Discovery of Large-Scale Gravitational Infall in a Massive Protostellar Cluster

We report Mopra (ATNF), Anglo-Australian Telescope, and Atacama Submillimeter Telescope Experiment observations of a molecular clump in Carina, BYF73 = G286.21+0.17, which give evidence of large-scale gravitational infall in the dense gas. From the millimetre and far-infrared data, the clump has mass ~ 2 x 10^4 Msun, luminosity ~ 2-3 x 10^4 Lsun, and diameter ~ 0.9 pc. From radiative transfer modelling, we derive a mass infall rate ~ 3.4 x 10^-2 Msun yr-1. If confirmed, this rate for gravitational infall in a molecular core or clump may be the highest yet seen. The near-infrared K-band imaging shows an adjacent compact HII region and IR cluster surrounded by a shell-like photodissociation region showing H2 emission. At the molecular infall peak, the K imaging also reveals a deeply embedded group of stars with associated H2 emission. The combination of these features is very unusual and we suggest they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation.Comment: v1: 23 pages single-column, 6 figures (some multipart) at end v2: 14 pages 2-column, 6 figures interspersed v3: edited to referee's comments with new sections and new figures; accepted to MNRAS, 20 pages 2-column, 8 figures (some multipart) intersperse

The role of perceptual information for episodic memory in children and young adults: electrophysiological and behavioral correlates of recollection and familiarity

In this dissertation, I will present the studies conducted during my doctoral studies. In spite of a lot of research in the last decades, the complex cognitive processes underlying human memory are not fully unraveled. Furthermore, the development of neuroscientific methods like functional mag-netic resonance imaging (fMRI) and event-related potentials (ERPs) have further build a founda-tion for new insights. Naturally, the utilization of these techniques led to further adaptation of both these techniques and the paradigms in which they have been employed. This can be observed in the research literature on episodic memory retrieval. Familiarity and recollection, have been found to be the chief factors at play during memory retrieval. The two processes have been thoroughly characterized in several studies and reviews (e.g., Mecklinger, 2000; Rugg & Curran, 2007; Yonelinas, 2002; Zimmer & Ecker, 2010), yet there are still open questions that have to be ad-dressed by researchers in this field (c.f., Leynes, Bruett, Krizan, & Veloso, 2017; MacLeod & Donaldson, 2017). In order to answer these questions, we conducted several studies during my doctoral studies. In Study 1, we developed a paradigm to investigated episodic memory using ERPs. In the study phase, pictorial stimuli were presented which at test were either perceptually identical, perceptually changed, or entirely new. Data collected from a sample of young adults revealed that the paradigm was suitable to elicit ERP correlates of both familiarity and recollection. As the newly developed paradigm yielded similar results as existing literature, we then applied this paradigm in two devel-opmental populations, second-graders and fifth-graders. According to the ERPs, the younger chil-dren seemed to rely on recollection alone, whereas ERPs of older children suggested the use of familiarity for perceptually identical items and only after intentional encoding. In a follow-up study two years later, we used the results from both studies to only slightly refine the paradigm, again administering it to young adults. In this study, Study 3, we found that ERP correlates were much smaller than in the earlier studies, hence we used a data-driven approach to detect time windows of interest. In spite of the large body of research on episodic memory, these studies serve to demon-strate that episodic memory is a complex interplay of several contributing cognitive processes which need to assessed carefully in order to unravel the key factors at play during familiarity and recollection

The role of perceptual information for episodic memory in children and young adults: electrophysiological and behavioral correlates of recollection and familiarity

In this dissertation, I will present the studies conducted during my doctoral studies. In spite of a lot of research in the last decades, the complex cognitive processes underlying human memory are not fully unraveled. Furthermore, the development of neuroscientific methods like functional mag-netic resonance imaging (fMRI) and event-related potentials (ERPs) have further build a founda-tion for new insights. Naturally, the utilization of these techniques led to further adaptation of both these techniques and the paradigms in which they have been employed. This can be observed in the research literature on episodic memory retrieval. Familiarity and recollection, have been found to be the chief factors at play during memory retrieval. The two processes have been thoroughly characterized in several studies and reviews (e.g., Mecklinger, 2000; Rugg & Curran, 2007; Yonelinas, 2002; Zimmer & Ecker, 2010), yet there are still open questions that have to be ad-dressed by researchers in this field (c.f., Leynes, Bruett, Krizan, & Veloso, 2017; MacLeod & Donaldson, 2017). In order to answer these questions, we conducted several studies during my doctoral studies. In Study 1, we developed a paradigm to investigated episodic memory using ERPs. In the study phase, pictorial stimuli were presented which at test were either perceptually identical, perceptually changed, or entirely new. Data collected from a sample of young adults revealed that the paradigm was suitable to elicit ERP correlates of both familiarity and recollection. As the newly developed paradigm yielded similar results as existing literature, we then applied this paradigm in two devel-opmental populations, second-graders and fifth-graders. According to the ERPs, the younger chil-dren seemed to rely on recollection alone, whereas ERPs of older children suggested the use of familiarity for perceptually identical items and only after intentional encoding. In a follow-up study two years later, we used the results from both studies to only slightly refine the paradigm, again administering it to young adults. In this study, Study 3, we found that ERP correlates were much smaller than in the earlier studies, hence we used a data-driven approach to detect time windows of interest. In spite of the large body of research on episodic memory, these studies serve to demon-strate that episodic memory is a complex interplay of several contributing cognitive processes which need to assessed carefully in order to unravel the key factors at play during familiarity and recollection

Neuronal oscillations reveal the processes underlying intentional compared to incidental learning in children and young adults.

This EEG study investigated the neuronal processes during intentional compared to incidental learning in young adults and two groups of children aged 10 and 7 years. Theta (3-8 Hz) and alpha (10-16 Hz) neuronal oscillations were analyzed to compare encoding processes during an intentional and an incidental encoding task. In all three age groups, both encoding conditions were associated with an increase in event-related theta activity. Encoding-related alpha suppression increased with age. Memory performance was higher in the intentional compared to the incidental task in all age groups. Furthermore, intentional learning was associated with an improved encoding of perceptual features, which were relevant for the retrieval phase. Theta activity increased from incidental to intentional encoding. Specifically, frontal theta increased in all age groups, while parietal theta increased only in adults and older children. In younger children, parietal theta was similarly high in both encoding phases. While alpha suppression may reflect semantic processes during encoding, increased theta activity during intentional encoding may indicate perceptual binding processes, in accordance with the demands of the encoding task. Higher encoding-related alpha suppression in the older age groups, together with age differences in parietal theta activity during incidental learning in young children, is in line with recent theoretical accounts, emphasizing the role of perceptual processes in mnemonic processing in young children, whereas semantic encoding processes continue to mature throughout middle childhood

Spectral changes in theta and alpha activity during encoding.

<p>(A) Time-frequency plots illustrate the relative signal changes upon stimulus onset for successfully encoded stimuli (i.e., subsequently remembered items with correct feature judgments). The signal changes depicted here are averaged over all electrodes, all participants in each group and both learning phases (incidental and intentional). (B) Topographical maps for event-related changes in individual theta and alpha activity during encoding. Signal changes are averaged over the entire stimulus presentation (1s), all participants in each age group and both learning phases (incidental and intentional).</p

Memory performance.

<p>Memory performance.</p

Electrode configuration and the clusters used for the statistical analyses.

<p>Electrodes were grouped along two dimensions, divided into 3 laterality (left, medial, right) by 3 caudality (frontal, central, parietal) clusters.</p

Spectral changes in theta and alpha activity during encoding.

<p>(A) Time-frequency plots illustrate the relative signal changes upon stimulus onset for successfully encoded stimuli (i.e., subsequently remembered items with correct feature judgments). The signal changes depicted here are averaged over all electrodes, all participants in each group and both learning phases (incidental and intentional). (B) Topographical maps for event-related changes in individual theta and alpha activity during encoding. Signal changes are averaged over the entire stimulus presentation (1s), all participants in each age group and both learning phases (incidental and intentional).</p

Posterior alpha suppression and corresponding response times.

<p>Graphs display the level of alpha-band suppression during and after stimulus presentation (stimulus: 0-1s, light gray), across electrodes of frontal and posterior electrode clusters and both phases. Dotted lines indicate mean response times for subsequent feature hits during encoding (±1 <i>SD</i>, gray), after stimulus offset until responses were given. Gray bars illustrate the result of a time-point-wise comparison against zero (<i>p</i> < .01).</p

Intentional learning is reflected in the theta frequency.

<p>(A) Difference topographies of event-related changes in theta between intentional (INT) and incidental (INC) encoding, for the entire duration of stimulus presentation. (B) Relative signal changes (rel. sig. change), in percent, for intentional and incidental encoding, at all electrodes of frontal (upper panel) and posterior clusters (lower panel). Asterisks indicate the results of <i>post hoc</i> t-tests between encoding conditions, for the entire time window of stimulus presentation (*** <i>p</i> < 001, ** <i>p</i> < 01, * <i>p</i> < 05). Bars below the graphs illustrate the time course of these differences (<i>p</i> < .05, time-point-wise).</p