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Search Results: 1 - 10 of 53149 matches for " David Comas "
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Unbalanced Multiple-Description Video Coding with Rate-Distortion Optimization
Comas David,Singh Raghavendra,Ortega Antonio,Marqués Ferran
EURASIP Journal on Advances in Signal Processing , 2003,
Abstract: We propose to use multiple-description coding (MDC) to protect video information against packet losses and delay, while also ensuring that it can be decoded using a standard decoder. Video data are encoded into a high-resolution stream using a standard compliant encoder. In addition, a low-resolution stream is generated by duplicating the relevant information (motion vectors, headers and some of the DCT coefficient) from the high-resolution stream while the remaining coefficients are set to zero. Both streams are independently decodable by a standard decoder. However, only in case of losses in the high resolution description, the corresponding information from the low resolution stream is decoded, else the received high resolution description is decoded. The main contribution of this paper is an optimization algorithm which, given the loss ratio, allocates bits to both descriptions and selects the right number of coefficients to duplicate in the low-resolution stream so as to minimize the expected distortion at the decoder end.
La evaluación de programas de ocio alternativo de fin de semana
Comas Domingo
Revista Espa?ola de Salud Pública , 2001,
A characterization of the rational normal curve
Gonzalo Comas
Mathematics , 2007,
Abstract: We give a characterization of the rational normal curve in terms of the rank function associated to a curve.
Utility-Preserving Differentially Private Data Releases Via Individual Ranking Microaggregation
David Sánchez,Josep Domingo-Ferrer,Sergio Martínez,Jordi Soria-Comas
Computer Science , 2015, DOI: 10.1016/j.inffus.2015.11.002
Abstract: Being able to release and exploit open data gathered in information systems is crucial for researchers, enterprises and the overall society. Yet, these data must be anonymized before release to protect the privacy of the subjects to whom the records relate. Differential privacy is a privacy model for anonymization that offers more robust privacy guarantees than previous models, such as $k$-anonymity and its extensions. However, it is often disregarded that the utility of differentially private outputs is quite limited, either because of the amount of noise that needs to be added to obtain them or because utility is only preserved for a restricted type and/or a limited number of queries. On the contrary, $k$-anonymity-like data releases make no assumptions on the uses of the protected data and, thus, do not restrict the number and type of doable analyses. Recently, some authors have proposed mechanisms to offer general-purpose differentially private data releases. This paper extends such works with a specific focus on the preservation of the utility of the protected data. Our proposal builds on microaggregation-based anonymization, which is more flexible and utility-preserving than alternative anonymization methods used in the literature, in order to reduce the amount of noise needed to satisfy differential privacy. In this way, we improve the utility of differentially private data releases. Moreover, the noise reduction we achieve does not depend on the size of the data set, but just on the number of attributes to be protected, which is a more desirable behavior for large data sets. The utility benefits brought by our proposal are empirically evaluated and compared with related works for several data sets and metrics.
t-Closeness through Microaggregation: Strict Privacy with Enhanced Utility Preservation
Jordi Soria-Comas,Josep Domingo-Ferrer,David Sánchez,Sergio Martínez
Computer Science , 2015, DOI: 10.1109/TKDE.2015.2435777
Abstract: Microaggregation is a technique for disclosure limitation aimed at protecting the privacy of data subjects in microdata releases. It has been used as an alternative to generalization and suppression to generate $k$-anonymous data sets, where the identity of each subject is hidden within a group of $k$ subjects. Unlike generalization, microaggregation perturbs the data and this additional masking freedom allows improving data utility in several ways, such as increasing data granularity, reducing the impact of outliers and avoiding discretization of numerical data. $k$-Anonymity, on the other side, does not protect against attribute disclosure, which occurs if the variability of the confidential values in a group of $k$ subjects is too small. To address this issue, several refinements of $k$-anonymity have been proposed, among which $t$-closeness stands out as providing one of the strictest privacy guarantees. Existing algorithms to generate $t$-close data sets are based on generalization and suppression (they are extensions of $k$-anonymization algorithms based on the same principles). This paper proposes and shows how to use microaggregation to generate $k$-anonymous $t$-close data sets. The advantages of microaggregation are analyzed, and then several microaggregation algorithms for $k$-anonymous $t$-closeness are presented and empirically evaluated.
Genetic origin, admixture, and asymmetry in maternal and paternal human lineages in Cuba
Isabel Mendizabal, Karla Sandoval, Gemma Berniell-Lee, Francesc Calafell, Antonio Salas, Antonio Martínez-Fuentes, David Comas
BMC Evolutionary Biology , 2008, DOI: 10.1186/1471-2148-8-213
Abstract: The Native American contribution to present-day Cubans accounted for 33% of the maternal lineages, whereas Africa and Eurasia contributed 45% and 22% of the lineages, respectively. This Native American substrate in Cuba cannot be traced back to a single origin within the American continent, as previously suggested by ancient DNA analyses. Strikingly, no Native American lineages were found for the Y-chromosome, for which the Eurasian and African contributions were around 80% and 20%, respectively.While the ancestral Native American substrate is still appreciable in the maternal lineages, the extensive process of population admixture in Cuba has left no trace of the paternal Native American lineages, mirroring the strong sexual bias in the admixture processes taking place during colonial times.At the time of the arrival of Columbus to Cuba in 1492, two different Native American groups inhabited the island: the Ciboneys, spread across the whole island, and the Tainos, mainly occupying the Central and Eastern regions of Cuba [1]. Although not much is known of Ciboney culture including their language, it is known that their economy was based on hunter-gathering (mainly fishing and hunting) and lacked pottery, unlike the Tainos, who were sedentary people living in large settlements and whose culture was supported by technically advanced agriculture. The social organization of the Tainos was based on chiefdoms, in which the caciques were the social authority. The Tainos spoke Arawakan, a language belonging to both the Equatorial sub-family and the Equatorial-Tucanoan family [1].Who first colonized the Caribbean islands is still a matter of debate. Geographical, archaeological and linguistic evidence [2-4], as well as ancient DNA data [5,6] suggest that the Caribbean was most likely populated by successive waves of migration originating in the Lower Orinoco Valley in South America, taking advantage of the close geographical proximity of the islands in the Caribbean. Therefo
Geographic stratification of linkage disequilibrium: a worldwide population study in a region of chromosome 22
Anna González-Neira, Francesc Calafell, Arcadi Navarro, Oscar Lao, Howard Cann, David Comas, Jaume Bertranpetit
Human Genomics , 2004, DOI: 10.1186/1479-7364-1-6-399
Genome-Wide and Paternal Diversity Reveal a Recent Origin of Human Populations in North Africa
Karima Fadhlaoui-Zid, Marc Haber, Bego?a Martínez-Cruz, Pierre Zalloua, Amel Benammar Elgaaied, David Comas
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0080293
Abstract: The geostrategic location of North Africa as a crossroad between three continents and as a stepping-stone outside Africa has evoked anthropological and genetic interest in this region. Numerous studies have described the genetic landscape of the human population in North Africa employing paternal, maternal, and biparental molecular markers. However, information from these markers which have different inheritance patterns has been mostly assessed independently, resulting in an incomplete description of the region. In this study, we analyze uniparental and genome-wide markers examining similarities or contrasts in the results and consequently provide a comprehensive description of the evolutionary history of North Africa populations. Our results show that both males and females in North Africa underwent a similar admixture history with slight differences in the proportions of admixture components. Consequently, genome-wide diversity show similar patterns with admixture tests suggesting North Africans are a mixture of ancestral populations related to current Africans and Eurasians with more affinity towards the out-of-Africa populations than to sub-Saharan Africans. We estimate from the paternal lineages that most North Africans emerged ~15,000 years ago during the last glacial warming and that population splits started after the desiccation of the Sahara. Although most North Africans share a common admixture history, the Tunisian Berbers show long periods of genetic isolation and appear to have diverged from surrounding populations without subsequent mixture. On the other hand, continuous gene flow from the Middle East made Egyptians genetically closer to Eurasians than to other North Africans. We show that genetic diversity of today's North Africans mostly captures patterns from migrations post Last Glacial Maximum and therefore may be insufficient to inform on the initial population of the region during the Middle Paleolithic period.
Una nueva especie del género Bathysciola Jeannel, 1910 de los Pirineos Centrales, Espa a (Coleoptera, Leiodidae, Cholevinae, Leptodirini)
Fresneda, J.,Comas, J.
Graellsia , 2007,
Abstract: A new species of the genus Bathysciola Jeannel, 1910 –Bathysciola fadriquei n. sp.– is described in the schiodtei group. The species was collected in a subterranean environment, in two caves in Sierra de Bernera, Bisaurín massif, Pyrenees of Huesca, Aragón, Spain. The most relevant characters of the genital structures were examined in detail: the new species is characterized by the complex phanerae of the internal sac of the aedeagus, with very large, triangular and strongly sclerotised apical phanerae presenting an associated external lobe. The taxonomic position of the new species is discussed. The study is completed with figures of the most characteristic structures, an identification key and distribution data. Se describe una nueva especie del género Bathysciola Jeannel, 1910 –Bathysciola fadriquei n. sp.– perteneciente al grupo schiodtei; ésta ha sido hallada en medio subterráneo profundo, en dos cuevas situadas en Sierra de Bernera, macizo del Bisaurín, Pirineo de Huesca, Aragón, Espa a. Los caracteres diferenciales se encuentran básicamente en las estructuras genitales: la nueva especie se caracteriza por presentar en el complejo faneroide del saco interno del edeago unas faneras apicales muy grandes, triangulares, fuertemente esclerotizadas, con un lóbulo exterior asociado. Se discute la posición taxonómica. Se completa el estudio con ilustraciones de las estructuras que permiten su diferenciación, clave de identificación y datos de distribución.
Graciela Blanco y Guillermo Banzato (comp.) 2009. La cuestión de la tierra pública en Argentina. A 90 a os de la obra de Miguel ángel Cárcano. Rosario: Prohistoria Ediciones. 208 p.
María Fernanda Comas
Mundo agrario , 2010,
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