Single-crystal EPR and DFT study of a <Superscript>VI</Superscript>Al–O<Superscript>−</Superscript>–<Superscript>VI</Superscript>Al center in jeremejevite: electronic structure and <Superscript>27</Superscript>Al hyperfine constants

Single-crystal electron paramagnetic resonance (EPR) spectra of a gem-quality jeremejevite, Al₆B₅O₁₅(F, OH)₃, from Cape Cross, Namibia, reveal an S = 1/2 hole center characterized by an ²⁷Al hyperfine structure arising from interaction with two equivalent Al nuclei. Spin-Hamiltonian parameters obtained from single-crystal EPR spectra at 295 K are as follows: g ₁ = 2.02899(1), g ₂ = 2.02011(2), g ₃ = 2.00595(1); A ₁/g _e β _e  = −0.881(1) mT, A ₂/g _e β _e  = −0.951(1) mT, and A ₃/g _e β _e  = −0.972(2) mT, with the orientations of the g ₃- and A ₃-axes almost coaxial and perpendicular to the Al–O–Al plane; and those of the g ₁- and A ₁-axes approximately along the Al–Al and Al–OH directions, respectively. These results suggest that this aluminum-associated hole center represents hole trapping on a hydroxyl oxygen atom linked to two equivalent octahedral Al³⁺ ions, after the removal of the proton (i.e., a ^VIAl–O⁻–^VIAl center). Periodic ab initio UHF and DFT calculations confirmed the experimental ²⁷Al hyperfine coupling constants and directions, supporting the proposed structural model. The ^VIAl–O⁻–^VIAl center in jeremejevite undergoes the onset of thermal decay at 300 °C and is completely bleached at 525 °C. These data obtained from the ^VIAl–O⁻–^VIAl center in jeremejevite provide new insights into analogous centers that have been documented in several other minerals.     

Thermodynamic and magnetic properties of surface Fe<Superscript>3+</Superscript> species on quartz: effects of gamma-ray irradiation and implications for aerosol–radiation interactions

Samples of a natural amethyst, pulverized in air, and irradiated for gamma-ray doses from 0.14 to 70 kGy, have been investigated by powder electron paramagnetic resonance (EPR) spectroscopy from 90 to 294 K. The powder EPR spectra show that the surface Fe³⁺ species on the gamma-ray-irradiated quartz differ from its counterpart without irradiation in both the effective g value and the observed line shape, suggesting marked radiation effects. This suggestion is supported by quantitatively determined thermodynamic properties, magnetic susceptibility, relaxation times, and geometrical radius. In particular, the surface Fe³⁺ species on gamma-ray-irradiated quartz has larger Gibbs and activation energies than its non-irradiated counterpart, suggesting radiation-induced chemical reactions. The shorter phase-memory time (T _m) but longer spin–lattice relaxation time (T ₁) of the surface Fe³⁺ species on the gamma-ray-irradiated quartz than that without irradiation indicate stronger dipolar interactions in the former. Moreover, the calculated geometrical radius of the surface Fe³⁺ species on the gamma-ray-irradiated quartz is three orders of magnitude larger than that of its counterpart on the as-is sample. These results provide new insights into radiation-induced aerosol nucleation, with relevance to atmospheric cloud formation and global climate changes.     

模拟降雨对齿肋赤藓(Syntrichia caninervis)生理特性的影响

新疆古尔班通古特沙漠地表具有发育完好的生物土壤结皮,本文以参与组成生物土壤结皮的优势藓类———齿肋赤藓(Syntrichia caninervis)为研究对象,在实验室内对其进行模拟降雨处理,降雨量分别为0mm(对照)、2mm、6mm、10mm和15mm,研究模拟降雨影响下齿肋赤藓植株含水量、光合色素含量及可溶性糖、游离脯氨酸、可溶性蛋白、抗氧化酶(SOD、CAT和POD)、丙二醛含量的变化,以探讨其对降雨的生理生化响应。结果表明:随降雨量的增加,齿肋赤藓植株含水量显著增加;随齿肋赤藓植株含水量的增加,其光合色素含量和可溶性蛋白含量显著增加;随降雨量增加,抗氧化酶(SOD、CAT和POD)活性和可溶性糖含量呈大致递减的趋势,游离脯氨酸和丙二醛含量呈先下降后上升的变化趋势。在干燥状态下齿肋赤藓通过提高体内保护酶(SOD、CAT和POD)活性,增加可溶性糖和游离脯氨酸含量来抵御外界干旱胁迫的环境;而降雨能够增加齿肋赤藓植株含水量,激活其光合生理活性,显著提高光合色素含量,但是降雨量过大又将加剧齿肋赤藓膜脂过氧化的程度。     

自动气象站的雷电防护

针对自动气象站安装在室外易遭雷击以及微电子装置的脆弱性,结合河南省自动气象站实际情况及设备的维护维修经验,探讨如何做好自动气象站雷电防护工作。     

Response spectrum of seismic design code for zones lack of near-fault strong earth- quake records

It was shown from the study on the recently near-fault earthquake ground motions that the near-fault effects were seldom considered in the existing Chinese seismic code. Referring to the UBC97 design concept for near-fault factors, based on the collected world-widely free-site records of near-fault earthquakes ground motions classified by earthquake magnitude and site condition, the attenuation relationship expressions of the acceleration spectrum demand at the key points within the long period and moderate period were established in term of the earthquake magnitude and the site condition. Furthermore, the near-fault factors’ expressions about the earthquake magnitude and the fault distance were deduced for the area lack of near-fault strong earthquake records. Based on the current Chinese Building Seismic Design Code, the near-fault effect factors and the modified design spectral curves, which were valuable for the seismic design, were proposed to analyze the seismic response of structures.     

应用注浆技术处理灌注桩离析问题

根据静压注浆原理,在桩顶钻孔到离析部位,高压注浆充实,浆液胶结凝固后可提高桩的抗压强度,达到补救桩质量的目的.     

层状云中对流泡特征及其在降水场中的作用

层状云中夹有对流泡对整个雨系降水的启动、发展以及降水场的分布、变化有很大作用，对寻找人工增雨最佳人工影响潜力区也有特殊意义。该文在总结大量历史资料的基础上，利用雷达、卫星、地面实况、天气、机载云雨探测和数值模拟等各种手段，对层状云中夹着的对流泡进行系统深入地研究，进而为人工增雨作业提供依据。     

莫里青断陷双阳组储层孔隙特征及影响因素分析

伊通盆地莫里青断陷储层发育六种孔隙类型，其中以溶蚀粒间孔隙、溶蚀粒内孔隙和填隙物内孔隙为主。孔隙结构类型主要有四种，以ⅢA、ⅢB级为主。研究表明在相同的成岩作用条件下，本区沉积相带控制着孔隙结构的平面分布特征；而在同样的沉积环境控制下，成岩作用对储层孔隙结构的纵向发育特征有着重要的影响。     

Non-Henry’s Law behavior of REE partitioning between fluorapatite and CaF2-rich melts: Controls of intrinsic vacancies and implications for natural apatites

The partitioning of rare-earth elements (REEs: Gd and multiple REEs), Sr, and Mn between fluorapatite and CaF₂-rich melts was investigated over a wide range of REE concentrations (i.e., from 0.8 ± 0.1 to 25,000 ± 2600 ppm Gd in fluorapatite) in two different sample assemblies (i.e., tightly covered Pt crucibles and sealed Pt capsules) at 1220 °C and atmospheric pressure. Attainment of equilibrium is indicated by selected reversal experiments. The partition coefficient D(Gd) decreases from ∼2 to ∼0.5 with increasing Gd in fluorapatite, hence a marked non-Henry’s Law behavior, but becomes independent of composition at and above ∼5000 and ∼1000 ppm Gd for experiments in Pt crucibles and Pt capsules, respectively. Non-Henry’s Law behavior is also observed in experiments involving multiple REEs. All REE patterns are convex upward in shape with maxima between Nd and Gd, and D(La)/D(Nd) and D(Nd)/D(Yb) decrease systematically with increasing total REEs in fluorapatite, suggesting that REE fractionations are partly related to non-Henry’s Law behavior. These experimental results and local structural data from previous electron paramagnetic resonance spectroscopic studies suggest that the non-Henry’s Law behavior of REE partitioning between fluorapatite and melt is controlled by intrinsic Ca²⁺ vacancies in the c-axis channels. The D(Sr) and D(Mn) values are independent of composition and, therefore, do not deviate from the Henry’s Law in their respective compositional ranges investigated in this study.Nonstoichiometry, such as Ca²⁺ and F⁻ vacancies in the c-axis channels, is well known in natural apatites, particularly in biogenic apatites. Therefore, the observed non-Henry’s Law behavior of REE partitioning is expected to have important implications for REE geochemical modeling involving apatites and for the uptake of REEs by natural apatites. Particularly, the non-Henry’s Law behavior of REE partitioning is at least partly responsible for the commonly observed, bell-shaped REE patterns in fossil biogenic apatites.     

地理核心素养视域下“教学设计与开发模型”的构建与实践——以湘教版高中地理新教材必修1“风成地貌”为例

本文尝试构建了地理核心素养视域下的"教学设计与开发模型",该模型包括表征核心素养、明确教学目标、设计评价方案、创设学习模块和选择教学材料五个部分,进一步以湘教版高中地理新教材必修1中的"风成地貌"为例,按照"听风—看风—捕风"的教学设计主线,对该模型在高中地理新教材中的运用进行了实践。