双螺杆冻胶纺丝法制备有机液体吸附功能纤维及其性能研究

在聚合釜中合成了BMA/HEMA二元共聚树脂,利用双螺杆纺丝机、采用冻胶纺丝技术制备了有机液体吸附功能纤维,研究了单体投料比中HEMA质量分数对纤维各种溶胀行为的影响,利用动态热机械分析仪(DMA)对纤维的动态力学性能进行了研究,同时利用环境扫描电子显微镜(SEM)观察了纤维的表面和断面形貌.结果表明,HEMA引入大分子后,所得纤维对有机液体甲苯、三氯乙烯具有吸附功能,且吸附过程符合sigmoidal模型中的Hill方程;随HEMA质量分数的增加,纤维对甲苯和三氯乙烯的饱和吸附量增大,对甲苯和三氯乙烯的最大吸附量分别可达10g/g和21g/g;随HEMA质量分数的增加,纤维剩余率增加的同时,使纤维对甲苯和三氯乙烯的握持能力增强;HEMA质量分数对纤维动态力学性能有突出影响,特别是链段运动受其影响更为明显;HEMA质量分数对纤维表面和断面形貌均有显著影响,特别是当HEMA质量分数为15wt%时,所得纤维表面出现了许多空洞,其断面存在许多尺寸不均的空洞.     

Synthesis and aggregation behavior of <Emphasis Type="Italic">N</Emphasis>-succinyl-o-carboxymethylchitosan in aqueous solutions

A simple and novel method was developed to successfully synthesize N-succinyl-O-carboxymethylchitosan (NSOCMCS) using N-acylation of chitosan with succinic anhydride. The NSOCMCS structure was characterized by Fourier transform infrared and ¹H nuclear magnetic resonance. The aggregation behaviors of NSOCMCS were studied using fluorescence spectroscopy, dynamic light scattering, and atomic force microscopy techniques. The critical aggregation concentration of NSOCMCS in water was determined to be 0.2–0.3 mg/ml. The apparent hydrodynamic radium of an NSOCMCS aggregate was dependent on the concentration. The aggregates demonstrated a much swollen association conformation in aqueous solution. The possible aggregation mechanisms for the NSOCMCS in water are discussed. Moreover, a driving force to form an open aggregation morphology was revealed in this study. Aggregation behaviors are important physicochemical properties of NSOCMCS, which impact the potential application in the biomedical field.     

Spectroscopic studies on 2,3,4,5-tetraphenylpyrylium salts with and without silver (I)-bridged structures

Two novel phenylated pyrylium compounds, silver (I)-bridged 2,3,4,5-tetraphenylpyrylium perchlorate (P1) and its silver (I)-free pyrylium ligand (P2) were prepared from 1,2,3,4-tetraphenylcyclopentadiene to examine their spectroscopic behaviors. The UV/vis absorption and fluorescent emission spectra of P1 and P2, measured in three solvents (acetonitrile, dichloromethane and toluene), reveal that the photophysical behaviors are closely related to silver (I) fragment, and strongly dependent on solvent polarity. In polar acetonitrile, P1 displays longer absorption wavelength and much lower fluorescent emission intensity than P2, although they exhibit much similarity in shape. In contrast, in nonpolar toluene, while P2 shows an apparent absorption band at 338 nm, P1 displays a tail-like line without absorption band observed. All the spectra obtained indicate a better coplanarity and a stronger intra-molecular charge transfer in P1 due to the effect of silver (I) fragment. Additionally, the 1H NMR spectra of P1 and P2, which were recorded under the same conditions, indicate that the silver (I) fragment reinforces pyrylium ring's capacity to localize the formal positive charge within the heterocyclic ring.     

Polymorphism of Acrylic and Methacrylic Acid Esters Containing Long Fluorocarbon Chains and Their Polymerizability

The molecular aggregation of acrylic and methacrylic acid esters containing long-fluorocarbon chains: 2-(perfluoroalkyl)ethyl acrylate (FF_nEA) and 2-(perfluoroalkyl)ethyl methacrylate (FF_nEMA) (F(CF₂)_nCH₂CH₂OCOC(X)=CH₂, where X=H, CH₃ and n=6, 8, 10) was investigated by differential scanning calorimetry (DSC) and temperature controlled X-ray powder diffraction measurement. These compounds exhibited some characteristic polymorphic behaviors depending on the length of fluorocarbon chain and the -position methyl group. The solid-state polymerization by -ray irradiation was studied for these compounds in the various crystal forms. In the solid-state polymerization, highest polymerizability was observed in the crystal form that exists in the highest temperature region for each compound.This revised version was published online in November 2005 with corrections to the Cover Date.     

Electroactive shape memory cyanate/polybutadiene epoxy composites filled with carbon black

Electroactive shape memory composites were synthesized using polybutadiene epoxy(PBEP) and bisphenol A type cyanate ester(BACE) filled with different contents of carbon black(CB). Dynamic mechanical analysis(DMA), scanning electron microscopy(SEM), electrical performance and electroactive shape memory behavior were systematically investigated. It is found that the volume resistivity decreased due to excellent electrical conductivity of CB, in turn resulting in good electroactive shape memory properties. The content of CB and applied voltage had significant influence on electroactive shape memory effect of developed BACE/PBEP/CB composites. Shape recovery can be observed within a few seconds with the CB content of 5 wt% and voltage of 60 V. Shape recovery time decreased with increasing content of CB and voltage. The infrared thermometer revealed that the temperature rises above the glass transition temperature faster with the increase of voltage and the decrease of resistance.     

Anodic voltammetric behaviors of methotrexate at a glassy carbon electrode and its determination in spiked human urine

The anodic voltammetric behavior of methotrexate was studied at glassy carbon electrode in acetate buffer (pH = 3.6) solution using cyclic, square-wave voltammetric and chronocoulometric techniques. The oxidation of methotrexate is an irreversible diffusion-controlled process. The oxidation mechanism was proposed and discussed in this work. The dependence of the current on pH, the concentration and nature of buffer, and instrumental parameters were investigated to optimize the experimental conditions for the determination of methotrexate. It was found that in the range of 8.0 × 10⁻⁷–2.0 × 10⁻⁵ mol/L, the currents measured by square-wave voltammetry presented a good linear property as a function of the concentrations of methotrexate. In addition, validation parameters, such as reproducibility, sensitivity and recovery were evaluated as well. The proposed method was also successfully applied for the determination of methotrexate in diluted human urine with good satisfactory.     

RUIN PROBABILITY IN A SEMI-MARKOV RISK MODEL WITH CONSTANT INTEREST FORCE AND HEAVY-TAILED CLAIMS

In the present paper, we consider a kind of semi-Markov risk model （SMRM） with constant interest force and heavy-tailed claims~ in which the claim rates and sizes are conditionally independent, both fluctuating according to the state of the risk business. First, we derive a matrix integro-differential equation satisfied by the survival probabilities. Second, we analyze the asymptotic behaviors of ruin probabilities in a two-state SMRM with special claim amounts. It is shown that the asymptotic behaviors of ruin probabilities depend only on the state 2 with heavy-tailed claim amounts, not on the state 1 with exponential claim sizes.     

一类具有无穷边界值的二次奇摄动边值问题

研究一类具有无穷边界值的二次奇摄动Robin边值问题解的存在性与解的渐进行为,重点关注边界值的奇异程度对解的边界层行为的影响;同时将所得的结果与Chang及Howes的结果(带正常边界值)进行比较.研究表明:(1)当边界值大小为O(1/)时,得到的边界层大小为O( ln ),这比Chang及Howes带正常边界值的情形提高了O(ln )量级;(2)增大边界值的奇性至O(1/ r),这里r >1,边界层大小的量级不变,依然为O( ln );(3)若要使得边界层大小为O(1),则边界值的大小需为O(e?1/).最后给出一个算例验证得到的结果.     

腹板开孔标准轻钢龙骨力学性能比较研究

腹板开孔轻钢龙骨作为一种有效的节能构件而被广泛应用于寒冷地区的轻钢龙骨复合住宅体系中.采用ANSYS非线性有限元方法系统分析了在轴压、弯矩、压弯基本荷载作用下,腹板开孔对标准轻钢龙骨的屈曲模式、变形、截面应力、承载力等方面力学性能的影响规律,给出龙骨腹板孔洞的合理取值范围.结果表明,常用孔洞参数范围内腹板开孔对龙骨承载力的降低幅度可以控制在10%以内;腹板开孔后龙骨整体变形能力降低,峰值应变相应减小,使龙骨的初始刚度略微增大.腹板孔洞长度是影响龙骨力学性能的重要参数,随孔洞长度增加,龙骨承载力下降,延性变差.     

剖面隐马氏模型训练算法的改进

利用剖面隐马氏模型获得多序列联配，一般需要经过初始化、训练、联配三个过程．然而，目前广泛采用的Baum—welch训练算法假设各条可观察序列互相独立，这与实际情况有所不符．本文对剖面隐马氏模型，给出可观察序列在互相不独立情况下的改进Baum—wlelch算法，在可观察序列两种特殊情况下（互相独立和一致依赖），得到了改进算法的具体表达式，讨论了一般情况下权重的选取方法．最后通过一个具体的蛋白质家族的多序列联配来说明改进算法的效果．