332 research outputs found
Enhancement of Superconductivity by Exchange Bias
In this work we study the transport properties of hybrids that consist of
exchange biased ferromagnets (FMs) combined with a low-Tc superconductor (SC).
Not only different FMs but also various structural topologies have been
investigated: results for multilayers of La(1-x)CaxMnO3 combined with Nb in the
form of [La0.33Ca0.67MnO3/La0.60Ca0.40MnO3]15/Nb, and for more simple
Ni80Fe20/Nb/Ni80Fe20 trilayers and Ni80Fe20/Nb bilayers are presented. The
results obtained in all hybrid structures studied in this work clearly uncover
that the exchange bias mechanism promotes superconductivity. Our findings
assist the understanding of the contradictory results that have been reported
in the recent literature regarding the transport properties of relative
FM/SC/FM spin valves
Giant increase in critical current density of KxFe2-ySe2 single crystals
By using post-annealing and quenching technique, we show that the critical
current density Jc,ab of KxFe2-ySe2 single crystals can be enhanced more than
one order of magnitude up to ~ 2.1 \times 10^4 A/cm^2 at 1.8 K. The scaling law
between normalized pinning force and reduced field for all measured
temperatures was observed, reflecting the presence of only one dominant pinning
mechanism. Analysis indicates presence of 3D point-like normal core pinning
sources in quenched KxFe2-ySe2 samples whereas dominant vortex interaction with
pinning centers is via spatial variations in Tc ("deltaTc pinning").Comment: 3 figures, 4 page
Effective ferromagnetic coupling between a superconductor and a ferromagnet in LaCaMnO/Nb hybrids
In this work we present magnetization data on hybrids consisting of
multilayers (MLs) of man- ganites [La0.33Ca0.67MnO3/La0.60Ca0.40MnO3]15 in
contact with a low-Tc Nb superconductor (SC). Although a pure SC should behave
diamagnetically in respect to the external magnetic field in our ML-SC hybrids
we observed that the magnetization of the SC follows that of the ML. Our
intriguing experimental results show that the SC below its TSC c becomes
ferromagnetically coupled to the ML. As a result in the regime where
diamagnetic behaviour of the SC was expected its bulk magne- tization switches
only whenever the coercive field of the ML is exceeded. By employing specific
experiments where the ML was selectively biased or not we demonstrate that the
ML inflicts its magnetic properties on the whole hybrid. Possible explanations
are discussed in connection to recent theoretical proposals and experimental
findings that were obtained in relative hybrids.Comment: To appear in Phys. Rev.
Pixel-level semantic understanding of ophthalmic images and beyond
Computer-assisted semantic image understanding constitutes the substrate of applications that range from biomarker detection to intraoperative guidance or street scene understanding for self-driving systems. This PhD thesis is on the development of deep learning-based, pixel-level, semantic segmentation methods for medical and natural images. For vessel segmentation in OCT-A, a method comprising iterative refinement of the extracted vessel maps and an auxiliary loss function that penalizes structural inaccuracies, is proposed and tested on data captured from real clinical conditions comprising various pathological cases. Ultimately, the presented method enables the extraction of a detailed vessel map of the retina with potential applications to diagnostics or intraoperative localization. Furthermore, for scene segmentation in cataract surgery, the major challenge of class imbalance is identified among several factors. Subsequently, a method addressing it is proposed, achieving state-of-the-art performance on a challenging public dataset. Accurate semantic segmentation in this domain can be used to monitor interactions between tools and anatomical parts for intraoperative guidance and safety. Finally, this thesis proposes a novel contrastive learning framework for supervised semantic segmentation, that aims to improve the discriminative power of features in deep neural networks. The proposed approach leverages contrastive loss function applied both at multiple model layers and across them. Importantly, the proposed framework is easy to combine with various model architectures and is experimentally shown to significantly improve performance on both natural and medical domain
B NMR detection of the magnetic field distribution in the mixed superconducting state of MgB
The temperature dependence of the magnetic field distribution in the mixed
superconducting phase of randomly oriented MgB powder was probed by B NMR spectroscopy. Below the temperature of the second critical () field, K, our spectra reveal two NMR signal
components, one mapping the magnetic field distribution in the mixed
superconducting state and the other one arising from the normal state. The
complementary use of bulk magnetization and NMR measurements reveals that
MgB is an anisotropic superconductor with a Tesla
anisotropy parameter
- β¦