Monica Meraz

FEEDBACK CONTROL OF THE CHEMOTHERAPY OF HIV

Using a model which describes the interaction of the immune system with the human immunodeficiency virus (HIV), we introduce a feedback control strategy of chemotherapy in an early treatment setting, where the control represents the percentage of effect chemotherapy has on the viral production. We seek to regulate the viral count by manipulating the percentage of effect chemotherapy has on the viral production. We show via numerical simulations that the proposed feedback control strategy can handle strong uncertainties in the HIV dynamics induced by imperfect modeling and sampled/delayed cell measurements.

Pentachlorophenol sorption in nylon fiber and removal by immobilized Rhizopus oryzae ENHE

This study describes pentachlophenol (PCP) sorption in nylon fiber in which Rhizopus oryzae ENHE was immobilized to remove the chemical compound. The experimental sorption data were analyzed using the Langmuir, Freundlich, and Redlich-Peterson isotherm models using non-linear error functions to fit the experimental data to the three models. Results showed that the isotherm obtained from the data fitted the three models used. However, the g parameter from Redlich-Peterson model showed that the isotherm obtained approaches the Freundlich model. This support reached the sorption equilibrium concentration at 3mg PCPg(-1)nylon. To study PCP removal capability by R. oryzae ENHE and to eliminate the error caused by PCP sorbed by the nylon fiber during its quantification, nylon fiber at PCP equilibrium sorption concentration was used to immobilize R. oryzae ENHE. It was found that this fungus grew within nylon fiber cubes in presence or not of PCP, even when PCP caused growth inhibition. Maximum biomass accumulated into nylon cubes without PCP was of 32 mg biomass g(-1)nylon and into nylon cubes at PCP equilibrium concentration was of 18 mg g(-1)nylon. The results showed that R. oryzae ENHE immobilized into nylon fiber removed 88.6% and 92% of PCP in cultures with 12.5 and 25 mg PCPL(-1), as initial concentration, respectively. This is the first work to report that a zygomycete, such as R. oryzae ENHE, immobilized into nylon fiber kept its potential to remove PCP.

Effect of lime concentration on gelatinized maize starch dispersions properties.

Maize starch was lime-cooked at 92 °C with 0.0-0.40% w/w Ca(OH)2. Optical micrographs showed that lime disrupted the integrity of insoluble remnants (ghosts) and increased the degree of syneresis of the gelatinized starch dispersions (GSD). The particle size distribution was monomodal, shifting to smaller sizes and narrower distributions with increasing lime concentration. X-ray patterns and FTIR spectra showed that crystallinity decreased to a minimum at lime concentration of 0.20% w/w. Lime-treated GSD exhibited thixotropic and viscoelastic behaviour. In the linear viscoelastic region the storage modulus was higher than the loss modulus, but a crossover between these moduli occurred in the non-linear viscoelastic region. The viscoelastic properties decreased with increased lime concentration. The electrochemical properties suggested that the amylopectin-rich remnants and the released amylose contained in the continuous matrix was firstly attacked by calcium ions at low lime levels (<0.20% w/w), disrupting the starch gel microstructure.

A simple rate model for the dynamics of immobilization of anaerobic bacteria on a plastic support

The dynamics of biofilm formation on polyethylene bioparticles in mesophilic anaerobic conditions, using an inverse fluidized bed as immobilization system, have been studied. The immobilization process was carried out using acetate and glucose as carbon sources. Scanning electron microscopy (SEM) showed cocci cells and Methanosaeta rods embedded into an exopolimeric substances (ESP) matrix. The acetoclastic activity was found to increase as soon as the lag biomass accumulation phase ended. The rate of immobilization was found to conform to a pseudo first order kinetics with good correlation. This kinetic model was used to estimate rate and equilibrium constants for the immobilization process. Rate properties have been explained in terms of attachment and detachment processes.

Inhibitory concentrations of 2,4D and its possible intermediates in sulfate reducing biofilms

Different concentrations of the herbicide 2,4-dichlorophenoxyacetic acid (2,4D) and its possible intermediates such as 2,4-dichlorophenol (2,4DCP), 4-chlorophenol (4CP), 2-chlorophenol (2CP) and phenol, were assayed to evaluate the inhibitory effect on sulfate and ethanol utilization in a sulfate reducing biofilm. Increasing concentrations of the chlorophenolic compounds showed an adverse effect on sulfate reduction rate and ethanol conversion to acetate, being the intermediate 2,4DCP most toxic than the herbicide. The monochlorophenol 4CP (600 ppm) caused the complete cessation of sulfate reduction and ethanol conversion. The ratio of the electron acceptor to the electron donor utilized as well as the sulfate utilization volumetric rates, diminished when chlorophenols and phenol concentrations were increased, pointing out to the inhibition of the respiratory process and electrons transfer. The difference found in the IC(50) values obtained was due to the chemical structure complexity of the phenolic compounds, the number of chlorine atoms as much as the chlorine atom position in the phenol ring. The IC(50) values (ppm) indicated that the acute inhibition on the biofilm was caused by 2,4DCP (17.4) followed by 2,4D (29.0), 2CP (99.8), 4CP (108.0) and phenol (143.8).

Zipf–Mandelbrot scaling law for world track records

World track records (WTR) can be fitted with a Zipf–Mandelbrot scaling law. Metabolic energy balances are used to describe the energy release dynamics during a race. It is shown that several hierarchical relaxation processes related to metabolic mechanisms can explain the power-law behavior of WTR.

Some remarks on the Langmuir–Hinshelwood kinetics

This work considered the Langmuir–Hinshelwood (LH) scheme for a single reactant. In a first step, the validity of the quasi-steady state approximation (QSSA) was revised in terms of nonlinear relaxation processes. It was found that the LH equation obtained from the QSSA is not valid most of the times, except for example in the case of high reactant concentrations when the relaxation time is small enough to reduce the order of the underlying system of differential equations. Subsequently, the observability properties of the LH equations were studied in order to find that the dynamical behavior of the adsorption complex can be reconstructed from measurements of the reactant trajectory. Finally, the estimation problem of the kinetic parameters based solely on the reactant concentration behavior was considered. It is then shown that the full set of kinetic parameters can be estimated from a single reactant depletion curve by solving a least-squares problem for the complete LH scheme. Numerical results were used to illustrate the findings of this work.

Biological degradation of a mixture of municipal wastewater and organic garbage leachate in expanded bed anaerobic reactors and a zeolite filter

Municipal wastewater was amended with organic garbage leachates at a concentration around 700 mgCOD(soluble)/L and fed to three different anaerobic systems to compare their performance: a down flow fluidized bed (DFFB), an expanded granular sludge bed (EGSB) and a zeolite-packed anaerobic filter reactor (ZPF). The DFFB and EGSB reactors were operated at HRT of 6 and 4 h and the ZPF reactor at 12 and 36 h. Organic loads rate for the DFFB reactor were 2.3+/-0.9 and 4.8+/-1.8 gCOD/L.d, with removal efficiencies around 40% and a methane productivity of 0.2+/-0.03 L/L(reactor).d. For the EGSB reactor, organic loads tested were 2.1+/-0.9 and 4.3+/-1.3 gCOD/L.d, removal efficiencies attained were of 77.6+/-12.7% and 84.4+/-4.9%, respectively at both conditions and total suspended solids were removed in 54.6+/-19.3%, while methane productivity at 4 h HRT was of 1.29+/-0.4 L/L(reactor).d. The ZPF reactor was operated at lower organic loading rates, 1.4+/-0.27 and 0.42+/-0.13 gCOD/L.d and attained removal efficiencies of 48+/-18% and 83+/-8%, respectively, reaching a methane productivity of 0.21+/-0.09 and 0.12+/-0.04 L/L(reactor).d, 83+/-8.0% of total suspended solids were retained in the reactor and as HRT was increased ammonium concentrations increased in 39%. Specific methanogenic activity in all systems was around 0.2 gCOD-CH(4)/gVSS d.

Control of enzyme activity in stirred bioreactors

In this work the problem of determining the feed rate policy of fresh enzyme into stirred bioreactors to offset the loss of activity due to enzyme deactivation is addressed. On the basis of a series-type deactivation mechanism with arbitrary deactivation kinetics, it is shown that the feed rate policy is a feedback function of the deactivation rate. From both the theoretical and the practical viewpoints, these results provide a useful tool in understanding enzyme deactivation, and in designing bioreactor operation.

Mathematical analysis of proportional-integral control for fixed bed bioreactors

This paper deals with the control of fixed bed bioreactors. The dynamics of these processes are described by a set of partial differential equations, which are reduced to ordinary differential equations by using a finite difference method. The task of this work is to demonstrate that a standard proportional-integral (PI) control law, which is based on the dynamics at the bioreactor output, can be used to regulate the operation of fixed bed bioreactors (eg, fermenters, biofilters, etc). The performance of the resulting control law is illustrated by simulation results on a fixed bed anaerobic waste water treatment process.