1,720,957 research outputs found
Free surface electrospinning from a wire electrode
Full text linkElectrostatic jetting from a free liquid surface offers an alternative to conventional electrospinning in which jets are emitted from spinnerets. In this work we analyze a system in which a wire electrode is swept (in a rotary motion) through a bath containing a polymeric solution in contact with a high voltage, resulting in entrainment of the fluid, the formation of liquid droplets on the wire and electrostatic jetting from each liquid droplet. Solutions of polyvinylpyrrolidone in ethanol were used as test systems to evaluate each stage of the process. The volumes of individual droplets on the wire were measured by photographic methods and correlated with the viscosity, density and surface tension of the liquid, and with system parameters such as electrode rotation rate and wire diameter. The local electric field in the absence of liquid entrainment was modeled using conventional electrostatics, and jet initiation was found to occur consistently at the angular position where the electric field exceeds a critical value of 34 kV/cm, regardless of rotation rate. Two operating regimes were identified. The first is an entrainment-limited regime, in which all of the entrained liquid is jetted from the wire electrode. The second regime is field-limited, in which the residence time of the wire electrode in an electric field in excess of the critical value is too short to deplete the fluid on the wire. The productivity of the system was measured and compared to the theoretical values of liquid entrainment. As expected, highest productivity occurred at high applied potentials and high rotation rates.Novartis-MIT Center for Continuous Manufacturin
Production of core/shell fibers by electrospinning from a free surface
Full text linkElectrostatic fiber formation (“electrospinning”) is the leading technology for production of continuous fibers with submicron diameter. Applications such as drug delivery and sensors benefit from the ability to produce submicron fibers with a core/shell morphology from electrified coaxial jets of two liquids. However, low productivity of the conventional needle-based coaxial process is a barrier for commercialization. We present a novel technology that overcomes this limitation by the development of coaxial jets directly from compound droplets of immiscible liquids entrained on wires, and control of mass transfer processes to produce uniform, core/shell fibers. The enabling feature of controlled evaporation by design of solution properties is verified by a simple mass transport model. Electron micrographs confirm the formation of fibers with the desired morphology. The proposed technology creates the opportunity to produce nanofibers with core/shell morphology on an industrial scale for a wide variety of applications.Novartis-MIT Center for Continuous Manufacturin
Humidity Control of Electrospun Membranes for Direct Contact Membrane Distillation
No full textA shortage in the supply of fresh water has prompted research in more effective methods of water distillation. One such method called direct contact membrane distillation (DCMD) is driven by the temperature gradient between the two sides of the membrane. It is not yet used in the industry because of the limited research in producing membranes specific for the process. A technique being used to create DCMD specific membranes is electrospinning.Citrus College RACE to STE
Development of Ceramic Metal Oxide Membranes By Means of Reactive Electrospinning
No full textExperts agree that carbon dioxide is the leading cause of the increase in global warming. To combat global climate change, Carbon Capture and Storage technology has been developed and implemented to reduce the amount of carbon dioxide and other malignant gases in the atmosphere. In efforts to contribute to this avenue of sustainable progress, we aimed to produce ceramic metal oxide membranes via reactive electrospinning with the intention of applying these novel nanofibrous membranes to greenhouse gas capture. Magnesium oxide membranes are considered viable candidates for adsorption processes because they exhibit high surface area, low density, high porosity and resistance to high temperatures and corrosion. The electrospinning solution consisted of 4MDa polyethylene oxide, acetic acid, magnesium methoxide, methanol and dichloromethane. During electrospinning, a voltage of 5-20 kV was applied to the solution in a flow-controlled needle housed in a humidity-controlled chamber. Once critical charge density was reached at the tip of the needle the solution formed a Taylor cone which ejected a continuous jet of magnesium oxide nanofibers. Another solution being pursued is composed of 4 MDa polyacrylic acid which substitutes for the dichloromethane and polyethylene oxide. Experimental data was collected for varying flow rates, supplied voltage, solution composition, substrate concentration and chamber humidity. Infrared spectroscopy followed for analysis of product chemical composition. Fiber diameter and porosity will be measured through Scanning Electron Microscopy (SEM). Ideally, the nanofibers will exhibit a ceramic quality denoted by a visible, consistent rigidity under SEM analysis
Humidity Control of Electrospun Membranes for Direct Contact Membrane Distillation
No full textA shortage in the supply of fresh water has prompted research in more effective methods of water distillation. One such method called direct contact membrane distillation (DCMD) is driven by the temperature gradient between the two sides of the membrane. It is not yet used in the industry because of the limited research in producing membranes specific for the process. A technique being used to create DCMD specific membranes is electrospinning
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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