Structure of mixed beta-lactoglobulin/pectin adsorbed layers at air/water interfaces; a spectroscopy study

Based on earlier reported surface rheological behaviour two factors appeared to be important for the functional behaviour of mixed protein/polysaccharide adsorbed layers at air/water interfaces: (1) protein/polysaccharide mixing ratio and (2) formation history of the layers. In this study complexes of beta-lactoglobulin (positively charged at pH 4.5) and low methoxyl pectin (negatively charged) were formed at two mixing ratios, resulting in negatively charged and nearly neutral complexes. Neutron reflection showed that adsorption of negative complexes leads to more diffuse layers at the air/water interface than adsorption of neutral complexes. Besides (simultaneous) adsorption of protein/polysaccharide complexes, a mixed layer can also be formed by adsorption of (protein/)polysaccharide (complexes) to a pre-formed protein layer (sequential adsorption). Despite similar bulk concentrations, adsorbed layer density profiles of simultaneously and sequentially formed layers were persistently different, as illustrated by neutron reflection analysis. Time resolved fluorescence anisotropy showed that the mobility of protein molecules at an air/water interface is hampered by the presence of pectin. This hampered mobility of protein through a complex layer could account for differences observed in density profiles of simultaneously and sequentially formed layers. These insights substantiated the previously proposed organisations of the different adsorbed layers based on surface rheological data.     

解Drucker-Prager塑性问题的二阶锥互补法

基于经典弹塑性理论中多数屈服准则具有凸锥数学结构的事实,将在大规模计算中更具潜力的锥规划法引入弹塑性分析。考虑到弹塑性流动理论有关联与非关联之分,本文提出利用锥型互补法求解弹塑性问题。具体以Drucker-Prager弹塑性模型为例,首先利用最大塑性功耗散原理和圆锥对偶理论等工具,建立了弹塑性本构方程的等价二阶锥互补模型;然后,基于参变量变分原理和有限元技术,建立了弹塑性增量分析的二阶锥线性互补模型;最后,利用一类半光滑Newton算法求解。数值算例表明了本文方法的有效性。     

颗粒材料内部滑动变形局部化的离散元模拟

颗粒材料在加载过程中表现出非常复杂的变形性质.在微观尺度上,单个颗粒的运动、单个孔隙胞元内的变形都是非均匀的,但也不是完全随机、没有规律可循的,而是呈现一定结构性的分布,如微带、剪切带等.本文用基于孔隙胞元的离散元方法对颗粒体进行双轴加载数值试验,模拟了以滑动变形表征的变形局部化现象.数值结果发现,对应加载过程中的不同...     

冠脉支架纵向柔顺性数值模拟

柔顺性是冠脉支架重要的力学性能之一。本文针对一种具有非对称结构的冠脉支架,利用有限元方法深入研究与弯曲方向有关的支架柔顺性,在柔顺性数值模拟中使该支架获得较大的弯曲曲率并且考虑了接触因素。在一个周期结构内的多个弯曲方向上分别进行模拟,详细研究了支架抗弯刚度的各向异性。计算结果显示：在支架自接触现象发生前,支架的柔顺性表...     

Tandem queueing networks with neighbor blocking and back-offs

We introduce a novel class of tandem queueing networks which arise in modeling the congestion behavior of wireless multi-hop networks with distributed medium access control. These models provide valuable insight in how the network performance in terms of throughput depends on the back-off mechanism that governs the competition among neighboring nodes for access to the medium. The models fall at the interface between classical queueing networks and interacting particle systems, and give rise to high-dimensional stochastic processes that challenge existing methodologies. We present various open problems and conjectures, which are supported by partial results for special cases and limit regimes as well as simulation experiments.     

Dynamics of species in a model with two predators and one prey

In this paper, we study a predator-prey model which has one prey and two predators with Beddington-DeAngelis functional responses. Firstly, we establish a set of sufficient conditions for the permanence and extinction of species. Secondly, the periodicity of positive solutions is studied. Thirdly, by using Liapunov functions and the continuation theorem in coincidence degree theory, we show the global asymptotic stability of such solutions. Finally, we give some numerical examples to illustrate the behavior of the model.     

苯丙烯酸羟基香豆素酯类化合物的合成

咖啡酸的酚羟基不作保护,直接与氯化亚砜作用生成酰氯,再与羟基香豆素类化合物完成缩合反应合成了一系列苯丙烯酸羟基香豆素酯类化合物(1a～1j),其结构经1H NMR和元素分析表征,其中1a,1c～1e为新化合物.     

Copper(II) Triflate Catalyzed Amination of 1,3‐Dicarbonyl Compounds

A method to prepare α,α‐acyl amino acid derivatives efficiently by Cu(OTf)₂+1,10‐phenanthroline (1,10‐phen)‐catalyzed amination of 1,3‐dicarbonyl compounds with PhI?NSO₂Ar is described. The mechanism is thought to initially involve aziridination of the enolic form of the substrate, formed in situ through coordination to the Lewis acidic metal catalyst, by the putative copper–nitrene/imido species generated from the reaction of the metal catalyst with the iminoiodane source. Subsequent ring opening of the resultant aziridinol adduct under the Lewis acidic conditions then provided the α‐aminated product. The utility of this method was exemplified by the enantioselective synthesis of a precursor of 3‐styryl‐2‐benzoyl‐L ‐alanine.     

Conversion of methanol to hydrocarbons: how zeolite cavity and pore size controls product selectivity

Liquid hydrocarbon fuels play an essential part in the global energy chain, owing to their high energy density and easy transportability. Olefins play a similar role in the production of consumer goods. In a post-oil society, fuel and olefin production will rely on alternative carbon sources, such as biomass, coal, natural gas, and CO(2). The methanol-to-hydrocarbons (MTH) process is a key step in such routes, and can be tuned into production of gasoline-rich (methanol to gasoline; MTG) or olefin-rich (methanol to olefins; MTO) product mixtures by proper choice of catalyst and reaction conditions. This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts.     

Copper(II) triflate catalyzed amination and aziridination of 2-alkyl substituted 1,3-dicarbonyl compounds

A method to prepare α-acyl-β-amino acid and 2,2-diacyl aziridine derivatives efficiently from Cu(OTf)(2) + 1,10-phenanthroline (1,10-phen)-catalyzed amination and aziridination of 2-alkyl substituted 1,3-dicarbonyl compounds with PhI═NTs is described. By taking advantage of the orthogonal modes of reactivity of the substrate through slight modification of the reaction conditions, a divergence in product selectivity was observed. In the presence of 1.2 equiv of the iminoiodane, amination of the allylic C-H bond of the enolic form of the substrate, formed in situ through coordination to the Lewis acidic metal catalyst, was found to selectively occur and give the β-aminated adduct. On the other hand, increasing the amount of the nitrogen source from 1.2 to 2-3 equiv was discovered to result in preferential formal aziridination of the C-C bond of the 2-alkyl substituent of the starting material and formation of the aziridine product.