The initial mass function and history of the star-formation rate in star-forming complexes in galaxies

The positions of star-forming complexes (SFCs) in color-luminosity, color-color, and chemical composition-luminosity diagrams are determined by the star-formation regime (history). Taking into account the fraction of Lyman continuum photons that are not absorbed by hydrogen, we find a strong correlation between the observed color indices and the total Lyman continuum flux from the stars in SFCs. The distribution of extragalactic SFCs in a plot of the slope of the initial mass function (IMF) versus the density of stars cannot be distinguished from this distribution for clusters in the Galaxy and the Large Magellanic Cloud, where the IMF slopes were derived directly from star counts.     

Comparison of <Emphasis Type="Italic">U BV R</Emphasis> photometry of giant HII regions in the galaxy NGC 628 with a detailed grid of evolutionary models for star clusters

We present the results of U BV RI CCD photometry of giant HII regions in the spiral galaxy NGC 628, acquired with the 1.5 m telescope of the Mt. Maidanak Observatory (Uzbekistan) with an angular resolution better than 1″. We estimate the ages and interstellar extinctions of these regions and identify the acting star-formation mode by comparing the observed color indices with a detailed grid of evolutionary models covering the entire range of parameters of the initial mass function and of ages of the young star-formation complexes, and taking into account two star-formation modes. We find a radial gradient of the interstellar extinction in NGC 628, which is consistent with the radial abundance gradient found earlier by other authors from independent spectrophotometry. Our age estimates agree with abundance estimates from independent observations.     

Timescales for mechanisms for the dynamical evolution of open star clusters

We have obtained the stellar velocity dispersion in three mutually perpendicular directions in the halos and cores of clusters as a function of time for several non-stationary open-cluster models. During the dynamical evolution of the open-cluster models, the velocity dispersions undergo oscillations that do not decay during 5–10 violent-relaxation timescales, τ _vr . We estimated the time for synchronization of the rotation of the open-cluster models and their motion around the center of the Galaxy, t _s , which, depending on the model parameters, is t _s ? (5–27)τ _vr . Synchronization mechanisms for the models are discussed. The disruption of the systems in the force field of the Galaxy is strongly affected by tidal friction. We have also estimated the time for the formation of a spherical stellar-velocity distribution in the cluster models, t _σ ? (6 ? 25)τ _vr . The impact of instability in the stellar motions in a cluster on the formation of a spherical velocity distribution in the open-cluster models is discussed. We have noted a tendency for a weakening of the dependence of the coarse phase density of the cluster on small initial perturbations of the stellar phase coordinates in the model cluster cores for times about five times longer than the violent-relaxation time.     

冥古宙的地层学属性:了解地球形成初期古地理背景和演变历史的重要线索*

在现行的前寒武纪地质年代表中,由于太古宙底界没有得到很好的定义,只是被粗略地置于大约4000,Ma,因此也造成了一个没有得到较好定义的“冥古宙”。2个重要的发现促使学者们对冥古宙的地层学属性进行修订:(1)在西澳大利亚Jack山脉太古宙砾岩中发现了真正古老的锆石晶体,其不仅可将地层时代延伸到4404,Ma,而且包含了有关地球早期环境条件较为丰富的信息; (2)在加拿大北部发现了大约4030,Ma的Acasta片麻岩。根据这些发现,并结合月球和陨石的测年数据,就产生了大量有关太阳系和地球早期历史的新知识,包括太阳系与地球的形成、初生地球时期的重要变化及其物质记录和生命的起源及早期进化,这成为修订冥古宙地层学属性的重要基础。修订后的冥古宙代表了地球演变历史的最早时段,即从太阳系和地球在T0=4567,Ma的形成,一直延续到地球上最古老岩石的出现(4030,Ma)。冥古宙还可被进一步划分为2个代:(1)“混沌代”(4567,Ma—4404±8,Ma);(2)“杰克山代”或“锆石代”(4404±8,Ma—4030,Ma)。由于没有保存相应的地层记录,因此冥古宙顶界(4030,Ma)与底界(4567,Ma)的年龄值,仅为一个计时性的年代界限。上述这个被赋予了明确地层学属性的冥古宙,不仅代表了前寒武纪地层学研究的一个重要进展,而且也为深入了解地球早期演变历史提供了许多重要的理念。     

Proper motions of open star clusters and the rotation rate of the galaxy

The mean proper motions of 167 Galactic open clusters with radial-velocity measurements are computed from the data of the Tycho-2 catalog using kinematic and photometric cluster membership criteria. The resulting catalog is compared to the results of other studies. The new proper motions are used to infer the Galactic rotation rate at the solar circle, which is found to be ω₀=+24.6±0.8 km s^?1 kpc^?1. Analysis of the dependence of the dispersion of ω₀ estimates on heliocentric velocity showed that even the proper motions of clusters with distances r>3 kpc contain enough useful information to be used in kinematic studies demonstrating that the determination of proper motions is quite justified even for very distant clusters.     

Pore-to-core simulations of flow with large velocities using continuum models and imaging data

We consider computational modeling of flow with small and large velocities at porescale and at corescale, and we address various challenges in simulation, upscaling, and modeling. While our focus is on voxel-based data sets from real porous media imaging, our methodology is verified first on synthetic geometries, and we analyze various scaling and convergence properties. We show that the choice of a voxel-based grid and representative elementary volume size can lead up to 10–20 % difference in calculated conductivities. On the other hand, the conductivities decrease significantly with flow rates, starting in a regime usually associated with the onset of inertia effects. This is accompanied by deteriorating porescale solver performance, and we continue our experiments up until about 50 % reduction in conductivities, i.e., to Reynolds number just under 1. To account for this decrease, we propose a practical power-based fully anisotropic non-Darcy model at corescale for which we calculate the parameters by upscaling.     

The possible existence of cloud-like clusters of microparticles at the libration points of a binary star

The possible existence of clusters of microscopic gas-dust particles forming gigantic clouds is demonstrated in the framework of the photogravitational three-body problem. These clouds are pulsating formations representing heterogeneous ensembles of particles of various sizes, densities, and susceptibilities to the radiation pressure, with each of the particles moving along its own trajectory. The conditions for the existence of co-linear and triangular libration points are derived by analyzing the dynamical equations describing the motion of a test particle in the gravitational-repulsive field of two gravitating and radiating bodies moving in an elliptical orbit about their common center of mass. The stability of these libration points is studied for various eccentricities e, mass parameters µ, and reduction coefficients characterizing the action of the stellar radiation on particles, and the results generalized in diagrams. We demonstrate the formation of clouds of particles located at multiple stable libration points. The extent of these clouds and their distances from the binary components are estimated. Scenarios for the subdivision of the clouds based on variations of e and µ are presented. The results of computations for a binary star with characteristics similar to those for α Cen are presented.     

Reconstructing images from projections using the maximum-entropy method. Numerical simulations of low-aspect astrotomography

The reconstruction of images from a small number of projections using the maximum-entropy method (MEM) with the Shannon entropy is considered. MEM provides higher-quality image reconstruction for sources with extended components than the Högbom CLEAN method, which is also used in low-aspect astrotomography. The quality of image reconstruction for sources with mixed structure containing bright, compact features embedded in a comparatively weak, extended base can be further improved using a difference-mapping method, which requires a generalization of MEM for the reconstruction of sign-variable functions. We draw conclusions based on the results of numerical simulations for a number of model radio sources with various morphologies.     

Star formation in extragalactic HII regions. Determination of parameters of the initial mass function

A method for using the colors of star-forming complexes to derive the slope and upper mass limit of the initial mass function (IMF) and the age of the complex is proposed in the framework of synthetic evolutionary models of star-cluster populations. The star-formation parameters of 105 complexes in 20 spiral and irregular galaxies are determined. The IMF slopes in different star-forming complexes differ appreciably, and their dependence on the luminosities and masses of the complexes is derived. The duration of the star-formation period increases with the luminosity of the complex, and complexes with longer star-formation periods are richer in metals. The slope of the integrated IMF in a Galaxy depends on the mass spectrum of its complexes, and the upper mass limit of the IMF is lower in early-type spirals.     

Sedimentary dynamics and evolutionary history of a Late Carboniferous Gondwanic lake in north-western Argentina

Lacustrine deposits are well represented in the lower part of the Late Carboniferous Agua Colorada Formation in the north-west Sierra de Narváez, Catamarca Province, Argentina. Lake Narváez was one of the several water bodies formed in the region immediately after the Gondwana glaciation. The lacustrine transport system has been divided into three distinct zones: delta, shallow lake and deep lake. Delta progradation proceeded from the ESE. Coarse-grained delta plain and turbidite delta front deposits suggest that the delta was formed close to the headwaters (‘short-headed stream delta’type). During periods of high discharge, river mouths acted as bypass zones and fine and very fine sands were transported further into the lake by underflow currents. The clastic material supplied by the deltaic system was partially reworked by wave action. Sands accumulated in unstable conditions at the upper delta front as a consequence of delta progradation. As a result of the addition of clastics in the steep delta front, turbidity currents were formed, spreading their load along the lower delta slope. Deep lacustrine deposits are typically stacked, forming two different kinds of progradational turbidite lobe sequences. Type I lobes were formed in a basinal setting and were probably detached from their feeder systems as a result of sediment-bypassing in a shallow lake during periods of low lake level. These turbidite lobes are replaced upwards by type II lobes, which were formed on the delta slope during periods of lake level rise that allowed the onset of delta progradation. The presence of highly deformed sandstone bodies suggests rapid depositional rates in a high slope setting, whereas the occurrence of hummocky cross-stratified sandstones indicates wave reworking of the sands initially emplaced by turbidity currents. Therefore, the inner part of type II lobes was formed above storm wave base. The depositional history of Lake Narváez can be traced through four evolutionary stages: lake transgression, formation of type I lobes, formation of type II lobes and delta progradation. Tectonic activity was probably important at the early stage of lake evolution, but the subsequent depositional history was mainly controlled by fluctuations of lake level.     

四川通江-南江-巴中地区长兴组层序地层特征及演化模式

本文以Vail的经典层序地层学和Cross的高分辨率层序地层学理论方法为指导,通过对层序界面、相序、叠置结构、测井曲线等标志的综合识别分析,将研究区长兴组划分为两个三级层序。在长兴组三级层序格架剖面建立的基础上,建立了长兴组层序地层演化模式,并从层序演化的角度探讨了长兴组沉积时期礁滩体的发育分布规律。     

Spatial estimation of geotechnical parameters for numerical tunneling simulations and TBM performance models

In this paper, we further elaborate on a methodology dedicated to the modeling of geotechnical data to be used as input in numerical simulation and TBM performance codes. The expression “geotechnical data” refers collectively to the spatial variability and uncertainty exhibited by the boundaries and the mechanical or other parameters of each geological formation filling a prescribed 3D domain. Apart from commercial design and visualization software such as AutoCAD Land Desktop^® software and 3D solid modelling and meshing pre-processors, the new tools that are employed in this methodology include relational databases of soil and rock test data, Kriging estimation and simulation methods, and a fast algorithm for forward or backward analysis of TBM logged data. The latter refers to the continuous upgrade of the soil or rock mass geotechnical model during underground construction based on feedback from excavation machines for a continuous reduction of the uncertainty of predictions in unsampled areas. The approach presented here is non-intrusive since it may be used in conjunction with a commercial or any other available numerical tunneling simulation code. The application of these tools is demonstrated in Mas-Blau section of L9 tunnel in Barcelona.     

Numerical evaluation of three non‐coaxial kinematic models using the distinct element method for elliptical granular materials

This paper presents a numerical evaluation of three non‐coaxial kinematic models by performing Distinct Element Method (DEM) simple shear tests on specimens composed of elliptical particles with different aspect ratios of 1.4 and 1.7. The models evaluated are the double‐shearing model, the double‐sliding free‐rotating model and the double slip and rotation rate model (DSR² model). Two modes of monotonic and cyclic simple shear tests were simulated to evaluate the role played by the inherent anisotropy of the specimens. The main findings are supported by all the DEM simple shear tests, irrespective of particle shape, specimen density or shear mode. The evaluation demonstrates that the assumption in the double‐shearing model is inconsistent with the DEM results and that the energy dissipation requirements in the double‐sliding free‐rotating model appear to be too restrictive to describe the kinematic flow of elliptical particle systems. In contrast, the predictions made by the DSR² model agree reasonably well with the DEM data, which demonstrates that the DSR² model can effectively predict the non‐coaxial kinematic behavior of elliptical particle systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Numerical simulations for effects of anisotropy and heterogeneity on well responses to slug tests

Because of their simplicity, assumptions of isotropy and homogeneity are often applied to slug test analyses, determining hydraulic conductivity of heterogeneous and anisotropic formations, in spite of their inherent unfitness. In this study, it was examined how anisotropy and heterogeneity of the formation affect well recovery curves and therefore estimates of hydraulic conductivity in slug tests. Using a finite element method (FEM) slug test model, several hypothetical slug tests in anisotropic and heterogeneous formations with known hydraulic parameters and actual formations of unknown parameters were analyzed. Error factors as a result of the assumptions of isotropy and homogeneity were quantified through sensitivity analyses of well recovery curves. Results of slug tests analyzed in this study indicate that: (1) the well recovery curves in slug tests do not show unique shape or signs reflecting the anisotropy and heterogeneity of the tested formation; (2) the assumption of isotropy does not deviate estimates of hydraulic conductivity significantly when the radial hydraulic conductivity is larger than the vertical one in the formation; (3) the assumption of homogeneity in a layered heterogeneous system has a high potential for errors in hydraulic conductivity estimation, however it can be avoided by placing the screened section apart from the adjacent layers; (4) a low permeability well skin skews the hydraulic conductivity of the original formation, depending on the size and hydraulic conductivity of the skin.     

隧道开挖与支护有限差分法分析

根据景德镇-黄山高速公路某隧道现场工程地质条件和隧道结构设计参数,采用有限差分法对喷射500 mm普通混凝土支护和喷射200 mm厚聚丙烯纤维混凝土支护两种支护结构,进行了施工过程的数值模拟分析。从围岩的应力、位移和塑性区分布3个方面对隧道围岩的稳定性进行了分析。模拟计算结果表明,采用喷射200 mm厚聚丙烯纤维混凝土支护结构的隧道围岩能够处于稳定状态。     

Coprecipitation in the barite isostructural family: 2. Numerical simulations of reactions and mass transport

Coprecipitation of barite with trace constituents was simulated with consideration of aqueous speciation and complexation, mixing properties for the binary solid solutions (Zhu, this issue), precipitation and dissolution kinetics, and advective-dispersive transport. Speciation-solubility modeling was used to reproduce BaSO₄-RaSO₄ coprecipitation experimental results, and to calculate CrO₄²⁻ aqueous concentrations in equilibrium with a Ba(SO₄,CrO₄) solid solution. Kinetic reaction path modeling was used to simulate the coprecipitation of barite with RaSO₄ to form an onion-like chemically zoned solid upon the cooling of oil field brine.A one-dimensional coupled reactive mass transport model shows a strikingly different transport pattern for the tracer Ra²⁺, when the dominant attenuation reaction is with solid solution (Ba, Ra) SO₄ as compared to the case when it is controlled by pure RaSO₄ and barite solids under local equilibrium conditions. A self-enrichment of Ra²⁺ in the groundwater and aquifer solid matrix—higher concentrations of Ra²⁺ downstream from the reaction front—results from the coprecipitation reaction and advective-dispersive transport. This self-enrichment process generates a secondary tracer source, which has tracer concentrations higher than that of the original source. On the other hand, coprecipitation reactions can reduce Ra²⁺ concentrations in groundwater to a much lower level (below ppb) than that of pure RaSO₄(c) solubility (near ppm), which has been used to establish the Ra²⁺ concentration limits in groundwater, soil, and nuclear waste repositories.     

Numerical MHD simulations of post-flare loop formation on the sun: Allowing for thermal-conductivity anisotropy

The process of post-flare loop formation, including the heating of flux tubes by hot chromospheric sources and their filling with plasma, is demonstrated by simulations in an MHD approximation. The loop is additionally heated at its apex by the interaction of oppositely directed plasma streams. Local coronal heating over the loop is also possible due to magnetic-field-line reconnection. A new version of the PERESVET code that can take into account anisotropy of the thermal conductivity of a plasma in a magnetic field was used for the computations.     

Discussion on the formation and evolutionary history of Shangyi-Longhua regional fault in northern Hebei Province

Shangyi-Longhua regional fault was EW distributed near northern Hebei Province, which was first active in the Late Neoarchean (Late Fuping) and still active in the Holocene and even today. Therefore, exploring its formation and evolutionary history is of great significance to study its geological structure, mineral distribution and the influence of Neotectonic movement on human beings in northern Hebei Province. The regional faults in Shangyi-Longhua are strong complex deformation zones through the census of the tectonic rocks and all kinds of directional structures in the fault zone. The ductile deformation and brittle deformation are alternating with characters of chronicity, multiphase activity, propensity and nature variation. Shangyi-Longhua regional fault is one of the important dividing lines of tectonic units of different levels in different periods in northern Hebei Province, which plays an important role in controlling the development and evolution of geological history on both sides. The authors redefined the structure superposition transformation relation and the development period, according to the superimposed relationship of the sturcture, the corresponding relationship between metamorphic degree of mylonites and the regional metamorphism, and the corresponding relationship between the movement model reflected by the shear-pointed fabric and the principal stress of the regional tectonic movement. Combined with the metamorphic mineral age of the predecessor tectonites, the authors divided the fault structure into two construction phases and nine tectonic active periods.     

冀北尚义—隆化区域断裂形成与演化历史探讨

尚义—隆化区域断裂呈近EW向分布于冀北地区,活动于新太古代晚期(阜平晚期),全新世至今仍有活动,探讨其形成与演化历史,对进一步研究冀北地区地质构造、矿产分布及新构造运动对人类活动的影响具有重要意义。通过统计该断裂中的构造岩及指向构造,发现尚义—隆化区域断裂为复杂的强变形带,韧性变形与脆性变形相间,具有长期及多期活动性、倾向及性质多变等特点; 尚义—隆化区域断裂是冀北地区不同时段不同级别构造单元的重要分界线之一,对两侧地质历史的发展及演化具有重要的控制作用。根据构造叠置关系、糜棱岩类变质程度与区域变质作用的对应关系,以及剪切指向组构反映的活动方式与区域构造运动主应力的对应关系,重新厘定了构造叠加改造关系及变形期次,结合前人构造岩的变质矿物年龄,将该断裂划分为2个构造阶段、9个构造活动期。     

Origin and evolutionary history of Anglonautilus (Nautilida,Cymatoceratidae) and a new species from the lower Aptian of Spain

The cymatoceratid nautilid genus Anglonautilus is distinguished from most other post-Triassic nautiloids by the occurrence of pronounced fold-like undulating ribs on the phragmocone and early body chamber. Anglonautilus praeundulatus n. sp. is described from the lower Aptian of eastern Spain. It is the first record of this genus from Spain and constitutes the oldest definite representative of the genus. This places the new species at the base of the evolutionary history of Anglonautilus. Its ornamental features confirm the previously assumed close relationship between Anglonautilus and Cymatoceras. An analysis of the ornamental pattern of all species hitherto referred to Anglonautilus indicates that there is an evolutionary lineage leading to the type species of the genus, A. undulatus, and a single successor (A. subalbensis). Several Late Cretaceous species hitherto identified as Anglonautilus (A. japonicus, A. mamiyai, A. suciensis) bear fold-like ribs superficially similar to typical representatives of Anglonautilus. The pattern of ornament in these taxa is very different at closer inspection, though. This suggests that these species developed independently from Cymatoceras. The undulations present in these taxa are interpreted here as a result of convergent evolution. They are therefore excluded from the genus Anglonautilus and provisionally referred to as “Anglonautilus” spp.