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关键词： Semantics  

摘要： Spatiotemporal representation is one of the critical areas receiving ongoing interest in GIScience. The ever-growing spatiotemporal big data, however, pose considerable challenges to temporal representation as existing methods predominantly use one-dimensional chronological timeline representations. Aiming to represent the lifespans of spatiotemporal objects, a temporal interval grid (TiGrid) is proposed based on a raster structure in two-dimensional space. The TiGrid is the lower-triangular part of a square matrix of order N, in which the column and row represent the start time and end time, respectively. Using the graphical transformation method, the lower-triangular matrix of the TiGrid is transformed to a rectangle matrix. The cells in a TiGrid can be converted into absolute world time using metadata such as the time resolution and start time. The TiGrid generating algorithm, the temporal topological relations, and the unary or binary operations in a TiGrid are defined. Furthermore, spatiotemporal constraint and snapshot retrieval methods are introduced based on the spatial semantics in the TiGrid. A prototype performed evaluation with the case of geotagged video retrieval. The experimental results show that a TiGrid with spatial indexing can efficiently retrieve mass objects with time-interval information. The TiGrid has the potential to be a new way for spatiotemporal modeling and geovisualization.

关键词： Calculations  

摘要： The hydration structure of cellulose is very important for understanding the hydrolysis of cellulose at the molecular level. In this paper, we report a joint experimental and theoretical study on x-ray absorption spectroscopy (XAS) of aqueous cellobiose, a disaccharide unit of cellulose. In the experimental part, high resolution measurements of the carbon K-edge XAS spectra were taken. In the theoretical part, ab initio molecular dynamics simulations and ensemble calculations of electronic excited states were performed to obtain the continuous XAS spectra. The XAS spectra were found to have three characteristic peaks at 289.3, 290.7, and 293.6 eV, each representing the absorption by carbon atoms of the alcohol group, the hemiacetal group, and both of these functional groups. It was found that the peak heights in the spectrum change considerably over the temperature range of 25-60 & DEG;C, which is a reflection of the number of hydrogen bonds between cellobiose and water. We suggest that this spectral change could be useful information for identifying the hydration of cellulose in various environments.

关键词： 高功率光纤激光器   光纤光栅   谐振腔腔镜   非线性效应抑制  

摘要： 目前光纤光栅在高功率连续光纤激光器中的应用主要有两个方面，一是作为谐振腔腔镜，二是用来抑制激光器的非线性效应。首先论述了光纤光栅作为腔镜技术的发展现状，然后着重论述了能够抑制光纤激光器中非线性效应的特殊光纤光栅的发展状况。并详细描述了倾斜布拉格光纤光栅抑制受激拉曼散射和受激布里渊散射、长周期光纤光栅抑制受激拉曼散射以及相移长周期光纤光栅抑制自相位调制或四波混频等非线性效应引起的光谱展宽的研究进展。最后展望了光纤光栅在高功率光纤激光器领域的发展趋势，认为光纤光栅将朝着更高承载功率与长波长方向发展，同时认为基于飞秒激光刻写的光纤光栅技术、能够同时抑制多种非线性效应的光纤光栅技术、以及基于光纤光栅的光纤激光器激光偏振控制技术等将成为新的研究热点。

关键词： Fused deposition modeling   Fracture toughness   Polycarbonate   Raster orientation   Semi-circular bending specimen  

摘要： Purpose The purpose of this paper is to study the Mode I fracture behavior of polycarbonate (PC) parts produced using fused deposition modeling (FDM). The focus of this study is on samples printed along the out-of-plane direction with different raster angles. Design/methodology/approach Tensile and Mode I fracture tests were conducted. Semi-circular bend specimens were used for the fracture tests, which were printed in four different raster patterns of (0/90), (15/-75) (30/-60) and (45/-45). Moreover, the finite element method (FEM) was used to determine the applicability of linear elastic fracture mechanics (LEFM) for the printed PC parts. The fracture toughness results, as well as the fracture path and the fracture surfaces, were studied to describe the fracture behavior of the samples. Findings Finite element results confirm that the use of LEFM is allowed for the tested PC samples. The fracture toughness results show that changing the direction of the printed rasters can have an effect of up to 50% on the fracture toughness of the printed parts, with the (+45/-45) and (0/90) orientations having the highest and lowest resistance to crack propagation, respectively. Moreover, except for the (0/90) orientation, the other samples have higher crack resistance compared to the bulk material. The fracture toughness of the tested PC depends more on the toughness of the printed sample, rather than its tensile strength. Originality/value The toughness and the energy absorption capability of the printed samples (with different raster patterns) were identified as the main properties affecting the fracture toughness of the AM PC parts. Because the fracture resistance of almost all the samples was higher than that of the base material, it is evident that by choosing the right raster patterns for 3D-printed parts, very high resistance to crack growth may be obtained. Also, using FEM and comparing the size of the plastic zones, it was concluded that, although the tensile curves s

关键词： Light absorption  

摘要： Enhancing the strength of optical absorption represents an important route toward improving the energy-efficiency of light-based technologies. Here, we experimentally and numerically explore how silicon substrates-long considered to be mere supporting structures for CMOS-compatible materials-can be exploited to improve optical absorption in the mid- to far-infrared spectral ranges, thus reducing the energy requirement for all-optical switching of magnetization. We show that infrared illumination of the metal through a 500 mu m-thick silicon substrate actually deposits more energy in the metal film (by a factor of almost 3) compared to the conventional approach of illuminating the metal directly. Our results reveal that silicon substrates can actually play a crucial role in the efficient optical delivery of energy to functional materials and will find application in a wide range of experiments and technologies involving mid- and far-infrared light.

摘要： 腰椎间盘突出症(lumbar disc herniation,LDH )是引起腰骶神经根压迫症的最常见病因[1],临床主要表现为坐骨神经痛或运动异常,甚至下肢瘫痪或大小便失禁等,严重影响患者生活质量[2].临床上对 LDH的诊断主要依据其临床特征及传统影像学表现,但特异性较低.近年来,研究[3-6 ]表明 MR 扩散张量成像(diffusion tensor imaging,DTI)不仅能在活体内显示纤维束的空间及解剖结构,还能对各向异性分数(fractional anisotropy,FA)值、表观扩散系数(apparent diffusion coefficient,ADC)值进行定量分析,在 LDH的诊治中具有较好的临床应用前景.本文围绕DTI的原理及其在LD H中的临床应用研究进展进行综述.

关键词： 2型糖尿病   糖尿病视网膜病变   视觉传导通路   扩散张量成像  

摘要： 目的 评估2型糖尿病(T2DM)患者视觉传导通路白质微结构完整性.方法 纳入T2DM患者65例,其中无糖尿病视网膜病变(NDR)39例,糖尿病视网膜病变(DR)26例;同时纳入非糖尿病的健康对照组(HC)31例.进行分段读出(RESOLVE)扩散张量成像(DTI),基于感兴趣区(ROI)分析视神经、视交叉、视束、视辐射的各向异性分数(FA)及表观扩散系数(ADC),采用单因素方差分析比较各组、各ROI的FA值及ADC值差异.结果 与HC组相比,在视神经、视交叉、视束及视辐射4个ROI,NDR组的FA值降低、ADC值增高,而DR组的FA值进一步较NDR组降低、ADC值增高(P<0.01或P<0.05).结论 RESOLVE-DTI序列可非侵入性地对T2DM患者视觉传导通路的微结构进行评估.T2DM患者视觉传导通路的神经纤维在并发视网膜病变之前可能已经受到损害,在并发视网膜病变之后损伤进一步加剧.