A kinetic model for methanol (MeOH) synthesis over Cu/ZnO/Al2O3/ZrO2 catalyst has been developed and selected to evaluate the effect of carbon dioxide on the reaction rates due to its high activity and stability. Detailed kinetic mechanism, on the basis of different sites on Cu for the adsorption of carbon monoxide and carbon dioxide, is applied, and the water−gas shift (WGS) reaction is included in order to provide the relationship between the hydrogenations of carbon monoxide and carbon dioxide. Parameter estimation results show that, among 48 reaction rates from different combinations of rate determining steps (RDSs) in each reaction, the surface reaction of a methoxy species, the hydrogenation of a formate intermediate HCO2, and the formation of a formate intermediate are the RDS for CO and CO2 hydrogenations and the WGS reaction, respectively. It is shown that the CO2 hydrogenation rate is much lower than the CO hydrogenation rate, and this affects the methanol production rate. However, carbon dioxide decreases the WGS reaction rate, which prevents methanol from converting to dimethyl ether, a byproduct. In such a way, a small fraction of carbon dioxide accelerates the production of methanol indirectly within a limited range, showing a threshold value of the CO2 fraction for the maximum methanol synthesis.

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Mammalian reproduction requires gonadotropin-releasing hormone (GnRH)-mediated signaling from brain neurons to pituitary gonadotropes. Because the pulses of released GnRH vary greatly in amplitude, we studied the biosynthetic response of the gonadotrope to varying GnRH concentrations, focusing on extracellular-regulated kinase (ERK) phosphorylation and egr1 mRNA and protein production. The overall average level of ERK activation in populations of cells increased non-cooperatively with increasing GnRH and did not show evidence of either ultrasensitivity or bistability. However, automated image analysis of single-cell responses showed that whereas individual gonadotropes exhibited two response states, inactive and active, both the probability of activation and the average response in activated cells increased with increasing GnRH concentration. These data indicate a hybrid single-cell response having both digital (switch-like) and analog (graded) features. Mathematical modeling suggests that the hybrid response can be explained by indirect thresholding of ERK activation resulting from the distributed structure of the GnRH-modulated network. The hybrid response mechanism improves the reliability of noisy reproductive signal transmission from the brain to the pituitary.Mammalian reproduction and the survival of a species rely on a precise orchestration of temporally and spatially distributed molecular events. The control of reproduction represents a difficult engineering problem, because noisy molecular processes within cells that occur on time scales of minutes must regulate brain, pituitary, and gonadal activity in a process with an overall periodicity of days to weeks, depending on the species. At the center of this coordinated reproductive activity lies the pituitary gonadotrope, which converts hormone signals secreted by the brain into the biosynthesis and secretion of pituitary hormones controlling gonadal responses.The hypothalamus secretes discrete pulses of gonadotropinreleasing hormone (GnRH) 2 (for a review, see Refs. 1-3). GnRH interacts with high affinity GnRH receptors on the gonadotrope membrane to modulate the biosynthesis and release of the gonadotropins luteinizing hormone and follicle-stimulating hormone (4 -6). The function of the reproductive axis depends on appropriate responses of the gonadotrope to GnRH despite the high interpulse variability in the amplitude of GnRH secreted by the brain (3,(7)(8)(9)(10)(11)(12). Elucidating the mechanisms underlying the response of the gonadotrope to varying concentrations of GnRH is important for understanding the design principles of this key response locus for mammalian physiology.GnRH directs two distinguishable gonadotrope activities, the biosynthesis of gonadotropins and their secretion. We focus here on the biosynthetic response. The GnRH receptor is a heptahelical G protein-coupled receptor that modulates a signaling network leading to activation of protein kinases and regulation of both transcription and translation (13). The gene network responses...

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A kinetic model of cobalt-based Fischer-Tropsch synthesis was developed through the detailed kinetic study of the reaction mechanism. Experimental evidence and previously reported theoretical analyses were used to suggest the mechanism and derive reaction rates for the formation of hydrocarbon products by applying the equilibrium constants of the adsorbents and the quasi steady state assumption to intermediate species on the surface of the catalyst. The comparison between experimental data and simulated results with kinetic parameters validated the effectiveness of the developed model. Further analysis showed that temperature and H 2 /CO ratio significantly influenced the entire distribution of hydrocarbon products. The effects of operating conditions were also predicted in accordance with previous work, thus demonstrating that the developed model can contribute to a better understanding of the kinetic mechanism of FT synthesis.

A mathematical model was developed for a continuous reactor in which free radical polymerization of methyl methacrylate (MMA) occurred. Elementary reactions considered in this study were initiation, propagation, termination, and chain transfers to monomer and solvent. The reactor model took into account the density change of the reactor content and the gel effect. To measure the conversion and weight-average molecular weight on line, the on-line densitometer and viscometer were installed in such a way that the measured values of density were used to calculate the conversion and the viscosity measurement along with conversion data was used to determine the weight-average molecular weight. A control system was designed for a continuous reactor using an extended Kalman filter (EKF)-based nonlinear model predictive controller (NLMPC) to control both the conversion and the weight-average molecular weight of the polymer product. The control input variables were the jacket inlet temperature and the feed flow rate. For the purpose of validating the control strategy, an on-line digital control experiment was conducted with an on-line densitometer and viscometer installed. Despite the complex and nonlinear features of the polymerization reaction system, the EKF-based NLMPC performed quite satisfactorily for the property control of the continuous polymerization reactor.

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