11,411 research outputs found

    Metallicity Effect on LMXB Formation in Globular Clusters

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    We present comprehensive observational results of the metallicity effect on the fraction of globular clusters (GC) that contain low-mass X-ray binaries (LMXB), by utilizing all available data obtained with Chandra for LMXBs and HST ACS for GCs. Our primary sample consists of old elliptical galaxies selected from the ACS Virgo and Fornax surveys. To improve statistics at both the lowest and highest X-ray luminosity, we also use previously reported results from other galaxies. It is well known that the LMXB fraction is considerably higher in red, metal-rich, than in blue, metal-poor GCs. In this paper, we test whether this metallicity effect is X-ray luminosity-dependent, and find that the effect holds uniformly in a wide luminosity range. This result is statistically significant (at >= 3 sigma) in LMXBs with luminosities in the range LX = 2 x 10^37 - 5 x 10^38 erg s-1, where the ratio of LMXB fractions in metal-rich to metal-poor GCs is R = 3.4 +- 0.5. A similar ratio is also found at lower (down to 10^36 erg s-1) and higher luminosities (up to the ULX regime), but with less significance (~2 sigma confidence). Because different types of LMXBs dominate in different luminosities, our finding requires a new explanation for the metallicity effect in dynamically formed LMXBs. We confirm that the metallicity effect is not affected by other factors such as stellar age, GC mass, stellar encounter rate, and galacto-centric distance.Comment: 21 pages, 5 figures, accepted in Ap

    Mobile moralities: ethical consumption in the digital realm

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    Ethical consumption, as a realm of production and exchange, as a framework for purchasing decisions and as political activism, is now well established in a range of nations. As a politics, it points to an interconnected but divergent set of concerns centred on issues of environmental sustainability, local and global economic and social justice, and community and individual wellbeing. While the subject of sustained critique, not least because of its apparent privileging of ‘the consumer’ as the locus of change, ethical consumption has garnered increasing attention. This is most recently evident in the development and widening use of ‘ethical consumption apps’ for mobile devices. These apps allow the user to both access ethical information on products and, potentially, to connect with a broader politics of consumption. However, in entering the digital realm ethical consumption also becomes embroiled in the complexities of digital technocultures and their ability to allow users of apps to be connected to each other, potentially building communities of interest and/or activism. This paper explores this emerging intersection of the ethical and the digital. It examines, in particular, whether such digital affordances affect the way ethical consumption itself may be conceived and pursued. Does the ethical consumption app work to collectivise or individualise, help to focus or fragment, speak of timidity or potential in relation to an oppositional politics of consumption? In confronting these issues, this paper suggests that contemporary ethical consumption apps – while full of political potential – remain problematic in that the turn to the digital has tended, so far, to accentuate the already individualising tendencies within a politics of ethical consumption. This speaks also, however, to a similar problematic in the politics of digital technocultures; the use of the digital does not automatically enable - merely through greater connectivity and information availability – forms of radical politics

    Birds of Freedom? Perspectives on Female Emancipation and Sri Lanka’s Liberation Tigers of Tamil Eelam

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    Over the last decade, females have been an integral part of fighting forces in both international conflicts and in armed struggle in at least 38 internal conflicts. While some scholars argue that recent wars have thrust women into new roles, enabling them to transform their social situations, identities and destinies, others question whether females achieve ‘emancipation’ through active participation in warfare. The Liberation Tigers of Tamil Eelam (LTTE) in Sri Lanka that has been engaged in conflict with the Sri Lankan government since 1983, and actively recruits female cadres, provides an interesting context to explore issues of female empowerment in the context of armed struggle. Drawing from interviews with four Sri Lankans living in Canada, this paper traces the perceived extent of female emancipation within the LTTE. While the participation of females in unconventional military roles represents a drastic change in behavior expected of Tamil women, the militant movement appears to reinforce existing patterns of gender constructions, ultimately impeding the attainment of meaningful empowerment for females

    Effect of magnetic Gd impurities on the superconducting state of amorphous Mo-Ge thin films with different thickness and morphology

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    pre-printWe studied the effect of magnetic doping with Gd atoms on the superconducting properties of amorphous Mo70Ge30 films. We observed that in uniform films deposited on amorphous Ge, the pair-breaking strength per impurity strongly decreases with film thickness initially and saturates at a finite value in films with thickness below the spin-orbit scattering length. The variation is likely caused by surface-induced magnetic anisotropy and is consistent with the fermionic mechanism of superconductivity suppression. In thin films deposited on SiN the pair-breaking strength becomes zero. Possible reasons for this anomalous response are discussed. The morphological distinctions between the films of the two types were identified using atomic force microscopy with a carbon nanotube tip

    Surface Modification of Melt Extruded Poly(ε-caprolactone) Nanofibers: Toward a New Scalable Biomaterial Scaffold.

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    A photochemical modification of melt-extruded polymeric nanofibers is described. A bioorthogonal functional group is used to decorate fibers made exclusively from commodity polymers, covalently attach fluorophores and peptides, and direct cell growth. Our process begins by using a layered coextrusion method, where poly(ε-caprolactone) (PCL) nanofibers are incorporated within a macroscopic poly(ethylene oxide) (PEO) tape through a series of die multipliers within the extrusion line. The PEO layer is then removed with a water wash to yield rectangular PCL nanofibers with controlled cross-sectional dimensions. The fibers can be subsequently modified using photochemistry to yield a "clickable" handle for performing the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction on their surface. We have attached fluorophores, which exhibit dense surface coverage when using ligand-accelerated CuAAC reaction conditions. In addition, an RGD peptide motif was coupled to the surface of the fibers. Subsequent cell-based studies have shown that the RGD peptide is biologically accessible at the surface, leading to increased cellular adhesion and spreading versus PCL control surfaces. This functionalized coextruded fiber has the advantages of modularity and scalability, opening a potentially new avenue for biomaterials fabrication

    IR-Level Versus Machine-Level If-Conversion for Predicated Architectures

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    If-conversion is a simple yet powerful optimization that converts control dependences into data dependences. It allows elimination of branches and increases available instruction level parallelism and thus overall performance. If-conversion can either be applied alone or in combination with other techniques that increase the size of scheduling regions. The presence of hardware support for predicated execution allows if-conversion to be broadly applied in a given program. This makes it necessary to guide the optimization using heuristic estimates regarding its potential benefit. Similar to other transformations in an optimizing compiler, if-conversion inherently su↵ers from phase ordering issues. Driven by these facts, we developed two algorithms for if-conversion targeting the TI TMS320C64x+ architecture within the LLVM framework. Each implementation targets a di↵erent level of code abstraction. While one targets the intermediate representation, the other addresses machine-level code. Both make use of an adapted set of estimation heuristics and prove to be successful in general, but each one exhibits di↵erent strengths and weaknesses. High-level if-conversion, applied before other control flow transformations, has more freedom to operate. But in contrast to its machine-level counterpart, which is more restricted, its estimations of runtime are less accurate. Our results from experimental evaluation show a mean speedup close to 14 % for both algorithms on a set of programs from the MiBench and DSPstone benchmark suites. We give a comparison of the implemented optimizations and discuss gained insights on the topics of ifconversion, phase ordering issues and profitability analysis
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