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.     

Design of molecular two-photon probes for in vivo imaging. 2H-Benzo[h]chromene-2-one derivatives

2H-Benzo[h]chromene-2-one derivatives showing appreciable water solubility, significant two-photon cross sections, high photostability, cell permeability, low toxicity, and ability to be converted to a protein TP probe have been developed by incorporating all of the needed functions within a small molecule.     

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.     

On the loss of ethylene from [C3H7O]+ ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {{\rm CHOH}}\limits^{\rm + } $\end{document}

The results of some ³C and ²H labelling experiments plus some measurements of reaction thermochemistry and translational energy releases, permit a significant simplification of the mechanistic pathways by which [C₃H₇O]⁺ ions of structure fragment by loss of C₂H₄. The relationships between these ions and some of their isomeric forms are explored and clarified.     

Specific and random fragmentations in the mass spectra of some neopentyl compounds

The mass spectra of neopentyl alcohol, bromide and chloride and some ¹³C and ²H labelled analogues have been studied. Most fragmentations of the molecular ions of these compounds occur by simple bond cleavages and do not involve rearrangement before fragmentation. We propose that in the [M ? CH₃]⁺ fragment ions, seven of the eight hydrogen atoms and all four carbon atoms are involved in randomisation when an ethylene molecule is ejected. The eighth hydrogen atom (which comes from a methyl group) is probably associated with the heteroatom. The neopentylcation, observed only in the mass spectrum of the bromide, fragments mainly by loss of an ethylene molecule, also containing randomly selected hydrogen and carbon atoms. The [C₄H₇]⁺ ion also was observed to undergo complete atom scrambling.     

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.     

Low-energy 3He+ ion scattering spectroscopy studies of D2 adsorption on W(211)

Direct physical evidence for occupation of a trough site by the β₂ state of deuterium adsorbed on W(211) has been obtained by angle-resolved ³He⁺/D(ads) ion-scattering spectroscopy (ISS) in combination with LEED/Auger. The W(211) surface is composed of close-packed 〈111〉 rows of W atoms separated by a wide channel. Previous thermal desorption studies have shown two clearly resolved hydrogen states: β₁ desorbing with a temperature maximum of ca. 60°C, and β₂ at ca. 400°C. Analyses of flash desorption, work-function, adsorption kinetics, stoichiometry and mixed adsorption further indicated that the more tightly bound β₂ form occupies a deep-trough position. In the present study, ISS polar-angle profiles were taken at an incident energy of 306 eV. With only the β₂ state populated, a ³He⁺ beam parallel to the close-packed 〈111〉 rows was found to scatter from D(ads) with a cutoff angle close to grazing incidence while for the perpendicular direction D(ads) scattering is observed only for angles greater than 18° away from grazing incidence. These measurements are consistent with the corrugated W(211) geometry and with the proposed β₂-D trough-site model.     

Enhanced diffraction from a grating on the surface of a negative-index metamaterial

We show by numerical simulation as well as by measurements on negative-index metamaterial wedge samples, that the unavoidable stepping of the refraction interface-due to the finite unit-cell size inherent to metamaterials-can give rise to a well-defined diffracted beam in addition to the negatively refracted beam. The direction of the diffracted beam is consistent with elementary diffraction theory; however, the coupling to this higher order beam is much larger than would be the case for a positive index material. The results confirm recent theoretical predictions of enhanced diffraction for negative-index grating surfaces.     

Anechoic chamber qualification: traverse method,inverse square law analysis method,and nature of test signal

Qualification of anechoic chambers is intended to demonstrate that the chamber supports the intended free-field environment within some permissible tolerance bounds. Key qualification issues include the method used to obtain traverse data, the analysis method for the data, and the use of pure tone or broadband noise as the chamber excitation signal. This paper evaluates the relative merits of continuous versus discrete traverses, of fixed versus optimal reference analysis of the traverse data, and of the use of pure tone versus broadband signals. The current practice of using widely space discrete sampling along a traverse is shown to inadequately sample the complexity of the sound field extant with pure tone traverses, but is suitable for broadband traverses. Continuous traverses, with spatial resolution on the order of 15% of the wavelength at the frequency of interest, are shown to be necessary to fully resolve the spatial complexity of pure tone qualifications. The use of an optimal reference method for computing the deviations from inverse square law is shown to significantly improve the apparent performance of the chamber for pure tone qualifications. Finally, the use of broadband noise as the test signal, as compared to pure tone traverses over the same span, is demonstrated to be a marginal indicator of chamber performance.