科研成果 by Year: 2014>

A highly efficient recognition phenomenon was observed between alkoxylated arylene-ethynylene macrocycles bearing identical side chains but different core size, which is based on van der Waals interactions between alkoxy chains. The ratio of both molecules and the environment of each molecule have been statistically analyzed to quantify the recognition efficiency.

As the world's second largest economy, China has experienced severe haze pollution, with fine particulate matter ( PM) recently reaching unprecedentedly high levels across many cities, and an understanding of the PM formation mechanism is critical in the development of efficient mediation policies to minimize its regional to global impacts. We demonstrate a periodic cycle of PM episodes in Beijing that is governed by meteorological conditions and characterized by two distinct aerosol formation processes of nucleation and growth, but with a small contribution from primary emissions and regional transport of particles. Nucleation consistently precedes a polluted period, producing a high number concentration of nano-sized particles under clean conditions. Accumulation of the particle mass concentration exceeding several hundred micrograms per cubic meter is accompanied by a continuous size growth from the nucleation-mode particles over multiple days to yield numerous larger particles, distinctive from the aerosol formation typically observed in other regions worldwide. The particle compositions in Beijing, on the other hand, exhibit a similarity to those commonly measured in many global areas, consistent with the chemical constituents dominated by secondary aerosol formation. Our results highlight that regulatory controls of gaseous emissions for volatile organic compounds and nitrogen oxides from local transportation and sulfur dioxide from regional industrial sources represent the key steps to reduce the urban PM level in China.

As the world's second largest economy, China has experienced severe haze pollution, with fine particulate matter ( PM) recently reaching unprecedentedly high levels across many cities, and an understanding of the PM formation mechanism is critical in the development of efficient mediation policies to minimize its regional to global impacts. We demonstrate a periodic cycle of PM episodes in Beijing that is governed by meteorological conditions and characterized by two distinct aerosol formation processes of nucleation and growth, but with a small contribution from primary emissions and regional transport of particles. Nucleation consistently precedes a polluted period, producing a high number concentration of nano-sized particles under clean conditions. Accumulation of the particle mass concentration exceeding several hundred micrograms per cubic meter is accompanied by a continuous size growth from the nucleation-mode particles over multiple days to yield numerous larger particles, distinctive from the aerosol formation typically observed in other regions worldwide. The particle compositions in Beijing, on the other hand, exhibit a similarity to those commonly measured in many global areas, consistent with the chemical constituents dominated by secondary aerosol formation. Our results highlight that regulatory controls of gaseous emissions for volatile organic compounds and nitrogen oxides from local transportation and sulfur dioxide from regional industrial sources represent the key steps to reduce the urban PM level in China.

The purpose of this study is to analyze the recent development of Chinese vocational colleges from two perspectives: the adoption of employability as a new institutional mission and organizational changes in six areas. The analysis is based on a multiple-case study. The analytical frameworks are developed from sociological theory and organizational theory. This study argues that vocational colleges in China are experiencing substantial transformations. At the macro level, they are transforming from a social institution to industry under the neoliberal argument for globalization. Colleges adopt employability as their new mission. At the micro level, there are considerable changes under the influence of the new mission, in terms of program goal, program development, curriculum development, dominant pedagogy, faculty development, and internal management. The changes fit the rhetoric of employability as a core competency. There is a tendency that Chinese vocational higher education institutions will degenerate into training organizations for employment.

Postgate annealing (PGA) in N-2/O-2 atmosphere at 300 degrees C for various annealing time is performed on enhancement mode AlGaN/GaN MOSFET fabricated using a self-terminating gate recess etching technique. After 45-min annealing, the device OFF-state leakage current decreases by more than two orders of magnitude and thus a low OFF-state leakage current of similar to 10(-13) A/mm is obtained at room temperature, resulting in an excellent ON/OFF current ratio of similar to 10(12). At 250 degrees C, the device still exhibits a low OFF-state leakage current of similar to 10(-9) A/mm and high ON/OFF current ratio of similar to 10(8). Meanwhile, a strong correlation between the OFF-state leakage current and mesa isolation current is observed as we change the annealing time: 1) the lower the mesa isolation current and 2) the lower the OFF-state leakage current and thus the higher the ON/OFF current ratio. It is the suppression of the mesa isolation current owing to the passivation of atomic layer deposition Al2O3 that leads to the improvement of the OFF-state leakage current and ON/OFF current ratio after PGA. Besides, the device shows no obvious change in terms of its threshold voltage and maximum drain current after PGA.