24,602 research outputs found


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    China's accession to the WTO poses great challenges to the Chinese agricultural sector, especially to the grain producers. Compared with major grain exporters in the world, most grain crops in China are high in production cost and weak in market competitiveness. This can be partly attributed to the fact that Chinese farmers are facing with poorer agricultural production infrastructures and inadequate public investment in agricultural research and extension, which leads to the lower efficiency in private inputs and thus higher private cost per unit of product. After China joining the WTO, protective and administrative measures conflicted with the URAA cannot be utilized as before. Alternative measures should be explored to provide help to farmers to improve competitiveness of their product. Public investment in agricultural research and other production infrastructures should be considered with high priority as one of the policy alternatives. This paper examines the effects of public investment in agricultural research on the reduction of production cost of major grain crops in China by using crop-specific data for the past 20 year. It is concluded that, increasing public investment in agricultural research, which is well within the "green box" policy framework and allowed by the WTO rules, is a plausible and effective measure to reduce grain producer's private input and to enhance the competitiveness of grain products. It is also of great significance to sustained food security in China.public investment, agricultural research, grain production, China, WTO, Crop Production/Industries, H540, Q170, Q180,

    A Generic Sample Splitting Approach for Refined Community Recovery in Stochastic Block Models

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    We propose and analyze a generic method for community recovery in stochastic block models and degree corrected block models. This approach can exactly recover the hidden communities with high probability when the expected node degrees are of order logn\log n or higher. Starting from a roughly correct community partition given by some conventional community recovery algorithm, this method refines the partition in a cross clustering step. Our results simplify and extend some of the previous work on exact community recovery, discovering the key role played by sample splitting. The proposed method is simple and can be implemented with many practical community recovery algorithms.Comment: 19 page

    Unconventional behavior of Dirac fermions in three-dimensional gauge theory

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    We study the unconventional behavior of massless Dirac fermions due to interaction with a U(1) gauge field in two spatial dimensions. At zero chemical potential, the longitudinal and transverse components of gauge interaction are both long-ranged. There is no fermion velocity renormalization since the system respects Lorentz invariance. At finite chemical potential, the Lorentz invariance is explicitly broken by the finite Fermi surface. The longitudinal gauge interaction is statically screened and becomes unimportant, whereas the transverse gauge interaction remains long-ranged and leads to singular renormalization of fermion velocity. The anomalous dimension of fermion velocity is calculated by means of the renormalization group method. We then examine the influence of singular velocity renormalization on several physical quantities, and show that they exhibit different behavior at zero and finite chemical potential.Comment: 9 pages, 4 figure

    On the characteristics of emulsion chamber family events produced in low heights

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    The uncertainty of the primary cosmic ray composition at 10 to the 14th power -10 to the 16th power eV is well known to make the study of the nuclear interaction mechanism more difficult. Experimentally considering, if one can identify effectively the family events which are produced in low heights, then an event sample induced by primary protons might be able to be separated. It is undoubtedly very meaningful. In this paper an attempt is made to simulate the family events under the condition of mountain emulsion chamber experiments with a reasonable model. The aim is to search for the dependence of some experimentally observable quantities to the interaction height