1,721,054 research outputs found
Ultrafast photoconductivity and charge carrier transport in semiconductor nanostructures: a study by terahertz spectroscopy
No full textTitle: Ultrafast photoconductivity and charge carrier transport in semiconductor nanostructures: a study by terahertz spectroscopy Author: Vladimir Pushkarev Institute: Institute of Physics of the Czech Academy of Sciences Supervisor of the doctoral thesis: doc. RNDr. Petr Kužel, Ph.D. Abstract: The thesis is devoted to a study of charge transport in nanostructured systems by means of time-resolved terahertz spectroscopy. We address various aspects of electron confinement in such systems, and the role of depolarization fields on the effective photoconductive response of samples. Accurate evaluation of localized carrier properties has been achieved using quantum mechanical calculations of the mobility. Theoretical interpretation of the terahertz conductivity spectra is based on the solution of the wave equation for the terahertz wave in inhomogeneous photoexcited media described in terms of VBD effective medium model developed in our laboratory. This approach is employed for investigation of the terahertz photoconductivity in two types of nanomaterials: superlattices of Si nanocrystals prepared by thermal decomposition of SiOx layers and lithographically prepared GaAs nanobars. Experimental spectra were measured at 300 and 20 K and for a wide range of photocarrier densities. A careful analysis of electron..
Ultrarychlá fotovodivost a transport náboje v polovodičových nanostrukturách: studium pomocí terahertzové spektroskopie
Full text linkNázev práce v češtině: Ultrarychlá fotovodivost a transport náboje v polovodičových nanostrukturách: studium pomocí terahertzové spektroskopie Autor: Vladimir Pushkarev Ústav: Fyzikální ústav Akademie věd České republiky Supervisor of the doctoral thesis: doc. RNDr. Petr Kužel, Ph.D. Abstrakt: Tato práce se věnuje studiu transportu náboje v nanostrukturovaných systémech pomocí časově rozlišené terahertzové spektroskopie. Zabývá se různými aspekty lokalizace elektronů v těchto systémech a rovněž vlivem depolarizačních polí na efektivní fotovodivou odezvu vzorků. Korektního vyhodnocení vlastností lokalizovaných nosičů náboje je dosaženo pomocí kvantově mechanických výpočtů jejich pohyblivosti. Teoretická interpretace spekter terahertzové vodivosti je založena na řešení vlnové rovnice pro terahertzové vlny v nehomogenních fotoexcitovaných prostředích popsaných pomocí tzv. VBD modelu efektivního prostředí vyvinutého v naší skupině. Tohoto přístupu jsme využili při studiu terahertzové fotovodivosti ve dvou typech nanomateriálů: v supermřížkách křemíkových nanokrystalů připravených termální dekompozicí vrstev SiOx a v litograficky připravených GaAs nanotyčinkách. Spektra byla měřena při 300 a 20 K a pro široký rozsah hustot opticky excitovaných nosičů náboje. Pečlivá analýza transportu elektronů v křemíkových...Title: Ultrafast photoconductivity and charge carrier transport in semiconductor nanostructures: a study by terahertz spectroscopy Author: Vladimir Pushkarev Institute: Institute of Physics of the Czech Academy of Sciences Supervisor of the doctoral thesis: doc. RNDr. Petr Kužel, Ph.D. Abstract: The thesis is devoted to a study of charge transport in nanostructured systems by means of time-resolved terahertz spectroscopy. We address various aspects of electron confinement in such systems, and the role of depolarization fields on the effective photoconductive response of samples. Accurate evaluation of localized carrier properties has been achieved using quantum mechanical calculations of the mobility. Theoretical interpretation of the terahertz conductivity spectra is based on the solution of the wave equation for the terahertz wave in inhomogeneous photoexcited media described in terms of VBD effective medium model developed in our laboratory. This approach is employed for investigation of the terahertz photoconductivity in two types of nanomaterials: superlattices of Si nanocrystals prepared by thermal decomposition of SiOx layers and lithographically prepared GaAs nanobars. Experimental spectra were measured at 300 and 20 K and for a wide range of photocarrier densities. A careful analysis of electron...Matematicko-fyzikální fakultaFaculty of Mathematics and Physic
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
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