Fingering convection and cloudless models for cool brown dwarf atmospheres

This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral type T and Y, whose modeling is a current challenge. Silicate and iron clouds are believed to disappear at the photosphere at the L/T transition, but cloudless models fail to reproduce correctly the spectra of T dwarfs, advocating for the addition of more physics, e.g. other types of clouds or internal energy transport mechanisms. We use a one-dimensional (1D) radiative/convective equilibrium code ATMO to investigate this issue. This code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the PT structure. Included opacity sources are H2-H2, H2-He, H2O, CO, CO2, CH4, NH3, K, Na, and TiO, VO if they are present in the atmosphere. We show that the spectra of Y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and NH3 quenching are taken into account. T dwarf spectra still have some reddening in e.g. J - H compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust.Comment: Accepted in ApJ

Near-Infrared Spectroscopy of the Y0 WISEP J173835.52+273258.9 and the Y1 WISE J035000.32-565830.2: the Importance of Non-Equilibrium Chemistry

We present new near-infrared spectra, obtained at Gemini Observatory, for two Y dwarfs: WISE J035000.32-565830.2 (W0350) and WISEP J173835.52+273258.9 (W1738). A FLAMINGOS-2 R=540 spectrum was obtained for W0350, covering 1.0 < lambda um < 1.7, and a cross-dispersed GNIRS R=2800 spectrum was obtained for W1738, covering 0.993-1.087 um, 1.191-1.305 um, 1.589-1.631 um, and 1.985-2.175 um, in four orders. We also present revised YJH photometry for W1738, using new NIRI Y and J imaging, and a re-analysis of the previously published NIRI H band images. We compare these data, together with previously published data for late-T and Y dwarfs, to cloud-free models of solar metallicity, calculated both in chemical equilibrium and with disequilibrium driven by vertical transport. We find that for the Y dwarfs the non-equilibrium models reproduce the near-infrared data better than the equilibrium models. The remaining discrepancies suggest that fine-tuning the CH_4/CO and NH_3/N_2 balance is needed. Improved trigonometric parallaxes would improve the analysis. Despite the uncertainties and discrepancies, the models reproduce the observed near-infrared spectra well. We find that for the Y0, W1738, T_eff = 425 +/- 25 K and log g = 4.0 +/- 0.25, and for the Y1, W0350, T_eff = 350 +/- 25 K and log g = 4.0 +/- 0.25. W1738 may be metal-rich. Based on evolutionary models, these temperatures and gravities correspond to a mass range for both Y dwarfs of 3-9 Jupiter masses, with W0350 being a cooler, slightly older, version of W1738; the age of W0350 is 0.3-3 Gyr, and the age of W1738 is 0.15-1 Gyr.Comment: Accepted on March 30 2016 for publication in Ap

Feasibility of self-structured current accessed bubble devices in spacecraft recording systems

The self-structured, current aperture approach to magnetic bubble memory is described. Key results include: (1) demonstration that self-structured bubbles (a lattice of strongly interacting bubbles) will slip by one another in a storage loop at spacings of 2.5 bubble diameters, (2) the ability of self-structured bubbles to move past international fabrication defects (missing apertures) in the propagation conductors (defeat tolerance), and (3) moving bubbles at mobility limited speeds. Milled barriers in the epitaxial garnet are discussed for containment of the bubble lattice. Experimental work on input/output tracks, storage loops, gates, generators, and magneto-resistive detectors for a prototype device are discussed. Potential final device architectures are described with modeling of power consumption, data rates, and access times. Appendices compare the self-structured bubble memory from the device and system perspectives with other non-volatile memory technologies

Inverse proximity effect in ss-wave and dd-wave superconductors coupled to topological insulators

We study the inverse proximity effect in a bilayer consisting of a thin $s$- or $d$-wave superconductor (S) and a topological insulator (TI). Integrating out the topological fermions of the TI, we find that spin-orbit coupling is induced in the S, which leads to spin-triplet $p$-wave ($f$-wave) correlations in the anomalous Green's function for an $s$-wave ($d$-wave) superconductor. Solving the self-consistency equation for the superconducting order parameter, we find that the inverse proximity effect can be strong for parameters for which the Fermi momenta of the S and TI coincide. The suppression of the gap is approximately proportional to $e^{-1/\lambda}$, where $\lambda$ is the dimensionless superconducting coupling constant. This is consistent with the fact that a higher $\lambda$ gives a more robust superconducting state. For an $s$-wave S, the interval of TI chemical potentials for which the suppression of the gap is strong is centered at $\mu_{TI} = \pm\sqrt{2mv_F^2\mu}$, and increases quadratically with the hopping parameter $t$. Since the S chemical potential $\mu$ typically is high for conventional superconductors, the inverse proximity effect is negligible except for $t$ above a critical value. For sufficiently low $t$, however, the inverse proximity effect is negligible, in agreement with what has thus far been assumed in most works studying the proximity effect in S-TI structures. In superconductors with low Fermi energies, such as high-$T_c$ cuprates with $d$-wave symmetry, we again find a suppression of the order parameter. However, since $\mu$ is much smaller in this case, a strong inverse proximity effect can occur at $\mu_{TI}=0$ for much lower values of $t$. Moreover, the onset of a strong inverse proximity effect is preceded by an increase in the order parameter, allowing the gap to be tuned by several orders of magnitude by small variations in $\mu_{TI}$.Comment: 11 pages, 4 figures, updated versio

Radiation of Neutron Stars Produced by Superfluid Core

We find that neutron star interior is transparent for collisionless electron sound, the same way as it is transparent for neutrinos. In the presence of magnetic field the electron sound is coupled with electromagnetic radiation and form the fast magnetosonic wave. We find that electron sound is generated by superfluid vortices in the stellar core. Thermally excited helical vortex waves produce fast magnetosonic waves in the stellar crust which propagate toward the surface and transform into outgoing electromagnetic radiation. The vortex radiation has the spectral index -0.45 and can explain nonthermal radiation of middle-aged pulsars observed in the infrared, optical and hard X-ray bands. The radiation is produced in the stellar interior which allows direct determination of the core temperature. Comparing the theory with available spectra observations we find that the core temperature of the Vela pulsar is T=8*10^8K, while the core temperature of PSR B0656+14 and Geminga exceeds 2*10^8K. This is the first measurement of the temperature of a neutron star core. The temperature estimate rules out equation of states incorporating Bose condensations of pions or kaons and quark matter in these objects. Based on the temperature estimate and cooling models we determine the critical temperature of triplet neutron superfluidity in the Vela core Tc=(7.5\pm 1.5)*10^9K which agrees well with recent data on behavior of nucleon interactions at high energies. Another finding is that in the middle aged neutron stars the vortex radiation, rather then thermal conductivity, is the main mechanism of heat transfer from the stellar core to the surface. Electron sound opens a perspective of direct spectroscopic study of superdense matter in the neutron star interiors.Comment: 43 pages, 7 figures, to appear in Astrophysical Journa

High magnetic field superconductivity in a two-band superconductor

When applying an external magnetic field to a superconductor, orbital and Pauli paramagnetic pairbreaking effects govern the limit of the upper critical magnetic field that can be supported before superconductivity breaks down. Experimental studies have shown that many multiband superconductors exhibit values of the upper critical magnetic field that violate the theoretically predicted limit, giving rise to many studies treating the underlying mechanisms that allow this. In this work we consider spin-splitting induced by an external magnetic field in a superconductor with two relevant bands close to the Fermi level, and show that the presence of interband superconducting pairing produces high-field reentrant superconductivity violating the Pauli-Chandrasekhar-Clogston limit for the value of the upper critical magnetic field

Heat kernel estimates and spectral properties of a pseudorelativistic operator with magnetic field

Based on the Mehler heat kernel of the Schroedinger operator for a free electron in a constant magnetic field an estimate for the kernel of E_A is derived, where E_A represents the kinetic energy of a Dirac electron within the pseudorelativistic no-pair Brown-Ravenhall model. This estimate is used to provide the bottom of the essential spectrum for the two-particle Brown-Ravenhall operator, describing the motion of the electrons in a central Coulomb field and a constant magnetic field, if the central charge is restricted to Z below or equal 86

Multiple mating and a low incidence of cuckoldry for nest-holding males in the two-spotted goby, Gobiusculus flavescens

Background: A major question in behavioural ecology concerns the relationship between genetic mating systems and the strength of sexual selection. In this study, we investigated the genetic mating system of the two-spotted goby (Gobiusculus flavescens), a useful fish model for the study of sexual selection whose genetic mating system remains uncharacterized. We developed four polymorphic microsatellite markers and used them to conduct parentage analyses on 21 nests collected during the breeding season to examine the rates of multiple mating by males and to test for evidence of alternative mating strategies.Results: Results of this study indicate that male G. flavescens mate with multiple females and enjoy confidence of paternity. We detected only one instance of sneaking, so cuckoldry contributed a very small percentage (~0.1%) of the total fertilizations in this population. Nests were nearly full and males that maintain larger nests have higher mating and reproductive success, irrespective of body size.Conclusion: Overall, our investigation shows that G. flavescens is similar to other, related gobies in that the nests of care-giving males often contain eggs from multiple females. However, G. flavescens differs from other gobies in displaying an extremely low rate of cuckoldry. The study of ecological factors responsible for this important<br /

Microhematuria in Postmenopausal Women: Adherence to Guidelines in a Tertiary Care Setting

In 2012, the American Urological Association released a revision of their asymptomatic microscopic hematuria (AMH) guidelines. Our objectives were to assess adherence to these guidelines and to describe the prevalence of urinary tract malignancy in postmenopausal women at our institution