Juglone Inactivates Pseudomonas aeruginosa through Cell Membrane Damage, Biofilm Blockage, and Inhibition of Gene Expression

Due to the strong drug resistance of Pseudomonas aeruginosa (P. aeruginosa), the inhibition effects of conventional disinfectants and antibiotics are not obvious. Juglone extracted from discarded walnut husk, as a kind of plant-derived antimicrobial agent, has the advantages of naturalness, high efficiency, and low residue, with a potential role in the inhibition of P. aeruginosa. This study elucidated the inhibitory effect of juglone on the growth of plankton and the formation of P. aeruginosa biofilm. The results showed that juglone (35 μg/mL) had an irreversible inhibitory effect on P. aeruginosa colony formation (about 107 CFU/mL). The integrity and permeability of the cell membrane were effectively destroyed, accompanied by disorder of the membrane permeability, mass leakage of the cytoplasm, and ATP consumption. Further studies manifested that juglone could induce the abnormal accumulation of ROS in cells and block the formation of the cell membrane. In addition, RT-qPCR showed that juglone could effectively block the expression of five virulence genes and two genes involved in the production of extracellular polymers, thereby reducing the toxicity and infection of P. aeruginosa and preventing the production of extracellular polymers. This study can provide support for the innovation of antibacterial technology toward P. aeruginosa in food.

Profile Optimization of Hydraulic, Polymeric, Sliding Seals by Minimizing an Objective Function of Leakage, Friction and Abrasive Wear

Hydraulic dynamic seals for reciprocating or alternating motion are machine elements with widespread applications in the automotive, aerospace, marine, pharmaceutical and several other industrial sectors. They have been under commercial development for many decades, and are often met in critical positions, consuming a considerable amount of energy during operation. An objective function of mass leakage rate, friction force and an abrasive-wear representative term is proposed in the present study to evaluate the performance of hydraulic, polymeric sliding seals under suitable constraints. Using Variational Calculus, analytical and numerical techniques, the objective function is minimized, resulting in an optimal seal profile that maximizes sealing performance for given, steady-state operating conditions, in additional consideration of the structural integrity and manufacturability of the modified seal. The obtained seal shape and related pressure distribution are reminiscent of those for U-cup and step seals, designs that dominate the industry. In the course of the mathematical analysis, some major obstacles are documented that show how sensitive and complicated sealing performance really is.

Mass-Conserved Wall Treatment of the Non-Equilibrium Extrapolation Boundary Condition in Lattice Boltzmann Method

In lattice Boltzmann simulations, the widely used non-equilibrium extrapolation method for velocity and pressure boundary conditions can cause a constant mass leakage under certain circumstances, particularly when an external force field is imposed on the fluid domain. The non-equilibrium distribution function at the boundary uses a first-order extrapolation method on the corresponding data of adjacent fluid nodes. In addition, based on this extrapolation method, the macroscopic velocity and density at the boundary nodes are obtained. Therefore, the corresponding equilibrium component of the distribution function can be calculated explicitly. Regarding the no-slip wall boundary condition, we found that the mass leakage primarily results from the extrapolation scheme for the density term in the equilibrium component of the distribution function at the boundary node. In this study, a mass-conserved wall treatment method is developed to correct the existing density term for guaranteeing the conservation of mass. Several benchmark test cases were simulated and compared to prove the justification of the newly developed mass-conserved boundary condition, and the results show a good agreement with those in the existing literature.

Experimental Analysis of Abradable Labyrinth Seal Leakage With Simulated Groove: Part 2

In the secondary flow path of centrifugal compressors, abradable seals are in high demand when higher efficiency is the main requirement. This is because abradable seals can maintain very tight clearances between static and rotating components compared to other sealing technology. However, due to the rubbing of the teeth into the abradable material, some grooves can form. The flow physics and mass leakage of abradable seals are strongly dependent on the presence of these grooves and their shape. For cases where no grooves are present, seal leakage is mainly a function of inlet pressure, pressure ratio across the seal and tooth radial clearance. Once grooves are formed, the flow physics and seal leakage also are a function of groove dimensions, tooth clearance and tooth axial position inside the groove. The scope of the present paper is to describe the experimental campaign that has been performed to validate the numerical analysis of part 1 of the paper [1]. The experimental test matrix investigates the groove and teeth positioning effects on seal leakages. To achieve higher accuracy, the key geometric parameters, such as radial and axial gaps, were controlled in the test sample during the tests. For cases where grooves are present the experimental measurements reveal that flow field strongly depends on groove dimensions, tooth radial clearance and tooth axial position. The authors, finally, found generally a good agreement between numerical predictions and measured data, both in terms of leakage and pressure drops across the teeth.