High-speed and acceleration micrometric jets induced by GHz streaming: A numerical study with direct numerical simulations

Gigahertz acoustic streaming enables the synthesis of localized microjets reaching speeds of up to meters per second, offering tremendous potential for precision micromanipulation. However, theoretical and numerical investigations of acoustic streaming at these frequencies remain so far relatively scarce due to significant challenges including: (i) the inappropriateness of classical approaches, rooted in asymptotic development, for addressing high-speed streaming with flow velocities comparable to the acoustic velocity; and (ii) the numerical cost of direct numerical simulations generally considered as prohibitive. In this paper, we investigate high-frequency bulk streaming using high-order finite difference direct numerical simulations. First, we demonstrate that high-speed micrometric jets of several meters per second can only be obtained at high frequencies, due to diffraction limits. Second, we establish that the maximum jet streaming speed at a given actuation power scales with the frequency to the power of 3/2 in the low attenuation limit and linearly with the frequency for strongly attenuated waves. Last, our analysis of transient regimes reveals a dramatic reduction in the time required to reach the maximum velocity as the frequency increases (power law in -5/2), leading to characteristic time on the order of μs at gigahertz frequencies, and hence accelerations within the Mega-g range.

Oscillations and Cavity Modes in the Circular Hydraulic Jump

We report spontaneous oscillations of circular hydraulic jumps created by the impact of a submillimeter water jet on a solid disk. The jet flow rate is shown to condition the occurrence of the oscillations while their period is independent of this parameter. The period, however, varies linearly with the disk radius. This dependency is rationalized by investigating surface gravity wave modes in the cavity formed by the disk. We show that the jump oscillation frequency systematically matches one of the surface wave disk-cavity eigenfrequencies, leading to the conclusion that the oscillations are self-induced by the interaction between the jump and surface wave eigenmodes.

HCV cure: an appropriate moment to reduce cannabis use in people living with HIV? (ANRS CO13 HEPAVIH data)

BACKGROUND

Thanks to direct-acting antivirals, hepatitis C virus (HCV) infection can be cured, with similar rates in HCV-infected and HIV-HCV co-infected patients. HCV cure is likely to foster behavioral changes in psychoactive substance use, which is highly prevalent in people living with HIV (PLWH). Cannabis is one substance that is very commonly used by PLWH, sometimes for therapeutic purposes. We aimed to identify correlates of cannabis use reduction following HCV cure in HIV-HCV co-infected cannabis users and to characterize persons who reduced their use.

METHODS

We used data collected on HCV-cured cannabis users in a cross-sectional survey nested in the ANRS CO13 HEPAVIH cohort of HIV-HCV co-infected patients, to perform logistic regression, with post-HCV cure cannabis reduction as the outcome, and socio-behavioral characteristics as potential correlates. We also characterized the study sample by comparing post-cure substance use behaviors between those who reduced their cannabis use and those who did not.

RESULTS

Among 140 HIV-infected cannabis users, 50 and 5 had reduced and increased their use, respectively, while 85 had not changed their use since HCV cure. Cannabis use reduction was significantly associated with tobacco use reduction, a decrease in fatigue level, paying more attention to one's dietary habits since HCV cure, and pre-HCV cure alcohol abstinence (p = 0.063 for alcohol use reduction).

CONCLUSIONS

Among PLWH using cannabis, post-HCV cure cannabis reduction was associated with tobacco use reduction, improved well-being, and adoption of healthy behaviors. The management of addictive behaviors should therefore be encouraged during HCV treatment.

Equivalence between angular spectrum-based and multipole expansion-based formulas of the acoustic radiation force and torque

Two main methods have been proposed to derive the acoustical radiation force and torque applied by an arbitrary acoustic field on a particle: The first one relies on the plane wave angular spectrum decomposition of the incident field (see Sapozhnikov and Bailey [J. Acoust. Soc. Am. 133, 661-676 (2013)] for the force and Gong and Baudoin [J. Acoust. Soc. Am. 148, 3131-3140 (2020)] for the torque), while the second one relies on the decomposition of the incident field into a sum of spherical waves, the so-called multipole expansion (see Silva [J. Acoust. Soc. Am. 130, 3541-3544 (2011)] and Baresch, Thomas, and Marchiano [J. Acoust. Soc. Am. 133, 25-36 (2013)] for the force, and Silva, Lobo, and Mitri [Europhys. Lett. 97, 54003 (2012)] and Gong, Marston, and Li [Phys. Rev. Appl. 11, 064022 (2019)] for the torque). In this paper, we formally establish the equivalence between the expressions obtained with these two methods for both the force and torque.

Acoustic radiation torque on a particle in a fluid: An angular spectrum based compact expression

In this work, a set of compact analytical formulas is derived expressing the three-dimensional acoustic radiation torque (ART) exerted on a particle of arbitrary shape embedded in a fluid and insonified by an arbitrary acoustic field. This formulation enables direct computation of the ART from the angular spectrum based beam shape coefficients introduced by Sapozhnikov and Bailey [J. Acoust. Soc. Am. 133, 661-676 (2013)] and the partial wave coefficients. It is particularly well suited to determine the ART exerted on a particle when the acoustic field is known in a source plane.

Spatially selective manipulation of cells with single-beam acoustical tweezers

Acoustical tweezers open major prospects in microbiology for cells and microorganisms contactless manipulation, organization and mechanical properties testing since they are biocompatible, label-free and have the potential to exert forces several orders of magnitude larger than their optical counterpart at equivalent power. Yet, these perspectives have so far been hindered by the absence of spatial selectivity of existing acoustical tweezers - i.e., the ability to select and move objects individually - and/or their limited resolution restricting their use to large particle manipulation only and/or finally the limited forces that they could apply. Here, we report precise selective manipulation and positioning of individual human cells in a standard microscopy environment with trapping forces up to ~200 pN without altering their viability. These results are obtained with miniaturized acoustical tweezers combining holography with active materials to synthesize specific wavefields called focused acoustical vortices designed to produce stiff localized traps with reduced acoustic power.

Sustained virological response to Do hepatitis C DAA treatments in migrants and non-migrants groups

Background

Although the efficacy of direct acting antivirals (DAA) against hepatitis C (HCV) has been widely proven, data lack on their effectiveness in the most vulnerable groups. In France, despite universal health coverage, migrants cumulate vulnerabilities including delays in screening that may affect both access to care and treatment effectiveness. We tested whether DAA-treated migrants had sustained virological response (SVR) rates comparable to not-migrants.

Methods

We used data collected in chronic HCV-infected patients of the ANRS CO22 HEPATHER cohort, receiving a first treatment with DAA, with follow-up from 2012 until 2022. SVR was measured by PCR, 12 weeks after the end of treatment. The main covariate was a 4-category variable comparing migrants and non-migrants, with or without other vulnerability conditions (including drug use, unhealthy alcohol use, living in poverty, being a man who have sex with men). We used a Poisson regression model to assess the relationship between this covariate and SVR after adjustment for significant predictors and potential confounders.

Results

The analysis included 5,080 individuals, of which 17% classified as migrants with at least one vulnerability, 10% as migrants with no vulnerability, 39% as non-migrants with at least one vulnerability and 35% as non-migrants with no vulnerability. Median [IQR] age was 57 [51-65] years, 56% of individuals were men, and 96% had SVR. The multivariable analysis showed no significant difference between the 4-category covariate and SVR. In addition, we found that SVR rates increased steadily during follow-up.

Conclusions

This is the first analysis exploring differences in SVR rates among migrants and not-migrants. The lack of significant differences found despite the power of the study suggests that migrants respond to DAA treatment as well as any other group of HCV-infected patients. These data can help advocating better screening and access to treatment for HCV-infected migrants in France.

Key messages

No significant differences were observed between migrants and non-migrants in terms of effectiveness of DAA treatment. These findings can help improving access to HCV care for migrants.

Folding a focalized acoustical vortex on a flat holographic transducer: Miniaturized selective acoustical tweezers

Acoustical tweezers based on focalized acoustical vortices hold the promise of precise contactless manipulation of millimeter down to submicrometer particles, microorganisms, and cells with unprecedented combined selectivity and trapping force. Yet, the widespread dissemination of this technology has been hindered by severe limitations of current systems in terms of performance and/or miniaturization and integrability. Here, we unleash the potential of focalized acoustical vortices by developing the first flat, compact, paired single electrode focalized acoustical tweezers. These tweezers rely on spiraling transducers obtained by folding a spherical acoustical vortex on a flat piezoelectric substrate. We demonstrate the ability of these tweezers to grab and displace micrometric objects in a standard microfluidic environment with unique selectivity. The simplicity of this system and its scalability to higher frequencies open tremendous perspectives in microbiology, microrobotics, and microscopy.

Nonspherical armoured bubble vibration

In this paper, we study the dynamics of cylindrical armoured bubbles excited by mechanical vibrations. A step by step transition from cylindrical to spherical shape is reported as the intensity of the vibration is increased, leading to a reduction of the bubble surface and a dissemination of the excess particles. We demonstrate through energy balance that nonspherical armoured bubbles constitute a metastable state. The vibration instills the activation energy necessary for the bubble to return to its least energetic stable state: a spherical armoured bubble. At this point, particle desorption can only be achieved through higher amplitude of excitation required to overcome capillary retention forces. Nonspherical armoured bubbles open perspectives for tailored localized particle dissemination with limited excitation power.

Dynamics of liquid plugs in prewetted capillary tubes: from acceleration and rupture to deceleration and airway obstruction

The dynamics of individual liquid plugs pushed at a constant pressure head inside prewetted cylindrical capillary tubes is investigated experimentally and theoretically. It is shown that, depending on the thickness of the prewetting film and the magnitude of the pressure head, the plugs can either experience a continuous acceleration leading to a dramatic decrease of their size and eventually their rupture or conversely, a progressive deceleration associated with their growth and an exacerbation of the airway obstruction. These behaviors are quantitatively reproduced using a simple nonlinear model [Baudoin et al., Proc. Natl. Acad. Sci. U. S. A., 2013, 110, 859] adapted here for cylindrical channels. Furthermore, an analytical criterion for the transition between these two regimes is derived and successfully compared with extensive experimental data. The potential implications of this work for pulmonary obstructive diseases are discussed.

SAW Synthesis With IDTs Array and the Inverse Filter: Toward a Versatile SAW Toolbox for Microfluidics and Biological Applications

Surface acoustic waves (SAWs) are versatile tools to manipulate fluids at small scales for microfluidics and biological applications. A nonexhaustive list of operations that can be performed with SAW includes sessile droplet displacement, atomization, division, and merging but also the actuation of fluids embedded in microchannels or the manipulation of suspended particles. However, each of these operations requires a specific design of the wave generation system, the so-called interdigitated transducers (IDTs). Depending on the application, it might indeed be necessary to generate focused or plane, propagating or standing, and aligned or shifted waves. Furthermore, the possibilities offered by more complex wave fields such as acoustical vortices for particle tweezing and liquid twisting cannot be explored with classical IDTs. In this paper, we show that the inverse filter technique coupled with an IDTs array enables us to synthesize all classical wave fields used in microfluidics and biological applications with a single multifunctional platform. It also enables us to generate swirling SAWs, whose potential for the on-chip synthesis of tailored acoustical vortices has been demonstrated lately. The possibilities offered by this platform are illustrated by performing many operations successively on sessile droplets with the same system.

Inverse Saffman-Taylor Experiments with Particles Lead to Capillarity Driven Fingering Instabilities

Using air to displace a viscous fluid contained in a Hele-Shaw cell can create a fingering pattern at the interface between the fluids if the capillary number exceeds a critical value. This Saffman-Taylor instability is revisited for the inverse case of a viscous fluid displacing air when partially wettable hydrophilic particles are lying on the walls. Though the inverse case is otherwise stable, the presence of the particles results in a fingering instability at low capillary number. This capillary-driven instability is driven by the integration of particles into the interface which results from the minimization of the interfacial energy. Both axisymmetric and rectangular geometries are considered in order to quantify this phenomenon.

Increased resistance to detachment of adherent microspheres and Bacillus spores subjected to a drying step

In various environments, including that of food processing, adherent bacteria are often subjected to drying conditions. These conditions have been shown to result in changes in the ability of biofilms to cross-contaminate food in contact with them. In this study, we investigated the consequences of a drying step on the further ability of adherent bacterial spores to resist detachment. An initial series of experiment was set up with latex microspheres as a model. A microsphere suspension was deposited on a glass slide and incubated at 25, 35 and 50°C for times ranging from 1h to 48h. By subjecting the dried slides to increasing water flow rates, we showed that both time and temperature affected the ease of microsphere detachment. Similar observations were made for three Bacillus spores despite differences in their surface properties, especially regarding their surface physicochemistry. The differences in ease of adherent spore detachment could not be clearly linked to the minor changes in spore morphology, observed after drying in various environmental conditions. In order to explain the increased interaction between spheres or spores and glass slides, the authors made several assumptions regarding the possible underlying mechanisms: the shape of the liquid bridge between the sphere and the substratum, which is greatly influenced by the hydrophilic/hydrophobic characters of both surfaces; the accumulation of soil at the liquid/air interface; the presence of trapped nano-bubbles around and/or under the sphere.

Dynamics of sessile and pendant drops excited by surface acoustic waves: Gravity effects and correlation between oscillatory and translational motions

When sessile droplets are excited by ultrasonic traveling surface acoustic waves (SAWs), they undergo complex dynamics with both oscillations and translational motion. While the nature of the Rayleigh-Lamb quadrupolar drop oscillations has been identified, their origin and their influence on the drop mobility remains unexplained. Indeed, the physics behind this peculiar dynamics is complex with nonlinearities involved both at the excitation level (acoustic streaming and radiation pressure) and in the droplet response (nonlinear oscillations and contact line dynamics). In this paper, we investigate the dynamics of sessile and pendant drops excited by SAWs. For pendant drops, so-far unreported dynamics are observed close to the drop detachment threshold with the suppression of the translational motion. Away from this threshold, the comparison between pendant and sessile drop dynamics allows us to identify the role played by gravity or, more generally, by an initial or dynamically induced stretching of the drop. In turn, we elucidate the origin of the resonance frequency shift, as well as the origin of the strong correlation between oscillatory and translational motion. We show that for sessile drops, the velocity is mainly determined by the amplitude of oscillation and that the saturation observed is due to the nonlinear dependence of the drop response frequency on the dynamically induced stretching.

Taming the degeneration of Bessel beams at an anisotropic-isotropic interface: Toward three-dimensional control of confined vortical waves

Despite their self-reconstruction properties in heterogeneous media, Bessel beams are known to degenerate when they are refracted from an isotropic to an anisotropic medium. In this paper, we study the converse situation wherein an anisotropic Bessel beam is refracted into an isotropic medium. It is shown that these anisotropic Bessel beams also degenerate, leading to confined vortical waves that may serve as localized particle trap for acoustical tweezers. The linear nature of this degeneration allows the three-dimensional control of this trap position by wavefront correction. Theory is confronted to experiments performed in the field of acoustics. A swirling surface acoustic wave is synthesized at the surface of a piezoelectric crystal by a microelectromechanical integrated system and radiated inside a miniature liquid vessel. The wavefront correction is operated with inverse filter technique. This work opens perspectives for contactless on-chip manipulation devices.

Capillary tube wetting induced by particles: towards armoured bubbles tailoring

In this paper, we report on the strongly modified dynamics of a liquid finger pushed inside a capillary tube, when partially wettable particles are lying on the walls. Particles promote the appearance of new regimes and enable the tailored synthesis of bubbles encapsulated in a monolayer of particles (so-called "armoured bubbles"). This remarkable behavior arises due to the collection of particles at the air-liquid interface, which modify the global energy balance and stabilize the interface. Armoured-bubbles are of primary interest in industrial processes since they display increased stability, interfacial rigidity and can even sustain non-spherical shapes. This work opens perspective for a low cost bubbles-on-demand technology enabling the synthesis of armoured bubbles with specific sizes, shapes and composition.

Cyclones and attractive streaming generated by acoustical vortices

Acoustical and optical vortices have attracted great interest due to their ability to capture and manipulate particles with the use of radiation pressure. Here we show that acoustical vortices can also induce axial vortical flow reminiscent of cyclones, whose topology can be controlled by adjusting the properties of the acoustical beam. In confined geometry, the phase singularity enables generating "attractive streaming" with the flow directed toward the transducer. This opens perspectives for contactless vortical flow control.

Scattering of ultrasonic shock waves in suspensions of silica nanoparticles

Experiments are carried out to assess, for the first time, the validity of a generalized Burgers' equation, introduced first by Davidson [J. Acoust. Soc. Am. 54, 1331-1342 (1973)] to compute the nonlinear propagation of finite amplitude acoustical waves in suspensions of "rigid" particles. Silica nanoparticles of two sizes (33 and 69 nm) have been synthesized in a water-ethanol mixture and precisely characterized via electron microscopy. An acoustical beam of high amplitude is generated at 1 MHz inside a water tank, leading to the formation of acoustical shock waves through nonlinear steepening. The signal is then measured after propagation in a cylinder containing either a reference solution or suspensions of nanoparticles. In this way, a "nonlinear attenuation" is obtained and compared to the numerical solution of a generalized Burgers' equation adapted to the case of hydrosols. An excellent agreement (corresponding to an error on the particles size estimation of 3 nm) is achieved in the frequency range from 1 to 40 MHz. Both visco-inertial and thermal scattering are significant in the present case, whereas thermal effects can generally be neglected for most hydrosols. This is due to the value of the specific heat ratio of water-ethanol mixture which significantly differs from unity.

Droplet displacements and oscillations induced by ultrasonic surface acoustic waves: a quantitative study

We present an experimental study of a droplet interacting with an ultrasonic surface acoustic wave. Depending on the amplitude of the wave, the drop can either experience an internal flow with its contact line pinned, or (at higher amplitude) move along the direction of the wave also with internal flow. Both situations come with oscillations of the drop free surface. The physical origins of the internal mixing flow as well as the drop displacement and surface waves are still not well understood. In order to give insights of the underlying physics involved in these phenomena, we carried out an experimental and numerical study. The results suggest that the surface deformation of the drop can be related to a combination between acoustic streaming effect and radiation pressure inside the drop.

On the influence of spatial correlations on sound propagation in concentrated solutions of rigid particles

In a previous paper [J. Acoust. Soc. Am. 121, 3386-3387 (2007)], a self-consistent effective medium theory has been used to account for hydrodynamic interactions between neighboring rigid particles, which considerably affect the sound propagation in concentrated solutions. However, spatial correlations were completely left out in this model. They correspond to the fact that the presence of one particle at a given position locally affects the location of the other ones. In the present work, the importance of such correlations is demonstrated within a certain frequency range and particle concentration. For that purpose, spatial correlations are integrated in our two-phase formulation by using a closure scheme similar to the one introduced by Spelt et al. [''Attenuation of sound in concentrated suspensions theory and experiments," J. Fluid Mech. 430, 51-86 (2001)]. Then, the effect is shown through a careful comparison of the results obtained with this model, the ones obtained with different self-consistent approximations and the experiments performed by Hipp et al. ["Acoustical characterization of concentrated suspensions and emulsions. 2. Experimental validation," Langmuir, 18, 391-404 (2002)]. With the present formulation, an excellent agreement is reached for all frequencies (within the limit of the long wavelength regime) and for concentrations up to 30% without any adjustable parameter.

An extended coupled phase theory for the sound propagation in polydisperse concentrated suspensions of rigid particles

An extension of the classical coupled phase theory is proposed to account for hydrodynamic interactions between neighboring rigid particles, which are essential to describe properly the sound propagation in concentrated suspensions. Rigorous ensemble-averaged equations are derived for each phase and simplified in the case of acoustical wave propagation. Then, closure is achieved by introducing a self-consistent scheme originally developed by Buyevich and Shchelchkova [Prog. Aerosp. Sci. 18, 121-151 (1978)] for incompressible flows, to model the transfer terms between the two phases. This provides an alternative to the effective medium self-consistent theory developed by Spelt et al. [J. Fluid Mech. 430, 51-86 (2001)] in which the suspension is considered as a whole. Here, a significantly simpler formulation is obtained in the long wavelength regime. Predictions of this self-consistent theory are compared with the classical coupled phase theory and with experimental data measuring the attenuation in concentrated suspensions of silica in water. Our calculation is shown to give a good description of the attenuation variation with volume fraction. This theory is also extended to the case of polydisperse suspensions. Finally, the link between the self-consistent theory and the different orders of the multiple scattering theory is clarified.

Preliminary findings from the National Pre-ESRD Education Initiative

Regardless of age or race, more patients preferred peritoneal dialysis (PD) than would be expected from the current ratio of patients treated with PD in the U.S. The percent of patients choosing PD seems to be largely influenced by the scope of information they receive prior to therapy initiation. In the absence of thorough treatment option education, a significant number of patients may be assigned a therapy when, in reality, they would have selected an alternative option. There is a need to further understand the correlation between a practice's PD utilization rate and the extent to which patients are given dialysis treatment options.

Brain damage in the premature infant. Early lesions and new aspects of sequelae

In spite of a significant decrease of the mortality and morbidity of neonates, cerebral damage in the premature infant remains the major concern for the neonatologist. Intraventricular hemorrhage (IVH) and necrosis of the white matter (leukomalacia) are the two main lesions. Early morphological aspects have been known for many years, but the use of computerized tomography (CT scan) and ultrasonography (US) through the anterior fontanelle have led to renewed interest and the general recognition of IVH. Localization, extent and frequency of the lesions can readily be established. However the early diagnosis of leukomalacia is still uncertain. Long survival, with mechanical ventilation of severely ill infants, has made it possible to follow the natural history of the lesions and has modified the relative frequency of their occurrence. Posthemorrhagic hydrocephalus, sclerosis of the centrum semiovale and multicystic encephalopathy are now commonly found at autopsy of infants who have survived for several weeks.