A numerical modelling of flow dynamics in a tidal river mouth of comprehensive morphology is assumed to be one of the most effective methods of both scientific research and civil engineering projects. Realistic results of simulations can be obtained only on the basis of field observations. This approach is realized for a 2D hydrodynamic model of the Northern Dvina River mouth area. The Northern Dvina delta has a very complicated distributary network and suffers from both spring snow-melt floods and autumn storm surges. The STREAM_2D software package based on the 2D shallow water equations was used for the model development. The model was calibrated and validated on the background of water level data at state gauges and special water discharges measurements in the essential delta branches during the semi-diurnal tidal cycles. Sensitivity tests were provided to evaluate the most significant reasons for model errors. It was discovered that the distribution of roughness coefficients amidst delta channels and floodplain does not affect the flow dynamics in the delta significantly. However, the tidal range variations over a neap-spring cycle and mean sea level changes along the delta marine edge are of major importance.
Presently, there is no generally accepted approach to automated measurement of pulse duration in cardiac cycles. This makes it difficult to compare the results obtained by different cardiograph models. At present, this problem is not very urgent because the duration of cardiopulses is still measured manually from the ECG records with an accuracy of about 10 msec [8, 13]. However, methods of comparison of the results of repeated examinations of the same patient during a significant length of time that are presently being introduced used into medical practice require the accuracy of the measurements to be at least 1 msec. Electrocardiographs providing such accuracy of measurements are available, but differences in algorithms of automated measurement in this case becomes a significant problem.The goal of this work was to consider various algorithms of measurement of duration, or, more precisely, various algorithms of determining the beginning and end of cardiopulses, which allows the duration of the pulse to be easily calculated. Development of such algorithms is one of the tasks of mathematical statistics. A comparative survey of algorithms given below treats this problem from the point of view of electrocardiography. Noise stability and accuracy of determination of the beginning of a pulse are chosen as the criteria for comparison of various algorithms.
Specific Physiological Features of the Be~nning of Cardiac Cycle PulsesRecent studies show [20] that the shape of cardiopulses at their beginning is rather complicated and has various phases. Each cardiopulse (especially the P wave) is preceded with a fluctuation process of spontaneous generation of artifacts (background myographic noise). At a certain moment in time, sinoatrial node ceils undergo collective excitation which is transmitted to adjacen t regions of the myocardial auricles. The steepness and shape of the leading edge of the excitation pulse are determined by the rate of excitation transmission and changes in the total volume of depolarized ceils. Initially, the process propagates in three dimensions, so it can be concluded that its rate is proportional to the third power of time. The measured rate is proportional to the third power of time because of the vector selectivity of ECG leads. Taking into account the thickness of myocardial walls (several mm in the region of the auricles), it can be concluded that the first steep phase of the process occurs within 1-4 msec. It is followed by a more flattened phase and the end of the pulse. The shape of P wave at its beginning is determined by the geometry of auricle muscles, anisotropy of excitation transmission rates, and vector selectivity of the lead.The process of appearance of the QRS complex is different from that described above. The QRS complex is preceded by the repolarization process in auricles and signals from the atrioventricular node, which transmit excitation with a delay to the His' bundle. A branched network of the His' bundle conducting paths distributes excitation over the endocardial pap...