Soil water retention and hydraulic conductivity dynamics following tillage

Soil bulk density (ρb) may be purposely reduced in agricultural fields using tillage to improve hydraulic properties. However, tillage alters the soil structure, resulting in unstable soils. As the soil stabilizes, ρb increases over time. While this is known, studies on soil hydraulic properties in tilled soils, including comparisons between tilled and non-tilled soils, commonly assume a rigid soil structure. This study presents changes in soil water retention and saturated hydraulic conductivity (Ksat) as ρb increased dynamically with time following tillage at a loam-textured field site. Over the summer of 2015, soil cores were collected at several depths below the surface following precipitation events. Soil water retention curves and Ksat were determined using pressure cells and the constant head method, respectively. Tillage reduced ρb to 0.94 g cm−3. Changes in ρb increased with depth, reaching a ρb of 1.11 g cm−3 in the 0–5 cm layer, and a ρb of 1.42 g cm−3 at the deepest tilled layer. Soil water retention curves were markedly steeper for samples with higher ρb, indicating an overall increase in water retained at a soil matric potential (Ψ) of −33 kPa. Evaluation of two modeling approaches for water retention as a function ρbindicated that changes in water retention with increases in ρb could be reasonably estimated if a matching point was used. No clear relationship between Ksat and ρbwas obvious for ρb \u3c 1.06 cm3 cm−3, but for ρb \u3e 1.06 cm3 cm−3, Ksat decreased markedly (order of magnitude) as ρb increased. Hydraulic properties varied strongly depending on time since tillage and soil depth, and results have implications for models of tilled soils, as well as for studies comparing tilled and non-tilled soils

Keck Hires Observations of the QSO First J104459.6+365605: Evidence for a Large Scale Outflow

This paper presents an analysis of a Keck HIRES spectrum of the QSO FIRST J104459.6+365605. The line of sight towards the QSO contains two clusters of outflowing clouds that give rise to broad blue shifted absorption lines. The outflow velocities of the clouds range from -200 to -1200 km/s and from -3400 to -5200 km/s, respectively. The width of the individual absorption lines ranges from 50 to more than 1000 km/s. The most prominent absorption lines are those of Mg II, Mg I, and Fe II. The low ionization absorption lines occur at the same velocities as the most saturated Mg II lines, showing that the Fe II, Mg I and Mg II line forming regions must be closely associated. Many absorption lines from excited states of Fe II are present, allowing a determination of the population of several low lying energy levels. From this we determine an electron density in the Fe II line forming regions of 4000 per cubic cm. Modelling the ionization state of the absorbing gas with this value of the electron density as a constraint, we find that the distance between the Fe II and Mg I line forming region and the continuum source is of order 700 parsec. From the correspondence in velocity between the Fe II, Mg I and Mg II lines we infer that the Mg II lines must be formed at the same distance. The Mg II absorption fulfills the criteria for Broad Absorption Lines defined by Weymann et al. (1991). This large distance is surprising, since BALs are generally thought to be formed in outflows at a much smaller distance from the nucleus.Comment: 34 pages, 11 figures. Accepted by The Astrophysical Journa

DE Canum Venaticorum : a bright, eclipsing red dwarf–white dwarf binary

Context. Close white dwarf–red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf–red dwarf binary with a relatively short (∼8.7 h) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. Aims. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters that we discuss in the framework of common-envelope evolution. Methods. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average lowresolution spectrum of DE CVn, we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system. Results. The derived ephemeris is HJDmin = 2 452 784.5533(1) + 0.3641394(2) × E. The red dwarf in DE CVn has a spectral type of M3V and the white dwarf has an effective temperature of 8 000 K. The inclination of the system is 86+3◦ −2 and the mass and radius of the red dwarf are 0.41 ± 0.06 M and 0.37+0.06 −0.007 R, respectively, and the mass and radius of the white dwarf are 0.51+0.06 −0.02 M and 0.0136+0.0008 −0.0002 R, respectively. Conclusions. We found that the white dwarf has a hydrogen-rich atmosphere (DA-type). Given that DE CVn has experienced a common-envelope phase, we can reconstruct its evolution and we find that the progenitor of the white dwarf was a relatively lowmass star (M ≤ 1.6 M). The current age of this system is 3.3−7.3 × 109 years, while it will take longer than the Hubble time for DE CVn to evolve into a semi-detached system

Volumetric evaluation of CT images of adrenal glands in primary aldosteronism

Objectives: To investigate whether adrenal volumetry provides better agreement with adrenal vein sampling (AVS) than conventional CT for subtyping PA. Furthermore, we evaluated whether the size of this contralateral adrenal was a prognostic factor for clinical outcome after unilateral adrenalectomy.Methods: We retrospectively analyzed volumes of both adrenal glands of the 180 CT-scans (88/180 with unilateral and 92/180 with bilateral disease) of the patients with PA included in the SPARTACUS trial of which 85 also had undergone an AVS. In addition, we examined CT-scans of 20 healthy individuals to compare adrenal volumes with published normal values.Results: Adrenal volume was higher for the left than the right adrenal (mean and SD: 6.49 ± 2.77 ml versus 5.25 ± 1.87 ml for the right adrenal; p &lt; 0.001). Concordance between volumetry and AVS in subtyping was 58.8%, versus 51.8% between conventional CT results and AVS (p = NS). The volumes of the contralateral adrenals in the patients with unilateral disease (right 4.78 ± 1.37 ml; left 6.00 ± 2.73 ml) were higher than those of healthy controls reported in the literature (right 3.62 ± 1.23 ml p &lt; 0.001; left 4.84 ± 1.67 ml p = 0.02). In a multivariable analysis the contralateral volume was not associated with biochemical or clinical success, nor with the defined daily doses of antihypertensive agents at 1 year follow-up.Conclusions: Volumetry of the adrenal glands is not superior to current assessment of adrenal size by CT for subtyping patients with PA. Furthermore, in patients with unilateral disease the size of the contralateral adrenal is enlarged but its size is not associated with outcome.</p

The long-lived Type IIn SN 2015da: Infrared echoes and strong interaction within an extended massive shell star star star

In this paper we report the results of the first similar to four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy greater than or similar to 10(51) erg. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be similar or equal to 8 M-circle dot, with an extreme mass-loss rate for the progenitor star similar or equal to 0.6 M-circle dot yr(-1), suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a fluxexcess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass greater than or similar to 0.4 x 10(-3) M-circle dot for the dustSpanish MICINN gran

Gopakumar-Vafa invariants via vanishing cycles

In this paper, we propose an ansatz for defining Gopakumar-Vafa invariants of Calabi-Yau threefolds, using perverse sheaves of vanishing cycles. Our proposal is a modification of a recent approach of Kiem-Li, which is itself based on earlier ideas of Hosono-Saito-Takahashi. We conjecture that these invariants are equivalent to other curve-counting theories such as Gromov-Witten theory and Pandharipande-Thomas theory. Our main theorem is that, for local surfaces, our invariants agree with PT invariants for irreducible one-cycles. We also give a counter-example to the Kiem-Li conjectures, where our invariants match the predicted answer. Finally, we give examples where our invariant matches the expected answer in cases where the cycle is non-reduced, non-planar, or non-primitive.Comment: 63 pages, many improvements of the exposition following referee comments, final version to appear in Inventione

The population of close double white dwarfs in the Galaxy

We present a new model for the Galactic population of close double white dwarfs. The model accounts for the suggestion of the avoidance of a substantial spiral-in during mass transfer between a giant and a main-sequence star of comparable mass and for detailed cooling models. It agrees well with the observations of the local sample of white dwarfs if the initial binary fraction is close to 50% and an ad hoc assumption is made that white dwarfs with mass less than about 0.3 solar mass cool faster than the models suggest. About 1000 white dwarfs brighter than V=15 have to be surveyed for detection of a pair which has total mass greater than the Chandrasekhar mass and will merge within 10 Gyr.Comment: 15 pages, 7 figures, to appear in Proc. ``The influence of binaries on stellar population studies'', Brussels, August 2000 (Kluwer, D. Vanbeveren ed.

Multi-dimensional modelling of X-ray spectra for AGN accretion-disk outflows III: application to a hydrodynamical simulation

We perform multi-dimensional radiative transfer simulations to compute spectra for a hydrodynamical simulation of a line-driven accretion disk wind from an active galactic nucleus. The synthetic spectra confirm expectations from parameterized models that a disk wind can imprint a wide variety of spectroscopic signatures including narrow absorption lines, broad emission lines and a Compton hump. The formation of these features is complex with contributions originating from many of the different structures present in the hydrodynamical simulation. In particular, spectral features are shaped both by gas in a successfully launched outflow and in complex flows where material is lifted out of the disk plane but ultimately falls back. We also confirm that the strong Fe Kalpha line can develop a weak, red-skewed line wing as a result of Compton scattering in the outflow. In addition, we demonstrate that X-ray radiation scattered and reprocessed in the flow has a pivotal part in both the spectrum formation and determining the ionization conditions in the wind. We find that scattered radiation is rather effective in ionizing gas which is shielded from direct irradiation from the central source. This effect likely makes the successful launching of a massive disk wind somewhat more challenging and should be considered in future wind simulations.Comment: 14 pages, 8 figures. Accepted for publication by MNRA