Design and synthesis of a tribranched phenylethynyl‐terminated aryl ether compound and its use as a reactive diluent for PETI‐5

In this study, a tribranched, phenylethynyl‐terminated aryl ether compound (Tri‐PE‐PAEK) was synthesized. This novel star‐shaped compound exhibits a good combination of properties, such as a low melting temperature (252 °C) and good solubility in aprotic solvents, as well as a low melt viscosity (0.1 P at 280 °C). All these advantages make it a good candidate material for modern processing techniques such as resin infusion and resin transfer molding, which are the most favorable methodologies for current economical manufacturing of polymer matrix/carbon fiber composites. Furthermore, after undergoing thermal curing to yield a network at 370 °C for 1 h, a cured sample exhibited an unexpectedly higher glass transition temperature (370 °C), storage modulus retention above the glass transition temperature, and good thermal stability. In addition, this compound can be used as a reactive diluent for phenylethynyl‐terminated imide oligomer, which has the molecular weight of 5000 g/mol (PETI‐5) to reduce its viscosity and lower the minimum temperature of the minimum viscosity. Meanwhile, the toughness of a cured blended resin can be greatly increased with the addition of just 10% Tri‐PE‐PAEK to PETI‐5. Further loading levels of Tri‐PE‐PAEK in the blending would lead to a higher storage modulus and a higher mechanical strength without compromising the thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4844–4854, 2007     

Study of isolated cubic GaN quantum dots by low-temperature cathodoluminescence

We report single dot spectroscopy of cubic GaN/AlN self-assembled quantum dots. Typical linewidths of the zero-phonon line between 2 and 8 meV are observed and interpreted in terms of charge fluctuations around a given quantum dot. The phonon sideband contribution in this emission, even at low temperature, reveals the importance of the acoustic phonon broadening mechanism which controls the exciton dephasing and may impose the real limits to the optical properties of GaN single QDs emission.     

中能区40Ar+197Au反应中轻粒子的发射时间测量

本文报道了25MeV/u ⁴⁰Ar+¹⁹⁷Au反应中粒子-粒子关联函数的实验结果.利用三体弹道模型从关联函数提取了轻粒子发射时间.轻粒子的平均发射时间随粒子能量而变化,从低能时的约300fm/c下降至高能时的约100fm/c.     

A semilinear non-classical pseudodifferential boundary value problem in the Sobolev spaces

We study the solvability of a semilinear non-classical pseudodifferential boundary value problem in the Sobolev spaces H_l,p,q, 1<p<∞, depending on a complex parameter q. To cite this article: Y.V. Egorov et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Synergistic photocatalytic and Fenton-like degradation of MO by nanocatalyst La0.7Sr0.3Mn0.85Fe0.15O3

Journal of Nanoparticle Research - The studies on the utilisation of supercritical fluids (SCFs) in processing chemicals and materials have garnered significant attention in the past two decades....     

多个硅通孔引起的热应力对迁移率和阻止区的影响

本文主要讨论了多个硅通孔引起的热应力对迁移率和阻止区的影响, 得到了器件沟道沿[100]方向时, 硅通孔之间的角度和间距对电子迁移率和阻止区的影响. 设定两种阻止区区域, 即迁移率变化分别为5%和10%的区域, 且主要考虑相邻TSV之间的区域. 仿真结果表明: 当硅通孔和X轴所成角度为π/4时, 电子迁移率变化和阻止区区域最小, 但是可布置器件区域不规则, 不易于布局. 随着间距的增加, 电子迁移率变化和阻止区区域逐渐增大, 趋向于单个TSV的情况; 当角度为0 时, 电子迁移率变化和阻止区区域变大, 可布置器件区域为硅通孔围成的中心小区域上, 形状比较规则, 便于布局. 而且随着间距的增加, 电子迁移率变化和阻止区区域越来越小, 趋向于单个硅通孔的情况.     

ARCJET ABLATION EXPERIMENT TO SIMULATE THE CHELYABINSK ASTEROID ENTRY 1)

烧蚀是小行星极高速进入地球大气层后最重要的现象之一,在很大程度上决定了小行星的质量/尺寸变化、飞行轨迹、甚至光辐射特性. 为观测小行星材料在超高速高温流场中的烧蚀现象,在电弧加热器上开展了模拟Chelyabinsk小行星事件典型弹道状态(速度约5.6 km/s,高度17 km,流星体直径1 m)的烧蚀实验. 试件为钝头外形,头部半径20 mm,半锥角18$^\circ$. 作为对比,试件分别采用玄武岩和碳钢材料. 成功记录了清晰的烧蚀动态过程,观察到两种材料试件表面的熔融损失流动、以及玄武岩试件的蒸发喷射和崩裂剥落等现象,全程测得烧蚀气体发射光谱、试件实时外形变化、表面热图变化等数据. 分析结果显示了两种材料明显不同的烧蚀现象和质量损失机制：碳钢在高温气流冲击作用下溅射成大量微小液滴,跟随气流高速流失;玄武岩质量损失以熔融物剪切流动为主,并伴随少量块状剥落及蒸发喷射. 烧蚀时间为4 s,玄武岩和碳钢的质量损失及驻点后退量分别为37.9 g,72.7 g以及7.3 mm,13.1 mm,估算玄武岩材料的有效烧蚀焓约为2.6 MJ/kg,两种材料的烧蚀光谱测量组分与电镜能谱扫描结果吻合.     

Finite element equilibrium analysis of creep using the mean value of the equivalent shear modulus

Summary The paper deals with the nonlinear creep analysis using equilibrium finite elements. In adopting a concept of the mean value of the equivalent shear modulus, a direct iterative procedure is proposed with the minimum calculation in the modification of the global stiffness matrix. The difficulties due to the incompressibility of the creep flow are overcome by a numerical artifice where the hydrostatic stress component is considered as a Lagrange parameter. Some numerical results are shown and compared with the analytical method.

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Sommario La memoria tratta l'analisi dello scorrimento viscoso non lineare usando l'equilibrio di elementi finiti. Adottando il concetto di valore medio di un modulo di taglio equivalente, si propone un procedimento iterattivo diretto con il minimo di calcolo nella modificazione della matrice di rigidezza globale. Le difficoltà dovute alla incomprimibilità dello scorrimento viscoso sono superate con un artificio numerico in cui la componente di sollecitazione idro-statica è considerata come un parametro di Lagrange. Vengono mostrati alcuni risultati numerici, e confrontati con il metodo analitico.

     

空间技术用固体润滑的发展现状与展望

本文对固体润滑在宇宙飞行器、人造卫星、空间站及空间运载系统中的应用进行了概述,并就其在降低空间机械部件的摩擦磨损、延长使用寿命、提高材料的耐高低温性和对宇宙气体或真空及储存环境的适应性等方面的研究工作发展现状作了评述,还对其未来的发展前景作了展望,指出其研究工作很有可能朝着润滑剂专业化的方向发展,预料固体润滑剂的复合效应将在解决许多新的空间机械润滑问题上发挥有效作用。作者认为,近几十年来在空间技术用固体润滑方面取得了长足的进步,但也还有大量的问题需要研究。     

Crosslinked nanofibrillated cellulose: poly(acrylic acid) nanocomposite films; enhanced mechanical performance in aqueous environments

Nanofibrillated cellulose (NFC) was compounded with poly(acrylic acid) (PAA) via solvent casting. Nanocomposite films were thermally-crosslinked to allow the formation of ester bonds between NFC and PAA, as confirmed by ¹³CNMR and infrared spectroscopy. The network morphology of the cellulose nanofibrils was left intact by the introduction of PAA and crosslinking. Water absorption and swelling was diminished by the introduction of crosslinking, due to the reduced number of vacant hydroxyl and carboxyl groups available to interact with water molecules. Crosslinking with PAA increased the activation energy required for thermal degradation. PAA effectively reinforced NFC, increasing Young’s modulus, tensile strength and glass transition temperature. Crosslinking imparted restraints on segmental motion of polymer chains, further enhancing the thermomechanical properties and retaining elasticity. Wet-strength properties were enhanced due to the reduced hydrophilicity of crosslinked nanocomposite films.