The Isothermal Melting Kinetics of Ultra-High Molecular Weight Polyethylene Crystals

The isothermal melting behaviors of ultra-high molecular weight polyethylene (UHMWPE) with different entangled states (i.e., nascent and melt-crystallized samples) are studied. For two kinds of UHMWPE samples, the result shows that the relative content of survived crystals (X_s) exponentially decreases with time and reaches a constant value. It is suggested that such a melting behavior is related to the observed nonlinear growth of crystals induced by the kinetically rejected entanglements accumulated at the growth front. Additionally, the exponential decay of X_s with time provides a characteristic melting time (τ) for the melting process. Compared to the melt-crystallized UHMWPE, the τ value of nascent UHMWPE is generally longer even in a higher temperature range, which is mainly because the former has a larger entanglement density difference. Furthermore, these observations demonstrate that UHMWPEs with different entangled states have an analogous melting mechanism since they exhibit a similar melting activation energy (≈1300 kJ mol⁻¹).     

基于材料边界概念的相变热传导变分原理及其数值计算

利用"材料边界"的概念,构造了伴有相变的热传导问题的泛函,建立了相变热传导问题的变分原理.在此基础上,采用有限元等效热容法求解温度场,并对相变单元的潜热、相界面位置的确定提出了处理方法.最后通过数值算例说明了方法的有效性.     

声呐信号处理中时域数字多波束成形的新方法

本文给出时域上数字多波束成形的一种新方法.它采用并行流水线结构,把数字滤波、升采样以及最优加权结合在一起,利用高速RAM和VLSI DSP芯片动态地构成一种高精度延时补偿的多波束数字信号处理系统.这种系统与传统波束成形比较,具有精度高,运算量少,编程容易,硬件结构紧凑的特点.文中给出设计的基本原理及硬件实现的方法。     

主被动拖线阵声呐中拖曳平台噪声和拖鱼噪声在浅海使用时的干扰特性

分析了主被动拖线阵声呐中拖曳平台的螺旋桨噪声和主动发射基阵(拖鱼)流噪声对被动接收基阵的干扰作用,指出在浅海声学环境下,直达波和海底、海面反射波会成为声呐系统的严重干扰。给出了拖曳平台和拖鱼在各种不同深度和缆长的情况下干扰源的入射角。从理论上计算了不同参数下干扰噪声对系统响应的影响,系统仿真结果可为声呐设计者抑制这种干扰提供途径。     

阵列指向性二次型约束稳健波束形成算法

提出了一种基于阵列指向性二次型约束的优化算法,以提高最小方差无畸变响应(MVDR)波束形成对方向矢量的稳健性。通过控制阵列波束指向附近的小区域的自适应波束图与期望波束图的加权平方误差,使波束主瓣区域内的信号畸变最小,同时保持了对约束区间外的干扰信号的抑制能力。数值结果表明:在理想阵形和阵形畸变情况下,无方位失配时,利用本文算法的阵列输出信号与干扰噪声比(SINR)与新近出现的球面约束稳健Capon方法相当,而存在方位失配时,本文算法均优于后者。     

Sn Anodes Protected by Intermetallic FeSn2 Layers for Long-lifespan Sodium-ion Batteries with High Initial Coulombic Efficiency of 93.8 %

With a theoretical capacity of 847 mAh g⁻¹, Sn has emerged as promising anode material for sodium-ion batteries (SIBs). However, enormous volume expansion and agglomeration of nano Sn lead to low Coulombic efficiency and poor cycling stability. Herein, an intermetallic FeSn₂ layer is designed via thermal reduction of polymer-Fe₂O₃ coated hollow SnO₂ spheres to construct a yolk-shell structured Sn/FeSn₂@C. The FeSn₂ layer can relieve internal stress, avoid the agglomeration of Sn to accelerate the Na⁺ transport, and enable fast electronic conduction, which endows quick electrochemical dynamics and long-term stability. As a result, the Sn/FeSn₂@C anode exhibits high initial Coulombic efficiency (ICE=93.8 %) and a high reversible capacity of 409 mAh g⁻¹ at 1 A g⁻¹ after 1500 cycles, corresponding to an 80 % capacity retention. In addition, NVP//Sn/FeSn₂@C sodium-ion full cell shows outstanding cycle stability (capacity retaining rate of 89.7 % after 200 cycles at 1 C).     

N,N,N＇,N＇-四苄基取代方块菁染料LB膜研究

方块菁染料在有机光导材料^[1,2]、有机太阳能存储^[2,3]、光记录^[4、有机光盘中红外吸收器^[4]以及光纤识别功能薄膜等领域中有着广泛应用前景.     

Experimental investigation of methane hydrate decomposition by depressurizing in porous media with 3-Dimension device

In order to simulate the behavior of gas hydrate formation and decomposition, a 3-Dimension experimental device was built, consisting of a high-pressure reactor with an inner diameter of 300 mm, effective height of 100 mm, and operation pressure of 16 MPa. Eight thermal resistances were mounted in the porous media at different depthes and radiuses to detect the temperature distribution during the hydrate formation/decomposition. To collect the pressure, temperature, and flux of gas production data, the Monitor and Control Generated System (MCGS) was used. Using this device, the formation and decomposition behavior of methane hydrate in the 20～40 mesh natural sand with salinity of 3.35 wt% was examined. It was found that the front of formation or decomposition of hydrate can be judged by the temperature distribution. The amount of hydrate formation can also be evaluated by the temperature change. During the hydrate decomposition process, the temperature curves indicated that the hydrate in the top and bottom of reactor dissociated earlier than in the inner. The hydrate decomposition front gradually moved from porous media surface to inner and kept a shape of column form, with different moving speed at different surface position. The proper decomposition pressure was also determined.     

Preparation and properties of chitosan nanocomposites with nanofillers of different dimensions

In this work, the chitosan ternary nanocomposites with two-dimensional (2D) clay platelets and one-dimensional (1D) CNTs have been successfully prepared by a simple solution-intercalation/mixing method in acid media. It was found that the thermal degradation temperature of chitosan (at 50% weight loss) could be only improved in about 20-30 °C by adding 3 wt% either clay or CNTs, however, almost 80 °C increase of degradation temperature could be achieved by adding 2 wt% clay and 1 wt% CNTs together. Dynamic mechanical measurement demonstrated an obviously improved storage modulus for chitosan/clay-CNTs than that for the corresponding binary chitosan/clay or chitosan/CNT nanocomposites with the same total filler content (3 wt%). For the solvent vapor permeation properties, a largely improved benzene vapor barrier property was observed only in chitosan/clay-CNT ternary nanocomposites and depended on the ratio of clay to CNTs. XRD, SEM and TEM results showed that both clay and CNTs could be well dispersed in the ternary nanocomposites with the nanotubes located around the clay platelets. FTIR showed an improved interaction between the fillers and chitosan by using both clay and CNTs. A much enhanced solid-like behavior was observed in the ternary nanocomposites, compared with the corresponding binary nanocomposites with the same total filler content, as indicated by rheological measurement. The unique synergistic effect of two-dimensional (2D) clay platelets and one-dimensional (1D) CNTs on the property enhancement could be tentatively understood as due to a formation of much jammed filler network with 1D CNTs and 2D clay platelets combined together. Our work demonstrates a good example for the preparation of high performance polymer nanocomposites by using nanofillers with different dimensions together.     

聚乳酸/聚氧化乙烯共混体系的热行为和力学性能及流变行为

采用熔融共混方法制备了聚乳酸与聚氧化乙烯的共混物.细致研究了重均分子量分别为2 kDa、10kDa1、00 kDa和600 kDa的聚氧化乙烯对聚乳酸的改性效果,并使用DSC、DMA及旋转流变仪等分析了共混物的相容性、热行为、力学性能和流变行为.结果表明,在聚氧化乙烯的组分含量不超过20 wt%的前提下,共混体系保持为完全相容体系,当聚氧化乙烯的分子量超过10 kDa时,其对聚乳酸的增塑效果,不随分子量增加而降低;增加聚氧化乙烯的分子量,可以提高材料的弹性模量和熔体强度.