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Multiphase flows are encountered in various industries, and the Coriolis flowmeter (CFM) is considered a high potential flowmeter for the metering of these flows. However, the decoupling effect and asymmetrical gas distribution in a CFM might decrease the accuracy of its multiphase flow metering The asymmetry of gas distribution in a CFM and its influence on the metering accuracy have only been qualitatively investigated in a few studies. The present paper quantitatively describes the gas distribution asymmetry in several CFMs under different flow conditions by numerical simulation. The simulation methodology is developed and validated by a results comparison with a conducted experiment and published data for bubbly, stratified and transitional flow regimes. U-shaped and triangle-shaped CFMs of different diameters are investigated at different gas volume fractions and flow rates. It is shown that the increase in the gas volume fraction and the reduction in the mixture flow rate lead to the increase in the gas distribution asymmetry. The strong correlation between the gas distribution asymmetry and the experimentally observed CFM error is demonstrated. The correction of the CFM error is proposed based on this correlation allowing the metering error to be decreased from 34% to 10% for the investigated conditions.

Numerical simulation is a widely used tool for Coriolis flowmeter (CFM) operation analysis. However, there is a lack of experimentally validated methodologies for the CFM simulation. Moreover, there is no consensus on suitable turbulence models and configuration simplifications. The present study intends to address these questions in a framework of a fluid-solid interaction simulation methodology by coupling the finite volume method and finite element method for fluid and solid domains, respectively. The Reynolds stresses (RSM) and eddy viscosity-based turbulence models are explored and compared for CFM simulations. The effects of different configuration simplifications are investigated. It is demonstrated that the RSM model is favorable for the CFM operation simulations. It is also shown that the configuration simplifications should not include the braces neglect or the equivalent flowmeter tube length assumption. The simulation results are validated by earlier experimental data, showing a less than 5% discrepancy. The proposed methodology will increase the confidence in CFM operation simulations and consequently provide the foundation for further studies of flowmeter usage in various fields.

Neurorobotic augmentation (e.g., robotic assist) is now in regular use to support individuals suffering from impaired motor functions. A major unresolved challenge, however, is the excessive cognitive load necessary for the human-machine interface (HMI). Grasp control remains one of the most challenging HMI tasks, demanding simultaneous, agile, and precise control of multiple degrees-of-freedom (DoFs) while following a specific timing pattern in the joint and human-robot task spaces. Most commercially available systems use either an indirect mode-switching configuration or a limited sequential control strategy, limiting activation to one DoF at a time. To address this challenge, we introduce a shared autonomy framework centred around a low-cost multi-modal sensor suite fusing: (a) mechanomyography (MMG) to estimate the intended muscle activation, (b) camera-based visual information for integrated autonomous object recognition, and (c) inertial measurement to enhance intention prediction based on the grasping trajectory. The complete system predicts user intent for grasp based on measured dynamical features during natural motions. A total of 84 motion features were extracted from the sensor suite, and tests were conducted on 10 able-bodied and 1 amputee participants for grasping common household objects with a robotic hand. Real-time grasp classification accuracy using visual and motion features obtained 100%, 82.5%, and 88.9% across all participants for detecting and executing grasping actions for a bottle, lid, and box, respectively. The proposed multimodal sensor suite is a novel approach for predicting different grasp strategies and automating task performance using a commercial upper-limb prosthetic device. The system also shows potential to improve the usability of modern neurorobotic systems due to the intuitive control design.

Background and Objective: This research aimed to present an improved side-vented needle and explore its availability as well as the corresponding irrigation strategy., Methods: A CFD model was used to simulate the irrigant flow in a simplified prepared round root canal with an apical delta respectively with different needles for irrigation. The needle types include flat end-tip needle, original side-vented needle, and improved side-vented needle. Different insertion depths and inlet velocities were contrastively studied, as well as the gap size between the bulb at the end tip of the improved side-vented needle and the root canal. The study includes a total of 13 schemes. Velocity, pressure, and shear stress in the root canal were measured to contrast the internal flow-field details and irrigation efficiencies between different schemes., Results: Poor irrigation replacement appeared in the schemes without enough needle insertion no matter which kind of needle has been used, though relatively lower pressure emerged at the apical foramen. On the contrary, deepening needle insertion not only brings better irrigant replacement but also higher apical foramen pressure. The original side-vented needle tends to make lower pressure at the apical foramen and simultaneously worse irrigant replacement as compared to the flat end-tip needle. The fluid entering the apical anatomy part deceases a lot as the original side-vented needle was replaced by the improved one. The scheme using the improved side-vented needle with gap size ratio and inlet velocity respectively equaling 5.0% and 5.50m/s can be considered the best one., Conclusions: The improved side-vented needle can ensure acceptable irrigant replacement performance without leading to a high-pressure level at the apical foramen. The gap between the bulb and the wall of the root canal is very crucial for the pressure at the apical. The ideal irrigation strategy is ensuring the gap equals zero. However, it is a little hard to realize during the whole procedure of the root canal preparation except the final step. Consequently, another strategy that keeping the value of gap size ratio as small as possible such as less than 15% and simultaneously ensuring lower-velocity coming fluid, is necessary in the non-final irrigation., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest whatsoever for this manuscript., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The aerobatic maneuvers of swifts could be very useful for micro aerial vehicle missions. Rapid arrests and turns would allow flight in cluttered and unstructured spaces. However, these decelerating aerobatic maneuvers have been difficult to demonstrate in flapping wing craft to date because of limited thrust and control authority. Here, we report a 26-gram X-wing ornithopter of 200-millimeter fuselage length capable of multimodal flight. Using tail elevation and high thrust, the ornithopter was piloted to hover, fly fast forward (dart), turn aerobatically, and dive with smooth transitions. The aerobatic turn was achieved within a 32-millimeter radius by stopping a dart with a maximum deceleration of 31.4 meters per second squared. In this soaring maneuver, braking was possible by rapid body pitch and dynamic stall of wings at relatively high air speed. This ornithopter can recover to glide stability without tumbling after a 90-degree body flip. We showed that the tail presented a strong stabilizing moment under high thrust, whereas the wing membrane flexibility alleviated the destabilizing effect of the forewings. To achieve these demands for high thrust, we developed a low-loss anti-whirl transmission that maximized thrust output by the flapping wings to 40 grams in excess of body weight. By reducing the reactive load and whirl, this indirect drive consumed 40% less maximum electrical power for the same thrust generation than direct drive of a propeller. The triple roles of flapping wings for propulsion, lift, and drag enable the performance of aggressive flight by simple tail control., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Supramolecular hydrogels based on inclusion complexation between cyclodextrins (CDs) and polymers have attracted much interest because of their potential for biomedical applications. It is also attractive to incorporate stimuli-responsive properties into the system to create "smart" hydrogels. Herein, a poly( N -isopropylacrylamide) (PNIPAAm) star polymer with a β-CD core and an adamantyl-terminated poly(ethylene glycol) (Ad-PEG) polymer were synthesized. They self-assembled into a thermoresponsive pseudo-block copolymer through host-guest complexation and formed supramolecular micelles with the change in environment temperature. Subsequently, an injectable polypseudorotaxane-based supramolecular hydrogel was formed between α-CD and the PEG chains of the pseudo-block copolymer. The hydrogel had a unique network structure involving two types of supramolecular self-assemblies between cyclodextrins and polymers, that is, the host-guest complexation between β-CD units and adamantyl groups and the polypseudorotaxane formation between α-CD and PEG chains. We hypothesize that the dual supramolecular hydrogel formed at room temperature may be enhanced by increasing the temperature over the lower critical solution temperature of PNIPAAm because of the hydrophobic interactions of PNIPAAm segments. Furthermore, if the hydrogel is applied for sustained delivery of hydrophobic drugs, the copolymer dissolved from the hydrogel could micellize and continue to serve as micellar drug carriers with the drug encapsulated in the hydrophobic core. Rheological tests revealed that the hydrophobic interactions of the PNIPAAm segments could significantly enhance the strength of the hydrogel when the temperature increased from 25 to 37 °C. As compared to hydrogels formed by α-CD and PEG alone, the sustained release property of this thermoresponsive hydrogel for an anticancer drug, doxorubicin (DOX), improved at 37 °C. The hydrogel dissolved slowly and released the pseudo-block copolymer in the form of micelles that continued to serve as drug carriers with DOX encapsulated in the hydrophobic core, achieving a better cellular uptake and anticancer effect than free DOX controls, even in multidrug-resistant cancer cells. According to these findings, the dual supramolecular hydrogel developed in this work with remarkable thermoresponsive properties might have potential for sustained anticancer drug delivery with enhanced therapeutic effect in multidrug-resistant cancer cells.

The effect of acute irradiation with 5Gy or fractionated exposure with 0.5Gy continuously for 10days (a total dose of 5Gy) was evaluated in an immature BALB/c mouse model. Radioprotective effect of ursolic acid (at 25mg/kg/daily administered 1h after acute or each of fractionated irradiations, and continuously for 30days) was also investigated. We found that both acute and fractionated irradiation at a total dose of 5Gy did not induce any mortality within 30days after exposure to postnatal day 26 (P26) BALB/c mice, but reduced animal weigh gain in the first few weeks. At 90days after irradiation, the weight of animals with acute irradiation was still significantly lower than the control group; no significant difference though was observed for those fractionatedly exposed mice compared to the control group. Behavioral tests indicated that acute irradiation at 5Gy induced deficits in learning and memory in the contextual fear conditioning test. The memory for novel object recognition was also impaired. Similar changes were not observed in mice with fractionated irradiation. Immunohistochemical study demonstrated clearly that acute and fractionated irradiations induced impairment of neurogenesis in the subgranular zone (SGZ) of the dentate gyrus although fractionated exposure induced much lesser loss of newly generated neurons. Ursolic acid administered at 25mg/kg/daily for 30days after irradiation greatly improved acute irradiation-induced deficits in contextual learning and memory and in novel object recognition memory although it exacerbated radiation-induced reduction of neurogenesis in SGZ., (Copyright © 2017. Published by Elsevier Inc.)

Irradiation of the brain in early human life may set abnormal developmental events into motion that last a lifetime, leading to a poor quality of life for affected individuals. While the effect of irradiation at different early developmental stages on the late human life has not been investigated systematically, animal experimental studies suggest that acute postnatal irradiation with ⩾0.1Gy may significantly reduce neurogenesis in the dentate gyrus and endotheliogenesis in cerebral vessels and induce cognitive impairment and aging. Fractionated irradiation also reduces neurogenesis. Furthermore, irradiation induces hippocampal neuronal loss in CA1 and CA3 areas, neuroinflammation and reduces gliogenesis. The hippocampal neurovascular niche and the total number of microvessels are also changed after radiation exposures. Each or combination of these pathological changes may cause cognitive impairment and aging. Interestingly, acute irradiation of aged brain with a certain amount of radiation has also been reported to induce brain hormesis or neurogenesis. At molecular levels, inflammatory cytokines, chemokines, neural growth factors, neurotransmitters, their receptors and signal transduction systems, reactive oxygen species are involved in radiation-induced adverse effect on brain development and functions. Further study at different omics levels after low dose/dose rate irradiation may not only unravel the mechanisms of radiation-induced adverse brain effect or hormesis, but also provide clues for detection or diagnosis of radiation exposure and for therapeutic approaches to effectively prevent radiation-induced cognitive impairment and aging. Investigation focusing on radiation-induced changes of critical brain development events may reveal many previously unknown adverse effects., (Copyright © 2016 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.)

Animal experimental studies indicate that acute or chronic low-dose ionizing radiation (LDIR) (≤100 mSv) or low-dose-rate ionizing radiation (LDRIR) (<6 mSv/h) exposures may be harmful. It induces genetic and epigenetic changes and is associated with a range of physiological disturbances that includes altered immune system, abnormal brain development with resultant cognitive impairment, cataractogenesis, abnormal embryonic development, circulatory diseases, weight gain, premature menopause in female animals, tumorigenesis and shortened lifespan. Paternal or prenatal LDIR/LDRIR exposure is associated with reduced fertility and number of live fetuses, and transgenerational genomic aberrations. On the other hand, in some experimental studies, LDIR/LDRIR exposure has also been reported to bring about beneficial effects such as reduction in tumorigenesis, prolonged lifespan and enhanced fertility. The differences in reported effects of LDIR/LDRIR exposure are dependent on animal genetic background (susceptibility), age (prenatal or postnatal days), sex, nature of radiation exposure (i.e. acute, fractionated or chronic radiation exposure), type of radiation, combination of radiation with other toxic agents (such as smoking, pesticides or other chemical toxins) or animal experimental designs. In this review paper, we aimed to update radiation researchers and radiologists on the current progress achieved in understanding the LDIR/LDRIR-induced bionegative and biopositive effects reported in the various animal models. The roles played by a variety of molecules that are implicated in LDIR/LDRIR-induced health effects will be elaborated. The review will help in future investigations of LDIR/LDRIR-induced health effects by providing clues for designing improved animal research models in order to clarify the current controversial/contradictory findings from existing studies., (© The Author 2017. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.)

The study of the interaction of bubbles with shock waves and ultrasound is sometimes termed 'acoustic cavitation'. It is of importance in many biomedical applications where sound waves are applied. The use of shock waves and ultrasound in medical treatments is appealing because of their non-invasiveness. In this review, we present a variety of acoustics-bubble interactions, with a focus on shock wave-bubble interaction and bubble cloud phenomena. The dynamics of a single spherically oscillating bubble is rather well understood. However, when there is a nearby surface, the bubble often collapses non-spherically with a high-speed jet. The direction of the jet depends on the 'resistance' of the boundary: the bubble jets towards a rigid boundary, splits up near an elastic boundary, and jets away from a free surface. The presence of a shock wave complicates the bubble dynamics further. We shall discuss both experimental studies using high-speed photography and numerical simulations involving shock wave-bubble interaction. In biomedical applications, instead of a single bubble, often clouds of bubbles appear (consisting of many individual bubbles). The dynamics of such a bubble cloud is even more complex. We shall show some of the phenomena observed in a high-intensity focused ultrasound (HIFU) field. The nonlinear nature of the sound field and the complex inter-bubble interaction in a cloud present challenges to a comprehensive understanding of the physics of the bubble cloud in HIFU. We conclude the article with some comments on the challenges ahead.

The concentration dependence of yield stress and dynamic moduli of kaolinite suspensions is studied. Complex electrostatic interactions between kaolinite platelets promote a more liquid-like behavior, with clay particles changing from attractive interactions to a face-face repulsive interaction as the mass fraction of clay particles increases. A yield stress model is developed based on the repulsive interaction between disk-shaped particles, which yields a good prediction of experimental observations when repulsive face-face interaction is dominant. The critical concentration when attractive interaction changes completely to face-face repulsive interaction is estimated from the theory. Four regions are identified in the variation of yield stress as a function of the concentration.

A boundary integral formulation for the solution of the Helmholtz equation is developed in which all traditional singular behaviour in the boundary integrals is removed analytically. The numerical precision of this approach is illustrated with calculation of the pressure field owing to radiating bodies in acoustic wave problems. This method facilitates the use of higher order surface elements to represent boundaries, resulting in a significant reduction in the problem size with improved precision. Problems with extreme geometric aspect ratios can also be handled without diminished precision. When combined with the CHIEF method, uniqueness of the solution of the exterior acoustic problem is assured without the need to solve hypersingular integrals.

Flow supercavitation begins when fluid is accelerated over a sharp edge, usually at the nose of an underwater vehicle, where phase change occurs and causes low density gaseous cavity to gradually envelop the whole object (supercavity) and thereby enabling higher speeds of underwater vehicles. The process of supercavity inception/development by means of "natural cavitation" and its sustainment through ventilated cavitation result in turbulence and fluctuations at the water-vapor interface that manifest themselves as major sources of hydrodynamic noise. Therefore in the present context, three main sources are investigated, namely, (1) flow generated noise due to turbulent pressure fluctuations around the supercavity, (2) small scale pressure fluctuations at the vapor-water interface, and (3) pressure fluctuations due to direct impingement of ventilated gas-jets on the supercavity wall. An understanding of their relative contributions toward self-noise is very crucial for the efficient operation of high frequency acoustic sensors that facilitate the vehicle's guidance system. Qualitative comparisons of acoustic pressure distribution resulting from aforementioned sound sources are presented by employing a recently developed boundary integral method. By using flow data from a specially developed unsteady computational fluid dynamics solver for simulating supercavitating flows, the boundary-element method based acoustic solver was developed for computing flow generated sound.

In our earlier studies, we have demonstrated that low and high intensity ultrasound can prevent barnacle cyprid settlement. In this study, we found that ultrasound treatment reduced the adhesion of newly metamorphosed barnacles up to 2 days' old. This was observed in the reduction of adhesion strength of the newly settled barnacles from ultrasound treated cyprids on silicone substrate compared to the adhesion strength of barnacles metamorphosed from cyprids not exposed to ultrasound. Atomic force microscopy (AFM) was used to analyze the effect of ultrasound on barnacle cyprid footprints (FPs), which are protein adhesives secreted when the larvae explore surfaces. The ultrasound treated cyprids were found to secrete less FPs, which appeared to spread a larger area than those generated by untreated cyprids. The evidence from this study suggests that ultrasound treatment results in a reduced cyprid settlement and footprint secretion, and may affect the subsequent recruitment of barnacles onto fouling release surfaces by reducing the ability of early settlement stage of barnacles (up to 2 days' old) from firmly adhering to the substrates. Ultrasound therefore can be used in combination with fouling release coatings to offer a more efficient antifouling strategy., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Two nonlinear models are proposed to investigate the focused acoustic waves that the nonlinear effects will be important inside the liquid around the scatterer. Firstly, the one dimensional solutions for the widely used Westervelt equation with different coordinates are obtained based on the perturbation method with the second order nonlinear terms. Then, by introducing the small parameter (Mach number), a dimensionless formulation and asymptotic perturbation expansion via the compressible potential flow theory is applied. This model permits the decoupling between the velocity potential and enthalpy to second order, with the first potential solutions satisfying the linear wave equation (Helmholtz equation), whereas the second order solutions are associated with the linear non-homogeneous equation. Based on the model, the local nonlinear effects of focused acoustic waves on certain volume are studied in which the findings may have important implications for bubble cavitation/initiation via focused ultrasound called HIFU (High Intensity Focused Ultrasound). The calculated results show that for the domain encompassing less than ten times the radius away from the center of the scatterer, the non-linear effect exerts a significant influence on the focused high intensity acoustic wave. Moreover, at the comparatively higher frequencies, for the model of spherical wave, a lower Mach number may result in stronger nonlinear effects., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Fractional flow reserve (FFR) is the gold standard to guide coronary interventions. However it can only be obtained via invasive angiography. The objective of this study is to propose a noninvasive method to determine FFRCT by combining computed tomography angiographic (CTA) images and computational fluid dynamics (CFD) technique. Utilizing the method, this study explored the effects of diameter stenosis (DS), stenosis length, and location on FFRCT. The baseline left anterior descending (LAD) model was reconstructed from CTA of a healthy porcine heart. A series of models were created by adding an idealized stenosis (with DS from 45% to 75%, stenosis length from 4 mm to 16 mm, and at 4 locations separately). Through numerical simulations, it was found that FFRCT decreased (from 0.89 to 0.74), when DS increased (from 45% to 75%). Similarly, FFRCT decreased with the increase of stenosis length and the stenosis located at proximal position had lower FFRCT than that at distal position. These findings are consistent with clinical observations. Applying the same method on two patients' CTA images yielded FFRCT close to the FFR values obtained via invasive angiography. The proposed noninvasive computation of FFRCT is promising for clinical diagnosis of CAD.

The complex dynamics of a single bubble of a few millimeters in size oscillating inside a narrow fluid-filled gap between two parallel plates is studied using high-speed videography. Two synchronized high-speed cameras were used to observe both the side and front views of the bubble. The front-view images show bubble expansion and collapse with the formation of concentric dark and bright rings. The simultaneous recordings reveal the mechanism behind these rings. The side-view images reveal two different types of collapse behavior of the bubble including a previously unreported collapse phenomenon that is observed as the gap width is changed. At narrow widths, the bubble collapses towards the center of the gap; when the width is increased, the bubble splits before collapsing towards the walls. The bubble dynamics is also observed to be unaffected by the hydrophobic or hydrophilic nature of the plate surface due to the presence of a thin film of liquid between each of the plates and the bubble throughout the bubble lifetime. It is revealed that such systems do not behave as quasi-two-dimensional systems; three-dimensional effects are important.

The invasion of red blood cells (RBCs) by malaria parasites is a complex dynamic process, in which the infected RBCs gradually lose their deformability and their ability to recover their original shape is greatly reduced with the maturation of the parasites. In this work, we developed two types of cell model, one with an included parasite, and the other without an included parasite. The former is a representation of real malaria-infected RBCs, in which the parasite is treated as a rigid body. In the latter, where the parasite is absent, the membrane modulus and viscosity are elevated so as to produce the same features present in the parasite model. In both cases, the cell membrane is modeled as a viscoelastic triangular network connected by wormlike chains. We studied the transient behaviors of stretching deformation and shape relaxation of malaria-infected RBCs based on these two models and found that both models can generate results in agreement with those of previously published studies. With the parasite maturation, the shape deformation becomes smaller and smaller due to increasing cell rigidity, whereas the shape relaxation time becomes longer and longer due to the cell's reduced ability to recover its original shape., (Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

The effect of cavitation bubbles on the removal of juvenile barnacles was documented using high speed photography. Using spark generated bubbles, the interaction between barnacle and cavitation bubble was examined in detail. The liquid jet generated by the bubble collapse was observed to be directed towards barnacle at different impact intensities, which is related to the dimensionless distance H' (H'=H/Rm), where H is the distance between bubble formation point and the top of barnacle, and Rm is the maximum bubble radius. At lower values of H', higher speed liquid jet was produced; consequently a larger impact pressure was generated. In general, barnacles are more easily removed at a younger stage. In older barnacles, the liquid jet impact was only able to remove the barnacle shells, leaving the base plate attached to the surface. This study indicates that cavitation can be used to remove attached barnacles, and it would be more efficient if it is applied during early stages of fouling, before the formation of hard calcareous structures., (Copyright © 2013 Elsevier B.V. All rights reserved.)

In this study, the effect of high-intensity focused ultrasound (HIFU) on Enterococcus faecalis on both planktonic suspensions and biofilms was investigated. E. faecalis persist in secondary dental infections as biofilms. Glass-bottom Petri dishes with biofilms were centered at the focal point of the HIFU wave generated by a 250-kHz transducer. Specimens were subjected to HIFU exposure at different periods of 30, 60 and 120 s. The viable bacteria, removal effect and bacterial viability of biofilms attached to the Petri dish surface were studied by colony-forming units (CFUs), scanning electron microscopy and confocal microscopy, respectively. The removal and bactericidal effects of HIFU are dependent on the exposure time. A significant reduction in biofilm thickness and CFU was found with the increase in HIFU exposure. The removal or bactericidal effect of HIFU was more significant starting from 60 s of exposure. This study highlighted the potential application of HIFU as a novel method for root canal disinfection., (Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

We study the forces and torques experienced by pill-shaped Janus particles of different aspect ratios where half of the surface obeys the no-slip boundary condition and the other half obeys the Navier slip condition of varying slip lengths. Using a recently developed boundary integral formulation whereby the traditional singular behavior of this approach is removed analytically, we quantify the strength of the forces and torques experienced by such particles in a uniform flow field in the Stokes regime. Depending on the aspect ratio and the slip length, the force transverse to the flow direction can change sign. This is a novel property unique to the Janus nature of the particles.

An experimental study of jets and sprays formed by a spark-induced bubble collapsing near a plate with a hole is presented. A Perspex plate with a hole at its center is placed in a half-filled water tank with its top face near the air-water interface. A bubble is created using a low-voltage electrical spark below the hole in the plate. The bubble expands against the hole, which pushes the liquid present within the hole and leads to an initial primary jet of water that emerges from the other end of the hole into air. The bubble subsequently collapses and leads to a second jet that is characterized by short bursts of liquid spray followed by a thicker continuous liquid column. The impact of the sprays onto the primary jet leads to perturbations in the jet and the breakup of the latter into fine droplets. The entire phenomenon is recorded using a high-speed camera to visualize the mechanism both within and outside the hole. The results give a clearer indication of the mechanism behind a recently reported phenomenon on the formation of impacting jets caused by bubble expansion and collapse at the micrometer length scale. The variation of the jet characteristics with parameters such as the position of the water-air interface with respect to the plate and the hole geometry (i.e., the hole diameter and the plate thickness) is also presented.

The complex variables method with mapping function was extended to solve the linear acoustic wave scattering by an inclusion with sharp/smooth corners in an infinite ideal fluid domain. The improved solutions of Helmholtz equation, shown as Bessel function with mapping function as the argument and fractional order Bessel function, were analytically obtained. Based on the mapping function, the initial geometry as well as the original physical vector can be transformed into the corresponding expressions inside the mapping plane. As all the physical vectors are calculated in the mapping plane (η,η), this method can lead to potential vast savings of computational resources and memory. In this work, the results are validated against several published works in the literature. The different geometries of the inclusion with sharp corners based on the proposed mapping functions for irregular polygons are studied and discussed. The findings show that the variation of angles and frequencies of the incident waves have significant influence on the bistatic scattering pattern and the far-field form factor for the pressure in the fluid., (© 2012 Acoustical Society of America)

Low frequency, low intensity ultrasound was demonstrated as an effective inhibitor of barnacle cyprid settlement. When the same substratum vibration amplitude (10.05 nm) and acoustic pressure (5 kPa) were applied, ultrasound at a frequency of 23 kHz significantly reduced cyprid settlement. The mechanism appeared to differ from the ultrasonic cavitation induced inhibition previously reported as no increased mortality was observed, and no change in the exploratory behaviour of cyprids was observed when they were exposed to this continuous ultrasonic irradiation regime. The application of ultrasound treatment in an intermittent mode of '5 min on and 20 min off' at 20-25 kHz and at the low intensity of 5 kPa produced the same effect as the continuous application of 23 kHz. This energy efficient approach to the use of low frequency, low intensity ultrasound may present a promising and efficient strategy regarding irradiation treatment for antifouling applications.

A method to create impacting jets at the micrometer length scale by means of a collapsing cavitation bubble is presented. A focused shock wave from a lithotripter leads to the nucleation of a cavitation bubble below a hole of 25 μm diameter etched in a silicon plate. The plate is placed at an air-water interface. The expansion and collapse of the bubble leads to two separate jets--an initial slow jet of velocity ∼10 m/s and a later faster jet of velocity ∼50 m/s. The jets subsequently impact coaxially, resulting in a circular sheet of liquid in the plane perpendicular to their axis. The sheet is characterized by a ring of droplets at its rim and breaks up into a spray as the shock pressure is increased. The results demonstrate an approach to create a high-speed jet and fine spray on demand at the micrometer scale.

Most real life bubble dynamics applications involve multiple bubbles, for example, in cavitation erosion prevention, ultrasonic baths, underwater warfare, and medical applications involving microbubble contrast agents. Most scientific dealings with bubble-bubble interaction focus on two similarly sized bubbles. In this study, the interaction between two oscillating differently sized bubbles (generated in tap water) is studied using high speed photography. Four types of bubble behavior were observed, namely, jetting toward each other, jetting away from each other, bubble coalescence, and a behavior termed the "catapult" effect. In-phase bubbles jet toward each other, while out-of-phase bubbles jet away from each other. There exists a critical phase difference that separates the two regimes. The behavior of the bubbles is fully characterized by their dimensionless separation distance, their phase difference, and their size ratio. It is also found that for bubbles with large size difference, the smaller bubble behaves similarly to a single bubble oscillating near a free surface.

Settlement inhibition of barnacle (Amphibalanus amphitrite) cypris larvae resulting from exposure to ultrasound was measured at three frequencies (23, 63, and 102 kHz), applied at three acoustic pressure levels (9, 15, and 22 kPa) for exposure times of 30, 150, and 300 s. The lowest settlement was observed for 23 kHz, which also induced the highest cyprid mortality. Cyprid settlement following exposure to 23 kHz at 22 kPa for 30 s was reduced by a factor of two. Observing surface exploration by the cyprids revealed an altered behaviour following exposure to ultrasound: step length was increased, while step duration, walking pace, and the fraction of cyprids exploring the surface were significantly reduced with respect to control cyprids. The basal area of juvenile barnacles, metamorphosed from ultrasound-treated cyprids was initially smaller than unexposed individuals, but normalised over two weeks' growth. Thus, ultrasound exposure effectively reduced cyprid settlement, yet metamorphosed barnacles grew normally.

The generation of arbitrarily shaped nonspherical laser-induced cavitation bubbles is demonstrated with a optical technique. The nonspherical bubbles are formed using laser intensity patterns shaped by a spatial light modulator using linear absorption inside a liquid gap with a thickness of 40 microm. In particular we demonstrate the dynamics of elliptic, toroidal, square, and V-shaped bubbles. The bubble dynamics is recorded with a high-speed camera at framing rates of up to 300,000 frames per second. The observed bubble evolution is compared to predictions from an axisymmetric boundary element simulation which provides good qualitative agreement. Interesting dynamic features that are observed in both the experiment and simulation include the inversion of the major and minor axis for elliptical bubbles, the rotation of the shape for square bubbles, and the formation of a unidirectional jet for V-shaped bubbles. Further we demonstrate that specific bubble shapes can either be formed directly through the intensity distribution of a single laser focus, or indirectly using secondary bubbles that either confine the central bubble or coalesce with the main bubble. The former approach provides the ability to generate in principle any complex bubble geometry.

Introduction: High-intensity focused ultrasound (HIFU) produces collapsing cavitation bubbles. This study aims to investigate the efficacy of collapsing cavitation bubbles to deliver antibacterial nanoparticles into dentinal tubules to improve root canal disinfection., Methods: In stage 1, experiments were performed to characterize the efficacy of collapsing cavitation bubbles to deliver the miniature plaster beads into a tubular channel model. In stage 2, experiments were conducted on root-dentin blocks to test the efficacy of HIFU applied at 27 kHz for 2 minutes to deliver antibacterial nanoparticles into dentinal tubules. After the stage 2 experiment, the samples were sectioned and analyzed using field-emission scanning electron microscopy and energy dispersive X-ray analysis., Results: The stage 1 experiment showed that collapsing cavitation bubbles using HIFU delivered plaster beads along the entire length of the tubular channel. It was observed from the stage 2 experiments that the diffusion of fluids alone was not able to deliver antibacterial nanoparticles into dentinal tubules. The collapsing cavitation bubbles treatment using HIFU resulted in significant penetration up to 1,000 microm of antibacterial nanoparticles into the dentinal tubules. The statistical analysis showed a highly significant difference in the depth of penetration of antibacterial nanoparticles between the two groups (<0.005)., Conclusion: The cavitation bubbles produced using HIFU can be used as a potential method to deliver antibacterial nanoparticles into the dentinal tubules to enhance root canal disinfection.

We present a coupled immersed interface method-boundary element method (IIM-BEM) numerical technique that predicts the behaviour of deformable cells under the effect of both hydrodynamic and electrical forces. This technique is applied to the study of a hybrid electrical-mechanical trap for single-cell trapping. We report on the effect of different combinations of electrode positions and mechanical properties of the trap on the maximum loading and unloading Reynolds numbers. We also report on the effect that cells moving with the flow have on cells which have been already trapped in a cavity.

High intensity pulsed ultrasound, interacting with microbubble contrast agents, is potentially useful for drug delivery, cancer treatment, and tissue ablation, among other applications. To establish the fundamental understanding on the interaction of a microbubble (in an infinite volume of water) with an ultrasound pressure field, a numerical study is performed using the boundary element method. The response of the bubble, in terms of its shape at different times, the maximum bubble radius obtained, the oscillation time, the jet velocity, and its translational movement, is studied. The effect of ultrasound intensity and initial bubble size is examined as well. One important outcome is the determination of the conditions under which a clear jet will be formed in a microbubble in its interaction with a specific sound wave. The high speed jet is crucial for the aforementioned intended applications.

The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillating vs. non-oscillating) on the dynamics of the shockwave-bubble interaction are discussed.

Ultrasonic cavitation bubble phenomena play a key role in numerous medical procedures such as ultrasound-assisted lipoplasty, phacoemulsification, lithotripsy, brain tumor surgery, muscle and bone therapies and intraocular or transdermal drug delivery. This study investigates numerically the interaction of a bubble with a bio-material (fat, skin, cornea, brain, muscle, cartilage or bone) involved in the treatments mentioned when subjected to an ultrasound field. A range of frequencies is used to study the bubble behavior in terms of its growth and collapse shapes, and the maximum jet velocity attained. Simulation results show complex dynamic behaviors of the bubble. In several cases a jet is formed directed away from the bio-material while in others, toward it. In certain cases, the bubble eventually breaks into two, with or without the formation of opposite penetrating jets. Very high maximum velocities of jets directing away or toward the bio-materials can be observed in some cases (700 to 900 ms(-1)).