Mesh optimisation based on Willmore energy

An algorithm for improving the quality of an initial triangulation on a fixed set of vertices is suggested. The edge flip operation is performed consecutively, aiming to minimise the discrete Willmore energy over a triangulated surface (or mesh). The Will- more energy of a surface is a function of Gaussian and mean curvature, and measures local deviation from a sphere. Virtual points are introduced in the triangulation to overcome the local invariance of Willmore energy under edge flips. Some experimental results are given

3D modelling and recognition

3D face recognition is an open field. In this paper we present a method for 3D facial recognition based on Principal Components Analysis. The method uses a relatively large number of facial measurements and ratios and yields reliable recognition. We also highlight our approach to sensor development for fast 3D model acquisition and automatic facial feature extraction

The influence of shear on the metabolite yield of Lactobacillus rhamnosus biofilms

Please read abstract in the article.http://www.elsevier.com/locate/nbthb201

Succinic acid production by Actinobacillus succinogenes in chemostat and biofilm cultures

Previously published results from a novel, homogeneously distributed shear, tubular fermenter used to study continuous chemostat (high shear) and biofilm (low shear) fermentations (Brink and Nicol, 2014a), were compared to results obtained in the same reactor at intermediate shear conditions as well as batch (biofilm) fermentations of Actinobacillus succinogenes. It was found that the steady-state volumetric production rates increased by nearly an order of magnitude (1.8 g.L−1.h−1 vs 15–17 g.L−1.h−1) as the shear was reduced from the chemostat (1.83 m.s−1) to the lower shear biofilm conditions. The biofilm results indicated similar volumetric production rates for the different shear conditions, while the measured extracellular polymeric substances (EPS) in the biofilm exhibited a significant shear dependence; EPS fractions of 0.50 ± 0.05 g.g−1 vs. 0.16 ± 0.02 g.g−1 for the low and intermediate shear conditions respectively. The cell-based biofilm production rates were shown to be dependent on shear conditions at succinic acid titres less than the growth-maintenance boundary (10 g.L−1), with a reduction in cellular production rate associated with an increase in shear. Under maintenance conditions the cell-based production rates appeared independent of the shear conditions in the fermenter, with the cell-based production rates decreasing with increasing succinic acid titres. The industrial implications are that for succinic acid titres in excess of 10 g.L-1, the same mass of biomass under intermediate shear conditions should exhibit a greater volumetric production rate due to the higher fraction of cells as opposed to EPS. The initial values for the batch cell-based succinic acid production rates corresponded to the steady-state values for biofilms grown under the same continuous conditions. However, during transient operation the production rates exceeded the steady-state values; a lag in the product inhibition response was observed. The transient production rates eventually ceased at succinic acid titres in excess of approximately 60–72 g.L−1; a residual glucose concentration of 20 g.L-1 was measured at the highest succinic acid titre (72 g.L-1), indicating product related inhibition as opposed to substrate depletion. The transient results indicate that a larger average cellbased production rate can be obtained during transient operation when compared to the steady fermentation conditions due to a lag in the succinic acid inhibition during transient operation.http://www.aidic.it/cetam2017Chemical Engineerin

Succinic acid production with Actinobacillus succinogenes : rate and yield analysis of chemostat and biofilm cultures

BACKGROUND: Succinic acid is well established as bio-based platform chemical with production quantities expecting to increase exponentially within the next decade. Actinobacillus succinogenes is by far the most studied wild organism for producing succinic acid and is known for high yield and titre during production on various sugars in batch culture. At low shear conditions continuous fermentation with A. succinogenes results in biofilm formation. In this study, a novel shear controlled fermenter was developed that enabled: 1) chemostat operation where self-immobilisation was opposed by high shear rates and, 2) in-situ removal of biofilm by increasing shear rates and subsequent analysis thereof. RESULTS: The volumetric productivity of the biofilm fermentations were an order of magnitude more than the chemostat runs. In addition the biofilm runs obtained substantially higher yields. Succinic acid to acetic acid ratios for chemostat runs were 1.28±0.2 g.g-1, while the ratios for biofilm runs started at 2.4 g.g-1 and increased up to 3.3 g.g-1 as glucose consumption increased. This corresponded to an overall yield on glucose of 0.48±0.05 g.g-1 for chemostat runs, while the yields varied between 0.63 g.g-1 and 0.74 g.g-1 for biofilm runs. Specific growth rates (μ) were shown to be severely inhibited by the formation of organic acids, with μ only 12% of μmax at a succinic acid titre of 7 g.L-1. Maintenance production of succinic acid was shown to be dominant for the biofilm runs with cell based production rates (extracellular polymeric substance removed) decreasing as SA titre increases. CONCLUSIONS: The novel fermenter allowed for an in-depth bioreaction analysis of A. succinogenes. Biofilm cells achieve higher SA yields than suspended cells and allow for operation at higher succinic acid titre. Both growth and maintenance rates were shown to drastically decrease with succinic acid titre. The A. succinogenes biofilm process has vast potential, where self-induced high cell densities result in higher succinic acid productivity and yield.http://www.microbialcellfactories.com/am201

Malic acid production by Aspergillus oryzae : the effect of alkaline-earth carbonate buffer identity

Malic acid is a specialty chemical that is currently mainly used in the food and beverage industry (market value of $182 million) but has a potential market value of$3.5 billion if used to produce maleic anhydride. The results from the study indicated that the production of malic acid by A. oryzae requires the presence of the alkaline earth metals calcium or magnesium in significant quantities. It was observed that replacing an amount of CaCO3 (240 g.l-1 CaCO3), significantly over that required for pH buffering (21 g.l-1 CaCO3), with an equivalent amount of MgCO3 (192 g.l-1 MgCO3 based on CO32+) results in similar malic acid yields and final malic acid titers. In contrast, a marked reduction in glucose consumption and malic acid production rates were observed. These observations are likely due to an evolutionary response to calcareous soils. These soils tend to immobilize minerals in solid precipitates resulting in nutrient depletion, while the production of malic acid solubilizes these minerals making them bioavailable. The higher rates observed for the calcium vs magnesium runs were likely a result of the stimulatory effect of Ca2+ on the ATP generating pathways as well as several regulatory responses within the fungal physiology. In addition, it was found that A. oryzae was capable of assimilating malic acid from the environment, therefore, minimizing the loss of valuable carbon due to malic acid excretion. This study provides invaluable information required for economically viable malic acid production by A. oryzae which could markedly reduce reliance on the petrochemical industry.http://www.aidic.it/cetam2023Chemical Engineerin

Rhizopus oryzae for fumaric acid production : optimising the use of a synthetic lignocellulosic hydrolysate

DATA AVAILABILITY STATEMENT : The data presented in this study are openly available at the University of Pretoria Research Data Repository at DOI: 10.25403/UPresearchdata.19883335.The hydrolysis of lignocellulosic biomass opens an array of bioconversion possibilities for producing fuels and chemicals. Microbial fermentation is particularly suited to the conversion of sugar-rich hydrolysates into biochemicals. Rhizopus oryzae ATCC 20344 was employed to produce fumaric acid from glucose, xylose, and a synthetic lignocellulosic hydrolysate (glucose–xylose mixture) in batch and continuous fermentations. A novel immobilised biomass reactor was used to investigate the co-fermentation of xylose and glucose. Ideal medium conditions and a substrate feed strategy were then employed to optimise the production of fumaric acid. The batch fermentation of the synthetic hydrolysate at optimal conditions (urea feed rate 0.625mgL1 h1 and pH 4) produced a fumaric acid yield of 0.439 g g1. A specific substrate feed rate (0.164 g L1 h1) that negated ethanol production and selected for fumaric acid was determined. Using this feed rate in a continuous fermentation, a fumaric acid yield of 0.735 g g1 was achieved; this was a 67.4% improvement. A metabolic analysis helped to determine a continuous synthetic lignocellulosic hydrolysate feed rate that selected for fumaric acid production while achieving the co-fermentation of glucose and xylose, thus avoiding the undesirable carbon catabolite repression. This work demonstrates the viability of fumaric acid production from lignocellulosic hydrolysate; the process developments discovered will pave the way for an industrially viable process.The National Research Foundation.https://www.mdpi.com/journal/fermentationam2023Chemical Engineerin

Internal mass transfer considerations in biofilms of succinic acid producing Actinobacillus succinogenes

The rumen bacterium Actinobacillus succinogenes is reputable for its high productivity, -yield and -titre fermentative production of succinic acid under biofilm conditions. The paper presents an analysis of internal mass transfer effects in biofilm fermentations of A. succinogenes. Internal mass transfer effects were investigated by batch fermentations using attached- and resuspended biofilms as biocatalysts. In the latter, the biofilms were resuspended after initial development to simulate mass transfer free (free cell) fermentations. Intrinsic kinetics for succinic production obtained from resuspended free cell fermentations predicted faster production rates than for the attached biofilms runs (biofilm thicknesses in the range of 120–200 µm), indicating internal mass transfer restrictions. A developed biofilm reaction diffusion model gave good predictions of attached biofilm batch results by accounting for internal mass transfer in the biofilm. Biofilm effectiveness factors ranged from 75% to 97% for all batches at the inception of batch conditions but increased with progression of batch operation due to increased succinic acid titres which inhibited production rates. Biofilm thickness and succinic acid concentrations were shown to have a significant effect on internal mass transfer. A simplified algorithm was developed to estimate the pseudo-steady state glucose penetration and biofilm effectiveness of A. succinogenes biofilms without the requirement to solve the overall mass transfer model. The results clearly showed that internal mass transfer need to be considered in biofilm fermentations involving A succinogenes as high biomass concentrations may not always equate to increased productivities if mass transfer effects dominate.The National Research Foundation (NRF) of South Africa and the Sugar Milling Research Institute (Durban, South Africa) via the Step-Bio program.https://www.elsevier.com/locate/cejhj2022Chemical Engineerin