There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Imagined communities: Reflections on the origin and spread of nationalism

The modern science of networks has brought significant advances to our understanding of complex systems. One of the most relevant features of graphs representing real systems is community structure, or clustering, i. e. the organization of vertices in clusters, with many edges joining vertices of the same cluster and comparatively few edges joining vertices of different clusters. Such clusters, or communities, can be considered as fairly independent compartments of a graph, playing a similar role like, e. g., the tissues or the organs in the human body. Detecting communities is of great importance in sociology, biology and computer science, disciplines where systems are often represented as graphs. This problem is very hard and not yet satisfactorily solved, despite the huge effort of a large interdisciplinary community of scientists working on it over the past few years. We will attempt a thorough exposition of the topic, from the definition of the main elements of the problem, to the presentation of most methods developed, with a special focus on techniques designed by statistical physicists, from the discussion of crucial issues like the significance of clustering and how methods should be tested and compared against each other, to the description of applications to real networks.

/pdf/community-detection-in-graphs-34rogm3r6p.pdf

Community detection in graphs

We envision new communication paradigms, using physical dynamic interconnectedness among people. Delay Tolerant Networks (DTNs) are a new communication paradigm to support such network environments, and our focus is a type of DTN that provides intermittent communication for humans carrying mobile devices: the Pocket Switched Network (PSN). Information propagation in PSNs is highly influenced by human connectivity networks, i.e. social networks. In our previous work, we have exploited constructing weighted networks using characteristics of pair connections such as the duration of contact time and frequency of contacts from time series of human connectivity network traces. The approach we took is based on empirical and heuristic and the focus is finding a single aggregated logical network structure. The physical network topology in the real world is time dependent and it is a complex task to describe its dynamics. This paper aims to identify dynamics of meeting groups in human connectivity traces, where meeting groups are expected to be a group interacting among the nodes in physical space. Thus, we define ‘meeting group’ differently from ‘community’. We exploit statistical approach that provides quantitative attributes to uncover meeting groups. We identify the power law behavior of meetings that is important for supporting to understanding dynamics of information flow between meeting groups and building group oriented communication protocol.

/pdf/dynamics-of-inter-meeting-time-in-human-contact-networks-1mp03volom.pdf

Dynamics of Inter-Meeting Time in Human Contact Networks

Universal Internet access has become critical to modern life, leading to many explorations of approaches to increase its availability. In this paper we report on a study of one such approach, PAWS, that seeks to understand the technical and social constraints of providing Internet access, free at the point of use, by sharing existing broadband subscribers' connections. We elaborate the technical and social context of our deployment, a deprived neighbourhood in a medium-sized British city, and discuss the constraints on and resulting architecture of this system, including the authentication and security mechanisms necessary for a service of this kind. We then report on the use of our deployment over a period of seven months from July 2013 to February 2014, including analyses of the performance and usage of the network. Our data show that PAWS is socially and technically feasible and has the potential to provide Internet access economically to many who are currently digitally disenfranchised. However, doing so requires overcoming numerous challenges, both technical and social.

A Feasibility Study of an In-the-Wild Experimental Public Access WiFi Network

Complex communication networks, more particular Mobile Ad Hoc Networks (MANET) and Pocket Switched Networks (PSN), rely on short range radio and device mobility to transfer data across the network. These kind of mobile networks contain duality in nature: they are radio networks at the same time also human networks, and hence knowledge from social networks can be also applicable here. In this paper, we demonstrate how identifying social communities can significantly improve the forwarding efficiencies in term of delivery ratio and delivery cost. We verify our hypothesis using data from five human mobility experiments and test on two application scenarios, asynchronous messaging and publish/subscribe service.

/pdf/identifying-social-communities-in-complex-communications-for-3ojnjc9a6w.pdf

Identifying Social Communities in Complex Communications for Network Efficiency.

The use of redundant audio encoding has been advocated for lossy networks like the Internet[1, 2] as a way of reducing the impact of loss in audioconferences. We present a model of loss and determine how the amount of redundancy should be varied with the loss rate. In addition, we make loss measurements and make a preliminary investigation of the position of redundant encodings relative to the original encoding.

/pdf/redundancy-control-in-real-time-internet-audio-conferencing-1y961cq038.pdf

Redundancy Control in Real-Time Internet Audio Conferencing

Universal access to Internet is crucial. Several initiatives have recently emerged to enable wider access to the Internet. Public Access WiFi Service (PAWS) enables free Internet access to all and is based on Lowest Cost Denominator Networking (LCDNet) -- a set of network techniques that enable users to share their home broadband network with the public. LCDNet takes advantage of the available unused capacity in home broadband networks and allows Less-than-Best Effort (LBE) access to these resources. LCDNet can enable third-party stakeholders, such as local governments, to setup, configure and operate home networks for public Internet access in cooperation with Internet Service Providers. Software-defined networking (SDN) creates new opportunities for the remote configuration and management of such networks at large scale. In this paper, we present Virtual Public Networks (VPuN), home networks created, deployed and managed through an evolutionary SDN control abstraction. This offers more flexibility to users and network operators, allowing them to share and control the network, while providing opportunities for new stakeholders to emerge as virtual network operators.

https://www.ikt.uni-hannover.de/uploads/tx_tkpublikationen/vpun_ewsdn_2013.pdf

Jon Crowcroft

Papers

Dynamics of Inter-Meeting Time in Human Contact Networks

A Feasibility Study of an In-the-Wild Experimental Public Access WiFi Network

Identifying Social Communities in Complex Communications for Network Efficiency.

Redundancy Control in Real-Time Internet Audio Conferencing

Virtual Public Networks