Spectral sequences of Type Ia supernovae. I. Connecting normal and sub-luminous SN Ia and the presence of unburned carbon

Type Ia supernovae are generally agreed to arise from thermonuclear explosions of carbon-oxygen white dwarfs. The actual path to explosion, however, remains elusive, with numerous plausible parent systems and explosion mechanisms suggested. Observationally, type Ia supernovae have multiple subclasses, distinguished by their lightcurves and spectra. This raises the question whether these reflect that multiple mechanisms occur in nature, or instead that explosions have a large but continuous range of physical properties. We revisit the idea that normal and 91bg-like supernovae can be understood as part of a spectral sequence, in which changes in temperature dominate. Specifically, we find that a single ejecta structure is sufficient to provide reasonable fits of both the normal type Ia supernova SN~2011fe and the 91bg-like SN~2005bl, provided that the luminosity and thus temperature of the ejecta are adjusted appropriately. This suggests that the outer layers of the ejecta are similar, thus providing some support of a common explosion mechanism. Our spectral sequence also helps to shed light on the conditions under which carbon can be detected in pre-maximum SN~Ia spectra -- we find that emission from iron can "fill in" the carbon trough in cool SN~Ia. This may indicate that the outer layers of the ejecta of events in which carbon is detected are relatively metal poor compared to events where carbon is not detected

The i-process and CEMP-r/s stars

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. We investigate whether the anomalous elemental abundance patterns in some of the C-enhanced metal-poor-r/s (CEMP-r/s) stars are consistent with predictions of nucleosynthesis yields from the i-process, a neutron-capture regime at neutron densities intermediate between those typical for the slow (s) and rapid (r) processes. Conditions necessary for the i-process are expected to be met at multiple stellar sites, such as the He-core and He-shell flashes in low-metallicity low-mass stars, super-AGB and post-AGB stars, as well as low-metallicity massive stars. We have found that single-exposure one-zone simulations of the i-process reproduce the abundance patterns in some of the CEMP-r/s stars much better than the model that assumes a superposition of yields from s and r-process sources. Our previous study of nuclear data uncertainties relevant to the i-process revealed that they could have a significant impact on the i-process yields obtained in our idealized one-zone calculations, leading, for example, to ∼ 0:7dex uncertainty in our predicted [Ba/La] ratio. Recent 3D hydrodynamic simulations of convection driven by a He-shell flash in post-AGB Sakurai's object have discovered a new mode of non-radial instabilities: the Global Oscillation of Shell H-ingestion. This has demonstrated that spherically symmetric stellar evolution simulations cannot be used to accurately model physical conditions for the i-process

SYSTEM AND METHOD FOR IMPROVING DATA ACQUISISTION CAPABILITY IN SPECTROSCOPIC ROTATABLE ELEMENT, ROTATING ELEMENT, MODULATION ELEMENT, AND OTHER ELLIPSOMETER AND POLARIMETER AND THE LIKE SYSTEMS

Disclosed is a System and method for controlling polarization State determining parameters of a polarized beam of light in an ellipSometer or polarimeter and the like System, (e.g. a modulation element ellipsometer System), So that they are in ranges wherein the Sensitivity, (of a Sample system characterizing PSI and DELTA value monitoring detector used to measure changes in Said polarization State resulting from interaction with a “composite Sample System,” comprised of a Sample System per Se.. and a beam polarization State determining variable retarder, to noise and measurement errors etc. therein), is reduced. The present invention allows determining Sample System per Se.. characterizing PSI and DELTA values, from Composite Sample System characterizing PSI and DELTA values, by compensating for the presence of present invention components, (VR1) and/or VR2), added to an ellipsometer or polarimeter and the like System. The present invention also improves the ability of an ellipSometer or polarimeter and the like System fitted with present invention components (VR1) and/or (VR2) to provide uSably accurate and precise Sample System characterizing PSI and DELTA determining data values, wherein a Sample System per Se.. investigating polarized beam of light is oriented at other than a Principal or Brewster Angle of Incidence thereto, the use of which Angle of Incidence would otherwise be difficult, if not impossible. Practice of the present invention also allows determination of the “Handedness” of a polarized beam of light, and of sample system Jones or Mueller Matrix component values. As well, the present invention provides means for making System components (VR1) and/or (VR2) added to an ellipsometer or components (VR1) and/or (VR2) added to an ellipsometer or parent when desired, without removal thereof from said ellipsometer or polarimeter System

A cross-sectional controlled developmental study of neuropsychological functions in patients with glutaric aciduria type I

Background: Glutaric aciduria type I (GA-I) is an inherited metabolic disease due to deficiency of glutaryl-CoA dehydrogenase (GCDH). Cognitive functions are generally thought to be spared, but have not yet been studied in detail. Methods: Thirty patients detected by newborn screening (n = 13), high-risk screening (n = 3) or targeted metabolic testing (n = 14) were studied for simple reaction time (SRT), continuous performance (CP), visual working memory (VWM), visual-motor coordination (Tracking) and visual search (VS). Dystonia (n = 13 patients) was categorized using the Barry-Albright-Dystonia Scale (BADS). Patients were compared with 196 healthy controls. Developmental functions of cognitive performances were analysed using a negative exponential function model. Results: BADS scores correlated with speed tests but not with tests measuring stability or higher cognitive functions without time constraints. Developmental functions of GA-I patients significantly differed from controls for SRT and VS but not for VWM and showed obvious trends for CP and Tracking. Dystonic patients were slower in SRT and CP but reached their asymptote of performance similar to asymptomatic patients and controls in all tests. Asymptomatic patients did not differ from controls, except showing significantly better results in Tracking and a trend for slower reactions in visual search. Data across all age groups of patients and controls fitted well to a model of negative exponential development. Conclusions: Dystonic patients predominantly showed motor speed impairment, whereas performance improved with higher cognitive load. Patients without motor symptoms did not differ from controls. Developmental functions of cognitive performances were similar in patients and controls. Performance in tests with higher cognitive demand might be preserved in GA-I, even in patients with striatal degeneration

Atomistic simulations of self-trapped exciton formation in silicon nanostructures: The transition from quantum dots to nanowires

Using an approximate time-dependent density functional theory method, we calculate the absorption and luminescence spectra for hydrogen passivated silicon nanoscale structures with large aspect ratio. The effect of electron confinement in axial and radial directions is systematically investigated. Excited state relaxation leads to significant Stokes shifts for short nanorods with lengths less than 2 nm, but has little effect on the luminescence intensity. The formation of self-trapped excitons is likewise observed for short nanostructures only; longer wires exhibit fully delocalized excitons with neglible geometrical distortion at the excited state minimum.Comment: 10 pages, 4 figure

The i-process and CEMP-r/s stars

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. We investigate whether the anomalous elemental abundance patterns in some of the C-enhanced metal-poor-r/s (CEMP-r/s) stars are consistent with predictions of nucleosynthesis yields from the i-process, a neutron-capture regime at neutron densities intermediate between those typical for the slow (s) and rapid (r) processes. Conditions necessary for the i-process are expected to be met at multiple stellar sites, such as the He-core and He-shell flashes in low-metallicity low-mass stars, super-AGB and post-AGB stars, as well as low-metallicity massive stars. We have found that single-exposure one-zone simulations of the i-process reproduce the abundance patterns in some of the CEMP-r/s stars much better than the model that assumes a superposition of yields from s and r-process sources. Our previous study of nuclear data uncertainties relevant to the i-process revealed that they could have a significant impact on the i-process yields obtained in our idealized one-zone calculations, leading, for example, to ∼ 0:7dex uncertainty in our predicted [Ba/La] ratio. Recent 3D hydrodynamic simulations of convection driven by a He-shell flash in post-AGB Sakurai's object have discovered a new mode of non-radial instabilities: the Global Oscillation of Shell H-ingestion. This has demonstrated that spherically symmetric stellar evolution simulations cannot be used to accurately model physical conditions for the i-process

Isolated oxygen defects in 3C- and 4H-SiC: A theoretical study

Ab initio calculations in the local-density approximation have been carried out in SiC to determine the possible configurations of the isolated oxygen impurity. Equilibrium geometry and occupation levels were calculated. Substitutional oxygen in 3C-SiC is a relatively shallow effective mass like double donor on the carbon site (O-C) and a hyperdeep double donor on the Si site (O-Si). In 4H-SiC O-C is still a double donor but with a more localized electron state. In 3C-SiC O-C is substantially more stable under any condition than O-Si or interstitial oxygen (O-i). In 4H-SiC O-C is also the most stable one except for heavy n-type doping. We propose that O-C is at the core of the electrically active oxygen-related defect family found by deep level transient spectroscopy in 4H-SiC. The consequences of the site preference of oxygen on the SiC/SiO2 interface are discussed