The Brazilian Tunable Filter Imager for the SOAR telescope

This paper presents a new Tunable Filter Instrument for the SOAR telescope. The Brazilian Tunable Filter Imager (BTFI) is a versatile, new technology, tunable optical imager to be used in seeing-limited mode and at higher spatial fidelity using the SAM Ground-Layer Adaptive Optics facility at the SOAR telescope. The instrument opens important new science capabilities for the SOAR community, from studies of the centers of nearby galaxies and the insterstellar medium to statistical cosmological investigations. The BTFI takes advantage of three new technologies. The imaging Bragg Tunable Filter concept utilizes Volume Phase Holographic Gratings in a double-pass configuration, as a tunable filter, while a new Fabry-Perot (FP) concept involves technologies which allow a single FP etalon to act over a large range of interference orders and spectral resolutions. Both technologies will be in the same instrument. Spectral resolutions spanning the range between 25 and 30,000 can be achieved through the use of iBTF at low resolution and scanning FPs beyond R ~2,000. The third new technologies in BTFI is the use of EMCCDs for rapid and cyclically wavelength scanning thus mitigating the damaging effect of atmospheric variability through data acquisition. An additional important feature of the instrument is that it has two optical channels which allow for the simultaneous recording of the narrow-band, filtered image with the remaining (complementary) broad-band light. This avoids the uncertainties inherent in tunable filter imaging using a single detector. The system was designed to supply tunable filter imaging with a field-of-view of 3 arcmin on a side, sampled at 0.12" for direct Nasmyth seeing-limited area spectroscopy and for SAM's visitor instrument port for GLAO-fed area spectroscopy. The instrument has seen first light, as a SOAR visitor instrument. It is now in comissioning phase.Comment: accepted in PAS

Virtual Communication Stack: Towards Building Integrated Simulator of Mobile Ad Hoc Network-based Infrastructure for Disaster Response Scenarios

Responses to disastrous events are a challenging problem, because of possible damages on communication infrastructures. For instance, after a natural disaster, infrastructures might be entirely destroyed. Different network paradigms were proposed in the literature in order to deploy adhoc network, and allow dealing with the lack of communications. However, all these solutions focus only on the performance of the network itself, without taking into account the specificities and heterogeneity of the components which use it. This comes from the difficulty to integrate models with different levels of abstraction. Consequently, verification and validation of adhoc protocols cannot guarantee that the different systems will work as expected in operational conditions. However, the DEVS theory provides some mechanisms to allow integration of models with different natures. This paper proposes an integrated simulation architecture based on DEVS which improves the accuracy of ad hoc infrastructure simulators in the case of disaster response scenarios.Comment: Preprint. Unpublishe

Time-Varying Graphs and Dynamic Networks

The past few years have seen intensive research efforts carried out in some apparently unrelated areas of dynamic systems -- delay-tolerant networks, opportunistic-mobility networks, social networks -- obtaining closely related insights. Indeed, the concepts discovered in these investigations can be viewed as parts of the same conceptual universe; and the formal models proposed so far to express some specific concepts are components of a larger formal description of this universe. The main contribution of this paper is to integrate the vast collection of concepts, formalisms, and results found in the literature into a unified framework, which we call TVG (for time-varying graphs). Using this framework, it is possible to express directly in the same formalism not only the concepts common to all those different areas, but also those specific to each. Based on this definitional work, employing both existing results and original observations, we present a hierarchical classification of TVGs; each class corresponds to a significant property examined in the distributed computing literature. We then examine how TVGs can be used to study the evolution of network properties, and propose different techniques, depending on whether the indicators for these properties are a-temporal (as in the majority of existing studies) or temporal. Finally, we briefly discuss the introduction of randomness in TVGs.Comment: A short version appeared in ADHOC-NOW'11. This version is to be published in Internation Journal of Parallel, Emergent and Distributed System

Optimal relaying in heterogeneous delay tolerant networks

In Delay Tolerant Networks (DTNs), there exists only intermittent connectivity between communication sources and destinations. In order to provide successful communication services for these challenged networks, a variety of relaying and routing algorithms have been proposed with the assumption that nodes are homogeneous in terms of contact rates and delivery costs. However, various applications of DTN have shown that mobile nodes should be divided into different classes in terms of their energy requirements and communication ability, and real application data have revealed the heterogeneous contact rates between node pairs. In this paper, we design an optimal relaying scheme for DTNs, which takes into account nodes’ heterogeneous contact rates and delivery costs when selecting relays to minimise the delivery cost while satisfying the required message delivery probability. Extensive results based on real traces demonstrate that our relaying scheme requires the least delivery cost and achieves the largest maximum delivery probability, compared with the schemes that neglect nodes’ heterogeneity

Strategic term rewriting and its application to a VDM-SL to SQL conversion

We constructed a tool, called VooDooM, which converts datatypes in Vdm-sl into Sql relational data models. The conversion involves transformation of algebraic types to maps and products, and pointer introduction. The conversion is specified as a theory of refinement by calculation. The implementation technology is strategic term rewriting in Haskell, as supported by the Strafunski bundle. Due to these choices of theory and technology, the road from theory to practise is straightforward.Fundação para a Ciência e a Tecnologia (FCT) - POSI/ICHS/44304/2002Agência de Inovação (ADI) - ∑!223