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Generation of Golomb Ruler Sequences and Optimization using Genetic Algorithms
No full textThe attractiveness of lightwave communications is the ability of silica-optical fibers to carry large amounts of information over long repeaterless spans. To utilize the available bandwidth, numerous channels at different wavelengths can be multiplexed on the same fiber. To increase system margins, higher transmitter powers or lower fiber losses are required. All these attempts to fully utilize the capabilities of silica fibers will ultimately be limited by nonlinear interactions between the information bearing lightwaves and the transmission medium. These optical nonlinearities can lead to interference, distortion and excess attenuation of the optical signals, resulting in system degradations. One of these nonlinearities is the four-wave mixing whereby two or more optical waves at different wavelengths mix to produce new optical waves at other wavelengths and generate interfering signals for other channels. This will degrade both detection and heterodyne systems.
Four-wave mixing (FWM) is a nonlinear process that occurs in materials such as silica with symmetric molecular structures and leads to generation of power at new optical frequencies from two or more co-propagating waves. The most significant negative effects of FWM are parametric gain and crosstalk in long haul, multi-channel Wavelength Division Multiplexed (WDM) systems. FWM efficiency is maximized at the zero dispersion wavelengths and for closely spaced input waves. Of particular concern is the case of WDM channels that are equally spaced in frequency as any FWM products will fall on frequencies used by other channels. By using unequal channel separations, the products of FWM can be made not to fall on allocated frequencies.
In an attempt to reduce FWM effect in WDM systems, many unequally spaced channel allocation methods were proposed. However, they resulted in increase of bandwidth requirement compared to equally spaced channel allocation. This is due to the constraint of the minimum channel spacing between each channel and that the difference in the channel spacing between any two channels is assigned to be distinct. As the number of channels increases, the bandwidth for the unequally spaced channel allocation methods increases proportionately.
In mathematics, the term 'Golomb Ruler' refers to a set of non-negative integers such that no distinct pairs of numbers from the set have the same difference. Since the difference between any two numbers is distinct, the new FWM frequencies generated would not fall into the one already assigned for the carrier channels. However, using conventional Golomb Rulers was not efficient as the operating bandwidth would be increased significantly as the existing methods. An Optimal Golomb Ruler (OGR) is the shortest Golomb Ruler possible for a given number of marks. Therefore, applying OGR to the channel allocation problem, it was possible to achieve the smallest distinct number to be used for the channel allocation. The OGRs were used to allocate the channels so as to restrict the expansion of the bandwidth.
The Golomb Rulers have to be optimized to form OGRs using an optimization technique.
There are several optimization techniques, the most common for engineering problems being stimulated annealing, evolution strategies and genetic algorithms. Simulated annealing probabilistically generates a sequence of states based on a cooling schedule to ultimately converge to the global optimum. Evolution strategies use mutations as search mechanisms and selection to direct the search toward the prospective regions in the search space. Genetic algorithms generate a sequence of populations by using a selection mechanism, and use crossover and mutation as search mechanisms. Thus, the genetic algorithms provide an alternative to traditional optimization techniques by using directed random searches to locate optimal solutions in complex landscapes.
The GA is a stochastic global search method that mimics the metaphor of natural biological evolution. GAs operate on a population of potential solutions applying the principle of survival of the fittest to produce better and better approximations to a solution. At each generation, a new set of approximations is created by the process of selecting individuals according to their level of fitness in the problem domain and breeding them together using operators borrowed from natural genetics. This process leads to the evolution of populations of individuals that are better suited to their environment than the individuals that are better suited to their environment than the individuals that they were created from, just as in natural adaptation.
In the present study, first of all a parametric run on fiber dispersion is performed to show dependency of four wave mixing on dispersion value. For operation near the zero dispersion wavelength, the FWM efficiency is maximized and as the dispersion increases, the power of the FWM products falls, that is, FWM effect decreases with increasing dispersion and vice-versa. Thus, for WDM systems deploying dispersion-shifted fibers to compensate for the dispersion induced in the fiber, it is a must to reduce FWM effect. In this concern, two algorithms for the generation of Golomb Ruler sequences are described. In the first algorithm, the modified extended quadratic congruence (EQC) sequences are generated and the second is the algorithm based on searching. These algorithms produce Golomb Rulers for any number of marks (channels). For both the algorithms, various examples of rulers for different number of marks are provided and bandwidth expansion factors are calculated that gives the factor of the bandwidth expanded with the use of unequal channel allocation in comparison with that of equal channel allocation. The total slot bandwidth and time requirements are calculated for different number of marks and compared for the two algorithms. It is seen that the bandwidth requirements for the search algorithm are less and in addition, the time required for the generation of sequences in search algorithm remains constant irrespective of the number of marks. Both these algorithm needed large bandwidth requirements. As the number of marks increases, the bandwidth increases exponentially. Optimization of the rulers means to have the short rulers, that is, the length of the rulers is minimized so as to conserve the bandwidth. Any optimization technique could be used here but for the NP-complete problems, like the Golomb Ruler, genetic algorithms are the best optimization technique to be used. Thus here the genetic algorithms are used to produce Optimal Golomb Rulers. The length of the rulers is the objective function to be minimized. As the number of generations increases, the length of the ruler and thus the bandwidth occupied tends to decrease, thus the rulers become more and more optimized, until no further improvements are there. This is the point where we get the optimal, or the shortest ruler. It is seen that by using genetic algorithms, bandwidth requirements become nearly one-third of that of the previous conventional algorithms, for the same number of channels.
The physical significance of this work is seen as the reduction of the four-wave mixing effect in WDM systems. As the difference between every pair of channels is unique, the additional frequencies produced by the FWM process do not tend to fall upon the already assigned frequencies. Hence the crosstalk, which is the main concern in WDM systems, is minimized enhancing the efficiency of the overall optical system.Thapar Institute of Engineering and Technology, Department of Electronics and Communication Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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