108,270 research outputs found
Medium access control, error control and routing in underwater acoustic networks: a discussion on protocol design and implementation
No full textThe journey of underwater communication which began from Leonardo’s era took four and a half centuries to find practical applications for military purposes during World War II. However, over the last three decades, underwater acoustic communications witnessed a massive development due to the advancements in the design of underwater communicating
peripherals and their supporting protocols. Successively, doors are opened for a wide range of applications to employ in the underwater environment, such as oceanography, pollution
monitoring, offshore exploration, disaster prevention, navigation assistance, monitoring, coastal patrol and surveillance. Different applications may have different characteristics and hence, may require different network architectures. For instance, routing protocols designed for unpartitioned multi-hop networks are not suitable for Delay-Tolerant Networks. Furthermore, single-hop networks do not need routing protocols at all. Therefore, before
developing a protocol one must study the network architecture properly and design it accordingly.
There are several other factors which should also be considered with the network architecture while designing an efficient protocol for underwater networks, such as long propagation delay, limited bandwidth, limited battery power, high bit error rate of the channel and several other adverse properties of the channel, such as, multi-path, fading and refractive behaviors. Moreover, the environment also has an impact on the performance of the protocols designed for underwater networks. Even temperature changes in a single day have an impact on the performance of the protocols. A good protocol designed for any network should consider some or all of these characteristics to achieve better performance.
In this thesis, we first discuss the impact of the environment on the performance of MAC and routing protocols. From our investigation, we discover that even temperature changes within a day may affect the sound speed profile and hence, the channel changes and the protocol performance vary. After that we discuss several protocols which are specifically designed for underwater acoustic networks to serve different purposes and for different network architectures. Underwater Selective Repeat (USR) is an error control protocol designed to assure reliable data transmission in the MAC layer. One may suspect that employing an error control technique over a channel which already suffers from long propagation delays is a burden. However, USR utilizes long propagation by transmitting multiple packets in a single RTT using an interlacing technique. After USR, a routing protocol for surveillance networks is discussed where some sensors are laid down at the bottom of the sea and some sinks are placed outside the area. If a sensor detects an asset within its detection range, it announces the presence of intruders by transmitting packets to the sinks. It may happen
that the discovered asset is an enemy ship or an enemy submarine which creates noise to jam the network. Therefore, in surveillance networks, it is necessary that the protocols have
jamming resistance capabilities. Moreover, since the network supports multiple sinks with similar anycast address, we propose a Jamming Resistance multi-path Multi-Sink Routing
Protocol (MSRP) using a source routing technique. However, the problem of source routing is that it suffers from large overhead (every packet includes the whole path information) with
respect to other routing techniques, and also suffers from the unidirectional link problem. Therefore, another routing protocol based on a distance vector technique, called Multi-path
Routing with Limited Cross-Path Interference (L-CROP) protocol is proposed, which employs a neighbor-aware multi-path discovery algorithm to support low interference multiple paths
between each source-destination pair. Following that, another routing protocol is discussed for next generation coastal patrol and surveillance network, called Underwater Delay-Tolerant
Network (UDTN) routing where some AUVs carry out the patrolling work of a given area and report to a shore based control-center. Since the area to be patrolled is large, AUVs
experience intermittent connectivity. In our proposed protocol, two nodes that understand to be in contact with each other calculate and divide their contact duration equally so that
every node gets a fair share of the contact duration to exchange data. Moreover, a probabilistic spray technique is employed to restrict the number of packet transmissions and for error correction a modified version of USR is employed.
In the appendix, we discuss a framework which was designed by our research group to realize underwater communication through simulation which is used in most of the simulations in this thesis, called DESERT Underwater (short for DEsign, Simulate, Emulate and Realize Test-beds for Underwater network protocols). It is an underwater extension of the
NS-Miracle simulator to support the design and implementation of underwater network protocols. Its creation assists the researchers in to utilizing the same codes designed for the
simulator to employ in actual hardware devices and test in the real underwater scenario
Contribution of Information and Communication Technology (ICT) in Country’S H-Index
No full textThe aim of this study is to examine the effect of Information and Communication Technology (ICT) development on country’s scientific ranking as measured by H-index. Moreover, this study applies ICT development sub-indices including ICT Use, ICT Access and ICT skill to find the distinct effect of these sub-indices on country’s H-index. To this purpose, required data for the panel of 14 Middle East countries over the period 1995 to 2009 is collected. Findings of the current study show that ICT development increases the H-index of the sample countries. The results also indicate that ICT Use and ICT Skill sub-indices positively contribute to higher H-index but the effect of ICT access on country’s H-index is not clear
On the paper “Symmetry analysis of wave equation on sphere” by H. Azad and M.T. Mustafa
No full textAbstractUsing the scalar curvature of the product manifold S2×R and the complete group classification of nonlinear Poisson equation on (pseudo) Riemannian manifolds, we extend the previous results on symmetry analysis of homogeneous wave equation obtained by H. Azad and M.T. Mustafa [H. Azad, M.T. Mustafa, Symmetry analysis of wave equation on sphere, J. Math. Anal. Appl. 333 (2007) 1180–1188] to nonlinear Klein–Gordon equations on the two-dimensional sphere
Cheladonta serrata Kudryashova, Neronov and Farang-Azad 1978
No full textCheladonta serrata Kudryashova, Neronov and Farang-Azad 1978: PAL Cheladonta (Susa) serrata Kudryashova, Neronov and Farang-Azad, 1978 Susa serrata, Kudryashova 1998 Cheladonta serrata, Stekolnikov et al. 2019cPublished as part of Nielsen, David H., Robbins, Richard G. & Rueda, Leopoldo M., 2021, Annotated world checklist of the Trombiculidae and Leeuwenhoekiidae (1758 - 2021) (Acari: Trombiculoidea), with notes on nomenclature, taxonomy, and distribution, pp. 1-243 in Zootaxa 4967 (1) on page 47, DOI: 10.11646/zootaxa.4967.1.1, http://zenodo.org/record/474551
Cell viability following 5-AzaD treatment.
No full textCell viability was detected by XTT following treatment of FaDu cells with increasing concentrations of 5-AzaD (0, 0.1, 0.5,1,2.5,5 and 10 μM) for 48 h (A). FaDu and normal fibroblast cells (NDHF) were treated with 5 μM of AzaD for a period of 24, 48 and 72 h (B). Untreated control cells, FaDu and NDHF, were exposed to 0.01% DMSO. Data were presented as mean ± SD of three independent experiments in which each treatment was performed in eight replicates, and are expressed as percentages of the respective untreated control cells that was defined as 100%. Statistical significance was determined by two-tailed Student’s t-test. Significance is indicated as **P<0.01, ***P<0.001.</p
Cheladonta firdousii Kudryashova, Neronov and Farang-Azad 1978
No full textCheladonta firdousii Kudryashova, Neronov and Farang-Azad, 1978: PAL Cheladonta firdousii, Stekolnikov et al. 2019cPublished as part of Nielsen, David H., Robbins, Richard G. & Rueda, Leopoldo M., 2021, Annotated world checklist of the Trombiculidae and Leeuwenhoekiidae (1758 - 2021) (Acari: Trombiculoidea), with notes on nomenclature, taxonomy, and distribution, pp. 1-243 in Zootaxa 4967 (1) on page 47, DOI: 10.11646/zootaxa.4967.1.1, http://zenodo.org/record/474551
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Corporate Social Responsibility Disclosure (CSRD) and Financial Distressed Risk (FDR): Does Institutional Ownership Matter?
No full textThis study aims to investigate the effect of corporate social responsibility disclosure (CSRD) on financial distressed risk (FDR) among firms listed on the Tehran Stock Exchange (TSE). This paper also examines whether there is a negative linkage between institutional ownership as a corporate governance mechanism and corporate bankruptcy. The final research purpose is to analyze if there is a moderating effect of institutional owners on the relationship between CSRD and FDR too. The study sample consists of 200 firms listed on the TSE between 2013 and 2018, and the statistical model is logistic regression. When FDR is assessed under both Article 141 of Iran’s business law and the Altman Z-score model, our results on the main research hypotheses are quite similar. Considering the social and cultural conditions and economic situation of the Iranian market, the results show that firms with a high level of CSR disclosure are not able to make themselves more creditworthy and do not have better access to financing, resulting in more financial insolvency. Our findings confirm institutional shareholders play a vital role in facilitating a firm’s emergence from bankruptcy. The results also demonstrate financial distress risk is less seen among companies with more institutional owners that disclose more CSR information. In other words, since the goals related to CSR are long-term and Iranian institutional investors have a long-term horizon towards the company, the presence of more institutional owners within a firm push managers to provide additional voluntary CSR disclosure so firms can maintain the trust of their shareholders at the highest possible level and prevent financial distress. Our additional analysis indicates there is a positive association between financial leverage and firm failure, whereas the current ratio and ROA are negatively connected with corporate bankruptcy. Finally, when FDR is assessed on the Altman Z-score model, our evidence supports a negative relation between purchase and sale-related party transactions and bankruptcy risk, which is consistent with the efficient transaction hypothesis
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