μSR studies of borocarbides

The muon‐spin‐relaxation technique has been utilized to characterize the magnetic properties of the borocarbide compounds RNi₂B₂C ( R=\,Tm, Er, Ho and Dy), which exhibit coexistence of superconductivity and magnetism. Some general features of their magnetic ground‐state and unusual results obtained in the Ho, Tm and Dy systems are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selective synthesis of some 5-hydrazono-5,6,7,8-tetrahydro-2H-1-benzopyran-2-ones

A simple, highly selective transformation of 5,6,7,8-tetrahydro-2H-1-benzopyran-2,5-diones 1–3 and 14 with some phenylhydrazines and heterocyclic hydrazines to 5-hydrazono-2H-1-benzopyran-2-ones 4–12 and 15–16 is described. Under more severe conditions the hydrazonoquinoline derivative 17 was obtained from the benzopyran derivative 3 and Phenylhydrazine.     

Pulsed NMRON measurements on insulators

Selective single and double quantum excitation pulsed NMRON has been utilized to obtain rotation patterns, free induction decays, and spin echoes in antiferromagnetic⁵⁴Mn−MnCl₂·4H₂O and the quasi-2 dimensional ferromagnet⁵⁴Mn−Mn(COOCH₃)₂·4H₂O. The pulsed technique is well suited to observing fast spin-lattice relaxation and T₁ values down to 100 ms have been measured in these systems. These short times may make magnetic insulators viable hosts for on-line experiments. The dependence on field and temperature of the⁵⁴Mn spin-lattice relaxation time T₁ has been investigated and a T₁ minimum at high fields observed in both systems. A spin-spin relaxation time T₂≈50 μs is measured in⁵⁴Mn−MnCl₂·4H₂O. The observation of NMRON in the paramagnetic phase of MnCl₂·4H₂O allows the resonant frequencies in the antiferromagnetic and paramagnetic phases to be compared, yielding a value for the zero point spin deviation in the former phase.     

Experimental and modeling study of shock‐tube oxidation of acetylene

Nine mixtures of acetylene and oxygen diluted in argon were studied behind reflected shock waves at temperatures of 1150–2132 K and pressures of 0.9–1.9 atm. Initial compositions were varied from very fuel‐lean to moderately fuel‐rich, covering equivalence ratios of 0.0625–1.66. Two more mixtures with added ethylene were used to boost the sensitivity to reactions of vinyl oxidation. The progress of reaction was monitored by laser absorption of CO molecules. The collected experimental data were subjected to extensive detailed chemical kinetics analysis. The initial kinetic model was assembled based on recent literature data and then optimized using the solution mapping technique. The analysis was extended to include recent experimental observations of Hidaka and co‐workers (Combust Flame 1996, 107, 401). The derived model reproduces closely both sets of experimental data, the result obtained by modifying nine rate coefficients and three enthalpies of formation of intermediate species. The identified parameter tradeoffs and justification for the changes are discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 391–414, 2003     

Search for magnetic fields due to anyons in high-T c superconductors

We have searched for anomalous internal magnetic fields in highT _c materials which are predicted to occur in anyon and flux phase models of superconductivity. The magnitude, anisotropy and temperature dependence of the observed fields inc-axis oriented samples of sintered YBa₂CuO₃O₇ and of thick-film Bi₂Sr₂CaCu₂O₈ are consistent with a conventional nuclear dipolar origin. An upper limit of ≲0.08 mT is set for any anomalous magnetic fields along thec-axis atμ ⁺ sites in bulk CuO₂ superconductors.     

Phase analysis of high-temperature superconductors by selective dissolution combined with ICP-AES

Summary An apparatus for the selective dissolution as a chemical method of phase analysis and its operating conditions are described. Using ICP-AES as determination method an example for the YBCO system is found in the phase YBa_2–0.04Cu_3+0.03O_x and a BSCCO system is found in three phases of 35.6% Bi₂(Sr,Ca)_4–0.08Cu_3–0.05O_x, 30.1% Bi₂(Sr,Ca)_3–0.09Cu_2–0.08O_x and 34.3% Bi₂(Sr,Ca)_2–0.07Cu_1–0.05O_x.     

Mass spectrometry of π-complexes of transition metals 38—keto-enol tautomerization of molecular ions of acetyl- and propionyl-ferrocenes in the gas phase

Fragmentation of the acetyl- and propionyl-ferrocenes under electron impact together with the rupture of C? CO bonds, characteristic of ketones, also includes elimination of water and migration of the OH group to the central metal atom, which is due to keto-enol tautomerization of the acyl group in molecular or fragment ions.     

A review of two decades of the analysis of hyperfine parameter distributions in Mössbauer spectroscopy: Difficulties,progress and prospects

We present a review of the most used methods used to obtain hyperfine parameter distributions and discuss the mathematical problems. The Czjzek model and extensions for an EFG distribution in random systems is critically reviewed