Urbanization, Rural-Urban Migration, Government Policies and Socioeconomic Development in China

This thesis is an attempt to characterize two aspects of Chinese urbanization and rural-urban migration: the influence of government policies and the effect of socioeconomic development. Because of frequent changes in government economic development strategies, ideology, population control, etc., rural-urban movement fluctuates significantly along with the policy changes. On the other hand, socioeconomic development in terms of higher literacy, more industrial and commercial establishments, intensive employment of agricultural machinery, etc., does seem to have a strong effect on the level of Chinese urbanization despite the government policies that have played a negative role for most of the time. An empirical analysis is done to validate this argument

Growth of massive black holes at their late stage

We derive the black hole mass density as a function of redshift with the bolometric luminosity function of AGN assuming that massive black holes grew via accreting the circumnuclear gases, in which the derived black hole mass density is required to match the measured local black hole mass density at z=0. ADAFs are supposed to present in low luminosity AGNs/normal galaxies, which are very hot and radiate mostly in the hard X-ray band. Most of the XRB is contributed by bright AGNs, and a variety of AGN population synthesis models were developed to model the observed XRB in the last two decades. Based on our derived black hole mass density, we calculate the contribution to the XRB from the ADAFs in faint AGNs/normal galaxies with a given Eddington ratio distribution, which is mostly in hard X-ray energy band with an energy peak at ~200 keV. The growth of massive black holes during ADAF phase can therefore be constrained with the observed XRB. Combining an AGN population synthesis model with our results, we find that the fitting on the observed XRB, especially at hard X-ray energy band with \ga 100 keV, is improved provided the contribution of the ADAFs in low luminosity AGNs/normal galaxies is properly included. It is found that less than ~15 per cent of local massive black hole mass density was accreted during ADAF phases. We suggest that more accurate measurements of the XRB in the energy band with \ga 100 keV in the future may help constrain the growth of massive black holes at their late stage. We also calculate their contribution to the extragalactic gamma-ray background, and find that less than ~1% of the observed EGRB is contributed by the ADAFs in these faint sources.Comment: 9 pages, 11 figures, accepted for publication in ApJ

Fractal Metamaterial Absorber with Three-Order Oblique Cross Dipole Slot Structure and its Application for In-band RCS Reduction of Array Antennas

To miniaturize the perfect metamaterial absorber, a fractal three-order oblique cross dipole slot structure is proposed and investigated in this paper. The fractal perfect metamaterial absorber (FPMA) consists of two metallic layers separated by a lossy dielectric substrate. The top layer etched a three-order oblique fractal-shaped cross dipole slot set in a square patch and the bottom one is a solid metal. The parametric study is performed for providing practical design guidelines. A prototype with a thickness of 0.0106λ (λ is the wavelength at 3.18 GHz) of the FPMA was designed, fabricated, measured, and is loaded on a 1×10 guidewave slot array antennas to reduce the in-band radar cross section (RCS) based on their surface current distribution. Experiments are carried out to verify the simulation results, and the experimental results show that the absorption at normal incidence is above 90% from 3.17 to 3.22GHz, the size for the absorber is 0.1λ×0.1λ, the three-order FPMA is miniaturized 60% compared with the zero-order ones, and the array antennas significantly obtain the RCS reduction without the radiation deterioration

Consistency of regularized spectral clustering

AbstractClustering is a widely used technique in machine learning, however, relatively little research in consistency of clustering algorithms has been done so far. In this paper we investigate the consistency of the regularized spectral clustering algorithm, which has been proposed recently. It provides a natural out-of-sample extension for spectral clustering. The presence of the regularization term makes our situation different from that in previous work. Our approach is mainly an elaborate analysis of a functional named the clustering objective. Moreover, we establish a convergence rate. The rate depends on the approximation property and the capacity of the reproducing kernel Hilbert space measured by covering numbers. Some new methods are exploited for the analysis since the underlying setting is much more complicated than usual. Some new methods are exploited for the analysis since the underlying setting is much more complicated than usual

The advection-dominated accretion flow+thin accretion disk model for two low-luminosity active galactic nuclei: M81 and NGC4579

It was found that the advection-dominated accretion flow (ADAF)+thin disk model calculations can reproduce the observed spectral energy distributions (SED) of the two low luminosity AGN, provided they are accreting at ~0.01-0.03 Eddington rates and the thin disks are truncated to ADAFs at ~100 R_s (Schwarzschild radii) for M81 and NGC4579 (Quataert et al., 1999). However, the black hole masses adopted in their work are about one order of magnitude lower than recent measurements on these two sources. Adopting the well estimated black hole masses, our ADAF+thin disk model calculations can reproduce the observed SEDs of these two LLAGN, if the black hole is accreting at 2.5e-4 Eddington rates with the thin disk truncated at 120 R_s for M81 (3.3e-3 and R_tr = 80R_s are required for NGC4579). The observed widths of the thermal X-ray iron lines at 6.8 keV are consistent with the Doppler broadening by the Keplerian motion of the gases in the transition zones at ~100R_s. The observed thermal X-ray lines provide a useful diagnosis on the physical properties of the transition zones. We calculate the thermal X-ray line emission from the transition zone between the ADAF and the thin disk with standard software package Astrophysical Plasma Emission Code (APEC), and the physical implications on the models of the transition zones are discussed.Comment: 10 pages, 2 figures, accepted by ChJA