Crystalline galliosilicate molecular sieves with the beta structure

Crystalline galliosilicates with the beta structure have been synthesized from alkali-free hydrogels with the composition Ga₂O₃:xSiO₂:12(TEA)₂O:1285H₂O, where x=40, 60, 80 and 100. The addition of an alkali (Ga₂O₃/Na₂O=1.0) to the hydrogel in the form of sodium gallate decreased crystallization times at 135°C to 10 days from 14 days. Crystallization reactions are not stoichiometric and the crystals' silica-to-gallia ratio (SGR) is always less than that in the parent hydrogel. Thermal analysis has shown that TEA ions first decompose and are then thermally desorbed, probably in the form of Hofmann decomposition products. Residual hydrocarbons are burned at T>400°C. The calcined crystals have surface area in the 500–625 m² g⁻¹ range. FTIR experiments with chemisorbed pyridine have shown that the isomorphous substitution of Al(IV) with Ga(IV) atoms decreases the acid-site strength and changes the relative B/L acid-site ratio of the crystals. IR spectra at a desorption temperature of 500°C revealed that all the pyridine desorbed from B sites but not from L sites in Ga-beta, whereas the Al-beta analog retained pyridine on both L and B sites. Microcalorimetry experiments with ammonia at 150°C have revealed the existence of different acid-site (B+L) strengths and site populations. The total number of sites available to NH₃ chemisorption and the number of strong acid sites show the same dependence on the SGR value of the crystals. ²⁹Si MAS-NMR spectra contain a resonance at −111 ppm attributed to T(4Si,0Ga) groups and a second resonance at −102 ppm attributed to T(3Si,1Ga) groups. ⁷¹Ga NMR spectra confirm that Ga(IV) is the dominant species and that Ga(VI) formation depends, in part, on the thermal pretreatment applied to the crystals. ¹H NMR results have revealed that after calcination in air at 500°C, there are residual hydrocarbon compounds in the beta microporous structure. This can be avoided if the organic template is decomposed in nitrogen at 500°C for 1 h and the decomposition products are removed oxidatively by a second calcination step in air at 550°C for 2 h.     

Knoevenagel condensation reaction over acid–base bifunctional nanocrystalline CexZr1−xO2 solid solutions

Highly thermally stable three-dimensional spongelike mesoporous Ce_xZr_1?xO₂ solid solutions consisting of nanometer size particles with different Ce/Zr compositions were synthesized by a modified sol–gel procedure using a triethanolamine/water mixture as a solvent to be used in liquid Knoevenagel condensation reaction. These materials were investigated in detail by means of X-ray diffraction (XRD), Raman spectroscopy, chemical analysis, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and adsorption microcalorimetry. The XRD, HRTEM and XPS studies proved the presence of nanocrystalline Ce_xZr_1?xO₂ solid solutions. These solid solutions showed excellent chemoselectivity in the classical Knoevenagel reaction. The large pore sizes (around 10 nm) highlight the possibility of using Ce_xZr_1?xO₂ as a support material for versatile catalytic systems. The results obtained from NH₃ and SO₂ adsorption microcalorimetry experiments successfully demonstrated the incorporation of ZrO₂ into the CeO₂ lattice resulting in both acidic and basic surface sites in a mixed oxide matrix.     

Melatonin Stimulates Dendrite Formation and Complexity in the Hilar Zone of the Rat Hippocampus: Participation of the Ca++/Calmodulin Complex

Melatonin (MEL), the main product synthesized by the pineal gland, stimulates early and late stages of neurodevelopment in the adult brain. MEL increases dendrite length, thickness and complexity in the hilar and mossy neurons of hippocampus. Dendrite formation involves activation of Ca²⁺/Calmodulin (CaM)-dependent kinase II (CaMKII) by CaM. Previous work showed that MEL increased the synthesis and translocation of CaM, suggesting that MEL activates CaM-dependent enzymes by this pathway. In this work we investigated whether MEL stimulates dendrite formation by CaMKII activation in organotypic cultures from adult rat hippocampus. We found that the CaMKII inhibitor, KN-62, abolished the MEL stimulatory effects on dendritogenesis and that MEL increased the relative amount of CaM in the soluble fraction of hippocampal slices. Also, PKC inhibition abolished dendritogenesis, while luzindole, an antagonist of MEL receptors (MT1/2), partially blocked the effects of MEL. Moreover, autophosphorylation of CaMKII and PKC was increased in presence of MEL, as well as phosphorylation of ERK1/2. Our results indicate that MEL stimulates dendrite formation through CaMKII and the translocation of CaM to the soluble fraction. Dendritogenesis elicited by MEL also required PKC activation, and signaling through MT1/2 receptors was partially involved. Data strongly suggest that MEL could repair the loss of hippocampal dendrites that occur in neuropsychiatric disorders by increasing CaM levels and activation of CaMKII.     

Analysis of medium manganese steel through cold-rolling and intercritical annealing or warm-rolling

ABSTRACT

Medium manganese steel is typically fabricated from hot-rolling followed by cold-rolling and intercritical annealing processes. However, a singular process, warm-rolling, is an appealing prospect. The microstructure, mechanical properties and texture of a 8?wt-% Mn–0.08?wt-% C steel was investigated by cold-rolling followed by intercritical annealing or warm-rolling. The product from both processes exhibited a highly refined microstructure as well as a large volume fraction of austenite. However, a slightly larger volume fraction as well as a more heterogeneous austenite morphology resulted from the warm-rolling process, associated with a higher work-hardening rate. Microstructural analysis revealed intense α-fibre components due to a higher strain following the warm-rolling process as well as a considerably high-angle grain boundary number which was associated with dislocation accumulation.

This paper is part of a Thematic Issue on Medium Manganese Steels.     

Characterization of polarization phenomenon in Al-Schottky CdTe detectors using a spectroscopic analysis method

CdTe radiation detectors equipped with Schottky contacts are known to show spectral response degradation over time under biasing. Nevertheless, they can be used as high-resolution spectrometers for X-rays and gamma-rays with moderate cooling and high voltage. Spectroscopic long-term measurements have been performed with Al/CdTe/Pt pixel detectors of 0.5, 1 and 2 mm thicknesses and ²⁴¹Am source from −13 to +16 °C to evaluate how long they can be operated. Experimental results are confronted to simulations using the charge accumulation model for electric field. Activation energy for collection efficiency stability and peak shift was measured at 1.0-1.2 eV although deep acceptor levels responsible for hole detrapping during polarization were evaluated by other methods at E_V +0.6-0.8 eV. The difference is probably due to a thermal effect of pre-polarization before biasing the detector.