Damage characteristics and surface description of near-wall materials subjected to ultrasonic cavitation.

For the analysis of ultrasonic cavitation erosion on the surface of materials, the ultrasonic cavitation erosion experiments for AlCu4Mg1 and Ti6Al4V were carried out, and the changes of surface topography, surface roughness, and Vickers hardness were explored. Cavitation pits gradually expand and deepen with the increase of experiment time, and Ti6Al4V is more difficult to erode by cavitation than AlCu4Mg1. After experiments, the cavitation damage characteristics such as the single pit, the rainbow ring area, the fisheye pit, and some small pits were observed, which can be considered to be induced by a single micro-jet impact, ablation effect caused by the high temperature, micro-jet impingement with a sharp angle, and multibeam micro-jets coupling impact or negative pressure in the local area produced by micro-jet impact, respectively. The surface roughness and Vickers hardness of the material increase slowly after rapid growth at different points in time as the experiment time increases. With the increase of the ultrasonic amplitude, both of them first increase and then decrease after the ultrasonic amplitude is greater than 10.8 µm. The increases in surface roughness and Vickers hardness tend to decrease as the viscosity coefficient increases. Ultrasonic cavitation can cause submicron surface roughness and increase surface hardness by 20.36%, so it can be used as a surface treatment method.

Ultrasonic cavitation damage characteristics of materials and a prediction model of cavitation impact load based on size effect.

High-speed micro-jet produced by cavitation collapse near the wall is the main mechanism of material damage, and cavitation pit is the most typical damage feature. The reason why high-pressure and high-speed micro-jet can only cause nano- and microscale cavitation pit is that the micro-jet is a short-term impact load of nano- and microscale, and the material shows size effect during the formation of pits. To further explore the cavitation damage characteristics and deformation mechanism of materials, the theoretical framework of indentation test and J-C constitutive model were adopted, and the size effect of materials during the process of cavitation pit formation was mainly considered, and the prediction models of cavitation impact load, impact pressure and velocity of micro-jet were established. The results showed that the equivalent stress and strain of cavitation pit and the impact pressure and velocity of micro-jet are only related to the diameter-to-depth ratio of pit without size effect, and also to the diameter of pit with size effect. Larger diameter and deeper depth of the pit infers greater cavitation impact load, and the influence of the pit diameter is more obvious. When considering the size effect, there is an additional size effect coefficient: 1+54hpα2µ2bdp2σJC2. In the selected size range of pit, the cavitation impact load, impact pressure and velocity of micro-jet predicted with size effect increase by 0.9408%-322.5% compared with those without size effect. The maximum increase ratio appears at the minimum of diameter-to-depth ratio of pit (dp = 2 µm and dh = 2 µm), that is, the smaller the pit diameter is and the greater the depth is, the greater the increase ratio is. Ten typical cavitation pits were selected for inversion analysis. The impact pressure and velocity of micro-jet with and without size effect are 473-1131 MPa and 355-848 m/s, and 427-604 MPa and 320-453 m/s, respectively. The predicted values increase by about 11%-88% when considering the size effect, and the micro-jet velocity predicted is closer to that observed by high-speed cameras, which confirms the necessity and rationality of size effect in the inversion analysis of cavitation pits.

Switching on the activity of 1,5-diaryl-pyrrole derivatives against drug-resistant ESKAPE bacteria: Structure-activity relationships and mode of action studies.

Antibiotic resistance represents a major threat worldwide. Gram-positive and Gram-negative opportunistic pathogens are becoming resistant to all known drugs mainly because of the overuse and misuse of these medications and the lack of new antibiotic development by the pharmaceutical industry. There is an urgent need to discover structurally innovative antibacterial agents for which no pre-existing resistance is known. This work describes the identification, synthesis and biological evaluation of a novel series of 1,5-diphenylpyrrole compounds active against a panel of ESKAPE bacteria. The new compounds show high activity against both wild type and drug-resistant Gram + ve and Gram-ve pathogens at concentrations similar or lower than levofloxacin. Microbiology studies revealed that the plausible target of the pyrrole derivatives is the bacterial DNA gyrase, with the pyrrole derivatives displaying similar inhibitory activity to levofloxacin against the wild type enzyme and retaining activity against the fluoroquinolone-resistant enzyme.