1,720,988 research outputs found
Crystallisation in fluorapatite-fluorphlogopite glass ceramics
No full textApatite based glass-ceramics are some of the most bioactive materials found todate. They do not require fibrous encapsulation and bond to bone directlythrough an apatite layer. Apatite based glass-ceramics exhibit relatively poorbiaxial flexural strength, hence limiting their applications to non-load bearingimplants. The addition of mica results in a material that is highly machinable, andprovided that a suitable interlocking microstructure can be produced, thestrength will be increased.The aim of this work is to investigate how altering the heat treatment affects thecrystallisation and the final mechanical properties of three differentcompositions of glass-ceramic. The glass system studied is the ternary glasssystem; barium fluorphlogopite (Bao.sMgafSiaAlOiojFz), fluorapatite(CaiofPO^eFz) and cordierite (MgzAUSisOis). The three compositions differ bythe mol% of fluorapatite forming feedstock in the precursor glass. Glass-ceramicsformed by heat-treating a glassy precursor are investigated using differentialscanning calorimetry, kinetic neutron diffraction and scanning electronmicroscopy. The mechanical properties of the samples are characterised by theirbiaxial flexural strength and Vickers hardness. The phases formed and themicrostructures of the samples are linked to the mechanical properties and anassessment of the final material's implant suitability is made
Crystal structures and phase transitions in the rare earth oxides
Full text linkThe lanthanoid sesquioxides exhibit a number of distinct structural phases. Below2000°C these oxides exist in three crystal systems, namely the A-type hexagonal phase,the B-type monoclinic phase and the C-type cubic phase. With increasing temperaturethe stability of these structures is generalised by the order C → B → A, although notevery oxide will exhibit all phases; this general transition is typical of the middlemembers of the group. Under ambient conditions, the A phase is preferred for La2O3 toPm2O3. Both the C and B phases exist for Sm2O3, Eu2O3 and Gd2O3. The C phase isstable at room temperature from Sm2O3 onwards, and at the high atomic number end ofthe series this phase is preferred.Traditionally, the structures of the heavier sesquioxides (Er2O3 to Lu2O3) have beenbelieved to be cubic from ambient temperature all the way up to their melting points.However, contrary to the current phase diagram, my work has shown that not only areB-type Sm2O3, Eu2O3 and Gd2O3 very stable at ambient temperature, but it is alsopossible to create 1% monoclinic Yb2O3 by heating and then quenching back toambient temperature.Of the lanthanoids, praseodymium and terbium are known for their existence in boththe +3 and +4 oxidation states. The praseodymium-oxygen system is notable for itsmultiple stoichiometries. This work presents kinetic data for the phi - beta phase and the sigma - thetaphase transitions in this system, the results obtained via high-temperature X-raypowder diffraction and differential scanning calorimetry.The crystal structures of B-type Gd2O3 and Yb2O3 are reported, the former obtainedusing both laboratory and synchrotron X-ray data and the latter using laboratory dataalone. It is proposed that this is the first time these two structures have been determinedfollowing the application of temperature alone, without the additional application ofpressure
Time resolved studies of metallic phase formation
No full textThe processes of phase formation and transformation in crystallised amorphous metallicmaterials can be investigated using a wide variety of techniques. Time and temperatureresolved neutron and x-ray scattering offers an insight into these processes in-situ oftenhighlighting the formation of metastable and unreported phases. In this work, time- andtemperature-resolved synchrotron x-ray diffraction and small angle neutron scatteringstudies are complemented with differential scanning calorimetry and transmissionelectron microscopy to gain a complete insight into the crystallisation and subsequentphase formation and transformation in two Fe-based metallic glasses: Cogo-xFe x B2o, x =20, 40 of current technological importance, and the Y-Fe system of academic interest.In Co4oFe4oB2o time resolved synchrotron x-ray diffraction shows that a a-(Co,Fe) solidsolution is formed in isolation irrespective of isothermal temperature treatment. Incontrast, temperature resolved synchrotron x-ray diffraction indicates a two-stagecrystallisation process; primary cc-(Co,Fe) phase formation is followed by polymorphiccrystallisation of (Co,Fe)2B. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) modelfor isothermal phase transformation kinetics indicates one-dimensional growth with adecreasing nucleation rate for the isolated a-(Co,Fe) solid solution.In a direct comparison, Co6oFe2oB2 o, is shown to undergo multi-phase crystallisationduring both isothermal and continuously heated temperature profiles. The JMAKmodel is in agreement to those for Co4oFe4oB2o, i.e. one dimensional growth with adecreasing nucleation rate.Secondly the Rare-Earth Transition Metal YeyFess is shown to crystallise fromelemental Y to the YFe2 Laves phase via a novel 'YFe' phase with suggested structureP6/mmm, a = 12.72A and c = 8.00A. Small angle neutron scattering data modelled to aLorentzian with variable power is in agreement with previously published kineticneutron diffraction and small angle scattering data highlighting the temperature andtime dependence of a critical scattering event evident at the point where the wholesample crystallises.xi
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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