The magnetorotational instability across the dead zone of protoplanetary disks

We examine the linear stability of a flow threaded by a weak, vertical magnetic field in a disk with a keplerian rotation profile and a vertical stratification of the ionization degree as that predicted for vast portions of protoplanetary disks. A quasi-global analysis is carried out, where the form of the perturbations in the vertical direction is determined. Considering the ohmic magnetic diffusivity of the gas, the conditions leading to the magnetorotational instability are analyzed as a function of the diffusivity at the disk surfaces, its vertical profile and the strength of the unperturbed magnetic field. For typical conditions believed to prevail in protoplanetary disks at radial distances between 0.1 and 10 AU, where the so-called dead zone is proposed to exist, we find that generally the instability is damped. This implies that, if the MRI is considered the only possible source of turbulence in protoplanetary disks, no viscous angular momentum transport occursat those radii.Comment: 33 pages, 8 figure

Online Harmonic/Percussive Separation Using Smoothness/Sparseness Constraints

(Abstract to follow

Oleaxonchium olearum gen. et sp. nov. (Nematoda, Dorylaimida) associated with an olive grove in the southern Iberian Peninsula, and new insights into the evolutionary relationships within Belondiridae

A new belondirid, dorylaimid taxon, Oleaxonchium olearum gen. et sp. nov., collected from an olive grove in the Andalusia region of Spain, is characterised, including its morphological description, morphometrics, SEM study, and molecular (18S-, 28S-rDNA) analyses. The new genus displays a unique combination of traits that distinguishes it from its closest genera: a rectangular lip region with sclerotized margins when observed in lateral view and visibly hexagonal in face view under SEM; a comparatively long cheilostom with thickened walls at its anterior part; a short isthmus-like section separating both pharyngeal regions; a mono-opistho-ovarian didelphic female genital system without pars refringens vaginae; and a short and rounded tail. The new species is characterised by its 2.44–2.87 mm long body, lip region 7–7.5 µm wide, odontostyle 10–10.5 µm long, neck 723–973 µm long, pharyngeal expansion occupying 63–72% of the total neck length, female anterior genital branch 4–6% of body length, tripartite posterior uterus 1.9–2.6 body diameters long, with a short intermediate section bearing sclerotized elements, vulva (V = 58–61) a transverse slit, caudal region 29–35 µm long (c = 74–89, c’ = 0.9–1.1), and male unknown. As derived from an integrative approach combining morphological and molecular data, the new genus is close to Metaxonchium, the polyphyly of Belondiridae is confirmed, and support is provided in favour of the monophyly of Axonchiinae

Modelling of bismuth segregation in InAsBi/InAs superlattices: Determination of the exchange energies

InAsBi dilute alloys are potential new candidates for the improvement of infrared optoelectronic devices such as photodetectors or lasers. In this work, InAsBi/InAs superlattices (SLs)with Bi contents ranging between 1 and 3% were grown by molecular beam epitaxy with different Bi fluxes and growth temperatures to analyze Bi segregation by cross sectional transmission electron microscopy techniques. Bi segregation profiles have been described layer-by-layer using a three-layer fluid exchange mechanism, extracting the values of the As/Bi exchange energies (E 1 , 1.26 ± 0.01 eV and E 2 , 1.36 ± 0.02 eV). A relationship to calculate the activation energies for exchange from the binding energies in III–V alloys is proposed, which would allow predicting them for other hitherto unknown compounds

Bihelical Magnetic Relaxation and Large Scale Magnetic Field Growth

A unified, three-scale system of equations accommodating nonlinear velocity driven helical dynamos, as well as time-dependent relaxation of magnetically dominated unihelical or bihelical systems is derived and solved herein. When opposite magnetic helicities of equal magnitude are injected on the intermediate and small scales, the large scale magnetic helicity grows kinematically (independent of the magnetic Reynolds number) to equal that on the intermediate scale. For both free and driven relaxation large scale fields are rapidly produced. Subsequently, a dissipation-limited dynamo, driven by growth of small scale kinetic helicity, further amplifies the large scale field. The results are important for astrophysical coronae fed with bihelical structures by dynamos in their host rotators. The large scale for the rotator corresponds to the intermediate scale for the corona. That bihelical magnetic relaxation can produce global scale fields may help to explain the formation of astrophysical coronal holes and magnetohydrodynamic outflows.Comment: LaTeX, 29 pages including figures, version in press, Physics of Plasma

On the migration of protogiant solid cores

The increase of computational resources has recently allowed high resolution, three dimensional calculations of planets embedded in gaseous protoplanetary disks. They provide estimates of the planet migration timescale that can be compared to analytical predictions. While these predictions can result in extremely short migration timescales for cores of a few Earth masses, recent numerical calculations have given an unexpected outcome: the torque acting on planets with masses between 5 M_Earth and 20 M_Earth is considerably smaller than the analytic, linear estimate. These findings motivated the present work, which investigates existence and origin of this discrepancy or ``offset'', as we shall call it, by means of two and three dimensional numerical calculations. We show that the offset is indeed physical and arises from the coorbital corotation torque, since (i) it scales with the disk vortensity gradient, (ii) its asymptotic value depends on the disk viscosity, (iii) it is associated to an excess of the horseshoe zone width. We show that the offset corresponds to the onset of non-linearities of the flow around the planet, which alter the streamline topology as the planet mass increases: at low mass the flow non-linearities are confined to the planet's Bondi sphere whereas at larger mass the streamlines display a classical picture reminiscent of the restricted three body problem, with a prograde circumplanetary disk inside a ``Roche lobe''. This behavior is of particular importance for the sub-critical solid cores (M <~ 15 M_Earth) in thin (H/r <~0.06) protoplanetary disks. Their migration could be significantly slowed down, or reversed, in disks with shallow surface density profiles.Comment: Accepted for publication in Ap

The Shapes of AGB Envelopes as Probes of Binary Companions

We describe how the large scale geometry of the circumstellar envelopes of asymptotic giant branch stars can be used to probe the presence of unseen stellar companions. A nearby companion modifies the mass loss by gravitationally focusing the wind towards the orbital plane, and thereby determines the shape of the envelope at large distances from the star. Using available simulations, we develop a prescription for the observed shapes of envelopes in terms of the binary parameters, envelope orientation, and type of observation. The prescription provides a tool for the analysis of envelope images at optical, infrared, and millimetre wavelengths, which can be used to constrain the presence of companions in well observed cases. We illustrate this approach by examining the possible role of binary companions in triggering the onset of axi-symmetry in planetary nebula formation. If interaction with the primary leads to axi-symmetry, the spherical halos widely seen around newly formed nebulae set limits on the companion mass. Only low mass objects may orbit close to the primary without observable shaping effects: they remain invisible until the interaction causes a sudden change in the mass loss geometry.Comment: 11 pages, 7 figures, to appear in MNRA

Compuestos fenólicos y capacidad antioxidante de genotipos de maíz pigmentado (azul/morado)

El maíz (Zea mays L.) es uno de los principales alimentos que constituyen la dieta de los mexicanos. Además, México es un país que cuenta con diversas razas de maíz con diferentes pigmentaciones. Los maíces con granos pigmentados se distinguen por presentar alto contenido de compuestos fenólicos y capacidad antioxidante, que pueden ser utilizados para el desarrollo de productos funcionales en beneficio de la salud. El objetivo de este trabajo fue evaluar y comparar el contenido de compuestos fenólicos (fenoles y flavonoides totales, antocianinas y taninos condensados), además de los niveles de capacidad antioxidante (DPPH y ABTS) en cinco genotipos de maíz azul/morado de diferentes razas (Kculli, Tuxpeño, Chalqueño y Cónicos), identificados como Morado Peruano (MPE), Morado Antonio Narro (MAN), Morado Veracruz (MV), Morado Sinaloa (MS) y Morado Poblano (MP). Los resultados obtenidos indican que los genotipos MPE y MAN presentaron los niveles más altos en fenoles totales y antocianinas, lo que resultó en mayores propiedades antioxidantes. El presente estudio permite identificar genotipos de maíz con alta concentración de compuestos antioxidantes que pueden ser utilizados para el desarrollo de suplementos alimenticios