Model-based control of the outlet temperature of a distributed solar collector eld is studied. An energy-based cont r o l l e r i s d e r i v ed using internal energy as a storage function and controlled variable. The controller relies on a distributed parameter nonlinear plant model and includes feedforward from the solar irradiation and inlet temperature. Stability of the closed loop is proved, and the method is experimentally veri ed to perform well on a pilot-scale solar power plant.

One of the major criticisms of ultrasound Doppler is its angle dependency, that is its ability to measure velocity components directly to or from the transducer only. The present article aims to investigate the impact of this angular error in a clinical setting. Apical two- and four-chamber views were recorded in 43 individuals, and the myocardium was marked by hand in each image. We assume that the main direction of the myocardial velocities is longitudinal and correct for the angular error by backprojecting measured velocities onto the longitudinal direction drawn. Strain was calculated from both corrected and uncorrected velocities in 12 segments for each individual. The results indicate that the difference between strain values calculated from corrected and uncorrected velocities is insignificant in 5 segments and within a decimal range in 11 segments. The biggest difference between measured and corrected strain values was found in the apical segments. Strain is also found to be more robust against angular error than velocities because the difference between corrected and uncorrected values is smaller for strain. Considering that there are multiple sources of noise in ultrasound Doppler measurements, the authors conclude that the angular error has so little impact on longitudinal strain that correction for this error can safely be omitted. (ECHOCARDIOGRAPHY, Volume 20, October 2003)

No abstract

Abstract-Aims: Using post-processing software it is possible to extract tissue velocities from colour-coded Doppler information in numerous positions in the myocardial wall. From velocity other variables such as displacement and deformation (strain) can be calculated. For adequate clinical assessment multiple measurements are needed. This is why reproducibility of the method must be evaluated. Methods: A moderately experienced observer measured systolic and diastolic basal velocity, displacement, strain rate and strain in right and left ventricular walls in 14 patients. The measurements were compared to those acquired by an experienced observer. Results: The inter-observer variability for the systolic longitudinal and radial velocity was 6.9% and 12.0% for the right and 5.8% and 11.9% for the left ventricle respectively. The results with the least reproducibility were obtained for the radial strain rate where the inter-observer variability was 27.9% and 16.2% for the right and left ventricles respectively. Left ventricular velocity measurements had slightly better reproducibility than right ventricular. Derived calculations had a larger variation. Conclusion: Basal velocity measurements and displacement calculations could be performed in the clinical routine by different observers with high reproducibility. Derived variables depending on multiple measuring locations could still be performed but with a method uncertainty of almost 15%.1 Keywords-Reproducibility, Doppler, tissue velocity, strain, strain rate. I. INTRODUCTIONExtraction of velocity profiles from colour coded tissue Doppler images is a modality that has been developed during the last decade [1,2]. Tissue Doppler measurement was first described by Isaaz et al. [3] and could at that time only be performed in one single spot during a heart cycle by using the high amplitude and low pass filtered information in an ordinary pulsed Doppler signal.By using cross correlation technique instead of Fourier spectral analysis myocardial velocities could be extracted as colour information instead of velocity curves. It has always been said that colour velocity only measures mean velocity but by pulsed Doppler real maximal velocities could also be acquired. This is true when velocities in hydraulic fluids like blood are measured but of less importance when velocity of tissue compartments is evaluated as e.g. myocardial wall velocity where all muscle fibres are more or less glued together resulting in small differences between minimum and maximum velocities. The concept of extracting velocity profiles from colour information has the advantage thatThe work is supported by the Swedish Heart Lung Foundation.nearly an infinite number of spatial locations could be evaluated from one single acquired heart beat giving valuable information about spatial differences in velocity profiles without too much biological time dependant variation. Earlier studies of reproducibility in pulsed tissue Doppler recordings have shown that the reproducibility is better for cardiac long axi...

No abstract