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Ionization state of cosmic hydrogen by early stars and quasars

Research in Astronomy and Astrophysics 2009年第6期9卷 665-681页

作者： Xiao-Chun Mao1,2 1 National Astronomical Observatories, chinese academy of sciences, beijing 100012, China 2 {4. university of chinese academy of sciences, beijing 10004., China National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China graduate university of chinese academy of {4. Beijing 100049 China

Cosmic hydrogen is reionized and maintained in its highly ionized state by the ultraviolet emission attributed to an early generation of stars and quasars. The Lyα opacity observed in absorption spectra of high-redshift quasars permits more stringent constraints on the ionization state of cosmic hydrogen. Based on density perturbation and structure formation theory, we develop an analytic model to trace the evolution of the ionization state in the post-overlap epoch of reionization, in which the bias factor is taken into account. For quasars, we represent an improved luminosity function by utilizing a hybrid approach for the halo formation rate that is in reasonable agreement with the published measurements at 2 ≤ z ≤ 6. Comparison with the classic Press-Schechter mass function of dark matter halos, we demonstrate that the biased mass distribution indeed enhances star formation efficiency in the overdense environment by more than 25 per cent following the overlap of ionized bubbles. In addition, an alternative way is introduced to derive robust estimates of the mean free path for ionizing photons. In our model, star-forming galaxies are likely to dominate the ionizing background radiation beyond z = 3, and quasars contribute equally above a redshift of z ～ 2.5. From 5 ≤ z ≤ 6, the lack of evolution in photoionization rate can thus be explained by the relatively flat evolution in star formation efficiency, although the mean free path of ionizing photons increases rapidly. Moreover, in the redshift interval z ～ 2 - 6, the expected mean free path and Gunn-Peterson optical depth obviously evolve by a factor of ～ 500 and ～50 respectively. We find that the relative values of critical overdensities for hydrogen ionization and collapse could be 4.0% at z ≈2 and 2% at z ≈6, suggesting a rapid overlap process in the overdense regions around instant quasars following reionization. We further illustrate that the absolute estimates of the fraction of neutral hydrogen computed fr

关键词： cosmology theory -- formation galaxies -- quasars general -- diffuse radiation -- intergalactic medium

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Monitoring of rice crop using ENVISAT ASAR data

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Science China Earth sciences 2006年第7期49卷 755-763页

作者： DONG Yanfang1, 2, SUN Guoqing1,3 & PANG Yong4.1. State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing Applications, chinese academy of sciences, beijing 100101, China 2. {4. university of chinese academy of sciences, beijing 100039, China 3. Department of Geography, university of Maryland, College Park, MD 2074., USA 4. Forest Remote Sensing Lab, Research Institute of Forest Resource and Information Technology, chinese academy of For-estry, beijing 100091, China 1. State Key Laboratory of Remote Sensing Science Institute of Remote Sensing Applications Chinese Academy of Sciences Beijing 100101 China 2. graduate university of chinese academy of {4. Beijing 100039 China 3. Department of Geography University of Maryland College Park MD 20742 USA 4. Forest Remote Sensing Lab Research Institute of Forest Resource and Information Technology Chinese Academy of Forestry Beijing 100091 China

Because of the cloudy conditions during the rice growth period, rice is one of the agri-cultural crops most suited to monitoring with the SAR instruments. Backscatter response measured by SAR is correlated with rice conditions, including height, density, biomass and structure, which are variable at different growing stages. In this paper, multi-date ENVISAT ASAR Alternating Polarization Mode (APMode) imageries were acquired during the rice crop growing cycle. At the same time, the rice parameters were measured in field. A continuous canopy model was used to compute the back-scattering from rice fields during the growth cycle, and the relationship between rice parameters and radar backscattering coefficients from both ASAR and modeling was analyzed. The effects of polari-zation, incidence angle and polarization on radar backscattering coefficients were analyzed. It was found that simulated radar backscatter has similar trends as ASAR data. This will be meaningful for the further research of rice parameters estimation from ASAR data. Different features show signifi-cantly different signatures in ASAR images and they follow some certain laws, so rice area can be accurately mapped by using multi-temporal SAR images, then rice yield can be estimated.

关键词： rice, ASAR, radar backscattering, model.

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Explicit analytical solutions of the anisotropic Brinkman model for the natural convection in porous media(Ⅱ)

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Science China(Physics,Mechanics & Astronomy) 2005年第4期48卷 422-430页

作者： CAI Ruixian1, GOU Chenhua1, 2 & ZHANG Na1 1. Institute of Engineering Thermophysics, chinese academy of sciences, beijing 100080, China 2. {4. School, chinese academy of sciences, beijing 100080, China 1. Institute of Engineering Thermophysics Chinese Academy of Sciences 100080 Beijing China 2. graduate School Chinese Academy of Sciences 10080 Beijing China

Some algebraically explicit analytical solutions are derived for the anisotropic Brinkman model―an improved Darcy model―describing the natural convection in porous media. Besides their important theoretical meaning (for example, in analyzing the non-Darcy and anisotropic effects on the convection), such analytical solutions can be the benchmark solutions that can promote the development of computational heat and mass transfer. Some solutions considering the anisotropic effect of permeability have been given previously by the authors, and this paper gives solutions including the anisotropic effect of thermal conductivity and the effect of heat sources.

关键词： explicit analytical solution, porous medium, natural convection, Brinkman model, anisotropic.

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Estimating surface evapotranspiration using combined MODIS and CBERS-02 data

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Science China(Technological sciences) 2005年第S2期48卷 145-160页

作者： XIN Xiaozhou1,2, LIU Qinhuo1, TANG Yong1,3, TIAN Guoliang1, GU Xingfa1, LI Xiaowen1,2, ZHENG Hongsheng4.& CHEN Jiayi4.1. State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing Applications, chinese academy of sciences, beijing 100101, China 2. Research Center for Remote Sensing and GIS, Department of Geography, beijing Normal university, beijing 100875, China 3. graduate university of chinese academy of sciences, beijing 100039, China 4. Department of Atmospheric Physics, Peking university, beijing 100871, China 1. State Key Laboratory of Remote Sensing Science Institute of Remote Sensing Applications Chinese Academy of Sciences 100101 Beijing China2. Research Center for Remote Sensing and GIS Department of Geography Beijing Normal University 100875 Beijing China3. Graduate University of Chinese Academy of Sciences 100039 Beijing China4. Department of Atmospheric Physics Peking University 100871 Beijing China

Spatial scale error is one of the most serious problems in the estimates of land surface heat fluxes of sensible and latent from satellite-borne data such as MODIS 1km resolution reflectance and emissive data. One of the feasible and economic ways to decrease the spatial scale error is to use high resolution land use class data together with the MODIS data. CBERS-02 data were used to produce land use class of Baiyangdian area, Hebei Province, China in the autumn of 2004. The area ratio of each class in MODIS pixel was calculated, and used to derive the heat fluxes of the mixed pixel. The results showed that the estimated heat fluxes of soil, sensible and latent have been changed remarkably after using the high resolution land class data. It could be concluded from the comparison between simulated and ground-measured fluxes as well as the theoretical analysis that high resolution land class data are useful to diminishing the scale error of heat fluxes estimated from low resolution satellite data.

关键词： surface evapotranspiration spatial scale error MODIS CBERS land class.

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Nonlinear autoregressive models with heavy-tailed innovation

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Science China Mathematics 2005年第3期48卷 333-340页

作者： JIN Yang & AN Hongzhi School of Statistics, Renmin university of China, beijing 100872, China academy of Mathematics and Systems Science, chinese academy of sciences, beijing 100080, China Sch. of Statistics Renmin Univ. of China Beijing 100872 China Acad. of Mathematics and Syst. Sci. Chinese Acad. of Sci. Beijing 100080 China

In this paper, we discuss the relationship between the stationary marginal tail probability and the innovation's tail probability of nonlinear autoregressive models. We show that under certain conditions that ensure the stationarity and ergodicity, one dimension stationary marginal distribution has the heavy-tailed probability property with the same index as that of the innovation's tail probability.

关键词： nonlinear autoregressive model, innovation, tail probability.

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A shortest path algorithm for moving objects in spatial network databases

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Progress in Natural Science:Materials International 2008年第7期18卷 893-899页

作者： Xiaolan Yin a,b,*, Zhiming Ding c, Jing Li a a Technology Center of Software Engineering, Institute of Software, chinese academy of Science, P.O. Box 8718, beijing 100080, China b graduate {4., chinese academy of sciences, beijing 10004., China c Technology Center of Basic Software, Institute of Software, chinese academy of sciences, beijing 100080, China Technology Center of Software Engineering Institute of Software Chinese Academy of Science P.O. Box 8718 Beijing 100080 China graduate university Chinese Academy of Sciences Beijing 100049 China Technology Center of Basic Software Institute of Software Chinese Academy of Sciences Beijing 100080 China

One of the most important kinds of queries in Spatial Network Databases (SNDB) to support location-based services (LBS) is the shortest path query. Given an object in a network, e.g. a location of a car on a road network, and a set of objects of interests, e.g. hotels, gas station, and car, the shortest path query returns the shortest path from the query object to interested objects. The studies of shortest path query have two kinds of ways, online processing and preprocessing. The studies of preprocessing suppose that the interest objects are static. This paper proposes a shortest path algorithm with a set of index structures to support the situation of moving objects. This algorithm can transform a dynamic problem to a static problem. In this paper we focus on road networks. However, our algorithms do not use any domain specific information, and therefore can be applied to any network. This algorithm’s complexity is O(klog2i), and traditional Dijkstra’s complexity is O((i + k)2).

关键词： Moving object Spatial network databases Shortest path index Shortest path

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The Koppelman-Leray formula on complex Finsler manifolds

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Science China Mathematics 2005年第6期48卷 847-863页

作者： QIU Chunhui & ZHONG Tongde School of Mathematical sciences, Xiamen university, Xiamen 361005, China academy of Mathematics and System sciences, {4. academy of sciences, beijing 100080, China 1. School of Mathematical sciences Xiamen University 361005 Xiamen China 2. academy of Mathematics and System sciences Chinese Academy of Sciences 100080 Beijing China

By means of the invariant integral kernel (the Berndtsson kernel), the complex Finsler metric and the non-linear connection associated with the Chern-Finsler connection to research into the integral representation theory on complex Finsler manifolds, theKoppelman and Koppelman-Leray formulas are obtained, and the - -equations are solved.

关键词： complex Finsler manifold, Chern-Finsler connection, invariant integral kernel, Koppelman-Lerayformulas, - -equation.

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A cumulant-based parameter estimation algorithm for near-field sources

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Progress in Natural Science:Materials International 2007年第8期17卷 900-905页

作者： Liang Junli~(1,2*) Yang Shuyuan~(1,2) Zhang Junying~3 (1.Institute of Acoustics,chinese academy of sciences,beijing 100080,China 2.{4. School,chinese academy of sciences,beijing 100039,China 3.National Laboratory of Radar Signal Processing,Xidian university,Xi'an 710071,China) [a]Institute of Acoustics Chinese Academy of Sciences Beijing China [b]graduate School Chinese Academy of Sciences Beijing China [c]National Laboratary of Radar Signal Processing Xidian University Xi'an China

To efficiently use the array aperture and avoid the complicated parameter pairing computation,this paper proposes a new cumulant-based algorithm for localizing near-field narrowband ***,this algorithm proposes a symmetric uniform linear ar- ray (ULA),and constructs three cumulant matrices by using the fourth-order cumulants of some properly chosen sensor outputs;second- ly,unlike the conventional parallel factor (PARAFAC) analysis models in data or subspace domain,it forms a three-way array (TWA) in the fourth-order cumulant domain using the three matrices,and analyzes the uniqueness of its low-rank decomposition;thirdly,it jointly estimates the frequency,the direction-of-arrival (DOA),and the range of each near-field source from the matrices via the low-rank de- composition of the *** simulation results are presented to validate the performance of our proposed method.

关键词： array signal processing localization cumulant parallel factor (PARAFAC) analysis three-way array (TWA)

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Effect of rock mass structure and block size on the slope stability——Physical modeling and discrete element simulation

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Science China(Technological sciences) 2005年第z1期48卷 1-17页

作者： LI Shihai1, LIAN Zhenzhong1,2 & J. G. Wang3 1. Institute of Mechanics, chinese academy of sciences, beijing 100080, China 2. {4. School, chinese academy of sciences, beijing 100060, China 3. Tropical Marine Science Institute, National university of Singapore, Singapore 119260 chinese Acad Sci Inst Mech Beijing 100080 Peoples R China chinese Acad Sci Grad Sch Beijing 100060 Peoples R China Natl Univ Singapore Trop Marine Sci Inst Singapore 119260 Singapore

This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.

关键词： rock masses, slope stability, DEM simulation, block size effect, joints configuration effect, limit equilibrium method.

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Application of the moist vorticity vector in the analysis of a heavy rainfall event in North China

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Progress in Natural Science:Materials International 2007年第12期17卷 1457-1465页

作者： Zhao Yu1,2,3, Wang Jianguo4.and Xue Deqiang2(1. Laboratory of Cloud-Precipitation Physics and Severe Storms, Institute of Atmospheric Physics, chinese academy of sciences, beijing 100029, China 2. Shandong Provincial Meteorological Observatory, Jinan 250031, China 3. {4. university of chinese academy of sciences, beijing 100039, China 4. Shandong Provincial Meteorological Bureau, Jinan 250031, China) Laboratory of Cloud-Precipitation Physics and Severe Storms Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China Shandong Provincial Meteorological Observatory Jinan 250031 China graduate university of chinese academy of {4. Beijing 100039 China Shandong Provincial Meteorological Bureau Jinan 250031 China

The moist vorticity vector (MVV), defined as (ζa×▽qv)/ρ introduced by Gao et al. is used to study a heavy rainfall event in North China. The MVV has zonal, meridional and vertical components in a three-dimensional framework. Analysis of domain-mean and mass-integrated quantities shows that the variation of the vertical component of the MVV closely follows the variation of the cloud hydrometeors, with a linear correlation coefficient of 0.95, indicating that the vertical component of the MVV is strongly associated with midlatitude convection. Further analysis shows that the vertical component of the MVV reflects the interaction between the horizontal vorticity and the horizontal specific humidity gradient, which can associate dynamic and thermodynamic processes with cloud microphysical processes. Thus, this study can help to understand how the interaction between circulations and clouds aids the development of convection, and the MVV can be used to trace the development and evolution of heavy rainfall.

关键词： moist vorticity vector heavy rainfall modeling study.

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