Abstract. Observed groundwater head and soil moisture profiles are assimilated into an integrated hydrological model. The study uses the ensemble transform Kalman filter (ETKF) data assimilation method with the MIKE SHE hydrological model code. The method was firstly tested on synthetic data in a catchment of less complexity (the Karup catchment in Denmark), and later implemented using data from real observations in a larger and more complex catchment (the Ahlergaarde catchment in Denmark). In the Karup model, several experiments were designed with respect to different observation types, ensemble sizes and localization schemes, to investigate the assimilation performance. The results showed the necessity of using localization, especially when assimilating both groundwater head and soil moisture. The proposed scheme with both distance localization and variable localization was shown to be more robust and provide better results. Using the same assimilation scheme in the Ahlergaarde model, groundwater head and soil moisture were successfully assimilated into the model. The hydrological model with assimilation showed an overall improved performance compared to the model without assimilation.
Atrial fibrillation (AF) is the most common cardiac arrhythmia. It is characterized by rapid and disorganized electrical activity in the atria. Atrial arrhythmias can be triggered from an ectopic focus, i.e., an abnormal impulse originating in an area other than the sinus node, generating reentrant waves. The regional ionic heterogeneities found in the atria cause a gradual shortening of the action potential duration (APD) with increased distance from the sinoatrial node. It is generally thought that the only electrophysiological consequence of the spatial dispersion of cardiac action potentials (AP) is the enhancement of reentry. This paper investigates the effect of a gradient in APD on arrhythmogenesis via computer simulations. A gradient of ionic properties was introduced into a computationally efficient computer model of the canine atria to produce a smooth distribution of APDs. The window of vulnerability for ectopic beat-induction of reentry was determined for both left atrium (LA) and the right atrium (RA) stimulation, with and without an APD gradient. The shortened windows of vulnerability in the RA, due to the addition of the APD gradient, suggests a protective mechanism against AF. The left atrial window of vulnerability was slightly longer from ionic dispersion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.