On Space-Time Capacity Limits in Mobile and Delay Tolerant Networks

We investigate the fundamental capacity limits of space-time journeys of information in mobile and Delay Tolerant Networks (DTNs), where information is either transmitted or carried by mobile nodes, using store-carry-forward routing. We define the capacity of a journey (i.e., a path in space and time, from a source to a destination) as the maximum amount of data that can be transferred from the source to the destination in the given journey. Combining a stochastic model (conveying all possible journeys) and an analysis of the durations of the nodes' encounters, we study the properties of journeys that maximize the space-time information propagation capacity, in bit-meters per second. More specifically, we provide theoretical lower and upper bounds on the information propagation speed, as a function of the journey capacity. In the particular case of random way-point-like models (i.e., when nodes move for a distance of the order of the network domain size before changing direction), we show that, for relatively large journey capacities, the information propagation speed is of the same order as the mobile node speed. This implies that, surprisingly, in sparse but large-scale mobile DTNs, the space-time information propagation capacity in bit-meters per second remains proportional to the mobile node speed and to the size of the transported data bundles, when the bundles are relatively large. We also verify that all our analytical bounds are accurate in several simulation scenarios.Comment: Part of this work will be presented in "On Space-Time Capacity Limits in Mobile and Delay Tolerant Networks", P. Jacquet, B. Mans and G. Rodolakis, IEEE Infocom, 201

Spatial Structure of Tourist Supply and Relations Between Sub-Regions : A Case Study in a Coastal Region, Greece

At the duration of previous decades has been realised important research with regard to the results and the repercussions of tourism in local level. Even if the tourism is often represented as industry of low impact, the researchers have begun to recognize the tourism as a factor of environmental change. The tourism is considered as the activity that eminently expresses spatial interaction. That means, that the characteristic elements two or more units of space affect each other. The effective spatial management of is an increasing competitive and complicated undertaking, that requires the help of economic, social and geographical elements for the process of planning and development. Taking into consideration the heterogeneous nature of the tourism phenomenon and organisational and functional structures of tourist destinations, especially the coastal areas, it is obvious that it is enough difficult to delimit with precision the tourism sector, as a single total of competences, that they are distinguished easily by the remainder policies of tourist destinations, and to record the spatial changes in the tourism. This work faces an important challenge in the field of tourism and the basic aim of this paper is to present the economic relations between sub-regions in a coastal area in Greece, and spatial concentration of economic activities and examination of communities in the sense of socio-economic characteristics, emphasising in the analysis of the correlation between employment in the tourism sector and other economic activities. Furthermore, the geographical distribution of tourist lodgings, constitutes a very widely used clue in the measurement of spatial fluctuations of tourist activity. This is owed because the tourist lodging constitutes one of the more important elements of tourist product with material substance, so that it can be also still measured, and data which concern in the geographical distribution of tourist lodgings, provide useful elements with regard to the importance of tourism and its spatial structure.

Low-energy excitations in strongly correlated materials: A theoretical and experimental study of the dynamic structure factor in V2O3

PACS number(s): 71.45.Gm, 71.15.−m, 71.30.+h.-- et al.This work contains an experimental and theoretical study of the dynamic structure factor at large momentum transfer |Q|∼4 Å−1 of the strongly correlated transition-metal oxide V2O3. We focus in particular on the transitions between d states that give rise to the spectra below 6 eV. We show that the main peak in this energy range is mainly due to t2g→egσ transitions, and that it carries a signature of the phase transition between the paramagnetic insulator and the paramagnetic metal that can already be understood from the joint density of states calculated at the level of the static local density approximation. Instead, in order to obtain theoretical spectra that are overall similar to the measured ones, we have to go beyond the static approximation and include at least crystal local field effects. The latter turn out to be crucial in order to eliminate a spurious peak and hence allow a safe comparison between theory and experiment, including an analysis of the strong anisotropy of the spectra.Use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. We are grateful for support by ETSF-I3 Grant No. 211956. Computer time was granted by IDRIS (544). F.I. also acknowledges financial support from the CEA program Transversal Nanosciences and M.G. from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG Proposal No. 267374), Spanish Grants No. FIS2011-65702-C02-01 and No. PIB2010US-00652, ACI-Promociona (ACI2009-1036), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT-319-07), Consolider nanoTHERM (Grant No. CSD2010-00044), and European Commission projects CRONOS (280879-2 CRONOS CPFP7) and THEMA (FP7-NMP-2008-SMALL-2, 228539).Peer reviewe

Indoor Positioning using the IEEE 802.11 Infrastructure

We propose a new indoor localization method which can be used to track a mobile node . Our method uses only the received signal strengths as input information . In addition our approach doesn't require any prior knowledge of the mobile node's motion and therefore doesn't use a cinematic motion model for tracking the mobile node. We discuss in detail the features of our approach and its resulting algorithm .We evaluate the performances of our algorithm using a real signal map

Spatial Structure of Tourist Supply and Relations Between Sub-Regions: A Case Study in a Coastal Region, Greece

At the duration of previous decades has been realised important research with regard to the results and the repercussions of tourism in local level. Even if the tourism is often represented as industry of low impact, the researchers have begun to recognize the tourism as a factor of environmental change. The tourism is considered as the activity that eminently expresses spatial interaction. That means, that the characteristic elements two or more units of space affect each other. The effective spatial management of is an increasing competitive and complicated undertaking, that requires the help of economic, social and geographical elements for the process of planning and development. Taking into consideration the heterogeneous nature of the tourism phenomenon and organisational and functional structures of tourist destinations, especially the coastal areas, it is obvious that it is enough difficult to delimit with precision the tourism sector, as a single total of competences, that they are distinguished easily by the remainder policies of tourist destinations, and to record the spatial changes in the tourism. This work faces an important challenge in the field of tourism and the basic aim of this paper is to present the economic relations between sub-regions in a coastal area in Greece, and spatial concentration of economic activities and examination of communities in the sense of socio-economic characteristics, emphasising in the analysis of the correlation between employment in the tourism sector and other economic activities. Furthermore, the geographical distribution of tourist lodgings, constitutes a very widely used clue in the measurement of spatial fluctuations of tourist activity. This is owed because the tourist lodging constitutes one of the more important elements of tourist product with material substance, so that it can be also still measured, and data which concern in the geographical distribution of tourist lodgings, provide useful elements with regard to the importance of tourism and its spatial structure

Performance of binary exponential backoff CSMA in WiFi and optimal routing in mobile ad hoc networks

International audienceIn this paper we show that the CSMA IEEE 802.11 protocol (Wifi) provides packet access delays asymptotics in power law. This very feature allows us to specify optimal routing via polynomial algorithm while the general case is NP-hard

Localization and Path Tracking Using the IEEE 802.11 Infrastructure

We propose a new localization method in order to estimate the position of wireless devices in real time, using already existent infrastructure (such as IEEE 802.11 access points). We present a filtering algorithm that computes the most likely path taken by a mobile node, based on signal strength measure- ments and a known signal strength map. In our approach we do not assume that the node mobility model is known. The algorithm calculates analytically in real time the optimal correction in the mobile node's estimated position, using current signal measurements. We discuss how this algorithm can be used in a practical implementation and we evaluate the performance of our method using numerical simulations

Atomic and itinerant effects at the transition metal x-ray absorption K-pre-edge exemplified in the case of V2_2O3_3

X-ray absorption spectroscopy is a well established tool for obtaining information about orbital and spin degrees of freedom in transition metal- and rare earth-compounds. For this purpose usually the dipole transitions of the L- (2p to 3d) and M- (3d to 4f) edges are employed, whereas higher order transitions such as quadrupolar 1s to 3d in the K-edge are rarely studied in that respect. This is due to the fact that usually such quadrupolar transitions are overshadowed by dipole allowed 1s to 4p transitions and, hence, are visible only as minor features in the pre-edge region. Nonetheless, these features carry a lot of valuable information, similar to the dipole L-edge transition, which is not accessible in experiments under pressure due to the absorption of the diamond anvil pressurecell. We recently performed a theoretical and experimental analysis of such a situation for the metal insulator transition of (V(1-x)Crx)2O3. Since the importance of the orbital degrees of freedom in this transition is widely accepted, a thorough understanding of quadrupole transitions of the vanadium K-pre-edge provides crucial information about the underlying physics. Moreover, the lack of inversion symetry at the vanadium site leads to onsite mixing of vanadium 3d- and 4p- states and related quantum mechanical interferences between dipole and quadrupole transitions. Here we present a theoretical analysis of experimental high resolution x-ray absorption spectroscopy at the V pre-K edge measured in partial fluorescence yield mode for single crystals. We carried out density functional as well as configuration interaction calculations in order to capture effects coming from both, itinerant and atomic limits