绝对正规范数空间上Ptolemy常数的计算

本文在二维绝对正规范数空间上给出了计算Ptolemy常数的一些新条件,得到的结论不仅包含了先前的一些结果,而且在一些具体的空间上给出了Ptolemy常数的新结果.     

空间几何常数与集值非扩张映射的不动点

本文利用凸刻画系数和正规结构系数,詹姆斯型常数和García-Falset系数之间的关系式,得到了空间上集值非扩张映射存在不动点的一些充分条件,这些结论不仅改进了一些文献中的结果,而且也对一些公开问题给出了解答.     

A new pH fluorescent molecular switch by modulation of twisted intramolecular charge transfer with protonation

A pH fluorescent molecular switch, BOPIM‐dma, a boron 2‐(2′‐pyridyl) imidazole complex derivatives, was investigated in aqueous system. BOPIM‐dma shows weak or no fluorescence in conventional solvents due to twisted intramolecular charge transfer (TICT). Upon protonation of the dimethylamino groups in BOPIM‐dma, its fluorescence was turned on ascribed to the inhibition of TICT. Its emission can be switched ‘on’ or ‘off’ between pH 2.4 and 4.0, and it undergoes a reversible protonation–deprotonation reaction with a pKa of 3.12. Copyright © 2013 John Wiley & Sons, Ltd.     

Two new oplopane sesquiterpenes from Artemisia gmelinii Web. ex Stechm.

Two new oplopane sesquiterpenes, gmelinin A（1） and gmelinin B（2）, were isolated from Artemisia gmelinii Web. ex Stechm. Their structures were established by spectroscopic techniques（mainly 1D and2 D NMR） and application of the modified Mosher method.     

First-principles study on the structure,elastic and electronic properties of hexagonal HfPtAl under pressure

We have investigated the structure, elastic and electronic properties in hexagonal HfPtAl by a first-principles ultrasoft pseudopotential of the plane wave within the density functional theory (DFT) plus the generalized gradient approximation (GGA) in the scheme of Perdew–Burke–Ernzerhof (PBE). All properties are calculated as a function of external pressure. The results of structural parameters have a good agreement with reported experiments and can predict the properties under pressure well. The hexagonal HfPtAl is mechanically stable and behaves in a ductile manner. The TDOS is occupied by Pt-d, Hf-d and Al-p.     

半导体制冷干燥装置在气相色谱法测定溶解态N2O中的应用

结合半导体制冷技术，建立了一种气相色谱在线除水方法，该法具有节约载气、减少干燥剂用量、样品消耗量小等优点。采用该装置，气相色谱法测定溶解态N2O，可有效消除水汽的干扰，仪器连续运行15h基线漂移的变异系数优于0．6％。     

A fully automatic system for underway N2O measurements based on cavity ring-down spectroscopy

N₂O is one of the most important greenhouse and ozone-depleting gases and has been the source of considerable concern in recent years. The oceans account for ~ 1/4 of the global N₂O emission budget; however, the oceanic N₂O source/sink characteristics are not well understood. To enhance the study of oceanic N₂O source/sink characteristics, our laboratory developed a fully automatic underway system for surface water N₂O concentration and atmospheric N₂O mole fraction measurements consisting of a cavity ring-down spectroscopy (CRDS) instrument and an upstream device. The developed device can be programmed to switch the CRDS measurements from the equilibrator headspace to the atmospheric sample and the reference gas sample. The surface water N₂O concentration is calculated from the equilibrium headspace N₂O mole fraction in the equilibrator. The response time of this equilibrator is ~ 3.4 min, and the estimated precision of this method for surface water N₂O measurements is better than 0.5% (relative standard deviation, RSD), which is one order of magnitude better than that of traditional gas chromatographic methods and can be further optimised. Data are acquired every 20 s, and the calibration frequency requirement of this system is approximately 7–10 days. This labor-saving underway system is a powerful tool for high-precision and high-resolution measurements of atmospheric and oceanic N₂O and can significantly improve the study of the characteristics of oceanic N₂O sources/sinks and their response to climate change.     

Facile fabrication of cerium niobate nano-crystalline fibers by electrospinning technology

In this study, one-dimensional (1D) cerium niobate nano-crystalline fibers were first prepared by a facile sol–gel and electrospinning process, followed by heat treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) were used to characterize the samples. It can be seen from SEM images that the as-prepared xerogel samples and those annealed at 900 °C presented uniform fibrous morphology, with the diameter of 100–300 nm and length of several centimeters. The XRD and FT-IR results showed that cerium niobate samples had well-crystallized phase of CeNbO_4.25 with the crystallite size of about 28.6 nm at a heat treatment temperature of 900 °C, which can also be validated with the TEM image. The AC impedance of annealed disks made from the CeNbO_4.25 nano-crystalline fibers has been probed.