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Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser
Gerber, S.,Yang, S.-L.,Zhu, D.,Soifer, H.,Sobota, J. A.,Rebec, S.,Lee, J. J.,Jia, T.,Moritz, B.,Jia, C.,Gauthier, A.,Li, Y.,Leuenberger, D.,Zhang, Y.,Chaix, L.,Li, W.,Jang, H.,Lee, J.-S.,Yi, M.,Dakovs American Association for the Advancement of Scienc 2017 Science Vol.357 No.6346
<P><B>A deeper look into iron selenide</B></P><P>In the past 10 years, iron-based superconductors have created more puzzles than they have helped resolve. Some of the most fundamental outstanding questions are how strong the interactions are and what the electron pairing mechanism is. Now two groups have made contributions toward resolving these questions in the intriguing compound iron selenide (FeSe) (see the Perspective by Lee). Gerber <I>et al.</I> used photoemission spectroscopy coupled with x-ray diffraction to find that FeSe has a very sizable electron-phonon interaction. Quasiparticle interference imaging helped Sprau <I>et al.</I> determine the shape of the superconducting gap and find that the electron pairing in FeSe is orbital-selective.</P><P><I>Science</I>, this issue p. 71, p. 75; see also p. 32</P><P>The interactions that lead to the emergence of superconductivity in iron-based materials remain a subject of debate. It has been suggested that electron-electron correlations enhance electron-phonon coupling in iron selenide (FeSe) and related pnictides, but direct experimental verification has been lacking. Here we show that the electron-phonon coupling strength in FeSe can be quantified by combining two time-domain experiments into a “coherent lock-in” measurement in the terahertz regime. X-ray diffraction tracks the light-induced femtosecond coherent lattice motion at a single phonon frequency, and photoemission monitors the subsequent coherent changes in the electronic band structure. Comparison with theory reveals a strong enhancement of the coupling strength in FeSe owing to correlation effects. Given that the electron-phonon coupling affects superconductivity exponentially, this enhancement highlights the importance of the cooperative interplay between electron-electron and electron-phonon interactions.</P>
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Migraine with Aura: Surface-Based Analysis of the Cerebral Cortex with Magnetic Resonance Imaging
Igor Petrusic,Marko Dakovic,Katarina Kacar,Jasna Zidverc-Trajkovic 대한영상의학회 2018 Korean Journal of Radiology Vol.19 No.4
Objective: Previous migraine studies have reported gray matter alterations in various cortical regions with conflicting results. This study aimed to explore a cortical morphometric difference in migraineurs with aura (MA) compared to healthy subjects (HS) and to delineate a possible difference between the cortical morphological features and different aura phenotypes. Materials and Methods: Forty-eight MA and 30 HS that were balanced by sex, age, and educational level were selected for this study. T2-weighted and three-dimensional T1-weighted magnetic resonance imaging (MRI) of the brain were acquired using a 1.5T MRI scanner. Surface-based morphometry from the MRI data was used to identify differences between the MA and HS group, and then between MA subgroups. The MA group was subdivided into migraineurs who experienced only visual aura (MVA) and migraineurs who had visual, somatosensory and dysphasic symptoms (MVA+). Results: The MVA+ group had significantly reduced cortical surface area of the left rostral middle frontal cortex compared with the MVA group (p < 0.001). Migraine patients had significantly reduced volume of the left fusiform gyrus relative to HS (p < 0.001). Also, the sulcal depth increased at the level of the left temporal pole in the MVA+ group relative to the MVA group (p < 0.001). The vertex-by-vertex analysis did not exhibit any significant difference in cortical thickness between MA and HS, and between MVA+ and MVA, when corrected for multiple comparisons. Conclusion: Migraineurs with aura demonstrates different morphometric features from HS in multiple cortical regions. MVA+ have different morphometric features in the left frontal and temporal lobe relative to MVA, which could be a source of distinct symptoms and serve as potential biomarkers of different MA subtypes.
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Subcortical Volume Changes in Migraine with Aura
Igor Petrusic,Marko Dakovic,Jasna Zidverc-Trajkovic 대한신경과학회 2019 Journal of Clinical Neurology Vol.15 No.4
Background and Purpose Various features of the cerebral cortex and white matter have been extensively investigated in migraine with aura (MwA), but the morphological characteristics of subcortical structures have been largely neglected. Te aim of this study was to identify possible differences in subcortical structures between MwA patients and healthy subjects (HS), and also to determine the correlations between the characteristics of migraine aura and the volumes of subcortical structures. Methods Tirty-two MwA patients and 32 HS matched by sex and age were analyzed in this study. Regional subcortical brain volumes were automatically calculated using the FSL/FMRIB Image Registration and Segmentation Tool sofware (https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/Glossary). A general linear model analysis was used to investigate diferences in the volume of subcortical structures between the MwA patients and HS. A partial correlation test was used to assess correlations between the volume of subcortical structures and characteristics of MwA. Results Te volumes of the right globus pallidus, lef globus pallidus, and lef putamen were signifcantly smaller in MwA patients than in HS (mean±SD): 1,427±135 mm 3 vs. 1,557± 136 mm 3 (p<0.001), 1,436±126 mm 3 vs. 1,550±139 mm 3 (p=0.001), and 4,235±437 mm 3 vs. 4,522±412 mm 3 (p=0.006), respectively. Tere were no signifcant relationships between subcortical structures and clinical parameters. Conclusions Tese fndings suggest that both the globus pallidi and lef putamen play signifcant roles in the pathophysiology of the MwA. Future studies should determine the cause-and-effect relationships, since these could not be discriminated in this study due to its cross-sectional design.
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