Solid colloidal particles inducing coalescence in bitumen-in-water emulsions

Silica particles are dispersed in the continuous phase of bitumen-in-water emulsions. The mixture remains dispersed in quiescent storage conditions. However, rapid destabilization occurs once a shear is applied. Observations under the microscope reveal that the bitumen droplets form a colloidal gel and coalesce upon application of a shear. We follow the kinetic evolution of the emulsions viscosity, eta, at constant shear rate: eta remains initially constant and exhibits a dramatic increase after a finite time, tau. We study the influence of various parameters on the evolution of tau: bitumen droplet size and volume fraction, silica diameter and concentration, shear rate, etc.

A fully predictive model for one-dimensional light attenuation byChlamydomonas reinhardtii in a torus photobioreactor

The light attenuation in a photobioreactor is determined using a fully predictive model. The optical properties were first calculated, using a data bank of the literature, from only the knowledge of pigments content, shape, and size distributions of cultivated cells which are a function of the physiology of the current species. The radiative properties of the biological turbid medium were then deduced using the exact Lorenz-Mie theory. This method is experimentally validated using a large-size integrating sphere photometer. The radiative properties are then used in a rectangular, one-dimensional two-flux model to predict radiant light attenuation in a photobioreactor, considering a quasi-collimated field of irradiance. Combination of this radiative model with the predictive determination of optical properties is finally validated by in situ measurement of attenuation profiles in a torus photobioreactor cultivating the microalgae Chlamydomonas reinhardtii, after a complete and proper characterization of the incident light flux provided by the experimental set-up.

Cheddar

This paper describes an Ada framework called Cheddar which provides tools to check if a real time application meets its temporal constraints. The framework is based on the real time scheduling theory and is mostly written for educational purposes. With Cheddar, an application is defined by a set of processors, tasks, buffers, shared resources and messages. Cheddar provides feasibility tests in the cases of monoprocessor, multiprocessor and distributed systems. It also provides a flexible simulation engine which allows the designer to describe and run simulations of specific systems. The framework is open and has been designed to be easily connected to CASE tools such as editors, design tools, simulators, ...

Soy glycinin microcapsules by simple coacervation method

Encapsulation of a dispersed oil phase (hexadecane) was realized by simple coacervation method using soy glycinin as the wall forming material. Suitable emulsification and coacervation conditions, that favor the formation of microcapsules wall, were identified and investigated. Mild acid (pH 2.0) and heat (55 degrees C) treatments of the reaction medium during the emulsification step enhanced significantly the deposition of coacervated glycinin around oil droplets. A pronounced correlation between glycinin concentration in the continuous phase, specific surface of the dispersed phase and the microencapsulation efficiency was also observed. Coacervation step study concerned the morphology and the stability of microcapsules. Controlled initiation of the coacervation, by slow readjustment of the pH, allowed a homogeneous precipitation of glycinin around oil droplets as well as the absence of aggregation phenomena. Since the morphology of microcapsules was considerably affected by a prolonged stirring of the reaction medium, the coacervation and reticulation time were optimized in order to preserve the homogeneity of the microcapsules size distribution and the microencapsulation efficiency.

Modelling responses to a smallpox epidemic taking into account uncertainty

Epidemiology and modelling are currently under pressure to build consistent scenarios of control in case of deliberate release of biological weapons. In order to assess the key parameters for the control of a smallpox outbreak in a large city (2 million inhabitants), we built a stochastic model to simulate the course of an epidemic controlled by ring vaccination and case isolation. Assuming a reference scenario with 100 index cases and implementation of intervention 25 days after the attack, the model forecasts an epidemic of 730 cases with an epidemic duration of 240 days. Setting intervention 20 days later would result in an almost fourfold increase in the epidemic size. A multivariate sensitivity analysis has selected three key parameters: the basic reproduction number (i.e. the number of secondary cases infected by one case in an entirely susceptible population, equal to 3 in the reference scenario), time to intervention, and proportion of traced and vaccinated contacts.

Photocatalytic: oxidation of volatile organic compounds present in airborne environment adjacent to sewage treatment plants

Emissions of volatile organic compounds (VOCs) from wastewater in municipal sewage or industrial wastewater treatment plants are often overlooked as sources of exposure to hazardous substances. The impact of such emissions on local airborne environments represents a growing source of scientific, toxicological and public health interest. Actually, VOCs are suspected to be quite dangerous for human health. Some of them belong to the family of odorous compounds and can cause serious annoyance in the neighbourhood of the emission sources. A way to remove VOCs released from sewers and wastewater treatment facilities could be to degrade them by photocatalytic oxidation. TiO2-based photocatalysts are known to be efficient for this kind of application. In the present work TiO2 P25 Degussa was deposited on glass supports. These materials were tested for the degradation of butanone-2 in a photocatalytic reactor. The influence of water vapour (relative humidity) was shown using the Langmuir-Hinshelwood kinetic model.

Comparison of different TiO2 photocatalysts for the gas phase oxidation of volatile organic compounds

Gas-solid photocatalyzed oxidation of air contaminants is being explored more and more for possible application to decontamination, purification and deodorization of enclosed atmospheres. Indoor air is characterized by a huge number of pollutants at low concentrations. Volatile organic compounds (VOC) represent the main indoor air pollutants category, and are of great concern since some of them can act negatively on human health. Several treatments exist to reduce VOC concentrations in gaseous effluents, but photocatalytic oxidation appears to be the most appropriate regarding indoor air specific constraints. It is then necessary to develop photocatalysts, which can possibly be used in an application such as indoor air-quality improvement. In the present work, three different TiO2-based materials were studied and compared for the photocatalytic oxidation of a typical pollutant of indoor air: methyl ethyl ketone. Kinetic studies were performed for each material in dry and humid air conditions, and the Langmuir-Hinshelwood model was satisfactorily applied in almost every case. A second approach consisted of determining methyl ethyl ketone degradation by-products. Acetaldehyde was found to be the main gaseous intermediate, and could be taken into account in the general Langmuir-Hinshelwood modeling.

Centrifugal partition chromatography: a survey of its history, and our recent advances in the field

Centrifugal partition chromatography (CPC) was introduced in 1982 by Sanki Eng. And for almost 20 years this company remained the only one manufacturing such an apparatus. A CPC instrument or a CPC column is a series of channels linked in cascade by ducts and aligned in cartridges or disks in a circle around a rotor; setting the rotor in motion submits this assembly to a constant centrifugal field. The originality of CPC is that it uses any biphasic liquid-liquid system as mobile and stationary phases. The United States branch of Sanki contributed greatly to the worldwide acceptance of the technique. Recent works performed in the Netherlands and in France have, by means of visualization of flow-patterns in CPC channels, contributed to a better knowledge of hydrodynamics and mass transfer phenomena. Nowadays research in our laboratory focuses on speediness and scale-up of the technique.

Swirling flow implementation in a photobioreactor for batch and continuous cultures ofporphyridium cruentum

Light is the main limiting factor in photoautotrophic-intensive production of microorganisms, and improvement of its use is an important concern for photobioreactor design and operation. Swirling flows, which are known to improve mass and photon transfers, were applied to annular light chambers of a photobioreactor and studied by simulation and microalgal culture. Two hydrodynamic conditions were compared: axial flow generating poor radial mixing, and tangential flow generating three-dimensional swirling motion. Batch and continuous cultures of the Rhodophyte Porphyridium cruentum were performed in a 100-L, 1.5-m(2), fully controlled photobioreactor with eight light chambers. The inlet design of these chambers was modified to create the hydrodynamic conditions for comparison. Various intensities of swirling motion were used, characterized by the velocity factor (VF), defined as the ratio between annular chamber flow and inlet aperture sections. Experiments were performed within the range of photon flux densities (PFD) optimizing the yield of light energy transformation into living substance for the species and the temperature used. Culture kinetics with swirling flows generated by apertures of VF = 2, 4, and 9 were compared with pseudoaxial VF = 2 chosen as reference. Batch cultures with VF = 4 swirling flow showed no significant difference, whereas continuous cultures proved more discriminating. Although no significant difference was obtained for VF = 2, a 7% increase of steady-state productivity and a 26% decrease in time required to reach this steady state were obtained with VF = 4 swirling flow. This beneficial effect of swirling flow could have accounted for increased mixing. Conversely, VF = 9 swirling flow resulted in a 9% decrease of steady-state productivity and a 9% increase in the time required to reach this steady state, a negative effect that could have accounted for increased shear stress. CO(2) bioconversion yield at steady state showed a 34% increase for VF = 4. These results suggest that swirling motion makes microalgal cultures more efficient, provided that the resulting adverse effects remain acceptable. Experimental investigation was completed by a theoretical approach in which simulation of continuous cultures of P. cruentum was based on the hydrodynamic conditions achieved in the photobioreactor. Although the results obtained with pseudoaxial flow were correctly predicted, simulations with swirling flow showed a marked enhancement of productivity not observed experimentally. The influence of side effects induced by increased mixing (particularly hydrodynamic shear stress) was considered with respect to modeling assumptions. Comparison of experimental results with theoretical simulation provided a better understanding of the mixing effect, a key factor in improving the efficiency of such bioprocesses.

Rational improvement of centrifugal partition chromatographic settings for the production of 5-n-alkylresorcinols from wheat bran lipid extract. I. Flooding conditions--optimizing the injection step

A dedicated CPC prototype permits direct flow pattern visualization in the partition cells of a CPC column. It was used to understand "flooding", a frequent phenomenon associated with large injections. A general strategy was developed to optimize the injection step in the framework of a particular preparative separation: the purification of 5-n-alkylresorcinols from a wheat bran lipid extract on a several hundred milligram scale. The construction of the "mobile phase/stationary phase/sample" pseudo ternary diagram characterizes the effect of the injected solution on mobile and stationary phases. The position of the binodal curve maximum indicates if the biphasic system is "robust" towards a large injection or not, and can be used for optimum mass load determination.