3,229 research outputs found

    Life Products of Stars

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    We attempt to document complete energetic transactions of stars in their life. We calculate photon and neutrino energies that are produced from stars in their each phase of evolution from 1 to 8 M_sun, using the state-of-the-art stellar evolution code, tracing the evolution continuously from pre-main sequence gravitational contraction to white dwarfs. We also catalogue gravitational and thermal energies and helium, and heavier elements that are stored in stars and those ejected into interstellar space in each evolutionary phase.Comment: 26 pages, including 8 figures and 3 tables. Submitted to ApJ

    The s-Process in Rotating Asymptotic Giant Branch Stars

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    (abridged) We model the nucleosynthesis during the thermal pulse phase of a rotating, solar metallicity AGB star of 3M_sun. Rotationally induced mixing during the thermal pulses produces a layer (~2E-5M_sun) on top of the CO-core where large amounts of protons and C12 co-exist. We follow the abundance evolution in this layer, in particular that of the neutron source C13 and of the neutron poison N14. In our AGB model mixing persists during the entire interpulse phase due to the steep angular velocity gradient at the core-envelope interface. We follow the neutron production during the interpulse phase, and find a resulting maximum neutron exposure of tau_max =0.04 mbarn^-1, which is too small to produce any significant s-process. In parametric models, we then investigate the combined effects of diffusive overshooting from the convective envelope and rotationally induced mixing. Models with overshoot and weaker interpulse mixing - as perhaps expected from more slowly rotating stars - yield larger neutron exposures. We conclude that the incorporation of rotationally induce mixing processes has important consequences for the production of heavy elements in AGB stars. Through a distribution of initial rotation rates it may lead to a natural spread in the neutron exposures obtained in AGB stars of a given mass - as appears to be required by observations. Our results suggest that both processes, diffusive overshoot and rotational mixing, may be required to obtain a consistent description of the s-process in AGB stars which fulfils all observational constraints. Finally, we find that mixing due to rotation within our current framework does increase the production of N15 in the partial mixing zone, however still falling short of what seems required by observations.Comment: 50 pages, 13 figures, ApJ in press, tentatively scheduled for v593 n2 August 20, 200

    Modeling lithium rich carbon stars in the Large Magellanic Cloud: an independent distance indicator ?

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    We present the first quantitative results explaining the presence in the Large Magellanic Cloud of some asymptotic giant branch stars that share the properties of lithium rich carbon stars. A self-consistent description of time-dependent mixing, overshooting, and nuclear burning was required. We identify a narrow range of masses and luminosities for this peculiar stars. Comparison of these models with the luminosities of the few Li-rich C stars in the Large Magellanic Cloud provides an independent distance indicator for the LMCComment: 7 pages, 2 figure

    Large-scale literature mining to assess the relation between anti-cancer drugs and cancer types

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    Background:There is a huge body of scientific literature describing the relation between tumor types and anti-cancer drugs. The vast amount of scientific literature makes it impossible for researchers and physicians to extract all relevant information manually.Methods:In order to cope with the large amount of literature we applied an automated text mining approach to assess the relations between 30 most frequent cancer types and 270 anti-cancer drugs. We applied two different approaches, a classical text mining based on named entity recognition and an AI-based approach employing word embeddings. The consistency of literature mining results was validated with 3 independent methods: first, using data from FDA approvals, second, using experimentally measured IC-50 cell line data and third, using clinical patient survival data.Results:We demonstrated that the automated text mining was able to successfully assess the relation between cancer types and anti-cancer drugs. All validation methods showed a good correspondence between the results from literature mining and independent confirmatory approaches. The relation between most frequent cancer types and drugs employed for their treatment were visualized in a large heatmap. All results are accessible in an interactive web-based knowledge base using the following link: https://knowledgebase.microdiscovery.de/heatmap.Conclusions:Our approach is able to assess the relations between compounds and cancer types in an automated manner. Both, cancer types and compounds could be grouped into different clusters. Researchers can use the inter-active knowledge base to inspect the presented results and follow their own research questions, for example the identification of novel indication areas for known drugs

    Transcranial magnetic stimulation in depression--lessons from the multicentre trials

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    Looking at novelties and advances in medicine in particular in the treatment of major depressive disorder no principally new antidepressant treatment strategy has been established in clinical routine in the last fifty years. However, regarding the considerable issue of treatment resistance in depression, new therapeutic strategies are urgently required. In this context, repetitive transcranial magnetic stimulation above the dorsolateral prefrontal cortex has been proposed as a potential new treatment option for depression; furthermore, in October 2008 a first rTMS-device (NeuroStar TMS Therapy Systemℱ) was approved by the FDA for the treatment of treatment resistant major refractory depression in adults. Yet, despite now nearly two decades of research in this field, no final answer concerning its validity for antidepressant treatment in the clinical practice is given. Numerous studies with small sample sizes and heterogeneous designs have been performed in this field yielding to different results. These were subjected to meta-analyses, assessing the antidepressant effect of rTMS, which are briefly summarized in this article. Further, multicentre-trials with larger numbers of patients were performed, which are presented and critically discussed here in more detail. This short review shall thus provide an overview of the current status of knowledge concerning rTMS in depression and it also provides some recommendations for future research in this field

    Revealing the mid-infrared emission structure of IRAS 16594-4656 and IRAS 07027-7934

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    TIMMI2 diffraction-limited mid-infrared images of a multipolar proto-planetary nebula IRAS 16594-4656 and a young [WC] elliptical planetary nebula IRAS 07027-7934 are presented. Their dust shells are for the first time resolved (only marginally in the case of IRAS 07027-7934) by applying the Lucy-Richardson deconvolution algorithm to the data, taken under exceptionally good seeing conditions (<0.5"). IRAS 16594-4656 exhibits a two-peaked morphology at 8.6, 11.5 and 11.7 microns which is mainly attributed to emission from PAHs. Our observations suggest that the central star is surrounded by a toroidal structure observed edge-on with a radius of 0.4" (~640 AU at an assumed distance of 1.6 kpc) with its polar axis at P.A.~80 degrees, coincident with the orientation defined by only one of the bipolar outflows identified in the HST optical images. We suggest that the material expelled from the central source is currently being collimated in this direction and that the multiple outflow formation has not been coeval. IRAS 07027-7934 shows a bright, marginally extended emission (FWHM=0.3") in the mid-infrared with a slightly elongated shape along the N-S direction, consistent with the morphology detected by HST in the near-infrared. The mid-infrared emission is interpreted as the result of the combined contribution of small, highly ionized PAHs and relatively hot dust continuum. We propose that IRAS 07027-7934 may have recently experienced a thermal pulse (likely at the end of the AGB) which has produced a radical change in the chemistry of its central star.Comment: 35 pages, 8 figures (figures 1, 2, 4 and 6 are in low resolution) accepted for publication in Ap

    Evolution and Nucleosynthesis of Zero Metal Intermediate Mass Stars

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    New stellar models with mass ranging between 4 and 8 Mo, Z=0 and Y=0.23 are presented. The models have been evolved from the pre Main Sequence up to the Asymptotic Giant Branch (AGB). At variance with previous claims, we find that these updated stellar models do experience thermal pulses in the AGB phase. In particular we show that: a) in models with mass larger than 6 Mo, the second dredge up is able to raise the CNO abundance in the envelope enough to allow a "normal" AGB evolution, in the sense that the thermal pulses and the third dredge up settle on; b) in models of lower mass, the efficiency of the CNO cycle in the H-burning shell is controlled by the carbon produced locally via the 3alpha reactions. Nevertheless the He-burning shell becomes thermally unstable after the early AGB. The expansion of the overlying layers induced by these weak He-shell flashes is not sufficient by itself to allow a deep penetration of the convective envelope. However, immediately after that, the maximum luminosity of the He flash is attained and a convective shell systematically forms at the base of the H-rich envelope. The innermost part of this convective shell probably overlaps the underlying C-rich region left by the inter-shell convection during the thermal pulse, so that fresh carbon is dredged up in a "hot" H-rich environment and a H flash occurs. This flash favours the expansion of the outermost layers already started by the weak thermal pulse and a deeper penetration of the convective envelope takes place. Then, the carbon abundance in the envelope rises to a level high enough that the further evolution of these models closely resembles that of more metal rich AGB stars. These stars provide an important source of primary carbon and nitrogen.Comment: 28 pages, 5 tables and 17 figures. Accepted for publication in Ap

    Matching anticancer compounds and tumor cell lines by neural networks with ranking loss

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    Computational drug sensitivity models have the potential to improve therapeutic outcomes by identifying targeted drug components that are likely to achieve the highest efficacy for a cancer cell line at hand at a therapeutic dose. State of the art drug sensitivity models use regression techniques to predict the inhibitory concentration of a drug for a tumor cell line. This regression objective is not directly aligned with either of these principal goals of drug sensitivity models: We argue that drug sensitivity modeling should be seen as a ranking problem with an optimization criterion that quantifies a drug’s inhibitory capacity for the cancer cell line at hand relative to its toxicity for healthy cells. We derive an extension to the well-established drug sensitivity regression model PaccMann that employs a ranking loss and focuses on the ratio of inhibitory concentration and therapeutic dosage range. We find that the ranking extension significantly enhances the model’s capability to identify the most effective anticancer drugs for unseen tumor cell profiles based in on in-vitro data

    The Three-Dimensional Mass Distribution in NGC 1700

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    A variety of modeling techniques is used with surface photometry from the literature and recently acquired high-accuracy stellar kinematic data to constrain the three-dimensional mass distribution in the luminous cuspy elliptical galaxy NGC 1700. First, we model the radial velocity field and photometry, and, using a Bayesian technique, estimate the triaxiality T and short-to-long axis ratio c in five concentric annuli between approximately 1 and 3 effective radii. The results are completely consistent with T being constant inside about 2.5 r_e (36 arcsec; 6.7/h kpc). Adding an assumption of constant T as prior information gives an upper limit of T < 0.16 (95% confidence); this relaxes to T < 0.22 if it is also assumed that there is perfect alignment between the angular momentum and the galaxy's intrinsic short axis. Near axisymmetry permits us then to use axisymmetric models to constrain the radial mass profile. Using the Jeans (moment) equations, we demonstrate that 2-integral, constant-M/L models cannot fit the data; but a 2-integral model in which the cumulative enclosed M/L increases by a factor of roughly 2 from the center out to 12/h kpc can. Three-integral models constructed by quadratic programming show that, in fact, no constant-M/L model is consistent with the kinematics. Anisotropic 3-integral models with variable M/L, while not uniquely establishing a minimum acceptable halo mass, imply, as do the moment models, a cumulative M/L_B approximately 10 h at 12/h kpc. We conclude that NGC 1700 represents the best stellar dynamical evidence to date for dark matter in elliptical galaxies.Comment: 26 pages, Latex, AASTeX v4.0, with 11 eps figures. To appear in The Astronomical Journal, January 1999. Figures 1 and 3 are color but are readable in b/
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