Charged particle spectra in16O induced nuclear collisions at the CERN SPS

Charged particle multiplicity distributions and pseudo-rapidity density distributions from¹⁶O induced nuclear collisions at 200 and 60A GeV are presented. The data were taken, using a minimumbias trigger, with the WA80 set-up at the CERN SPS. In this presentation we focus on how the yield of charged particles depends on the projectile energy, the mass number of the target nucleus and the energy measured in a uranium-plastic sampling calorimeter covering angles close to zero degrees. The data are compared to simulations from the event generator FRITIOF.     

Untersuchung eines Li-Cr-Ferrits mit Hilfe des Mößbauer-Effekts

The hyperfine-structure spectra of the 14.4 keVγ-ray of the nucleus⁵⁷Fe in the spinel type ferrite (Li ₀₅ ⁺ Fe _1.3 ³⁺ Cr _1.2 ³⁺ O ₄ ^2? ) have been measured through the use of the Mößbauer effect. These measurements were performed on powder samples at different temperatures between 88 °K and 633 °K. For the Fe³⁺ ions at both the tetrahedral (A) and octahedral (B) sites at 88 °K the effective magnetic fieldH at the Fe nuclei is the same and equal to 504±4 kG. The temperature dependence ofH _A however is different fromH _B . Application of an external magnetic field of 20 kG shows that the sign ofH _A is positive and the sign ofH _B is negative. As the temperature is increased a considerable broadening of the magnetic hfs-lines (and especially of the outer pair of lines) is observed. No theoretical discussion directly applicable to these measurements is as yet available. In the paramagnetic phase a well resolved doublet is obtained. It appears that this doublet must be interpreted as a quadrupole splitting.     

ESR of exchange coupled Cr3+ pairs in the dimer Di-μ-Diphenylphosphinatoacetyl-Acetonatochromium(III) (DPACr)

DPACr is a dimeric phosphinate in which the pairs of Cr³⁺ ions are superexchange coupled via -OPO- bridges. The consequences of site anisotropy and inequivalence are demonstrated in the ESR spectra and can be derived using a perturbation scheme on the appropriate Hamiltonian. First and second order fine structure, multiplet shifts, g-shifts and g-anisotropies are discussed. This dimeric system is the simplest member of a class of poly(chromium phosphinates).     

Relating Categorical Semantics for Intuitionistic Linear Logic

There are several kinds of linear typed calculus in the literature, some with their associated notion of categorical model. Our aim in this paper is to systematise the relationship between three of these linear typed calculi and their models. We point out that mere soundness and completeness of a linear typed calculus with respect to a class of categorical models are not sufficient to identify the most appropriate class uniquely. We recommend instead to use the notion of internal language when relating a typed calculus to a class of models. After clarifying the internal languages of the categories of models in the literature we relate these models via reflections and coreflections. Mathematics Subject Classifications (2000) 03G30, 03B15, 18C50, 03B20.     

Polyreaktionen in orientierten Systemen. 6. Mitt. Mizellare Assoziationen in 4-Vinylpyridiniumsalzl?sungen

Ohne Zusammenfassung     

Relaxationsphänomene in Mössbauerspektren von Magnetisierten paramagnetischen Substanzen. I [(Fe x,Al1-x )NH4(SO4)2· 12H2O]

The Fe³⁺-spin in alums of type (Fe _x , A1_1-x )NH₄(SO₄)₂ · 12 H₂O interacts (i) with the crystal lattice viaLS-coupling, and (ii) with the spins of the adjacent Fe³⁺-ions via magnetic dipole-dipole interaction. These interactions lead to a time fluctuation of the spin direction, characterized by correlation times τ _c and τ′ _c of increasing order. The times may be deduced from the⁵⁷Fe-Mössbauer spectra of the alums, τ _c from the width, and τ′ _c ≈τ _c from the position of the hyperfine structure lines. The theoretical interpretation of the Mössbauer spectra is relatively simple, when (i) the spin-lattice interaction gets frozen in, and (ii) a strong applied magnetic fieldH _a decouples the spins of the Fe³⁺-ion and the⁵⁷Fe-nucleus. The spectra were taken, therefore, at 4.2 °K and 8 kOe≦H _a ≦ 54 kOe. According to the 1/r ³-dependence of the magnetic dipole-dipole interaction τ _c should be related tox, the Fe-concentration, τ _c ·x≈τ₀=const. Forx≧0.5 our experimental results are in agreement with this rule when τ₀=(1.5±0.5) · 10^?9 s. For an alum withx=0.26, however, the observed spectra cannot be explained in terms of temporal spin fluctuations, at least not in the framework of the models which are available now. Here, presumedly, the electron spins of adjacent Fe³⁺-ions are coupled to more or less isolated and, consequently, relatively stationary spin clusters of various sizes, leading to many time independent internal magnetic fields. A treatment of this proposal is in preparation.     

Reduction of hexachloroiridate (IV) by benzene-1,2-diol in aqueous perchloric acid

The kinetics of the reaction between benzene-1,2-diol(catechol) and hexachloroiridate (IV) have been measured in aqueous acidic perchlorate solutions by the stopped-flow method. The reaction is second order overall, and first order in each reactant. A reverse reaction also occurs, but it is much slower than the forward process. Observed rate constants are dependent on acidity, but the variation can be attributed to activity rather than mechanistic effects. The reaction appears to proceed predominantly by an outer sphere electron transfer mechanism, yielding o-benzoquinone and hexachloroiridate (III), although monoaquopentachloroiridate (III) is formed also at the higher [catechol]/[IrCl₆^2?]ratios.