On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

fMRI syntactic and lexical repetition effects reveal the initial stages of learning a new language

Contains fulltext : 158692.pdf (publisher's version ) (Open Access)When learning a new language, we build brain networks to process and represent the acquired words and syntax and integrate these with existing language representations. It is an open question whether the same or different neural mechanisms are involved in learning and processing a novel language compared to the native language(s). Here we investigated the neural repetition effects of repeating known and novel word orders while human subjects were in the early stages of learning a new language. Combining a miniature language with a syntactic priming paradigm, we examined the neural correlates of language learning online using functional magnetic resonance imaging (fMRI). In left inferior frontal gyrus (LIFG) and posterior temporal cortex the repetition of novel syntactic structures led to repetition enhancement, while repetition of known structures resulted in repetition suppression. Additional verb repetition led to an increase in the syntactic repetition enhancement effect in language-related brain regions. Similarly the repetition of verbs led to repetition enhancement effects in areas related to lexical and semantic processing, an effect that continued to increase in a subset of these regions. Repetition enhancement might reflect a mechanism to build and strengthen a neural network to process novel syntactic structures and lexical items. By contrast, the observed repetition suppression points to overlapping neural mechanisms for native and new language constructions when these have sufficient structural similarities.9 p

Implicit artificial syntax processing: genes, preference, and bounded recursion

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Effective connectivity of cortical and subcortical regions during unification of sentence structure

Contains fulltext : 90249.pdf (publisher's version ) (Closed access)In a recent fMRI study we showed that left posterior middle temporal gyrus (LpMTG) subserves the retrieval of a word's lexical-syntactic properties from the mental lexicon (long-term memory), while left posterior inferior frontal gyrus (LpIFG) is involved in unifying (on-line integration of) this information into a sentence structure (Snijders et al., 2009). In addition, the right IFG, right MTG, and the right striatum were involved in the unification process. Here we report results from a psychophysical interactions (PPI) analysis in which we investigated the effective connectivity between LpIFG and LpMTG during unification, and how the right hemisphere areas and the striatum are functionally connected to the unification network. LpIFG and LpMTG both showed enhanced connectivity during the unification process with a region slightly superior to our previously reported LpMTG. Right IFG better predicted right temporal activity when unification processes were more strongly engaged, just as LpIFG better predicted left temporal activity. Furthermore, the striatum showed enhanced coupling to LpIFG and LpMTG during unification. We conclude that bilateral inferior frontal and posterior temporal regions are functionally connected during sentence-level unification. Cortico-subcortical connectivity patterns suggest cooperation between inferior frontal and striatal regions in performing unification operations on lexical-syntactic representations retrieved from LpMTG

Mean-based neural coding of voices

Contains fulltext : 116568.pdf (Publisher’s version ) (Closed access)The social significance of recognizing the person who talks to us is obvious, but the neural mechanisms that mediate talker identification are unclear. Regions along the bilateral superior temporal sulcus (STS) and the inferior frontal cortex (IFC) of the human brain are selective for voices, and they are sensitive to rapid voice changes. Although it has been proposed that voice recognition is supported by prototype-centered voice representations, the involvement of these category-selective cortical regions in the neural coding of such “mean voices” has not previously been demonstrated. Using fMRI in combination with a voice identity learning paradigm, we show that voice-selective regions are involved in the mean-based coding of voice identities. Voice typicality is encoded on a supra-individual level in the right STS along a stimulus-dependent, identity-independent (i.e., voice-acoustic) dimension, and on an intra-individual level in the right IFC along a stimulus-independent, identity-dependent (i.e., voice identity) dimension. Voice recognition therefore entails at least two anatomically separable stages, each characterized by neural mechanisms that reference the central tendencies of voice categories.10 p

Beyond the language given: The neural correlates of inferring speaker meaning

Item does not contain fulltextEven though language allows us to say exactly what we mean, we often use language to say things indirectly, in a way that depends on the specific communicative context. For example, we can use an apparently straightforward sentence like “It is hard to give a good presentation” to convey deeper meanings, like “Your talk was a mess!” One of the big puzzles in language science is how listeners work out what speakers really mean, which is a skill absolutely central to communication. However, most neuroimaging studies of language comprehension have focused on the arguably much simpler, context-independent process of understanding direct utterances. To examine the neural systems involved in getting at contextually constrained indirect meaning, we used functional magnetic resonance imaging as people listened to indirect replies in spoken dialog. Relative to direct control utterances, indirect replies engaged dorsomedial prefrontal cortex, right temporo-parietal junction and insula, as well as bilateral inferior frontal gyrus and right medial temporal gyrus. This suggests that listeners take the speaker's perspective on both cognitive (theory of mind) and affective (empathy-like) levels. In line with classic pragmatic theories, our results also indicate that currently popular “simulationist” accounts of language comprehension fail to explain how listeners understand the speaker's intended message

Break-up related 2170–2120 Ma mafic dykes across the North Atlantic craton : Final dismembering of a North Atlantic-Dharwar craton connection?

Progress with supercontinental reconstructions relies on accurate age determinations for continental geological units such as mafic dyke swarms. Here we present zircon and baddeleyite U-Pb ID-TIMS isotope data of six mafic dykes from the Archean North Atlantic craton in present-day southern West and South-East Greenland. Two dykes in southern West Greenland yield crystallization ages of 2021 ± 4 Ma, for the NE-trending Hamborgersund dyke, and 2125 ± 9 Ma, for the E-trending Angissunguaq dyke. Additional age determinations of mafic dykes from South-East Greenland are 2166 ± 8 Ma and 2158 ± 8 Ma for two E–W trending dykes, herein named the Skjoldungen dykes, and 2137 ± 11 and 2124 ± 11 for two ENE and NE trending dykes, respectively. The name Ruinnæsset dykes is proposed for this slightly younger, ca. 2137–2124 Ma, generation of dykes in SE Greenland, and Nuuk dykes for coeval ca. 2125 Ma dykes in SW Greenland. The Skjoldungen and the Ruinnæsset dykes have primordial mantle geochemical signatures, with only minor LILE-enrichments. These signatures differ from other, more ‘lithospheric’ Proterozoic dykes within the region, and may reflect highly attenuated lithospheric extension during their emplacement. Coeval mafic magmatism in North Atlantic and Dharwar cratons suggests that these two fragments coexisted within a common Paleoproterozoic supercraton. A lack of younger age-matches further argue for ca. 2170–2140 Ma rifting and subsequent break-up of this Dharwar-North Atlantic connection, prior to the 2137–2124 Ma emplacement of the Ruinnæsset dykes. Other global age correlations are discussed and a likely paleogeographic reconstruction of North Atlantic craton together with the Dharwar and Superior cratons within a Paleoproterozoic supercraton is presented

Integration of word meaning and world knowledge in language comprehension

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