The controlled release behavior and pH‐ and thermo‐sensitivity of alginate/poly(vinyl alcohol) blended hydrogels

Poly(vinyl alcohol) (PVA) was blended with sodium alginate (Alg) in various ratios and crosslinked with calcium chloride and made into hydrogel membranes. The dependence of the swelling behavior of these Alg‐Ca/PVA hydrogels on pH was investigated. The temperature‐dependent swelling behavior of the semi‐interpenetrating network (semi‐IPN) hydrogels was examined at temperatures from 2 to 45°C and the enthalpy of mixing (ΔH_mix) was determined at various temperatures. The molecular structure of the hydrogels was studied by infrared spectroscopy and their water structure in the semi‐IPN hydrogels was measured by differential scanning calorimetry (DSC). The influence of Ca²⁺ content on the network structure of Alg‐Ca/PVA hydrogels was investigated in terms of the compressive elastic modulus, effective crosslinking density, and the polymer–solvent interaction parameter based on the Flory theory. The loading of alizarin red S (ARS) followed the Langmuir isotherm mechanism and the release kinetics of ARS from the Alg‐Ca/PVA hydrogels followed the Fickian diffusion mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

Geometric Effects on Conductance in Single Molecule Electron Transport Junctions

We studied electron transport properties of a dithiol‐benzene molecule covalently bonded between two gold electrodes by combining ab initio calculations for the central molecule and a green function method to calculate electron transport. Due to the large computational demand, this type of calculations usually involves certain ways of simplification. The simplification commonly used is to fix the contact surface of the electrodes by ignoring the disturbance of the Au contact surface by contacting with the central molecule, i.e. without scattering region relaxation. In this study, we intended to resolve the difference between models with and without the above simplification. The large conductance found in our models without scattering region relaxation is due to the highly symmetric arrangement of the Au contact surface and those layers near the contact. The disturbance of the Au contact surface by the contact of the central molecule is important since the increase of the Au‐S bond and the distortion of the Au atom on the FCC site can lower the transmission coefficient between the two electrodes. In order to obtain better results, the model should include scattering region relaxation. However, when such relaxation is not applicable or demands too much calculation resource, the center molecule of the electronic transport junction should be at least optimized by the calculation level including electronic correlation, i.e. post‐HF methods.     

Efficient experimental design tools for exploring large simulation models

Simulation experiments are typically faster, cheaper and more flexible than physical experiments. They are especially useful for pilot studies of complicated systems where little prior knowledge of the system behavior exists. One key characteristic of simulation experiments is the large number of factors and interactions between factors that impact decision makers. Traditional simulation approaches offer little help in analyzing large numbers of factors and interactions, which makes interpretation and application of results very difficult and often incorrect. In this paper we implement and demonstrate efficient design of experiments techniques to analyze large, complex simulation models. Looking specifically within the domain of organizational performance, we illustrate how our approach can be used to analyze even immense results spaces, driven by myriad factors with sometimes unknown interactions, and pursue optimal settings for different performance measures. This allows analysts to rapidly identify the most important, results-influencing factors within simulation models, employ an experimental design to fully explore the simulation space efficiently, and enhance system design through simulation. This dramatically increases the breadth and depth of insights available through analysis of simulation data, reduces the time required to analyze simulation-driven studies, and extends the state of the art in computational and mathematical organization theory.     

Capping the upper and lower rims of calix[4]arenes by aryl dinitrile oxide reactions

1,3-Dipolar cycloadditions of upper- and lower-rim diallylcalix[4]arenes (1 and 3) with aryl dinitrile oxides provide a unique and efficient way of capping the calix[4]arenes. When dinitrile oxides reacted with 5-allylcalix[4]arene 7, they underwent a 1,3-dipolar cycloaddition on one side and an electrophilic substitution on the other side, which led to a novel type of asymmetric calix[4]arenes (9 and 12).     

Li6PO5Br and Li6PO5Cl: The first Lithium‐Oxide‐Argyrodites

The title compounds Li₆PO₅Br (Fand Li₆PO₅Cl (F represent the first oxidic argyrodites in general and the first lithiumoxoargyrodites in particular. The overall crystal structure corresponds to the cubic high temperature (HT) modification of all known cubic argyrodites, however, with a seemingly small but important difference concerning the lithium positions. In all other HT argyrodites with similar lithium content the 24 lithium atoms per unit cell are disordered over a 48 fold position in close vicinity to a 24 fold one causing a high mobility of the Li⁺. In the title compounds, however, they occupy the 24 fold one in a strictly ordered manner thus establishing a planar triangular first sphere coordination environment. This detail is of great importance for the amount of the specific lithium ionic conductivity and for the possible phase transition to an LT (low temperature) modification accompanied by an ordering of the disordered lithium atoms. Apparently the latter transition is suppressed in the title compounds because the Li⁺ are already frozen out in the cubic (HT = LT) form. The initially open question how this structural peculiarity influences the ionic conductivity (strengthening or weakening in comparison to oxygen free argyrodites?) is answered by a series of impedance measurements. The specific lithium ionic conductivity of the title compounds in the range 313 K < T < 518 K is significantly lower than in oxygen free argyrodites.     

Limit theorems for sums of dependent random variables

Summary In Lai and Stout [7] the upper half of the law of the iterated logarithm (LIL) is established for sums of strongly dependent stationary Gaussian random variables. Herein, the upper half of the LIL is established for strongly dependent random variables {X _i} which are however not necessarily Gaussian. Applications are made to multiplicative random variables and to f(Z _i ) where the Z _i are strongly dependent Gaussian. A maximal inequality and a Marcinkiewicz-Zygmund type strong law are established for sums of strongly dependent random variables X _i satisfying a moment condition of the form E¦S _a,n ¦^pg(n), where , generalizing the work of Serfling [13, 14].Research supported by the National Science Foundation under grant NSF-MCS-78-09179Research supported by the National Science Foundation under grant NSF-MCS-78-04014