Multi-excitonic complexes in single InGaN quantum dots

Cathodoluminescence spectra employing a shadow mask technique of InGaN layers grown by metal organic chemical vapor deposition on Si(111) substrates are reported. Sharp lines originating from InGaN quantum dots are observed. Temperature dependent measurements reveal thermally induced carrier redistribution between the quantum dots. Spectral diffusion is observed and was used as a tool to correlate up to three lines that originate from the same quantum dot. Variation of excitation density leads to identification of exciton and biexciton. Binding and anti-binding complexes are discovered.Comment: 3 pages, 4 figure

Polarized emission lines from A- and B-type excitonic complexes in single InGaN/GaN quantum dots

Cathodoluminescence measurements on single InGaN/GaN quantum dots (QDs) are reported. Complex spectra with up to five emission lines per QD are observed. The lines are polarized along the orthogonal crystal directions [1120] and [1100]. Realistic eight-band k·p electronic structure calculations show that the polarization of the lines can be explained by excitonic recombinations involving hole states which are formed either by the A or the B valence band

Polarized Emission Lines from Single InGaN/GaN Quantum Dots: Role of the Valence-band Structure of Wurtzite Group-III Nitrides

We present a study of the polarization properties of emission lines from single InGaN/GaN quantum dots (QDs). The QDs, formed by spinodal decomposition within ultra-thin InGaN quantum wells, are investigated using single-QD cathodoluminescence (CL). The emission lines exhibit a systematic linear polarization in the orthogonal crystal directions [1 1 -2 0] and [-1 1 0 0]--a symmetry that is non-native to hexagonal crystals. Eight-band k.p calculations reveal a mechanism that can explain the observed polarizations: The character of the hole(s) in an excitonic complex determines the polarization direction of the respective emission if the QD is slightly elongated. Transitions involving A-band holes are polarized parallel to the elongation; transitions involving B-type holes are polarized in the orthogonal direction. The energetic separation of both hole states is smaller than 10 meV. The mechanism leading to the linear polarizations is not restricted to InGaN QDs, but should occur in other wurtzite-nitride QDs and in materials with similar valence band structure.Comment: Conf. Proc. of the MSS-13 in Genova 2007, accepted at Physica

Spatial correction improves accuracy of catheter positioning during ablation of premature ventricular contractions: differences between ventricular outflow tracts and other localizations

Abstract Background Hybrid activation mapping is a novel tool to correct for spatial displacement of the mapping catheter due to asymmetrical contraction of myocardium during premature ventricular contractions (PVC). The aim of this study is to describe and improve our understanding of spatial displacement during PVC mapping as well as options for correction using hybrid activation mapping. Methods and results We analyzed 5798 hybrid mapping points in 40 acquired hybrid maps of 22 consecutive patients (age 63 ± 16 years, 45% female) treated for premature ventricular contractions (PVCs). Median PVC-coupling interval was 552 ms (IQR 83 ms). Spatial displacement was determined by measuring the dislocation of the catheter tip during PVC compared to the preceding sinus beat. Mean spatial displacement was 3.8 ± 1.5 mm for all maps. The displacement was 1.3 ± 0.4 mm larger for PVCs with non-outflow-tract origin compared to PVCs originating from the ventricular outflow tracts (RVOT/LVOT; p = 0.045). Demographic parameters, PVC-coupling-interval and chamber of origin had no significant influence on the extent of spatial displacement. Conclusion Ectopic activation of the ventricular myocardium during PVCs results in spatial displacement of mapping points that is significantly larger for PVCs with non-outflow-tract origin. The correction for spatial displacement may improve accuracy of radiofrequency current (RFC)-application in catheter ablation of PVCs

Digitales Lehren und Lernen chirurgischer Fertigkeiten (nicht nur) in Zeiten der Pandemie: Ein Bericht über ein Blended-Learning-Projekt

Due to the COVID-19 pandemic, digital teaching approaches should be used wherever possible. In this article we report on our project for digital teaching and learning of surgical skills.The compulsory elective "Intensivkurs Chirurgische Techniken" for medical students starting with semester 5 was designed as a blended learning course. One week before the face-to-face class, the students receive the learning and teaching material online in a Moodle course. In the face-to-face class, live demos of procedures (e.g. performing skin and intestinal sutures) are presented by the teachers. The learners then perform the practical procedures and record themselves with the camera of an iPad. They publish their videos in the Moodle course via an Opencast plugin. The implementation of an annotation tool enables everyone in the Moodle course to add free-text comments to selected parts of the videos (video-assisted feedback and coaching).As a result of the pandemic, the face-to-face class is being moved to a digital learning environment. For this purpose, we are extending the existing system with a web conference tool (BigBlueButton).Vor dem Hintergrund der COVID-19-Pandemie sollen Lehrveranstaltungen nach Möglichkeit digital stattfinden. In diesem Beitrag berichten wir über unser Lehrprojekt zum digitalen Lehren und Lernen chirurgischer Fertigkeiten.Die Wahlpflichtveranstaltung "Intensivkurs Chirurgische Techniken" für Medizinstudierende ab dem 5. Semester wurde in einem Blended-Learning-Format konzipiert. Eine Woche vor Beginn der Präsenzphase werden den Studierenden die Lernmaterialien für die Veranstaltung in einem Moodle Kurs zur Verfügung gestellt. In der Präsenzphase werden Übungen zu Haut- und Darmnähten in Live-Demos durch die Dozierenden präsentiert. Anschließend führen die Lernenden die praktischen Übungen durch und zeichnen sich dabei mit der Kamera eines iPad auf. Mithilfe eines Opencast-Plugins veröffentlichen sie ihre Videos im Moodle Kurs. Die Einbindung eines Annotation Tool ermöglicht allen Teilnehmenden im Moodle Kurs einzelne Stellen der Videos mit Freitext zu kommentieren (videogestütztes Feedback und Coaching).In Folge der Pandemie soll nun auch die Präsenzphase digital durchgeführt werden. Dafür wird das vorhandene System um eine Webkonferenzlösung (BigBlueButton) erweitert

New method for the in situ determination of AlxGa1-xN composition in MOVPE by real-time optical reflectance

This paper reports on the in situ determination of the Al-content in AlxGa1-xN layers deposited by MOVPE on sapphire and silicon substrates by means of optical reflectance. The accuracy of the conventional in situ method which utilizes the dependence of the refractive index and the extinction coefficient on Al-content is compared to that of the new dispersion approach. The limits and possibilities of the new approach will be discussed. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

An integrated approach to coastal and biological observations

Maritime economy, ecosystem-based management and climate change adaptation and mitigation raise emerging needs on coastal ocean and biological observations. Integrated ocean observing aims at optimizing sampling strategies and cost-efficiency, sharing data and best practices, and maximizing the value of the observations for multiple purposes. Recently developed cost-effective, near real time technology such as gliders, radars, ferrybox, and shallow water Argo floats, should be used operationally to generate operational coastal sea observations and analysis. Furthermore, value of disparate coastal ocean observations can be unlocked with multi-dimensional integration on fitness-for-the-purpose, parameter and instrumental. Integration of operational monitoring with offline monitoring programs, such as those for research, ecosystem-based management and commercial purposes, is necessary to fill the gaps. Such integration should lead to a system of networks which can deliver data for all kinds of purposes. Detailed integration activities are identified which should enhance the coastal ocean and biological observing capacity. Ultimately a program is required which integrates physical, biogeochemical and biological observation of the ocean, from coastal to deep-sea environments, bringing together global, regional, and local observation efforts