Abstract

Abstract
Achievable secrecy rates over a multiple-input multiple-output multipleeavesdropper (MIMOME) wiretap channel are considered, when the legitimate users have perfect knowledge only of the legitimate channel state and the eavesdropper channel is drawn from a (possibly unknown) continuous probability density. Legitimate users are assumed to deploy more antennas than the eavesdropper. A signaling transmission based on K-class Gaussian mixture model (GMM) distributions is proposed, which can be considered as an artificial-noise augmented signal, where the noise statistics are data-dependent. The proposed scheme is shown to achieve the secrecy capacity, log K, in the high signal-to-noise ratio (SNR) regime. Moreover, the tradeoff between secrecy and reliability at finite SNR is explored via the characterization of an upper bound to the error probability at the legitimate receiver, an upper bound to themutual information leakage to the eavesdropper and via numerical simulations. © Springer International Publishing Switzerland 2016.

Abstract
Pulido et al. (Annals Oper Res 158:133–141, 2008) present an extension of the classical bankruptcy problem (O’Neill in Math Social Sci 2:345–371, 1982) where the involved agents have, apart from the claims vector, an additional reference vector. To analyze this extended problem, they propose the extreme and the diagonal approaches, both of them restricted to the case in which the reference vector is lower than the claims vector. We note that if the claims and the reference vectors are interchanged, the allocation proposed by the extreme approach varies. Therefore, by introducing the idea of impartiality, in the current approach, we propose an extension of their model in which no relation is assumed between the claims and reference vectors. © 2015, Sociedad de Estadística e Investigación Operativa.

Abstract

Abstract
Searching for health information is one of the most popular activities on the Web. In this domain, users frequently encounter difficulties in query formulation, either because they lack knowledge of the proper medical terms or because they misspell them. To overcome these difficulties and attempt to retrieve higher-quality content, we developed a query suggestion system that provides alternative queries combining the users' native language and English language with lay and medico-scientific terminology. To assess how the language and terminology impact the use of suggestions, we conducted a user study with 40 subjects considering their English proficiency, health literacy and topic familiarity. Results show that suggestions are used most often at the beginning of search sessions. English suggestions tend to be preferred to the ones formulated in the users' native language, at all levels of English proficiency. Medico-scientific suggestions tend to be preferred to lay suggestions at higher levels of health literacy.

Abstract
A palladium (Pd)-based optical metamaterial has been designed, fabricated and characterized for its application in hydrogen sensing. The metamaterial can replace Pd thin films in optical transmission schemes for sensing with performances far superior to those of conventional sensors. This artificial material consists of a palladium-alumina metamaterial fabricated using inexpensive and industrial-friendly bottom-up techniques. During the exposure to hydrogen, the system exhibits anomalous optical absorption when compared to the well-known response of Pd thin films, this phenomenon being the key factor for the sensor sensitivity. The exposure to hydrogen produces a large variation in the light transmission through the metamembrane (more than 30% with 4% in volume hydrogen-nitrogen gas mixture at room temperature and atmospheric pressure), thus avoiding the need for sophisticated optical detection systems. An optical homogenization model is proposed to explain the metamaterial response. These results contribute to the development of reliable and low-cost hydrogen sensors with potential applications in the hydrogen economy and industrial processes to name a few, and also open the door to optically study the hydrogen diffusion processes in Pd nanostructures.