89 research outputs found
Depinning and dynamics of vortices confined in mesoscopic flow channels
We study the behavior of vortex matter in artificial flow channels confined
by pinned vortices in the channel edges (CE's). The critical current is
governed by the interaction with static vortices in the CE's. We study
structural changes associated with (in)commensurability between the channel
width and the natural row spacing , and their effect on . The
behavior depends crucially on the presence of disorder in the CE arrays. For
ordered CE's, maxima in occur at matching ( integer), while
for defects along the CE's cause a vanishing . For weak CE
disorder, the sharp peaks in at become smeared via nucleation
and pinning of defects. The corresponding quasi-1D row configurations can
be described by a (disordered)sine-Gordon model. For larger disorder and
, levels at of the ideal lattice strength
. Around 'half filling' (), disorder causes new
features, namely {\it misaligned} defects and coexistence of and
rows in the channel. This causes a {\it maximum} in around mismatch,
while smoothly decreases towards matching due to annealing of the
misaligned regions. We study the evolution of static and dynamic structures on
changing , the relation between modulations of and transverse
fluctuations and dynamic ordering of the arrays. The numerical results at
strong disorder show good qualitative agreement with recent mode-locking
experiments.Comment: 29 pages, 32 figure
Prefrontal cortex gyrification index in twins: an MRI study
Cortical development and folding seems to be under environmental as well as genetic control. The aim of our study was to estimate the genetic influence on gyrification and cortical volumes, comparing prefrontal gyrification index (GI) in monozygotic (MZ) and dizygotic (DZ) twin pairs, and unrelated pairs. Twenty-four subjects (6 pairs of MZ and 6 pairs of DZ twins) were included in this study. Prefrontal cortical folding (gyrification) was measured by an automated and manual version of the gyrification index (A-GI, M-GI) according to previously published protocols. MR-imaging was performed and 3 representative slices were selected from coronar MR-imaging scans. The volumes of the total brain, temporal lobes, prefrontal lobes, and cerebellum were analyzed, too. To evaluate similarity in GI, absolute differences in GI, and brain volumes as well as intraclass correlations of twin pairs were compared with regard to twin status. Finally, a control group of unrelated pairs was assembled from the first two study groups and analyzed. Compared to unrelated pairs, twin pairs exhibited more similarity concerning different brain volumes and a trend to more similarity concerning A-GI. MZ twins did not present more similarity concerning GI (automatically and manually measured) and volume measurements compared to DZ twins. Different factors, like intrauterine factors, postnatal development conditions, and especially environmental factors might account for the differences between related and unrelated pairs. The nonexistence of a pronounced similarity in MZ twins compared to DZ twins concerning prefrontal GI raises questions about the extent of genetic influence on GI
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