The mass spectra of some pyridazines,pyrido-pyridazines and related compounds

The mass spectral fragmentation behaviour of substituted sulphur containing pyridazines, pyrido (2,3-d) pyridazines and pyrido-thiazolo-pyridazines has been investigated and fragmentation patterns proposed.     

MR imaging of diplomyelia.

We present an unusual case of duplication of the fifth lumbar vertebra and sacrum in a 6-year-old boy. The spinal cord was also duplicated and tethered by bone spurs bilaterally. The imaging features and the embryological basis of diplomyelia are discussed.     

Heavy to light transitions in the heavy quark limit and the determination of |V UB |

We discuss semileptonic decays of heavy mesons into light pseudoscalar and vector mesons. Exploiting the symmetries arising in the heavy quark limit we use the known data on semileptonicD decays to predict the corresponding rates for semileptonicB decays. These consideration may serve as a model independent way to extract theub matrix element of the CKM matrix.Supported by a grant of Deutsche Forschungsgemeinschaft     

Zur Theorie der Photospaltung des Deuterons bei mittleren Energien

The differential cross-section for the photo-disintegration of the deuteron has been calculated on the basis of a phenomenological theory for energies up to 80 MeV, assuming the validity of Siegert's theorem. We have used the Hulth'en wavefunction with a 4% D-state admixture for the ground state. The final state potential has been approximated by a square-well of a given radius, the depth of which has been calculated from the phase-shifts given by Marshak. For both the ground state and the final states a hard-core of radius 0,4 · 10^?13 cm is introduced. We have considered only the electric and magnetic dipole transitions. For the isotropic term we have obtained a fairly constant value which agrees, with the experimentally observed energy-dependence but is about 20% smaller than the experimental value. The coefficient of the sin² Θ-term agrees well with the experimental results.     

Transport coefficients in the mixed state of dirty superconductors

We present a general formalism for the calculation of electronic transport properties in inhomogeneous superconducting alloys, neglecting fluctuations of the self-consistent potentials. All previously known results can easily be rederived as limiting cases and for the first time the ultrasonic absorption and thermal conductivity are determined numerically throughout the whole mixed state regime.     

Pion-pion interaction andK 2x03C0;x03C0;x03C0;-decay

The enhancement of theK _2π ⁺ -decay compared to theK _2π ⁰ -decay is discussed on the basis of the\(|\mathop {\Delta {\rm I}}\limits^ \to | = \tfrac{1}{2}\)-rule. The enhancement factor is calculated by dispersion methods which yield an expression depending only on the phase shift of the two pion system in theJ=0,I=0,2 state. This expression has been studied in the framework of simple models for the two-pion interaction in order to obtain a survey of the possibilities for the cause of the anomalous large ratioK _2π ⁺ /K _2π ⁰ . Only characteristic cases have been considered and, as far as possible, experimental results of theπ-π-interaction are taken into account.     

γ5-Invarianz und Paritätserhaltung bei starken Wechselwirkungen

It is shown in this paper, that it is possible to construct parity conserving baryonpion interactions which areγ-invariant in exactly the same manner as electromagnetic and weak interactions.     

Transport properties of quantum dots

Linear and nonlinear transport through a quantum dot that is weakly coupled to ideal quantum leads is investigated in the parameter regime where charging and geometrical quantization effects coexist. The exact eigenstates and spins of a finite number of correlated electrons confined within the dot are combined with a rate equation. The current is calculated in the regime of sequential tunneling. The analytic solution for an Anderson impurity is given. The phenomenological charging model is compared with the quantum mechanical model for interacting electrons. The current-voltage characteristics show Coulomb blockade. The excited states lead to additional fine-structure in the current voltage characteristics. Asymmetry in the coupling between the quantum dot and the leads causes asymmetry in the conductance peaks which is reversed with the bias voltage. The spin selection rules can cause a ‘spin blockade’ which decreases the current when certain excited states become involved in the transport. In two-dimensional dots, peaks in the linear conductance can be suppressed at low temperatures, when the total spins of the corresponding ground states differ by more than 1/2. In a magnetic field, an electron number parity effect due to the different spins of the many-electron ground states is predicted in addition to the vanishing of the spin blockade effect. All of the predicted features are consistent with recent experiments.