Search in Publications

Found 6674 publications

Initial value selection of the model parameters in the curve fitting phase of the dynamic SPECT imaging

Balazs Benyo Péter Somogyi Gábor Hesz Katalin Kovacs Zsófia Barna Akos Szlavecz

Publication Name: IFAC Papersonline

Publication Date: 2018-01-01

Volume: 51

Issue: 27

Page Range: 241-246

Description:

The dynamic SPECT (Single Photon Emission Computed Tomography) reconstruction algorithm developed in our prior work reconstructs the parameters of the time activity curve for each image voxel directly from the projection images. In each iterations of the SPECT reconstruction beyond the static 3D MLEM (Maximum Likelihood Expectation Maximization) step, the algorithm performs a fitting process for each voxel in order to estimate the parameters describing the function of the examined organ considering that the time frames are not independent from each other. In real cases the fitted curve is nonlinear function of these parameters, it is usually described as the sum of exponential functions. In order to estimate the parameters properly, an iterative root-finding method is applied. In the current study the Newton-Raphson method is used. The selection of a proper initial value for the root-finding method is critical in order to achieve convergence of the fitting process. If the initial guess is not appropriate, the root-finding algorithm can diverge or converge to an inappropriate parameter set that can result in unacceptable reconstructed parameters. This affects then the subsequent MLEM iterations, also neighboring voxels and breaks the reconstruction. In this work we investigated different methods to calculate the initial values of the fitting process and evaluated the reconstructed parameter set of the dynamic SPECT reconstruction algorithm. Three different methods are investigated, one that uses the fitted parameters of the previous MLEM iteration, one that is based on the sum of the geometrical series of the exponentials and one that calculates the best guess using both methods. The three methods were compared by benchmark reconstruction cases using a mathematical phantom. In each reconstruction different initial value selection method was applied then the time activity curves of the voxels belonging to the same tissue were statistically evaluated using the reconstructed parameters. In the study no significant differences were found in the mean value of the reconstructed parameters. The standard deviation of the parameters was similar between the two simple approaches, however, the combination of the methods resulted in better statistical performance.

Open Access: Yes

DOI: 10.1016/j.ifacol.2018.11.635

Heritability Estimates of Age at First Calving and Correlation Analysis in Angus Cows Bred in Hungary

Szabolcs Bene Judit Márton Ferenc Szabó

Publication Name: Animals

Publication Date: 2024-12-01

Volume: 14

Issue: 24

Page Range: Unknown

Description:

This study aimed to examine the age at first calving (AFC) in Hungarian Angus herds. This study was conducted on the basis of data from 2955 registered cows, classified into five groups (based on different Angus types), and 200 breeding bulls, which were the sires of the cows. The data were made available by the Hungarian Hereford, Angus, and Galloway Breeders’ Association. The variance and covariance components, heritability, breeding value (BV), and genetic trends of AFC between 1998 and 2021 were evaluated. A general linear model (univariate analysis of variance) was used to examine the various effects, while best linear unbiased prediction was used to estimate the population genetic parameters and BV, and linear regression analysis was used for the trend analysis. The average AFC obtained was 28.1 ± 0.1 months (SD = 5.3 months), showing a relatively large variance (CV = 18.9%). The environmental factors that influenced the development of the phenotype were the cow’s birth season (28.99%, p < 0.01), cow’s birth year (28.7%, p < 0.01), the cow’s sire (18.32%, p < 0.01), and the herd (11.77, p < 0.05). The cow’s color variant (8.10%, p > 0.05) was not significant and did not influence the AFC in this study. The direct heritability of AFC (h2 = 0.51 ± 0.06) was higher than data in the literature (0.38 ± 0.05); however, the maternal heritability was low (h2m = 0.00 ± 0.03). The correlation between direct and maternal genetic effects was zero (rdm = −0.97 ± 1.00). The phenotypic trend of AFC increased by +0.03 months per year, which was not statistically significant. The genetic trend calculation showed no significant changes. Based on the h2 and BV results, it seems that selecting a suitable sire can effectively reduce the AFC of daughters. Since AFC is also an important trait in economic terms, it would be appropriate to include AFC BV in the bull catalog.

Open Access: Yes

DOI: 10.3390/ani14243715

Fractal properties of AlGeNi layers on GaAs surfaces

L. M. Molnár Bernadett Varga Imre Mojzes Szilvia Nagy

Publication Name: Vacuum

Publication Date: 2009-08-25

Volume: 84

Issue: 1

Page Range: 251-253

Description:

The thermal interactions of thin AlGe and AlNiGe layers with a bulk GaAs monocrystal were investigated. The heat treatment of these systems was carried out in the working chamber of a scanning electron microscope. The SEM pictures were analysed using a fractal mathematical technique. It was found that the surface of the samples has fractal character. No temperature dependence of the fractal dimension was observed. The samples were also studied using the structural entropy versus filling factor maps of the samples in order to find their localization properties. The SEM pictures of AlGe perform mostly as a Gaussian functions, whereas the AlNiGe samples show usually a behaviour with exponential decay. © 2009 Elsevier Ltd. All rights reserved.

Open Access: Yes

DOI: 10.1016/j.vacuum.2009.06.005

Immigration and competitiveness - some methodological questions

Tünde Patay

Publication Name: Deturope

Publication Date: 2017-01-01

Volume: 9

Issue: 3

Page Range: 207-220

Description:

Immigrants can contribute significantly to the economic and social development of regions or urban areas. Some key figures on migration are thus traditionally used in studies on local development. Beyond the usual description of migratory movements, two research fields are often in the centre of controversies, namely the labour market and the inclusion of immigrants. Comparing the European regions, the phases of urban development as well as the relevant internal and external factors present a mixed picture in Europe. At the same time, the dynamics of migratory movements and the reactions of national and subnational policies also vary. The Member States of the European Union aim to harmonise their definitions and data on migration issues, however, the daily practice leads us to the questions of reliability and comparability of migration statistics; and the interdisciplinary character of migration research offers the use of variable research methods. The aim of this study, as a part of a presentation at a conference on urban development, is to describe some key methodological issues of migration research exploring the typical questions. The first part of the paper calls attention to the importance of data quality, processing and interpretation, describing the research methods mainly used in studies on immigration. The second part summarizes the significance of immigration in regional competitiveness, pointing out the possible "stumbling stones" in the relevant migration studies. Some of these factors, the areas that are mainly in the centre of scientific and political debates, are discussed in this paper, namely the labour market challenges and issues relating to the different aspects of segregation.

Open Access: Yes

DOI: 10.32725/det.2017.030

A new algorithm to determine optimal transfer opportunities in a public transport network

Agoston Winkler

Publication Name: Pollack Periodica

Publication Date: 2009-08-01

Volume: 4

Issue: 2

Page Range: 135-143

Description:

Transfer opportunities play an important role in modeling public transport networks. Finding the optimal transfer locations is essential for providing valuable passenger information in order to support journey planning. Furthermore, using this information makes possible to accelerate general-purpose shortest path algorithms, making transit assignments more efficient. However, determining optimal transfer opportunities in a dense network is not an easy task. This paper presents the principles of a possible solution, and a new algorithm based on them, illustrated with actual examples. The algorithm has a polynomial complexity; therefore it can be used easily in practice.

Open Access: Yes

DOI: 10.1556/Pollack.4.2009.2.14

Efficient fuzzy cognitive modeling for unstructured information

Tamás D. Gedeon László T. Kóczy Kok Wai Wong

Publication Name: IEEE International Conference on Fuzzy Systems

Publication Date: 2006-12-01

Volume: Unknown

Issue: Unknown

Page Range: 358-363

Description:

This paper presents an efficient fuzzy cognitive modeling which can handle granulation, organisation and causation. This cognitive modeling technique consists of multiple levels where the lowest level includes details required to make a decision or to transfer to the next stage. This Fuzzy Cognitive Modeling will enhance the usability of fuzzy theory in modeling complex systems as well as facilitating complex decision making process based on ill structured or missing information or data. © 2006 IEEE.

Open Access: Yes

DOI: 10.1109/FUZZY.2006.1681737

Probabilistic Topology Optimization Framework for Geometrically Nonlinear Structures Considering Load Position Uncertainty and Imperfections

Oveys Ghodousian Hamed Fathnejat R. M. Movahedi Muayad Habashneh

Publication Name: Mathematics

Publication Date: 2024-12-01

Volume: 12

Issue: 23

Page Range: Unknown

Description:

In this manuscript, a novel approach to topology optimization is proposed which integrates considerations of uncertain load positions, thereby enhancing the reliability-based design within the context of structural engineering. Extending the conventional framework to encompass imperfect geometrically nonlinear analyses, this research discovers the intricate interplay between nonlinearity and uncertainty, shedding light on their combined effects on probabilistic analysis. A key innovation lies in treating load position as a stochastic variable, augmenting the existing parameters, such as volume fraction, material properties, and geometric imperfections, to capture the full spectrum of variability inherent in real-world conditions. To address these uncertainties, normal distributions are adopted for all relevant parameters, leveraging their computational efficacy, simplicity, and ease of implementation, which are particularly crucial in the context of complex optimization algorithms and extensive analyses. The proposed methodology undergoes rigorous validation against benchmark problems, ensuring its efficacy and reliability. Through a series of structural examples, including U-shaped plates, 3D L-shaped beams, and steel I-beams, the implications of considering imperfect geometrically nonlinear analyses within the framework of reliability-based topology optimization are explored, with a specific focus on the probabilistic aspect of load position uncertainty. The findings highlight the significant influence of probabilistic design methodologies on topology optimization, with the defined constraints serving as crucial conditions that govern the optimal topologies and their corresponding stress distributions.

Open Access: Yes

DOI: 10.3390/math12233686

Comparative Analysis of Stress Serration Characteristics in AlMg3 Alloys †

Dóra Harangozó Imre Czinege

Publication Name: Engineering Proceedings

Publication Date: 2025-01-01

Volume: 113

Issue: 1

Page Range: Unknown

Description:

Aluminum–magnesium alloys show the Portevin–Le Chatelier (PLC) effect. The aim of this publication is to provide a detailed analysis of the evaluation methods of this phenomenon using tensile tests at a strain rate range of 10−3 s−1, where A and A + B stress serrations can be observed. Four smoothing and analytical functions are evaluated in detail as reference functions, which are compared based on their serration amplitude and frequency characteristics. The studied functions are the moving average and Savitzky–Golay smoothing method, as well as the Voce and polynomial analytic functions. The two smoothing methods and smoothing window sizes are compared to obtain the best reference function parameters.

Open Access: Yes

DOI: 10.3390/engproc2025113026

The finite element modeling of rigid inclusion-supported embankment

E. Koch Rashad Alsirawan

Publication Name: Pollack Periodica

Publication Date: 2022-01-01

Volume: 17

Issue: 2

Page Range: 86-91

Description:

The design of supported embankments on soft soil is a common challenge for civil engineers. This article aims to evaluate the performance of three advanced constitutive models for predicting the behavior of soft soils, i.e., hardening soil, hardening soil model with small-strain stiffness, and soft soil creep. A case study of a rigid inclusion-supported embankment is used for this purpose. Plaxis 3D program was adopted to predict the settlements in subsoil layers and vertical stresses in the load transfer platform. Comparison between field measurements and result of Plaxis 3D modeling was performed. Results demonstrate that soft soil creep model yields predictions in a good agreement with the field measurements, while hardening soil small strain model gives slightly worst predictions.

Open Access: Yes

DOI: 10.1556/606.2021.00504