The nature of marbled Terra Sigillata slips: a combined μXRF and μXRD investigation

In addition to the red terra sigillata production, the largest Gallic workshop (La Graufesenque) made a special type of terra sigillata, called “marbled” by the archaeologists. Produced exclusively at this site, this pottery is characterized by a surface finish made of a mixture of yellow and red slips. Because the two slips are intimately mixed, it is difficult to obtain the precise composition of one of the two constituents without contamination from the other. In order to obtain very precise correlation at the appropriate scale between the color aspect and the elemental and mineralogical phase distributions in the slip, combined electron microprobe, X-ray micro spectroscopies and micro diffraction on cross-sectional samples were performed. The aim of this study is to discover how potters were able to produce this unique type of terra sigillata and especially this particular slip of an intense yellow color. Results show that the yellow component of marbled sigillata was made from a titanium-rich clay preparation. The color is due to the formation of a pseudobrookite (TiFe₂O₅) phase in the yellow part of the slip, the main characteristics of that structure being considered nowadays as essential for the fabrication of stable yellow ceramic pigments. Its physical properties such as high refractive indices and a melting point higher than that of most silicates widely used as ceramic colorants are indeed determinant for this kind of application. Finally, the red parts have a similar composition (elementary and mineralogical) to the one of standard red slip.     

Linear and nonlinear optical properties of ZnO nanorod arrays

Polarization-dependent linear absorption, second-harmonic generation （SHG） and 3rd-order nonlinearities of wellaligned ZnO nanorod arrays have been investigated with ps pulses. The depressed spectral width and the enhanced intensity of reflective SHG along the long axis of ZnO nanorods were observed by using p-polarized pulses, which is explained by the optical confinements. The nonlinear absorption coefficient measured with s-polarization reached the maximum 4.0×10^4cm/GW at the wavelength -750nm, which revealed a large two-photon resonance absorption attributed to the quantum confined exciton when the polarization is vertical to the long axis of ZnO nanorod.     

人造复眼成像系统研究的新进展

人造复眼成像系统具有体积小、功耗低、视角范围广等优点，是一种应用前景非常广阔的光成像系统。综述了人造复眼成像系统的研究背景及最新的研究进展，其中包宿基于不同仿生设计理念的各种新型人造复眼结构以及能够实现诸如彩色成像、指纹识别、全视角成像等新功能的实验系统；展望了人造复眼成像系统今后的研究方向。     

Quantum phase transition and entanglement in Li atom system

By use of the exact diagonalization method, the quantum phase transition and entanglement in a 6-Li atom system are studied. It is found that entanglement appears before the quantum phase transition and disappears after it in this exactly solvable quantum system. The present results show that the von Neumann entropy, as a measure of entanglement, may reveal the quantum phase transition in this model.     

A practical synthesis of L-ribose

L-Ribose was synthesized by a simple four-step method with overall yield of 76.3% from a protected L-arabinose derivative, which is a compatible intermediate for the synthesis of L-deoxyribose. The key step of this strategy is the Swern oxidation and subsequent stereoselective reduction accompanied by inversion of the 2-hydroxy group of protected L-arabinose.     

Preparation and characterization of silica-pillared derivatives from kanemite

The silica-pillared derivatives from kanemite (NaHSi(2)O(5).3H(2)O) were prepared by intercalation of dialkyldimethylammonium (DADMA) ion and pillaring with tetraethylorthosilicate. The formation of silica pillars between the silicate sheets was demonstrated by X-ray diffraction, (29)Si CP/MAS NMR, and TEM observation. The basal spacing depended on the chain length of DADMA. Nitrogen adsorption study showed that the specific surface area was enlarged over 1000 m(2) g(-1) by the pillaring and that the pore size was in the micropore region. Water and benzene adsorption isotherms revealed that the surface properties of the pillared derivatives show hydrophobic character.     

Structural and Physical Properties of New Conducting Cation Radical Salts with Te-Based Counteranions, Tetraiodotellurate(II) and Hexaiododitellurate(II)

This article reports preparation, structure, and conducting property of several cation radical salts of organic donors tetramethyltetrathiafulvalene (TMTTF), ethylenedithiotetrathiafulvalene (EDT-TTF), bis(ethylenedithio)tetrathiafulvalene (ET), bis(ethylenedithio)tetraselenafulvalene (BETS) and hexamethylenetetraselenafulvalene (HMTSF) with two novel planar Te-based dianions, TeI₄²⁻ and Te₂I₆²⁻. (ET)₅Te₂I₆ 1 and (BETS)₅Te₂I₆ 2 are isostructural. In these Te₂I₆²⁻ salts, intermolecular short I···I contacts form a supramolecular corrugated anion sheet. Donor arrangement is similar to the θ-type. With lowering temperature, the resistivity of 1 shows a gradual increase followed by a sharp upturn at 110 K. 2 is metallic down to 120 K and shows a gradual increase of the resistivity followed by a clear transition to an insulating state around 60 K. Crystal structure of (ET)₄TeI₄ 3 is based on the “herring bone” arrangement of ET molecules similar to the α-type. 3 shows a semiconductive behavior around room temperature followed by a transition to an insulating state at 210 K. (EDT-TTF)₄TeI₄ 4, a semiconductor, exhibits a unique two-dimensional arrangement of dimerized EDT-TTF molecules.     

BF3.OEt2-mediated cycloaddition of O-tert-butyldimethylsilyloximes having olefin moieties: intramolecular cycloaddition of N-borano-nitrones

Treatment of O-tert-butyldimethylsilyloximes having olefin moieties in the molecules with BF3.OEt2 results in efficient generation of N-borano-nitrones, which undergo intramolecular cycloaddition at room temperature to afford N-nonsubstituted cycloadducts after work-up.     

Nucleophilic addition reaction of 2-trimethylsilyloxyfuran to N-gulosyl-C-alkoxymethylnitrones: synthetic approach to polyoxin C

[reaction: see text] The stereoselectivity of nucleophilic addition of 2-trimethylsilyloxyfuran to N-gulosyl-C-alkoxymethylnitrones was investigated. It was found that the selectivity was highly dependent on the bulkiness of the C-substituent of the nitrone. The major adducts were elaborated into the key intermediate of polyoxin C.     

Conversion of quassinoids for enhancement of inhibitory effect against Epstein-Barr virus early antigen activation. Introduction of lipophilic side chain and esterification of diosphenol

Introduction of a senecioyl group into shinjulactones B and C, and esterification of the diosphenol moiety in brusatol and brucein A enhanced inhibitory effect against Epstein-Barr virus early antigen activation.