Excitons and shallow impurities in GaAs-Ga1-xAlxAs semiconductor heterostructures within a fractional-dimensional space approach: Magnetic-field effects

The fractional-dimensional space approach is extended to study exciton and shallow-donor states in symmetric-coupled GaAs-Ga1-xAlxAs multiple quantum wells. In this scheme, the real anisotropic 'exciton (or shallow donor) plus multiple quantum well' semiconductor system is mapped, for each exciton (or donor) state, into an effective fractional-dimensional isotropic environment, and the fractional dimension is essentially related to the anisotropy of the actual semiconductor system. Moreover, the fractional-dimensional space approach was extended to include magnetic-field effects in the study of shallow-impurity states in GaAs-Ga1-xAlxAs quantum wells and superlattices. In our study, the magnetic field was applied along the growth direction of the semiconductor heterostructure, and introduces an additional degree of confinement and anisotropy besides the one imposed by the heterostructure barrier potential. The fractional dimension is then related to the anisotropy introduced both by the heterostructure barrier potential and magnetic field. Calculations within the fractional-dimensional space scheme were performed for the binding energies of 1s-like heavy-hole direct exciton and shallow-donor states in symmetric-coupled semiconductor quantum wells, and for shallow-impurity states in semiconductor quantum wells and superlattices under growth-direction applied magnetic fields. Fractional-dimensional theoretical results are shown to be in good agreement with previous variational theoretical calculations and available experimental measurements.6119131041311

Self-similarity and anti-self-similarity of the effective Lande g(perpendicular to) factor in GaAs-(Ga,Al)As Fibonacci superlattices under in-plane magnetic fields

A theoretical study of the effects of in-plane magnetic fields on the Lande g(perpendicular to) factor associated to conduction electrons in GaAs-(Ga,Al)As Fibonacci superlattices is presented. We have used the Ogg-McCombe effective Hamiltonian, which includes nonparabolic and anisotropy effects, in order to describe the electron states in the Fibonacci heterostructure. We have expanded the corresponding electron envelope wave functions in terms of harmonic-oscillator wave functions, and obtained the Lande g(perpendicular to) factor for magnetic fields related by even powers of the golden mean tau=(1+root 5)/2. Theoretical results for GaAs-(Ga,Al)As Fibonacci superlattices, under magnetic-field values scaled by tau(2n), clearly exhibit a self-similar (for even n) or anti-self-similar (for odd n) behavior for the Lande g(perpendicular to) factors, as appropriate.74

Magnetic-field effects on shallow impurities in semiconductor GaAs-(Ga,Al)As quantum wells and superlattices within a fractional-dimensional space approach

We have used the fractional-dimensional space approach to study the effects of applied magnetic fields on shallow-impurity states in GaAs-(Ga,Al)As quantum welts and superlattices. In this scheme, a semiconductor heterostructure is treated as isotropic in an effective fractional-dimensional space, and the value of the fractional dimension is associated to the degree of anisotropy introduced both by the heterostructure barrier potential and applied magnetic field. Theoretical fractional-dimensional calculations for shallow-impurity states in GaAs-(Ga,Al)As semiconductor quantum wells and superlattices, under magnetic fields applied along the growth direction, were shown to be in overall agreement with available experimental measurements and previous variational calculations. (C) 2000 Elsevier Science B.V. All rights reserved.8323924

A theoretical resonant-tunnelling approach to electric-field effects in quasiperiodic Fibonacci GaAs-(Ga,Al)As semiconductor superlattices

A theoretical resonant-tunnelling approach is used in a detailed study of the electronic and transmission properties of quasiperiodic Fibonacci GaAs-(Ga,Al)As semiconductor superlattices, under applied electric fields. The theoretical scheme is based upon an exact solution of the corresponding Schroedinger equations in different wells and barriers, through the use of Airy functions, and a transfer-matrix technique. The calculated quasibound resonant energies agree quite well with previous theoretical parameter-based results within a tight-binding scheme, in the particular case of isolated Fibonacci building blocks. Theoretical resonant-tunnelling results for S-4 and S-5 generations of the quasiperiodic Fibonacci superlattice reveal the occurrence of anticrossings of the resonant levels with applied electric fields, together with the conduction-and valence-level wave function localization properties and electric-field-induced migration to specific regions of the semiconductor quasiperiodic heterostructure. Finally, theoretical resonant-tunnelling calculations for the interband transition energies are shown to be in quite good quantitative agreement with previously reported experimental photocurrent measurements.10163557356

Electron Lande g factor in GaAs-(Ga,Al)As quantum wells under applied magnetic fields: Effects of Dresselhaus spin splitting

The effects of the Dresselhaus spin splitting on the Lande g factor associated with conduction electrons in GaAs-(Ga,Al)As quantum wells are studied by using the nonparabolic Ogg-McCombe effective Hamiltonian. The g factor and cyclotron effective mass are calculated as functions of applied magnetic fields (along both the growth and in-plane directions) and GaAs well widths of the heterostructure. Present calculations indicate that in GaAs-(Ga,Al)As heterostructures, the inclusion of the Dresselhaus term leads to very small corrections in the effective Lande factor. Taking into account the effects of nonparabolic and anisotropic terms in the Hamiltonian is fundamental in obtaining quantitative agreement with experimental measurements. Moreover, the present results suggest that previous theoretical work on the Dresselhaus spin-splitting effects on the effective Lande factor should be viewed with caution if nonparabolic and anisotropic effects are not taken into account. (c) 2008 American Institute of Physics.104

Notes for genera – Ascomycota

Knowledge of the relationships and thus the classification of fungi, has developed rapidly with increasingly widespread use of molecular techniques, over the past 10--15 years, and continues to accelerate. Several genera have been found to be polyphyletic, and their generic concepts have subsequently been emended. New names have thus been introduced for species which are phylogenetically distinct from the type species of particular genera. The ending of the separate naming of morphs of the same species in 2011, has also caused changes in fungal generic names. In order to facilitate access to all important changes, it was desirable to compile these in a single document. The present article provides a list of generic names of Ascomycota (approximately 6500 accepted names published to the end of 2016), including those which are lichen-forming. Notes and summaries of the changes since the last edition of `Ainsworth Bisby's Dictionary of the Fungi' in 2008 are provided. The notes include the number of accepted species, classification, type species (with location of the type material), culture availability, life-styles, distribution, and selected publications that have appeared since 2008. This work is intended to provide the foundation for updating the ascomycete component of the ``Without prejudice list of generic names of Fungi'' published in 2013, which will be developed into a list of protected generic names. This will be subjected to the XIXth International Botanical Congress in Shenzhen in July 2017 agreeing to a modification in the rules relating to protected lists, and scrutiny by procedures determined by the Nomenclature Committee for Fungi (NCF). The previously invalidly published generic names Barriopsis, Collophora (as Collophorina), Cryomyces, Dematiopleospora, Heterospora (as Heterosporicola), Lithophila, Palmomyces (as Palmaria) and Saxomyces are validated, as are two previously invalid family names, Bartaliniaceae and Wiesneriomycetaceae. Four species of Lalaria, which were invalidly published are transferred to Taphrina and validated as new combinations. Catenomycopsis Tibell Constant. is reduced under Chaenothecopsis Vain., while Dichomera Cooke is reduced under Botryosphaeria Ces. De Not. (Art. 59)