世界経済・社会統計 = World development indicators

Unmanned aerial vehicles (UAVs) have enormous potential in the public and civil domains. These are particularly useful in applications, where human lives would otherwise be endangered. Multi-UAV systems can collaboratively complete missions more efficiently and economically as compared to single UAV systems. However, there are many issues to be resolved before effective use of UAVs can be made to provide stable and reliable context-specific networks. Much of the work carried out in the areas of mobile ad hoc networks (MANETs), and vehicular ad hoc networks (VANETs) does not address the unique characteristics of the UAV networks. UAV networks may vary from slow dynamic to dynamic and have intermittent links and fluid topology. While it is believed that ad hoc mesh network would be most suitable for UAV networks yet the architecture of multi-UAV networks has been an understudied area. Software defined networking (SDN) could facilitate flexible deployment and management of new services and help reduce cost, increase security and availability in networks. Routing demands of UAV networks go beyond the needs of MANETS and VANETS. Protocols are required that would adapt to high mobility, dynamic topology, intermittent links, power constraints, and changing link quality. UAVs may fail and the network may get partitioned making delay and disruption tolerance an important design consideration. Limited life of the node and dynamicity of the network lead to the requirement of seamless handovers, where researchers are looking at the work done in the areas of MANETs and VANETs, but the jury is still out. As energy supply on UAVs is limited, protocols in various layers should contribute toward greening of the network. This paper surveys the work done toward all of these outstanding issues, relating to this new class of networks, so as to spur further research in these areas.

Survey of Important Issues in UAV Communication Networks

Summary) The abstract should follow the structure of the article (relevance, degree of exploration of the problem, the goal, the main results, conclusion) and characterize the theoretical and practical significance of the study results. The abstract should not contain wording echoing the title, cumbersome grammatical structures and abbreviations. The text should be written in scientific style. The volume of abstracts (summaries) depends on the content of the article, but should not be less than 250 words. All abbreviations must be disclosed in the summary (in spite of the fact that they will be disclosed in the main text of the article), references to the numbers of publications from reference list should not be made. The sentences of the abstract should constitute an integral text, which can be made by use of the words “consequently”, “for example”, “as a result”. Avoid the use of unnecessary introductory phrases (eg, “the author of the article considers...”, “The article presents...” and so on.)

/pdf/ministry-of-education-and-science-of-the-russian-federation-7m2jn0xnm1.pdf

Ministry of Education and Science of the Russian Federation

Hafnia (HfO2) and hafnium-based materials are traditionally regarded as technologically important materials in the nuclear industry, a consequence of their exceptionally high neutron absorption coefficient. Following the discovery of transformation toughening in the mid 1970s, a considerable research effort has been devoted to zirconia (ZrO2)-toughened ceramics (ZTCs). They are considered to be potentially useful materials for structural applications at low and intermediate temperatures (T 1000 °C) is related to the low temperature of the tetragonal to monoclinic transformation in ZrO2. On the basis that HfO2 exhibits a similar crystal structure and in particular that its tetragonal to monoclinic transformation temperature (∼1700 °C) is approximately 700 °C higher than that for ZrO2, it has been suggested that high-temperature transformation toughening could be possible in HfO2-toughened ceramics (HTCs). Although the concepts behind this suggestion are universally appreciated, only a limited success has been made of the fabrication and the microstructural and mechanical property evaluation of these materials. The fracture toughness values obtained so far in HfO2 toughened ceramics are, in fact, considerably lower than those obtained in their ZrO2 counterparts. A great deal of further research work is therefore required in order to understand fully and to exploit toughened ceramics in the HfO2-based and HfO2-containing systems. This review covers the science and technology of HfO2 and HfO2-toughened ceramics in terms of processing, phase transformation, microstructure, and mechanical properties.

Hafnia and hafnia-toughened ceramics

Providing connectivity to around half of the world population living in rural or underprivileged areas is a tremendous challenge, but, at the same time, a unique opportunity. Access to the Internet would provide the population living in these areas a possibility to progress on the educational, health, environment, and business levels. In this article, a survey of technologies for providing connectivity to rural areas, which can help address this challenge, is provided. Although access/fronthaul and backhaul techniques are discussed in this article, it is noted that the major limitation for providing connectivity to rural and underprivileged areas is the cost of backhaul deployment. In addition, energy requirements and cost-efficiency of the studied technologies are analyzed. In fact, the challenges faced for deploying an electricity network, as a prerequisite for deploying communication networks, are huge in these areas, and they are granted an important share of the discussions in this article. Furthermore, typical application scenarios in rural areas are discussed, and several country-specific use cases are surveyed. The main initiatives by key international players aiming to provide rural connectivity are also described. Moreover, directions for the future evolution of rural connectivity are outlined in this article. Although there is no single solution that can solve all rural connectivity problems, building gradually on the current achievements in order to reach ubiquitous connectivity, while taking into account the particularities of each region and tailoring the solution accordingly, seems to be the most suitable path to follow.

/pdf/a-key-6g-challenge-and-opportunity-connecting-the-base-of-385d3hceqi.pdf

A Key 6G Challenge and Opportunity—Connecting the Base of the Pyramid: A Survey on Rural Connectivity

2nd IFIP International Symposium on Wireless Communications and Information Technology in Developing Countries, CSIR, Pretoria, South Africa, 6-7 October 2008

Simple pragmatic approach to mesh routing using BATMAN

Predicting the performance of ad hoc networking protocols for mesh networks has typically been performed by making use of software based simulation tools. Experimental study and validation of such predictions is a vital to obtaining more realistic results, but may not be possible under the constrained environment of network simulators. This paper presents an experimental comparison of OLSR using the standard hysteresis routing metric and the ETX metric in a 7 by 7 grid of closely spaced Wi-Fi nodes to obtain more realistic results. The wireless grid is first modelled to extract its ability to emulate a real world multi-hop ad hoc network. This is followed by a detailed analysis of OLSR in terms of hop count, routing traffic overhead, throughput, delay, packet loss and route flapping in the wireless grid using the hysteresis and ETX routing metric. It was discovered that the ETX metric which has been extensively used in mesh networks around the world is fundamentally flawed when estimating optimal routes in real mesh networks and that the less sophisticated hysteresis metric shows better performance in large dense mesh networks.

/pdf/comparison-of-two-routing-metrics-in-olsr-on-a-grid-based-2mqjifujwa.pdf

Comparison of two routing metrics in OLSR on a grid based mesh network

Mobile telephony brings clear economic and social benefits to its users. As handsets have become more affordable, ownership has reached staggering numbers, even in the most remote areas of the world. However, network coverage is often lacking in low population densities and low income rural areas of the developing world, where big telecoms often defer from deploying expensive infrastructure. To solve this coverage gap, we propose VillageCell, a low-cost alternative to high-end cell phone networks. VillageCell relies on software defined radios and open-source solutions to provide free local and cheap long-distance communication for remote regions. Our architecture is simple and easy to deploy, yet robust and requires no modification to GSM handsets. Through measuring the call quality metrics and the system capacity under a realistic rural-area network load, we show that VillageCell is indeed an attractive solution for rural area voice connectivity.

/pdf/villagecell-cost-effective-cellular-connectivity-in-rural-2iak7thtb8.pdf

VillageCell: cost effective cellular connectivity in rural areas

While Internet connectivity has reached a significant part of the world's population, those living in rural areas of the developing world are still largely disconnected. Recent efforts have provided Internet connectivity to a growing number of remote locations, yet Internet traffic demands cause many of these networks to fail to deliver basic quality of service needed for simple applications. For an in-depth investigation of the problem, we gather and analyze network traces from a rural wireless network in Macha, Zambia. We supplement our analysis with on-site interviews from Macha, Zambia and Dwesa, South Africa, another rural community that hosts a local wireless network. The results reveal that Internet traffic in rural Africa differs significantly from the developed world. We observe dominance of web-based traffic, as opposed to peer-to-peer traffic common in urban areas. Application-wise, online social networks are the most popular, while the majority of bandwidth is consumed by large operating system updates. Our analysis also uncovers numerous network anomalies, such as significant malware traffic. Finally, we find a strong feedback loop between network performance and user behavior. Based on our findings, we conclude with a discussion of new directions in network design that take into account both technical and social factors.

Traffic characterization and internet usage in rural Africa

There have been a number of rural wireless networks providing Internet access over the last decade but little is known about how the Internet is being used, how these networks perform and whether they follow similar trends when compared with Internet usage patterns in developed regions. We analyse a set of network traces from the Linknet wireless network in Zambia, which provides Internet access to approximately 300 residents of a rural village using a satellite link and a combination of point-to-point links, hotspots and wireless mesh networks. Our analysis reveals largely web-based traffic as opposed to the peer-to-peer traffic dominance that one finds in urban areas. Social networking sites receive the most hits, and large file downloads from operating system repositories contribute the most to the bandwidth consumption. A number of network pathologies in the gateway as well as the wireless mesh network are also analysed and a set of recommendations conclude the work.

https://dritte.org/nsdr10/files/nsdr10_paper07.pdf

Internet usage and performance analysis of a rural wireless network in Macha, Zambia

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