Inferring Geodesic Cerebrovascular Graphs: Image Processing, Topological Alignment and Biomarkers Extraction

A vectorial representation of the vascular network that embodies quantitative features - location, direction, scale, and bifurcations - has many potential neuro-vascular applications. Patient-specific models support computer-assisted surgical procedures in neurovascular interventions, while analyses on multiple subjects are essential for group-level studies on which clinical prediction and therapeutic inference ultimately depend. This first motivated the development of a variety of methods to segment the cerebrovascular system. Nonetheless, a number of limitations, ranging from data-driven inhomogeneities, the anatomical intra- and inter-subject variability, the lack of exhaustive ground-truth, the need for operator-dependent processing pipelines, and the highly non-linear vascular domain, still make the automatic inference of the cerebrovascular topology an open problem. In this thesis, brain vessels’ topology is inferred by focusing on their connectedness. With a novel framework, the brain vasculature is recovered from 3D angiographies by solving a connectivity-optimised anisotropic level-set over a voxel-wise tensor field representing the orientation of the underlying vasculature. Assuming vessels joining by minimal paths, a connectivity paradigm is formulated to automatically determine the vascular topology as an over-connected geodesic graph. Ultimately, deep-brain vascular structures are extracted with geodesic minimum spanning trees. The inferred topologies are then aligned with similar ones for labelling and propagating information over a non-linear vectorial domain, where the branching pattern of a set of vessels transcends a subject-specific quantized grid. Using a multi-source embedding of a vascular graph, the pairwise registration of topologies is performed with the state-of-the-art graph matching techniques employed in computer vision. Functional biomarkers are determined over the neurovascular graphs with two complementary approaches. Efficient approximations of blood flow and pressure drop account for autoregulation and compensation mechanisms in the whole network in presence of perturbations, using lumped-parameters analog-equivalents from clinical angiographies. Also, a localised NURBS-based parametrisation of bifurcations is introduced to model fluid-solid interactions by means of hemodynamic simulations using an isogeometric analysis framework, where both geometry and solution profile at the interface share the same homogeneous domain. Experimental results on synthetic and clinical angiographies validated the proposed formulations. Perspectives and future works are discussed for the group-wise alignment of cerebrovascular topologies over a population, towards defining cerebrovascular atlases, and for further topological optimisation strategies and risk prediction models for therapeutic inference. Most of the algorithms presented in this work are available as part of the open-source package VTrails

A Survey on Wireless Security: Technical Challenges, Recent Advances and Future Trends

This paper examines the security vulnerabilities and threats imposed by the inherent open nature of wireless communications and to devise efficient defense mechanisms for improving the wireless network security. We first summarize the security requirements of wireless networks, including their authenticity, confidentiality, integrity and availability issues. Next, a comprehensive overview of security attacks encountered in wireless networks is presented in view of the network protocol architecture, where the potential security threats are discussed at each protocol layer. We also provide a survey of the existing security protocols and algorithms that are adopted in the existing wireless network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term evolution (LTE) systems. Then, we discuss the state-of-the-art in physical-layer security, which is an emerging technique of securing the open communications environment against eavesdropping attacks at the physical layer. We also introduce the family of various jamming attacks and their counter-measures, including the constant jammer, intermittent jammer, reactive jammer, adaptive jammer and intelligent jammer. Additionally, we discuss the integration of physical-layer security into existing authentication and cryptography mechanisms for further securing wireless networks. Finally, some technical challenges which remain unresolved at the time of writing are summarized and the future trends in wireless security are discussed.Comment: 36 pages. Accepted to Appear in Proceedings of the IEEE, 201

Synchronization in complex networks

Synchronization processes in populations of locally interacting elements are in the focus of intense research in physical, biological, chemical, technological and social systems. The many efforts devoted to understand synchronization phenomena in natural systems take now advantage of the recent theory of complex networks. In this review, we report the advances in the comprehension of synchronization phenomena when oscillating elements are constrained to interact in a complex network topology. We also overview the new emergent features coming out from the interplay between the structure and the function of the underlying pattern of connections. Extensive numerical work as well as analytical approaches to the problem are presented. Finally, we review several applications of synchronization in complex networks to different disciplines: biological systems and neuroscience, engineering and computer science, and economy and social sciences.Comment: Final version published in Physics Reports. More information available at http://synchronets.googlepages.com

Proposta de um protocolo de roteamento autoconfigurável para redes mesh em Bluetooth Low Energy (BLE) baseado em proactive source routing

Orientador: Yuzo IanoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A Internet das Coisas (Internet of Things ¿ IoT) visa a criação de ambientes inteligentes como domótica, comunicação intra-veicular e redes de sensores sem fio (Wireless Sensor Network ¿ WSN), sendo que atualmente essa tecnologia vem crescendo de forma rápida. Uma das tecnologias sem fio utilizada para aplicações de curta distância que se encontra mais acessível à população, em geral, é o Bluetooth. No final de 2010, o Bluetooth Special Interest Group (Bluetooth SIG), lançou a especificação Bluetooth 4.0 e, como parte dessa especificação, tem-se o Bluetooth Low Energy (BLE). O BLE é uma tecnologia sem fio de baixíssimo consumo de potência, que pode ser alimentada por uma bateria tipo moeda, ou até mesmo por indução elétrica (energy harvesting). A natureza do Bluetooth (e BLE) é baseada na conexão do tipo Mestre/Escravo. Muitos estudos mostram como criar redes mesh baseadas no Bluetooth clássico, que são conhecidas como Scatternets, onde alguns nós são utilizados como escravos com o objetivo de repassar os dados entre os mestres. Contudo, o BLE não tinha suporte para a mudança entre mestre e escravo até o lançamento da especificação Bluetooth 4.1, em 2013. A capacidade de uma tecnologia sem fio para IoT de criar uma rede ad-hoc móvel (Mobile Ad-hoc Network ¿ MANET) é vital para poder suportar uma grande quantidade de sensores, periféricos e dispositivos que possam coexistir em qualquer ambiente. Este trabalho visa propor um novo método de autoconfiguração para BLE, com descoberta de mapa de roteamento e manutenção, sem a necessidade de mudanças entre mestre e escravo, sendo compatível com os dispositivos Bluetooth 4.0, assim como com os 4.1 e mais recentes. Qualquer protocolo de mensagens pode aproveitar o método proposto para descobrir e manter a topologia de rede mesh em cada um dos seus nósAbstract: Nowadays, the Internet of Things (IoT) is spreading rapidly towards creating smart environments. Home automation, intra-vehicular interaction, and wireless sensor networks (WSN) are among the most popular applications discussed in IoT literature. One of the most available and popular wireless technologies for short-range operations is Bluetooth. In late 2010, the Bluetooth Special Interest Group (SIG) launched the Bluetooth 4.0 Specification, which brings Bluetooth Low Energy (BLE) as part of the specification. BLE characterises as being a very low power wireless technology, capable of working on a coin-cell or even by energy scavenging. Nevertheless, the nature of Bluetooth (and BLE) has always been a connection-oriented communication in a Master/Slave configuration. Several studies exist showing how to create mesh networks for Classic Bluetooth, called Scatternets, by utilizing some nodes as slaves to relay data between Masters. However, BLE didn¿t support role changing until the 4.1 Specification released in 2013. The capability of a wireless technology to create a Mobile Ad-Hoc Network (MANET) is vital for supporting the plethora of sensors, peripherals, and devices that could coexist in any IoT environment. This work focuses on proposing a new autoconfiguring dynamic address allocation scheme for a BLE Ad-Hoc network, and a network map discovery and maintenance mechanism that doesn¿t require role changing, thus being possible to implement it in 4.0 compliant devices as well as 4.1 or later to develop a MANET. Any ad-hoc routing protocol can utilise the proposed method to discover, keep track, and maintain the mesh network node topology in each of their nodesDoutoradoTelecomunicações e TelemáticaDoutor em Engenharia ElétricaCAPE

Flexible Application-Layer Multicast in Heterogeneous Networks

This work develops a set of peer-to-peer-based protocols and extensions in order to provide Internet-wide group communication. The focus is put to the question how different access technologies can be integrated in order to face the growing traffic load problem. Thereby, protocols are developed that allow autonomous adaptation to the current network situation on the one hand and the integration of WiFi domains where applicable on the other hand

Methods for improving resilience in communication networks and P2P overlays

Resilience to failures and deliberate attacks is becoming an essential requirement in most communication networks today. This also applies to P2P Overlays which on the one hand are created on top of communication infrastructures, and therefore are equally affected by failures of the underlying infrastructure, but which on the other hand introduce new possibilities like the creation of arbitrary links within the overlay. In this article, we present a survey of strategies to improve resilience in communication networks as well as in P2P overlay networks. Furthermore, our intention is to point out differences and similarities in the resilience-enhancing measures for both types of networks. By revising some basic concepts from graph theory, we show that many concepts for communication networks are based on well-known graph-theoretical problems. Especially, some methods for the construction of protection paths in advance of a failure are based on very hard problems, indeed many of them are in NP and can only be solved heuristically or on certain topologies. P2P overlay networks evidently benefit from resilience-enhancing strategies in the underlying communication infrastructure, but beyond that, their specific properties pose the need for more sophisticated mechanisms. The dynamic nature of peers requires to take some precautions, like estimating the reliability of peers, redundantly storing information, and provisioning a reliable routing