Structural characterization of high-pressure C–Na<Subscript>2</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript> by single-crystal diffraction and <Superscript>29</Superscript>Si MAS NMR

Single crystals of C–Na₂Si₂O₅ have been synthesized from the hydrothermal recrystallization of a glass. The title compound is monoclinic, space group P2₁/c with Z= 8 and unit-cell parameters a= 4.8521 (4)Å, b=23.9793(16)Å, c=8.1410(6)Å, β=90.15(1)° and V=947.2(2)ų. The structure has been determined by direct methods and belongs to the group of phyllosilicates. It is based on layers of tetrahedra with elliptically six-membered rings in chair conformation. The sequence of directedness within a single ring is UDUDUD. The sheets are parallel to (010) with linking sodium cations in five- and sixfold coordination. Concerning the shape and the conformation of the rings, C–Na₂Si₂O₅ is closely related to β-Na₂Si₂O₅. However, both structures differ in the stacking sequences of the layers. A possible explanation for the frequently observed polysynthetic twinning of phase C is presented. In the ²⁹Si MAS-NMR spectrum of C–Na₂Si₂O₅ four well-resolved lines of equal intensity are observed at ?86.0, ?86.3, ?87.4, and ?88.2?ppm. The narrow range of isotropic chemical shifts reflects the great similarity of the environments of the different Si sites. This lack of pronounced differences in geometry renders a reliable assignment of the resonance lines to the individual sites on the basis of known empiric correlations and geometrical features impossible.     

Origin of seleniferous cherts in Yutangba Se deposit,southwest Enshi,Hubei Province

At the top of the Lower Permian Maokou Formation limestones are developed carbonaceous cherts(Plm3),which constitute the dominant seleniferous layer of the Yutangba Se deposit.The cherts contain as much Se as 1646×10?6 on average.In addition,they are rich in organic carbon,Al2O3,Si2O,but poor in S.In addition to Se,as well as Mo,Cd,V,and Co,etc are also highly enriched in the cherts.The chert samples are characterized by low ?REE,slight LREE enrichment,relatively heavy Si isotope enrichment,and insignificant variations in ? 30Si value within the range of 1.1‰-1.2‰.Generally,it can be judged from the major element,trace element and REE data and the Si isotopic characteristics that the Yutangba seleniferous cherts were formed in the shallow sea to semi-deep sea anoxic environments and their formation is controlled chiefly by bio-chemical processes.     

Silicon isotope fractionation between plant parts in banana: In situ vs. in vitro

We recently showed that silicon isotopic fractionation in banana (Musa acuminata Colla, cv Grande Naine) was related to phytolith production, and therefore to silica content in plant. The present study focuses on isotopic fractionation between the different plant parts. Silicon isotopic compositions were measured using a Nu plasma multicollector plasma source mass spectrometer (MC–ICP–MS) operating in dry plasma mode. The results are expressed as δ²⁹Si relatively to the NBS28 standard, with an average precision and accuracy of ± 0.08‰ (± 2σ). On mature banana (Musa acuminata Colla, cv Grande Naine) from Cameroon, δ²⁹Si ranged from + 0.13‰ in the petiole to + 0.49‰ in the lamina, yielding to a 0.36‰ change towards heavier isotopic composition in the upper parts of the plant. This strongly accords with results obtained on in vitro banana plantlets cultivated in hydroponics, where the δ²⁹Si increase from pseudostems to lamina is 0.26‰. These preliminary results on in situ banana show a trend of intra-plant fractionation comparable with that of in vitro hydroponics banana plantlets and with previous data obtained on bamboo.     

基于传统文化的河道景观治理应用研究

探讨传统文化在河道景观治理工程中的应用。首先,分析了国内有关河道景观设计的研究现状,引出了基于传统文化的河道景观治理理念;其次,以泗河---曲阜段的河道景观治理为例,依托其深厚的地域特色文化底蕴,以孔子提倡的儒家文化为纽带,以儒家“中庸”思想作为设计理念和依据,以“儒风”、“书院”、“英杰”、“六经”等史迹、史料为线索,借由抽象的方式表达出儒家“中庸”的思想本质,展现孔子时期传承教化的历史画卷以及先贤的古朴遗风,同时塑造出自然与人文和谐共存的标志性景观图式;结果表明：将传统文化的延续性与都市生活的现代性有机地融合,重现了河流原有的、多姿多彩的自然风情,实现了河流“生态性”和”城市性”的平衡统一,打造了“充满活力和文化的河流”,赋予了河流“生命和灵魂”。     

大水式金矿床稳定同位素、稀土元素地球化学研究

大水式金太床是近年来在西秦岭地区发现的一个国内外十分罕见的金矿类型,具有极为独特的矿化特征。通过对矿区热液方解石、硅质岩矿石、硅化灰岩及原岩、岩浆岩等地质体碳－氧、硅－氧、碳－氢－氧同位素和稀土元素地球化学特征的系统研究揭示,成矿物质中碳为氧化作用改造的深成岩浆碳,硅具深部岩浆或岩浆热水来源的特点,成矿流体具岩浆水与建造水混合之特点,各种矿石稀土配分曲线和δＥｕ、δＣｅ值均与岩浆岩类似或接近而与地     

西藏蛇绿岩豆荚状铬铁矿中简单氧化物矿物组合及其超高压成因

最近在西藏罗布莎蛇绿岩豆荚状铬铁矿中,发现包括金刚石、柯石英和某些简单氧化物,诸如SiO2、MgO、Fe2O3、Cr2O3、Al2O3以及(Si,Ti)O2等组成的矿物群。这些矿物是非常复杂的由70~80种矿物组成的地幔矿物群的一部分。这充分证实在地幔中存在简单氧化物。高压-高温相平衡实验表明,硅酸盐矿物在下地幔条件才可分解成FeO、MgO和SiO2等简单氧化物(>670km)。因此有理由认为罗布莎简单氧化物可能来自下地幔深部。     

地下水^32硅年龄的测定方法—液体闪烁计数法

用Fe(OH) 3共沉淀从天然水中提取纯化SiO2 ,回收率在 30 %～ 98% ,然后提取32 P ,将H3PO4溶液和PicoflourLLT混合制备计数溶液 ,用液体闪烁计数法测量32 P的放射性 ,计算32 Si的放射性浓度 ,最后确定地下水的年龄。通过对河北平原浅层地下水的32 Si年龄进行测定 ,所得的32 Si年龄为 92 9 89a± 1 7 87a,与1 4 C的校正年龄一致