12,877 research outputs found

    On the Brauer groups of symmetries of abelian Dijkgraaf-Witten theories

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    Symmetries of three-dimensional topological field theories are naturally defined in terms of invertible topological surface defects. Symmetry groups are thus Brauer-Picard groups. We present a gauge theoretic realization of all symmetries of abelian Dijkgraaf-Witten theories. The symmetry group for a Dijkgraaf-Witten theory with gauge group a finite abelian group AA, and with vanishing 3-cocycle, is generated by group automorphisms of AA, by automorphisms of the trivial Chern-Simons 2-gerbe on the stack of AA-bundles, and by partial e-m dualities. We show that transmission functors naturally extracted from extended topological field theories with surface defects give a physical realization of the bijection between invertible bimodule categories of a fusion category and braided auto-equivalences of its Drinfeld center. The latter provides the labels for bulk Wilson lines; it follows that a symmetry is completely characterized by its action on bulk Wilson lines.Comment: 21 pages, 9 figures. v2: Minor changes, typos corrected and references added. v3: Typos correcte

    Optical Identification of He White Dwarfs Orbiting Four Millisecond Pulsars in the Globular Cluster 47 Tucanae

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    We used ultra-deep UV observations obtained with the Hubble Space Telescope to search for optical companions to binary millisecond pulsars (MSPs) in the globular cluster 47 Tucanae. We identified four new counterparts (to MSPs 47TucQ, 47TucS, 47TucT and 47TucY) and confirmed those already known (to MSPs 47TucU and 47TucW). In the color magnitude diagram, the detected companions are located in a region between the main sequence and the CO white dwarf cooling sequences, consistent with the cooling tracks of He white dwarfs of mass between 0.15 Msun and 0.20 Msun. For each identified companion, mass, cooling age, temperature and pulsar mass (as a function of the inclination angle) have been derived and discussed. For 47TucU we also found that the past accretion history likely proceeded in a sub-Eddington rate. The companion to the redback 47TucW is confirmed to be a non degenerate star, with properties particularly similar to those observed for black widow systems. Two stars have been identified within the 2-sigma astrometric uncertainty from the radio positions of 47TucH and 47TucI, but the available data prevent us from firmly assessing whether they are the true companions of these two MSPs.Comment: 27 pages, 7 figures, Accepted for publication by Ap

    A Comprehensive Approach to Addressing Gender Equity in STEM Subjects at Four-Year Universities in England

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    England is among the many nations aspiring to increase highly qualified and diversified human resources in science, technology, engineering, and mathematics (STEM) fields. Gender disparities in enrollment and persistence in STEM undergraduate education in England are replicated internationally. Despite the expansion of higher education in England, women remain underrepresented in STEM subjects. Politicians have voiced their worries over the economy’s overall health and security due to the inadequate number of women in STEM fields in England. While numerous studies have documented gender disparities in STEM subjects in England, there is still a need for better understanding about how to promote gender equity in STEM from early childhood to higher education. In this chapter, we examine the difference in early educational achievement in mathematics and science subjects and students’ plan to study STEM subjects by gender. We also examine women’s odds of studying STEM subjects in England after controlling for academic performance and social class characteristics. We particularly test gendered differences in studying STEM at prestigious Russell Group universities. We analyze data from the British Department of Education’s Longitudinal Study of Young People in England (also known as Next Steps). Finally, we highlight factors that policy makers, researchers, instructors, and STEM workforce members should consider to close gender gaps in STEM undergraduate education

    Neonatal thrombocytopenic purpura: report of two cases and review of literature

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    Severe neonatal thrombocytopenia is a hematological emergency that can be due to increased platelet destruction(such as immune-mediated and peripheral platelet consumption) or congenital failure of platelet production. The definitive diagnosis of the underlying cause of neonatal thrombocytopenic purpurais based on both clinical and laboratory findings.Case report; We present two infants with persistent severe thrombocytopenia of distinct aetiologies: neonatal alloimmune thrombocytopenic purpura and hepatitis B virus exposure. Their clinical course, haematological profile and treatments are discussed.Conclusion: This reportreiterates the need to think laterally while considering the differential diagnoses of neonatal thrombocytopenic purpura. Moreover, ithighlightsits treatment challenges in peripheral health facilities, especially in resource-limited settings

    Bayesian optimization of the PC algorithm for learning Gaussian Bayesian networks

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    The PC algorithm is a popular method for learning the structure of Gaussian Bayesian networks. It carries out statistical tests to determine absent edges in the network. It is hence governed by two parameters: (i) The type of test, and (ii) its significance level. These parameters are usually set to values recommended by an expert. Nevertheless, such an approach can suffer from human bias, leading to suboptimal reconstruction results. In this paper we consider a more principled approach for choosing these parameters in an automatic way. For this we optimize a reconstruction score evaluated on a set of different Gaussian Bayesian networks. This objective is expensive to evaluate and lacks a closed-form expression, which means that Bayesian optimization (BO) is a natural choice. BO methods use a model to guide the search and are hence able to exploit smoothness properties of the objective surface. We show that the parameters found by a BO method outperform those found by a random search strategy and the expert recommendation. Importantly, we have found that an often overlooked statistical test provides the best over-all reconstruction results

    Radio Timing and Optical Photometry of the Black Widow System PSR J1953+1846A in the Globular Cluster M71

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    We report on the determination of the astrometric, spin and orbital parameters for PSR J1953+1846A, a "black widow" binary millisecond pulsar in the globular cluster M71. By using the accurate position and orbital parameters obtained from radio timing, we identified the optical companion in ACS/Hubble Space Telescope images. It turns out to be a faint (m_F606W>=24, m_F814W>=23) and variable star located at only ~0.06" from the pulsar timing position. The light curve shows a maximum at the pulsar inferior conjunction and a minimum at the pulsar superior conjunction, thus confirming the association with the system. The shape of the optical modulation suggests that the companion star is heated, likely by the pulsar wind. The comparison with the X-ray light curve possibly suggests the presence of an intra-binary shock due to the interaction between the pulsar wind and the material released by the companion. This is the second identification (after COM-M5C) of an optical companion to a black widow pulsar in a globular cluster. Interestingly, the two companions show a similar light curve and share the same position in the color magnitude diagram.Comment: Accepted for publication by ApJ; 33 Pages, 10 Figures, 3 Table
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