Thermally Assisted Heterogeneous Cavitation through Gas Supersaturation.

We demonstrate that besides gaseous pockets also a gas supersaturated spot on a substrate can be a nucleus for cavitation. The supersaturation is achieved by either a formerly dissolved bubble or by heating locally the surface below the boiling temperature. The experiments are conducted in a thin film of water; one side of the water film is in contact with a gold coated substrate that is heated by a continuous laser through plasmonic heating. For nucleation of a bubble, the pressure at the heated spot is reduced by a transient rarefaction wave. The experimental findings suggest that the local gas supersaturation is responsible to nucleate cavitation and thus connects the phase transitions of cavitation and boiling. Additionally, the pressure waves in the liquid gap are studied numerically.

Ion adsorption stabilizes bulk nanobubbles.

The mechanism leading to the extraordinary stability of bulk nanobubbles in aqueous solutions remains an outstanding problem in soft matter, modern surface science, and physical chemistry science. In this work, the stability of bulk nanobubbles in electrolyte solutions under different pH levels and ionic strengths is studied. Nanobubbles are generated via the technique of ultrasonic cavitation, and characterized for size, number concentration and zeta potential under ambient conditions. Experimental results show that nanobubbles can survive in both acidic and basic solutions with pH values far away from the isoelectric point. We attribute the enhanced stability with increasing acidity or alkalinity of the aqueous solutions to the effective accumulation of net charges, regardless of their sign. The kinetic stability of the nanobubbles in various aqueous solutions is evaluated within the classic DLVO framework. Further, by combining a modified Poisson-Boltzmann equation with a modified Langmuir adsorption model, we describe a simple model that captures the influence of ion species and bulk concentration and reproduce the dependence of the nanobubble's surface potential on pH. We also discuss the apparent contradiction between quantitative calculation by ion stabilization model and experimental results. This essentially requires insight into the structure and dynamics of interfacial water on the atomic-scale.

How bulk nanobubbles are stable over a wide range of temperatures.

HYPOTHESIS: Bulk nanobubbles are nanoscopic gaseous domains in an aqueous solution. Their surprising long-term stability remains controversial due to the widespread assumption that spherical bubbles cannot achieve stable equilibrium. To uncover the intrinsic mechanisms underlying stabilization, the thermodynamic behavior of nanobubbles in water over a wide range of temperatures is explored. EXPERIMENTS: Bulk nanobubbles with a typical radius of 50 - 200 nm are generated using acoustic cavitation. Increasing temperature significantly narrows the bubble-size distribution and their mean radius shrinks to a minimum of approx. 50 nm at 45 °C. For higher temperatures a slight increase is observed. The thermal induced shrinkage is reversible: upon cooling they return to the original state. FINDINGS: The observation can be explained with a charge-stabilization mechanism. The intricate balance of competing interactions between water self-ionization and mobility of ions on the surface gives rise to this non-monotonic dependency. Nanobubbles consequently undergo charge loss at lower temperatures and charge conservation at higher temperatures, corresponding to their shrinkage and slight expansion. With theoretical calculations, we further quantity the equilibrium properties of nanobubbles and their zeta potential under various initial conditions. The temperature-sensitive nature of bulk nanobubbles offers a vital step forward exploring and industrializing their stability.

Spreading of soap bubbles on dry and wet surfaces.

The spreading of soap bubbles after forming contact with a substrate is experimentally studied. We find for dry glass substrate that the rim of the spreading soap bubble follows the well known scaling law for inertia dominated spreading [Formula: see text] [Eggers, J., Lister, J., and Stone, H., J. Fluid Mech. 401, 293-310 (1999)]. Varying the viscosity of the soap solutions and the coating of the glass does not affect this spreading behavior qualitatively. Yet, on a wetted surface, the rim obtains a constant radial velocity. Here, the rim splits into two and this new rim trails the main rim. Interestingly, the central film enclosed by the two rims develops radially oriented wrinkles.

Partitioning of dissolved chlorinated ethenes into vegetable oil.

Food-grade soybean oil (SoyOil) has been used to enhance in situ anaerobic bioremediation at sites contaminated with chlorinated ethenes (CEs). The abiotic interactions of SoyOil with the CEs may be significant and need to be better understood. The oil: water partition coefficients (Kp) of dissolved CEs into SoyOil were measured in batch tests and ranged from 22 to 1200 with increasing chlorination. CE mixtures significantly reduced the Kp for tetrachloroethene (PCE), but not the other CEs. Simple flow tests were used to quantify the mass transfer coefficients (kL) of dissolved CEs into SoyOil. Higher kL values corresponded to the CEs with higher diffusivity in water. CE mixtures reduced the kL for all of the CEs. The results can be used to predict abiotic interactions and distribution of contaminant mass expected after SoyOil injection, and thus provide a more accurate estimate of the mass of CEs removed due to enhanced biodegradation.

Prenatal screening for major congenital heart disease: assessing performance by combining national cardiac audit with maternity data.

OBJECTIVE: Determine maternity hospital and lesion-specific prenatal detection rates of major congenital heart disease (mCHD) for hospitals referring prenatally and postnatally to one Congenital Cardiac Centre, and assess interhospital relative performance (relative risk, RR). METHODS: We manually linked maternity data (3 hospitals prospectively and another 16 retrospectively) with admissions, fetal diagnostic and surgical cardiac data from one Congenital Cardiac Centre. This Centre submits verified information to National Institute for Cardiovascular Outcomes Research (NICOR-Congenital), which publishes aggregate antenatal diagnosis data from infant surgical procedures. We included 120 198 unselected women screened prospectively over 11 years in 3 maternity hospitals (A, B, C). Hospital A: colocated with fetal medicine, proactive superintendent, on-site training, case-review and audit, hospital B: on-site training, proactive superintendent, monthly telemedicine clinics, and hospital C: sonographers supported by local obstetrician. We then studied 321 infants undergoing surgery for complete transposition (transposition of the great arteries (TGA), n=157) and isolated aortic coarctation (CoA, n=164) screened in hospitals A, B, C prospectively, and 16 hospitals retrospectively. RESULTS: 385 mCHD recorded prospectively from 120 198 (3.2/1000) screened women in 3 hospitals. Interhospital relative performance (RR) in Hospital A:1.68 (1.4 to 2.0), B:0.70 (0.54 to 0.91), C:0.65 (0.5 to 0.8). Standardised prenatal detection rates (funnel plots) demonstrating inter-hospital variation across 19 hospitals for TGA (37%, 0.00 to 0.81) and CoA (34%, 0.00 to 1.06). CONCLUSIONS: Manually linking data sources produced hospital-specific and lesion-specific prenatal mCHD detection rates. More granular, rather than aggregate, data provides meaningful feedback to improve screening performance. Automatic maternal and infant record linkage on a national scale, requires verified, prospective maternity audit and integration of health information systems.

COMPASS: a novel risk-adjustment model for catheter ablation in pediatric and congenital heart disease patients.

BACKGROUND: Robust risk-adjustment algorithms are often necessary if data from clinical registries is to be used to compare rates of important clinical outcomes between participating centers. Although such algorithms have been successfully developed for surgical and catheter-based cardiac interventions in children, outcomes of pediatric and congenital catheter ablation have not been modeled with respect to case mix. METHODS: A working group was appointed by the Pediatric and Congenital Electrophysiology Society to develop a risk-adjustment algorithm for use in conjunction with a modernized, multicenter registry database. Expert consensus was used to develop relevant outcome measures, an inclusive list of possible predictors, and estimates of associated incremental risk. Historical data from the Pediatric Radiofrequency Ablation Registry was reanalyzed using multivariate regression to create statistical models of ablation outcomes. RESULTS: Acute ablation failure and serious adverse event rates were modeled as outcomes. Statistical modeling was performed on 4486 cases performed in 19 centers. For ablation failure rate, a simple model including general category of arrhythmia mechanism and presence of structural congenital heart disease accounted for ∼71% of outcome variance. The model was useful for identification of between-center variability in the historical data set. Although expert consensus predicted the need for a more complex model, predicted univariate effects were similar to those generated by statistical modeling. Serious adverse events were too infrequent to permit statistical association with any predictive variable, but could be compared with the mean rate observed among all centers. CONCLUSION: A substantial component of the intercenter variability of acute ablation outcomes in a historical database of pediatric and congenital ablation patients may be accounted for by a simple statistical model, exposing variations in outcome specific to centers. This will be a useful initial model for use a modern registry for pediatric catheter ablation outcomes.