焙烧温度对CuCe/AC催化剂甲醇氧化羰基化性能的影响

采用先浸渍Ce后浸渍Cu的方法制备了活性炭(AC)负载CuCe催化剂,考察了焙烧温度对CuCe/AC催化剂表面结构及其催化甲醇气相氧化羰基化合成碳酸二甲酯(DMC)性能的影响,并采用XRD、XPS和H2-TPR等表征分析了活性组分含量和价态等性质。结果表明,催化剂中高价态的Cu~(2+)逐渐被还原为低价态的Cu~+和Cu~0,催化剂中发生Cu~(2+)→Cu~+→Cu~0的还原变化过程。催化剂经450℃焙烧处理后,催化剂中仍然存在一定量的Cu_2O晶相,表明Ce与Cu的相互作用抑制了部分Cu_2O的还原。当焙烧处理温度为300℃时,催化剂中的Cu~+含量达到最高,此时催化剂的活性达到最优,DMC的时空收率、选择性以及甲醇转化率分别为143.4mg/(g·h)、85.2%和4.1%。     

Controller design for network‐based Markovian jump systems with unreliable communication links

This article is concerned with observer and controller design for networked control systems, where the considered plant refers to a class of discrete‐time communication delay Markovian jump systems. In the study, random packet losses and output quantization are considered simultaneously. The packet losses considered here includes sensor to controller and controller to actuator sides, which are modeled as two Bernoulli distributed white sequences, respectively. An observer‐based control scheme is developed to stabilize the closed‐loop systems. Finally, an illustrative example is provided to show the applicability of the proposed control method. © 2016 Wiley Periodicals, Inc. Complexity 21: 623–634, 2016     

Even-electron ions: a systematic study of the neutral species lost in the dissociation of quasi-molecular ions

The collision-induced dissociations of the even-electron [M + H](+) and/or [M - H](-) ions of 121 model compounds (mainly small aromatic compounds with one to three functional groups) ionized by electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) have been studied using an ion trap instrument, and the results are compared with the literature data. While some functional groups (such as COOH, COOCH(3), SO(3)H in the negative ion mode, or NO(2) in both the positive and negative ion modes) generally promote the loss of neutrals that are characteristic as well as specific, other functional groups (such as COOH in the positive ion mode) give rise to the loss of neutrals that are characteristic, but not specific. Finally, functional groups such as OH and NH(2) in aromatic compounds do not lead to the loss of a neutral that reflects the presence of these substituents. In general, the dissociation of [M + H](+) and [M - H](-) ions generated from aliphatic compounds or compounds containing an aliphatic moiety obeys the even-electron rule (loss of a molecule), but deviations from this rule (loss of a radical) are sometimes observed for aromatic compounds, in particular for nitroaromatic compounds. Thermochemical data and ab initio calculations at the CBS-QB3 level of theory provide an explanation for these exceptions. When comparing the dissociation behaviour of the even-electron [M + H](+) and/or [M - H](-) ions (generated by ESI or APCI) with that of the corresponding odd-electron [M](+) ions (generated by electron ionization, EI), three cases may be distinguished: (1) the dissociation of the two ionic species differs completely; (2) the dissociation involves the loss of a common neutral, yielding product ions differing in mass by one Da, or (3) the dissociations lead to a common product ion.     

抗杂散电容电桥

本文介绍一种以方波驱动的抗杂散电容交流电桥,在不进行补偿的条件下,提高测量精度一个数量级以上。     

电路参数对外电极气体放电过程影响的计算机分析

本文通过对外电极气体放电物理过程的计算机模拟,研究了一些主要电学参量(包括电源电压、外电路阻抗、介质层电容和介质层上的壁电荷等)对放电过程的影响.文中给出了关于放电电流、辐射亮度和电功损耗等项放电特性随外电路阻抗变化的一维数值分析实例.     

Advanced AC calorimetry of polycaprolactone in melting region

The new capabilities of AC calorimetry, when working at frequencies above the classical limit were demonstrated. The appropriate frequency range of classical AC calorimetry was substantially enlarged. It was shown that the advanced AC calorimetry can be applied for studying dynamic heat capacity of polymers in the frequency range 0.1–1 Hz. Thus, the processes with characteristic time as short as ca. 5 s was registered. The advanced AC technique was applied for investigation of the melting kinetics in polycaprolactone. It was found that melting in polycaprolactone is related to an activated process. The activation of the melting process after a step heating is described by a stretched exponent and the decay of the melting by only one exponent at short times. The dependencies of the exponent on temperature and thermal treatment were investigated at frequencies in the range 0.1–1Hz and modulation amplitudes 0.005–0.2 K.     

AC impedance and state-of-charge analysis of a sealed lithium-ion rechargeable battery

A 7.2 V, 1.25 Ah sealed lithium-ion rechargeable battery has been studied for estimating its state-of-charge (SOC) by AC impedance. The dispersion of impedance data over the frequency range between 100 kHz and 25 mHz comprises an inductive part and two capacitive parts. As the inductive behaviour of the battery is attributed to the porous nature of the electrodes, only the capacitive components have been examined. The data obtained at several SOC values of the battery have been analyzed by a non-linear least-squares fitting procedure. The presence of two depressed semicircles in the capacitive region of the Nyquist plots necessitated the use of an electrical equivalent circuit containing constant phase elements instead of capacitances. The impedance parameters corresponding to the low-frequency semicircle have been found useful for predicting the SOC of the battery, mainly because the magnitude of these parameters and their variations are more significant than those of the high-frequency semicircle. The frequency maximum (f _max) of the semicircle, the resistive component (Z′) corresponding to f _max, the phase angle (φ) in the 5.0 Hz–0.1 Hz frequency range, the equivalent series resistance (R _s) and the equivalent series capacitance (C _s) have been identified as suitable parameters for predicting the SOC values of the lithium-ion battery. Received: 23 September 1998 / Accepted: 22 February 1999     

A note on overpotential dependence of AC impedance data

Charge-transfer resistance [R _ct = (dη/di)_{η = 0}] and Tafel plots of current density (i) versus overpotential (η) data are generally known to yield values of the energy-transfer coefficient (α) and exchange current density (i _o) of an electrochemical reaction. In the present investigation, the resistance (dη/di)_η≠0 that could be calculated by differentiating a wide range of i−η curves was also shown to provide the values of α and i _o, by plotting ln(dη/di)_η≠0 against η. Since α and i _o could also be evaluated directly from the experimental DC polarization data, the procedure was not of significant importance. Nevertheless, it was considered important in evaluating α and i _o from AC impedance data, because the procedure was based on data analysis, which was much simpler than that reported in the literature. A cobalt electrode prepared from fine metal powder was used in 1 M KOH electrolyte and the hydrogen evolution reaction was studied by AC impedance at several potentials. The resistance values measured from the complex plane impedance diagram were plotted against the potential, and the values of α and i _o were evaluated. Received: 8 October 1998 / Accepted: 11 January 1999     

环形叶栅中二次流与损失的数值模拟

1引言三维叶栅中的损失主要由叶型损失、端部损失及二次流损失等组成。而其中的二次流损失,由于在损失总量中往往占有很大的比重,且又强烈依赖于叶栅几何形状等本身的特点,因而十分受到关注。许多学者分别用计算或试验的方法来研究二次流动,已经做了大量的工作（如文献1～8）。然而,以往大部分的研究往往局限于直列叶栅,对沿径向非等截面的环形叶棚的详细研究甚少。本文基于非正交曲线坐标与非正交速度分量下完全守恒型的Navier－Stokes方程,采用时间推进法与Baldwin－Lomax湍流模型,数值求解环形叶栅内部的粘性流场,得到了十分…     

New experimental evidence of the structural modification in single crystal Bi2Sr2CaCu2Oy by X-ray diffraction observation

The variations of the high angle 00 peak-shape by means of X-ray l scans of the 00l fundamental reflections were investigated in detail for a highly oriented Bi₂Sr₂CaCu₂O_y (Bi2212) crystal with sufficiently small intrinsic mosaicity and the same crystal annealed in air at 250, 300, 400, 600, and 750°C for 20 h in consequence. For the first time, we observed a new additional reflection almost overlapped original 00l fundamental reflection at annealing temperature below 400°C by X-ray diffraction measurement, which shows that there coexisted two sets of lattice periodicity in the c-direction of the annealed crystal. The new additional reflection appeared at 250°C and disappeared at 400°C. Its intensity was increased at 300°C. The measurements of the AC susceptibility, c-axis parameter and full width at half maximum (FWHM) of the 00 peaks showed that the new additional reflection was associated with the oxygen diffusion in CuO₂ planes and the changes of strain field. The results provide the new experimental evidence that the structural distortion is more sensitive to the oxygen diffusion in CuO₂ planes than to that in Bi–O layers.