Growth and characterization of c-plane AlGaN on γ-LiAlO2

This study demonstrates a pure c-plane AlGaN epilayer grown on a γ-LiAlO₂ (1 0 0) (LAO) substrate with an AlN nucleation layer grown at a relatively low temperature (LT-AlN) by metal-organic chemical vapor deposition (MOCVD). The AlGaN film forms polycrystalline film with m- and c-plane when the nucleation layer grows at a temperature ranging from 660 to 680 °C. However, a pure c-plane AlGaN film with an Al content of approximately 20% can be obtained by increasing the LT-AlN nucleation layer growth temperature to 700 °C. This is because the nuclei density of AlN increases as the growth temperature increases, and a higher nuclei density of AlN deposited on LAO substrate helps prevent the deposition of m-plane AlGaN. Therefore, high-quality and crack-free AlGaN films can be obtained with a (0 0 0 2) ω-rocking curve FWHM of 547 arcsec and surface roughness of 0.79 nm (root-mean-square) using a 700-°C-grown LT-AlN nucleation layer.     

固相微萃取-气相色谱/质谱法测定博物馆空气中总挥发性有机物

采用固相微萃取-气相色谱/质谱(SPME-GC/MS)法测定博物馆室内空气中总挥发性有机物(TVOC)的含量,建立了一种更适合于博物馆室内空气中TVOC的检测方法.对7种挥发性有机物标样进行SPME-GC/MS定性定量分析,进样口温度230 ℃,柱温:起始温度45 ℃,保持3 min,以16 ℃/min的速率程序升温至250 ℃,保持5 min.结果表明,该方法在0.014～0.914 μg/L浓度范围内具有良好的线性关系,最低检出限在1.4～14 ng/L之间,相对标准偏差小于5.28%.该方法方便快捷、对待测物的选择性高、重复性好、采样无需电源、无需溶剂.     

Joint Distribution of Rises and Falls

The marginal distributions of the number of rises and the number of falls have been used successfully in various areas of statistics, especially in non-parametric statistical inference. Carlitz (1972, Duke Math. J. 39, 268–269) showed that the generating function of the joint distribution for the numbers of rises and falls satisfies certain complex combinatorial equations, and pointed out that he had been unable to derive the explicit formula for the joint distribution from these equations. After more than two decades, this latter problem remains unsolved. In this article, the joint distribution is obtained via the probabilistic method of finite Markov chain imbedding for random permutations. A numerical example is provided to illustrate the theoretical results and the corresponding computational procedures.     

Hahn-echoes from N in solids by the stray-field method: prospects for imaging using Long Echo-Train Summation

We have observed Hahn-echoes resulting from Powles–Mansfield pulse-sequences for a variety of nitrogen containing solids which exhibit a range of ¹⁴N electric quadrupole coupling constants (C_q) from 0 to 4.9 MHz. Long echo-decays were frequently obtained which allowed the collection of many echoes in one echo-train, so that the method of Long Echo-Train Summation (LETS), could be used to accumulate signal. A one-dimensional STRAFI-profile is shown for solid ammonium nitrate. The spatial resolution is discussed as a function of C_q.     

X射线显微术

综述了Ｘ射线显微术的基本原理，成像模式和技术及其在生命科学，材料科学等方面应用的新进展，同时简述了Ｘ线射显微术应用过程中应注意的几个问题。     

A unified tabu search algorithm for vehicle routing problems with soft time windows

The different ways of allowing time window violations lead to different types of the vehicle routing problems with soft time windows (VRPSTW). In this paper, different types of VRPSTW are analysed. A unified penalty function and a unified tabu search algorithm for the main types of VRPSTW are presented, with which different types of VRPSTW can be solved by simply changing the values of corresponding parameters in the penalty function. Computational results on benchmark problems are provided and compared with other methods in the literature. Some best known solutions for the benchmark problems in the literature have been improved with the proposed algorithm.     

平面电磁波性质的推导与讨论

简洁推导平面电磁波的基本关系式并由此讨论平面电磁波的性质．     

Symmetric identities on Bernoulli polynomials

In this paper, we obtain a generalization of an identity due to Carlitz on Bernoulli polynomials. Then we use this generalized formula to derive two symmetric identities which reduce to some known identities on Bernoulli polynomials and Bernoulli numbers, including the Miki identity.     

正赝复合全景像全息术

本文提出一种利用正、赝再现像,将物体的正、反两面信息复合在一起的全息术.在一张全息干板片上,可以同时看到物体的两面,增强立体效果和艺术感.文中介绍了原理、方法和结果.