Thermal Degradation of Adsorbed Bottle-Brush Macromolecules: When Do Strong Covalent Bonds Break Easily?

The scission kinetics of bottle-brush molecules in solution and on an adhesive substrate is modeled by means of Molecular Dynamics simulation with Langevin thermostat. Our macromolecules comprise a long flexible polymer backbone with L segments, consisting of breakable bonds, along with two side chains of length N, tethered to segments of the backbone with grafting density σ_g. In agreement with recent experiments and theoretical predictions, we find that bond cleavage is significantly enhanced on a strongly attractive substrate even though the chemical nature of the bonds remains thereby unchanged. Our simulation results indicate that the mean life time of covalent bonds decreases by more than an order of magnitude upon adsorption even for brush molecules with comparatively short side chains . The distribution of scission probability along the bonds of the backbone is found to change significantly when the length and/or the grafting density of the side chains are varied. The tension, experienced by the covalent bonds is found to grow steadily with increasing σ_g. The mean life time declines with growing contour length L as , and also with growing side chain length N. The probability distribution of fragment lengths at different times is compatible with experimental observations and reveals a two-stage (initially fast, then slow) process with different rates. The variation of the mean length L(t) of the fragments with elapsed time characterizes the thermal degradation process as a first order reaction.     

Biodegradation of Polyhydroxyalkanoate Films in Natural Environments

Summary: Biodegradation of film specimens from polyhydroxyalkanoates (PHAs) of two types – poly-3-hydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) – was analysed in different environments: tropical sea waters of the South China Sea (Nha Trang, Vietnam) and soils in the environs of Hanoi (Vietnam), Nha Trang (Vietnam) and Krasnoyarsk (Siberia, Russia). In seawater, the mass loss of the specimens of both types was almost equal. However, in tropical soils, PHB degraded quicker than PHBV. In the Siberian soil, the degradation rate of the PHBV was generally higher than that of PHBV. Analysis of molecular mass of PHA specimens showed its decreasing during biodegradation. In the tropical sea conditions, PHA degrading microorganisms were represented by bacteria of Enterobacter, Bacillus and Gracilibacillus genera. Among PHA degrading bacteria, Burkholderia, Alcaligenes, Bacillus, Mycobacterium and Streptomyces genera were identified in Vietnamese soils, and Variovorax, Stenotrophomonas, Acinetobacter, Pseudomonas, Bacillus and Xanthomonas genera in Siberian soils. Micromycetes of Gongronella, Paecilomyces, Penicillium and Trichoderma genera exhibited PHA degrading activity in Vietnamese soils, and Paecilomyces, Penicillium, Acremonium, Verticillium and Zygosporium genera – in Siberian soils.     

Cathodic and Anodic Electroactive Product from Acidic Cleavage of Cepradine

Abstract

The isolation and identification of a cathodic degradation product from cephradine after acidic hydrolysis in presence of 1% formaldehyde is reported. Also, the electroactivity of an anodic degradation product is described. However, this product has not been identified.

Each electroactive product exhibits a diffusion-controlled polarographic wave and their respectives limiting currents show a linear dependence with the cephradine concentration. These characteristics are applied for analytical pur poses.

Synthetic samples exhibit 99.4 and 100.4% recoveries for the cathodic and anodic product respectively.     

钛电极苯酚降解反应动力学的Monte Carlo模拟

应用Monte Carlo方法,结合化学反应随机过程理论,模拟钛电极上苯酚电催化氧化反应机理,研究苯酚降解时间、初始浓度、电极的催化性能及反应中间产物对降解过程的影响.结果表明:苯酚浓度随时间变化逐渐降低并渐趋稳定,苯酚初始浓度较高时降解速率快,具有较高催化性能的电极对降解第1步反应的影响较大,可有效减少中间产物停留时间,但控制第1步反应则对降解过程尤其是第2步反应的产物有明显影响,而控制第2步反应对降解过程影响很小.     

Prediction of elastic strain recovery of a formed steel sheet considering stiffness degradation

The aim of this work is to show first, how the springback of a steel sheet drawn part is affected by the stiffness degradation, as it results from the damage evolved during forming process, and second, to build a respective modeling approach to take this degradation into account. For the consideration of the orthotropic elastic properties degradation we develop an approach, based on the Mori-Tanaka theory, where damage is considered by inclusion of ellipsoidal cavities. The respective void shape evolution is proposed to be identified with the measurements of elastic modulus in two perpendicular directions during the uniaxial tensile test of a flat specimen at different loading stages. The proposed approach is coupled with the Gurson-Tvergaard-Needleman (GTN) plastic potential, though it could be substituted by almost any other continuum damage model. At the end the presented approach is experimentally validated by a simple springback test, developed by authors. A very good agreement between by calculation predicted and measured springback amount is observed.     

CCL非线性平衡吸附条件下填埋场渗滤液运移过程数值分析

采用Langmuir等温吸附方程表示黏土对渗滤液中某种污染物的非线性吸附,依据污染物在多孔介质中运移机理,建立了渗滤液在饱和多孔介质运移的一维数学模型。在考虑填埋场采用压实黏土衬里防渗层、垃圾生物降解生成污染物的特性、在填埋场下含有一定厚度含水层等实际情况下,采用有限差分法求解控制方程。通过参数对比计算与分析表明,与线性吸附相比,非线性吸附使得污染物的穿透能力增强,污染物浓度随时间变化曲线尖锐而狭窄、峰值浓度出现时间提前、曲线有尾部拖长现象。组合参数Sl对污染物运移影响较大,当Sl取值较大时,可降低污染物浓度,"挫峰"能力增强,污染物浓度随时间变化曲线表现出线性吸附性质。参数K1对污染物运移影响较参数Sl小。压实黏土衬里的渗透系数较低时,弥散控制污染物运移,且弥散系数较大和较小时,穿透曲线分别表现出线性吸附性质和非线性性质。     

混凝土的弹塑性损伤双面本构模型

针对混凝土材料拉压应变空间下损伤机制的不同,结合连续损伤力学和塑性理论建立了一个全新的本构模型。该模型中损伤和塑性变形的演变由应变空间的同一个非弹性曲面来控制,但对拉压应变空间中非弹性曲面的演变分别采用了随动强化法则和各向同性演化规律。计算结果表明,该模型能较好地描述混凝土材料在单轴及多轴单调加载和低周反复荷载下的典型非线性特征。     

水力空化与臭氧联合降解油田污水初步试验研究

针对油田开采后期,污水成分复杂且各种常规水处理方法都有其局限性的问题,提出了水力空化技术与臭氧氧化技术联合工艺处理污水的设想.利用臭氧氧化与空化效应,采用多孔孔板建立了水力空化污水处理系统,对油田现场污水进行了尝试性的试验研究.分别对水力空化和臭氧各自单独降解与两者联合降解水样COD的效果作了对比分析.结果表明,孔板入口压力在0.19MPa附近以及系统的进气量在70 L/h时COD的去除率相对较高;水力空化与臭氧联合降解的效果明显优于两者单独降解的效果;同时说明水力空化与臭氧在降解COD过程中存在互相强化的关系,孔板型空化水处理系统对降低油污水的COD含量具有一定的作用,但效率并不高,但对分析水力空化技术作为油田污水辅助处理技术的可行性,有一定参考价值.     

降解-CTMABr组装介-微孔分子筛的实验研究

通过考察实验影响因素以在最佳条件合成一种具有潜在应用价值的高水热稳定性材料。通过降解NaY分子筛形成其前驱体,以CTMABr（十六烷基三甲基溴化铵）为模板剂合成介-微孔分子筛。XRD和FT-IR表征结果表明材料的孔壁含有沸石结构单元,在750℃,100%水蒸汽中处理2h后介孔结构依然存在。研究认为在最佳条件下合成的材料是一种高水热稳定性的孔壁含有沸石结构单元的介孔材料,且与直接制备分子筛前驱体的过程相比,降解微孔分子筛制备前驱体有沸石回收和成本低廉两方面的优点。     

三氧化钨纳米片的制备及其光催化性质研究

利用化学沉淀法和水热法制备单斜相和正交相WO3纳米片,通过X射线衍射(XRD)、扫描电子显微镜(SEM)对合成产物进行表征.以合成的WO3光催化降解次甲基蓝染料为模型,研究光催化反应的影响因素,比较不同物相WO3的催化性能,测定单斜相和正交相WO3的带隙能.与正交相产物相比,单斜相WO3的带隙能较小,更容易发生电子吸光和跃迁,产生数量较多的电子-空穴对,因而具有较高的光催化活性.