13,598 research outputs found

    Systematic Blueshift of Line Profiles in the Type IIn Supernova 2010jl: Evidence for Post-Shock Dust Formation?

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    Type IIn SNe show spectral evidence for strong interaction between their blast wave and dense circumstellar material (CSM) around the progenitor star. SN2010jl was the brightest core-collapse SN in 2010, and it was a Type IIn explosion with strong CSM interaction. Andrews et al. recently reported evidence for an IR excess in SN2010jl, indicating either new dust formation or the heating of CSM dust in an IR echo. Here we report multi-epoch spectra of SN2010jl that reveal the tell-tale signature of new dust formation: emission-line profiles becoming systematically more blueshifted as the red side of the line is blocked by increasing extinction. The effect is seen clearly in the intermediate-width (400--4000 km/s) component of Hα\alpha beginning roughly 30d after explosion. Moreover, we present near-IR spectra demonstrating that the asymmetry in the hydrogen-line profiles is wavelength dependent, appearing more pronounced at shorter wavelengths. This evidence suggests that new dust grains had formed quickly in the post-shock shell of SN 2010jl arising from CSM interaction. Since the observed dust temperature has been attributed to an IR echo and not to new dust, either (1) IR excess emission at λ<5Ό\lambda < 5 \mum is not a particularly sensitive tracer of new dust formation in SNe, or (2) some assumptions about expected dust temperatures might require further study. Lastly, we discuss one possible mechanism other than dust that might lead to increasingly blueshifted line profiles in SNeIIn, although the wavelength dependence of the asymmetry argues against this hypothesis in the case of SN2010jl.Comment: 6 pages, 4 figures, submitted to A

    Students on the Edge: Evaluating an Academic Support Group

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    This qualitative case study evaluated the effectiveness of the Academic Skills Discussion Group, a new retention intervention targeting undergraduate students on academic probation. This intervention utilized a support group structure to provide social and academic supports to academically-poor students. These supports incorporated didactic educational presentations and interpersonal discussions relating to life change and college expectations. The case comprised one pilot administration of the intervention for three student group members. Data was collected from pre/post-intervention resiliency surveys, grade point average comparisons, journal-entry analysis and semi-structured exit interviews. The researcher conducted inductive data analysis by coding participant statements for meaning, calculating and comparing survey results, and triangulating findings. Analysis provided case descriptions and themes regarding how participating in the intervention influenced students’ resiliency, adjustment, and academic performance. Findings indicate that for most students, participation in the program coincided with improved academic performance and increased connectivity to the academic environment. Evaluative descriptions break down the recruitment strategy, examine benefits of participation and address future enhancements to the delivery of the intervention. Implications for higher education applications and future use of small group interventions are discussed

    Cessation of X-ray Pulsation of GX 1+4

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    We report results from our weekly monitoring campaign on the X-ray pulsar GX 1+4 with the {\em Rossi X-ray Timing Explorer} satellite. The spin-down trend of GX 1+4 was continuing, with the pulsar being at its longest period ever measured (about 138.7 s). At the late stage of the campaign, the source entered an extended faint state, when its X-ray (2-60 keV) flux decreased significantly to an average level of ∌3×10−10ergscm−2s−1\sim 3 \times 10^{-10} ergs cm^{-2} s^{-1}. It was highly variable in the faint state; the flux dropped to as low as ∌3×10−11ergscm−2s−1\sim 3 \times 10^{-11} ergs cm^{-2} s^{-1}. In several observations during this period, the X-ray pulsation became undetectable. We can, therefore, conclude conservatively that the pulsed fraction, which is normally ≳\gtrsim 70% (peak-to-peak), must have decreased drastically in those cases. This is very similar to what was observed of GX 1+4 in 1996 when it became similarly faint in X-ray. In fact, the flux at which the cessation of X-ray pulsation first occurred is nearly the same as it was in 1996. We suggest that we have, once again, observed the propeller effect in GX 1+4, a phenomenon that is predicted by theoretical models of accreting X-ray pulsars.Comment: 13 pages, 9 figures (available at http://www.physics.purdue.edu/~cui/ftp/cuifigs.tar.gz). To appear in Ap

    It’s Part-Time but Still Not as We Know it!” – A Further Evaluation of a Flexible Learning MEng

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    This paper reports on the evaluation of the effectiveness of delivery of a flexible learning MEng (Hons) Engineering course at Bournemouth University (BU) and its integration with level 3, 4 & 5 courses delivered at a local Further Education College. The research aims to improve the delivery of the MEng programme by better understanding the effectiveness of operation over the 3 academic cycles now operated for this programme. The course was developed as part of an HESTEM National Programme project and provides an opportunity for engineers to take higher education qualifications while remaining in full time employment. The evaluation takes the perspective of both academics and students. The underlying pedagogy of the programme has been based on the Constructivist approach to learning delivered via blended learning. The paper evaluates how the use of both staff/student and student/student online forums, were modified and how the face to face tutorials on campus became the important mode of delivery. The paper discusses the challenges students’ and academics found in moving from a ‘day-release’ mode of learning to a virtual environment and from Further to Higher Education and explores the now integrated nature of the programme

    Food-Borne Chemical Carcinogens and the Evidence for Human Cancer Risk

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    Commonly consumed foods and beverages can contain chemicals with reported carcinogenic activity in rodent models. Moreover, exposures to some of these substances have been associated with increased cancer risks in humans. Food-borne carcinogens span a range of chemical classes and can arise from natural or anthropogenic sources, as well as form endogenously. Important considerations include the mechanism(s) of action (MoA), their relevance to human biology, and the level of exposure in diet. The MoAs of carcinogens have been classified as either DNA-reactive (genotoxic), involving covalent reaction with nuclear DNA, or epigenetic, involving molecular and cellular effects other than DNA reactivity. Carcinogens are generally present in food at low levels, resulting in low daily intakes, although there are some exceptions. Carcinogens of the DNA-reactive type produce effects at lower dosages than epigenetic carcinogens. Several food-related DNA-reactive carcinogens, including aflatoxins, aristolochic acid, benzene, benzo[a]pyrene and ethylene oxide, are recognized by the International Agency for Research on Cancer (IARC) as causes of human cancer. Of the epigenetic type, the only carcinogen considered to be associated with increased cancer in humans, although not from low-level food exposure, is dioxin (TCDD). Thus, DNA-reactive carcinogens in food represent a much greater risk than epigenetic carcinogens

    Strong exciton-photon coupling with colloidal nanoplatelets in an open microcavity

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    Colloidal semiconductor nanoplatelets exhibit quantum size effects due to their thickness of only few monolayers, together with strong optical band-edge transitions facilitated by large lateral extensions. In this article we demonstrate room temperature strong coupling of the light and heavy hole exciton transitions of CdSe nanoplatelets with the photonic modes of an open planar microcavity. Vacuum Rabi splittings of 66±166 \pm 1 meV and 58±158 \pm 1 meV are observed for the heavy and light hole excitons respectively, together with a polariton-mediated hybridisation of both transitions. By measuring the concentration of platelets in the film we compute the transition dipole moment of a nanoplatelet exciton to be Ό=(575±110)\mu = (575 \pm 110) D. The large oscillator strength and fluorescence quantum yield of semiconductor nanoplatelets provide a perspective towards novel photonic devices, combining polaritonic and spinoptronic effects.Comment: 9 pages, 4 figure
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