National Autonomous University of Mexico

About: National Autonomous University of Mexico is a education organization based out in Mexico City, Distrito Federal, Mexico. It is known for research contribution in the topics: Population & Galaxy. The organization has 72868 authors who have published 127797 publications receiving 2285543 citations. The organization is also known as: UNAM & Universidad Nacional Autónoma de México.

On the corotation torque in a radiatively inefficient disk

Abstract: We consider the angular momentum exchange at the corotation resonance between a two-dimensional gaseous disk and a uniformly rotating external potential, assuming that the disk flow is adiabatic. We first consider the linear case for an isolated resonance, for which we give an expression of the corotation torque that involves the pressure perturbation and which reduces to the usual dependence on the vortensity gradient in the limit of a cold disk. Although this expression requires the solution of the hydrodynamic equations, it provides some insight into the dynamics of the corotation region. In the general case, we find an additional dependence on the entropy gradient at corotation. This dependence is associated with the advection of entropy perturbations. These are not associated with pressure perturbations. They remain confined to the corotation region, where they yield a singular contribution to the corotation torque. In a second part, we check our torque expression by means of customized two-dimensional hydrodynamical simulations. In a third part, we contemplate the case of a planet embedded in a Keplerian disk, assumed to be adiabatic. We find an excess of corotation torque that scales with the entropy gradient, and we check that the contribution of the entropy perturbation to the torque is in agreement with the expression obtained from the linear analysis. We finally discuss some implications of the corotation torque expression for the migration of low-mass planets in the regions of protoplanetary disks where the flow is radiatively inefficient on the timescale of the horseshoe U-turns.

Electro-Fenton and photoelectro-Fenton degradation of indigo carmine in acidic aqueous medium

Abstract: Acidic aqueous solutions containing concentrations of the dye indigo carmine up to 09 g l−1 have been degraded by environmentally friendly electrochemical methods such as electro-Fenton and photoelectro-Fenton using an undivided cell with a Pt or boron-doped diamond (BDD) anode and an O2-diffusion cathode at 350 °C The great oxidation ability of these systems is due to the large production of hydroxyl radical ( OH) at the anode surface from water oxidation and in the medium mainly from Fenton's reaction between catalytic Fe2+ and cathodically generated H2O2 Complete mineralization is feasible using electro-Fenton with a BDD anode and 10 mM Fe2+ and when 10 mM Fe2+ and 025 mM Cu2+ are combined as catalysts in photoelectro-Fenton with a Pt anode The first method yields similar degradation rate in the pH range 20–40, whereas the second one is more potent up to 044 g l−1 of the dye at pH 30 Mineralization is enhanced with increasing current density and initial dye concentration The indigo carmine decay always follows a pseudo zero-order reaction Isatin 5-sulfonic acid, indigo and isatin are detected as aromatic products, which are degraded to oxalic and oxamic acids The electro-Fenton process with BDD yields the destruction of Fe3+-oxalate and Fe3+-oxamate complexes by OH at the anode surface In the presence of Fe2+ and Cu2+ the photoelectro-Fenton process with Pt involves the photolysis of Fe3+-oxalate complexes under the action of UVA light, while competitive Cu2+-oxalate and Cu2+-oxamate complexes are mineralized with OH produced by Fenton's reaction The nitrogen of the dye is mainly converted into NH4+