Morphological and structural effects of NaOH added to silica

The effects of addition of NaOH (from 0.5 to 3%) upon the morphological and structural properties of a commercial silica support have been investigated in the range from 300 to 780° C: samples have been characterized by means of surface area, pore volume, pore and particle size distribution measurements, chemical and X-ray analysis, electron and optical microscopy observations. Results of various techniques were allied in showing the prevalency, at the lowest temperatures (<600° C), of surface modifications involving chemical reaction and incipient sintering while at the highest temperatures (>600° C) modifications entail the entire mass which undergoes a crystallization process. The singular presence of keatite, not hitherto reported for similar systems, allowed an interpretation of the crystallization process in terms of the sequence: amorphous cristobalite (keatite) quartz.     

High-temperature chemical heat pump based on reversible catalytic reactions of cyclohexane-dehydrogenation/benzene-hydrogenation: Comparison of the potentialities of different flow diagrams

The authors compare various flow diagrams for high temperature chemical heat pumps (HTCHP) based on the reversible cyclohexane-dehydrogenation/benzene-hydrogenation reactions. A new technological flow diagram for HTCHP is suggested. The peculiarity of this diagram is a multipurpose use of hydrogen-permeable membranes. A comparative thermodynamic analysis of the flow diagrams under consideration is undertaken in order to examine the influence of various factors on the heat efficiency and coefficient of performance of the heat pump. It is shown that the use of the hydrogen-permeable membranes in principle allows one to improve the performance of the HTCHPs and to extend the field of their application in comparison with the HTCHPs based on the flow diagrams suggested earlier.     

The influence of iron in synthetic zeolites on the decomposition of perborate

Commercial Grace 4A Zeolite exchanged with Fe³⁺ ions, pumice from different geological flows and their hydrothermally derived zeolites have been characterised as to the distribution and structural configuration of the iron content. Decomposition capacity of perborate (active constituent of detergent formulations) is not only determined by the total Fe content of the zeolite but also by the oxidation state, electron configuration and coordination. For a similar oxygen coordination, structural Fe²⁺ is more active in the decomposition of perborate than Fe³⁺. Exchanged Fe³⁺ ions of zeolites exhibit higher perborate decomposition capacity than structural Fe³⁺ or the Fe³⁺ of iron oxide.     

Mechanism of O2 evolution on TiO2 photoanodes

The mechanism of O₂ evolution over titanium oxide photoanodes has been studied by relating structural properties, derived from XRD and XPS, and electrochemical properties currents, (cyclic voltammetry and flatband potentials) to the performance in PEC cells of five specimens of lowest and highest photoelectrochemical efficiency.     

Forecasting nonlinear time series with neural network sieve bootstrap

A new method to construct nonparametric prediction intervals for nonlinear time series data is proposed. Within the framework of the recently developed sieve bootstrap, the new approach employs neural network models to approximate the original nonlinear process. The method is flexible and easy to implement as a standard residual bootstrap scheme while retaining the advantage of being a nonparametric technique. It is model-free within a general class of nonlinear processes and avoids the specification of a finite dimensional model for the data generating process. The results of a Monte Carlo study are reported in order to investigate the finite sample performances of the proposed procedure.     

New-generation of cryogenic sapphire microwave oscillators for space, metrology, and scientific applications

This article reports on the characterization of cryogenic sapphire oscillators (CSOs), and on the first test of a CSO in a real field installation, where ultimate frequency stability and continuous operation are critical issues, with no survey. Thanks to low-vibration liquid-He cryocooler design, Internet monitoring, and a significant effort of engineering, these oscillators could bridge the gap from an experiment to a fully reliable machine. The cryocooler needs scheduled maintenance every 2 years, which is usual for these devices. The direct comparison of two CSOs demonstrates a frequency stability of 5 × 10(-16) for 30 s ≤ τ ≤ 300 s integration time, and 4.5 × 10(-15) at 1 day (1 × 10(-14) typical). Two prototypes are fully operational, codenamed ELISA and ULISS. ELISA has been permanently installed the new deep space antenna station of the European Space Agency in Malargu?e, Argentina, in May 2012. ULISS is a transportable version of ELISA, modified to fit in a small van (8.5 m(2) footprint). Installation requires a few hours manpower and 1 day of operation to attain full stability. ULISS, intended for off-site experiments and as a technology demonstrator, and has successfully completed two long-distance travels.