Browsing by Author "Liao, Y. H."

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Anomalous anticrossing of neutral exciton states in GaAs/AlGaAs quantum dots
(2014-03-12)
Kumar, S.
;
Zallo, E.
;
Liao, Y. H.
;
Lin, P. Y.
;
Trotta, R.
We study the effects of heavy hole-light hole (HH-LH) mixing on fine-structure and polarization properties of neutral excitons ( X-0) confined in single GaAs/AlGaAs quantum dots (QDs) under the application of anisotropic biaxial stress. In the large HH-LH mixing regime, these properties are substantially different from the usually observed properties in the case of small or no mixing. By varying the applied stress, the mixing in the initially strain-free QDs changes from similar to 0 to similar to 70% and an anomalous anticrossing of the X-0 bright states is observed. The latter is attributed to stress-induced rotation of the in-plane principal axis of the QD confinement potential. We show that the analysis of free-excitonic emission of bulk GaAs surrounding the QDs not only allows estimation of the stress and mixing in the QDs, but also provides the quantum-confinement-induced HH-LH splitting of the as-grown QDs.
COMPARISON OF THE PROPULSION PERFORMANCE OF AEROSPIKE AND BELL-SHAPED NOZZLE USING HYDROGEN PEROXIDE MONOPROPELLANT UNDER SEA-LEVEL CONDITION
(2019-06-01)
Lai, A.
;
Wei, S. S.
;
Lai, C. H.
;
Chen, J. L.
;
Liao, Y. H.
This study investigates numerically the performance of applying aerospike nozzle in a hydrogen peroxide mono-propellant propulsion system. A set of governing equations, including continuity, momentum, energy and species conservation equations with extended k-epsilon turbulence equations, are solved using the finite-volume method. The hydrogen peroxide mono-propellant is assumed to be fully decomposed into water vapor and oxygen after flowing through a catalyst bed before entering the nozzle. The aerospike nozzle is expected to have high performance even in deep throttling cases due to its self-compensating characteristics in a wide range of ambient pressure environments. The results show that the thrust coefficient efficiency (C-f,C-eta) of this work exceeds 90% of the theoretical value with a nozzle pressure ratio (PR) in the range of 20 similar to 45. Many complex gas dynamics phenomena in the aerospike nozzle are found and explained in the paper. In addition, performance of the aerospike nozzle is compared with that of the bell-shape nozzle.