49 research outputs found
Resonance fluorescence revival in a voltage-controlled semiconductor quantum dot
We demonstrate systematic resonance fluorescence recovery with near-unity
emission efficiency in single quantum dots embedded in a charge-tunable device
in a wave-guiding geometry. The quantum dot charge state is controlled by a
gate voltage, through carrier tunneling from a close-lying Fermi sea,
stabilizing the resonantly photocreated electron-hole pair. The electric field
cancels out the charging/discharging mechanisms from nearby traps toward the
quantum dots, responsible for the usually observed inhibition of the resonant
fluorescence. Fourier transform spectroscopy as a function of the applied
voltage shows a strong increase of the coherence time though not reaching the
radiative limit. These charge controlled quantum dots act as quasi-perfect
deterministic single-photon emitters, with one laser pulse converted into one
emitted single photon
Near-critical spreading of droplets
We study the spreading of droplets in a near-critical phase-separated liquid
mixture, using a combination of experiments, lubrication theory and
finite-element numerical simulations. The classical Tanner's law describing the
spreading of viscous droplets is robustly verified when the critical
temperature is neared. Furthermore, the microscopic cut-off length scale
emerging in this law is obtained as a single free parameter for each given
temperature. In total-wetting conditions, this length is interpreted as the
thickness of the thin precursor film present ahead of the apparent contact
line. The collapse of the different evolutions onto a single Tanner-like master
curve demonstrates the universality of viscous spreading before entering in the
fluctuation-dominated regime. Finally, our results reveal a counter-intuitive
and sharp thinning of the precursor film when approaching the critical
temperature, which is attributed to the vanishing spreading parameter at the
critical point
High domain wall velocity at zero magnetic field induced by low current densities in spin-valve nanostripes
Current-induced magnetic domain wall motion at zero magnetic field is
observed in the permalloy layer of a spin-valve-based nanostripe using
photoemission electron microscopy. The domain wall movement is hampered by
pinning sites, but in between them high domain wall velocities (exceeding 150
m/s) are obtained for current densities well below 10^{12} \unit{A/m^2},
suggesting that these trilayer systems are promising for applications in domain
wall devices in case of well controlled pinning positions. Vertical spin
currents in these structures provide a potential explanation for the increase
in domain wall velocity at low current densities.Comment: Published version, Applied Physics Express 2, 023003 (2009)
http://dx.doi.org/10.1143/APEX.2.02300
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
Bolomètres à électrons chauds à supraconducteurs haute température critique pour les ondes submillimétriques (élaboration et caractérisations)
PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
Microwave behaviour of HTS circuits based on ion-irradiated Josephson junctions
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