Phase Stability and Physical Properties of Cubic and Tetragonal ZrO2 in the System ZrO2–Y2O3–Ta2O5

The cubic ( c -ZrO₂) and tetragonal zirconia ( t -ZrO₂) phase stability regions in the system ZrO₂–Y₂O₃–Ta₂O₅ were delineated. The c -ZrO₂ solid solutions are formed with the fluorite structure. The t -ZrO₂ solid solutions having a c/a axial ratio (tetragonality) smaller than 1.0203 display high fracture toughness (5 to 14 MPa · m^1/2), and their instability/transformability to monoclinic zirconia ( m -ZrO₂) increases with increasing tetragonality. On the other hand, the t -ZrO₂ solid solutions stabilized at room temperature with tetragonality greater than 1.0203 have low toughness values (2 to 5 MPa · m^1/2), and their transformability is not related to the tetragonality.     

The far infra-red spectrum of poly(vinyl chloride)

The far infra-red spectrum of a poly(vinyl chloride) sample prepared by the urea clathrate (UC) route has been measured at various temperatures in the range 60 to 320 K. The results, taken in conjunction with those for two less highly ordered polymers, indicate that a revision of the assignments of earlier workers, based on normal coordinate calculations and on the measured spectra of secondary alkyl chlorides such as 2-chlorobutane, is required. The band at 65 cm^?1 is attributed to a lattice mode and is not indicative of weak hydrogen bonds of the type CH…ClC. However, it is suggested that the band at 185 cm^?1, which is particularly clear and sharp with the UC polymer, probably originates from an interaction of this type, occurring specifically at tight chain folds.     

骨料颗粒与多孔材料显微结构关系的研究

本文阐述了多孔材料的孔隙率与生产工艺的关系 ,结合显微结构分析了骨料粒径及其分布对多孔材料的孔隙率、抗折强度的影响。     

Crystal lattice deformation and the mesophase in poly(ethylene terephthalate) uniaxially drawn by solid-state coextrusion

The development of crystalline and mesophase structure on drawing of poly(ethylene terephthalate) (PET) has been studied. The uniaxial drawing has been done by solid-state coextrusion from 50 to 90°C. The unit-cell parameters of stress-induced crystallites in extrudates have been determined as a function of extrusion draw ratio (EDR) up to 4.4 and at an extrusion temperature (ET) above T_g, at 70 and 90°C. The higher the EDR, the longer the c-axis chain direction, the shorter the a and b axes and the smaller the unit-cell volume. In comparison with the conventional lattice parameters obtained by Bunn and Fisher, the highest elongation of the c axis is near 10%. These features imply that the lattice of stress-induced crystallites is far from the closest packing. Coextrudates made below the T_g of PET differ markedly from those made above T_g. Wide-angle X-ray diffraction (WAXD) patterns of PET extruded at 50°C (below T_g) even at high draw ratio exhibit small and/or imperfect crystallites. They appear much as a mesophase. The distance between macromolecular chains ranges from 3.2 to 5.4 Å. The shortest value in the mesophase approaches the interplanar crystal distance of 3.4 Å for the (100) crystal face, on which the benzene rings lie. The crystalline peak separation of the PET, WAXD curve has been evaluated to obtain absolute crystallinities and the content of mesophase and amorphous phase.     

1H nuclear magnetic resonance study of polyurethane prepolymers from toluene diisocyanate and polypropylene glycol

Polyurethane prepolymers prepared from toluene 2,4‐diisocyanate, toluene 2,6‐diisocyanate, and polypropylene glycol with a ratio between the isocyanate and hydroxyl groups equal to 2 were analyzed by ¹H nuclear magnetic resonance (NMR) spectroscopy in acetone‐d₆. Different temperatures and concentrations were used. Toluene 2,4‐dimethylurethane and toluene 2,6‐dimethylurethane were synthesized and used as model compounds to assign prepolymers signals. Measurements of spin–lattice relaxation time T₁ by “inversion recovery” experiments were carried out on toluene 2,4‐diisocyanate, toluene 2,6‐diisocyanate, toluene 2,4‐dimethylurethane, toluene 2,6‐dimethylurethane, and polyurethane prepolymers. Differences in T₁ times were used to interpret prepolymers spectra, by means of the strong observed effect on protons due to the presence of adjacent isocyanate groups. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 347–357, 2003     

Experiments and simulation of low-velocity impact characteristics on carbon fiber composite lattice core sandwich structures

Since composite sandwich structures are susceptible to low-velocity impact damage,a thorough characterization of the loading and damage process during impact is important.In the present paper,the low-velocity impact response of carbon fiber composites lattice structures is investigated by experimental and numerical methods.Impact tests on composite plates are performed using an instrumented drop-weight machine(Instron 9250HV)and a new damage mode is observed.A three-dimensional finite element model is built by ABAQUS/Explicit and user subroutine(VUMAT)to predict the peak loading and simulate the complicated damage problem.The numerical predictions are in good agreement with the experimental results.     

汉语语音文档检索中后验概率的索引方法

基于音节Lattice形式的语音识别结果来实现汉语语音文档检索,不但可以成功规避词表外词问题,而且Lattice这种多候选形式也能有效补偿识别错误对检索性能的影响.在基于音节Lattice的汉语语音文档检索研究中,针对已有索引方法的不足,提出了一种基于后验概率的索引方法,对向量空间模型进行改进,以音节和K步邻接音节对作为索引项,以它们在语音文档中的后验概率值作为索引项权重.检索实验表明,文中的方法更适用于基于音节Lattice的语音文档检索任务,各项改进都达到了预期效果.     

Application of ACO algorithm in protein structure prediction

The hydrophobic-polar (HP) lattice model is an important simplified model for studying protein folding. In this paper, we present an improved ACO algorithm for the protein structure prediction. In the algorithm, the "lone"ethod is applied to deal with the infeasible structures, and the "oint mutation and reconstruction"ethod is applied in local search phase. The empirical results show that the presented method is feasible and effective to solve the problem of protein structure prediction, and notable improvements in CPU time are obtained.     

一种格缩减辅助MIMO检测的非线性量化算法

针对格缩减辅助MIMO检测中,采用格缩减技术后导致星座畸变,引起变换域信号非线性联合量化复杂度高的问题,提出了一种排序反馈的非线性量化算法。该算法同时考虑了变换星座的边界和各元素之间的相关性,且根据量化误差的大小选择信号元素量化判决的顺序,依次量化判决信号的各个元素。仿真证明,基于该算法的格缩减辅助MIMO检测其性能要优于无排序反馈量化和逐元素独立量化的格缩减辅助MIMO检测,且能很好的逼近最大似然检测的性能,在平坦块衰落信道下,算法复杂度为多项式复杂度。     

索穹顶与单层网壳组合结构的模型试验研究

研究索穹顶与单层网壳组合的新型空间结构的受力性能.设计肋环型索穹顶与肋环双斜杆型单层网壳组合的结构,对其进行下部索穹顶预应力张拉试验以及结构在全跨和半跨荷载下的静力性能试验.根据试验结果对试验的计算模型进行修正,并将结构在全跨和半跨荷载下的试验实测数据与理论分析结果进行比较.结果表明,实测数据与理论分析之间差异较小,模型设计和试验方法合理,理论分析方法正确.修正的计算模型能准确反映结构的力学性能.