High temperature combustion: Approaching equilibrium using nuclear networks

A method for integrating the chemical equations associated with nuclear combustion at high temperature is presented and extensively checked. Following the idea of E. M\"uller, the feedback between nuclear rates and temperature was taken into account by simultaneously computing molar fraction changes and temperature response in the same matrix. The resulting algorithm is very stable and efficient at calculating nuclear combustion in explosive scenarios, especially in those situations where the reacting material manages to climb to the nuclear statistical equilibrium regime. The numerical scheme may be useful not only for those who carry out hydrodynamical simulations of explosive events, but also as a tool to investigate the properties of a nuclear system approaching equilibrium through a variety of thermodynamical trajectories.Comment: 31 pages, 11 figures, accepted for publication in the ApJ

Detailed Spectral Modeling of a 3-D Pulsating Reverse Detonation Model: Too Much Nickel

We calculate detailed NLTE synthetic spectra of a Pulsating Reverse Detonation (PRD) model, a novel explosion mechanism for Type Ia supernovae. While the hydro models are calculated in 3-D, the spectra use an angle averaged hydro model and thus some of the 3-D details are lost, but the overall average should be a good representation of the average observed spectra. We study the model at 3 epochs: maximum light, seven days prior to maximum light, and 5 days after maximum light. At maximum the defining Si II feature is prominent, but there is also a prominent C II feature, not usually observed in normal SNe Ia near maximum. We compare to the early spectrum of SN 2006D which did show a prominent C II feature, but the fit to the observations is not compelling. Finally we compare to the post-maximum UV+optical spectrum of SN 1992A. With the broad spectral coverage it is clear that the iron-peak elements on the outside of the model push too much flux to the red and thus the particular PRD realizations studied would be intrinsically far redder than observed SNe Ia. We briefly discuss variations that could improve future PRD models.Comment: 15 pages, 4 figures, submitted to Ap

Axisymmetric smoothed particle hydrodynamics with self-gravity

The axisymmetric form of the hydrodynamic equations within the smoothed particle hydrodynamics (SPH) formalism is presented and checked using idealized scenarios taken from astrophysics (free fall collapse, implosion and further pulsation of a sun-like star), gas dynamics (wall heating problem, collision of two streams of gas) and inertial confinement fusion (ICF, -ablative implosion of a small capsule-). New material concerning the standard SPH formalism is given. That includes the numerical handling of those mass points which move close to the singularity axis, more accurate expressions for the artificial viscosity and the heat conduction term and an easy way to incorporate self-gravity in the simulations. The algorithm developed to compute gravity does not rely in any sort of grid, leading to a numerical scheme totally compatible with the lagrangian nature of the SPH equations.Comment: 17 pages, 10 figures, 1 Table. Accepted for publication in MNRA

Constraining deflagration models of Type Ia supernovae through intermediate-mass elements

The physical structure of a nuclear flame is a basic ingredient of the theory of Type Ia supernovae (SNIa). Assuming an exponential density reduction with several characteristic times we have followed the evolution of a planar nuclear flame in an expanding background from an initial density 6.6 10^7 g/cm3 down to 2 10^6 g/cm3. The total amount of synthesized intermediate-mass elements (IME), from silicon to calcium, was monitored during the calculation. We have made use of the computed mass fractions, X_IME, of these elements to give an estimation of the total amount of IME synthesized during the deflagration of a massive white dwarf. Using X_IME and adopting the usual hypothesis that turbulence decouples the effective burning velocity from the laminar flame speed, so that the relevant flame speed is actually the turbulent speed on the integral length-scale, we have built a simple geometrical approach to model the region where IME are thought to be produced. It turns out that a healthy production of IME involves the combination of not too short expansion times, t_c > 0.2 s, and high turbulent intensities. According to our results it could be difficult to produce much more than 0.2 solar masses of intermediate-mass elements within the deflagrative paradigma. The calculations also suggest that the mass of IME scales with the mass of Fe-peak elements, making it difficult to conciliate energetic explosions with low ejected nickel masses, as in the well observed SN1991bg or in SN1998de. Thus a large production of Si-peak elements, especially in combination with a low or a moderate production of iron, could be better addressed by either the delayed detonation route in standard Chandrasekhar-mass models or, perhaps, by the off-center helium detonation in the sub Chandrasekhar-mass scenario.Comment: 9 pages, 5 figures, 2 table

Specific gene correction of the AGXT gene and direct cell reprogramming for the treatment of Primary Hyperoxaluria Type 1

P428 Primary Hyperoxaluria Type 1 (PH1) is an inherited rare metabolic liver disease caused by the deficiency in the alanine: glyoxylate aminotransferase enzyme (AGXT), involved in the glyoxylate metabolism. The only potentially curative treatment is organ transplantation. Thus, the development of new therapeutic approaches for the treatment of these patients appears as a priority.We propose the combination of site-specific gene correction and direct cell reprogramming for the generation of autologous phenotypically healthy induced hepatocytes (iHeps) from skin-derived fibroblast of PH1 patients. For the correction of AGXT mutations, we have designed specific gene editing tools to address gene correction by two different strategies, assisted by CRISPR/Cas9 system. Accurate specific point mutation correction (c.853T-C) has been achieved by homologydirected repair (HDR) with ssODN harbouring wild-type sequence. In the second strategy, an enhanced version ofAGXTcDNAhas been inserted near the transcription start codon of the endogenous gene, constituting an almost universal correction strategy for PH1 mutations. Direct reprogramming of fibroblasts has been conducted by overexpression of hepatic transcription factors and in vitro culture in defined media. In vitro characterization of healthy induced hepatocytes (iHeps) has demonstrated hepatic function of the reprogrammed cells. PH1 patient fibroblasts and , ,

Systematically Asymmetric Heliospheric Magnetic Field: Evidence for a Quadrupole Mode and Non-axisymmetry with Polarity Flip-flops

Recent studies of the heliospheric magnetic field (HMF) have detected interesting, systematic hemispherical and longitudinal asymmetries which have a profound significance for the understanding of solar magnetic fields. The in situ HMF measurements since 1960s show that the heliospheric current sheet (HCS) is systematically shifted (coned) southward during solar minimum times, leading to the concept of a bashful ballerina. While temporary shifts can be considerably larger, the average HCS shift (coning) angle is a few degrees, less than the $7.2^{\circ}$ tilt of the solar rotation axis. Recent solar observations during the last two solar cycles verify these results and show that the magnetic areas in the northern solar hemisphere are larger and their intensity weaker than in the south during long intervals in the late declining to minimum phase. The multipole expansion reveals a strong quadrupole term which is oppositely directed to the dipole term. These results imply that the Sun has a symmetric quadrupole S0 dynamo mode that oscillates in phase with the dominant dipole A0 mode. Moreover, the heliospheric magnetic field has a strong tendency to produce solar tilts that are roughly opposite in longitudinal phase. This implies is a systematic longitudinal asymmetry and leads to a "flip-flop" type behaviour in the dominant HMF sector whose period is about 3.2 years. This agrees very well with the similar flip-flop period found recently in sunspots, as well as with the observed ratio of three between the activity cycle period and the flip-flop period of sun-like stars. Accordingly, these results require that the solar dynamo includes three modes, A0, S0 and a non-axisymmetric mode. Obviously, these results have a great impact on solar modelling.Comment: 13 pages, 4 figures, Solar Physics, Topical Issue of Space Climate Symposium, in pres