5,166 research outputs found

    Sequential Classification of Hyperspectral Images

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    Hyperspectral imaging has become increasingly popular in applications such as agriculture, food, and environment. Rich spectral information of hyperspectral images leads to new possibilities and new challenges in data processing. In this chapter, we consider the hyperspectral classification problems in consideration of sequential data collection, which is a frequent setting in industrial pushboom imaging systems. We present related techniques including data normalization, dimension reduction, classification, and spatial information integration and the way to accommodate these techniques to the context of sequential data collecting and processing. The propose scheme is validated with real data collected in our laboratory. The methodology of result assessment is also presented

    Creating democratic citizens? The political effects of the Internet in China

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    This study explores the perplexing role of the Internet in authoritarian settings. We disentangle the political impact of the Internet along two distinct dimensions, indirect effects and direct effects. While the direct effects of the exposure to the Internet shape political attitudes in a manifest and immediate way, the indirect effects shape various political outcomes via instilling fundamental democratic orientations among citizens. In authoritarian societies such as China, we argue the indirect effects of the Internet as a value changer tend to be potent, transformative and persistent. But the direct effects of the Internet as a mere alternative messenger are likely to be markedly contingent. Relying on the newly developed method of causal mediation analysis and applying the method to data from a recent survey conducted in Beijing, we find strong empirical evidence to support our argument on the two-dimensional impacts of the Internet on authoritarian nations

    Social trust and grassroots governance in rural China

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    The relationship between social trust and governance has been one of the focal points of the academic and policy-making communities. Empirical studies on this relationship, however, have focused mostly on democracies. The scarcity of such studies in authoritarian countries has left many important questions unanswered: Is social trust associated with effective governance only in democratic settings? Can social trust improve the quality of governance in non-democracies as well? Drawing on data from 2005 China General Social Survey—a representative survey conducted nationwide at both the individual- and village-level in rural China, this paper attempts to answer these questions empirically by examining the relationship between social trust and the quality of governance in rural China. The findings reveal that different types of social trust—particularized trust and generalized trust—correspond with different effects in rural governance: whereas villagers’ trust in people whom they knew personally was positively and significantly associated with the provision of various public goods and services, their trust in strangers had virtually no impact on rural governance

    Statistical Properties of Multiple Optical Emission Components in Gamma-Ray Bursts and Implications

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    Well-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are complied from the literature. Multiple optical emission components are extracted with power-law function fits to these lightcurves. We present a systematical analysis for statistical properties and their relations to prompt gamma-ray emission and X-ray afterglow for each component. We show that peak luminosity in the prompt and late flares are correlated and the evolution of the peak luminosity may signal the evolution of the accretion rate. No tight correlation between the shallow decay phase/plateau and prompt gamma-ray emission is found. Assuming that they are due to a long-lasting wind injected by a compact object, we show that the injected behavior favors the scenarios of a long-lasting wind after the main burst episode. The peak luminosity of the afterglow onset is tightly correlated with Eiso, and it is dimmer as peaking later. Assuming that the onset bump is due to the fireball deceleration by the external medium, we examine the Gamma_0-Eiso relation and find that it is confirmed with the current sample. Optical re-brightening is observed in 30 GRBs in our sample. It shares the same relation between the width and the peak time as found in the onset bump, but no clear correlation between the peak luminosity and Eiso as observed in the onset bumps is found. Although its peak luminosity also decays with time, the slope is much shallower than that of the onset peak. We get L t^{-1}_{p}$, being consistent with off-axis observations to an expanding external fireball in a wind-like circum medium. The late re-brightening may signal another jet component. Mixing of different emission components may be the reason for the observed chromatic breaks in different energy bands.Comment: 10 pages, 5 figures, to be published by IJMPD (Proceedings of "The Third Galileo - Xu Guangqi meeting", Beijing, October 11-15, 2011

    Algorithms for square root of semi-infinite quasi-Toeplitz MM-matrices

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    A quasi-Toeplitz MM-matrix AA is an infinite MM-matrix that can be written as the sum of a semi-infinite Toeplitz matrix and a correction matrix. This paper is concerned with computing the square root of invertible quasi-Toeplitz MM-matrices which preserves the quasi-Toeplitz structure. We show that the Toeplitz part of the square root can be easily computed through evaluation/interpolation at the mm roots of unity. This advantage allows to propose algorithms only for the computation of correction part, whence we propose a fixed-point iteration and a structure-preserving doubling algorithm. Moreover, we show that the correction part can be approximated by solving a nonlinear matrix equation with coefficients of finite size followed by extending the solution to infinity. Numerical experiments showing the efficiency of the proposed algorithms are performed
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