Rapid mechanical deformation of poly(ethylene terephthalate) fibers at temperatures above the glass transition

The mechanical properties of poly(ethylene terephthalate) (PET) fibers at temperatures above the glass transition are investigated by means of a specially constructed device. Measurements of the deformation rate and of the “dynamic” stress-strain curves of the fibers are performed in nearly isothermal regime (after initial rapid heating) in a temperature interval 100–200°C. The results reported in the present work demonstrate that the high-temperature mechanical characteristics of rapidly crystallizing polymers can be deduced to a satisfactory precision, while keeping the crystallinity development at low level. Our investigations indicate that if the high-temperature deformation is sufficiently fast, the polymer behavior is similar to the deformation at sub-T_g temperatures. Based on this similarity, a qualitative model of the deformation in the high-temperature region is proposed. The proposed model is fundamentally equivalent to the models describing mechanical deformation of glassy polymers at temperatures below the glass transition. ©1995 John Wiley & Sons, Inc.     

Effects of hydrogen at high temperature on ZnAl2O4 and Sn−ZnAl2O4

ZnAl₂O₄ and Sn?ZnAl₂O₄ were synthesized by coprecipitation, sol-gel and impregnation methods. These materials were calcined and treated in H₂ at 1073 K. Thermal analysis (DTA and TG), nitrogen physisorption (BET method), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used as characterization techniques. H₂ treatment promoted Al_xZn_y crystallization in the coprecipitated and impregnated samples. When tin was added to zinc aluminate, the tin acted as a protective shell against high-temperature reduction, independently of the preparation technique.     

The attenuation of oscillatory thermocapillary convection in the oxide melt by a transverse magnetic field

The effect of a transverse magnetic field on the oscillatory thermocapillary convection in the NaBi(WO4)2 melt was studied by using the in-situ observation system. The oscillation was attenuated when the 60 mT magnetic field was applied, as shown by the decrease in the amplitude and the frequency. Furthermore, the oscillation under smaller temperature difference was stabilized after the magnetic field was applied. The magnetic effect could be due to the Lorentz force generated by the interaction between motional ions and the vertical magnetic field. The ionic conductivities were measured to demonstrate the effect of the magnetic field. The solid ionic electrical conductivity increases with the temperature rise, and the melt ionic electrical conductivity was measured to be about 2.0×10-4 Ω-1·cm-1. Experimental results manifest that the effect of the magnetic field on anions and cations in the melt makes the flow change to the direction normal to the applied field, so the flow is more orderly and the oscillation is suppressed.     

精铸热锻模具钢的合金成分设计及其高温磨损性能研究

探讨了精铸热锻模具钢合金化设计的依据和合金成分设计较佳的参数范围,开发出高耐磨精铸热锻模具钢,采用MG-2000型销-盘式高温摩擦磨损试验机在干摩擦、400℃条件下,研究了精铸热锻模具钢的高温磨损性能.结果表明:合金成分设计参数应控制为V/C在3.00～3.60之间,C余在0.10～0.25之间,Cr/Cr Mo在0.68～0.85之间,Cr/C余＞16.60,Mo/C余＞16.00;所研制的精铸热锻模具钢的淬火组织为马贝复相组织,回火后碳化物以弥散析出的V4C3为主,含有少量Cr和Mo的碳化物,Cr、Mo主要固溶于α-Fe中,以保证精铸热锻模具钢的热强性和热稳定性;精铸模具钢具有较好的高温耐磨性,磨损率明显低于H13钢.其磨损机制为氧化磨损,即在精铸热锻模具钢的高温磨损表面形成Fe3O4和Fe2O3.     

Reverse Engineering Analysis of the High-Temperature Reversible Oligomerization and Amyloidogenicity of PSD95-PDZ3

PSD95-PDZ3, the third PDZ domain of the post-synaptic density-95 protein (MW 11 kDa), undergoes a peculiar three-state thermal denaturation (N ↔ I_n ↔ D) and is amyloidogenic. PSD95-PDZ3 in the intermediate state (I) is reversibly oligomerized (RO: Reversible oligomerization). We previously reported a point mutation (F340A) that inhibits both ROs and amyloidogenesis and constructed the PDZ3-F340A variant. Here, we “reverse engineered” PDZ3-F340A for inducing high-temperature RO and amyloidogenesis. We produced three variants (R309L, E310L, and N326L), where we individually mutated hydrophilic residues exposed at the surface of the monomeric PDZ3-F340A but buried in the tetrameric crystal structure to a hydrophobic leucine. Differential scanning calorimetry indicated that two of the designed variants (PDZ3-F340A/R309L and E310L) denatured according to the two-state model. On the other hand, PDZ3-F340A/N326L denatured according to a three-state model and produced high-temperature ROs. The secondary structures of PDZ3-F340A/N326L and PDZ3-wt in the RO state were unfolded according to circular dichroism and differential scanning calorimetry. Furthermore, PDZ3-F340A/N326L was amyloidogenic as assessed by Thioflavin T fluorescence. Altogether, these results demonstrate that a single amino acid mutation can trigger the formation of high-temperature RO and concurrent amyloidogenesis.     

单晶光纤制备及高温传感器研究进展

单晶光纤(single-crystal fiber),是一种纤维形态的晶体材料,凭借优异的物理和化学性能以及大长径比的结构特点在国防及民生领域都有着广泛的应用前景。随着导模法、激光加热基座法以及微下拉法等生长技术的日渐成熟,单晶光纤迎来了科学研究和应用发展的黄金时期,其材料种类以及应用方向均呈现多元化发展态势,其中面向高温传感领域的高熔点氧化物单晶光纤凭借其耐高温、抗氧化、结构紧凑等特点在强氧化、强辐射、强腐蚀、强电磁干扰等极端环境中展现出了巨大的应用潜力。近年来,研究者们不断将光学、声学等传感技术与单晶光纤介质相结合,在保持传感器结构灵活性的基础上,拓宽了常规玻璃光纤传感器的使用温度,同时弥补了热电偶等传统接触式测温技术在恶劣环境中寿命较低的缺陷。本文以单晶光纤的制备技术为出发点,回顾了单晶光纤的发展历史,分析了单晶光纤三种主要制备方法的技术特点及发展现状。同时,总结了单晶光纤在高温传感领域的主要研究成果,展望了单晶光纤高温传感技术的应用前景。     

渐近非对称陀螺分子H122C16O的高温光谱

在直接计算分子配分函数的基础上,将无转动跃迁偶极矩平方近似为一常数,计算了渐近非对称陀螺分子H¹²₂C¹⁶O 100000-000000跃迁在中等温度和高温下的线强度. 计算结果在500K时与HITRAN数据库的结果吻合相当好.在温度高达3000K时与HITRAN数据库的结果仍符合较好,表明分子配分函数和线强度的高温计算是可靠的.在此基础上,进一步计算了渐近非对称陀螺分子H¹²₂C¹⁶O 100000-000000跃迁带在极端高温4000和5000K的线强度并报道其模拟光谱.计算结果对大气分子高温光谱的实验测量和理论研究均有一定的参考价值. 关键词： 高温光谱 渐近非对称陀螺分子 配分函数 甲醛     

铁基超导体中的反铁磁序和自旋动力学

类似于其他非常规超导材料,铁基高温超导电性通常出现在静态长程反铁磁序被抑制之后,并且强烈的自旋涨落始终与超导电性相伴相生,因此理解磁性相互作用是建立铁基超导微观机理的重要前提.中子散射作为研究凝聚态物质中磁性相互作用的有力工具,在揭示铁基超导电性的磁性起源方面起到了关键作用.本文系统总结了近十年来铁基超导材料的中子散射研究结果,包括铁基超导材料中的静态磁结构、磁性相变、动态磁激发、电子向列相等,并探讨它们与超导电性之间的关系.     

铋层状结构压电陶瓷及敏感元件高温特性研究

介绍了铋层状结构压电陶瓷的特点和改性试验所获得的一些结果。针对压电活性低,采取A位复合置换方式对CBT(CaBi4Ti4O15)基材料进行改性研究,特别研究了改性后材料的高温特性,结果表明,改性材料的压电性能、居里温度、高温电阻率等参数有大的改善,qC达800℃以上,d33达18 pC/N以上,在500℃时体电阻率大于106Ω·cm,高温敏感元件在430℃连续保温170 h,绝缘电阻大于1.5 MΩ。     

高功率单高阶模倒置表面浮雕结构垂直腔面发射激光器

提出并研究了一种带有环形出光孔的倒置表面浮雕结构垂直腔面发射激光器.该器件最突出的结构特点在于,支持稳定的单高阶横向模式激射.在输入电流为六倍阈值电流时,输出功率高达9.8 m W,边模抑制比将近30 d B.在外界为360 K高温时,输出功率仍可达4 m W.且其远场表现出的高斯光束发散角较小.