Robust control with uncertainty estimation for feedback linearizable systems: application to control of distillation columns

The goal of this paper is to describe a linearizing feedback adaptive control structure which leads to a high quality regulation of the output error in the presence of uncertainties and external disturbances. The controller consists of three elements: a nominal input–output linearizing compensator, a state observer and an uncertainty estimator, which provides the adaptive part of the control structure. In this way, the feedback controller, based on the disturbance observer, compensates for external disturbances and plant uncertainties. The effectiveness of the controller is demonstrated on a distillation column via numerical simulations. ©     

Corrosion relationships as a function of time and surface roughness on a structural AE44 magnesium alloy

Pit initiation, growth, and coalescence corrosion mechanisms of an AE44 magnesium alloy subjected to a salt-water environment were quantified. Stereological quantities were evaluated using optical microscopy, scanning electron microscopy, and laser beam profilometry. Three corrosion mechanisms clearly arose: pitting, intergranular, and general. Pitting began as the result of localized galvanic dissolution between the intermetallics and magnesium matrix. Intergranular corrosion arose as pits coalesced. General corrosion arose by dissolution and regeneration of a Mg(OH)₂ film at a continuous rate. Stereological quantification demonstrated that the corrosion pit number density and pit radius size distribution initially increased before decreasing due to pit coalescence.     

Coatings for corrosion protection of porous substrates in gasifier components

Deposition of several coatings by Chemical Vapor Deposition in a Fluidized Bed was studied inside porous coupons made of 409 steel. Four different coating systems were studied: TiAlSiN/TiAl/SS409, TiAlSiN/TiAlSi/SS409, TiAlN/Nb/TiAl/SS409 and TiSiN/Nb/TiSi/SS409. Though coating thickness decreased with depth inside the porous filter, the formation of Ti-based ceramic films with thicknesses around 1 micrometer was observed 0.5 mm inside the bulk of the samples. Coated substrates were exposed to a simulated coal gas at 643 K for 300 hours, in order to study their corrosion resistance under conditions that mimic a porous metal particulate filter of a coal gasification system. Some of the coatings did not provide enough protection against corrosion at the bulk of the porous coupons, and iron sulfide crystals were formed that plugged the pores. On the other hand, the TiSiN/Nb/TiSi/SS409 system showed no sign of corrosion.     

DIMENSIONLESS CORRELATION FOR THE HEAT TRANSFER COEFFICIENT IN A BATCH-INDIRECT ROTARY DRIER

A batch-indirect rotary drier heated with steam was experimentally operated to obtain data of moisture content and temperature versus time for soy meal and fish meal. Operation conditions were as follow: steam pressure (1 to 4 bar), rotation speed (3.7 to 11.6 r.p.m.) and rate of vapor extraction (0.059 to 0.256 m/s).

From experimental data the effective heat transfer coefficient between the hot surface and the bed of solids was determined. These data were correlated by means of dimensional analysis as a function of the drying process variables. The equation obtained for the effective Nusselt number predicts adequately the effective heat transfer coefficient, for both substrates, in the range of the operating variables studied.     

Robust estimators under semi‐parametric partly linear autoregression: Asymptotic behaviour and bandwidth selection

Abstract. In this article, under a semi‐parametric partly linear autoregression model, a family of robust estimators for the autoregression parameter and the autoregression function is studied. The proposed estimators are based on a three‐step procedure, in which robust regression estimators and robust smoothing techniques are combined. Asymptotic results on the autoregression estimators are derived. Besides combining robust procedures with M‐smoothers, predicted values for the series and detection residuals, which allow to detect anomalous data, are introduced. Robust cross‐validation methods to select the smoothing parameter are presented as an alternative to the classical ones, which are sensitive to outlying observations. A Monte Carlo study is conducted to compare the performance of the proposed criteria. Finally, the asymptotic distribution of the autoregression parameter estimator is stated uniformly over the smoothing parameter.     

Colistin Resistance in Aeromonas spp.

The increase in the use of antimicrobials such as colistin for the treatment of infectious diseases has led to the appearance of Aeromonas strains resistant to this drug. However, resistance to colistin not only occurs in the clinical area but has also been determined in Aeromonas isolates from the environment or animals, which has been determined by the detection of mcr genes that confer a resistance mechanism to colistin. The variants mcr-1, mcr-3, and mcr-5 have been detected in the genus Aeromonas in animal, environmental, and human fluids samples. In this article, an overview of the resistance to colistin in Aeromonas is shown, as well as the generalities of this molecule and the recommended methods to determine colistin resistance to be used in some of the genus Aeromonas.     

Application of adsorptive voltammetry to assess the stability of modified alanine aminotransferases

Alanine aminotransferase has been stabilized by using chemical modification with both bis(imidates) (of varying length) and succinic anhydride. The voltammetric behavior of the native enzyme and its various modified forms has been studied by using both cyclic voltammetry and differential pulse adsorptive voltammetry. A distinctive accumulation pattern was found for each of the stabilized enzymes at the static mercury drop electrode with respect to the native alanine aminotransferase. Adsorptive voltammetry was demonstrated to be a useful technique to assess the extent of chemical modification of this enzyme, which is indirectly related to their stability for use in biotechnological processes. The sue of differential pulse adsorptive voltammetry, after a preconcentration of the enzyme for 300 s at the electrode surface, has yielded a detection limit of 1.0 x 10(-9) M.     

Effect of addition of cryoprotectants on the mechanical properties, colour and sensory attributes of fresh and frozen/thawed mashed potatoes

Cryoprotectants such as hydrocolloids (amidated low-methoxyl (ALM) and high methoxyl (HM) pectins), kappa- and iota-carrageenans (k-C and i-C), xanthan gum (XG)) and dairy proteins [whey protein (WP), sodium caseinate (SC)] were added to mashed potatoes to investigate ways of improving the effects of freezing and thawing. It was found that each hydrocolloid and protein, depending on concentration, affected the mechanical properties [instrumental textural profile analysis (ITPA), cone penetration (CP) test], the total colour difference (ΔE*) with respect to fresh control (FC) and the sensory attributes of fresh (F) and frozen/thawed (F/T) mashed potatoes in a different way. In the F/T samples, adding 5 and 8 g kg⁻¹ ALM, 3, 5 and 8 g kg⁻¹ k-C, 1.5, 3, 5 and 8 g kg⁻¹ i-C and 1.5, 5 and 15 g kg⁻¹ WP significantly increased ITPA consistency. Also, adding 2.5 and 5 g kg⁻¹ XG significantly increased ITPA consistency of the F/T product. In both F and F/T samples, k-C provided the highest ITPA consistency and also high CP average force evidencing a stronger synergistic effect in κ-C/denatured milk protein systems, although the excessive thickening and stickiness provided was judged undesirable by the panellists. Adding 8 g kg⁻¹ HM pectin had a disruptive effect on the mashed potatoes and decreased both ITPA consistency and CP average force. In all cases, freezing and thawing reinforced the gel structure of the products as compared to F and FC counterparts. The ΔE* values were higher in F samples containing ALM and HM pectins. Dairy proteins affected the taste and odour of the mashed potatoes and were judged unacceptable in the sensory analysis. Samples containing 0.5 and 1.5 g kg⁻¹ added XG were preferred organoleptically due to the creamy mouthfeel it produced. ITPA consistency correlated well with sensory texture attributes.     

Development of a predictive model for polymer/solvent diffusion coefficient calculations

A new calculation procedure for free‐volume parameters is considered in this work by using viscosity prediction methods and the Levenberg‐Marquardt calculation scheme. All parameters used in the Vrentas–Duda free‐volume theory can be estimated from pure component properties. The prediction results are compared with experimental data for some polymer/solvent systems. The diffusion coefficient calculated by Vrentas–Duda theory can be used in the modeling of membrane separation processes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Impact of Ethanol on Benzene Plume Lengths: Microbial and Modeling Studies

Recent legislation in several states has called for the removal of methyl tert-butyl ether (MTBE) from gasoline. In order to comply with Federal Clean Air Act requirements for carbon monoxide and ozone attainment, ethanol is being considered as a replacement for MTBE. The objective of this study is to evaluate the potential impact of ethanol on benzene plume lengths in subsurface environments following accidental spills of ethanol-blended gasoline. Two types of studies were conducted here. First, laboratory studies were performed using a pure culture indigenous to a gasoline-contaminated aquifer to evaluate the effect of ethanol on the rate of benzene biodegradation under aerobic conditions. Results from microbial studies showed that the biodegradation of 25 mg/L benzene was severely inhibited in the presence of 25 mg/L ethanol. While the enzymes responsible for benzene biodegradation by the culture were inducible, ethanol degradation appeared to be constitutive. Second, a two-dimensional model was developed to quantify the impact of ethanol on benzene plume lengths using weighted-average aerobic and anaerobic biodegradation rates for benzene in the presence and absence of ethanol. Model simulations indicated that benzene plume lengths are likely to increase by 16–34% in the presence of ethanol.