THE INVERSE FLUIDIZATION AIRLIFT BIOREACTOR, PART I: HYDRODYNAMIC STUDIES

The inverse fiuidization airlift bioreactor offers a simple solution to the problem of handling shear sensitive cultures and/or systems requiring biofilm growth control. This unit combines in a single vessel the hydrodynamic behavior of concentric tube airlift aerators or contactors and liquid-solid fluidized beds. The effects of the diameter of the concentric tubes, liquid level, bed properties and gas flow rate on gas holdup, bed expansion and liquid circulation velocity were investigated in this study. The Zuber and Findlay relation (1965) gives satisfactory results for gas holdup. The inverse bed expansion can be predicted by the Richardson and Zaki correlation (1953). The liquid circulation velocity can be calculated using a mechanical energy balance     

Study of xenon thermal migration in sintered titanium nitride using nuclear micro-probe

Micro-Rutherford backscattering spectrometry experiments were performed on a set of sintered titanium nitride samples implanted with xenon to a depth of about 150 nm. Implanted samples were annealed at 1500 °C during 5 h. Xe depth profile and its lateral distribution on the surface were measured. Surface morphology was observed using scanning electron microscopy. The results reveal that the microstructure plays an important role on xenon release. Moreover, the crystalline orientation of each grain could be a key parameter to explain the heterogeneous evolution of the surface during thermal treatments as well as Xe release from surface.     

Rheological and high gelling properties of mango (Mangifera indica) and ambarella (Spondias cytherea) peel pectins

Ambarella and mango peels are good sources of pectins (15–20%), with high degree of methylation (60–78%) and high molar masses. Ambarella and mango ( Améliorée and Mango varieties) peel pectins were extracted using HCl or oxalic acid/ammonium oxalate (OAAO). Purified pectins were analysed for their flow behaviour and phase diagrams were established at pH 3 as sucrose vs. pectin concentration. The gelation kinetics and mechanical spectra of these pectin gels were studied and compared to those of commercial citrus (lime) pectins. At a concentration of 1% (w/v), all pectic solutions had a shear thinning behaviour but at 0.6% (w/v), only OAAO-extracted pectins exhibited such behaviour. Phase diagrams showed that at pH 3, gelation of OAAO mango extracted pectins was possible at low polymer concentration (0.2%; w/w) for a sucrose concentration of 60% (w/w). OAAO-extracted pectins exhibited a higher gelling ability than HCl-extracted ones. Sucrose (45–50%) and pectin (0.2–0.6%) concentration had a deep impact on the gel strength. Our results enable to conclude that the OAAO extraction from mango and ambarella peels allowed the recovery of pectins that exhibit high gelling properties.     

Rheology-structure properties of waxy maize starch–gellan mixtures

Dynamic oscillatory shear and confocal laser scanning microscopy were used, respectively, to study the viscoelastic properties and ultrastructure of mixtures of unmodified waxy maize starch (3%) and gellan (0.005–0.05%), pasted at 75 and 90 °C. The two temperatures resulted in different rheological properties and ultrastructure. At 75 °C swollen and partially disrupted granules were observed, while at 90 °C the dominant feature was the presence of granule remnants. Addition of gellan produced mixtures with different elastic properties depending on the extent of granular disruption and gellan concentration in the mixture. Below 0.02% gellan, swollen and disrupted starch granules were surrounded by compact, yet slightly interconnected, gellan networks resulting in enhanced blends at both temperatures. Above such gellan concentration no enhancement was observed and gellan dominated the viscoelastic behavior of the mixtures because of the existence of more evenly distributed networks with swollen or disrupted starch granules exerting a weakening effect on the resulting structure.     

Sensor-Based Control Architecture for a Car-Like Vehicle

This paper presents a control architecture endowing a car-like vehicle moving in a dynamic and partially known environment with autonomous motion capabilities. Like most recent control architectures for autonomous robot systems, it combines three functional components: a set of basic real-time skills, a reactive execution mechanism and a decision module. The main novelty of the architecture proposed lies in the introduction of a fourth component akin to a meta-level of skills: the sensor-based manoeuvers, i.e., general templates that encode high-level expert human knowledge and heuristics about how a specific motion task is to be performed. The concept of sensor-based manoeuvers permit to reduce the planning effort required to address a given motion task, thus improving the overall response-time of the system, while retaining the good properties of a skill-based architecture, i.e., robustness, flexibility and reactivity. The paper focuses on the trajectory planning function (which is an important part of the decision module) and two types of sensor-based manoeuvers, trajectory following and parallel parking, that have been implemented and successfully tested on a real automatic car-like vehicle placed in different situations.     

Isolation of DNA from the uncultured "Candidatus Liberobacter" species associated with citrus Huanglongbing by RAPD

"Candidatus Liberobacter," the uncultured bacterium associated with citrus Huanglongbing (HLB) disease, is an alpha-Proteobacteria, and two species, "Candidatus L. africanum" and "Candidatus L. asiaticum, " have been characterized by sequence analysis of the 16S rDNA and beta operon (rplKAJL-rpoBC) genes. These genes were isolated by PCR and random cloning of DNA from infected plants. However, this strategy is laborious and allowed selection of only three Liberobacter DNA fragments. In this paper, we described isolation of additional genes using Random Amplified Polymorphic DNA (RAPD). In total, 102 random 10-mer primers were used in PCR reactions on healthy and Liberobacter-infected plant DNA. Eight DNA bands amplified from infected plant DNA were cloned and analyzed. Six of them were found to be part of the Liberobacter genome by sequence and hybridization experiments. On these DNA fragments, four genes were identified: nusG, pgm, omp, and a hypothetical protein gene. These results indicate that RAPD can be used to clone DNA of uncultured organisms.     

Pressure-less spark plasma sintering effect on non-conventional necking process during the initial stage of sintering of copper and alumina

In the present study, we focus on the characterization of the necking mechanisms during the early stages of pressure-less spark plasma sintering (PL-SPS) compared to conventional sintering (CS) of two different types of powdered materials (Cu and α-Al₂O₃). SEM observations of the evolution of particle morphology and necks from the as-received powders to sintered ones show the nature of the neck between particles which were either in contact or not. For alumina, no particular necking process (melt or viscous bridge) was observed regardless of the sintering conditions (PL-SPS and CS), even for a very high heating rate 455 °C/min. For copper, this neck morphology is unequivocally not typical of conventional ones, thus, suggesting mass transport by an ejection mechanism. This particular morphology was seen occasionally. In comparison, the conventionally sintered Cu particles presented a smoother surface, with conventional curved necks suggesting the contribution of surface diffusion mechanisms. Based on partial pressure calculations, a direct thermal effect might not explain the observed non-conventional neck for copper. On the other hand, local field enhancement effect and local favourable thermal breakdown voltage conditions are described and discussed in order to support the experimental results.     

Statistical distribution of the convergence time of evolutionaryalgorithms for long-path problems

The behavior of a (1+1)-ES process on Rudolph's binary long k paths is investigated extensively in the asymptotic framework with respect to string length l. First, the case of k=l^α is addressed. For α⩾1/2, we prove that the long k path is a long path for the (1+1)-ES in the sense that the process follows the entire path with no shortcuts, resulting in an exponential expected convergence time. For α<1/2, the expected convergence time is also exponential, but some shortcuts occur in the meantime that speed up the process. Next, in the case of constant k, the statistical distribution of convergence time is calculated, and the influence of population size is investigated for different (μ+λ)-ES. The histogram of the first hitting time of the solution shows an anomalous peak close to zero, which corresponds to an exceptional set of events that speed up the expected convergence time with a factor of l². A direct consequence of this exceptional set is that performing independent (1+1)-ES processes proves to be more advantageous than any population-based (μ+λ)-ES     

SENEQUE: a multi-scaling GIS interface to the Riverstrahler model of the biogeochemical functioning of river systems

The Riverstrahler model describes the biogeochemical functioning of an entire river system, from 100 to 100,000 km(2) or more, taking into account the constraints set by the morphology of the drainage network, the meteorological/hydrological conditions, and the inputs of material from point and non-point sources in the watershed. This tool has been applied for research purpose to several river systems differing in terms of hydrological regime and anthropogenic influences. In order to improve its capabilities and its generic dimension, as well as to develop a user-friendly interface allowing its transfer to non-specialist users including managers, the model has been coupled to a GIS interface. This gives the user the possibility to visualize the available geospatial database, to select the best geographical representation of the drainage network, to automatically prepare the corresponding input files required for the model, to pilot the model calculation and to visualize the results. The coupling with a GIS interface has considerably improved the capabilities of the Riverstrahler model. The code of the model is now entirely generic and can be run on any river system for which a suitable database is available. Its spatial resolution can be adapted to the requirement of the relevant problem, from the highest level, where each elementary watershed is individualized, to the lower level, where the whole basin is idealized as one basin with tributaries of each order having the same characteristics. As an illustration of the new potentialities offered by the coupling of Riverstrahler with a GIS through the SENEQUE interface, the results of a same modeling scenario are compared at different spatial resolutions. For the first time, with on-line coupling to a geodatabase, the effect of increasing the spatial resolution of the drainage network representation on the performance of the Riverstrahler model has been examined. At the outlet of the basin, the water quality results were found invariant to a large degree, whatever the details of its representation in the calculations. This result justifies the use of a low resolution representation of the upstream watershed when results are required only at the outlet of the basin.