5,758 research outputs found
Peculiarities of neutron waveguides with thin Gd layer
Peculiarities of the formation of a neutron enhanced standing wave in the
structure with a thin highly absorbing layer of gadolinium are considered in
the article. An analogue of the poisoning effect well known in reactor physics
was found. The effect is stronger for the Nb/Gd/Nb system. Despite of this
effect, for a Nb/Gd bilayer and a Nb/Gd/Nb trilayer placed between Al2O3
substrate and Cu layer, it is shown theoretically and experimentally that one
order of magnitude enhancement of neutron density is possible in the vicinity
of the Gd layer. This enhancement makes it possible to study domain formation
in the Gd layer under transition of the Nb layer(s) into the superconducting
state (cryptoferromagnetic phase).Comment: 5 pages, 2 figure
Open Source Dataset and Machine Learning Techniques for Automatic Recognition of Historical Graffiti
Machine learning techniques are presented for automatic recognition of the
historical letters (XI-XVIII centuries) carved on the stoned walls of St.Sophia
cathedral in Kyiv (Ukraine). A new image dataset of these carved Glagolitic and
Cyrillic letters (CGCL) was assembled and pre-processed for recognition and
prediction by machine learning methods. The dataset consists of more than 4000
images for 34 types of letters. The explanatory data analysis of CGCL and
notMNIST datasets shown that the carved letters can hardly be differentiated by
dimensionality reduction methods, for example, by t-distributed stochastic
neighbor embedding (tSNE) due to the worse letter representation by stone
carving in comparison to hand writing. The multinomial logistic regression
(MLR) and a 2D convolutional neural network (CNN) models were applied. The MLR
model demonstrated the area under curve (AUC) values for receiver operating
characteristic (ROC) are not lower than 0.92 and 0.60 for notMNIST and CGCL,
respectively. The CNN model gave AUC values close to 0.99 for both notMNIST and
CGCL (despite the much smaller size and quality of CGCL in comparison to
notMNIST) under condition of the high lossy data augmentation. CGCL dataset was
published to be available for the data science community as an open source
resource.Comment: 11 pages, 9 figures, accepted for 25th International Conference on
Neural Information Processing (ICONIP 2018), 14-16 December, 2018 (Siem Reap,
Cambodia
On the feasibility to study inverse proximity effect in a single S/F bilayer by Polarized Neutron Reflectometry
Here we report on a feasibility study aiming to explore the potential of
Polarized Neutron Reflectometry (PNR) for detecting the inverse proximity
effect in a single superconducting/ferromagnetic bilayer. Experiments,
conducted on the V(40nm)/Fe(1nm) S/F bilayer, have shown that experimental spin
asymmetry measured at T = 0.5TC is shifted towards higher Q values compared to
the curve measured at T = 1.5TC. Such a shift can be described by the
appearance in superconducting vanadium of magnetic sub-layer with thickness of
7 nm and magnetization of +0.8 kG.Comment: Changes in the 2nd version: small mistypes are corrected. Manuscript
submitted to JETP let. 4 pages, 2 figure
Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy
While magnetoresistance (MR) has generally been found to be symmetric in
applied field in non-magnetic or magnetic metals, we have observed
antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and
transport measurements show that the antisymmetric MR is due to the appearance
of domain walls that run perpendicular to both the magnetization and the
current, a geometry existing only in materials with perpendicular magnetic
anisotropy. As a result, the extraordinary Hall effect (EHE) gives rise to
circulating currents in the vicinity of the domain walls that contributes to
the MR. The antisymmetric MR and EHE have been quantitatively accounted for by
a theoretical model.Comment: 17 pages, 4 figure
Heavy MSSM Higgs Bosons at CMS: "LHC wedge" and Higgs-Mass Precision
The search for MSSM Higgs bosons will be an important goal at the LHC. In
order to analyze the search reach of the CMS experiment for the heavy neutral
MSSM Higgs bosons, we combine the latest results for the CMS experimental
sensitivities based on full simulation studies with state-of-the-art
theoretical predictions of MSSM Higgs-boson properties. The experimental
analyses are done assuming an integrated luminosity of 30 or 60 fb^-1. The
results are interpreted as 5 \si discovery contours in MSSM M_A-tan_beta
benchmark scenarios. Special emphasis is put on the variation of the Higgs
mixing parameter mu. While the variation of mu can shift the prospective
discovery reach (and correspondingly the ``LHC wedge'' region) by about Delta
tan_beta= 10, the discovery reach is rather stable with respect to the impact
of other supersymmetric parameters. Within the discovery region we analyze the
accuracy with which the masses of the heavy neutral Higgs bosons can be
determined. An accuracy of 1-4% should be achievable, depending on M_A and
tan_beta.Comment: Talk given by G.W. at EPS07 (Manchester, July 2007) and talk given by
S.H. at SUSY07 (Karlsruhe, July 2007). 4 pages, 2 figure
Evidence for nonmonotonic magnetic field penetration in a type-I superconductor
Polarized neutron reflectometry (PNR) provides evidence that nonlocal
electrodynamics governs the magnetic field penetration in an extreme low-k
superconductor. The sample is an indium film with a large elastic mean free
path (11 mkm) deposited on a silicon oxide wafer. It is shown that PNR can
resolve the difference between the reflected neutron spin asymmetries predicted
by the local and nonlocal theories of superconductivity. The experimental data
support the nonlocal theory, which predicts a nonmonotonic decay of the
magnetic field.Comment: 5 pages, 4 figures, LaTex, corrected typos and figure
Magnetic and Superconducting Phase Diagram of Nb/Gd/Nb trilayers
We report on a study of the structural, magnetic and superconducting
properties of Nb(25nm)/Gd()/Nb(25nm) hybrid structures of a
superconductor/ ferromagnet (S/F) type. The structural characterization of the
samples, including careful determination of the layer thickness, was performed
using neutron and X-ray scattering with the aid of depth sensitive
mass-spectrometry. The magnetization of the samples was determined by SQUID
magnetometry and polarized neutron reflectometry and the presence of magnetic
ordering for all samples down to the thinnest Gd(0.8nm) layer was shown. The
analysis of the neutron spin asymmetry allowed us to prove the absence of
magnetically dead layers in junctions with Gd interlayer thickness larger than
one monolayer. The measured dependence of the superconducting transition
temperature has a damped oscillatory behavior with well defined
positions of the minimum at =3nm and the following maximum at =4nm;
the behavior, which is in qualitative agreement with the prior work (J.S. Jiang
et al, PRB 54, 6119). The analysis of the dependence based on Usadel
equations showed that the observed minimum at =3nm can be described by the
so called "" to "" phase transition of highly transparent S/F
interfaces with the superconducting correlation length nm in
Gd. This penetration length is several times higher than for strong
ferromagnets like Fe, Co or Ni, simplifying thus preparation of S/F structures
with which are of topical interest in superconducting
spintronics
Systematic XAFS investigations of the structural evolution of ytrrium-enriched oxides in ODS ferritic steels by advanced synchrotron source at ESRF
- …