Boron nitride (BN) and carbon are chemical analogues of each other and share similar structures such as one-dimensional nanotubes, two-dimensional nanosheets characterized by sp2 bonding, and three-dimensional diamond structures characterized by sp3 bonding. However, unlike carbon which can be metallic in one, two, and three dimensions, BN is an insulator, irrespective of its structure and dimensionality. On the basis of state-of-the-art theoretical calculations, we propose a tetragonal phase of BN which is both dynamically stableand metallic. Analysis of its band structure, density of states, and electron localization function confirms the origin of the metallic behavior to be due to the delocalized B 2p electrons. The metallicity exhibited in the studied three-dimensional BN structures can lead to materials beyond conventional ceramics as well as to materials with potential for applications in electronic devices.
Lake Yilong in Southwestern China has been under serious eutrophication threat during the past decades; however, the lake water remained clear until sudden sharp increase in Chlorophyll a (Chl a) and turbidity in 2009 without apparent change in external loading levels. To investigate the causes as well as examining the underlying mechanism, a three-dimensional hydrodynamic and water quality model was developed, simulating the flow circulation, pollutant fate and transport, and the interactions between nutrients, phytoplankton and macrophytes. The calibrated and validated model was used to conduct three sets of scenarios for understanding the water quality responses to various load reduction intensities and ecological restoration measures. The results showed that (a) even if the nutrient loads is reduced by as much as 77%, the Chl a concentration decreased only by 50%; and (b) aquatic vegetation has strong interaction with phytoplankton, therefore requiring combined watershed and in-lake management for lake restoration. (c) 2013 Elsevier Ltd. All rights reserved.
This paper estimates the labor supply functions for health care professionals in China using Census-based data in 2005. The rapid economic growth and population aging in China led to a substantial increase in the demand for health care services and the derived demand for health care professionals in recent years. However, the increase in the supply of doctors and nurses lags behind the growth in demand, raising the question of whether the excess demand should be met by expanding the health care manpower or by inducing the existing personnel to work more hours through wage increase. Our findings indicate that wage rate adjustment has a significant impact on the length of working time among the self-employed practitioners (with an estimated short-run elasticity of 0.575), while the labor supply of hospital employees is inelastic due to their fixed payment scheme. Instead, hours worked in the employee group are related to non-wage factors such as asset holdings and the hospital ownership type. An important policy implication of our study is that adjustments of labor compensation methods and hospital ownership structure are potentially effective approaches for coping with the excess demand for health care professionals and improving the quality of health care in China.
A series of PDI dimers featuring various arylene linkers are developed as electron acceptors in organic solar cells. Using P3HT as the donor, power conversion efficiency of up to 2.3% is achieved with two PDI dimers having spirobifluorene linkers. The results indicate that such non-planar, three-dimensional structures effectively suppress self-aggregation and crystallization of the PDI units, which is favourable for their solar cell performance.
In this review, a non-standard application of high-resolution transmission electron microscope (HRTEM), namely the creation of so-called NanoLaboratory for the nanomaterial property studies within its pole piece, is presented. The most modern research trends with respect to nanotube, graphene and nanowire, as well as electrical, mechanical and electromechanical properties are demonstrated. In addition, the unique possibilities of modeling real technological processes inside HRTEM, for example, the performance of Li-ion batteries, are illustrated. The contribution particularly highlights the recent research endeavors of our Tsukuba group in line with all the above-mentioned directions of in situ TEM.
