Time–frequency higher‐order spectra with adjustment to the instantaneous frequency variation

Novel time–frequency techniques are proposed: the short time instantaneous higher‐order spectra (HOS) with adjustment to measured or known a priori time variation of the instantaneous frequency of transient signals. It is shown that the proposed transforms are more effective than the non‐instantaneous HOS (i.e. without adjustment to time variation of the instantaneous frequency) in recognizing a non‐stationary nonlinearity. Copyright © 2008 John Wiley & Sons, Ltd.     

In vivo electrochemical impedance measurement on single cell membrane

The electrochemical characteristics of the plasma membranes of single cells and organelles were investigated. Silicon fabrication technology was used to produce a metal ultra-microelectrode (UME). Furthermore, the UME was characterized in a cell medium using electrochemical impedance spectroscopy (EIS). A single rat fibroblast cell, or chloroplast purified from Peperomia metallica leaves, was immobilized by a micropipette after which the UME was inserted into its cytosolic space through cell membrane using a piezo actuator. An in vivo EIS measurement between the UME and the counter electrode outside of a single cell was taken. The measurements were analyzed using equivalent circuits in order to estimate the membrane impedance of a single cell.     

芴衍生物TF-CF1的发光性质研究

芴类化合物是一种刚性平面联苯结构的电致发光材料,因具有宽的能隙、高的发光效率等优点,备受专家学者的关注。文章结合作者的工作实践,简述TF1可以作为一种有机电致发光的潜能型材料。     

Comparative study on the growth mechanisms of PAHs

The efficiencies of recently proposed, phenyl addition/cyclization (PAC), methyl addition/cyclization (MAC) and a popular hydrogen abstraction/acetylene addition (HACA) mechanisms have been examined experimentally by detecting the gas phase reaction products of pyrolysis of toluene with/without addition of benzene + acetylene by using vacuum ultraviolet (VUV) single photon ionization (SPI) time of flight mass spectrometry (TOFMS). Besides the observation of verities of large polycyclic aromatic hydrocarbons (PAHs), intense mass peaks of indene, phenylacetylene and propyne confirmed a remarkable quenching of the major active species, benzyl, phenyl and methyl radicals by acetylene. In spite of quenching, only benzyl contributed products were diminished while phenyl and methyl contributed products were enhanced. Uniquely observed symmetrical PAHs; corrannulene/coronene; formed by the active involvement of PAC, HACA and/or MAC mechanisms, reflects the interdependencies of these mechanisms. Individually, PAC was found highly efficient for endless growth, HACA for filling triple fusing site and MAC for expanding cyclotetra/pentafused into benzenoid structure, respectively.     

The origin of the complex character of the Ohmic impedance

The local and global Ohmic response for an electrode exhibiting geometry-induced potential and/or current distributions has recently been shown to be represented by a frequency-dependent complex impedance. A physical explanation for this result is provided in terms of the radial contribution to local current density and the decrease in current density along the current lines. Experiments performed with Cu/Al and Mg/Al galvanic couples show that, in regions where a radial current density does not exist, the local Ohmic impedance is independent of position; whereas, in regions where the radial current density cannot be neglected, the local Ohmic impedance is a function of position. Simulations performed on recessed electrodes show that, even in the absence of a radial current, an axial variation of current density gives rise to a complex Ohmic impedance. The complex character of the Ohmic impedance shows that an equivalent circuit, using the usual two-terminal resistor to represent the Ohmic contribution of the electrolyte, provides an inadequate representation of an electrode with geometry-induced current and potential distributions.     

基于信号强度的改进型井下测距算法的研究

针对现有信号强度测距法计算误差较大的问题，研究射频天线性能参数对电磁波传输的影响，提出将天线阻抗特性与能量接收相联系，将水平极化衰减率应用于求解天线回路上任意微分长度元的电磁波功率密度，从而建立了符合井下射频天线特性的信号能量与传输距离的关系式，推导出求解井下基站与目标之间距离的改进型信号强度测距法。选取相同的巷道环境验证了算法改进前后对目标的定位能力，结果表明经过改进后算法得出的目标位置与改进前相比更加准确，定位误差缩小6.9 m2，且改进后算法与改进前相比大幅减少全巷道内基站的布设数量，提高了基站的利用率，充分证明提出的改进型信号强度测距法更加适合井下巷道中的目标测距及定位，计算结果更加准确可靠。     

Durable high-performance Sm0.5Sr0.5CoO3–Sm0.2Ce0.8O1.9 core-shell type composite cathodes for low temperature solid oxide fuel cells

Sm_0.5Sr_0.5CoO₃ (SSC)-Sm_0.2Ce_0.8O_1.9 (SDC) core-shell composite cathodes are synthesized via a polymerizable complex method, and the durability of a cell incorporating the cathodes is examined. Nanocrystalline SSC powders have been coated onto the surfaces of SDC cores to enable the formation of a rigid backbone structure, over which the catalyst phase is effectively dispersed. A symmetrical SSC-SDC |SDC| SSC-SDC half-cell exhibits a polarization resistance of 0.098 Ω cm² at 650 °C. The durability and microstructure of the cathode are investigated by electrochemical impedance spectroscopy and thermo-cycle tests at temperatures in the range of 100 °C-650 °C. After 30 cycles, the polarization resistance is found to increase by 9.04 × 10⁻² Ω cm², a 3.56% rise with respect to the initial resistance. Coarsening of the SSC catalyst phase has been prevented with the use of core-shell type powders, as confirmed by a nearly constant low frequency polarization resistance and a microstructural analysis. The performance of a unit cell comprised of the core-shell type cathode exhibits 1.07 W cm⁻² at 600 °C and 0.62 W cm⁻² at 550 °C.     

Electrochemical tuning of titania nanotube morphology in inhibitor electrolytes

The electrochemical behavior of fluorine containing electrolytes and its influence in controlling the lateral dimensions of TiO₂ nanotubes is thoroughly investigated. Potentiostatic anodization is carried out in three different electrolytes, viz., aqueous hydrofluoric acid (HF), HF containing dimethyl sulphoxide (DMSO) and HF containing ethylene glycol (EG). The experiments were carried out over a broad voltage range from 2 to 200 V in 0.1-48 wt% HF concentrations and different electrolytic compositions for anodization times ranging from 5 s to 70 h. The chemistry that dictates how the nature of electrolytes influences the morphology of nanotubes is discussed. Electrochemical impedance spectra were recorded for varying compositions of all the electrolytes. It was observed that composition of the electrolyte and its fluorine inhibiting nature has significant impact on nanotube formation as well as in controlling the aspect ratio. The inhibiting nature of EG is helpful in holding fluorine at the titanium anode, thereby allowing controlled etching at appropriate voltages. Thus our study demonstrates that HF containing EG is a promising electrolytic system providing wide tunability in lateral dimensions and aspect ratio of TiO₂ nanotubes by systematically varying the anodization voltage and electrolyte composition.     

AC impedance and state-of-charge analysis of alkaline zinc/manganese dioxide primary cells

Alternating current impedance data of alkaline Zn/MnO₂ cells were analysed in view of identification of suitable parameters, which depend on the state-of-charge (SOC) of the cells. The impedance of a slightly discharged cell was found to possess impedance considerably lesser than that of an undischarged cell. The data in the form of Nyquist plot contained an inductance part at very high frequencies, a capacitive semicircle at high frequencies and a diffusion linear spike at low frequencies. The low frequency linear spike gradually transformed into a capacitive semicircle with the decrease of SOC of the cell, which was attributed to the nature of the reactions at the Zn anode. Of several impedance parameters that were examined, equivalent series capacitance (C _s) was found to have a strong dependence on SOC of the alkaline Zn/MnO₂ cells. There was a continuous change in a partially discharged cell during its ageing, which was reflected by transformation of low frequency data into a clear semicircle.     

两种杯[6]芳烃的红外光谱和拉曼光谱研究

研究了两种对－叔丁基杯〔６〕芳烃的红外和拉曼光谱。对－叔丁基杯〔６〕芳烃Ｉ的环状的分子内缔合氢键和部分甲基化的（１，３，５－三甲基）－对－叔丁基杯（６）芳烃Ⅱ的三中心氢键在红外光谱中有明显反映杯（６）芳烃的ｐｉｎｃｈｅｄ ｃｏｎｅ（紧锥型）构象也得到了证明，而两种杯（６）芳烃氢键构象和强度的不同导致了二者的拉曼谱图也存在较大的差异。