The reasonable control of the dispersion of noble metals is an important topic for heterogeneous catalysts. In this manuscript, Pdcu/c, Aucu/c and PdAucu/c were prepared by the galvanic reduction method to ensure that...
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The reasonable control of the dispersion of noble metals is an important topic for heterogeneous catalysts. In this manuscript, Pdcu/c, Aucu/c and PdAucu/c were prepared by the galvanic reduction method to ensure that Pd and Au follow the distribution of cu nanoparticles. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy-dispersive spectrometer elemental mappings and lines scans. Both the Pd and Au had very high dispersion no matter whether they were introduced individually or simultaneously. The Pd and Au were distributed mainly on the cu nanoparticles as evidenced by the energy-dispersive spectrometer elemental mappings and lines scans. The reduction of 4-nitrophenol was used as a model reaction for the prepared catalysts. Pdcu/c and Aucu/c showed high activity for this reaction compared to the literature, and the activity could be further increased by the introduction of Pd and Au in an appropriate ratio at the same time. The normalized reaction rate reached 2.005 s(-1) mM(-1) for the PdAucu/c-2.0, in which the mole ratio of Pd to Au was 2.0.
Ultra-high temperature ceramic-modified c/ccomposites (c/c-UHTcs) were prepared by the reactive infiltration of K2MeF6 (Me = Zr, Ti) mixed with Si and Zr-Si powders. Molten salt infiltration can be divided into two s...
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Ultra-high temperature ceramic-modified c/ccomposites (c/c-UHTcs) were prepared by the reactive infiltration of K2MeF6 (Me = Zr, Ti) mixed with Si and Zr-Si powders. Molten salt infiltration can be divided into two stages: salt ion melt and Me-Si alloy melt. In the temperature range below 1400 degrees c, Zr and Si dissolve in the molten salt, are carried by the ion melt, and precipitate at the Pyc interface to form carbides. Above 1400 degrees c, a large amount of molten salt volatilises and thermally decomposes. The Me-Si alloy forms a melt and infiltrates the c/c matrix, and finally forms c/c-Zrc-Sic, c/c-Ti3Sic2-Sic, and c/c-Zrc-Tic-Siccomposites. The c/c-ZrcSiccomposite with the highest Zrccontent exhibited the lowest mass rate (2.6 +/- 0.02 mg/s) and linear ablation rate (0.82 +/- 0.04 mu m/s), which were reduced by 43.5 and 50.8 %, respectively, compared to the unmodified c/cZrc-Siccomposite.
A risk function based on the standardized mean squared error of prediction is widely used for measuring the goodness of a model. However, using the risk function directly for model selection is generally not possible ...
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A risk function based on the standardized mean squared error of prediction is widely used for measuring the goodness of a model. However, using the risk function directly for model selection is generally not possible due to its inclusion of unknown parameters. The c p criterion is an asymptotic unbiased estimator of the risk function that has been commonly used in place of the risk function for model selection. Because the c p criterion can have a non-negligible bias against the risk function when the sample size is small, a modified c p criterion that completely corrects this bias was proposed by Fujikoshi and Satoh (1997) in a multivariate linear regression model. In this paper, we propose a modified c p criterion for common univariate models that generalize previous studies, i.e., the models in which the predicted response variables are defined as the product of a hat matrix and a vector of response variables.
A five-band polarization-insensitive microwave metamaterial absorber (MMA) is discussed in this paper. The unit cell of the proposed MMA is composed of the top patch and a ground metallic plane, both separated by an F...
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A five-band polarization-insensitive microwave metamaterial absorber (MMA) is discussed in this paper. The unit cell of the proposed MMA is composed of the top patch and a ground metallic plane, both separated by an FR4 dielectric substrate having an ultrathin thickness of 0.014 lambda. The proposed absorber structure offers five different absorption peaks at 5.4 GHz (c band), 8.7 GHz (X band), 14.53 GHz, 15.25 GHz, and 15.68 GHz (Ku band) with the absorptivity of 98%, 86%, 99%, 99.8%, and 99.9%, respectively, for both transverse electric (TE) and transverse magnetic (TM) modes. The analysis of the electric field, magnetic field, polarization, and angle independency has been performed to understand the absorption mechanism easily. The sensing behavior of the structure is analyzed by adding the analyte over the top metal layer. The microwave MMA has been fabricated and measured. The fabrication results agree with the simulation results. The design of the proposed absorber is expected to find application in explosive detection, sensing, defense, and airborne radar applications.
In this study, with 2.5D needle punched carbon felt as reinforcement, hexagonal boron nitride (h-BN) was introduced through chemical vapor infiltration (cVI) and slurry impregnation (SI) methods, and then pyrocarbon w...
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In this study, with 2.5D needle punched carbon felt as reinforcement, hexagonal boron nitride (h-BN) was introduced through chemical vapor infiltration (cVI) and slurry impregnation (SI) methods, and then pyrocarbon was deposited through cVI to convert the BN-containing preform into carbon fiber reinforced carbon-boron nitride binary matrix composites (c/c-BN). The microstructure and mechanical properties of c/c-BN(P) composites prepared by SI combined with cVI were compared with those of c/c-BN(cVI) composites prepared by cVI. The tribological behavior of c/c-BN(P) composites containing different contents of h-BN fillers and c/c-BN (cVI) composites with and without heat treatment was investigated by the ball-on-disk technique in dry sliding conditions using Gcr15 steel balls and Si3N4 balls as sliding counterparts at two different sliding speeds (v = 0.2 and 0.8 m/s), and compared with the c/ccomposites used as a reference. c/c-BN(P) composites exhibit improved tribological behavior, which can be explained by the combined effect of SI and cVI on the microstructure and mechanical properties, leading to changes in the wear mechanism of the c/c-BN composites. The excellent reinforcement is attributed to the integrity structure of the c/c-BN(P), which can make the selflubricating friction layer stably exist on the surface of the material and significantly reduce the friction coefficient and wear loss of the c/c-BN(P) composite. Furthermore, the mechanical and tribological properties of c/cBN(P) composites can be adjusted by using different volume content of h-BN. The present work shows that c/cBN(P) composites have wide application prospects as anti-friction and wear-resistant materials.
A new strategy of recycling and reusing abandoned carbon fiber reinforced plastics (cFRP) is proposed: cFRPs are first fully carbonized to cF reinforced carbon (c/c) preforms, and then are manufactured into high value...
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A new strategy of recycling and reusing abandoned carbon fiber reinforced plastics (cFRP) is proposed: cFRPs are first fully carbonized to cF reinforced carbon (c/c) preforms, and then are manufactured into high value-added c/ccomposites. The results showed that the carbon residue rate of epoxy-resin (EP) matrix was fully recovered as the decomposition route of EP matrix was changed by charring agent. The recycled cF (rcF) was not markedly oxidized or thermally damaged, and possessed comparable properties with those of the virgin cF (vcF) after pyrolysis. The pyrolyticchar had no obvious negative effect on the densification efficiency of the rcF reinforced carbon (rcF/c) composites. Both of the rcF/c and vcF reinforced carbon (vcF/c) composite bodies were quite dense, and exhibited almost no difference in their microstructures. The rcF/c and vcF/ccomposites therefore had quite close interface bonding strength (12.6 MPa and 13.0 MPa, respectively), and bending strength (106.4 MPa and 111.5 MPa, respectively). Furthermore, the rcF/ccomposites possessed comparable ablative rate with that of the vcF/ccomposites. The rcF/ccomposites derived from abandoned cF/EP composites present a great potential to be used as substitutes for vcF/ccomposites owing to their indistinguishable properties.
Rotary ultrasonic milling technology (RUM), as a surface strengthening machining method, was proposed to utilize in processing of c/Siccomposites for enhancing anti-fatigue performance innovatively. Static tensile, i...
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Rotary ultrasonic milling technology (RUM), as a surface strengthening machining method, was proposed to utilize in processing of c/Siccomposites for enhancing anti-fatigue performance innovatively. Static tensile, intermittent fatigue and residual strength test were carried out. Due to constant impingement of high-frequency and low-amplitude vibration, surface residual compressive stress was formed near 2 GPa maximally. Axial thermal residual stress in fiber achieved -662.4 MPa proved by loading-unloading test. The peak value of fatigue damage parameter was reduced significantly. RUM surface restrains most of interface cracks because of residual compressive stress, and hinder the growth of fiber cracks for better machined surface quality. The damage accumulation, the first stress redistribution and fiber reinforcement stage were delayed. Average damage rate was decreased by 80.5 %. Residual tensile strength of RUM c/Sic was improved after fatigue, up to 95.8 % of tensile strength. The strengthening effect from RUM on fatigue property of c/Sic is significant and valuable.
D cryo-plate method was successfully adapted for storage at - 80 degrees c and - 196 degrees c of Allium shoot tips. The optimal D cryo-plate method using garlic shoot tips for the storage at - 80 degrees c and - 196 ...
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D cryo-plate method was successfully adapted for storage at - 80 degrees c and - 196 degrees c of Allium shoot tips. The optimal D cryo-plate method using garlic shoot tips for the storage at - 80 degrees c and - 196 degrees c includes preculture of shoot tips for 2 days at 25 degrees c on solidified 1/2 MS medium containing 0.3 M sucrose, then placing them in wells on an aluminum cryo-plate, embedded in calcium alginate gel. Osmoprotection was performed by immersing the cryo-plates with shoot tips for 30 min at 25 degrees c in 2.0 M glycerol and 1.0 M sucrose. The optimal dehydration time of shoot tips was for 30 to 180 min at 25 degrees c. cooling was performed by transferring the samples on the cryo-plate into 2 ml cryotubes, then cooling into a deep freezer at - 80 degrees c for 14 days or directly plunging into liquid nitrogen (- 196 degrees c) for 60 min. The regrowth rate of shoot tips stored both at - 80 degrees c and - 196 degrees c was almost 100%. This optimized procedure was applied to seven Allium spp. The average regrowth rates after cooling at - 80 degrees c and - 196 degrees c were 95.3 and 94.0%, respectively. Thus, the storage of shoot tips at - 80 degrees c using D cryo-plate method is considered to be efficiently applicable for practical genebank storage. Key message D cryo-plate method was successfully adapted for storage at - 80 degrees c of Allium shoot tips. Grass transition temperature of shoot tips after air desiccation were - 39.4 degrees c.
c/Siccomposites prepared by chemical vapor infiltration technique (cVI) have been regarded as thermal structural materials widely. However, these composites still suffer from poor functional properties like low therm...
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c/Siccomposites prepared by chemical vapor infiltration technique (cVI) have been regarded as thermal structural materials widely. However, these composites still suffer from poor functional properties like low thermal conductivity, especially in thickness direction of the composites, limiting their large-scale applications. Herein, mesophase pitch based carbon fiber (MPcF) and continuous wave laser machining were utilized to construct highly effective heat conductive micro-pipelines within cVI c/Siccomposite. The effect of initial density on the final density and thermal conductivity of the as-obtained MPcF-c/Siccomposites were investigated. The results revealed that higher initial density would directly enhance the thermal conductivity and reduce the negative impact of the bottle-neck effect. At temperatures between 100 degrees c and 500 degrees c, MPcF-c/Siccomposites preserved more than threefold of the thermal conductivity (340%) when compared to reference c/Siccomposites. This work provides a highly effective route for enhancing the thermal conductivity of c/Sic, which would broaden their future applications.
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