Ideal Structure (ideal + structure)

Distribution by Scientific Domains

Selected Abstracts

Structure and Properties of Poly(, -caprolactone) Networks with Modulated Water Uptake

Jorge L. Escobar Ivirico
Abstract Summary: A PCL macromonomer was obtained by the reaction of PCL diol with methacrylic anhydride. The effective incorporation of the polymerizable end groups was assessed by FT-IR and 1H NMR spectroscopy. PCL networks were then prepared by photopolymerization of the PCL macromonomer. Furthermore, the macromonomer was copolymerized with HEA, with the aim of tailoring the hydrophilicity of the system. A set of hydrophilic semicrystalline copolymer networks were obtained. The phase microstructure of the new system and the network architecture was investigated by DSC, IR, DMS, TG, dielectric spectroscopy and water sorption studies. The presence of the hydrophilic units in the system prevented PCL crystallization on cooling; yet there was no effect on the glass transition process. The copolymer networks showed microphase separation and the , relaxation of the HEA units moved to lower temperatures as the amount of PCL in the system increased. Ideal structure, compatible with the experimental results, for the hydrophilized poly(, -caprolactone) networks with modulated water uptake. [source]

Quantifying distortion from ideal closest-packing in a crystal structure with analysis and application

Richard M. Thompson
A parameter, Ucp, that quantifies the distortion of the anion skeleton in a crystal from ideal closest-packing has been developed. It is a measure of the average isotropic displacement of the observed anions from their ideal equivalents. An ideal closest-packed structure can be fit to an observed structure by varying the radius of the ideal spheres, orientation and translation, such that Ucp is minimized. Ideal structures were fit to the M1M2TO4 polymorphs, pyroxenes and kyanite. The distortions of these crystals were analyzed in terms of the two parameters, Ucp and the ideal radius. Changes in structures due to temperature, pressure and compositional effects were characterized in terms of these parameters. [source]

Generalization of the B *-algebra (C0(X),, ,,)

Jorma Arhippainen
Abstract We give a generalization of the Stone,Weierstrass property for subalgebras of C (X), with X a completely regular Hausdorff space. In particular, we study in this paper some subalgebras of C0(X), with X a locally compact Hausdorff space, provided with weighted norm topology. By using the Stone,Weierstrass property, we then describe the ideal structure of these algebras. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Characterization within and around the Limbal Epithelial Crypt

Purpose: The Limbal Epithelial Crypt (LEC) is an anatomical structure that is found between the junction of the cornea and sclera and is in a unique position to make it an ideal structure to examine further. Previous studies have demonstrated the LEC to have properties that suggest it may be a stem cell niche. Basal cells of the LEC are significantly smaller than basal cells found in adjacent rete pegs, and morphologically they have a higher nuclear:cytoplasmic ratio. We set out to examine LEC further by exploring the surrounding LEC matrix proteins, and with known differentiation markers. Methods: Donated corneo-sclero rims were cut into eight equal sized pieces and frozen. Each piece was cut into 7,m serial sections, and was examined by microscopy for LEC structures. Identified LEC was collected on slides and stored until they were fixed in acetone and processed by standard immunofluorescence techniques for each differentiation marker. Results: Tenacin C was more positively taken up by the basement membrane of the LEC compared with the surrounding limbus. In addition, staining for desmoglein was negative against isolated small subpopulations of cells within the basal regions of the LEC. Conclusions: The LEC structure demonstrates properties that may identify this as a possible stem cell niche. Further studies are necessary to determine the significance of the LEC in its role in stem cell maintenance. [source]

New Microporous Materials for Acetylene Storage and C2H2/CO2 Separation: Insights from Molecular Simulations

CHEMPHYSCHEM, Issue 10 2010
Michael Fischer
Abstract Force-field based grand-canonical Monte Carlo simulations are used to investigate the acetylene and carbon dioxide uptake capacity, as well as the C2H2/CO2 adsorption selectivity of three novel microporous materials: Magnesium formate, Cu3(btc)2, and cucurbit[6]uril. Because no comparable computational studies of acetylene adsorption have been reported so far, the study focuses on systems for which experimental data are available to permit a thorough validation of the simulation results. The results for magnesium formate are in excellent agreement with experiment. The simulation predicts a high selectivity for acetylene over CO2, which can be understood from a detailed analysis of the structural features that determine the affinity of Mg-formate towards C2H2. For Cu3(btc)2, preliminary calculations reveal the necessity to include the interaction of the sorbate molecules with the unsaturated metal sites, which is done by means of a parameter adjustment based on ab-initio calculations. In spite of the high C2H2 storage capacity, the C2H2/CO2 selectivity of this material is very modest. The simulation results for the porous organic crystal cucurbit[6]uril show that the adsorption characteristics that have been observed experimentally, particularly the very high isosteric heat of adsorption, cannot be understood when an ideal structure is assumed. It is postulated that structural imperfections play a key role in determining the C2H2 adsorption behavior of this material, and this proposition is supported by additional calculations. [source]

Car,Parrinello Molecular Dynamics Study of DCl Hydrate Crystals,

CHEMPHYSCHEM, Issue 9 2005
Atte Sillanpää Dr.
Abstract Three DCl hydrates have been studied using Car,Parrinello (CP) molecular dynamics. The structural results at low temperatures (T<350 K) agree with experiment and previously published CP results. The monohydrate has been shown to be built from D3O+and Cl,ions. The dihydrate is built exclusively from D5O2+and Cl,ions. The trihydrate consists of D2O, D5O2+, and Cl,ions. Thus, the DCl hydrates are excellent systems for studying ideal D3O+and D5O2+ions. The data from these ideal structures can be compared to high-concentration acid,liquid simulations. [ClD,,,Cl],ions were detected at amorphous and fluid conditions after melting the di- and trihydrate crystals. The experimentally observed spectral continuum can be explained by combining the Eigen and Zundel spectra, and interpolating between the shared deuterium frequencies of the latter and the stretching band of the former. [source]