零通量方法原位测定给水度

本文简略介绍了零通量面（ＺＦＰ）方法原位测定给水度的原理、计算,并给出了在银北平原江南试区人工调控地下水位条件下和天津万军套洼试点天然条件下应用ＺＦＰ方法原位测定给水度的具体实例。结果表明,给水度测定值与测参历时有关,对单一岩性而言,其值逐渐增大,经过相当时间后将趋于某一稳定值,其原因是非饱和带释水存在滞后作用,所以它也是反映不同释水过程的一个参数,其值是在一个范围内变化。另外给水度测定值与包气带及潜水位变动带的岩性有关,土层质地越粘重给水度值越小,包气带释水的滞后作用影响越明显。同时,潜水位降落的起始位置不同对多层地质结构的给水度测定值影响也不同。而且给水度的测定值还与潜水埋深及包气带土壤剖面初始含水量有关。     

Analysis of oil lens removal by extraction through a seepage face

Removal of LNAPL (oil) from an aquifer is described using a multiphase flow model. At the well boundary seepage face conditions are imposed. These conditions are implemented in a numerical model and withdrawal in a twodimensional domain is simulated for two different geometries of the oil lens and for varied values of the physical parameters. Assuming vertical equilibrium, the oil flow equation is reduced by vertical integration. The well boundary condition is approximated by imposing zero oil lens thickness. Similarity solutions of the reduced equations for the two geometries show good agreement with the numerical results in most cases.     

莺歌海盆地上新统双壳类贝壳的锶含量及其意义

锶（Ｓｒ）是碳酸盐沉积物及软体动物介壳中的重要微量元素之一,Ｓｒ含量和Ｓｒ／Ｃａ比值的变化明显受沉积相的控制。因此,锶作为地球化学指标具有一定的环境意义。通过对南海北部莺歌海盆地莺６井上新统双壳类贝壳中的Ｓｒ含量和Ｓｒ／Ｃａ比值的变化与环境、成岩作用关系的研究,发现莺歌海盆地上新世沉积环境为上陆坡→潮下带→潮间带,所得结论与双壳类的生态环境和地层沉积相的综合分析结果一致。     

膨胀土胀缩性评价中有关问题的研究

膨胀土吸水膨胀、失水收缩,产生地表变形,进而导致建筑物破坏。本文就现行膨胀土胀缩性指标试验及地基变形量评价计算中有关问题进行了研究,认为以天然含水量为起始含水量测定土样胀缩率是不合适的,建议以缩限为起点进行膨胀试验,以胀限为起点进行收缩试验,采用加荷膨胀量（而非卸荷膨胀量）参加有荷载下的膨胀率计算。膨胀土地基勘察必须结合场地条件分析可能影响土体含水量变化的因素,对同一工程采用几种方法评价,互相对比、参照。     

The Stellar Content of Active Galaxies

We present the results of a long-slit spectroscopic study of 38 active and four normal galaxies. Stellar absorption features, continuum colours and their radial variations are analysed in an effort to characterize the stellar population in these galaxies and detect the presence of a featureless continuum underlying the starlight spectral component. Spatial variations of the equivalent widths of conspicuous absorption lines and continuum colours are detected in most galaxies. Star-forming rings, in particular, leave clear fingerprints in the equivalent widths and colour profiles. We find that the stellar populations in the inner regions of active galaxies present a variety of characteristics, and cannot be represented by a single starlight template. Dilution of the stellar lines by an underlying featureless continuum is detected in most broad-lined objects, but little or no dilution is found for most of the 20 type 2 Seyferts in the sample. Colour gradients are also ubiquitous. In particular, all but one of the observed Seyfert 2s are redder at the nucleus than in its immediate vicinity. Possible consequences of these findings are briefly outlined.     

Pre-enriched, not primordial ellipticals

We follow the chemical evolution of a galaxy through star formation and its feedback into the interstellar medium (ISM), starting from primordial gas and allowing for gas to inflow into the region being modelled. We attempt to reproduce observed spectral line strengths for early-type galaxies in order to constrain their star formation histories (SFH). The efficiencies and times of star formation are varied, as are the amount and duration of inflow. We evaluate the chemical enrichment and the mass of stars made with time. Single stellar population (SSP) data are then used to predict line strengths for composite stellar populations. The results are compared with observed line strengths in 10 ellipticals, including some features which help to break the problem of age–metallicity degeneracy in old stellar populations. We find that the elliptical galaxies modelled require high metallicity SSPs (> 3 Z⊙) at later times. In addition, the strong lines observed cannot be produced by an initial starburst in primordial gas, even if a large amount of inflow is allowed for during the first few × 10⁸ yr. This is because some pre-enrichment is required for lines in the bulk of the stars to approach the observed line strengths in ellipticals. These strong lines are better modelled by a system with a delayed burst of star formation, following an early SFH which can be a burst or more steady star formation. Such a model is representative of star formation in normal ellipticals or spirals, respectively, followed by a starburst and gas inflow during a merger or strong interaction with a gas-rich galaxy. Alternatively, a single initial burst of normal stars with a Salpeter initial mass function could produce the observed strong lines if it followed some pre-enrichment process which did not form long-lived stars (e.g. population III stars).     

Stellar evolution models for Z = 0.0001 to 0.03

We have calculated a grid of empirically well tested evolutionary tracks with masses M between 0.5 and 50 M⊙, spaced by approximately 0.1 in log M , and with metallicities Z  = 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02 and 0.03. We use a robust and fast evolution code with a self-adaptive non-Lagrangian mesh, which employs the mixing-length theory but treats convective mixing as a diffusion process, solving simultaneously for the structure and the chemical composition. The hydrogen and helium abundances are chosen as functions of the metallicity: X  = 0.76 − 3.0 Z Y  = 0.24 + 2.0 Z .   Two sets of models were computed, one without and one with a certain amount of enhanced mixing or 'overshooting'. This amount has been empirically chosen by means of various sensitive tests for overshooting: (1) the luminosity of core helium burning (blue loop) giants of well-known mass, (2) the width of the main sequence as defined by double-lined eclipsing binaries with well-measured masses and radii, and (3) the shape and implied stellar distribution of isochrones of various open clusters. The first two tests have been the subject of previous papers, the third test is discussed in this paper. On the basis of these tests, we recommend the use of the overshooting models for masses above about 1.5M ⊙.   We describe here the characteristics of the models, the procedure for constructing isochrones for arbitrary age and metallicity from the models, and the performance of these isochrones for several intermediate-age and old open clusters. All original models are available in electronic form and we describe the means by which they may be obtained.     

Stellar population synthesis with more degrees of freedom than observables

In order to derive the stellar population of a galaxy or a star cluster, it is a common practice to fit its spectrum by a combination of spectra extracted from a data base (e.g. a library of stellar spectra). If the data to be fitted are equivalent widths, the combination is a non-linear one and the problem of finding the 'best' combination of stars that fits the data becomes complex. It is probably because of this complexity that the mathematical aspects of the problem did not receive a satisfying treatment; the question of the uniqueness of the solution , for example, was left in uncertainty. In this paper we complete the solution of the problem by considering the underdetermined case where there are fewer equivalent widths to fit than stars in the data base (the overdetermined case was treated previously). The underdetermined case is interesting to consider because it leaves space for the addition of supplementary astrophysical constraints. In fact, it is shown in this paper that when a solution exists it is generally not unique. There are infinitely many solutions, all of them contained within a convex polyhedron in the solutions vector space. The vertices of this polyhedron are extremal solutions of the stellar population synthesis. If no exact solution exists, an approximate solution can be found using the method described for the overdetermined case. Also provided is an algorithm able to solve the problem numerically; in particular all the vertices of the polyhedron are found.     

Morphology of star formation regions in irregular galaxies

The location of H  II regions, which indicates the locus of present star formation in galaxies, is analysed for a large collection of 110 irregular galaxies (Irr) imaged in Hα and nearby continuum. The analysis is primarily by visual inspection, although a two-dimensional quantitative measure is also employed. The two different analyses yield essentially identical results. H  II regions appear preferentially at the edges of the light distribution, predominantly on one side of the galaxy, contrary to what is expected from stochastic self-propagating star formation scenarios. This peculiar distribution of star-forming regions cannot be explained by a scenario of star formation triggered by an interaction with extragalactic gas, or by a strong one-armed spiral pattern.