The LOFAR Two-metre Sky Survey (LoTSS) is a deep 120-168 MHz imaging survey that will eventually cover the entire northern sky. Each of the 3170 pointings will be observed for 8 h, which, at most declinations, is sufficient to produce ∼5 resolution images with a sensitivity of ∼100 µJy/beam and accomplish the main scientific aims of the survey, which are to explore the formation and evolution of massive black holes, galaxies, clusters of galaxies and large-scale structure. Owing to the compact core and long baselines of LOFAR, the images provide excellent sensitivity to both highly extended and compact emission. For legacy value, the data are archived at high spectral and time resolution to facilitate subarcsecond imaging and spectral line studies. In this paper we provide an overview of the LoTSS. We outline the survey strategy, the observational status, the current calibration techniques, a preliminary data release, and the anticipated scientific impact. The preliminary images that we have released were created using a fully automated but direction-independent calibration strategy and are significantly more sensitive than those produced by any existing large-area low-frequency survey. In excess of 44 000 sources are detected in the images that have a resolution of 25 , typical noise levels of less than 0.5 mJy/beam, and cover an area of over 350 square degrees in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45• 00 00 to 57• 00 00 ).

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ObjectiveExposure based large-group one-session treatments (LG-OSTs) proved feasible in different situational fears and showed promising short- and long-term outcomes. Based on prior LG-OST protocols we explored feasibility and effectiveness of an LG-OST protocol in four cohorts of individuals highly fearful of heights (N = 104). Moreover, we aimed to identify predictors of LG-OST outcome in order to provide individualized treatment recommendations in the future.MethodsParticipants’ fear of heights was assessed at pre- and post-treatment as well as at 5 months follow-up using questionnaires and a behavioral approach test (BAT). Pre-treatment indices of negative emotional traits and positive mental health, the extent by which fear-evoking expectancies were violated during exposure, and post-treatment group perception processes were assessed in order to predict the outcome.ResultsThe LG-OST procedure proved feasible and effective in terms of both subjective and behavioral fear of heights. Post-treatment effects sizes of questionnaires assessing fear of heights ranged between d = 0.94 – 1.43. After the treatment, about half of the participants (49.5%) were able to ascend an aerial fire ladder up to a maximum of 30 m (vs. pre-treatment 17.3%). Follow up results showed the long-term stability of effects. Among psychological constructs, positive mental health and expectancy violation were the strongest predictors of LG-OST long-term outcome.ConclusionWe conclude that exposure based LG-OSTs are feasible, effective and very efficient compared to individual face-to-face settings. Thus, they represent very promising treatment alternatives for situational fears including fear of heights. Moreover, clinical research may benefit from LG-OST protocols as its high standardization may facilitate the search for mediators and moderators of exposure outcomes.