The failure mechanism and size effect during the quasi-static and dynamic shear tests of hat-shaped specimens were investigated in this study. Three types of specimens with different shear ring ...thicknesses (800, 400, and 50 μm) were designed. Quasi-static tests were carried out using an electronic universal testing machine, while dynamic impact tests were carried out using split Hopkinson pressure bar (SHPB) tests. The adiabatic temperature rises with different strain rates, and the shear ring thickness was calculated. We found that the adiabatic temperature rises of the specimens with shear ring thicknesses of 800 and 400 μm were much larger than those of the specimens with shear ring thicknesses of 50 μm. The failure surfaces after the SHPB test were investigated via scanning electron microscopy, and the failure surfaces after the SHPB test could be divided into three zones: tensile, shear, and impact zones. The effect of the shear ring thickness and impact speed on the failure surface morphology was discussed. The typical shear stress–strain curves could be divided into three sections: elastic, plastic rise, and plastic plateau sections. Subsequently, a modified Johnson–Cook constitutive model was employed to fit the shear stress–strain results, and the fitted curves showed good agreement with the tested curves.
Guided by the theoretical prediction, a new MAX phase V
2
SnC was synthesized experimentally for the first time by reaction of V, Sn, and C mixtures at 1000 °C. The chemical composition and crystal ...structure of this new compound were identified by the cross-check combination of first-principles calculations, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and high resolution scanning transmission electron microscopy (HR-STEM). The stacking sequence of V
2
C and Sn layers results in a crystal structure of space group P6
3
/mmc. The
a
- and
c
-lattice parameters, which were determined by the Rietveld analysis of powder XRD pattern, are 0.2981(0) nm and 1.3470(6) nm, respectively. The atomic positions are V at 4f (1/3, 2/3, 0.0776(5)), Sn at 2d (2/3, 1/3, 1/4), and C at 2a (0, 0, 0). A new set of XRD data of V
2
SnC was also obtained. Theoretical calculations suggest that this new compound is stable with negative formation energy and formation enthalpy, satisfied Born-Huang criteria of mechanical stability, and positive phonon branches over the Brillouin zone. It also has low shear deformation resistance
c
44
(second-order elastic constant,
c
ij
) and shear modulus (
G
), positive Cauchy pressure, and low Pugh’s ratio (
G/B
= 0.500 < 0.571), which is regarded as a quasi-ductile MAX phase. The mechanism underpinning the quasi-ductility is associated with the presence of a metallic bond.
Rubber trees in southern China are often impacted by natural disturbances, and accurate rubber tree crown segmentation and property retrieval are of great significance for forest cultivation ...treatments and silvicultural risk management. Here, three plots of different rubber tree clones, PR107, CATAS 7-20-59 and CATAS 8-7-9, that were recently impacted by hurricanes and chilling injury were taken as the study targets. Through data collection using ground-based mobile light detection and ranging (LiDAR) technology, a weighted Rayleigh entropy method based on the scanned branch data obtained from the region growing algorithm was proposed to calculate the trunk inclination angle and crown centre of each tree. A watershed algorithm based on the extracted crown centres was then adopted for tree crown segmentation, and a variety of tree properties were successfully extracted to evaluate the susceptibility of different rubber tree clones facing natural disturbances. The results show that the angles between the first-order branches and trunk ranged from 35.1–67.7° for rubber tree clone PR107, which is larger than the angles for clone CATAS 7-20-59, which ranged from 20.2–43.2°. Clone PR107 had the maximum number of scanned leaf points, lowest tree height and a crown volume that was larger than that of CATAS 7-20-59, which generates more frontal leaf area to oppose wind flow and reduces the gaps among tree crowns, inducing strong wind loading on the tree body. These factors result in more severe hurricane damage, resulting in trunk inclination angles that are larger for PR107 than CATAS 7-20-59. In addition, the rubber tree clone CATAS 8-7-9 had the minimal number of scanned leaf points and the smallest tree crown volume, reflecting its vulnerability to both hurricanes and chilling injury. The results are verified by field measurements. The work quantitatively assesses the susceptibility of different rubber tree clones under the impacts of natural disturbances using ground-based mobile LiDAR.
To characterize P adsorption-desorption in the riverbed sediments, we studied sediment physicochemical parameters affecting P dynamics, adsorption-desorption parameters such as P desorption maximum, ...equilibrium P concentration and P desorption capacity of bed sediments by a batch experiment. The results showed that the adsorption-desorption rate of phosphorus on sediment obviously increased, then slightly decreased, and finally reached equilibrium at 90 min of reaction. The desorption concentration of phosphorus on the surface of sediment was 0.45 mg/L when the rotational speed was 250 r/min. The increase of sediment concentration facilitated the transformation of phosphorus from dissolved state to adsorbed state. When the sediment particle size was less than 0.074 mm, the equilibrium adsorption and desorption capacity of phosphorus were 0.47 mg/g and 0.43 mg/L, respectively. In addition, high temperature was beneficial to the adsorption of phosphorus, but rarely affect the desorption of phosphorus in the sediment. The pH value of solution has little impact on the adsorption and desorption of phosphorus.
Since the summer of 2022, the whole world has suffered the abnormal weather phenomena of high ambient temperature. Equipment for refrigeration, particularly portable refrigeration equipment, is ...crucial for personal protection in high-temperature environments, but cooling performance and miniaturization have been challenging issues. A portable air conditioner based on a semiconductor refrigeration device for human body cooling was developed. The total weight of the device is 450 g. The overall power consumption of the device is 82 W and the energy consumption ratio of semiconductor cooling plate is 0.85. The semiconductor refrigeration technology is based on the Peltier effect, supplemented by a DC fan to send the cooling air out to a specified position or zone. The structural parts are manufactured by 3D printing technology to make the overall size of the device more compact. The air volume and cooling performance of the device were analyzed by computational fluid dynamics simulation and the temperature distribution was measured by an infrared thermal imager and other instruments, and the measured results agreed with the CFD simulation results. The test ambient temperature was 20 °C. The measurement results showed that the wind speed of the hot air outlet was 6.92 m/s and that of the cold air outlet was 8.24 m/s. The cold air surface temperature reached a stable state of 13.9 °C in about 4 min, while the hot air surface temperature reached a stable state of 47.2 °C.
Ti-6Al-4V titanium alloy is a typical difficult-to-cut material used in many fields. The selection of cutting parameters exerts tremendous influences on the material removal process. Finite element ...numerical simulation is a low-cost method to obtain optimized cutting parameters. Finite element simulation requires the study of machining properties of machined materials. The material removal and related physical phenomena during machining are characterized by the dynamic mechanical properties of the machined material. In this paper, the dynamic mechanical properties of Ti-6Al-4V have been tested by the high temperature split Hopkinson pressure bar system to obtain true stress–strain curves under different conditions. The sensitivity of strain and temperature of Ti-6Al-4V has been analyzed. The influence of temperature-dependent specific heat capacity, which has been tested by a laser thermal conductivity tester, on adiabatic temperature rise has been considered. Adiabatic temperature rise has been calculated separately with constant specific heat capacity and temperature-dependent specific heat capacity. True stress–strain curves have been switched to true stress–strain isothermal curves to analyze separately the influence of strain rate and temperature on true stress. Based on true stress–strain isothermal curves, the constitutive models of power-law and Johnson–Cook have been introduced to fit the experimental results. The fitting results of the two constitutive models have been compared with the experiment results, which have an average error less than 6%.
The flexure hinge is a kind of micro-displacement adjustment device with application prospects because of its high displacement resolution, positioning accuracy and repeatability. In this study, a ...micro-displacement worktable with four degrees of freedom (X→, Z→, X︵, Z︵) was designed. The micro-displacement worktable was composed of three different flexure hinges. The adjustment ranges and adjustment accuracy of flexure hinges in terms of their respective degrees were improved. The micro-displacement worktable performance was examined by FEA (Finite Element Method). The maximum displacement that was adjusted in X→ and Z→ was 1.67 µm and 1.74 µm. The maximum angle adjusted in the X︵ and Z︵ direction was 14.90° and 18.58°. A test platform was developed for micro-displacement worktable performance tests. The simulation results showed a good agreement with the experimental results.
With the intensification of climate change, understanding the impacts of climate change on the water cycle is vital for integrated watershed management. Based on the precipitation and temperature ...data from 1980 to 2018, the climatic change characteristics of the Three Gorges Reservoir Area were analyzed. The Soil and Water Assessment Tool (SWAT) was used to simulate the spatial and temporal distribution of runoff and water quality. The result indicated that precipitation showed clear inter-annual fluctuation, and the maximum and minimum temperatures showed an increasing trend with rates of 0.38 °C/10a and 0.29 °C/10a, respectively. The moving averages revealed that the annual averages of runoff, total nitrogen (TN), and total phosphorus (TP) loads showed a decreasing trend followed by an increasing trend, which experienced strong inter-annual fluctuations. The hydrological processes changed significantly at different spatial scales, and the most affected area was the middle and head of reservoir area. The highest correlation was found between precipitation and runoff (0.91), followed by TP (0.81), and TN (0.60), while extreme precipitation could result in a high probability of water pollution events. These findings provide useful information to support the utilization of water resources, especially in the face of strong climate change impacts.
Phytochromes (phys) are red and far-red photoreceptors that control plant development and growth by promoting the proteolysis of a family of antagonistically acting basic helix-loop-helix ...transcription factors, the PHYTOCHROME-INTERACTING FACTORs (PIFs). We have previously shown that the degradation of PIF1 and PIF3 requires HEMERA (HMR). However, the biochemical function of HMR and the mechanism by which it mediates PIF degradation remain unclear. Here, we provide genetic evidence that HMR acts upstream of PIFs in regulating hypocotyl growth. Surprisingly, genomewide analysis of HMR- and PIF-dependent genes reveals that HMR is also required for the transactivation of a subset of PIF direct-target genes. We show that HMR interacts with all PIFs. The HMR-PIF interaction is mediated mainly by HMR’s N-terminal half and PIFs’ conserved active-phytochrome B binding motif. In addition, HMR possesses an acidic nine-aminoacid transcriptional activation domain (9aaTAD) and a loss-of-function mutation in this 9aaTAD impairs the expression of PIF target genes and the destruction of PIF1 and PIF3. Together, these in vivo results support a regulatory mechanism for PIFs in which HMR is a transcriptional coactivator binding directly to PIFs and the 9aaTAD of HMR couples the degradation of PIF1 and PIF3 with the transactivation of PIF target genes.
Traditional hydrodynamic models face the significant challenge of balancing the demands of long prediction spans and precise boundary conditions, large computational areas, and low computational ...costs when attempting to rapidly and accurately predict the nonlinear spatial and temporal characteristics of fluids at the basin scale. To tackle this obstacle, this study constructed a novel deep learning framework with a hydrodynamic model for the rapid spatiotemporal prediction of hydrodynamics at the basin scale, named U-Net-ConvLSTM. A validated high-fidelity hydrodynamic mechanistic model was utilized to build a 20-year hydrodynamic indicator dataset of the middle and lower reaches of the Han River for the training and validation of U-Net-ConvLSTM. The findings indicate that the R2 value of the model surpassed 0.99 when comparing the single-step prediction results with the target values. Additionally, the required computing time fell by 62.08% compared with the hydrodynamic model. The ablation tests demonstrate that the U-Net-ConvLSTM framework outperforms other frameworks in terms of accuracy for basin-scale hydrodynamic prediction. In the multi-step-ahead prediction scenarios, the prediction interval increased from 1 day to 5 days, while consistently maintaining an R2 value above 0.7, which demonstrates the effectiveness of the model in the missing boundary conditions scenario. In summary, the U-Net-ConvLSTM framework is capable of making precise spatiotemporal predictions in hydrodynamics, which may be considered a high-performance computational solution for predicting hydrodynamics at the basin scale.
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