Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

落锤试验测定船板的无塑性转变温度

无塑性转变温度是安全设计的重要参量，广泛应用于材料研究和产品质量控制过程。利用落锤试验方法，测定了AH36级船板的无塑性转变温度为-25℃，并对试验结果进行了评定。结果表明，落锤试验方法简单，试验数据重复性好，当船板的服役温度高于NDTT时，基本保证船板不会发生脆断。     

Influence of grain boundaries on short crack growth behaviour of IGSCC

Understanding short crack behaviour is essential for predicting the lifetime of light water reactor components. However, crack growth rates of short cracks are unsteady due to microstructural obstacles such as grain boundaries. On the other hand, the statistical behaviour of short cracks can be deduced from crack size distributions. Some papers have pointed out that the crack size distributions obtained by stress corrosion cracking tests showed a kink in the distribution line. This kink suggests that the short crack growth rate is slow compared with that of long cracks. And it can be thought that the slow growth rate is caused by the microstructural obstacles. This study investigated the influence of grain boundaries on the short crack growth behaviour of intergranular stress corrosion cracking. A crack growth simulation model, which considered the mechanical effects of the crack kink and bifurcation by grain boundaries, was developed. The crack depth distribution obtained by the simulation also exhibited a kink in the distribution line as seen in the experimental results. This suggests that grain boundaries play an important role in short crack growth behaviour.     

住宅投资与地方经济增长——基于湖南省1999-2012年数据的实证研究

运用1999-2012年的湖南省住宅投资和GDP季度数据,对住宅投资与经济增长之间的领先与滞后关系进行了实证研究.结果表明,住宅投资与GDP之间只存在单向的因果关系;广义脉冲响应函和方差分解分析也显示,GDP对住宅投资的影响远大于住宅投资对GDP的影响,GDP的走势对于住宅投资起着决定性影响,而住宅投资对于GDP的贡献很小.本结论对于地方政府的房地产投资政策具有一定参考价值.     

电荷束团非均匀密度分布引起的发射度增长

直线加速器中电荷束团的非线性效应是导致束流发射度增长的一个重要原因。文中给出了直线加速器中几种常见的非均匀密度分布的有限长空间电荷束团所具有的非线性自场能，即纵向非均匀电荷密度分布分别为水袋型，抛物线型，而横向密度分布为均匀型，水袋型，抛物线型及高期型等各种组合非均匀密度分布的自场能公式，并得到了由束团非线性的均匀电荷密度分布引起的束流发射度增长。     

流动沸腾条件下窄通道内的汽泡生长和冷凝

针对过冷沸腾条件下窄通道内的汽泡生长和冷凝进行实验研究。实验中观察到了两类汽泡的生长和冷凝,分别称为第1类汽泡和第2类汽泡。其中第1类汽泡生长速度较快,且在滑移离开核化点之后迅速冷凝消失。而第2类汽泡的生长速度较慢,且滑移很长一段距离后也不会冷凝消失,具有更长的存活时间。两类汽泡的生长可采用不同的关系式进行预测,且生长冷凝特性均表现出很强的随机性,体现出汽泡周围环境的微小变化对汽泡行为的影响。     

Hydrogen plasma treatment of very thin p-type nanocrystalline Si films grown by RF-PECVD in the presence of B(CH3)3

Abstract

We have characterized the structure and electrical properties of p-type nanocrystalline silicon films prepared by radio-frequency plasma-enhanced chemical vapor deposition and explored optimization methods of such layers for potential applications in thin-film solar cells. Particular attention was paid to the characterization of very thin (～20 nm) films. The cross-sectional morphology of the layers was studied by fitting the ellipsometry spectra using a multilayer model. The results suggest that the crystallization process in a high-pressure growth regime is mostly realized through a subsurface mechanism in the absence of the incubation layer at the substrate-film interface. Hydrogen plasma treatment of a 22-nm-thick film improved its electrical properties (conductivity increased more than ten times) owing to hydrogen insertion and Si structure rearrangements throughout the entire thickness of the film.     

One of the Primary Functions of Tissue-Resident Pluripotent Pericytes Cells May Be to Regulate Normal Organ Growth and Maturation: Implications for Attempts to Repair Tissues Later in Life

Adult mesenchymal stem cells were reported more than 30 years ago. Since then, their potential to repair and regenerate damaged or diseased tissues has been studied intensively in both preclinical models and human trials. Most of the need for such tissue repair/regeneration is in older populations, so much of the effort has been performed with autologous cells in older patients. However, success has been difficult to achieve. In the literature, it has been noted that such progenitor cells from younger individuals often behave with more vigorous activity and are functionally enhanced compared to those from older individuals or animals. In addition, cells with the characteristics of mesenchymal stem cells or pluripotent mesenchymal regulatory cells exist in nearly all tissues and organs as pericytes since fetal life. Such evidence raises the possibility that one of the primary roles of these organ-specific cells is to regulate organ growth and maturation, and then subsequently play a role in the maintenance of organ integrity. This review will discuss the evidence to support this concept and the implications of such a concept regarding the use of these progenitor cells for the repair and regeneration of tissues damaged by injury or disease later in life. For the latter, it may be necessary to return the organ-specific progenitor cells to the functional state that contributed to their effectiveness during growth and maturation rather than attempting to use them after alterations imposed during the aging process have been established and their function compromised.     

Direct vapor phase growth process and robust photoluminescence properties of large area MoS2 layers

There has been growing research interest in the use of molybdenum disulfide in the fields of optoelectronics and energy harvesting devices, by virtue of its indirect-to-direct band gap tunability. However, obtaining large area thin films of MoS2 for future device applications still remains a challenge. In the present study, the amounts of the precursors （S and MOO3） were varied systematically in order to optimize the growth of highly crystalline and large area MoS2 layers by the chemical vapor deposition method. Careful control of the amounts of precursors was found to the key factor in the synthesis of large area highly crystalline flakes. The thickness of the layers was confirmed by Raman spectroscopy and atomic force microscopy. The optical properties and chemical composition were studied by photoluminescence （PL） and X-ray photoelectron spectroscopy. The emergence of strong direct excitonic emissions at 1.82 eV （A-exciton, with a normalized PL intensity of -55 × 10^3） and 1.98 eV （B-exciton, with a normalized PL intensity of -5 × 10^3） of the sample at room temperature clearly indicates the high luminescence quantum efficiency. The mobility of the films was found to be 0.09 cm^2/（V.s） at room temperature. This study provides a method for the controlled synthesis of high-quality two-dimensional （2D） transition metal dichalcogenide materials, useful for applications in nanodevices, optoelectronics and solar energv conversion.