含Eu3+离子的Na2O-K2 O-SiO2-Al2O3系统玻璃的制备及其变温发射光谱与结构特性

通过高温熔融法制备了含Eu^3 离子的Na2O-K2O-SiO2-Al2O3系统玻璃。在488nm波长光的激发下，系统地研究了上述玻璃从77K到700K温度范围的变温发光特征。发现总的荧光强度首先随温度的升高而大幅度升高，然后随温度的升高而减少，用声子辅助吸收与热激活过程及温度淬灭效应定性地解释了上述强度的变化，同时测量与分析了Eu^3 离子的晶格场参量。结果表明，Eu^3 离子与氧离子的距离随着温度升高而变短，而Eu^3 离子的配位数不随温度而变化。     

Confirming the lattice contraction in CdSe nanocrystals grown in a glass matrix by Raman scattering

This work gives the evidence of the lattice contraction in CdSe nanocrystals (NCs) grown in a glass matrix. The CdSe NCs were investigated by atomic force microscopy (AFM), optical absorption (OA), and Raman spectroscopy. The average size of CdSe NCs can be estimated by AFM images. Using the OA spectra and the effective‐mass approximation, it was also possible to estimate the average sizes of CdSe NCs, which agree very well with the AFM data. These results showed that the CdSe NCs grow with increasing time of heat treatment. The blue shift of the longitudinal optical (LO) modes and surface optical (SO) phonon modes with an increase in the average radius of the NCs, shown in the Raman spectra, was explained by the lattice contraction in CdSe NCs caused by thermodynamic interactions at the interface with the host glass matrix. Copyright © 2010 John Wiley & Sons, Ltd.     

景观湖水质的三维荧光指纹

荧光光谱法灵敏度高、选择性强、测量快速便捷,而三维荧光光谱更有信息丰富的优点。荧光光谱与水样具有一一对应的关系,就像水样指纹一样,被称为“水质荧光指纹”。 该文采用三维荧光光谱法研究了北京两个相邻景观湖四季的水质变化。两湖湖水均具有明显的类蛋白质和类腐殖酸的荧光,且类蛋白质的荧光强度较强。荧光强度与自然和人为活动的相关性表明,两湖湖水水质随季节变化明显,春夏季节水质相对较好,秋冬季节水质相对较差;以游船为主的娱乐湖的水质主要受藻类和植物生长等自然因素的影响,而种植等人为因素对植物观赏湖的水质的影响十分重要。由此可见,湖水水质的变化是由湖的功能决定的。在春秋人工清理藻类和植物的残余有利于保护湖体水质。     

Learning-based compressed sensing for infrared image super resolution

This paper presents an infrared image super-resolution method based on compressed sensing (CS). First, the reconstruction model under the CS framework is established and a Toeplitz matrix is selected as the sensing matrix. Compared with traditional learning-based methods, the proposed method uses a set of sub-dictionaries instead of two coupled dictionaries to recover high resolution (HR) images. And Toeplitz sensing matrix allows the proposed method time-efficient. Second, all training samples are divided into several feature spaces by using the proposed adaptive k-means classification method, which is more accurate than the standard k-means method. On the basis of this approach, a complex nonlinear mapping from the HR space to low resolution (LR) space can be converted into several compact linear mappings. Finally, the relationships between HR and LR image patches can be obtained by multi-sub-dictionaries and HR infrared images are reconstructed by the input LR images and multi-sub-dictionaries. The experimental results show that the proposed method is quantitatively and qualitatively more effective than other state-of-the-art methods.     

Comparative study of optical analysis methods for thin films

Three popular optical analysis methods (the transfer-matrix method, the Tinkham formula, and Beer's law) have been used for analyzing the optical spectra of thin films. While the transfer-matrix method is an accurate method, the Tinkham formula and Beer's law are approximate methods. Here we investigated the three methods using measured transmittance spectra of insulating transition-metal dichalcogenide (TMD) thin films on a quartz substrate. Three different semiconducting 2H-TMD systems (MoS₂, MoSe₂, and MoTe₂) were measured and analyzed. The optical conductivities obtained from the measured transmittance spectra using the transfer-matrix method and Tinkham formula and the absorption coefficients obtained using the transfer-matrix method and Beer's law were compared. The comparisons show some discrepancies. The reasons for the discrepancies between the results obtained via the two different methods were examined and the application limitations of the Tinkham formula and Beer's law were discussed.     

Side Information Generation Scheme Based on Coefficient Matrix Improvement Model in Transform Domain Distributed Video Coding

In order to effectively improve the quality of side information in distributed video coding, we propose a side information generation scheme based on a coefficient matrix improvement model. The discrete cosine transform coefficient bands of the Wyner–Ziv frame at the encoder side are divided into entropy coding coefficient bands and distributed video coding coefficient bands, and then the coefficients of entropy coding coefficient bands are sampled, which are divided into sampled coefficients and unsampled coefficients. For sampled coefficients, an adaptive arithmetic encoder is used for lossless compression. For unsampled coefficients and the coefficients of distributed video coding coefficient bands, the low density parity check accumulate encoder is used to calculate the parity bits, which are stored in the buffer and transmitted in small amount upon decoder request. At the decoder side, the optical flow method is used to generate the initial side information, and the initial side information is improved according to the sampled coefficients by using the coefficient matrix improvement model. The experimental results demonstrate that the proposed side information generation scheme based on the coefficient matrix improvement model can effectively improve the quality of side information, and the quality of the generated side information is improved by about 0.2–0.4 dB, thereby improving the overall performance of the distributed video coding system.     

一种处理原子核多体问题的有效方法

由二级散射矩阵元出发计算了核物质内强子的二级自能修正, 并且归纳了一种研究原子核多体问题的有效方法. 另外, 还讨论了各种密度相关的相对论多体方法之间的关系.     

密度矩阵重正化群的异构并行优化

密度矩阵重正化群方法（DMRG）在求解一维强关联格点模型的基态时可以获得较高的精度,在应用于二维或准二维问题时,要达到类似的精度通常需要较大的计算量与存储空间.本文提出一种新的DMRG异构并行策略,可以同时发挥计算机中央处理器（CPU）和图形处理器（GPU）的计算性能.针对最耗时的哈密顿量对角化部分,实现了数据的分布式存储,并且给出了CPU和GPU之间的负载平衡策略.以费米Hubbard模型为例,测试了异构并行程序在不同DMRG保留状态数下的运行表现,并给出了相应的性能基准.应用于4腿梯子时,观测到了高温超导中常见的电荷密度条纹,此时保留状态数达到10⁴,使用的GPU显存小于12 GB.