1,720,968 research outputs found
A Textbook Solution for Dynamic Strings
Get PDFWe consider the problem of maintaining a collection of strings while efficiently supporting splits and concatenations on them, as well as comparing two substrings, and computing the longest common prefix between two suffixes. This problem can be solved in optimal time O(log N) whp for the updates and O(1) worst-case time for the queries, where N is the total collection size [Gawrychowski et al., SODA 2018]. We present here a much simpler solution based on a forest of enhanced splay trees (FeST), where both the updates and the substring comparison take O(log n) amortized time, n being the lengths of the strings involved. The longest common prefix of length l is computed in O(log n + log2 l) amortized time. Our query results are correct whp. Our simpler solution enables other more general updates in O(log n) amortized time, such as reversing a substring and/or mapping its symbols. We can also regard substrings as circular or as their omega extension
BAT-LZ out of hell
Get PDFDespite consistently yielding the best compression on repetitive text collections, the Lempel-Ziv parsing has resisted all attempts at offering relevant guarantees on the cost to access an arbitrary symbol. This makes it less attractive for use on compressed self-indexes and other compressed data structures. In this paper we introduce a variant we call BAT-LZ (for Bounded Access Time Lempel-Ziv) where the access cost is bounded by a parameter given at compression time. We design and implement a linear-space algorithm that, in time O(nlog3 n), obtains a BAT-LZ parse of a text of length n by greedily maximizing each next phrase length. The algorithm builds on a new linear-space data structure that solves 5-sided orthogonal range queries in rank space, allowing updates to the coordinate where the one-sided queries are supported, in O(log3 n) time for both queries and updates. This time can be reduced to O(log2 n) if O(nlog n) space is used. We design a second algorithm that chooses the sources for the phrases in a clever way, using an enhanced suffix tree, albeit no longer guaranteeing longest possible phrases. This algorithm is much slower in theory, but in practice it is comparable to the greedy parser, while achieving significantly superior compression. We then combine the two algorithms, resulting in a parser that always chooses the longest possible phrases, and the best sources for those. Our experimentation shows that, on most repetitive texts, our algorithms reach an access cost close to log2 n on texts of length n, while incurring almost no loss in the compression ratio when compared with classical LZ-compression. Several open challenges are discussed at the end of the paper
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
On Data Structures for Texts and Permutations
Get PDFDue to the exponential growth of genomic data, constructing dedicated data structures has become the principal bottleneck in common bioinformatics applications. A large number of algorithms for constructing and processing data structures on texts exist in the literature, but they are faced with the challenge of keeping up with the volume of new data. Especially in pangenomics, where numerous genomes of the same species are produced and processed together, one can hope to modify existing algorithms or introduce new ones to exploit the repetitiveness that is contained within this kind of datasets.
In the first part of this thesis, we will focus on speeding up the computation of a key data structure used in bioinformatics: the matching statistics. We propose various heuristics aimed at improving the running time for the computation of the matching statistics for large sets of similar strings.
Then we introduce a compressed representation of the matching statistics. The new representation is shown to be very small in practice while retaining all the information needed for allowing fast random access. This permitted us to use this new representation for constructing other fundamental data structures, namely the suffix array and the Burrows-Wheeler Transform (BWT). Next, we study the topic of merging BWTs, where data belonging to distinct sets is dissimilar. Here, the matching statistics are used to speed up the merging phase, where the algorithm exploits areas of high difference between the two sets.
In the second part of the thesis, we show how to handle dynamic strings and dynamic permutations. The dynamic setting is of high interest due to the fast pace at which data is produced nowadays. We present new data structures that are simple and elegant and handle both strings and permutations using a common underlying idea: a forest of splay trees. Splay trees are binary search trees which are particularly well suited for a dynamic setting. Moreover, they are easy to understand and to implement, and have therefore high practical applicability. In the last chapter of this part, we present a simple data structure whose application has significantly improved a recent algorithm for combinatorial generation of permutations.
Finally, in the last part, we study the problem of efficient access to Lempel-Ziv-compressed text. The Lempel-Ziv compression (LZ77) is one of the most well-known and most used methods for compressing large amounts of repetitive data. An open problem is how to access arbitrary characters without the need to decompress the whole input. In this thesis, we propose new heuristics to build different kinds of LZ-like parsings that allow constant time access to characters while in compressed form, without compromising the compression ratio by more than a small percentage w.r.t.\ the original LZ parse.
All of these new algorithms have been implemented and tested against the main competitors in the respective fields, and they have shown good results.
We close with an outlook to future research
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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