Accuracy of the Judd—Ofelt theory

The accuracy of the Judd-Ofelt theory is investigated in several rare earth doped glasses. Using a normalized method to fit the experimental data, we show that an average accuracy of 5 to 15% is often obtained. However, large errors (up to 35%) can be found on some transitions, even in the case of ions usually considered as well described by the theory. These errors tend also to depend strongly on the materials so that prediction of the accuracy of a calculated intensity is difficult. The Judd-Ofelt parameters found with the normalized method may also differ from those computed in the usual way. Moreover, even in relatively close compositions, quality of the fits can largely vary, weakening possible correlations between compositions and Judd-Ofelt parameters.     

微量氧氛围中八乙烯基POSS低温(180℃)热氧老化机理研究

通过1 H-NMR,13 C-NMR,29 Si-NMR表征物质老化前后结构变化;采用FTIR,MALDI-TOF,ESR,TG-IR联用,DSC等分析手段跟踪老化过程中特征基团、分子量、活性中心、质量损失和焓变情况,对八乙烯基POSS(OVPOSS)在180℃微量氧气氛围的热氧老化行为进行了研究.采用微量氧气方法以减少乙烯基基团热氧老化过程中的过氧化反应,以观察可能存在的其他反应机理.实验表明老化过程中不饱和双键逐渐转化成饱和单键,老化过程存在C自由基中心和放热效应,且分子量增大趋势明显,质量变化略微,说明八乙烯基POSS在微量氧气氛围中的低温(180℃)热氧老化过程存在自由基聚合历程.     

Mechanical properties and inhomogeneous nanostructures of dicyandiamide-cured epoxy resins

Dicyandiamide (DICY)-cured epoxy resins are important materials for structural adhesives and matrix resins for fiber reinforced prepregs. The objective of this study was to examine the mechanical and physical properties as well as the gel structures of the cured resins and discuss the relationships among them. Diglycidyl ether of bisphenol-A (DGEBA) oligomers were chosen as the common chemical structure of the epoxy resins. Four kinds of resin mixtures were formulated using the seven types of DGEBA oligomers having different molecular weight distributions. Three resin formulations having bimodal-type molecular weight distributions were designed to have almost identical rubbery plateau values of the storage modulus in dynamic mechanical analyses after curing, means that they had almost equivalent average crosslink density and basic chemical structure. However, the toughness, ductility, and environmental (heat and solvent) resistance of these three formulations were different. Atomic force microscopy revealed the existence of inhomogeneous nanoscale gel structures in these cured resins. The morphological differences in the gel structures in terms of their size, the connectivity, and the relative magnitude of the heterogeneity would cause the difference in several properties of the DICY-cured epoxy resins. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1425–1434, 2007     

A combined isotropic-kinematic hardening model for the simulation of warm forming and subsequent loading at room temperature

A coupled isotropic-kinematic hardening material model was developed based on phenomenological observations of performed two stage experiments on a medium carbon steel – SAE 1144, where the first deformation is performed at elevated temperatures and the second deformation at room temperature. Above all, deformations with orthogonal loading at various temperatures were investigated in order to determine the influence of the loading direction as well as of the temperature. Bergström’s theory of work hardening as well as the nonlinear kinematic hardening of an Armstrong–Frederick type were used as a basis for the model development. In the proposed model a relationship between material coefficients of the classical Bergström model and temperature was investigated. The aim of the new material model was to introduce the least possible amount of new parameters as well as to facilitate the mathematical determination of parameters during the fitting of the model with experimental data. The developed model was implemented in an in-house FE-Code in order to simulate the material behavior due to the dynamic strain aging and the hardening behavior after the dynamic strain aging process. Representative simulation results were compared with the experimental data in order to validate the efficiency and the application range of the model.     

固态发射机散热系统的设计

根据一般的散热理论,探讨了大功率 Ｄ Ｍ Ｏ Ｓ场效应管 Ｂ Ｌ Ｆ１４７ 的热传输过程,计算出 ４００ Ｗ 全固态发射机功放部分的散热面积,并设计了其散热通道及过热保护电路     

关于矽钢片涡流问题的讨论

通过定量分析,表明矽钢片的涡流其单体体积的涡损都和其厚度的平方成正比。     

Effect of Aging on the Stability of Ceramic Foams Prepared by Thermostimulated Sol-Gel Process

This work presents a new route of preparation of zirconium ceramic foams based on the thermostimulated sol-gel process. This method produces gelled bodies with up to 90% of porosity in the wet gel and can be used to make complex-shaped components. Unfortunately, the shrinkage during the drying step allows to a catastrophic reduction (>50%) of the foam porosity. To improve the foam stability we carried out a systematic study of the effect of gel foam aging on the drying process. Samples were aged in closed vessel at 25°C during different time period (from 6 to 240 h). The shrinkage and the mass loss during drying at 50°C were measured in situ, using a non-contact technique performed with a special apparatus. The results show that the total linear shrinkage decreases from 46% to 8% as the aging period increase from 6 to 240 h. This behavior is followed by a small change of total mass loss, from 42 to 54%. It indicates that by aging the structural stiffness of the foams increases due to secondary condensation reactions. Thus, by controlling the aging period, the porosity can be increased from 67 to 75% and the average size of mesopores of dried foams can be screened from 0.3 to 0.9 m. Finally, these results demonstrate that the thermostimulated sol-gel transition provides a potential route to ceramic foams manufacture.     

水杨酸类糖酯化合物的合成及其生物活性

将水杨酸及乙酰水杨酸分别与溴代糖作用, 合成了10个水杨酸类糖酯化合物. 所有化合物经元素分析和1H NMR确认了其结构, 并证明产物为β-构型, 反应具有立体专一性. 生物活性初步测定结果表明, 该类化合物具有一定的诱导活性, 且一些化合物的诱导活性好于水杨酸.     

Ni－海泡石催化剂的热稳定性和抗毒性

Ｎｉ－海泡石催化剂的热稳定性和抗毒性曹声春，杨礼嫦，彭峰，周军，郭栋材（湖南大学化工系，长沙４１００８２）关键词镍，海泡石，负载型催化剂，耐热性，抗毒性，苯，环己烷国内外现行的苯加氢过程主要采用Ｎｉ－ＡＩ。Ｏ。催化剂．但它存在耐热性差、易中毒、活性温...     

RFLP Tagging of a Gene Pm12 for Powdery Mildew Resistance in Wheat (Triticum aestivum L. )

A dominant gene, Pml2, conferring the resistance to powdery mildew (Erysiphe graminis) has been transferred to wheat from Aegilops speltoides. Sixteen RFLP probes were used to test Line 31 and its parents, showing that Line 31 is a 6B/6S translocation lines. The linkage analysis by five probes indicates that Pm12 is located on the chromosome 6B/6S, and tightly flanked by an RFLP marker α-Amy-1 (1.1 cM), identified by RFLP and isozyme analysis. This approach is equally applicable to the identification of other transferred alien genes and the segments of alien chromosome introgressed into wheat.