Effects of electron-electron interactions on excitonic absorption in charged self-assembled quantum dots

We investigate theoretically the effects of electron-electron interactions on excitonic absorption in charged, lens-shaped, self-assembled quantum dots (SAD). The electronic shells of SAD are filled with N electrons according to generalized Hund's rules. In absorption, an exciton is added to the electronic system. The electronic part of the exciton couples in a nontrivial way to resonant electronic configurations of SAD through direct and exchange interaction while the mobile valence hole contributes through the entanglement of many-electron configurations. The two processes result in an excitonic absorption spectrum that reflects the filling of electronic shells. These processes are illustrated by detailed calculations of absorption spectra for few-electron complexes.6120137531376

Salivary Glucose Oxidase from Caterpillars Mediates the Induction of Rapid and Delayed-Induced Defenses in the Tomato Plant

Caterpillars produce oral secretions that may serve as cues to elicit plant defenses, but in other cases these secretions have been shown to suppress plant defenses. Ongoing work in our laboratory has focused on the salivary secretions of the tomato fruitworm, Helicoverpa zea. In previous studies we have shown that saliva and its principal component glucose oxidase acts as an effector by suppressing defenses in tobacco. In this current study, we report that saliva elicits a burst of jasmonic acid (JA) and the induction of late responding defense genes such as proteinase inhibitor 2 (Pin2). Transcripts encoding early response genes associated with the JA pathway were not affected by saliva. We also observed a delayed response to saliva with increased densities of Type VI glandular trichomes in newly emerged leaves. Proteomic analysis of saliva revealed glucose oxidase (GOX) was the most abundant protein identified and we confirmed that it plays a primary role in the induction of defenses in tomato. These results suggest that the recognition of GOX in tomato may represent a case for effector-triggered immunity. Examination of saliva from other caterpillar species indicates that saliva from the noctuids Spodoptera exigua and Heliothis virescens also induced Pin2 transcripts

Longitudinal Changes of Fixation Location and Stability Within 12 Months in Stargardt Disease: ProgStar Report No. 12

Purpose: To investigate the natural history of Stargardt disease (STGD1) using fixation location and fixation stability. // Design: Multicenter, international, prospective cohort study. // Methods: Fixation testing was performed using the Nidek MP-1 microperimeter as part of the prospective, multicenter, natural history study on the Progression of Stargardt disease (ProgStar). A total of 238 patients with ABCA4-related STGD1 were enrolled at baseline (bilateral enrollment in 86.6%) and underwent repeat testing at months 6 and 12. // Results: Outcome measures included the distance of the preferred retinal locus from the fovea (PRL) and the bivariate contour ellipse area (BCEA). After 12 months of follow-up, the change in the eccentricity of the PRL from the anatomic fovea was −0.0014 degrees (95% confidence interval [CI], −0.27 degrees, 0.27 degrees; P = .99). The deterioration in the stability of fixation as expressed by a larger BCEA encompassing 1 standard deviation of all fixation points was 1.21 degrees squared (deg2) (95% CI, −1.23 deg2, 3.65 deg2; P = .33). Eyes with increases and decreases in PRL eccentricity and/or BCEA values were observed. // Conclusions: Our observations point to the complexity of fixation parameters. The association of increasingly eccentric and unstable fixation with longer disease duration that is typically found in cross-sectional studies may be countered within individual patients by poorly understood processes like neuronal adaptation. Nevertheless, fixation parameters may serve as useful secondary outcome parameters in selected cases and for counseling patients to explain changes to their visual functionality

The role of finite hole mass in the negatively charged exciton in two dimensions

The role of finite hole mass on the ground and excited states of the negatively charged exciton in two dimensions is discussed. We present results of configuration-interaction calculation using exact excitonic states and results of a variational calculation of the ground-state energy to elucidate the interplay of finite hole mass and electron-electron interactions. (C) 2001 Elsevier Science B.V. All rights reserved.9471672

Excitonic absorption in a quantum dot

The excitonic absorption spectrum of a single quantum dot is investigated theoretically and experimentally. The spectrum is determined by an interacting electron-valence-hole complex. We show that the mixing of quantum configurations by two-body interactions leads to distinct absorption spectra controlled by the number of confined electronic shells. The theoretical results are compared with results of photoluminescence excitation spectroscopy on a series of single self-assembled In0.60Ga0.40As quantum dots.85238939

On the cross-over between 2-dimensional and 3-dimensional growth in Si/Ge-n/Si quantum wells

We report Raman scattering and low temperature photoluminescence measurements performed on a series of Molecular-Beam-Epitaxy-grown Si/Ge-n/Si quantum wells with n varying from 3 to 6. Our results are consistent with a gradual evolution of the Si/Ge interface which starts with Ge segregation and formation of terraces for low Ge coverage, to smooth 2-dimensional Ge layers, bounded by interfacial alloy layers, for coverages superior to 4-monolayers. (C) 1998 Elsevier Science Ltd. All rights reserved.107735936