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Determining the stress intensity factor (SIF) for cracked engineering structures under different loading conditions is one of the core issues of fracture analysis. A slender fin-shaped shell possesses both shell and beam characteristics, in the cross section of which some complex cracks, such as the circumferential and T-shaped cracks, may arise. There will be different singular stress fields next to crack tips for a cracked fin-shaped shell under bending. Based on the conservation law and elementary mechanics, a technique to determine SIFs is proposed in this article, which is simple and easy to understand. The SIFs calculated using the present method agree well with FEM results even if elementary mechanics is used.

MicroRNAs are emerging as important regulators of cardiac function. This study investigated the role of microRNA-24 (miR-24) in ischemic cardiomyocytes, based on the observation that miR-24 expression was significantly enhanced in the ischemic myocardium of rats. Using primary cultured rat cardiomyocytes, cell injury was induced by ischemic conditions, and the cells were evaluated for changes in lactate dehydrogenase (LDH) release, cell viability, apoptosis and necrosis. The results showed that miR-24 was increased in myocytes exposed to ischemia. When miR-24 was further overexpressed in ischemic myocytes using the mimic RNA sequence, LDH release was reduced, cell viability was enhanced, and apoptosis and necrosis rates were both decreased. By contrast, a deficiency in miR-24 resulted in the largest LDH release, lowest cell viability and highest apoptosis and necrosis rates in normal and ischemic myocytes, with significant changes compared to that of non-transfected myocytes. Additionally, the mRNA and protein levels of the pro-apoptotic gene, BCL2L11, were down-regulated by miR-24 overexpression and up-regulated by miR-24 deficiency. The luciferase reporter assay confirmed BCL2L11 to be a target of miR-24. Overall, this study showed a protective role for miR-24 against myocardial ischemia by inhibiting BCL2L11, and may represent a potential novel treatment for ischemic heart disease.

The application of photoconductive switches in military, medical equipment and communications is gradually expanding. The research on high voltage RF output of photoconductive switches is becoming more and more important. A high voltage and high power RF photoconductive switch was developed by using vanadium-nitrogen doped 4H-SiC as substrate and hetero-planar electrode structure. The on-resistance is tested by the applied bias voltage over a range of different ranges. The test results show that the bias voltage of the photoconductive switch developed by this method can reach 10kV, which is positively correlated with the on-resistance of the photoconductive switch, and the voltage resistance of the 4H-SiC photoconductive switch has been effectively improved, and it has the characteristics of large output power, stable output waveform and small jitter, and can obtain low on-resistance with lower optical energy.

Globally, up to 10% of the total annual rice production is wasted due to excessively high moisture content during storage. Mechanized drying of rice is an important measure to reduce this loss. However, traditional hot-air rice dryers have issues such as low drying rates and high energy consumption. This paper introduces a new type of gas-catalytic infrared rice dryer, including its working principle and components. By using drying rate and fissuring rate as evaluation indicators before and after drying, the performance of this dryer is compared with that of traditional hot-air dryers. Further, a three-factor, three-level orthogonal experimental method was employed. Batch processing capacity, conveyor belt speed, and tempering time were selected as variables to calculate the optimal operating conditions of the gas-catalytic infrared rice dryer using the comprehensive balance method. Experimental results show that under nine different operating conditions, the gas-catalytic infrared rice dryer outperforms the traditional hot-air dryer. The drying rate of the gas-catalytic infrared dryer increased by 215.15% compared to the traditional hot-air dryer, and the fissuring rate decreased by 86%. The orthogonal experimental results indicate that, based on a comprehensive evaluation of moisture content difference and fissuring rate, the gas-catalytic infrared dryer achieves the best drying effect when the conveyor belt speed is 1.92 m/min and the tempering time is 40 minutes. These research findings provide important references for further optimization of rice drying technology.

This study aimed to investigate the vasoactivity of sulfur dioxide (SO2), a novel gas identified from vascular tissue, in rat thoracic aorta. The thoracic aorta was isolated, cut into rings, and mounted in organ-bath chambers. After equilibrium, the rings were gradually stretched to a resting tension. Isometric tension was recorded under the treatments with vasoconstrictors, SO2 derivatives, and various drugs as pharmacological interventions. In endothelium-intact aortic rings constricted by 1 μM phenylephrine (PE), SO2 derivatives (0.5 – 8 mM) caused a dosedependent relaxation. Endothelium removal and a NOS inhibitor L-NAME reduced the relaxation to low doses of SO2 derivatives, but not that to relatively high doses (≥ 2 mM). In endotheliumdenuded rings, SO2 derivatives attenuated vasoconstriction induced by high K+ (60 mM) or CaCl2 (0.01-10 mM). The relaxation to SO2 derivatives in PE-constricted rings without endothelium was significantly inhibited by blockers of ATPsensitive K+ (KATP) and Ca2+-activated K+ (KCa) channels, but not by those of voltage-dependent K+ channels, Na+-K+-ATPase or Na+-Ca2+ exchanger. SO2 relaxed vessel tone via endotheliumdependent mechanisms associated with NOS activation, and via endothelium-independent mechanisms dependent on the inhibition of voltage-gated Ca2+ channels, and the opening of KATP and KCa channels.

Fracture is one of the most common failure of engineering structure and the stress intensity factor is the key parameter used to decide whether the structure will crack or not. This essay is based on the concept of conservation law and the tension theory in mechanics of material. It analyzes the stress intensity factor of circumferential periodic cracks on tube with stiffened plates, it obtains the specific expression of stress intensity factor of circumferential periodic cracks on tube with stiffened plates under tension. Finite element method is used for checking the stress intensity factor of cracks and proving the accuracy of expression's results. The method which proposed in this essay is easy to calculate and can get the closed solution.

The effect of Zn on the microstructure evolution of Mg-7Gd-3Y-1Nd-xZn-0.5Zr (x=1.0, 2.0) (wt.%) alloys during homogenization and ageing heat treatment has been investigated systemically. The results indicate that as-cast 1 Zn alloy is composed mainly of α-Mg, Mg5(RE, Zn) eutectic phase, (Mg, Zn)3RE eutectic phase, stacking faults and block-like compounds rich in RE. Increasing of Zn content result in the disappearance of Mg5(RE, Zn) eutectic phase, but the volume fraction of 14H-typ LPSO phase is increasing, which has made it even more difficult to dissolve into the matrix during homogenization. After homogenization at 520 °C for 48 h, the 14H LPSO phase remains in the alloys with 2 wt.% Zn, but only compounds rich in RE can be seen in the alloy with 1 wt.%Zn. After ageing at 240°C for 18 h, the coherent β′ phase can be found both in 1Zn and 2Zn alloys, resulting in the increase of mechanical properties. The β′, β1 and stacking faults can be found in 1Zn and 2Zn alloys after ageing at 240°C for 100 h. However, it can be concluded that Zn can suppress the formation of LPSO phases but impede the precipitation of β′ and β1 during the aging process. The as-aged alloy with 1% Zn addition shows the optimal mechanical properties.

The hot deformation behavior of Mg-12Gd-1MM-0.6Zr (wt.%) magnesium alloy was tested by Gleeble-1500D hot simulator with reduction of 60% and strain rates from 0.001 to 1 s−1 at the temperature range from 753 to 793 K. The results show that the flow stress is influenced by both, temperatures and strain rates. At constant temperatures, flow stress is increased with strain rate, while at constant strain rates, it decreased with temperature. The constitutive equation of Mg-12Gd-1MM-0.6Zr alloy during hot compression was constructed by the linear regression analysis. Average activation energy and stress exponent were 227.94 kJ/mol and 2.87, respectively. The processing map was plotted and analyzed via the dynamic material model. The most proper ranges for hot deformation temperature and strain rate were found to be 763 to 783 K and 0.01 to 0.1 s−1, respectively.

The microstructures and electrical conductivity of extruded Mg-5.38 wt.%Zn-0.88 wt.%Mn (ZM51) magnesium alloys under four different heat treatments (T5: single aging, two-stage aging; T6:T4+single aging, T4+two-stage aging) were investigated by optical microscopy (OM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and conductivity test. The results show that the electrical conductivity of alloys after different heat treatments was increased with the aging time increasing identically. The conductivity of T6 ZM51 alloy is lower than that of T5 treatment alloy, and the conductivity of alloy with two-stage aging is higher than that of alloys with single-stage aging. In the two-stage aging, the time of pre-aging at low temperature formed dense GP zones which can serve as the nucleation core of the β1' phases, and the formed β1' phases are more diffuse and fine, and the scattering of free electrons are lower. The electrical conductivity of the alloy increased first and then reduced with the increase of the pre-aging time, and the reason is that the alloys form a more diffuse GP zones after pre-aging for 32h, which can be used as the heterogeneous nucleation core of β1' phases, so that the precipitation of the β1' phases are more finely dispersed, thereby increasing the scattering capacity of free electrons.

Microstructure and mechanical properties of Mg-5wt.% Sn-xAl as-cast alloys were studied, for the Al content ranged from 0.5 to 3.0wt.%. It was found that Al element was mainly distributed in Mg17Al12 phase in as-cast alloys, and its increase rose the Mg17Al12 phase share. There were no ternary phases in these alloys. Only two forms of Mg2Sn and Mg17Al12 phases were detected, namely (i) Mg17Al12 phase attached to the end of Mg2Sn phase and (ii) Mg2Sn phase enclosed by Mg17Al12 phases. The grain sizes of these alloys got refined with the growing content of Al element, and 1.5wt% Al content corresponded to the grain size of 33.5um. As for the mechanical properties, the ultimate tensile and yield strengths of the alloys were improved at larger contents of Al. The Mg-5wt.%Sn-3.0wt% alloy had the highest ultimate tensile and yield strengths of 212 and 167MPa, respectively, while Mg-5wt.%Sn-1.5wt%Al alloy had the best elongation of 16.5%.