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SiCf/SiC composites were prepared by melt infiltration（MI）process，chemical vapor infiltration combined with precursor infiltration and pyrolysis（CVI+PIP）process and precursor infiltration and pyrolysis（PIP）process，respectively. The microstructures，compositions and properties of SiCf/SiC composites prepared by different processes before and after water-oxygen corrosion at 1300 ℃ were characterized by scanning electron microscopy and its accompanying EDS and X-ray diffractometer. The results show that the distributions of oxygen elements of the fracture surface is obviously different in the composites prepared by different processes，and the phases after corrosion are closely related to the preparation processes. The strength retention rate and modulus retention rate of SiCf/SiC composites prepared by MI process are 84% and 76% after water oxygen corrosion at 1300 ℃ for 50 hours. The strength retention rate of SiCf/SiC composites prepared by CVI+PIP is 64%，and the modulus is increased by 6%. The SiCf/SiC composites prepared by PIP process has a strength retention rate of 49% and a modulus increase of 17%. The composite materials prepared by MI process show oxidation mass gain，while the composite materials prepared by CVI+PIP and PIP process show oxidation mass loss，which are mainly related to its microstructures and compositions.

SiC/SiC composites have the characteristics of high hardness and brittleness, and they are typical difficult materials to process. Laser processing is mainly used to prepare cooling holes. Millisecond and nanosecond lasers mainly use photothermal action to rapidly heat the target material, melt and gasify it, and remove the material with the help of high-speed gas flow. Due to the short pulse duration and high peak power of nanosecond laser, it is easier to realize the gasification of materials, and the thermal effect caused is less. In this paper, millisecond and nanosecond lasers are used to make holes in SiC/SiC composites respectively. The results show that for cooling holes with a diameter of 0.6 mm and an inclination angle of 25 °, the processing time of nanosecond laser is 8.7 times longer than that of millisecond laser. The two kinds of laser processed holes have certain taper, in which the hole cone angle of nanosecond laser processing is 2.12 ° and that of millisecond laser processing is 1.49 °. There are residues in the inner, outlet end and inlet end of the hole processed by millisecond laser, and there are obvious remelting oxidation zone and heat affected zone around the hole. However, there is no obvious residue inside the hole processed by nanosecond laser, there is discoloration at the inlet end of the laser, there is no discoloration at the outlet end, and there is no obvious remelting oxidation zone and heat affected zone. The results of elemental analysis show that both kinds of laser processing can cause the oxidation of materials.

Laminating method is one of the key factors affecting the thermal shock resistance of SiCf/SiC composites prepared by prepreg paving process. Based on the cohesion model, 1200 ℃ high temperature water quenching tests and finite element simulation studies were carried out on SiCf/SiC composite square samples with different orthogonal lay-up methods, which were prepared by the precursor immersion pyrolysis(PIP) process. The results show that the surface temperature of the sample drops sharply during the water quenching process, and there is a large temperature difference between the core and the surface. The temperature difference between the corner and the core can reach up to 1077 ℃. The main failure modes are interlaminar delamination and matrix cracking, and the delamination position is related to the layering method. Moreover, significant differences in the delamination displacement can be observed, due to the difference in the orthogonal lay-up mode: tacking displacement of the main interlaminar delamination of [0/90] and [0/90/0] can reach 0.61 mm, while the [0/0/90/90] layer cracking displacement is only 0.04 mm. In addition, the cracking displacement of the main interlaminar delamination increases gradually with the increase of water quenching time, while the secondary cracks will undergo crack closure after opening.

SiCf/SiC composites with the polycarbosilane and silicon carbide fiber of different pyrolytic carbon (PyC) interphase thicknesses as the reinforcement phase were fabricated by a polymer impregnation and pyrolysis (PIP) method. And SiC whisker was introduced into the SiCf/SiC composites to further improve its performance. It is found that the mechanical properties of SiCf/SiC composites have outstanding tensile strength, fracture toughness and flexural strength of 192.3 MPa, 446.9 MPa and 11.4 MPa·m1/2,, when the PyC interphase thickness is about 230 nm. After the introduction of SiC whisker, into the SiCf/SiC composite matrix, the toughening mechanisms such as whisker pull-out, whisker bridging and crack deflection increase the energy consumption when the crack is transferred in the matrix, and the fracture toughness and bending strength of the composite are increased by 22.9% and 9.1% respectively.

SiCf/SiC composites are consisted of SiC fibers, SiC matrix and interphase. The interphase can transfer stresses from matrix to SiC fibers and deflects microcracks, at the same time, it protects SiC fibers from chemical erosion during the preparation and use of materials, which plays a very important role in regulating the properties of SiCf/SiC composites. In this paper, the effects of precursor gas ratio, carrier gas, deposition pressure, temperature on the deposition rate and microstructure of interphase during the chemical vapor infiltration (CVI) process are summarized. It will be the key and difficult point in the research of SiCf/SiC composite interphase to select appropriate process conditions and prepare BN and its composite multilayer with ideal structure.

Vascular endothelial cells are exposed to shear stresses with disturbed vs. laminar flow patterns, which lead to proinflammatory vs. antiinflammatory phenotypes, respectively. Effective treatment against endothelial inflammation and the consequent atherogenesis requires the identification of new therapeutic molecules and the development of drugs targeting these molecules. Using Connectivity Map, we have identified vitexin, a natural flavonoid, as a compound that evokes the gene-expression changes caused by pulsatile shear, which mimics laminar flow with a clear direction, vs. oscillatory shear (OS), which mimics disturbed flow without a clear direction. Treatment with vitexin suppressed the endothelial inflammation induced by OS or tumor necrosis factor-α. Administration of vitexin to mice subjected to carotid partial ligation blocked the disturbed flow-induced endothelial inflammation and neointimal formation. In hyperlipidemic mice, treatment with vitexin ameliorated atherosclerosis. Using SuperPred, we predicted that apurinic/apyrimidinic endonuclease1 (APEX1) may directly interact with vitexin, and we experimentally verified their physical interactions. OS induced APEX1 nuclear translocation, which was inhibited by vitexin. OS promoted the binding of acetyltransferase p300 to APEX1, leading to its acetylation and nuclear translocation. Functionally, knocking down APEX1 with siRNA reversed the OS-induced proinflammatory phenotype, suggesting that APEX1 promotes inflammation by orchestrating the NF-κB pathway. Animal experiments with the partial ligation model indicated that overexpression of APEX1 negated the action of vitexin against endothelial inflammation, and that endothelial-specific deletion of APEX1 ameliorated atherogenesis. We thus propose targeting APEX1 with vitexin as a potential therapeutic strategy to alleviate atherosclerosis.

Abstract Background Cell death induced by poly(ADP-ribose) (PAR) and mediated by apoptosis-inducing factor (AIF) is well-characterized in models of ischemic tissue injury, but their roles in cancer cell death after chemotherapy are less understood. Methods Here we investigated the roles of PAR and AIF by RNA interference (RNAi) in MDA-MB-231 and MCF-7 breast adenocarcinoma cells after chemotherapy. Differences in effects were statistically tested by analysis-of-variance and unpaired student’s t-test. Results Silencing of AIF by RNAi led to decreased MDA-MB-231 and MCF-7 breast cancer cell death after chemotherapy, which demonstrates a critical role for AIF. RNAi silencing of PAR glycohydrolase (PARG), the primary enzyme that catalyzes the hydrolysis of PAR, led to increased PAR levels but decreased cell death. Further investigation into the possible role of PAR in apoptosis revealed decreased caspase-3/7/8/9 activity in PARG-null cells. Interestingly, the pharmacologic inhibition of caspase activity in PARG-silenced breast cancer cells led to increased cell death after chemotherapy, which indicates that an alternative cell death pathway is activated due to elevated PAR levels and caspase inhibition. AIF silencing in these cells led to profound protection from chemotherapy, which demonstrates that the increased cell death after PARG silencing and caspase inhibition was mediated by AIF. Conclusions The results show a role for AIF in breast cancer cell death after chemotherapy, the ability of PAR to regulate caspase activity, and the ability of AIF to substitute as a primary mediator of breast cancer cell death in the absence of caspases. Thus, the induction of cell death by PAR/AIF may represent a novel strategy to optimize the eradication of breast tumors by activating an alternative cell death pathway.

BackgroundTo map and quantify the proton exchange rate (kex) of brain tissues using improved omega plots in ischemic stroke patients and to investigate whether kex can serve as a potential endogenous surrogate imaging biomarker for detecting the metabolic state and the pathologic changes due to ischemic stroke.New methodThree sets of Z-spectra were acquired from seventeen ischemic stroke patients using a spin echo-echo planar imaging sequence with pre-saturation chemical exchange saturation transfer (CEST) pulse at B1 of 1.5, 2.5, and 3.5 μT, respectively. Pixel-wise kex was calculated from improved omega plot of water direct saturation (DS)-removed Z-spectral signals.ResultsThe derived kex maps can differentiate infarcts from contralateral normal brain tissues with significantly increased signal (893 ± 52 s-1vs. 739 ± 34 s-1, P