I Always Feel Like Somebody's Watching Me. Measuring Online Behavioural Advertising

Online Behavioural targeted Advertising (OBA) has risen in prominence as a method to increase the effectiveness of online advertising. OBA operates by associating tags or labels to users based on their online activity and then using these labels to target them. This rise has been accompanied by privacy concerns from researchers, regulators and the press. In this paper, we present a novel methodology for measuring and understanding OBA in the online advertising market. We rely on training artificial online personas representing behavioural traits like 'cooking', 'movies', 'motor sports', etc. and build a measurement system that is automated, scalable and supports testing of multiple configurations. We observe that OBA is a frequent practice and notice that categories valued more by advertisers are more intensely targeted. In addition, we provide evidences showing that the advertising market targets sensitive topics (e.g, religion or health) despite the existence of regulation that bans such practices. We also compare the volume of OBA advertising for our personas in two different geographical locations (US and Spain) and see little geographic bias in terms of intensity of OBA targeting. Finally, we check for targeting with do-not-track (DNT) enabled and discovered that DNT is not yet enforced in the web.Comment: To appear in ACM CoNEXT 2015, Heidelberg, Germany. Please cite the conference version of this pape

blocks_3d: Software for general 3d conformal blocks

We introduce the software blocks_3d for computing four-point conformal blocks of operators with arbitrary Lorentz representations in 3d CFTs. It uses Zamolodchikov-like recursion relations to numerically compute derivatives of blocks around a crossing-symmetric configuration. It is implemented as a heavily optimized, multithreaded, C++ application. We give performance benchmarks for correlators containing scalars, fermions, and stress tensors. As an example application, we recompute bootstrap bounds on four-point functions of fermions and study whether a previously observed sharp jump can be explained using the "fake primary" effect. We conclude that the fake primary effect cannot fully explain the jump and the possible existence of a "dead-end" CFT near the jump merits further study

The Gross-Neveu-Yukawa Archipelago

We perform a bootstrap analysis of a mixed system of four-point functions of bosonic and fermionic operators in parity-preserving 3d CFTs with O(N) global symmetry. Our results provide rigorous bounds on the scaling dimensions of the O(N)-symmetric Gross-Neveu-Yukawa (GNY) fixed points, constraining these theories to live in isolated islands in the space of CFT data. We focus on the cases N = 1, 2, 4, 8, which have applications to phase transitions in condensed matter systems, and compare our bounds to previous analytical and numerical results.Comment: 51 pages, 8 figures, 3 appendices; v2: small corrections and clarifications to match JHEP versio

blocks_3d: Software for general 3d conformal blocks

We introduce the software blocks_3d for computing four-point conformal blocks of operators with arbitrary Lorentz representations in 3d CFTs. It uses Zamolodchikov-like recursion relations to numerically compute derivatives of blocks around a crossing-symmetric configuration. It is implemented as a heavily optimized, multithreaded, C++ application. We give performance benchmarks for correlators containing scalars, fermions, and stress tensors. As an example application, we recompute bootstrap bounds on four-point functions of fermions and study whether a previously observed sharp jump can be explained using the "fake primary" effect. We conclude that the fake primary effect cannot fully explain the jump and the possible existence of a "dead-end" CFT near the jump merits further study.Comment: 33 pages + appendice

Pressure Induced Hydration Dynamics of Membranes

Pressure-jump initiated time-resolved x-ray diffraction studies of dynamics of the hydration of the hexagonal phase in biological membranes show that (i) the relaxation of the unit cell spacing is non-exponential in time; (ii) the Bragg peaks shift smoothly to their final positions without significant broadening or loss in crystalline order. This suggests that the hydration is not diffusion limited but occurs via a rather homogeneous swelling of the whole lattice, described by power law kinetics with an exponent $\beta = 1.3 \pm 0.2$.Comment: REVTEX 3, 10 pages,3 figures(available on request),#

Pressure Induced Topological Phase Transitions in Membranes

Some highly unusual features of a lipid-water liquid crystal are revealed by high pressure x-ray diffraction, light scattering and dilatometric studies of the lamellar (bilayer $L_{\alpha}$) to nonlamellar inverse hexagonal ($H_{II}$) phase transition. (i) The size of the unit cell of the $H_{II}$ phase increases with increasing pressure. (ii) The transition volume, $\Delta V_{bh}$, decreases and appears to vanish as the pressure is increased. (iii) The intensity of scattered light increases as $\Delta V_{bh}$ decreases. Data are presented which suggest that this increase is due to the formation of an intermediate cubic phase, as predicted by recent theoretical suggestions of the underlying universal phase sequence.Comment: 12 pages, typed using REVTEX 2.

On the nature and impact of self-similarity in real-time systems

In real-time systems with highly variable task execution times simplistic task models are insufficient to accurately model and to analyze the system. Variability can be tackled using distributions rather than a single value, but the proper charac- terization depends on the degree of variability. Self-similarity is one of the deep- est kinds of variability. It characterizes the fact that a workload is not only highly variable, but it is also bursty on many time-scales. This paper identifies in which situations this source of indeterminism can appear in a real-time system: the com- bination of variability in task inter-arrival times and execution times. Although self- similarity is not a claim for all systems with variable execution times, it is not unusual in some applications with real-time requirements, like video processing, networking and gaming. The paper shows how to properly model and to analyze self-similar task sets and how improper modeling can mask deadline misses. The paper derives an analyti- cal expression for the dependence of the deadline miss ratio on the degree of self- similarity and proofs its negative impact on real-time systems performance through system¿s modeling and simulation. This study about the nature and impact of self- similarity on soft real-time systems can help to reduce its effects, to choose the proper scheduling policies, and to avoid its causes at system design time.This work was developed under a grant from the European Union (FRESCOR-FP6/2005/IST/5-03402).Enrique Hernández-Orallo; Vila Carbó, JA. (2012). On the nature and impact of self-similarity in real-time systems. Real-Time Systems. 48(3):294-319. doi:10.1007/s11241-012-9146-0S294319483Abdelzaher TF, Sharma V, Lu C (2004) A utilization bound for aperiodic tasks and priority driven scheduling. IEEE Trans Comput 53(3):334–350Abeni L, Buttazzo G (1999) QoS guarantee using probabilistic deadlines. 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Social features of online networks: the strength of intermediary ties in online social media

An increasing fraction of today social interactions occur using online social media as communication channels. Recent worldwide events, such as social movements in Spain or revolts in the Middle East, highlight their capacity to boost people coordination. Online networks display in general a rich internal structure where users can choose among different types and intensity of interactions. Despite of this, there are still open questions regarding the social value of online interactions. For example, the existence of users with millions of online friends sheds doubts on the relevance of these relations. In this work, we focus on Twitter, one of the most popular online social networks, and find that the network formed by the basic type of connections is organized in groups. The activity of the users conforms to the landscape determined by such groups. Furthermore, Twitter's distinction between different types of interactions allows us to establish a parallelism between online and offline social networks: personal interactions are more likely to occur on internal links to the groups (the weakness of strong ties), events transmitting new information go preferentially through links connecting different groups (the strength of weak ties) or even more through links connecting to users belonging to several groups that act as brokers (the strength of intermediary ties).Comment: 14 pages, 18 figure

The dynamics of experiential learning: Microprocesses and adaptation in a professional service INV

In international new ventures (INVs), experiential learning happens in quick succession and across a wide number of diverse contexts. Yet, we lack an empirical understanding of the microprocesses through which INVs learn and adapt in their foreign expansion. Understanding those microprocesses is important because timely adaptation can save the venture time and resources, thus promoting sustainable growth. In this study, we investigate the dynamics of experiential learning and adaptation in the internationalisation process of an INV in the professional service sector. Findings from our study illustrate that the firm applies deliberate experiential learning by developing, revising, and finalising criteria for important dimensions in the international growth process, and adapts its internationalisation practices accordingly. We further show that deliberate experiential learning is predicated on an actively and closely monitored learning process, involving critical evaluation, adjustment of criteria, and acceptance of affordable mistakes, as opposed to learning by defaul