Two-electron singlet states in semiconductor quantum dots with Gaussian confinement: A single-parameter variational calculation

The problem of two electrons in a three-dimensional quantum dot with Gaussian confinement is investigated for the singlet pairing by a variational method with a very simple wavefunction containing only a single parameter and a Jastrow-like factor, which is shown to yield fairly good results for deep confining potentials. The calculation is also performed for a few realistic semiconductor quantum dots and the phase diagrams for the two-electron singlet states are obtained for these materials. The pair density function is calculated for several parameter values and its peak positions are obtained as a function of the confinement length and the depth of the potential to study the behaviour of the electron-pair size. The size of the bound pair of electrons is also obtained by directly calculating the average distance between the two electrons in three different ways and compared with the pair correlation results. It is furthermore shown that, other properties remaining the same, the two-electron energy and the electron-pair size depend crucially on the effective electronic mass and the dielectric constant of the material. Finally, the ways of improving the wavefunction are also indicated. © IOP Publishing Ltd

Quantum size effect on the phonon-induced Zeeman splitting in a GaAs quantum dot with Gaussian and parabolic confining potentials

The Zeeman splitting of the ground and the first excited level of a Gaussian GaAs quantum dot is studied in the presence of electron-longitudinal-optical (LO)-phonon interaction incorporating the spin of the electron and is compared with the case of a parabolic dot. It is shown that the Zeeman splitting is suppressed because of the polaronic interaction and becomes strongly size dependent, but the parabolic confinement overestimates this Zeeman suppression. It is also shown that although the energy levels are split because of the spin-field interaction, the cyclotron frequencies and the Zeeman lines are independent of the electron spin in the dipole transition. © 2008 Elsevier B.V. All rights reserved

Polaronic effects in a Gaussian quantum dot

The problem of an electron interacting with longitudinal-optical (LO) phonons is investigated in an N-dimensional quantum dot with symmetric Gaussian confinement in all directions using the Rayleigh-Schrödinger perturbation theory, a variant of the canonical transformation method of Lee-Low-Pines, and the sophisticated apparatus of the Feynman-Haken path-integral technique for the entire range of the coupling parameters and the results for N = 2 and N = 3 are obtained as special cases. It is shown that the polaronic effects are quite significant for small dots with deep confining potential well and the parabolic potential is only a poor approximation of the Gaussian confinement. The Feynman-Haken path-integral technique in general gives a good upper bound to the ground state energy for all values of the system parameters and therefore is used as a benchmark for comparison between different methods. It is shown that the perturbation theory yields for the ground state polaron self-energy a simple closed-form analytic expression containing only Gamma functions and in the weak-coupling regime it provides the lowest energy because of an efficient partitioning of the Gaussian potential and the subsequent use of a mean-field kind of treatment. The polarization potential, the polaron radius and the number of virtual phonons in the polaron cloud are obtained using the Lee-Low-Pines-Huybrechts method and their variations with respect to different parameters of the system are discussed. © 2007 Elsevier Ltd. All rights reserved

The Statistical Investigation on Posidonia Oceanica (L.) Delile Meadows in Izmir, Turkey

WOS: 000271501900010In this study, variance analysis technique on unbalanced data was examined, and in this sense, Type II (fitting constants) methods were studied. The aim of this study was to show that meaningful evaluations can be performed even in unbalanced conditions and to contribute to the present investigations in biological area. In the implementation part of the study, the juvenile leaf densities of Posidonia oceanica-which is a sea grass that grows in Izmir Bay, and has very important ecological effects-in various regions and in various depths were determined. The results revealed that depth affect number of juvenile leaf (d.f. = 3, F = 523.90, R (2) = 0.998, p < 0,01). There were significant differences among region (d.f. = 3, F = 41.53, p < 0.01), site (d.f. = 1, F = 19.65, p < 0.01). As a result of Tukey ANOVA test it can be said that there were significant differences among Urla-Gulbah double dagger e (p < 0.001), Urla-Fo double dagger a (p < 0.001), Karaburun-Gulbah double dagger e (p < 0.001), Karaburun-Fo double dagger a (p < 0.001). It was found that Fo double dagger a had the highest juvenile leaf counts (782.15 +/- 435.71) whereas Urla had the lowest juvenile leaf counts (231.46 +/- 175.67). The mean juvenile leaf counts in Izmir was (496.23 +/- 377.61). it can be said that juvenile leaf counts in Karaburun(Island) had (448.13 +/- 250.85), and Fo double dagger a(Island) had (888.65 +/- 497.39).Scientific and Technical Research Council of TurkeyTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); Aegean University Research FundEge University [TBAG-1638 197T032]This study was funded by the Scientific and Technical Research Council of Turkey and Aegean University Research Fund (TBAG-1638 197T032)

The statistical investigation on posidonia oceanica (L.) delile meadows in Izmir, Turkey

In this study, variance analysis technique on unbalanced data was examined, and in this sense, Type II (fitting constants) methods were studied. The aim of this study was to show that meaningful evaluations can be performed even in unbalanced conditions and to contribute to the present investigations in biological area. In the implementation part of the study, the juvenile leaf densities of Posidonia oceanica-which is a sea grass that grows in Izmir Bay, and has very important ecological effects-in various regions and in various depths were determined. The results revealed that depth affect number of juvenile leaf (d. f.=3, F=523.90, R2=0.998, p&lt;0,01). There were significant differences among region (d.f.=3, F=41.53, p&lt;0.01), site (d.f.=1, F=19.65, p&lt;0.01). As a result of Tukey ANOVA test it can be said that there were significant differences among Urla-Gülbahçe (p&lt;0.001), Urla-Foça (p&lt;0.001), Karaburun-Gülbahçe (p&lt;0.001), Karaburun-Foça (p&lt;0.001). It was found that Foça had the highest juvenile leaf counts (782.15±435.71) whereas Urla had the lowest juvenile leaf counts (231.46±175.67). The mean juvenile leaf counts in Izmir was (496.23±377.61). it can be said that juvenile leaf counts in Karaburun(Island) had (448.13±250.85), and Foça(Island) had (888.65±497.39). © Springer Science + Business Media B.V. 2008.TBAG-1638 197T032Acknowledgements This study was funded by the Scientific and Technical Research Council of Turkey and Aegean University Research Fund (TBAG-1638 197T032). -