1,720,953 research outputs found
Droplet condensation in turbulent jets
No full textThe evaporation and condensation process of liquid droplets, advected by a turbu- lent flow is found in many technological applications - ranging from aeronautical/power- plants engines up to the rather new discipline of Particle Engineering in the biotech industry - and in many natural phenomena, such as cloud formation and meteorology. A better understanding of droplets nucleation, transport, evaporation/condensation and vapour mixing is crucial for the efficiency of these devices as well as it would be to improve weather forecasting.
The phase change is a multi-scale phenomena ranging from the nano scale, at which droplets nucleate, to the micro and macro scales where the turbulent flow advects both the droplets and their vapour. Although droplet laden flows have been extensively studied, several issues are still in place, especially when dealing with multi-phase turbulent flows. Many phenomena, such as small scales clustering of droplets (considered as inertial particles) or preferential spatial accumulation, have been observed and understood under the simplifying assumption of the one-way cou- pling regime, where the disperse phase does not modify the carrier fluid. Nonetheless, a deeper understanding of multiphase flows demands at least for two-way coupling effects, accounting for the inter-phase mass, momentum and energy exchanges. Homogeneous nucleation of liquid droplets occurs when a hot vapour stream mixes with a cooler and dry external flow. Even though many applications could benefit from a better understanding of droplet nucleation in turbulence, nowadays it has been investigated only experimentally, given all the aforementioned difficulties on modelling the multi-physics phenomena occurring in such a complex turbulent flow. In fact, the nonlinear interplay between turbulent fluctuations and homogeneous nucleation, immediately leads to non-trivial cross-coupling phenomena between the gas and the liquid phase. Their modelling reveals to be crucial for detailed numerical investigations to be reliable.
Classical Nucleation Theory (CNT) prescribes a rate for the homogenous nucleation of droplets, per unit time and volume. It also provides for an estimate of the critical radius at which – eventually – each droplet nucleates. The droplet nucleation itself basically occurs when a stable molecules cluster size is reached, thus everything strongly depends on the local thermodynamical state. While the equations describ- ing mass, momentum and energy exchange, between droplets and the turbulent flow are still formulated on phenomenological ground, a rigorous derivation of the fluid flow equations still lacks. In the present work a first attempt to tackle this challenging physical problem will be presented: modelling the mass, momentum and energy transfer, with appropriate boundary conditions, at the interface between the two phases. Starting from the low-Mach number formulation of the Navier-Stokes equations for the gaseous phase, an analytical decomposition of the flow field allows
– within the point particle approximation, for the disperse phase – to reallocate the boundary conditions at the droplets surface as equivalent source/sink terms on the carrier phase, without any ad-hoc assumption. However this methodology still needs an estimate for the fluxes at the droplet surface, at any length-scale. Two different models for the mass transfer, have been tested and employed here to be validated against the available experimental investigations found in literature.
In the present study a full description of the droplet nucleation in a vapour turbulent jet is provided by means of Direct Numerical Simulation (DNS). No turbulence model has been considered, since all the relevant scales of turbulent motion have been resolved on the computational grid. To capture the inter-phase exchanges the so-called Exact Regularised Point-Particle method (ERPP) has been adopted, proving again its suitability for High Performance Computing simulations (HPC) on massively parallel machines, handling billions particles. In the point-particle ap- proximation and within the Eulerian-Lagrangian approach, here adopted to describe respectively the carrier and disperse phase dynamics, each droplets is described as point mass. The relevance of the inter-phase coupling effects is thoroughly discussed, by comparing the results obtained accounting for the droplets back-reaction with those obtained neglecting it. It is already known how a disperse phase does affect the carrier phase dynamics, modulating turbulence, stretching the shape of the jet, but always preserving the (statuary) jet self-similarity found in the one-way coupling regime. Beyond turbulence modulation, the droplets back-reaction is mainly effective on the temperature and vapour fields of the carrier phase, heavily altering the local thermodynamical fluctuations, thus affecting the related droplet nucleation rate. This way, one is able to completely characterise the phase change process, to measure any droplet trajectory followed in a Lagrangian way and to fully characterise any observable from a statistical point of view.
Considerable effects of the droplets back-reaction on the nucleation rate emerged, by decreasing the amount of vapour – due to nucleation/condensation – and heating up, to a lesser extent, the dry environment. Both effects decrease the vapour saturation and the nucleation rate that strongly depends on it. The intensity of these effects is related to the number of back-reacting nucleated droplets, thus at lower concen- trations the nucleation rate is almost insensitive to it. However, for higher vapour concentration, it is not possible to neglect the particles back-reaction, especially being these an additional source of turbulent fluctuations that ultimately impacts on the mean nucleation rate. In fact, the droplets redistribute vapour through condensation/evaporation and temperature by releasing/absorbing heat, along their trajectory. In other words, the particles back-reaction serves as an additional source of fluctuations not to be disregarded. It is reasonable to hypothesise that it is not possible to effectively model the back-reaction effects, discussed so far, rather than to simply evolve each single droplet as it has been done in the present DNS simulations. Under this respect, the present contribution constitutes an absolute novelty in the aerosol community shedding light on the the two-way coupling effects that were revealed to be crucial in the overall nucleation process and turbulent transport of the droplets
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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