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Keywords = heat pulse velocity

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26 pages, 4943 KiB  
Article
Ultrasonic Pulse Velocity for Real-Time Filament Quality Monitoring in 3D Concrete Printing Construction
by Luis de la Flor Juncal, Allan Scott, Don Clucas and Giuseppe Loporcaro
Buildings 2025, 15(14), 2566; https://doi.org/10.3390/buildings15142566 - 21 Jul 2025
Viewed by 291
Abstract
Three-dimensional (3D) concrete printing (3DCP) has gained significant attention over the last decade due to its many claimed benefits. The absence of effective real-time quality control mechanisms, however, can lead to inconsistencies in extrusion, compromising the integrity of 3D-printed structures. Although the importance [...] Read more.
Three-dimensional (3D) concrete printing (3DCP) has gained significant attention over the last decade due to its many claimed benefits. The absence of effective real-time quality control mechanisms, however, can lead to inconsistencies in extrusion, compromising the integrity of 3D-printed structures. Although the importance of quality control in 3DCP is broadly acknowledged, research lacks systematic methods. This research investigates the feasibility of using ultrasonic pulse velocity (UPV) as a practical, in situ, real-time monitoring tool for 3DCP. Two different groups of binders were investigated: limestone calcined clay (LC3) and zeolite-based mixes in binary and ternary blends. Filaments of 200 mm were extruded every 5 min, and UPV, pocket hand vane, flow table, and viscometer tests were performed to measure pulse velocity, shear strength, relative deformation, yield stress, and plastic viscosity, respectively, in the fresh state. Once the filaments presented printing defects (e.g., filament tearing, filament width reduction), the tests were concluded, and the open time was recorded. Isothermal calorimetry tests were conducted to obtain the initial heat release and reactivity of the supplementary cementitious materials (SCMs). Results showed a strong correlation (R2 = 0.93) between UPV and initial heat release, indicating that early hydration (ettringite formation) influenced UPV and determined printability across different mixes. No correlation was observed between the other tests and hydration kinetics. UPV demonstrated potential as a real-time monitoring tool, provided the mix-specific pulse velocity is established beforehand. Further research is needed to evaluate UPV performance during active printing when there is an active flow through the printer. Full article
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23 pages, 1184 KiB  
Article
Time-Resolved Photoacoustic Response of Thin Semiconductors Measured with Minimal Volume Cell: Influence of Photoinduced Charge Carriers
by Slobodanka P. Galovic, Dragana K. Markushev, Dragan D. Markushev, Katarina Lj. Djordjevic, Marica N. Popovic, Edin Suljovrujic and Dragan M. Todorovic
Appl. Sci. 2025, 15(13), 7290; https://doi.org/10.3390/app15137290 - 28 Jun 2025
Viewed by 226
Abstract
When a semiconducting sample is illuminated by an intensity-modulated monochromatic light beam with photon energy exceeding the band gap, part of the absorbed energy is directly converted into heat through photon–lattice interactions. This gives rise to a heat source that closely follows the [...] Read more.
When a semiconducting sample is illuminated by an intensity-modulated monochromatic light beam with photon energy exceeding the band gap, part of the absorbed energy is directly converted into heat through photon–lattice interactions. This gives rise to a heat source that closely follows the temporal profile of the optical excitation, known as the fast heat source. Simultaneously, another portion of the absorbed energy is used to generate electron-hole pairs. These charge carriers diffuse together and recombine via electron–electron and electron–hole interactions, transferring their kinetic energy to the lattice and producing additional heating of the sample. This indirect heating mechanism, associated with carrier recombination, is referred to as the slow heat source. In this study, we develop a model describing surface temperature variations on the non-illuminated side of a thermally thin semiconductor exposed to a rectangular optical pulse, explicitly accounting for the contribution of surface charge carrier recombinations. Using this model, we investigate the influence of surface recombination velocity and the material’s plasma properties on the time-domain temperature response for both plasma-opaque and plasma-transparent samples. Our results demonstrate that charge carrier recombinations can significantly affect the transient photoacoustic signal recorded using a minimum volume cell, highlighting the potential of time-resolved photoacoustic techniques for probing the electronic properties of semiconductors. Full article
(This article belongs to the Special Issue Advances in Photoacoustic and Photothermal Phenomena)
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13 pages, 3624 KiB  
Article
Quasi-One-Dimensional Thermodynamic Analysis of Radially Expanding Laser-Supported Detonations
by Yuma Itakura, Kyohei Kato, Kimiya Komurasaki, Hokuto Sekine and Hiroyuki Koizumi
Aerospace 2025, 12(7), 584; https://doi.org/10.3390/aerospace12070584 - 28 Jun 2025
Viewed by 295
Abstract
Repetitively pulsed (RP) laser propulsion is regarded as an alternative to chemical rockets for space launches, potentially offering remarkable cost reductions. Understanding the physics of laser-supported detonation (LSD) is important for designing a high-performance propulsion system. Experimentally observed LSD propagation velocities are reportedly [...] Read more.
Repetitively pulsed (RP) laser propulsion is regarded as an alternative to chemical rockets for space launches, potentially offering remarkable cost reductions. Understanding the physics of laser-supported detonation (LSD) is important for designing a high-performance propulsion system. Experimentally observed LSD propagation velocities are reportedly lower than the Chapman–Jouguet (C-J) velocity; hence, a previous study that examined two-dimensional expansion behind the LSD to perform Hugoniot analysis using computational fluid dynamics (CFD) simulation resulted in strong detonation solution. In the present study, the effects of varying the relationship between heating and propagation velocity are investigated using CFD simulations. The findings indicate that a weak detonation solution was obtained with more realistic input of heating rate distribution and the pressure behind the LSD wave was lower than that in C-J detonation by a factor of three. The input LSD propagation velocity was changed by ±30% in the CFD simulation to examine the case of faster propagation in helium and slower propagation in argon and even so, a weak detonation mode was maintained. However, the input relaxation distance from the electron temperature to heavy particle temperature that is shorter in a light gas such as helium can produce a solution of C-J or strong detonation. Full article
(This article belongs to the Special Issue Laser Propulsion Science and Technology (2nd Edition))
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18 pages, 1390 KiB  
Article
Durability and Mechanical Analysis of Basalt Fiber Reinforced Metakaolin–Red Mud-Based Geopolymer Composites
by Ouiame Chakkor
Buildings 2025, 15(12), 2010; https://doi.org/10.3390/buildings15122010 - 11 Jun 2025
Cited by 1 | Viewed by 533
Abstract
Cement is widely used as the primary binder in concrete; however, growing environmental concerns and the rapid expansion of the construction industry have highlighted the need for more sustainable alternatives. Geopolymers have emerged as promising eco-friendly binders due to their lower carbon footprint [...] Read more.
Cement is widely used as the primary binder in concrete; however, growing environmental concerns and the rapid expansion of the construction industry have highlighted the need for more sustainable alternatives. Geopolymers have emerged as promising eco-friendly binders due to their lower carbon footprint and potential to utilize industrial byproducts. Geopolymer mortar, like other cementitious substances, exhibits brittleness and tensile weakness. Basalt fibers serve as fracture-bridging reinforcements, enhancing flexural and tensile strength by redistributing loads and postponing crack growth. Basalt fibers enhance the energy absorption capacity of the mortar, rendering it less susceptible to abrupt collapse. Basalt fibers have thermal stability up to about 800–1000 °C, rendering them appropriate for geopolymer mortars designed for fire-resistant or high-temperature applications. They assist in preserving structural integrity during heat exposure. Fibers mitigate early-age microcracks resulting from shrinkage, drying, or heat gradients. This results in a more compact and resilient microstructure. Using basalt fibers improves surface abrasion and impact resistance, which is advantageous for industrial flooring or infrastructure applications. Basalt fibers originate from natural volcanic rock, are non-toxic, and possess a minimal ecological imprint, consistent with the sustainability objectives of geopolymer applications. This study investigates the mechanical and thermal performance of a geopolymer mortar composed of metakaolin and red mud as binders, with basalt powder and limestone powder replacing traditional sand. The primary objective was to evaluate the effect of basalt fiber incorporation at varying contents (0.4%, 0.8%, and 1.2% by weight) on the durability and strength of the mortar. Eight different mortar mixes were activated using sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions. Mechanical properties, including compressive strength, flexural strength, and ultrasonic pulse velocity (UPV), were tested 7 and 28 days before and after exposure to elevated temperatures (200, 400, 600, and 800 °C). The results indicated that basalt fiber significantly enhanced the performance of the geopolymer mortar, particularly at a content of 1.2%. Specimens with 1.2% fiber showed up to 20% improvement in compressive strength and 40% in flexural strength after thermal exposure, attributed to the fiber’s role in microcrack bridging and structural densification. Subsequent research should concentrate on refining fiber type, dose, and dispersion techniques to improve mechanical performance and durability. Examinations of microstructural behavior, long-term durability under environmental settings, and performance following high-temperature exposure are crucial. Furthermore, investigations into hybrid fiber systems, extensive structural applications, and life-cycle evaluations will inform the practical and sustainable implementation in the buildings. Full article
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20 pages, 1843 KiB  
Article
Fractional Dynamics of Laser-Induced Heat Transfer in Metallic Thin Films: Analytical Approach
by M. A. I. Essawy, Reham A. Rezk and Ayman M. Mostafa
Fractal Fract. 2025, 9(6), 373; https://doi.org/10.3390/fractalfract9060373 - 10 Jun 2025
Viewed by 609
Abstract
This study introduces an innovative analytical solution to the time-fractional Cattaneo heat conduction equation, which models photothermal transport in metallic thin films subjected to short laser pulse irradiation. The model integrates the Caputo fractional derivative of order 0 < p ≤ 1, addressing [...] Read more.
This study introduces an innovative analytical solution to the time-fractional Cattaneo heat conduction equation, which models photothermal transport in metallic thin films subjected to short laser pulse irradiation. The model integrates the Caputo fractional derivative of order 0 < p ≤ 1, addressing non-Fourier heat conduction characterized by finite wave speed and memory effects. The equation is nondimensionalized through suitable scaling, incorporating essential elements such as a newly specified laser absorption coefficient and uniform initial and boundary conditions. A hybrid approach utilizing the finite Fourier cosine transform (FFCT) in spatial dimensions and the Laplace transform in temporal dimensions produces a closed-form solution, which is analytically inverted using the two-parameter Mittag–Leffler function. This function inherently emerges from fractional-order systems and generalizes traditional exponential relaxation, providing enhanced understanding of anomalous thermal dynamics. The resultant temperature distribution reflects the spatiotemporal progression of heat from a spatially Gaussian and temporally pulsed laser source. Parametric research indicates that elevating the fractional order and relaxation time amplifies temporal damping and diminishes thermal wave velocity. Dynamic profiles demonstrate the responsiveness of heat transfer to thermal and optical variables. The innovation resides in the meticulous analytical formulation utilizing a realistic laser source, the clear significance of the absorption parameter that enhances the temperature amplitude, the incorporation of the Mittag–Leffler function, and a comprehensive investigation of fractional photothermal effects in metallic nano-systems. This method offers a comprehensive framework for examining intricate thermal dynamics that exceed experimental capabilities, pertinent to ultrafast laser processing and nanoscale heat transfer. Full article
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31 pages, 7884 KiB  
Article
Magnetic Pulse Welding of Dissimilar Materials: Weldability Window for AA6082-T6/HC420LA Stacks
by Mario A. Renderos Cartagena, Edurne Iriondo Plaza, Amaia Torregaray Larruscain, Marie B. Touzet-Cortina and Franck A. Girot Mata
Metals 2025, 15(6), 619; https://doi.org/10.3390/met15060619 - 30 May 2025
Viewed by 660
Abstract
Magnetic pulse welding (MPW) is a promising solid-state joining process that utilizes electromagnetic forces to create high-speed, impact-like collisions between two metal components. This welding technique is widely known for its ability to join dissimilar metals, including aluminum, steel, and copper, without the [...] Read more.
Magnetic pulse welding (MPW) is a promising solid-state joining process that utilizes electromagnetic forces to create high-speed, impact-like collisions between two metal components. This welding technique is widely known for its ability to join dissimilar metals, including aluminum, steel, and copper, without the need for additional filler materials or fluxes. MPW offers several advantages, such as minimal heat input, no distortion or warping, and excellent joint strength and integrity. The process is highly efficient, with welding times typically ranging from microseconds to milliseconds, making it suitable for high-volume production applications in sectors including automotive, aerospace, electronics, and various other industries where strong and reliable joints are required. It provides a cost-effective solution for joining lightweight materials, reducing weight and improving fuel efficiency in transportation systems. This contribution concerns an application for the automotive sector (body-in-white) and specifically examines the welding of AA6082-T6 aluminum alloy with HC420LA cold-rolled micro-alloyed steel. One of the main aspects for MPW optimization is the determination of the process window that does not depend on the equipment used but rather on the parameters associated with the physical mechanisms of the process. It was demonstrated that process windows based on contact angle versus output voltage diagrams can be of interest for production use for a given component (shock absorbers, suspension struts, chassis components, instrument panel beams, next-generation crash boxes, etc.). The process window based on impact pressures versus impact velocity for different impact angles, in addition to not depending on the equipment, allows highlighting other factors such as the pressure welding threshold for different temperatures in the impact zone, critical transition speeds for straight or wavy interface formation, and the jetting/no jetting effect transition. Experimental results demonstrated that optimal welding conditions are achieved with impact velocities between 900 and 1200 m/s, impact pressures of 3000–4000 MPa, and impact angles ranging from 18–35°. These conditions correspond to optimal technological parameters including gaps of 1.5–2 mm and output voltages between 7.5 and 8.5 kV. Successful welds require mean energy values above 20 kJ and weld specific energy values exceeding 150 kJ/m2. The study establishes critical failure thresholds: welds consistently failed when gap distances exceeded 3 mm, output voltage dropped below 5.5 kV, or impact pressures fell below 2000 MPa. To determine these impact parameters, relationships based on Buckingham’s π theorem provide a viable solution closely aligned with experimental reality. Additionally, shear tests were conducted to determine weld cohesion, enabling the integration of mechanical resistance isovalues into the process window. The findings reveal an inverse relationship between impact angle and weld specific energy, with higher impact velocities producing thicker intermetallic compounds (IMCs), emphasizing the need for careful parameter optimization to balance weld strength and IMC formation. Full article
(This article belongs to the Topic Welding Experiment and Simulation)
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14 pages, 9950 KiB  
Article
Investigation of the Laser Material Interaction of Lithium Copper Foils Under Different Process Gases for All-Solid-State Batteries
by Lars O. Schmidt, Houssin Wehbe, Sven Hartwig and Maja W. Kandula
Batteries 2025, 11(5), 195; https://doi.org/10.3390/batteries11050195 - 15 May 2025
Cited by 1 | Viewed by 552
Abstract
Lithium metal exhibits strong adhesive properties and a highly reactive nature, which complicates conventional mechanical separation methods. Laser cutting, as a contactless process, is possible under a defined drying room atmosphere. However, it is a costly process and therefore not suitable for industrial [...] Read more.
Lithium metal exhibits strong adhesive properties and a highly reactive nature, which complicates conventional mechanical separation methods. Laser cutting, as a contactless process, is possible under a defined drying room atmosphere. However, it is a costly process and therefore not suitable for industrial usage. Consequently, the development of a cost-effective process gas is imperative for the future implementation of lithium metal. In this research, the laser cutting of 30 µm lithium copper composite foil is performed under different process gases (nitrogen and argon) and ambient atmospheres with different water contents to determine the ablation potential depended on the process gas. To assess the laser–material interaction, the impact of pulse repetition frequency and cutting velocity on the material behavior was investigated. To this end, the ablation behavior, the resulting cutting edges, and the electrochemical performance were thoroughly explored. The findings reveal a dependence of the ablation behavior on the water content in the ambient atmosphere, as well as a reduced energy input for a complete shot through when using an inert gas. The resulting cutting edges result in nearly similar outcomes with regard to the heat-affected zone. The electrochemical performance illustrates the influence of the laser process with different gases, taking into account the changed electrochemical impedance spectroscopy. Full article
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25 pages, 7571 KiB  
Article
The Effect of Industrial Byproducts Fly Ash and Quartz Powder on Cement Properties and Environmental Benefits Analysis
by Yonghong Miao, Yudong Luo, Yulong Zheng, Zenian Wang, Zhaochang Zhang, Xiaoyong Wang and Guiyu Zhang
Appl. Sci. 2025, 15(9), 5093; https://doi.org/10.3390/app15095093 - 3 May 2025
Viewed by 505
Abstract
Using industrial byproducts to replace cement is an important way to reduce carbon emissions from the cement industry. In this study, the effects of two industrial byproducts, fly ash (FA) and quartz powder (QZ), as supplementary cementitious materials (SCMs) on the macroscopic properties [...] Read more.
Using industrial byproducts to replace cement is an important way to reduce carbon emissions from the cement industry. In this study, the effects of two industrial byproducts, fly ash (FA) and quartz powder (QZ), as supplementary cementitious materials (SCMs) on the macroscopic properties and microstructure of cement-based materials were experimentally investigated. The results of the compressive strength and ultrasonic pulse velocity experiments showed that QZ significantly mitigated the decrease in strength and ultrasonic pulse velocity caused by the reduction in cement dosage in the early stage. Moreover, the 28-day compressive strength of the FA group was comparable to that of the control group, and regression analysis indicated a negligible effect of FA addition on 28-day compressive strength. X-ray diffraction and Fourier transform infrared spectroscopy experiments showed that QZ can promote the hydration reaction in the early stage. Scanning electron microscopy images revealed that a layer of hydration products can form on the surface of FA after 28 days of hydration. Hydration heat experiments indicated that FA significantly reduces the release of hydration heat, while QZ promotes the formation of ettringite through nucleation effects in the early stage of hydration, thereby accelerating the release of hydration heat. Thermogravimetric analysis after 28 days showed that the amount of hydration products and calcium hydroxide produced decreased with the addition of cementitious materials. Finally, the use of FA and QZ was analyzed for carbon emissions and energy consumption. The results showed that using these two cementitious materials significantly reduces carbon dioxide emissions and energy consumption. Full article
(This article belongs to the Section Civil Engineering)
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17 pages, 4763 KiB  
Article
An Analysis of a Cement Hydration Process Using Glass Waste from Household Appliances as a Supplementary Material
by Karolina Bekerė, Jurgita Malaiškienė and Jelena Škamat
Processes 2025, 13(3), 840; https://doi.org/10.3390/pr13030840 - 13 Mar 2025
Cited by 2 | Viewed by 772
Abstract
Due to the significant increase in consumerism, the amount of household appliance waste has been growing, particularly in the form of glass. This study explores the possibility of using this glass (HAGw) as a replacement additive in cement-based products. The article examines the [...] Read more.
Due to the significant increase in consumerism, the amount of household appliance waste has been growing, particularly in the form of glass. This study explores the possibility of using this glass (HAGw) as a replacement additive in cement-based products. The article examines the properties of HAGw, including its chemical composition (XRF), mineral composition (XRD), particle morphology, and size distribution. Scanning electron microscopy (SEM) analysis revealed that HAGw particles could partially crystallise, forming needle-shaped minerals. When replacing 10%, 20%, and 30% of cement with dispersive HAGw, the rate of cement hydration remains unchanged; however, the amount of heat released decreases proportionally to the amount of waste used. Thermogravimetric analysis indicated that substituting a part of the cement with HAGw reduces the amount of portlandite over longer curing periods, indicating the pozzolanic activity of the glass, while the quantity of calcium silicate hydrates (C-S-H) remains similar to the control sample. In the microstructure of the samples, numerous agglomerates of glass particles are formed, increasing the porosity of the cement matrix and reducing its strength. However, over time, the surface of the glass particles begins to dissolve, leading to the formation of new cement hydrates that gradually fill the voids. This process enhances cement density, increases the ultrasonic pulse velocity, and improves compressive strength, particularly after 90 days, compared to the properties of the samples at 7 and 28 days of curing. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))
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32 pages, 23330 KiB  
Article
Study on the Combustion Behavior of Inhomogeneous Partially Premixed Mixtures in Confined Space
by Yanfei Li, Xin Zhang, Lichao Chen and Ying Liu
Energies 2025, 18(4), 899; https://doi.org/10.3390/en18040899 - 13 Feb 2025
Cited by 1 | Viewed by 632
Abstract
Reasonably configuring the concentration distribution of the mixture to achieve partially premixed combustion has been proven to be an effective method for improving energy utilization efficiency. However, due to the significant influence of concentration non-uniformity and flow field disturbances, the combustion behavior and [...] Read more.
Reasonably configuring the concentration distribution of the mixture to achieve partially premixed combustion has been proven to be an effective method for improving energy utilization efficiency. However, due to the significant influence of concentration non-uniformity and flow field disturbances, the combustion behavior and mechanisms of partially premixed combustion have not been fully understood or systematically analyzed. In this study, the partially premixed combustion characteristics of methane–hydrogen–air mixtures in a confined space were investigated, focusing on the combustion behavior and key parameter variation patterns under different equivalence ratios (0.5, 0.7, 0.9) and hydrogen contents (10%, 20%, 30%, 40%). The global equivalence ratio and degree of partial premixing of the mixture were controlled by adjusting the fuel injection pulse width and ignition timing, thereby regulating the concentration field and flow field distribution within the combustion chamber. The constant-pressure method was used to calculate the burning velocity. Results show that as the mixture formation time decreases, the degree of partial premixing increases, accelerating the heat release process, increasing burning velocity, and shortening the combustion duration. It exhibits rapid combustion characteristics, particularly during the initial combustion phase, where flame propagation speed and heat release rate increase significantly. The burning velocity demonstrates a distinct single-peak profile, with the peak burning velocity increasing and its occurrence advancing as the degree of partial premixing increases. Additionally, hydrogen’s preferential diffusion effect is enhanced with increasing mixture partial premixing, making the combustion process more efficient and concentrated. This effect is particularly pronounced under low-equivalence-ratio (lean burn) conditions, where the combustion reaction rate improves more significantly, leading to greater combustion stability. The peak of the partially premixed burning velocity occurs almost simultaneously with the peak of the second-order derivative of the combustion pressure. This phenomenon highlights the strong correlation between the combustion reaction rate and the dynamic variations in pressure. Full article
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20 pages, 6285 KiB  
Article
The Impact of Differently Prepared Mixed Plastic Waste Granules on the Structure and Properties of Concrete
by Jurgita Malaiškienė, Jelena Škamat, Andrius Kudžma, Renata Boris and Darius Bačinskas
Sustainability 2025, 17(3), 1052; https://doi.org/10.3390/su17031052 - 27 Jan 2025
Viewed by 1429
Abstract
The relatively low production cost and short lifespan of plastic products contribute significantly to the annual accumulation of plastic waste, raising serious environmental concerns. Conventional disposal methods like landfill and incineration not only waste valuable resources but also result in substantial secondary pollution. [...] Read more.
The relatively low production cost and short lifespan of plastic products contribute significantly to the annual accumulation of plastic waste, raising serious environmental concerns. Conventional disposal methods like landfill and incineration not only waste valuable resources but also result in substantial secondary pollution. In response to the imperatives of sustainable development and environmental protection, in this work, different preparation methods (mechanical processing; heating and covering with milled sand and glass; covering plastic granules with polymers and then mineral materials such as microsilica and waste metakaolin; using other chemical additives) for plastic granules from waste and their influence on the properties of cementitious materials were studied. Lightweight concrete properties such as density, ultrasound pulse velocity, flexural and compressive strength, water absorption, and the interaction zone between the cement matrix and plastic granules were analyzed. It was determined that one-third by volume of natural aggregate can be replaced with specially prepared plastic granules from waste, obtaining a bending strength of the lightweight concrete of about 5 MPa, a compressive strength at 28 days of approximately 30 to 35 MPa, a density of about 1850 kg/m3, and an ultrasound pulse velocity of 3900 m/s. Full article
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22 pages, 4284 KiB  
Article
Dynamics of Photoinduced Charge Carrier and Photothermal Effect in Pulse-Illuminated Narrow Gap and Moderate Doped Semiconductors
by Slobodanka Galovic, Katarina Djordjevic, Milica Dragas, Dejan Milicevic and Edin Suljovrujic
Mathematics 2025, 13(2), 258; https://doi.org/10.3390/math13020258 - 14 Jan 2025
Cited by 2 | Viewed by 985
Abstract
When a sample of semiconducting material is illuminated by monochromatic light, in which the photon energy is higher than the energy gap of the semiconductor, part of the absorbed electromagnetic energy is spent on the generation of pairs of quasi-free charge carriers that [...] Read more.
When a sample of semiconducting material is illuminated by monochromatic light, in which the photon energy is higher than the energy gap of the semiconductor, part of the absorbed electromagnetic energy is spent on the generation of pairs of quasi-free charge carriers that are bound by Coulomb attraction. Photo-generated pairs diffuse through the material as a whole according to the density gradients established, carrying part of the excitation energy and charge through the semiconducting sample. This energy is indirectly transformed into heat, where the excess negatively charged electron recombines with a positively charged hole and causes additional local heating of the lattice. The dynamic of the photoexcited charge carrier is described by a non-linear partial differential equation of ambipolar diffusion. In moderate doped semiconductors with a low-level injection of charge carriers, ambipolar transport can be reduced to the linear parabolic partial differential equation for the transport of minority carriers. In this paper, we calculated the spectral function of the photoinduced charge carrier distribution based on an approximation of low-level injection. Using the calculated distribution and inverse Laplace transform, the dynamics of recombination photoinduced heat sources at the surfaces of semiconducting samples were studied for pulse optical excitations of very short and very long durations. It was shown that the photoexcited charge carriers affect semiconductor heating depending on the pulse duration, velocity of surface recombination, lifetime of charge carriers, and their diffusion coefficient. Full article
(This article belongs to the Special Issue Transport Phenomena Equations: Modelling and Applications)
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21 pages, 3054 KiB  
Article
Two-Dimensional Analysis of Air–Water Interaction in Actual Water Pipe-Filling Processes
by Duban A. Paternina-Verona, Oscar E. Coronado-Hernández, Vicente S. Fuertes-Miquel, Alfonso Arrieta-Pastrana and Helena M. Ramos
Water 2025, 17(2), 146; https://doi.org/10.3390/w17020146 - 8 Jan 2025
Cited by 2 | Viewed by 1457
Abstract
This paper investigates air–water interactions during a controlled filling process of an actual water pipeline using a two-dimensional Computational Fluid Dynamics (CFD) model. The main objectives are to understand the dynamic interaction of these fluids through water inflow patterns, pressure pulses, and air-pocket [...] Read more.
This paper investigates air–water interactions during a controlled filling process of an actual water pipeline using a two-dimensional Computational Fluid Dynamics (CFD) model. The main objectives are to understand the dynamic interaction of these fluids through water inflow patterns, pressure pulses, and air-pocket dynamics based on contours. This study uses an existing cast iron pipeline 485 m in length, a nominal diameter of 400 mm, and an air valve with a nominal diameter of 50 mm. The methodology of this CFD model includes the Partial Volume of Fluid (pVoF) method for air–water interface tracking, a turbulence model, mesh sensitivity and numerical validation with pressure and velocity measurements. Results highlight the gradual pressurization of pipelines and air pocket behavior at critical points and show the thermodynamic interaction concerning heat transfer between gas and liquid. This study advances the application of CFD in actual water pipelines, offering a novel approach to air pocket management. Full article
(This article belongs to the Special Issue Design and Management of Water Distribution Systems)
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13 pages, 3913 KiB  
Article
Configuration of Low-Cost Miniature Heat Pulse Probes to Monitor Heat Velocity for Sap Flow Assessments in Wheat (Triticum durum L.)
by Oscar Parra-Camara, Luis A. Méndez-Barroso, R. Suzuky Pinto, Jaime Garatuza-Payán and Enrico A. Yépez
Grasses 2024, 3(4), 320-332; https://doi.org/10.3390/grasses3040024 - 14 Nov 2024
Viewed by 1146
Abstract
Heat velocity (Vh) is a key metric to estimate sap flow which is linked to transpiration rate and is commonly measured using thermocouples implanted in plant stems or tree trunks. However, measuring transpiration rates in the Gramineae family, characterized by thin [...] Read more.
Heat velocity (Vh) is a key metric to estimate sap flow which is linked to transpiration rate and is commonly measured using thermocouples implanted in plant stems or tree trunks. However, measuring transpiration rates in the Gramineae family, characterized by thin and hollow stems, is challenging. Commercially available sensors based on the measurement of heat velocity can be unaffordable, especially in developing countries. In this work, a real-time heat pulse flux monitoring system based on the heat ratio approach was configured to estimate heat velocity in wheat (Triticum durum L.). The heat velocity sensors were designed to achieve optimal performance for a stem diameter smaller than 5 mm. Sensor parameterization included the determination of casing thermal properties, stabilization time, and time to achieve maximum heat velocity which occurred 30 s after applying a heat pulse. Heat velocity sensors were able to track plant water transport dynamics during phenological stages with high crop water demand (milk development, dough development, and end of grain filling) reporting maximum Vh values in the order of 0.004 cm s−1 which scale to sap flow rates in the order of 3.0 g h−1 comparing to reports from other methods to assess sap flow in wheat. Full article
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21 pages, 8600 KiB  
Article
Influence of Detonation Spraying Parameters on the Microstructure and Mechanical Properties of Hydroxyapatite Coatings
by Zhuldyz Sagdoldina, Marcin Kot, Daryn Baizhan, Dastan Buitkenov and Laila Sulyubayeva
Materials 2024, 17(21), 5390; https://doi.org/10.3390/ma17215390 - 4 Nov 2024
Cited by 1 | Viewed by 1184
Abstract
The process of osteointegration depends significantly on the surface roughness, structure, chemical composition, and mechanical characteristics of the coating. In this regard, an important direction in the development of medical materials is the development of new techniques of surface modification and the creation [...] Read more.
The process of osteointegration depends significantly on the surface roughness, structure, chemical composition, and mechanical characteristics of the coating. In this regard, an important direction in the development of medical materials is the development of new techniques of surface modification and the creation of bioactive ceramic coatings. Calcium-phosphate materials based on hydroxyapatite have been proposed as bioactive ceramic coatings on titanium implants for the effective acceleration of bone tissue healing. To obtain bioactive ceramic coatings, pulse power sources are best suited, namely detonation spraying, in which the energy of the explosion of gas mixtures is used as a source of pulse action. The pulse mode of operation in the detonation spraying method is preferable for the formation of bioactive ceramic coatings. It provides a high velocity of hydroxyapatite particles, which promotes their effective fixation on the titanium substrate, while minimizing the heating of the material. This approach preserves the substrate structure and improves the coating adhesion. Four different types of coatings with varying O2/C2H2 molar ratios, ranging from 2.6 to 3.7, were obtained using detonation spraying. Powders and obtained coatings of hydroxyapatite were studied by Raman spectroscopy and XRD structural analysis. The results of XRD phase analysis showed the partial conversion of the hydroxyapatite phase to the α-tricalcium phosphate (α-TCP) phase during the detonation spraying process. The results obtained by Raman spectroscopy indicate that hydroxyapatite is the main phase in coatings. All hydroxyapatite-based coatings exhibited hydrophobic properties, which was confirmed by contact-angle values above 90° in wettability tests, characteristic of hydrophobic surfaces. The adhesive strength of the coatings was measured by the scratch test method. Tribological tests were conducted using the ball-on-disk method under both dry conditions and in Ringer’s solution. This approach enabled the evaluation of wear resistance and friction coefficient of the coatings in different environments, simulating both lubrication-free conditions and those resembling physiological environments. Full article
(This article belongs to the Special Issue Advances in Tribological and Other Functional Properties of Materials)
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