1,721,130 research outputs found
Empirical analysis of the impact of queries on watermarked relational databases
No full textRobust relational database watermarking techniques aim to preserve the watermark in the protected assets despite daily updates and malicious attacks. Nevertheless, most techniques do not analyze the root of operations that can degrade the embedded watermark signal, being that the case of Structured Query Language (SQL) queries for relational data. In this paper, we perform an empirical analysis of the role played by different types of SQL queries in the persistence and degradation of a watermark signal in a relational data set. According to the type of operation, we present a set of alternatives for the watermark detection process, contributing to the extraction of an ownership copyright signals threshold. Moreover, our proposal allows data owners to consider variations for the selected watermarking technique, according to the suspected malicious operation performed in the copy of available data. Finally, we give evidence of the importance of some features to be considered when selecting a watermark source, making possible the resilience against update operations that affect a high amount of protected data and the enhancement of a partially detected watermark
Relational data watermarking resilience to brute force attacks in untrusted environments
No full textWatermarking techniques for relational data that aim at robustness face the challenge of guaranteeing watermark persistence despite aggressive attacks. Nevertheless, attackers cannot compromise watermark detection to their will since they must ensure the usability of the stolen data. Attacks that constitute a potential master-key for false ownership claims focus on leaking or compromising values used for watermark synchronization. For instance, brute-force attacks attempt to guess the values of parameters used for watermark embedding. The chances for brute-force attacks of successfully performing illegal watermark detection increases in untrusted environments where the leaks of parameters are common. In this paper, (i) we show how brute-force attacks succeed even if not all watermark detection parameters’ values are correctly guessed, (ii) we define the role played by each parameter in robustness, and (iii) we formalize a method for improving the resilience of existing watermarking techniques in scenarios lacking trust. According to the experimental results, watermarking approaches to which our proposal has been applied benefit in terms of robustness and security requirements, extending the deployment opportunities for other techniques
The distribution of lenticular galaxies in the phase space of present-day galaxy cluster regions
No full textWe investigate the environmental impact of cluster regions on the evolution of nearby S0 galaxies, focusing on their distinct quiescent and star-forming (SF) subpopulations. We select a sample of clusters by crossmatching optical and X-ray data and extract a subset of 14 systems with maximally relaxed cores by applying strict virialization and substructure tests. A projected phase space (PPS) diagram is generated from the stack of relaxed clusters up to 3 virial radii to assess the locations of quiescent and SF S0s and their cluster infall histories. Additionally, we compare the radial line-of-sight velocity dispersion (VDLOS) and specific star-formation rate (SSFR) profiles for the different S0 subpopulations, using other Hubble types as benchmarks. Our study shows that quiescent S0s, the dominant class in the entire cluster region, concentrate preferentially at low radii in the PPS diagram, while SF S0s are more abundant in the outskirts. Despite this segregation, both subpopulations show similar VDLOS profiles in the cluster core -indicating an advanced stage of dynamical relaxation-, but that resemble those of late-type galaxies beyond the virial radius. This finding, combined with the distinct PPS distributions of both S0 subpopulations, which lead to mean infall times Gyr longer for quiescent S0s but that are shorter than those expected for ancient infallers, suggests that a substantial fraction of S0s present in the core region arrive via secondary infall. We also find evidence in the SSFR profiles that star formation in S0s begins to decline beyond the virialized core, likely due to preprocessing in infalling groups. Our results support a delayed-then-rapid quenching scenario for SF S0s in cluster regions, where their centrally concentrated star formation persists for an extended period before abruptly ending ( Gyr) after their first pericenter passage
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
A Quantile-Based Watermarking Approach for Distortion Minimization
Get PDFDistortion-based watermarking techniques embed the watermark by performing tolerable changes in the digital assets being protected. For relational data, mark insertion can be performed over the different data types of the database relations’ attributes. An important goal for distortion-based approaches is to minimize as much as possible the changes that the watermark embedding provokes into data, preserving their usability, watermark robustness, and capacity. This paper proposes a quantile-based watermarking technique for numerical cover type focused on preserving the distribution of attributes used as mark carriers. The experiments performed to validate our proposal show a significant distortion reduction compared to traditional approaches while maintaining watermark capacity levels. Also, positive achievements regarding robustness are visible, evidencing our technique’s resilience against subset attacks
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
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