Miloš Ivanović

Computer search for trees with minimal ABC index

The ABC index is a degree-based molecular structure descriptor, that found chemical applications. Finding the connected graph(s) of a given order whose ABC index is minimal is a hitherto unsolved problem, but it is known that these must be trees. In this paper, by combining mathematical arguments and computer-based modeling we establish the basic structural features of the minimum-ABC trees.

Adaptive system for dam behavior modeling based on linear regression and genetic algorithms

Most of the existing methods for dam behavior modeling require a persistent set of input parameters. In real-world applications, failures of the measuring equipment can lead to a situation in which a selected model becomes unusable because of the volatility of the independent variables set. This paper presents an adaptive system for dam behavior modeling that is based on a multiple linear regression (MLR) model and is optimized for given conditions using genetic algorithms (GA). Throughout an evolutionary process, the system performs real-time adjustment of regressors in the MLR model according to currently active sensors. The performance of the proposed system has been evaluated in a case study of modeling the Bocac dam (at the Vrbas River located in the Republic of Srpska), whereby an MLR model of the dam displacements has been optimized for periods when the sensors were malfunctioning. Results of the analysis have shown that, under real-world circumstances, the proposed methodology outperforms traditional regression approaches.

Radiology Services Costs and Utilization Patterns Estimates in Southeastern Europe—A Retrospective Analysis from Serbia

OBJECTIVE Assessment of costs matrix and patterns of prescribing of radiology diagnostic, radiation therapy, nuclear medicine, and interventional radiology services. Another aim of the study was insight into drivers of inappropriate resource allocation. METHODS An in-depth, retrospective bottom-up trend analysis of services consumption patterns and expenses was conducted from the perspective of third-party payer, for 205,576 inpatients of a large tertiary care university hospital in Serbia (1,293 beds) from 2007 to 2010. RESULTS A total of 20,117 patients in 2007, 17,436 in 2008, 19,996 in 2009, and 17,579 in 2010 were radiologically examined, who consumed services valued at €2,713,573.99 in 2007, €4,529,387.36 in 2008, €5,388,585.15 in -2009, and €5,556,341.35 in 2010. CONCLUSIONS The macroeconomic crisis worldwide and consecutive health policy measures caused a drop in health care services diversity offered in some areas in the period 2008 to 2009. In spite of this, in total it increased during the time span observed. The total cost of services increased because of a rise in overall consumption and population morbidity. An average radiologically examined patient got one frontal chest graph, each 7th patient got an abdomen ultrasound examination, each 19th patient got a computed tomography endocranium check, and each 25th patient got a head nuclear magnetic resonance. Findings confirm irrational prescribing of diagnostic procedures and necessities of cutting costs. The consumption patterns noticed should provide an important momentum for policymakers to intervene and ensure higher adherence to guidelines by clinicians.

Hemodynamic Flow Modeling Through an Abdominal Aorta Aneurysm Using Data Mining Tools

Geometrical changes of blood vessels, called aneurysm, occur often in humans with possible catastrophic outcome. Then, the blood flow is enormously affected, as well as the blood hemodynamic interaction forces acting on the arterial wall. These forces are the cause of the wall rupture. A mechanical quantity characteristic for the blood-wall interaction is the wall shear stress, which also has direct physiological effects on the endothelial cell behavior. Therefore, it is very important to have an insight into the blood flow and shear stress distribution when an aneurysm is developed in order to help correlating the mechanical conditions with the pathogenesis of pathological changes on the blood vessels. This insight can further help in improving the prevention of cardiovascular diseases evolution. Computational fluid dynamics (CFD) has been used in general as a tool to generate results for the mechanical conditions within blood vessels with and without aneurysms. However, aneurysms are very patient specific and reliable results from CFD analyses can be obtained by a cumbersome and time-consuming process of the computational model generation followed by huge computations. In order to make the CFD analyses efficient and suitable for future everyday clinical practice, we have here employed data mining (DM) techniques. The focus was to combine the CFD and DM methods for the estimation of the wall shear stresses in an abdominal aorta aneurysm (AAA) underprescribed geometrical changes. Additionally, computing on the grid infrastructure was performed to improve efficiency, since thousands of CFD runs were needed for creating machine learning data. We used several DM techniques and found that our DM models provide good prediction of the shear stress at the AAA in comparison with full CFD model results on real patient data.

A 3-D model of ligand transport in a deforming extracellular space

Cells communicate through shed or secreted ligands that traffic through the interstitium. Force-induced changes in interstitial geometry can initiate mechanotransduction responses through changes in local ligand concentrations. To gain insight into the temporal and spatial evolution of such mechanotransduction responses, we developed a 3-D computational model that couples geometric changes observed in the lateral intercellular space (LIS) of mechanically loaded airway epithelial cells to the diffusion-convection equations that govern ligand transport. By solving the 3-D fluid field under changing boundary geometries, and then coupling the fluid velocities to the ligand transport equations, we calculated the temporal changes in the 3-D ligand concentration field. Our results illustrate the steady-state heterogeneities in ligand distribution that arise from local variations in interstitial geometry, and demonstrate that highly localized changes in ligand concentration can be induced by mechanical loading, depending on both local deformations and ligand convection effects. The occurrence of inhomogeneities at steady state and in response to mechanical loading suggest that local variations in ligand concentration may have important effects on cell-to-cell variations in basal signaling state and localized mechanotransduction responses.

Elastic grid resource provisioning with WoBinGO

In this paper, we present the WoBinGO (Work Binder Genetic algorithm based Optimization) framework for solving optimization problems over a Grid. It overcomes the shortcomings of earlier static pilot-job frameworks, by: (1) providing elastic resource provisioning thus avoiding unnecessary occupation of Grid resources; (2) providing friendliness towards other batching queue users thanks to adaptive allocation of jobs with limited lifetime. It hides the complexity of the underlying Grid environment, allowing the users to concentrate on the optimization problems. Theoretical analysis of possible speed-up is presented. An empirical study using an artificial problem, as well as a real-world calibration problem of a leakage model at the Visegrad power plant were performed. The obtained results show that despite WoBinGOs adaptive and frugal allocation of computing resources, it provides significant speed-up when dealing with problems that have computationally expensive evaluations. Moreover, the benchmarks were performed in order to estimate the influence of the limited job lifetime feature on the queuing time of other batching jobs, compared to a static pilot-job infrastructure. Framework for optimization using parallel GA over Grid and HPC resources.Provides elastic resource provisioning avoiding unnecessary occupation of resources.Automatic adaptive allocation of jobs with limited lifetime.Limited job lifetime provides friendliness towards other batching queue users.The complexity of underlying Grid infrastructure is hidden from the user.

Computer program Neutron_CR-39 for simulation of neutrons from an Am–Be source and calculation of proton track profiles

Abstract A computer program called Neutron_CR-39.F90 for neutron simulation through a PADC detector and its detection was described and developed. In this work the neutron Am–Be source was considered for simulation. It was shown that the most intensive secondary particles, created in neutron interactions with the detector, are protons. The programming steps are outlined with detailed description of neutron simulation, determination of latent tracks of created protons, as well as, their development after detector etching in the same and opposite direction of particle motion. The outputs of the code are parameters of created protons (coordinates of starting and stopping points, direction angles of particles, initial and deposited energies) and number of visible tracks per incident neutron. Program summary Program title: Neutron_CR-39 Catalogue identifier: AEIU_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEIU_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 140 004 No. of bytes in distributed program, including test data, etc.: 2 213 012 Distribution format: tar.gz Programming language: Fortran 90 Computer: PCs and workstations Operating system: Unix, Linux, Windows 95+ RAM: 256 MB Classification: 17.5, 18 External routines: For the Windows installation the entire code must be linked with the PORTLIB library. Nature of problem: The neutrons do not cause ionizations in the detector, and consequently no tracks are produced directly by them in the PADC. Due to the elastic and nonelastic interaction of neutrons with the atoms of PADC, recoil nuclei and secondary particles are created producing latent intrinsic tracks. After chemical etching in aqueous NaOH solution these tracks become visible under optical microscope and usually density of visible tracks is measured. Optical microscopes are often used for this purpose but the process is relatively tedious and time consuming. The present computer program has been written for neutron simulation through PADC detector; determination of parameters of secondary particles; calculation track profiles of secondary particles emitted in the same and opposite direction as etchant progression. The outputs of the code are parameters of secondary particles (coordinates of starting and stopping points, direction angles of particles, initial and deposited energies) and number of visible tracks per incident neutron. Solution method: A computer program is prepared to simulate neutronʼs interactions in a PADC by the Monte Carlo method using the Neutron data library ENDF/B-VII [B. Milenkovic, D. Nikezic, N. Stevanovic, Radiat. Meas. 45 (2010) 1338]. The parameters of the emitted secondary particles (emission angle, initial energy, deposited energy and starting and stopping coordinates) were stored in an enclosed file. The subroutine for calculation of track profiles by a finite difference method for particles emitted in the same direction was developed [D. Nikezic, N. Stevanovic, D. Kostic, S. Savovic, K.C.C. Tse, K.N. Yu, Radiat. Meas. 43 (2008) S76]. It was shown that there are many tracks formed in the opposite direction than the etchant progression. The method for calculation of track profiles for these particles is developed in [B. Milenkovic, N. Stevanovic, D. Krstic, D. Nikezic, Radiat. Meas. 44 (2009) 57]. It is very different than the method for track in the same direction. The separate subroutine for this purpose was developed here. Additional comments: The program distribution file contains an executable which enables the program to be run on a Windows machine. The source code is also provided, but in order to build an executable the PORTLIB must be available. Running time: Running time depends mainly on the neutron number for simulation, source and detector geometry and removed layer required by the user. Running time is several minutes.

Software tools for automatic generation of finite element mesh and application of biomechanical calculation in medicine

Cardiovascular diseases are common and a special difficulty in their curing is diagnostics. Modern medical instruments can provide data that is much more adequate for computer modeling. Computer simulations of blood flow through the cardiovascular organs give powerful advantages to scientists today. The motivation for this work is raw data that our Center recently received from the University Clinical center in Heidelberg from a multislice CT scanner. In this work raw data from CT scanner was used for creating a 3D model of the aorta. In this process we used Gmsh, TetGen (Hang Si) as well as our own software tools, and the result was the 8-node (brick) mesh on which the calculation was run. The results obtained were very satisfactory so...

Market risk management in a post-Basel II regulatory environment

We propose a novel method of Mean-Capital Requirement portfolio optimization. The optimization is performed using a parallel framework for optimization based on the Nondominated Sorting Genetic Algorithm II. Capital requirements for market risk include an additional stress component introduced by the recent Basel 2.5 regulation. Our optimization with the Basel 2.5 formula in the objective function produces superior results to those of the old (Basel II) formula in stress scenarios in which the correlations of asset returns change considerably. These improvements are achieved at the expense of reduced cardinality of Pareto-optimal portfolios. This reduced cardinality (and thus portfolio diversification) in periods of relatively low market volatility may have unintended consequences for banks’ risk exposure.

Numerical solution of Stefan problem with variable space grid method based on mixed finite element/finite difference approach

Purpose The purpose of this paper is to improve the accuracy and stability of the existing solutions to 1D Stefan problem with time-dependent Dirichlet boundary conditions. The accuracy improvement should come with respect to both temperature distribution and moving boundary location. Design/methodology/approach The variable space grid method based on mixed finite element/finite difference approach is applied on 1D Stefan problem with time-dependent Dirichlet boundary conditions describing melting process. The authors obtain the position of the moving boundary between two phases using finite differences, whereas finite element method is used to determine temperature distribution. In each time step, the positions of finite element nodes are updated according to the moving boundary, whereas the authors map the nodal temperatures with respect to the new mesh using interpolation techniques. Findings The authors found that computational results obtained by proposed approach exhibit good agreement with the exact solution. Moreover, the results for temperature distribution, moving boundary location and moving boundary speed are more accurate than those obtained by variable space grid method based on pure finite differences. Originality/value The authors’ approach clearly differs from the previous solutions in terms of methodology. While pure finite difference variable space grid method produces stable solution, the mixed finite element/finite difference variable space grid scheme is significantly more accurate, especially in case of high alpha. Slightly modified scheme has a potential to be applied to 2D and 3D Stefan problems.