1,720,995 research outputs found
Ignition and extinction fronts in counterflowing premixed reactive gases
Full text linkWe describe two-dimensional steady propagating flame fronts in the stagnation mixing layer between two opposed streams of the same reactive mixture, the propagation taking place in the direction perpendicular to the plane of strain. The front, which is curved by the nonuniform flow field, separates a chemically frozen region from a region with a twin-flame configuration. The front velocity is calculated in terms of the Lewis number, Le(F), and the Damkohler number, Da. Da, equal to the inverse of the Karlovitz number, is defined as the ratio of the strain time to the transit time through the planar unstrained flame. For the cases corresponding to large Da, difficult to tackle numerically, analytical expressions are given, characterizing the flame shape, and the variation of the burning rate along the flame front from the nose up to the planar trailing branches. For moderately large and low values of Da, the study is carried out numerically, yielding, in particular, the propagation velocity in terms of Da, for different values of Le(F). Different combustion regimes are thus described including flames propagating toward the unburnt mixture, or ignition fronts, standing flames and retreating flames, or extinction fronts. We also describe stationary cylindrical flames of finite-extent, or 2D burning spots. In particular, a critical Lewis number is found, below which negative propagation speeds do not exist while the 2D burning spots mentioned may be encountered. Typically, these exist only for sufficiently small Le(F) if the Da is within a range [Da(min), Da(max)], depending on Le(F). For Da < Da(min), the 2D spots are quenched, whereas as Da is increased, they grow in size, tending to give birth to propagating (ignition) fronts; Da(max) is indeed found to be the smallest Da allowing for ignition fronts. We notice that the range of existence of the 2D spots, for a given Le(F), can overlap with that of retreating (extinction) fronts, and possibly with that of 3D spots, or flame balls, in this flow. However, the 3D case is not addressed in this work
Evaluation of faba bean breeding lines under different rainfed conditions
No full textDrought is one of the major factors limiting faba bean (Vicia faba L.) production in Mediterranean region with irregular water distribution and moisture level below than 500 mm. A major objective of any breeding program in this region is to develop drought-tolerant/resistant genotypes of faba bean that are well adapted to a wide range of environments, since environmental variation causes differential genotypic responses. The objective of this study was to evaluate the response of eight faba bean drought tolerant breeding lines - selected in Tel Hadya (Syria) with moisture level below 300 mm - and three cultivars under rainfed conditions in two stations (Terbol and Kfardan) of the International Center for Agricultural Research in the Dry Areas (ICARDA) representing two different agro-climatic zones in Bekaa, Lebanon during 2008/2009 cropping season. The breeding lines were compared in terms of growth vigor, yield, yield components, harvest index and water use efficiency in both locations. The seasonal accumulated rainfall in Kfardan station (289 mm) was 42% less than that recorded in Terbol station (501 mm). Genotypic variations for several yield characters were recorded in both locations. Plant height, number of nods per plant, number of lateral branches and internodes’ length were higher in Terbol by 14%, 50%, 25% and 48%, respectively, than those recorded in Kfardan. Highest grain yields were recorded in Terbol station by the genotypes ILB1814 (Syrian local large) and ILB1266 (Aguadolce), followed by DT/B7 9013, ILB 1270 Reina Blanca and DT/B7 9005. Similarly in Kfardan, the genotype DT/B7 9013 had the highest grain yield, followed by ILB 1814 (Syrian local large), DT/B7 9005, DT/B7 9043 and ILB 1266 (Aguadolce). The biological yield, total biomass, grain yield, harvest index, number of pods per plant and the number of seeds per plant recorded in Terbol were higher by 39%, 16%, 77%, 30%, 54%, and 53%, respectively, than those recorded in Kfardan. This means lines yielding good under low rainfall area may not perform well under high rainfall environments. The biomass water use efficiency (WUEb) ranged from 0.4 to 0.61 kg m-3 in Terbol and from 0.63 to 0.89 kg m-3 in Kfardan, whereas the grain water use efficiency (WUEg) ranged from 0.32 to 0.61 kg m-3 in Terbol and from 0.36 to 0.55 kg m-3 in Kfardan. The WUEb was significantly higher (by 50%) in kfardan than in Terbol whereas the WUEg in Kfardan was significantly lower (by 8%) than that in Terbol. Thus it seems that the remobilization of assimilates is limited in Kfardan due to the severe terminal drought
LIST OF PUBLICATIONS OF JOEL DAOU Refereed Journal Publications References
No full text[3] Al-Malki, F and Daou, J. Triple-flame propagation against a Poiseuille flow in a channel with porous walls. Combustion Theory and Modelling (2013). [4] Pearce, P. and Daou, J. The effect of gravity and thermal expansion on the propagation of a triple flame in a horizontal channel. Combustion and Flame 160, 28002809 (2013). [5] Daou,J. Strainedpremixed flames: effect ofheat-loss, preferential diffusion, and the reversibility of the chemical reaction. Combustion Theory and Modelling 15:437-454 (2011). [6] Daou, J. and Al-Malki, F. Triple flame propagation in a parallel flow: an asymptotic study. Combustion Theory and Modelling 14:177-202 (2010). [7] Daou, J. Asymptotic analysis of flame propagation in weakly-strained mixing layers under a reversible chemical reaction. Combustion Theory and Modelling, 13:189-213 (2009). [8] Daou, J., Al-Malki, F. and Ronney, P. Generalized Flames Balls. Combustio
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
Premixed edge-flames under transverse enthalpy gradients
Full text linkWe describe flame propagation between two opposed reactive streams which may differ in their composition and temperature. A two-dimensional counterflow configuration and an irreversible Arrhenius reaction are adopted, along with the constant density approximation. Attention is focused on the influence of two nondimensional parameters. The first one, denoted by γ, represents the difference in the enthalpy of the feed streams. The second one, ε, quantifies the ratio between the characteristic chemical time and the strain time. After a general formulation of the problem, we begin by an analysis of the one-dimensional case consisting of two parallel planar flames of unequal strength. The flames behavior is described analytically and numerically. In particular, two extinction regimes are identified: for values of γ smaller than a critical value γ*, the flames extinguish by quenching against each other at the stagnation plane; for γ > γ* they extinguish while at a finite distance from each other which increases with γ. These behaviors are similar to those, known in the literature, associated with the influence of Lewis numbers on the extinction of twin-flames. We then describe the propagation of two-dimensional flame fronts along the stagnation line, in a direction perpendicular to the plane of strain. The flame front is thus curved under the combined effects of the flow field and the transverse enthalpy gradient in the frozen mixture ahead of it; far behind the state of the gas is that of the pair of flat flames introduced above. The problem is studied numerically and complemented by an analytical description of the fast-chemistry situations corresponding to small values of ε. In particular we describe, for different fixed values of γ, the evolution of ignition fronts, characterized by a positive propagation speed, to extinction fronts, characterized by negative speeds, as ε is increased. In addition to the marked change in the flame shape, the most noticeable effect of an increase in γ is the decrease in the propagation speed of the flame front. These effects are associated with the increased front curvature for higher values of γ, along with a shift of the front leading edge towards the stream with higher enthalpy
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