The copper matrix composites were prepared by spark plasma sintering (SPS). The current-carrying friction and wear tests were carried out on a self-made HST-100 high-speed current-carrying friction and wear tester, and the effect of the graphite content on the current-carrying friction and wear properties of the composite material was studied. The results show that with an increase in graphite content, the average friction coefficient and wear rate of the two materials decreased significantly, the fluctuation amplitude of the friction coefficient was also significantly reduced, and the average friction coefficient of copper-coated graphite composite with graphite content of 10 wt.% was 0.100; when the graphite content was the same and more than 5.0 wt.%, the average friction coefficient and wear rate of copper–graphite composites were slightly higher than copper–copper-coated graphite composites; the current-carrying efficiency and current-carrying stability of the copper matrix composite were obviously higher than that of copper material; there was a mechanical wear area and arc erosion area on the wear surface of the composites, with the increase in graphite content, the adherence and the tear of the mechanical wear area weakened, the rolling, plastic deformation increased, and the surface roughness decreased obviously. The surface roughness of the wear surface of copper–copper-coated graphite composites with graphite content of 10 wt.% was 3.17 μm. The forms of arc erosion included melting and splashing, and were mainly distributed in the friction exit area.
Cancer is a type of malignant affliction threatening human health worldwide; however, the molecular mechanism of cancer pathogenesis remains to be elusive. The oncogenic hedgehog (Hh) pathway is a highly evolutionarily conserved signaling pathway in which the hedgehog-Patched complex is internalized to cellular lysosomes for degradation, resulting in the release of Smoothened inhibition and producing downstream intracellular signals. Noncoding RNAs (ncRNAs) with diversified regulatory functions have the potency of controlling cellular processes. Compelling evidence reveals that Hh pathway, ncRNAs, or their crosstalk play complicated roles in the initiation, metastasis, apoptosis and drug resistance of cancer, allowing ncRNAs related to the Hh pathway to serve as clinical biomarkers for targeted cancer therapy. In this review, we attempt to depict the multiple patterns of ncRNAs in the progression of malignant tumors via interactions with the Hh crucial elements in order to better understand the complex regulatory mechanism, and focus on Hh associated ncRNA therapeutics aimed at boosting their application in the clinical setting.
Copper-graphite composites were prepared by spark plasma sintering (SPS) with copper powder and copper-coated graphite powder. The effect of particle size of raw material powder on the current-carrying friction properties of copper-graphite composites was studied. The results show that the friction coefficient of the composites decreased with the decrease of the particle size of copper-coated graphite powder, the friction coefficient of the composites increased with the decrease of the particle size of the copper powder, the wear rate of the composites increased with the decrease of the particle size of the copper-coated graphite powder, and the wear rate of the composites increased significantly with the decrease of the particle size of the copper-coated graphite powder. The current carrying properties of composites with different particle size ratios and QCr0.5 pairs are good and fluctuate little. The current-carrying friction properties of 150 μm copper powder and 75 μm copper-coated graphite powder were found to be the best. The wear surface could be divided into mechanical wear area and arc erosion area. The main area of arc erosion was less than 15% of the total area, and it was mainly distributed in the friction outlet area. The main forms of mechanical wear included furrow, rolling deformation, cold welding, and tearing, among other forms. Graphite film was formed on the surface. The surface quality of the composite prepared by 150 μm copper powder and 75 μm copper-coated graphite powder was the best, the Sa was 3.22 μm, rolling deformation was the most adequate, no large tear pit and furrow appeared, and the carbon content on the worn surface was much higher than that in the composite. The behavior of arc erosion was mainly melting and splashing, and the particle size of the original powder had little effect on it.
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