181 research outputs found
Epitaxy, stoichiometry, and magnetic properties of Gd-doped EuO films on YSZ (001)
We have succeeded in preparing high-quality Gd-doped single-crystalline EuO
films. Using Eu-distillation-assisted molecular beam epitaxy and a systematic
variation in the Gd and oxygen deposition rates, we have been able to observe
sustained layer-by-layer epitaxial growth on yttria-stabilized cubic zirconia
(001). The presence of Gd helps to stabilize the layer-by-layer growth mode. We
used soft x-ray absorption spectroscopy at the Eu and Gd M4,5 edges to confirm
the absence of Eu3+ contaminants and to determine the actual Gd concentration.
The distillation process ensures the absence of oxygen vacancies in the films.
From magnetization measurements we found the Curie temperature to increase
smoothly as a function of doping from 70 K up to a maximum of 125 K. A
threshold behavior was not observed for concentrations as low as 0.2%.Comment: 8 pages, 9 figure
Laser sounding of instantaneous and mean speed of wind using correlation method
The correlation methods for laser sounding of wind speed are based on mutual processing of lidar signals scattered from several spatially separated volumes at each altitude investigated. The time of atmospheric aerosol transport between the scattering volumes estimated by the position of maximum of the mutual correlation function is the measure of corresponding wind speed. In this case the distance between the scattering volumes (the measuring base), defining the time of aerosol movement through the measuring base also determines the lidar possibilities for measuring the instantaneous (during the time interval of several seconds) or the mean wind speed (some minutes). Based on the experimental investigations performed using two lidars, these possibilites are analyzed
Frequency of vitreoretinal adhesion in retinal vessels in patients with axial myopia of different age groups
Purpose. Finding out the frequency and structures posterior vitreous detachment (PVD), the proportion of local vitreoretinal adhesion in topographical zones of large retinal vessels of posterior pole of the eye in patients of different age groups with axial myopia.Material and methods. Clinical material was 82 eyes (41 patients). The age of patients ranged from 18 to 70 years. According to the age category, which is determined by the WHO classification, all patients were divided into 3 groups. The 1st group (18-44 years old) included 12 people (24 eyes); the 2nd group (45–59 years old) included 14 people (28 eyes); the 3rd group (60–74 years old) included 15 people (30 eyes).Results. In the 1st group PVD was not detected in 11 eyes (45.8%); in 13 eyes there were various variants of PVD (54.2%). In the 2nd group PVD was not detected in 9 eyes (32.1%); in 19 eyes there were various variants of PVD (67.9%). In the 3rd group PVD was not detected in 5 eyes (16.7%); in 25 eyes (83.3%) there were various variants of PVD. In this group, there was statistically significant predominance of partial PVD with fixation of the posterior hyaloid membrane to inner limiting membrane (PHM to ILM).Conclusion. In the group of elderly patients with axial myopia (60– 75 years), statistically significant increase in incidence of local adhesion of PHM to ILM in the projection of large retinal vessels was revealed in comparison with young and middle-aged groups (10 cases versus 1 and 2, respectively, p<0.05). This feature must be taken in examination and subsequent management of these patients
Abrikosov vortex escape from a columnar defect as a topological electronic transition in vortex core
We study microscopic scenario of vortex escape from a columnar defect under
the influence of a transport current. For defect radii smaller than the
superconducting coherence length the depinning process is shown to be a
consequence of two subsequent topological electronic transitions in a trapped
vortex core. The first transition at a critical current is associated
with the opening of Fermi surface segments corresponding to the creation of a
vortex--antivortex pair bound to the defect. The second transition at a certain
current is caused by merging of different Fermi surface segments,
which accompanies the formation of a freely moving vortex.Comment: 5 pages, 4 figure
The Bean-Livingston barrier at a superconductor/magnet interface
The Bean-Livingston barrier at the interface of type-II
superconductor/soft-magnet heterostructures is studied on the basis of the
classical London approach. This shows a characteristic dependence on the
geometry of the particular structure and its interface as well as on the
relative permeability of the involved magnetic constituent. The modification of
the barrier by the presence of the magnet can be significant, as demonstrated
for a cylindrical superconducting filament covered with a coaxial magnetic
sheath. Using typical values of the relative permeability, the critical field
of first penetration of magnetic flux is predicted to be strongly enhanced,
whereas the variation of the average critical current density with the external
field is strongly depressed, in accord with the observations of recent
experiments.Comment: RevTeX 4; revised version; accepted in Journal of Physics: Condensed
Matte
Electronic Structure of Vortices Pinned by Columnar Defects
The electronic structure of a vortex line trapped by an insulating columnar
defect in a type-II superconductor is analysed within the Bogolubov-de Gennes
theory. For quasiparticle trajectories with small impact parameters defined
with respect to the vortex axis the normal reflection of electrons and holes at
the defect surface results in the formation of an additional subgap spectral
branch. The increase in the impact parameter at this branch is accompanied by
the decrease of the excitation energy. When the impact parameter exceeds the
radius of the defect this branch transforms into the Caroli--de
Gennes--Matricon one. As a result, the minigap in the quasiparticle spectrum
increases with the increase in the defect radius. The scenario of the spectrum
transformation is generalized for the case of arbitrary vorticity.Comment: 7 pages, 4 figure
Armenia and Belarus: caught between the EU's and Russia's conditionalities?
This article looks into Armenia's and Belarus’ engagement with the European Union's (EU) and Russia's conditionalities, the two EU Eastern Partnership (EaP) countries that are also members of the Russia-led Eurasian Economic Union (EAEU). While paying attention to political, economic (including energy and technical) as well as security dimensions of the EU's and Russia's approaches, as proposed in the present special section, the article demonstrates that the conditionalities extended by the EU and Russia to the two countries in question have differed. In their turn, Armenia and Belarus have reacted differently to Russia's and the EU's conditionalities. Against the backdrop of the changing significance ascribed to both the EU's and Russia's policies towards their common neighbourhood since the 1990s, the present contribution identifies and analyses factors that account for the diverging positions of Armenia and Belarus, including the type of regime, the geopolitical considerations, the stakes in the economic and energy spheres and the predisposition to integration. The article shows that in the resulting complex context, Armenia and Belarus have been able to influence the shape and content of the EU's and Russia's conditionalities, although in a different way and to a different extent.Ministry of Education and Science (UID/CPO/ 00758/2013
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