Bubble Rims Research Articles

High speed observation of damage created by a collapse of a single cavitation bubble

One of the remaining open questions in cavitation erosion research is the one on the importance of the microjet and the shock wave on the formation of the pit. Up until now, no successful attempt has been made to study this in detail, mainly because the damage could only be detected and evaluated after several successive bubble collapses.A bubble with a maximum diameter of up to 3.3 mm was created during photoionization using a Nd:YAG laser. The damage was observed on a 9 µm thick aluminum foil attached to a glass substrate. Two high speed cameras were simultaneously used. One captured the dynamics of the bubble, while the other recorded the damage of the foil.We also observed the collapse of a bubble in the presence of shear flow, where most of the damage is created by the microjet mechanism. Sometimes, the collapse of the bubble rim, at the rebound of the initial bubble causes pits in a well-known circular pattern. From the recordings at the very fastest acquisition rate, we determined that the material deforms and then partially relaxes, while a significant deformation remains. The whole process is only 2–3 µs long.

A Molecular Line Investigation of the Interaction between Mid-infrared Bubbles and the Interstellar Medium

Abstract We used the Green Bank Telescope to detect molecular lines observed toward mid-infrared bubbles N62, N65, N90, and N117. The bubbles were selected from Watson et al., who detected non-Gaussian CS (1–0) emission lines toward the bubbles. Two of the bubbles are adjacent to infrared dark clouds (IRDCs); we examined these sources for evidence of interaction between the bubble rim and IRDC. The other two bubbles contain young stellar objects (YSOs) interior to the bubble rim; in these sources, we observed the gas near the YSOs. We detect CS (1–0) emission toward all of the sources, and in several pointings the CS emission shows non-Gaussian line shapes. HC3N (5–4), C34S (1–0), CH3OH (1–0), and SiO (v = 0) (1–0) were also detected in some pointings. We calculate column densities and abundances for the detected molecules. We compare the velocity of optically thick CS emission with the velocity of the other optically thin lines to look for evidence of infall. We find that even in pointings with non-Gaussian CS emission, our detections do not support an infall model. We interpret the kinematics of the gas in N62, N65, and N117 as likely evidence of multiple clouds along the line of sight moving at slightly offset velocities. We do not detect evidence of bubble rims interacting with IRDCs in N62 or N90. The gas interior to bubbles appears more disrupted than the gas in the IRDCs. N65 shows significantly stronger emission lines than the other sources, as well as the most complicated non-Gaussian line shapes.

THE MILKY WAY PROJECT AND ATLASGAL: THE DISTRIBUTION AND PHYSICAL PROPERTIES OF COLD CLUMPS NEAR INFRARED BUBBLES

ABSTRACT We present a statistical study of the distribution and physical properties of cold, dense material in and around the inner Galactic Plane near-infrared bubbles as cataloged by the Milky Way Project citizen scientists. Using data from the Atacama Pathfinder Experiment (APEX) Telescope Large Area Survey of the Galaxy 870 μm survey, we show that 48 ± 2% of all cold clumps in the studied survey region ( , ) are found in close proximity to a bubble, and 25 ± 2% appear directly projected toward a bubble rim. A two-point correlation analysis confirms the strong correlation of massive cold clumps with expanding bubbles. It shows an overdensity of clumps along bubble rims that grows with increasing bubble size, which shows how interstellar medium material is reordered on large scales by bubble expansion around regions of massive star formation. The highest column density clumps appear to be resistent to the expansion, remaining overdense toward the bubbles’ interior rather than being swept up by the expanding edge. Spectroscopic observations in ammonia show that cold dust clumps near bubbles appear to be denser, hotter, and more turbulent than those in the field, offering circumstantial evidence that bubble-associated clumps are more likely to be forming stars. These observed differences in physical conditions persist beyond the region of the bubble rims.

Influence of intermittent flow sub-patterns on erosion-corrosion in horizontal pipe

Thinning of pipe wall due to erosion and corrosion has resulted in many catastrophic failures and huge economic losses in petroleum refineries (Wood et al., 2013) and nuclear power stations (Ahmed, 2012). The intermittent structure of two-phase flow through pipe (intermittent flow regime) is an important factor responsible for such erosion and corrosion. The present research is an effort to develop a regime map showing possible erosion and corrosion phenomena due to intermittent flows in pipe. In this direction, flow visualization experiments are carried out for three distinct sub-regimes of intermittent flow namely, plug flow with or without bubble rim, less aerated slug flow and highly aerated slug flow. Images captured at a rate of 1600 frames per second at 288 diameter downstream of inlet are utilised for analysing the dynamics of intermittent flow structure in terms of expansion, contraction, breaking, coalescence, collapse, and collision of bubbles. Quantitative measurements of intermittent flow characteristics (including plug/slug frequency, plug/slug velocity and length of liquid plug/slug) and their influence on erosion-corrosion phenomena in the pipe are reported in detail. Based on these qualitative and quantitative analysis, a regime map for prediction of erosion-corrosion phenomena in pipes is established as a function of inlet flow conditions for both the phases. Transition boundaries for four distinct erosion-corrosion phenomena: shear stress induced erosion, cavitation erosion, liquid impact induced erosion and flow accelerated corrosion are represented in the map and eight distinct regimes of erosion-corrosion are illustrated. The regime map is represented in terms of non-dimensional superficial Reynolds numbers of both the phases to account for pipe diameter, flow rate and fluid viscosity. This erosion-corrosion regime map developed in this research will immensely aid to the effective design of piping systems and optimization of operating conditions for safer operation of petroleum refineries and nuclear power stations.

Dimensions and the Profile of Surface Nanobubbles: Tip–Nanobubble Interactions and Nanobubble Deformation in Atomic Force Microscopy

The interactions between argon surface nanobubbles and AFM tips on HOPG (highly oriented pyrolitic graphite) in water and the concomitant nanobubble deformation were analyzed as a function of position on the nanobubbles in a combined tapping mode and force-volume mode AFM study with hydrophilic and hydrophobic AFM tips. On the basis of the detailed analysis of force-distance curves acquired on the bubbles, we found that for hydrophobic tips the bubble interface may jump toward the tip and that the tip-bubble interaction strength and the magnitude of the bubble deformation were functions of vertical and horizontal position of the tip on the bubble and depended on the bubble size and tip size and functionality. The spatial variation is attributed to long-range attractive forces originating from the substrate under the bubbles, which dominate the interaction at the bubble rim. The nonuniform bubble deformation leads to a nonuniform underestimation of the bubble height, width, and contact angle in conventional AFM height data. In particular, scanning with a hydrophobic tip resulted in severe bubble deformation and distorted information in the AFM height image. For a typical nanobubble, the upward deformation may extend up to tens of nanometers above the unperturbed bubble height, and the lateral deformation may constitute 20% of the bubble width. Therefore, only scanning with a hydrophilic tip and no direct contact between the tip and the bubble may reduce nanobubble deformation and provide reliable AFM images that can be used to estimate adequately the unperturbed nanobubble dimensions. The deformation of the bubble shape and underestimation of the bubble size lead to the conclusion that the profile of surface nanobubbles is much closer than previously thought to a nearly flat bubble profile and hence that the Laplace pressure is much closer to the atmospheric pressure. Together with line pinning, this may explain the long nanobubble lifetimes observed previously. The findings presented in this report hold independently of the material that constitutes the interrogated nanoscale surface features.

THE MILKY WAY PROJECT: LEVERAGING CITIZEN SCIENCE AND MACHINE LEARNING TO DETECT INTERSTELLAR BUBBLES

We present Brut, an algorithm to identify bubbles in infrared images of the Galactic midplane. Brut is based on the Random Forest algorithm, and uses bubbles identified by >35,000 citizen scientists from the Milky Way Project to discover the identifying characteristics of bubbles in images from the Spitzer Space Telescope. We demonstrate that Brut's ability to identify bubbles is comparable to expert astronomers. We use Brut to re-assess the bubbles in the Milky Way Project catalog, and find that 10-30% of the objects in this catalog are non-bubble interlopers. Relative to these interlopers, high-reliability bubbles are more confined to the mid plane, and display a stronger excess of Young Stellar Objects along and within bubble rims. Furthermore, Brut is able to discover bubbles missed by previous searches -- particularly bubbles near bright sources which have low contrast relative to their surroundings. Brut demonstrates the synergies that exist between citizen scientists, professional scientists, and machine learning techniques. In cases where "untrained" citizens can identify patterns that machines cannot detect without training, machine learning algorithms like Brut can use the output of citizen science projects as input training sets, offering tremendous opportunities to speed the pace of scientific discovery. A hybrid model of machine learning combined with crowdsourced training data from citizen scientists can not only classify large quantities of data, but also address the weakness of each approach if deployed alone.

A statistical study of gaseous environment of Spitzer interstellar bubbles

The expansion of interstellar bubbles is suggested to be an important mechanism of triggering material accumulation and star formation. In this work, we investigate the gaseous environment of a large sample of interstellar bubbles identified by the Spitzer space telescope, aiming to explore the possible evidence of triggered gas accumulation and star formation in a statistical sense. By cross-matching 6124 Spitzer interstellar bubbles from the Milky Way Project (MWP) and more than 2500 Galactic H ii regions collected by us, we obtain the velocity information for 818 MWP bubbles. To study the gaseous environment of the interstellar bubbles and get rid of the projection effect as much as possible, we constrain the velocity difference between the bubbles and the 13CO(1−0) emission extracted from the Galactic Ring Survey (GRS). Three methods: the mean azimuthally averaged radial profile of 13CO emission, the surface number density of molecular clumps and the angular cross-correlation function of MWP bubbles and the GRS molecular clumps are adopted. Significant over density of molecular gas is found to be close to the bubble rims. 60 per cent of the studied bubbles were found to have associated molecular clumps. By comparing the clump-associated and the clump-unassociated MWP interstellar bubbles, we reveal that the bubbles in associations tend to be larger and thicker in physical sizes. From the different properties shown by the bubble-associated and bubble-unassociated clumps, we speculate that some of the bubble-associated clumps result from the expansion of bubbles. The fraction of the molecular clumps associated with the MWP bubbles is estimated to be about 20 per cent after considering the projection effect. For the bubble-clump complexes, we found that the bubbles in the complexes with associated massive young stellar object(s) (MYSO(s)) have larger physical sizes, hence the complexes tend to be older. We propose that an evolutionary sequence might exist between the relatively younger MYSO-unassociated bubble-clump complexes and the MYSO-associated complexes.

THE INTERSTELLAR BUBBLES OF G38.9–0.4 AND THE IMPACT OF STELLAR FEEDBACK ON STAR FORMATION

We present a study of the star formation (SF) region G38.9-0.4 using publicly available multiwavelength Galactic Plane surveys from ground- and space-based observatories. This region is composed of four bright mid-IR bubbles and numerous infrared dark clouds. Two bubbles, N 74 and N 75, each host a star cluster anchored by a single O9.5V star. We identified 162 young stellar objects (YSOs) and classify 54 as stage I, 7 stage II, 6 stage III, and 32 ambiguous. We do not detect the classical signposts of triggered SF, i.e., star-forming pillars or YSOs embedded within bubble rims. We conclude that feedback-triggered SF has not occurred in G38.9-0.4. The YSOs are preferentially coincident with infrared dark clouds. This leads to a strong correlation between areal YSO mass surface density and gas mass surface density with a power law slope near 1.3, which closely matches the Schmidt-Kennicutt Law. The correlation is similar inside and outside the bubbles and may mean that the SF efficiency is neither enhanced nor supressed in regions potentially influenced by stellar feedback. This suggests that gas density, regardless of how it is collected, is a more important driver of SF than stellar feedback. Larger studies should be able to quantify the fraction of all SF that is feedback-triggered by determining the fraction SF, feedback-compressed gas surrounding HII regions relative to that already present in molecular clouds.

INVESTIGATION OF MOLECULAR CLOUD STRUCTURE AROUND INFRARED BUBBLES: CARMA OBSERVATIONS OF N14, N22, AND N74

We present CARMA observations in 3.3 mm continuum and several molecular lines of the surroundings of N14, N22, and N74, three infrared bubbles from the GLIMPSE catalog. We have discovered 28 compact continuum sources and confirmed their associations with the bubbles using velocity information from HCO+ and HCN. We have also mapped small-scale structures of N2H+ emission in the vicinity of the bubbles. By combining our data with survey data from GLIMPSE, MIPSGAL, BGPS, and MAGPIS, we establish about half of our continuum sources as star-forming cores. We also use survey data with the velocity information from our molecular line observations to describe the morphology of the bubbles and the nature of the fragmentation. We conclude from the properties of the continuum sources that N74 likely is at the near kinematic distance, which was previously unconfirmed. We also present tentative evidence of molecular clouds being more fragmented on bubble rims compared to dark clouds, suggesting that triggered star formation may occur, though our findings do not conform to a classic collect-and-collapse model.

Big bubble technique dissection plane: histological and ultrastructural comparative analysis on both white and clear margin dissected corneas

AbstractPurpose Pneumodissection or 'big‐bubble' technique (BBT) is used to separate Descemet’s membrane (DM) and stroma in both deep anterior lamellar keratoplasty and Descemet’s membrane endothelial keratoplasty. It has been reported that BBT may produce two typer of bubble outlines: clear or white margin. It seems that the components of the posterior lamella obtained with each bubble rims also differ. Our aim is to compare BBT dissection plane using histological and electron microscopy (EM) analysis on eye‐bank corneas.Methods BBT was carried out on donor corneas unsuitable for transplantation for reasons other than corneal disease.Corneoscleral discs were mounted on an artificial anterior chamber and BBT was carried out using a 27G needle. 5 samples which had a bubble with white margin and 5 with clear margin were fixed in formalin and sent for histology followed by EM.Results Samples in which the edge of the bubble had a white margin showed variable residual stroma adherent to DM. When the edge of the bubble was clear no residual stroma was seen attached to a bare, smooth DM. The anterior lamellae of the cases without residual stroma were also analysed. These showed no evidence of DM elements excluding the unlikely possibility of intra‐Descemet’s dissection plane. The findings were confirmed by EM in all cases. These showed intact banded DM in all posterior lamellae but only those with a white bubble outline had attached residual stromal collagen.Conclusion In eye bank corneas the histological elements of the posterior lamella dissected using BBT can be predicted depending on the margin of the bubble obtained. Assumptions that pneumodissection in BBT routinely bares DM need to be revisited.

THE MILKY WAY PROJECT: A STATISTICAL STUDY OF MASSIVE STAR FORMATION ASSOCIATED WITH INFRARED BUBBLES

The Milky Way Project citizen science initiative recently increased the number of known infrared bubbles in the inner Galactic plane by an order of magnitude compared to previous studies. We present a detailed statistical analysis of this dataset with the Red MSX Source catalog of massive young stellar sources to investigate the association of these bubbles with massive star formation. We particularly address the question of massive triggered star formation near infrared bubbles. We find a strong positional correlation of massive young stellar objects (MYSOs) and H II regions with Milky Way Project bubbles at separations of < 2 bubble radii. As bubble sizes increase, a statistically significant overdensity of massive young sources emerges in the region of the bubble rims, possibly indicating the occurrence of triggered star formation. Based on numbers of bubble-associated RMS sources we find that 67+/-3% of MYSOs and (ultra)compact H II regions appear associated with a bubble. We estimate that approximately 22+/-2% of massive young stars may have formed as a result of feedback from expanding H II regions. Using MYSO-bubble correlations, we serendipitously recovered the location of the recently discovered massive cluster Mercer 81, suggesting the potential of such analyses for discovery of heavily extincted distant clusters.

DEEPCHANDRAOBSERVATIONS OF EDGES AND BUBBLES IN THE NGC 5846 GALAXY GROUP

We use a combined 120 ks Chandra exposure to analyze X-ray edges produced by non-hydrostatic gas motions (sloshing) from galaxy collisions, and cavities formed by AGN activity. Evidence for gas sloshing is seen in the spiral morphology and multiple cold front edges in NGC 5846's X-ray surface brightness distribution, while lack of spiral structure in the temperature map suggests the perturbing interaction was not in the plane of the sky. Density and spectral modeling across the edges indicate the relative motion of gas in the cold fronts is at most transonic. Evidence for AGN activity is seen in two inner bubbles at 0.6 kpc, filled with 5 GHz and 1.5 GHz radio plasma and coincident with Halpha emission, and in a ghost bubble at 5.2 kpc west of NGC 5846's nucleus. The outburst energy and ages for the inner (ghost) bubbles are ~10^{55} ergs and ~2 Myr (~ 5 x 10^{55} ergs and 12 Myr), respectively, implying an AGN duty cycle of 10 Myr. The inner bubble rims are threaded with 9 knots, whose total 0.5-2 keV X-ray luminosity is 0.3 x10^{40} ergs, a factor ~2-3 less than that of the surrounding rims, and 0.7 keV mean temperature is indistinguishable from that of the rims. We suggest that the knots may be transient clouds heated by the recent passage of a shock from the last AGN outburst. We also observe gas stripping from a cE galaxy, NGC 5846A, in a 0.5 kpc long (~10^5 Msolar) hot gas tail, as it falls towards NGC 5846.

A VERY DEEPCHANDRAOBSERVATION OF A2052: BUBBLES, SHOCKS, AND SLOSHING

We present the first results from a very deep (∼650 ks) Chandra X-ray observation of A2052, as well as archival Very Large Array radio observations. The data reveal detailed structure in the inner parts of the cluster, including bubbles evacuated by radio lobes of the active galactic nucleus (AGN), compressed bubble rims, filaments, and loops. Two concentric shocks are seen, and a temperature rise is measured for the innermost one. On larger scales, we report the first detection of an excess surface brightness spiral feature. The spiral has cooler temperatures, lower entropies, and higher abundances than its surroundings, and is likely the result of sloshing gas initiated by a previous cluster–cluster or sub-cluster merger. Initial evidence for previously unseen bubbles at larger radii related to earlier outbursts from the AGN is presented.

Pulsed-laser-induced damage in rat corneas: time-resolved imaging of physical effects and acute biological response

Laser-induced damage is studied in the rat corneal epithelium and stroma using a combination of time-resolved imaging and biological assays. Cavitation bubble interactions with cells are visualized at a higher spatial resolution than previously reported. The shock wave is observed to propagate through the epithelium without cell displacement or deformation. Cavitation bubble expansion is damped in tissue with a reduction in maximum size in the range of 54 to 59%, as compared to 2-D and 3-D cultures. Bubble expansion on nanosecond timescales results in rupture of the epithelial sheet and severe compression of cell layers beyond the bubble rim. In the stroma, the dense collagen lamellae strongly damped bubble expansion, thus resulting in reduced damage. The acute biological response of this tissue to laser pulses is characterized by confocal fluorescence microscopy. A viability assay of the epithelium reveals that only cells around the immediate site of laser focus are killed, while cells seen to undergo large deformations remain alive. Actin morphology in cells facing this mechanical stress is unchanged. Collagen microstructure in the stroma as revealed by second-harmonic imaging around the ablation site shows minimal disruption. These cellular responses are also compared to in vitro 2-D and 3-D cell cultures.

A spherical-cap bubble moving at terminal velocity in a viscous liquid

The nonlinear Navier–Stokes equations governing steady, laminar, axisymmetric flow past a deformable bubble are solved by the Galerkin finite-element method simultaneously with a set of elliptic partial differential equations governing boundary-fitted mesh. For Reynolds number 20 ≤ Re ≤ 500, numerical solutions of spherical-cap bubbles are obtained at capillary number Ca = 1. Increasing Ca to 2 leads to a highly curved, cusp-like bubble rim that seems to correspond to skirt formation. The computed steady, axisymmetric spherical-cap bubbles with closed, laminar wakes compare reasonably with the available experimental results, especially for Re ≤ 100. By exploring the parameter space (for Re ≤ 200), a sufficient condition for steady axisymmetric solutions of bubbles with the spherical-cap shape is found to be roughly Ca &gt; 0.4. The basic characteristics of spherical-cap bubbles of Ca ≥ 0.5, for a given Re ≥ 50, are found to be almost independent of the value of Ca (or Weber number We ≡ Re Ca). At a fixed Re ≥ 50, continuation by increasing Ca (or We) from a spherical bubble solution cannot lead to solutions of spherical-cap bubbles, but rather to a turning point at We slightly greater than 10 where the solution branch folds back to reduced values of Ca (or We). Yet continuation by reducing Ca (or We) from a spherical-cap bubble solution cannot arrive at a spherical bubble solution for Re ≥ 50, but rather at solutions with bubbles having more complicated shapes such as a sombrero, etc. Without thorough examinations of the solution stability, multiple steady axisymmetric solutions are shown to exist in the parameter space for a given set of parameters.

A deep Chandra observation of the Perseus cluster: shocks and ripples

We present preliminary results from a deep observation lasting almost 200 ks of the centre of the Perseus cluster of galaxies around NGC 1275. The X-ray surface brightness of the intracluster gas beyond the inner 20 kpc, which contains the inner radio bubbles, is very smooth apart from some low-amplitude quasi-periodic ripples. A clear density jump at a radius of 24 kpc to the north-east, about 10 kpc out from the bubble rim, appears to be due to a weak shock driven by the northern radio bubble. A similar front may exist around both inner bubbles but is masked elsewhere by rim emission from bright cooler gas. The continuous blowing of bubbles by the central radio source, leading to the propagation of weak shocks and viscously dissipating sound waves seen as the observed fronts and ripples, gives a rate of working which balances the radiative cooling within the inner 50 kpc of the cluster core.

Experimental studies of wakes behind circularly capped bubbles

The wake behind a circularly capped bubble rising in fluids of different viscosity has been experimentally investigated using aspirin powder for flow visualization and high-speed photography synchronized with pressure-time measurements to measure the pressure field. The bubble plus its primary wake with a cusped tail is observed to contain symmetric pressure minima within the primary wake. Adjacent to the boundary wake is a free shear layer which contains large-scale vortices generated near the bubble rim that remain essentially stationary to an observer in the laboratory reference frame. The change in wake geometry and the transition to an ellipsoidal bubble shape as fluid viscosity increases is documented.The airfoil shape of the boundary of the circularly capped bubble and its closed primary wake is modelled using a Joukowski transformation in which the Joukowski constant is adjusted to match the experimental and potential-flow pressures along the bubble cap. The model successfully predicts the frontal pressure field, and the wake size and shape. The Davies &amp; Taylor bubble-cap boundary condition is also verified.