具有多个中介变量的中介效应估计①

因果中介分析是调查自变量通过中介变量对因变量的影响,以揭示其因果机制。近年来,中介分析研究成果越来越多,但主要针对一个中介变量模型。面对多个中介变量的复杂情况,构造了具有多个中介变量的中介模型,提出了中介效应的估计,并对直接效应和间接效应进行了模拟研究,模拟结果表明提出的估计效果良好。     

助理模具工程师应用性人才能力培养的探讨

应用型高技能是高职高专院校人才培养的目标。结合社会对人才的要求,提出了培养助理模具工程师为目标的教改理念,并为我校模具专业学生能力培养提出具体的助理模具工程师标准,在本校模具专业进行了教改实践。结果表明采用设计、制造和装配一条龙的实践教学过程,能够使培养的学生的能力达到助理工程师标准。     

Simulation on effect of metal/graphene hybrid transparent electrode on characteristics of GaN light emitting diodes

In order to decrease the Schottky barrier height and sheet resistance between graphene(Gr) and the p-GaN layers in GaN-based light-emitting diodes(LEDs), some transparent thin films with good conductivity and large work function are essential to insert into Gr and p-GaN layers. In this work, the ultra-thin films of four metals(silver(Ag), golden(Au), nickel(Ni), platinum(Pt)) are explored to introduce as a bridge layer into Gr and p-GaN, respectively. The effect of a different combination of Gr/metal transparent conductive layers(TCLs) on the electrical, optical, and thermal characteristics of LED was investigated by the finite element methods. It is found that both the TCLs transmittance and the surface temperature of the LED chip reduces with the increase of the metal thickness, and the transmittance decreases to about 80% with the metal thickness increasing to 2 nm. The surface temperature distribution, operation voltage, and optical output power of the LED chips with different metal/Gr combination were calculated and analyzed. Based on the electrical, optical, and thermal performance of LEDs, it is found that 1.5-nm Ag or Ni or Pt, but 1-nm Au combined with 3 layered(L) Gr is the optimal Gr/metal hybrid transparent and current spreading electrode for ultra-violet(UV) or near-UV LEDs.     

石墨烯纳米带的可控制备研究进展

石墨烯纳米带是宽度为纳米尺度的石墨烯条带,根据其边缘构型的不同可以分为锯齿型石墨烯纳米带和扶手型石墨烯纳米带.纳米尺度导致的量子限域效应和边缘构型引起的边缘效应能够调节石墨烯纳米带的电子结构,打开石墨烯的带隙.而且,石墨烯纳米带具有极大的长宽比和极高比例的边缘原子,为通过结构裁剪实现功能定制提供了无限可能.这些几何和电子结构特性使得石墨烯纳米带在电子器件等诸多领域比石墨烯具有更大的应用潜力,因此,石墨烯纳米带的相关研究一直是纳米材料领域的热点.基于此,本综述首先介绍了石墨烯纳米带的结构和性质,全面介绍了石墨烯纳米带的制备方法,相应的制备方法可以分为两部分:(1)自上而下法:通过等离子体、离子束、扫描隧道显微镜和金属纳米颗粒对石墨烯和碳纳米管进行刻蚀和切割,制备石墨烯纳米带.该方法面临最大挑战在于如何提高刻蚀和切割精度.(2)自下而上法:利用含碳前驱体,如有机化合物、碳氢化合物气体以及碳化硅等,制备石墨烯纳米带.该方法利于实现原子精度的结构控制,尤其是化学气相沉积法有望实现低成本、规模化制备.最后展望石墨烯纳米带研究的挑战和前景.我们相信,随着材料和技术的创新发展,石墨烯纳米带必将成为一...