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关键词： aerosol optical depth (AOD)   absorption aerosol optical depth (AAOD)   black carbon (BC)   angstrom ngstrom Exponent (AE   a)   single scattering albedo (SSA   omega)   depolarization ratio (DPR, delta(p))  

摘要： Black carbon (BC) absorption aerosol optical depth (AAOD(BC)) defines the contribution of BC in light absorption and is retrievable using sun/sky radiometer measurements provided by Aerosol Robotic Network (AERONET) inversion products. In this study, we utilized AERONET-retrieved depolarization ratio (DPR, delta p), single scattering albedo (SSA, omega), and angstrom ngstrom Exponent (AE, a) of version 3 level 2.0 products as indicators to estimate the contribution of BC to the absorbing fractions of AOD. We applied our methodology to the AERONET sites, including North and South America, Europe, East Asia, Africa, India, and the Middle East, during 2000-2018. The long-term AAOD(BC) showed a downward tendency over Sao Paulo (-0.001 year(-1)), Thessaloniki (-0.0004 year(-1)), Beijing (-0.001 year(-1)), Seoul (-0.0015 year(-1)), and Cape Verde (-0.0009 year(-1)) with the highest values over the populous sites. This declining tendency in AAOD(BC) can be attributable to the successful emission control policies over these sites, particularly in Europe, America, and China. The AAOD(BC) at the Beijing, Sao Paulo, Mexico City, and the Indian sites showed a clear seasonality indicating the notable role of residential heating in BC emissions over these sites during winter. We found a higher correlation between AAOD(BC) and fine mode AOD at 440 nm at all sites except for Beijing. High pollution episodes, BC emission from different sources, and aggregation properties seem to be the main drivers of higher AAOD(BC) correlation with coarse particles over Beijing.

关键词： aerosol scattering   atmospheric attenuation   direct-to-Earth communication   free-space optics   molecular absorption lines   optical space-ground links  

摘要： Free-space radio-frequency (RF) communication links for intersatellite or satellite-to-ground communications are getting increasingly constraint by the insufficient spectrum availability and limited data rate of RF technology. With the advent of large satellite mega-constellation networks for global communications coverage, this limitation of classical RF communication becomes even more critical. Therefore, the establishment of point-to-point free-space optical link technology (FSO) in space will become of paramount importance in future systems, where the application will be for data-relays links, or for mega-constellations inter-satellite links, as well as for direct data downlinks, or from deep-space probes to ground. Further advantages of optical FSO-besides spectrum availability-is its increased power efficiency, higher data rates, avoidance of interference, and inherent protection against interception. When, however, these optical communication links have to pass through Earth's atmosphere, attenuation and scattering effects do influence the signal transmission. In this publication, we investigate the effects of atmospheric attenuation, including the effects of molecular absorption as well as aerosol scattering and absorption, for typical wavelength regions used for FSO, dependent on the link geometries. Based on transmission-simulation databases, we show useful spectral ranges and their specific attenuation strength. Free spectral transmission windows dependent on atmospheric quality and elevation angle are identified for reliable and efficient use of the optical transmission technology in space applications.

关键词： Graphene oxide nanosheet   DFT functionals   Absorption capacity   Optoelectronic   Non-linear optical  

摘要： We studied the absorption capacity, optoelectronic and non-linear optical (NLO) properties of graphene oxide nanosheet (GON) and its doped derivatives with aluminum (-Al) atoms. The investigations have been performed using three functionals (B3LYP, B3LYP-D3 and omega B97XD) of the density functional theory (DFT) associated to the basis set 6-31+G(d,p). Aluminum atoms were incorporated into GON at different sites in order to search for suitable candidates that could lead to the enhancement of NLO properties and decrease the band gap value of pristine graphene oxide. As per our molecular investigations, several doped molecular design schemes based on push-pull models of GON were proposed. The best electronic and NLO configurations responses highlight the doped derivatives which were obtained by replacement of carbon atoms which support the functional groups present on the honeycomb lattice of GON with -Al atoms.

关键词： 张量  

ISBN: (纸本)9787030717849

摘要： 本书共9章，主要内容包括：张量的背景知识、复张量基本概念、多复变量实值函数球面优化与US-特征对计算、U-特征值计算的迭代算法、最大U-特征值计算的多项式优化方法、纯态量子态纠缠测度的数值计算、埃尔米特张量与混合量子态基本理论、埃尔米特张量与混合量子态可分性判别和分解算法，以及对称埃尔米特可分性判别及其应用。

关键词： X-ray absorption near edge spectroscopy   Vesicles   Oxides   Scattering   Extended X-ray absorption fine structure  

摘要： We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O-2, with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O-2-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike Co3O4 under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.

关键词： Solar cell efficiency  

摘要： In this work, scattering properties of a metal-dielectric structure are carried out in the optical range. In the proposed structure design, the absorption coefficient reaches more than 80% and has an almost constant character in the entire visible spectrum. Based on the obtained simulation results, such structures can be utilized in the field of solar energy storage applications. A review of works in the field of plasmonic solar cells is given, where the efficiency is usually increased due to the confinement of incident radiation in the active region of photoelectric conversion using localized modes, which are concentrated at the surface of conducting nanoparticles. That is, such batteries are operated in narrow wavelength intervals. However, in this article, the assumed solar cell efficiency enhancement can be achieved by incorporating the entire optical range due to the proposed metamaterial structure.

关键词： 面肌痉挛   扩散张量成像   脑白质   痉挛评分  

摘要： 目的 探讨面肌痉挛(H FS)患者全脑白质结构的异常以及与临床特征的相关性.方法 26例H FS患者(患者组)和29例健康志愿者(对照组)纳入本研究.应用基于纤维束的空间统计方法(TBSS)分析患者组与对照组各项扩散张量成像(DTI)参数的差异,并与患者的面部肌肉痉挛程度进行相关分析.结果 与对照组相比,患者组胼胝体膝部和体部、双侧下纵束和下额枕束、左侧上纵束、放射冠前部、后部及上部、双侧内囊后肢以及左侧丘脑后辐射等白质纤维束存在广泛异常.进一步分析发现,患者组部分各向异性分数(FA)值降低伴有径向扩散系数(RD)值和平均扩散系数(MD)值升高的脑区仅局限于右侧下纵束和下额枕束,同时,该区的RD值与患者的痉挛评分呈正相关性.结论 H FS患者脑白质完整性存在一定缺陷,尤其表现在右侧下纵束和下额枕束的RD值异常,这为评估该病的病理生理特征提供了影像学依据.

关键词： Copper   Oxidation state   Electronic structure   Ligands   Energy  

摘要： A series of organometallic copper complexes in formal oxidation states ranging from +1 to +3 have been characterized by a combination of Cu K-edge X-ray absorption (XAS) and Cu K beta valence-to-core X-ray emission spectroscopies (VtC XES). Each formal oxidation state exhibits distinctly different XAS and VtC XES transition energies due to the differences in the Cu Z(eff), concomitant with changes in physical oxidation state from +1 to +2 to +3. Herein, we demonstrate the sensitivity of XAS and VtC XES to the physical oxidation states of a series of N-heterocyclic carbene (NHC) ligated organocopper complexes. We then extend these methods to the study of the [Cu(CF3)(4)](-) ion. Complemented by computational methods, the observed spectral transitions are correlated with the electronic structure of the complexes and the Cu Z(eff). These calculations demonstrate that a contraction of the Cu 1s orbitals to deeper binding energy upon oxidation of the Cu center manifests spectroscopically as a stepped increase in the energy of both XAS and K beta(2,5) emission features with increasing formal oxidation state within the [Cun+(NHC2)](n+) series. The newly synthesized Cu(III) cation [Cu-III(NHC4)](3+) exhibits spectroscopic features and an electronic structure remarkably similar to [Cu(CF3)(4)](-), supporting a physical oxidation state assignment of low-spin d(8) Cu(III) for [Cu(CF3)(4)](-). Combining XAS and VtC XES further demonstrates the necessity of combining multiple spectroscopies when investigating the electronic structures of highly covalent copper complexes, providing a template for future investigations into both synthetic and biological metal centers.

关键词： BiFeO3   Bandgap   Magnetic properties   First principle calculations   Reflection loss  

摘要： Tunable microwave absorption characteristics are highly desirable for industrial applications such as antenna, absorber, and biomedical diagnostics. Here, we report BiNdxCrxFe1-2xO3 (x = 0, 0.05, 0.10, 0.15) nanoparticles (NPs) with electromagnetic matching, which exhibit tunable magneto-optical and feasible microwave absorption characteristics for microwave absorber applications. The experimental results and theoretical calculations demonstrate the original bismuth ferrite (BFO) crystal structure, while Nd and Cr injection in the BFO structure may cause to minimize dielectric losses and enhance magnetization by producing interfacial defects in the spinel structure. Nd and Cr co-doping plays a key role in ordering the BFO crystal structure, resulting in improved microwave absorption characteristics. The BiNd0.10Cr0.10Fe1.8O3 (BNCF2) sample exhibits a remarkable reflection loss (RL) of -37.7 dB with a 3-mm thickness in the 10.15 GHz-10.30 GHz frequency region. Therefore, Nd and Cr doping in BFO nanoparticles opens a newpathway to construct highly efficient BFO-based materials for tunable frequency, stealth, and microwave absorber applications. (c) 2021 Elsevier Inc. All rights reserved.

关键词： Redox reactions   Reaction mechanisms   Oligomers   Energy   Selenium  

摘要： Selenium X-ray absorption spectroscopy (XAS) has found widespread use in investigations of Se-containing materials, geochemical processes, and biologically active sites. In contrast to sulfur K beta X-ray emission spectroscopy (XES), which has been found to contain electronic and structural information complementary to S XAS, Se K beta XES remains comparatively underexplored. Herein, we present the first Se Valence-to-Core (VtC) XES studies of reduced Se-containing compounds and FeSe dimers. Se VtC XES is found to be sensitive to changes in covalent Se bonding interactions (Se-Se/Se-C/Se-H bonding) while being relatively insensitive to changes in Fe oxidation states as selenide bridges in FeSe dimers ([Fe2Se2](2+) vs [Fe2Se2](+)). In contrast, Se K beta HERFD XAS is demonstrated to be quite sensitive to changes in the Fe oxidation state with Se K beta HERFD XAS demonstrating experimental resolution equivalent to K alpha HERFD XAS. Additionally, computational studies reveal both Se VtC XES and XAS to be sensitive to selenium protonation in FeSe complexes.