322,990 research outputs found
Visita di Stefano Basagni (Northeastern University)
No full textprogettazione, valutazione e test di protocolli per reti di sensori.01/01/201
Design and Evaluation of Protocol Stacks for Underwater Communications
No full textThe project revolves around three themes: (i) understanding the physics of acoustic propagation and its impact on the design of communication algorithms and network protocols, (ii) design of network protocols that are theoretically sound and suited to the needs of underwater applications, and (iii) experimental demonstration. The latter activity will benefit from Prof. Basagni collaborations with Woods Hole Oceanograhic Institute and with La Spezia NURC (Nato Underwater Research Center). Such collaborations will allow us to test our ideas in real settings, using equipments whose cost (in the million of Euros) would otherwise be not affordable, having impact on cutting edge ocean engineering
Heat or light? Tools of choice for on-surface synthesis
No full textIn recent years, direct on-surface synthesis in UHV has been exploited as a promising strategy to obtain thermally and chemically stable structures by covalent bonding of suitable precursors. So far, covalent linking of organic molecules onto metal, semiconducting and bulk insulator surfaces has been mostly carried out thermally. Heat supplied to the system promotes the formation of covalent bonds between the monomeric building units either simultaneously with the surface diffusion phenomena it promotes (i.e. under dynamic bond-forming conditions) or as a trigger, after a pre-assembly step into a surface-supported supramolecular, non-covalent network. However, heat as a tool for on-surface synthesis has the ambivalent status of a pharmakon, since it has the capacity to be beneficial and detrimental to the production and to the structural quality of the covalently-linked network at the same time. The close interplay between molecular surface diffusion, chemical reactivity and temperature, in fact, often hampers the possibility to independently control reaction initiation and surface mobility, ultimately leading to highly defective covalent networks, poorly ordered on the long range. Photochemically activated reactions are a potentially powerful tool to stabilize self-organized structures without disrupting the long-range order. Yet, to date photo-initiated on-surface reactions are still rather uncommon, since the processes following light absorption are not completely understood and, in particular, the role of the substrate is still poorly characterized in quantitative terms: the high quenching rate of electronically excited species on metal surfaces, which inhibits the photophysical processes commonly observed in the gas phase and in solution; the presence of new, surface-related excitation and relaxation pathways; the occurrence of charge-transfer-mediated photochemistry are but a few important issues. Based on the recent experience of our group in this field [1–6], in this talk I will provide some hints on the necessary conditions to be fulfilled to make either heat or light – or a combination of both – the tool of choice for the successful on-surface synthesis of long range-ordered covalent networks. References [1] F. Sedona, M. Di Marino, M. Sambi, T. Carofiglio, E. Lubian, M. Casarin, and E. Tondello. ACS Nano 4, 5147 (2010) [2] A. Basagni, L. Colazzo, F. Sedona, M. Di Marino, T. Carofiglio, E. Lubian, D. Forrer, A. Vittadini, M. Casarin, A. Verdini, A. Cossaro, L. Floreano and M. Sambi. Chem. Eur. J. 20, 14296 (2014) [3] A. Basagni, F. Sedona, C. A. Pignedoli, M. Cattelan, L. Nicolas, M. Casarin, and M. Sambi. J. Am. Chem. Soc. 137, 1802 (2015) [4] A. Basagni, L. Ferrighi, M. Cattelan, L. Nicolas, K. Handrup, L. Vaghi, A. Papagni, F. Sedona, C. Di Valentin, S. Agnoli and M. Sambi. Chem. Commun. 51, 12593 (2015) [5] S. Tognolini, S. Ponzoni, F. Sedona, M. Sambi and S. Pagliara. Phys. Chem. Lett. 6, 3632 (2015) [6] A. Basagni, G. Vasseur, C. A. Pignedoli, M. Vilas-Varela, D. Peña, L. Nicolas, L. Vitali, J. Lobo-Checa, D. G. de Oteyza, F. Sedona, M. Casarin, J. E. Ortega, and M. Sambi. ACS Nano 10, 2644 (2016
On the difficulty of finding walks of length k
No full textWe characterize the computational complexity of the following combinatorial problem: Given a directed graph G = (V, E) endowed with a length function w : E ⇀ N, a pair of nodes s and t in V and an integer k ≥ 0, does G contain a walk π from s to t of length exactly k? We show that the problem is NP-complete when G is a directed graph, an undirected graph, or a directed acyclic graph. The problem becomes NL-complete when w is a unary function
A logarithmic lower bound for time-spread multiple access protocols
No full textTime-Spread Multiple-Access (TSMA) protocols are scheduled access protocols for mobile multi-hop radio networks that guarantee deterministic access to the shared channel regardless of the possibility of radio interference. In scheduled access methods, time is considered to be slotted and time slots are cyclically organized into frames. In general, the shorter the frame, the more efficient the protocol. An Ω(log log n) lower bound is known on the minimum length of the frame of TSMA protocols in networks with n nodes. In this note we improve that lower bound by characterizing the multiple access to the radio channel as a combinatorial problem. The proposed characterization allows us to prove that no TSMA protocols can successfully schedule the transmissions of the nodes of a multi-hop radio network in frames with less than log n time slots
Bluetooth Scatternet Formation and Scheduling: An Integrated Solution
No full textBuilding and deploying multi-hop networks of Bluetooth devices (aka scatternets) concerns devising methods for forming piconets, connecting them through shared gateways, and scheduling the presence of these gateways among the piconets they interconnect (inter-piconet scheduling). There are several types of gateways, and their efficient scheduling is affected by the gateway type. Scatternet formation and scheduling have been dealt with separately in the past. This leads to network performance degradation because of the missed opportunity of designing scatternet formation protocols that best address scheduling requirements and vice-versa. In this paper we propose SS-Blue, an integrated mechanism for the joint design of scatternet formation and scheduling. Specifically, we enhance an efficient scatternet formation protocol by adopting methods for piconets interconnection that favor types of gateways which will result in a better performing inter-piconet scheduling. At the same time, a fair and traffic adaptive mechanism is proposed to schedule all types of gateways (inter-piconet scheduling), and for managing intra-piconet scheduling, i.e., for scheduling traffic transmission within a piconet. Our solution is evaluated through extensive simulations. Our results show that SS-Blue succeeds in producing scatternets whose gateways are efficiently scheduled. The combination of the proposed intra- and inter-piconet scheduling is shown to be remarkably effective in favoring packet forwarding with very low end-to-end latency
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