Saddle-Node Bifurcation to Jammed State for Quasi-One-Dimensional Counter Chemotactic Flow

The transition of a counter chemotactic particle flow from a free-flow state to a jammed state in a quasi-one-dimensional path is investigated. One of the characteristic features of such a flow is that the constituent particles spontaneously form a cluster that blocks the path, called a path-blocking cluster (PBC), and causes a jammed state when the particle density is greater than a threshold value. Near the threshold value, the PBC occasionally desolve itself to recover the free flow. In other words, the time evolution of the size of the PBC governs the flux of a counter chemotactic flow. In this paper, on the basis of numerical results of a stochastic cellular automata (SCA) model, we introduce a Langevin equation model for the size evolution of the PBC that reproduces the qualitative characteristics of the SCA model. The results suggest that the emergence of the jammed state in a quasi-one-dimensional counter flow is caused by a saddle-node bifurcation.Comment: 5pages, 8figure

Coupling photosynthetic biogas upgrading with the astaxanthin production using Neochloris sp

The feasibility of coupling photosynthetic biogas upgrading with astaxanthin production by Neochloris sp. using real centrate as a feedstock was herein evaluated. To maximize astaxanthin production, this study focused on optimizing the cultivation conditions such as light intensity, culture medium, and composition of biogas. A light intensity of 300 μmol m-2 s-1 showed the highest specific growth rate (0.34 d-1) and total suspended solid of biomass (0.33±0.03 g L-1) of microalgae compared to other light intensity (0, 100, 500, 800 μmol m-2 s-1). When the headspace in the bottles was filled with air, mineral salt medium showed higher growth (0.78±0.007 g L-1) than other medium conditions (10% diluted centrate from domestic wastewater, 10% diluted centrate adjusted initial pH of 7, and 10% diluted centrate with activated sludge aliquot). On the other hand, when biogas was injected into the headspace in the bottles, 10% diluted centrate showed a higher specific growth rate (0.58-1.1 d-1) and TSS (2.57±0.92~6.98±0.029 g L-1) because pH control by CO2 dissolution prevented growth inhibition by free ammonia. In terms of biogas upgrading, CO2 of the headspace in the bottles was removed by 82.8-99.8% and decarbonization of biogas was achieved. Interestingly, biogas containing 600 ppm H2S revealed a two-fold higher biomass yield than biogas without H2S. When 5000 ppm of H2S, growth inhibition occurred, but addition of activated sludge aliquot was effective to remove H2S by sulfur oxidizing bacteria, and microalgae grew (4.36±0.057 g L-1). Thus, this study indicated that Neochloris sp. could validated the proof of concept with biogas containing 600 ppm H2S. Comparison of the maximum biomass yield with different dilution centrate under a headspace of biogas with 600 ppm H2S showed no significant differences. Astaxanthin yield were 0.072% of dry biomass (MSM), 0.024% (10% diluted centrate), 0.028% (50% diluted centrate), and 0.177% (raw centrate (100% centrate)) on day 10. From these results, 100% centrate can be utilized for Neochloris sp. cultivation. Thus, photosynthetic biogas upgrading using Neochloris sp. can support the valorization of residual effluents such as digestate and biogas in the form of high added value pigments and biomass.Departamento de Ingeniería Química y Tecnología del Medio AmbienteMáster en Ingeniería Ambienta

Segregation pattern reorientation of granular mixture on horizontally oscillating tray

Reorientation of the segregation pattern of a binary granular mixture on a two-dimensional hor- izontally oscillating tray is numerically realized. The mixture consists of large-and-heavy particles and small-and-light particles, the segregation pattern of which shows a transition between a striped pattern perpendicular to the oscillation and that parallel to the oscillating direction according to the change of area-fractions of two types of particles. The transition mechanism is discussed on the basis of a simplified 1-dimensional dynamics.Comment: 10 pages, 6 figure