Model of cold crystallization of uniaxially oriented poly(ethylene terephthalate) fibers

The differential scanning calorimeter heating curves of uniaxially oriented poly(ethylene terephthalate) (PET) fibers with three peaks were analyzed by using a newly proposed equation. The diffusion-controlled crystallization theory is suitable for describing cold crystallization of uniaxially oriented PET fibers. A crystallization model was proposed based on the kinetic parameters obtained. The model embraces the three sub-processes of crystallization corresponding to different growth geometries. The first sub-process corresponds to the nucleation of ordered molecular segments or the radial growth of preformed nucleus, resulting in the shorter bundle-like entities. The second sub-process corresponds to further growth of the bundle-like crystallites along chain direction, resulting in the longer bundle-like entities. The third sub-process corresponds to the three-dimensional growth of crystallites relating to the random segments, resulting in the spherical entities.     

基于攻击树模型的数传电台传输安全性评估

数传电台在数据采集与监视控制系统中广泛应用,其传输安全也受到越来越大的挑战。文章为了系统分析评估数据采集与监视控制系统中数传电台传输的安全性,针对数传电台传输阶段可能存在的风险,采用攻击树建模方法,对传统攻击树进行改进,重新定义了攻击节点,量化了叶子节点的攻击风险,建立了以威胁数据采集与监视控制系统安全为攻击目标的攻击树模型,在攻击树的基础上可以直观地反映各种可能的攻击图景。并根据攻击树计算出了各攻击图景发生的概率,根据多攻击图景考虑系统总的安全性。最后利用安全性灵敏度,定量分析各攻击方式发生概率变化对系统安全性的影响,找出对系统安全性影响较大的关键方式,提出提高系统安全水平的措施。文中攻击树模型可以用于评估系统风险,区分不同攻击方式对系统的不同安全威胁程度,由此为决策者采取相应的数传电台传输保护措施提供依据。     

一种基于PE文件的信息隐藏方法的研究与实现

通过研究PE文件的格式,分析了目前存在的冗余空间进行信息隐藏的不足,利用PE文件资源结构提出一种基于PE文件的信息隐藏方法,通过将信息隐藏于PE文件资源节中,隐藏后PE文件的大小没有改变,而且也不破坏原PE文件的执行,最终达到将信息分散隐藏的目的,提高信息的隐蔽性.     

MBS树脂合成技术的中试研究(Ⅲ)MBS胶乳的凝聚

阐述了聚合物乳液的凝聚机理和MBS接枝胶乳的凝聚工艺,在MBS胶乳凝聚小试研究和MBS接枝胶乳中试研究的基础上进行了MBS接枝胶乳凝聚的中试研究,着重研究了凝聚剂种类、用量和加料方式以及凝聚温度、水胶比等对MBS粉料堆密度和粒度分布的影响,确定了MBS胶乳的凝聚工艺,为5 000 t/a MBS树脂生产装置提供了设计依据.     

纳米ZSM-5沸石上丁烯芳构化反应

用小型固定床加压反应器研究了液化石油气（C4 LPG）中的丁烯在纳米ZSM-5型催化剂DLG-1上的低温芳构化反应，重点考察了原料中二烯烃和碱性氮杂质，以及反应温度、压力和C4 LPG进料重量空速（WHSV LPG）条件对催化剂芳构化反应活性及稳定性的影响。结果表明：原料中的二烯烃和碱性氮杂质都能加速催化剂失活，其中碱性氮的失活作用比二烯烃大。反应温度、压力和进料重量空速都对催化剂性能有显著影响，最佳反应条件为450℃、2. 0 MPa和WHSV LPG=0. 83 h-1。反应温度、压力和进料空速过高都会导致催化剂积炭失活速度加快。     

New liquid membrane technology for simultaneous extraction and stripping of copper(II) from wastewater

In this paper, a new liquid membrane technique, hollow fiber renewal liquid membrane (HFRLM), is presented, which is based on the surface renewal theory, and integrates the advantages of fiber membrane extraction, liquid film permeation and other liquid membrane processes. The results from the system of CuSO₄+D2EHPA in kerosene+HCl show that the HFRLM process is very stable. The liquid membrane is renewed constantly during the process, the direct contact of organic droplets and aqueous phase provides large mass transfer area. These effects can significantly reduce the mass transfer resistance in the lumen side. Then the mixture of feed phase and organic phase flowing through the lumen side gives a higher mass transfer rate than that of stripping phase and organic phase, because the aqueous layer diffusion of feed phase is the rate-controlling step. The overall mass transfer coefficient increases with increasing flow rates and D2EHPA concentration in the organic phase, and with decreasing initial copper concentration in the feed phase. The overall mass transfer coefficient also increases with increasing pH in the feed phase, and reaches a maximum value at pH of 4.44, then decreases. Also, there is a favorable w/o volume ratio of 20:1 to 30:1 for this process. Compared with hollow fiber supported liquid membrane and hollow fiber membrane extraction processes, HFRLM process has a high mass transfer rate. Mathematical model for the HFRLM process based on the surface renewal theory is developed. The calculated results are in good agreement with experimental results under the conditions studied.     

A novel method of utilizing the biomass resource: Rapid liquefaction of wheat straw and preparation of biodegradable polyurethane foam (PUF)

In the paper, wheat straw was rapidly liquefied in the mild condition. The optimum liquefaction effect was obtained at steam-explosion pre-treatment of wheat straw, liquefaction temperature of 140 °C, solvent/wheat straw ratio of 6:1, glycol (EG):glycerol = 5, sulfuric acid of 5%, and wheat straw of water content of 150%. During the liquefaction, cellulose, semi-cellulose and lignin are decomposed, which results in changes of hydroxyl value, acid value, viscosity and weight-average molecular weight of the reaction system. The liquefaction product was used to prepare polyurethane foam. Compared with the normal PUF, the foam had similar mechanical properties and better water absorption and biodegradability.     

Properties and pervaporation separation of hydroxyl‐terminated polybutadiene‐based polyurethane/poly(methyl metharcylate) interpenetrating networks membranes

Hydroxyl‐terminated polybutadiene (HTPB), 4,4′‐dicyclohexyl methane diiscyanate (H₁₂MDI), and 1,4‐butane diol are used to synthesize polyurethane (PU) solutions by two‐stage process. Interpenetrating networks (IPNs) of HTPB‐based PU and poly(methyl methacrylate) (PMMA) with HTPB/MMA (wt/wt % ratio) = 2.0, 1.5, 1.0, 1.5, 0.8, and 0.6, which are designated as IPN1 to IPN5, respectively, are synthesized by sequential polymerization technique. Thermal properties, tensile strength, and contact angle of membranes increase with the increase of MMA content, while the elongation of membranes show the reverse trend. Characterization of membranes are investigated by C?C/C?O absorption ratio and infrared absorption frequency shiftment. These PU and IPN membranes are used for the separation of ethanol/water and isopropanol/water solution by pervaporation test. IPN3 membrane possesses the largest pervaporation permeability and the separation factor. The pervaporation results of ethanol/water feed has the same trend as that of isopropyl alcohol (IPA)/water solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

双模板法CeO2/g-C3N4形貌结构特征及湿式催化性能

利用微波辅助双模板法、软模板法制备了一系列的CeO₂/g-C₃N₄复合催化材料,通过XRD、N₂吸附-脱附、XPS、SEM和TEM等方式对材料进行表征,并对其湿式催化性能进行研究。结果表明,双模板法制备的D-CeO₂/g-C₃N₄复合材料表现出立方相CeO₂和层叠g-C₃N₄的特征,比表面积和孔径较大,属于介孔结构,表面存在Ce^₃₊和Ce^₄₊,有利于氧空位的形成。加入1 g嵌段共聚物 F127,使用无水乙醇溶液为溶剂,调节混合液呈碱性,微波辐射反应120 min后得到的D-CeO₂/g-C₃N₄(7.5)样品,结构完整均匀,具有最佳形貌特征。控制反应温度75 ℃,D-CeO₂/g-C₃N₄(7.5)投加0.7 g,H₂O₂投加 0.5 mL,初始pH值为5时,100 mg/L的苯酚溶液COD去除率可达80%以上。 D-CeO₂/g-C₃N₄(7.5) 复合催化材料使用五次以后仍可达60%以上的催化降解效果。     

像素聚类改进二进制描述子鲁棒性

目标：本文通过挖掘图像局部区域特征信息,提出了一种鲁棒性更高的二进制描述子。针对BRIEF关于旋转和视角变化鲁棒性差的问题,本文通过图像补丁分层处理、增加关键点图像补丁个数来捕获更多的局部特征信息,对BRIEF描述子改进。方法：首先,根据灰度序列对补丁内所有像素点分类,像素的一个聚类形成了一个亚补丁,然后在每个亚图像补丁上进行类似BRIEF的随机测试。其次,由于原图像补丁大小、尺度大小影响补丁的像素点成分,从而影响像素聚类的效果,所以在原图像关键点周围分割出多个不同大小的图像补丁,或是将原图像补丁根据尺度金字塔确定几个尺度大小不同的补丁,然后再对图像补丁进行分层、测试。所构建的描述子不仅包含了补丁像素的灰度比较信息,而且包含了灰度排序信息和像素群聚信息,提高了描述子的鲁棒性。结果：通过性能对比实验,发现所提的描述子的性能提高了,而且好于对比的浮点描述子。结论：所以挖掘图像补丁的特征信息能提高二进制描述子的鲁棒性。