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

This work does the statistical quality-of-service (QoS) analysis of a block-fading device-to-device (D2D) link in a multi-tier cellular network that consists of a macro-BS (BSMC) and a micro-BS (BSmC) which both operate in full-duplex (FD) mode. For the D2D link under consideration, we first formulate the mode selection problem-whereby D2D pair could either communicate directly, or, through the BSmC, or, through the BSMC-as a ternary hypothesis testing problem. Next, to compute the effective capacity (EC) for the given D2D link, we assume that the channel state information (CSI) is not available at the transmit D2D node, and hence, it transmits at a fixed rate r with a fixed power. This allows us to model the D2D link as a Markov system with six-states. We consider both overlay and underlay modes for the D2D link. Moreover, to improve the throughput of the D2D link, we assume that the D2D pair utilizes two special automatic repeat request (ARQ) schemes, i.e., Hybrid-ARQ (HARQ) and truncated HARQ. Furthermore, we consider two distinct queue models at the transmit D2D node, based upon how it responds to the decoding failure at the receive D2D node. Eventually, we provide closed-form expressions for the EC for both HARQ-enabled D2D link and truncated HARQ-enabled D2D link, under both queue models. Noting that the EC looks like a quasi-concave function of r, we further maximize the EC by searching for an optimal rate via the gradient-descent method. Simulation results provide us the following insights: i) EC decreases with an increase in the QoS exponent, ii) EC of the D2D link improves when HARQ is employed, iii) EC increases with an increase in the quality of self-interference cancellation techniques used at BSmC and BSMC in FD mode.

Effective Capacity Analysis of HARQ-enabled D2D Communication in Multi-Tier Cellular Networks

Users predominantly access their email via mobile devices. This presents a two-fold challenge to the email applications. First, email's update from multiple devices has to be eventually reconciled with the server. Prioritization of updates is difficult and maybe undesirable. Solving this problem requires a data store with the complete history of email changes. Second, legacy email protocols don't provide an optimal email synchronization and access in mobile environment. In this paper we are proposing to take advantage of the Internet of Things (IoT) phenomena. In IoT environment a user may have multiple interconnected in-home low-end devices with publicly accessible address. In this architecture we move the email application from the central service into user's in-home and mobile devices, store complete email history on each device, and replace legacy IMAP and SMTP protocols with a synchronization protocol found in Distributed Version Control Systems(DVCS). This addresses the email reconciliation issue, optimizes the bandwidth usage, and intrinsically puts the user in control of her data. We analyze a number of stores and synchronization implementations and compare them with the open source Dovecot email server.

My home is my post-office: evaluation of a decentralized email architecture on internet-of-things low-end device

— With the advances in mobile technologies, smart mobile computing devices have become increasingly affordable and powerful, leading to a significant growth in both the number of advanced mobile users and their bandwidth demands. Moreover multimedia streaming to these high-end mobile devices has become widespread. However, multimedia applications are known to be resource-hungry and in order to cope with this explosion of data traffic, operators have started deploying different, overlapping radio access network technologies. One important challenge in such a heterogeneous wireless environment is to ensure an Always Best Experience to the mobile user, anywhere and anytime. This paper proposes the Quality Utility, a realistic mapping function of the received bandwidth to user satisfaction for multimedia streaming applications. The Quality Utility is mapped to a Google Nexus One Android Mobile device and validated through objective and subjective tests.

Middlesex University Research Repository An open access repository of Middlesex University research

Future advances in conferencing will make it feasible to build servers which collaborate to provide services similar to those of an airline booking system over the networks. Such servers should be able to support real-time queries and modifications to the information stored. We present the management requirements for the services that are providd by these servers.

Teleservice requirements for management

MeshSim is a platform for developing wireless ad-hoc network communication protocols. It supports two operation modes: Firstly, simulated mode, in which all nodes of the network run as processes in a given machine with arbitrary configuration parameters. Secondly, device mode, in which the code is deployed to individual devices with their own radios. The main feature of MeshSim is that the code that runs in simulated mode is the same code that runs on device mode. This is achieved via network interface abstraction. It allows the design, development and test of ad-hoc network protocols while isolating external variables (simulated mode), that can be later deployed and tested on real devices (device mode).

https://dl.acm.org/doi/pdf/10.1145/3124087.3124089

Jon Crowcroft

Papers

Effective Capacity Analysis of HARQ-enabled D2D Communication in Multi-Tier Cellular Networks

My home is my post-office: evaluation of a decentralized email architecture on internet-of-things low-end device

Middlesex University Research Repository An open access repository of Middlesex University research

Teleservice requirements for management

Demo: MeshSim: A Wireless Ad-Hoc Network Development Platform