Digital holographic microscopy is used for characterizing the profiles of mean velocity, viscous and Reynolds shear stresses, as well turbulence level in inner part turbulent boundary layers over several super-hydrophobic surfaces (SHSs) with varying roughness/texture characteristics. The friction numbers vary from 693 to 4496, normalized root square values roughness $(k_{rms}^{+})$ 0.43 3.28. wall stress estimated sum at top elements slip velocity obtained profile same elevation. For flow...

Abstract Collective behaviour is typically thought to arise from individuals following fixed interaction rules. The possibility that rules may change under different circumstances has thus only rarely been investigated. Here we show local interactions in flocks of wild jackdaws ( Corvus monedula ) vary drastically contexts, leading distinct group-level properties. Jackdaws interact with a number neighbours (topological interactions) when traveling roosts, but coordinate based on spatial...

In this work, we experimentally investigated the impact of surface roughness on drag reduction as well plastron stability superhydrophobic surfaces (SHSs) in turbulent flows. A series SHSs were fabricated by spraying hydrophobic nanoparticles sandpapers. By changing grit size sandpapers from 240 to 1500, root mean square height (krms) varied 4 14 μm. The experiments performed a channel flow facility, where speed (Um) 0.5 4.4 m/s, and Reynolds number (Rem) based Um changed 3400 26 400. was...

Gas diffusion rates in and out of superhydrophobic surfaces transitional turbulent boundary layers are observed measured at varying Reynolds numbers, pressures, dissolved gas concentrations. Results show a power-law correlation between the Sherwood friction number.

As one of nature's most striking examples collective behaviour, bird flocks have attracted extensive research. However, we still lack an understanding the attractive and repulsive forces that govern interactions between individuals within how these influence neighbours' relative positions ultimately determine shape flocks. We address issues by analysing three-dimensional movements wild jackdaws ( Corvus monedula) in containing 2-338 individuals. quantify social interaction large, airborne...

Super-hydrophobic surface (SHS), which traps micro/nano-scale gas bubbles on solid walls, has been reported to greatly reduce bacterial adhesion and biofouling. However, it is unclear whether how the trapped adhesion. Here, we examine role of by measuring spatial distributions attached bacteria SHS using scanning electron microscopy (SEM). Two SHSs, one with regular micro-grooves, other randomly roughed textures at micro/nano-scales, both created aluminum substrates, were tested. We found...

In this work, we experimentally studied bubble formation on the superhydrophobic surface (SHS) under a constant gas flow rate and at quasi-static regime. SHS with radius RSHS ranging from 4.2 to 19.0 mm was used. We observed two bubbling modes A B, depending RSHS. mode for small RSHS, contact line fixed rim of SHS, angle (θ) initially reduced, then maintained as constant, finally increased. B large continuously expanded, θ slowly reduced. For both modes, during necking, retracts, close...

Abstract We experimentally studied the effect of gas flow rate Q on bubble formation a superhydrophobic surface (SHS). varied in range 0.001 < Q/Q cr 0.35, where is critical value for transition from quasi‐static regime to dynamic regime. The geometrical parameters and forces acting were calculated. found that as increase, detached volume ( V d ) increased. After proper normalization, relationship between generally agreed with those observed bubbles detaching hydrophilic hydrophobic...

The gas (or plastron) trapped between micro/nano-scale surface textures, such as that on superhydrophobic surfaces, is crucial for many engineering applications, including drag reduction, heat and mass transfer enhancement, anti-biofouling, anti-icing, self-cleaning. However, the longevity of plastron significantly affected by diffusion, a process where molecules slowly diffuse into ambient liquid. In this work, we demonstrated could be extended using gas-soluble gas-permeable...

The rapid, cohesive turns of bird flocks are one the most vivid examples collective behaviour in nature, and have attracted much research. Three-dimensional imaging techniques now allow us to characterize kinematics turning their group-level consequences precise detail. We measured wild jackdaws executing two contexts: during transit roosts anti-predator mobbing. All reduced speed turns, probably because constraints on individual flight capability. Turn rates increased with angle turn so...

Tracking the movements of birds in three dimensions is integral to a wide range problems animal ecology, behaviour and cognition. Multi-camera stereo-imaging has been used track three-dimensional (3D) motion dense flocks, but precise localization remains challenge due imaging resolution depth direction optical occlusion. This paper introduces portable system with improved accuracy simple stereo-matching algorithm that can resolve allows us decouple body wing motion, thus measure not only...

Although the longevity of superhydrophobic surface (SHS) induced by diffusive gas transfer has been extensively studied, scaling relation between SHS and undersaturation level liquid is still an open question. In this study, we address question performing experiments where plastron decay visualized a nonintrusive optical technique based on light reflection, diffusion introduced using with low dissolved concentrations, measured status entire surface. We find that (tf) follows relation: tf ∼...

This paper deals with two issues affecting the application of digital holographic microscopy (DHM) for measuring spatial distribution particles in a dense suspension, namely discriminating between real and virtual images accurate detection particle center. Previous methods to separate fields have involved applications multiple phase-shifted holograms, combining reconstructed axially displaced analysis intensity distributions weakly scattering objects. Here, we introduce simple approach based...

Digital inline holography (DIH) has long been used to measure the three-dimensional (3D) distribution of micrometer particles in suspensions. However, DIH experiences a virtual image problem that limits particle density and placement hologram plane relative sample volume. Here, we apply virtual-image-free phase retrieval digital (PRDH) detect opaque 3D volumes exceed $ 2000\;{\rm particles}/{{\rm mm}^3} $2000particles/mm3. PRDH is based on recording two holograms whose planes are displaced...

Abstract We perform a numerical study of the longevity super-hydrophobic surface (SHS) in under-saturated, stationary liquid. numerically solve spatial-temporal evolution gas concentration liquid, time-variation mass flux out plastron, as well time required for plastron to be fully dissolved (i.e., lifetime). find that profiles at different times are self-similar, and reduces with (t) rate 1/t0.5. In addition, we examine impact texture parameters, including pitch, fraction, height, advancing...

A comparison of the movement characteristics between bacteria with and without wall accumulation could potentially elucidate mechanisms biofilm formation. However, authors previous studies have mostly focused on motion that exhibit accumulation. Here, we applied digital holographic microscopy to compare three-dimensional (3D) motions two bacterial strains (Shewanella japonica UMDC19 Shewanella sp. UMDC1): one exhibiting higher concentrations near solid surfaces, other showing similar in...

When using inline digital holographic microscopy (DHM) and placing the hologram plane within a particle suspension, both real virtual images come into focus during reconstruction, limiting our ability to resolve three-dimensional (3D) distribution. Here, we propose new method distinguish between in 3D reconstruction field. This is based on use of weak scatterers, fact that scatterers display distinct intensity distributions along optical axis. We experimentally demonstrate this by localizing...

The measurement of the volume blood cells is important for clinical diagnosis and patient management. While digital holography microscopy has been used to obtain such information, previous off-axis setups usually involve a separated reference beam are thus not very easy implement. Here, we use simple in-line Gabor setup without separation measure shape mounted on glass slides. Inherent holograms, reconstructed phase object affected by virtual image noise, producing errors in cell...

One shortcoming of digital in-line holography (DIH) is the low axial position accuracy due to elongated particle traces in reconstruction field. Here, we propose a method that improves localization DIH when applying it track motion weak phase particles dense suspensions. The proposed detects positions based on local intensities field consisting scattering and incident waves. We perform both numerical experimental tests demonstrate has higher than previous reconstructed scattered show an...

The gas (or plastron) trapped between micro/nano-scale surface textures, such as that on superhydrophobic surface, is crucial for many engineering applications, including drag reduction, heat and mass transfer enhancement, anti-biofouling, anti-icing, self-cleaning. However, the longevity of plastron significantly affected by diffusion, a process where molecular slowly diffuses into ambient liquid. In this work, we demonstrated can be extended using soluble permeable polydimethylsiloxane...

This paper discusses the effect of hologram plane position on tracking particle motions in a 3D suspension using digital holography microscopy. We compare two optical configurations where is located either just outside or middle suspension. In both cases, we record axially separated holograms cameras and subsequently adopt an iterative phase retrieval approach to solve virtual image problem. measure settling 2 µm spheres mm thick sample containing 300 1500particles/mm3. show that setup...