圆柱壳大开孔问题——单圆孔的理论解

从Ｄｏｎｎｅｌｌ圆柱壳方程出发，利用复变函数与保角映射的方法，将圆柱壳展开面上的开孔边界线保角晨射成单位圆，并在映射平面上给出了逼近大开孔圆柱壳方程解答的完备函数逼近序列，进而利用边界条件和正交函数展开的方法得到了自由孔边应力集中系数的表达式，最后，对具有开孔率的圆柱壳在不同荷载条件下的自由孔口边界上的应力集中的系数进行了计算，此种方法，同时研究圆柱壳开非圆大孔和接管等问题提供了可能性。     

Partitioned partial least squares regression with application to a batch fermentation process

The performance of Partial Least Squares regression (PLS) in predicting the output with multivariate cross‐ and autocorrelated data is studied. With many correlated predictors of varying importance PLS does not always predict well and we propose a modified algorithm, Partitioned Partial Least Squares (PPLS). In PPLS the predictors are partitioned into smaller subgroups and the important subgroups with high prediction power are identified. Finally, regular PLS analysis using only those subgroups is performed. The proposed Partitioned PLS (PPLS) algorithm is used in the analysis of data from a real pharmaceutical batch fermentation process for which the process variables follow certain profiles during a specific fermentation period. We observed that PPLS leads to a more accurate prediction of the yield of the fermentation process and an easier interpretation, since fewer predictors are used in the final PLS prediction. In the application important issues such as alignment of the profiles from one batch to another and standardization of the predictors are also addressed. For instance, in PPLS noise magnification due to standardization does not seem to create problems as it might in regular PLS. Finally, PPLS is compared to several recently proposed functional PLS and PCR methods and a genetic algorithm for variable selection. More specifically for a couple of publicly available data sets with near infrared spectra it is shown that overall PPLS has lower cross‐validated error than PLS, PCR and the functional modifications hereof, and is similar in performance to a more complex genetic algorithm. Copyright © 2011 John Wiley & Sons, Ltd.     

固相萃取-超高压液相色谱-串联质谱测定水中19种抗生素

应用固相萃取(SPE)及液相色谱-串联质谱(LC-MS/MS)技术,建立了水中痕量(ng/L)四环素类、磺胺类、大环内酯类、喹诺酮类和β-内酰胺类5类共19种抗生素的同时定量检测方法。水样通过HLB萃取小柱富集后,以C18反相色谱柱为分析柱,乙腈-0.1%甲酸溶液为流动相,采用LC-MS/MS进行定量分析。选择电喷雾正电离源(ESI+),多反应监测模式(MRM),内标法定量。19种抗生素在0.5~1 000μg/L范围内均具有良好的线性关系,方法的定量下限(S/N=10,1 000倍浓缩)为0.1~0.5 ng/L。以纯水和河水(黄浦江水)作为基底,13C-咖啡因为内标物,加标质量浓度为20、100 ng/L时,抗生素的平均加标回收率分别为75%~125%和77%~132%,相对标准偏差(RSD)分别为1.7%~6.9%和0.9%~6.5%,表明所建立的测试方法准确可靠。研究结果表明,黄浦江水受到了抗生素污染,共检出15种抗生素,检出的四环素类、磺胺类、大环内酯类、喹诺酮类及β-内酰胺类抗生素污染质量浓度分别为13.0~56.9、12.2~103.4、53.8~84.8、3.1~26.2、16.5~181.6 ng/L。     

The mean activity coefficients of LaCl3 in dilute aqueous solution at 298.15 K

The electromotive forces of a symmetrical concentration cell with transference, Ag; AgCl|LaCl₃ (m*):LaCl₃ (m)|AgCl; Ag, were measured over the concentration range from 8.762 × 10⁻⁴ mol kg⁻¹ to 6.788 × 10⁻² mol kg⁻¹ at 298.15 K to obtain the mean activity coefficients of LaCl₃. The mean activity coefficient for reference solution at 298.15 K and the ion size parameter for LaCl₃ in the extended Debye–Hückel equation are evaluated by using an approach extrapolating concentration to unlimited dilution. A modified Debye–Hückel equation with new parameters has been established for the studied concentration range. A comparison is done of the thermodynamic data of LaCl₃ that are determined by this experiment with those reported by previous literatures, and evaluated by some models.     

pePC-SAFT: Modeling of polyelectrolyte systems: 1. Vapor–liquid equilibria

A molecular thermodynamic model for polyelectrolyte systems—called pePC-SAFT—is proposed. The effect of charged monomers within the polyelectrolyte chain is explicitly taken into account in the reference term by replacing the hard-chain contribution of the PC-SAFT model by a charged-hard-chain contribution. Moreover, counterion condensation is accounted for to determine the effective number of charges along the polyion as well as of free counterions. The electrostatic contribution of the free counterions is described by a Debye–Hückel term.     

Heteroscedastic controlled calibration model applied to analytical chemistry

In chemical analyses performed by laboratories, one faces the problem of determining the concentration of a chemical element in a sample. In practice, one deals with the problem using the so‐called linear calibration model, which considers that the errors associated with the independent variables are negligible compared with the former variable. In this work, a new linear calibration model is proposed assuming that the independent variables are subject to heteroscedastic measurement errors. A simulation study is carried out in order to verify some properties of the estimators derived for the new model and it is also considered the usual calibration model to compare it with the new approach. Three applications are considered to verify the performance of the new approach. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigation of the effects of 24 bio-matrices on the LC-MS/MS analysis of morinidazole

This study compares and evaluates the effect of various matrices on liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) analysis. Permanent post-column infusion (PCI) was used to quantify matrix effects. In this way, the suppressed or enhanced signal of the target material resulting from different co-eluting matrix components could be assessed. Twenty-four biological samples from in vivo and in vitro experiments were selected for this study. In addition, 7 sample components were further analyzed after sample preparation by protein precipitation. Multiple regression analysis was used to investigate the collinear relationship between matrix effects and co-eluted components at different time intervals. We found that salt was the dominant factor which impacted changes in signal detection. In order to eliminate it, we used ammonium formate as a modifier of the mobile phase which resulted in charge-state redistribution profiles so that a homogeneous matrix formed. By employing pulse gradient chromatography in the presence of 5 mM ammonium formate, favorable improvements of enhanced signal intensity and reduced matrix effects were obtained. These experiments also indicated the feasibility of using analogue IS during bio-analysis which contributed to an overall faster assay that would be suitable for drug discovery and development purposes.     

New way to crosslink chitosan in aqueous solution

In this paper, the reaction between o-phthaldialdehyde and free NH₂ of chitosan is investigated; at a very low molar ratio between the two reactants ([dialdehyde]/[NH₂] ∼ 2.5 × 10⁻⁴), an increase of the apparent molecular weight is obtained as evidenced from the rheological behaviour. Then, three non-ionic polysaccharides (galactomannan, maltodextrins, methylcellulose) are oxidised to 10% with sodium metaperiodate to obtain polyaldehydic derivatives able to react with free NH₂ of chitosan after their direct dissolution into chitosan solution at a molar ratio [monosaccharide units]/[NH₂ ] ∼ 0.6. Stable swollen porous gels are obtained with an excellent yield in the presence of a reducing agent (NaBH₃CN) chosen to reduce the Schiff base; nearly no influence of the structure of the initial non-ionic polysaccharides is observed when the polysaccharides are oxidized in the same conditions. Different parameters for the reaction of oxidized methylcellulose (Me-ox) with chitosan are tested: influence of the degree of oxidation (up to 50%), and of the oxidised methylcellulose concentration. The larger is the degree of oxidation or the Me-ox concentration, the lower is the degree of swelling (i.e., the larger is the degree of chitosan cross-linkage). The swollen gels formed immediately after reaction are isolated and re-swell in aqueous acidic conditions, a good solvent of initial chitosan, to purify the gel and determine the yield of the reaction and the swelling degree. At the end, preliminary tests of biodegradability of these new gels are performed using specific enzymatic degradation with lysozyme and cellulase in the case of chitosan/Me-ox cogels chosen as example.     

Study of the high temperature reactions of a hindered aryl phosphite (Hostanox PAR 24) used as a processing stabiliser in polyolefins

The processing stabilising performance of various phosphorous antioxidants in polyolefins is affected significantly by their chemical composition. In order to explore the mechanism of stabilisation, the reactions of a hindered aryl phosphite [tris(2,4-di-tert-butylphenyl)phosphite (DTBPP), Hostanox PAR 24] were investigated at temperatures corresponding to polyethylene processing. The thermal and thermo-oxidative stability of the additive was determined by differential scanning calorimetric (DSC) and thermogravimetric methods. DTBPP was heat treated under argon and oxygen at 200 and 240 °C. The stabiliser was reacted at 200 °C with azobisisobutyronitrile (AIBN) in oxygen-free environment (carbon centred radicals) and under oxygen (peroxy radicals), with dicumyl peroxide (DCP) in oxygen atmosphere (oxy radicals), and with cumene hydroperoxide (CHP) under argon. The reaction products were identified by FT-IR, HPLC and HPLC-MS. The results revealed that besides the known reactions of hindered aryl phosphites, thermal decomposition and recombination reactions also take place above the melting point of the antioxidant. DTBPP does not react with molecular oxygen, but its decomposition is accelerated by oxygen and especially by radicals. Accordingly, the heat-stability of phosphorous stabilisers also has to be taken into account in their application, as it is one of the factors which influence the processing stabilisation of polyolefins.     

Statistical quality control for ternary ordinal quality data

The paper considers various aspects of statistical quality control by means of sample data received on a ternary ordinal scale. A new method for evaluating quality level and dispersion, free of any latent numerical scale assumptions, is proposed. The emphasis is on working with large samples, which enable the statistical analysis, estimation and control by the use of approximate analytical expressions of these measures to be considerably simplified. Two complementary studies demonstrate the usage of the proposed approach. Copyright © 2010 John Wiley & Sons, Ltd.