Electric potential and energy band in ZnO nanofiber tuned by local mechanical loading

Recent success in strain engineering has triggered tremendous interest in its study and potential applications in nanodevice design. In this paper, we establish a coupled piezoelectric/semiconducting model for a wurtzite structure ZnO nanofiber under the local mechanical loading. The energy band structure tuned by the local mechanical loading and local length is calculated via an eight-band k·p method, which includes the coupling of valance and conduction bands. Poisson's effect on the distribution of electric potential inversely depends on the local mechanical loading. Numerical results reveal that both the applied local mechanical loading and the local length exhibit obvious tuning effects on the electric potential and energy band. The band gap at band edges varies linearly with the applied loading. Changing the local length shifts the energy band which is far away from the band edges. This study will be useful in the electronic and optical enhancement of semiconductor devices.     

ELECTRICALLY FORCED VIBRATION OF A THICKNESS-TWIST MODE PIEZOELECTRIC RESONATOR WITH NON-UNIFORM ELECTRODES

We study the effect of electrodes with varying thickness on thickness-twist vibration of a piezoelectric plate resonator of crystals of 6 mm symmetry.An exact theoretical analysis is performed.Results show that non-uniform electrodes have a strong effect on mode shapes,and suggest the possibility of using nonuniform electrodes for strong energy trapping.     

脂润滑条件下激光微精处理零件的抗擦伤性能研究

采用ＳＲＶ试验机和Ｔｉｍｋｅｎ试验机，对脂润滑条件下经激光微精处理的３种铸铁与ＧＣｒ１５钢的抗擦伤性能进行了研究。结果表明：激光微精处理使其抗擦伤性能均大幅度提高，其中合金铸铁经激光微精处理后可在蜗轮摩擦副中代替青铜使用。     

Collective buckling of a two-dimensional array of nanoscale columns

Periodic soft nanostructures are building blocks for small devices. However, mechanical failure in the form of structure buckling or distortion from their original shape is often reported when the dimension of these soft structures were reduced to below submicron scale. Such a phenomenon seriously limits a reliable impact of these nanostructures to greater applications. Current understandings of buckling of soft 2-D nanostructures are limited. The substrate for these soft nanostructures is usually very compliant. Neighboring nanostructures could interact through the deformation of the substrate. We analyze the collective buckling of a two-dimensional array of nanoscale columns with their lower ends built into an elastic substrate. Buckling of these nanostructures is mathematically described by an eigenvalue problem. Numerical analyses show patterned collapse for these 2-D nanostructures, qualitatively matching reported experimental findings. Our efforts are useful toward the understanding and manufacturing of many two-dimensional nanoscale features.     

化学高考结构效度初探

任何考试总是为了一定的测量目的而编制的,判断它是否有效（效度）,主要看它达到测验目标的程度。如果通过考试能测量出所要测量的特性,我们称这次考试是有效的。     

化学高考预测效度研究初探

化学高考预测效度研究初探卫子光,韩家勋,苑庆兰,卫丽君一、引言就我国高考而言,其直接目的是选拔普通高校的合格新生。考试要从水平相近的考生群体中区分出哪些是最适合进一步培养的人才。所以,高考与人才的预测有着直接关系,这种考试的预测与将来实际发生的事情的...     

Improvement of light power and efficiency droop in GaN-based LEDs using graded InGaN hole reservoir layer

InGaN-based light-emitting diodes with graded indium composition p-type InGaN hole reservoir layer (HRL) are numerically investigated using the APSYS simulation software. It is found that by gradient increasing indium composition in growth direction of the p-InGaN HRL can improve light output power, lower current leakage and efficiency droop. Based on numerical simulation and analysis, these improvements on the electrical and optical characteristics are attributed mainly to tailoring energy band in p–n junction vicinal region, and finally enhanced the hole injection efficiency and electron blocking efficiency.     

正交试验设计法简介

一项科学试验要达到预期的目的,除有正确的指导思想外,还和方法十分有关。试验安排得好,次数不多就能获得成效;如果试验的计划安排不妥,盲目试验,不仅增加试验次数,延长周期,造成人力、物力、时间上的浪费,而且有时还会导致试验的失败。     

天津国际化学教育研讨会概况

天津国际化学教育研讨会于1988年6月13日至16日在天津师范大学举行。这是由国家科委批准,天津师范大学和美国坦普尔大学共同组织召开的,在我国首次举行的一次重要国际化学教育会议。会议的目的是探讨中等学校化学教育如何适应当今科学技术的发展和社会的需要,以及这两个方面相结合的问题。