Polycation Structure Mediates Expression of Lyophilized Polycation/pDNA Complexes

Lyophilization of polycation/pDNA complexes provides stable, long‐term storage of complexes prior to clinical use but also reduces gene delivery efficiency. We examined whether polycation structure mediates effects of lyophilization on gene expression. Linear and branched PEI of the same molecular weight were used as a model system. Interestingly, pDNA/linear PEI complexes led to much smaller effects on gene expression following lyophilization compared with branched PEI complexes. The effect of polycation structure correlated with changes in dissociation ability of pDNA/PEI complexes. These results will be useful for developing new gene delivery vehicles.

     

Hydrogen bond perturbation in hen egg white lysozyme by external electromagnetic fields: a nonequilibrium molecular dynamics study

Nonequilibrium molecular dynamics simulations of a charge-neutral mutant of hen egg white lysozyme have been performed at 300 K and 1 bar in the presence of external microwave fields (2.45 to 100 GHz) of an rms electric field intensity of 0.05 V ?(-1). A systematic study was carried out of the distributions of persistence times and energies of each intraprotein hydrogen bond in between breakage and reformation, in addition to overall persistence over 20 ns simulations, vis-á-vis equilibrium, zero-field conditions. It was found that localized translational motion for formally charged residues led to greater disruption of associated hydrogen bonds, although induced rotational motion of strongly dipolar residues also led to a degree of hydrogen bond perturbation. These effects were most apparent in the solvent exposed exterior of hen egg white lysozyme, in which the intraprotein hydrogen bonds tend to be weaker.     

Differential water sorption studies on Kevlar 49 and As-polymerized poly(p-phenylene terephthalamide): determination of water transport properties

Water vapor sorption experiments have been conducted on Kevlar 49 at 30 degrees C over a range of water vapor pressures in 0-90% of saturation and on the as-polymerized form of the material at 30, 45, and 60 degrees C over a series of water vapor pressures of 0-60%, 0-25%, and 0-15%, respectively. For each of the differential steps in water vapor pressure, dynamic uptake curves were generated and analyzed according to a number of different mathematical models, including Fickian, Coaxial cylindrical, and intercalation models. The intercalation model was demonstrated to be the most successful model and considered two time-scales involved in the diffusion process, i.e., a penetrant-diffusive time-scale and a polymer-local-matrix-relaxation time-scale. The success of this model reinforces previously reported adsorption and desorption isotherms which suggested that water may penetrate into the surface layers of the polymer crystallite through a process known as intercalation.     

Partial Regularity for Singular Solutions to the Monge‐Ampère Equation

We prove that solutions to the Monge‐Ampère inequality in ?ⁿ are strictly convex away from a singular set of Hausdorff (n‐1)‐dimensional measure zero. Furthermore, we show this is optimal by constructing solutions to det D²u = 1 with singular set of Hausdorff dimension as close as we like to n‐1. As a consequence we obtain W^2,1 regularity for the Monge‐Ampère equation with bounded right‐hand side and unique continuation for the Monge‐Ampère equation with sufficiently regular right‐hand side. © 2015 Wiley Periodicals, Inc.     

Space environmental testing of flexible coverglass alternatives based on siloxanes

With the development of thin-film, high-efficient III–V solar cells using the epitaxial lift-off technique, flexible solar panels for space applications can be designed. Besides new deployment options, this also reduces the mass and thus launch costs of a satellite. One requirement for such a flexible panel configuration is the replacement of the brittle coverglass, which shields the solar cells from the harsh space environment, by a flexible alternative. In this work we have tested several compositions of a polysiloxane candidate material for a flexible shielding layer by exposing them to high energy UV and electron radiation at elevated temperatures. It was found that irradiation by electrons with a fluence corresponding to 15 years in space produces little degradation. UV radiation, on the other hand, has a more pronounced impact on the material properties, causing a discolouration of the transparent material and for some compositions even cracking of the samples.     

A Framework for Characterizing Middle School Students' Statistical Thinking

People make use of quantitative information on a daily basis. Professional education organizations for mathematics, science, social studies, and geography recommend that students, as early as middle school, have experience collecting, organizing, representing, and interpreting data. However, research on middle school students' statistical thinking is sparse. A cohesive picture of middle school students' statistical thinking is needed to better inform curriculum developers and classroom teachers. The purpose of this study was to develop and validate a framework for characterizing middle school students' thinking across 4 processes: describing data, organizing and reducing data, representing data, and analyzing and interpreting data. The validation process involved interviewing, individually, 12 students across Grades 6 through 8. Results of the study indicate that students progress through 4 levels of thinking within each statistical process. These levels of thinking were consistent with the cognitive levels postulated in a general developmental model by Biggs and Collis (1991).