Acoustic Emission Mechanism and Source Modeling of Dynamic Crack Detection in Steel Structure

Cracks are dangerous and frequently observed defects in steel structures. Therefore, the understanding of the mechanism of crack is very important to structure safety. Although the mechanism of static crack has been widely studied by researchers, the mechanism of dynamic crack has been left out and seldom been discussed. In this paper, a modeling method for acoustic emission (AE) source of dynamic crack was proposed for the mechanism revelation. In the method, AE signal was related to crack stress based on the theory of elasto-dynamics; the crack stress was inversely modeled from AE signal by employing half-space Green's function and de-convolution procedure. When the method was applied to an AE testing for dynamic crack in steel structure, AE source function representing the time history of crack stress was obtained. The crack stress was found to be a step-like function with a pulse, and with it the mechanism and transient dynamic process of crack growth (crack initiation and propagation) was recovered. The results indicated that, the modeling method is effective for the study on the mechanism of dynamic crack

miR-24 is involved in vertebrate LC-PUFA biosynthesis as demonstrated in marine teleost Siganus canaliculatus

Recently, microRNAs (miRNAs) have emerged as crucial regulators of lipid metabolism. However, the miRNA-mediated regulatory mechanism on long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA) biosynthesis in vertebrates remains largely unknown. Here, we address a potentially important role of miRNA-24 (miR-24) in the regulation of LC-PUFA biosynthesis in rabbitfish Siganus canaliculatus. miR-24 showed significantly higher abundance in liver of rabbitfish reared in brackish water than in seawater for fish fed vegetable oil diets and in S. canaliculatus hepatocyte line (SCHL) cells incubated with alpha-linolenic acid (ALA) than the control group. Similar expression patterns were also observed on the expression of sterol regulatory element-binding protein-1 (srebp1) and LC-PUFA biosynthesis related genes. While opposite results were observed on the expression of insulin-induced gene 1 (insig1), an endoplasmic reticulum membrane protein blocking Srebp1 proteolytic activation. Luciferase reporter assays revealed rabbitfish insig1 as a target of miR-24. Knockdown of miR-24 in SCHL cells resulted in increased Insig1 protein, and subsequently reduced mature Srebp1 protein and expression of genes required for LC-PUFA biosynthesis, and these effects could be attenuated after additional insig1 knockdown. Opposite results were observed with overexpression of miR-24. Moreover, increasing endogenous insig1 by knockdown of miR-24 inhibited Srebp1 processing and consequently suppressed LC-PUFA biosynthesis in rabbitfish hepatocytes. These results indicate a potentially critical role for miR-24 in regulating LC-PUFA biosynthesis through the Insig1/Srebp1 pathway by targeting insig1. This is the first report of miR-24 involved in LC-PUFA biosynthesis and thus may provide knowledge on the regulatory mechanisms of LC-PUFA biosynthesis in vertebrates

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements