Zoltán Horváth

7102083557

Publications - 36

Estimating the air quality standard exceedance areas and the spatial representativeness of urban air quality stations applying microscale modelling

F. Martín V. Rodrigues J. Bartzis I. Sakellaris Zoltán Horváth X. Jurado N. Reiminger P. Thunis C. Cuvelier S. Janssen J. Sousa E. Rivas L. Tarrason M. G. Villani N. Masey S. Hamilton J. L. Santiago F. Russo J. Stocker R. Jackson G. Tinarelli L. Környei R. San José J. L. Pérez-Camanyo G. Sousa Santos D. Barbero

Publication Name: Science of the Total Environment

Publication Date: 2025-08-01

Volume: 988

Issue: Unknown

Page Range: Unknown

Description:

This study builds upon the findings of a FAIRMODE intercomparison exercise conducted in a district of Antwerp, Belgium, where a comprehensive dataset of air pollutant measurements (air quality stations and passive samplers) was available. Long-term average NO2 concentrations at very high spatial resolution were estimated by several dispersion modelling systems (Martín et al., 2024) to investigate the ability of these to capture the detailed spatial distribution of NO2 concentrations at the microscale in urban environments. In this follow-up research, we extend the analysis by evaluating the capability of these modelling systems to predict the NO2 annual limit value exceedance areas (LVEAs) and spatial representativeness areas (SRAs) for NO₂ at two reference air quality stations. The different modelling approaches used are based on CFD, Lagrangian, Gaussian, and AI-driven models. The different modelling approaches are generally good at predicting the LVEA and SRAs of urban air quality stations, although a small SRA (corresponding to low concentration tolerances or the traffic station) is more difficult to predict correctly. However, there are notable differences in performance among the modelling systems. Those based on CFD models seem to provide more consistent results predicting LVEAs and SRAs. Then, lower accuracy is obtained with AI-based systems, Lagrangian models, and Gaussian models with street canyon parameterizations. The Gaussian models with street-canyon parametrizations show significantly better results than models using simply a Gaussian dispersion parametrization. Furthermore, little differences are observed in most of the statistical indicators corresponding to the LVEA and SRA estimates obtained from the unsteady full month CFD simulations compared to those from the scenario-based CFD simulation methodologies, but there are some noticeable differences in the LVEA or SRA (traffic station, 10 % tolerance) sizes. The number of scenarios does not seem to be relevant to the results. Different bias correction methodologies are explored.

Open Access: Yes

DOI: 10.1016/j.scitotenv.2025.179824

Using dispersion models at microscale to assess long-term air pollution in urban hot spots: A FAIRMODE joint intercomparison exercise for a case study in Antwerp

F. Martín Ákos Kovács V. Rodrigues Bence Liszkai J. Bartzis I. Sakellaris Zoltán Horváth X. Jurado N. Reiminger P. Thunis C. Cuvelier S. Janssen J. Sousa E. Rivas M. G. Villani J. L. Santiago F. Russo J. Stocker R. Jackson G. Tinarelli L. Környei R. San José J. L. Pérez-Camanyo G. Sousa Santos D. Barbero

Publication Name: Science of the Total Environment

Publication Date: 2024-05-15

Volume: 925

Issue: Unknown

Page Range: Unknown

Description:

In the framework of the Forum for Air Quality Modelling in Europe (FAIRMODE), a modelling intercomparison exercise for computing NO2 long-term average concentrations in urban districts with a very high spatial resolution was carried out. This exercise was undertaken for a district of Antwerp (Belgium). Air quality data includes data recorded in air quality monitoring stations and 73 passive samplers deployed during one-month period in 2016. The modelling domain was 800 × 800 m2. Nine modelling teams participated in this exercise providing results from fifteen different modelling applications based on different kinds of model approaches (CFD – Computational Fluid Dynamics-, Lagrangian, Gaussian, and Artificial Intelligence). Some approaches consisted of models running the complete one-month period on an hourly basis, but most others used a scenario approach, which relies on simulations of scenarios representative of wind conditions combined with post-processing to retrieve a one-month average of NO2 concentrations. The objective of this study is to evaluate what type of modelling system is better suited to get a good estimate of long-term averages in complex urban districts. This is very important for air quality assessment under the European ambient air quality directives. The time evolution of NO2 hourly concentrations during a day of relative high pollution was rather well estimated by all models. Relative to high resolution spatial distribution of one-month NO2 averaged concentrations, Gaussian models were not able to give detailed information, unless they include building data and street-canyon parameterizations. The models that account for complex urban geometries (i.e. CFD, Lagrangian, and AI models) appear to provide better estimates of the spatial distribution of one-month NO2 averages concentrations in the urban canopy. Approaches based on steady CFD-RANS (Reynolds Averaged Navier Stokes) model simulations of meteorological scenarios seem to provide good results with similar quality to those obtained with an unsteady one-month period CFD-RANS simulations.

Open Access: Yes

DOI: 10.1016/j.scitotenv.2024.171761

A MILP approach combined with clustering to solve a special petrol station replenishment problem

Tamás Hajba Bálint Psenák Dániel Heitz Zoltán Horváth

Publication Name: Central European Journal of Operations Research

Publication Date: 2024-03-01

Volume: 32

Issue: 1

Page Range: 95-107

Description:

Vehicle routing problem is a well-known optimization problem in the logistics area. A special case of the vehicle routing problem is the station replenishment problem in which different types of fuel types have to be transported from the depots to the customers. In this paper we study the replenishment problem of a European petrol company. The problem contains several additional constraints such as time windows, different sized compartment vehicles, and restrictions on the vehicles that can serve a customer. We introduce a mixed integer linear programming model of the problem. To reduce the size complexity of the MILP model the customers are clustered and, based on the clusters, additional constraints are added to the MILP model. The resulting MILP model is tested on real problems of the company. The results show that combining the MILP model with clustering improves the effectiveness of the model.

Open Access: Yes

DOI: 10.1007/s10100-023-00849-1

A physics-based reduced order model for urban air pollution prediction

L. Környei Gianluigi Rozza Giovanni Stabile Moaad Khamlich Zoltán Horváth

Publication Name: Computer Methods in Applied Mechanics and Engineering

Publication Date: 2023-12-01

Volume: 417

Issue: Unknown

Page Range: Unknown

Description:

This article presents an innovative approach for developing an efficient reduced-order model to study the dispersion of urban air pollutants. The need for real-time air quality monitoring has become increasingly important, given the rise in pollutant emissions due to urbanization and its adverse effects on human health. The proposed methodology involves solving the linear advection–diffusion problem, where the solution of the Reynolds-averaged Navier–Stokes (RANS) equations gives the convective field. At the same time, the source term consists of an empirical time series. However, the computational requirements of this approach, including microscale spatial resolution, repeated evaluation, and low time scale, necessitate the use of high-performance computing facilities, which can be a bottleneck for real-time monitoring. To address this challenge, a problem-specific methodology was developed that leverages a data-driven approach based on Proper Orthogonal Decomposition with regression (POD-R) coupled with Galerkin projection (POD-G) endorsed with the discrete empirical interpolation method (DEIM). The proposed method employs a feedforward Neural Network (NN) to non-intrusively retrieve the reduced-order convective operator required for online evaluation. The numerical framework was validated on synthetic emissions and real wind measurements. The results demonstrate that the proposed approach significantly reduces the computational burden of the traditional approach and is suitable for real-time air quality monitoring. Overall, the study advances the field of reduced order modeling and highlights the potential of data-driven approaches in environmental modeling and large-scale simulations.

Open Access: Yes

DOI: 10.1016/j.cma.2023.116416

Kriging-Assisted Multi-Objective Optimization Framework for Electric Motors Using Predetermined Driving Strategy

Peter Koros György Istenes Zoltan Pusztai Ferenc Friedler Zoltán Horváth

Publication Name: Energies

Publication Date: 2023-06-01

Volume: 16

Issue: 12

Page Range: Unknown

Description:

In this paper, a multi-objective optimization framework for electric motors and its validation is presented. This framework is suitable for the optimization of design variables of electric motors based on a predetermined driving strategy using MATLAB R2019b and Ansys Maxwell 2019 R3 software. The framework is capable of managing a wide range of objective functions due to its modular structure. The optimization can also be easily parallelized and enhanced with surrogate models to reduce the runtime. The framework is validated by manufacturing and measuring the optimized electric motor. The method’s applicability for solving electric motor design problems is demonstrated via the validation process. A test application is also presented, in which the operating points of a predetermined driving strategy provide the input for the optimization. The kriging surrogate model is used in the framework to reduce the runtime. The results of the optimization and the framework’s benefits and drawbacks are discussed through the provided examples, in addition to displaying the properly applicable design processes. The optimization framework provides a ready-to-use tool for optimizing electric motors based on the driving strategy for single- or multi-objective purposes. The applicability of the framework is demonstrated by optimizing the electric motor of a world recorder energy-efficient race vehicle. In this application, the optimization framework achieved a 2% improvement in energy consumption and a 9% increase in speed at a rated DC voltage, allowing the motor to operate at desired working points even with low battery voltage.

Open Access: Yes

DOI: 10.3390/en16124713

Complex-Geometry 3D Computational Fluid Dynamics with Automatic Load Balancing

József Bakosi L. Környei Marc Charest Jacob Waltz Aditya Pandare Mátyás Constans Paula Rutherford Ákos Kovács Zoltán Horváth

Publication Name: Fluids

Publication Date: 2023-05-01

Volume: 8

Issue: 5

Page Range: Unknown

Description:

We present an open-source code, Xyst, intended for the simulation of complex-geometry 3D compressible flows. The software implementation facilitates the effective use of the largest distributed-memory machines, combining data-, and task-parallelism on top of the Charm++ runtime system. Charm++’s execution model is asynchronous by default, allowing arbitrary overlap of computation and communication. Built-in automatic load balancing enables redistribution of arbitrarily heterogeneous computational load based on real-time CPU load measurement at negligible cost. The runtime system also features automatic checkpointing, fault tolerance, resilience against hardware failure, and supports power- and energy-aware computation. We verify and validate the numerical method and demonstrate the benefits of automatic load balancing for irregular workloads.

Open Access: Yes

DOI: 10.3390/fluids8050147

Response to Artificial intelligence-based colorectal polyp histology prediction using narrow-band image-magnifying colonoscopy: a stepping stone for clinical practice

István Rácz Andras Horvath Zoltán Horváth

Publication Name: Clinical Endoscopy

Publication Date: 2022-09-01

Volume: 55

Issue: 5

Page Range: 701-702

Description:

No description provided

Open Access: Yes

DOI: 10.5946/ce.2022.123.1

Multi-objective Optimization of Electric Motors with a Kriging Surrogate Model

György Istenes Zoltán Horváth

Publication Name: 2022 22nd International Symposium on Electrical Apparatus and Technologies Siela 2022 Proceedings

Publication Date: 2022-01-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

Since the electric drive systems are already used in numerous cars and other vehicles as well, the widely varying fields of applications require custom motor design. The most efficient tool for different specified motor designs is the multi-objective optimization tool based on validated simulations. An electrical motor optimization system with a kriging surrogate model based on FEM simulations is developed. The application of this system is presented in this paper. The models and the simulations were created in ANSYS Maxwell and MATLAB. The optimization was performed with the multi-objective genetic optimization algorithm by MATLAB which can be controlled by a simple input-output MATLAB interface.

Open Access: Yes

DOI: 10.1109/SIELA54794.2022.9845694

Artificial Intelligence-Based Colorectal Polyp Histology Prediction by Using Narrow-Band Image-Magnifying Colonoscopy

István Rácz Henriett Regoczi Noemi Kranitz Andras Horvath Gyöngyi Kiss Zoltán Horváth

Publication Name: Clinical Endoscopy

Publication Date: 2022-01-01

Volume: 55

Issue: 1

Page Range: 113-121

Description:

Background/Aims: We have been developing artificial intelligence based polyp histology prediction (AIPHP) method to classify Narrow Band Imaging (NBI) magnifying colonoscopy images to predict the hyperplastic or neoplastic histology of polyps. Our aim was to analyze the accuracy of AIPHP and narrow-band imaging international colorectal endoscopic (NICE) classification based histology predictions and also to compare the results of the two methods. Methods: We studied 373 colorectal polyp samples taken by polypectomy from 279 patients. The documented NBI still images were analyzed by the AIPHP method and by the NICE classification parallel. The AIPHP software was created by machine learning method. The software measures five geometrical and color features on the endoscopic image. Results: The accuracy of AIPHP was 86.6% (323/373) in total of polyps. We compared the AIPHP accuracy results for diminutive and non-diminutive polyps (82.1% vs. 92.2%; p=0.0032). The accuracy of the hyperplastic histology prediction was significantly better by NICE compared to AIPHP method both in the diminutive polyps (n=207) (95.2% vs. 82.1%) (p<0.001) and also in all evaluated polyps (n=373) (97.1% vs. 86.6%) (p<0.001) Conclusions: Our artificial intelligence based polyp histology prediction software could predict histology with high accuracy only in the large size polyp subgroup.

Open Access: Yes

DOI: 10.5946/ce.2021.149

Numerical Simulation of Coupled Electromagnetic and Thermal Problems in Permanent Magnet Synchronous Machines

A. Lotfi Dániel Marcsa V. Chabannes C. Prudhomme Zoltán Horváth

Publication Name: Lecture Notes in Computational Science and Engineering

Publication Date: 2021-01-01

Volume: 139

Issue: Unknown

Page Range: 693-701

Description:

The main objective of our task is to develop mathematical models, numerical techniques to analyse the thermal effects in electric machines, to implement the developed algorithm in multiprocessor or multi-core environments and to apply them to industrial use cases. In this study, we take into account coupled character of the electromagnetic and thermal features of the physical process. Both thermal and electromagnetic processes are considered transient, solved by means of the FEM method on independent meshes and the time-discretization is realized using time operator splitting. Two examples are presented to assess the accuracy of the developed coupled solvers and the numerical results are compared with the experimental ones, which are obtained from a prototype machine.

Open Access: Yes

DOI: 10.1007/978-3-030-55874-1_68

Computation of sensitivity of periodically excited dynamical systems

Mate Antali Zoltán Horváth

Publication Name: Journal of Engineering Mathematics

Publication Date: 2018-12-01

Volume: 113

Issue: 1

Page Range: 123-142

Description:

In the optimization of continuous-time dynamical systems, it can be important to numerically calculate the parametric sensitivity of some long-time-averaged quantities in the system. These computations are challenging for typical numerical methods in the presence of oscillations, which can originate from the internal structure of an autonomous dynamical system or be caused by an external periodic excitation. The case of periodic excitation is motivated by the problem of heat conduction in mechanical parts in engines, where the mean strength of the heat fluctuation can be an important parameter in the engineering design. In this work, approaches to transform periodically excited systems into autonomous systems appropriate for sensitivity analysis were investigated. The least-squares shadowing method is used to compute the sensitivities, and the effect of different kinds of transformation compared. The resulting numerical method is presented using the motivating example of heat conduction.

Open Access: Yes

DOI: 10.1007/s10665-018-9977-3

Invariance Preserving Discretization Methods of Dynamical Systems

Yunfei Song Tamás Terlaky Zoltán Horváth

Publication Name: Vietnam Journal of Mathematics

Publication Date: 2018-12-01

Volume: 46

Issue: 4

Page Range: 803-823

Description:

In this paper, we consider local and uniform invariance preserving steplength thresholds on a set when a discretization method is applied to a linear or nonlinear dynamical system. For the forward or backward Euler method, the existence of local and uniform invariance preserving steplength thresholds is proven when the invariant sets are polyhedra, ellipsoids, or Lorenz cones. Further, we also quantify the steplength thresholds of the backward Euler methods on these sets for linear dynamical systems. Finally, we present our main results on the existence of uniform invariance preserving steplength threshold of general discretization methods on general convex sets, compact sets, and proper cones both for linear and nonlinear dynamical systems.

Open Access: Yes

DOI: 10.1007/s10013-018-0305-z

A novel unified approach to invariance conditions for a linear dynamical system

Yunfei Song Tamás Terlaky Zoltán Horváth

Publication Name: Applied Mathematics and Computation

Publication Date: 2017-04-01

Volume: 298

Issue: Unknown

Page Range: 351-367

Description:

In this paper, we propose a novel, simple, and unified approach to explore sufficient and necessary conditions, i.e., invariance conditions, under which four classic families of convex sets, namely, polyhedra, polyhedral cones, ellipsoids, and Lorenz cones, are invariant sets for a linear discrete or continuous dynamical system. For discrete dynamical systems, we use the Theorems of Alternatives, i.e., Farkas lemma and S-lemma, to obtain simple and general proofs to derive invariance conditions. This novel method establishes a solid connection between optimization theory and dynamical system. Also, using the S-lemma allows us to extend invariance conditions to any set represented by a quadratic inequality. Such sets include nonconvex and unbounded sets. For continuous dynamical systems, we use the forward or backward Euler method to obtain the corresponding discrete dynamical systems while preserves invariance. This enables us to develop a novel and elementary method to derive invariance conditions for continuous dynamical systems by using the ones for the corresponding discrete systems. Finally, some numerical examples are presented to illustrate these invariance conditions.

Open Access: Yes

DOI: 10.1016/j.amc.2016.10.007

Strong stability preserving explicit peer methods

Rüdiger Weiner Helmut Podhaisky Zoltán Horváth

Publication Name: Journal of Computational and Applied Mathematics

Publication Date: 2016-04-01

Volume: 296

Issue: Unknown

Page Range: 776-788

Description:

In this paper we study explicit peer methods up to order p=13 which have the strong stability preserving (SSP) property. This class of general linear methods has the favourable property of a high stage order. The effective SSP coefficient is maximized by solving a nonlinear constraint optimization problem numerically to high precision. The coefficient matrices of the optimized methods are sparse in a very structured way. Linear multistep methods are obtained as a special case of only one stage.

Open Access: Yes

DOI: 10.1016/j.cam.2015.11.005

Integrated urban air pollution dispersion modelling framework and application in air quality prediction of the city of győr

É V.P. Rácz L. Környei Balázs Szintai István Harmati György Istenes Bence Liszkai Péter Zsebők Zoltán Horváth

Publication Name: Harmo 2016 17th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes Proceedings

Publication Date: 2016-01-01

Volume: 2016-May

Issue: Unknown

Page Range: 410-414

Description:

Model accuracy versus model running time - urban air pollution dispersion modellers have to balance between them when selecting models to be implemented. CFD based models seem to be the best candidates for an accurate model that can be validated at urban scale at highest level on the price of a longer running time. In this paper we shall introduce 3DAirQC software framework which addresses a portable and validated CFD model for air quality prediction and control.

Open Access: Yes

DOI: DOI not available

Invariance conditions for nonlinear dynamical systems

Yunfei Song Tamás Terlaky Zoltán Horváth

Publication Name: Springer Optimization and Its Applications

Publication Date: 2016-01-01

Volume: 115

Issue: Unknown

Page Range: 265-280

Description:

Recently,Horváth et al. (Appl Math Comput,submitted) proposed a novel unified approach to study,i.e.,invariance conditions,sufficient and necessary conditions,under which some convex sets are invariant sets for linear dynamical systems. In this paper,by utilizing analogous methodology,we generalize the results for nonlinear dynamical systems. First,the Theorems of Alternatives,i.e.,the nonlinear Farkas lemma and the S-lemma,together with Nagumo’s Theorem are utilized to derive invariance conditions for discrete and continuous systems. Only standard assumptions are needed to establish invariance of broadly used convex sets,including polyhedral and ellipsoidal sets. Second,we establish an optimization framework to computationally verify the derived invariance conditions. Finally,we derive analogous invariance conditions without any conditions.

Open Access: Yes

DOI: 10.1007/978-3-319-42056-1_8

MILP models for the optimization of real production lines

Tamás Hajba Zoltán Horváth

Publication Name: Central European Journal of Operations Research

Publication Date: 2015-12-01

Volume: 23

Issue: 4

Page Range: 899-912

Description:

A special class of the permutation flow shop problems (PFSPs) with makespan minimization which contains repeated jobs, limited buffer sizes between the machines and fixed number of palettes that carry the jobs on the production line is introduced in this paper. We define the related PB-R-PFSP, the Permutation with Repetition Flow Shop Problem with Palettes and Buffers, and construct new mixed integer linear programming (MILP) models for this problem. The effectiveness of the MILP models and the influence of the number of palettes and buffers on the problems are investigated experimentally.

Open Access: Yes

DOI: 10.1007/s10100-014-0337-8

On Preservation of Positivity in Some Finite Element Methods for the Heat Equation

Panagiotis Chatzipantelidis Vidar Thomée Zoltán Horváth

Publication Name: Computational Methods in Applied Mathematics

Publication Date: 2015-10-01

Volume: 15

Issue: 4

Page Range: 417-437

Description:

We consider the initial boundary value problem for the homogeneous heat equation, with homogeneous Dirichlet boundary conditions. By the maximum principle the solution is nonnegative for positive time if the initial data are nonnegative. We complement in a number of ways earlier studies of the possible extension of this fact to spatially semidiscrete and fully discrete piecewise linear finite element discretizations, based on the standard Galerkin method, the lumped mass method, and the finite volume element method. We also provide numerical examples that illustrate our findings.

Open Access: Yes

DOI: 10.1515/cmam-2015-0018

Steplength thresholds for invariance preserving of discretization methods of dynamical systems on a polyhedron

Yunfei Song Tamás Terlaky Zoltán Horváth

Publication Name: Discrete and Continuous Dynamical Systems Series A

Publication Date: 2015-07-01

Volume: 35

Issue: 7

Page Range: 2997-3013

Description:

Steplength thresholds for invariance preserving of three types of discretization methods on a polyhedron are considered. For Taylor approximation type discretization methods we prove that a valid steplength threshold can be obtained by finding the first positive zeros of a finite number of polynomial functions. Further, a simple and efficient algorithm is proposed to numerically compute the steplength threshold. For rational function type discretization methods we derive a valid steplength threshold for invariance preserving, which can be computed by using an analogous algorithm as in the first case. The relationship between the previous two types of discretization methods and the forward Euler method is studied. Finally, we show that, for the forward Euler method, the largest steplength threshold for invariance preserving can be computed by solving a finite number of linear optimization problems.

Open Access: Yes

DOI: 10.3934/dcds.2015.35.2997

Small-scale differences of urban nox exposition in field measurement data

É V.P. Rácz Zoltán Horváth

Publication Name: Wit Transactions on Ecology and the Environment

Publication Date: 2014-09-23

Volume: 191

Issue: Unknown

Page Range: 1513-1522

Description:

Local differences in air pollution levels of different positions of even close points along a street can be dramatic due to mainly meteorological parameters and local geometry. Air pollution monitoring systems provide a huge amount of temporal data, but the number of monitoring sites is far from sufficient for fine spatial investigations. On the other hand, for reliable air pollution modelling and correct prediction of expositions, a more detailed spatial distribution of samples is needed. Small-scale differences and street canyons are often investigated by models. However, such small-scale real field data from direct measurements are rarely available. In this paper we provide evidence by measurements to the existence of significant small-scale differences in air pollution levels and provide data for model validation. Hence, we performed measurements inside a single crossing and along three main roads in the city of Győr. Air samples were sucked into Tedlar bags and NOx concentration was determined by a gas analyser using a chemiluminescent method. On the sampling days manual traffic counting and noise measurements were performed and meteorological data were also taken at the same time. Daily rhythm and spatiotemporal variation of NOx expositions were investigated and compared to traffic data and data from the two monitoring containers of Győr. We observed a similar daily profile as expected in an average workday out of heating season: a sharp peak in the morning and a wider rise of nitrogen oxide concentration in the afternoon. Canyon effects were detected inside the investigated crossing. It caused a difference in pollutant levels of the two sides of the street. Despite a relatively small number of sampling sites, significant differences were detected both inside the crossing level and between main streets at p = 0.055.

Open Access: Yes

DOI: 10.2495/SC141282

On the control of a vehicle dynamics problem

Tihamér A. Kocsis Adrián Németh Zoltán Horváth

Publication Name: 2014 IEEE International Electric Vehicle Conference Ievc 2014

Publication Date: 2014-01-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

In this paper we present an approach to find the controlled invariant sets of a nonlinear dynamical system. Our method explores the state space and determines the set of those initial values where the system can be stabilized with a bounded control function. A continuous closed-loop feedback rule can also be obtained from this procedure. We illustrate the numerical results of our method on a problem describing the behaviour of actuators controlling the lateral dynamics of a vehicle.

Open Access: Yes

DOI: 10.1109/IEVC.2014.7056192

New effective MILP models for PFSPs arising from real applications

Tamás Hajba Zoltán Horváth

Publication Name: Central European Journal of Operations Research

Publication Date: 2013-12-01

Volume: 21

Issue: 4

Page Range: 729-744

Description:

Permutation flow shop problems (PFSPs) with makespan minimization that model production lines working in industry often have some special features: they are typically large-scale and the jobs can be sorted into types so that jobs of the same type have equal processing time values at each machine. We define the related R-PFSP, the Permutation with Repetition Flow Shop Problem, which is of less complexity if the number of types is bounded. Moreover, a subproblem set of R-PFSPs, the RL-PFSP is considered too, where only those permutations are in the design space in which subsequent tuples of a certain size contain jobs of the same type. We construct adequate new MILP models for R-PFSPs and RL-PFSPs and investigate their effectiveness experimentally. We demonstrate that via our new MILP models significantly larger problems can be solved than via the classical MILP models. © 2012 Springer-Verlag.

Open Access: Yes

DOI: 10.1007/s10100-012-0263-6

Integrated experimental design and nonlinear optimization to handle computationally expensive models under resource constraints

János D. Pintér Zoltán Horváth

Publication Name: Journal of Global Optimization

Publication Date: 2013-09-01

Volume: 57

Issue: 1

Page Range: 191-215

Description:

In many real-world applications of optimization, the underlying descriptive system model is defined by computationally expensive functions: simulation modules, numerical models and other "black box" model components are typical examples. In such cases, the model development and optimization team often has to rely on optimization carried out under severe resource constraints. To address this important issue, recently a Regularly Spaced Sampling (RSS) module has been added to the Lipschitz Global Optimizer (LGO) solver suite. RSS generates non-collapsing space filling designs, and produces corresponding solution estimates: this information is passed along to LGO for refinement within the given resource (function evaluation and/or runtime) limitations. Obviously, the quality of the solution obtained will essentially depend both on model instance difficulty and on the admissible computational effort. In spite of this general caveat, our results based on solving a selection of non-trivial global optimization test problems suggest that even a moderate amount of well-placed sampling effort enhanced by limited optimization can lead at least to reasonable or even to high quality results. Our numerical tests also indicate that LGO's overall efficiency is often increased by using RSS as a presolver, both in resource-constrained and in completed LGO runs. © 2012 Springer Science+Business Media, LLC.

Open Access: Yes

DOI: 10.1007/s10898-012-9882-7

Mucosal healing effect of mesalazine granules in naproxen-induced small bowel enteropathy

Milan Szalai Valéria Kovács István Rácz Henriett Regoczi Gyöngyi Kiss Zoltán Horváth

Publication Name: World Journal of Gastroenterology

Publication Date: 2013-01-01

Volume: 19

Issue: 6

Page Range: 889-896

Description:

AIM: To investigate the effect of mesalazine granules on small intestinal injury induced by naproxen using capsule endoscopy (CE). METHODS: This was a single center, non-randomized, open-label, uncontrolled pilot study, using the PillCam SB CE system with RAPID 5 software. The Lewis Index Score (LIS) for small bowel injury was investigated to evaluate the severity of mucosal injury. Arthropathy patients with at least one month history of daily naproxen use of 1000 mg and proton pump inhibitor co-therapy were screened. Patients with a minimum LIS of 135 were eligible to enter the 4-wk treatment phase of the study. During this treatment period, 3 × 1000 mg/d mesalazine granules were added to ongoing therapies of 1000 mg/d naproxen and 20 mg/d omeprazole. At the end of the 4-wk combined treatment period, a second small bowel CE was performed to re-evaluate the enteropathy according to the LIS results. The primary objective of this study was to assess the mucosal changes after 4 wk of mesalazine treatment. RESULTS: A total of 18 patients (16 females), ranging in age from 46 to 78 years (mean age 60.3 years) were screened, all had been taking 1000 mg/d naproxen for at least one month. Eight patients were excluded from the mesalazine therapeutic phase of the study for the following reasons: the screening CE showed normal small bowel mucosa or only insignificant damages (LIS < 135) in five patients, the screening esophagogastroduodenoscopy revealed gastric ulcer in one patient, capsule technical failure and incomplete CE due to poor small bowel cleanliness in two patients. Ten patients (9 female, mean age 56.2 years) whose initial LIS reached mild and moderate-to-severe enteropathy grades (between 135 and 790 and ≥ 790) entered the 4-wk therapeutic phase and a repeat CE was performed. When comparing the change in LIS from baseline to end of treatment in all patients, a marked decrease was seen (mean LIS: 1236.4 ± 821.9 vs 925.2 ± 543.4, P = 0.271). Moreover, a significant difference between pre-and post-treatment mean total LIS was detected in 7 patients who had moderate-tosevere enteropathy gradings at the inclusion CE (mean LIS: 1615 ± 672 vs 1064 ± 424, P = 0.033). CONCLUSION: According to the small bowel CE evaluation mesalazine granules significantly attenuated mucosal injuries in patients with moderate-to-severe enteropathies induced by naproxen. © 2013 Baishideng. All rights reserved.

Open Access: Yes

DOI: 10.3748/wjg.v19.i6.889

Multi-threaded Bacterial Iterated Greedy heuristics for the Permutation Flow Shop Problem

Krisztián Balázs L. T. Koczy Zoltán Horváth

Publication Name: Cinti 2012 13th IEEE International Symposium on Computational Intelligence and Informatics Proceedings

Publication Date: 2012-12-01

Volume: Unknown

Issue: Unknown

Page Range: 63-66

Description:

This paper proposes approaches for combining Iterated Greedy techniques, as state-of-the-art methods, with bacterial evolutionary algorithms based on a hybrid technique involving the Multi-Threaded Iterated Greedy heuristic and a memetic algorithm in order to efficiently solve the Permutation Flow Shop Problem on parallel computing architectures. In the present work three novel approaches are proposed by combining a variant of the Bacterial Memetic Algorithm and the recently proposed Bacterial Iterated Greedy technique with the mentioned hybrid multi-threaded approach. The techniques thus obtained are evaluated via simulation runs carried out on a series of data from the well-known Taillard's benchmark problem set. Based on the experimental results the multi-threaded hybrid methods are compared to each other and to the original techniques (i.e. to the techniques without bacterial algorithms). © 2012 IEEE.

Open Access: Yes

DOI: 10.1109/CINTI.2012.6496734

Pantoprazole before endoscopy in patients with gastroduodenal ulcer bleeding: Does the duration of infusion and ulcer location influence the effects?

Milan Szalai Tibor Kárász István Rácz Nóra Dancs Andrea Szabó Zoltán Horváth Mihály Csöndes

Publication Name: Gastroenterology Research and Practice

Publication Date: 2012-11-19

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

The aim of this study was to investigate the effect of preemptive pantoprazole infusion on early endoscopic findings in patients with acute ulcer bleeding. Records of 333 patients admitted with acute ulcer bleeding were analyzed. Ulcer bleeders were given either 80 mg bolus of pantoprazole followed by continuous infusion of 8 mg per hour or saline infusion until endoscopy. In 93 patients saline infusion whereas in 240 patients bolus plus infusion of pantoprazole was administrated with mean (±SD) durations of 5.45±12.9 hours and 6.9±13.2 hours, respectively (P=0.29). Actively bleeding ulcers were detected in 46/240 (19.2) of cases in the pantoprazole group as compared with 23/93 (24.7) in the saline infusion group (P=0.26). Different durations of pantoprazole infusion (04 hours, >4 hours, and >6 hours) had no significant effect on endoscopic and clinical outcome parameters in duodenal ulcer bleeders. Gastric ulcer bleeders on pantoprazole infusion longer than 4 and 6 hours before endoscopy had actively bleeding ulcers in 4.3 and 5 compared to the 19.5 active bleeding rate in the saline group (P=0.02 and P=0.04). Preemptive infusion of high-dose pantoprazole longer than 4 hours before endoscopy decreased the ratio of active bleeding only in gastric but not in duodenal ulcer patients. © 2012 Istvan Rácz et al.

Open Access: Yes

DOI: 10.1155/2012/561207

Hybrid Bacterial Iterated Greedy heuristics for the Permutation Flow Shop Problem

Krisztián Balázs L. T. Koczy Zoltán Horváth

Publication Name: 2012 IEEE Congress on Evolutionary Computation CEC 2012

Publication Date: 2012-10-04

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

This paper proposes approaches for combining the Iterated Greedy (IG) technique, as a presently state-of-the-art method, with a recently proposed adapted version of the Bacterial Evolutionary Algorithm (BEA) in order to efficiently solve the Permutation Flow Shop Problem. The obtained techniques are evaluated via simulation runs carried out on the well-known Taillard's benchmark problem set. Based on the experimental results the hybrid methods are compared to each other and to the original techniques (i.e. to the original IG and BEA algorithms). © 2012 IEEE.

Open Access: Yes

DOI: 10.1109/CEC.2012.6256167

Different Chromosome-based Evolutionary Approaches for the Permutation Flow Shop Problem

Krisztián Balázs L. T. Koczy Zoltán Horváth

Publication Name: Acta Polytechnica Hungarica

Publication Date: 2012-05-28

Volume: 9

Issue: 2

Page Range: 115-138

Description:

This paper proposes approaches for adapting chromosome-based evolutionary methods to the Permutation Flow Shop Problem. Two types of individual representation (i.e. encoding methods) are proposed, which are applied on three different chromosome based evolutionary techniques, namely the Genetic Algorithm, the Bacterial Evolutionary Algorithm and the Particle Swarm Optimization method. Both representations are applied on the two former methods, whereas one of them is used for the latter optimization technique. Each mentioned algorithm is involved without and with local search steps as one of its evolutionary operators. Since the evolutionary operators of each technique are established according to the applied representation, this paper deals with a total number of ten different chromosome-based evolutionary methods. The obtained techniques are evaluated via simulation runs carried out on the well-known Taillard's benchmark problem set. Based on the experimental results the approaches for adapting chromosome based evolutionary methods are compared to each other.

Open Access: Yes

DOI: DOI not available

Fast tomographic reconstruction on parallel hardware

Gábor Takács G. Veres Zoltán Horváth

Publication Name: Aip Conference Proceedings

Publication Date: 2010-12-01

Volume: 1281

Issue: Unknown

Page Range: 1793-1796

Description:

Tomographic reconstruction is the mathematical procedure of approximating a function f, based on the integrals of f along a set of line sections. The need for fast tomographic reconstruction arises for example in the challenging problem of real time control of some plasma parameters in a fusion reactor. In this paper, we present a fast algorithm for tomographic reconstruction. A good property of our approach is that it fits well to hardware with two levels of parallelism (e.g. a GPU cluster). We also propose an objective evaluation method for measuring the quality of reconstruction on real datasets where f is unknown. We will demonstrate that our algorithm is able to perform more than 50 000 reconstructions per second at reasonably good quality, running on a relatively cheap hardware. © 2010 American Institute of Physics.

Open Access: Yes

DOI: 10.1063/1.3498232

Performance of CFD codes on CPU/GPU clusters

Manfred Liebmann Zoltán Horváth

Publication Name: Aip Conference Proceedings

Publication Date: 2010-12-01

Volume: 1281

Issue: Unknown

Page Range: 1789-1792

Description:

The paper investigates the scalability of a parallel Euler solver, using the Vijayasundaram method, on CPU and GPU clusters. The aim of this research is to develop efficient parallel CFD codes on unstructured meshes. We present the relevant algorithms and some benchmark results, which show overall efficiency of the solver. © 2010 American Institute of Physics.

Open Access: Yes

DOI: 10.1063/1.3498230

Large scale simulations of the euler equations on GPU clusters

Manfred Liebmann Craig C. Douglas Zoltán Horváth Gundolf Haase

Publication Name: Proceedings 9th International Symposium on Distributed Computing and Applications to Business Engineering and Science Dcabes 2010

Publication Date: 2010-11-05

Volume: Unknown

Issue: Unknown

Page Range: 50-54

Description:

The paper investigates the scalability of a parallel Euler solver, using the Vijayasundaram method, on a GPU cluster with 32 Nvidia Geforce GTX 295 boards. The aim of this research is to enable large scale fluid dynamics simulations with up to one billion elements. We investigate communication protocols for the GPU cluster to compensate for the slow Gigabit Ethernet network between the GPU compute nodes and to maintain overall efficiency. A diesel engine intake-port and a nozzle, meshed in different resolutions, give good real world examples for the scalability tests on the GPU cluster. © 2010 IEEE.

Open Access: Yes

DOI: 10.1109/DCABES.2010.17

The value of routine second-look endoscopy in the management of the acute gastroduodenal ulcer bleeding

Tibor Kárász Márta Jánoki Hussam Saleh István Rácz Nóra Dancs Katalin Szocs Andrea Szabó Zoltán Horváth Mihály Csöndes

Publication Name: Orvosi Hetilap

Publication Date: 2009-10-01

Volume: 150

Issue: 42

Page Range: 1932-1936

Description:

The role of routine second-look endoscopy in the management of patients with acute peptic ulcer bleeding is controversial. A more precise identification of higher risk patient group, based on both clinical and endoscopic criteria, is needed to determine whether there are high-risk patients who may benefit from this management strategy. Aim: Or aim was to find out whether scheduled second-look endoscopy has any beneficial effect in the clinical outcome. Methods: Both endoscopic and clinical data were analyzed in 274 acute gastroduodenal ulcer bleeding patients. The need for repeated endoscopic haemostatic intervention was used as a measure to evaluate the potential beneficial effect of the second look endoscopy. Patients were categorized according to the Forrest classification detected during the emergency endoscopy. Results: In the subgroup of actively bleeding patients (Forrest Ia, Ib) a second endoscopic haemostasis was performed in 23.8% of cases. In the patient subgroup with visible vessel ulcers (Forrest IIa) and in those with adherent clot covered ulcers (Forrest IIb) the needs for a repeated haemostasis were 13.0% and 13.3% respectively. Despite the not statistically significant differences, remarkable clinical impact was noted favoring scheduled second look endoscopy in patients with initially active ulcer bleeding. Conclusion: In the light of the retrospective study results it may be concluded that the scheduled second look endoscopy strategy offers a beneficial clinical outcome for selected patients estimated to be a very high risk of re-bleeding following the initial endoscopic therapy for active bleeding.

Open Access: Yes

DOI: 10.1556/OH.2009.28725

On the positivity step size threshold of Runge-Kutta methods

Zoltán Horváth

Publication Name: Applied Numerical Mathematics

Publication Date: 2005-05-01

Volume: 53

Issue: 2-4

Page Range: 341-356

Description:

In the first part of this paper we determine the largest step size of Runge-Kutta (RK) methods for which the corresponding numerical approximations are positive (component-wise non-negative) for arbitrary positive initial vector, whenever the underlying initial value problem (IVP) possesses the related positivity preserving property. We prove that step size thresholds for certain classes of positive IVPs guaranteeing positivity that we derived in a former paper are strict for irreducible and non-confluent RK methods. Investigating the strict positivity step size thresholds we can see that these are rather small if at all positive: often they are, roughly speaking, inverse proportional to the Lipschitz constant of the problem. However, for certain (stiff) IVPs with some particular initial vectors, e.g., for some "smooth" vectors in semi-discretized diffusion problems, we experience preservation of positivity with much larger step sizes than the strict positivity step size threshold. To catch this phenomenon, in the second part of the paper we construct positively invariant sets of positive vectors and derive step size thresholds for the discrete version of the positive invariance. The resulting threshold for discrete positive invariance is, roughly speaking, inverse proportional to the one-sided Lipschitz constant only and is shown in good accordance with some displayed computational experiments. © 2004 IMACS. Published by Elsevier B.V. All rights reserved.

Open Access: Yes

DOI: 10.1016/j.apnum.2004.08.026

On the positivity of matrix-vector products

Zoltán Horváth

Publication Name: Linear Algebra and Its Applications

Publication Date: 2004-12-01

Volume: 393

Issue: 1-3

Page Range: 253-258

Description:

In this paper we examine the positivity of Rv where R∈R N×N, v∈RN, v≥0 with R=r(τA), r is a given (rational) function, A∈RN×N and τ∈(0,∞). Here we mean by positivity the ordering w.r.t. an arbitrary order cone, which includes the classical entrywise positivity of vectors. Since the requirement R≥0 leads to very severe restrictions on r and τ we construct a positive cone ℘=℘(A) and determine τ*=τ*(r,℘) such that r(τA)℘⊂℘ for all τ∈[0,τ*]. Finally we give an example arising from applications to partial differential equations where our results explain actual computations much better than the general theory on R≥0. © 2004 Elsevier Inc. All rights reserved.

Open Access: Yes

DOI: 10.1016/j.laa.2004.03.012

Construction of two-sided bounds for initial-boundary value problems

C. Grossmann Zoltán Horváth

Publication Name: Applied Numerical Mathematics

Publication Date: 2002-08-01

Volume: 42

Issue: 1-3

Page Range: 177-187

Description:

The present paper extends the bounding operator approach developed for boundary value problems to the case of initial-boundary value problems (IBVPs). Following the general principle of bounding operators enclosing methods for the case of partial differential equations are discussed. In particular, continuous discretization methods with an appropriate error bound controlled shift and monotone extensions of Rothe's method for parabolic problems are investigated. © 2001 IMACS. Published by Elsevier Science B.V. All rights reserved.

Open Access: Yes

DOI: 10.1016/S0168-9274(01)00149-0

Positivity of Runge-Kutta and diagonally split Runge-Kutta methods

Zoltán Horváth

Publication Name: Applied Numerical Mathematics

Publication Date: 1998-01-01

Volume: 28

Issue: 2-4

Page Range: 309-326

Description:

In this paper we study positivity of general Runge-Kutta (RK) and diagonally split Runge-Kutta (DSRK) methods when applied to the numerical solution of positive initial value problems for ordinary differential equations. Here we mean by positivity that the nonnegativity of the components of the initial vector is preserved. First we state and prove a theorem that gives conditions under which a general RK or DSRK method is positive on arbitrary positive problem set. Then we study problems which are simultaneously positive and dissipative. For such problems we give the maximal step size that - under a solvability assumption on the algebraic equations defining the method - guarantees positivity. We show how the step size threshold is governed by the radius of positivity, which is an inherent property of the scheme. This result ensures that we can construct DSRK methods which are unconditionally positive and have an order higher than 1. Note that such a method does not exist between the classical methods. Investigating the radius of positivity of RK methods further we can get rid of the additional solvability condition. In this way we can give a complete positivity analysis for RK methods. We calculate the positivity threshold for some methods, which are of practical interest. Finally we prove a theorem which generalizes the well-known result of Bolley and Crouzeix to nonlinear problems. © 1998 Elsevier Science B.V. and IMACS. All rights reserved.

Open Access: Yes

DOI: 10.1016/S0168-9274(98)00050-6