On decay of large amplitude bubble of disoriented chiral condensate

The time evolution of initially formed large amplitude bubble of disoriented chiral condensate (DCC) is studied. It is found that the evolution of this object may have a relatively long pre-decay stage. Simple explanation of such delay of the DCC bubble decay is given. This delay is related to the existence of the approximate solutions of multi-soliton type of the corresponding radial sine-Gordon equation in (3+1) dimensions at large bubble radius.Comment: 6 pages, LaTeX, 5 PostScript figure

Universality in a Class of Q-Ball Solutions: An Analytic Approach

The properties of Q-balls in the general case of a sixth order potential have been studied using analytic methods. In particular, for a given potential, the initial field value that leads to the soliton solution has been derived and the corresponding energy and charge have been explicitly evaluated. The proposed scheme is found to work reasonably well for all allowed values of the model parameters.Comment: 9 Pages, 6 Figure

Metal-insulator transition induced by 16O -18O oxygen isotope exchange in colossal negative magnetoresistance manganites

The effect of 16O-18O isotope exchange on the electric resistivity was studied for (La(1-y)Pr(y))0.7Ca0.3MnO3 ceramic samples. Depending on y, this mixed perovskite exhibited different types of low-temperature behavior ranging from ferromagnetic metal (FM) to charge ordered (CO) antiferromagnetic insulator. It was found that at y=0.75, the substitution of 16O by 18O results in the reversible transition from a FM to a CO insulator at zero magnetic field. The applied magnetic field (H >= 2 T) transformed the sample with 18O again to the metallic state and caused the increase in the FM transition temperature Tc of the 16O sample. As a result, the isotope shift of Tc at H = 2 T was as high as 63 K. Such unique sensitivity of the system to oxygen isotope exchange, giving rise even to the metal-insulator transition, is discussed in terms of the isotope dependence of the effective electron bandwidth which shifts the balance between the CO and FM phases.Comment: 5 pages (RevTeX), 2 eps figures included, to appear in J. Appl. Phys. 83, (1998

Kink-antikink interactions in the double sine-Gordon equation and the problem of resonance frequencies

We studied the kink-antikink collision process for the "double sine-Gordon" (DSG) equation in 1+1 dimensions at different values of the potential parameter $R>0$. For small values of $R$ we discuss the problem of resonance frequencies. We give qualitative explanation of the frequency shift in comparison with the frequency of the discrete level in the potential well of isolated kink. We show that in this region of the parameter $R$ the effective long-range interaction between kink and antikink takes place.Comment: 9 pages, LaTeX, 4 figures (eps

Ferromagnetism in the Mott insulator Ba2NaOsO6

Results are presented of single crystal structural, thermodynamic, and reflectivity measurements of the double-perovskite Ba2NaOsO6. These characterize the material as a 5d^1 ferromagnetic Mott insulator with an ordered moment of ~0.2 Bohr magnetons per formula unit and TC = 6.8(3) K. The magnetic entropy associated with this phase transition is close to Rln2, indicating that the quartet groundstate anticipated from consideration of the crystal structure is split, consistent with a scenario in which the ferromagnetism is associated with orbital ordering.Comment: 5 pages, 5 figures, added reference

The bubbles of matter from multiskyrmions

The multiskyrmions with large baryon number B given by rational map (RM) ansaetze can be described reasonably well within the domain wall approximation, or as spherical bubbles with energy and baryon number density concentrated at their boundary. A special class of profile functions is considered approximating the true profile and domain wall behaviour at the same time. An upper bound is obtained for the masses of RM multiskyrmions which is close to the calculated masses, especially at large B. The gap between rigorous upper and lower bounds for large B multiskyrmions is less than 4%. The basic properties of such bubbles of matter are investigated, some of them being of universal character, i.e. they do not depend on baryon number of configuration and on the number of flavors. As a result, the lagrangian of the Skyrme type models provides field theoretical realization of the bag model of special kind.Comment: 7 pages, no figure

The dynamical background of polar mesosphere winter echoes from simultaneous EISCAT and ESRAD observations

On 30 October 2004 during a strong solar proton event, layers of enhanced backscatter from altitudes between 55 and 75km have been observed by both ESRAD (52MHz) and the EISCAT VHF (224MHz) radars. These echoes have earlier been termed Polar Mesosphere Winter Echoes, PMWE. After considering the morphology of the layers and their relation to observed atmospheric waves, we conclude that the radars have likely seen the same phenomenon even though the radars' scattering volumes are located about 220km apart and that the most long-lasting layer is likely associated with wind-shear in an inertio-gravity wave. An ion-chemistry model is used to determine parameters necessary to relate wind-shear induced turbulent energy dissipation rates to radar backscatter. The model is verified by comparison with electron density profiles measured by the EISCAT VHF radar. Observed radar signal strengths are found to be 2-3 orders of magnitude stronger than the maximum which can be expected from neutral turbulence alone, assuming that previously published results relating radar signal scatter to turbulence parameters, and turbulence parameters to wind shear, are correct. The possibility remains that some additional or alternative mechanism may be involved in producing PMWE, such as layers of charged dust/smoke particles or large cluster ions

Crystal Structure, Electrical Conductivity and Hydration of the Novel Oxygen-Deficient Perovskite La2 ScZnO5.5, Doped with MgO and CaO

This paper demonstrates the possibility of creating oxygen deficiency in perovskites A+3 B+3 O3 by introducing two types of cations with different charges into the B-sublattice. For this, it is proposed to introduce a two-charged cation, for example, Zn2+, as an alternative to alkaline earth metals. Previ-ously, this possibility was demonstrated for aluminate LaAlO3 and indate LaInO3 . In this article, we have focused on the modification of the scandium-containing perovskite LaScO3 . The novel oxygen-deficient perovskite La2 ScZnO5.5 and doped phases La1.9 Ca0.1 ScZnO5.45, La2 Sc0.9 Ca0.1 ZnO5.45, and La2 Sc0.9 Mg0.1 ZnO5.45 were obtained via a solid-state reaction process. Their phase composition and hydration were investigated by XRD and TGA + MS techniques. The conductivities of these materials were measured by the electrochemical impedance technique under atmospheres of various water vapor partial pressures. All phases crystallized in orthorhombic symmetry with the Pnma space group. The phases were capable of reversible water uptake; the proton concentration increased in the order of La2 ScZnO5.5 < La2 Sc0.9 Mg0.1 ZnO5.45 < La2 Sc0.9 Ca0.1 ZnO5.45 ≈ La1.9 Ca0.1 ScZnO5.45 and reached ~90% hydration limit for Ca2+-doped phases. The total conductivities increased withthe increase inthe free lattice volume inthe sequence of σLa2 ScZnO5.5 < σLa2 Sc0.9 Mg0.1 ZnO5.45 < σLa1.9 Ca0.1 ScZnO5.45 < σLa2 Sc0.9 Ca0.1 ZnO5.45, the activation energy decreased in the same sequence. The sample La2 Sc0.9 Ca0.1 ZnO5.45 showed the highest conductivity of about 10−3 S·cm−1 at 650◦ C (dry air pH2 O = 3.5·10−5 atm). Water incorporation was accompanied by an increase in conductivity in wet air (pH2 O = 2·10−2 atm) due to the appearance of proton conductivity. The sample La2 Sc0.9 Ca0.1 ZnO5.45 showed a conductivity of about 10−5 S·cm−1 at 350◦ C (pH2 O = 2·10−2 atm). A comparison of conductivities of obtained phase La2 ScZnO5.5 with the conductivities of La2 AlZnO5.5 and La2 InZnO5.5 was made; the nature of the B-cation did not significantly affect the total conductivity. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Acknowledgments: The study was financially supported by the Ministry of Education and Science of the Russian Federation (state assignment no. AAAA-A20-120061990010-7)