Transfer Matrix method for computation of electron transmission through aperiodic MQW
This paper presents the Eigen values and corresponding Eigen functions for the electron states in an aperiodic and asymmetric Multiple Quantum Well structure. A faster, simpler, and accurate algorithm based on Transfer Matrix method has been introduced for solving time independent Schrödinger equation in the most general case of aperiodic and asymmetric MQW structure. The MQWs are aperiodic with varying well and barrier widths and asymmetric i.e., having different materials and effective masses for the different regions of the wells and barriers. Adjacent wells are coupled through the barriers. Effect of barrier width on the tunneling properties has also been investigated. The theoretical results are compared with experimental results of Giorgetta et all [1]. Results of the computation based on the general model agree well with experimental data.
Resonant Tunneling in Fibonacci Series Multiple Quantum Wells Nanostructures
Tunneling of electrons through the Fibonacci series multiple quantum wells (FMQWs) has been studied theoretically within unified transfer matrix approach. The characterisation of light-emitting one-dimensional photonic quasicrystals based on excitonic resonances is reported. The structures consist of GaAs/AlGaAs multiple quantum wells satisfying a Fibonacci sequence. The resulting band structure causes photons to become confined within the wells, where they occupy discrete quantized states. We have obtained an expression for the transmission coefficient of the Fibonacci series MQW nanostructures using analytical Transfer matrix method (ATMM) and found the resonance state within the photonic wells. These resonant states occur due to split pairs and coupling between degenerate states. The active photonic quasicrystals are good light emitters. The lack of periodicity in the Fibonacci series MQW results in resonant tunneling and strong emission. The resonant state describe here can be used to develop new types of optical devices, photonicswitching devices, detectors and optoelectronic devices.
Full-scale measurements of SO2 gas phase concentrations and slurry compositions in a wet flue gas desulphurisation spray absorber
Abstract Two measurement campaigns were carried out at ENERGI E2's Asnaes Power plant, unit 5. The unit has a capacity of 620 MW e and is equipped with a wet flue gas desulphurisation (FGD) plant employing a counter-current spray absorber with five spray levels. In the first campaign, the power plant was firing Orimulsion ® with 2.85 wt% S resulting in a flue gas concentration of SO 2 exceeding 2000 ppmv. In the second campaign, the fuel applied was a low-S blended coal and the SO 2 concentration in the raw gas was around 400 ppmv. A novel probe for in situ sampling of gas phase concentrations in wet FGD spray absorbers was developed and applied for measuring axial profiles of the SO 2 gas phase concentrations in the absorber. The expected decrease in SO 2 concentrations along the height of the absorber was found in the spray section (from height 26.5 to 36.2 m) whereas the SO 2 concentration above the holding tank and below the gas inlet was quite low probably due to long local residence times in the region. Horizontal variations, due to somewhat different flow conditions near the column wall were investigated and the SO 2 concentrations were found to be higher near the wall. Measurements at different gross loads showed that the SO 2 gas phase concentration at a given position inside the absorber was roughly linearly related to the L/G ratio in the measuring interval. Turning off one of the lower spray levels, while burning coal with low S content, did not lower the overall removal efficiency of the absorber. However, the SO 2 gas phase concentration inside the lower part of the absorber was increased by a factor of 2–3. Measurements of slurry pH at different positions showed a decrease of approximately 0.5 units from the upper to the lower part of the absorber. The full-scale measurements provide a detailed set of experimental data for validation of mathematical models of a wet FGD spray absorber.