M. Meilūnas

Numerical simulation of the heat conduction in electrical cables

Abstract The modelling of the heat conduction in electrical cables is a complex mathematical problem. To get a quantitative description of the thermo‐electrical characteristics in the electrical cables, one requires a mathematical model for it. It must involve the different physical phenomena occurring in the electrical cables, i.e. heat conduction, convection and radiation effects, description of heat sources due to current transitions. Since the space in mobile systems is limited and weight is always reduced, wire conductor sizes must be kept as small as possible. Thus the main aim is to determine optimal conductor cross‐sections for long standing loads. In this paper we develop and validate a set of mathematical models and numerical algorithms for the heat transfer simulation in cable bundles. The numerical algorithms are targeted to the two‐dimensional transient heat transfer mathematical models. Finally, a validation procedure for the coefficient validation of the differential equations is carried ou...

Automatic contouring of segmented human brain ischemic stroke region on ct images 1

Abstract Investigation of the relationship between stroke area size and patient status implies evaluation of the stroke area location, volume and shape. Computed tomography (CT) examination became very popular in such type of investigations due to its moderate price and less discomfort for patient in comparison with other techniques. We propose an algorithm for segmented CT images post‐processing, which consists of several stages: filtering of CT slices, smoothing and extension of stroke region boundary, filling of stroke space, and computing of stroke volume via all slices. Post‐processing of several CT images using this technique showed that all accidental points can be filtered successfully and therefore the aim of ischemie stroke area determination can be reached. We are convinced that the quality of initial information (results of stroke area segmentation) plays a crucial role for later image processing.

Generating of reformat slices in neural and cardio‐tomography

Abstract A lot of medical diagnostics problems are related to the reconstruction of three dimension (3D) images from the cross sections of the regions of interest. Such reconstructions are very desirable for evaluation of disease or planning of surgical treatment. This paper reviews recent 3D preprocessing work of authors in human brain blood vessels structure recognition and localization of aneurysms as well as analysis of the right ventricular of the human heart. Here we present some approximation techniques for generation of reformatted images.

An algorithm for partitioning of right heart ventricle medial axis

Abstract A right heart ventricle has a complex and irregular shape, this obscures analysis of ventricle surface movements. We are trying to quantitative evaluate morphological changes of right ventricle surface, these changes appear during heart beat cycle, between different age groups, due to heart diseases, and other factors. A method for such evaluation would open new possibilities for insights into heart function, disease course extrapolation and other. We see this as a multistage task, where the first step is partitioning whole surface into smaller, more manageable regions, and the second step is to analyse each region separately. In this paper we present a new algorithm for partitioning the medial axis of right heart ventricle surface. Such partitioning leads to division of surface into smaller regions with clear shape. The proposed algorithm first computes medial axis from sampled ventricle surface. Later, the medial axis is filtered and smoothed, and third, we compute curvature map and use it as w...

Numerical simulation of the conductivity relaxation in the high resistivity semiconductor

Abstract A theoretical model describing the relaxation of charge carriers in semiconductors of high resistance under the influence of the laser pulses is presented. It is demonstrated that parameters of the trapping states relevant to the processes of the conductivity relaxation can be defined by fitting the experimental data. Time evolution of the conductivity of the GaAs bulk semiconductor under the influence of nanosecond and picosecond laser pulses is considered. Effect of two laser pulses, when the first one results in population of the trapping state and the second one induces its depopulation, is also considered.

Computing Volume of the Heart's Right Ventricle Using 2D Echocardiography Images

AbstractThis paper presents a new way for computing the volume of the hearts right ventricle. The technique involves manual marking of three critical contours of the ventricles regions on 2D echocardiography images. The contours are then deformed semi-automatically to keep them orthogonal and concurrent in four-chamber plane, transverse (short-axis) plane, and lateral plane. The ventricles surface is generated and its volume computed automatically. The proposed model was validated by comparing its estimate with actual measurements using 3D echocardiography imaging.

Numerical analysis of nonlinear model of excited carrier decay

This paper presents a mathematical model for photo-excited carrier decay in a semiconductor. Due to the carrier trapping states and recombination centers in the bandgap, the carrier decay process is defined by the system of nonlinear differential equations. The system of nonlinear ordinary differential equations is approximated by linearized backward Euler scheme. Some a priori estimates of the discrete solution are obtained and the convergence of the linearized backward Euler method is proved. The identifiability analysis of the parameters of deep centers is performed and the fitting of the model to experimental data is done by using the genetic optimization algorithm. Results of numerical experiments are presented.

Glycemia monitoring: The problem of exogenous insulin input

Abstract We present the system of two nonlinear difference‐differential equations with lag which is a mathematical model of self‐regulation of sugar level in blood. We analyze the pathological case, i.e. describe the concrete patients glycemia self‐regulation system and diet. The model helps to determine the dosage and tactics of the traditional insulinotherapy practicing discrete inputs of insulin into the organism with the help of injections.

NUMERICAL METHODS FOR A VISCOUS INCOMPRESSIBLE HEAVY LIQUID MOTION EQUATIONS

Santrauka Darbe nagrinėjamas sunkiojo nespūdžiojo skyscio tekėjimo uždavinys, kai dalis pavirsiaus yra laisva. Skaitiskai sprendžiant tokius uždavinius svarbiausios dviproblemos. Pirmoji—netiesinio Navjė-Stokso uždavinio diskrecioji aproksimacija srityje su fiksuotu pavirsiumi, o antroji problema—judancių pavirsių skaitinis aproksimavimas. Darbe suformuluoti trys algoritmai pagrindiniam uždaviniui spresti. Pirmajame panaudota konstruktyvi Puchnaciovo diferencialinio uždavinio sprendinio egzistencijos įrodymo schema. Siuo metodu iteracinio proceso metu netiesinis Navjė-Stokso uždavinys sprendžiamas fiksuotoje erdvės srityje ir tikslinamas laisvasis srities pavirsius. Tai isskaido uždavinį į du paprastesnius uždavinius, kurių kiekvieno sprendimas yra pakankamai nuodugniai isnagrinėtas literatūroje. Tiriama Puchnaciovo metodo konvergavimo sritis. Antrasis algoritmas gaunamas sprendžiant linearizuotą nestacionarų Navjė-Stokso uždavinį, t.y. nereikalaujame, kad kiekvienoje isorinėje iteracijoje netiesinė diskr...