Are Type Ia Supernovae Reliable Distance Indicators？     

Lian-Zhong Lü 《中国天文和天体物理学报》2007,7(5):649-656

Recent applications of type Ia supernovae(SNe Ia)in cosmology have successfully revealed the accelerating expansion of the universe.However,as distance indicators used in measuring the expansion history of the universe and probing the nature of dark energy,these objects must pass more strict tests.We propose a K-S test to investigate if there exists any systematic bias when deriving the luminosity distances under the standard candle assumption. Two samples,one comprising 71 high-redshift SNe Ia and the other,44 nearby ones,are used in our investigation.We find that it is likely there exists a bias in the adopted samples,which is probably caused by a systematic error,e.g.in the color parameter used in the luminosity calibration and a bias may be caused by the SN evolution or by varying properties of the dust surrounding the SNe Ia.  相似文献   

Dehydration reaction and isotope front transport induced by CO₂ infiltration at Nuliyam, South India     

D. H. JACKSON  M. SANTOSH 《Journal of Metamorphic Geology》1992,10(3):365-382

The field relations from a quarry at Nuliyam, South India, illustrate dehydration of an amphibolite facies gneiss to granulite facies charnockite by CO₂ influx, over a scale of 30 m. Both the calc-silicate source of the fluids and the full extent of their penetration into the gneiss are preserved in a continuous section. Fluid flow is by a hydraulic fracture mechanism, but is thought to be pervasive. The sharp reaction front predicted by the continuum mechanical theory for advective fluid transport is not observed. The front spreading is on too large a scale for either diffusive or dispersive control and is due to local kinetic disequilibrium between the fluid and rock, although the divariant nature of the reaction may also have a limited effect. The time-integrated fluid flux varies from the instantaneous porosity at the fluid front to 20 vol. % adjacent to the calc-silicate. Carbon isotope budgets suggest that decarbonation of the calc-silicate by a Rayleigh fractionation process provides a sufficient source for the CO₂ influxing into the gneiss. Graphite abundances vary from 0.01 to 0.1% (by weight), it is principally derived by precipitation from the fluid and may be modelled from phase equilibria. Carbon isotope fronts coincide with the reaction front on the scale of sampling, although isotopic disequilibrium between graphite and inclusion-CO₂ also implies local fluid-rock disequilibrium.  相似文献   

恒星导星器设计的新方案     

徐家岩  王正明 《时间频率学报》1992,15(2):121-125

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The clustering of luminous red galaxies in the Sloan Digital Sky Survey imaging data     

Nikhil Padmanabhan  David J. Schlegel  Uro&#; Seljak  Alexey Makarov  Neta A. Bahcall  Michael R. Blanton  Jonathan Brinkmann  Daniel J. Eisenstein  Douglas P. Finkbeiner  James E. Gunn  David W. Hogg  &#;eljko Ivezi&#;  Gillian R. Knapp  Jon Loveday  Robert H. Lupton  Robert C. Nichol  Donald P. Schneider  Michael A. Strauss  Max Tegmark  Donald G. York 《Monthly notices of the Royal Astronomical Society》2007,378(3):852-872

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On the deprojection of clusters of galaxies combining X-ray, Sunyaev–Zeldovich temperature decrement and gravitational lensing maps     

M. Sereno 《Monthly notices of the Royal Astronomical Society》2007,380(3):1207-1218

Knowledge of the intrinsic shape of galaxy clusters is very important in investigating cosmic structure formation and astrophysical processes. The reconstruction of the 3D structure usually relies on deprojecting 2D X-ray, Sunyaev–Zeldovich (SZ) and/or gravitational lensing observations. As known, a joint analysis of these data sets can provide the elongation of the cluster along the line of sight together with its length and width in the plane of the sky. An unbiased measurement of the Hubble constant can be also inferred. Due to some intrinsic degeneracies, the observational constraints obtained from such projected data sets are not enough to allow an unique inversion. In general, the projected maps can be at the same time compatible with prolate, oblate and with many triaxial configurations. Even a prolate cluster might be interpreted as an oblate system and vice versa. Assuming that the cluster is axially symmetric is likely to overestimate the intrinsic ellipticity, whereas the system always looks rounder performing the inversion under the hypothesis of a triaxial cluster aligned with the line of sight. In general, analysing triaxial clusters under the prolate or oblate assumption may introduce strong biases even when the clusters are actually near to axial symmetry whereas the systematics introduced assuming the cluster to be aligned with the line of sight are more under control.  相似文献   

Measurement and prediction of water movement in a field soil: The matrix-macropore dichotomy     

K. R. J. Smettem  P. J. Ross 《水文研究》1992,6(1):1-10

The saturated and unsaturated flow properties of a field soil under two tillage treatments were obtained with ponded rings and disc permeameters of dissimilar radii. No difference was observed between tillage treatments but the flow properties displayed a distinct macropore-matrix dichotomy, with K changing by an order of magnitude as ψ₀ went from just - 30 mm to zero. Accurate prediction of time to incipient ponding was achieved using both numerical and analytical models calibrated with field hydraulic properties that were characteristic of the soil matrix. However, extension of the numerical model to the prediction of the wetting front development under non-ponded conditions was less accurate due to localized preferred wetting It is hypothesized that at this site, localized concentration of rainfall and hence, preferred wetting, May, occur by interception and stemflow associated with lines of standing stubble present in the original seeding slots.  相似文献   

A robust method for measuring the Hubble parameter     

M.A. Hendry  S. Rauzy  S.P. Goodwin  J. Gribbin 《Monthly notices of the Royal Astronomical Society》2001,324(3):717-724

We obtain a robust, non-parametric, estimate of the Hubble constant from the linear diameters and rotation velocities of galaxies in the recent KLUN sample, calibrated using Cepheid distances to Hubble Space Telescope Key Project galaxies. There are two key features that make our analysis considerably more robust than previous work. First, the method is independent of the spatial distribution of galaxies and is insensitive to Malmquist bias. It may, therefore, be applied to more distant samples than so-called 'plateau' methods – making it much less vulnerable to the impact of peculiar motions in the Local Supercluster. Secondly, we include information on the galaxy rotation velocities in a fully non-parametric manner: unlike the conventional Tully–Fisher relation we reconstruct a robust estimate of the cumulative distribution function of galaxy diameter at given rotation velocity, without requiring the assumption of, for example, a linear Tully–Fisher relation with symmetric Gaussian residuals.
Using this robust method we find H ₀=65±6 km s⁻¹ Mpc⁻¹ from our analysis – in excellent agreement with many recent determinations of the Hubble parameter, although somewhat larger than previous results using galaxy diameters.  相似文献   

Mapping Paleo‐Fire Boundaries from Binary Point Data: Comparing Interpolation Methods     

Amy Hessl  Jennifer Miller  James Kernan  David Keenum  Don McKenzie 《The Professional geographer》2007,59(1):87-104

Fire history studies have traditionally emphasized temporal rather than spatial properties of paleo‐fire regimes. In this study we compare four methods of mapping paleo‐fires in central Washington from binary point data: indicator kriging, inverse distance weighting, Thiessen polygons, and an expert approach. We evaluate the results of each mapping method using a test (validation) dataset and receiver operating characteristic plots. Interpolation methods perform well, but results vary with fire size and spatial pattern of points. Though all methods involve some subjectivity, automated interpolation methods perform well, are replicable, and can be applied across varying landscapes.  相似文献   

模糊理论在遥感图像分类中的应用   总被引：1，自引：0，他引：1  

王荣华  干嘉元  过仲阳  吴佳勤 《上海国土资源》2007,(4):52-55

利用2000年假彩色遥感图像,采用模糊C-均值法中的欧氏距离和马氏距离法对崇明东滩的遥感图像进行了处理。通过对白色覆盖物、未耕种土地、一号水稻田、水体和二号水稻田的分类结果表明,欧氏距离的聚类结果优于马氏距离。  相似文献   

北京顺义地裂缝带的活动特征及减灾措施   总被引：1，自引：1，他引：1  

任俊杰  张世民  唐荣余 《城市地质》2007,2(1):33-38

本文详细调查了北京顺义地裂缝带的展布和成灾特征,实测了地裂缝灾害最为严重的橡胶二厂内地裂缝的位置和建筑物破坏范围,并综合已有关于顺义地裂缝成因的研究,认为顺义地裂缝带的防治应以控制地下水的开采为根本措施。基于地裂缝的发育程度及成灾特点,在不考虑构造因素的前提下,提出了橡胶二厂建筑用地规划中安全距离的避让方案,即以主破裂带为中心基准线,西北侧建筑安全距离为12m,东南侧建筑安全距离为16m。  相似文献