Bubble Wall Thickness Research Articles

Neon excess in pumice: volcanological implications

We measured the noble gas abundance and Ne and Ar isotopic compositions in pumice samples from Japan and the Eolian Islands, Italy. The goal was to give clues on the mechanism of air incorporation into pumice and its relationship with eruption processes. The samples contain large excesses of atmospheric Ne over Ar, with 20 Ne/ 36 Ar ratios up to 600 times the atmospheric ratio. This excess is produced by the preferential diffusion of Ne over Ar in pumice vesicles during volcanic eruptions. The 20 Ne/ 36 Ar ratios measured in pumice reflect the initial quenching temperature, the cooling rate of the eruption column and the bubble's wall thickness. The final Ne amount is likely to be proportional to the volume of preserved vesicles in pumice. Calculations indicate that the fraction of isolated vesicles are less than 10% of the total, suggesting that a few amount of gas is preserved in pumice after deposition.

Defect formation in first order phase transitions with damping

Within the context of first order phase transitions in the early universe, we study the influence of a coupling between the [global U(1)] scalar driving the transition and the rest of the matter content of the theory. The effect of the coupling on the scalar is simulated by introducing a damping term in its equations of motion. Following a previous paper, in which we studied the influence that this coupling has on individual bubble collisions and on topological defect formation, we proceed here to quantify the impact these effects have on the number of defects created per nucleated bubble, ${n}_{d}.$ To a good accuracy, we find that ${n}_{d}$ goes through two different regimes as we increase the value of the damping coefficient $\ensuremath{\gamma}.$ The first regime has ${n}_{d}$ changing as ${n}_{d}\ensuremath{\propto}{\ensuremath{\gamma}}^{\ensuremath{-}1/2},$ whereas for the second one ${n}_{d}\ensuremath{\propto}{\ensuremath{\gamma}}^{\ensuremath{-}3/4}.$ In a first approximation, the divide between the two regimes is estimated to be at values $\ensuremath{\gamma}$ such that $\ensuremath{\gamma}{\ensuremath{\delta}}_{m}\ensuremath{\sim}2R$ (where $R$ and ${\ensuremath{\delta}}_{m}$ are the bubble radius and wall thickness, respectively).

The unphysical nature of `warp drive'

We will apply the quantum-inequality-type restrictions to Alcubierre's warp drive metric on a scale in which a local region of spacetime can be considered `flat'. These are inequalities that restrict the magnitude and extent of the negative energy which is needed to form the warp drive metric. From this we are able to place limits on the parameters of the `warp bubble'. It will be shown that the bubble wall thickness is on the order of only a few hundred Planck lengths. Then we will show that the total integrated energy density needed to maintain the warp metric with such thin walls is physically unattainable.

Radiatively induced first-order phase transitions the necessity of the renormalization group

We advocate a (Wilson) renormalization-group (RG) treatment of finite-temperature first-order phase transitions, in particular those driven by radiative corrections such as occur in the standard model, and other spontaneously broken gauge theories. We introduce the scale-dependent coarse-grained free energy S Λ [ φ] which we explicitly calculate, using the Wilson RG and a (4 − ε)-expansion, for a scalar toy model that shares many features of the gauged case. As argued by Langer and others, the dynamics of the phase transition are described by S Λ [ φ] with 1/Λ of order the bubble wall thickness, and not by the usual (RG-improved) finite-temperature effective action which is reproduced by S Λ [ φ] for Λ → 0. We argue that for weakly first-order transitions (such as that in the he (4 − ε)-expansion is necessary to control an inevitable growth of the effective scale-dependent coupling towards the strong-coupling regime, and that diagrammatic resummation techniques are unlikely to be appropriate.

Dynamics of diffusive bubble growth in magmas: Isothermal case

We have conducted a parametric study and developed a new cell model describing diffusion‐induced growth of closely spaced bubbles in magmatic systems. The model accounts for (1) the effects of advection of melt resulting from bubble growth, and its affect on the local concentration profile; (2) dynamic resistance of the viscous melt during diffusive growth; (3) diffusion of volatiles in response to evolving concentration gradients; (4) mass balance between dissolved volatiles and gas inside the bubble; (5) changes in the equilibrium saturation concentration at the bubble‐melt interface; (6) total pressure within the bubble consisting of ambient, surface tension, and dynamic pressures. The results of this study reveal that bubble growth depends strongly on ambient pressure, volatile oversaturation in the melt, and diffusivity coefficients, but only weakly on bubble separation and initial bubble radius. Increased volatile oversaturation increases growth rate to the point at which it actually reduces time for complete bubble growth. This counterintuitive result is due to significant advective volatile flux toward the bubble interface during growth. Viscosity controls growth dynamics only for cases of high viscosity (>104 Pa s). The documentation of the evolution of gas fraction in the melt and bubble wall thickness as a function of time makes it possible to estimate bubble disruption thresholds which bear on volcanic eruption mechanisms. Model results can be applied to the larger‐scale problem of magmatic degassing in terms of bubble coalescence, flotation and the development of foams in magma chambers and vent systems, and ultimately to the dynamics of eruption mechanisms.

A preliminary investigation of the permeation of some permanent gases through foam membranes

To evaluate gas permeation properties of foam membranes, a preliminary investigation of the permeation of O 2, N 2, and CO 2 through a monolayer of foam bubbles formed on an aqueous glycerol solution with saponin as surfactant was carried out in a new static foam membrane test cell. Foam stability, a prerequisite to meaningful measurement, was highest with a 70% glycerol solution. Using the notion of an average foam bubble, time-dependent measurements of gas composition above foam bubbles and foam bubble height reduction yielded values of permeation parameters from the solution of appropriate mass balance equations. The O 2 permeation parameter defined by the ratio of the O 2 permeability coefficient and the foam bubble wall thickness was found to have a value comparable to that of a 1-mil-thick silicone rubber film. The O 2N 2 separation factor, found to be around 2 for the same system, is comparable also to that of a silicone rubber film. Significant absorption of CO 2 in the surfactant liquid solution suggests limitations of this new foam permeation cell to gases with extremely limited solubility.