1,721,113 research outputs found
Nanometric oxides for functional materials
No full textThis thesis describes the synthesis and application of complex metal oxide nanoparticles. The work is focussed on three core areas; the synthesis of CoFe2O4 nanoparticles and their application as CO oxidation catalysts, the controlled assembly of functionalised CoFe2O4 and BaTiO3 nanoparticles and the preparation and characterisation of magnetoelectric composites from chemically-bonded nanoparticle assemblies.
Chapter 1 gives an introduction to the history of nanotechnology, recent
developments in the synthesis of nanoparticles and other areas key to the work
described herein.
In Chapter 2 details the synthetic and analytical techniques employed.
Chapter 3 describes the synthesis and characterisation of CoFe2O4 nanoparticles, and
their application as catalysts in the CO oxidation reaction. Nanoparticles were
prepared with a range of controlled sizes and were found to be active CO oxidation
catalysts. Analysis of their size-dependent activity and stability is performed.
Chapter 4 describes the assembly of CoFe2O4 and BaTiO3 nanoparticles by direct
functionalisation of the nanoparticle surfaces using complementary organic
functional molecules. Characterisation of the functionalised nanoparticles and
assemblies is performed, and the extensibility of the developed functionalisation and
assembly protocol is tested using particles with different sizes and morphologies.
In Chapter 5 the assembled nanoparticles discussed in Chapter 4 are processed into
dense ceramics with a view to preparing magnetoelectric composites. The
magnetoelectric properties are tested, and optimisation of the ceramics is performed
by modification of the starting nanoparticle sizes, composite composition and
processing conditions. The composites are tested against control samples prepared by
traditional grinding and firing, and characterisation of the ceramics using XRD and
electron microscopy provides and insight as to why their magnetoelectric properties
differ to those prepared by the traditional technique.
The work contained in this thesis has been published in the following papers: -
G. Evans, I. V. Kozhevnikov, E. F. Kozhevnikova, J. B. Claridge, R. Vaidhyanathan,
C. Dickinson, C. D. Wood, A. I. Cooper, M. J. Rosseinsky, “Particle-size Activity
Relationship for CoFe2O4 Nanoparticle CO Oxidation Catalysts,” J. Mater. Chem.
2008, 18, 5518.
G. Evans, G. V. Duong, M. J. Ingleson, Z. Xu, J. T. A. Jones, Y. Z. Khimyak, J. B.
Claridge, M. J. Rosseinsky, “Chemical Bonding Assembly of Multifunctional Oxide
Nanocomposites,” Adv. Funct. Mater. 2010, 20, 231
Multifunctional magnetic nanoparticles for biomedical applications
No full textThe objective of this thesis was to develop and prepare multifunctional magnetic nanoparticles with targeting and bimodal imaging capabilities for cancer diagnostic applications.
Superparamagnetic iron oxide nanoparticles (SPIONs) were the key component in the multifunctional nanoparticles prepared. In a first approach, alkoxysilane ligands were used to introduce functional groups such as amino, bromo, iodo, nitrile, and vinyl on the surface of SPIONs. Physicochemical analyses showed that each silane ligand formed a dense silane monolayer covalently attached to the nanoparticle surface. The amino-functionalised SPIONs were successfully modified yielding amino and carboxylic acid-bifunctionalised SPIONs using a succinylation reaction. This nanoparticle system showed no cytotoxicity during cell viability evaluations. Further conjugation with fluorescent dye and antibodies produced targeted bimodal optical/magnetic resonance imaging (MRI) agents, confirmed by good contrast enhancement capabilities. The conjugated antibody successfully enabled the targeted delivery of SPIONs to pancreatic cancer cells in vitro. The targeting efficiency and the nanoparticle cellular uptake were monitored using fluorescence and confocal microscopy.
In a second approach, hydrophobic and monodisperse SPIONs were coated with amphiphilic polyoxazoline to produce colloidally stable magneto-micelles. This magneto-micellar system showed high colloidal stability in water, phosphate buffered saline as well as at different pH values. Fluorescent dyes were successfully co-assembled into the magneto-micelles providing for the localisation of the nanoparticles in the cells by confocal microscopy. Antibodies conjugated to nontoxic magneto-micelles allowed for binding to specific receptors present on pancreatic cancer cells. The targeting efficiency and accumulation of the antibody labelled magneto-micelles into pancreatic cancer cells was evaluated using live cell confocal microscopy. Their performance as MRI contrast agents was evaluated using relaxivity measurements and it was shown that the clustering effect of the SPIONs within the core of the micelle is particularly favourable for enhancing the contrast on MRI images. Both approaches provided efficient routes of preparation of multifunctional platforms to achieve the desired targeting and bimodal imaging capabilities
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
New cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs)
Get PDFThe work presented in this thesis focuses on the synthesis of long axis A-site ordered perovskites, which have ordered oxygen vacancies. The materials discussed have also been assessed as potential cathodes for solid oxide fuel cells (SOFCs), targeting an intermediate temperature (IT) SOFC operating range of 500 800 °C.
In chapter 3 of this thesis, a 16ap phase (ap = 1 perovskite unit, ABO3-δ), Y2.24Ba2.28Ca3.48Fe7.44Cu0.56O21-δ, was first observed in a powder X-ray diffraction (PXRD) pattern that resulted from the attempted Cu doping of a 10ap phase (Y0.9Ba1.7Ca2.4Fe5 xCuxO13 δ). This phase was indexed as ap √2 × 16ap × ap √2 by selective area electron diffraction (SAED). Mössbauer spectroscopy identified that Fe3+ existed in three different coordination environments and a Rietveld refinement was carried out using combined powder synchrotron (S) XRD and powder neutron diffraction (ND) data. High Angle Annular Scanning Transmission Electron Diffraction (HAADF-STEM) confirmed the A-site ordering from the refinement.
The 16ap phase exhibited good thermal stability, CO2 stability and chemical compatibility with state of the art electrolytes (GDC, SDC and LSGM), as well as a close matching thermal expansion coefficient (TEC) with the same electrolytes. Although possessing low electronic conductivity, 3.5 S.cm-1 at 750 °C, a good area specific resistance (ASR) of 0.12 Ω.cm2 at 750 °C was achieved, within the IT-SOFC operating range.
In chapter 4, a 10ap phase, Y0.9Ca2.4Sr1.7Fe5O13-δ (YCSFO), was discussed. The space group Imma was identified from SXRD data, while the structure was closely related to brownmillerite. A Rietveld refinement carried out with the addition of SXRD data collected at the K absorption edge for Sr determined A-site ordering. The ASR of YCSFO was three times higher than that of the 16ap phase, highlighting the ordering of oxygen vacancies.
The final phases investigated in chapter 5 of this thesis belong to a family of Co doped 10ap phases (Y0.9Ba1.7Ca2.4Fe5 xCoxO13 δ). A range of compositions were synthesised by varying the cation ratios, in order to obtain high Co content phase pure samples. The highest Co content was x = 1.85 for compositions Y1.24Ba1.85Ca1.91Fe3.15Co1.85O13-δ (annealed in O2) and Y1.6Ba1.8Ca1.6Fe3.15Co1.85O13-δ. AC impedance measurements carried out showed that increased Co content reduced the ASR, with the values at 700 °C of 0.19 Ω.cm2 and 0.23 Ω.cm2 respectively
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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