1,721,228 research outputs found
The utility of L-tyrosine based polycarbonate copolymers containing poly(ethylene glycol) as a degradable carrier for the release of a hydrophobic peptide molecule:
No full textThe utility of biodegradable polymers as localized drug delivery carriers is an ongoing area of research where investigators attempt to deliver a wide range of hydrophobic small molecules and peptides. The long-term (> 1 year), controllable and sustained release of such molecules from these solid carriers has not been demonstrated due to the complexity of the reaction-diffusion mechanisms that occur in these hydrated polymers. The goal of the present research was to characterize the release of the hydrophobic peptide voclosporin from a class of biodegradable amorphous polymers based on desaminotyrosyl-tyrosine alkyl ester (DTR) and desaminotyrosyl-tyrosine ester, (DT), and the monomer polyethylene glycol (PEG). Four areas of study were presented: (i) the modulation of drug release and polymer erosion as a function of poly(DTR-co-y % DT-co-z % PEG1K carbonate) homo-, co- and terpolymer compositions, (ii) the changes in polymer morphology and a proposed theory to account for drug retention exhibited by these polymers after prolonged hydration, (iii) the instability of voclosporin in the presence of the terpolymer carriers and the need for formulations containing antioxidants and (iv) the demonstration of selected PEG-containing polycarbonate formulations as a drug delivery vehicle for potential ophthalmic applications. The polycarbonate terpolymers were shown to undergo hydration-induced microphase separation, where the mobility of the PEG1K length in the composition enabled this behavior. The limited access of water to regions containing only PEG was believed to cause both drug retention and a slowdown in polymer erosion in these matrices. Drug-polymer interaction between DTE-co-DT segments of the polymer and voclosporin was also suspected to play a role in drug retention. In vivo in vitro correlation (IVIVC) values of 3 to 4 obtained from rabbit implantation studies implied that both drug release and polymer resorption would be enhanced if these carriers were placed within the human body. Select tyrosine-based polycarbonate terpolymer matrices were well tolerated in the sensitive regions of the rabbit’s eye. An outcome of this research is the development of a polymer platform that can serve as an implantable medical device matrix to deliver drugs to patients for the treatment of chronic diseases and disorders of the eye.Ph.D.Includes bibliographical references (p. 183-187)by Isaac John Kha
Simulation of the effects of sensorineural hearing loss
Full text linkThesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 103-112).by Isaac John Graf.M.S
Quantal analysis of synaptic transmission in CA1 pyramidal cells of the rat hippocampus
No full textThe hippocampal formation is an area of the limbic system involved in a number of brain functions including learning and memory. It is also involved in the pathogenesis of epilepsy. Using the recently developed recording technique of whole-cell patch-clamp in brain slices, the synaptic and cellular mechanisms of CA1 pyramidal neurons were investigated in rat hippocampal slices in vitro. Two components to the excitatory postsynapti currents (EPSCs), evoked by afferent stimulation, were observed, a fast AMPA receptor-mediated event accounting for 90-95% of peak EPSC amplitude, and a small, slow NMDA receptor-mediated component. The local anaesthetic, N-(2,6-dimethyl-phenylcarbamoylmethyl)triethylammonium bromide (QX-314; 10-20mM), was found to block all voltage-gated Na+ conductances in CA1 cells when applied intracellularly, and blocked a conductance which exhibited characteristics of the anomalous rectifier IQ. EPSCs, however, were not blocked by intracellular QX-314. The space-clamp properties of CA1 cells were also investigated. The incomplete voltage control of EPSCs and voltage-gated Ca2+ currents indicated that CA1 pyramidal cells were poorly space-clamped. However, proximal areas of the cell were under better voltage control than the distal. Excitatory synaptic transmission in area CA1 was investigated using quantal analysis. EPSCs were evoked by a minimal stimulation protocol with a `bridge' of axons sectioned in the stratum radiatum between the stimulating and recording sites. Precise positioning of a monopolar stimulating electrode enabled a small population of synapses to be selectively activated, and this was confirmed by input-output relationships. Data sets were analysed using Bayesian statistics and amplitude distributions were constructed. Initial studies indicated only a low number of data sets exhibiting regular fluctuations in EPSC amplitude. However, non-equivalent subsets of EPSCs were observed within the majority of data sets, which exhibited different rise times and quantal amplitudes. Data sets separated into subsets with `fast' and `slow' rise times, exhibited regular quantal fluctuations in EPSC amplitude, providing strong evidence for quantal transmission at these synapses.</p
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
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