检索结果-南通市图书馆

Transformations and non-degenerate maps

在线全文

学校读者我要写书评

暂无评论

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, beijing 100080, china graduate school, chinese academy of sciences, beijing 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.

Geometry of Broad Line Regions of Active Galactic Nuclei

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2008年第1期8卷 50-62页

作者： Xiao-Rong Lü1 Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, chinese academy of sciences, beijing 1.0049 2 graduate school of chinese academy of sciences, beijing 1.0049 Key Laboratory for Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 graduate school of chinese academy of sciences Beijing 100049

It has long remained an open question as to the geometry of the broad line region （BLR） in active galactic nuclei （AGNs）. The reverberation mapping technique which measures the response of the broad emission lines to the ionizing continuum, when combined with multiwavelength continuum fitted by sophisticated accretion disks, provides a way of probing the BLR geometry. We analyze a sample of 35 AGNs, which have been monitored by the reverberation mapping campaign. In view of energy budget, the reverberation-based BH masses are found to be in agreement with those obtained by accretion disk models in two thirds of the present sample while the reverberation mapping methods underestimate the BH masses in about one third of objects, as also suggested by CoUin et al. in a recent work. We point out that there are obviously two kinds of BLR geometry, which are strongly dependent on the Eddington ratio, and separated by the value LBol/LEdd - 0.1. These results prefer a scenario of the disk and wind configuration of the BLR and identify the Eddington ratio as the physical driver regulating the wind in the BLR.

关键词： accretion, accretion disks - galaxies active - galaxies Seyfert - quasars general

A novel operation mode for spaceborne polarimetric SAR

在线全文

学校读者我要写书评

暂无评论

Science china(Information sciences) 2011年第4期54卷 884-897页

作者： QI WeiKong 1,2 & YU WeiDong 1 1 Institute of Electronics,chinese academy of sciences,beijing 100190,china 2 graduate school of chinese academy of sciences,beijing 100039,china Institute of Electronics Chinese Academy of Sciences Beijing China graduate school of chinese academy of sciences Beijing China

A novel operation mode for spaceborne polarimetric SAR,named polarization space-division adding polarization code-division (PSD-PCD) operation mode,is proposed in this paper through combining polarimetric SAR with elevation digital beam-forming (DBF) on *** a pulse repetition interval the up-chirp LFM sub-pulse is transmitted with horizontal polarization antenna,and with some delay the down-chip LFM subpulse is transmitted with vertical polarization antenna to realize code *** every sub-aperture receives returns from ground,SAR system uses range DBF to separate echoes relative to different sub-pulses in order to realize space *** system PRF is equal to that of single-polarization SAR,and elevation DBF help reduce range ambiguity ***,the main system parameters,including PRF,delay between two sub-pulses,radar equation and ambiguity are analyzed and compared with those of single-polarization *** results demonstrate the feasibility and validity of PSD-PCD operation mode.

关键词： spaceborne synthetic aperture radar (SAR) polarimetry digital beamforming (DBF) operation mode ambiguity ratio polarization space-division polarization code-division

Effects of cosmological constant on motion of UHECR particles

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

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 100039, china graduate school of chinese academy of sciences, beijing 100039, 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

在线全文

学校读者我要写书评

暂无评论

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 school of chinese academy of sciences, beijing 100039, 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.

Comparative study of pollination biology of two closely related alpine Primula species,namely Primula beesiana and *** (Primulaceae)

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Systematics and Evolution 2010年第2期48卷 109-117页

作者： 1,2Zhi-Kun WU 1Chang-Qin ZHANG 1(Kunming Institute of Botany,chinese academy of sciences,Kunming 650204,china) 2(graduate school of chinese academy of sciences,beijing 1.0049,china) (Kunming Institute of Botany Chinese Academy of Sciences Kunming 650204 China) (graduate school of chinese academy of sciences Beijing 100049 China)

The comparative pollination biology of a population of Primula beesiana,a population of ***,and an overlapping population of these two species in Yulong Shan,Yunnan Province,china,was studied in 2004 and *** results indicate that both *** and *** are typical heterostylous and obligate outcrossing species;the main pollinators of the two species were bees and *** the sites of all three populations,the main pollinating visitors of the two species showed preference for one of the two species,resulting in the ethological isolation of the two species by the *** ethological isolation contributes to the reproductive isolation of the two species,which supports the hypothesis that *** and *** are two distinct *** reproductive isolation of the two species (ethological isolation) is probably an important mechanism in maintaining species boundaries in the genus and has contributed to the species diversification of Primula in the *** addition,gene exchanges between *** and *** has occurred to some extent in the overlapping population,but whether natural hybridization has contributed to species diversification in Primula remains to be determined.

关键词： pollination biology Primula beesiana Primula bulleyana reproductive isolation

The identity of some taxa of Schizophragma (Saxifragaceae)

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Systematics and Evolution 2009年第2期47卷 151-161页

作者： 1,2Wei LIU 1Xiang-Yun ZHU 1(Institute of Botany,chinese academy of sciences,beijing 100093,china) 2(graduate University of chinese academy of sciences,beijing 1.0049,china) Institute of Botany Chinese Academy of Sciences Beijing 100093 China graduate University of chinese academy of sciences Beijing 100049 China

After examining a large number of type and authoritative specimens of Schizophragma Siebold & Zucc.,*** *** and *** *** Rehder were reduced to synonyms of *** Rehder and *** *** *** was reduced to synonym of *** *** crassum *** *** was treated as the correct name of *** ***(Chun) *** name *** *** Rehder is *** taxonomic treat-ment is supported by leaf epidermal characters.

关键词： leaf epidermis new synonym reinstatement Schizophragma

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

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

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 school 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.

Ionization state of cosmic hydrogen by early stars and quasars

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

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 graduate University of chinese academy of sciences, beijing 1.0049, china National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China graduate University of chinese academy of sciences 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 430% 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