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Transformations and non-degenerate maps

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Science China Mathematics 2005年第z1期48卷 195-205页

作者： LI Baokui & WANG Yuefei Institute of Mathematics, academy of Mathematics and System sciences, chinese academy of sciences, {5. 100080, China graduate school, chinese academy of sciences, {5. 100080, China Institute of Mathematics Academy of Mathematics and System Sciences Chinese Academy of Sciences Beijing China graduate school Chinese Academy of Sciences Beijing China

We shall prove the equivalences of a non-degenerate circle-preserving map and a M(o)bius transformation in ^Rn, of a non-degenerate geodesic-preserving map and an isometry in Hn of a non-degenerate line-preserving map and an affine transformation in Rn. That a map is non-degenerate means that the image of the whole space under the map is not a circle, or geodesic or line respectively. These results hold without either injective or surjective, or even continuous assumptions, which are new and of a fundamental nature in geometry.

关键词： M(o)bius transformation, circle-preserving map, non-degenerate map.

Infrared Galaxies in the Nearby Universe

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chinese Journal of Astronomy and Astrophysics 2008年第6期8卷 643-652页

作者： Jian-Ling Wang 1 National Astronomical Observatories,chinese academy of sciences,beijing 100012,China 2 graduate {5. of chinese academy of sciences,beijing 100049,China National Astronomical Observatories Chinese Academy of Science

We used the Sloan Digital Sky Survey （SDSS） Data Release 5.（DR5. to study the morphological properties of 113. nearby infrared （IR） galaxies, most of which are brighter than 15.9 mag in r-band. This sample was drawn from a cross-correlation of the Infra-Red Astronomical Satellite （IRAS） point source catalog redshift survey with DR5.at z ≤ 0.08. Based on this IR galaxy sample, we constructed five volume-limited sub-samples with IR luminosity ranging from 10^9.5.L⊙ to 10^12L⊙. By deriving the IR luminosity functions （LF） for different morphological types, we found that normal spiral galaxies are the dominant population below LIR ~ 8 ~ 10^10 L⊙; while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond LIR ≈ 5.× 10^10L⊙. As the IR luminosity decreases, the IR galaxies become more compact and have lower stellar masses. The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe, while, in contrast, the contribution from peculiar galaxies is only 39%.

关键词： galaxies evolution galaxies interactions galaxies starburst infrared galaxies galaxies luminosity function

Effects of cosmological constant on motion of UHECR particles

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Science China(Physics,Mechanics & Astronomy) 2005年第1期48卷 44-56页

作者： CHEN Shaoxia & CHANG Zhe Institute of High Energy Physics, chinese academy of sciences, beijing 10003., China graduate {5. of chinese academy of sciences, beijing 10003., China Institute of High Energy Physics Chinese Academy of Sciences Beijing 100039 China graduate school Chinese Academy of Sciences Beijing 100039 China

Recent astronomical observations manifest that about two-thirds of the whole energy in the Universe is contributed by a small positive cosmological constant A (> 0). Then, an asymptotically de Sitter spacetime is premised naturally. However, physics in the de Sitter spacetime is very different from that in the Minkowski spacetime. As the first step, a covariant formalism of the kinematics in the de Sitter spacetime is presented here. By solving exactly the equations of motion for a field, we obtain the dispersion relation of a free particle. It is noticed that the dispersion relation is dependent on the degree of freedom of angular momentum of the particle. We show the threshold anomaly of the ultra high energy cosmic ray disappears naturally in the framework of the de Sitter kinematics.

关键词： ultrahigh energy cosmic ray, cosmological constant, curved spacetime.

Recent advances in the data analysis method of functional magnetic resonance imaging and its applications in neuroimaging

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Progress in Natural Science:Materials International 2006年第8期16卷 785-795页

作者： TIAN Jie, YANG Lei and HU Jin (Institute of Automation, chinese academy of sciences, beijing 100080, China graduate {5. of chinese academy of sciences, beijing 10003., China) Institute of Automation Chinese Academy of Sciences Beijing 100080 China. graduate school of chinese academy of sciences Beijing 100039 China

Functional magnetic resonance imaging (fMRI) has opened a new area to explore the human brain. The fMRI can reveal the deep insights of spatial and temporal changes underlying a broad range of brain function, such as motor, vision, memory and emotion, all of which are helpful in the clinical investigation. In this paper, we introduce some recent-developed algorithms for fMRI signal detection such as model-driven method (general linear model, deconvolution model, non-linear model, etc. ) and data-driven method (principle component analysis, independent component analysis, self-organization mapping, clustered constrained non-negative matrix factorization, etc. ). We also propose several important applications of neuroimaging and point out their shortcomings and future perspectives.

关键词： fMR1 data analysis neuroimaging.

An Efficient High-Resolution Shock-Capturing Scheme for Multi-Dimensional Flows I. Hydrodynamics

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chinese Journal of Astronomy and Astrophysics 2006年第6期6卷 680-688页

作者： Cong Yu National Astronomical Observatories / Yunnan Astronomical Observatory, chinese academy of sciences, Kunming 65.011 graduate school of chinese academy of sciences, beijing 100049 National Astronomical Observatories / Yunnan Astronomical Observatory Chinese Academy of Sciences graduate school of chinese academy of sciences

Many problems at the forefront of theoretical astrophysics require a treatment of dynamical fluid behavior. We present an efficient high-resolution shock-capturing hydrodynamic scheme designed to study such phenomena. We have implemented a weighted, essentially non-oscillatory （WENO） scheme to fifth order accuracy in space, lILLE approximate Riemann solver is used for the flux computation at cell interface, which does not require spectral decomposition into characteristic waves and so is computationally friendly. For time integration we apply a third order total variation diminishing （TVD） Runge-Kutta scheme. Extensive testing and comparison with schemes that *** characteristic decomposition are carried out demonstrating the ability of our scheme to address challenging open questions in astrophysics.

关键词： accretion - hydrodynamics- method numerical - shock waves

A new approach of cascade utilization of the chemical energy of fuel

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Progress in Natural Science:Materials International 2006年第5期16卷 518-523页

作者： HAN Wei, JIN Hongguang and LIN Rumou ( Institute of Engineering Thermophysics, chinese academy of sciences, beijing 100080, China graduate {5. of the chinese academy of sciences, beijing 100080, China) Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100080 China graduate school of the chinese academy of sciences Beijing 100080 China

The indirect release of chemical energy of fuel is investigated, and a new mechanism is proposed to identify the cascade utilization of chemical energy of fuel more clearly. Based on the concept of energy level, the internal phenomenon of the indirect chemical energy release is disclosed, and the equations of energy level describing the utilization of chemical energy and thermal energy during the indirect chemical energy release process are obtained. From theoretical analysis, we find that the superiority of the indirect chemical energy release of fuel comes from the cascade utilization of the fuel's chemical energy. Moreover, the cascade utilization of chemical energy is verified by the investigation of CRGT (chemically recuperated gas turbine). As a result, the thermal exergy obtained from the chemical energy release of fuel increases by 2 % -3 % . The results obtained here may help a deeper understanding of indirect chemical energy release of fuel and provide a theoretical basis for the synthesis of innovative energy systems.

关键词： chemically recuperated gas turbine methane/steam reforming chemical energy level cascade utilization.

Reconstruction of temperature series in China for the last 5.00 years

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Progress in Natural Science:Materials International 2006年第8期16卷 838-845页

作者： GE Quansheng, WANG Shunbing and ZHENG Jingyun (Institute of Geographical sciences and Natural Resources Research, chinese academy of sciences, beijing 100101, China {5. school of the chinese academy of sciences, beijing 10003., China) Institute of Geographical sciences and Natural Resources Research Chinese Academy of Sciences Beijing 100101 China. graduate school of The chinese academy of sciences Beijing 100039 China

A temperature series with a 100 year resolution for the last 5.00 years in China has been reconstructed by using 31 longterm temperature proxy series selected from recent publications in the last 20 years. The proxy records include pollens, stalagmites, lake-sediments, peat, ice cores and historical documents. The result reveals that in the millennial scale temperature variation it was warm in 305.-25. BC and it was cold in 25. BC-195. AD. In the above two periods there were many stages of sub-scale temperature fluctuations. The result also shows an obvious temperature discrepancy on the century to multi-century scale between the Eastern Monsoon Region, the Qinghai-Tibet Region and the Northwestern Region in 285. BC, 235. BC, 13.0 BC, 95.-35. BC, 5.-25. AD, and 5.0 AD. A comparison between the reconstructed series of this paper and some North Hemisphere temperature series indicates that in the longterm scale change, the temperature change in China is in phrase with that of the Northern Hemisphere during the last 5.00 years, while on the century to multi-century scale there are differences at the beginning and end times, which may imply that temperature change does not occur simultaneously in different regions.

关键词： temperature series the last 5.00 years China.

Structure of augmentation quotients of finite homocyclic abelian groups

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Science China Mathematics 2007年第9期50卷 1280-1288页

作者： Guo-ping TANG school of Mathematical sciences,graduate University of chinese academy of sciences,beijing 100049,China school of Mathematical sciences Graduate University of Chinese Academy of Sciences Beijing China

Let G be a finite abelian group and its Sylow p-subgroup a direct product of copies of a cyclic group of order p r , i.e., a finite homocyclic abelian group. Let Δ n (G) denote the n-th power of the augmentation ideal Δ(G) of the integral group ring ?G. The paper gives an explicit structure of the consecutive quotient group Q n (G) = Δ n (G)/Δ n+1(G) for any natural number n and as a consequence settles a problem of Karpilovsky for this particular class of finite abelian groups.

关键词： integral group ring augmentation ideal consecutive quotient of augmentation ideal 16S34 20C05

Valuations on arithmetic surfaces

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Science China Mathematics 2009年第1期52卷 66-76页

作者： XU Ning Department of Mathematics, graduate school of chinese academy of sciences, {5. 100049, China Department of Mathematics Graduate School of Chinese Academy of Sciences Beijing China

In this paper, we give the definition of the height of a valuation and the definition of the big field ? p,G , where p is a prime and G ? ? is an additive subgroup containing 1. We conclude that ? p,G is a field and ? p,G is algebraically closed. Based on this the author obtains the complete classification of valuations on arithmetic surfaces. Furthermore, for any m ? p,G n ∈ ?, let V m,n be an ∝-vector space of dimension n - m + 1, whose coordinates are indexed from m to n. We generalize the definition of ? p,G , where p is a prime and G ? V m,n is an additive subgroup containing 1. We also conclude that ? p,G is a field if m ? 0 ? n.

关键词： valuation height rank totally ordered group big field transcendental number 14J10