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

A Canonical Biomechanical Vocal Fold Model

The present article aimed at constructing a canonical geometry of the human vocal fold (VF) from subject-specific image slice data. A computer-aided design approach automated the model construction. A subject-specific geometry available in literature, three abstractions (which successively diminished in geometric detail) derived from it, and a widely used quasi two-dimensional VF model geometry were used to create computational models. The first three natural frequencies of the models were used to characterize their mechanical response. These frequencies were determined for a representative range of tissue biomechanical properties, accounting for underlying VF histology. Compared with the subject-specific geometry model (baseline), a higher degree of abstraction was found to always correspond to a larger deviation in model frequency (up to 50% in the relevant range of tissue biomechanical properties). The model we deemed canonical was optimally abstracted, in that it significantly simplified the VF geometry compared with the baseline geometry but can be recalibrated in a consistent manner to match the baseline response. Models providing only a marginally higher degree of abstraction were found to have significant deviation in predicted frequency response. The quasi two-dimensional model presented an extreme situation: it could not be recalibrated for its frequency response to match the subject-specific model. This deficiency was attributed to complex support conditions at anterior-posterior extremities of the VFs, accentuated by further issues introduced through the tissue biomechanical properties. In creating canonical models by leveraging advances in clinical imaging techniques, the automated design procedure makes VF modeling based on subject-specific geometry more realizable

Синтез и исследование наночастиц магнетита и композитов на его основе

В работе наночастицы Fe3O4 и композиты Fe3O4/rGO с высокой намагниченностью насыщения были синтезированы методом совместного осаждения в различных условиях с добавлением лимонной кислоты для применения в области биомедицины. Исследовано влияние условий синтеза и добавления лимонной кислоты на магнитные свойства полученных образцов.In this work, Fe3O4 nanoparticles and Fe3O4/rGO composites with high saturation magnetization were synthesized by co-precipitation under various conditions with the addition of citric acid for use in the field of biomedicine. The influence of the conditions of synthesis and addition of citric acid on the magnetic properties of the obtained samples was investigated

In vitro experimental investigation of voice production

The process of human phonation involves a complex interaction between the physical domains of structural dynamics, fluid flow, and acoustic sound production and radiation. Given the high degree of nonlinearity of these processes, even small anatomical or physiological disturbances can significantly affect the voice signal. In the worst cases, patients can lose their voice and hence the normal mode of speech communication. To improve medical therapies and surgical techniques it is very important to understand better the physics of the human phonation process. Due to the limited experimental access to the human larynx, alternative strategies, including artificial vocal folds, have been developed. The following review gives an overview of experimental investigations of artificial vocal folds within the last 30 years. The models are sorted into three groups: static models, externally driven models, and self-oscillating models. The focus is on the different models of the human vocal folds and on the ways in which they have been applied

Mean velocity (arrow length) of the liquid in the sections given in Fig. 7 for Case 1 (top) and reference case (bottom).

<p>Mean velocity (arrow length) of the liquid in the sections given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061548#pone-0061548-g007" target="_blank">Fig. 7</a> for Case 1 (top) and reference case (bottom).</p

Computational domain and mesh topology in the region of interest (ROI) of the venom channel.

<p>Computational domain and mesh topology in the region of interest (ROI) of the venom channel.</p

Boundary conditions used for the simulations.

<p>Boundary conditions used for the simulations.</p

Cross-section positions at various downstream locations: lateral (top) and top view (bottom).

<p>S indicates the midline of the channel. Note the curvature of the midline in the top graph.</p