The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Kaz Adamowski - One of the best experts on this subject based on the ideXlab platform.
-
scaling model of a rainfall intensity duration Frequency Relationship
Hydrological Processes, 2006Co-Authors: John Bougadis, Kaz AdamowskiAbstract:Intensity-duration-Frequency (IDF) Relationships are currently constructed based on an at-site Frequency analysis of rainfall data separately for different durations. These Relationships are not accurate and reliable since they depend on many assumptions such as distribution selection for each duration; they require a large number of parameters, and are not time-independent. In this study, scaling properties of extreme rainfall are examined to establish scaling behaviour of statistical non-central moments over different durations. A scale invariance concept is explored for disaggregation (or downscaling) of rainfall intensity from low to high resolution and is applied to the derivation of scaling IDF curves. These curves are developed for gauged sites based on scaling of the generalized extreme value (GEV) and Gumbel probability distributions. Numerical analysis was performed on annual maximum rainfall series for the province of Ontario, for storm durations of 5, 10, 15, and 30 min (the typical time of concentration for small urban catchments) and 1, 2, 6, 12, and 24 h (the typical time of concentration for larger rural watersheds). Results show that rainfall does follow a simple scaling process. Estimates found from the scaling procedure are comparable to estimates obtained from traditional techniques; however, the scaled approach was more efficient and gives more accurate estimates compared with the observed rainfall total at all stations.
H Just - One of the best experts on this subject based on the ideXlab platform.
-
Influence of the force—Frequency Relationship on haemodynamics and left ventricular function in patients with non-failing hearts and in patients with dilated cardiomyopathy
European Heart Journal, 1994Co-Authors: G Hasenfuss, Christian Holubarsch, H.-p. Hermann, K. Astheimer, B. Pleske, H JustAbstract:In isolated human myocardium it was shown that a positive force-Frequency Relationship occurs in non-failing myocardium; however, the force-Frequency Relationship was found to be inverse in myocardium from failing human hearts. In order to investigate the clinical relevance of these experimental findings, the influence of heart rate changes on haemodynamics and left ventricular function was studied in eight patients without heart failure and in nine with failing dilated cardiomyopathy (NYHA II–III). Right ventricular pacing was performed at a rate slightly above sinus rate and at 100, 120 and 140 beats. min−1 Haemodynamic parameters were obtained by right heart catheterization and by high-fidelity left ventricular pressure measurements. Left ventricular angiography was performed at basal pacing rate and at 100 and 140 beats. min−1 With increasing heart rate, cardiac index increased in patients with normal left ventricular function from 2·9 ± 0·2 to 3·5 ± 0·21. min−1. m−2 ( P
-
influence of the force Frequency Relationship on haemodynamics and left ventricular function in patients with non failing hearts and in patients with dilated cardiomyopathy
European Heart Journal, 1994Co-Authors: G Hasenfuss, Christian Holubarsch, H.-p. Hermann, K. Astheimer, B. Pleske, H JustAbstract:In isolated human myocardium it was shown that a positive force-Frequency Relationship occurs in non-failing myocardium; however, the force-Frequency Relationship was found to be inverse in myocardium from failing human hearts. In order to investigate the clinical relevance of these experimental findings, the influence of heart rate changes on haemodynamics and left ventricular function was studied in eight patients without heart failure and in nine with failing dilated cardiomyopathy (NYHA II–III). Right ventricular pacing was performed at a rate slightly above sinus rate and at 100, 120 and 140 beats. min−1 Haemodynamic parameters were obtained by right heart catheterization and by high-fidelity left ventricular pressure measurements. Left ventricular angiography was performed at basal pacing rate and at 100 and 140 beats. min−1 With increasing heart rate, cardiac index increased in patients with normal left ventricular function from 2·9 ± 0·2 to 3·5 ± 0·21. min−1. m−2 ( P <0·01) and decreased continuously in patients with dilated cardiornyopathy from 2·6 ± 0·1 to 2·2 ± 0·11. min−1 . m−2 ( P <0·05). With increasing heart rate, the maximum rate of left ventricular pressure rise increased in non-failing hearts from 1388 ± 86 to 1671 ± 88 mmHg. s−1 ( P <0·01) and did not change in failing hearts. Ejection fraction decreased from 27 ± 3% to 19 ± 2% in patients with dilated cardiomyopathy ( P <0·05) when the pacing rate was changed from 84 ± 2 beats. min−1 to 140 beats. min−1, which was associated with a significantly increase in end-systolic volume without significantly changes in end-diastolic volume. In patients with normal left ventricular function, when the pacing rate was changed from 85 ± 3 beats. min−1 to 140 beats. min−1, end-diastolic volume decreased significantly by 13%, whereas left ventricular end-systolic volume and ejection fraction did not significantly change. Left ventricular systolic and end-diastolic pressures did not significantly change with pacing tachycardia in either group. The Frequency-related changes in left ventricular volumes and pressures indicate that the differrent haemodynamic effects of pacing tachycardia in both groups of patients result predominantly from Frequency effects on myocardial function and not from Frequency effects on preload or afterload. These data indicate that recent experimental findings of positive force-Frequency effects in non-failing and negative force-Frequency effects in failing human myocardium are relevant for the intact heart.
-
Alterations of the force-Frequency Relationship in the failing human heart depend on the underlying cardiac disease.
Basic research in cardiology, 1992Co-Authors: B Pieske, M Böhm, G Hasenfuss, C Holubarsch, R Schwinger, H JustAbstract:We investigated the force-Frequency Relationship (0.5-3 Hz) in non-failing human myocardium and in end-stage failing human myocardium due to dilated cardiomyopathy or subacute myocarditis. In non-failing myocardium, force of contraction increased with increasing stimulation Frequency. In end-stage heart failure, the force-Frequency Relationship was inverse in myocardium from dilated cardiomyopathy, but was similar to control in myocardium from subacute myocarditis. After increasing extracellular Ca(2+)-concentration from 2.5 to 7.2 mM, the shape of the force-Frequency Relationship was not changed in nonfailing myocardium. In dilated cardiomyopathy, the decline in force with increasing frequencies was even more pronounced at 7.2 mM compared to 2.5 mM extracellular Ca2+. In subacute myocarditis, at Ca2+ 7.2 mM, increasing frequencies increased force in the lower Frequency range (less than 1.75 Hz) only, whereas at higher stimulation rates force declined again. These results indicate that (1.) alterations of the force-Frequency Relationship in the failing human heart depend on the underlying cardiac disease and/or the time-course of the disease, and (2.) an increase in the extracellular Ca(2+)-concentration aggravates changes in the force-Frequency Relationship in the failing myocardium.
-
Alterations of the force-Frequency Relationship in the failing human heart depend on the underlying cardiac disease.
Basic Research in Cardiology, 1992Co-Authors: B Pieske, G Hasenfuss, C Holubarsch, R Schwinger, Michael Böhm, H JustAbstract:We investigated the force-Frequency Relationship (0.5–3 Hz) in non-failing human myocardium and in end-stage failing human myocardium due to dilated cardiomyopathy or subacute myocarditis. In non-failing myocardium, force of contraction increased with increasing stimulation Frequency. In end-stage heart failure, the force-Frequency Relationship was inverse in myocardium from dilated cardiomyopathy, but was similar to control in myocardium from subacute myocarditis. After increasing extracellular Ca2+-concentration from 2.5 to 7.2 mM, the shape of the force-Frequency Relationship was not changed in nonfailing myocardium. In dilated cardiomyopathy, the decline in force with increasing frequencies was even more pronounced at 7.2 mM compared to 2.5 mM extracellular Ca2+.In subacute myocarditis, at Ca2+ 7.2 mM, increasing frequencies increased force in the lower Frequency range (< 1.75 Hz) only, whereas at higher stimulation rates force declined again. These results indicate that (1.) alterations of the force-Frequency Relationship in the failing human heart depend on the underlying cardiac disease and/or the time-course of the disease, and (2.) an increase in the extracellular Ca2+-concentration aggravates changes in the force-Frequency Relationship in the failing myocardium.
Ibrahim H Elsebaie - One of the best experts on this subject based on the ideXlab platform.
-
developing rainfall intensity duration Frequency Relationship for two regions in saudi arabia
Journal of King Saud University: Engineering Sciences, 2012Co-Authors: Ibrahim H ElsebaieAbstract:Abstract Intensity–duration–Frequency (IDF) Relationship of rainfall amounts is one of the most commonly used tools in water resources engineering for planning, design and operation of water resources projects. The objective of this research is to derive IDF Relationship of rainfall at Najran and Hafr Albatin regions in the kingdom of Saudi Arabia (KSA). These Relationships are useful in the design of urban drainage works, e.g. storm sewers, culverts and other hydraulic structures. Two common Frequency analysis techniques were used to develop the IDF Relationship from rainfall data of these regions. These techniques are: Gumbel and the Log Pearson Type III distribution (LPT III). An equation for estimating rainfall intensity for each region was derived using both techniques. The results obtained using Gumbel distribution are slightly higher than the results obtained using the LPT III distribution. Rainfall intensities obtained from these two methods showed good agreement with results from previous studies on some parts of the study area. The chi-square goodness-of-fit test was used to determine the best fit probability distribution. The parameters of the IDF equations and coefficient of correlation for different return periods (2, 5, 10, 25, 50 and 100) are calculated by using non-linear multiple regression method. The results obtained showed that in all the cases the correlation coefficient is very high indicating the goodness of fit of the formulae to estimate IDF curves in the region of interest.
John Bougadis - One of the best experts on this subject based on the ideXlab platform.
-
scaling model of a rainfall intensity duration Frequency Relationship
Hydrological Processes, 2006Co-Authors: John Bougadis, Kaz AdamowskiAbstract:Intensity-duration-Frequency (IDF) Relationships are currently constructed based on an at-site Frequency analysis of rainfall data separately for different durations. These Relationships are not accurate and reliable since they depend on many assumptions such as distribution selection for each duration; they require a large number of parameters, and are not time-independent. In this study, scaling properties of extreme rainfall are examined to establish scaling behaviour of statistical non-central moments over different durations. A scale invariance concept is explored for disaggregation (or downscaling) of rainfall intensity from low to high resolution and is applied to the derivation of scaling IDF curves. These curves are developed for gauged sites based on scaling of the generalized extreme value (GEV) and Gumbel probability distributions. Numerical analysis was performed on annual maximum rainfall series for the province of Ontario, for storm durations of 5, 10, 15, and 30 min (the typical time of concentration for small urban catchments) and 1, 2, 6, 12, and 24 h (the typical time of concentration for larger rural watersheds). Results show that rainfall does follow a simple scaling process. Estimates found from the scaling procedure are comparable to estimates obtained from traditional techniques; however, the scaled approach was more efficient and gives more accurate estimates compared with the observed rainfall total at all stations.
Masao Endoh - One of the best experts on this subject based on the ideXlab platform.
-
force Frequency Relationship in intact mammalian ventricular myocardium physiological and pathophysiological relevance
European Journal of Pharmacology, 2004Co-Authors: Masao EndohAbstract:Abstract The force–Frequency Relationship (FFR) is an important intrinsic regulatory mechanism of cardiac contractility. The FFR in most mammalian ventricular myocardium is positive; that is, an increase in contractile force in association with an increase in the amplitude of Ca2+ transients is induced by elevation of the stimulation Frequency, which reflects the cardiac contractile reserve. The Relationship is different depending on the range of Frequency and species of animal. In some species, including rat and mouse, a ‘primary-phase’ negative FFR is induced over the low-Frequency range up to approximately 0.5–1 Hz (rat) and 1–2 Hz (mouse). Even in these species, the FFR over the Frequency range close to the physiological heart rate is positive and qualitatively similar to that in larger mammalian species, although the positive FFR is less prominent. The integrated dynamic balance of the intracellular Ca2+ concentration ([Ca2+]i) is the primary cellular mechanism responsible for the FFR and is determined by sarcoplasmic reticulum (SR) Ca2+ load and Ca2+ flux through the sarcolemma via L-type Ca2+ channels and the Na+-Ca2+ exchanger. Intracellular Na+ concentration is also an important factor in [Ca2+]i regulation. In isolated rabbit papillary muscle, over a lower Frequency range ( 2.5 Hz), the contractile force is dissociated from the amplitude of Ca2+ transients probably due to complex cellular mechanisms, including oxygen limitation in the central fibers of isolated muscle preparations, while the amplitude of Ca2+ transients increases further with increasing Frequency (‘secondary-phase’ negative FFR). Calmodulin (CaM) may contribute to a positive FFR and the Frequency-dependent acceleration of relaxation, although the role of calmodulin has not yet been established unequivocally. In failing ventricular myocardium, the positive FFR disappears or is inverted and becomes negative. The activation and overexpression of cardiac sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) is able to reverse these abnormalities. Frequency-dependent alterations of systolic and diastolic force in association with those of Ca2+ transients and diastolic [Ca2+]i levels are excellent indicators for analysis of cardiac excitation-contraction coupling, and for evaluating the severity of cardiac contractile dysfunction, cardiac reserve capacity and the effectiveness of therapeutic agents in congestive heart failure.