95 research outputs found
Activated Transport in the individual Layers that form the =1 Exciton Condensate
We observe the total filling factor =1 quantum Hall state in a
bilayer two-dimensional electron system with virtually no tunnelling. We find
thermally activated transport in the balanced system with a monotonic increase
of the activation energy with decreasing below 1.65. In the
imbalanced system we find activated transport in each of the layers separately,
yet the activation energies show a striking asymmetry around the balance point.
This implies that the gap to charge-excitations in the {\em individual} layers
is substantially different for positive and negative imbalance.Comment: 4 pages. 4 figure
Spin effects in the magneto-drag between double quantum wells
We report on the selectivity to spin in a drag measurement. This selectivity
to spin causes deep minima in the magneto-drag at odd fillingfactors for
matched electron densities at magnetic fields and temperatures at which the
bare spin energy is only one tenth of the temperature. For mismatched densities
the selectivity causes a novel 1/B-periodic oscillation, such that negative
minima in the drag are observed whenever the majority spins at the Fermi
energies of the two-dimensional electron gasses (2DEGs) are anti-parallel, and
positive maxima whenever the majority spins at the Fermi energies are parallel.Comment: 4 pages, 3 figure
Scanned Potential Microscopy of Edge and Bulk Currents in the Quantum Hall Regime
Using an atomic force microscope as a local voltmeter, we measure the Hall
voltage profile in a 2D electron gas in the quantum Hall (QH) regime. We
observe a linear profile in the bulk of the sample in the transition regions
between QH plateaus and a distinctly nonlinear profile on the plateaus. In
addition, localized voltage drops are observed at the sample edges in the
transition regions. We interpret these results in terms of theories of edge and
bulk currents in the QH regime.Comment: 4 pages, 5 figure
10Kin1day: a bottom-up neuroimaging initiative
We organized 10Kin1day, a pop-up scientific event with the goal to bring together neuroimaging groups from around the world to jointly analyze 10,000+ existing MRI connectivity datasets during a 3-day workshop. In this report, we describe the motivation and principles of 10Kin1day, together with a public release of 8,000+ MRI connectome maps of the human brain
ATLAS pixel detector electronics and sensors
The silicon pixel tracking system for the ATLAS experiment at the Large Hadron Collider is described and the performance requirements are summarized. Detailed descriptions of the pixel detector electronics and the silicon sensors are given. The design, fabrication, assembly and performance of the pixel detector modules are presented. Data obtained from test beams as well as studies using cosmic rays are also discussed
The Resource Curse and Rentier States in the Caspian Region : A Need for Context Analysis
Although much attention is paid to the Caspian region with regard to energy issues, the domestic
consequences of the region’s resource production have so far constituted a neglected field of research.
A systematic survey of the latest research trends in the economic and political causalities of
the resource curse and of rentier states reveals that there is a need for context analysis. In reference
to this, the paper traces any shortcomings and promising approaches in the existent body of literature
on the Caspian region. Following on from this, the paper then proposes a new approach; specifically,
one in which any differences and similarities in the context conditions are captured. This
enables a more precise exploration of the exact ways in which they form contemporary post-Soviet
Caspian rentier states.Obwohl der Region am Kaspischen Meer im Zuge von Energiediskursen groĂźe Aufmerksamkeit zuteil
wird, stellen die innerstaatlichen Folgen der Ressourcenproduktion in der Region ein bislang
vernachlässigtes Forschungsfeld dar. Ein systematischer Überblick über die jüngsten Forschungstrends
zu wirtschaftlichen und politischen Kausalzusammenhängen des Ressourcenfluchs und zu
Rentierstaaten offenbart die Notwendigkeit von Kontextanalysen. Hierauf Bezug nehmend, analysiert
der Aufsatz sowohl die Mängel als auch viel versprechende Ansätze in der betreffenden Literatur
zur Region am Kaspischen Meer. Der Aufsatz stellt letztendlich einen neuen Ansatz vor, der
Unterschiede und Gemeinsamkeiten in den Kontextbedingungen erfasst, um zu erforschen, wie diese
die gegenwärtigen post-sowjetischen Rentierstaaten in der Region am Kaspischen Meer tatsächlich
prägen
The genetic architecture of the human cerebral cortex
The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson’s disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder
Reproducibility in the absence of selective reporting : An illustration from large-scale brain asymmetry research
Altres ajuts: Max Planck Society (Germany).The problem of poor reproducibility of scientific findings has received much attention over recent years, in a variety of fields including psychology and neuroscience. The problem has been partly attributed to publication bias and unwanted practices such as p-hacking. Low statistical power in individual studies is also understood to be an important factor. In a recent multisite collaborative study, we mapped brain anatomical left-right asymmetries for regional measures of surface area and cortical thickness, in 99 MRI datasets from around the world, for a total of over 17,000 participants. In the present study, we revisited these hemispheric effects from the perspective of reproducibility. Within each dataset, we considered that an effect had been reproduced when it matched the meta-analytic effect from the 98 other datasets, in terms of effect direction and significance threshold. In this sense, the results within each dataset were viewed as coming from separate studies in an "ideal publishing environment," that is, free from selective reporting and p hacking. We found an average reproducibility rate of 63.2% (SD = 22.9%, min = 22.2%, max = 97.0%). As expected, reproducibility was higher for larger effects and in larger datasets. Reproducibility was not obviously related to the age of participants, scanner field strength, FreeSurfer software version, cortical regional measurement reliability, or regional size. These findings constitute an empirical illustration of reproducibility in the absence of publication bias or p hacking, when assessing realistic biological effects in heterogeneous neuroscience data, and given typically-used sample sizes
The genetic architecture of the human cerebral cortex
The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder
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