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Modularity of residually reducible Galois representations and Eisenstein ideals
Get PDFThe purpose of this thesis is to explain modularity of residually reducible Galois representations. More precisely, for a given reducible mod l representation, we want to classify the set of newforms whose associated mod l representations are isomorphic to it.We describe the partial result of the above classification
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Security of Genus 3 Curves in Cryptography
Get PDFThe Discrete Logarithm Problem (DLP) in the abelian group of -valued points on an elliptic curve has been successfully used as a building block for a wide variety of both public key encryption schemes and digital signature schemes. Since the size of is roughly , to have a security level of at least bits against generic collision attacks, such as Pollard rho, one must take to be at least bits.Neil Koblitz suggested using instead the group of -valued points on the Jacobian of a genus hyperelliptic curve . The upshot is that the size of is roughly , so to obtain a security level of bits against Pollard rho one needs to take to be at least bits.When everything works out well. As in the case of elliptic curves, the most efficient known attack against the DLP is Pollard rho, which runs in time . There are very efficient ways of doing arithmetic on the Jacobian of a genus curve (or rather on the Kummer surface), and with the increase in efficiency coming from using smaller fields ( at least bits), such genus cryptosystems are fast enough to be competitive with elliptic curve cryptosystems.When g>3 there is an efficient index calculus algorithm for breaking the DLP, which is why such curves are not considered to be useful for cryptographic purposes. Moreover, there is no efficient enough way of doing arithmetic on such high-dimensional Jacobians.When the situation is much more complicated. There is an index calculus algorithm which breaks the DLP on the Jacobian of a hyperelliptic genus curve in time . Note for comparison that Pollard rho runs in time . For practical field sizes ( at least bits) the difference between these complexities is quite significant. Nevertheless, this index calculus algorithm might not be fast enough to be a significant threat and the practicality of the attack is highly debatable. But genus hyperelliptic curves suffer also from another much worse security problem. Namely, it might be possible to compute an isogeny from the hyperelliptic Jacobian to another isogenous abelian variety, which has a good chance of being the Jacobian of a non-hyperelliptic genus curve over the same base field. If such an isogeny can be computed explicitly enough, the DLP can be mapped to the Jacobian of the non-hyperelliptic curve and solved using an even faster index calculus algorithm by Claus Diem, with complexity . This sounds bad, but again the practicality of Diem's attack is debatable. The main problem turns out to be that both the hyperelliptic and the non-hyperelliptic algorithms require vast amounts of memory. Therefore the security of genus hyperelliptic curves depends strongly on the practical performance of Diem's index calculus and the feasibility of computing isogenies explicity.We develop and study, both in theory and in practice, a new index calculus algorithm for attacking non-hyperelliptic genus curves. Our attack is related to Diem's index calculus, but improves it in several aspects. We obtain detailed space and time complexity estimates for our algorithm, making all hidden factors in the -notation explicit. We discuss time-memory trade-offs and practical ways of dealing with the massive memory requirements. Finally we discuss ways of generating hyperelliptic genus curves in such a way that performing isogeny attacks becomes particularly difficult. This is done by generating input data for the genus CM method of Weng in a very careful way, allowing us to precisely control which isogenies the attacker can use to reach non-hyperelliptic Jacobians
Cohomological realization of a family of 1-motives
No full textAbstractThe author studies a class of 1-motives which he encountered in his work joint work with Jacquinot (J. Number Theory 24, No. 3, 1986). A 1-motive M was attached in this previous work to each triple (A, f, α), where A is an abelian variety, f: A → A′ a homomorphism from A to its dual, and α a point on A. It was stated, without proof, at that time that the 1-motive M generates the same “Galois groups” (in a literal sense if one discusses n-torsion points of 1-motives, or else in the sense of Mumford-Tate groups if one works over C) as the simpler 1-motive M = [Z → A] which “is” α. The present article refines that observation by proving that the cohomological realizations of M may be derived from those of M, and vice versa, by linear algebra constructions. More precisely, let T(M) and T(M) be the modules of “n-division points” of M and M, where n ≥ 1 is an integer. The latter module is an evident quotient of the former. The author shows that, in the other direction, T(M) may be recovered from T(M) as a specific subquotient of T(M)⊗ 2
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
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