Temperature and Strain Rate Dependence on the Tensile Mechanical Properties, Constitutive Equations, and Fracture Mechanisms of MarBN Steel.

The effect of strain rate and temperature on the thermomechanical behavior and microstructure of MarBN steel is studied with the strain rates of 5 × 10-3 and 5 × 10-5 s-1 from room temperature (RT) to 630 °C. At high strain rates of 5 × 10-3 s-1, the Holloman and Ludwigson equations can better predict tensile plastic properties. In contrast, under low strain rates of 5 × 10-5 s-1, coupling of the Voce and Ludwigson equations appears to predict the flow relationship at RT, 430, and 630 °C. However, the deformation microstructures have the same evolution behavior under strain rates and temperatures. Geometrically necessary dislocations appear along the grain boundaries and increase the dislocation density, which results in the formation of the low-angle grain boundaries and a decrease in the number of twinning. The strengthening sources of MarBN steel include grain boundary strengthening, dislocation interactions, and multiplication. The fitted R2 values of these models (JC, KHL, PB, VA, ZA) to plastic flow stress at 5 × 10-5 s-1 are greater than 5 × 10-3 s-1 for MarBN steel. Due to the flexibility and minimum fitting parameters, the phenomenological models of JC (RT and 430 °C) and KHL (630 °C) give the best prediction accuracy under both strain rates.

Analysis of the Tensile Deformation Behaviors and Microstructure Characterization under Various Temperatures of MarBN Steel by EBSD.

The uniaxial tensile behavior of MarBN steel with a constant strain rate of 5 × 10-5 s-1 under various temperatures ranging from room temperature to 630 °C was analyzed. This study aimed to identify the effect of the temperature on the tensile behavior and to understand the microstructure deformation by electron backscatter diffraction. The tensile results showed that the yield and ultimate tensile strength decreased with increasing temperature. Serrated flow was observed from 430 °C to 630 °C. The electron backscatter diffraction analysis showed that the low-angle grain boundaries decreased at the medium deformation and increased at the maximum deformation. In contrast, they decreased with increasing temperatures. In addition, the number of voids increased with the increasing plastic strain. As the strain increased, the voids joined together, and the tiny cracks became larger and failed. Three mechanisms were responsible for the tensile deformation failure at various temperatures: grain rotation, the formation and rearrangement of low angle grain boundaries, and void nucleation and propagation. Finally, the formation of the low-angle grain boundaries and voids under different degrees of deformation is discussed.

Tensile Behavior, Constitutive Model, and Deformation Mechanisms of MarBN Steel at Various Temperatures and Strain Rates.

To reduce harmful gas emission and improve the operational efficiency, advanced ultra-supercritical power plants put forward higher requirements on the high temperature mechanical properties of applied materials. In this paper, the tensile behavior and deformation mechanisms of MarBN steel are discussed at different strain rates (5 × 10-3 s-1, 5 × 10-4 s-1, and 5 × 10-5 s-1) under room temperature and 630 °C. The results show that the tensile behavior of the alloy is dependent on temperature and strain rate, which derived from the balance between the average dislocation velocity and dislocation density. Furthermore, observed dynamic recrystallized grains under severe deformation reveal the existence of dynamic recovery at 630 °C, which increases the elongation compared to room temperature. Finally, three typical constitutive equations are used to quantitatively describe the tensile deformation behavior of MarBN steel under different strain rates and temperatures. Meanwhile, the constitutive model of flow stress for MarBN steel is developed based on the hyperbolic sine law.

NtAGO1 positively regulates the generation and viral resistance of dark green islands in Nicotiana tabacum.

Dark green islands (DGIs) are the outcome of post-transcriptional gene silencing (PTGS) in antiviral immunity, but their characteristics related to PTGS remain largely unknown. In this study, the cucumber mosaic virus (CMV) was inoculated on Nicotiana tabacum plants to explore the PTGS features of DGIs. Our results showed that higher expressions of PTGS-associated genes, especially NtAGO1, present in DGIs. To investigate the role of NtAGO1 in the generation and the antiviral effect of DGIs, NtAGO1 was then over-expressed or knocked out in N. tabacum plants through agrobacterium-mediated genetic transformation. The results showed that more DGIs with larger areas appeared on NtAGO1 over-expressed plants, accompanied by less virus accumulation, less reactive oxygen species production, and seldom membrane damage, whereas fewer DGIs appeared on NtAGO1 knockout plants with more damage on infected plants. In addition, the NtAGO1-participated antiviral process could promote the transduction of the salicylic acid-mediated defense pathway. Taken together, our results indicate that DGIs are maintained by a stronger PTGS mechanism, and NtAGO1 positively regulates the generation and viral resistance of DGIs in N. tabacum.

Thevetiaflavone from Wikstroemia indica ameliorates PC12 cells injury induced by OGD/R via improving ROS­mediated mitochondrial dysfunction.

Cerebral ischemia and following reperfusion affects many people worldwide. To discover efficient therapeutic approaches, numerous natural products have been investigated. The current study investigated the protective effects of thevetiaflavone, a natural flavonoid obtained from Wikstroemia indica, and the associated mechanisms using PC12 cells induced by oxygen and glucose deprivation. As a result, thevetiaflavone improves cell viability and suppresses the leakage of lactate dehydrogenase from the cytoplasm. Further investigation of the mechanisms demonstrated that thevetiaflavone decreases overproduction of ROS and ameliorates ROS­mediated mitochondrial dysfunction, including collapse of mitochondrial membrane potential and mitochondrial permeability transition pore opening. Thevetiaflavone reduces the intracellular Ca2+ level, which is closely associated with mitochondrial function and interplays with ROS. Furthermore, thevetiaflavone inhibits apoptosis in PC12 cells through upregulating the expression of Bcl­2 and downregulating that of Bax and caspase­3 in addition to increasing the activity of caspase­3. These results further indicate the protective effects of thevetiaflavone in vivo and its application in the clinic.

Cutaneous protothecosis in patient with diabetes mellitus and review of published case reports.

Protothecosis is an opportunistic infection caused by Prototheca, usually called as saprophytes, and is frequently found in natural and living surroundings with low virulence, but may cause chronic infection in immunocompromised individuals. We report a case of cutaneous protothecosis with zopfii var. portoricensis infection in a 66-year-old diabetic woman following hand surgery on middle right finger. Mycology study showed that smooth, creamy white, yeast-like colonies grown after necrotic tissue was cultured on Sabouraud dextrose agar at both 37 and 25°C. The organism was then identified as Prototheca zopfii var. portoricensis by molecular identification and also found from histopathology of the lesion. The lesion got improved with intravenous amphotericin B and itraconazole.