102,478 research outputs found
Self-consistent simulation of Magnum-PSI target in SOLPS-ITER with a Finite Element Wall model
Full text linkIdentification of coronary resistance and compliance in the dog
No full textProceedings of the 37th Annual Conference on Engineering in Medicine and Biology (ACEMB), Los Angeles, Californi
Identification of canine coronary resistance and intramyocardial compliance on the basis of the waterfall model
No full textTotal systemic arterial compliance and aortic characteristic impedance in the dog as a function of pressure: A model based study
No full textTotal arterial compliance and aortic characteristic impedance as a function of pressure in the anesthetized closed chest dog (n = 5) were studied. The three-element windkessel (consisting of a peripheral resistance, a total systemic arterial compliance, and an aortic characteristic impedance) was assumed as an arterial model. Aortic pressure was varied by pacing the heart at different rates after the production of atrioventricular block and by administration of Angiotensin and Hydralazine. Model parameters were estimated by two different methods. The first was based on a computerized optimization procedure using all the information contained in the aortic pressure and flow waveforms. The second method used the diastolic decay of aortic pressure to compute total arterial compliance and used the arterial input impedance spectrum to compute aortic characteristic impedance. Total arterial compliance and aortic characteristic impedance changed with pressure. The parameter optimization procedure yielded values of total arterial compliance ranging from 0.20 to 1.4 ml/mmHg and values of aortic characteristic impedance ranging from 0.05 to 0.42 mmHg sec/ml. Values of parameters estimated on the basis of the impedance spectrum and diastolic pressure decay were similar. Compliance values as a function of mean aortic pressure could be fitted with a bell-shaped curve similar to that found from in vitro studies of aortic segments. Characteristic impedance values as a function of mean aortic pressure could be fitted with a parabolic function the minimum of which was found in the range of control to high pressures (90-160 mmHg)
Heat transport in the canine left ventricular wall
No full text The rate of rise of local myocardial temperature (dT/dt) evoked by left coronary artery main stem occlusion has been proposed in the literature as a measure of local metabolic heat production, assuming heat loss due to diffusion to be negligible. In a previous study (ten Velden, G. H. M., G. Elzinga, and N. Westerhof. Circ. Res. 50: 63-73, 1982), we showed that this assumption was not valid. With this information in mind, in an attempt to study local metabolism, we compared, in anesthetized dogs, the dT/dt with the temperature distribution over the left ventricular wall. We found the value of dT/dt to be reproducible in time and to reproducibly depend on location. Negative values as well as positive values were measured; values even higher than the maximal possible temperature slope, calculated from the energy equivalent of left ventricular oxygen consumption and the specific heat of cardiac tissue, were found. Transmural distribution of the dT/dt showed positive values epicardially and negative values endocardially, while, as previously shown, a parabola-like shape of the transmyocardial temperature distribution existed. Our findings demonstrate that dT/dt by left coronary main stem occlusion cannot be used as a measure of local myocardial heat production. </jats:p
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Material parameter identification for modelling the left ventricle in the healthy state
No full textIncludes bibliographical references.An idealized truncated ellipsoidal model, was used to simulate a healthy canine left ventricle. Passive behaviour of the myocardium was modelled using the constitutive model of Usyk. In addition, active behaviour of the myocardium was modelled by the active stress law of Guccione. Furthermore, the load faced by the left ventricle in ejecting blood into the arterial system, was modelled with the three element Windkessel model of Westerhof. The model was calibrated to pressure-volume data, which was adaptedfrom the work of Kerckhoffs. The projected Levenberg-Marquardt algorithm was used to identify material parameters. Identification of the anisotropic constants in the model of Usyk proved to be difficult, with the calibration algorithm often converging to parameter values that produced numerical instability. An idealized truncated ellipsoidal model, was used to simulate a healthy canine left ventricle. Passive behaviour of the myocardium was modelled using the constitutive model of Usyk. In addition, active behaviour of the myocardium was modelled by theactive stress law of Guccione. Furthermore, the load faced by the left ventricle in ejecting blood into the arterial system, was modelled with the three element Windkessel model of Westerhof. The model was calibrated to pressure-volume data, which was adapted from the work of Kerckhoffs. The projected Levenberg-Marquardt algorithm was used to identify material parameters. Identification of the anisotropic constants in the model of Usyk proved to be difficult, with the calibration algorithm often converging to parameter values that produced numerical instability. An idealized truncated ellipsoidal model, was used to simulate a healthy canine left ventricle. Passive behaviour of the myocardium was modelled using the constitutive model of Usyk. In addition, active behaviour of the myocardium was modelled by the active stress law of Guccione. Furthermore, the load faced by the left ventricle in ejecting blood into the arterial system, was modelled with the three element Windkessel model of Westerhof. The model was calibrated to pressure-volume data, which was adaptedfrom the work of Kerckhoffs. The projected Levenberg-Marquardt algorithm was used to identify material parameters. Identification of the anisotropic constants in the model of Usyk proved to be difficult, with the calibration algorithm often converging to parameter values that produced numerical instability. An idealized truncated ellipsoidal model, was used to simulate a healthy canine left ventricle. Passive behaviour of the myocardium was modelled using the constitutive model of Usyk. In addition, active behaviour of the myocardium was modelled by the active stress law of Guccione. Furthermore, the load faced by the left ventricle in ejecting blood into the arterial system, was modelled with the three element Windkessel model of Westerhof. The model was calibrated to pressure-volume data, which was adapted from the work of Kerckhoffs. The projected Levenberg-Marquardt algorithm was used to identify material parameters. Identification of the anisotropic constants in the model of Usyk proved to be difficult, with the calibration algorithm often converging to parameter values that produced numerical instability
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