Composition and thermal stability of SiO2-based hybrid materials TEOS-MTEOS system

Hybrid materials with different amounts of organics permanently bound on the inorganic network obtained in the TEOS-MTEOS (tetraethoxysilan-methyltriethoxysilan) system are used for obtaining coatings with different optical and mechanical properties. To study the thermal stability of the mentioned materials, compositions with different molar ratios of the precursors were prepared. The influence of the solvent and water amounts on the gelation process was also investigated. The gels obtained were characterised by IR spectrometry and their decomposition temperatures were determined by DTA/TG. Thermal stability of the gels is rather influenced by their composition than the conditions of the gelation process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radiation dose contribution from coal-slags used as structural building material

A significant dose contribution on the population could be derived from coal slags used as isolation material. Extremely high natural activities are measured in the coal slag, derived from the region of the settlement Ajka, Hungary. In some buildings monitored, the elevated -doses were nearly 5–10 times higher than the world average ones. The annual average indoor radon concentrations from the slag exceeded 400 Bq/m³ and in some cases up to 1200 Bq/m³. Due to the elevated exposure and the radon concentrations in the dwellings the annual dose was estimated to 8–24 mSv/y more than 5–10 times of the world average one.     

Angle-resolved x-ray photoelectron spectroscopy

In this review, various aspects of angle-resolved x-ray photoelectron spectroscopy (ARXPS) as applied to solid state- and surface chemical- studies are discussed. Special requirements for $\text{instrumentation}$ are first considered. The use of $\text{grazing-emission}$ angles to enhance surface sensitivity and study surface concentration profiles of various types is then discussed. Various effects that may limit the accuracy of such measurements such as surface roughness, electron refraction, and elastic scattering are considered. Several examples of surface-specific electronic structure changes as studied by grazing-emission ARXPS (e.g., valence-band narrowing and core-level shifts) are also reviewed. The use of $\text{grazing-incidence}$ geometries for surface enhancement is also briefly considered. Single-crystal studies providing additional types of information via ARXPS are next discussed. For core-level emission from single-crystal substrates or adsorbed overlayers, $\text{x-ray photoelectron diffraction (XPD)}$ is found to produce considerable fine structure in polar- or azimuthal- scans of intensity. Such XPD effects can be very directly related to the atomic geometry near a surface, for example, through simple intramolecular or intermolecular scattering processes. A straightforward single scattering or kinematical theory also appears to describe such effects rather well, thus far permitting several structures to be solved by analyses of azimuthal intensity scans. Likely future developments and possible limitations of such XPD structure studies are also discussed. Finally, $\text{valence-band ARXPS}$ is considered, and it is shown that pronounced direct-transition effects can be observed provided that the specimen Debye-Waller factor is not too small. A simple free-electron final-state model is found to predict these direct-transition effects very well, and future studies at low temperatures and with higher angular resolution seem promising.     

X-ray photoelectron angular distributions with dispersion-compensating x-ray and electron optics

A general model for predicting instrumental effects on intensifies and line-shapes in angle-resolved X-ray photoemission experiments is presented. This     

CIRCULAR DICHROISM SPECTRA OF SYSTEM I PARTICLES FROM NORMAL CHLOROPLASTS AND CAROTENOID-DEFICIENT MUTANTS OF MAIZE

Abstract— Circular dichroism (CD) spectra were studied in System I particles prepared by digitonin fragmentation of chloroplasts of normal maize and carotenoid-deficient mutants. CD bands of pigment molecules were found to be higher in particles than in solutions. This phenomenon was most pronounced for the particles containing the carotenoid composition of normal chloroplast lamellae. The CD signal of chlorophylls bound to particles of carotenoid-deficient chloroplasts was closer to that found in solutions. This indicates that aggregation and/or binding of chlorophylls in carotenoid-deficient mutants may be less extensive than in normal chloroplasts.     

Photoelectric cross-sections for fixed-orientation atomic orbitals: Relationship to the plane-wave final state approximation and angle-resolved photoemission

Differential photoelectric cross sections for fixed-orientation p- and d-orbitals have been derived within the one-electron, central-potential model and the dipole approximation for a completely general experimental geometry. Also, for the special geometry of a polarized source with polarization parallel to the electron emission direction, it is shown that such cross sections are exactly proportional to the probability distribution of the initial orbital, a result equivalent to that derived by using a plane-wave final-state approximation. Detailed numerical calculations of cross sections for Cu3 and O2p orbitals in various geometries and at various energies exhibit significant differences in comparison to plane-wave cross sections. By contrast, certain prior angular-resolved X-ray photoemission studies of single-crystal valence bands are found to have been carried out in an experimental geometry that fortuitously yields cross-sections close to the plane-wave predictions.