Ueber die Brechungsexponenten von Salzl?sungen

Ohne Zusammenfassung     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

High-resolution (e,e') study of isovector M1 and M2 transitions in the oxygen isotopes: (III). 18O

The excitation energy region in ¹⁸O from about E_x = 11–27 MeV has been studied with low-momentum transfer, but high-resolution inelastic electron scattering. Two sharp lines are prominent in the spectra, corresponding to the excitation of T = 2 levels at 16.399 ± 0.005 MeV and 18.871 ± 0.005 MeV of J^π = 2^? and 1⁺, respectively. In contradiction to theoretical predictions no more strong M2 transitions could be found. Broad peaks were observed at 18.5, 19.7, 20.2, 22.5 and 23.8 MeV, the latter two are due to the giant dipole resonance as known from photonuclear reactions. The spectra show in addition considerable fine structure and the application of a cross correlation function technique for its analysis resulted in the location of twelve more low multipolarity weak transitions in the excitation energy range between 16 and 19 MeV. Tentative J^π assignments are given for these levels. The spectra of isospin T = 2 states of A = 18 nuclei are discussed in view of the existing experimental and theoretical work. Finally, the pattern of the isovector M1 and M2 strength distributions of all the three oxygen isotopes ^16,17,18O is discussed.     

Structures and properties of anionic clay minerals

The Mössbauer spectra of pyroaurite-sjögrenite-type compounds (PTC) (layered anion exchangers) are discussed with reference to the crystal structure, cation order, and crystallite morphology. It is shown that cation-ordered layers are produced in the synthesis of carbonate and sulphate types of green rust. In contrast, synthetic and natural pyroaurite only occurs as disordered types. The redox chemistry of Fe(III) within the metal hydroxide layer is illustrated with examples of electrochemical oxidation and reversible reduction by boiling glycerol. The chemistry of iron in the interlayer is exemplified by the intercalation of Fe-cyanide complexes in hydrotalcite. This reaction may be used as a probe for the charge distribution in the interlayer.     

An HFB scheme in natural orbitals

We present a formulation of the Hartree-Fock-Bogoliubov (HFB) equations which solves the problem directly in the basis of natural orbitals. This provides a very efficient scheme which is particularly suited for large scale calculations on coordinate-space grids.     

The asymptotic number of labeled connected graphs with a given number of vertices and edges

Let c(n, q) be the number of connected labeled graphs with n vertices and q ≤ N = (2n ) edges. Let x = q/n and k = q ? n. We determine functions w_k ? 1. a(x) and φ(x) such that c(n, q) ? w_k(q^N)eⁿφ(x)+a(x) uniformly for all n and q ≥ n. If ? > 0 is fixed, n→ ∞ and 4q > (1 + ?)n log n, this formula simplifies to c(n, q) ? (N^q) exp(–ne^?2q/n). on the other hand, if k = o(n^1/2), this formula simplifies to c(n, n + k) ? 1/2 w_k (3/π)^1/2 (e/12k)^k/2nⁿ?^(3k?1)/2.     

Structure analyses of Ba-silicate glasses

The structures of four different Ba-silicate glasses were analysed applying a broad spectrum of diffraction and spectroscopic methods, atomic force microscopy and computer simulations. This collaborative study offers new insights into the influence of the network modifier BaO. 3 at.% carbon were incorporated into two of the glasses with the intention to obtain additional information about the effect of partial substitution of carbon for oxygen on the considered structures. A structure model for Ba-silicate glasses with compositions close to BaSi₂O₅ is discussed that differs with respect to other models proposed in previous studies. We propose that [SiO₄] tetrahedra do not exclusively form six-membered rings, but also considerable numbers of smaller rings arranged in (slightly) folded layers which alternate with barium layers and/or barium chains. Additionally, the occurrence of tetrahedral chains, possibly isolated rings and of regions in which the [SiO₄] tetrahedra form a silica-like network is assumed.     

Finite element approximation in quantum field theory

Lattices are conventionally used to regulate quantum field theory. However, lattices have a number of drawbacks, one of the most noteworthy being the awkwardness which arises in treating the first difference operator associated with the fermion kinetic energy. We propose here an alternative to the conventional lattice formulation of quantum field theories. This alternative is based on the method of finite elements, which has been a powerful tool in continuum mechanics and fluid dynamics for many years. We believe that this method may be advantageous in quantum field theory because it treats bosons and fermions on a nearly equal footing. This is possible because in the finite element method one does not introduce a finite difference approximation for derivatives. In this paper, we adapt the finite element technique to quantum field theory, and apply it to several elementary field theory models.     

Nuclear structure effects on the neutrinoless double beta decay

The nuclear matrix elements of the 0ν ββ decay of⁷⁶Ge,⁸²Se,¹⁰⁰Mo,^128,130Te,¹³⁶Xe and¹⁵⁰Nd are calculated in the proton-neutron quasiparticle RPA with theG-matrix of the Paris potential. It is shown that the matrix elements are not sensitive to details of nuclear structure, in contrast to the 2ν ββ decay. We investigate effects of ground-state correlations and those of short-range correlations on the suppression of the nuclear matrix elements. We also discuss effective values of the neutrino mass which are deduced from experimental 0ν ββ decay half-lives.