Testing the homogeneity of the Universe using gamma-ray bursts

In this paper, we study the homogeneity of the GRB distribution using a subsample of the Greiner GRB catalogue, which contains 314 objects with redshift $0<z<2.5$ (244 of them discovered by the Swift GRB Mission). We try to reconcile the dilemma between the new observations and the current theory of structure formation and growth. To test the results against the possible biases in redshift determination and the incompleteness of the Greiner sample, we also apply our analysis to the 244 GRBs discovered by Swift and the subsample presented by the Swift Gamma-Ray Burst Host Galaxy Legacy Survey (SHOALS). The real space two-point correlation function (2PCF) of GRBs, $\xi(r),$ is calculated using a Landy-Szalay estimator. We perform a standard least-$\chi^2$ fit to the measured 2PCFs of GRBs. We use the best-fit 2PCF to deduce a recently defined homogeneity scale. The homogeneity scale, $R_H$, is defined as the comoving radius of the sphere inside which the number of GRBs $N(<r)$ is proportional to $r^3$ within $1\%$, or equivalently above which the correlation dimension of the sample $D_2$ is within $1\%$ of $D_2=3$. For the Swift subsample of 244 GRBs, the correlation length and slope are $r_0= 387.51 \pm 132.75~h^{-1}$Mpc and $\gamma = 1.57\pm 0.65$ (at $1\sigma$ confidence level). The corresponding scale for a homogeneous distribution of GRBs is $r\geq 7,700~h^{-1}$Mpc. The results help to alleviate the tension between the new discovery of the excess clustering of GRBs and the cosmological principle of large-scale homogeneity. It implies that very massive structures in the relatively local Universe do not necessarily violate the cosmological principle and could conceivably be present.Comment: 7 pages, 5 figures, accepted by Astronomy & Astrophysics. The data used in this work (e.g. Tables 1 and 2) are publicly available online in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A

Finslerian MOND versus the Strong Gravitational Lensing of the Early-type Galaxies

The gravitational lensing of Bullet Clusters and early-type galaxies pose serious challenges on the validity of MOND. Recently, Finslerian MOND, a generalization of MOND in the framework of Finsler gravity, has been proposed to explain the mass discrepancy problem of Bullet Cluster 1E 0657\ 558. In this paper, we check the validity of the Finslerian MOND in describing the strong gravitational lensing of early-type galaxies. The investigation on ten strong lenses of the CASTLES samples shows that there is no strong evidence for the existence of dark matter.Comment: 11 pages, 2 figures, 2 table

Managing Triads in a Military Avionics Service Maintenance Network in Taiwan

Purpose – The purpose of this paper is to investigate how different types of triad structures, and the management mechanisms adopted by the focal company, affect cooperative performance. Design/methodology/approach – This paper uses a social network perspective to examine the triad management phenomenon in the military avionics maintenance context, which is closely associated with the field of operations management. Findings – This paper demonstrates that different triad structures and management mechanisms influence perceived cooperative performance. Four main findings emerged: in a triad, a firm playing a bridging role perceives higher cooperative performance than when playing a peripheral role in the triad or being located in a fully connected triad. When a firm plays the bridging role in a triad, and has a high level of trust, this leads to higher perceived cooperative performance. When a firm plays a peripheral role in a triad, high levels of coordination mechanism combined with high levels of trust result in higher levels of perceived cooperative performance. In a fully linked triad, when the coordination mechanism is well developed, the level of trust is high, so that the resulting level of perceived cooperation is high. Originality/value – This paper extends the knowledge of triad management by providing an in-depth study of a well-defined network setting with exceptionally high-level access to the most senior executives. In practice, this paper shows how to manage differen