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Giant change in IR light transmission in La_{0.67}Ca_{0.33}MnO_{3} film near the Curie temperature: promising application in optical devices
Transport, magnetic, magneto-optical (Kerr effect) and optical (light
absorption) properties have been studied in an oriented polycrystalline
La_{0.67}Ca_{0.33}MnO_{3} film which shows colossal magneto-resistance. The
correlations between these properties are presented. A giant change in IR light
transmission (more than a 1000-fold decrease) is observed on crossing the Curie
temperature (about 270 K) from high to low temperature. Large changes in
transmittance in a magnetic field were observed as well. The giant changes in
transmittance and the large magneto-transmittance can be used for development
of IR optoelectronic devices controlled by thermal and magnetic fields.
Required material characteristics of doped manganites for these devices are
discussed.Comment: 7 pages, 7 figures, submitted to J. Appl. Phy
Crystal structures and proton dynamics in potassium and cesium hydrogen bistrifluoroacetate salts with strong symmetric hydrogen bonds
The crystal structures of potassium and cesium bistrifluoroacetates were
determined at room temperature and at 20 K and 14 K, respectively, with the
single crystal neutron diffraction technique. The crystals belong to the I2/a
and A2/a monoclinic space groups, respectively, and there is no visible phase
transition. For both crystals, the trifluoroacetate entities form dimers linked
by very short hydrogen bonds lying across a centre of inversion. Any proton
disorder or double minimum potential can be rejected. The inelastic neutron
scattering spectral profiles in the OH stretching region between 500 and 1000
cm^{-1} previously published [Fillaux and Tomkinson, Chem. Phys. 158 (1991)
113] are reanalyzed. The best fitting potential has the major characteristics
already reported for potassium hydrogen maleate [Fillaux et al. Chem. Phys. 244
(1999) 387]. It is composed of a narrow well containing the ground state and a
shallow upper part corresponding to dissociation of the hydrogen bond.Comment: 31 pages, 7 figure
Discretized rotation has infinitely many periodic orbits
For a fixed k in (-2,2), the discretized rotation on Z^2 is defined by
(x,y)->(y,-[x+ky]). We prove that this dynamics has infinitely many periodic
orbits.Comment: Revised after referee reports, and added a quantitative statemen
Nonlocal aspects of -symmetries and ODEs reduction
A reduction method of ODEs not possessing Lie point symmetries makes use of
the so called -symmetries (C. Muriel and J. L. Romero, \emph{IMA J.
Appl. Math.} \textbf{66}, 111-125, 2001). The notion of covering for an ODE
is used here to recover -symmetries of as
nonlocal symmetries. In this framework, by embedding into a
suitable system determined by the function ,
any -symmetry of can be recovered by a local symmetry of
. As a consequence, the reduction method of Muriel and
Romero follows from the standard method of reduction by differential invariants
applied to .Comment: 13 page
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