Structural,magnetic and optical properties of vanadium doped zinc oxide: Systematic first-principles investigations

The electronic structural, magnetic and optical properties of pure and V-doped ZnO are investigated by first-principles calculations based on the density functional theory. With the introduction of V atoms, the spin-splitting near the Fermi level leads to a net magnetic moment of the system. A significant possibility of room temperature ferromagnetism (RTFM) originated from the Ruderman–Kittel–Kassuya–Yosida (RKKY) exchange is predicted. Oxygen vacancy is positive to enhance the ferromagnetism while zinc vacancy is negative. With respect to the optical properties, the presence of V atoms was found to have an obvious influence on the transmittivity, especially in the low energy region. A slight V-doping can keep a high optical transmission and smoothly modulate the optical bandgap.     

Observation of capillary discharge Ne-like Ar 46.9?nm laser with pre-pulse and main-pulse delay time in the domain of 2–130?μs

We demonstrated the lasing of Ne-like Ar 46.9?nm pumped by capillary discharge with the delay time between pre-pulse and main-pulse ranging from 2 to 130???s. Results show that the laser output reduced significantly when the delay time is much longer than 12???s. The temporal evolution of spontaneous radiation emitted from pre-ionized plasma implies that the observed reduction of the laser output is caused by the axial non-uniformity of pre-ionized plasma density and the decrease of pre-ionized plasma density.     

An investigation of preservice teachers’ use of guess and check in solving a semi open-ended mathematics problem

Open-ended problems have been regarded as powerful tools for teaching mathematics. This study examined the problem solving of eight mathematics/science middle-school teachers. A semi-structured interview was conducted with (PTs) after completing an open-ended triangle task with four unique solutions. Of particular emphasis was how the PTs used a specific heuristic strategy. The results showed that the primary strategy PTs employed in attempting to solve the triangle problem task was guess and check; however, from the PTs’ reflections, we found there existed misapplications of guess and check as a systematic problem-solving strategy. In order to prepare prospective teachers to effectively teach, teacher educators should pay more attention to the mathematical proficiency of PTs, particularly their abilities to systematically and efficiently use guess and check while solving problems and explain their solutions and reasoning to middle-school students.     

InGaN/GaN多量子阱LED载流子泄漏与温度关系研究

通过测量光电流,直接观察了InGaN/GaN量子阱中载流子的泄漏程度随温度升高的变化关系。当LED温度从300K升高到360K时,在相同的光照强度下,LED的光电流增大,说明在温度上升之后,载流子从量子阱中逃逸的数目更多,即载流子泄漏比例增大。同时,光电流的增大在激发密度较低的时候更为明显,而且光电流随温度的增加幅度与激发光子的能量有关。用量子阱-量子点复合模型能很好地解释所观察到的实验现象。实验结果直接证明,随着温度的升高,InGaN/GaN量子阱中的载流子泄漏将显著增加,而且在低激发密度下这一效应更为明显。温度升高导致的载流子泄漏增多是InGaN多量子阱LED发光效率随温度升高而降低的重要原因。     

A nonsmooth Levenberg-Marquardt method for vertical complementarity problems

A nonsmooth Levenberg-Marquard (LM) method with double parameter adjusting strategies is presented for solving vertical complementarity problems based on the computation of an element of a vextor-valued minimum function’s B-differential in this paper. At each iteration, the LM parameter is adjusted based on the norm of the vector-valued minimum function and the ratio between the actual reduction and the predicted reduction. Under the local error bound condition, which is strictly weaker than nonsingular assumption, the local convergence rate is discussed. Finally, the numerical tests indicate that the present algorithm is effective.