Hydrophobic polyphenylalanine-grafted hyperbranched polyethylenimine and its in vitro gene transfection

A series of amphiphilic multi‐armed PPn copolymers were prepared by ROP of Phe‐NCA with PEI‐25k as a macroinitiator. The particle size of the PPn/DNA complexes was about 100 nm and the zeta potentials were below 20 mV. An MTT assay demonstrated that all the PPn copolymers had lower cytotoxicity compared to PEI‐25k. In vitro gene transfection studies were also conducted in HeLa, 293 and CT 26 cells. The optimal quantity of hydrophobic phenylalanine segments in PP80 led to higher transfection efficiency in various cell lines based on this study. The results indicate that PP80 was the best candidate for gene delivery among these PPn copolymers.

     

Pseudo-likelihood methodology for partitioned large and complex samples

Large data sets, either coming from a large number of independent replications, or because of hierarchies in the data with large numbers of within-unit replication, may pose challenges to the data analyst up to the point of making conventional inferential methods, such as maximum likelihood, prohibitive. Based on general pseudo-likelihood concepts, we propose a method to partition such a set of data, analyze each partition member, and properly combine the inferences into a single one. It is shown that the method is fully efficient for independent partitions, while with dependent sub-samples efficiency is sometimes but not always equal to one. It is argued that, for important realistic settings, efficiency is often very high. Illustrative examples enhance insight in the method’s operation, while real-data analysis underscores its power for practice.     

微极流体蠕动泵经由滑移边界管道输送的Stokes流动

计及管道边界条件滑移的影响,研究微极流体蠕动泵,经由圆柱形管道输运的Stokes流动.壁面运动的控制方程为正弦波方程.使用润滑理论,得到了轴向速度、微转动向量、流函数、压力梯度、摩擦力和机械效率的解析数值解.用图形表示出构成参数,如像耦合参数、微极参数和表征蠕流泵特性的滑移参数、摩擦力和俘获现象的影响.数值计算表明,当耦合参数较大时,需要蠕动泵的压力更大,而微极参数和滑移参数正相反.俘获团块的大小随耦合参数和微极参数的减小而缩小,而随滑移参数的增大而缩小.     

DEA模型在资金分配和管理中的应用

资金的合理使用,是经济活动中的一个非常重要的问题.利用DEA的理论、方法模型,探讨资金的使用效率、分配的合理性,以及最佳资金预算的确定方法.涉及的DEA模型结构属于非参数的最优化DEA模型,以及DEA平行网络结构.模型中所使用的生产可能集是可以评价是否呈现"拥挤"迹象的.     

银行间债券市场的外部效率:基于商业银行的视角

以参与我国银行间债券市场的商业银行为研究对象,运用面板数据模型检验银行间债券市场的外部效率对于商业银行经营绩效的影响.实证结果表明:我国银行间债券市场的发展对于商业银行的盈利能力和流动性管理水平均有较强的外部正效率,而对于商业银行传统盈利模式和风险管理则具有负面影响.建议商业银行应利用银行间债券市场的外部正效率提高其资产负债管理水平,通过提升自身经营管理水平来降低银行间债券市场外部负效率对自身的影响;此外监管当局还应该降低小型金融机构进入银行间债券市场的门槛,以发挥该市场外部正效率对化解区域金融风险的作用.     

Shell particles, trials, tribulations and triumphs

The concept of pellicular particles was imagined by Horváth and Lipsky fifty years ago. They were initially intended for the analysis of macromolecules. Later, shell particles were prepared. The rational behind this concept was to improve column efficiency by shortening the pathways that analyte molecules must travel and, so doing, to improve their mass transfer kinetics. Several brands of superficially porous particles were developed and became popular in the 1970s. However, the major improvements in the manufacturing of high-quality, fully porous particles, that took place in the same time, particularly by making them finer and more homogeneous, hampered the success of shell particles, which eventually disappeared. Recently, the pressing needs to improve analytical throughputs forced particle manufacturers to find a better compromise between the demands for higher column efficiency that require short diffusion paths of analyte molecules in columns and the need for columns that can be operated with the conventional instruments for liquid chromatography, which operate with moderate column back-pressures. This lead to the apparition of a new generation of columns packed with shell particles, which bring chromatographic columns to a level of efficiency undreamed of a few years ago. This evolution is reviewed, the reason that motivated it, and the consequences of their success are discussed.     

Accurate measurements of peak variances: importance of this accuracy in the determination of the true corrected plate heights of chromatographic columns

The true efficiency of a column is derived from the differences between the variances of the peak profiles of the same compound recorded in the presence and the absence of the chromatographic column. These variances are usually derived using one of three methods: (1) the retention time of the peak apex and its half-height width; (2) the moments of the best fit between the experimental data and a hybrid response function, e.g., an exponentially convoluted Gaussian; or (3) the exact moments of the experimental band profiles. Comparisons of the results of these methods show that the first method is always inaccurate because all the band profiles recorded are strongly tailing. The peak fit method is accurate only for 4.6mm I.D. columns operated with instruments having low extra-column volume but fails for short narrow-bore columns due to the severe tailing of peaks passing through the complex channels of the extra-column volumes and to the inaccuracies in the fit of experimental data to the selected function. Although far better, the moment method may be inaccurate when the zero dead volume union used to measure the extra-column peak variances has a higher permeability than the column, causing the upstream part of the instrument to operate under comparatively low pressures.     

Peristaltic flow of MHD Jeffrey fluid through finite length cylindrical tube

The present investigation studies the peristaltic flow of the Jeffrey fluid through a tube of finite length. The fluid is electrically conducting in the presence of an applied magnetic field. Analysis is carried out under the assumption of long wavelength and low Reynolds number approximations. Expressions of the pressure gradient, volume flow rate, average volume flow rate, and local wall shear stress are obtained. The effects of relaxation time, retardation time, Hartman number on pressure, local wall she...     

Collision efficiency of two nanoparticles with different diameters in Brownian coagulation

The collision efficiency of two nanoparticles with different diameters in the Brownian coagulation is investigated. The collision equations are solved to obtain the collision efficiency for the dioctyl phthalate nanoparticle with the diameter changing from 100 nm to 750 nm in the presence of the van der Waals force and the elastic deformation force. It is found that the collision efficiency decreases as a whole with the increase of both the particle diameter and the radius ratio of two particles. There exists an abrupt increase in the collision efficiency when the particle diameter is equal to 550 nm. Finally, a new expression is presented for the collision efficiency of two nanoparticles with different diameters.     

Analysis of energy consumption in microwave and convective drying process of multi-layered porous material inside a rectangular wave guide

This work applies the first law of thermodynamics to estimate the ratio of energy utilization in microwave drying process using a rectangular waveguide. Two porous packed bed systems are considered such as attaching fine bed on coarse bed (F-C) and attaching coarse bed on fine bed (C-F). The effects of layered configuration and layered thickness on drying rate, power absorbed efficiency, specific energy consumption (SEC), and energy efficiency are studied in detail. The results show that the variations of all parameters have strongly affected on microwave penetration depth and power absorbed within the packed bed. Furthermore, F-C bed with equal layer thickness corresponds to great energy efficiency.