Double-diffusive instabilities of a shear-generated magnetic layer

Previous theoretical work has speculated about the existence of double-diffusive magnetic buoyancy instabilities of a dynamically evolving horizontal magnetic layer generated by the interaction of forced vertically sheared velocity and a background vertical magnetic field. Here we confirm numerically that if the ratio of the magnetic to thermal diffusivities is sufficiently low then such instabilities can indeed exist, even for high Richardson number shear flows. Magnetic buoyancy may therefore occur via this mechanism for parameters that are likely to be relevant to the solar tachocline, where regular magnetic buoyancy instabilities are unlikely.Comment: Submitted to ApJ

The Evolution of a Double Diffusive Magnetic Buoyancy Instability

Recently, Silvers, Vasil, Brummell, & Proctor (2009), using numerical simulations, confirmed the existence of a double diffusive magnetic buoyancy instability of a layer of horizontal magnetic field produced by the interaction of a shear velocity field with a weak vertical field. Here, we demonstrate the longer term nonlinear evolution of such an instability in the simulations. We find that a quasi two-dimensional interchange instability rides (or "surfs") on the growing shear-induced background downstream field gradients. The region of activity expands since three-dimensional perturbations remain unstable in the wake of this upward-moving activity front, and so the three-dimensional nature becomes more noticeable with time.Comment: 9 pages; 3 figures; accepted to appear in IAU symposium 27

A Contracting, Turbulent, Starless Core in the Serpens Cluster

We present combined single-dish and interferometric CS(2--1) and N2H+(1--0) observations of a compact core in the NW region of the Serpens molecular cloud. The core is starless according to observations from optical to millimeter wavelengths and its lines have turbulent widths and ``infall asymmetry''. Line profile modeling indicates supersonic inward motions v_in>0.34 km/s over an extended region L>12000AU. The high infall speed and large extent exceeds the predictions of most thermal ambipolar diffusion models and points to a more dynamical process for core formation. A short (dynamic) timescale, ~1e5 yr=L/v_in, is also suggested by the low N2H+ abundance ~1e-10.Comment: 11 pages including 2 figures. Accepted for publication in the Astrophysical Journal Letter

Synchronisation of the superimposed training method for channel estimation in the presence of DC-offset

The superimposed training method estimates the channel from the induced first-order cyclostationary statistics exhibited by the received signal. In this paper, using vector space decomposition, we show that the information needed for training sequence synchronisation, and for DC-offset estimation, can be extracted from the first-order cyclostationary statistics as well. Necessary and sufficient conditions for channel computation and equalisation are derived, when training sequence synchronisation and DC-offset removal are required. The computational burden of the practical implementation of the method presented here is much lighter than for existing algorithms. At the same time, simulation results show that the performance, in terms of the MSE of the channel estimates and BER, is not diminishedwhen compared to these existing algorithms

Vortex ratchet reversal: The role of interstitial vortices

Triangular arrays of Ni nanotriangles embedded in superconducting Nb films exhibit unexpected dynamical vortex effects. Collective pinning with a vortex lattice configuration different from the expected fundamental triangular "Abrikosov state" is found. The vortex motion which prevails against the triangular periodic potential is produced by channelling effects between triangles. Interstitial vortices coexisting with pinned vortices in this asymmetric potential, lead to ratchet reversal, i.e. a DC output voltage which changes sign with the amplitude of an applied alternating drive current. In this landscape, ratchet reversal is always observed at all magnetic fields (all numbers of vortices) and at different temperatures. The ratchet reversal is unambiguously connected to the presence of two locations for the vortices: interstitial and above the artificial pinning sites.Comment: 21 pages, 4 figures, 1 Tabl

Recovering star formation histories: Integrated-light analyses vs stellar colour-magnitude diagrams

Accurate star formation histories (SFHs) of galaxies are fundamental for understanding the build-up of their stellar content. However, the most accurate SFHs - those obtained from colour-magnitude diagrams (CMDs) of resolved stars reaching the oldest main sequence turnoffs (oMSTO) - are presently limited to a few systems in the Local Group. It is therefore crucial to determine the reliability and range of applicability of SFHs derived from integrated light spectroscopy, as this affects our understanding of unresolved galaxies from low to high redshift. To evaluate the reliability of current full spectral fitting techniques in deriving SFHs from integrated light spectroscopy by comparing SFHs from integrated spectra to those obtained from deep CMDs of resolved stars. We have obtained a high signal--to--noise (S/N $\sim$ 36.3 per \AA) integrated spectrum of a field in the bar of the Large Magellanic Cloud (LMC) using EFOSC2 at the 3.6 meter telescope at La Silla Observatory. For this same field, resolved stellar data reaching the oMSTO are available. We have compared the star formation rate (SFR) as a function of time and the age-metallicity relation (AMR) obtained from the integrated spectrum using {\tt STECKMAP}, and the CMD using the IAC-star/MinnIAC/IAC-pop set of routines. For the sake of completeness we also use and discuss other synthesis codes ({\tt STARLIGHT} and {\tt ULySS}) to derive the SFR and AMR from the integrated LMC spectrum. We find very good agreement (average differences $\sim$ 4.1 $\%$) between the SFR(t) and the AMR obtained using {\tt STECKMAP} on the integrated light spectrum, and the CMD analysis. {\tt STECKMAP} minimizes the impact of the age-metallicity degeneracy and has the advantage of preferring smooth solutions to recover complex SFHs by means of a penalized $\chi^2$. [abridged]Comment: 23 pages, 24 figures. Accepted for publication in A&A (6 Sep 2015

A History of Trauma is Associated with Aggression, Depression, Non-Suicidal Self-Injury Behavior, and Suicide Ideation in First-Episode Psychosis.

The association between trauma and psychosis outcomes is well-established, and yet the impact of trauma on comorbid clinical symptoms-such as aggression, non-suicidal self-injury behavior (NSSIB), suicide ideation, and suicide behavior-for those with psychosis is unclear. To effectively treat those with first-episode psychosis (FEP) and a history of trauma, we need to understand the impact of trauma on their whole presentation. FEP participants were recruited from an Early Psychosis Program (N = 187, ages 12-35, 72.2% male). Clinicians gathered history of trauma, aggression, and suicide data, and rated current symptom severity and functioning. Data was coded using clinician rated measures, self-report measures, and retrospective clinical chart review. Regression analyses examined whether trauma was associated with a history of aggression, suicidal ideation, suicide behavior, NSSIB, symptoms, and functioning. Trauma was associated with aggression, aggression severity and type of aggression (aggression towards others). Trauma was also associated with depression severity, suicide ideation, most severe suicide ideation, and NSSIB. Trauma was not associated with suicide behavior, severity of suicide behavior or psychosocial functioning. Integrating trauma treatment into FEP care could reduce rates of depression, aggression, suicide ideation, and NSSIB for those with a history of trauma. To reduce suicide attempt occurrence and improve functioning, more research is needed

Late Quaternary monogenetic volcanoes along Río Salado, Sothwest Mendoza Province, Argentina

On the eastem flank of the Andes, to the north of Río Salado in southwest Mendoza Province (35º07'S-35º10'S), there are 4 monogenetic cones with blocky lava flows. A western group of small volcanoes, Hoyada, Lagunita and Loma Negra, with a total volume of -0.2 km3, are composed of amphibole-bearing basaltic andesite, and the eastem, more voluminous Hoyo Colorado volcano, with 0.44 km3 is composed of olivine (+ oxidised amphibole) basaltic andesite. Although data indicate they were emitted through successive, strombolian eruptions, they are overall coeval and the youngest Late Pleistocene volcanoes located in an "extra-Andean" setting, -70 km east of the main volcanic front. The magmas of the westem group of monogenetic cones show petrographic and geochemical characteristics that support processes of crustal interaction during ascent. In contrast, the magmas of the Hoyo Colorado volcano had a more direct ascent. Structural characteristics of the basement rocks to the volcanoes and the current seismotectonic activity of the Andes at this latitude indicate that the monogenetic cones of Río Salado were emplaced in a dominantly compressive tectonic regime