1,720,966 research outputs found
The disturbance of thermosolutal convection by g-jitter
No full textn this paper we review the disturbance of thermosolutal convection by g-jitter in two configurations (1) a horizontal layer of fluid and (2) directional solidification. We find that in both situations g-jitter provides a rich dynamical response resulting in both synchronous and asynchronous modes as well as resonant behaviour. It may act to both stabilise or destabilise the system, with the precise response depending on the parameter regime. Our knowledge of the response of thermosolutal convection in the presence of periodic acceleration is very limited. The results presented here, albeit limited in extent, suggest that the response of the system is rich and complex and not easily predictable. In view of this, further carefully coordinated modelling and experimentation (in both terrestrial gravity and microgravity) is necessary to characterise and effectively control this behaviour based upon a sound understanding of the underlying fundamental physical mechanisms
Simulations of experimentally observed dendritic growth behaviour using a phase-field model
No full textAn anisotropic phase-field model is used to simulate numerically dendritic solidification for a pure material in two dimensions. The phase-field model has been formulated to include the effect of four-fold anisotropy in both the surface energy and interfacial kinetics. The computations presented here are intended to model qualitatively experimentally observed dendritic solidification morphology. In particular, we simulate the growth into an undercooled melt of two dendrite tips which have formed as the result of a splitting event. The computation exhibits the competition between the two growing dendrite branches and the eventual predominance of one branch. Also, we simulate the effect of time-periodic forcing of an isolated dendrite tip on the mechanism of sidebranch formation. Although it is not yet computationally feasible to adequately verify convergence of the phase-field solutions, the phase-field simulations presented show many of the qualitative features observed in dendritic growth experiments
Prediction of solute trapping at high solidification rates using a diffuse interface phase-field theory of alloy solidification
No full textA phase-field model for solidification of a binary alloy is developed that includes gradient energy contributions for the phase field and for the composition field. When the gradient energy coefficient for the phase field is smaller than that for the solute field, planar steady-state solutions exhibit a reduction in segregation in the liquid phase ahead of an advancing front (solute trapping), and in the limit of high solidification speeds predict alloy solidification with no redistribution of composition. Comparison is made with the Aziz model of solute trapping
Convective stability in the Rayleigh-Benard and directional solidification problems - high-frequency gravity modulation
No full textThe effect of vertical, sinusoidal, time-dependent gravitational acceleration on the onset of solutal convection during directional solidification is analyzed in the limit of large modulation frequency-OMEGA. When the unmodulated state is unstable, the modulation amplitude required to stabilize the system is determined by the method of averaging, and is O(OMEGA). Comparison of the results from the averaged equations with numerical solutions of the full linear stability equations (based on Floquet theory) show that the difference is O(OMEGA-1/2). When the unmodulated state is stable, resonant modes of instability occur at large modulation amplitude. These are analyzed using matched asymptotic expansions to elucidate the boundary-layer structure for both the Rayleigh-Benard and directional solidification configurations. The leading-order term for the modulation amplitude is of O(OMEGA-2); the first-order correction of O(OMEGA-3/2) is calculated, and the results are compared with numerical solutions of the full linear stability equations. Based on these analyses, a thorough examination of the dependence of the stability criteria on the unmodulated Rayleigh number, Schmidt number, and distribution coefficient, is carried out
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
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