An alternative design approach for Fractional Order Internal Model Controllers for time delay systems.

INTRODUCTION: Fractional Order Internal Model Control (FO-IMC) extends the capabilities of the classical IMC approach into the generalized domain of fractional calculus. When dealing with processes that exhibit time delays, implementation of such controllers in a classical feedback loop requires the approximation of the fractional order terms, as well as of the corresponding time delays. OBJECTIVES: The present study proposes an alternative design procedure of FO-IMC controllers based on a novel approximation method of the process time delay, proving the efficiency of the proposed method and its suitability for time delay systems. METHODS: The generalized IMC control laws are obtained analytically, based on a novel approximation of time delay, the Non-Rational Transfer Function approach. RESULTS: Several numerical examples are chosen to illustrate the efficiency of the proposed approach. In addition, a vertical take-off and landing unit exhibiting second order plus time delay dynamics is chosen to experimentally validate the proposed control strategy. The obtained results are used to compare the proposed tuning strategy with a popular FO-IMC tuning approach, based on the Taylor series approximation of the time delay. CONCLUSION: All the chosen examples, both numerical and experimental ones, validate the proposed method. The overall closed loop results obtained with the proposed approach demonstrate an improved performance compared to the existing method. Ultimately, the purpose of the paper to provide an alternative design strategy that extends the existing FO-IMC control field is reached.

A comparison of propofol-to-BIS post-operative intensive care sedation by means of target controlled infusion, Bayesian-based and predictive control methods: an observational, open-label pilot study.

PURPOSE: We evaluated the feasibility and robustness of three methods for propofol-to-bispectral index (BIS) post-operative intensive care sedation, a manually-adapted target controlled infusion protocol (HUMAN), a computer-controlled predictive control strategy (EPSAC) and a computer-controlled Bayesian rule-based optimized control strategy (BAYES). METHODS: Thirty-six patients undergoing short lasting sedation following cardiac surgery were included to receive propofol to maintain a BIS between 40 and 60. Robustness of control for all groups was analysed using prediction error and spectrographic analysis. RESULTS: Although similar time courses of measured BIS were obtained in all groups, a higher median propofol effect-site concentration (CePROP) was required in the HUMAN group compared to the BAYES and EPSAC groups. The time course analysis of the remifentanil effect-site concentration (CeREMI) revealed a significant increase in CeREMI in the EPSAC group compared to BAYES and HUMAN during the case. Although similar bias and divergence in control was found in all groups, larger control inaccuracy was observed in HUMAN versus EPSAC and BAYES. Spectrographic analysis of the system behavior shows that BAYES covers the largest spectrum of frequencies, followed by EPSAC and HUMAN. CONCLUSIONS: Both computer-based control systems are feasible to be used during ICU sedation with overall tighter control than HUMAN and even with lower required CePROP. EPSAC control required higher CeREMI than BAYES or HUMAN to maintain stable control. Clinical trial number: NCT00735631.

Modeling of the lung impedance using a fractional-order ladder network with constant phase elements.

The self similar branching arrangement of the airways makes the respiratory system an ideal candidate for the application of fractional calculus theory. The fractal geometry is typically characterized by a recurrent structure. This study investigates the identification of a model for the respiratory tree by means of its electrical equivalent based on intrinsic morphology. Measurements were obtained from seven volunteers, in terms of their respiratory impedance by means of its complex representation for frequencies below 5 Hz. A parametric modeling is then applied to the complex valued data points. Since at low-frequency range the inertance is negligible, each airway branch is modeled by using gamma cell resistance and capacitance, the latter having a fractional-order constant phase element (CPE), which is identified from measurements. In addition, the complex impedance is also approximated by means of a model consisting of a lumped series resistance and a lumped fractional-order capacitance. The results reveal that both models characterize the data well, whereas the averaged CPE values are supraunitary and subunitary for the ladder network and the lumped model, respectively.

Parametric models for characterizing respiratory input impedance.

This study compares a manifold of parametric models reported in the literature with two novel parametric models for identifying human input respiratory impedance. The analysis is carried out on typical patient data obtained with the forced oscillations technique (FOT), on three sets of representative diagnosed subjects: healthy, asthma and COPD. The performance of the models is characterized by the error between the true respiratory impedance of the patient and the estimated impedance by the parametric models. The optimal solutions of the nonlinear estimations are compared. The resulting parameter values are discussed with respect to both model structure and physiological insight.

Pancreas divisum: a teenager with calculi in the duct of Santorini. Report of a case treated by double drainage procedure.

Since the age of sixteen, a teenager suffers from acute recurrent pancreatitis with a weight loss of 17 kg, without evident etiologic factor. At laparotomy the duct of Wirsung is absent; calculi are found in a grossly dilated duct of Santorini and the minor papilla is stenosed with periductal fibrosis and a large retention pseudocyst. Recurrent pancreatitis is cured by sphincteroplasty of the minor papilla and side-to-side pancreatico-jejunostomy. After a follow-up of 17 months the recurrent pancreatitis seems cured by sphincteroplasty of the minor papilla and side-to-side pancreatico-jejunostomy.

A fatal intoxication due to doxepin.

A fatal intoxication due to doxepin, a tricyclic antidepressant, is described. Concentrations of doxepin and its metabolite, desmethyldoxepin, were measured in blood, urine, myocardial, and other tissues using thin layer chromatography (TLC) and gas chromatography equipped with a flame-ionisation detector (GC/FID). The developed technique also permitted the quantitative determination of the cis and trans isomers of doxepin. A very remarkable concentration ratio of doxepin:desmethyldoxepin was observed in myocardial tissues. A detailed report on the possible significance is described.