependent effects directly impact local less‐mobile residence times and associated contact time for biogeochemical reaction. The simulations indicate that for the sediment textures explored here, less‐mobile porosity exchange is dominated by variable rates of advection through the domain, rather than diffusion of solute, for typical low‐to‐moderate rate (approximately 3–40 cm/day) hyporheic fluid fluxes. Overall, our model‐based results show that less‐mobile porosity may be expected in a range of natural hyporheic sediments and that changes in flowpath orientation and magnitude will impact less‐mobile exchange parameters. These temporal dynamics can be assessed with the geoelectrical experimental tracer method applied at laboratory and field scales.     

韧性剪切带构造岩类质量平衡分析

本文概要介绍了韧性剪切带研究的新方法——构造岩类质量平衡分析法。     

湘南晚泥盆世佘田桥期碳酸盐块状流沉积特征

湘南晚泥盆世佘田桥期表现为东西两侧高而中部低陷的古地理面貌。两侧为碳酸盐台地,中间为深水台盆。在台盆、台地之间斜坡地带和台盆边缘,堆积了类型繁多的碳酸盐块状流沉积物。它们由两类在成因和分布上有密切联系的沉积体系组成,一类为重力崩落或滑移体系,包括岩崩、滑动和滑塌沉积,另一类为重力流体系,包括碎屑流、浊流和颗粒流沉积。在层序上它们虽作有规律的组合层序,但并不是完整的类型,而出现较大的变异性。已发现的组合层序有①滑塌沉积—碎屑流沉积,②碎屑流—高密度浊流—低密度浊流沉积,③变密度颗粒流—浊流沉积。它们沿近南北向的台盆的两侧边缘呈条带状分布,东侧位于临武香花岭至桂阳莲塘一带,重力流厚度可达150m左右,西侧位于道县虎岩坝至双牌县城一带,重力流厚只30—50m,反映了台盆边缘两侧构造活动强度不一致,东侧强,西侧弱。     

Long baseline interferometric observations of long period variable stars

Recent observations of long-period variable stars at spatial resolutions from approximately 1 arcsec to several milli-arcsecs have provided new insights into pulsation, dust formation, and mass-loss of AGB stars. These insights have come from long baseline interferometric observations obtained across a wide range of wavelengths, from the optical, through the infrared, to wavelengths as long as several millimeters. The present status and recent results from long baseline interferometry, particularly at optical and infrared wavelengths, are discussed. Such results include diameters and limb-darkening, surface features, mode of pulsation, location of SiO masers, inner radii of dust shells, physical conditions in the dust formation zone and of the inner regions of the dust shells. The results are interpreted in terms of present models of dust formation and mass-loss.     

Nonlinear models of pulsation and mass loss

We briefly discuss the current status of our radiation-hydrodynamical models of pulsation in various stellar objects and of dust-driven mass loss in LPVs. We emphasize the importance of a future combined modelling of pulsation and mass loss in AGB stars which has to be based on reliable physical and numerical methods.     

东秦岭地区浅隐花岗岩体遥感识别模式

在含金地层分布区，研究揭示隐伏岩浆热源活动特征及基底导岩导矿构造特征是寻找隐伏金矿床的技术关键。本文依据花岗岩体侵位动力学及热力学机制，阐明了线、环同现构造影像的形成机理及其所揭示的地质内涵，指出了环形影像构造成因的多解性，提出了如何从纷杂的“环、线”影像构造中提取出反映岩体侵位这一特定影像构造的原则及其重要性，以遥感技术为主导，综合应用地质、物化探技术，建立了“环状影像构造－斜磁化场－重力亏损场－岩浆期后热液活动中心的多元信息同现”隐伏成矿花岗岩体的遥感综合判读模式，实现了遥感解译由模糊—定性—定量化的综合解译判读过程。论证了东秦岭一些地区存在着规模宏大的燕山期浅隐伏成矿花岗岩体，并定量解译了隐伏花岗岩体的形态、产状及规模，指出金及其伴生元素的含矿热液活动受隐伏岩浆活动及基底导岩导矿构造双重因素控制     

The dynamics of velocity fluctuations in the solar wind – I. Coronal mass ejections

In this paper we present a simple, analytic model for the dynamical evolution of supersonic velocity fluctuations at the base of the ambient solar wind. These fluctuations result in the formation of dense working surfaces that travel down the wind. It is shown how the initial parameters of the fluctuations (velocity, density and duration) are related to the characteristics of the working surfaces far from the Sun (for instance at the Earth). We apply the model to the evolution of the coronal mass ejections in the IP medium, finding that the model is in good agreement with satellite observations of these phenomena, thus providing physical insight into their dynamical evolution. Our model may contribute to future 'space weather forecasting' on the Earth, based on detailed satellite monitoring of the solar corona.     

Spectral analyses of [WCL]-type central stars

The optical spectra of the seven late-type Wolf-Rayet central stars NGC-40 (PNG 120.0+09.8, subtype [WC8]), He 2-99 (PNG 309.0–04.2, [WC9]), BD+30°3639 (PN G 064.7+05.0, [WC9]), CPD-56°8032 (PNG 332.9–09.9, [WC11]), He2-113 (PNG 321.0+03.9, [WC11]), M4-18 (PNG 146.7+07.6, [WC11]) and K2-16 (PNG 352.9+11.4, [WC11]) are analyzed by means of spherically expanding model atmospheres. The NLTE simulations account for the elements hydrogen, helium, carbon and oxygen. As main results effective temperature, element abundances and final velocity of the wind are determined for each star. Assuming distances or luminosities for the objects, also the stellar radii and the mass-loss rates can be fixed. The results of these analyses establish empirical constraints for the evolutionary status of WC-type central stars as post-AGB objects and provide input for modeling their planetary nebulae.