Structural and electrical properties of γ-alumina - lithium sulphate films

Li₂SO₄ as a model ionic conductor has received very much attention over several decades. Especially, in recent years Li₂SO₄ and Li₂SO₄-Al₂O₃ have been mentioned as promising proton conducting electrolytes for applications such as intermediate temperature fuel cells and novel cogeneration systems regarding H₂S handling devices. This has encouraged us to strive towards further improvement of the properties of the materials to meet the demands of the applications. In order to improve the properties of this system, a new process, a suspension technique, has been recently developed to prepare nanostructured powder and thin film Li₂SO₄-Al₂O₃ membranes. The powders and thin films have a well crystallised structure composed of two phases, Li₂SO₄ and γ-Al₂O₃, and excellent mechanical strength. The thin film thickness is in the scale of a few to several mm with a smooth and shining surface and a homogeneous macroscopic structure. It is a very interesting phenomenon that all samples show no significant conductivity increase at the temperature of the phase transition (∼ 577 °C) from β to α phase of pure Li₂SO₄. This transition has important significance for applications. The conductivity of the two-phase film materials has been greatly enhanced, where the xLi₂SO₄-(1-x)Al₂O₃ (x=58) sample shows the highest conductivity, about 1 S/cm at 600 °C; the activation energy decreases with increasing Li₂SO₄ content. These results agree with the so called composite effect for the conductivity enhancement observed earlier for two-phase bulk materials. Based on the four-step proton conducting mechanism in sulphate-based materials, this work may propose a new mechanism. The protons might jump in a water network associated with the water molecular re-orientation, which is accompanied with the single proton jump of the four-step transportation among SO ₄ ²⁻ groups from one Li₂SO₄ molecule to another. The former mechanism occur in the interfacial region between the Li₂SO₄ and the Al₂O₃ grains, while the latter occur in the bulk of the Li₂SO₄ grains. These thin film materials are intended for use as proton conducting ceramic membranes in applications such as desulphurisation and fuel cell co-generation plants. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

On the semi-hyponormal n-tuple of operators

The theory of singular integral model and trace formula is extended to the context of hyponormal or semi-hyponormal n-tuple of operators. The spectrum of noncommutative n-tuple of operators is examined.     

Simulation of the Burridge-Knopoff model of earthquakes with variable range stress transfer

Simple models of earthquake faults are important for understanding the mechanisms for their observed behavior, such as Gutenberg-Richter scaling and the relation between large and small events, which is the basis for various forecasting methods. Although cellular automaton models have been studied extensively in the long-range stress transfer limit, this limit has not been studied for the Burridge-Knopoff model, which includes more realistic friction forces and inertia. We find that the latter model with long-range stress transfer exhibits qualitatively different behavior than both the long-range cellular automaton models and the usual Burridge-Knopoff model with nearest-neighbor springs, depending on the nature of the velocity-weakening friction force. These results have important implications for our understanding of earthquakes and other driven dissipative systems.     

On the bound of the Lyapunov exponents for continuous systems

In this paper, both upper bounds and lower bounds for all the Lyapunov exponents of continuous differential systems are determined. Several examples are given to show the application of the estimates derived here.     

Inverse energy cascade correlated with turbulent-structure generation in toroidal plasma

We report the first experimental observation of the inverse energy cascade correlated with the generation of large turbulent structures. Spectral energy is nonlinearly transferred from the unstable region of the spectrum into large coherent structures and into broadband turbulence in agreement with theoretical expectations. These results are obtained by producing plasma in the H-1 heliac whose parameters allow a single-field, Hasegawa-Mima-type model to be used for the spectral energy transfer analysis.     

MASSIS: a mass spectrum simulation system 1. Principle and method

A mass spectrum simulation system was developed. The simulated spectrum for a given target structure is computed based on the cleavage knowledge and statistical rules established and stocked in pivot databases: cleavage rule knowledge, function groups, small fragments and fragment-intensity relationships. These databases were constructed from correlation charts and statistical analysis of large population of organic mass spectra using data mining techniques. Since 1980, several systems were proposed for mass spectrum simulation, but in present there is no any commercial software available. This shows the complexity and difficulties in the development of a such system. The reported mass spectral simulation system in this paper could be the first general software for organic chemistry use     

Imaging the velocity profiles in tubeless siphon flow by NMR microscopy

We report on the use of NMR micro-imaging to observe flow within a tubeless siphon. The flow is maintained in a visco-elastic liquid of high extensional viscosity, namely 0.5% w/v 8 million Dalton polyethylene oxide in water. The velocity profiles reveal a significant velocity gradient in the vertical direction as well as a transition from near-Poiseuille flow at the pipe entrance to plug flow far from the pipe entrance towards the base of the tubeless siphon.     

Sensitivity enhancement of HCACO by using an HMQC magnetization transfer scheme

Previous theoretical calculations have demonstrated that the multiquantum relaxation rate of (1)H(alpha)-(13)C(alpha)(R(MQ)) is, on average, 1.3 +/- 0.4 or 1.7 +/- 0.6 times slower than the single-quantum relaxation rate of (13)C(alpha)(R(C)) for a sample with or without, respectively, amide protons. By taking advantage of this fact and by using the PEP sensitivity enhancement scheme, an HMQC version of the HCACO experiment has been developed. We demonstrate that this new experiment is 23 and 55% more sensitive than the original HSQC version of the HCACO experiment, at constant times of 7 and 27 ms, respectively, for a sample of the BC domain of the ciliary neurotrophic factor receptor protein dissolved in D(2)O at 20 degrees C.     

Broadband dispersion compensation using microstructure fibers

Beijing University of Posts and Telecommunications, Beijing 100876Dispersion and dispersion slope compensation of 10-Gb/s pulses using microstructure fibers (MFs) is demonstrated experimentally. A 26-m MF is used to compensate the dispersion of 2-km standard singe mode fiber in a 20-nm range in C band. The experimental results show that a significant improvement can be achieved in the quality of the observed pulses with the dispersion compensation. Moreover, the further research shows that the MF can compensate the anomalous dispersion of a single mode fiber within ±0.27 ps/(nm·km) over a 50-nm wavelength range from 1520 to 1570 nm.     

Novel fluorene-alt-thienylenevinylene-based copolymers: tuning luminescent wavelength via thiophene substitution position

The design, synthesis and characterization of three novel fluorene-alt-thienylenevinylene-based copolymers have been reported. All these polymers consist of similar repeating unit, while thiophene unit with different substitution position is incorporated to well tune the conjugation degree that realizes multi-color luminance. These polymers show emission maxima in the blue, orange and red region of the visible spectrum. Considering the compatibility of luminescent materials with similar structure units, our methodology provides a facile and effective way for designing multi-color luminescent polymeric blending to realize full color electroluminescent (EL) devices. All these polymers have been successfully tested in single-layer sandwiched EL devices.