1,720,996 research outputs found
Identifying spinel phases in nearly monodisperse iron oxide colloidal nanocrystals
No full textNearly monodisperse iron oxide colloidal nanocrystals prepared by nonhydrolytic high-temperature solution method were obtained with two different sizes and degrees of oxidation. The characterization of the structural features of the nanocrystals was performed by a multitechnique approach including transmission electron microscopy, X-ray diffraction and X-ray absorption spectroscopy, energy filtered electron microscopy imaging, and SQUID magnetometry. The different techniques provided complementary information on the local oxidation state of iron in the iron oxide nanoparticles, the stability of the phases, the exact crystal structure, and the compositional homogeneity. X-ray diffraction, transmission electron microscopy, and extended X-ray absorption spectroscopy show that the addition of oxidizer to the iron precursor gives rise to monodisperse polycrystalline nanoparticles made out of FeO plus a spinel phase. X-ray absorption near-edge structure, which is very sensitive to the oxidation state and local environment of iron in the different iron oxides, was used to distinguish among isostructural spinel phases of iron (II, III) oxide (magnetite) and iron(III) oxide (maghemite). Single-crystalline spinel nanoparticles are obtained upon sequential oxidation: in smaller nanoparticles a mixture of mainly Fe(3)O(4) and gamma-Fe(2)O(3) is present, whereas the larger nanoparticles are made out of gamma-Fe(2)O(3), as also supported by SQUID magnetization measurements. The importance of a multitechnique approach for the elucidation of the compositional and structural details in addition to geometrical parameters in the characterization of nanocrystalline iron oxides is pointed out
Selective growth of PbSe on one or both tips of colloidal semiconductor nanorods
No full textPbSe nanocrystals with rock-salt structure are grown on the tips of colloidal CdS and CdSe nanorods. The facets of wurtzite rods provide a
substrate with various degrees of reactivity for the growth of PbSe. The presence of dangling Cd bonds may explain subtle differences
between nonequivalent facets resulting in the selective nucleation of PbSe only on one of the two tips of each CdS rod. This approach has
the potential to facilitate the fabrication of heterostructures with tailored optical and electronic properties
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
Laser-induced vapor nanobubbles for efficient delivery of macromolecules in live cells
No full textMacromolecular agents such as nucleic acids and proteins need to be delivered into living cells for therapeutic purposes. Among physical methods to deliver macromolecules across the cell membrane, laser- induced photoporation using plasmonic nanoparticles is a method that is receiving increasing attention in recent years. By irradiating gold nanoparticles bound to the cell membrane with laser light, nanosized membrane pores can be created. Pores are formed by localized heating or by vapour nanobubbles (VNBs) depending on the incident laser energy. Macromolecules in the surrounding cell medium can then diffuse through the transiently formed pores into the cytoplasm. While both heating and VNBs have been reported before for permeabilization of the cell membrane, it remains unclear which of both methods is more efficient in terms of cell loading with minimal cytotoxicity. In this study we report that under condition of a single 7 ns laser pulse VNBs are substantially more efficient for the cytosolic delivery of macromolecules. We conclude that VNB formation is an interesting photoporation mechanism for fast and efficient macromolecular delivery in live cells
Efficient delivery of quantum dots in live cells by gold nanoparticle mediated photoporation
No full textThere is considerable interest in using Quantum Dots (QDs) as fluorescent probes such for cellular imaging due to unique advantages in comparison with conventional molecular dyes. However, cytosolic delivery of QDs into live cells remains a major challenge. Here we demonstrate highly efficient delivery of PEG-coated QDs into live cells by means of laser-induced vapour nanobubbles. Using this procedure we succeeded in high-throughput loading of similar to 80% of cells while maintaining a cell viability of similar to 85
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
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