Franc Runovc

Cardiovascular physiology: simulation of steady state and transient phenomena by using the equivalent electronic circuit

By using commercially available software it is readily possible to design electronic circuits and to analyze them. By introducing the concept of equivalent quantities a simulation of various physiological phenomena is possible. This includes the steady state as well as various complex transient phenomena. This paper describes the use of an equivalent electronic circuit in simulating the cardiovascular system. It allows a stepwise upgrading. The first step is a one-ventricle circuit similar to the Starling heart-lung preparation. The final step is an equivalent circuit allowing simulation of various normal as well as pathological states (e.g. effects of heart rate, negative intrathoracic pressure, exercise, hemorrhage, heart failure, and hypertension). The degree of disturbance can be set by adjusting the value of single components. Following this, the optimal type of compensation (e.g. the increase in blood volume in failure of the right ventricle; systemic venoconstriction in failure of the left ventricle) of the basic disturbance can be searched for, activated and the consequences studied. The described approach has been found a useful tool in teaching physiology and pathophysiology for postgraduate medical students.

Simulation of cardiovascular physiology: the diastolic function(s) of the heart

The cardiovascular system was simulated by using an equivalent electronic circuit. Four sets of simulations were performed. The basic variables investigated were cardiac output and stroke volume. They were studied as functions (i) of right ventricular capacitance and negative intrathoracic pressure; (ii) of left ventricular relaxation and of heart rate; and (iii) of left ventricle failure. It seems that a satisfactory simulation of systolic and diastolic functions of the heart is possible. Presented simulations improve our understanding of the role of the capacitance of both ventricles and of the diastolic relaxation in cardiovascular physiology.

MODELLING OF RADIONUCLIDE MIGRATION THROUGH THE GEOSPHERE WITH RADIAL BASIS FUNCTION METHOD AND GEOSTATISTICS

Abstract The modelling of radionuclide transport through the geosphere is necessary in the safety assessment of repositories for radioactive waste. A number of key geosphere processes need to be considered when predicting the movement of radionuclides through the geosphere. The most important input data are obtained from field measurements, which are not available for all regions of interest. For example, the hydraulic conductivity, as input parameter, varies from place to place. In such cases geostatistical science offers a variety of spatial estimation procedures. To assess the long term safety of a radioactive waste disposal system, mathematical models are used to describe the complicated groundwater flow, chemistry and potential radionuclide migration through geological formations. The numerical solution of partial differential equations (PDEs) has usually been obtained by finite difference methods (FDM), finite element methods (FEM), or finite volume methods (FVM). Kansa introduced the concept of solving PDEs using radial basis functions (RBFs) for hyperbolic, parabolic and elliptic PDEs. The aim of this study was to present a relatively new approach to the modelling of radionuclide migration through the geosphere using radial basis functions methods and to determine the average and sample variance of radionuclide concentration with regard to spatial variability of hydraulic conductivity modelled by a geostatistical approach. We will also explore residual errors and their influence on optimal shape parameters.

Seismometer self-noise estimation using a single reference instrument

A new method is presented for the self-noise estimation of a seismometer using a single, side-by-side, reference instrument and taking into consideration the misalignment in the orientation of both seismometers. The self-noise of seismometers is extracted directly from the measurements without using any information relating to the transfer functions. This procedure can be applied if the self-noise of the reference seismometer is well known and defined, or if the self-noise of the reference seismometer is sufficiently below the self-noise of the tested instrument and can be neglected. The latter case applies to this study. An algorithm is also developed where we apply self-noise data in order to determine the orientation misalignment between two seismometers, which is then resolved in three-dimensional space. This new method provides an estimate of the self-noise and can also be used to extract some parameters of the installed seismic system in comparison with the reference seismic system, such as generator constants and seismometer orientation or to eliminate unwanted noise sources, which have their origin in the seismic station’s design. The new technique was applied to the CMG-3ESPC and CMG-40T seismometers, where an STS-2 instrument served as the reference seismometer.

The use of equivalent electronic circuits in simulating physiological processes

This paper is a report on one of the modern approaches to teaching physiology to postgraduate medical students. The aim is to promote qualitative as well as quantitative analog thinking about physiological processes. To meet this aim the concept of equivalent electronic circuits was introduced in teaching. Two examples of simulation of physiological phenomena by equivalent electronic circuits are described: (1) a pump for building-up the concentration gradient of a solute and (2) drug distribution in body compartments after single or repeated administration and extracellular volume measurement. The use of the latter circuit in teaching was tested in two generations of postgraduate medical students. They showed an increasing interest for this type of teaching because simulation graphs were almost identical to those shown in textbooks and physicians manuals.

Determination of a seismometer’s generator constant, azimuth, and orthogonality in three-dimensional space using a reference seismometer

To accurately predict the performance of a seismometer, knowledge of its key parameters is required. We present a new method that requires a single reference instrument to estimate some of the important parameters of the seismometer, such as the ratio of the generator constants, the orthogonality deviation, and the rotation in space and in the horizontal plane with regards to the reference instrument. The procedure is performed in the three-dimensional spaces where the Euler rotation theorem is applied in order to define a transformation, which is then used to transform the detection of the reference seismometer as well as the detection of the instrument under test. The estimated transformation matrix is defined as an upper triangular matrix, where its elements contain the information regarding the parameters of the tested seismometer, which are then evaluated using the Euler angles. The new method has been verified on a pair consisting of two STS-2 seismometers and on a pair consisting of one CMG-3T and one STS-2 seismometer.

Simulation of some short-term control mechanisms in cardiovascular physiology

The equivalent electronic circuit, developed to simulate cardiovascular physiology, is upgraded to incorporate negative feedback loops. In this way homeostasis of the arterial pressure is simulated in exercise, in haemorrhage, in the insufficiency of the aortic valve, and in hypervolemia. The results show that homeostasis supports the cardiovascular system by modulating Starling mechanism(s) in exercise, haemorrhage and hypervolemia. In aortic insufficiency it seems that only Starling mechanism(s) can maintain cardiac output and arterial pressure.

A comparison of the effectiveness of using the meshless method and the finite difference method in geostatistical analysis of transport modeling

Disposal of radioactive waste in geological formations is a great concern with regards to nuclear safety. The general reliability and accuracy of transport modeling depends predominantly on input data such as hydraulic conductivity, water velocity, radioactive inventory, and hydrodynamic dispersion. The most important input data are obtained from field measurements, but they are not always available. One way to study the spatial variability of hydraulic conductivity is geostatistics. The numerical solution of partial differential equations (PDEs) has usually been obtained by finite difference methods (FDM), finite element methods (FEM), or finite volume methods (FVM). These methods require a mesh to support the localized approximations. The multiquadric (MQ) radial basis function method is a recent meshless collocation method with global basis functions. Solving PDEs using radial basis function (RBF) collocations is an attractive alternative to these traditional methods because no tedious mesh generation is required. We compare the meshless method, which uses radial basis functions, with the traditional finite difference scheme. In our case we determine the average and standard deviation of radionuclide concentration with regard to spatial variability of hydraulic conductivity that was modeled by a geostatistical approach.

The development and analysis of 3D transformation matrices for two seismometers

The records of ground motion, measured by broadband seismometers, serve for a wide range of scientific research activities. Accordingly, the knowledge of key parameters of seismometers is important for providing reliable results. In most common quality control procedures, the tested seismometer is installed side by side with the reference seismometer. Then, a three-dimensional matrix transforming recordings from one unit to another is needed. The quality of a design of this transformation matrix depends on the mathematical background of a chosen procedure, on the quality of a recorded seismic signal, and on the used bandwidth. In this paper, we present five different mathematical techniques to calculate transformation matrices. One of these techniques is applied in the time domain while the four others use the frequency domain. The methods were verified by two different cases, where different pairs of seismometers were installed on different locations. In all cases, the procedure, reducing the “average” self-noise gives the best result, regards to the decision criteria.

The Influence of Geostatistical Data on the Reliability of the Meshless Method in Transport Modeling

The disposal of radioactive waste in geological formation is of great importance for nuclear safety. A number of key geosphere processes need to be considered when predicting the movement of radionuclides through the geosphere. The main goal of this research is to investigate the influence of geostatistical data on reliability and accuracy of computational modelling. We chose the Kansa meshless method that uses radial basis functions as the mathematical solution technique. The aim of this study is to determine the average and sample variance of radionuclide concentration with regard to spatial variability of hydraulic conductivity modelled by geostatistical approach.