You never surf alone. Ubiquitous tracking of users' browsing habits

In the early age of the internet users enjoyed a large level of anonymity. At the time web pages were just hypertext documents; almost no personalisation of the user experience was o ered. The Web today has evolved as a world wide distributed system following specific architectural paradigms. On the web now, an enormous quantity of user generated data is shared and consumed by a network of applications and services, reasoning upon users expressed preferences and their social and physical connections. Advertising networks follow users' browsing habits while they surf the web, continuously collecting their traces and surfing patterns. We analyse how users tracking happens on the web by measuring their online footprint and estimating how quickly advertising networks are able to pro le users by their browsing habits

Sources of intrinsic rotation in the low flow ordering

A low flow, $\delta f$ gyrokinetic formulation to obtain the intrinsic rotation profiles is presented. The momentum conservation equation in the low flow ordering contains new terms, neglected in previous first principles formulations, that may explain the intrinsic rotation observed in tokamaks in the absence of external sources of momentum. The intrinsic rotation profile depends on the density and temperature profiles and on the up-down asymmetry.Comment: 20 page

Tidal nitrogen and phosphorus exchange in the Palmones River estuary (Algeciras Bay, Cadiz)

The estuary of the Palmones River is a shallow fluvial catchment area, which had suffered major hydrodynamic changes over the last decade related to the construction of a dam. The estuary acts as a nutrient sink, and its catchment area shows high eutrophication (Pérez-Lloréns, Fernández and Niell, 1989; Clavero, Niell and Fernández, 1997). Nutrient concentration, salinity and evolution of current speed were monitored at the mouth of the estuary during a complete tidal cycle in the spring of 1997. The authors found strong water- column stratification, which enabled them to determine the input and output estuarine fluxes, using a two-box model. The deepest water mass, with a relatively constant composition, is responsible for the nutrient input into the estuary. Surface waters export nutrients to adjacent coastal zones, although this phenomenon has an obvious seasonal component. Net balance reveals a silicate, phosphate and ammonia output and frequent nitrogen forms (nitrite and nitrate) inputs.El estuario del río Palmones es una cuenca fluvial de escasa profundidad que, en la última década, ha sufrido un represamiento, originando importantes cambios en su hidrodinámica. El estuario se comporta como un sumidero de nutrientes y su cuenca experimenta una alta eutrofización (Pérez Lloréns, Fernández y Niell, 1989; Clavero, Niell and Fernández, 1997). Se ha seguido la evolución de la concentración de nutrientes, salinidad y velocidades de corriente en la desembocadura del estuario durante ciclos de marea completos en la primavera de 1997. Debido a la intensa estratificación encontrada en la columna de agua, los flujos de entrada y salida del estuario se han cuantificado mediante un modelo de dos cajas. La masa de agua más profunda, con una composición relativamente constante, es responsable de una entrada de nutrientes en el estuario. Por el contrario, las aguas más superficiales exportan nutrientes a otras zonas adyacentes, aunque este fenómeno tiene una clara componente estacional. El balance neto pone de manifiesto una salida de silicato, fosfato y amonio y una entrada en el sistema de formas asiduas de nitrógeno (nitrito y nitrato).Instituto Español de Oceanografí

Hamiltonian description of singular Lagrangian systems with spontaneously broken time translation symmetry

Shapere and Wilczek recently found some singular Lagrangian systems which spontaneously breaks time translation symmetry. The common feature of their models is that the energy functions are multivalued in terms of the canonical phase space variables and the symmetry breaking ground states are all located at the brunching point singularities. By enlarging the phase space and making use of Dirac's theory on constrained Hamiltonian systems, we present the Hamiltonian description of some of the models discussed by Shapere and Wilczek and found that both the multivaluedness and the brunching point singularities can be avoided, while the spontaneous breaking oftime translation becomes more transparent. It is also shown that the breaking of time translation is always accompanied by the breaking of time reversal.Comment: 13 page

Robust Stability and Optimality Conditions for Parametric Infinite and Semi-Infinite Programs

This paper primarily concerns the study of parametric problems of infinite and semi-infinite programming, where functional constraints are given by systems of infinitely many linear inequalities indexed by an arbitrary set T, where decision variables run over Banach (infinite programming) or finite-dimensional (semi-infinite case) spaces, and where objectives are generally described by nonsmooth and nonconvex cost functions. The parameter space of admissible perturbations in such problems is formed by all bounded functions on T equipped with the standard supremum norm. Unless the index set T is finite, this space is intrinsically infinite-dimensional (nonreflexive and nonseparable) of the l(infinity)-type. By using advanced tools of variational analysis and generalized differentiation and largely exploiting underlying specific features of linear infinite constraints, we establish complete characterizations of robust Lipschitzian stability (with computing the exact bound of Lipschitzian moduli) for parametric maps of feasible solutions governed by linear infinite inequality systems and then derive verifiable necessary optimality conditions for the infinite and semi-infinite programs under consideration expressed in terms of their initial data. A crucial part of our analysis addresses the precise computation of coderivatives and their norms for infinite systems of parametric linear inequalities in general Banach spaces of decision variables. The results obtained are new in both frameworks of infinite and semi-infinite programming