1,720,954 research outputs found
Modelling the stability of ternary solid dispersions
No full textThis thesis provides a mathematical analysis of the stability of some ternary solid dispersions using thermodynamic theory. Solid dispersions have been developed to improve the solubility of poorly soluble drugs. Traditional solid dispersions typically consist of two components - a drug and a hydrophilic polymer, the purpose of the polymer being to improve the solubility of the drug when administered orally. More recently, ternary dispersions (that is, systems with three components) have been developed. Ternary dispersions provide an extra degree of freedom to enable system designers to optimize both the stability and solubility properties of the dispersion. Unstable dispersions may phase separate, thereby limiting their shelf life. In this thesis, I mathematically model ternary solid dispersions with a view to identifying parameter regimes that lead to favourable and unfavourable stability properties for the dispersion. A systematic study of this kind has hitherto been lacking in the literature.
The methodology used is as follows. The solid dispersions are modelled using Flory- Huggins solution theory, a well-established thermodynamic model in polymer science for polymer blends. The stability properties of the dispersions are determined by constructing phase diagrams using the Gibbs free energy of mixing. The phase diagrams determine whether a particular ternary composition is stable or unstable or metastable. The requisite numerical calculations to construct the diagrams are carried out by programs that I wrote using the mathematical packages Maple and MATLAB.
Thermodynamic theory determines the broad character of the ultimate state of the mixture, but yields no information on how the mixture evolves to that state, or what the detailed character of the final state is for unstable compositions. To address these issues, a partial differential equations model is developed to describe the dispersion mixture evolution, and some simulations of this model are also presented.
A few notable results are as follows. For polymer-polymer-drug ternary systems, it is found that for desirable stability properties to be possible, the two polymers need to be compatible (in a sense that has been described quantitatively). Also, the stability behaviour can be finely dependent on the asymmetry between how the two polymers interact with the drug. Closed loops of immiscibility are shown to be theoretically possible. For polymer-surfactant-drug ternary systems, it is shown that the stability behaviour can be sensitive to the character of the interaction between the polymer and the surfactant, and the molecular weight of the surfactant. Numerous other predictions are made
Essays on crude oil price differentials, oil price shocks, and the economy of Saudi Arabia
Get PDFDoctor of PhilosophyDepartment of EconomicsLance J. BachmeierThis dissertation incorporates three essays to examine the price differential between different-quality crude oils and the effect of oil price shocks on the Saudi economy. The first essay examined how price differences depending on crude oil quality have different regimes using a Markov switching model. The main difference between the two regimes is in the mean; the mean in the first regime shows no difference from zero, whereas the mean in the second regime is significantly positive, indicating consistency with a capacity constraint.
The second essay compared two situations: one involving three shocks applying Kilian’s (2009) methodology versus one with only one shock to investigate whether considering a single shock is sufficient. Using three shocks showed a difference in how Saudi Arabia’s industrial production and consumer price index respond to oil supply and demand shocks, suggesting that it is not sufficient to consider only one shock.
Finally, the third essay explored the reactions of Saudi Arabia’s stock market to oil market shocks using Kilian’s (2009) methodology and found that Saudi Arabia’s stock sectors react differently to oil price shocks. Saudi Arabia’s stock sectors reacted positively to oil-specific demand shocks but negatively to oil supply shocks; they showed no response to aggregate demand shocks
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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