53 research outputs found
Anisotropic spin-density distribution and magnetic anisotropy of strained LaSrMnO thin films: Angle-dependent x-ray magnetic circular dichroism
Magnetic anisotropies of ferromagnetic thin films are induced by epitaxial
strain from the substrate via strain-induced anisotropy in the orbital magnetic
moment and that in the spatial distribution of spin-polarized electrons.
However, the preferential orbital occupation in ferromagnetic metallic
LaSrMnO (LSMO) thin films studied by x-ray linear dichroism
(XLD) has always been found out-of-plane for both tensile and compressive
epitaxial strain and hence irrespective of the magnetic anisotropy. In order to
resolve this mystery, we directly probed the preferential orbital occupation of
spin-polarized electrons in LSMO thin films under strain by angle-dependent
x-ray magnetic circular dichroism (XMCD). Anisotropy of the spin-density
distribution was found to be in-plane for the tensile strain and out-of-plane
for the compressive strain, consistent with the observed magnetic anisotropy.
The ubiquitous out-of-plane preferential orbital occupation seen by XLD is
attributed to the occupation of both spin-up and spin-down out-of-plane
orbitals in the surface magnetic dead layer.Comment: 20 pages, 4 figure
Testing the potential of a virtual reality neurorehabilitation system during performance of observation, imagery and imitation of motor actions recorded by wireless functional near-infrared spectroscopy (fNIRS)
Background
Several neurorehabilitation strategies have been introduced over the last decade based on the so-called simulation hypothesis. This hypothesis states that a neural network located in primary and secondary motor areas is activated not only during overt motor execution, but also during observation or imagery of the same motor action. Based on this hypothesis, we investigated the combination of a virtual reality (VR) based neurorehabilitation system together with a wireless functional near infrared spectroscopy (fNIRS) instrument. This combination is particularly appealing from a rehabilitation perspective as it may allow minimally constrained monitoring during neurorehabilitative training.
Methods
fNIRS was applied over F3 of healthy subjects during task performance in a virtual reality (VR) environment: 1) 'unilateral' group (N = 15), contralateral recording during observation, motor imagery, observation & motor imagery, and imitation of a grasping task performed by a virtual limb (first-person perspective view) using the right hand; 2) 'bilateral' group (N = 8), bilateral recording during observation and imitation of the same task using the right and left hand alternately.
Results
In the unilateral group, significant within-condition oxy-hemoglobin concentration Î[O2Hb] changes (mean ± SD ÎŒmol/l) were found for motor imagery (0.0868 ± 0.5201 ÎŒmol/l) and imitation (0.1715 ± 0.4567 ÎŒmol/l). In addition, the bilateral group showed a significant within-condition Î[O2Hb] change for observation (0.0924 ± 0.3369 ÎŒmol/l) as well as between-conditions with lower Î[O2Hb] amplitudes during observation compared to imitation, especially in the ipsilateral hemisphere (p < 0.001). Further, in the bilateral group, imitation using the non-dominant (left) hand resulted in larger Î[O2Hb] changes in both the ipsi- and contralateral hemispheres as compared to using the dominant (right) hand.
Conclusions
This study shows that our combined VR-fNIRS based neurorehabilitation system can activate the action-observation system as described by the simulation hypothesis during performance of observation, motor imagery and imitation of hand actions elicited by a VR environment. Further, in accordance with previous studies, the findings of this study revealed that both inter-subject variability and handedness need to be taken into account when recording in untrained subjects. These findings are of relevance for demonstrating the potential of the VR-fNIRS instrument in neurofeedback applications
Leishmanicidal Active Constituents from Nepalese Medicinal Plant Tulsi (Ocimum sanctum L.)
Oxidosqualene Cyclases from Cell Suspension Cultures of Betula platyphylla var. japonica: Molecular Evolution of Oxidosqualene Cyclases in Higher Plants
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