Bacterial swarmer cells in confinement: A mesoscale hydrodynamic simulation study

A wide spectrum of Peritrichous bacteria undergo considerable physiological changes when they are inoculated onto nutrition-rich surfaces and exhibit a rapid and collective migration denoted as swarming. Thereby, the length of such swarmer cells and their number of flagella increases substantially. In this article, we investigated the properties of individual E. coli-type swarmer cells confined between two parallel walls via mesoscale hydrodynamic simulations, combining molecular dynamics simulations of the swarmer cell with the multiparticle particle collision dynamics approach for the embedding fluid. E. coli-type swarmer cells are three-times longer than their planktonic counter parts, but their flagella density is comparable. By varying the wall separation, we analyze the confinement effect on the flagella arrangement, on the distribution of cells in the gap between the walls, and on the cell dynamics. We find only a weak dependence of confinement on the bundle structure and dynamics. The distribution of cells in the gap changes from a geometry-dominated behavior for very narrow to fluid-dominated behavior for wider gaps, where cells are preferentially located in the gap center for narrower gaps and stay preferentially next to one of the walls for wider gaps. Dynamically, the cells exhibit a wide spectrum of migration behaviors, depending on their flagella bundle arrangement, and ranges from straight swimming to wall rolling

Modelling the Mechanics and Hydrodynamics of Swimming E. coli

The swimming properties of an E. coli-type model bacterium are investigated by mesoscale hy- drodynamic simulations, combining molecular dynamics simulations of the bacterium with the multiparticle particle collision dynamics method for the embedding fluid. The bacterium is com- posed of a spherocylindrical body with attached helical flagella, built up from discrete particles for an efficient coupling with the fluid. We measure the hydrodynamic friction coefficients of the bacterium and find quantitative agreement with experimental results of swimming E. coli. The flow field of the bacterium shows a force-dipole-like pattern in the swimming plane and two vor- tices perpendicular to its swimming direction arising from counterrotation of the cell body and the flagella. By comparison with the flow field of a force dipole and rotlet dipole, we extract the force- dipole and rotlet-dipole strengths for the bacterium and find that counterrotation of the cell body and the flagella is essential for describing the near-field hydrodynamics of the bacterium

Binding kinetics of membrane-anchored receptors and ligands: molecular dynamics simulations and theory

The adhesion of biological membranes is mediated by the binding of membrane-anchored receptor and ligand proteins. Central questions are how the binding kinetics of these proteins is affected by the membranes and by the membrane anchoring of the proteins. In this article, we (i) present detailed data for the binding of membrane-anchored proteins from coarse-grained molecular dynamics simulations, and (ii) provide a theory that describes how the binding kinetics depends on the average separation and thermal roughness of the adhering membranes, and on the anchoring, lengths, and length variations of the proteins. An important element of our theory is the tilt of bound receptor-ligand complexes and transition-state complexes relative to the membrane normals. This tilt results from an interplay of the anchoring energy and rotational entropy of the complexes and facilitates the formation of receptor-ligand bonds at membrane separations smaller than the preferred separation for binding. In our simulations, we have considered both lipid-anchored and transmembrane receptor and ligand proteins. We find that the binding equilibrium constant and binding on-rate constant of lipid-anchored proteins are considerably smaller than the binding constant and on-rate constant of rigid transmembrane proteins with identical binding domains.Comment: 13 pages, 6 figures; to appear in J. Chem. Phy

The research of polishing nozzle quality based on discrete element method

In order to get further study for the effect of abrasive grains to the wall of the workpiece during polishing process, a new method of discrete element that carry out the numerical simulation with DEM is put forward, and the visual calculation is performed for the abrasive grain movement in the nozzle. The interaction of particles-particles or particles-workpiece wall during the polishing process and the tracks of single grain in the workpiece are analyzed by observing the distribution of abrasive grain in the workpiece at different time. The surface removal mechanism of abrasive grains to the workpiece material is discussed by analyzing the collision process of particles to the workpiece wall. The wear level of the abrasive grains to the inner surface of the workpiece is studied through the force of abrasive grain to the workpiece wall consumption, and finally explore the cutting effect of particles to workpiece wall. As a consequence, the abrasive flow processing experiment is carried out. The surface roughness of the large hole and small hole of the nozzle are detected by stylus measurement. The conclusion shows that the surface roughness for the large hole and the small hole before the experiment is1.741 μm and 1.201 μm, its 0.801 μm, 0.651 μm after it. Further roughness tests are performed on the surface of the pores by means of a grating surface measuring instrument. The result indicates that the surface roughness reduces from 2.67 μm to 0.697 μm, 0.728 μm, 0.782 μm. Apparently, the surface roughness of the hole is sharply reduced, which has a smooth and flat inner surface, the effectiveness and reliability of the abrasive flow are verified

Effects of different inlet velocity on the polishing quality of abrasive flow machining

In order to study the effect of different inlet velocity on the polishing quality of abrasive flow machining, this paper takes the variable diameter pipe as an example. The fluid dynamic pressure and total energy of abrasive particles under coupling field with different inlet velocities were carried out by using computational fluid dynamics software. The results of numerical analysis show that the polishing quality becomes better with the increase of the inlet velocity. At the same inlet velocity, the smaller the pipe diameter is, the higher the polishing quality will be. Therefore, the optimum inlet velocity can be selected by numerical simulation according to the size of the aperture of workpiece in the actual processing, which can provide technical support for the production

Numerical analysis in viscosity-temperature characteristics of solid-liquid two-phase abrasive flow polishing

The non-linear tube is widely used in military and civil fields and the general performance of the machine depends on the internal channel surface quality of it. The effective ways to improving the surface quality is solid-liquid two-phase abrasive flow polishing technology. So, the numerical analysis about the internal channel of non-linear tube polished by abrasive flow is implemented to analyze the effect of viscosity-temperature characteristics of abrasive flow polishing on the internal channel surface quality. Turbulent kinetic energy, intensity and viscosity, nephogram of the dynamic pressure distribution, and corresponding relation of temperature and turbulent kinetic energy, near the wall of non-linear tube, are received from the simulation in different initial turbulent kinetic energy and temperature which provides a theoretical basis for controlling the surface quality

Study on the polishing of curved pipe parts by solid liquid two phase abrasive flow

In order to study the effect of abrasive flow on the polishing quality of the elbow parts, 90° elbow is used as the research object. The dynamic pressure and wall shear force of different incident angle flow is numerically simulated by setting the process parameters of elbow polishing, which shows that the properly increase entrance angle can improve the uniformity and reliability of abrasive flow polishing, and then, the numerical simulation analysis of turbulence viscosity and wall shear force for different incident pressures are also simulated. It indicates that the properly enhance inlet pressure is helpful to improve the polishing effect and polishing uniformity. Finally, the abrasive grain polishing test is carried out. After the measurement by Mahr stylus measuring instrument, the surface roughness decreases from 1.968 μm to 0.212 μm, which confirm the effectiveness of abrasive flow processing. The roughness value of the inside at the bend after the polishing of the abrasive grain is 0.274 μm by the measurement of the NT1100 Grating Surface Roughness Meter under the pressure condition of 7 MPa. By comparing the polishing effect of the pipe at different pressure and inflow angle, it is found that increase the pressure and inlet angle can improve the polishing effect of the abrasive flow on the curved pipe, but at the same time the uniformity of the polishing is decreased, in other words, the roughness gap at different positions of the elbow will increase. Therefore, it is exceedingly necessary to make some adjustments when in the actual operation

Quality analysis of T-tube with solid-liquid two-phase abrasive flow polished

For the problem affected by speed and uneven grinding in abrasive flow with non-linear pipe, the T-tube is regarded as the research object, the numerical simulation of the flow state of the abrasive flow under different inlet velocities is carried out by using the large eddy simulation (LES). The dynamic pressure, turbulent kinetic energy, turbulence intensity and wall shear force under different inlet conditions are compared and analyzed. We can see from the numerical analysis that with the increase of inlet velocity, the dynamic pressure, turbulent kinetic energy, turbulence intensity and wall shear force also increase, and the polished effect is improved. The surface roughness and surface morphology of the T-tube workpiece before and after polished of abrasive flow are measured, the surface roughness decreased from 3.633 μm to 1.201 μm. Therefore, the effectiveness of the abrasive flow polished inner channel structure is confirmed, Also the credibility of numerical analysis is verified and provides theoretical support for the development of abrasive flow polished technology

All-Inorganic Perovskite Solar Cells With Both High Open-Circuit Voltage and Stability

Metal halide perovskite solar cells based on all-inorganic CsPbBr3 have attracted considerable attentions recently, due to their high open-circuit voltage and good stability. However, the fabrication of CsPbBr3 film is limited by the poor solubility of cesium precursors in organic solvents by the one-step method. Here, we successfully fabricated CsPbBr3 film solar cells by employing colloid nanocrystal. The effects of technique parameters, including purification times, anneal temperatures, and spin-coating times on film morphology, optical spectra, and device performance are investigated in detail. The highest power conversion efficiency of 4.57% has been achieved based on a large open-circuit voltage of 1.45 V and a large short-circuit current of 9.41 mA cm−2. A large open-circuit voltage results from the reduced non-radiative energy loss channels and defect states while a large short-circuit current is related to the high conductivity induced by the removal of organic ligands with the increased nanocrystal electronic coupling. Furthermore, excellent stability in air is disclosed on the unencapsulated device suggesting the enormous potential for developing high open-circuit photovoltaic devices with high stability in future