Interlaminar shear fatigue properties of a two-dimensional carbon fibre reinforced silicon carbide composite were investigated at room temperature (RT) and 900°C in air. The interlaminar shear strength (ILSS) of the survived specimens was determined to reveal the damage mechanisms. The composite presents excellent resistance to the fatigue at RT. The fatigue limits at 900°C are much lower than that at RT. Moreover, ILSS can be enhanced for the survived composite to some extent. The damage involves the matrix cracking and interfacial debonding. Such damage offers the channels for the oxidation of the pyrolytic carbon interface and carbon fibres, and leads to the decrease in the fatigue limits at 900°C.
As an important measure of the sponge city, green roofs have received extensive attention in recent years. To investigate the inter-annual changes in runoff quality of green roofs with different vegetation types, three green roofs with different vegetation cover (Sedum lineare, Portulaca grandiflora, and a non-vegetated control) were set up in Beijing. The influences of vegetation and monitoring period on runoff quality from the green roofs were evaluated using the plant growth characteristics and the quality of rainwater and runoff from the green roofs during the rainy season of 2017-2019. The results showed that all three green roofs were the sinks of NH4+-N, and the average mass concentration reduction rates were between 50.1% and 79.2%. However, all three green roofs were sources of PO43--P, DCr, DCu, and DNi. The green roofs covered with S. lineare and P. grandiflora were sinks of NO3--N in 2017, and the average mass concentration reduction rates were 71.4% and 99.5%, respectively, but they became sources of NO3--N in both 2018 and 2019. However, the non-vegetated control was the source of NO3--N in all three rainy seasons. Both vegetation type and length of monitoring period had significant effects on the mass concentrations of NO3--N, PO43--P, DNi, and DCu in runoff from the green roofs (P<0.05) but had no significant effects on the mass concentrations of NH4+-N and DCr in runoff from the green roofs (P>0.05). In 2017-2019, the mass concentrations of NO3--N in runoff from the non-vegetated control and the green roofs covered by S. lineare and the mass concentration of PO43--P in runoff from the green roof covered by P. grandiflora increased yearly. The mass concentrations of DNi and DCu in runoff from all three green roofs increased in 2018 but dropped in 2019. Among the green roofs with different vegetation types, the green roof covered by P. grandiflora showed better NO3--N retention capacity than that of the other green roofs but may have increased the concentrations of PO43--P, DNi, and DCu in the runoff.
In this study, under the heating rate of 1300 °C/min, the thermal shock tests of 2D C/SiC composites with different thermal shock cycles and temperature differences (680 °C, 980 °C, 1280 °C) were carried out. Based on thermal shock damage mechanisms, a two-step residual properties prediction model using thermal-mechanic-oxygen coupling and cross-scale methods was established. The damage field calculation and residual properties prediction were carried out according to the thermal shock condition in the first. The test results show that matrix cracking caused by thermal gradient stress, interfacial debonding caused by thermal mismatch and fiber failure caused by oxidation are the main reasons for thermal shock damage of 2D C/SiC composites. The prediction results show that the residual strength, stiffness and stress–strain curve of the thermal shock obtained by the prediction have little difference from the test results, which reflects the accuracy of the prediction model.
CYP71 belongs to cytochrome P450 (CYP) monooxygenase superfamily, which is functionally diverse and participates in shikimic acid pathway and the secondary metabolism of tryptophan. We identified 58 MaCYP71s and 14 MbCYP71s from the Musa acuminata Colla and Musa balbisiana Colla, and investigated the biological function of the banana CYP71 gene family. Analysis of conserved domain motifs showed that MaCYP71 was more conservative than MbCYP71. Through cluster analysis, MaCYP71 could be divided into 11 subgroups, and MbCYP71 could be divided into 4 subgroups. The expansion of the MaCYP71s might result from the combined actions of tandem and segmental duplications 17% of the MaCYP71 were found to be potentially responsive to low temperature. Exon skipping was the main alternative splicing events of MaCYP71. According to FPKM value and qPCR analysis of MaCYP71 at low temperature, the expressions of MaCYP71A1-4, MaCYP78A6-2, MaCYP78A5-5, and MaCYP78A6-3 at 4°C and 0°C were significantly higher than those at 28°C, which reflected their possible association with response to low-temperature stress. Fifteen members of MaCYP71 family were mainly regulated by miRNA (miR398 and novel_7. 15). MaCYP71s were targeted by 26 lncRNA genes, of which 13 lncRNAs were upregulated in expression at 4°C. From the above studies, it was suggested that MaCYP71 play a vital role in response to low-temperature stress in banana.
The surface of Ti17 alloy was strengthened by electrospark deposition systems with silicon bronze electrode in the medium of argon and silicon oil,respectively.The microstructure,phase constitution,hardness and wear resisting of the strengthening layer were investigated by means of SEM,XRD,glow discharge optical emission spectrometer,microhardness tester and MM200 abrasion tester,respectively.The results show that the depth of strengthening layer obtained in argon and silicon oil is about 10μm and 5μm,its microhardness is 550HV and 494HV,respectively.The strengthening layer deposited in argon is composed of Ti_3Cu,Cu phase primarily and a small quantity of TiSi_2 and Ti,but the strengthening layer formed in silicon oil consists of phases of Ti_3Cu,Cu and a small quantity of TiO,Ti_2N and Ti_3SiC_2.The results of wear tests show that the abrasion mass loss of the non-strengthened samples is about 56 times of that of samples strengthened in argon and 24 times of that of samples strengthened in silicon oil,respectively.The abrasion mechanism of substrate sample is oxidation abrasion and adhesion abrasion,but abrasive wear prevails for the strengthened samples by electrospark depositon due to the strengthening layer peeling off.
Single-mode operation while maintaining a high-quality factor have always been key factors for building high-performance semiconductor lasers. Here, single CsPbBr3 perovskite microwire with a width of ∼3 μm is served as an active microresonator in which a typical single-mode laser output with a quality factor of 3000 is realized through the intrinsic self-absorption effect in success. Simultaneously, we observed the evolution of cavity modes in different dimensional perovskite microresonators and discussed the internal mechanisms of mode evolution and single-mode output in depth. The synergistic effect of intrinsic self-absorption and cavity size is the dominant factor for single-mode lasing output. It provides a feasible approach for the subsequent construction of high-quality electrically pumped single-mode lasers.
The oxidation damage evolution law of ceramic matrix composites prepared by chemical vapor infiltration (CVI) process was analyzed. Considering the effects of temperature and oxidation time, prediction models of elastic modulus about fiber and cell were established based on the distribution of microcracks in matrix and the oxidation process of interface, fiber and matrix. The prediction results show that the tensile elastic moduli of carbon fiber (Cf)/SiC and SiC fiber (SiCf)/SiC composites decrease more obviously with the increase of temperature and oxidation time. The elastic prediction model was verified by the tensile tests of the composites after high temperature oxidation. The error between the prediction results and the test results of SiCf/SiC composites with BN interphase after oxidation at 1000 ℃ for different time is no more than 2%, and the error between the prediction results and the test results of Cf/SiC composites with PyC interphase after oxidation at 700℃ for different time is no more than 7%.
In this article, a hybrid model for the current-voltage (I-V) characteristic and its high-order derivatives of III-V FETs is presented. The proposed model divides the entire operating region into several subregions and chooses optimum models in each subregion. The artificial neural network (ANN) techniques are employed to smoothly link the boundaries. The validity of this model has been verified by comparing the measurement and modeled results of a GaAs pHEMT.
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