1,720,985 research outputs found
Molecular beam epitaxy of tailored (In,Ga)As/GaAs quantum dot heterostructures
Get PDFDiese Arbeit behandelt das Wachstum von selbstorganisierten (In,Ga)As/GaAs Quantenpunkten (QDs) mittels Molekularstrahlepitaxie auf GaAs(100)-Substraten. Das InAs/GaAs-Materialsystem ist ausgereift, was die Herstellung von komplexen Heterostrukturen mit hoher Qualität ermöglicht. (In,Ga)As-QDs sind mögliche Halbleiterquantenemitter, welche auch räumlich positioniert gewachsen werden können. Das macht InAs/GaAs zu einem attraktiven Materialsystem für Anwendungen in der Quantenkommunikation.Zunächst wird das Wachstum von (In,Ga)AsAs QDs mit niedriger Dichte für Einzelpunktspektroskopie durch einen Indiumgradienten-Ansatz diskutiert. Dazu wird die Substratrotation während der InAs-Deposition gestoppt, wodurch ein In-Gradient auf der Oberfläche entsteht. Die Emissionswellenlängen der QDs sollen bei 900-1000 nm liegen damit Siliziumdetektoren genutzt werden können. Um die Emissionsenergie der QDs zu kontrollieren wird die Indiumflush-Technik angewandt oder InxGa1-xAs QDs hergestellt.Anschließend wird eine vereinfachte Gradientenmethode zum Wachstum von QD-Molekülen mit niedrigen Dichten verwendet, wobei der Indiumgradienten-Ansatz mit verspannungsinduzierter Nukleation kombiniert wird. Dabei wird auch der Einfluss der unteren Quantenpunktschicht auf die obere Quantenpunktschicht untersucht, indem die abgeschiedene InAs-Menge bei konstanter Barrierendicke verändert wird.Im letzten Teil wird eine Technologie behandelt, bei der positionierte QDs auf strukturierten Substraten gewachsen werden. Dazu werden Löcher mit einer Größe von wenigen Nanometern in das Substrat geätzt um als Nukleationsorte für QDs während des Überwachsens zu fungieren. Der Prozess wurde so optimiert, dass sich in jedem Loch ein einzelner QD bildet.This work is focused on the growth of self-assembled (In,Ga)As/GaAs quantum dots (QDs) by the molecular beam epitaxy on the GaAs(100) substrate. The InAs/GaAs is a mature material system which allows precise fabrication of the complex heterostructures of a high quality. The InAs QDs are promising semiconductor quantum emitters and it is also possible to grow them in a spatially controlled manner which allows novel device fabrications. All this together makes InAs/GaAs a very attractive material system for the applications in the field of quantum communication.In the first part of the thesis, the growth of low density (In,Ga)As QDs for single dot spectroscopy is realized by an In-gradient approach. In this approach, the substrate rotation is paused during InAs deposition, which results in a density gradient on the substrate surface. The emission wavelength of the QDs should be around 900-1000 nm so that the efficient Si-detection technology can be used. In this thesis the emission energy tuning of QDs is done by the In-flush technique or by growing InxGa1-xAs QDs.In the second part of the thesis, we demonstrate a simplified gradient method to grow low density quantum dot molecules, utilizing the In-gradient approach and strain induced nucleation. The influence of the bottom QD layer on the growth of the top QD layer is studied by varying InAs amount for the top layer growth while keeping the interdot barrier thickness constant.In the last part of the thesis, the patterning and regrowth technology for the site-controlled QDs fabrication is discussed. In the process, the nanohole arrays are patterned on the substrate for preferential nucleation of QDs during the regrowth process. The nanohole patterning and the QD growth process is optimized for single QD per hole occupancy.by Nand Lal Sharma (India) ; [1. Gutachter: Prof. Dr. Dirk Reuter, 2. Gutachter: Prof. Dr. Artur Zrenner]Tag der Verteidigung: 09.11.2017Universität Paderborn, Dissertation, 201
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Cutaneous sarcoidosis: Clinical profile of 23 Indian patients
No full textBackground: Sarcoidosis is a multisystem disease of undetermined
etiology. Indian studies on cutaneous sarcoidosis are not many and
mainly comprise case reports. Aims: This retrospective study was
carried out to assess the clinical profile of sarcoidosis patients
presenting with cutaneous lesions. Methods: All histopathologically
proven cases of cutaneous sarcoidosis seen consecutively between 1999
and 2004 were studied. Their age, sex, presenting features, evolution
of disease and laboratory parameters were analyzed. Results: A total
of 23 patients (F:M 15:8) between 31 to 78 years (mean 44.3 years) of
age had the mean duration of skin lesions of 1.4 years. Six patients
had one to four lesions; two patients each had scar sarcoidosis and
angiolupoid and one patient each had recurrent erythema nodosum, leg
lymphedema and subcutaneous sarcoidosis. Others showed combination of
papules, nodules, plaques and psoriasiform lesions. Peripheral lymph
nodes were involved in two patients. Among 10 patients of pulmonary
involvement, three had become symptomatic four months to four years
after the cutaneous lesions. Routine laboratory investigations
including serum calcium estimation were normal in all cases. Serum
angiotensin-converting enzyme levels were raised in 3 out of 6
patients. Asymptomatic lytic lesions of digital bones were detected in
hand X-ray of one patient. Conclusion: Skin lesions of sarcoidosis are
like the tip of an iceberg indicating more changes in other organs. The
symptomatology and abnormal laboratory results do not necessarily
correlate with the severity of cutaneous involvement in general
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