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81.
The role of extra-framework and framework aluminium in wet-ion exchanged Fe-ZSM5 has been studied using 29Si NMR and 27Al triple quantum magic angle spinning (3QMAS) NMR. A series of samples were studied, the parent material, the wet ion exchanged Fe-ZSM5 and Fe-ZSM5 that has been used in the decomposition of N2O with varying reaction conditions. Various framework and extra-framework aluminium species have been identified. It was found that cationic Fe species prefer to replace the Brønsted acid protons in their charge balancing role at those aluminium sites associated with the largest quadrupolar product. The framework aluminium atoms that pertain to the smaller quadrupolar product, which are either charge balanced by extra-framework aluminium or a proton, are much less prone to exchange. In the catalytic decomposition of N2O it seemed that water present in small amounts enhances the catalytic activity. However, water also decreases the long term stability and performance by dealuminating the zeolite framework. With a high amount of water present, Fe-ZSM5 was destabilised and catalytically inferior. 相似文献
82.
We study the stability of topological order against local perturbations by considering the effect of a magnetic field on a spin model--the toric code--which is in a topological phase. The model can be mapped onto a quantum loop gas where the perturbation introduces a bare loop tension. When the loop tension is small, the topological order survives. When it is large, it drives a continuous quantum phase transition into a magnetic state. The transition can be understood as the condensation of "magnetic" vortices, leading to confinement of the elementary "charge" excitations. We also show how the topological order breaks down when the system is coupled to an Ohmic heat bath and relate our results to error rates for topological quantum computations. 相似文献
83.
Matthias Echternach Louisa Traser Michael Markl Bernhard Richter 《Journal of voice》2011,25(6):670-677
Purpose
Professional male altos (countertenors) mostly use a register function, which is considered to be derived from falsetto. However, the sound produced differs in professional altos compared with the modal register or falsetto of untrained voices. The aim of this study was to analyze differences of the vocal tract shapes in male alto register functions.Material and Methods
Dynamic real-time magnetic resonance imaging of eight frames per second was used to analyze the vocal tract profile in seven professional male altos who sang on the vowel /a/, an ascending and descending scale from G3 (196 Hz) to E4 (330 Hz). The scale included their register transition from modal register to stage (counter) falsetto and naïve falsetto.Results
Register transitions from modal register to stage falsetto were associated with increased lip opening, jaw retraction, elevation and back positioning of the tongue, pharynx narrowing, uvula elevation, drop of larynx height, and tilting of the larynx. Differences between stage and naïve falsetto were found mostly with regard to lip opening and pharynx width.Conclusions
The differences between the vocal tract configurations might have an impact on the acoustic characteristics observed in professional male alto register functions. 相似文献84.
Calmano T Siebenmorgen J Reichert F Fechner M Paschke AG Hansen NO Petermann K Huber G 《Optics letters》2011,36(23):4620-4622
We fabricated waveguides in Pr:SrAl(12)O(19) crystals by direct femtosecond laser writing. The propagation losses were calculated to be as low as 0.16 dB/cm at a wavelength of 633 nm. Laser oscillation in a diode-pumped waveguide at a wavelength of 643.5 nm was realized. The output power of the waveguide laser was 28.1 mW at a slope efficiency of 8%. 相似文献
85.
Raúl Pérez-Ruiz Robert Fichtler Yrene Diaz Miara Matthieu Nicoul Dominik Schaniel Helfried Neumann Matthias Beller Dirk Blunk Axel G. Griesbeck Axel Jacobi von Wangelin 《Journal of fluorescence》2010,20(3):657-664
The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy. UV spectra in gas phase and DMSO solution were calculated by TD-DFT which revealed the existence of two low-energy excited singlet states with strong pH-sensitivity. 相似文献
86.
Johannes Tauer Heinrich Kofler Elisabeth Schwarz Ernst Wintner 《Central European Journal of Physics》2010,8(2):242-248
Laser ignition is considered to be one of the most promising future concepts for internal combustion engines. It combines the legally required reduction of pollutant emissions and higher engine efficiencies. The igniting plasma is generated by a focused pulsed laser beam. Having pulse durations of a few nanoseconds, the pulse energy E p for reliable ignition amounts to the order of 10 mJ. Different methods of laser ignition with an emphasis on fiber-based systems will be discussed and evaluated. 相似文献
87.
88.
We study dc charge and spin transport through a weakly coupled quantum dot, driven by a nonadiabatic periodic change of system parameters. We generalize the model of Tien and Gordon to simultaneously oscillating voltages and tunnel couplings. When applying our general result to the two-parameter charge pumping in quantum dots, we find interference effects between the oscillations of the voltage and tunnel couplings. We show that these interference effects may explain recent measurements in metallic islands. Furthermore, we discuss the possibility to electrically pump a spin current in presence of a static magnetic field. 相似文献
89.
90.
The initial value problem for a model Boltzmann equation of a two dimensional gas with a continuous or discrete energy distribution function and a transition probability δ(? - ?') is solved exactly; ? and ?' are the total energies before and after collision. 相似文献