Volumetric Oscillation Research Articles

Autonomous Motion of Hydrogels Driven by Semi-Interpenetrating Chemical Processing Systems.

Developing artificial autonomous materials is crucial for a deeper understanding of the emergence of life-like behavior. In nature, cells achieve autonomy through chemical processing systems incorporated into soft material-based frameworks. Inspired by natural cells, we herein describe a straightforward methodology for constructing artificial autonomous materials consisting of a polymer-based chemical processing system and a hydrogel-based soft framework. Using a material comprising a hydrogel framework devoid of active components in combination with semi-interpenetrating self-oscillating linear polymers, we discovered that semi-interpenetrating polymer-based chemical processing systems drive the autonomous motion of the hydrogel framework. The material exhibited autonomous volumetric oscillation powered by the Belousov-Zhabotinsky reaction. Furthermore, the autonomous behavior is controllable by changing the content of the chemical processing system incorporated into the hydrogel framework. Our findings shed light on a class of autonomous materials based on polymer-based chemical processing systems with soft frameworks.

The pressure-volume relationship in an ideal Stirling refrigerator

Hysteresis losses in the heat transfer between compressing or expanding gas and the adjacent wall is said to play an important role in Stirling machines, where it increases the amount of required p-V work. Previous studies have linked hysteresis loss with the pressure phase shift. In the context of this research, the effect of the pressure phase shift on the net p-V work in a single space is examined.A Sage model of a single space piston-cylinder device is used to investigate the underlying mechanisms of the pressure phase shift. The Sage model is validated using an experimental piston seal rig. In addition, the time dependence of heat transfer is discussed along with how it affects the pressure phase shift, using an iterative model. The Schmidt equations were manipulated to determine the phase shift between pressure and volumetric oscillation in an ideal Stirling refrigerator.The results of this investigation are surprising. It was found that even in the case of an idealized Stirling refrigerator, the phase shift between pressure and volume is non-zero in order to produce a refrigeration effect.

Emergent Synchronous Volumetric Oscillation in Hierarchically Structured Self-Oscillating Gel Clusters.

Emergent properties accompanying synchronization among oscillators are vital characteristics in biological systems. Belousov-Zhabotinsky (BZ) oscillators are an artificial model to study the emergence and synchronization in life. This research represents a self-oscillating gel system with clusterable properties to experimentally examine synchronous and emergent properties at a fundamental hierarchical level. Incorporating acrylic acid (AAc) moieties within the gel network facilitates cluster formation through hydrogen bonding in an acidic BZ substrate solution. Upon clustering, both homogeneous and heterogeneous gel assemblies─ranging from double to quadruple clusters─exhibit increased and synchronized periods and amplitudes during the BZ reaction. Notably, in heterogeneous clusters, gel units with initially short periods and small volumetric amplitudes display a significant increase, aligning with the lonfger periods and larger amplitudes of other elements within the cluster, an emergent property. This research can pave the way for a better understanding of synchronous and emergent properties in biological oscillators such as cardiomyocytes.

Fabrication of submillimeter-sized spherical self-oscillating gels and control of their isotropic volumetric oscillatory behaviors.

In this study, we established a fabrication method and analyzed the volumetric self-oscillatory behaviors of submillimeter-sized spherical self-oscillating gels. We validated that the manufactured submillimeter-sized spherical self-oscillating gels exhibited isotropic volumetric oscillations during the Belousov-Zhabotinsky (BZ) reaction. In addition, we experimentally elucidated that the volumetric self-oscillatory behaviors (i.e., period and amplitude) and the oscillatory profiles depended on the following parameters: (1) the molar composition of N-(3-aminopropyl)methacrylamide hydrochloride (NAPMAm) in the gels and (2) the concentration of Ru(bpy)3-NHS solution containing an active ester group on conjugation. These clarified relationships imply that controlling the amount of Ru(bpy)3 in the gel network could influence the gel volumetric oscillation during the BZ reaction. These results of submillimeter-sized and spherical self-oscillating gels bridge knowledge gaps in the current field because the gels with corresponding sizes and shapes have not been systematically explored yet. Therefore, our study could be a cornerstone for diverse applications of (self-powered) gels in various scales and shapes, including soft actuators exhibiting life-like functions.

Explaining the working mechanism of laser-activated irrigation and its action on microbial biofilms: A high-speed imaging study.

Laser-activated irrigation (LAI) using pulsed erbium lasers has been studied with regard to canal cleaning, but its working mechanism remains poorly understood. This study sought to unravel the method of action of LAI and to assess its effect on bacterial biofilms in a root canal model, by means of high-speed imaging. A root canal model consisting of dentine and glass walls was used. Visualization of the canal space during activation was achieved with a high-speed camera, capturing 20-s activation series at 50 000 frames per second. Recordings were made of canal models filled with water, models filled with water containing glass microspheres, and models with a biofilm (an undefined biofilm originating from oral samples, a 1-week-old Enterococcus faecalis biofilm or a 11-day-old multispecies biofilm) grown on the dentine walls. LAI parameters were 2940 nm, 15 Hz, 50 μs, 20 mJ and 400 μm conical tip held at orifice level. Quantitative (measurement of size, life time and timing of cavitation bubbles; velocity and amplitude of root canal content movement) and qualitative (descriptive) analysis of the intracanal events was performed using imaging software. During the implosion of the primary bubble, smaller cavitation bubbles emerged throughout the entire canal. This process began in the coronal canal part and continued in the apical direction. Expansion of these bubbles was followed by an implosion, and this volumetric change over a time span of a few 100 μs resulted in a very rapid vertical movement of the canal content with a mean amplitude of 900 μm. The succession of these movements with every pulse, resulted in biofilm detachment from the root canal walls and the gradual displacement of fragments coronally, until their complete removal. The pattern of the biofilm removal was the same for all groups. LAI was able to remove biofilm from the root canal models. The hydrodynamic effect of LAI is based on the generation of small cavitation bubbles throughout the entire canal, far from the primary bubble. Their volumetric oscillation results in a small yet very fast vertical movement of the root canal content and local liquid streaming on each pulse, resulting in biofilm detachment and coronal displacement.

Magnetic Nanobubble Mechanical Stress Induces the Piezo1-Ca2+ -BMP2/Smad Pathway to Modulate Neural Stem Cell Fate and MRI/Ultrasound Dual Imaging Surveillance for Ischemic Stroke.

Neural stem cells (NSCs) are used to treat various nervous system diseases because of their self-renewal ability and multidirectional differentiation potential. However, an insufficient ability to track their migration in vivo and poor control over their survival and differentiation efficiency are two major critical challenges for clinical application. Here, it is shown that when magnetic nanobubbles (MNBs), which are assembled from magnetic nanoparticles, are internalized by NSCs, intramembrane volumetric oscillation of the MNBs induces an increase in intracellular hydrostatic pressure and cytoskeleton force, resulting in the activation of the Piezo1-Ca2+ mechanosensory channel. This subsequently triggers the BMP2/Smad biochemical signaling pathway, leading to differentiation of NSCs into the neuronal phenotype. Signaling through the Piezo1-Ca2+ -BMP2/Smad pathway can be further accelerated by application of an external shear stress force using low-intensity pulsed ultrasound. More importantly, magnetic resonance imaging and ultrasound imaging surveillance of NSCs based on MNB labeling can be leveraged to provide NSC therapeutic outcomes. Both the in vitro and in vivo findings demonstrate that a bubble nanostructure-induced physical force can modulate and control the mechanical signaling pathway regulating stem cell development.

Region-dependent volumetric oscillation of self-oscillating gels with gradient transducers.

Heartbeats with different ventricular contractions vary with heart regions, which can be described as anisotropy. Herein, we report self-oscillating gels which exhibit region-dependent anisotropic volumetric oscillation behavior similar to that of the heart. We installed a (Ru(bpy)3) gradient transducer on self-oscillating gels by employing slow and unidirectional diffusion in the gels and dipping part of the gel into a Ru(bpy)3-NHS solution. We found that the spatial distribution of Ru(bpy)3 in the gel caused region-dependent swelling/deswelling behavior depending on the redox state. We also confirmed that gel regions with smaller Ru(bpy)3 amounts exhibit lower amplitudes than those with larger amounts of Ru(bpy)3 during the Belousov-Zhabotinsky (BZ) reaction. These results are important in the design of self-oscillating soft actuators or machines, such as a biomimetic pump with desirable anisotropic oscillating behavior.

Comb Filter Saw-Resonator Traveling Wave

Owing to the use of surface acoustic waves, the frequency range of this type of filter is expanded to the high frequency range and can reach several gigahertz. To implement filters on surface waves, piezoelectrics like a quartz plate are used. However, quartz is rarely used for the manufacture of broadband filters. Barium titanate or lithium niobate is commonly used.The difference in the operation of SAW filters from quartz or piezoceramic filters is that not a volumetric oscillation of the piezoelectric is used, but a wave propagating over the surface. In order to prevent body waves that could distort the frequency response, special constructive measures are taken. Most of the advantages of SAW devices are directly related to their physical structure: low weight and dimensions; linear (or defined by requirements) phase; shape factor approaching unity (very high squareness); exceptional out-of-band suppression; temperature stability. Since the center frequency and the shape of the frequency response are determined by the topology, they do not require complex settings in the equipment and cannot be upset during operation. Manufacturing technology compatible with semiconductor manufacturing allows them to be produced in large volumes with high reproducibility. Filtering devices on distributed components are considered. Since narrow band filters are constructed on surface - acoustic waves, there are difficulties in providing the vertex of the amplitude - frequency characteristic uniformity. When designing and creating new high-frequency electronics components, there is a need to reduce filter losses and harmonization. Offered the design and mathematical model of a comb filter based on a ring resonator of surface - acoustic waves and two waveguides on surface - acoustic waves, which are connected to a ring resonator at opposite points taking into account integral losses. This model helps to consider and calculate the propagation of waves inside the annular resonator in the light of losses. A topological scheme is described, which is described by the distribution of the energy of the signal and the coefficients of division. The division coefficients are represented as mathematical relations. The solutions of the amplitude and phase expressions by the method of successive approximations are presented. Reducing the loss in the filter and reducing the effect of the partition coefficient lead to an increase in the figure of merit of the ring resonator, which allows to take this into account when designing, since the characteristic moves to the range of higher damping values. We get a result that significantly reduces the bandwidth attenuation of the filter due to the loss reduction. The result obtained is described in the form of a linear circuit with feedback. The obtained characteristics are inherent in the comb filters, and the result is explained by the fact that the investigated structure is presented in the form of a linear circuit with delay and feedback. Also, it can be concluded that the advantages of the SAW are light weight and dimensions, temperature stability and relative ease of design and manufacture.

Natural convection combined with surface radiation in a rotating cavity with an element of variable volumetric heat generation

Thermogravitational convection and surface radiation in a rotating chamber with an element of variable volumetric thermal generation has been studied. The analyzed chamber has two thermally-insulated horizontal borders, two isothermal vertical walls of the low temperature and variable heat-generated element on the bottom border. The cavity rotates with a constant angular velocity. Mathematical model has been formulated in non-dimensional stream function and vorticity functions. The important equations have been worked out by the finite difference technique on uniform grid. The impacts of the Taylor number, surface emissivity, and heat source volumetric heat generation oscillation frequency on heat and mass transfer have been investigated. It has been found that the surface emissivity and the volumetric heat generation oscillation frequency can improve the heat transfer in a rotating cavity. A rise of the surface emissivity illustrates the total energy transport enhancement and a diminution of the average heater temperature, while a rise of the volumetric heat generation oscillation frequency characterizes a reduction of the average heater temperature.

Mixed convection–radiation in lid-driven cavities with nanofluids and time-dependent heat-generating body

The cooling process of electronic devices having heat-generating elements is a major challenge allowing to develop electronics industry. Therefore, a creation of novel cooling techniques is an important task that can be solved numerically taking into account the multiparametric character of this problem. The mixed convection heat transfer combined with thermal radiation in a lid-driven cavity filled with an alumina–water nanofluid under the effect of sinusoidal time-dependent heat-generating solid element is studied numerically. The partial differential equations formulated in stream function–vorticity variables are solved by the finite difference method. Effects of the Rayleigh number, Reynolds number, thermal radiation parameter, heater location, volumetric heat flux oscillation frequency and nanoparticles volume fraction on liquid flow and heat transfer are analyzed. It has been found that an addition of nanoparticles leads to reduction of the heater temperature, while convective flow rate decreases also.

Numerical simulations and experimental validation on passive acoustic emissions during bubble formation

In this paper, the volume of fluid (VOF) model in conjunction with continuum surface force (CSF) model is applied to numerically investigate the single bubble formation process in the bubble columns. Meanwhile, the hybrid method (large-eddy simulation (LES) and acoustic analogy method) is used for bubble acoustic prediction. Experimental results provide a reliable validation of the numerical results. Adaptive filtering technique and time–frequency analyses are adapted for the numerical acoustic data at the gas velocity of 0.1m/s. The spectrum and spectrogram approaches indicate that the numerical acoustic data covers two principal frequency components, in which, one is the bubble generation rate and the other is the natural frequency of volumetric bubble oscillation. By combining the studies of flow field and acoustic signals, volumetric bubble oscillation is found to be excited by an axial water jet up into the bubble, immediately following the bubble detachment. The results of this study lead to the proposition that numerical simulation method could be applied to well understanding of the physics behind the passive acoustic emission.

Linear oscillation of gas bubbles in a viscoelastic material under ultrasound irradiation

Acoustically forced oscillation of spherical gas bubbles in a viscoelastic material is studied through comparisons between experiments and linear theory. An experimental setup has been designed to visualize bubble dynamics in gelatin gels using a high-speed camera. A spherical gas bubble is created by focusing an infrared laser pulse into (gas-supersaturated) gelatin gels. The bubble radius (up to 150 μm) under mechanical equilibrium is controlled by gradual mass transfer of gases across the bubble interface. The linearized bubble dynamics are studied from the observation of spherical bubble oscillation driven by low-intensity, planar ultrasound driven at 28 kHz. It follows from the experiment for an isolated bubble that the frequency response in its volumetric oscillation was shifted to the high frequency side and its peak was suppressed as the gelatin concentration increases. The measurement is fitted to the linearized Rayleigh–Plesset equation coupled with the Voigt constitutive equation that models the behavior of linear viscoelastic solids; the fitting yields good agreement by tuning unknown values of the viscosity and rigidity, indicating that more complex phenomena including shear thinning, stress relaxation, and retardation do not play an important role for the small-amplitude oscillations. Moreover, the cases for bubble-bubble and bubble-wall systems are studied. The observed interaction effect on the linearized dynamics can be explained as well by a set of the Rayleigh–Plesset equations coupled through acoustic radiation among these systems. This suggests that this experimental setup can be applied to validate the model of bubble dynamics with more complex configuration such as a cloud of bubbles in viscoelastic materials.

Source mechanism of small long‐period events at Mount St. Helens in July 2005 using template matching, phase‐weighted stacking, and full‐waveform inversion

AbstractLong‐period (LP, 0.5‐5 Hz) seismicity, observed at volcanoes worldwide, is a recognized signature of unrest and eruption. Cyclic LP “drumbeating” was the characteristic seismicity accompanying the sustained dome‐building phase of the 2004–2008 eruption of Mount St. Helens (MSH), WA. However, together with the LP drumbeating was a near‐continuous, randomly occurring series of tiny LP seismic events (LP “subevents”), which may hold important additional information on the mechanism of seismogenesis at restless volcanoes. We employ template matching, phase‐weighted stacking, and full‐waveform inversion to image the source mechanism of one multiplet of these LP subevents at MSH in July 2005. The signal‐to‐noise ratios of the individual events are too low to produce reliable waveform inversion results, but the events are repetitive and can be stacked. We apply network‐based template matching to 8 days of continuous velocity waveform data from 29 June to 7 July 2005 using a master event to detect 822 network triggers. We stack waveforms for 359 high‐quality triggers at each station and component, using a combination of linear and phase‐weighted stacking to produce clean stacks for use in waveform inversion. The derived source mechanism points to the volumetric oscillation (∼10 m3) of a subhorizontal crack located at shallow depth (∼30 m) in an area to the south of Crater Glacier in the southern portion of the breached MSH crater. A possible excitation mechanism is the sudden condensation of metastable steam from a shallow pressurized hydrothermal system as it encounters cool meteoric water in the outer parts of the edifice, perhaps supplied from snow melt.

Numerical analysis of weld pool oscillation in laser welding

Volume of fluid (VOF) numerical simulation was used to investigate melt flow and volumetric oscillation of conduction-mode pulsed laser weld pools. The result is compared to high speed video stream of titanium laser spot welding experiment. The total simulation time is 10ms with the first 5 ms being heating and melting under constant laser irradiation and the remaining 5 ms corresponding to re-solidification of the weld pool. During the melting process, the liquid pool did not exhibit periodic oscillation but was continually depressed by the evaporation recoil pressure. After the laser pulse, the weld pool was excited into volumetric oscillation by the release of pressure on its surface and oscillation of the weld pool surface was analyzed. The simulation model suggested adjusting thermal diffusivity to match cooling rate and puddle diameter during solidification which is distinguishable from previous weld pool simulation. The frequency continuously increased from several thousand cycles per second to tens of thousands of cycles per second as the weld pool solidified and its diameter decreased. The result is the first trial of investigation of small weld pool oscillation in laser welding although there have been several reports about arc welding.

High-intensity focused ultrasound heating of large tissue region enhanced by cavitation bubbles at multiple focal spots

High-intensity focused ultrasound (HIFU) causes selective tissue necrosis through heating and is used for a noninvasive treatment of cancer therapy. However, it has a problem of a long treatment time for a large tumor. To improve the throughput of the treatment, the development of a highly efficient method is needed. It is known that cavitation bubbles enhance the heating effect of ultrasound during ultrasonic irradiation because the increase in the energy dissipation is caused by the volumetric oscillation of cavitation bubbles. In this study, cavitation bubbles were generated at multiple spots by changing focal position of high-intensity ultrasound. Immediately after generating the bubbles, the bubbles were exposed to a wide-focused ultrasound which covers all the cavitation sites for the cavitation-enhanced heating in a large region. The behavior of the cavitation bubbles at multiple spots in a tissue-mimicking gel was observed by high-speed photography, and the coagulation performance of the developed...

An Attribution of Cavitation Resonance: Volumetric Oscillations of Cloud

In order to further verify the proposed theory of cavitation resonance, as well as to proceed the investigations into microscopic level, a series of studies are being carried out on the Warwick venturi. The analysis of the oscillation characteristics of the cavitation resonance has conclusively verified the macro-mechanism proposed through previous studies on other cavitating flows by the authors. The initial observations using high-speed photographic approach have revealed a new attribution of cavitation resonance. That is, the volumetric oscillation of cavitation cloud is associated with the cavitation resonance, which is a collective behaviour of the bubbles in the cloud.

Direct numerical simuiation of bubble-cluster's dynamic characteristics

A Direct Numerical Simulation (DNS) for understanding the dynamic response of bubble cluster to pulses of pressure perturbations has been studied by using a front-tracking method. The results show that owing to high nonlinearity, the bubble shape and volume oscillations caused by passing by pressure wave will be transformed into an in-phase volumetric oscillation of whole bubble cluster at a particular low-frequency. The value of the frequency is independent of the pulse excitations but the characteristics of the bubble cluster such as its bubble size, bulk void fraction and its spacial distribution etc. It is believed that this study provides important information for us to understand the coupling mechanism of cavitation cloud involved in cavitation resonance, a phenomenon noticed by one of the authors more than two decades ago.

The influence of surface adsorption on microbubble dynamics

In a pure liquid, the behaviour of a gas or vapour microbubble is determined primarily by its size, the ambient pressure and the properties of the surrounding liquid. In practice, however, adsorption of a dissolved substance from the surrounding liquid onto the microbubble surface will often take place, producing a thin coating which can significantly affect both the microbubble's stability and its dynamic response. This can have important implications in a wide range of applications, including underwater acoustics, cavitation detection, medical imaging and drug delivery. The aim of this paper is to review the existing theoretical treatments of coated microbubbles and to present and discuss some recent developments. It will be shown that the presence of the coating can substantially modify the amplitude of microbubble volumetric oscillation, resonance characteristics and relative amplitude in tension and compression. Finally, the need for improved understanding of the dynamic behaviour of surface coatings at high frequencies will be discussed.

A Study on the Hydrodynamic Load in a Water Pool When Discharged Air Forms a Bubble Cloud (PVP2006-ICPVT11-93281)

This paper presents a numerical and qualitative study on the expected hydrodynamic load-reducing effect of bubbly medium near a volumetrically oscillating bubble. In this study, the bubble or bubble cloud is assumed to be spherically symmetric, and its motion is analyzed as a one-dimensional compressible two-phase flow in the radial direction in spherical coordinates. We adopted the cubic interpolated pseudoparticle combined unified procedure method, which is a unified analysis method for both compressible and incompressible fluids proposed by Yabe and Wang (1991, “Unidied Numerical Procedure for Compressible and Incompressible Fluid,” J. Phys. Soc. Jpn., 60, pp. 2105–2108) in order to treat interaction among gas, liquid, and two-phase medium and to avoid large numerical dissipation at density discontinuities. To verify the analysis program we developed, we analyzed free oscillations of a bubble with a unity void fraction and of a bubble cloud with an initial void fraction of 0.5, and found that the natural frequency from numerical results is well reproduced with an error of 0.9% for the bubble and 5% for the bubble cloud as compared to those obtained on a theoretical basis. Using this method, we analyzed the free oscillation of a bubble cloud in which a bubble with a unity void fraction is covered by a bubbly medium layer with an initial void fraction of 0.5. Numerical results show that the amplitude of pressure oscillation inside the bubble is about halved and that a higher mode of oscillation appears when a bubbly medium layer covers the bubble. The measured results from a blowdown test we previously reported also show a similar higher mode of oscillation. The amplitude of pressure oscillation in the water region was apparently reduced when a thick bubbly medium layer covers the bubble. Thus, if the bubbly medium are ejected from sparger holes prior to the ejection of a high-pressure bubble, the bubbly medium might reduce the hydrodynamic load induced in a water pool made by volumetric oscillation of the bubble.

Novel methods of micro-object trapping by acoustic radiation force

It is expected that micro object trapping by acoustic radiation force is a useful method in future drug delivery systems in order to concentrate the payloads at desired position. In this paper, two novel methods of micro object trapping are presented. First method is micro object trapping by seed bubbles. This method uses seed bubbles, which have higher sensitivity to the ultrasonic wave, in order to trap micro objects, which are difficult to trap by conventional methods due to low volumetric oscillation under the ultrasonic wave. The Bjerkne’s force, which is produced by a secondary wave radiated from the seed bubbles, traps the target objects making bi-layer seed bubbletarget object mass. The Second method is micro bubble trapping by bubble nonlinear oscillation. Two ultrasonic waves with different frequencies (pumping and control waves) are introduced simultaneously. The frequency of the control wave is set to a harmonic frequency of the pumping wave. If the bubbles flow into the cross area of two waves, nonlinear oscillation by high intensity pumping wave generates the Bjerkne’s force, producing multiple traps with narrow separation along the control wave propagation direction. In order to demonstrate these methods, experiments using an ultrasonic wave contrast agent are shown.