Absence Of Bubbles Research Articles

Bubbling potential as a measure of the charge of gas bubbles in aqueous environment

Gas bubbles in aqueous environment cause changes in electrical potential of the electrodes containing a ceramic porous plug. It was found that collision and interception of bubbles and porous plug surface are responsible for the observed phenomenon. In the course of collision bubble approaches porous plug surface to a certain distance within diffuse layer of air/water interface. At that distance the electrostatic potential of gas bubble affects the electrode potential. Reversible redox electrodes cannot serve as a bubbling indicator electrode due to relaxation of the electrode reactions. Bubbling potential is defined as the difference of indicator electrode potential in presence and absence of bubbles. It provides information on the isoelectric point of the gas bubbles, and may be recalculated to ζ-potentials using the Gouy–Chapman theory. For that purpose, the distance between electrokinetic slip plane and plane of bubble contact with porous plug surface should be known. This distance was estimated to be between 6 and 10nm. As electrokinetic potential, the bubbling potential is also significantly reduced by increasing electrolyte concentration, which is markedly more pronounced for counterions of higher charge. The effect of pH and several various electrolytes on argon bubbles was examined and discussed. Measurement of bubbling potential is fast and reproducible and may be used as a useful tool for examination of gas/water interfaces.

Arbitrage Theory with State-Price Deflators

The aim of this article is to develop some mathematical results for the existence of asset price bubbles, which is consistent with the martingale analysis of financial markets. More specifically, this article studies the relation between the divergence of the sum of dividend-price ratios and the absence of bubbles. The framework used describes a contemporary model of a securities market built in an environment with both uncertainty and a countable number of trading dates. The market allows trading of a finite number of corporate securities. In this context, no arbitrage condition is characterized by the existence of a state-price deflator across an infinite time horizon.

When bubbles burst: econometric tests based on structural breaks

Speculative bubbles have played an important role ever since in financial economics. During an ongoing bubble it is relevant for investors and policy-makers to know whether the bubble continues to grow or whether it is already collapsing. Prices are typically well approximated by a random walk in absence of bubbles, while periods of bubbles are characterised by explosive price paths. In this paper we first propose a conventional Chow-type testing procedure for a structural break from an explosive to a random walk regime. It is shown that under the null hypothesis of a mildly explosive process a suitably modified Chow-type statistic possesses a standard normal limiting distribution. Second, a monitoring procedure based on the CUSUM statistic is suggested. It timely indicates such a structural change. Asymptotic results are derived and small-sample properties are studied via Monte Carlo simulations. Finally, two empirical applications illustrate the merits and limitations of our suggested procedures.

Decompression vs. Decomposition: Distribution, Amount, and Gas Composition of Bubbles in Stranded Marine Mammals

Gas embolic lesions linked to military sonar have been described in stranded cetaceans including beaked whales. These descriptions suggest that gas bubbles in marine mammal tissues may be more common than previously thought. In this study we have analyzed gas amount (by gas score) and gas composition within different decomposition codes using a standardized methodology. This broad study has allowed us to explore species-specific variability in bubble prevalence, amount, distribution, and composition, as well as masking of bubble content by putrefaction gases. Bubbles detected within the cardiovascular system and other tissues related to both pre- and port-mortem processes are a common finding on necropsy of stranded cetaceans. To minimize masking by putrefaction gases, necropsy, and gas sampling must be performed as soon as possible. Before 24 h post mortem is recommended but preferably within 12 h post mortem. At necropsy, amount of bubbles (gas score) in decomposition code 2 in stranded cetaceans was found to be more important than merely presence vs. absence of bubbles from a pathological point of view. Deep divers presented higher abundance of gas bubbles, mainly composed of 70% nitrogen and 30% CO2, suggesting a higher predisposition of these species to suffer from decompression-related gas embolism.

Convection heat transfer anisotropy in a bubbling viscous pool—Application to molten core–concrete interaction

In the absence of bubbling, natural convection in an internally heated pool is largely anisotropic. There are large heat transfers to the upper and lateral walls, while the heat transfer to the cooled lower surface is small. Bubbling is a well-known mean of increasing the heat transfer coefficients, especially at the lower wall. The heat transfer between an internally heated pool and its walls has been experimentally studied while air bubbles were produced through a grid drilled with holes installed at the lower interface. Sugar solutions have been used as simulant the high temperature corium melts that would be produced during molten core-concrete interaction with respect to [Deckwer, W.-D.,1992. Bubble Column Reactors. John Wiley & Sons, Chichester (English Translation)] heat transfer model. Without any gas bubbling, natural convection in the pool exhibits a large anisotropy with a small heat transfer to the bottom wall. This is due to the building of a thermal gradient through the pool height. Bubbling with superficial gas velocity as low as 1 mm/s is sufficient to destabilize these layers in water and homogenize the pool. For more viscous fluids, it has been possible to determine a threshold between these regimes.

¿Qué aporta el láser Revolix® en las nefrectomías parciales?

Partial nephrectomy is a technique that requires extensive manipulation and control of the renal vessels. In this paper we will evaluate the contribution of Revolix laser to the minimally invasive and nephron sparing renal surgery over the years 2005-2008. We have used the Revolix laser (Thulium), with a wavelength of 2013 nm in the infrared (invisible) spectrum, which can work in a continue or pulsed manner. Its chromophore target is water. Two different techniques may be employed: vaporization (side firing fiber) or vaporresection (frontal fiber). In all cases we used the frontal fiber (rigifib, flexifib and percufib), for vaporresection between 12 and 15 watts. A total of nine patients underwent treatment between 2005 and 2008. We performed one laparoscopic partial nephrectomy and eight open partial nephrectomies through a lumbar incision. In all partial nephrectomies except three (open) the pedicle was clamped. All patients, seven males and two females, had a favourable outcome, without relevant complications. The cases were six tumors in the left kidney and 3 in the right. Mean tumor size was 3.5 cm, being seven of them localized in the lower pole and two in the upper pole. Mean surgical time was 135 minutes with conventional open surgery and 210 minutes with laparoscopic partial nephrectomy. Estimated blood loss was 156 cc for laparoscopic partial nephrectomy and 260 cc for open surgery. One case was performed under renal hypothermia with 50 minutes ischemia time. Revolix laser offers an excellent haemostasis and precise dissection of the renal cortex. The absence of bubbles and the minimal formation of gases favour its use in laparoscopic surgery. It coagulates vessels of up to 1.6 mm allowing good sealing of the bloody surface. With the use of this type of laser surgical times are shorter, because there is no need to perform sutures of the renal parenchyma.

Time reversal of acoustic waves in the nonlinear regime: basic physics and application to ultrasound contrast imaging

Time reversal invariance of acoustic waves propagation remains valid even in the nonlinear regime in nondissipative media. This very interesting property that was extensively used in linear acoustics can also find potential applications in the nonlinear regime. Harmonic imaging coupled to the use of contrast agents is a topic of wide interest in ultrasonic medical imaging. Images are built at twice the excitation frequency that corresponds to the resonance frequency of the bubbles embedded in the medium. Consequently, the contrast becomes important between areas of low and high concentration of bubbles. However, at a high mechanical index, the harmonic components of backscattered echoes depends on the intrinsic nonlinear properties of tissues as well as the bubble's resonance. The focused beam is generating harmonics during its nonlinear propagation. It results in a degradation of the harmonic image contrast. Time reversal is an elegant way to find the emission codes allowing us to cancel the harmonic components due to nonlinear propagation of the ultrasonic beam. In the absence of bubbles, if the backscattered echoes are time-reversed and reemitted by the array, the harmonic components of the resulting wavefront are transferred back to the fundamental frequency during propagation. Experiments conducted with 1D-linear arrays illustrate these cancellation techniques.

Light transfer in bubble sparged photobioreactors for H 2 production and CO 2 mitigation

This paper presents a parametric study simulating light transfer in a photobioreactor containing gas bubbles and filamentous cyanobacteria Anabaena variabilis suspended in water. To the best of our knowledge, this paper presents for the first time a model for such system: (i) using a consistent set of radiation characteristics of the medium derived from experimental data and from Mie theory; (ii) accounting for anisotropic scattering by both the bubbles and the filamentous microorganisms; (iii) considering the spectral dependency of radiation characteristics in the spectral range from 400 to 700 nm using a box model, and (iv) evaluating light transfer in a photobioreactor containing genetically engineered microorganisms with reduced pigment content. The steady-state one-dimensional radiation transfer equation is solved using the modified method of characteristics and a quadrature with 24 directions per hemisphere adapted to forward scattering media. The parameters investigated include the bacteria concentration, the bubble radius, and the void fraction, as well as the approximate scattering phase function. It was established that the strongly forward scattering by the bubbles must be accounted for and the truncated phase function (TPF) is recommended. In the absence of bubbles, ignoring in-scattering by the bacteria leads to errors as high as 20%. On the other hand, accounting for in-scattering with isotropic phase function gives acceptable results. Moreover, genetically reducing the pigment content of the microorganisms by an order of magnitude increases the significance of forward scattering of light by the microorganisms. This in turn, increases the penetration depth and can be accounted for by either the Henyey–Greenstein or the TPF approximations. Finally, the model presented can also be applied to (i) other types of microorganisms such as unicellular green algae or photosynthetic bacteria, (ii) different photobioreactor processes such as food product or pharmaceutical production, or (iii) photochemical reactors.

Forming nanometer TiO 2 sheets by nonaqueous tape casting

The condition for the preparation of stable nanometer TiO 2 slurries by nonaqueous tape casting was indentified. To acquire stable low-viscosity slurries, the influences of solvent, dispersant and solid content on the rheological properties were investigated. The azeotropic mixtures (ethanol/methyl ethyl ketone) and Polyester/Polyamine Copolymer (KD-1) could serve as good solvent and dispersant, respectively. The slurries of nanometer TiO 2 behaved as near Newtonian up to a solid loading of 34 vol.%. Films of TiO 2 had very good qualities, such as homogeneity, surface quality, absence of bubbles and cracks, which indicated that slurries at selected conditions met the needs of tape casting process. The relative density of 24 and 34 vol.% sintered sheet was 51 and 69%, respectively. Results indicated the density increased with the solid content, sintering temperature and pressure.

Longitudinal photographic observation of the occurrence of bubbles in pit and fissure sealants.

The purpose of this study was to employ photographic evaluation to observe the presence or absence of bubbles in pit and fissure sealants Concise and Prisma Shield, at 7 days, 18 months, 36 months and 11 years after accomplishment of treatment.Methods:A hematoxylin-based staining solution was applied to the occlusal surface at the study periods, which allowed assessment of the sealing material on the surface. All occlusal surfaces were photographed and the photographs corresponding to each period were subjected to photographic evaluation.Results:There was statistically significant difference only at 18 months, with a significantly higher number of specimens with bubbles for the Prisma Shield sealant compared to the Concise, whereas the groups were similar at all other study periods. On the other hand, separate analysis of subsequent periods of the sealants did not reveal any significant difference.Conclusions:According to the results of the present longitudinal investigation, it may be concluded that the sealing materials showed that bubbles came into and went out with time. However, this fact did not interfere with its clinical purpose, provided the remaining material covers the expected region of pits and fissures.

Surfactants Reduce Platelet–Bubble and Platelet–Platelet Binding Induced by In Vitro Air Embolism

The effect of gas bubbles on platelet behavior is poorly characterized. The authors assessed platelet-bubble and platelet-platelet binding in platelet-rich plasma in the presence and absence of bubbles and three surface-active compounds. Platelet-rich plasma was prepared from blood drawn from 16 volunteers. Experimental groups were surfactant alone, sparging (microbubble embolization) alone, sparging with surfactant, and neither sparging nor surfactant. The surfactants were Pluronic F-127 (Molecular Probes, Eugene, OR), Perftoran (OJSC SPC Perftoran, Moscow, Russia), and Dow Corning Antifoam 1510US (Dow Corning, Midland, MI). Videomicroscopy images of specimens drawn through rectangular glass microcapillaries on an inverted microscope and Coulter counter measurements were used to assess platelet-bubble and platelet-platelet binding, respectively, in calcium-free and recalcified samples. Histamine-induced and adenosine diphosphate-induced platelet-platelet binding were measured in unsparged samples. Differences between groups were considered significant for P < 0.05 using analysis of variance and the Bonferroni correction. Sixty to 100 platelets adhered to bubbles in sparged, surfactant-free samples. With sparging and surfactant, few platelets adhered to bubbles. Numbers of platelet singlets and multimers not adherent to bubbles were different (P < 0.05) compared both with unsparged samples and sparged samples without surfactant. No significant platelet-platelet binding occurred in uncalcified, sparged samples, although 20-30 platelets adhered to bubbles. Without sparging, histamine and adenosine diphosphate provoked platelet-platelet binding with and without surfactants present. Sparging causes platelets to bind to air bubbles and each other. Surfactants added before sparging attenuate platelet-bubble and platelet-platelet binding. Surfactants may have a clinical role in attenuating gas embolism-induced platelet-bubble and platelet-platelet binding.

The relationship between critical flux and fibre movement induced by bubbling in a submerged hollow fibre system

Bubbling has been used to enhance various processes. In this paper we deal with the effect of bubbling on submerged hollow fibre membranes, where bubbling is applied to prevent severe membrane fouling. Previous work with submerged hollow fibres has observed that significant fibre movement can be induced by bubbling and that there is a qualitative relationship between fibre movement and filtration performance. Therefore, the aim of the present research has been to analyse the link between bubbling, fibre movement and critical flux, identified as the flux at which the transmembrane pressure (TMP) starts to rise. Tests were performed on vertical isolated fibres with a model feed of yeast suspension. The fibres were subject to steady bubbling from below. The parameters of interest were the fibre characteristics, such as tightness, diameter and length, as well as feed concentration. The results confirmed that the critical fluxes are affected by the fibre characteristics and feed concentration. Higher critical flux values can be achieved by using loose fibres, smaller diameters and longer fibres. The enhancement is partially linked to fibre movement and this is confirmed by improved performance when fibres are subject to mechanical movement in the absence of bubbling.

Internal waves in a three-layer bubbly waveguide

Abstract In many oceanic situations, clouds, or layers of bubbles are present which may influence the larger-scale dynamics. A two-dimensional model of a diluted locally monodisperse mixture of an incompressible fluid with gas bubbles is used to model and study such situations. The problem is simplified by ignoring the horizontal variability in the structure of the bubble layer and by focusing instead on the vertical variability. We consider waves propagating horizontally in the oceanic waveguide, assuming that bubbles are confined to a thin upper layer of the otherwise homogeneous upper ocean, and using a three layer model to represent this situation. The presence of the depth-dependent distribution of bubbles introduces an effective stratification and considerably changes the value of the buoyancy frequency N l in the absence of bubbles, replacing it with an effective value N, where N 2 = N l 2 + g α g 0 [ ( ln n 0 ) z + 3 α g 0 ( ln R 0 ) z ] / ( 1 - α g 0 ) (here α g 0 is the void fraction, n 0 is the number density, and R 0 is the radius of bubbles in the basic state).This leads to the possibility of existence of the internal waves in the otherwise homogeneous upper mixed layer. Also the presence of the bubbly layer causes significant changes to the dispersion relation for the usual internal waves.

The Effect of Bubbles on Internal Waves

Abstract The influence of gas bubbles on the properties of internal waves in a continuously stratified fluid is studied in the framework of a two-dimensional model of a diluted locally monodisperse mixture of an incompressible fluid with gas bubbles. The model takes into account the depth dependence of the void fraction of the bubbles, surface tension on the walls of the bubbles, and an effective viscosity, which accounts for the fluid viscosity, thermal damping, and other dissipative mechanisms. It is shown that bubbles, when present in the upper part of the ocean, change the value of the buoyancy frequency Nl in the absence of bubbles, replacing it with an effective value N, where N2 ≈ N2l + gαg0(lnn0)z (αg0 is the void fraction and n0 is the number density of the bubbles). First, plane linear waves in a uniformly stratified Boussinesq fluid are considered, and it is shown that there are two classes of plane waves. One class, the “bubble” wave, may propagate with frequencies higher than the effective bu...

Surfactants attenuate gas embolism-induced thrombin production.

There are no pharmacologic strategies to prevent embolism bubble-induced blood clot formation. The authors conducted experiments to measure thrombin production in sheared whole blood in the presence and absence of bubbles and three surface-active compounds. Blood samples were obtained from six volunteers seven times. The thrombin-specific substrate Boc-VPR-MCA was added to citrated blood diluted with HEPES-buffered saline. Experimental groups were as follows: sparging (air microbubble embolization) with surfactant present; sparging alone; surfactant alone; and neither surfactant nor sparging. The surfactants were Dow Corning Antifoam 1510US, Perftoran, and Pluronic F-127. Blood was sheared by a cone-plate viscometer at 100 and 500 s-1 for 5, 10, and 20 min at 37 degrees C, pipetted into excess stop buffer, and evaluated fluorimetrically. Mean values of fluorescence intensity +/- SDs for each group were compared using ANOVA. Differences were considered significant at P < 0.05 using the Bonferroni correction. For fixed shear rate, thrombin production increased 2.3- to 5.7-fold (P < 0.05) as shear duration lengthened. For fixed shear duration, thrombin production increased 1.9- to 3.9-fold (P < 0.05) with increasing shear rate. For fixed shear rate and duration, sparging increased thrombin production 2.1- to 3.7-fold (P < 0.05). Surfactant addition without sparging did not change thrombin production (P > 0.05). Surfactants attenuated thrombin production in sparged samples 31.8-70.9% (P < 0.05). Thrombin production is shear rate and duration-dependent. Sparging increases thrombin production. Surfactants added before sparging attenuate thrombin production. Surfactants may have a clinical application to attenuate gas embolism-induced clotting.

A numerical study of fluidization behavior of Geldart A particles using a discrete particle model

This paper reports on a numerical study of fluidization behavior of Geldart A particles by use of a 2D soft-sphere discrete particle model (DPM). Some typical features, including the homogeneous expansion, gross particle circulation in the absence of bubbles, and fast bubbles, can be clearly displayed if the interparticle van der Waals forces are relatively weak. An anisotropy of the velocity fluctuation of particles is found in both the homogeneous fluidization regime and the bubbling regime. The homogeneous fluidization is shown to represent a transition phase resulting from the competition of three kinds of basic interactions: the fluid–particle interaction, the particle–particle collisions (and particle–wall collisions) and the interparticle van der Waals forces. In the bubbling regime, however, the effect of the interparticle van der Waals forces vanishes and the fluid–particle interaction becomes the dominant factor determining the fluidization behavior of Geldart A particles. This is also evidenced by the comparisons of the particulate pressure with other theoretical and experimental results.

Constrast enhancement in harmonic imaging using time reversal processing

Harmonic imaging coupled to the use of contrast agents has become a topic of wide interest in ultrasonic medical imaging. Instead of achieving images at the fundamental frequency of the emission signals, images are built at twice the excitation frequency that corresponds to the resonance frequency of the bubbles embedded in the medium. Consequently, the contrast becomes important between areas of low and high concentration of bubbles. However, at a high mechanical index, the harmonic components of backscattered echoes depends on the intrinsic nonlinear properties of tissues as well as the bubble’s resonance. The focused beam is generating harmonics during its nonlinear propagation. It results in a degradation of the harmonic image contrast. Time reversal is an elegant way to find the emission codes allowing us to cancel the harmonic components due to nonlinear propagation of the ultrasonic beam and so to recover an optimal image contrast. Indeed, the wave equation in a nonlinear regime remains time reversal invariant: in the absence of bubbles, if the backscattered echoes are time-reversed and reemitted by the array, the harmonic components of the resulting wavefront are transferred back to the fundamental frequency during propagation. Experiments conducted with 1-D-linear arrays illustrate this cancellation technique.

Hydrodynamics and heat transfer in bubbly flow in the turbulent boundary layer

In the work presented is a new approach to modelling the bubbly flow in the boundary layer. The approach is based on summation of dissipation energy coming from the shearing turbulent flow in the absence of bubbles and the dissipation contribution from the presence of bubbles. As a result we obtain the dissipation of equivalent single phase turbulent flow. The model has been solved using the method of asymptotic correction to provide an explicit differential equation describing the velocity profile. That can be solved with the assumption of constant void fraction distribution to yield the analytical velocity profile. Alternatively, author has developed his own model of lateral void migration, which is distinct from other models by virtue of presence of another rotational velocity. Velocity distributions calculated using the new model have been compared against the experimental data of turbulent bubble flows with small void fraction. A good consistency between calculations performed using a new model and available experimental data has been obtained. Additionally, a solution of the temperature field is also given. In the case of a constant void fraction distribution analytical distribution of the Nusselt number is given or the set of differential equations needs to be solved.

Surfactant Scavenging and Surface Deposition by Rising Bubbles

When bubbles rise through a liquid they are known to scavenge dissolved surface-active materials (surfactants). Small bubbles in the size range of tens of micrometers quickly become covered with surfactants in any but the cleanest conditions. This has the effect of immobilizing the bubble surface and affecting the drag and therefore the bubble rise speed. A large number of bubbles rising as a cloud toward a free surface will populate the bulk surface with surfactants at a richness that far exceeds that which would occur in the absence of bubbling. However, in addition to the increased deposition of surfactants on the bulk surface, the random and agitated motions of the rising bubbles induce mixing of the liquid. In a companion paper (R. L. Stefan and A. J. Szeri, submitted for publication) the mixing properties of a bubble cloud rising toward a free surface were determined. In the present work, a model for the uptake of surfactants by bubbles and subsequent deposition on the bulk surface is developed including the crucial feature of bubble-induced fluid mixing. It is found that the mixing of desorbed surfactant down into the bulk is key to predicting what will be the enrichment of the bulk surface.

Analysis of the heat transfer coefficient during potato frying

The objective of this work was to study the dependence of the heat transfer coefficient ( h) on the water loss rate of potato during frying. An indirect method was used where a metal piece with the same geometry of the potato pieces was placed on top of various potato samples at different frying times, and its temperature was recorded for 20–30 s. Another method consisted of direct recording of the temperature within a potato slice, close to the surface. Water loss rate was estimated by image analysis of bubbles. After immersion in hot oil, the potato temperature increases and water starts vapourising, leaving the surface in the form of bubbles that flow through the oil. The water loss rate increases until complete drying of the potato surface and then decreases till the end of frying. The h value showed the same behaviour increasing up by two times in relation to the values measured in the absence of bubbling, with maximum values depending on the oil temperature and potato geometry (443–750 W m −2 K −1). The percentage of heat transferred to the potato that is used for water evaporation showed an increase with time up to complete surface drying.