1,720,968 research outputs found
Distributed connected dominating set techniques for energy-efficient topology control in wireless sensor networks.
No full textDespite the considerable research efforts devoted to extending the lifetime of wireless sensor networks (WSNs) by making them more energy efficient, there are still a number of unresolved issues. Among the possible solutions for improving their overall energy efficiency, topology control has significant potential. Distributed topology control is a difficult problem, and optimal solutions are not possible except for very simple topologies. Because of this, heuristic methods are used, but the solutions proposed in the research literature are usually tested with overly simplistic simulation models and consequently they fail to perform satisfactorily in real networks. The research project reported in this thesis proposes three new topology control methods that are tested on highly realistic simulation models calibrated with data collected on an experimental wireless sensor network. These models accurately handle interference effects, realistic transmission ranges and imperfect communication links. Additionally, the correctness of the proposed methods was verified using theoretical analysis. Two leading algorithms were used as benchmarks. Based on the outcomes of a thorough literature review and analysis of existing techniques, distributed connected dominating set (CDS) approach was selected as the starting point for the design of the proposed algorithms. The proposed algorithms are not only distributed but also use localized information for computing a CDS. Given that the CDS serves various tasks in a WSN, a fair load distribution strategy was adopted to prolong the network lifetime. This strategy takes into account the remaining energy levels at each node when choosing the eligible CDS nodes. The first topology control technique called the three-phase single initiator (TPSI) was developed to form a small CDS for medium and dense networks (i.e., in deployments when average node degree is relatively high) with minimal communication overhead, computational complexity and energy consumption. The simulation results demonstrate that the TPSI algorithm generates a small CDS for both medium and dense networks but not for sparse networks. These results also prove that the impact of network density on performance of an algorithm is significant and cannot be ignored. The second technique, single-phase single initiator (SPSI) on the other hand was proposed for applications that require fast convergence, and is best suited to WSN applications that have sparse topologies. The simulation results show that SPSI can generate a small CDS for sparse networks using low message overhead and energy consumption, and compute a CDS faster than the TPSI algorithm. The third one, the Two-phase multiple initiator (TPMI) algorithm adapts well to dynamic topology changes, thus it is suitable for applications that require frequent topology updates. Instead of relying on a single initiator to construct the CDS as in the TPSI and SPSI, the TPMI algorithm uses multiple initiators. The simulation results show that although the CDS size of TPMI is larger than the ones generated by TPSI or SPSI, it outperforms them in terms of energy consumption, network lifetime and convergence time in networks with rapidly changing topologies. Best suited algorithm for a particular installation can be selected manually, or by using some measurement techniques, the structure of a network can be probed to activate the optimal method automatically
Distributed connected dominating set techniques for energy-efficient topology control in wireless sensor networks.
No full textDespite the considerable research efforts devoted to extending the lifetime of
wireless sensor networks (WSNs) by making them more energy efficient, there
are still a number of unresolved issues. Among the possible solutions for improving
their overall energy efficiency, topology control has significant potential.
Distributed topology control is a difficult problem, and optimal solutions are not
possible except for very simple topologies. Because of this, heuristic methods
are used, but the solutions proposed in the research literature are usually tested
with overly simplistic simulation models and consequently they fail to perform
satisfactorily in real networks.
The research project reported in this thesis proposes three new topology control
methods that are tested on highly realistic simulation models calibrated with data
collected on an experimental wireless sensor network. These models accurately
handle interference effects, realistic transmission ranges and imperfect communication
links. Additionally, the correctness of the proposed methods was verified
using theoretical analysis. Two leading algorithms were used as benchmarks.
Based on the outcomes of a thorough literature review and analysis of existing
techniques, distributed connected dominating set (CDS) approach was selected
as the starting point for the design of the proposed algorithms. The proposed
algorithms are not only distributed but also use localized information for computing
a CDS. Given that the CDS serves various tasks in a WSN, a fair load
distribution strategy was adopted to prolong the network lifetime. This strategy
takes into account the remaining energy levels at each node when choosing the
eligible CDS nodes.
The first topology control technique called the three-phase single initiator (TPSI)
was developed to form a small CDS for medium and dense networks (i.e., in
deployments when average node degree is relatively high) with minimal communication
overhead, computational complexity and energy consumption. The
simulation results demonstrate that the TPSI algorithm generates a small CDS
for both medium and dense networks but not for sparse networks. These results
also prove that the impact of network density on performance of an algorithm is
significant and cannot be ignored.
The second technique, single-phase single initiator (SPSI) on the other hand was
proposed for applications that require fast convergence, and is best suited to WSN
applications that have sparse topologies. The simulation results show that SPSI
can generate a small CDS for sparse networks using low message overhead and
energy consumption, and compute a CDS faster than the TPSI algorithm.
The third one, the Two-phase multiple initiator (TPMI) algorithm adapts well to dynamic
topology changes, thus it is suitable for applications that require frequent
topology updates. Instead of relying on a single initiator to construct the CDS as
in the TPSI and SPSI, the TPMI algorithm uses multiple initiators. The simulation
results show that although the CDS size of TPMI is larger than the ones generated
by TPSI or SPSI, it outperforms them in terms of energy consumption, network
lifetime and convergence time in networks with rapidly changing topologies.
Best suited algorithm for a particular installation can be selected manually, or by
using some measurement techniques, the structure of a network can be probed to
activate the optimal method automatically
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Improving the realibility of zinc oxide surge arrester / Azrina Abd Aziz and Tapan K. Saha
Full text linkReliable surge arresters can avoid unnecessary costs associated with equipment damage and ineffective lightning protection techniques. The most recent advance in the arrester is the Zinc Oxide arrester. However, some of the arresters can be damaged during their operation. The major cause of failure of the arresters is the surface flashover. This study aim to examine the surface flashover effect on ZnO arresters and develop method to reduce its effect and enhance the performance of the arrester. The experiment was designed to study the surface flashover effects. The ZnO blocks supplied by manufacturers were tested under different environments during multipulse currents. The observed degradation was qualitatively explained in terms of physical changes on the blocks and their electrical characteristics. The study found that the environments surrounding the ZnO blocks had no impact on surface flashover. The major finding leads to the possible contribution of the quality of surface material coating in protecting the blocks from surface flashover
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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