Multiple Bubbles Research Articles

Inertial Cavitation Behaviors Induced by Nonlinear Focused Ultrasound Pulses.

Inertial cavitation induced by pulsed high-intensity focused ultrasound (pHIFU) has previously been shown to successfully permeabilize tumor tissue and enhance chemotherapeutic drug uptake. In addition to HIFU frequency, peak rarefactional pressure ( p- ), and pulse duration, the threshold for cavitation-induced bioeffects has recently been correlated with asymmetric distortion caused by nonlinear propagation, diffraction and formation of shocks in the focal waveform, and therefore with the transducer F -number. To connect previously observed bioeffects with bubble dynamics and their attendant physical mechanisms, the dependence of inertial cavitation behavior on shock formation was investigated in transparent agarose gel phantoms using high-speed photography and passive cavitation detection (PCD). Agarose phantoms with concentrations ranging from 1.5% to 5% were exposed to 1-ms pulses using three transducers of the same aperture but different focal distances ( F -numbers of 0.77, 1.02, and 1.52). Pulses had central frequencies of 1, 1.5, or 1.9 MHz and a range of p- at the focus varying within 1-18 MPa. Three distinct categories of bubble behavior were observed as the acoustic power increased: stationary near-spherical oscillation of individual bubbles, proliferation of multiple bubbles along the pHIFU beam axis, and fanned-out proliferation toward the transducer. Proliferating bubbles were only observed under strongly nonlinear or shock-forming conditions regardless of frequency, and only where the bubbles reached a certain threshold size range. In stiffer gels with higher agarose concentrations, the same pattern of cavitation behavior was observed, but the dimensions of proliferating clouds were smaller. These observations suggest mechanisms that may be involved in bubble proliferation: enhanced growth of bubbles under shock-forming conditions, subsequent shock scattering from the gel-bubble interface, causing an increase in the repetitive tension created by the acoustic wave, and the appearance of a new growing bubble in the proximal direction. Different behaviors corresponded to specific spectral characteristics in the PCD signals: broadband noise in all cases, narrow peaks of backscattered harmonics in the case of stationary bubbles, and broadened, shifted harmonic peaks in the case of proliferating bubbles. The shift in harmonic peaks can be interpreted as a Doppler shift from targets moving at speeds of up to 2 m/s, which correspond to the observed bubble proliferation speeds.

Concentration profile, energy, and weak limits of radial solutions to semilinear elliptic equations with Trudinger–Moser critical nonlinearities

We investigate the next Trudinger–Moser critical equations, $$\begin{aligned} {\left\{ \begin{array}{ll} -\Delta u=\lambda ue^{u^2+\alpha |u|^\beta }&{}\text { in }B, u=0&{}\text { on }\partial B, \end{array}\right. } \end{aligned}$$ where $$\alpha >0$$ , $$(\lambda ,\beta )\in (0,\infty )\times (0,2)$$ and $$B\subset {\mathbb {R}}^2$$ is the unit ball centered at the origin. We classify the asymptotic behavior of energy bounded sequences of radial solutions. Via the blow–up analysis and a scaling technique, we deduce the limit profile, energy, and several asymptotic formulas of concentrating solutions together with precise information of the weak limit. In particular, we obtain a new necessary condition on the amplitude of the weak limit at the concentration point. This gives a proof of the conjecture by Grossi et al. (Math Ann, to appear) in 2020 in the radial case. Moreover, in the case of $$\beta \le 1$$ , we show that any sequence carries at most one bubble. This allows a new proof of the nonexistence of low energy nodal radial solutions for $$(\lambda ,\beta )$$ in a suitable range. Lastly, we discuss several counterparts of our classification result. Especially, we prove the existence of a sequence of solutions which carries multiple bubbles and weakly converges to a sign-changing solution.

Bubble Detection in Housing Market: Evidence From a Developing Country

There is an upward trend in housing prices around the world, and Pakistan is no different either; being a developing county, it is facing a rising population. Due to this, the demand for housing has exceeded its supply and in turn rinsing their prices. This study is the first attempt to identify housing price bubbles in Pakistan from 1972 to 2018. The data are available on an annual basis, and to capture the price volatility, it is converted into a quarterly and monthly format. The Generalized Supremum Augmented Dickey–Fuller (GSADF) test is used to detect multiple bubbles. Monthly data showed more episodes of bubbles than yearly and quarterly data; in each case, it reported two periods of bubble episodes. The results of the house price dynamics suggest a higher return with high risk in the short run.

A hybrid simulation of gravitational wave production in first-order phase transitions

The LISA telescope will provide the first opportunity to probe the scenario of a first-order phase transition happening close to the electroweak scale. In thermal transitions, the main contribution to the GW spectrum comes from the sound waves propagating through the plasma. Current estimates of the GW spectrum are based on numerical simulations of a scalar field interacting with the plasma or on analytical approximations — the so-called sound shell model. In this work we present a novel setup to calculate the GW spectra from sound waves. We use a hybrid method that uses a 1d simulation (with spherical symmetry) to evolve the velocity and enthalpy profiles of a single bubble after collision and embed it in a 3d realization of multiple bubble collisions, assuming linear superposition of the velocity and enthalpy. The main advantage of our method compared to 3d hydrodynamic simulations is that it does not require to resolve the scale of bubble wall thickness. This makes our simulations more economical and the only two relevant physical length scales that enter are the bubble size and the fluid shell thickness (that are in turn enclosed by the box size and the grid spacing). The reduced costs allow for extensive parameter studies and we provide a parametrization of the final GW spectrum as a function of the wall velocity and the fluid kinetic energy.

Pulsed ultrasound propagation through polydisperse contrast agent suspensions

Gas microbubbles stabilised by a surfactant or polymer coating are widely used in echocardiography and, increasingly, for quantitative studies of tissue perfusion. It is their highly nonlinear response to ultrasound excitation that makes them such effective contrast agents. It is this property also, however, that leads to image artefacts and difficulties in obtaining accurate quantitative information. There are few theoretical models describing the response of a contrast agent population that take into account both nonlinear behaviour and multiple bubble interactions. Computational complexity arises when the medium contains a polydisperse bubble population because a nonlinear ordinary differential equation (ODE) governing the bubble response must be computed for the current radius of each bubble size R0 present at each spatial location at every time step, which unfortunately makes the numerical model impractical for real-time clinical use. Further complexity occurs when near-resonant microbubbles shed their lipid coating drastically transforming the suspension’s acoustic response to subsequent pulses. In this work, we investigate approximations that can significantly reduce the computational complexity and demonstrate that, under certain parameter regimes, these approximations can simulate the nonlinear propagation of a repeated ultrasound pulses through a polydisperse contrast agent suspension to reasonably high accuracy.

Cystitis Emphysematous on CT

Emphysematous cystitis is a rare form of lower urinary tract infection characterized by the presence of gas in the lumen and/ or bladder wall. The main cause is diabetes, especially in cases of poor balance or bladder neuropathy, but also in cases of immunosuppression. It is secondary to anaerobic glucose metabolism, which leads to the production of CO2. This leads to parietal emphysema by parietal gas dissection, which can spread in severe forms to the peri bladder cellulo-fat space. Not recommended for diagnosis, the abdomen without preparation may find pneumovesia or pelvic hydroaeriosis. Ultrasonography shows parietal bladder air bubbles with shadow cones. The CT scan shows multiple diffuse circumferential air bubbles in the bladder wall without digestive fistula (Figure 1; Figure 2: blues arrows). The germs involved are aerobic and anaerobic, but especially Escherichia Coli and Klebsiella pneumoniae. The prognosis depends on the early diagnosis and antibiotic treatment.

Detecting multiple bubbles in the Seoul housing market based on GSADF test

본 연구는 한국의 서울시 25개 지역구의 다중거품의 존재여부를 검정한다. 분석시점은 2002년 12월부터 2020년 4월까지의 월별자료를 이용하였다. 본 연구는 현재가치모형을 토대로 GSADF 검정을 통해 분석한다. GSADF test 결과 서울 25개지역구 중 21개 지역구에서 2-5개의 다중거품이 존재했다. 그리고 이러한 다중거품은 평균 9개월동안 지속되었다. 강남지역과 비교해서 강북지역에서 더 많은 다중거품이 발견되었으며 거품의 지속기간 또한 강북지역이 더 높게 나타났다. 한편 시점별로 보면 2015년 이전에는 강남지역에서는 거품이 발견되지 않았으나 강북지역의 경우에는 2006년과 2012년으로 거품시작시점이 두가지로 나타났다. 그러나 2015년부터 2019년까지는 서울시 25개 모든 지역구에서 거품이 나타났다.

Fate of the False Vacuum: Finite Temperature, Entropy, and Topological Phase in Quantum Simulations of the Early Universe

Despite being at the heart of the theory of the "Big Bang" and cosmic inflation, the quantum field theory prediction of false vacuum tunneling has not been tested. To address the exponential complexity of the problem, a table-top quantum simulator in the form of an engineered Bose-Einstein condensate (BEC) has been proposed to give dynamical solutions of the quantum field equations. In this paper, we give a numerical feasibility study of the BEC quantum simulator under realistic conditions and temperatures, with an approximate truncated Wigner (tW) phase-space method. We report the observation of false vacuum tunneling in these simulations, and the formation of multiple bubble 'universes' with distinct topological properties. The tunneling gives a transition of the relative phase of coupled Bose fields from a metastable to a stable 'vacuum'. We include finite temperature effects that would be found in a laboratory experiment and also analyze the cut-off dependence of modulational instabilities in Floquet space. Our numerical phase-space model does not use thin-wall approximations, which are inapplicable to cosmologically interesting models. It is expected to give the correct quantum treatment including superpositions and entanglement during dynamics. By analyzing a nonlocal observable called the topological phase entropy (TPE), our simulations provide information about phase structure in the true vacuum. We observe a cooperative effect in which the true vacua bubbles representing distinct universes each have one or the other of two distinct topologies. The TPE initially increases with time, reaching a peak as the multiple universes are formed, and then decreases with time to the phase-ordered vacuum state. This gives a model for the formation of universes with one of two distinct phases, which is a possible solution to the problem of particle-antiparticle asymmetry.

Fluid interface calorimetry

HypothesisAmphiphilic molecules spontaneously adsorb to fluid polar-nonpolar interfaces. The timescale of such adsorption depends on the molecular size and structure of the solute. This process should be accompanied by a power heat exchange that could be detected by commercial isothermal calorimeters. ExperimentsAir is injected in the bulk of different aqueous solutions contained in the sample cell of an isothermal titration calorimeter. The formation of the resulting bubbles leads to a liquid/air interface to which the solute molecules spontaneously adsorb. Continuous injection experiments to produce multiple bubbles as well as experiments with static bubbles stand from the capillary tip, aiming to observe slow adsorption processes, were performed. FindingsThe power associated with the formation, growth and release of air bubbles in different liquids was measured. Different independent contributions that can be associated to the pressure change in the gas phase, the evaporation-condensation of the solvent, the increase of interfacial area, the change in the heat capacity of the sample cell content, and the release of the bubble were observed. The periodic pattern produced by the continuous injection of air at a constant rate is used to determine the surface tension of different liquids, including solutions of different molecules and (bio)macromolecules.

Taming the Bubble

Taming the Bubble

The effect of surface wettability on flow boiling characteristics within microchannels

The process of flow boiling within micro-passages plays a very important role in many industrial applications. However, there is still a lack of understanding of the effect of an important controlling parameter: surface wettability. In this paper, an advanced numerical investigation on the effect of wettability characteristics on single and multiple bubble growth during saturated flow boiling conditions within a microchannel is performed. The 3D numerical simulations are conducted with the open-source Computational Fluid Dynamics (CFD) toolbox OpenFOAM, utilising a custom user-enhanced Volume Of Fluid (VOF) solver. The proposed solver enhancements involve an appropriate treatment for spurious velocities dampening, an improved dynamic contact angle treatment, as well as the implementation of a phase-change model in the fluid domain also accounting for Conjugate Heat Transfer (CHT) with the solid domain. In total, three sets of simulations of hydrophilic and hydrophobic surfaces with constant heat and mass flux were performed. In the first set, a single bubble seed was patched close to the inlet of the microchannel and the Heat Transfer Coefficient (HTC) along the channel interface was measured until the nose of the bubble reaches the outlet. The bubble growth and transport process within the channel were analysed, with a minor effect of the wettability characteristics on the HTC observed. In the second set of simulations, multiple recurring nucleation events at the same position were simulated; observing that in such more realistic cases the effect of wettability in the HTC was more profound. Finally, simulations with multiple nucleation sites and recurring nucleation events were conducted to analyse cases closer to reality. These results show indeed that surface wettability plays a significant role on the HTC, with the hydrophilic and hydrophobic cases performing approximately 43.9% and 17.8% higher respectively, compared to the single-phase reference simulations. Additionally, it is found that the dominant heat transfer mechanisms for the hydrophilic and hydrophobic surface are liquid film evaporation and contact line evaporation, respectively, and that for the proposed simulation parameters liquid film evaporation can be considered as a more efficient heat transfer mechanism compared to contact line evaporation.

Price bubbles in Beijing carbon market and environmental policy announcement

This paper examines price bubbles in the relatively new carbon emission trading scheme of Beijing carbon market by employing a recently proposed econometric test which can stamp the occurrence and burst of financial bubbles. We find multiple bubbles in Beijing carbon market over the sample period between January 2014 to April 2018, and that the occurrences of carbon price bubbles are closely related to the announcements of environmental policies by the Chinese government. Comparing our results to the EU ETS, we find that the volatility of carbon price in Beijing market is higher than EU, and interestingly, the bubbles in Beijing market occur when the price volatility is relatively low, while in EU market the bubbles correspond to the peaks of volatility. Our empirical results provide insightful policy implications in the context of the actual China’s carbon market reform. To achieve effective stabilization of carbon price, policymakers should publicize alert notifications of the price fluctuations, and strengthen the carbon markets supervision and promote its improvement.

Trapping Multielectron Bubbles Using a Point Paul Trap

We demonstrate an experimental setup to trap multielectron bubbles in bulk liquid He4 using a point Paul trap. The experimental configuration is based on dc and rf electric fields applied to planar electrodes such as to trap the bubbles at a certain location. We have performed numerical simulations to estimate the experimental parameters at which stable trapping can occur, which matched with the experimental results. Compared to the linear Paul traps reported earlier by our group, point Paul traps allow more efficient loading and better optical access for viewing the trapped bubbles, and will allow simultaneous storage and investigation of multiple electron bubbles in the future.

Identifying price bubble periods in the Bitcoin market-based on GSADF model

The advert of cryptocurrency era is signified by the luanch of Bitcoin, which has been considered as a milestone event. Ever since its emergence, Bitcoin has experienced rapid price increase along with great price fluctuations. This paper aims to explore the beginning and the culmination of possible speculative bubbles the Bitcoin market. Based on the daily closing price of Bitstamp, a major Bitcoin exchange platform, from September 13, 2011 to October 12, 2020, this paper adopts GSADF (generalized sup augmented Dickey–Fuller) to explore the existence of the bubble in the Bitcoin market, estimate the time of emergence and collapse of the bubble, investigate the causes of the bubbles based on its time order, and attempts to put forward some policy suggestions. Through this study, we have found that: (1) There are a lot of speculative bubbles. During the research period, there were a total of four long bubbles (i.e. 2013.01.25–2013.04.05; 2013.11.05–2013.12.10; 2017.04.27–2017.07.05; 2017.07.15 –2018.01.09) and four short bubbles (2016.06.08–2016.06.18; 2016.12.30–2017.01.15; 2017.02.22 –2017.03.07; 2019.06.19 –2019.06.25). (2) The emergence and burst of bubbles were mostly related to the occurrence of relevant events and policies. (3) Bitcoin market is far from mature. A key policy risk triggering the speculative behavior is policy announcement. The prominent innovation of this paper is that the latest developed bubble detection method GSADF has been employed in the Bitcoin market. This method can detect the existence of multiple Bitcoin bubbles and their durations.

Nonlinear dynamics of acoustic bubbles excited by their pressure-dependent subharmonic resonance frequency: influence of the pressure amplitude, frequency, encapsulation and multiple bubble interactions on oversaturation and enhancement of the subharmonic signal

Nonlinear behavior of bubbles, and most importantly $$\frac{1}{2}$$ -order subharmonics (SH), are used to increase the contrast-to-tissue ratio (CTR) in diagnostic ultrasound (US) and to monitor bubble-mediated therapeutic US. It is shown experimentally and numerically that when bubbles are sonicated with a frequency that is twice their resonance frequency ( $$f_\mathrm{r}$$ ), SHs at half the excitation frequency are generated at the minimum excitation pressure. Thus, $$f=2f_\mathrm{r}$$ is defined as the SH resonance frequency. SHs increase rapidly with pressure and reach an upper limit of the achievable SH signal strength. Numerous studies have investigated the pressure threshold of SH oscillations; however, conditions to enhance the saturation level of SHs have not been investigated. In this paper, nonlinear dynamics of bubbles excited at frequencies in the range of $$f_\mathrm{r}<f<2f_\mathrm{r}$$ is studied for different sizes of bubbles (400 nm–8 $$\upmu \mathrm{m}$$ ). In agreement with previous studies, we show that the SH resonance frequency is pressure dependent and decreases as pressure increases. When a bubble is sonicated with its pressure-dependent SH resonance frequency, oscillations undergo a saddle node bifurcation from a P1 or P2 regime to a P2 oscillation regime with higher amplitude. The saddle node bifurcation is concomitant with over-saturation of the SH and UH amplitude and eventual enhancement of the upper limit of SH and UH strength (e.g., $$\approx $$ 7 dB in UH amplitude). This can increase the CTR and signal-to-noise ratio in applications. Here, we show that the highest non-destructive SH amplitude occurs when $$f\approxeq 1.6-1.8f_\mathrm{r}$$ . In the case of interacting bubbles, $$f_\mathrm{r}$$ and pressure threshold of SH emissions decrease with increasing concentration, and supersaturation amplitude decreases above an upper limit of concentration.

Influence of multiple air bubbles on the collapse strength of a cavitation bubble

Studying the effect of multiple air bubbles on the collapse strength of a cavitation bubble can aid in understanding the mechanism of air entrainment alleviating the cavitation erosion and enhance the aeration effects in hydraulic engineering. A cavitation bubble is generated by the spark-generated system. Air bubbles are arranged in three manners: two air bubbles on the same side, one air bubble on either side, and four air bubbles around. The intensity of the cavitation bubble collapse noise is estimated using a hydrophone. The results show that, in the range in which the air bubbles can interact with the cavitation bubble, the relative distance, size, and number of the air bubbles and cavitation bubble can considerably influence the migration direction, the oscillation time and the collapse sound pressure of the cavitation bubble. For the first time, it is observed that air bubbles split a cavitation bubble into two subcavitation bubbles. In aeration methods, under the same aeration concentration, the air bubbles should be small, numerous, and evenly distributed.

Activating Bubble's Escape, Coalescence, and Departure under an Electric Field Effect.

In this paper, we present the results of applying an electric field to activate bubbles' escape, coalescence, and departure. A simple electrowetting-on-dielectric device was utilized in this bubble dynamics study. When a copper electrode wire inserted into deionized water was positioned on one side of single or multiple bubbles, the bubble tended to continuously escape from its initial position as the voltage was turned on. Contact angle imbalance at different sides of the bubble was observed, which further promoted the bubble's escape. An analysis model with an electromechanical framework was developed to study the charging time difference on two sides of the bubble, which generated a wettability gradient and capillary force to propel it away from the electrode. Sine, ramp, and square alternating current waveforms with 60 V amplitude and 2 Hz frequency were tested for comparison. It was shown that all waveforms promoted the bubble's escape; the square wave shape manifested the farthest escape capability, followed by sine and ramp waves. An upper view of several bubbles aligning in triangle, square, pentagon, and hexagon shapes demonstrated that the bubbles tended to move outward when the electrode is placed at the geometric centers. Experiments with an electrode on one side and several bubbles positioned in a line were conducted. In these cases, the bubbles closer to the electrode reacted faster than those farther from the electrode, resulting in coalescence. Once the bubble size became larger, it departed either by overcoming the disjoining pressure in a thin film of water or via the buoyancy force in a thick film of water. Controlling bubble dynamics by the electric field, including escape, coalescence, and departure provides an active and reversible approach to move bubbles or increase departure frequency in many fluid mechanics and heat transfer studies.

The soft commodities multiple bubbles tests: evidence from the New York Futures Markets

ABSTRACT The soft commodity is a high-frequency trading market. We use the right-tailed unit root tests of Phillips et al. to investigate asset bubbles within and to detect explosive episodes on each soft commodity sample date set. Our empirical test uses weekly data from New York soft commodity market and finds bubbles existed in each of the soft commodities. The test model allows us to exam each bubble’s origination and termination dates using date-stamping in the recursive procedure. We found that the soft commodities bubble is more relevant to the man-made factor.

Fatal Necrotizing Fasciitis Following Uncomplicated Colonoscopic Polypectomy: A Case Report

Necrotizing fasciitis (NF) is a life-threatening infection that can be caused by various procedures or surgery and may develop in healthy elderly patients. Here, we report a case of a 66-year-old man with diabetes mellitus who underwent colonoscopic polypectomy, without complications. However, he visited the emergency department 24 hours after the procedure complaining of abdominal pain. Abdominopelvic computed tomography revealed multiple air bubbles in the right lateral abdominal muscles. After a diagnosis of NF was made, immediate surgical debridement was performed. However, despite three sessions of extensive surgical debridement and best supportive care at the intensive care unit, the patient died because of sepsis and NF-associated multiple-organ failure. In conclusion, physicians should pay special attention to the possibility of NF if a patient with risk factors for NF develops sepsis after colonoscopic polypectomy.

Do crude oil price bubbles occur?

The Generalized Supremum Augmented Dickey-Fuller (GSADF) test is employed to conclude whether crude oil price (OP) experiences multiple bubbles. The technique has distinctions to detect multiple bubbles along with its beginning and ending point. Oil is extremely significant due to its strategic position and several factors influence OP. The outcomes display the existence of bubbles which imply that OP deviates three times. This indicates the beginning and termination of bubbles coincide with a particular crisis. The expansion of the world economy, the mismatch between demand-supply of oil, dollar depreciation, excess supply by Organization of the Petroleum Exporting Countries, shale oil production of the U.S., and low demand by the emerging economies are the leading factors of OP bubbles. The main contributions are the investigation of the OP bubble, its determinants and the different technique of GSADF to detect OP bubbles. Moreover, the greater economic certainty and political stability ensure a smooth supply of OP can lessen unexpected fluctuation. The symmetric information can minimize market speculation, improve market efficiency, help investors make reasonable investment decisions, and minimize potential price risks.