FLOC SIZE REDUCTION IN THE TURBULENT ENVIRONMENT

The dynamic behavior of the particle size distribution (PSD) in wastewater treatment processes results from the interaction of a random growth process with nonlinear, stochastic hydrodynamics. Successful modeling of the PSD response to high dissipation conditions depends upon accurate quantification of the breakage mode, the local dissipation rate, transition probability, and the daughter particle size distribution; the inferential determination of these quantities from PSD data is difficult, at best. Direct photographic observation of floc breakup in a turbulent jet apparatus and in the Impeller stream of a baffled, agitated tank has provided opportunities to measure both the breakage mode and the daughter particle size distribution for individual parent floes. These data have been used in successful PSD modeling in lean, batch systems characterized by irreversible breakage.     

A polynomial regression model for the response of various accelerating techniques on maize wine maturation

Statistical analysis was conducted to interpret the recently observed effects of various accelerating techniques on maize wine maturation (Chang, A. C. (2004). The effects of different accelerating techniques on maize wine maturation. Food Chemistry, 86, 61). Instead of the previously reported simple linear relationship between the concentrations of the key components of maize wine in the final product and the number of treatments or the dosage, various types of non-linear behaviours were observed. A general polynomial regression model is used to describe these behaviours, and the adjustable parameters were estimated from the experimental data. The performance of the proposed regression model, which plays a key role in the design of an efficient accelerating process, was satisfactory. Some specific variations of the key components of maize wine, as a function of the number of treatments or the dosage, were observed.     

Dynamic seeding and perfusion culture of hepatocytes with galactosylated vegetable sponge in packed-bed bioreactor

A galactose moiety was introduced into the fiber surface of a vegetable sponge by the covalent binding of lactobionic acid. The galactosylated sponge was used as scaffold for the culture of rat hepatocytes in a packed-bed bioreactor. Hepatocytes could be dynamically seeded into and uniformly distributed throughout the scaffold, and the immobilized cells maintained high albumin and urea production rates during long-term perfusion culture. The hepatocytes showed an increasing albumin production rate from 49 to 109 microg/10(6) cells/d over the 7-d culture.     

A STOCHASTIC ANALYSIS OF COKE DEPOSITION

The phenomenon of coke deposition on catalyst surface is analyzed stochastically. In contrast to a conventional deterministic approach, derivation of the governing equations of the phenomenon is based on probability laws. The resulting representation provides the information on both the mean or macroscopic and the fluctuating characteristics about the system under consideration. The deposition of coke is assumed to be reversible, i.e., deposited coke has a certain probability of escaping the surface. The applicability of the model developed is justified through analyzing available experimental data appeared in the literature.     

Bioactive collagen-grafted poly-L-lactic acid nanofibrous membrane for cartilage tissue engineering

Biodegradable nanofibrous membrane was prepared from poly-L-lactic acid by electrospinning and used as a scaffold for cartilage tissue engineering. Operating parameters during the electrospinning process were studied in terms of their influences on fiber diameter, membrane porosity and pore size. In order to improve cell attachment and growth, nanofibrous membrane was subject to DC-pulsed oxygen plasma treatment, followed by acrylic acid grafting and collagen coating by covalent binding of collagen to carboxylic moieties of the polyacrylic acid. The membrane was fully characterized for its physical and chemical properties. Primary chondrocyte cells seeded into the membrane proliferated well and maintain high viability within the membrane from Confocal Laser Scanning Microscopy. Cell differentiation was confirmed by secretion of glycoaminoglycan and collagen during the cultivation period. Scanning electron microscope observation of the cell-scaffold construct confirms the tight attachment of cells to nanofibers and in-growth of cells into the interior of the membrane with proper maintenance of morphology and structure of chondrocytes.     

Superparamagnetic iron oxide nanoparticles for delivery of tissue plasminogen activator

Magnetic nanoparticle (MNP) modified by carboxymethyl dextran (CMD) was synthesized and characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, superconducting quantum interference device, dynamic light-scattering, thermogravimetric analysis, and X-ray diffraction. CMD coating on the particle surface provides abundant -COOH functional groups for conjugating with a thrombolytic drug, recombinant tissue plasminogen activator (rtPA). CMD-coated MNP (CMD-MNP) prepared with higher CMD/MNP ratios had higher CMD content, less iron content, more -COOH surface groups, smaller hydrodynamic diameter, and smaller saturation magnetization. The in vitro biocompatibility study using lactate dehydrogenase assays indicated that CMD-MNP elicited no cell cytotoxicity. The optimum drug loading could be achieved by contacting 0.25 mg rtPA with 5 mg CMD-MNP where all rtPA is immobilized to the magnetic nanocarrier with full retention of its thrombolytic activity.     

Effects of Moisture on Pyrolysis of Polypropylene

The thermal degradation kinetics of polypropylene (PP) in steam was investigated with a thermal gravimetric analysis (TGA) reaction system. The experiments were carried out in the 500–800 K temperature range at various constant heating rates of 1, 2, and 5 K∕min. The partial pressure of steam in the system was adjusted to 0.24 atm, which is seen in most municipal solid waste (MSW) incinerators in Taiwan. The results indicated that the water molecule significantly enhanced the thermal degradation rate of PP. The corresponding activation energy, preexponential factor, and reaction order were determined. It was found that thermal degradation of PP in steam can be adequately described by an overall rate equation.     

Analysis of co-extrusion process for preparation of gradient index plastic optical fiber

The fabrication of gradient index plastic optical fiber in a closed co-extrusion process is simulated theoretically. The concentration dependency of the diffusivities of monomers in host polymer is taken into account on the basis of a modified free volume theory together with a generalized Flory-Huggins theory for a three-component polymer solution. The applicability of the model derived is justified by fitting it to the experimental data reported in the literature, and its performance is found to be satisfactory. We show that the diffusion of a mobile phase in a polymer solution is dependent upon the structure and the concentration of polymer, and the concentration of the other mobile phase present.     

Effects of double-layer polarization and electroosmotic flow on the electrophoresis of a finite cylinder along the axis of a cylindrical pore

The electrophoresis of a rigid, finite cylindrical particle along the axis of a long cylindrical pore is analyzed theoretically under the conditions of arbitrary surface potential and double-layer thickness. The effects of double-layer polarization and electroosmotic flow on the electrophoretic behavior of the particle are discussed. We show that if both the particle and the pore are positively charged, the mobility of the particle has a local minimum as the thickness of double layer varies. Also, if the level of the surface potential of the particle is sufficiently high and its aspect ratio is sufficiently large, then its mobility may change its sign twice as the thickness of double layer (or the concentration of electrolytes) varies. These findings are of practical significance in designing an electrophoresis operation because it will influence the prediction of the charged conditions on a particle if electrophoresis is used as an analytical tool, and the separation efficiency, if it is adopted as a separation technique.     

SUPERSATURATION, INDUCTION PERIOD, AND METASTABLE ZONE WIDTH OF CaCl2—Na2C03—HCl SYSTEM

The supersaturation, induction period, and mctastablc zone width ofan aqueous supersaturated solution of CaC₂—Na₂C0₃—HCl system are studied in the present paper. The supersaturation is varied and predicted within a reasonable accuracy when a specified amount of HCl(_aq) is added into the aqueous supersaturated CaC₂—Na₂C0₃—HCl solution. It is found that the decrease of solution supersaturation at low pH is caused mainly by the decrease of carbonate ions. Then, the induction periods are estimated by using the coagulation theory and they can be expressed as a function of supersaturation alone, which results from different values of reagent concentration and pH. Finally, the theoretical metastable zone widths based on arbitrary induction periods are obtained. Meanwhile, the induction periods are measured at various levels of reagent concentration and solution pH by applying the conductivity method. Accordingly, the metastable zone widths are determined experimentally and compared with the theoretical results. It is concluded that the present method is an useful tool for determining the metastable zone width of aqueous supersaturated CaC₂—Na₂C0₃—HCl solution.