科研成果

研究在30°安息角的沙坡面上,单一粒径球形沙粒的运动状态。假设沙粒无滑动且碰撞时角动量守恒,则扰动沙粒经过不超过5次的滚动、抛射、再滚动后,即进入与初条件无关的周期性运动,其频率为0.39g/D（1/2）,与鸣沙流的梯度相近,临界抛射角稳定在51.2°,抛射过程沙粒自旋角速度为16 r/min。自保持的周期性决定了沙粒的整体协同运动,是鸣沙发声及频率自锁的根本原因。

<正>未来很可能存在于机器交互的界面中,但是大量的技术、伦理问题都要在人机交互的阶段解决。希望读者看到这个标题后,可以会心地一笑。就像宁财神在《龙门客栈》的一版预告片中打出"1024"的时候,草榴一族好像接收到了族人发出的暗号,激动万分——1024等于草榴,草榴等于"无尺度"、"无节制"、"无下限"的分享。

纵观2013年的慕课发展可以看出,慕课全球化态势已经凸显,慕课与正规教育结合的各类实验做法初见成效,围绕慕课的相关研究发现也在本年度小试锋芒。本文系统梳理了2013年慕课运动的4条发展路径,以此作为2013年慕课观察之总结。

In this paper, we report the device performance of a high-voltage normally off Al2O3/GaN MOSFET on the Si substrate. Normally off operation is obtained by multiple cycles of O-2 plasma oxidation and wet oxide-removal gate recess process. The recessed normally off GaN MOSFET with 3 mu m gate-drain distance exhibits a maximum drain current of 585 mA/mm at 9 V gate bias. The threshold voltage of the MOSFET is 2.8 V with a standard derivation of 0.2 V on the sample with an area of 2 x 2 cm(2). The gate leakage current is below 10(-6) mA/mm during the whole gate swing up to 9 V and the I-ON/I-OFF ratio is larger than 10(9), indicating the good quality of Al2O3 gate insulator. The MOSFET with 10 mu m gate-drain distance shows a three terminal OFF-state breakdown voltage (BV) of 967 V at zero gate-source bias with a drain leakage current criterion of 1 mu A/mm. The specific ON-resistance (R-ON,R- SP) of the device is 1.6 m Omega . cm(2) and the power figure of merit (BV2/R-ON,R- SP) is 584 MW/cm(2).

Although new particle formation accounts for about 50% of the global aerosol production in the troposphere, the chemical species and mechanism responsible for the growth of freshly nucleated nanoparticles remain largely uncertain. Here we show large size growth when sulfuric acid nanoparticles of 4-20 nm are exposed to epoxide vapors, dependent on the particle size and relative humidity. Composition analysis of the nanoparticles after epoxide exposure reveals the presence of high molecular weight organosulfates and polymers, indicating the occurrence of acid-catalyzed reactions of epoxides. Our results suggest that epoxides play an important role in the growth of atmospheric newly nucleated nanoparticles, considering their large formation yields from photochemical oxidation of biogenic volatile organic compounds.