A consistency analysis for the numerical solution of boundary integral equations

A method is presented for assessing the nature of the error incurred in the boundary integral equation (BIE) solution of both harmonic and biharmonic boundary value problems (BVPs). It is shown to what order of accuracy the governing partial differential equation is actually represented by the approximating numerical scheme, and how raising the order of the boundary ‘shape functions’ affects this representation. The effect of varying both the magnitude and the aspect ratio of the solution domain is investigated; it is found that the present technique may suggest an optimum nondimensional scaling for the BIE solution of a particular harmonic or biharmonic BVP.     

Significant improving H+/VO2+ permselectivity of Nafion membrane by modification with PDDA in aqueous isopropanol

The modification of Nafion® membranes with poly(diallyldimethylammonium chloride) (PDDA) in aqueous solutions of isopropanol has been investigated. A remarkable decrease in vanadyl ion permeability (by 3.5 orders of magnitude), accompanied by a decrease in proton conductivity sixfold at most, was found for Nafion membranes modified in 30–35 wt% isopropanol solutions providing a high swelling of the membranes. The Bradford reagent has been used for the detection of PDDA on the membrane surface.     

Copolyesteramides—II. Anionic copolymers of ε-caprolactam with ε-caprolactone. Preparation and general properties

The N-sodiocaprolactam-catalysed anionic polymerisation of ε-caprolactam is activated by ε-caprolactone which itself acts as a comonomer, yielding copolyesteramides. At lower temperatures and lower catalyst concentrations, copolymerisation of the lactone is favoured over that of lactam; higher temperatures, higher catalyst concentrations and longer reaction times cause a more equal incorporation of the two comonomers giving products with molecular weights in the order of 10⁴ and with NH(CH₂)₅CO and O(CH₂)₅CO unit contents approximating to those in the reactant feeds. The T_g's of the products lie between those of the homopolymer extremes but the T_m vs composition relationship displays a shallow eutectic minimum at ca 20% NH(CH₂)₅CO group content and, for given NH(CH₂)₅CO group contents, is sensitive to changes in the technique of copolymerisation. Alternatingly-sequenced NH(CH₂)₅CO/O(CH₂)₅CO copolymers prepared by polycondensation also differ from anionic copolymers of similar sub-unit stoichiometry. The property differences imply differences of chain-sequential order and hence complexity in the mechanism of the anionic copolymerisation.     

Copolyesteramides—III. Anionic copolymers of ε-caprolactam with ε-caprolactone. Crystalline character and mechanical properties

The crystalline character of anionic copolymers of ε-caprolactam with ε-caprolactone and of some alternatingly-sequenced analogues has been studied and investigations made of the mechanical and dynamic mechanical properties of the anionic copolymers. The anionic copolymers are crystalline over the whole range of compositions. Depending on the proportions of NH(CH₂)₅CO and O(CH₂)₅CO units and the thermal history of the copolymers, the crystalline phases present are either wholly of polyamide type or composed of co-existing and mutually incompatible polyamide and polyester entities. However, the constituents appear to be miscible in the amorphous phase. The mechanical properties of the copolymers (like their crystalline melting temperatures) change discontinuously with composition, showing minima in the values of initial modulus, yield stress and breaking stress at ca 25–40% amide-group content where dual crystallinity exists. In addition to their variation with composition, the properties are also affected by changes in the procedure of anionic copolymerisation.     

我国高原低氧训练研究的文献计量规律分析

通过中国知网期刊全文数据库(CNKI)检索2000～2011年我国高原低氧训练研究论文971篇. 采用信息计量分析, 证实了幂函数符合其文献增长规律、洛特卡定律符合作者分布规律、布拉德福定律符合机构和期刊分布规律, 且布鲁克斯公式和Logistic模型分别适用于表征机构分布曲线和期刊分布曲线.     

Effect of filler incorporation route on the properties of polysulfone–silver nanocomposite membranes of different porosities

Flat sheet porous polysulfone–silver nanocomposite membranes were synthesized by the wet phase inversion process. The effects of casting mixture composition and nanoparticle incorporation route on the morphological and separation properties of prepared membranes were studied by comparing nanocomposites of different preparations with silver-free controls. Silver nanoparticles were either synthesized ex situ and then added to the casting solution as an organosol or produced in the casting solution via in situ reduction of ionic silver by the polymer solvent. Nanocomposite membranes of three types differing in skin porosity and macrovoid structure were prepared. The structure and properties of nanocomposites were interpreted in terms of the coupling between the processes of nanoparticle formation and gelling of the polymer-rich phase during phase inversion. Larger nanoparticles preferentially located in the skin layer were observed in composites prepared via the ex situ method while in situ reduction of silver led to formation of smaller nanoparticles homogeneously distributed along the membrane cross-section. In some cases, incorporation of nanoscale silver formed ex situ resulted in macrovoid widening and an order of magnitude decrease in hydraulic resistance accompanied by only a moderate decrease in rejection. The accessibility of the silver nanoparticles embedded in the membrane was quantitatively assessed by the degree of the growth inhibition of a membrane biofilm due to the ionic silver released by the nanocomposites and was found to depend on the method of silver incorporation.     

Quantification of immunoglobulin G and characterization of process related impurities using coupled Protein A and size exclusion high performance liquid chromatography

The present work describes two HPLC-UV methods for multi-protein quantification using (i) only a Protein A sensor cartridge (Protein A HPLC) and (ii) the same Protein A cartridge in combination with a size exclusion HPLC column (PSEC-HPLC). The possibility to simultaneously quantify immunoglobulin G (IgG) besides a non-binding protein such as bovine serum albumin (BSA) increases the applicability of Protein A HPLC. Its most pronounced feature is its independence of the buffer system, pH-value and salt content of the investigated sample solvent, which includes cell media. A comparison with the state-of-the-art, the photometrical Bradford method, shows that Protein A HPLC is as sensitive as Bradford, but that it comes with an extended linear range of 4 orders of magnitude, ranging from 0.15 [μg abs] to 1 [mg abs] absolute injected protein amount. The applicability of the PSEC-HPLC method is demonstrated for the analysis of real cell culture feed samples. While Protein A binds IgG, the SEC-column distributes the feed impurities by their molecular weight. The peak area ratios of IgG and the feed impurities of interest are then plotted against the collected sample fraction. These Protein A-Size-Exclusion-Chromatographic diagrams (PSEC-plot) combine the performance information of feed impurities and IgG in a single plot. Further it is shown that both methods are suitable for the performance evaluation of antibody purification media using static as well as dynamic binding experiments performed on DEAE-Fractogel and Capto Adhere. The investigated test samples were “mock” protein solutions with increasing complexity ranging from simple PBS buffer to serum free cell media and “real” cell culture feed solutions.     

Increasing the amount of phosphoric acid enhances the suitability of Bradford assay for proteomic research

The Bradford assay is one of the most commonly used methods for protein quantification. However, in proteomic research, the lysis buffer generally used for dissolving proteins can cause some interference to the assay. The dye reagent of classical Bradford assay contains 8.50% (w/v) phosphoric acid, which is an important factor relating to the color yield of the assay. In this study, the phosphoric acid content in dye reagent was increased to 9.35% (w/v), 10.20% (w/v), and 11.05% (w/v) to evaluate the changes of interference and the effects of lysis buffer on the interaction between proteins and dye reagent. Results show that lysis buffer not only causes background interference but also affects the protein–dye chromogenic process. Analysis of different components in the lysis buffer showed that carrier ampholyte is the main factor that introduces interference to the Bradford assay. Detergents are well‐known interfering compounds in the Bradford assay, but CHAPS and octyl b‐D‐glucopyranoside only cause slight interference. When the amount of phosphoric acid was increased from 8.50%(w/v) to 10.20% (w/v), the sensitivity of the Bradford assay to proteins in lysis buffer was increased, and the interference delivered by lysis buffer was considerably reduced.