Impact and usage of the shear thickening fluid (STF) material in damping vibration of bolted flange joints

Bolted flange joints in fuzes undergo high acceleration during penetration, along with nonlinear responses which are forced reaction, structural vibrations, and shock effects. Vibrations of high frequencies aggregate noises and make it harder for the signal processing of fuzes. This study proposed an effective and innovative method of suppressing vibrations of high frequencies caused by impact loading. Shear thickening fluids (STFs) were stuffed into bolted flange joints. A damper of 57 vol/vol% dense silica particle-ethylene glycol suspension was inserted into gaps between the surfaces of the incident bar and the flange. Based on a modified split Hopkinson pressure bar, pulse widths, amplitudes, and structural frequencies of both impact and vibrational response regions were evaluated to examine the effectiveness of the STF damper. The amplitude and pulse width in the vibrational response region were significantly reduced, since this suspension forms jamming clusters subjected to impulses, attenuating the shockwaves. The STF fillers under various lengths of projectiles from 50 mm-400 mm were discussed to validate effectiveness. Further comparisons with epoxy resin fillers with various curing times indicated that the STF inhibited high frequency oscillations as a protector, and damped the dominant frequency of the original structure. However, experimental data showed that the transmission pulse of the incident bar was similar to joints without protection, indicating that the force transmission ratio was not affected by the fillers. These results show the feasibility of STFs as energy absorbers for vibration reduction of bolted flange joints

MicroRNA-210-5p Contributes to Cognitive Impairment in Early Vascular Dementia Rat Model Through Targeting Snap25

Vascular dementia (VD) is the most common form of dementia in elderly people. However, little is understood about the role of microRNAs (miRNAs) involved in cognitive impairment in early VD. Here, a VD model induced by chronic cerebral ischemia and fetal bovine serum (FBS)-free cell model that detects synapse formation was established to investigate the function of miRNAs in early VD. The microarray analysis and real-time reverse transcription polymerase chain reaction (RT-PCR) showed that miR-210-5p increased significantly in the hippocampus of rats with 4 weeks of ischemia. The VD model rats also displayed significant cognitive deficits and synaptic loss. The overexpression of miR-210-5p decreased the synaptic number in primary hippocampal neurons, whereas specific suppression of miR-210-5p resulted in the formation of more synapses. Additionally, intracerebroventricular (ICV) injection of miR-210-5p agomir to VD rats aggravated phenotypes of cognitive impairment and synaptic loss. These VD-induced phenotypes were effectively attenuated by miR-210-5p antagomir. Moreover, bioinformatic prediction revealed that synaptosomal-associated protein of 25 KDa (Snap25) mRNA is targeted by miR-210-5p. The miR-210-5p decreased the luciferase activities of 3’ untranslated region (3’UTR) of Snap25 mRNA. Mutation of predicted miR-210-5p binding sites in the 3’ UTR of Snap25 mRNA abolished the miR-210-5p-induced decrease in luciferase activity. Western blot and immunofluorescence staining confirmed that miR-210-5p targets Snap25. Finally, RT-quantitative PCR (qPCR) and immunofluorescence staining detected that miR-210-5p agomir downregulated Snap25 expression in the cornu ammonis1 (CA1) region of hippocampi in VD rats, whereas miR-210-5p antagomir upregulated Snap25 expression. Altogether, miR-210-5p contributes to cognitive impairment in chronic ischemia-induced VD model through the regulation of Snap25 expression, which potentially provides an opportunity to develop a new therapeutic strategy for VD

Ultrahigh cavitation erosion resistant metal-matrix composites with biomimetic hierarchical structure

Cavitation erosion significantly impairs the serviceability of hydroelectric turbines and causes tremendous economic loss. Therefore, the demand for materials with effective resistance to cavitation erosion is imperative. Here, a novel nickel (Ni)-tungsten carbide (WC) composite coating with biomimetic hierarchical structure (BHS) is proposed. The BHS imitates cuttlebone in microscale and abalone nacre in nanoscale. In microscale, a threedimensional cross-linking eutectic network of Ni-WC sandwiches divides Ni matrix into many small cells, which effectively inhibits crack propagation to an individual cell, controlling the damage caused by cavitation erosion. In nanoscale, numerical modelling results further reveal that the Ni-WC sandwiches can reduce the tensile stress triggered by cavitation impact and dissipate the impact energy, giving rise to ultrahigh cavitation erosion resistance behaviour. The design of similar structures may promote the development of other metal-matrix composites, establishing new methods for developing material systems with advanced properties

Carbon Nanotube-Directed 7 GPa Heterocyclic Aramid Fiber and Its Application in Artificial Muscles

Poly(p-phenylene-benzimidazole-terephthalamide) (PBIA) fibers with excellent mechanical properties are widely used in fields that require impact-resistant materials such as ballistic protection and aerospace. The introduction of heterocycles in polymer chains increases their flexibility and makes it easier to optimize the fiber structure. However, the inadequate orientation of polymer chains is one of the main reasons for the large difference between the measured and theoretical mechanical properties of PBIA fibers. Herein, carbon nanotubes (CNTs) are selected as an orientation seed. Their structural features allow CNTs to orient during the spinning process, which can induce an orderly arrangement of polymers and improve the orientation of the fiber microstructure. To ensure the complete 1D topology of long CNTs (approximate to 10 mu m), PBIA is used as an efficient dispersant to overcome dispersion challenges. The p-CNT/PBIA fibers (10 mu m single-walled carbon nanotube 0.025 wt%) exhibit an increase of 22% in tensile strength and 23% in elongation, with a maximum tensile strength of 7.01 +/- 0.31 GPa and a reinforcement efficiency of 893.6. The artificial muscle fabricated using CNT/PBIA fibers exhibits a 34.8% contraction and a 25% lifting of a 2 kg dumbbell, providing a promising paradigm for high-performance organic fibers as high-load smart actuators. The damage-free single-walled carbon nanotubes (SWNTs) dispersed using poly(p-phenylene-benzimidazole-terephthalamide) (PBIA) are selected as the orientation seed to improve the fiber microstructure and the mechanical properties. The p-SWNT/PBIA fibers exhibit an increase of 22% in tensile strength and 23% in elongation, with a maximum tensile strength of 7.01 +/- 0.31 GPa and a reinforcement efficiency of 893.6.imag