57Fe Mössbauer spectra and magnetic data from the kagomé antiferromagnet H3O-jarosite

⁵⁷Fe Mössbauer spectra are presented from (H₃O)Fe₃(SO₄)₂(OH)₆ (or H₃O-jarosite), which is a model kagomé antiferromagnet which features geometrical frustration and spin-glass-like behaviour. Dynamic scaling of the freezing temperature as a function of frequency is observed over a large frequency range, which indicates the presence of a spin-glass transition. A fast relaxation model between “up” and “down” states, separated by an energy gap, is presented to account for the shape of the Mössbauer spectra below the freezing temperature. From a calculation of the Electric Field Gradient tensor, it is suggested that H₃O-jarosite is an XY-Heisenberg antiferromagnet, where the Fe³⁺ moments lie in the kagomé planes.     

Debye temperature and magnetic ordering in K x Ba1−x Fe2S3

⁵⁷Fe Mössbauer measurements are reported for the series K _x Ba_1?x Fe₂S₃, x ≤ 0.3, at temperatures between 4.2 K ≤ T ≤ 294 K. A decrease of the Debye temperature from 435 to 405 K with x, indicates a weakening of the stiffness of the Fe sublattice. The ordering temperatures, taken from the appearance of magnetic hyperfine splitting in the spectra, are approximately 40 K lower for x ≥ 0.1. The values of the centre shift and the small temperature dependence of the quadrupole splitting strongly supports that similar to the border compound BaFe₂S₃ also the K containing samples should be characterised as mixed valence compounds.     

First observation of 55, 56Zn

In an experiment at the SISSI/LISE3 facility of GANIL, the most proton-rich zinc isotopes ^55,56Zn have been observed for the first time. The experiment was performed using a high-intensity ⁵⁸Ni beam at 74.5 MeV/nucleon impinging on a nickel target. The identification of ^55,56Zn opens the way to ⁵⁴Zn, a good candidate for two-proton radioactivity according to theoretical predictions. Received: 31 October 2000 / Accepted: 9 November 2000     

Totally geodesic Kähler immersions in view of curves of order two

In this paper, we characterize of totally geodesic Kähler immersions by extrinsic shapes of some curves having points of order 2.     

Measurement of Spectral Emissivity and Thermal Conductivity of Zirconia by Thermal Radiation Calorimetry

The hemispherical total emissivity of partially stabilized zirconia has been obtained by a spectral analysis of the normal emission spectra between 400–850 K. Thermal conductivity was evaluated with this emissivity and temperature gradient in the sample. Effects of the scattering of the radiation in a ceramic sample are also investigated. In addition, specific heat capacity was measured by thermal radiation calorimetry. Current results are compared with those reported for tetragonal zirconia with the same yttria content and for monoclinic phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

A global characterization of the Fu?ík spectrum for a system of ordinary differential equations

The Fu?ík spectrum for systems of second order ordinary differential equations with Dirichlet or Neumann boundary values is considered: it is proved that the Fu?ík spectrum consists of global C¹ surfaces, and that through each eigenvalue of the linear system pass exactly two of these surfaces. Further qualitative, asymptotic and symmetry properties of these spectral surfaces are given. Finally, related problems with nonlinearities which cross asymptotically some eigenvalues, as well as linear-superlinear systems are studied.     

New Estimates for the Bottom of the Spectrum of Schrödinger Operators

We obtain a bound for the bottom of the negative spectrum of Schrödinger operators on weighted Riemannian manifolds in terms of F-Sobolev inequalities. Also, we show how an estimate for the first negative eigenvalue implies the F-Sobolev inequality.     

The geometry of L-manifolds

A class of almost contact metric structures generalizing those of quasi-Sasakian and trans-Sasakian structures is introduced and studied. Its subclass consisting of normal structures locally conformal to quasi-Sasakian structures is investigated in detail.     

Calculating the coefficients of a discrete elliptic equation from spectral data

A numerical analytical algorithm is developed for calculating the coefficients of a discrete two-dimensional elliptic equation from given eigenvalues and certain symmetry conditions imposed on the basis eigenfunctions.