Buoyancy driven bubbly flows: scaling of velocities in bubble columns operated in the heterogeneous regime

The hydrodynamics of bubble columns in the heterogeneous regime is revisited. Focusing on air-water systems at large aspect ratio, we show from dimensional analysis that buoyancy equilibrates inertia, and that velocities scale as $(gD\varepsilon)^{1/2}$, where $D$ is the bubble column diameter, $\varepsilon$ the void fraction and $g$ the gravitational acceleration. From new experiments in a $0.4$m diameter column with ${\cal{O}}(10^3)$ particle Reynolds number bubbles and from a detailed analysis of published data, we confirm the self-organization prevailing in the heterogeneous regime, and that the liquid flow rate is only set by the column diameter $D$. Besides, direct liquid and gas velocity measurements demonstrate that the relative velocity increases above the terminal velocity $U_T$ in the heterogeneous regime, and that it tends to $\sim 2.4 U_T$ at very large gas superficial velocities $V_{sg}$. The proposed velocity scaling is shown to hold for liquid and gas mean velocities and for their standard deviations. Furthermore, it is found to be valid over a wide range of conditions, corresponding to Froude numbers $Fr=V_{sg}/(gD)^{1/2}$ from 0.02 to 0.5. Then, the relevance of this scaling for coalescing media is discussed. Moreover, following the successful prediction of the void fraction with a Zuber \& Findlay approach at the beginning of the heterogeneous regime, we show how the void fraction is correlated with $Fr$. Further investigations are finally suggested to connect the increase in relative velocity with meso-scale structures known to exist in the heterogeneous regime

Buoyancy driven bubbly flows: role of meso-scale structures on the relative motion between phases in bubble columns operated in the heterogeneous regime

The hydrodynamics of bubble columns in the heterogeneous regime is investigated from experiments with bubbles at large particle Reynolds numbers and without coalescence. The void fraction field $\varepsilon$ at small scales, analyzed with Vorono\"i tessellations, corresponds to a Random Poisson Process (RPP) in homogeneous conditions but it significantly differs from a RPP in the heterogeneous regime. The distance to a RPP allows identifying meso-scale structures, namely clusters, void regions and intermediate regions. A series of arguments demonstrate that the bubble motion is driven by the dynamics of these structures. Notably, bubbles in clusters (respectively in intermediate regions) are moving up faster, up to 3.5 (respectively 2) times the terminal velocity, than bubbles in void regions those absolute velocity equals the mean liquid velocity. Besides, the mean unconditional relative velocity of bubbles is recovered from mean relative velocities conditional to meso-scale structures, weighted by the proportion of bubbles in each structure. Assuming buoyancy-inertia equilibrium for each structure, the relative velocity is related with the characteristic size and concentration of meso-scale structures. By taking the latter quantities values at large gas superficial velocities, a cartoon of the internal flow structure is proposed. Arguments are put forward to help understanding why the relative velocity scales as $(gD\varepsilon)^{1/2}$ (with $D$ the column's diameter and $g$ gravity's acceleration). The proposed cartoon seems consistent with a fast-track mechanism that, for the moderate Rouse numbers studied, leads to liquid velocity fluctuations proportional to the relative velocity. The potential impact of coalescence on the above analysis is also commented.Comment: arXiv admin note: substantial text overlap with arXiv:2203.0741

Impact du développement des palmeraies familiales sur la déforestation et dans les ménages au Cameroun

Une étude a été conduite au sein de 208 exploitants familiaux dans le but d’estimer l’impact de l’expansion de l’élaéiculture sur la déforestation et les revenus des ménages au Cameroun. La méthode de l’Effet Moyen du Traitement a été utilisée dans une modélisation Probit. Les résultats montrent que le taux de déforestation causé par les producteurs ayant obtenu le matériel végétal sélectionné (Tenera) d’une source formelle, est significativement supérieur à celui des producteurs qui se sont  approvisionnés dans des sources informelles. Les facteurs qui déterminent cette déforestation sont l’âge et la politique agricole. L’âge est enrelation étroite avec l’aptitude à posséder les facteurs de production (terre, capital et travail) qui deviennent plus rares lorsque le producteur est jeune, c’est-à-dire moins de 30 ans. Dans les ménages des exploitantsfamiliaux, l’élaéiculture contribue à plus de 50% au revenu agricole annuel. Cette activité donne également de l’huile de palme nécessaire pour la consommation familiale. Ces résultats ont déclenché une réflexion sur l’opportunité d’élaborer un outil d’aide aux politiques agricoles prenant en compte les objectifs d’accroître la production nationale d’huile de palme et celui de gérer durablement des ressources forestières.Mots clés: Déforestation, exploitants familiaux, impact, palmier à huile

Tramsission de la politique monétaire: le cas des pays de la CEMAC

This article analyzes the process by which the monetary policy influences economies of the six countries of the Economic and Monetary Community of Central Africa (CEMAC) during the period 1980-2008. After having identified the channels of interest rate, credit and currency, we show that the monetary policy ended in differentiated effects on the economies of the sub-region. In particular, extent of the shocks on the variables of the monetary transmission led to important differences between the countries with short and long-term

Tramsission de la politique monétaire: le cas des pays de la CEMAC

This article analyzes the process by which the monetary policy influences economies of the six countries of the Economic and Monetary Community of Central Africa (CEMAC) during the period 1980-2008. After having identified the channels of interest rate, credit and currency, we show that the monetary policy ended in differentiated effects on the economies of the sub-region. In particular, extent of the shocks on the variables of the monetary transmission led to important differences between the countries with short and long-term

Tramsission de la politique monétaire: le cas des pays de la CEMAC

This article analyzes the process by which the monetary policy influences economies of the six countries of the Economic and Monetary Community of Central Africa (CEMAC) during the period 1980-2008. After having identified the channels of interest rate, credit and currency, we show that the monetary policy ended in differentiated effects on the economies of the sub-region. In particular, extent of the shocks on the variables of the monetary transmission led to important differences between the countries with short and long-term

Permanent Genetic Resources added to Molecular Ecology Resources Database 1 February 2013-31 March 2013

This article documents the addition of 142 microsatellite marker loci to the Molecular Ecology Resources database. Loci were developed for the following species: Agriophyllum squarrosum, Amazilia cyanocephala, Batillaria attramentaria, Fungal strain CTeY1 (Ascomycota), Gadopsis marmoratus, Juniperus phoenicea subsp. turbinata, Liriomyza sativae, Lupinus polyphyllus, Metschnikowia reukaufii, Puccinia striiformis and Xylocopa grisescens. These loci were cross-tested on the following species: Amazilia beryllina, Amazilia candida, Amazilia rutila, Amazilia tzacatl, Amazilia violiceps, Amazilia yucatanensis, Campylopterus curvipennis, Cynanthus sordidus, Hylocharis leucotis, Juniperus brevifolia, Juniperus cedrus, Juniperus osteosperma, Juniperus oxycedrus, Juniperus thurifera, Liriomyza bryoniae, Liriomyza chinensis, Liriomyza huidobrensis and Liriomyza trifolii. © 2013 John Wiley & Sons Ltd.Peer Reviewe

Developing Local Currency Bond Markets for Long-term Development Financing in Sub-Saharan Africa

This article discusses the role that local currency bond markets (LCBMs) can play in the long-term financing of sustainable development of Sub-Saharan African (SSA) economies and presents an empirical analysis of the factors which may hinder or promote the development of such markets in SSA. Using a new dataset for 27 SSA countries, our findings support earlier research on SSA and other regions, showing that LCBM development is related to country size, larger banking systems, greater trade openness and better regulatory frameworks and the rule of law. Foreign investor participation broadens the investor base and can give a boost to LCBM development, yet it may also increase volatility of international capital flows. Hence, with view to the experience of emerging economies in other regions, capital market liberalisation should be pursued only very cautiously and in pace with solid financial and institutional development

Hepatitis C Virus Infection May Lead to Slower Emergence of P. falciparum in Blood

International audienceBACKGROUND: Areas endemic for Plasmodium falciparum, hepatitis B virus (HBV) and hepatitis C virus (HCV) overlap in many parts of sub-Saharan Africa. HBV and HCV infections develop in the liver, where takes place the first development stage of P. falciparum before its further spread in blood. The complex mechanisms involved in the development of hepatitis may potentially influence the development of the liver stage of malaria parasites. Understanding the molecular mechanisms of these interactions could provide new pathophysiological insights for treatment strategies in Malaria. METHODOLOGY: We studied a cohort of 319 individuals living in a village where the three infections are prevalent. The patients were initially given a curative antimalarial treatment and were then monitored for the emergence of asexual P. falciparum forms in blood, fortnightly for one year, by microscopy and polymerase chain reaction. PRINCIPAL FINDINGS: At inclusion, 65 (20.4%) subjects had detectable malaria parasites in blood, 36 (11.3%) were HBV chronic carriers, and 61 (18.9%) were HCV chronic carriers. During follow-up, asexual P. falciparum forms were detected in the blood of 203 patients. The median time to P. falciparum emergence in blood was respectively 140 and 120 days in HBV- and HBV+ individuals, and 135 and 224 days in HCV- and HCV+ individuals. HCV carriage was associated with delayed emergence of asexual P. falciparum forms in blood relative to patients without HCV infection. CONCLUSIONS: This pilot study represents first tentative evidence of a potential epidemiological interaction between HBV, HCV and P. falciparum infections. Age is an important confounding factor in this setting however multivariate analysis points to an interaction between P. falciparum and HCV at the hepatic level with a slower emergence of P. falciparum in HCV chronic carriers. More in depth analysis are necessary to unravel the basis of hepatic interactions between these two pathogens, which could help in identifying new therapeutic approaches against malaria

Publisher Correction: Science diplomacy for plant health

Correction to: Nature Plants https://doi.org/10.1038/s41477-020-0744-x, published online 11 August 2020.1 Pág.An amendment to this paper has been published and can be accessed via a link at the top of the paper.In the version of this Comment originally published, in the penultimate paragraph of the section “Steps towards global phytosanitary research coordination” the second sentence incorrectly defined IPPC as ‘Intergovernmental Panel on Climate Change’, though it was cor rectly defined earlier as ‘International Plant Protection Convention’; the sentence has now been corrected to read “Ideally, they should benefit from the reputation of a United Nations mandate convention, such as the IPPC…”Peer reviewe