Calcareous sand containing weak particles originated from the deposition of skeletal residue of marine organisms is susceptible to significant particle crushing under compression and shearing. The ...breakage of grains results in excessive deformation and foundation failure. This study focuses on the mechanical properties and particle crushing of calcareous sand retrieved from Nansha Island, South China Sea. A series of isotropically drained and undrained triaxial compression tests were performed on reconstituted calcareous sand samples at different initial densities and at a wide range of confining stresses. The amount of particle crushing for calcareous sand after shearing was measured and quantified. Experimental results demonstrate that the shear response of calcareous sand had been well interpreted within the critical state framework. The amount of particle crushing for calcareous sand increases with increasing density and confining stress. Compared with the undrained condition, a larger amount of particle crushing of calcareous sands is observed in the drained triaxial compression test. Stress-dilatancy curves exhibit similar varying tendency for calcareous sand. Multiple critical state lines for calcareous sands with different initial densities are identified in the void ratio and logarithm of the mean stress plane. Considering the variation in stress ratio at the critical state induced by particle crushing, all stress paths are normalized to determine the state bounding surface for calcareous sand at varying densities and stresses.
•Particle crushing for calcareous sand is jointly governed by density, stress level, and drainage condition.•Particle crushing-induced position shift of critical state line is observed for calcareous sand.•Bounding state surface is identified for calcareous sand at various initial densities.
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•Bio-inspired solar steam generation using floating plasmonic membranes (PMs) proposed.•High steam generation efficiency of 85% achieved at illumination power of 10kWm−2.•PMs enhanced ...the productivity of a solar still for seawater desalination by ∼80%.
Efficient solar-enabled evaporation plays a critical role in solar power-based concentration systems, photochemical plants, seawater desalination technologies, etc. However, traditional processes for solar steam generation usually depend on high-temperature heating of the bulk liquid, which requires highly concentrated solar power and suffers from high energy and optical losses. Therefore, the enhancement of solar steam generation by bio-inspired interface solar heating is proposed in this work. In this study, easy-to-prepare, flexible, and reusable plasmonic membranes (PMs) were fabricated for realizing the bio-inspired interface solar heating and continuous steam transportation through the micropores of the membranes. A solar steam generation efficiency of ∼85% was achieved at an illumination power of 10kWm−2. The effects of Au concentration in the membranes and optical power on the steam generation efficiency were systemically studied. The observed high evaporation rate and efficiency were attributed to three main factors: high (∼90%) and broadband solar absorption, efficient photo-thermal conversion due to high plasmon dissipation losses, and fast capillary flow in the membrane micropores. Finally, the application of PMs in a single basin solar still system for seawater desalination was investigated and the PMs exhibited great performance on enhancing the productivity of clean water.
The bearing capacity of the dredged calcareous soil in the Nansha Islands, South China Sea typically exceeds that of terrigenous dredger fill. Furthermore, the shear strength of calcareous soil ...exceeds that of siliceous sand under identical conditions. It is mainly caused by the interparticle obstruction between calcareous soil particles. To explore the obstruction mechanism of calcareous soil particles, a series of triaxial tests were performed on calcareous soils under both consolidated undrained (CU) and consolidated drained (CD) conditions, respectively. Particle shape characteristics and particle crushing were also investigated to study the formation mechanism of obstruction force. Test results indicate that irregular particle shape is the prerequisite for the emergence of particle obstruction in calcareous soils. A simple obstruction-dilatation model was developed to describe the relationship among particle obstruction, dilation and particle crushing. The obstruction force varies greatly during the shearing process, which is mainly influenced by particle size and stress level. Under low confining pressure, particle obstruction results in dilatation and increases internal friction angle. In contrast, obstruction causes particle breakage, increases the apparent cohesion, and ultimately decreases the effective internal friction angle under high confining pressures. The particle obstruction of calcareous soil noticeably improves shear strength. Therefore, the effect of particle obstruction on strength should be considered in coral reef engineering design work.
•The causes of particle occlusion of Calcareous soil were analyzed.•Irregular particle shape is the prerequisite for producing particle occlusion.•Particle occlusion causes shear dilatation and increases internal friction angle.•A simple obstruction-dilatation model was developed.
In this paper, a novel direct solar steam generation method is proposed that realizes highly efficient vapour generation. The strategy was inspired by the evaporation of sweat from the human skin and ...the transpiration of plants in biological systems. A micro-porous structured broadband absorption paper-based carbon nanotube (CNT) film was prepared by a facile vacuum filtration process, and was utilized as both the solar harvesting surface and steam generation skin. The excellent optical absorptivity and water conductivity of CNTs make great contributions to the solar steam generation. The heat and mass transfer properties on the direct solar steam generation performance of CNT films was investigated. The evaporation rate and temperature distribution of the steam generation system were experimentally studied to evaluate the evaporation performance. The results demonstrate that the bio-inspired solar heating of CNT films has significant advantages for enhancing direct solar steam generation compared to those of direct volumetric solar heating. Through this research, it was found that the localized photo-heating of floating CNT films at the water-air interface and the fast capillary flow through the porous structures of the films enhanced the solar steam generation process. This bio-inspired direct solar steam generation method using carbon nanotube films has great potential in a variety of industrial applications, including electrical power generation, freshwater distillation, and solar hygiene systems.
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•A novel bio-inspired direct solar steam generation method was proposed.•Porous and broadband absorption CNT films were prepared via a facile method.•Heat and steam flow through the micro-porous CNT films were studied.•Broadband absorption CNT films improved the efficiency of solar steam by up to 400%.
•Optical properties of core-shell NPs were discussed systematically.•Absorption efficiency can be adjusted by the core-shell or mixing ratios of NPs.•Optimized parameters of the core-shell NPs for ...solar absorption were obtained.•Efficiency of Au-decorated SiO2 NPs was superior to Au NPs and SiO2 NPs.
In this study, the properties of various types of core-shell nanoparticles (NPs) were evaluated using the finite difference time domain (FDTD) method towards the enhancement of solar absorption performance. Results showed that the resonance wavelength of SiO2@Au NPs lay in the 540–900 nm range, covering the near-infrared and visible regions. The resonance wavelength of SiO2@Ag NPs lay in the 390–830 nm range, covering the entire visible region. SiO2@Au nanofluid with a core-shell ratio of φ = 0.2 exhibited the highest solar absorption efficiency with 64% less Au consumption compared to pure Au NPs. For mixed nanofluids, the mixtures featuring core-shell ratios of 0.1 and 0.6 with mixing ratios of 0.5 for SiO2@Au and 0.6 for SiO2@Ag gave the highest absorption efficiencies. In addition, the peak solar absorption efficiency of a mixed nanofluid of SiO2@Au (φ = 0.1) and SiO2@Ag (φ = 0.4) with a mixing ratio of 0.58 was as high as 94.4%. Solar thermal conversion experiments revealed that, under the same conditions, a Au-decorated SiO2 nanofluid showed a comparable efficiency to the calculated solar absorption efficiency of the SiO2@Au core-shell nanofluid (∼95.2%); it was as high as 95.9%, higher than those of Au NPs and SiO2 NPs. These results showed that adjusting the core-shell ratios and tuning the mixing ratios of different nanofluids are two efficient methods to enhance the solar absorption efficiencies of SiO2@Au and SiO2@Ag NPs under the optimal conditions.
•Processes of light absorption and heating of NPs have been investigated numerically.•Absorption power per volume is introduced to evaluate the overall solar absorption.•Results show that Au and Cu ...NPs have the highest solar absorption efficiency.•Au cube obtains a higher solar heating temperature than the Au sphere and cylinder.
Solar heating with plasmonic nanoparticles (NPs) has great potential for application in optical storage, solar thermal collectors, and thermo-photovoltaic technologies. The performance of solar thermal conversion applications depends on the NP parameters. Herein, we present a comparative analysis of the solar absorption properties of noble metallic NPs (Au, Ag, Cu, and Al), to determine suitable parameters for effective solar heating by using the finite-difference time-domain method and the finite-element method. Results show that light absorption plays a major role in the interaction of light with the small NP size, small sphericity, or small dielectric constant of the surrounding environment. Au and Cu NPs have higher solar absorption power and absorption ratio. The NP size has little effect on the peak absorption wavelength. A Au sphere smaller than 30 nm has greater solar absorption ability for the solar heating process when considering the absorption power per unit volume. The solar absorption power first increases rapidly and subsequently decreases slightly with increasing dielectric constant, and can become as high as 0.0045 nW when the dielectric constant is 1.33–2.5 in the calculation samples. The solar scattering power and solar absorption power decrease with increasing sphericity, i.e., ranging from cubic to cylindrical and spherical. Finally, simulation results of NP solar heating show that the Au cube obtains a higher maximum temperature than the Au sphere and Au cylinder, which further verifies that Au NPs with low sphericity can significantly enhance solar heating ability in the simulation cases.
Anatomic contour zirconia crowns are widely used in clinical dental practice because of their mechanical reliability and improved appearance. However, few studies have performed clinical evaluations ...of the esthetics of these crowns in terms of color and translucency gradient.
The purpose of this clinical trial was to compare the esthetic effect and color-matching behaviors of anatomic contour zirconia crowns manufactured with 3-dimensional (3D) gel deposition and dry milling methods.
Twenty-seven premolar teeth of 27 participants received 2 identical anatomic contour zirconia crowns fabricated by additive 3D gel deposition or dry milling. Color differences (ΔE) between the crown and natural control teeth were measured by a dental shade-matching device. Subjective color matching was rated by professionals using an extended visual rating scale for appearance match (EVRSAM) and by participants using a visual analog scale (VAS). Data were analyzed by using repeated measures ANOVA, the Bonferroni test, paired Student t test, Pearson chi-square test, and Wilcoxon test (α=.05).
Significant differences were found in ΔE between zirconia crown and core types (P<.05); however, there was no significant interaction between these factors (P>.05). The average ΔE of crowns made by wet deposition and dry milling were 2.45 ±1.60 and 4.55 ±1.54 (P<.05). The mean crown ΔE was significantly higher if a gold cast post-and-core was placed rather than a prefabricated fiber post and composite core (P<.05). Consistent with these findings, subjective color matching was significantly higher in the wet deposition group than in the dry milling group as rated by EVRSAM and VAS (P<.05).
Anatomic contour zirconia crowns fabricated by additive wet deposition were better matched to adjacent teeth and had excellent esthetics in terms of color and translucency gradient.
Optimization of control parameters for plasma spraying process is of great importance in thermal spray technology development. Engineers may limit themselves to local optimal solution by considering ...countable potential design solutions when selecting the plasma spray parameters in practice. This work proposes one decision support model by employing convolutional neural network (CNN) to explore the suitability of preliminary design. The approach aims to help engineers select global optimal solution with short time and low labor cost by invoking the models' capability of extracting potential features of in-flight particle characteristics. Simulation results make it possible to analyze new spraying process and train the designed model under the condition of insufficient experience and data. Firstly, the distributions of particle status obtained from simulation results act as the input and the control parameters are the output. Secondly, the projections between the in-flight particles and the control parameters are built implicitly and analyzed through CNN models. Thirdly, we validate the statistical information of particle state distributions through visualizing the feature maps and filters. Finally, the trained CNN models are verified by the fitted Gaussian distributions with basically consistent results. By building projections of in-flight particles and control parameters, new entrants and apprentices are capable of deducing the control parameters with the help of the pre-trained CNN model, thus cutting down the threshold for new practitioners.
•Reverse process of plasma spray is modeled, which provide guidance in the optimization.•Convolutional Neural Network (CNN) considers distribution features of in-flight particle status.•Relationship between in-flight particle status and control parameters is analyzed by CNN.•CNN model can greatly reduce the computing resources and time cost
AbstractRing shear tests were performed in this work to investigate the characteristics of shear band formation and particle breakage for calcareous sands sampled from the South China Sea. The tests ...focused on the formation of shear band and the evolution of particle breakage under various levels of loading stress, together with sensitivity analyses of the initial sample grading and shear rate. The breakage of particles has a significant influence on the stress-strain relationship, volumetric deformation, and final grading of calcareous sands. In particular, the calcareous sand specimen tends to remain at a constant volume and a stable grading at shear strains larger than 2,000%. The change of the microstructure of calcareous sands during shearing has been illustrated by scanning electron microscopy (SEM) images, showing clear evolution of particle breakage and surface smoothness within the shear band. A considerable amount of fine particles (<0.074 mm) was produced during the tests, and the final complete particle-size distribution was obtained with a laser diffraction particle-size analyzer. The findings of this study improve the understanding of calcareous sands by showing that they can be crushed readily under normal loading stress levels as long as the shear strain continues.
Graphene oxide (GO) films with two-dimensional structure were successfully prepared via the modified Hummer method. It is proven that redox method is a promising way to synthesize GO films on a large ...scale. Comprehensive characterizations of the properties of GO films were conducted. TEM and DFM analyses showed that GO sheets prepared in this study had single and double lamellar layer structure and a thickness of 2~3 nm. X-ray diffraction (XRD) was selected to measure the crystal structure of GO sheet. Fourier-transform infrared spectra analyzer (FT-IR) was used to certify the presence of oxygen-containing functional groups in GO films. The tests of UV-VIS spectrometer and TGA analyzer indicated that GO sheet possessed excellent optical response and outstanding thermal stability. Elemental analyzer (EA) and X-ray photoelectron spectroscope (XPS) analyzed the components synthetic material. Simultaneously, chemical structure of GO sheet was described in this study. Discussion and references for further research on graphene are provided.
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