New faint optical spectrophotometric standards: hot white dwarfs from the Sloan Digital Sky Survey

The spectral energy distributions for pure-hydrogen (DA) hot white dwarfs can be accurately predicted by model atmospheres. This makes it possible to define spectrophotometric calibrators by scaling the theoretical spectral shapes with broad-band photometric observations – a strategy successfully exploited for the spectrographs onboard the Hubble Space Telescope ( HST ) using three primary DA standards. Absolute fluxes for non-DA secondary standards, introduced to increase the density of calibrators in the sky, need to be referred to the primary standards, but a far better solution would be to employ a network of DA stars scattered throughout the sky. We search for blue objects in the sixth data release of the Sloan Digital Sky Survey (SDSS) and fit DA model fluxes to identify suitable candidates. Reddening needs to be considered in the analysis of many of these stars. We propose a list of nine pure-hydrogen white dwarfs with absolute fluxes with estimated uncertainties below 3 per cent, including four objects with estimated errors <2 per cent, as candidates for spectrophotometric standards in the range  14 < g < 18  , and provide model-based fluxes scaled to match the SDSS broad-band fluxes for each. We apply the same method to the three HST DA standards, linking the zero point of their absolute fluxes to ugr magnitudes transformed from photometry obtained with the US Naval Observatory 1-m telescope. For these stars, we estimate uncertainties of <1 per cent in the optical, finding good consistency with the fluxes adopted for HST calibration.     

2006年5—9月雷暴天气及各种物理量指数的统计分析

对2006年5-9月全国雷暴天气时空特征进行了统计分析,结果表明:雷暴天气的发生具有明显的短时局地特征,大多数发生在17-20时,上午11时发生最少.全国范围发生过雷暴天气的站点不到总数的三分之一.从空间分布来看,广东、广西及云南三省(区)是雷暴发生最为频繁的省份,内蒙古中西部、新疆北部、青海北部等地则发生较少.此外,统计分析各物理量指数后发现,各种物理量指数对于雷暴等强对流天气发生呈现出不同的概率分布特征,其中最主要的特征是当雷暴等强对流性天气发生时,存在3个高概率区域,每个区域对应物理量指数值相对集中在一个特定范围内.     

MODIS BRIGHTNESS TEMPERATURE DATA ASSIMILATION UNDER CLOUDY CONDITIONS: METHODS AND IDEAL TESTS

Clouds have important effects on the infrared radiances transmission in that the inclusion of cloud effects in data assimilation can not only improve the quality of the assimilated atmospheric parameters greatly, but also minimize the initial error of cloud parameters by adjusting part of the infrared radiances data. On the basis of the Grapes-3D-var (Global and Regional Assimilation and Prediction Enhanced System), cloud liquid water, cloud ice water and cloud cover are added as the governing variables in the assimilation. Under the conditions of clear sky, partly cloudy cover and totally cloudy cover, the brightness temperature of 16 MODIS channels are assimilated respectively in ideal tests. Results show that when the simulated background brightness temperatures are lower than the observation, the analyzed field will increase the simulated brightness temperature by increasing its temperature and reducing its moisture, cloud liquid water, cloud ice water, and cloud cover. The simulated brightness temperature can be reduced if adjustment is made in the contrary direction. The adjustment of the temperature and specific humidity under the clear sky conditions conforms well to the design of MODIS channels, but it is weakened for levels under cloud layers. The ideal tests demonstrate that by simultaneously adding both cloud parameters and atmospheric parameters as governing variables during the assimilation of infrared radiances, both the cloud parameters and atmospheric parameters can be adjusted using the observed infrared radiances and conventional meteorological elements to make full use of the infrared observations.     

矿床工业指标优化及其对矿山可持续发展的意义:以紫金山金矿为例

矿床工业指标的优化应体现动态性和及时性的原则,建立起能反映各有关参数间动态联系的数学模型,在生产成本、产品价格、生产技术等有较大变化时及时进行优化,从而有效地保护和科学、合理地开发利用矿产资源,实现可持续发展。本文以福建紫金山金矿为例,论述了矿床工业指标优化的原则和可行性,阐述了矿床工业指标优化参数的选择和论证过程,以及增加矿产资源储量,提高资源利用率,延长矿山服务年限,实现矿山可持续发展的意义。     

CSAMT视电阻率曲线对水平层状大地的识别与分辨

在三层和五层介质模型上,通过改变各电性层层参数并进行相应的数值计算,比较并分析了可控源音频大地电磁法卡尼亚视电阻率曲线对各层信息的识别与分辨能力。上部覆盖层厚度的增大和电阻率的减小使视电阻率曲线对下部信息的分辨能力下降,而下部地层层参数变化的影响则相对较小;低阻薄夹层对曲线的影响主要由其纵向电导所决定,纵向电导越大异常值越明显;高阻夹层对曲线的影响则取决于其厚度埋深比,比值越大高阻层越易于分辨,而曲线对高阻层电阻率值变化反应不敏感;在10%的分辨标准下,当低阻夹层纵向电导大于覆盖层的0.2倍、高阻夹层电阻率大于围岩5倍以上并且厚度埋深比大于0.2时,各有可分辨异常。相邻高低阻层差异的增大将使曲线的震荡假异常更加明显,导致分辨能力下降。     

SCS2D程序反演参数的应用效果分析

SCS2D程序中反演参数应用不当将使反演的地电模型与实际的地电模型产生较大的差别。通过对该软件反演参数圆滑系数、模型顶层厚度、初始背景模型的应用效果分析,为正确选择应用各参数、提高资料的反演精度打下基础。     

带权重的相关函数在半解析模型和SDSS数据中的应用

基于半解析模型和SDSS DR4(Sloan Digital Sky Survey Data Release 4),研究了环境对星系性质的影响.通过对以颜色、恒星形成率和恒星质量的带权重的相关函数的测量,发现半解析模型在颜色和恒星质量上与SDSS数据符合得比较好,而恒星形成率则在SDSS数据中表现为与环境无关.此结论证实了半解析模型对星系中部分性质与环境关系的预测,但对于恒星形成率为何与环境无关仍有待研究.     

Measuring ΩM and ΩΛ with long‐duration gamma‐ray bursts

Gamma‐ray bursts (GRBs) are one of the most luminous events in the Universe. In addition, the Universe itself is almost transparent to γ ‐rays, making GRBs detectable up to very high redshifts. As a result, GRBs are very suitable to probe the cosmological parameters. This work shows the potential of long‐duration GRBs for measuring the cosmological parameters Ω_M and Ω_Λ by comparing the observed log N ‐log P distribution with the theoretical one. Provided that the GRBs rate and luminosity function are well determined, the best values and 1σ confidence intervals obtained are Ω_M = 0.22^+0.05_–0.03 and Ω_Λ = 1.06^+0.05_–0.10. Finally, a set of simulations show the ability of the method to measure Ω_M and Ω_Λ (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)