Horseshoe drag in three-dimensional globally isothermal disks

We study the horseshoe dynamics of a low-mass planet in a three-dimensional, globally isothermal, inviscid disk. We find, as reported in previous work, that the boundaries of the horseshoe region (separatrix sheets) have cylindrical symmetry about the disk´s rotation axis. We interpret this feature as arising from the fact that the whole separatrix sheets have a unique value of Bernoulli´s constant, and that this constant does not depend on altitude, but only on the cylindrical radius, in barotropic disks. We next derive an expression for the torque exerted by the horseshoe region on the planet, or horseshoe drag. Potential vorticity is not materially conserved as in two-dimensional flows, but it obeys a slightly more general conservation law (Ertel´s theorem) that allows an expression for the horseshoe drag identical to the expression in a two-dimensional disk to be obtained. Our results are illustrated and validated by three-dimensional numerical simulations. The horseshoe region is found to be slightly narrower than previously extrapolated from two-dimensional analyses with a suitable softening length of the potential. We discuss the implications of our results for the saturation of the corotation torque, and the possible connection to the flow at the Bondi scale, which the present analysis does not resolve.Fil: Masset, F. S.. Universidad Nacional Autónoma de México; MéxicoFil: Benítez Llambay, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentin

Phase diagram of Landau-Zener phenomena in coupled one-dimensional Bose quantum fluids

We study stationary and dynamical properties of the many-body Landau-Zener dynamics of a Bose quantum fluid confined in two coupled one-dimensional chains, using a many-body generalization recently reported [Y.-A. Chen et al.], within the decoupling approximation and the one-level band scheme. The energy spectrum evidences the structure of the avoided level crossings as a function of the on-site inter particle interaction strength. On the dynamical side, a phase diagram of the transfer efficiency across ground-state and inverse sweeps is presented. A totally different scenario with respect to the original single-particle Landau-Zener scheme is found for ground-state sweeps, in which a breakdown of the adiabatic region emerges as the sweep rate decreases. On the contrary, the transfer efficiency across inverse sweeps reveals consistent results with the single-particle Landau-Zener predictions. In the strong coupling regime, we find that there is a critical value of the on-site interaction for which the transfer of particles starts to vanish independently of the sweep rate. Our results are in qualitative agreement with those of the experimental counterpart.Comment: 15 pages, submitted to Phys. Rev. A (new version

Beyond Invalidation: Unorthodox Forms of Judicial Review of Constitutional Amendments and Constitution-amending Case Law in Colombia

Judicial invalidation of constitutional amendments has garnered the attention of scholars in the last few years. Questions like whether and how a court should quash an amendment are at the forefront of contemporary comparative-constitutional-law and constitutional-theory inquiries. This excessive focus on annulment, however, has neglected some other nonconventional forms of judicial involvement regarding amendments. Taking Colombia as a case study, this article shows that the Constitutional Court has also had the power to initiate amendments, define their content, rewrite their text, and promulgate them. As these novel judicial interventions that go beyond invalidation resemble the prerogatives commonly vested on the amendment power, this research terms them ‘constitution-amending case law’, offers an in-depth exploration of them, and proposes a typology of such a jurisprudence. Lastly, the article ends with a cautionary note about the challenges this type of constitution-amending case law faces from the perspective of democracy and democratic backsliding.            

Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures

Spin Hall effects have surged as promising phenomena for spin logics operations without ferromagnets. However, the magnitude of the detected electric signals at room temperature in metallic systems has been so far underwhelming. Here, we demonstrate a two-order of magnitude enhancement of the signal in monolayer graphene/Pt devices when compared to their fully metallic counterparts. The enhancement stems in part from efficient spin injection and the large resistivity of graphene but we also observe 100% spin absorption in Pt and find an unusually large effective spin Hall angle of up to 0.15. The large spin-to-charge conversion allows us to characterise spin precession in graphene under the presence of a magnetic field. Furthermore, by developing an analytical model based on the 1D diffusive spin-transport, we demonstrate that the effective spin-relaxation time in graphene can be accurately determined using the (inverse) spin Hall effect as a means of detection. This is a necessary step to gather full understanding of the consequences of spin absorption in spin Hall devices, which is known to suppress effective spin lifetimes in both metallic and graphene systems.Comment: 14 pages, 6 figures. Accepted in 2D Materials. https://doi.org/10.1088/2053-1583/aa882

The ALHAMBRA photometric system

This paper presents the characterization of the optical range of the ALHAMBRA photometric system, a 20 contiguous, equal-width, medium-band CCD system with wavelength coverage from 3500A to 9700A. The photometric description of the system is done by presenting the full response curve as a product of the filters, CCD and atmospheric transmission curves, and using some first and second order moments of this response function. We also introduce the set of standard stars that defines the system, formed by 31 classic spectrophotometric standard stars which have been used in the calibration of other known photometric systems, and 288 stars, flux calibrated homogeneously, from the Next Generation Spectral Library (NGSL). Based on the NGSL, we determine the transformation equations between Sloan Digital Sky Survey (SDSS) ugriz photometry and the ALHAMBRA photometric system, in order to establish some relations between both systems. Finally we develop and discuss a strategy to calculate the photometric zero points of the different pointings in the ALHAMBRA project.Comment: Astronomical Journal on the 14th of January 201

Mergers and the outside-in formation of dwarf spheroidals

We use a cosmological simulation of the formation of the Local Group to explore the origin of age and metallicity gradients in dwarf spheroidal galaxies. We find that a number of simulated dwarfs form "outside-in", with an old, metal-poor population that surrounds a younger, more concentrated metal-rich component, reminiscent of dwarf spheroidals like Sculptor or Sextans. We focus on a few examples where stars form in two populations distinct in age in order to elucidate the origin of these gradients. The spatial distributions of the two components reflect their diverse origin; the old stellar component is assembled through mergers, but the young population forms largely in situ. The older component results from a first episode of star formation that begins early but is quickly shut off by the combined effects of stellar feedback and reionization. The younger component forms when a late accretion event adds gas and reignites star formation. The effect of mergers is to disperse the old stellar population, increasing their radius and decreasing their central density relative to the young population. We argue that dwarf-dwarf mergers offer a plausible scenario for the formation of systems with multiple distinct populations and, more generally, for the origin of age and metallicity gradients in dwarf spheroidals.Comment: 10 pages, 8 figures, Accepted for publication in MNRA

Exact solution of the two-dimensional Dirac oscillator

In the present article we have found the complete energy spectrum and the corresponding eigenfunctions of the Dirac oscillator in two spatial dimensions. We show that the energy spectrum depends on the spin of the Dirac particle.Comment: revtex, 6pp. IVIC-CFLE 93/0

One-dimensional image reconstruction by exponential filtering in infrared stellar speckle interferometry: application to IRC +10216

Exponential filtering, together with an improved version of the iterative Fourier-transform algorithm, is applied to image reconstruction from one-dimensional infrared stellar speckle interferometry data. The performance of the method is checked first by computer simulations with both noiseless and noisy data and then with a realistic simulation of one-dimensional infrared stellar speckle interferometry. We have seen no problems with convergence. The only problem that we found was an expected noisy appearance of the results when noisy data were simulated. Finally, the method was applied to observational specklegrams of the infrared source IRC +10216, in two standard photometric bands: K and M (2.2 and 5 m, respectively). The reconstruction in K of a north-south scan clearly shows three components inside a circumstellar shell. On the other hand, in the M band only a wing on the north side of the main component is resolvable.This paper was published in Journal of the Optical Society of America A, and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: [article URL]. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Peer reviewe

Three rate-constant kinetic model for permanganate reactions autocatalyzed by colloidal manganese dioxide: the oxidation of L-phenylalanine

The reduction of permanganate ion to MnO2 Mn2O3 soluble colloidal mixed oxide by L-phenylalanine in aqueous phosphate-buffered neutral solutions has been followed by a spectrophotometric method, monitoring the decay of permanganate ion at 525 nm and the formation of the colloidal oxide at 420 nm. The reaction is autocatalyzed by the manganese product and three rate constants have been required to fit the experimental absorbance-time kinetic data. The reaction shows base catalysis and the values of the activation parameters at different pHs have been determined. A mechanism including both the non-autocatalytic and the autocatalytic reaction pathways, and in agreement with the available experimental data, has been proposed. Some key features of this mechanism are the following: (i) of the two predominant forms of the amino acid, the anionic form exhibits a stronger reducing power than the zwitterionic form; (ii) the non-autocatalytic reaction pathway starts with the transfer of the hydrogen atom in the position of the amino acid to permanganate ion; and (iii) the autocatalytic reaction pathway involves the reduction of Mn(IV) to Mn(II) by the amino acid and the posterior re-oxidation of Mn(II) to Mn(IV) by permanganate ion