10,944 research outputs found

    Limits on stable iron in Type\,Ia supernovae from NIR spectroscopy

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    We obtained optical and near-infrared spectra of Type\,Ia supernovae (SNe\,Ia) at epochs ranging from 224 to 496 days after the explosion. The spectra show emission lines from forbidden transitions of singly ionised iron and cobalt atoms. We used non-local thermodynamic equilibrium (NLTE) modelling of the first and second ionisation stages of iron, nickel, and cobalt to fit the spectra using a sampling algorithm allowing us to probe a broad parameter space. We derive velocity shifts, line widths, and abundance ratios for iron and cobalt. The measured line widths and velocity shifts of the singly ionised ions suggest a shared emitting region. Our data are fully compatible with radioactive 56^{56}Ni decay as the origin for cobalt and iron. We compare the measured abundance ratios of iron and cobalt to theoretical predictions of various SN\,Ia explosion models. These models include, in addition to 56^{56}Ni, different amounts of 57^{57}Ni and stable 54,56^{54,56}Fe. We can exclude models that produced only 54,56^{54,56}Fe or only 57^{57}Ni in addition to 56^{56}Ni. If we consider a model that has 56^{56}Ni, 57^{57}Ni, and 54,56^{54,56}Fe then our data imply that these ratios are 54,56^{54,56}Fe / 56^{56}Ni =0.272±0.086=0.272\pm0.086 and 57^{57}Ni / 56^{56}Ni =0.032±0.011=0.032\pm0.011.Comment: 10 pages, 7 figures, Accepted for publication in A&

    The Rising Light Curves of Type Ia Supernovae

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    We present an analysis of the early, rising light curves of 18 Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF) and the La Silla-QUEST variability survey (LSQ). We fit these early data flux using a simple power-law (f(t)=α×tn)(f(t) = {\alpha\times t^n}) to determine the time of first light (t0)({t_0}), and hence the rise-time (trise)({t_{rise}}) from first light to peak luminosity, and the exponent of the power-law rise (nn). We find a mean uncorrected rise time of 18.98±0.5418.98 {\pm} 0.54 days, with individual SN rise-times ranging from 15.9815.98 to 24.724.7 days. The exponent n shows significant departures from the simple 'fireball model' of n=2n = 2 (or f(t)t2{f(t) \propto t^2}) usually assumed in the literature. With a mean value of n=2.44±0.13n = 2.44 {\pm} 0.13, our data also show significant diversity from event to event. This deviation has implications for the distribution of 56Ni throughout the SN ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The range of n found also confirms that the 56Ni distribution is not standard throughout the population of SNe Ia, in agreement with earlier work measuring such abundances through spectral modelling. We also show that the duration of the very early light curve, before the luminosity has reached half of its maximal value, does not correlate with the light curve shape or stretch used to standardise SNe Ia in cosmological applications. This has implications for the cosmological fitting of SN Ia light curves.Comment: 19 pages, 19 figures, accepted for publication in MNRA

    Intercellular Interactions in PC12 Cells Overexpressing Beta/A4 Amyloid

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    The amyloid precursor protein (APP) is an integral membrane component of eukaryotic cells. A variety of research approaches have addressed the contribution of the β amyloid peptide region of the APP to neuritic plaque structure and formation in the Alzheimer disease brain as well as the relationship between β amyloid accumulation and the occurrence of dementia. However, there is limited information available concerning the cellular consequences of amyloid deposition. The present studies were undertaken to investigate the relationship between β amyloid and intercellular junctions. Transfected PC12 cell lines, that overexpress the β amyloid peptide, exhibit structural and functional alterations at the cell surface and tend to form aggregates more readily than normal control cells. Intermediate junctions were the most common intercellular interactions of both normal and transfected cells. However, the control and transfected cells differed since areas of continuous and extensive junctions were readily seen in transfected cells and infrequently seen in control cells. The data suggest that excess accumulation of β amyloid is associated with the junctional apparatus and may be related to increased intercellular adhesion

    Outcome following valve surgery in Australia: Development of an enhanced database module

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    Background: Valvular heart disease, including rheumatic heart disease (RHD), is an important cause of heart disease globally. Management of advanced disease can include surgery and other interventions to repair or replace affected valves. This article summarises the methodology of a study that will incorporate enhanced data collection systems to provide additional insights into treatment choice and outcome for advanced valvular disease including that due to RHD. Methods: An enhanced data collection system will be developed linking an existing Australian cardiac surgery registry to more detailed baseline co-morbidity, medication, echocardiographic and hospital separation data to identify predictors of morbidity and mortality outcome following valve surgery. Discussion: This project aims to collect and incorporate more detailed information regarding pre and postoperative factors and subsequent morbidity. We will use this to provide additional insights into treatment choice and outcome. © 2017 The Author(s)

    Autobiographical memory: A candidate latent vulnerability mechanism for psychiatric disorder following childhood maltreatment

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    BACKGROUND: Altered autobiographical memory (ABM) functioning has been implicated in the pathogenesis of depression and post-traumatic stress disorder and may represent one mechanism by which childhood maltreatment elevates psychiatric risk. AIMS: To investigate the impact of childhood maltreatment on ABM functioning. METHOD: Thirty-four children with documented maltreatment and 33 matched controls recalled specific ABMs in response to emotionally-valenced cue words during functional magnetic resonance imaging (fMRI). RESULTS: Children with maltreatment experience showed reduced hippocampal and increased middle temporal and para-hippocampal activation during positive ABM recall compared to peers. During negative ABM recall they exhibited increased amygdala activation, and greater amygdala connectivity with the salience network. CONCLUSIONS: Childhood maltreatment is associated with altered ABM functioning, specifically reduced activation in areas encoding specification of positive memories, and greater activation of the salience network for negative memories. This pattern may confer latent vulnerability to future depression and post-traumatic stress disorder

    CO_2 on Titan

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    A sharp stratospheric emission feature at 667 cm^(−1) in the Voyager infrared spectra of Titan is associated with the ν_2 Q branch of CO_2. A coupling of photochemical and radiative transfer theory yields an average mole fraction above the 110 mbar level of ƒCO_2 = 1.5 ± ^(1.5)_(0.8) x 10^(-9), with most of the uncertainty being due to imprecise knowledge of the vertical distribution. CO_2 is found to be in a steady state, with its abundance being regulated principally by the ∼72 K cold trap near the tropopause and secondarily by the rate at which water-bearing meteoritic material enters the top of the atmosphere. An influx of water about 0.4 times that at the top of the terrestrial atmosphere is consistent with a combination of the observed CO_2 abundance and a steady state CO mole fraction of 1.1×10^(−4); the theoretical value for CO is close to the value observed by Lutz et al. (1983), although there are large margins for error in both numbers. If steady state conditions for CO prevail, little information is available regarding the evolution of Titan's atmosphere
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