Determination of constant‐volume combustion energy for the complexes of zinc nitrate with three amino acids

Five solid complexes of zinc with L‐α‐methionine, L‐α‐phenylalanine and L‐α‐histidine were prepared. The constant‐volume combustion energies of the complexes, ΔE_c (coordination), were determined by a precise rotating bomb calorimeter at 298.15 K. They were ‐ 2969.03 ± 0.34, ‐2929.46 ± 1.59, ‐9597.13 ± 6.12, ‐4378.98 ± 3.27 and ‐14047 ± 6.75 kJ/mol, respectively. Their standard enthalpies of combustion, ΔH^θ_m,c(coordination, s, 298.15 K), and standard enthalpies of formation, ΔH^θ_m,f (coordination, s, 298.15 K), were calculated. They were ‐2959.73 ± 0.34, ‐2923.88 ± 1.59, ‐9649.18 ± 6.12, ‐4373.40 ± 3.27, ‐14048.53 ± 6.75 kj/mol and ‐1180.94 ± 0.92, ‐1401.26 ± 1.77, ‐2501.69 ± 6.50, ‐1381.47 ± 3.49, ‐1950.19 ± 7.65 kJ/mol, respectively.     

陶瓷/VDF-TrFE 0-3型铁电复合物的三阶非线性介电系数

在自建的非线性介电测试装置上测得了PT,BT、PZT和VDF-TrFE共聚物形成的0-3型铁电复合物厚片的三阶非线性介电系数ε3.研究发现,三种复合物的ε3都随陶瓷组分含量的上升而增大.测试场强升高,测得的ε3值减小,但对高陶瓷含量(φ＞0.4)的BT/VDF-TrFE和PZT/VDF-TrFE复合物则在6MV/m场强下出现极小值.二相都被预极化的复合物小于仅陶瓷相被预极化的ε3值.PZT/VDF-TrFE复合物的温度依赖关系显示了与(-阶)介电系数类似的表观热滞后现象.高PZT含量的复合物在相变区出现较大的ε3值.     

CuCl/沸石双功能羰基化催化剂催化合成叔碳酸

Bifunctional carbonylation catalysts were prepared by introducing both of acidic and metallic sites into zeolites, such as β, M and Y, by which tertiary butyl acid was synthesized under mild reaction conditions. The effects of reaction temperature and the copper amount as well as the acid strength on the catalytic activity were investigated. The results show that when the content of cuprous for β, M and Y are 2 35%, 2 48% and 7 13% respectively, the carbonylation activity of the related sample is the greatest. In the reaction temperature range, lower temperature is favorable for yielding acid and higher temperature is favorable for yielding ester. The catalytic activity increases with the increase of the acid strength. The in situ FT IR study shows that Cu(Ⅰ) is the metallic active site.     

Asymptotic behaviour of a Brownian motion on exterior domains

We study the asymptotic behaviour of the transition density of a Brownian motion in ?, killed at ∂?, where ? ^c is a compact non polar set. Our main result concern dimension d = 2, where we show that the transition density p ^? _t (x, y) behaves, for large t, as u(x)u(y)(t(log t)²)⁻¹ for x, y∈?, where u is the unique positive harmonic function vanishing on (∂?) ^r , such that u(x) ∼ log ∣x∣. Received: 29 January 1999 / Revised version: 11 May 1999     

RAFT Polymerization: Adding to the Picture

SUMMARY: Factors affecting the choice of RAFT agent [RSC(Z) = S] for a given polymerization are discussed. For polymerization of methyl methacrylate (MMA), tertiary cyanoalkyl trithiocarbonates provide very good control over molecular weight and distribution and polymerizations show little retardation. The secondary trithiocarbonate RAFT agents with R = CHPh(CN) also gives good control but an inhibition period attributed to slow reinitiation is manifest. Radical induced reduction with hypophosphite salts provides a clean and convenient process for removal of thiocarbonylthio end groups of RAFT-synthesized polymers. Two methods providing simultaneous control over stereochemistry and molecular weight distribution of chains formed by radical polymerization are reported. Polymerization of MMA in the presence of scandium triflate provides a more isotactic PMMA. A similar RAFT polymerization with trithiocarbonate RAFT agents also provides control and avoids issues of RAFT agent instability seen with dithiobenzoate RAFT agents in the presence of Lewis acids. RAFT polymerization of tetramethylammonium methacrylate at 45 °C provides a more syndiotactic PMMA of controlled molecular weight and distribution (after methylation; mm:mr:rr 2:21:77 compared to 3:35:62 when formed by bulk polymerization of MMA).     

晶型转变对尼龙11分子链运动的影响

Two crystal forms (α and δ′ form) of nylon 11 were prepared by melting, ice water bath quenching and annealing. The characteristic of chain movement of two forms was investigated using dielectric relaxation spectroscopy in the frequency range from 42 Hz to 5 MHz. The dielectric temperature spectra at different frequencies show that the primary α relaxation corresponding to the chain segment movement is located at higher temperature in α form, indicating the chain segment movement is restricted after δ′→α crystal transition. The activation energy of secondary β relaxation remained almost unchanged for two forms, but the relaxation time was longer and the relaxation strength was weaker for α form, confirming that the local relaxation was also restricted to some extent after δ′→α crystal transition.     

半化学法制备0.5Pb(Mg1/2W1/2)O3-0.5PbTiO3粉体的反应机理探讨

半化学法制备0.5Pb(Mg1/2W1/2)O3-0.5PbTiO3粉体的反应机理探讨;钨镁酸铅;钙钛矿相;半化学法;反应机理     

微柱高效液相色谱法测定大鼠脑微透析液中 的乙酰胆碱和胆碱

用所建立的微柱高效液相色谱分离、柱后固定化酶反应器酶解、电化学检测器检测的方法, 对用不同浓度异氟醚麻醉前后的大鼠脑微透析液中的乙酰胆碱和胆碱的浓度进行了测定。在 乙酰胆碱和胆碱的浓度为10～ 2 000 nmol/L 时,其浓度分别与各自相应峰高的线性 关系良好,两者的检测限(以信噪比为3计)均可达5 nmol/L 。微透析液中乙酰胆碱和胆碱的含量在大鼠清醒时最高,随着异氟醚吸入浓度的增加,乙酰胆碱和胆碱含量明显降低。在大鼠海马和脑皮层中乙酰胆碱浓度的降低与大鼠吸入异氟醚的浓度相关( P ＜     

基于微腔效应增强单层二硫化钨光吸收

提出基于金属薄膜-分布式布拉格反射器微腔效应增强单层二硫化钨光吸收的多层薄膜结构。运用光学传输矩阵理论研究了其输运特性,发现由于金属薄膜-分布式布拉格反射器的微腔效应,在间隔层和覆盖层之间形成电场强度极大值,有效促进入射光与单层二硫化钨的相互作用。综合优化金属层、间隔层和覆盖层厚度,单层二硫化钨在612 nm处的光吸收提高了38倍,达到78.42%。进一步探讨了光入射角、分布式布拉格反射器周期、间隔层折射率与单层二硫化钨光吸收的关系。研究结果表明,上述结构参数的变化可有效调控单层二硫化钨的吸收峰值。研究结果为制备高性能单层二硫化钨光电探测器等新型光电子器件提供了新思路。