Optimal control analysis and Practical NMPC applied to refrigeration systems.

This work is focused on optimal control of mechanical compression refrigeration systems. A reduced-order state-space model based on the moving boundary approach is proposed for the canonical cycle, which eases the controller design. The optimal cycle (that satisfying the cooling demand while maximizing efficiency) is defined by three variables, but only two inputs are available, therefore the controllability of the proposed model is studied. It is shown through optimization simulations how optimal cycles for a range of the cooling demand turn out not to be achieved by keeping the degree of superheating to a minimum. The Practical NMPC and a well-known feedback-plus-feedforward strategy from the literature are compared in simulation, both showing trouble in reaching the optimal cycle, which agrees with the controllability study.

Prevalence of dementia subtypes in El Prat de Llobregat, Catalonia, Spain: the PRATICON study.

BACKGROUND: Studies on dementia subtypes show a wide variation in the prevalence of Alzheimer's disease (AD) and vascular dementia (VD) worldwide. However, studies reporting on Lewy body dementia (LBD) and frontotemporal dementia (FTD) are sparse. AIMS: To describe the prevalence of dementia and subtypes. METHOD: A 34% sample of 5,150 subjects aged 70 years and over in El Prat de Llobregat (Barcelona) were screened by the Mini-Mental State Examination. When scoring <24, participants were assessed to establish a diagnosis. RESULTS: There were 165 subjects diagnosed with dementia (prevalence of 9.4%). Subtypes of dementia were: AD 69.1%, VD 12.7%, LBD 9.1%, FTD 3% and secondary dementia 1.8%. Prevalences were: AD 6.5%, VD 1.2%, LBD 0.9% and FTD 0.3%. CONCLUSIONS: AD and VD were the most common type of dementia. Prevalence of dementia, AD and FTD were similar to those reported, while prevalence of VD and LBD were lower.

Quantification of dideoxycytidine in human plasma by gas chromatography/mass spectrometry.

A gas chromatographic/mass spectrometric procedure has been developed for the quantification in plasma of dideoxycytidine (DDC), a candidate anti-AIDS drug. The assay uses an extraction with ethyl acetate containing 10% methanol followed by three derivatization steps: (i) reaction with t-butyl dimethyl chlorosilane to silylate the 5'-hydroxyl group; (ii) pentafluorobenzoylation of the amino group with pentafluorobenzoyl chloride; (iii) methylation of the ring nitrogen adjacent to the amino group with diazomethane. The resulting derivative is quantified using stable isotope dilution, selective ion monitoring and methane negative chemical ionization mass spectrometry. Plasma concentrations of DDC were measured over a range of 2-200 ng ml-1 using 1 ml plasma for extraction.