A mechanism implicating plastoglobules in thylakoid disassembly during senescence and nitrogen starvation

Plastoglobules are lipid droplets present in all plastid types. In chloroplasts, they are connected to the thylakoid membrane by the outer lipid half-bilayer. The plastoglobule core is composed of neutral lipids most prominently the prenylquinones, triacylglycerols, fatty acid phytyl esters but likely also unknown compounds. During stress and various developmental stages such as senescence, plastoglobule size and number increase due to the accumulation of lipids. However, their role is not limited to lipid storage. Indeed, the characterization of the plastoglobule proteome revealed the presence of enzymes. Importantly it has been demonstrated that these participate in isoprenoid lipid metabolic pathways at the plastoglobule, notably in the metabolism of prenylquinones. Recently, the characterization of two phytyl ester synthases has established a firm metabolic link between PG enzymatic activity and thylakoid disassembly during chloroplast senescence and nitrogen starvation

Comprehensive experimental investigation of counter-current bubble column hydrodynamics: Holdup, flow regime transition, bubble size distributions and local flow properties

In this paper, we apply a variety of experimental techniques to investigate the influence of the counter-current mode on bubble column hydrodynamics. We study an air-water bubble column, which is 5.3 m in height and has an inner diameter of 0.24 m, and we consider gas superficial velocities in the range of 0.004-0.20 m/s and liquid superficial velocities up to -0.09 m/s. The experimental investigation consists of holdup, gas disengagement, image analysis and optical probe measurements. The holdup measurements are compared with the literature and are used to investigate the flow regime transition. The gas disengagement measurements are used to further investigate the flow regime transition and study the structure of the holdup curve. The image analysis is used to study the bubble shapes and size distributions near the sparger and in the developed region of the column; in particular, the image analysis is applied to different gas velocities in the homogeneous regime in both the batch and counter-current modes. The optical probe is used to acquire radial profiles of the local properties (i.e., local void fraction and bubble rise velocity) to study the flow properties and further investigate the flow regime transition. Comparing the results from the different techniques, the influence of the gas superficial velocity and the liquid superficial velocity is discussed considering all main aspects of the two-phase flow, from the local flow properties to the global flow features. The counter-current mode is found to increase the holdup, reduce the bubble rise velocity, destabilize the homogeneous regime and change the local flow properties. © 2016 Elsevier Ltd

Identification and Characterisation of Technological Topics in the Field of Molecular Biology

This paper focuses on methodological approaches for characterising the specific topics within a technological field based on scientific literature data. We introduce a diachronic clustering analysis approach and some bibliometric indicators. The results are visualised with the software-tool Stanalyst [1]. We are applying our methods to the field "Molecular Biology". This field has grown a great deal in the last decade

Influence of electrolyte concentration on holdup, flow regime transition and local flow properties in a large scale bubble column

We experimentally investigate the influence of the electrolyte concentration on holdup, flow regime transition and local flow properties in a large scale bubble column, with air and water as working fluids. The column is 0.24 m inner diameter, 5.3 m height and the air is introduced by a spider sparger up to a superficial gas velocity of 0.2 m/s. The influence of five NaCl concentrations are investigated by using gas holdup and optical probe measurements. The gas holdup measurements are used for analysing the flow regime transition between the homogeneous and the transition regime and the optical probe is used for studying the local flow characteristics at different radial positions. The presence of NaCl - up to a critical concentration - increases the gas holdup. The increase in the gas holdup is due to the inhibition of the coalescence between the bubbles and, thus, the extension of the homogeneous regime. The results are in agreement with the previous literature on smaller bubble columns

Bubble size distributions and shapes in annular gap bubble column

An understanding of the bubble properties, size distributions and shapes is of fundamental importance for comprehending flow dynamics and mass transfer phenomena in bubble column reactors. A large number of studies have focused on open tube bubble columns, and the knowledge concerning bubble columns with internals is still limited. This paper contributes to the existing discussion experimentally investigating a counter-current annular bubble column with 0.24. m inner diameter and two internal pipes. The experimental investigation consists in holdup measurements and image analysis. The former is used for identifying the flow regime transition and studying the bubble column hydrodynamics, whereas the latter is used for investigating the bubble shapes and size distributions. The definition of the transition point is important because the size distribution and bubble shapes depend on the operating conditions and a change of the bubble properties is expected near the transition. The image analysis is applied at different superficial gas and liquid velocities, corresponding to a gas holdup between 2.9% and 9.6%. It is difficult to measure bubble size distribution accurately in large-diameter bubble columns owing to the overlapping of bubbles, even at low void fractions, and-in an annular gap bubble column-the fact that cap bubbles have also been reported in the homogeneous flow regime. The use of a bubble image analysis method to study the bubbly flows in a large-diameter annular gap bubble column is described. In the proposed method, each bubble is approximated and reconstructed using an ellipse. The proposed approach is used to quantify the bubble size distribution, as well as to study the bubble shape and orientation as function of the superficial gas and liquid velocities. The experimental data obtained are used to develop a correlation between non-dimensional parameters and aspect ratios. Also, the experimental data are compared with non-dimensional diagrams from the literature, revealing good agreement. Finally, the image analysis is used for supporting the flow regime transition prediction in the stability analysis method: the virtual mass formulation is obtained by using the aspect ratio correlation provided by the image analysis. The stability analysis-supported by the image analysis-was able to predict the transition point in very good agreement with experimental data and performed better than literature correlations. © 2015 Elsevier Inc

Influence of internals on counter-current bubble column hydrodynamics: Holdup, flow regime transition and local flow properties

Bubble columns are frequently studied without considering internals (open tube bubble columns). However, in most industrial applications, internal devices are often added to control heat transfer, to foster bubble break-up or to limit liquid phase back mixing. These elements can have significant effects on the multiphase flow inside the bubble column reactor and the prediction of these effects is still hardly possible without experimentation. In this paper, we study experimentally a counter-current gas-liquid bubble column in the open tube and annular gap configurations. In the annular gap bubble column, two vertical internal tubes are considered. The column has an inner diameter of 0.24 m, and the global and local hydrodynamic properties are studied using gas holdup measurements and a double-fiber optical probe. The gas holdup measurements are compared with the literature and used to investigate the flow regime transition. A double-fiber optical probe is used to acquire midpoint data and radial profiles of the local properties to study the flow properties and to further investigate the flow regime transition. The counter-current mode is found to increase the holdup, decrease the bubble velocity and cause regime transition at lower superficial gas velocity. The holdup curves in the annular gap and open tube configurations are similar in shape and values, suggesting that the presence of internals has a limited influence on the global hydrodynamic. In addition, it is found that the presence of the internals stabilizes the homogeneous regime in terms of transition gas velocity and holdup. © 2016 Elsevier Ltd

Computational fluid dynamics simulation of the heterogeneous regime in a large-scale bubble column

Bubble columns are used in many industrial applications, but the complex fluid dynamics phenomena has limited their design and optimization processes. Computational Fluid Dynamics (CFD) is a promising tool to investigate the complex multi-scale flow physics characterising multiphase reactors. In this work, a CFD Eulerian-Eulerian modelling approach is developed to describe the hydrodynamics of a large-scale bubble column operated over a wide range of superficial gas velocities (0.0188 – 0.20 m/s). Available experimental results were used for the model validation. A drag law for oblate bubbles was considered and coupled with a drag modification function to include the effects of bubble–bubble interactions. The numerical approach was tested considering a mono-dispersed approximation and including coalescence and breakup by using a Population Balance Model (PBM). The role played by the lift force was investigated and, for the reactor configuration considered, it turned out to be essential in the description of the local flow properties

Aspect ratio of bubbles in different liquid media:a novel correlation

The bubble shape is a required parameter in the modeling and design of multiphase reactors. This communication contributes to the broader discussion and closes the knowledge gap by providing a practical correlation for the bubble shape. The correlation is based on a very large experimental dataset, encompassing a wide range of Morton numbers (Log10(Mo) in the range of −10.8 and 2.3), flow conditions (single bubbles and dense bubbly flows) and considering both gravity-driven flows and flows with an extra-external pressure gradient (counter-current flows). The experimental data were post-processed to derive a simple and physics-based correlation, relating the bubble aspect ratio to the bubble Reynolds and Eötvös numbers. This correlation provides a more accurate description and covers a wider range of applicability compared with literature correlations. As such, it can be helpful in the estimation of the interfacial area and velocity of a dispersed phase rising in a continuous phase.</p