Mössbauer analysis of the state of iridium and platinum in supported catalysts

The state of iridium and platinum in supported noble metal catalysts was investigated by Mössbauer spectroscopy. With iridium, conventional absorption experiments with the 73 KeV γ-rays of¹⁹³Ir were preformed; platinum was studied in source experiments using the 77 KeV resonance in¹⁹⁷Au. First results for pure Pt catalysts on silica supports and for a used automotive catalytic converter are presented. In Pt-rich bimetallic Pt?Ir catalysts on amorphous silica, both Pt and Ir were studied after different treatments.     

Hartree–Fock versus quantum Monte Carlo study of persistent current in a one-dimensional ring with single scatterer

We calculate the persistent current of interacting spinless electrons in a one-dimensional ring containing a single δ barrier. We use the self-consistent Hartree–Fock method and the quantum Monte Carlo method which gives fully correlated solutions. Our Hartree–Fock method treats the non-local Fock term in a local approximation and also exactly (if the ring is not too large). Treating the Fock term exactly we attempt to support our previous Hartree–Fock result obtained in the local approximation, in particular the persistent current behaving like I∝L^-1-α, where L is the ring length and α>0 is the power depending only on the electron–electron interaction. Finally, we use the Hartree–Fock solutions as an input for our quantum Monte Carlo calculation. The Monte Carlo results exhibit only small quantitative differences from the Hartree–Fock results.     

Precise pion electroproduction in thep(e,e′ π+)n reaction at W=1125 MeV

The reactione+p →> e+π ⁺+n at c.m. energyW=1125MeV and momentum transfer Q²=0.117GeV²/c₂ has been measured. The transverse and longitudinal structure functions have been separated by varying the polarization of the virtual photon (Rosenbluth plot) with a 3 to 4% error. In addition the longitudinal-transverse interference term has been determined measuring the right-left asymmetry with an accuracy of 3%. The experimental data are compared to model calculations, and the sensitivity of the results to the axial and pion formfactors is discussed.     

Baryon chiral perturbation theory A.D. 1994

In these lectures, the status of baryon chiral perturbation theory is reviewed. Particular emphasis is put on the two-flavor sector and the physics related to electromagnetic probes. I discuss in some detail the structure of the effective Lagrangian at next-to-leading order, the meaning of low-energy theorems in Compton scattering and pion photoproduction, and confront the chiral predictions with the existing data. Some remaining problems and challenges are outlined.Lectures given at the Indian-Summer School on Electron Scattering from Nucleons and Nuclei, Prague, Czech Republic, September 1994.First, I would like to thank the organizers for their kind invitation and hospitality. I am also grateful to Véronique Bernard and Norbert Kaiser for fruitful collaborations and allowing me to present some material before publication. I would like to thank Gerhard Ecker and Jürg Gasser for sharing with me their insight into the chiral dynamics.     

Mössbauer studies of Inca ceramics

To obtain information on the firing of inca ceramics, 7 samples from different locations were studied by Mössbauer spectroscopy including a detailed laboratory refiring procedure. The glaze typical for the surface of this ware was studied by Mössbauer scattering.     

C60 under pressure-bulk modulus and equation of state

C₆₀ has been investigated under pressure up to 13 GPa using angular dispersive X-ray scattering and a diamond anvil cell. The resolution of the experimental setup allows to examine the volume decrease dV/dp under pressure even for pressures of a tenth of a GPa. The obtained data of numerous experimental runs result in a bulk modulus of 13.4 GPa, which is much smaller than the value reported by Duclos et al. [1]. At 170 K and 70 K a bulk modulus of 14.2 GPa and 14.7 GPa was obtained, respectively. The pressure induced fcc-sc transition at 300 K was clearly visible at approx. 0.3 GPa with a jump in the lattice parameter of 0.05 Å. With increasing pressure we found an extreme change in dV/dp, which disables the usage of common equations of state (EOS), like the Murnaghan [2] or Birch [3] equation. Considering the small compressibility of the fullerence molecules we suggest a modified EOS to describe the experimental data.     

Vertex 2-isomorphism

Whitney's theorem on 2-isomorphism characterizes the set of graphs having the same cycles as a given graph, where a cycle is regarded as a set of edges. In this paper, vertex 2-isomorphism is defined and used to prove a vertex analogue of Whitney's theorem. The main theorem states that two connected graphs have the same set of cycles, where a cycle is now regarded as a set of vertices, if and only if one can be obtained from the other by a sequence of simple operations. © 1992 John Wiley & Sons, Inc.     

Policies,requirements and surveys concerning frequency for participation in proficiency testing schemes

This paper focuses on policies and requirements concerning the frequency for participation in proficiency testing (PT) and provides an overview of the frequency for which PT activities are offered in 25 testing fields. Recent international surveys are summarised.