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关键词： 青少年抑郁症   自杀未遂   扩散张量成像   各向异性分数  

摘要： 目的 探讨青少年自杀未遂抑郁症患者不同脑区微观结构的变化特点.方法 选取30例青少年自杀未遂抑郁症患者(抑郁组)和30例性别、年龄、受教育年限相匹配的正常健康者(对照组),所有被试均为右利手,对所有受试者进行17项汉密尔顿抑郁量表(HAMD-17)评分,并行常规MRI和扩散张量成像(DTI)扫描,分别测量双侧额上回、额中回、额下回、前扣带回、纹状体及双侧海马的平均表观扩散系数(ADC)及各向异性分数(FA)值,比较2组间的差异.结果 所有受试者常规MRI均未见明显异常,抑郁组与对照组各脑区ADC值比较差异无统计学意义(P>0.05),抑郁组双侧额中回、额下回、前扣带回、纹状体及双侧海马的FA值低于对照组,差异均有统计学意义(P<0.05).结论 DTI技术的FA值能定量反映青少年自杀未遂抑郁症患者不同脑区的微观结构变化,这种细微结构异常可能对青少年自杀行为进行早期预警.

关键词： chemical fuel   multivariate analysis   NMR   reaction mechanism   time resolved XAS and NMR   XANES   XAS  

摘要： The satisfactory rationalization of complex reactive pathways in solution chemistry may greatly benefit from the combined use of advanced experimental and theoretical complementary methods of analysis. In this work, we combine X-Ray Absorption and H-1 NMR spectroscopies with state-of-the-art Multivariate Curve Resolution and theoretical analyses to gain a comprehensive view on a prototypical reaction involving the variation of the oxidation state and local structure environment of a selected metal ion coordinated by organic ligands. Specifically, we investigate the 2-cyano-2-phenylpropanoic acid reduction of the octahedral complex established by the Cu2+ ion with terpyridine to the tetrahedral complex formed by Cu+ and neocuproine. Through our interdisciplinary approach we gain insights into the nature, concentration time evolution and structures of the key metal (XAS measurements) and organic (H-1 NMR measurements) species under reaction. We believe our method may prove to be useful in the toolbox necessary to understand the mechanisms of reactive processes of interest in solution.

关键词： Excited states  

摘要： Time-resolved X-ray absorption spectroscopy is emerging as a uniquely powerful tool to probe coupled electronic-nuclear dynamics in photo-excited molecules. Theoretical studies to date have established that time-resolved X-ray absorption spectroscopy is an atom-specific probe of excited-state wave packet passage through a seam of conical intersections (CIs). However, in many molecular systems, there are competing dynamical pathways involving CIs of different electronic and nuclear character. Discerning these pathways remains an important challenge. Here, we demonstrate that time-resolved X-ray absorption spectroscopy (TRXAS) has the potential to resolve competing channels in excited-state non-adiabatic dynamics. Using the example of 1,3-butadiene, we show how TRXAS discerns the different electronic structures associated with passage through multiple conical intersections. trans-1,3-Butadiene exhibits a branching between polarized and radicaloid pathways associated with ethylenic "twisted-pyramidalized" and excited-state cis-trans isomerization dynamics, respectively. The differing electronic structures along these pathways give rise to different XAS signals, indicating the possibility of resolving them. Furthermore, this indicates that XAS, and other core-level spectroscopic techniques, offer the appealing prospect of directly probing the effects of selective chemical substitution and its ability to affect chemical control over excited-state molecular dynamics.

关键词： CO2 reduction reaction (CO2RR)   metal intercalation   layered structures   electrochemistry   copper catalyst   in situ XAS  

摘要： The electrochemical conversion of carbon dioxide (CO2) to useful chemical fuels is a promising route toward the achievement of carbon neutral and carbon negative energy technologies. Copper (Cu)- and Cu oxide-derived surfaces are known to electrochemically convert CO2 to high-value and energy-dense products. However, the nature and stability of oxidized Cu species under reaction conditions are the subject of much debate in the literature. Herein, we present the synthesis and characterization of copper-titanate nanocatalysts, with discrete Cu-O coordination environments, for the electrochemical CO2 reduction reaction (CO2RR). We employ real-time in situ X-ray absorption spectroscopy (XAS) to monitor Cu species under neutral-pH CO2RR conditions. Combination of voltammetry and on-line electrochemical mass spectrometry with XAS results demonstrates that the titanate motif promotes the retention of oxidized Cu species under reducing conditions for extended periods, without itself possessing any CO2RR activity. Additionally, we demonstrate that the specific nature of the Cu-O environment and the size of the catalyst dictate the long-term stability of the oxidized Cu species and, subsequently, the product selectivity.

摘要： Testing method of optical constants for optical thin films based onspectro-photo-metric method 发布日期:2021-10-18 归口单位:中国材料与试验团体标准委员会光电材料及产品领域委员(CSTM/FC60)

关键词： Crystals   X-ray absorption near edge spectroscopy   Ligands   Chemical calculations   Molybdenum  

摘要： X-ray spectroscopy using high-energy-resolution fluorescence detection (HERFD) has critically increased the information content in X-ray spectra. We extend this technique to the tender X-ray range and present a study at the L-3-edge of molybdenum. We show how information on the oxidation state, phase composition, and local environment in molybdenum-based compounds can be obtained by analyzing the HERFD L-3 X-ray absorption near-edge structure (XANES). We demonstrate that the chemical shift of the L-3-edge HERFD spectra follows a parabolic dependence on the oxidation state and show that a qualitative analysis of high-resolution spectra can help to estimate parameters such as distortion of a ligand environment and radial order of atoms around the absorber. In certain cases, the spectra allow disentangling the contributions from bond lengths and angles to the distortion of the ligand polyhedron. Comparison of the high-resolution spectra with theoretical simulations shows that the single-electron approximation is able to reproduce the spectral shape. The results of this work may be useful in every branch of physics, inorganic and organometallic chemistry, catalysis, materials science, biochemistry, and mineralogy where observed changes in performance or chemical properties of Mo-based compounds, accompanied by small changes in spectral shape, are to be related to the details of electronic structure and local atomic environment.

关键词： X-rays   Absorption   Basis sets   Chemical calculations   Mathematical methods  

摘要： The simulation of X-ray absorption spectra requires both scalar and spin-orbit (SO) relativistic effects to be taken into account, particularly near L- and M-edges where the SO splitting of core p and d orbitals dominates. Four-component Dirac-Coulomb Hamiltonian-based linear damped response time-dependent density functional theory (4c-DR-TDDFT) calculates spectra directly for a selected frequency region while including the relativistic effects variationally, making the method well suited for X-ray applications. In this work, we show that accurate X-ray absorption spectra near L-2,L-3- and M-4,M-5- edges of closed- shell transition metal and actinide compounds with different central atoms, ligands, and oxidation states can be obtained by means of 4c-DR-TDDFT. While the main absorption lines do not change noticeably with the basis set and geometry, the exchange-correlation functional has a strong influence with hybrid functionals performing the best. The energy shift compared to the experiment is shown to depend linearly on the amount of Hartee-Fock exchange with the optimal value being 60% for spectral regions above 1000 eV, providing relative errors below 0.2% and 2% for edge energies and SO splittings, respectively. Finally, the methodology calibrated in this work is used to reproduce the experimental L-2,L-3-edge X-ray absorption spectra of [RuCl2(DMSO)(2)(Im)(2)] and [WCl4(PMePh2)(2)], and resolve the broad bands into separated lines, allowing an interpretation based on ligand field theory and double point groups. These results support 4c-DR-TDDFT as a reliable method for calculating and analyzing X-ray absorption spectra of chemically interesting systems, advance the accuracy of state-of-the art relativistic DFT approaches, and provide a reference for benchmarking more approximate techniques.

关键词： Dielectric metamaterial   UV-light trapping   Monolayer graphene   Polarization-insensitive  

摘要： With the aim of improving UV light trapping capability in monolayer graphene, a nanomesh metamaterial absorber is proposed, which exhibits the polarization-insensitive feature due to the geometrical symmetry. Through the functional combination of magnetic resonance and UV mirror, the absorption of unpolarized UV light in monolayer graphene can reach 99.5% under normal incidence. The absorption enhancement is induced by the magnetic resonance mode between the dielectric silica nanomesh and the calcium fluoride base layer. The effects of geometric parameters on the absorption spectra are systematically investigated. The proposed structure shows insensitive to manufacturing deviations, which can maintain at a high UV absorption rate of more than 99% within the nanomesh width ranging from 50 nm to 90 nm. Furthermore, after delicate optimization of the geometric parameters, two sharp resonances with absorbance more than 90% can be excited simultaneously inside the absorber. Our work provides an important theoretical guide for the design of optoelectronic devices based on two-dimensional materials in the UV range.

关键词： Magnetic circular dichroism   Ni-Co-Mn-In   Pulsed magnetic field   Field-induced reverse transformation   Metamagnetic shape memory alloy  

摘要： In this study, X-ray absorption spectroscopy (XAS) experiments for Ni45Co5Mn36.7In13.3 metamagnetic shape memory alloy were performed under high magnetic fields up to 12 T using a pulsed magnet. Field-induced reverse transformation from martensite phase to austenite phase caused considerable changes in the magnetic circular dichroism (MCD) signals and the magnetic moments of the Mn, Ni, and Co with ferro-magnetic coupling were determined. The spin magnetic moment, Mspin, and orbital magnetic moment, Morb, of Mn atom in the induced austenite ferromagnetic phase, estimated based on the sum-rule analysis, were 3.19 and 0.08 mu B, respectively, resulting in an Morb / Mspin ratio of 0.03. In the element-specific magnetization curves obtained at 150 K, metamagnetic behavior associated with the field-induced reverse transformation was clearly observed and the transformation magnetic fields could be detected. There was almost no change in the magnetically averaged XAS spectrum for Mn-L2,3 edges between in the martensite and in the mag-netic field-induced austenite phases, however, it was visible for Ni. This implies that Ni 3d-electrons mainly contribute to martensitic transformation. (c) 2021 Elsevier B.V. All rights reserved.

关键词： Materials Science   general   Biomaterials   Nanotechnology   Inorganic Chemistry   Materials Engineering   Applied and Technical Physics  

摘要： The global shift to electricity as the main energy carrier will require innovation in electrochemical energy storage (EES). EES systems are the key to the "electron energy economy," minimizing losses and increasing reliability between energy supply and demand. However, steep challenges such as cost, cycle/calendar life, energy density, material availability, and safety limit widespread adoption of batteries for large-scale grid and vehicle applications. Battery innovation that meets today's challenges will require new chemistries, which can originate from understanding charge transport phenomena at multiple time and length scales. The advancement of operando characterization can expedite this progress as changes can be observed during battery function. This article highlights progress in bulk and interfacial operando characterization of batteries. Specifically, a case study involving Fe3O4 is provided demonstrating that combining X-ray absorption spectroscopy and isothermal microcalorimetry can provide real-time characterization of productive faradaic redox processes and parasitic interfacial reactions during (de)lithiation.