The Effect of Surface Geometry of Solid Wall On the Collapse of a Cavitation Bubble

The objective of this paper is to reveal the influence of different surface geometric conditions on the dynamic behavior characteristics of a laser-induced bubble collapse. A high-speed camera system was used to record the oscillation process of the laser-induced bubble on plane solid walls with different roughness and a wall containing reentrant cavities full of water or gas. The focus is on the quantitative analysis of the morphological characteristics of the cavitation bubble near the solid wall under different surface forms during the first two oscillation period. The results show that the dimensionless ratio γ, defined as the distance from the center of the bubble to the wall divided by the maximum radius of the bubble, has a great influence on the change of the cavitation shape in the direction of the vertical wall. Different surface geometries without gas in our cases have no significant effect on the collapse time of cavitation bubbles. While for the surface containing gas, the direction of movement of the bubble accompanying the micro-jet will greatly change during the collapse of the cavitation bubble, and the collapse time seems to be independent of the dimensionless ratio γ. These achievements shed the light for the engineering to avoid the damage of the micro-jet caused by design suitable surface geometry.

A computational method for detecting aspect ratio and problematic features in additive manufacturing

In metal additive manufacturing, geometries with high aspect ratio (AR) features are often associated with defects caused by thermal stresses and other related build failures. Ideally, excessively high AR features would be detected and removed in the design phase to avoid unwanted failure during manufacture. However, AR is scale and orientation independent and identifying features across all scales and orientations is exceptionally challenging. Furthermore, not all high AR features are as easy to recognise as thin walls and fine needles. There is therefore a pressing need for further development in the field of problematic features detection for additive manufacturing processes. In this work, a dimensionless ratio (D1/D2) based on two distance metrics that are extracted from triangulated mesh geometries is proposed. Based on this method, geometries with different features (e.g. thin wall, helices and polyhedra) were generated and evaluated to produce metrics that are similar to AR. The prediction results are compared with known theoretical AR values of typical geometries.By combining this metric with mesh segmentation, this method was further extended to analyse the geometry with complex features. The proposed method provides a powerful, general and promising way to automatically detect high AR features and tackle the relevant defect issues prior to manufacture.

Floating and sinking of self-assembled spheres on liquid-liquid interfaces: rafts versus stacks

The floating and sinking of objects on fluid-fluid interfaces occurs in nature, and has many important implications in technology. Here, we study the stability of floating self-assembled spheres on an oil-water interface, and how the sphere deposition geometry affects the size limits of the assemblies before they collapse and sink through the interface. Specifically, we compare the critical size of particle rafts to particle stacks. We show that, on liquid-liquid interfaces, monolayer rafts and stacked sphere exhibit different scaling of the critical number of spheres to the Bond number - the dimensionless ratio of buoyancy to interfacial tension effects. Our results indicate that particle stacks will sink with a lower threshold number of particles than particle rafts. This finding may have important implications to engineering applications where interfacial assemblies are not monolayers.

Floating and sinking of self-assembled spheres on liquid-liquid interfaces: rafts versus stacks

The floating and sinking of objects on fluid-fluid interfaces occurs in nature, and has many important implications in technology. Here, we study the stability of floating self-assembled spheres on an oil-water interface, and how the sphere deposition geometry affects the size limits of the assemblies before they collapse and sink through the interface. Specifically, we compare the critical size of particle rafts to particle stacks. We show that, on liquid-liquid interfaces, monolayer rafts and stacked sphere exhibit different scaling of the critical number of spheres to the Bond number - the dimensionless ratio of buoyancy to interfacial tension effects. Our results indicate that particle stacks will sink with a lower threshold number of particles than particle rafts. This finding may have important implications to engineering applications where interfacial assemblies are not monolayers.

Wall Effects On the Flow Dynamics of a Rigid Sphere in Motion

The presence of a wall near a rigid sphere in motion is known to disturb the particle fore and aft flow field symmetry and to affect the hydrodynamic force. An Immersed Boundary Direct Numerical Simulation (IB-DNS) is used in this study to determine the wall effects on the dynamics of a free-falling sphere and the drag of a sphere moving at a constant velocity. The numerical results are validated by comparison to the published experimental, numerical, and analytical data. The pressure and velocity fields are numerically computed when the particle is in the vicinity of the wall; the transverse (lift) and longitudinal (drag) parts of the hydrodynamic force are calculated; its rotational velocity is also investigated in the case of a free-falling sphere. The flow asymmetry also causes the particle to rotate. The wall effect is shown to be significant when the dimensionless ratio of the wall distance to the particle diameter, L/D, is less than 3. The wall effects are more pronounced and when the particle Reynolds number, Re, is less than 10. Based on the computational results, a useful correlation for the wall effects on the drag coefficients spheres is derived in the range 0.75 < L/D < 3 and 0.18 < Re < 10.

Intracellular coupling modulates biflagellar synchrony

Beating flagella exhibit a variety of synchronization modes. This synchrony has long been attributed to hydrodynamic coupling between the flagella. However, recent work with flagellated algae indicates that a mechanism internal to the cell, through the contractile fibres connecting the flagella basal bodies, must be at play to actively modulate flagellar synchrony. Exactly how basal coupling mediates flagellar coordination remains unclear. Here, we examine the role of basal coupling in the synchronization of the model biflagellate Chlamydomonas reinhardtii using a series of mathematical models of decreasing levels of complexity. We report that basal coupling is sufficient to achieve inphase, antiphase and bistable synchrony, even in the absence of hydrodynamic coupling and flagellar compliance. These modes can be reached by modulating the activity level of the individual flagella or the strength of the basal coupling. We observe a slip mode when allowing for differential flagellar activity, just as in experiments with live cells. We introduce a dimensionless ratio of flagellar activity to basal coupling that is predictive of the mode of synchrony. This ratio allows us to query biological parameters which are not yet directly measurable experimentally. Our work shows a concrete route for cells to actively control the synchronization of their flagella.

Optimization of the distance between the rows in solar collectors’ arrays

The article presents some results of the analysis of the influence of the distance between the collectors’ rows in thermal solar systems on the degree of self-shading. For the purposes of the study, the dimensionless ratio Ks between the required minimum distance between the rows, guaranteeing the absence of self-shading, and the height of the collectors, was used. A simulation study was performed for specific climatic conditions and the annual solar radiation incident on the collectors’ array at different degrees of self-shading was determined. Its annual financial equivalent for various alternative heat sources (electricity, natural gas, wood pellets, district heating and gas oil) was assessed, as well as the necessary investment costs for construction of the solar system. A regression relationship between the coefficient of net present value NPVQ and Ks was derived and its optimal values were established, which ensure the achievement of maximum economic efficiency of the system operation for the considered replaced heat sources.

Nuclear spin relaxation as a probe of zeolite acidity: a combined NMR and TPD investigation of pyridine in HZSM-5

The relative surface affinities of pyridine within microporous HZSM-5 zeolites are explored using two-dimensional 1H nuclear magnetic resonance (NMR) relaxation time measurements. The dimensionless ratio of longitudinal-to-transverse nuclear spin relaxation...

Role of ratio-based metrics in cardiology

In cardiovascular studies, two related parameters that determine the same physical variable are often recorded. Interpretation of the calculated indicators presented in the form of ratios and differences is difficult, since they can be associated with several combinations of primary data giving the same value.Aim. To find a way to overcome this limitation and take a more comprehensive approach.Material and methods. We analyzed the data on left ventricular volume and blood pressure (BP) in 275 patients (women — 207), obtained using echocardiography and BP monitor. To calculate a lost companion (c) value based on a difference or dimensionless ratio, we applied the Pythagorean theorem. The lost companion isdefined as the hypotenuse in each study area. To calculate the pulse pressure companion (PP), the following formula was used: PP(c)=Ö(SBP2+SBP2). Similar methods were applied to ejection fraction (EF), augmentation pressure (AG) and AG/PP ratio, resulting in the ratio called augmentation index (AIx).Results. 1. Mean blood pressure (MBP) acts as a surrogate for the PP companion (PPc) values (R=0,970, N=257). 2. We have identified correlations between PPc and pulse wave velocity (R=0,397, N=193), and AGc with AIx (75) (R=0,662, N=198). 3. EF has an inverse relationship with the end diastolic volume (EDV) (R=-0,559, N=187), and the ventricular-arterial coupling (VAC) correlates with ESV (r=-0,627, N=180). 4. Comparison of EDV and VACc revealed R of 0,949.Conclusion. Companions calculated from the available data can have significant additional diagnostic value without the need for additional measurements. It is important to note that the combination of traditional ratio-based and suggested companions allows for more accurate data on individual patients.

Role of combined cell membrane and wall mechanical properties regulated by polarity signals in cell budding

The budding yeast, Saccharomyces cerevisiae, is a prime biological model to study mechanisms underlying asymmetric growth. Previous studies have shown that, prior to yeast bud emergence, polarization of a conserved small GTPase, Cdc42, must be established. Additionally, hydrolase changes the mechanical properties of the cell wall and plasma membrane with the periplasm between them (cell surface). However, how the surface mechanical properties in the emerging bud are different from the properties of the mother cell and their role in bud formation are not well understood. We hypothesize that the polarized chemical signal alters the local dimensionless ratio of stretching to bending stiffness of the cell surface of the emerging yeast bud. To test this hypothesis, a novel three-dimensional coarse-grained particle-based model has been developed which describes inhomogeneous mechanical properties of the cell surface. Model simulations suggest that regulation of the dimensionless ratio of stretching to bending stiffness of the cell surface is necessary to initiate bud formation. Furthermore, model simulations predict that bud shape depends strongly on the experimentally observed molecular distribution of the polarized signaling molecule Cdc42, while the neck shape of the emerging bud is strongly impacted by the properties of the chitin and septin ring. This 3D model of asymmetric cell growth can also be used for studying viral budding and other vegetative reproduction processes performed via budding.