In this paper we study a negatively charged exciton （NCE）, which is trapped by a two-dimensional （2D） parabolic potential. By using matrix diagonalization techniques, the correlation energies of the low-lying stat...In this paper we study a negatively charged exciton （NCE）, which is trapped by a two-dimensional （2D） parabolic potential. By using matrix diagonalization techniques, the correlation energies of the low-lying states with L=0, 1, and 2 are calculated as a function of confinement strength. We find that the size effects of different states are different. This phenomenon can be explained as a hidden symmetry, which is originated purely from symmetry. Based on symmetry, the features of the low-lying states are discussed in the influence of the 2D parabolic potential well. It is found that the confinement may cause accidental degeneracies between levels with different low-excited states. It is shown that the effect of quantum confinement on the binding energy of the heavy hole is stronger than that of a light hole.展开更多
An investigation of the optical properties of a hydrogenic donor in spherical parabolic quantum dots hasbeen performed by using the matrix diagonalization method.The optical absorption coefficient between the ground(L...An investigation of the optical properties of a hydrogenic donor in spherical parabolic quantum dots hasbeen performed by using the matrix diagonalization method.The optical absorption coefficient between the ground(L=0) and the first excited state (L=1) have been examined based on the computed energies and wave functions.The results are presented as a function of the incident photon energy for the different values of the confinement strength.These results show the effects of the quantum size and the impurity on the optical absorption coefficient of a donorimpurity quantum dot.展开更多
Using the method of matrix diagonalization, we investigate an off-center D^- in a spherical quantum dot （QD） subjected to a parabolic potential confinement. We discuss the effect of the position of an impurity in th...Using the method of matrix diagonalization, we investigate an off-center D^- in a spherical quantum dot （QD） subjected to a parabolic potential confinement. We discuss the effect of the position of an impurity in the QD on the binding energy of the D system, Eurthermore, we compare a negatively charged donor D^- with a neutral donor DO confined by a spherical QD with a parabolic potentiM. The results have clearly demonstrate the so-called quantum size effect. The binding energy is dependent on the confining potential hw0 and the impurity ion distance D.展开更多
To date, only a handful of studies have investigated the interlocutor effects on peer-peer test discourse, and they focus almost exdusively on the paired format in the Cambridge speaking tests, which is mostly a discu...To date, only a handful of studies have investigated the interlocutor effects on peer-peer test discourse, and they focus almost exdusively on the paired format in the Cambridge speaking tests, which is mostly a discussion type collaborative task. In the oral English test administered by a Chinese university under the present study, role-play is a major test type. This study chose for analysis three out of over 100 video recordings of test takers participating in role- play-based interaction. The author adopted conversation analysis （CA） and Young＇s （2000） constructivist, practice-oriented view of interaction and competence to assist the interpretation of speech exchange throughout the interaction. It is evident from the data that learners make use of various interactional resources and employ different strategies in the assessment- based role play. It could be tentatively concluded from the conversation analysis of the paired interaction that the interaction framework together with the participants＇ strategic competence in negotiating their own interactional resources, to a great extent, determines their joint performance of the collaborative task. The configuration of pairing in terms of proficiency is found to have an impact on joint interaction performance and strategic use. The implications of the current study include： interactional competence could be more readily accessed via role play than discussion type of pair work; qualitative conversation analysis of test takers＇ actual practices can reveal what quantitative methods are unable to detect, and therefore is an indispensable complement.展开更多
基金supported by National Natural Science Foundation of China under Grant No.10775035
文摘In this paper we study a negatively charged exciton （NCE）, which is trapped by a two-dimensional （2D） parabolic potential. By using matrix diagonalization techniques, the correlation energies of the low-lying states with L=0, 1, and 2 are calculated as a function of confinement strength. We find that the size effects of different states are different. This phenomenon can be explained as a hidden symmetry, which is originated purely from symmetry. Based on symmetry, the features of the low-lying states are discussed in the influence of the 2D parabolic potential well. It is found that the confinement may cause accidental degeneracies between levels with different low-excited states. It is shown that the effect of quantum confinement on the binding energy of the heavy hole is stronger than that of a light hole.
基金Supported by National Natural Science Foundation of China under Grant No.10775035
文摘An investigation of the optical properties of a hydrogenic donor in spherical parabolic quantum dots hasbeen performed by using the matrix diagonalization method.The optical absorption coefficient between the ground(L=0) and the first excited state (L=1) have been examined based on the computed energies and wave functions.The results are presented as a function of the incident photon energy for the different values of the confinement strength.These results show the effects of the quantum size and the impurity on the optical absorption coefficient of a donorimpurity quantum dot.
基金supported by the National Natural Science Foundation of China under Grant No.10775035
文摘Using the method of matrix diagonalization, we investigate an off-center D^- in a spherical quantum dot （QD） subjected to a parabolic potential confinement. We discuss the effect of the position of an impurity in the QD on the binding energy of the D system, Eurthermore, we compare a negatively charged donor D^- with a neutral donor DO confined by a spherical QD with a parabolic potentiM. The results have clearly demonstrate the so-called quantum size effect. The binding energy is dependent on the confining potential hw0 and the impurity ion distance D.
文摘To date, only a handful of studies have investigated the interlocutor effects on peer-peer test discourse, and they focus almost exdusively on the paired format in the Cambridge speaking tests, which is mostly a discussion type collaborative task. In the oral English test administered by a Chinese university under the present study, role-play is a major test type. This study chose for analysis three out of over 100 video recordings of test takers participating in role- play-based interaction. The author adopted conversation analysis （CA） and Young＇s （2000） constructivist, practice-oriented view of interaction and competence to assist the interpretation of speech exchange throughout the interaction. It is evident from the data that learners make use of various interactional resources and employ different strategies in the assessment- based role play. It could be tentatively concluded from the conversation analysis of the paired interaction that the interaction framework together with the participants＇ strategic competence in negotiating their own interactional resources, to a great extent, determines their joint performance of the collaborative task. The configuration of pairing in terms of proficiency is found to have an impact on joint interaction performance and strategic use. The implications of the current study include： interactional competence could be more readily accessed via role play than discussion type of pair work; qualitative conversation analysis of test takers＇ actual practices can reveal what quantitative methods are unable to detect, and therefore is an indispensable complement.
