Role of vapor-phase diffusion in selective-area MOVPE of InGaN/GaN MQWs

Selective-area growth (SAG) of InGaN/GaN multiple quantum wells (MQWs) was performed by metalorganic vapor phase epitaxy (MOVPE). The layers of a blue light-emitting diode (LED), that includes five InGaN quantum wells, were grown on a patterned GaN template on a sapphire substrate. In order to elucidate the contribution of vapor-phase diffusion of group-III precursors to the in-plane modulation of luminescence wavelength, the width of a stripe selective growth area was 60 μm that is sufficiently larger than the typical surface diffusion length, with the mask width varied stepwise between 30 and 240 μm. The distribution of the luminescence wavelength from the MQWs was measured with cathode luminescence (CL) across the stripe growth area. The peak wavelength ranged between 420 and 500 nm. The peak shifted to longer wavelengths and became broader as the measured point approached to the mask edge. Such a shift in the peak wavelength exhibited parabolic profile in the growth area and the wider mask shifted the entire peak positions to longer wavelengths. These trends clearly indicate that the vapor-phase diffusion play a dominant role in the in-plane modulation of the luminescence wavelength in the SA-MOVPE of InGaN MQWs, when the size of a growth area and/or the mask width exceeds approximately 10 μm.     

The even Orlicz Minkowski problem

The classical Minkowski problem leads to the Lp Minkowski problem and now to the Orlicz Minkowski problem. Existence is demonstrated for the even Orlicz Minkowski problem. A byproduct is a new approach to the solution of the classical Minkowski problem.     

Molecular Dynamics Simulations and Steered Molecular Dynamics Simulations of Glabridin Bound to Wild Type and V30A Mutant Transthyretin: Ligand-linked Perturbation of Tertiary Conformation

Transthyretin(TTR), as a tetrameric protein, functions as a neuroprotector. The native TTR homotetramer dissociates into dimers and monomers. Dimers and monomers self-assemble into amyloid fibrils, and this process can lead to some diseases. Native TTR homotetramer is a widely accepted model for TTR amyloid formation. In this study, simulations using molecular dynamics(MD) and steered MD(SMD) were performed to explore the mechanisms for glabridin(Glab), a specific inhibitor for TTR binding, for V30A mutant and wild-type(WT) TTR. MD simulation results indicate that, compared with Glab binding to WT and V30A mutant, the WT TTR could lead to the collapse of β-strands from Ser52 to His56 at chain A. This phenomenon facilitated the easy dissociation of chains A and C. Calculations of the binding free energy between the two chains showed that the V30A-Glab TTR complex displayed a lower binding energy than other systems(WT TTR and WT-Glab TTR). Then, SMD simulation was performed to explore the unbinding pathway for Glab through the WT and V30A mutant TTR. The results show that Lys15(chain A) produced a hydrogen bond with Glab at the force peak via the WT TTR tunnel. Meanwhile, in the V30A TTR mutant, the hydrogen bond between Lys15(chain A) and Glab was broken at the force peak. This condition was beneficial for Glab to be taken off from the protein. Our theoretical results will be useful in designing a new specific inhibitor of TTR protein to control the TTR homotetramer dissociation.     

基于M积分的脆性材料微缺陷等效损伤面积/体积表征

随着脆性材料在工程中的广泛应用,对脆性材料中微缺陷进行统一的损伤水平标定,具有重要的科学研究和工程应用价值. 本研究提出一种基于M积分的材料等效损伤面积/体积标定方法, 以具有相同M积分值的圆孔面积或球孔体积来标定 复杂微缺陷构型的损伤水平,从而实现不同类型微缺陷真实损伤水平的统一表征. 首先,基于Lagrangian能量密度函数推导 了M积分定义式,并简述了M积分的物理意义,基于域积分方法实现二维/三维M积分的数值计算. 随后,提出了基 于M积分的材料缺陷等效损伤面积/体积标定方法,以圆孔面积/球孔体积来标定复杂微缺陷材料系统的损伤水平. 最后, 针对单轴拉伸载荷作用下的二维/三维脆性体含不同缺陷构型,具体计算了椭圆孔、裂纹以及双裂纹、双孔洞、裂纹和孔洞干 涉等复杂缺陷构型情况下的等效损伤面积/体积,并详细分析了缺陷之间的干涉效应及影响因素. 本研究旨在基于M积分等 效方法量化脆性材料中各类微缺陷造成的损伤程度,实现损伤等级标定,有益于工程材料及结构的损伤容限设计及完整性评估.      

MOVING MODEL ANALYSIS OF THE INITIAL COMPRESSION WAVE IN TUNNEL FOR HIGH-SPEED TRAINS1)

利用动模型实验方法,主要研究列车头型横截面变化对初始压缩波的影响。结果表明,在列车最大横截面积和流线型部分长度相同的情况下,列车头部流线型部分的平均横截面积和截面变化率均会对初始压缩波的压力峰值产生影响,平均横截面积决定了初始压缩波形成时的强度大小,截面变化率则通过影响初始压缩波的压力梯度,决定在隧道传播过程中初始压缩波压力峰值的衰减程度。     

Binder melt: Quantification using SEM/EDS and its effects on composite solid propellant combustion

The present study reports the development of a novel technique to quantify binder melt on the surface of the propellant. Non-aluminized AP-HTPB propellants of 86% particulate loading are used to illustrate the technique. Elemental maps of unburnt and extinguished propellant surface are obtained using EDS (Energy Dispersive Spectroscopy). Overlap between the elements is identified and the elemental maps are processed to calculate AP and binder area exposed in unburnt and extinguished samples. The AP area exposed is found to be around 72.3% and 63.3% for unburnt and extinguished samples, respectively, indicating a reduction in AP exposed area with extinguished samples. This has been attributed to the binder melt discussed in literature but never quantified. Simulations have been carried out to analyze and understand the effects of this binder melt. A random packing algorithm is used to simulate propellant packs. Also, a methodology to account for binder melt layer is introduced and is used to capture AP exposed areas. Effect of binder melt in propellants with different solid loading and varying particle size is discussed. It is shown that fine AP particles are more prone to being covered by binder melt than the coarse AP particles. A possible explanation to the behavior of plateau burning propellants observed in literature has been provided through this analysis.     

3D aluminum/silver hierarchical nanostructure with large areas of dense hot spots for surface‐enhanced raman scattering

Plasmonic nanomaterials possessing large‐volume, high‐density hot spots with high field enhancement are highly desirable for ultrasensitive surface‐enhanced Raman scattering (SERS) sensing. However, many as‐prepared plasmonic nanomaterials are limited in available dense hot spots and in sample size, which greatly hinder their wide applications in SERS devices. Here, we develop a two‐step physical deposition protocol and successfully fabricate 3D hierarchical nanostructures with highly dense hot spots across a large scale (6 × 6 cm²). The nanopatterned aluminum film was first prepared by thermal evaporation process, which can provide 3D quasi‐periodic cloud‐like nanostructure arrays suitable for noble metal deposition; then a large number of silver nanoparticles with controllable shape and size were decorated onto the alumina layer surfaces by laser molecular beam epitaxy, which can realize large‐area accessible dense hot spots. The optimized 3D‐structured SERS substrate exhibits high‐quality detection performance with excellent reproducibility (13.1 and 17.1%), whose LOD of rhodamine 6G molecules was 10^?9 M. Furthermore, the as‐prepared 3D aluminum/silver SERS substrate was applied in detection of melamine with the concentration down to 10^?7 M and direct detection of melamine in infant formula solution with the concentration as low 10 mg/L. Such method to realize large‐area hierarchical nanostructures can greatly simplify the fabrication procedure for 3D SERS platforms, and should be of technological significance in mass production of SERS‐based sensors.     

Design Rules for Metal-Organic Framework Stability in High-Pressure Hydrogen Environments

Stability of metal-organic frameworks (MOFs) under hydrogen is of particular importance for a diverse range of applications, including catalysis, gas separations, and hydrogen storage. Hydrogen in gaseous form is known to be a strong reducing agent and can potentially react with the secondary building units of a MOF and decompose the porous framework structure. Moreover, rapid pressure swings expected in vehicular hydrogen storage could create significant mechanical stresses within MOF crystals that cause partial or complete pore collapse. In this work, we examined the stability of a structurally representative suite of MOFs by testing them under both static (70 MPa) and dynamic hydrogen exposure (0.5 to 10 MPa, 1000 pressure cycles) at room temperature. We aim to provide stability information for development of near room-temperature hydrogen storage media based on MOFs and suggest framework design rules to avoid materials unstable for hydrogen storage under relevant technical conditions.     

A型恒星光谱线指数岭回归有效温度的预测分析

天文光谱线指数数据能够较好地保留着恒星的物理特征信息,为此借助线指数特征数据构建多参数模型,有利于更好地回归分析数据的共变关系及谱线的内在规律。世界上光谱获取率最高的施密特天文望远镜LAMOST发布的观测光谱都已经过标记,利用天文可视化工具分析这些标记的恒星光谱线指数会产生预测因子自相关,多元线性回归时因变量存在共线性,导致方差较大、得到最小二乘回归系数不稳定,虽不影响使用回归的有效性,但较难从回归方程中得到独立预测因子的评估系数。利用LAMOST巡天光谱数据中A型恒星Lick线指数为数据源,选取有效温度T_eff为7 000～8 500 K,取信噪比大于50的光谱特征值实现回归分析恒星参数T_eff值,经箱线图呈现DR5星表中,A型光谱86 097条具备T_eff值大样本光谱数据的整体分布,统计分析26种线指数的特征值后,选取分布相似且带宽为12 Å的kp12,halpha12和hgamma12字段,减少解释线指数变量的数目,优化冗余变量方差膨胀因子（VIF）系数。实验选取两两变量间观测数据集,局部拟合回归散点、同样的数据源使用散点图的总体轮廓生成高密度散点图,利用色差透明性突出显示数据密集区域。结果表明多元线性回归和岭回归算法都能从低分辨率光谱中确定A型恒星的有效温度,但经过共线性数据分析有偏估计实验,使用岭回归分析寻找最佳模型,能更准确地确定恒星有效温度,进而得到预测A型恒星有效温度及谱线回归特性。     

大宝山多金属矿床氧化微粒的X射线衍射和近红外光谱分析及其意义

利用XRD和NIR技术对大宝山东岗岭组下亚组氧化矿中7个氧化物样品微粒进行分析,其中前4个样品为同一标高,后3个样品为不同标高。XRD,NIR研究结果表明随着氧化程度的加深（04-2→04-3→04-4）,Al-OH矿物吸收峰位所对应的波长不断加大（2 160.72→2 163.05→2 200.36 nm）,说明矿物中的阳离子Al被取代,产生贫Al现象;且对应的峰的强度从7.08×10-4, 7.83×10-3到6.66×10-2,说明Al-OH矿物的含量不断上升;另外SO2-₄矿物所对应的吸收峰位（1 938.80→1 946.94→1 926.47 nm）的强度从5.635×10-2, 1.82×10-2到1.668×10-2,说明随着氧化的进行,SO2-₄矿物的含量不断下降, 结合前人研究, 我们可以推测出早期形成的铜多金属硫化物矿床在后期发生强烈氧化作用, 使得硫化矿体氧化, 其中的硫经氧化形成强酸性硫酸溶液, 围岩受到硫酸溶液的腐蚀, 转变成松散的黏土;在04-2, 04-3, 13-1号样品中发现钠明矾石和钾明矾石,矾类矿物的大量发现说明该矿区的氧化淋滤作用仍在进行;通过XRD与NIR技术发现了石英、绢云母、方解石、绿帘石、角闪石、透闪石、金云母、绿泥石、高岭土等矿物,很好的反映出蚀变类型,且与此区域的地质特征相吻合,目前近红外已开始用于矿床勘查中的蚀变填图。通过光谱分析发现了矿床深部氧化过程与阳离子取代间的关系, 并以光谱学的视角验证了前人对于大宝山矿床成因的解释。研究表明一方面XRD和NIR可以有效的分析土壤和岩石的矿物成分,从而为该地区矿床矿石研究提供服务;另一方面NIR可以波长的迁移情况反映离子交代,峰的尖锐程度反映结晶程度,峰的强度反映矿物含量,这些独具的优势使其可以从微观角度研究矿物的氧化。不过有一点需要指出来,和近红外与X射线衍射在其他领域的研究相比,这两种技术在地质学的应用需要进一步加深,包括地质学应用的理论基础研究和光谱的分析解释手段,以尽量做到不仅可以通过光谱技术分析出所对应的矿物类型还能快速分析出不同矿物的含量及同一矿物的不同构型。