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A mathematical model was formulated to simulate cell growth, plasmid loss and recombinant protein production during the aerobic culture of a recombinant yeast S. cerevisiae. Model development was based on three simpli®ed metabolic events in the yeast: glucose fermentation, glucose oxidation and ethanol oxidation. Cell growth was expressed as a composite of these metabolic events. Their contributions to the total speci®c growth rate depended on the activities of the pacemaker enzyme pools of the individual pathways. The pacemaker enzyme pools were regulated by the speci®c glucose uptake rate. The effect of substrate concentrations on the speci®c growth rate was described by a modi®ed Monod equation. It was assumed that recombinant protein formation is only associated with oxidative pathways. Plasmid loss kinetics was formulated based on segregational instability during cell division by assuming constant probability of plasmid loss. Experiments on batch fermentation of recombinant S. cerevisiae C468/pGAC9 (ATCC 20690), which expresses Aspergillus awamori glucoamylase gene and secretes glucoamylase into the extracellular medium, were carried out in an airlift bioreactor in order to evaluate the proposed model. The model successfully predicted the dynamics of cell growth, glucose consumption, ethanol metabolism, glucoamylase production and plasmid instability. Excellent agreement between model simulations and our experimental data was achieved. Using published experimental data, model agreement was also found for other recombinant yeast strains. In general, the proposed model appears to be useful for the design, scale-up, control and optimization of recombinant yeast bioprocesses.

The radiation absorption profiles on the surfaces of TiO films in a corrugated IntroductionAs a potential water-treatment technology, photocatalysis has been extensively studied during the last two decades. In this process an oxide semiconductor, usually TiO , is pho-2 toexcited upon absorbing photons with appropriate energy levels. The photoexcited semiconductor produces electrons Ž . and holes that is, electron vacancies that can migrate to the solid surface and initiate a series of oxidation and reduction reactions that can simultaneously oxidize toxic organic water Ž . Ž pollutants Matthews, 1987 , kill microorganisms Belhacova . et al., 1999 Despite the profuse work on the photochemical process and areas of potential applications, a similar research effort has not been reported on the related engineering issues. There is Correspondence concerning this article should be addressed to W. A. Anderson. still a shortage of studies on the design and scale-up of photocatalytic reactors based on radiative and reactor performance models. Of the limited number of reactor-engineering-related publications, radiation fields were modeled rigor-Ž ously in only a few studies Romero et al., 1997; Pasquali et . al., 1996; Cabrera et al., 1994; Marinangeli and Ollis, 1977 . The effect of the recapture of reflected photons on the radiation absorption of an immobilized catalyst film has not yet been reported.Radiative transfer in absorbing, reacting, and scattering reaction media has been properly described by a set of Ž . integral-differential equations Cassano et al., 1995 . A heterogeneous medium may be regarded as optically homogeneous provided that the smallest inhomogeneities are sufficiently small compared to the wavelength of the photon. The Ž . radiation fields in pseudo homogeneous photoreactors have been described using the local volumetric rate of energy ab-Ž . sorption LVREA and modeled with the Lambert-Beer's law Ž . Ž Rizzuti, 1985 and the principles of geometric optics Roger . and Villermaux, 1979 . However, the LVREA is not appropriate for describing the radiation absorption profiles on immobilized catalyst films.In this work, a new term, the local-area-specific rate of Ž . energy absorption LASREA , was adopted to characterize The water flows through the long triangular channels formed by the corrugations and the lamp sleeves, shown in Section A-A. The photocatalyst is immobilized on the surface of the corrugations and illuminated by the lamps. For solar illumination, only one corrugated plate would be illuminated on the one side pointed at the sun.the radiation absorption profiles in heterogeneous photoreactors. The LASREA on the surfaces of the TiO films in a 2 corrugated-plate photocatalytic reactor was modeled based on the principles of geometric optics, the absorption and reflection characteristics of the catalyst film, and the refraction properties of the reaction medium and reactor components. Effects of the radiation sources, the photon recapture through multiple reflection, and the geometry of the...

AxMoO3(H20)y has been shown to undergo substantial exfoliation of the layer structure in water wheen A = Li. Although extensive exfoliation of the Na form is not observed, sufficient swelling occurs to enable the insertion of large polyoxycations of Al, Ga, Zr, Ti and Cr between the layers of MoO3 by ion exchange with colloidal dispersions of NaXMoO3. This represents the first such "pillaring" reactions for MoO3. Interlayer expansions are observed to range from 7 to 14Å in these materials. In some cases, the orientation of the oxide cluster between the layers can also be determined by 1D electron density mapping. We have also shown that this method can be applied to the insertion of conductive polymers via incorporation of a water-soluble precursor polymer. The sulfonium ionomer precursor of poly (p-phenylene vinylene) has been intercalated in MoO3, to form a novel polymer/oxide layered structure. Data for the heat-treated [PPV]32MoO3 films show an order of magnitude increase in conductivity over that of pristine NaxMoO3.

We demonstrate a chirped-pulse amplification system that simultaneously amplifies two pulses from a dual-wavelength oscillator in a single regenerative amplifier. The two wavelengths can be tuned from 800 to 890 nm. The total energy of 1.5 mJ can be variably split between the two pulses. The pulses are 150 fs in duration and have 60-fs timing jitter.