Slug Phase Research Articles

Rapid production of biodiesel in a microchannel reactor at room temperature by enhancement of mixing behaviour in methanol phase using volume of fluid model

The demand for biodiesel to reduce consumption of fossil fuels has motivated engineers to design a rapid and safe production process. However, the slow mass transfer of multiphase transesterification reaction hinders the overall reaction time. A continuous process using a microchannel reactor was proven to achieve complete reaction time in 40 s with high oil conversion of 98.6% due to the enhancement of mixing inside the methanol slug phase. The reaction was successfully performed at ambient room environment, without heating element in the reactor that reduces the design complexity and makes the operation energy efficient and safer. The enhancement of reaction was investigated based on the hydrodynamic factors such as interfacial area and mixing. Three-dimensional Computational Fluid Dynamics (CFD) simulation shows a torus-shaped recirculation structure inside methanol slug that enhances mixing. Microchannel reactor has been proven to enhance the mixing and capable in having faster, highly efficient, and safer process.

Organism motility in an oxygenated shallow-marine environment 2.1 billion years ago

Evidence for macroscopic life in the Paleoproterozoic Era comes from 1.8 billion-year-old (Ga) compression fossils [Han TM, Runnegar B (1992) Science 257:232-235; Knoll et al. (2006) Philos Trans R Soc Lond B 361:1023-1038], Stirling biota [Bengtson S et al. (2007) Paleobiology 33:351-381], and large colonial organisms exhibiting signs of coordinated growth from the 2.1-Ga Francevillian series, Gabon. Here we report on pyritized string-shaped structures from the Francevillian Basin. Combined microscopic, microtomographic, geochemical, and sedimentologic analyses provide evidence for biogenicity, and syngenicity and suggest that the structures underwent fossilization during early diagenesis close to the sediment-water interface. The string-shaped structures are up to 6 mm across and extend up to 170 mm through the strata. Morphological and 3D tomographic reconstructions suggest that the producer may have been a multicellular or syncytial organism able to migrate laterally and vertically to reach food resources. A possible modern analog is the aggregation of amoeboid cells into a migratory slug phase in cellular slime molds at times of starvation. This unique ecologic window established in an oxygenated, shallow-marine environment represents an exceptional record of the biosphere following the crucial changes that occurred in the atmosphere and ocean in the aftermath of the great oxidation event (GOE).

Modelling mass transfer in liquid-liquid slug flow in a microchannel

Liquid-liquid slug flow regime is characterised by the presence of strong internal circulation which enhances mass transfer. In this work, we develop a mathematical model for conjugate mass transfer in the liquid-liquid slug flow regime in a microchannel. A Lagrangian approach is adopted where the behaviour of a unit cell in the channel is analysed in a moving reference frame. The system is analysed for two cases when (I) the slug is in direct contact with the channel wall and (II) there is a thin film of continuous fluid surrounding the slug. A novel contribution of this work is the extension of the stream function formulation to determine the flow structures in multiply connected domains made up of two liquids in a pressure driven flow. The primary objective of the work is to understand the influence of the flow patterns (which is determined by fluid properties and operating conditions) on the mass transfer of a solute from the slug to the continuous phase. Towards this, the species transport equation is solved numerically using the velocity field obtained. The reliability of the model developed is validated with experiments reported in the literature. This study gives us insights on the influence of the film on the hydrodynamics and its contribution to mass transfer. A key finding of this study is that the rate of mass transfer can be enhanced if the continuous phase has higher viscosity than the slug phase.

Cold hardiness, adaptive strategies, and invasion of slugs of the genus Deroceras (Gastropoda, Pulmonata) in northeastern Asia

Abstract-Four species of slugs have been identified in the vicinity of Magadan: Deroceras laeve, D. altaicum, D. reticulatum, and D. agreste. They exemplify three different life cycle schemes, with D. reticulatum and D. altaicum wintering at the egg phase; D. laeve, at the slug phase; and D. agreste, at either phase. The D. altaicum and D. reticulatum slugs and D. laeve eggs are intolerant of subzero temperatures. D. laeve’s tolerate freezing and survive at temperatures below −28°C. The eggs of other species, which lose up to 35% of water upon cooling, can withstand temperatures as low as −15 to −17°C (D. altaicum), −25°C (D. agreste), and −35°C (D. reticulatum). According to preliminary data, D. agreste slugs survive at temperatures down to −10°C. The almost ubiquitous distribution of D. laeve in regions with cool summers (including zonal tundras) is accounted for not so much by the high rate of ontogeny as by its significant cold hardiness and ability to winter at different phases of the life cycle (except for the egg phase), which allows the period of development to be prolonged for the next seasons. The last is confirmed by the fact that the slugs collected before and after hibernation proved to have identical patterns of distribution by body weight. Three species of slugs introduced in the vicinity of Magadan fail to spread inland. In the case of D. reticulatum, this is explained primarily by the fact that the frost-free season in inland areas is too short to allow these slugs to complete ontogeny and lay eggs. The barriers to their expansion appear to be insuperable, since this process remains unsuccessful over no less than 75–80 years.

The extracellular matrix of the Dictyostelium discoideum slug.

In this review, we detail the current understanding of the extracellular matrix (ECM) of the migratory slug phase of the cellular slime mould, Dictyostelium discoideum. We describe some structural and non-structural molecules which comprise the ECM, and how these molecules reflect both plant and animal ECM systems. We also describe zones of the multicellular slug that are known to make ECM components, including the role of the prestalk cells and the slug epithelium-like layer. Finally, we review the contributions of studies on mutants to our understanding of the ECM of D. discoideum, and relate this to differentiation and development in more complex eukaryotic systems.

Remobilizing surfactant retarded fluid particle interfaces. I. Stress-free conditions at the interfaces of micellar solutions of surfactants with fast sorption kinetics

Surfactant molecules adsorb onto the interfaces of moving fluid particles and are convected to regions in which the surface flow converges. Accumulation of surfactant in these regions creates interfacial tension gradients that retard the surface flow. In this study it is argued theoretically and demonstrated experimentally that fluid movement on the surface of a drop or bubble can remain unhindered in the presence of a single adsorbed surfactant if, relative to the convective rate of transport of adsorbed surfactant along the surface, desorption is fast, and the bulk concentration is high enough so that diffusion away from the particle is fast. For this circumstance, a uniform surface concentration of surfactant is maintained, and no gradients in surface tension arise to retard the surface velocity. The fluid particle flow behaves as it would in the absence of surfactant save that it has a reduced, uniform surface tension. The remobilization of surfactant-laden interfaces of fluid particles is demonstrated experimentally in a three-phase periodic slug flow in a capillary tube in which a train of alternating air and aqueous slugs ride on an annular wetting film of fluorocarbon oil. Surfactant, dissolved in the aqueous slug phase, adsorbs onto and retards the aqueous–oil interface. The hydrodynamics of this flow is such that small changes in the mobility of this interface create large shear rates in the oil layer. This significantly increases the pressure drop required to drive the slug train at constant velocity. Three surface adsorbers are used to demonstrate surface remobilization: The polyethoxy, nonionic surfactants Triton X-100 and Brij-35, which have fast desorption kinetics and do not retard the surface flow at high concentrations and, as a counter example, the desorption hindered protein bovine serum albumin, which is shown to be unable to remobilize an interface even at high concentration.

Genetic Analysis of the Slug Stage of Dictyostelium discoideum

During the course of development, cells of Dictyostelium discoideum are able to produce a multicellular body (a ‘slug’) which is capable of movement over the substratum. This phase, which is induced by production of ammonia by the starving cells, may last for hours or days depending on environmental stimuli. In order to probe the regulatory system controlling formation and duration of the slug phase, mutants were isolated that remained in the slug phase for an extended period. Thirty-two such ‘slugger’ mutants were analysed by parasexual genetic techniques and placed into 10 complementation groups (slgA-slgJ). The linkage groups bearing representatives of these complementation groups were determined by segregation of diploids formed between mutants and tester strains. Phenotypic studies of mutants indicated that members of slgD, slgE and slgG were over-sensitive to the ammonia slug-inducing stimulus.

Changes in morphogenesis and developmental enzyme levels in Dictyostelium discoideum after gamma irradiation.

Changes in the levels of specific activity of two enzymes believed to be involved in developmental regulation were observed after irradiating differentiating cells of Dictyostelium discoideum. Stimulation of the levels of specific activity of alkaline phosphatase occured after irradiation at the beginning of development and at the end of the aggregation period, but not after irradiation at the beginning of aggregation. A stimulation in UDP-glucose pyrophosphorylase specific activity was also observed, but to a lesser extent and only after irradiation at the end of aggregation. Dose-dependent delays in the appearance of peaks of specific activity were noted. The delay per unit dose was less when irradiation took place at the beginning of development as opposed to the beginning or end of the aggregation period. Radiation-induced delays in progression through visible developmental stages were almost identical to delays in enzyme appearance. Other radiation effects on morphogenesis included the induction of a migratory slug phase.