Near-field frequency attenuation of vibrations from blasting using a full-field solution

This study analyses the frequency content of vibrations from blasting in the near field using a vibration prediction model called full-field solution (FFS). For that purpose, the frequency content of recorded signals and synthetic waveforms obtained through the FFS using dominant and mean frequencies have been compared and correlated with the geometrical distance to the blastholes. The study shows that the model overestimates the dominant and mean frequencies in the entire frequency domain, which may require tailoring the source function to a lower frequency content. However, it attenuates the frequency content as distance increases. Additionally, the study shows that the mean frequencies may be used as a better estimator of the frequency content than the dominant frequencies.

Constructing elastic distinguishability metrics for location privacy

With the increasing popularity of hand-held devices, location-based applications and services have access to accurate and real-time location information, raising serious privacy concerns for their users. The recently introduced notion of geo-indistinguishability tries to address this problem by adapting the well-known concept of differential privacy to the area of location-based systems. Although geo-indistinguishability presents various appealing aspects, it has the problem of treating space in a uniform way, imposing the addition of the same amount of noise everywhere on the map. In this paper we propose a novel elastic distinguishability metric that warps the geometrical distance, capturing the different degrees of density of each area. As a consequence, the obtained mechanism adapts the level of noise while achieving the same degree of privacy everywhere. We also show how such an elastic metric can easily incorporate the concept of a “geographic fence” that is commonly employed to protect the highly recurrent locations of a user, such as his home or work. We perform an extensive evaluation of our technique by building an elastic metric for Paris’ wide metropolitan area, using semantic information from the OpenStreetMap database. We compare the resulting mechanism against the Planar Laplace mechanism satisfying standard geo-indistinguishability, using two real-world datasets from the Gowalla and Brightkite location-based social networks. The results show that the elastic mechanism adapts well to the semantics of each area, adjusting the noise as we move outside the city center, hence offering better overall privacy.1

GUESS

The increasing availability of mobile networks and devices motivate the development of new paradigms of interaction between users, and between a user and the surrounding environment. When the position of a user is known, location-aware applications can adapt their behaviour accordingly to that position. This usual behaviour of location-aware applications can be enhanced in order to turn these applications pro-active, providing services that can be helpful to the user before he/she asks for them. For this kind of behaviour, location-aware applications need to anticipate the user’s position, predicting where the user is going to be in the future. This chapter discusses the prediction of movement in space by looking at the topological constraints existing in the geographical space in which the user is moving. The obtained results show that the topological distance can be used as an alternative or as a complement to the geometrical distance normally used in map-matching techniques.

Constraints on a strong X-ray flare in the Seyfert galaxy MCG–6-30-15

We discuss implications of a strong flare event observed in the Seyfert galaxy MCG–6-30-15 assuming that the emission is due to localized magnetic reconnection. We conduct detailed radiative transfer modeling of the reprocessed radiation for a primary source that is elevated above the disk. The model includes relativistic effects and Keplerian motion around the black hole. We show that for such a model setup the observed time-modulation must be intrinsic to the primary source. Using a simple analytical model we then investigate time delays between hard and soft X-rays during the flare. The model considers an intrinsic delay between primary and reprocessed radiation, which measures the geometrical distance of the flare source to the reprocessing sites. The observed time delays are well reproduced if one assumes that the reprocessing happens in magnetically confined, cold clouds.