209 research outputs found
Spin-charge conversion in disordered two-dimensional electron gases lacking inversion symmetry
We study the spin-charge conversion mechanisms in a two-dimensional gas of
electrons moving in a smooth disorder potential by accounting for both
Rashba-type and Mott's skew scattering contributions. We find that quantum
interference effects between spin-flip and skew scattering give rise to
anisotropic spin precession scattering (ASP), a direct spin-charge conversion
mechanism that was discovered in an earlier study of graphene decorated with
adatoms [C. Huang \emph{et al.} Phys.~Rev.~B \textbf{94} 085414.~(2016)]. Our
findings suggest that, together with other spin-charge conversion mechanisms
such as the inverse galvanic effect, ASP is a fairly universal phenomenon that
should be present in disordered two-dimensional systems lacking inversion
symmetry.Comment: 9 pages, 2 figure
V-Net: Fully Convolutional Neural Networks for Volumetric Medical Image Segmentation
Convolutional Neural Networks (CNNs) have been recently employed to solve
problems from both the computer vision and medical image analysis fields.
Despite their popularity, most approaches are only able to process 2D images
while most medical data used in clinical practice consists of 3D volumes. In
this work we propose an approach to 3D image segmentation based on a
volumetric, fully convolutional, neural network. Our CNN is trained end-to-end
on MRI volumes depicting prostate, and learns to predict segmentation for the
whole volume at once. We introduce a novel objective function, that we optimise
during training, based on Dice coefficient. In this way we can deal with
situations where there is a strong imbalance between the number of foreground
and background voxels. To cope with the limited number of annotated volumes
available for training, we augment the data applying random non-linear
transformations and histogram matching. We show in our experimental evaluation
that our approach achieves good performances on challenging test data while
requiring only a fraction of the processing time needed by other previous
methods
Optimal input configuration of dynamic contrast enhanced MRI in convolutional neural networks for liver segmentation
Most MRI liver segmentation methods use a structural 3D scan as input, such
as a T1 or T2 weighted scan. Segmentation performance may be improved by
utilizing both structural and functional information, as contained in dynamic
contrast enhanced (DCE) MR series. Dynamic information can be incorporated in a
segmentation method based on convolutional neural networks in a number of ways.
In this study, the optimal input configuration of DCE MR images for
convolutional neural networks (CNNs) is studied. The performance of three
different input configurations for CNNs is studied for a liver segmentation
task. The three configurations are I) one phase image of the DCE-MR series as
input image; II) the separate phases of the DCE-MR as input images; and III)
the separate phases of the DCE-MR as channels of one input image. The three
input configurations are fed into a dilated fully convolutional network and
into a small U-net. The CNNs were trained using 19 annotated DCE-MR series and
tested on another 19 annotated DCE-MR series. The performance of the three
input configurations for both networks is evaluated against manual annotations.
The results show that both neural networks perform better when the separate
phases of the DCE-MR series are used as channels of an input image in
comparison to one phase as input image or the separate phases as input images.
No significant difference between the performances of the two network
architectures was found for the separate phases as channels of an input image.Comment: Submitted to SPIE Medical Imaging 201
Computerâ aided detection of retained surgical needles from postoperative radiographs
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/136033/1/mp12011.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/136033/2/mp12011_am.pd
Magneto-spin Hall conductivity of a two-dimensional electron gas
It is shown that the interplay of long-range disorder and in-plane magnetic
field gives rise to an out-of-plane spin polarization and a finite spin Hall
conductivity of the two-dimensional electron gas in the presence of Rashba
spin-orbit coupling. A key aspect is provided by the electric-field induced
in-plane spin polarization. Our results are obtained first in the
\textit{clean} limit where the spin-orbit splitting is much larger than the
disorder broadening of the energy levels via the diagrammatic evaluation of the
Kubo-formula. Then the results are shown to hold in the full range of the
disorder parameter by means of the quasiclassical Green
function technique.Comment: 5 pages, 1 figur
Optimal Charge-to-Spin Conversion in Graphene on Transition-Metal Dichalcogenides
When graphene is placed on a monolayer of semiconducting transition metal dichalcogenide (TMD) its band structure develops rich spin textures due to proximity spin-orbital effects with interfacial breaking of inversion symmetry. In this work, we show that the characteristic spin winding of low-energy states in graphene on a TMD monolayer enables current-driven spin polarization, a phenomenon known as the inverse spin galvanic effect (ISGE). By introducing a proper figure of merit, we quantify the efficiency of charge-to-spin conversion and show it is close to unity when the Fermi level approaches the spin minority band. Remarkably, at high electronic density, even though subbands with opposite spin helicities are occupied, the efficiency decays only algebraically. The giant ISGE predicted for graphene on TMD monolayers is robust against disorder and remains large at room temperature
Covariant Conservation Laws and the Spin Hall Effect in Dirac-Rashba Systems
We present a theoretical analysis of two-dimensional Dirac-Rashba systems in the presence of disorder and external perturbations. We unveil a set of exact symmetry relations (Ward identities) that impose strong constraints on the spin dynamics of Dirac fermions subject to proximity-induced interactions. This allows us to demonstrate that an arbitrary dilute concentration of scalar impurities results in the total suppression of nonequilibrium spin Hall currents when only Rashba spin-orbit coupling is present. Remarkably, a finite spin Hall conductivity is restored when the minimal Dirac-Rashba model is supplemented with a spin–valley interaction. The Ward identities provide a systematic way to predict the emergence of the spin Hall effect in a wider class of Dirac-Rashba systems of experimental relevance and represent an important benchmark for testing the validity of numerical methodologies
- …