1,720,964 research outputs found
Badanie mechanizmów sprzężonych reakcji przeniesienia elektronu i transferu międzyfazowego
No full textData from project entitled 'Investigation into the mechanisms of coupled electron and phase transfer reactions'</p
Preparation of glass nanopores for the coulter counting of transient nanobubbles
No full textConventional characterisation techniques have so far provided insufficient explanations for the existence of bulk nanobubbles. This thesis proposes an alternative Coulter counting approach that has not yet been applied to nanobubbles and could help elucidate the reasons for their stability. The work herein details the procedure used to obtain glass nanopores and to apply them to the Coulter counting of ultrasonically generated bulk nanobubbles. Tungsten nanoelectrodes are prepared from the electrochemical etching of microwires and the electrochemistry of tungsten is explored in order to characterise and size these electrodes. Nanoelectrodes prepared in this fashion give reproducible diameters of ≈ 100 nm and show electrochemical traits similar to those seen with microelectrodes. Chemical etching of the nanoelectrodes yields glass nanopores that are sized and compared to the nanoelectrodes using voltammetry, simulations, and the Coulter counting of polystyrene nanoparticles. Using a unique differential approach, the sensitivity of the Coulter counting apparatus is shown to increase dramatically. Nanopores are then used to detect and size the transient bulk nanobubbles that are generated during the ultrasonication of potassium chloride solutions with a piston-like emitter. These nanobubbles are distinguished apart from nanoparticles, which are detected in the absence of a local acoustic environment, and microbubbles, which are shown to oscillate in the presence of a local acoustic environment
The in situ electrochemical detection of microbubble oscillations during motion through a channel
No full textBubble oscillation has many applications, from driving local fluid motion to cleaning. However, in order to exploit their action, a full understanding of this motion, particularly in confined spaces (such as crevices etc. which are important in ultrasonic decontamination) is important. To this end, here we show how a Coulter counter can be used to characterize microbubbles produced through the ultrasonication of electrolytes. These microbubbles are shown to exist in relatively high concentrations while bubble activity is driven by ultrasound. Detection of these microbubbles, and their oscillatory behaviour, is achieved via translocation through a cylindrical glass microchannel (GMC). The microbubbles oscillate within the 40 μm channel employed and this behaviour is observed to change over the translocation period. This is attributed to the acoustic environment present or changes to the physical conditions in the interior of the chamber compared to the exterior. High-speed imaging confirms the presence of microbubbles as they move or ‘skate’ across the surface of the structures present before translocating through the channel. The observations are useful as they show that microbubble oscillation occurs within small structures, is preceded by surface confined bubbles and could be enhanced through pressure driven flow through a structure
Generation and in situ electrochemical detection of transient nanobubbles
No full textNanobubbles are fascinating but controversial objects. Although there is strong evidence for the existence of surface bound nanobubbles, the possibility of stable nanobubbles in the bulk remains in question. In this work, we show how ultrasonication of electrolytes can create transient bulk nanobubbles. To do this, glass nanopores are used as Coulter counters to detect nanobubbles. During ultrasonication, these transient bulk nanobubbles are shown to exist in relatively high concentrations while bubble activity on the surface of a solid media close to the pore is driven by ultrasound. However, the transient nature of these bubbles is evident upon termination of the ultrasonic source. High-speed imaging suggests that these transient nanobubbles originate from the fragmentation of larger bubbles, which skate over the surface of the structure in the acoustic field present. Transient nanobubbles as small as ∼100 nm in radius are detected. In contrast to previous work with microbubbles, no evidence for the oscillation of these nanobubbles during translocation was found. The novel experimental approach presented here provides strong evidence for the existence of transient nanobubbles in bulk solution.</p
An analytical differential resistance pulse system relying on a time shift signal analysis – applications in Coulter counting
No full textImproving the sensitivity and ultimately the range of particle sizes that can be detected with a single pore extends the versatility of the Coulter counting technique. Here, to enable a pore to have greater sensitivity, we have developed and tested a novel differential resistive pulse sensing (DiS) system for sizing particles. To do this, the response was generated through a time shift approach utilizing a “self-servoing regime” to enable the final signal to operate with a zero background in the absence of particle translocation. The detection and characterization of a series of polystyrene particles, forced to translocate through a cylindrical glass microchannel (GMC) by a suitable static pressure difference using this approach, is demonstrated. An analytical response, which scales with the size of the particles employed, was verified. Parasitic capacitive effects are discussed; however, translocations on the millisecond time scale can be detected with high sensitivity and accuracy using the approach described
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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