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Found 6423 publications

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

Health issues using 5G frequencies from an engineering perspective: Current review

György Wersényi

Publication Name: Open Engineering

Publication Date: 2022-01-01

Volume: 12

Issue: 1

Page Range: 1060-1077

Description:

The possible adverse health effects of electromagnetic field (EMF) exposure have been in research focus since radio waves were introduced to telecommunication. Broadcast radio systems, satellites, and mobile communication devices use different bands of the radio spectrum, antennas, modulations, and radiated power. The proliferation of cellular networks and mobile phones as user devices have brought transmitting and receiving antennas in the close proximity of the human body and the head. Hundreds of experiments have been conducted to prove and disprove adverse health effects of exposure. Literature reviews of experimental results have also followed the current developments in technology; however, an exhaustive analysis performed on the methodologies has revealed many flaws and problems. This article focuses on the latest results on frequency bands mostly used for 5G below and above 6 GHz in the mmWave band. Current results do not indicate significant health effects and responses below the current safety limits. Nevertheless, further research directions can be identified, especially for mmWave radiation.

Open Access: Yes

DOI: 10.1515/eng-2022-0387

The Effect of Heat Treatment on the Mechanical Properties of Continuously Fibre-Reinforced Standardised Specimens

Robert Magai Balazs Molnar

Publication Name: International Journal of Automotive Science and Technology

Publication Date: 2025-12-17

Volume: 9

Issue: 1st Future of Vehicles Conf.

Page Range: 22-27

Description:

This study investigates the influence of post-printing heat treatments on the mechanical characteristics of 3D-printed specimens strengthened with continuous Kevlar filaments. After their fabrication, the specimens underwent thermal annealing at temperatures of 100 °C and 150 °C for either 1 or 3 hours. To assess the effects of these treatments on mechanical performance, tensile tests and microscopic analyses were performed. The findings indicated that the most significant enhancement was observed in specimens annealed at 150 °C for 1 hour, which resulted in an approximately 20% increase in tensile strength compared to untreated samples. Heat treatments at 100 °C for 1 hour and 3 hours led to moderate improvements of 5–8%, whereas extended treatment at 150 °C for 3 hours resulted in a reduction of about 10% in tensile strength. Microscopy revealed that brief, high-temperature treatment enhanced interlayer bonding and decreased internal stress without harming the structure, while prolonged thermal exposure led to local delamination and compromised fibre–matrix adhesion. These results suggest that controlled post-printing heat treatment can enhance the mechanical properties of continuous fibre-reinforced composites, though excessive heat exposure can lead to degradation. Therefore, careful optimisation of temperature and duration is crucial. The outcomes offer valuable insights for improving the structural performance of additively manufactured continuous fibre-reinforced components.

Open Access: Yes

DOI: 10.30939/ijastech.1752437

Development of a reduced fat and lactose-free dairy spread containing viable lactic acid bacteria – part 1: Technology of manufacture

Gábor Kátay László Varga

Publication Name: Elelmiszervizsgalati Kozlemenyek

Publication Date: 2019-01-01

Volume: 65

Issue: 2

Page Range: 2470-2485

Description:

The popularity of buttercream, considered to be a reduced energy, cheaper version of butter with a better function of use, has been constant in Hungary for three and a half decades. Our objective was to develop a new type of functional buttercream manufacturing technology. In order to achieve this, the pressure value resulting in parameters ensuring the adequate texture and good adsorption of the finished product during the one-stage homogenization of 30% fat cream was determined, as well as to what extent the viscosity of cream and its ease of handling are affected by ho-mogenization. It has been found that the criteria for the homogenization effect can be achieved by single homogenization of a 30% fat cream containing a milk protein con-centrate serving as the raw material for the new type of butter product on a single-stage homogenization machine at 65 °C and 15 MPa (150 bar). Due to the increased viscosity of the cream treated this way, the use of a tubular or scraped-surface heat exchanger is recommended. Our reduced fat, lactose-free buttercream with live cul-ture can be manufactured safely with the technology developed, and with the enzyme and starter cultures used, the lactose content of the product will be less than 0.1%.

Open Access: Yes

DOI: DOI not available

Analysis and Measurement of Bending Stiffness of Wound String According to Higher Order Frequencies

Mate Antali Péter Szalai

Publication Name: Advances in Transdisciplinary Engineering

Publication Date: 2024-01-01

Volume: 59

Issue: Unknown

Page Range: 263-268

Description:

Bass strings of piano are manufactured by winding a wire around a core string. At these strings, the bending stiffness is not negligible. This effect modifies the higher harmonics of the string compared to the harmonic spectrum of the ideal string. This inharmonicity is even more significant in upright pianos. The effect has recently received renewed attention in the literature. In the present paper, the authors present a dynamic measurement for determining the bending stiffness of the piano strings. By using the so-called inharmonicity coefficient, the spectrum of the string is predicted, and the deviation from the ideal string is determined.

Open Access: Yes

DOI: 10.3233/ATDE240554

Multiresolution modeling of cavity resonators in microwave systems

András Fehér Brigita Sziova János Pipek Szilvia Nagy

Publication Name: 2016 13th International Conference on Synthesis Modeling Analysis and Simulation Methods and Applications to Circuit Design Smacd 2016

Publication Date: 2016-07-25

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

Multiresolution analysis or wavelet analysis provides a toolbox not only for signal processing, but also for synthesis of complex systems. Wavelets can be used for modeling complex parts of microwave circuits, such as cavity resonators. The differential equations describing the physical behavior of the device can be discretized using multiple resolutions simultaneously, i.e., high resolutions, where the details of the geometry demand it, and low resolutions, where the geometry is smooth. Using wavelet analysis offers the possibility of systematic and adaptive refinement, where the result is not sufficiently precise. Our method gives an approximation for the error of the solution in order to make it possible to decide, whether refinements are necessary.

Open Access: Yes

DOI: 10.1109/SMACD.2016.7520651

Digital twins in the food supply chain: Taking stock and moving forward

Dániel Róbert Szabó Abderahman Rejeb Karim Rejeb Donia Khalfallah John G. Keogh

Publication Name: Cogent Food and Agriculture

Publication Date: 2026-01-01

Volume: 12

Issue: 1

Page Range: Unknown

Description:

Digital twin technology is transforming food supply chains through real-time monitoring, predictive simulation, and optimization. This study synthesizes existing research on digital twin applications in agri-food systems and identifies intellectual structures, thematic trends, and research gaps. Following PRISMA guidelines, a bibliometric analysis was conducted on 148 Scopus-indexed journal articles published between January 2019 and September 2025, using keyword co-occurrence and bibliographic coupling. Results show a sharp growth in publications since 2021, led mainly by India, Italy, and the United States, with most studies appearing in engineering and computer science journals. Keyword co-occurrence revealed four clusters: technological enablers of digital twins; supply-chain decision-making for resilience and sustainability; postharvest and cold-chain management; and human-centred digital twins for the food industry and precision agriculture. Bibliographic coupling confirmed these themes and indicated a shift from descriptive monitoring toward prescriptive digital twins that actively support decision-making. The review consolidates a fragmented field, highlights current biases such as the focus on horticulture and limited longitudinal validation, and emphasizes the need for interoperability, governance, and standardized metrics. It proposes future research directions for advancing predictive, resilient, and sustainable food systems.

Open Access: Yes

DOI: 10.1080/23311932.2026.2673255

The Hungarian EU Presidency-A newcomer's experience in a novel institutional framework

Balázs Horváthy Réka Friedery

Publication Name: Acta Juridica Hungarica

Publication Date: 2012-03-01

Volume: 53

Issue: 1

Page Range: 103-114

Description:

No description provided

Open Access: Yes

DOI: 10.1556/AJur.53.2012.1.10

Environmental Sustainability, Digitalisation, and the Entrepreneurial Perception of Distances as Drivers of SMEs’ Internationalisation

Roland Zsolt Szabó Borbála Szedmák Anna Tajti Péter Bera

Publication Name: Sustainability Switzerland

Publication Date: 2023-02-01

Volume: 15

Issue: 3

Page Range: Unknown

Description:

The complex relationship between sustainability, digitalization, entrepreneurship and internationalization has received less academic attention, although each of these topics is an important research area on its own. Thus, our research aims to understand the effect of environmental sustainability, the usage of digital systems, and the entrepreneurial perception of distances on the intention to export in the case of SMEs. The authors have developed a survey to examine three main hypotheses. Based on the answers of 315 SMEs, the article highlights that the communication of environmental sustainability, the usage of ERP systems, and the perception of cultural distance as opportunities to foster internationalisation.

Open Access: Yes

DOI: 10.3390/su15032487