164 research outputs found
Final Report for Full-Scale Load Monitoring of Rubble Mound Breakwaters:description of work completed by Aalborg University
Four-Wave Mixing in Landau-Quantized Graphene
International audienceFor Landau-quantized graphene, featuring an energy spectrum consisting of a series of nonequidis-tant Landau levels, theory predicts a giant resonantly-enhanced optical nonlinearity. We verify the nonlinearity in a degenerate time-integrated four-wave mixing (FWM) experiment in the mid-infrared spectral range, involving the Landau levels LL −1 , LL 0 and LL 1. A rapid dephasing of the optically induced microscopic polarization on a timescale shorter than the pulse duration (∼4 ps) is observed, while a complementary pump-probe experiment under the same experimental conditions reveals a much longer lifetime of the induced population. The FWM signal shows the expected field dependence with respect to lowest order perturbation theory for low fields. Saturation sets in for fields above ∼ 6 kV/cm. Furthermore, the resonant behavior and the order of magnitude of the third-order susceptibility are in agreement with theoretical calculations
Is 8:30 a.m. Still Too Early to Start School? A 10:00 a.m. School Start Time Improves Health and Performance of Students Aged 13-16.
While many studies have shown the benefits of later school starts, including better student attendance, higher test scores, and improved sleep duration, few have used starting times later than 9:00 a.m. Here we report on the implementation and impact of a 10 a.m. school start time for 13 to 16-year-old students. A 4-year observational study using a before-after-before (A-B-A) design was carried out in an English state-funded high school. School start times were changed from 8:50 a.m. in study year 0, to 10 a.m. in years 1-2, and then back to 8:50 a.m. in year 3. Measures of student health (absence due to illness) and academic performance (national examination results) were used for all students. Implementing a 10 a.m. start saw a decrease in student illness after 2 years of over 50% (p < 0.0005 and effect size: Cohen's d = 1.07), and reverting to an 8:50 a.m. start reversed this improvement, leading to an increase of 30% in student illness (p < 0.0005 and Cohen's d = 0.47). The 10:00 a.m. start was associated with a 12% increase in the value-added number of students making good academic progress (in standard national examinations) that was significant (<0.0005) and equivalent to 20% of the national benchmark. These results show that changing to a 10:00 a.m. high school start time can greatly reduce illness and improve academic performance. Implementing school start times later than 8:30 a.m., which may address the circadian delay in adolescents' sleep rhythms more effectively for evening chronotypes, appears to have few costs and substantial benefits
Symmetry-breaking supercollisions in Landau-quantized graphene
Recent pump-probe experiments performed on graphene in a perpendicular
magnetic field have revealed carrier relaxation times ranging from picoseconds
to nanoseconds depending on the quality of the sample. To explain this
surprising behavior, we propose a novel symmetry-breaking defect-assisted
relaxation channel. This enables scattering of electrons with single
out-of-plane phonons, which drastically accelerate the carrier scattering time
in low-quality samples. The gained insights provide a strategy for tuning the
carrier relaxation time in graphene and related materials by orders of
magnitude
Regional Flow and Deformation Analysis of Basin-Fill Aquifer Systems Using Stress-Dependent Parameters
Field-induced compensation of magnetic exchange as the origin of superconductivity above \texorpdfstring{40\,T}{40~T} in \texorpdfstring{\UTe}{UTe2}
The potential spin-triplet heavy-fermion superconductor \UTe exhibits
signatures of multiple distinct superconducting phases. For field aligned along
the axis, a metamagnetic transition occurs at \HmT. It
is associated with magnetic fluctuations that may be beneficial for the
field-enhanced superconductivity surviving up to \Hm. Once the field is tilted
away from the towards the axis, a reentrant superconducting phase
emerges just above \Hm. In order to better understand this remarkably
field-resistant superconducting phase, we conducted magnetic-torque and
magnetotransport measurements in pulsed magnetic fields. We determine the
record-breaking upper critical field of \HcT and its
evolution with angle. Furthermore, the normal-state Hall effect experiences a
drastic suppression indicative of a reduced band polarization above \Hm in the
angular range around caused by a partial compensation between the
applied field and an exchange field. This promotes the Jaccarino-Peter effect
as a possible mechanism for the reentrant superconductivity above \Hm.Comment: Main text: 27 pages, 4 figure, supplement: 10 pages, 5 figure
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