Income Inequality in China and its Influencing Factors

inequality, China, Kuznets curve

Rural-Urban Income Disparity and WTO Impact on China’s Agricultural Sector: Policy Considerations

Agricultural and Food Policy,

Sustainability of China's Economic Growth

no abstract provide

Silicon-germanium nanowire heterojunctions: Optical and electrical properties

Semiconductor nanowires are quasi-one-dimensional objects with unique physical properties and strong potential in nanophotonics, nanoelectronics, biosensing, and solar cell devices. The next challenge in the development of nanowire functional structures is the nanowire axial heterojunctions, especially lattice mismatched heterojunctions. Si and Ge have a considerable lattice mismatch of ~ 4.2% as well as a mismatch in the coefficient of thermal expansion, and the formation of a Si1-xGex transition layer at the heterointerface creates a non-uniform strain and modifies the band structures of the adjacent Si and Ge nanowire segments. These nanostructures are produced by catalytic chemical vapor deposition employing vapor-liquid-solid mechanism on (111) oriented p-type Si substrate, and they exhibit unique structural properties including highly localized strain, and short-range interdiffusion/intermixing revealed by transmission electron microscopy, scanning electron microscopy and energy dispersive x-ray spectroscopy. Our studies of the structural properties of axial Si-Ge nanowire heterojunctions show that despite the 4.2% lattice mismatch between Si and Ge they can be grown without a significant density of structural defects. The lattice mismatch induced strain is partially relieved due to spontaneous SiGe intermixing at the heterointerface during growth and lateral expansion of the Ge segment of the nanowire, which is in part due to a higher solubility of Ge in metal precursors. The mismatch in Ge and Si coefficients of thermal expansion and low thermal conductivity of Si/Ge nanowire heterojunctions are proposed to be responsible for the thermally induced mechanical stress detected under intense laser radiation. The performed electrical measurements include current-voltage, conductance-voltage, transient electrical measurements under various applied voltages at temperatures ranging from 20 to 400K. We find that Si-Ge nanowire heterojunctions exhibit strong current instabilities associated with flicker noise and damped oscillations with frequencies close to 10-30 MHz. Flicker (or 1/f ) noise is characterized and analyzed on carrier number fluctuation model and mobility fluctuation model noise mechanism, respectively. The proposed explanation is based on a carrier transport mechanism involving electron transitions from Ge to Si segments of the NWs, which requires momentum scattering, causes electron deceleration at the Ge-Si heterointerface and disrupts current flow. Both Si/Ge heterojunctions and NW surface states are demonstrated to be the two dominant elements that strongly influence the electrical characteristics of nanowires

Generating functions and short recursions, with applications to the moments of quadratic forms in noncentral normal vectors

Using generating functions, the top-order zonal polynomials that occur in much distribution theory under normality can be recursively related to other symmetric functions (power-sum and elementary symmetric functions, Ruben, Hillier, Kan, and Wang). Typically, in a recursion of this type the k -th object of interest, d k say, is expressed in terms of all lower-order d j's. In Hillier, Kan, and Wang we pointed out that, in the case of top-order zonal polynomials (and generalizations of them), a shorter (i.e., fixed length) recursion can be deduced. The present paper shows that the argument in generalizes to a large class of objects/generating functions. The results thus obtained are then applied to various problems involving quadratic forms in noncentral normal vectors.

Computationally efficient recursions for top-order invariant polynomials with applications

The top-order zonal polynomials Ck(A),and top-order invariant polynomials Ck1,...,kr(A1,...,Ar)in which each of the partitions of ki,i = 1,..., r,has only one part, occur frequently in multivariate distribution theory, and econometrics - see, for example Phillips (1980, 1984, 1985, 1986), Hillier (1985, 2001), Hillier and Satchell (1986), and Smith (1989, 1993). However, even with the recursive algorithms of Ruben (1962) and Chikuse (1987), numerical evaluation of these invariant polynomials is extremely time consuming. As a result, the value of invariant polynomials has been largely confined to analytic work on distribution theory. In this paper we present new, very much more efficient, algorithms for computing both the top-order zonal and invariant polynomials. These results should make the theoretical results involving these functions much more valuable for direct practical study. We demonstrate the value of our results by providing fast and accurate algorithms for computing the moments of a ratio of quadratic forms in normal random variables.