三芳基咪唑类化合物的合成及其双光子吸收性能研究

双光子吸收是指物质分子或原子在强激光激发下同时吸收两个光子,从基态跃迁到两倍光子能量激发态的过程。目前,双光子吸收材料已广泛地应用到双光子激发显微[1]、频率上转换激射[2-3]、光学限幅、三维光信息存储[4]以及光生物学等领域。但在已报道的双光子诱导上转换荧光的有机     

程序涂渍柱“柱效能程序效应”的研究

本文从理论上给出程序柱“柱效能程序效应”的概念并导出了函数关系式,通过计算机可计算柱效能程序效应与柱内各变量之间的关系,实践证明实验数据的变化趋势与理论数据相符。     

Thermal and thermoxidative degradations of starch and thermosensitive starch-g-BAM copolymers

Summary Thermal degradation under N₂atmosphere and thermoxidative degradation under air atmosphere of increasingly grafting efficiency values (i.e. GE%=0.0 to 35.5) for starch and starch grafted with N-tert-butylacrylamide thermosensitive copolymers (starch-g-BAM) by Ozawa and Kissinger methods using thermogravimetric analysis (TG) and differential scanning calorimetry techniques (DSC) at 10, 30 and 50% mass losses respectively have been studied. Influence of physical inter and intra molecular interactions on grafting and consequently on activation energy of degradation (E_a,d) was investigated using Ozawa's method, whereas linear dependence of E_a,don GE% by scaling relations using Kissinger's method was determined. Furthermore, the thermoxidative degradation induces the possibility of molecular rearrangement, cyclization and partial crosslinking that is deduced from the activation energy of degradation (E_a,d) and residual mass of TG profile. Thermal stability of starch does not alter as a result of different grafting efficiency percentages.     

Structural Efficiency and Microstructural Modeling of Wet Gels and Aerogels

We present a microstructural model of aerogels that includes the effect of particle necks, tortuosity and dangling ends on the scaling of elastic moduli with density. Relative neck radii can be determined for sintering series of silica aerogels and for Resorcinol Formaldehyde (RF) aerogels produced with different catalyst concentrations. The density of elastically ineffective dangling ends and the tortuosity can be estimated using information from thermal conductivity and elastic modulus measurements in silica aerogels. Typical values for the load bearing mass range from >50% for high density and heat treated aerogels to <10% of the total mass for low density wet-gels.     

Practical limitations of capillary gas chromatography

Glass capillary gas chromatography is a high resolution separation method which allows the qualitative and quantitative analysis of even complex mixtures, which may contain many components–also isomeric–in a wide range of volatilities, polarities and concentrations. The principal limitation of gas chromatographic application is given by an insufficient volatility of the species to be separated. Elevated temperatures have to be applied if the application range is to be extended and to achieve steep peak profiles, i.e. low detection limits at high resolution. The use of elevated temperatures is limited, of course, by the temperature stability of both the solvent (stationary liquid and support) and the solutes. The problems of trace analysis for low volatility compounds at high resolution and its limitational parameters regarding sampling, separation and detection are discussed. The applicability of glass capillary columns in this field is influenced by the following parameters: tailing behaviour; irreversible adsorption of polar and decomposition of unstable solutes; thermal stability of stationary liquid (including the support deactivation); separation efficiency and sample capacity (film thickness). Multidimensional gas chromatography using capillary columns coupled either with a packed or another capilllary column for preseparations may be applied with advantage in the analysis of complex mixtures.     

咪唑类化合物-CuCl络合催化剂在甲醇氧化羰基化反应中的催化性能

研究了咪唑及其衍生物配合CuCl对甲醇液相氧化羰化合成碳酸二甲酯的催化性能。筛选出溶解性好、腐蚀性小且催化活性高的多功能助催剂。实验结果表明，反应体系中加入N-甲基咪唑后，CuCl可以完全溶解。当催化剂的浓度为0.2 mol/L, N-甲基咪唑与CuCl的量为4∶1，反应温度为120 ℃，反应压力为2.40 MPa，CO与O2的进气比2∶1，反应3 h的条件下甲醇的摩尔转化率为15.4%，选择性为98%以上。从腐蚀性试验结果看，50 ℃时，加入N-甲基咪唑化合物后，Q235钢在CuCl/CH3OH/H2O/CO/O2体系中的腐蚀速率为0.22mm/a，缓蚀效率为94.5%。动力学研究表明，反应近似为一级，加入N-甲基咪唑后，反应速率常数为0.15 min－1。     

Effect of mobile phase density gradients on efficiency in packed column supercritical fluid chromatography

Summary The efficiency of packed columns was measured as a function of flow rate, temperature, outlet density, and the density differential across the column, unsing pure carbon dioxide as the mobile phase. Although density differentials are often blamed for a serious loss in efficiency in packed column supercritical fluid chromatography, the results show that efficiency was not a function of the density differential. Peak shapes suggest that apparent loss in efficiency is actually due to inadequate solubility of the solute in carbon dioxide.     

Efficiency of connected binary block designs when a single observation is unavailable

In this paper the problem of finding the design efficiency is considered when a single observation is unavailable in a connected binary block design. The explicit expression of efficiency is found for the resulting design when the original design is a balanced incomplete block design or a group divisible, singular or semiregular or regular with ₁>0, design. The efficiency does not depend on the position of the unavailable observation. For a regular group divisible design with ₁>0, the efficiency depends on the position of the unavailable observation. The bounds, both lower and upper, on the efficiency are given in this situation. The efficiencies of designs resulting from a balanced incomplete block design and a group divisible design are in fact high when a single observation is unavailable.The work of the first author is sponsored by the Air Force Office of Scientific Research under Grant AFOSR-90-0092.On leave from Indian Statistical Institute, Calcutta, India. The work of the third author was supported by a grant from the CMDS, Indian Institute of Management, Calcutta.     

Anodic behavior of nickel-based alloys in the electrolytic production of NF3

The Ni-based alloys, such as Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si, prepared by hot isostatic pressing (HIP) at 1000 °C under 2 × 10⁸ Pa for 2 h were employed as the anodes for electrolytic production of NF₃. The current efficiencies for NF₃ formation were 42-38, 52-40, 52-47, 63-62, 50 and 41% for Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si alloys, respectively. The current efficiencies only on Ni-Cu alloys with Cu concentrations lower than 10 mol% were almost the same as those on Ni sheet and HIPed Ni anodes, whereas those on the other alloys used in this study were smaller compared with those on both Ni anodes. On the other hand, the current losses caused by anodic dissolution of Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si alloy electrodes were 7.95-4.42, 6.40-7.02, 5.60-6.30, 3.34-6.33, 5.10 and 0.18%, respectively. The anode consumptions of Ni-5 mol% Cu and Ni-5 mol% Si alloys were almost the same or smaller compared with those of Ni sheet and HIPed Ni electrodes, though those of other alloys used were large compared with those of both Ni anodes. Consequently, addition of Cu to the nickel matrix is available for a cheaper cost of anode with keeping a same current efficiency as that on the Ni anode and addition of Si to the nickel matrix is effective for decreasing anode consumption largely. A Ni sheet electrode containing a trace of impurities, such as Co, Mn, Ag and Al, is also favorable as the anode for electrolytic production of NF₃.     

Rapid determination of desorption efficiency, and analysis of solvent mixtures for occupational exposure studies

Summary An analytical procedure has been developed for simultaneous determination of solvent mixture vapors to enable evaluation of occupational exposure. To determine the desorption efficiency the volatile components of the solvent mixtures were generated from a glass tube filled with glass wool. This device is easy to prepare and use. These vapors were then collected in activated charcoal tubes and analyzed by capillary gas chromatography. The method was tested with a mixture of 22 solvents, including aliphatic and aromatic hydrocarbons, alcohols, ethers, esters, and ketones, all at low concentrations. All the components were detected. When a 99∶1 mixture of carbon disulfide-dimethylformamide was used for desorption the efficiency was>75% for most of the solvents.