The optical light curve of GRB 970228 refined

We present the R and V light curves of the optical counterpart of GRB 970228. A critical analysis of all the available data is made in light of the results achieved in the recent GRB Symposium held in Huntsville and by considering the latest information from the HST images on the underlying nebulosity.Comment: 3 pages, 2 .ps figures, Nuclear Physics style file espcrc2.sty included. To appear in the proceedings of the conference "The Active X-Ray Sky: Results from BeppoSAX and Rossi-XTE", Rome, Italy, 21-24 October, 1997. L. Scarsi, H. Bradt, P. Giommi and F. Fiore editors, Nuc. Phys. B Proc. Supp

Push & Pull: autonomous deployment of mobile sensors for a complete coverage

Mobile sensor networks are important for several strategic applications devoted to monitoring critical areas. In such hostile scenarios, sensors cannot be deployed manually and are either sent from a safe location or dropped from an aircraft. Mobile devices permit a dynamic deployment reconfiguration that improves the coverage in terms of completeness and uniformity. In this paper we propose a distributed algorithm for the autonomous deployment of mobile sensors called Push&Pull. According to our proposal, movement decisions are made by each sensor on the basis of locally available information and do not require any prior knowledge of the operating conditions or any manual tuning of key parameters. We formally prove that, when a sufficient number of sensors are available, our approach guarantees a complete and uniform coverage. Furthermore, we demonstrate that the algorithm execution always terminates preventing movement oscillations. Numerous simulations show that our algorithm reaches a complete coverage within reasonable time with moderate energy consumption, even when the target area has irregular shapes. Performance comparisons between Push&Pull and one of the most acknowledged algorithms show how the former one can efficiently reach a more uniform and complete coverage under a wide range of working scenarios.Comment: Technical Report. This paper has been published on Wireless Networks, Springer. Animations and the complete code of the proposed algorithm are available for download at the address: http://www.dsi.uniroma1.it/~novella/mobile_sensors

Making space for hybridity: Industrial heritage naturecultures at West Carclaze Garden Village, Cornwall

This is the final version. Available on open access from Elsevier via the DOI in this recordThe paper explores the diverse forms of renaturing and reinscription which arise from the materiality of industrial decline and the desire to make space for nature in new peri-urban developments. As productive use is sought for post-operational spaces, remnant industrial objects and ecologies are either removed or incorporated into new landscape narratives and forms. When they are retained, the status of such remnants often remains unstable, as their identities are (re)inscribed through diverse and sometimes competing value frameworks. Instability and ambivalence are particularly pronounced in relation to features that straddle categories of nature and society: nature-culture assemblages produced through both industrial and ecological processes. In this paper, we examine two such assemblages at West Carclaze, Cornwall, in the SW of the UK, a site shaped by the process of china clay extraction and now undergoing redevelopment as a ‘garden village’. The paper considers an artificial hill formed of clay-processing waste and a rare bryophyte species which depends for its survival on ongoing industrial process. Both of these objects represent a category which we describe as ‘industrial heritage naturecultures’ – hybrid entities whose recognition potentially signals a new willingness to accept the blurring of nature-society distinctions in planning and heritage management contexts.Arts and Humanities Research Council (AHRC

Fast network configuration in Software Defined Networking

Software Defined Networking (SDN) provides a framework to dynamically adjust and re-program the data plane with the use of flow rules. The realization of highly adaptive SDNs with the ability to respond to changing demands or recover after a network failure in a short period of time, hinges on efficient updates of flow rules. We model the time to deploy a set of flow rules by the update time at the bottleneck switch, and formulate the problem of selecting paths to minimize the deployment time under feasibility constraints as a mixed integer linear program (MILP). To reduce the computation time of determining flow rules, we propose efficient heuristics designed to approximate the minimum-deployment-time solution by relaxing the MILP or selecting the paths sequentially. Through extensive simulations we show that our algorithms outperform current, shortest path based solutions by reducing the total network configuration time up to 55% while having similar packet loss, in the considered scenarios. We also demonstrate that in a networked environment with a certain fraction of failed links, our algorithms are able to reduce the average time to reestablish disrupted flows by 40%

Where horses run free? Autonomy, temporality and rewilding in the Côa Valley, Portugal

This is the final version of the article. Available from Wiley via the DOI in this record.This paper builds on work about rewilding and human-animal relations by focusing on Portugal's Côa Valley, where a concentration of prehistoric rock art animal figures shares a landscape with a rewilding pilot which seeks to re-establish a population of wild horses. In response to recent geographical debates, the paper offers a sustained, situated analysis of the temporalities of rewilding and related claims to nonhuman autonomy. In the Côa Valley, ancient images of animal others are enrolled in efforts to return ‘wild’ horses to the landscape, but conceptions of wildness and domesticity, and autonomy and temporality, remain fluid and unfixed--even as they are implicated in the production of bounded spaces and invoked in present day management imperatives. To conclude, we argue for an appreciation of degrees of animal autonomy in rewilding contexts, moving beyond the binaries that often seem to be the focus of rewilding debates. Understanding of these degrees of autonomy, we argue, must be grounded in histories of landscape co-habitation and co-production, and consider the intersection of past cultural tradition and conceptions of desired future-natures.Research for this article was supported by Heritage Futures, an Arts and Humanities Research Council (AHRC) “Care for the Future: Thinking Forward through the Past” Theme Large Grant (AH/M004376/1), awarded to Rodney Harrison (principal investigator), Caitlin DeSilvey, Cornelius Holtorf and Sharon Macdonald. The project receives generous additional support from its host universities and partner organizations (see www.heritage-futures.org for further information). Antony Lyons (Heritage Futures senior creative fellow) participated in fieldwork in Portugal and shared his perspectives with the authors. A first draft of this article was completed while Caitlin DeSilvey was resident at the Centre for Advanced Study in Oslo, Norway, as a fellow on a research project led by Bjørnar Olsen, After Discourse: Things, Archaeology and Heritage in the 21st Century

P&P protocol: local coordination of mobile sensors for self-deployment

The use of mobile sensors is of great relevance for a number of strategic applications devoted to monitoring critical areas where sensors can not be deployed manually. In these networks, each sensor adapts its position on the basis of a local evaluation of the coverage efficiency, thus permitting an autonomous deployment. Several algorithms have been proposed to deploy mobile sensors over the area of interest. The applicability of these approaches largely depends on a proper formalization of rigorous rules to coordinate sensor movements, solve local conflicts and manage possible failures of communications and devices. In this paper we introduce P&P, a communication protocol that permits a correct and efficient coordination of sensor movements in agreement with the PUSH&PULL algorithm. We deeply investigate and solve the problems that may occur when coordinating asynchronous local decisions in the presence of an unreliable transmission medium and possibly faulty devices such as in the typical working scenario of mobile sensor networks. Simulation results show the performance of our protocol under a range of operative settings, including conflict situations, irregularly shaped target areas, and node failures.Comment: Technical repor

Dynamic Effects of Wind Loads on a Gravity Damper

AbstractThe gravity damper is safety device used for the air treatment that prevent overpressure inside the unit through the opening. It is a normally closed valve under the effect of the gravity force, which, under the action of the incident air flow, allows to manage any excess mass. Clearly, although the device is rather simple and therefore reliable, the operating conditions may prove burdensome, especially if the gravity dampers are applied to installations of energy transformation, such as the gas turbines; this is mainly due to the need to develop large masses of air at speeds rather incurred. This article describes an experiment carried out on a gravity damper designed to be installed in a gas turbine. The characterization has been performed in numerical (CFD-FEM), considering both the mode shapes and the natural frequencies of the device in working condition as well as any phenomenon of detachment of the fluid that can trigger vortex shedding and subsequently validated in the wind tunnel facilities of the University of Perugia. In particular, what is wanted to be highlighted is the fact that, after a preliminary analysis, it has been clearly evident that, under the operating conditions, the structure would be affected by phenomena of vortex shedding. The shedding frequency is next to some natural frequencies of the structure, with obvious repercussions on the integrity of the structure. An experimental vibration analysis performed in the wind tunnel at flow regime has in fact allowed to identify the phenomenon of lock-in

ASCA and BeppoSAX observations of the peculiar X-ray source 4U1700+24/HD154791

The X-ray source 4U1700+24/HD154791 is one of the few galactic sources whose counterpart is an evolved M star. In X-rays the source shows extreme erratic variability and a complex and variable spectrum. While this strongly suggests accretion onto a compact object, no clear diagnosis of binarity was done up to now. We report on ASCA and BeppoSAX X-ray broad band observations of this source and on ground optical observations from the Loiano 1.5 m telescope.Comment: 5 pages, 4 figures, uses aipproc.sty, to appear in Proceedings of the Fifth Compton Symposiu