Expansion dynamics of a dipolar Bose-Einstein condensate

Our recent measurements on the expansion of a chromium dipolar condensate after release from an optical trapping potential are in good agreement with an exact solution of the hydrodynamic equations for dipolar Bose gases. We report here the theoretical method used to interpret the measurement data as well as more details of the experiment and its analysis. The theory reported here is a tool for the investigation of different dynamical situations in time-dependent harmonic traps.Comment: 12 pages. Submitted to PR

Diffusion-limited deposition of dipolar particles

Deposits of dipolar particles are investigated by means of extensive Monte Carlo simulations. We found that the effect of the interactions is described by an initial, non-universal, scaling regime characterized by orientationally ordered deposits. In the dipolar regime, the order and geometry of the clusters depend on the strength of the interactions and the magnetic properties are tunable by controlling the growth conditions. At later stages, the growth is dominated by thermal effects and the diffusion-limited universal regime obtains, at finite temperatures. At low temperatures the crossover size increases exponentially as T decreases and at T=0 only the dipolar regime is observed.Comment: 5 pages, 4 figure

Academic culture in doctoral education: are companies making a difference in the experiences and practices of doctoral students in Portugal?

Aim/Purpose: This article examines the experience and practice of doctoral students by focus-ing on different dimensions of the PhD socialization process. It addresses the question of whether university collaborations with businesses influence the ex-perience and practice of PhD students. Background: The study explores the academic culture in the PhD process through the analy-sis of the experiences and practices of doctoral students in two groups - those without business collaborations (academic trajectories) and those with business collaborations (hybrid trajectories). Academic trajectories are seen as traditional academic disciplinary based doctoral education, while hybrid trajectories cross boundaries collaborating with companies in the production of new knowledge.Methodology: The article uses a qualitative methodology based on extensive interviews and analysis of the curriculum vitae of fourteen Portuguese PhD students in three scientific domains (engineering and technology sciences, exact sciences, and so-cial sciences). The doctoral program profiles were defined according to a survey applied to the directors of all doctoral programs in Portugal. Contribution: The study contributes to the reflection on the effects of collaboration with companies, in particular on the trajectories and experiences of doctoral stu-dents. It contributes to the understanding of the challenges associated with business collaborations.info:eu-repo/semantics/publishedVersio

A thorough analysis of the short- and mid-term activity-related variations in the solar acoustic frequencies

The frequencies of the solar acoustic oscillations vary over the activity cycle. The variations in other activity proxies are found to be well correlated with the variations in the acoustic frequencies. However, each proxy has a slightly different time behaviour. Our goal is to characterize the differences between the time behaviour of the frequency shifts and of two other activity proxies, namely, the area covered by sunspots and the 10.7cm flux. We define a new observable that is particularly sensitive to the short-term frequency variations. We then compare the observable when computed from model frequency shifts and from observed frequency shifts obtained with the Global Oscillation Network Group (GONG) for cycle 23. Our analysis shows that on the shortest time-scales the variations in the frequency shifts seen in the GONG observations are strongly correlated with the variations in the area covered by sunspots. However, a significant loss of correlation is still found. We verify that the times when the frequency shifts and the sunspot area do not vary in a similar way tend to coincide with the times of the maxima of the quasi-biennial variations seen in the solar seismic data. A similar analysis of the relation between the 10.7cm flux and the frequency shifts reveals that the short-time variations in the frequency shifts follow even more closely those of the 10.7cm flux than those of the sunspot area. However, a loss of correlation between frequency shifts and 10.7cm flux variations is still found around the same times.Comment: 7 pages, 6 figures, accepted for publication in MNRA

On the relation between activity-related frequency shifts and the sunspot distribution over the solar cycle 23

The activity-related variations in the solar acoustic frequencies have been known for 30 years. However, the importance of the different contributions is still not well established. With this in mind, we developed an empirical model to estimate the spot-induced frequency shifts, which takes into account the sunspot properties, such as area and latitude. The comparison between the model frequency shifts obtained from the daily sunspot records and those observed suggests that the contribution from a stochastic component to the total frequency shifts is about 30%. The remaining 70% is related to a global, long-term variation. We also propose a new observable to investigate the short- and mid-term variations of the frequency shifts, which is insensitive to the long-term variations contained in the data. On the shortest time scales the variations in the frequency shifts are strongly correlated with the variations in the total area covered by sunspots. However, a significant loss of correlation is still found, which cannot be fully explained by ignoring the invisible side of the Sun when accounting for the total sunspot area. We also verify that the times when the frequency shifts and the sunspot areas do not vary in a similar way tend to coincide with the times of the maximum amplitude of the quasi-biennial variations found in the seismic data.Comment: 4 pages, 2 figures, proceedings of the Joint TASC2 - KASC9 Workshop - SPACEINN - HELAS8 Conference "Seismology of the Sun and the Distant Stars 2016: Using Today's Successes to Prepare the Future". To be published by the EPJ Web of Conference

Observation of dipole-dipole interaction in a degenerate quantum gas

We have investigated the expansion of a Bose-Einstein condensate (BEC) of strongly magnetic chromium atoms. The long-range and anisotropic magnetic dipole-dipole interaction leads to an anisotropic deformation of the expanding Cr-BEC which depends on the orientation of the atomic dipole moments. Our measurements are consistent with the theory of dipolar quantum gases and show that a Cr-BEC is an excellent model system to study dipolar interactions in such gases.Comment: 4 pages, 2 figure

Inductive learning spatial attention

This paper investigates the automatic induction of spatial attention from the visual observation of objects manipulated on a table top. In this work, space is represented in terms of a novel observer-object relative reference system, named Local Cardinal System, defined upon the local neighbourhood of objects on the table. We present results of applying the proposed methodology on five distinct scenarios involving the construction of spatial patterns of coloured blocks

Detection and resolution of normative conflicts in multi-agent systems : a literature survey

Peer reviewedPostprin