Search Results (173)

This study presents an experimental investigation into the dynamic response and blast resistance of aluminum foam-cored sandwich panels with varied face sheet thicknesses under impulsive loading conditions. The primary focus is on analyzing how the thickness of front and back face sheets affects the deformation behavior and energy absorption capabilities of the sandwich panels. By employing a 3D digital image correlation (3D-DIC) system coupled with post-test analyses, the dynamic responses and permanent deformations were quantitatively characterized. Failure modes of the core layers, front face sheets, and back face sheets were identified and discussed. The results demonstrated that sandwich panels with thick front face sheets exhibited superior blast resistance and energy absorption performance than their thin-front counterparts under high localized impulsive loading. The findings provide important comparative insights about face sheet thickness distribution effects, though further studies with broader thickness variations are needed to establish comprehensive design guidelines. Full article

To enhance the impact resistance and protective performance of ship double-bottom liquid tanks, a liquid storage structure with unequal panel strength was designed. Drop hammer impact experiments and finite element simulations were carried out under ten different working conditions. Based on the experimental and numerical findings, the failure morphology, dynamic response, energy absorption characteristics, and protection mechanisms of the structure were systematically analyzed. By quantifying the plastic limit ratio between the front and rear wall panels, the relationship between strength matching and energy dissipation was revealed. The findings demonstrate that reducing the strength of the rear wall panel promotes large-deflection plastic deformation, which facilitates directional energy dissipation and reduces both the deformation and energy absorption of the bottom panel. Furthermore, the strength matching between the front and rear panels causes asymmetry in the dynamic response during impact. Increasing the plastic limit ratio enhances the protective capability of the structure, providing a valuable reference for the design of unequal-strength double-bottom liquid tanks in ships. Full article

Resin Transfer Molding (RTM) is a widely used composite manufacturing process where liquid resin is injected into a closed mold filled with a fibrous preform. By applying this process, large pieces with complex shapes can be produced on an industrial scale, presenting excellent properties and quality. A true physical phenomenon occurring in the RTM process, especially when using vegetable fibers, is related to the absorption of resin by the fiber during the infiltration process. The real effect is related to the slowdown in the advance of the fluid flow front, increasing the mold filling time. This phenomenon is little explored in the literature, especially for non-isothermal conditions. In this sense, this paper does a numerical study of the liquid injection process in a closed and heated mold. The proposed mathematical modeling considers the radial, three-dimensional, and transient flow, variable injection pressure, and fluid viscosity, including the effect of liquid fluid absorption by the reinforcement (fiber). Simulations were carried out using Computational Fluid Dynamic tools. The numerical results of the filling time were compared with experimental results, and a good approximation was obtained. Further, the pressure, temperature, velocity, and volumetric fraction fields, as well as the transient history of the fluid front position and injection fluid volumetric flow rate, are presented and analyzed. Full article

In carbazole-substituted phthalocyanine complexes 2,3,9,10,16,17,23,24-octakis-(3,6-dibromo-9Hcarbazol) phthalocyaninato zinc(II) (Pc 2) and 2,3,9,10,16,17,23,24-Octakis-(9H-carbazol-9-yl) phthalocyaninato zinc(II) (Pc 4) and their conjugated complexes to graphene quantum dots (GQDs), we studied the nonlinear absorption and propagating of picosecond pulse trains. Each pulse train contains 25 subpulses with width 100 ps seperated by space 13 ns. During the interaction with pulse trains, the structures of Pcs can be simplified to the five-state energy model. In our calculations, the coupled rate equations and two-dimensional paraxial field were solved using the Crank–Nicholson numerical method. The effects of substituted carbazoles and conjugated GQDs were investigated. Pcs and their conjugated complexes with GQDs exhibit optical limiting (OL) properties, and GQDs could decrease the OL of Pcs. One-photon absorption cross section ${\sigma }_{S_0{S}_1}$ or ${\sigma }_{T_1{T}_2}$ is the critical factor to determine the limiting value of energy transmittance in weak- or strong-intensity regions, respectively. The two-step two-photon absorption (TPA) tunnel $(S_0\to S_1)\times (T_1\to T_2)$ is the main absorption mechanism; therefore, the effective population transfer time ${\tau }_{ST}$ from $S_0$ to $T_1$ is another critical factor that is determined by one-photon absorption cross section ${\sigma }_{S_0{S}_1}$ and intersystem crossing time ${\tau }_{isc}$. Through further exploration it is found that a high incident intensity will lead to an asymmetric shape of output intensity due to different absorption mechanisms in the front and latter subpulses of the pulse train. Full article

We report new medium-resolution spectroscopy covering the wavelength range from 0.6 to 2.4 $\mathsf{\mu }$m, as well as multi-epoch, multi-wavelength photometry, of the Class I high-mass embedded young stellar object Mol 12 (IRAS 05373+2349). It is embedded ($A_V\simeq 12$) in the centre of a dense core at a distance of 1.59 kpc from the Sun and has a total luminosity of $1.74\times {10}^3{L}_{\odot }$. The spectra show a large number of permitted atomic emission lines, mostly for Fe, H, C, N, and Ca, that originate in the inner zones of a very active protoplanetary disc and no photospheric absorption lines. Conspicuously, the He I line at 1.0830 $\mathsf{\mu }$m displays a complex P-Cygni profile. Also, the first overtone CO emission band-heads at 2.3 $\mathsf{\mu }$m are seen in emission. From the strengths of the principal emission lines, we determined the accretion rate and luminosity to be $\dot{M}\sim {10}^{-5}{M}_{\odot }$ y⁻¹ and $L_{\mathrm{acc}}\sim {10}^3{L}_{\odot }$, respectively. Decade-long light curves show a series of irregular brightness dips of more than four magnitudes in r, becoming shallower as the wavelength increases and disappearing at $\lambda >3\mathsf{\mu }$m. The colour–magnitude diagrams suggest the occurrence of a series of eclipses caused by the passage of small dust cloudlets in front of the star, producing more than 10 magnitudes of extra extinction. Full article

The biological role of the fluorescence of flowers is a matter of debate. Anthocyanins are a group of compounds that are weakly fluorescent; their fluorescence in flowers has been rarely studied. This study aimed to compare the absorption and fluorescence spectra of anthocyanins extracted from several anthocyanin-containing autumn flowers and examine changes in these spectra during the storage of petals at cold-room and room temperatures and during the storage of dried petals. Petals of red clover Trifolium pratense, pink petunia Petunia × hybrida, Pelargonium horatum, Pelargonium. zonale, Pelargonium. peltatum, red and pink Begonia semperflorens, Buddleja japonica, and purple Chrysanthemum were studied. The results demonstrate that it is possible to distinguish between petals of various flowers based on the absorption spectra of petal extracts and the fluorescence spectra of petal extracts and intact petals. Spectral changes during storage were not always unidirectional and progressive; the most common one was the increase in the intensity of the fluorescence band at 500–560 nm at the excitation wavelength of 460 nm. These results point to the possibility of using fluorescence measurements to identify and estimate the freshness of petal-based material in herbalism, forensic analysis, and the food industry. The measurement of the spectra of whole petals or their fragments by front-face fluorimetry, including common plate readers, may be especially useful due to its simplicity and rapidity. Full article

The rise in temperature worldwide, especially in hot regions with extreme weather conditions, has made climate change one of the critical issues that degrades the solar photovoltaic (PV) system performance. In this paper, a new design of solar cells based on plasmonic thin-film Silver (Ag) technology is introduced. The new design is characterized by enhancing thermal effects, optical power absorption, and output power significantly, thus compensating for the deterioration in the solar cells efficiency when the ambient temperature rises to high levels. The temperature distribution on a PV solar module is determined using a three-dimensional computational fluid dynamics (CFD) model that includes the front glass, crystalline cells, and back sheet. Experimental and analytical results are presented to validate the CFD model. The parameters of temperature distribution, absorbed optical power, and output electrical power are considered to evaluate the device performance during daylight hours in summer. The effects of solar radiation falling on the solar cell, actual temperature of the environment, and wind speed are investigated. The results show that the proposed cells’ temperature is reduced by 1.2 °C thanks to the plasmonic Ag thin-film technology, which leads to enhance 0.48% real value as compared to that in the regular solar cells. Consequently, the absorbed optical power and output electrical power of the new solar cells are improved by 2.344 W and 0.38 W, respectively. Full article

Methanol is a promising low-carbon fuel that can effectively reduce environmental pollution from ships compared to traditional fuels. The timing of methanol injection is a major factor affecting the performance of internal combustion engines, and either too late or too early injection can severely impact the combustion efficiency of an engine. This paper focused on a 4135Aca marine diesel engine produced by the Shanghai Diesel Engine Factory in China. Using CONVERGE/3.0 software for numerical simulation, the study analyzed the impact of methanol injection timing on the combustion and emission characteristics of marine diesel engines. It was found that the determination of methanol injection timing should comprehensively consider the effects of the combustion start point, mixture quality, flame front propagation speed, and evaporation heat absorption. Appropriate methanol injection timing can improve the combustion duration, cylinder pressure, and heat release rate, enhancing the power performance of marine diesel engines. This study shows that methanol injection at −30 °CA can effectively control the in-cylinder combustion process, improve combustion efficiency, and significantly reduce the emissions of pollutants such as soot (by 60.5%), HC (by 3.6%), CO (by 95.3%), etc. However, it can lead to an increase in NOx (by 3.7%) generation under high-temperature conditions. This research can provide a certain reference for the engineering application of methanol direct injection engines for ships. Full article

Polyurethane foam (PF) is a versatile polymer widely used in various applications. By changing the composition of polyol and isocyanate, these foams can be classified into rigid polyurethane foams (PUFRs) and flexible polyurethane foams (PUFFs). The flexible polyurethane foam (PUFFs) is well known for its sound absorption capacities; nevertheless, its flammability poses significant safety hazards. The purpose of this study is to look into how flexible polyurethane foam reacts to fire, specifically its combustion properties, and the risks that come with them. The study aims to find out the rates of horizontal and vertical burning, the make-up of the reaction products, and the temperatures that build up inside the polyurethane foam mass when a support pole is placed in front of the stage and sound-absorbing material is added to stop stage sounds from reverberating. There were performed experiments to determine the fire behavior of the samples in contact with an ignition source in the form of a small flame and experiments to determine the ignition temperature of the sound-absorbing sponge, where it was found that vertical position accelerates combustion, and in practical applications, this aspect must be considered for fire prevention. To determine the combustion gases, several methods were used, namely spectrophotometric, ion chromatography, and gas-chromatographic methods. Analysis of the gases resulting from the combustion of the sound-absorbing sponge indicates the presence of dangerous toxic compounds (hydrogen cyanide, carbon monoxide, and hydrochloric acid), which can endanger human health in the event of a fire. Full article

The timing jitter of a single-photon avalanche diode (SPAD) plays a critical role in the design and optimization of front-end circuits. This paper proposes a simplified timing jitter model based on Verilog-A. This model uses random numbers to determine the locations of photon absorptions and carrier avalanches based on absorption and avalanche probabilities, thereby achieving a calculation of the response time. By introducing photon detection probability, the model has corrected the response time obtained under ideal assumptions and achieved compatibility with excess bias voltage effects, which can describe the Gaussian peak of the timing jitter concisely and effectively. The simulation results are in good agreement with the measurement results, demonstrating the advantages of this model in terms of accuracy, flexibility, and adaptability. The model provides support for the collaborative optimization of the design of SPAD devices and circuits. Full article

The Helmholtz resonance acoustic metamaterial is an effective sound absorber in the field of noise reduction, especially in the low-frequency domain. To overcome the conflict between the number of Helmholtz resonators and the volume of the rear cavity for each chamber with a given front area of single-layer metamaterial, a novel acoustic metamaterial of interlayer parallel connection of multiple Helmholtz resonators (IPC–MHR) is proposed in this study. The developed IPC–MHR consists of several layers, and the Helmholtz resonators among different layers are connected in parallel. The sound absorption property of IPC–MHR is studied by finite element simulation and further optimized by particle swarm optimization algorithm, and it is validated by standing wave tube measurement with the sample fabricated by additive manufacturing. The average sound absorption coefficient in the discrete frequency band [200 Hz, 300 Hz] U [400 Hz, 600 Hz] U [800 Hz, 1250 Hz] is 0.7769 for the IPC–MHR with four layers. Through the optimization of the thickness of each layer, the average sound absorption coefficient in 250–750 Hz is up to 0.8068. Similarly, the optimized IPC–MHR with six layers obtains an average sound absorption coefficient of 0.8454 in 300–950 Hz, which exhibits an excellent sound absorption performance in the low-frequency range with a wide band. The IPC–MHR can be used to suppress obnoxious noise in practical applications. Full article

Ternary lithium-ion batteries (LIBs) have the advantages of high energy density and high charging efficiency, and they are the preferred energy source for long-life new energy vehicles. However, when thermal runaway (TR) occurs in the ternary LIB, an open flame is easily produced. The burning phenomenon is intense, and the rapid of TR propagation is high; consequently, vehicle-level fire accidents are easily induced. These accidents have become the biggest obstacle restricting the batteries’ development. Therefore, this study investigates the TR behavior of ternary LIBs at the cell and module levels. The addition of an insulation layer alone, including ceramic nano fibers, glass fiber aerogel, and phase-change composite materials, cannot prevent TR propagation. To completely block the TR propagation, we developed a safety prevention strategy, combining the phase-change composite materials with a commercial liquid cooling plate. This approach provides a three-level TR protection mechanism that includes heat absorption, heat conduction, and heat insulation. The use of a 2 mm thick phase change composite material combined with a liquid cooling plate effectively prevents the TR propagation between60 Ah ternary LIBs with 100%SOCs.. The front surface temperature of the adjacent cell is maintained near 90 °C, with its maximum temperature consistently stays below 100 °C. This study successfully demonstrates the blockage of TR propagation and offers valuable insights for the thermal safety design of high-specific-energy LIBs; the aim is to improve the overall safety of battery packs in practical applications. Full article

Respiratory diseases pose a significant threat to global public health, as exemplified by the COVID-19 pandemic. Molecular communication (MC), as a new method in communication systems, provides a framework for the modeling of diseases. Current studies, however, largely restrict MC models to transmission scenarios involving a single source and single receiver, leaving scenarios with multiple receivers insufficiently explored. This study investigates respiratory virus transmission through air, applying a single-input-multiple-output (SIMO) MC model to analyze the in vitro transmission process. In this context, a COVID-19-positive individual can transmit the virus to multiple recipients, modeled as a SIMO MC system where the affected person is the transmitter, susceptible individuals are receivers, and the intervening air serves as the communication channel. A theoretical model is developed to elucidate the virus transmission process, yielding foundational analytical expressions for the absorption probability. Numerical data validate the model and reveal factors influencing the cumulative reception probability. The results indicate that both the distance and angle between the transmitter and receiver significantly impact the absorption probability, which decreases with increasing distance and angle. Optimal absorption occurs when the receiver is directly in front of the emitter. These findings introduce a new perspective on viral transmission mechanisms and provide a scientific basis for future prevention and control measures. Full article

Approximate analytical solutions to a degenerate reaction–diffusion model with power-law absorption (source) and production (sink) terms have been developed. The integral-balance method applied to a preliminary transformed model and by a direct integration approach has provided physically reasonable results. The model equation scaling has revealed the characteristic length and times scales and the Fourier number as the controlling dimensionless group. Full article

This study presents numerical and experimental investigations on an oscillating water column (OWC) wave energy device integrated into a sloping breakwater. Regular waves were generated in a physical wave tank to investigate the hydrodynamic performance and extraction efficiency of the small-scale nested OWC device. Simultaneously, to complement various scenarios, numerical simulations were conducted using the open-source computational fluid dynamics platform OpenFOAM. The volume of fluid (VOF) method was employed to capture the complex evolution of the air–water interface, and an artificial source term (Forchheimer flow region) was introduced into the Navier–Stokes equations to replace the power take-off (PTO) system. By analyzing wave reflection properties, energy absorption efficiency, and wave run-up, the hydrodynamic characteristics of the inclined OWC device were explored. The comparison between the numerical and experimental results indicate a good consistence. A smaller front wall draft broadens the high-efficiency frequency bandwidth. For relatively long waves, increasing the air chamber width enhances energy conversion efficiency and reduces wave run-up. The optimal configuration was achieved with the following dimensionless parameters: front wall draft $a/h=1/3$, air chamber width $d_1/h=2/9$, and slope $i=2$. Due to the sloped structure, when compared with a vertical OWC, long waves can more easily enter the chamber. This causes the efficient frequency bandwidth to shift towards the low frequency range, allowing more wave energy to be converted into pneumatic energy. As a result, wave run-up is reduced, enhancing the protective function of the breakwater. Full article