Volume‐dependent potential approach for tungsten

A scheme to produce density‐of‐states‐(DOS)‐dependent potentials for d‐metals on the basis of the local density approximation calculations is suggested. As an example this scheme is applied to construct a DOS‐dependent potential for tungsten. The second moment of the tungsten DOS is calculated. We show that the obtained potentials give a good agreement of cohesive properties with the experimental data. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 343–348, 1999     

Generalized metrics and generalized twistor spaces

Mathematische Zeitschrift - The twistor construction for Riemannian manifolds is extended to the case of manifolds endowed with generalized metrics (in the sense of generalized geometry à la...     

Compact complex surfaces with geometric structures related to split quaternions

We study the problem of existence of geometric structures on compact complex surfaces that are related to split quaternions. These structures, called para-hypercomplex, para-hyperhermitian and para-hyperkähler, are analogs of the hypercomplex, hyperhermitian and hyperkähler structures in the definite case. We show that a compact 4-manifold carries a para-hyperkähler structure iff it has a metric of split signature together with two parallel, null, orthogonal, pointwise linearly independent vector fields. Every compact complex surface admitting a para-hyperhermitian structure has vanishing first Chern class and we show that, unlike the definite case, many of these surfaces carry infinite-dimensional families of such structures. We provide also compact examples of complex surfaces with para-hyperhermitian structures which are not locally conformally para-hyperkähler. Finally, we discuss the problem of non-existence of para-hyperhermitian structures on Inoue surfaces of type S⁰$S^0$ and provide a list of compact complex surfaces which could carry para-hypercomplex structures.     

Commutative medial ternary groupoids

The paper studies the class of commutative medial ternary groupoids. A construction of ternary semiterms is given and it is proved that the equational theory of medial commutative ternary groupoids is solvable, namely, an algorithm is found, which in allmedial commutative ternary groupoids verifies the validity of the identity u = v for any pair (u, v) of terms. A construction of free medial commutative ternary groupoids is given, and it is proved that anymedial commutative ternary groupoid has a convex linear representation.     

Effect of hydrogen absorption on the magnetic properties of some Zr-3d laves phase binary and pseudobinary intermetallics

Magnetization measurements have been performed on ZrCr₂, ZrMn₂, Zr(Cr_xFe_1−x)₂(x = 0.2, 0.5, 0.75) and Zr(Cr_x Co_1−x)₂ (x = 0.75, 0.4) before and after hydrogenation. In all cases both the magnetic moments and the magnetic ordering temperatures (whenever present) appeared to be significantly larger in the hydride phases. The increase of the magnetic ordering temperatures is in a qualitative agreement (but not a quantitative one) with the negative pressure effects on T_c in ZrFe₂.     

Electron spin echo modulation and relaxation in polythiophene

Electron spin echo measurements on neutral poly (thiophene) show a clear modulation of the spin-echo decay. Analysis of the modulation and its Fourier transformed (ω) power spectrum indicates that the wave function of the spin defect is extended over ～ 25 proton nuclei. The functional behavior of the longitudinal relaxation, T₁, versus temperature is very similar to that observed previously for (CH)_x, although T₁ values for poly (thiophene) are significantly longer.     

Relaxation and exchange in a nuclear cooling agent: NMR and EPR in single crystal PrNi5

NMR of Pr and ESR of Gd in single crystals of PrNi₅ are observed to exhibit a dramatic increase of the resonance linewidth with temperature in the range 1.2K ? T ? 10K. The observations are interpreted, within the framework of a crystal field spin Hamiltonian model calculation, in terms of low frequency fluctuations of the Pr ions induced by Pr-Pr exchange coupling. A fitting procedure of the theory to the experimental data enabled us to extract the various Pr-Pr and Pr-Gd exchange parameters. The former yield independent information concerning the lowest temperature that can be achieved in nuclear cooling experiments.     

Eta-Einstein condition on twistor spaces of odd-dimensional Riemannian manifolds

In this note, we find the conditions on an odd-dimensional Riemannian manifolds under which its twistor space is eta-Einstein. This can be used to yield an Einstein metric on the tangent sphere bundle of any 3-dimensional manifold of positive constant curvature.