273 research outputs found

    A high-order finite volume method for Maxwell's equations in heterogeneous and time-varying media

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    We develop a finite volume method for Maxwell's equations in materials whose electromagnetic properties vary in space and time. We investigate both conservative and non-conservative numerical formulations. High-order methods accurately resolve fine structures that develop due to the varying material properties. Numerical examples demonstrate the effectiveness of the proposed method in handling temporal variation and its efficiency relative to traditional 2nd-order FDTD.Comment: 15 pages, 8 figure

    Newly Identified Star Clusters in M33. III. Structural Parameters

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    We present the morphological properties of 161 star clusters in M33 using the Advanced Camera For Surveys Wide Field Channel onboard the Hubble Space Telescope using observations with the F606W and F814W filters. We obtain, for the first time, ellipticities, position angles, and surface brightness profiles for a significant number of clusters. On average, M33 clusters are more flattened than those of the Milky Way and M31, and more similar to clusters in the Small Magellanic Cloud. The ellipticities do not show any correlation with age or mass, suggesting that rotation is not the main cause of elongation in the M33 clusters. The position angles of the clusters show a bimodality with a strong peak perpendicular to the position angle of the galaxy major axis. These results support the notion that tidal forces are the reason for the cluster flattening. We fit King and EFF models to the surface brightness profiles and derive structural parameters including core radii, concentration, half-light radii and central surface brightness for both filters. The surface brightness profiles of a significant number of clusters show irregularities such as bumps and dips. Young clusters (Log age < 8) are notably better fitted by models with no radial truncation (EFF models), while older clusters show no significant differences between King or EFF fits. M33 star clusters seem to have smaller sizes, smaller concentrations, and smaller central surface brightness as compared to clusters in the MW, M31, LMC and SMC. Analysis of the structural parameters presents a age-radius relation also detected in other star cluster systems. The overall analysis shows differences in the structural evolution between the M33 cluster system and cluster systems in nearby galaxies. These differences could have been caused by the strong differences in these various environments.Comment: 30 pages, 12 figures, accepted for publication in MNRA

    Testing the chemical tagging technique with open clusters

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    Context. Stars are born together from giant molecular clouds and, if we assume that the priors were chemically homogeneous and well-mixed, we expect them to share the same chemical composition. Most of the stellar aggregates are disrupted while orbiting the Galaxy and most of the dynamic information is lost, thus the only possibility of reconstructing the stellar formation history is to analyze the chemical abundances that we observe today. Aims. The chemical tagging technique aims to recover disrupted stellar clusters based merely on their chemical composition. We evaluate the viability of this technique to recover co-natal stars that are no longer gravitationally bound. Methods. Open clusters are co-natal aggregates that have managed to survive together. We compiled stellar spectra from 31 old and intermediate-age open clusters, homogeneously derived atmospheric parameters, and 17 abundance species, and applied machine learning algorithms to group the stars based on their chemical composition. This approach allows us to evaluate the viability and efficiency of the chemical tagging technique. Results. We found that stars at different evolutionary stages have distinct chemical patterns that may be due to NLTE effects, atomic diffusion, mixing, and biases. When separating stars into dwarfs and giants, we observed that a few open clusters show distinct chemical signatures while the majority show a high degree of overlap. This limits the recovery of co-natal aggregates by applying the chemical tagging technique. Nevertheless, there is room for improvement if more elements are included and models are improved.Comment: accepted for publication in Astronomy and Astrophysics. Corrected typo

    Bringing research alive through stories: reflecting on research storytelling as a public engagement method

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    Stories are vital in making sense of our lives – and research. Consequently, 12 researchers from the University of Sheffield underwent a three-month training process from September to November 2019 to learn how to shape their research experiences into accessible, ten-minute, spoken stories. This culminated in a storytelling evening as part of the Economic and Social Research Council’s Festival of Social Science, at which researchers from different disciplines discussed various nature–society dynamics in diverse field sites in the Global South. By reflecting on the training process and the performance through qualitative interviews with storytellers and audience members, our study answers the research question: What lessons emerge from an interdisciplinary group of researchers engaging with research storytelling for public engagement? Our study addresses gaps in the literature by focusing on interdisciplinary research storytelling, spoken ten-minute stories, bringing together storytellers’ and audience’s viewpoints, and providing practical recommendations for researchers and practitioners. We argue that research storytelling can have diverse benefits for both researchers and listeners by promoting learning in an accessible format, boosting self-confidence and helping (un/re)learn scholarly communication. However, professional guidance and peer support, as well as ethical sensitivity, are crucial

    Total Degree Formula for the Generic Offset to a Parametric Surface

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    We provide a resultant-based formula for the total degree w.r.t. the spatial variables of the generic offset to a parametric surface. The parametrization of the surface is not assumed to be proper.Comment: Preprint of an article to be published at the International Journal of Algebra and Computation, World Scientific Publishing, DOI:10.1142/S021819671100680

    Stellar populations of galaxies in the ALHAMBRA survey up to z∌1z \sim 1. II. Stellar content of quiescent galaxies within the dust-corrected stellar mass−-colour and the UVJUVJ colour−-colour diagrams

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    Our aim is to determine the distribution of stellar population parameters (extinction, age, metallicity, and star formation rate) of quiescent galaxies within the rest-frame stellar mass−-colour and UVJUVJ colour−-colour diagrams corrected for extinction up to z∌1z\sim1. These novel diagrams reduce the contamination in samples of quiescent galaxies owing to dust-reddened galaxies, and they provide useful constraints on stellar population parameters. We set constraints on the stellar population parameters of quiescent galaxies combining the ALHAMBRA multi-filter photo-spectra with our SED-fitting code MUFFIT, making use of composite stellar population models. The extinction obtained by MUFFIT allowed us to remove dusty star-forming (DSF) galaxies from the sample of red UVJUVJ galaxies. The distributions of stellar population parameters across these rest-frame diagrams are revealed after the dust correction and are fitted by the LOESS method to reduce uncertainty effects. Quiescent galaxy samples defined via classical UVJUVJ diagrams are typically contaminated by a ∌20\sim20% fraction of DSF galaxies. A significant part of the galaxies in the green valley are actually obscured star-forming galaxies (∌30−65\sim30-65%). Consequently, the transition of galaxies from the blue cloud to the red sequence, and hence the related mechanisms for quenching, seems to be much more efficient and faster than previously reported. The rest-frame stellar mass−-colour and UVJUVJ colour−-colour diagrams are useful for constraining the age, metallicity, extinction, and star formation rate of quiescent galaxies by only their redshift, rest-frame colours, and/or stellar mass. Dust correction plays an important role in understanding how quiescent galaxies are distributed in these diagrams and is key to performing a pure selection of quiescent galaxies via intrinsic colours.Comment: (37 pages, 29 figures, accepted for publication in A&A

    The Gaia-ESO Survey: Detailed Abundances in the Metal-poor Globular Cluster NGC 4372

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    We present the abundance analysis for a sample of 7 red giant branch stars in the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part of the Gaia-ESO Survey. This is the first extensive study of this cluster from high resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = -2.19 ±\pm 0.03 and find no evidence for a metallicity spread. This metallicity makes NGC 4372 one of the most metal-poor galactic globular clusters. We also find an {\alpha}-enhancement typical of halo globular clusters at this metallicity. Significant spreads are observed in the abundances of light elements. In particular we find a Na-O anti-correlation. Abundances of O are relatively high compared with other globular clusters. This could indicate that NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al spread is also present which spans a range of more than 0.5 dex in Al abundances. Na is correlated with Al and Mg abundances at a lower significance level. This pattern suggests that the Mg-Al burning cycle is active. This behavior can also be seen in giant stars of other massive, metal-poor clusters. A relation between light and heavy s-process elements has been identified.Comment: 14 pages, 14 figures, accepted for publication in A&

    BCR-ABL1-induced expression of HSPA8 promotes cell survival in chronic myeloid leukaemia

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    In order to determine new signal transduction pathways implicated in chronic myeloid leukaemia (CML), we performed a gene expression profile comparison between CD34+ cells from CML patients and healthy donors. Functional studies were performed using the Mo7e and Mo7e-p210 cell lines. Expression of CCND1 (Cyclin D1), as well as the chaperone HSPA8, which is important for regulation of CCND1, were significantly upregulated in CD34+ CML cells. Upregulation of HSPA8 was dependent, at least in part, on STAT5 (signal transducer and activator of transcrition 5)-dependent transcriptional activation, as demonstrated by chromatin immunoprecipitation. The presence of HSPA8 in the nuclear protein fraction as well as its binding to CCND1 suggests that it may contribute to stabilization of the CCND1/CDK4 complex, which, in turn, may participate in proliferation of CML cells. Treatment of CML cells with the specific HSPA8 inhibitor 15-deoxyspergualin induced inhibition of CML cell viability but did not induce apoptosis. In conclusion, our studies suggest that STAT5-mediated activation of HSPA8 induces nuclear translocation and activation of the CCND1/CDK4 complex leading to increased proliferation of CML cells, deciphering a new pathway implicated in CML and supporting a potential role of chaperone inhibitors in the treatment of CML

    Down-Regulation of hsa-miR-10a in Chronic Myeloid Leukemia CD34+ Cells Increases USF2-Mediated Cell Growth

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    MicroRNAs (miRNA) are small noncoding, single-stranded RNAs that inhibit gene expression at a posttranscriptional level, whose abnormal expression has been described in different tumors. The aim of our study was to identify miRNAs potentially implicated in chronic myeloid leukemia (CML). We detected an abnormal miRNA expression profile in mononuclear and CD34+ cells from patients with CML compared with healthy controls. Of 157 miRNAs tested, hsa-miR-10a, hsa-miR-150, and hsa-miR-151 were down-regulated, whereas hsa-miR-96 was up-regulated in CML cells. Down-regulation of hsa-miR-10a was not dependent on BCR-ABL1 activity and contributed to the increased cell growth of CML cells. We identified the upstream stimulatory factor 2 (USF2) as a potential target of hsa-miR-10a and showed that overexpression of USF2 also increases cell growth. The clinical relevance of these findings was shown in a group of 85 newly diagnosed patients with CML in which expression of hsa-miR-10a was down-regulated in 71% of the patients, whereas expression of USF2 was up-regulated in 60% of the CML patients, with overexpression of USF2 being significantly associated with decreased expression of hsa-miR-10a (P = 0.004). Our results indicate that down-regulation of hsa-miR-10a may increase USF2 and contribute to the increase in cell proliferation of CML implicating a miRNA in the abnormal behavior of CML
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