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

Opinions from people, evident in surveys and microblogging, for instance, may have bias or low user participation due to legitimate concerns about privacy and anonymity. To provide sender (the participant) anonymity, the identity of the message sender must be hidden from the message recipient (the opinion collector) and the contents of the actual message hidden from any intermediate actors (such as, routers) that may be responsible for relaying the message. We propose a novel one-way message routing scheme based on probabilistic forwarding that guarantees message privacy and sender anonymity through cryptographic means; utilising an additively homomorphic public-key cryptosystem along with a symmetric cipher. Our scheme involves intermediate relays and can work with either a centralised or a decentralised registry that helps with connecting the relays to each other. In addition to theoretical analysis, we demonstrate a real-world prototype built with HTML5 technologies and deployed on a public cloud environment. The prototype allows anonymous messaging over HTTP(S), and has been run inside HTML5 browsers on mobile application environments with no configurations at the network level. While we leave constructing the reverse path as future work, the proposal contained in this paper complete and has practical applications in anonymous surveys and microblogging.

https://hal.inria.fr/hal-01416208/document

Lightweight Practical Private One-Way Anonymous Messaging

The simulation models used in mobile ad hoc network research have been criticised for lack of realism. While credited with ease of understanding and implementation, they are often based on theoretical models, rather than real world observations. Criticisms have centred on radio propagation or mobility models. In this work, we take an integrated approach to modelling the real world that underlies a mobile ad hoc network. While pointing out the correlations between the space, radio propagation and mobility models, we use mobility as a focal point to propose a new framework, MIRRORS, that captures real world behaviour. We give the formulation of a specific model within the framework and present simulation results that reflect topology properties of the networks synthesised. Compared with the existing models studied, our model better represent real world topology properties and presents a wider spectrum of variation in the metrics examined, due to the model encapsulating more detailed dynamics. While the common approach is to focus on performance evaluation of existing protocols using these models, we discuss protocol design opportunities across layers in view of the simulation results.

/pdf/mirrors-an-integrated-framework-for-capturing-real-world-11luhhciwu.pdf

MIRRORS: An integrated framework for capturing real world behaviour for models of ad hoc networks

In this paper, we provide (i) a rigorous general theory to elicit conditions on (tail-dependent) heavy-tailed cyber-risk distributions under which a risk management firm might find it (non)sustainable to provide aggregate cyber-risk coverage services for smart societies, and (ii)a real-data driven numerical study to validate claims made in theory assuming boundedly rational cyber-risk managers, alongside providing ideas to boost markets that aggregate dependent cyber-risks with this http URL the best of our knowledge, this is the only complete general theory till date on the feasibility of aggregate cyber-risk management.

Aggregate Cyber-Risk Management in the IoT Age: Cautionary Statistics for (Re)Insurers and Likes

The success of Wi-Fi technology as an efficient and low-cost last-mile access solution has enabled massive spontaneous deployments generating storms of beacons all across the globe. Emerging location systems are using these beacons to observe mobility patterns of people through portable or wearable devices and offers promising use-cases that can help to solve critical problems in the developing world. In this paper, we design and develop a novel prototype to organise these spontaneous deployments of Access Points into what we call virtual cells (vcells). We compute virtual cells from a list of Access Points collected from different active scans for a geographical region. We argue that virtual cells can be encoded using Bloom filters to implement the location process. Lastly, we present two illustrative use-cases to showcase the suitability and challenges of the technique.

Peer provided cell-like networks built out of thin air

Java is a relatively new, cross-platform, object-oriented language, which has rapidly evolved into an entire operating environment, encompassing most real-world programming requirements. Traditionally, its interpreted nature has been regarded as a severe restriction against real-time application implementation. However, constant performance improvements with subsequent releases of the language, as well as its technical advantages in networking and multithreading support, have recently allowed its use for multimedia delivery by a variety of sources. In this text, presented are experiences on relevant work carried out during the last three years, almost immediately after Java’s public release, at the Department of Computer Science, University College London (UCL-CS). Java’s suitability for (soft) real-time media is verified, and current issues that need to be addressed, including workarounds for common implementation problems, are also examined. In addition, a performance-oriented case study, based on audio transmission over packet networks, an area where UCL-CS enjoys worldwide recognition, is included. The advent of higher speed access (e.g., 33.6-56 Kbps modems, but also xDSL, cable modems, etc.), combined with wide backbone connectivity and progress in software (applications and protocols), proved in practice the suitability of packet networks to carry multimedia (audio, graphics, video, etc.) information. During recent years, there has been considerable work on this field, with a significant number of relevant tools seeing publicity ([5] , [15] , [34] ). Most of these applications are implemented in C and/or C++, for performance and functionality reasons. Recently, however, a number of efforts to develop multimedia applications using a relative newcomer, Java, have been recorded ([1] , [8] , [14] , [17] , [30] ). The Department of Computer Science at University College London (UCL-CS) has long-term research and development experience in Networked Multimedia, and in particular audio and video conferencing, with several previous and current projects in the area ([35] ). With the advent of the Java programming language and its rapid evolution as the preferred platform for many, significant effort has been put into investigating its applicability for multimedia applications, with emphasis being given to audio ([1] , [8] ).

Jon Crowcroft

Papers

Lightweight Practical Private One-Way Anonymous Messaging

MIRRORS: An integrated framework for capturing real world behaviour for models of ad hoc networks

Aggregate Cyber-Risk Management in the IoT Age: Cautionary Statistics for (Re)Insurers and Likes

Peer provided cell-like networks built out of thin air

Java performance for multimedia applications