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In this study, a comparative study of carbon fiber reinforced polymer (CFRP) bar and steel–carbon fiber composite bar (SCFCB) reinforced coral concrete beams was made through a series of experimental tests and theoretical analyses. The flexural capacity, crack development and failure modes of CFRP and SCFCB-reinforced coral concrete were investigated in detail. They were also compared to ordinary steel-reinforced coral concrete beams. The results show that under the same conditions of reinforcement ratios, the SCFCB-reinforced beams exhibit better performance than CFRP-reinforced beams, and stiffness is slightly lower than that of steel-reinforced beams. Under the same load conditions, the crack width of SCFCB beams was between that of steel-reinforced beams and CFRP bar-reinforced beams. Before the steel core yields, the crack growth rate of SCFCB beam is similar to the steel-reinforced beams. SCFCB has a higher strength utilization rate—about 70–85% of its ultimate strength. Current design guidance was also examined based on the test results. It was found that the existing design specifications for FRP-reinforced normal concrete is not suitable for SCFCB-reinforced coral concrete structures. [ABSTRACT FROM AUTHOR]

In order to improve the brittle characteristics of coral cement-based composites and increase their toughness, an experimental study was carried out on the basic mechanical properties of PVA (polyvinyl alcohol) fiber-reinforced coral cement-based composites, taking into account the fiber content and length-to-diameter ratio (L/D). The results showed that PVA fibers can effectively improve the mechanical properties of concrete, especially its tensile strength. At the same time, PVA fibers improved the damage characteristics of cement-based composites and had obvious toughening and brittleness reduction effects. The PVA fibers, with a volume content of 1.5% and an L/D of 225, had the best performance in reinforcing the overall performance of the coral cement-based composites. Too many PVA fibers or a large length-to-diameter ratio would make it difficult for the fibers to contribute to toughness and cracking resistance and even cause defects in the matrix, reducing the mechanical properties. The tensile stress-strain curves of PVA fiber-reinforced coral cement-based composites were consistent with the trilinear constitutive model curves and showed the tensile characteristic of strain hardening after the occurrence of the main cracks. [ABSTRACT FROM AUTHOR]

Corn-peanut intercropping is an important element of China's agricultural planting model as it confers ecological benefits and increases yield. The aim of this study was to explore the productivity differences between intercropping and monoculture by using the 13C isotope tracer labelling method. Corn hybrid Denghai 618 (DH618) and peanut variety Huayu 22 (HY22) were used as test materials under three planting methods, single corn, SM; single peanut, SP; and corn-peanut intercropping, IM and IP, respectively, during two growing seasons. The results showed that IM increased yield by 59.7% and 62.3% compared with SM, respectively. IP reduced yield by 31.3% and 32.3% compared with SP, respectively. IM significantly increased the photosynthetic rate, leaf area, 13C assimilation distribution, and dry matter accumulation of summer corn, which led to an increase in the kernel number and grain yield. The decrease in intercropped peanut yield was mainly caused by a decrease in the full-pod rate and number of pods per plant. The decrease in peanut yield did not affect the production of intercropping benefit due to the larger intercropping advantage and land equivalence ratio. Corn-peanut intercropping yielded greater economic benefits than monoculture. These results showed the utility of the peanut-corn intercropping model. [ABSTRACT FROM AUTHOR]

The appropriate increase of planting densities is the key to the obtainment of high-yield maize (Zea mays L.). However, lodging is a major constraint to limit grain yield under increased planting density in present maize production. Effects of population density on stalk lodging and agronomic traits were investigated using two maize cultivars Denghai 618 (DH618, low stalk with low spike height) and Xianyu335 (XY335, high stalk with high spike height). Four levels of density treatment were imposed by 1.5, 6.0, 7.5, and 9.0 × 104 plants ha−1. Results showed that bending strength, rind penetration strength, maximum bending strength, dry weight, and internode diameter of maize were significantly decreased with the increase of planting density. The change range of XY335 with the increase of planting density was significantly larger than that of DH618, showing a high sensitivity to planting density. In addition, the thickness of cortex and vascular bundle sclerenchyma cells was significantly reduced with the increase of planting density. Compared with 1.5 × 104 plants ha−1, the thickness of the above-ground third internode stem cortex was decreased by 9.64%, 12.72%, and 20.77% for DH618, and 19.26%, 30.49%, and 37.45% for XY335 at 6.0, 7.5, and 9.0 × 104 plants ha−1, respectively. The thickness of vascular bundle sclerenchyma cells at 1.5 × 104 plants ha−1 was decreased by 7.75%, 12.44%%, and 17.89% for DH618, 10.18%, 15.21%, and 24.73% for XY335, compared to those at 6.0, 7.5, and 9.0 × 104 plants ha−1, respectively. Visibly, with the increase of planting density, the thickness of cortex and vascular bundle sclerenchyma cells, and the number of vascular bundles were all significantly decreased, resulting in the increase of lodging rate. However, the extent of variation in these parameters for short-plant height hybrid was less than those for high-plant height hybrid, and the yield of short-plant height hybrid was greater than that of high-plant height hybrid, indicating that short-plant height hybrid has better resistance to lodging with higher yield at higher planting density. Therefore, lodging resistance and yield can be improved through selection and breeding strategies that achieving synergistic development of diameter, dry weight per unit, and cortex thickness in maize basal internodes. [ABSTRACT FROM AUTHOR]

FRP (Fiber Reinforced Polymer) Bar reinforced coral concrete beam is a new type of structural member that has been used more and more widely in marine engineering in recent years. In order to study and predict the flexural performance of CFRP reinforced coral concrete beams, the flexural rigidity, crack morphology and failure mode of concrete were studied in detail. The results show that under the condition of similar reinforcement ratio, the flexural rigidity of CFRP reinforced coral concrete beam is significantly lower than that of ordinary reinforced concrete beam. Increasing the cross-section reinforcement ratio within a certain range can increase the bending stiffness of the test beam or reduce the deflection, but the strength utilization rate of CFRP reinforcement is greatly reduced. The short-term bending stiffness of the CFRP reinforced coral concrete beam calculated by the existing standard formula is obviously higher. This paper proposes a modified formula for introducing the strain inhomogeneity coefficient (ψ) of CFRP bars and considers the relative slip between CFRP bars and coral concrete to predict the short-term flexural stiffness of coral concrete beams reinforced by CFRP bars. The formula was verified with the test results, and it was proved that the formula has a good consistency with the test results. [ABSTRACT FROM AUTHOR]

To explore the response of summer maize leaf senescence, photosynthetic characteristics, and yield to the depth of one-time base application of controlled-release urea, which provides a theoretical basis for the light and simplified production of summer maize. Seven treatments were set up with Zhengdan 958 as the material under field conditions, including no nitrogen fertilizer (CK), surface spreading (DP0), furrow application depth of 5 cm (DP5), 10 cm (DP10), 15 cm (DP15), 20 cm (DP20), 25 cm (DP25). The results showed that under the same nitrogen application rate, there are significant differences in the effects of summer maize leaf senescence and photosynthetic characteristics with the increase of fertilization depth, and DP10 and DP15 have the best effects. The LAI of DP10 and DP15 increased by 5.1% and 5.5% compared to DP0 at tasseling stage, and chlorophyll content increased by 6.8% and 7.3% in 10 days after tasseling. Compared with DP0, superoxide dismutase (SOD) increased by 13.1% and 10.5%, the content of soluble protein increased significantly, while the content of malondialdehyde (MDA) decreased by 9.8% and 10.8%, respectively. In addition, Pn and Gs of the ear-leaf significantly increased by 13.9%, 16.5%, and 26.1% and 31.9% at tasseling stage, respectively, over DP0, while Ci decreased by 22.3% and 26.4%, respectively; meanwhile, the photochemical quenching (qP) and quantum yield (ΦPSII) of the reaction center of photosystem II (PSII) of the ear-leaf were significantly improved, the non-photochemical quenching (NPQ) was significantly reduced. The yield of DP10 and DP15 heightened significantly; two-year average value increased by 5.7% and 6.0% compared with DP0; the kernels per spike and 1000-kernels weight increased by 4.8%, 5.2%, and 4.1%, 5.2%, respectively. Comprehensive analysis of LAI, chlorophyll content, various protective enzyme activities and MDA, soluble protein content showed that 10–15 cm is the appropriate fertilization depth when the nitrogen application rate of controlled-release urea is 225 kg N per hectare. In consequence, optimizing fertilization depth of controlled-release urea as a simplified fertilization mode could improve the nitrogen utilization efficiency and obtain higher yield in summer maize, which provides technical support for large-scale application of controlled-release urea. [ABSTRACT FROM AUTHOR]

In this study, fatigue crack tests of CuNi2Si alloys using the replica technique under symmetrical tensile-compression loading, and rotational-bending loading were carried out with the same nominal stress amplitude. Observation and analysis results indicate that under different load types, the cracks display a trend of slow initiation growth and then rapid growth. The critical point is identified at the approximate value of 0.8 of the fatigue life fraction, and the crack growth rate of the sample under tensile-compression load is approximately an order of magnitude higher than that under rotational-bending load, resulting in the average life of the former being significantly shorter than the latter. Combining the observation results of the fractographical analysis and the surface-etched sample replica film, it can be seen that whether it is a tensile-compression load or a rotational-bending load, cracks mainly propagate in intergranular mode after initiation. [ABSTRACT FROM AUTHOR]