220 research outputs found
An Evaluation of Non-Contrastive Self-Supervised Learning for Federated Medical Image Analysis
Privacy and annotation bottlenecks are two major issues that profoundly
affect the practicality of machine learning-based medical image analysis.
Although significant progress has been made in these areas, these issues are
not yet fully resolved. In this paper, we seek to tackle these concerns head-on
and systematically explore the applicability of non-contrastive self-supervised
learning (SSL) algorithms under federated learning (FL) simulations for medical
image analysis. We conduct thorough experimentation of recently proposed
state-of-the-art non-contrastive frameworks under standard FL setups. With the
SoTA Contrastive Learning algorithm, SimCLR as our comparative baseline, we
benchmark the performances of our 4 chosen non-contrastive algorithms under
non-i.i.d. data conditions and with a varying number of clients. We present a
holistic evaluation of these techniques on 6 standardized medical imaging
datasets. We further analyse different trends inferred from the findings of our
research, with the aim to find directions for further research based on ours.
To the best of our knowledge, ours is the first to perform such a thorough
analysis of federated self-supervised learning for medical imaging. All of our
source code will be made public upon acceptance of the paper
Design aspects of dual gate GaAs nanowire FET for room temperature charge qubit operation: A study on diameter and gate engineering
The current work explores a geometrically engineered dual gate GaAs nanowire
FET with state of the art miniaturized dimensions for high performance charge
qubit operation at room temperature. Relevant gate voltages in such device can
create two voltage tunable quantum dots (VTQDs) underneath the gates, as well
as can manipulate their eigenstate detuning and the inter-dot coupling to
generate superposition, whereas a small drain bias may cause its collapse
leading to qubit read out. Such qubit operations, i.e., Initialization,
Manipulation, and Measurement, are theoretically modeled in the present work by
developing a second quantization filed operator based Schrodinger-Poisson
self-consistent framework coupled to non-equilibrium Greens function formalism.
The study shows that the Bloch sphere coverage can be discretized along polar
and azimuthal directions by reducing the nanowire diameter and increasing the
inter-dot separation respectively, that can be utilized for selective
information encoding. The theoretically obtained stability diagrams suggest
that downscaled nanowire diameter and increased gate separation sharpen the
bonding and anti-bonding states with reduced anticrossing leading to a gradual
transformation of the hyperbolic current mapping into a pair of straight lines.
However, the dephasing time in the proposed GaAs VTQD-based qubit may be
significantly improved by scaling down both the nanowire diameter and gate
separation. Therefore, the present study suggests an optimization window for
geometrical engineering of a dual gate nanowire FET qubit to achieve superior
qubit performance. Most importantly, such device is compatible with the
mainstream CMOS technology and can be utilized for large scale implementation
by little modification of the state of the art fabrication processes
IDEAL: Improved DEnse locAL Contrastive Learning for Semi-Supervised Medical Image Segmentation
Due to the scarcity of labeled data, Contrastive Self-Supervised Learning
(SSL) frameworks have lately shown great potential in several medical image
analysis tasks. However, the existing contrastive mechanisms are sub-optimal
for dense pixel-level segmentation tasks due to their inability to mine local
features. To this end, we extend the concept of metric learning to the
segmentation task, using a dense (dis)similarity learning for pre-training a
deep encoder network, and employing a semi-supervised paradigm to fine-tune for
the downstream task. Specifically, we propose a simple convolutional projection
head for obtaining dense pixel-level features, and a new contrastive loss to
utilize these dense projections thereby improving the local representations. A
bidirectional consistency regularization mechanism involving two-stream model
training is devised for the downstream task. Upon comparison, our IDEAL method
outperforms the SoTA methods by fair margins on cardiac MRI segmentation
Non-equilibrium VLS-grown stable ST12-Ge thin film on Si substrate: A study on strain-induced band-engineering
The current work describes a novel method of growing thin films of stable
crystalline ST12-Ge, a high pressure polymorph of Ge, on Si substrate by a
non-equilibrium VLS-technique. The study explores the scheme of band
engineering of ST12-Ge by inducing process-stress into it as a function of the
growth temperature and film thickness. In the present work, ST12-Ge films are
grown at 180 C - 250 C to obtain thicknesses of ~4.5-7.5 nm, which possess
extremely good thermal stability up to a temperature of ~350 C. Micro-Raman
study shows the stress induced in such ST12-Ge films to be compressive in
nature and vary in the range of ~0.5-7.5 GPa. The measured direct band gap is
observed to vary within 0.688 eV to 0.711 eV for such stresses, and four
indirect band gaps are obtained to be 0.583 eV, 0.614-0.628 eV, 0.622-0.63 eV
and 0.623-0.632 eV, accordingly. The corresponding band structures for
unstrained and strained ST12-Ge are calculated by performing DFT simulation,
which shows that a compressive stress transforms the fundamental band gap at
M-G valley from indirect to direct one. Henceforth, the possible route of
strain induced band engineering in ST12-Ge is explored by analyzing all the
transitions in strained and unstrained band structures along with
substantiation of the experimental results and theoretical calculations. The
investigation shows that unstrained ST12-Ge is a natural n-type semiconductor
which transforms into p-type upon incorporation of a compressive stress of ~5
GPa, with the in-plane electron effective mass components at M-G band edge to
be ~0.09 me. Therefore, such band engineered ST12-Ge exhibits superior mobility
along with its thermal stability and compatibility with Si, which can have
potential applications to develop high-speed MOS devices for advanced CMOS
technology
Antimagnetic rotation and sudden change of electric quadrupole transition strength in 143Eu
Lifetimes of the states in the quadrupole structure in 143Eu have been
measured using the Doppler shift attenuation method as well as parity of the
states in the sequence has been firmly identified from polarization measurement
using the Indian National Gamma Array. The decreasing trends of the deduced
quadrupole transition strength B(E2) with spin, along with increasing J (2)
/B(E2) values before band crossing, conclusively establish the origin of these
states as arising out of antimagnetic rotation. The abrupt increase in the
B(E2) values after the band crossing in the quadrupole band, a novel feature
observed in the present experiment, may indicates the crossing of different
shears configurations resulting in re-opening of shears structure. The results
are well reproduced by numerical calculation within the framework of
semi-classical geometric model.Comment: 6 pages, 4 postscript figure
Synthesis and structure of new pyrochlore-type oxides Ln2ScNbO7 (Ln = Pr, Nd, Eu, Gd, Dy)
We report the synthesis and structural study of mixed oxides in the Ln2ScNbO7
series. New phases with Ln = Pr, Eu, Gd and Dy are obtained. All crystallize in
the cubic pyrochlore structure type, space group F-d3m, with no Sc-Nb ordering
on the B-site. The structures are determined by Rietveld refinement. The
evolution of cell parameters, interatomic distances and angles as a function of
lanthanide cation size is discussed. Magnetic measurements show the absence of
ordering down to 2 K, in agreement with the presence of strong geometric
frustration in the lanthanide sublattice. The europium phase shows a peculiar
magnetic behaviour; its magnetic susceptibility becomes constant below ca 50 K.
This feature confirms the behaviour observed previously on Eu2Ti2O7 and is
ascribed to crystal field effects
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