Periodica Polytechnica (Budapest University of Technology and Economics)
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Exploring the Universe of Lean Startup: A Four-dimensional Review
Full text linkThe lean startup (LS) methodology has become a widely used tool by entrepreneurs around the world. Despite its popularity, there are doubts about its scientific validity, particularly from an academic perspective. This article presents a literature review of the LS methodology. A search was conducted in the Scopus database, and 57 scientific articles were selected for analysis. The results are classified into four main categories: literature review, theoretical development and conceptual framework, measurement and effectiveness testing, and practical application. The findings indicate that while the methodology is still in a developmental phase, it is effective in promoting innovation and adaptability in various business contexts. Future research should focus on quantitative studies and longitudinal research to provide solid empirical evidence of its effectiveness, as well as explore its adaptation to different cultural, industrial, and geographical contexts
Mechanical and Thermal Characterization of Graphene and TiO2-Reinforced 4032 Aluminum Alloy for Piston Applications Using Mean Field Homogenization
Full text linkThe impact of adding graphene and titanium dioxide (TiO2) nanoparticles to a 4032 aluminum alloy for use in piston applications is examined in this paper. Mori-Tanaka micromechanical modelling and mean-field homogenization were used to examine the characteristics of the composites. Mechanically, the findings demonstrated that the graphene-reinforced composite outperformed the TiO2-reinforced composite and the base material without reinforcement in terms of tensile strength, elastic modulus. The TiO2-reinforced composite, however, had a higher Poisson's ratio, suggesting that lateral deformation was more likely when crushed axially. The graphene-reinforced composite also had less overall deformation and density than the TiO2-reinforced composite and showed a lower Poisson's ratio. Thermally, the graphene-reinforced composite exhibited higher thermal conductivity, which was particularly significant for piston cooling, and showed overall higher performance characteristics for piston applications. This study sheds light on the use of Mori-Tanaka modelling and mean-field homogenization to forecast the mechanical and thermal characteristics of metal matrix composites
Investigation of the Thermal Stability of High Energy Ball Milled SiC Nanoparticles Using Thermogravimetric and Differential Thermal Analysis
Full text linkIn this paper, an attempt has been made to analyze the thermal stability of silicon carbide (SiC) particles using thermogravimetric and differential thermal analysis (TGA/DTA). The SiC particles were made by using a high-energy ball milling (HEBM) process to break down micro-sized particles into nano-sized ones. The HEBM was conducted over 60 h, with samples collected at intervals of 15, 30, 45, and 60 h. The samples were further characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to examine changes in crystallinity and particle morphology. XRD analysis revealed shifts in peak positions, indicating structural changes induced by the milling process. SEM and TEM analyses showed a more homogeneous structure in the milled samples. TGA/DTA analysis demonstrated that nanosized SiC particles exhibited reduced thermal stability. Milling for a longer time caused mass loss to increase, ranging from 2% to 4.24%, at temperatures from 30 °C to 1000 °C and a heating rate of 20 °C/min in a nitrogen atmosphere. These findings show that nanosized SiC particles could be useful in high-temperature situations, especially in fields that need materials that are very stable at high temperatures
Adsorption of Phenol Using Activated Carbon Derived from Polystyrene, Paper and Wood Mixtures
Full text linkThe removal of phenol from wastewater is essential due to its toxicity, persistence, and environmental risks. Among various treatment methods, activated carbon (AC) adsorption is widely preferred for its efficiency and cost-effectiveness. This study examines the production of AC from polystyrene (PS), paper, and wood ‒ common components of refuse-derived fuel (RDF) ‒ and evaluates their phenol adsorption capacity. The aim was to assess potential interactions during thermal treatment and their impact on adsorption performance. The results showed that for most mixtures, co-carbonization reduced adsorption capacity compared to separately activated components, indicating negative thermal interactions. However, a positive adsorption-related synergy was observed for the PS/wood mixture. BET surface area analysis revealed that paper-containing mixtures exhibited significantly lower surface areas than expected, likely due to the inhibition of gasification reactions, resulting in reduced adsorption performance. This study highlights how RDF components influence AC properties and provides insights for optimizing waste-derived adsorbents in wastewater treatment
An Improved Design of UWB Slotted Antipodal Vivaldi Antenna for Through-Wall Imaging (TWI) Systems
Full text linkThis paper presents an improved design of an Ultra-Wideband (UWB) Slotted Antipodal Vivaldi Antenna (SAVA) for through-wall imaging (TWI) systems. The antenna, featuring slots on both flares, is designed on a 1.58 mm thick Rogers 5880 material substrate and operates within the 3 GHz to 10 GHz range. The slots, both rectangular and circular, contribute to the improved performance of the antenna. Experimental testing of the fabricated antenna reveals a measured ∣S11∣ of less than or equal to -10 dB and a Voltage Standing Wave Ratio (VSWR) below 2. The antenna exhibits an improved radiation pattern and achieving maximum simulated gain of 11.7 dB within the operating range. The measured results align well with the simulated ones, thereby validating the design method. The proposed design, characterized by a compact aperture width, offers high gain, ultra-wide bandwidth, and directional radiation characteristics. These features make it suitable for TWI systems. This work contributes to the ongoing advancements in antenna design for imaging systems
Investigation of the Applicability of a Hybrid Foaming System in a Mixed Plastic Waste Matrix
Full text linkIn our research, we investigated the chemical foaming of mixed plastic waste granulate (VMHD) using a combination of endothermic and exothermic foaming agents. We found that increasing the exothermic foaming agent improved cell distribution but reduced flexibility and impact resistance. The highest porosity (30.04%) was achieved with 0.5% endothermic and 3.5% exothermic foaming agents. Our results indicate that the proper ratio of foaming agents is crucial for optimizing the mechanical properties of the material
New Cross-section Model for Full Bore Ball-valves
Full text linkThe energy-efficient control of heating systems is a highly perspective issue. Retrofitting old heating systems require flow control valves which can provide linear control of flowrate; therefore, an accurate model is needed to be able to use simulation methods to efficiently optimize these systems. The Simscape toolbox of MATLAB/Simulink, widely used in engineering practice, includes a ball valve model that can be used as a throttle; however, the model may not be sufficiently accurate. In this research, a comprehensive mathematical model describing the flow cross-section of a ball valve is presented. An experimental system was built to be able to verify simulated data, thus validate the developed model. The developed and Simscape model is compared to measured data which shows a significant accuracy improvement. This study presents a new improved ball-valve model that considers the real geometry of the valve providing accurate simulation results, making it possible to simulate retrofitted systems with ball-valves
Safe Robust Framework for Reinforcement Learning-based Control of Indoor Vehicles
Full text linkThe paper presents the design of a safe data-aided steering control for indoor vehicles using the robust supervisory framework. The goal of the method is to achieve the combination of the effective motion with reinforcement learning (RL) based control and the guaranteed safe motion with robust control. The RL-based control through the Proximal Policy Optimization (PPO) method is designed in which actor and critic agents are used. The supervisory robust control is selected in the form with which robust stability against an additional input disturbance can be guaranteed. The effectiveness of the combination through simulations and experimental test scenarios is illustrated. For test purposes, an F1TENTH type small-scaled test vehicle is used, whose lap time is minimized through the proposed control system
Organization of Transport Services and Transport Process Safety
Full text linkThe research aims to address the basic principles and methods of organizing transport and ensuring safety in the transport process to improve the efficiency and security of logistics operations. The study addressed key aspects including selecting the right mode of transport, route planning, selecting reliable carriers, ensuring cargo and vehicle security, staff training, legal compliance and risk management, which helped to optimize logistics operations and minimize risks. Particular attention was devoted to ensuring the safety of cargo and vehicles, including measures to protect against theft, damage and other risks. The study found that the efficient organization of transport services and ensuring the safety of the transport process are key factors in optimizing logistics operations and minimizing risks. An analysis of transport mode selection, route planning and security methods helped identify strategies to improve processes. The importance of choosing reliable carriers and complying with the law confirms the importance of proper management of logistics operations. Effective management of the transport process and safety leads to cost savings and improved customer service. In addition, the study revealed the need for regular staff training in security and effective risk management to successfully implement logistics strategies. Thus, an integrated approach to transport and security is the basis for successful logistics operations. The study provides recommendations for improving transport efficiency and safety, which is of practical importance for logistics companies