In situ study of the temperature stability of TiO1.05 titanium monooxide using synchrotron radiation

The temperature stability of cubic TiO1.05 titanium monooxide is investigated. An in situ X-ray structural analysis is performed using synchrotron radiation in a high temperature vacuum chamber. It is found that under poor vacuum and at high heating rates of up to 1250 C, the structural transformations in TiO1.05 occur at 630 C. In particular, there is a phase transition from TiO1.05 (space group Fm-3m) to rhombohedraic Ti2O3 (space group R-3c) via Ti2.5O3 (space group Immm). © 2013 Allerton Press, Inc

Synthesis of octahydro-2H-chromen-4-ol from vanillin and isopulegol over acid modified montmorillonite clays: Effect of acidity on the Prins cyclization

Two calcium-rich natural layered aluminosilicates containing 90–95 wt.% montmorillonite were chemically activated using 0.125–3.0 M HCl solutions. Structural and textural properties were characterized by X-ray diffraction, elemental analysis and N2-adsorption/desorption analyses. According to infrared spectroscopy using pyridine as probe molecule, the amount of Brønsted acid sites increased when increasing HCl concentration. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2H-chromen-4-ol, carried out in toluene at 35 °C. It was found that the amount of Brønsted acid sites and the microporosity of the catalysts are key factors for the control of the reaction rate and the selectivity towards octahydro-2H-chromen-4-o

Determination of Debye Temperatures and Lamb-Mössbauer Factors for LnFeO3 Orthoferrite Perovskites (Ln = La, Nd, Sm, Eu, Gd)

Lanthanide orthoferrites have wide-ranging industrial uses including solar, catalytic and electronic applications. Here a series of lanthanide orthoferrite perovskites, LnFeO3 (Ln = La; Nd; Sm; Eu; Gd), prepared through a standard stoichiometric wet ball milling route using oxide precursors, has been studied. Characterisation through X-ray diffraction and X-ray fluorescence confirmed the synthesis of phase-pure or near-pure LnFeO3 compounds. 57Fe Mössbauer spectroscopy was performed over a temperature range of 10 K to 293 K to observe hyperfine structure and to enable calculation of the recoil-free fraction and Debye temperature (θD) of each orthoferrite. Debye temperatures (Ln = La 474 K; Nd 459 K; Sm 457 K; Eu 452 K; Gd 473 K) and recoil-free fractions (Ln = La 0.827; Nd 0.817; Sm 0.816; Eu 0.812; Gd 0.826) were approximated through minimising the difference in the temperature dependent experimental Centre Shift (CS) and theoretical Isomer Shift (IS), by allowing the Debye temperature and Isomer Shift values to vary. This method of minimising the difference between theoretical and actual values yields Debye temperatures consistent with results from other studies determined through thermal analysis methods. This displays the ability of variable-temperature Mössbauer spectroscopy to approximate Debye temperatures and recoil-free fractions, whilst observing temperature induced transitions over the temperature range observed. X-ray diffraction and Rietveld refinement show an inverse relationship between FeO6 octahedral volume and approximated Debye temperatures. Raman spectroscopy show an increase in the band positions attributed to soft modes of Ag symmetry, Ag(3) and Ag(5) from La to GdFeO3 corresponding to octahedral rotations and tilts in the [010] and [101] planes respectively

Ionospheric storms monitored by ground and space based GPS techniques

Ionospheric storms affect accuracy, reliability and availability of global navigation satellite systems (GNSS). On the other hand, ground and space based GNSS techniques enable the capability to explore different temporal and spatial aspects of ionospheric perturbations. We discuss ionospheric perturbation features of several severe storms by combining ground and space based GPS measurements to get a more detailed view on the perturbation mechanism. Deduced is the temporal and horizontal structure of the ionosphere at both hemispheres based on 30 s sampled high latitude TEC data from the ground tracking network of the International GPS Service (IGS). Whereas the ground based measurements show strong horizontal perturbation induced convection of plasma crossing the pole from day- to night-side, the spaceborne measurements on CHAMP indicate a severe vertical redistribution of the ionospheric plasma during the selected events. Presented are also some average features of ionospheric storms as observed over the European region since 10 years

Monitoring the generation and propagation of ionospheric disturbances and effects on GNSS positioning

To gain a more comprehensive view of the powerful and dynamic plasma processes occurring during ionospheric storms, ground- and space-based observations using Global Navigation Satellite System (GNSS) signals have been analyzed. Several case and statistical studies of ionospheric storms are presented, clearly showing the generation and propagation of ionospheric disturbances. Discussed are the capabilities of advanced techniques for routine monitoring of the ionosphere and studying the ionospheric perturbations. It is concluded that the permanent monitoring of the ionosphere-plasmasphere system can play a significant role in mitigating adverse space weather effects on GNSS-based positioning

Ionospheric Radio Occultation Measurements Onboard CHAMP

The GPS radio occultation measurements of the ionosphere have been performed onboard CHAMP since 11 April 2001. More than 115000 vertical electron density profiles have been derived so far by a model assisted retrieval technique. The talk addresses the capabilities of the ionospheric radio occultation (IRO) technique for routinely monitoring the global ionosphere with the purpose of deriving value added data products and studying ionospheric perturbations. Discussed are the model assisted retrieval technique, operational data processing and results from the validation of vertical electron density profiles. These profiles may not only be used to validate other models, but they also provide a good data basis for developing new models of key ionospheric parameters such as the critical frequency, density peak height, and plasma scale height. Such models would help us to improve retrieval procedures and tomographic reconstruction techniques. Travelling ionospheric irregularities (TIDs) and other types of ionospheric irregularities may be studied on the basis of CHAMP radio occultation measurements. Shown are the latitudinal distribution and the diurnal and seasonal dynamics of the irregularities. The most prominent feature is the significant enhancement of winter time TID activities over the polar regions. Thanks to the operational data processing capabilities, the data products may also contribute to the space weather monitoring of the ionosphere