3D flow in the venom channel of a spitting cobra: do the ridges in the fangs act as fluid guide vanes?

The spitting cobra Naja pallida can eject its venom towards an offender from a distance of up to two meters. The aim of this study was to understand the mechanisms responsible for the relatively large distance covered by the venom jet although the venom channel is only of micro-scale. Therefore, we analysed factors that influence secondary flow and pressure drop in the venom channel, which include the physical-chemical properties of venom liquid and the morphology of the venom channel. The cobra venom showed shear-reducing properties and the venom channel had paired ridges that span from the last third of the channel to its distal end, terminating laterally and in close proximity to the discharge orifice. To analyze the functional significance of these ridges we generated a numerical and an experimental model of the venom channel. Computational fluid dynamics (CFD) and Particle-Image Velocimetry (PIV) revealed that the paired interior ridges shape the flow structure upstream of the sharp 90° bend at the distal end. The occurrence of secondary flow structures resembling Dean-type vortical structures in the venom channel can be observed, which induce additional pressure loss. Comparing a venom channel featuring ridges with an identical channel featuring no ridges, one can observe a reduction of pressure loss of about 30%. Therefore it is concluded that the function of the ridges is similar to guide vanes used by engineers to reduce pressure loss in curved flow channels

The Belle II Physics Book

We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB $e^+e^-$ collider. Belle II collected its first collisions in 2018, and is expected to operate for the next decade. It is anticipated to collect 50/ab of collision data over its lifetime. This book is the outcome of a joint effort of Belle II collaborators and theorists through the Belle II theory interface platform (B2TiP), an effort that commenced in 2014. The aim of B2TiP was to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: B physics, charm, tau, quarkonium, electroweak precision measurements and dark sector searches. It is composed of nine working groups (WGs), which are coordinated by teams of theorist and experimentalists conveners: Semileptonic and leptonic B decays, Radiative and Electroweak penguins, phi_1 and phi_2 (time-dependent CP violation) measurements, phi_3 measurements, Charmless hadronic B decay, Charm, Quarkonium(like), tau and low-multiplicity processes, new physics and global fit analyses. This book highlights "golden- and silver-channels", i.e. those that would have the highest potential impact in the field. Theorists scrutinised the role of those measurements and estimated the respective theoretical uncertainties, achievable now as well as prospects for the future. Experimentalists investigated the expected improvements with the large dataset expected from Belle II, taking into account improved performance from the upgraded detector.Comment: 689 page

Self-cleaning ability of the skin of <i>B. rhinoceros</i>.

<p><b>A–C,</b> Photographic images of an exuvium of <i>B. rhinoceros</i>. <b>A,</b> The exuvium at daylight before dusting it with the redwop. <b>B,</b> The exuvium under black light after dusting it with the redwop. <b>C,</b> The same exuvium under black light after fogging it for 30 min at an inclination of 20°. <b>D,</b> SEM-image of the <i>B. rhinoceros</i> scale with black and pale regions after contamination with the redwop dust and subsequent fogging. The (black) areas showing the characteristic micro- and nanostructure are free of the redwop particles. The (pale) areas showing the inconspicuous microstructure and no nanostructures are covered by a dense layer of the redwop particles.</p

Photographic image of the skin of a living individual of <i>B. rhinoceros</i> after sprinkling with water.

<p>Whereas the rest of the skin is evenly wetted and shiny on black coloured scales appear black and matt further on, because they are not covered by water. There are only droplets in the keel regions of the scales (white arrows).</p

Contact angle measurements on scales of <i>B. rhinoceros</i>.

<p><b>A,</b> Static contact angles of 1 µl droplets of water (H₂O, hatched bars), diiodomethane (CH₂I₂, white bars), and ethylene glycol (C₂H₆O₂, black bars) on ventral and dorsal pale and black scales on the exuvium of <i>B. rhinoceros</i>. Error bars indicate standard deviations of contact angles of ten individual measurements. <b>B,</b> Behavior of water droplets on the black- and white-coloured areas of the dorsal scale of <i>B. rhinoceros</i>. On the black area, the droplet remains in a spherical state due to the superhydrophobic properties of the underlying microstructure. In the pale area, the droplet spreads out and largely covers the area. The microstructure of this area has no superhydrophobic effect.</p

Parameters used for the CFD study.

<p>Parameters used for the CFD study.</p

Cross-sectional distribution of helicity with sectional streamlines at various downstream locations (cf. Fig. 7): blue −0.05, red +0.05.

<p>Min. and maximum values of relative helicity are given. Case 1 (A) and reference case (B).</p

SEM image of a parasagittal section (d = dentin) of a <i>N. pallida</i> fang.

<p>(A) The exit orifice (e) as well as the symmetrical ridges (r) are displayed. (B) SEM image of the inner surface of the channel in high magnification. The surface is smooth in the micron dimension. No microstructures are visible that might affect the venom flow.</p