The structure and stability of extended, inclined circumplanetary disc or ring systems

ABSTRACT Large dips in the brightness for a number of stars have been observed, for which the tentative explanation is occultation of the star by a transiting circumplanetary disc or ring system. In order for the circumplanetary disc/rings to block the host star’s light, the disc must be tilted out of the planet’s orbital plane, which poses stability problems due to the radial extent of the disc required to explain the brightness dip durations. This work uses N-body integrations to study the structure and stability of circumplanetary disc/ring systems tilted out of the planet’s orbital plane by the spinning planet’s mass quadrupole. Simulating the disc as a collection of test particles with orbits initialized near the Laplace surface (equilibrium between tidal force from host star and force from planet’s mass quadrupole), we find that many extended, inclined circumplanetary discs remain stable over the duration of the integrations ($\sim 3\!-\!16 \, {\rm Myr}$). Two dynamical resonances/instabilities excite the particle eccentricities and inclinations: the Lidov-Kozai effect which occurs in the disc’s outer regions, and ivection resonance which occurs in the disc’s inner regions. Our work places constraints on the maximum radial extent of inclined circumplanetary disc/ring systems, and shows that gaps present in circumplanetary discs do not necessarily imply the presence of exomoons.

Assessment of Surfactant Flooding With Variations of Slug Injection Strategies in Waterflooded Reservoir

Injection of surfactant into waterflooded reservoir which has considerably high water saturation may cause a reduction in surfactant efficiency by means of surfactant dilution and adsorption. Therefore, to maintain expected lowest interfacial tension (IFT) condition, large amount of surfactant, which leads to higher cost, is inevitable. Several studies have observed that reduction in surfactant concentration slug at the late time can cause a shift in surface equilibrium, resulting in desorption of retained active surfactant agents and therefore, it is possible to obtain benefit from this phenomenon to achieve longer period of the lowest IFT condition while maintaining the amount of surfactant used. Hence, this study aims to evaluate effects of two-slug surfactant flooding compared to single-slug while maintaining amount of surfactant used constant in waterflooded reservoir. The performance is evaluated based on additional oil recovery using STAR® reservoir simulation program. Simulated results indicated that two-slug surfactant injection yields better oil recovery than conventional single-slug surfactant flooding due to benefit of sacrificial adsorption and desorption process of active surfactant. Selecting type of two-slug surfactant flooding strategy would depend on surfactant concentration of single-slug which is chosen for modification; whereas, the selection of magnitude of concentration contrast between two slugs would depend on placement of surfactant mass ratio.

Practical corrections for p(H,D) measurements in mixed H2O/D2O biological buffers

Changes in the p(H,D) measured in H2O and D2O may be small since the glass electrode's surface equilibrium changes too.

Analysis of the Equilibrium Approximation in Chemical Ablation of Thermal Protective Systems

A quasi-steady-state ablation model is used to investigate the behavior of thermochemically ablating systems in equilibrium and nonequilibrium surface thermochemistry regimes. The model is simplified to allow extraction of relevant nondimensional parameters and comparison with existing experimental data on solid carbon combustion. Good agreement is found between model predictions and experimental data, and the data and model are collapsed in terms of the B number and surface Damkohler number. A new formulation for the surface Damkohler number is proposed, and a relationship between the B number and this Damkohler number is derived for the surface equilibrium and nonequilibrium regimes. The Damkohler formulation is applied to the reentry scenario, and the behavior of the B number in this context is explored. Nondimensional parameters governing behavior in the nonequilibrium regime are determined for graphite oxidation, and the results are extrapolated to more complex surface thermochemistry conditions.