Near-threshold η-meson production in the dd↦He η reaction

The dd↦⁴Heη reaction has been investigated near threshold using the ANKE facility at COSY-Jülich. Both total and differential cross-sections have been measured at two excess energies, Q = 2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q = - 2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition into partial amplitudes and their consequences for the determination of the s-wave ηα scattering length are discussed.     

Relaxation,postponement, and features of the attractor in a driven varactor oscillator

The driven varactor oscillator is investigated by numerical integration of its ODEs using the standard model of circuit theory. Attention is given to some properties of the basic relaxation mechanism. For time dependent amplitudes of the sinusoidal driving voltage the post-ponement of the bifurcations is characterized by transient Lyapunov numbers. The postponement of the first bifurcation shows the same dependence on the sweep velocity as in the case of the nonautonomous quadratic map. The shapes of the attractors are displayed in extended phase space. Generalized Renyi-dimensionsD ₀ andD ₁ have been determined in the chaotic region. A corresponding twodimensional Pioncaré map indicates selfsimilarity.     

Low-energy πN partial wave analysis

An energy-independent partial-wave analysis has been performed on pion-nucleon elastic and charge-exchange differential cross sections and elastic polarizations, for lab. momenta below 500 MeV/c. The amplitudes were constrained by a simultaneous fixed momentum transfer analysis, which leads to a unique and smooth solution. The masses and widths of Δ⁺⁺ and Δ⁰ have been redetermined from total cross sections as m_Δ⁺⁺ = 1230.9 ± 0.3 MeV, m_Δ⁰ = 1233.6 ± 0.5 MeV, Γ_Δ⁺⁺ = 111 ± 1 MeV and Γ_Δ⁰ = 113 ± 1.5 MeV. For the pion-nucleon coupling constant the value |² = 0.079 ± 0.001 was obtained.     

Mass spectra of bithiophthalide and related compounds

High resolution mass spectra of biphlhalidu ( 1 ), bithiophthalide ( 2 ), and thioindigo ( 3 ) were investigated and the major fragmentation patterns were elucidated. The simultaneous loss of two sulfur atoms from the molecular ion of 2 was particularly noteworthy.