CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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The classification of eye diseases from fundus images based on CNN and pretrained models
Get PDFVisual impairment affects more than a billion people worldwide due to insufficient care or inadequate vision screening. Computer-aided diagnosis using deep neural networks is a promising approach, it can analyse and process retinal fundus images, providing valuable reference data for doctors in clinical diagnosis or screening. This study aims to achieve an accurate classification of fundus images, including images of healthy patients as well as those with diabetic retinopathy, cataracts, and glaucoma, using a convolutional neural network (CNN) architecture and several pretrained models (AlexNet, GoogleNet, ResNet18, ResNet50, YOLOv3, and VGG 19). To enhance the training process, a mirror effect technique was applied to augment the volume of data. The experimental study resulted in very satisfactory outcomes, with the GoogleNet model paired with the SGDM optimiser achieving the highest accuracy (92.7 %)
Reverse engineering of pump as turbine for CFD analysis
Get PDFReverse engineering (RE) using 3D scanning is already a relatively technologically simple and cost-effective method. For water turbines, this is particularly true for RE of larger machines. With microturbines, there is a lot of pressure to minimise costs, even at the cost of reduced accuracy. Using an existing micro-PAT (Pump as Turbine) as an example, we showed the approach to assessing these microturbines, starting with scanning the entire internal flow profile of the turbine, reconstructing the surface into a 3D model, and numerically assessing it using CFD (Computational Fluid Dynamics). A different approach is necessary compared to standard large machines, whose dimensions allow troublefree scanning of the flow parts of the turbine. Using CFD, we assessed the reconstructed geometry of the PAT. Two significant findings were made: the importance of high-quality 3D scanning by combining several cheaper 3D scanners and the necessity for reliable in-situ measurements for a successful CFD validation. Our future focus involves optimising PAT runner geometry in turbine mode to enhance energy production at the site and, at the same time, eliminating existing cavitation
Non-homogeneity effect on the vibration of the rectangular visco-elastic plate subjected to the linear temperature effect with quadratic thickness variation in both directions
Get PDFThe present work investigates the effect of non-homogeneity on the vibration of a rectangular visco-elastic plate. The plate is subjected to linear temperature variation in the x-direction with quadratic thickness variation in both directions. The quadratic variation has been considered in the material density of the plate only along the x-axis, and it is assumed that non-homogeneity transpires because of this variation. The governing differential equation is solved using the Rayleigh-Ritz technique. All four edges of the plate should be clamped to drive the frequency equation. Deflection and time period have been evaluated for several combinations of values of the thermal constant, constant of nonhomogeneity, taper constants, and length-to-width ratio (aspect ratio) for the first two vibrationmodes of the clamped plate. The results presented are compared with those found in the literature
Sustainable transitions in age-friendly communities in Europe: a participatory approach
Get PDFThe ageing European population is driving the demand for age-friendly communities that support older individuals’ health and well-being. As communities navigate this transition, Transition Design emerges as a promising approach for addressing complex social and environmental challenges. This study explores the potential of Transition Design to create age-friendly communities in Europe. Drawing on examples from several European countries, this paper describes the key principles of Transition Design and how they can be applied to the development of age-friendly communities. This article highlights the importance of participatory processes in involving older people and other stakeholders in the design process, and discusses the role of technology in creating more accessible and inclusive environments. It also considers some of the challenges of implementing a transition design approach in a European context. In conclusion, this study asserts that Transition Design offers a promising approach for creating sustainable, inclusive, and responsive age-friendly communities
Utilization of high fly ash dosage to reduce cement consumption in concrete formulations
Get PDFThe concrete production is responsible for high proportion of total carbon dioxide emission due to enormous consumption of Portland cement. This traditional binder system is due to high autogenous emission during calcination the main carrier of such negative environmental impact. The effective way to reduce the use of Portland cement is to replace that this binding material exhibiting lower energy demandingness. This paper deals with the utilization of fly ash as Portland cement replacement, which is frequently applied in concrete industry. The paper deals the highest replacement level in accordance with valid regulations. The experimental program was focused on the properties of fresh concrete mixture and basic physical and mechanical properties of hardened concrete. The attained results confirmed good potential of this approach, however the increase of plasticizer dosage was necessary to maintain a similar consistency of fresh mixture. That is why the fresh mixture exhibited lower level of air content
Characteristics of fibres based on secondary raw materials and their use in concrete technology
Get PDFDifferent types of fibres in cementitious composites, particularly in concrete, are currently used for a number of reasons. Fibres are being added to improve mechanical properties (especially steel and glass fibres), to increase the durability – to reduce occurrence of microcracks during the concrete aging (mainly synthetic and cellulose fibres), or to increase the fire resistance (polypropylene fibres). Within the study, characterization of different types of alternative fibres (fibres generated during waste recycling that would otherwise end in incinerators or landfills) with possible use in cementitious composites. These were fibres from recycled PET bottles, paper, and mineral wool, whose properties were compared to the traditionally used cellulose and polypropylene fibres. In the experimental part, the thickness, length, shape, and surface of individual fibres were monitored by an optical microscope. Furthermore, the amount of heat of combustion was determined by the calorimetric method, and the differential thermal analysis (DTA) was carried out for determination of the impact of high temperature on monitored fibres. The microstructure of fibres was monitored using a scanning electron microscope. The focus of the experimental study was on fibres usable in concrete and capable of enduring high temperature stress
EFFECT OF SEGMENT DISLOCATION ON THE MECHANICAL PROPERTIES OF LINED TUNNELS IN A COMPLEX ENVIRONMENT
Get PDFIn complex environments, tunnels with a lined structure are more affected by the dislocation of a segment. This study uses finite element simulations to further investigate the relationship between environmental changes and segments in lined tunnels. Tunnels with and without a lining are simulated under varying strata resistance, buried depth, and water level conditions. The horizontal and vertical displacements and stress changes in the two tunnels are compared when segment dislocation occurs. The results show that the lateral displacement of the tunnel is relatively stable and less influenced by external loads. However, the longitudinal displacement change is the opposite, and it increases significantly when the displacement exceeds 10 mm. When the lined tunnel is subjected to a large external load and misalignment occurs, the performance of the tube sheet joint bolts deteriorates, resulting in a stress decrease. Furthermore, the lined tunnel exhibits an increased ability to resist deformation and does not exactly follow the law of small displacements from small misalignments. When a large misalignment occurs, the lined tunnel may be damaged by elliptical deformation along the 45° direction, and its internal forces would be much larger than those of the unlined tunnel
Plasma treated water as a tool for sustainable applications
Get PDFPlasma treated water was prepared by non-thermal plasma systems using plasma interaction above or inside liquid or in a remote bubbling regime. Plasma treated water prepared from distilled, tap or water solutions was characterised by physical properties (pH, conductivity) and colorimetric determination of stable chemical species (hydrogen peroxide, nitrites, and nitrates). Its quality was evaluated with respect to its possible utilization in sustainable agriculture and medicine applications
Acoustic Radiation Patterns of Different Polygon Piston Surfaces
No full textTransducers are used in acoustic remote sensing and several other modern applications. The radiating surface geometry of a single acoustic transducer affects its beam pattern and has a cumulative effect on the overall performance of an array configuration. In addition, the transducers with polygon radiating surfaces provide more compact structure in an array than the circular pistons due to their flat surface edges. However, until now, the radiation patterns of acoustic polygonal pistons have not been exclusively studied and documented. In this study, the directional factors of acoustic pistons with polygonal surfaces of three to ten sides were derived analytically from the first principle using the Rayleigh integral. These directional factors were used to synthesise and characterise the radiation patterns of the piston sources in comparison with the baffled circular piston of an equivalent surface area. The rectangular, the triangular, and the rest of the polygons have the same performance with the circular piston when the surface diameter is not higher than 0.5λ, 0.28λ and 0.43λ, respectively. The main lobe of the acoustic emissions from the square is very close to that of the circular piston whose diameter is greater than a wavelength while that of the rectangle is wider. The results show that the radiating surface perimeter and symmetry are the two most critical factors affecting the beam characteristics of a piston source rather than the surface area or the number of sides. The theoretical results were validated using the finite element method with an excellent compliance
Understanding intrinsic stress effects on vibrational response of silicon nanowires
Get PDFSilicon nanowires have become integral components in nanoelectromechanical systems and nanoelectronics. This article explores the intricate relationship between intrinsic stress and mechanical behavior in silicon nanowires. Utilizing a comprehensive approach involving Raman characterization, resonance testing, and thermal processing, the study investigates the induced intrinsic stresses within silicon nanowires. The findings reveal the introduction of 1.4G Pa of intrinsic stress and a 1.3 MHz frequency shift to silicon nanowire through thermal processing. These results underscore the importance of understanding and utilizing intrinsic stresses in silicon nanowires for the advancement of nextgeneration nanoelectromechanical systems. Overall, this article contributes to the ongoing efforts aimed at fully realizing the potential of silicon nanowires in various scientific and technological domains