Dataset Information

A Fluctuating State in the Framework Compounds (Ba,Sr)Al2O4.

ABSTRACT: The structural fluctuation in hexagonal Ba(1-x)Sr(x)Al2O4 with a corner-sharing AlO4 tetrahedral network was characterized at various temperatures using transmission electron microscopy experiments. For x???0.05, soft modes of q ~ (1/2, 1/2, 0) and equivalent wave vectors condense at a transition temperature (TC) and form a superstructure with a cell volume of 2a?×?2b?×?c. However, TC is largely suppressed by Sr-substitution, and disappears for x???0.1. Furthermore, the q ~ (1/2, 1/2, 0) soft mode deviates from the commensurate value as temperature decreases and survives in nanoscaled regions below ~200 K. These results strongly suggest the presence of a new quantum criticality induced by the soft mode. Two distinct soft modes were observed as honeycomb-type diffuse scatterings in the high-temperature region up to 800 K. This intrinsic structural instability is a unique characteristic of the framework compound and is responsible for this unusually fluctuating state.

SUBMITTER: Ishii Y

PROVIDER: S-EPMC4725368 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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A Fluctuating State in the Framework Compounds (Ba,Sr)Al2O4.

Ishii Yui Y Tsukasaki Hirofumi H Tanaka Eri E Mori Shigeo S

Scientific reports 20160113

The structural fluctuation in hexagonal Ba(1-x)Sr(x)Al2O4 with a corner-sharing AlO4 tetrahedral network was characterized at various temperatures using transmission electron microscopy experiments. For x ≤ 0.05, soft modes of q ~ (1/2, 1/2, 0) and equivalent wave vectors condense at a transition temperature (TC) and form a superstructure with a cell volume of 2a × 2b × c. However, TC is largely suppressed by Sr-substitution, and disappears for x ≥ 0.1. Furthermore, the q ~ (1/2, 1/2, 0) soft mo ...[more]

PMID: 26758625

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Project description:Functional and effective connectivity are known to change systematically over time. These changes might be explained by several factors, including intrinsic fluctuations in activity-dependent neuronal coupling and contextual factors, like experimental condition and time. Furthermore, contextual effects may be subject-specific or conserved over subjects. To characterize fluctuations in effective connectivity, we used dynamic causal modelling (DCM) of cross spectral responses over 1- min of electroencephalogram (EEG) recordings during rest, divided into 1-sec windows. We focused on two intrinsic networks: the default mode and the saliency network. DCM was applied to estimate connectivity in each time-window for both networks. Fluctuations in DCM connectivity parameters were assessed using hierarchical parametric empirical Bayes (PEB). Within-subject, between-window effects were modelled with a second-level linear model with temporal basis functions as regressors. This procedure was conducted for every subject separately. Bayesian model reduction was then used to assess which (combination of) temporal basis functions best explain dynamic connectivity over windows. A third (between-subject) level model was used to infer which dynamic connectivity parameters are conserved over subjects. Our results indicate that connectivity fluctuations in the default mode network and to a lesser extent the saliency network comprised both subject-specific components and a common component. For both networks, connections to higher order regions appear to monotonically increase during the 1- min period. These results not only establish the predictive validity of dynamic connectivity estimates - in virtue of detecting systematic changes over subjects - they also suggest a network-specific dissociation in the relative contribution of fluctuations in connectivity that depend upon experimental context. We envisage these procedures could be useful for characterizing brain state transitions that may be explained by their cognitive or neuropathological underpinnings.

Dataset Information

A Fluctuating State in the Framework Compounds (Ba,Sr)Al2O4.

Publications

A Fluctuating State in the Framework Compounds (Ba,Sr)Al2O4.

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