Searching for cluster substructure using APM and ROSAT data

We present a detailed study of the morphological features of 22 rich galaxy clusters. Our sample is constructed from a cross-correlation of optical (Abell+APM) data with X-ray (0.1 - 2.4) keV ROSAT pointed observations. We systematically compare cluster images and morphological parameters in an attempt to reliably identify possible substructure in both optical and the X-ray images. To this end, we compute various moments of the optical and X-ray surface-brightness distribution such as the ellipticities, center-of-mass shifts and ellipsoidal orientations. We assess the significance of our results using Monte Carlo simulations. We find significant correlations between the optical and X-ray morphological parameters, indicating that in both parts of the spectrum it is possible to identify correctly the dynamical state of a cluster. Most of our clusters (17/22) have a good 1-to-1 correspondence between the optical and the X-ray images and about 10 appear to have strong indications of substructure. This corresponds to a minimum percentage of order 45 per cent which is in very good accordance with other similar analyses. Finally, 5 out of 22 systems seem to have distinct subclumps in the optical which are not verified in the X-ray images, and thus are suspect of being due to optical projection effects. These results will serve as a useful guide in interpreting subsequent analyses of large optical cluster catalogues.Comment: 15 pages, including 9 figures, MNRAS in press, revised versio

Building Community and Collaboration Applications for MMOGs

Supporting collaborative activities among the online players are one of the major challenges in the area of Massively Multiplayer Online Games (MMOG), since they increase the richness of gaming experience and create more engaged communities. To this direction, our study has focused on the provision of services supporting and enhancing the players' in-game community and collaboration activities. We have designed and implemented innovative tools exploiting a game adaptation technology, namely, the In-game Graphical Insertion Technology (IGIT), which permits the addition of web-based applications without any need from the game developers to modify the game at all, nor from the game players to change their game installation. The developed tools follow a design adapted to the MMOG players' needs and are based on the latest advances on Web 2.0 technology. Their provision is performed through the core element of our system, which is the so-called Community Network Game (CNG) Server. One of the important features provided by the implemented system's underlying framework is the utilization of enhanced Peer-to-Peer (P2P) technology for the distribution of user-generated live video streams. In this paper, we focus on the architecture of the CNG Server as well as on the design and implementation of the online community and collaboration tools

Examining the value of flexible logistics offerings

In the order fulfilment and retail industry, the provision of fast and low cost delivery services has received significant focus over the last decade. What is often neglected is other factors that contribute to a customer's overall experience like customisation and flexibility of deliveries, especially in cases when a customer's needs and plans change between order placement and order delivery. This paper explores the value of a flexible type of logistics offering in which the customer is able to change the order requirements (such as delivery date) after the order has been placed. In particular, we focus on the interactions between a retailer and a customer in agreeing and executing such logistics orders. We examine the benefits of this type of flexible logistics offerings because flexibility and customisation are critical factors for the success of omni-channel commerce. Such offerings are clearly connected with recent developments in digital technologies as these technologies are essential for the implementation. Our results indicate that flexible logistics offerings can be beneficial both for retailers and for customers. They also highlight the importance of receiving orders that do not fully meet the requirements of a customer.</p