294 research outputs found
Observation of the spin-orbit gap in bilayer graphene by one-dimensional ballistic transport
We report on measurements of quantized conductance in gate-defined quantum
point contacts in bilayer graphene that allow the observation of subband
splittings due to spin-orbit coupling. The size of this splitting can be tuned
from 40 to 80 eV by the displacement field. We assign this gate-tunable
subband-splitting to a gap induced by spin-orbit coupling of Kane-Mele type,
enhanced by proximity effects due to the substrate. We show that this
spin-orbit coupling gives rise to a complex pattern in low perpendicular
magnetic fields, increasing the Zeeman splitting in one valley and suppressing
it in the other one. In addition, we observe the existence of a spin-polarized
channel of 6 e/h at high in-plane magnetic field and of signatures of
interaction effects at the crossings of spin-split subbands of opposite spins
at finite magnetic field.Comment: 5 pages, 4 figures, Supplement 6 figure
Anisotropic susceptibility of ferromagnetic ultrathin Co films on vicinal Cu
We measure the magnetic susceptibility of ultrathin Co films with an in-plane
uniaxial magnetic anisotropy grown on a vicinal Cu substrate. Above the Curie
temperature the influence of the magnetic anisotropy can be investigated by
means of the parallel and transverse susceptibilities along the easy and hard
axes. By comparison with a theoretical analysis of the susceptibilities we
determine the isotropic exchange interaction and the magnetic anisotropy. These
calculations are performed in the framework of a Heisenberg model by means of a
many-body Green's function method, since collective magnetic excitations are
very important in two-dimensional magnets.Comment: 7 pages, 3 figure
Europe-wide air pollution modeling from 2000 to 2019 using geographically weighted regression
Previous European land-use regression (LUR) models assumed fixed linear relationships between air pollution concentrations and predictors such as traffic and land use. We evaluated whether including spatially-varying relationships could improve European LUR models by using geographically weighted regression (GWR) and random forest (RF). We built separate LUR models for each year from 2000 to 2019 for NO2, O3, PM2.5 and PM10 using annual average monitoring observations across Europe. Potential predictors included satellite retrievals, chemical transport model estimates and land-use variables. Supervised linear regression (SLR) was used to select predictors, and then GWR estimated the potentially spatially-varying coefficients. We developed multi-year models using geographically and temporally weighted regression (GTWR). Five-fold cross-validation per year showed that GWR and GTWR explained similar spatial variations in annual average concentrations (average R(2) = NO2: 0.66; O3: 0.58; PM10: 0.62; PM2.5: 0.77), which are better than SLR (average R(2) = NO2: 0.61; O3: 0.46; PM10: 0.51; PM2.5: 0.75) and RF (average R(2) = NO2: 0.64; O3: 0.53; PM10: 0.56; PM2.5: 0.67). The GTWR predictions and a previously-used method of back-extrapolating 2010 model predictions using CTM were overall highly correlated (R(2) > 0.8) for all pollutants. Including spatially-varying relationships using GWR modestly improved European air pollution annual LUR models, allowing time-varying exposure-health risk models
Inhibitory Control Across the Preschool Years: Developmental Changes and Associations with Parenting
The normative developmental course of inhibitory control between 2.5 and 6.5 years, and associations with maternal and paternal sensitivity and intrusiveness were tested. The sample consisted of 383 children (52.5% boys). During four annual waves, mothers and fathers reported on their children’s inhibitory control using the Children\u27s Behavior Questionnaire. During the first wave, mothers’ and fathers’ sensitivity and intrusiveness were observed and coded with the Emotional Availability Scales. Inhibitory control exhibited partial scalar invariance over time, and increased in a decelerating rate. For both mothers and fathers, higher levels of sensitivity were associated with a higher initial level of children\u27s inhibitory control, whereas higher levels of intrusiveness predicted a slower increase in children\u27s inhibitory control
Evaporation and fluid dynamics of a sessile drop of capillary size
Theoretical description and numerical simulation of an evaporating sessile
drop are developed. We jointly take into account the hydrodynamics of an
evaporating sessile drop, effects of the thermal conduction in the drop and the
diffusion of vapor in air. A shape of the rotationally symmetric drop is
determined within the quasistationary approximation. Nonstationary effects in
the diffusion of the vapor are also taken into account. Simulation results
agree well with the data of evaporation rate measurements for the toluene drop.
Marangoni forces associated with the temperature dependence of the surface
tension, generate fluid convection in the sessile drop. Our results demonstrate
several dynamical stages of the convection characterized by different number of
vortices in the drop. During the early stage the street of vortices arises near
a surface of the drop and induces a non-monotonic spatial distribution of the
temperature over the drop surface. The initial number of near-surface vortices
in the drop is controlled by the Marangoni cell size which is similar to that
given by Pearson for flat fluid layers. This number quickly decreases with
time, resulting in three bulk vortices in the intermediate stage. The vortices
finally transform into the single convection vortex in the drop, existing
during about 1/2 of the evaporation time.Comment: 23 pages, 12 figure
Gas Dynamic Virtual Nozzle for Generation of Microscopic Droplet Streams
As shown by Ganan-Calvo and co-workers, a free liquid jet can be compressed
in iameter through gas-dynamic forces exerted by a co-flowing gas, obviating
the need for a solid nozzle to form a microscopic liquid jet and thereby
alleviating the clogging problems that plague conventional droplet sources of
small diameter. We describe in this paper a novel form of droplet beam source
based on this principle. The source is miniature, robust, dependable, easily
fabricated, and eminently suitable for delivery of microscopic liquid droplets,
including hydrated biological samples, into vacuum for analysis using vacuum
instrumentation. Monodisperse, single file droplet streams are generated by
triggering the device with a piezoelectric actuator. The device is essentially
immune to clogging
A combined first and second order variational approach for image reconstruction
In this paper we study a variational problem in the space of functions of
bounded Hessian. Our model constitutes a straightforward higher-order extension
of the well known ROF functional (total variation minimisation) to which we add
a non-smooth second order regulariser. It combines convex functions of the
total variation and the total variation of the first derivatives. In what
follows, we prove existence and uniqueness of minimisers of the combined model
and present the numerical solution of the corresponding discretised problem by
employing the split Bregman method. The paper is furnished with applications of
our model to image denoising, deblurring as well as image inpainting. The
obtained numerical results are compared with results obtained from total
generalised variation (TGV), infimal convolution and Euler's elastica, three
other state of the art higher-order models. The numerical discussion confirms
that the proposed higher-order model competes with models of its kind in
avoiding the creation of undesirable artifacts and blocky-like structures in
the reconstructed images -- a known disadvantage of the ROF model -- while
being simple and efficiently numerically solvable.Comment: 34 pages, 89 figure
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