342 research outputs found
On the hierarchy of partially invariant submodels of differential equations
It is noticed, that partially invariant solution (PIS) of differential
equations in many cases can be represented as an invariant reduction of some
PIS of the higher rank. This introduce a hierarchic structure in the set of all
PISs of a given system of differential equations. By using this structure one
can significantly decrease an amount of calculations required in enumeration of
all PISs for a given system of partially differential equations. An equivalence
of the two-step and the direct ways of construction of PISs is proved. In this
framework the complete classification of regular partially invariant solutions
of ideal MHD equations is given
Magnetic anisotropy in strained manganite films and bicrystal junctions
Transport and magnetic properties of LSMO manganite thin films and bicrystal
junctions were investigated. Manganite films were epitaxially grown on STO,
LAO, NGO and LSAT substrates and their magnetic anisotropy were determined by
two techniques of magnetic resonance spectroscopy. Compare with cubic
substrates a small (about 0.3 persentage), the anisotropy of the orthorhombic
NGO substrate leads to a uniaxial anisotropy of the magnetic properties of the
films in the plane of the substrate. Samples with different tilt of
crystallographic basal planes of manganite as well as bicrystal junctions with
rotation of the crystallographic axes (RB - junction) and with tilting of basal
planes (TB - junction) were investigated. It was found that on vicinal NGO
substrates the value of magnetic anisotropy could be varied by changing the
substrate inclination angle from 0 to 25 degrees. Measurement of magnetic
anisotropy of manganite bicrystal junction demonstrated the presence of two
ferromagnetically ordered spin subsystems for both types of bicrystal
boundaries RB and TB. The magnitude of the magnetoresistance for TB - junctions
increased with decreasing temperature and with the misorientation angle even
misorientation of easy axes in the parts of junction does not change. Analysis
of the voltage dependencies of bicrystal junction conductivity show that the
low value of the magnetoresistance for the LSMO bicrystal junctions can be
caused by two scattering mechanisms with the spin- flip of spin - polarized
carriers due to the strong electron - electron interactions in a disordered
layer at the bicrystal boundary at low temperatures and the spin-flip by anti
ferromagnetic magnons at high temperatures.Comment: 26 pages, 10 figure
Classification of conservation laws of compressible isentropic fluid flow in n>1 spatial dimensions
For the Euler equations governing compressible isentropic fluid flow with a
barotropic equation of state (where pressure is a function only of the
density), local conservation laws in spatial dimensions are fully
classified in two primary cases of physical and analytical interest: (1)
kinematic conserved densities that depend only on the fluid density and
velocity, in addition to the time and space coordinates; (2) vorticity
conserved densities that have an essential dependence on the curl of the fluid
velocity. A main result of the classification in the kinematic case is that the
only equation of state found to be distinguished by admitting extra
-dimensional conserved integrals, apart from mass, momentum, energy, angular
momentum and Galilean momentum (which are admitted for all equations of state),
is the well-known polytropic equation of state with dimension-dependent
exponent . In the vorticity case, no distinguished equations of
state are found to arise, and here the main result of the classification is
that, in all even dimensions , a generalized version of Kelvin's
two-dimensional circulation theorem is obtained for a general equation of
state.Comment: 24 pages; published version with misprints correcte
Evidence for spin-triplet superconducting correlations in metal-oxide heterostructures with non-collinear magnetization
Heterostructures composed of ferromagnetic La0.7Sr0.3MnO3, ferromagnetic
SrRuO3, and superconducting YBa2Cu3Ox were studied experimentally. Structures
of composition Au/La0.7Sr0.3MnO3/SrRuO3/YBa2Cu3Ox were prepared by pulsed laser
deposition, and their high quality was confirmed by X-ray diffraction and
reflectometry. A non-collinear magnetic state of the heterostructures was
revealed by means of SQUID magnetometry and polarized neutron reflectometry. We
have further observed superconducting currents in mesa-structures fabricated by
deposition of a second superconducting Nb layer on top of the heterostructure,
followed by patterning with photolithography and ion-beam etching. Josephson
effects observed in these mesa-structures can be explained by the penetration
of a triplet component of the superconducting order parameter into the magnetic
layers.Comment: 10 pages, 6 figure
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