Browsing by Author "Lu, HM"

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A computational efficient algorithm for protein sequence classification
(2003)
Li, YM
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Lu, HM
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友訊交大聯合研發中心
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D Link NCTU Joint Res Ctr
In this paper we present statistical algorithms to classify the stability of proteins by their sequence. A protein sequence consists of successive amino acid codes and can be considered as multivariate categorical data. Based on the statistical variance analysis for data set in each group (stable or unstable protein), the weights are calculated and become an important clue for the effects of the combination of amino acids codes on protein stability. Once the weights for every combination of amino acid codes have been decided, we can assign each protein a score presenting its stability. The distribution of the score for a stable protein is different from the score of an unstable protein. Our algorithm is well suit in the protein stability analysis by its sequence. We propose weighting algorithms and compare them as the results of protein stability classification. It provides an alternative for the protein stability classification and a predictable result as the reference before the protein mutation.
A computational investigation of electron energy states for vertically coupled semiconductor quantum dots
(2003)
Li, YM
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Lu, HM
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友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We study the electron energy state for single and vertically coupled quantum dots (QDs). Our realistic three-dimensional (3D) modeling for narrow gap semiconductor QDs considers: (1) the effective one electronic band Hamiltonian; (2) the energy- and position-dependent electron effective mass approximation; (3) a finite height hard-wall confinement potential; and (4) the Ben Daniel-Duke boundary conditions. A robust nonlinear iterative algorithm is applied to solve the model for disk- (DI-) and conical- (CO-) shaped QDs. For single QD, we find that the most stable against the dot size deviations (between dots of the same base radius) is the electron energy spectra of the CO-shaped QDs. For vertically coupled QDs with the fixed dot size, the energy spectra can be controlled by an interdot distance between two dots. Due to weak interaction of wavefunctions, electron energies of the CO-shaped coupled QDs are less dependent on the inter-distance than that of the DI-shaped coupled QDs. This investigation is related to optical spectra and useful in optoelectronics applications.
An investigation of magnetic field effects on energy states for nanoscale InAs/GaAs quantum rings and dots
(2003-03-01)
Li, YM
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Lu, HM
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友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
In this paper, we investigate the electron-hole energy states and energy gap in three-dimensional (313) InAs/GaAs quantum rings and dots with different shapes under external magnetic fields. Our realistic model formulation includes: (i) the effective mass Hamiltonian in non-parabolic approximation for electrons, (ii) the effective mass Hamiltonian in parabolic approximation for holes, (iii) the position- and energy-dependent quasi-particle effective mass approximation for electrons, (iv) the finite hard wall confinement potential, and (v) the Ben Daniel-Duke boundary conditions. To solve the 3D non-linear problem without any fitting parameters, we have applied the nonlinear iterative method to obtain self-consistent solutions. Due to the penetration of applied magnetic fields into torus ring region, for ellipsoidal- and rectangular-shaped quantum rings we find nonperiodical oscillations of the energy gap between the lowest electron and hole states as a function of external magnetic fields. The nonperiodical oscillation is different from 1D periodical argument and strongly dependent on structure shape and size. The result is useful to study magneto-optical properties of the nanoscale quantum rings and dots.
Dependence of energy gap on magnetic field in semiconductor nano-scale quantum rings
(2003-06-10)
Li, YM
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Lu, HM
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Voskoboynikov, O
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Lee, CP
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Sze, SM
We study the electron and hole energy states for a complete three-dimensional (3D) model of semiconductor nanoscale quantum rings in an external magnetic field. In this study, the model formulation includes: (i) the position dependent effective mass Hamiltonian in non-parabolic approximation for electrons, (ii) the position dependent effective mass Hamiltonian in parabolic approximation for holes, (iii) the finite hard wall confinement potential, and (iv) the Ben Daniel-Duke boundary conditions. To solve this 3D non-linear problem, we apply the non-linear iterative method to obtain self-consistent solutions. We find a non-periodical oscillation of the energy band gap between the lowest electron and hole states as a function of external magnetic fields. The result is useful in describing magneto-optical properties of the nano-scale quantum rings. (C) 2003 Elsevier Science B.V. All rights reserved.
Electron transition energy for vertically coupled InAs/GaAs semiconductor quantum dots and rings
(2004-04-01)
Li, YM
;
Lu, HM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We investigate the transition energy of vertically coupled quantum dots and rings (VCQDs and VCQRs) with a three-dimensional (3D) model under an applied magnetic field. The model formulation includes (1) the position-dependent effective mass Hamiltonian in the nonparabolic approximation for electrons, (2) the position-dependent effective mass Hamiltonian in the parabolic approximation for holes, (3) the finite hard-wall confinement potential, and (4) the Ben Daniel-Duke boundary conditions. We explore small VCQDs and VCQRs with disk (DI) and conical (CO) shapes. For small VCQDs and VCQRs, the electron-hole transition energy is dominated by the interdistance d which plays a crucial role in the tunable states of structures. Under zero magnetic field, there is about 25% variation in the electron ground state energy for both InAs/GaAs DI-shaped VCQDs and VCQRs with d varying from 0.4 nm to 4.8 nm. The energy spectra of the CO-shaped VCQDs are the most stable against the structure interdistance deviations (among dots and rings of the same volume). For a fixed d, VCQDs show diamagnetic shift; contrarily, VCQRs imply a nonperiodical transition among the lowest electron energy states. The energy band gap of VCQRs oscillates nonperiodically between the lowest electron and holes states as a function of external magnetic fields. Our investigation is constructive for studying the magneto-optical phenomena of the nanoscale semiconductor artificial molecules.
Energy states and magnetization in nanoscale quantum rings
(2002-10-15)
Voskoboynikov, O
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Li, YM
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Lu, HM
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Shih, CF
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Lee, CP
In this paper we calculate electron energy states and magnetization for torus shaped nanoscale quantum rings with external magnetic fields. We use the three-dimensional effective one-band Hamiltonian, the energy and position-dependent quasiparticle effective mass approximation, and the Ben Daniel-Duke boundary conditions. The dependence of the energy spectrum on the sizes and shapes of the quantum rings was calculated and the result agrees with experimental observations. Penetration of the magnetic field into torus region results in an aperiodic oscillation of magnetization at zero temperature. It saturates with the increasing of the magnetic field strength.
Geometric variations and magnetic field effects on electron energy states of InAs/GaAs quantum rings
(2003-04-01)
Li, YM
;
Lu, HM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We study electron energy states in three-dimensional (313) narrow-gap semiconductor quantum rings with ellipsoidal-shape torus (EST) and cut-bottom EST (CBEST) under an applied magnetic field. Our model includes the effective one-electronic-band Hamiltonian, the energy- and position-dependent electron effective mass approximation, and the Ben Daniel-Duke boundary condition. It is solved by the nonlinear iterative method to obtain a "self-consistent" solution numerically. The electron energy dependence on the inner radius, height, and lateral width is investigated for InAs/GaAs quantum rings with EST and CBE T shapes. The height and lateral width play a crucial role in varying the energy spectra of the rings. When the magnetic field is applied on a fixed-size CBEST ring, we find that there is a nonperiodical transition among the lowest electron energy states. Compared with the well-known ID Aharonov-Bohm periodical oscillation, the electron energy levels increase and oscillate nonperiodically when the magnetic field is increased. Our calculation for single-electron magnetization shows that the magnetization is nonperiodical and is a negative function of magnetic field.