Four-nucleon shell-model calculations in a Faddeev-like approach

We use equations for Faddeev amplitudes to solve the shell-model problem for four nucleons in the model space that includes up to 14 hbar Omega harmonic-oscillator excitations above the unperturbed ground state. Two- and three-body effective interactions derived from the Reid93 and Argonne V8' nucleon-nucleon potentials are used in the calculations. Binding energies, excitations energies, point-nucleon radii and electromagnetic and strangeness charge form factors for 4He are studied. The structure of the Faddeev-like equations is discussed and a formula for matrix elements of the permutation operators in a harmonic-oscillator basis is given. The dependence on harmonic-oscillator excitations allowed in the model space and on the harmonic-oscillator frequency is investigated. It is demonstrated that the use of the three-body effective interactions improves the convergence of the results.Comment: 22 pages, 13 figures, REVTe

Experiments in vortex avalanches

Avalanche dynamics is found in many phenomena spanning from earthquakes to the evolution of species. It can be also found in vortex matter when a type II superconductor is externally driven, for example, by increasing the magnetic field. Vortex avalanches associated with thermal instabilities can be an undesirable effect for applications, but "dynamically driven" avalanches emerging from the competition between intervortex interactions and quenched disorder constitute an interesting scenario to test theoretical ideas related with non-equilibrium dynamics. However, differently from the equilibrium phases of vortex matter in type II superconductors, the study of the corresponding dynamical phases - in which avalanches can play a role - is still in its infancy. In this paper we critically review relevant experiments performed in the last decade or so, emphasizing the ability of different experimental techniques to establish the nature and statistical properties of the observed avalanche behavior.Comment: To be published in Reviews of Modern Physics April 2004. 17 page

Strangeness Photoproduction at the BGO-OD Experiment

BGO-OD is a newly commissioned experiment to investigate the internal structure of the nucleon, using an energy tagged bremsstrahlung photon beam at the ELSA electron facility. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating meson photoproduction. The extensive physics programme for open strangeness photoproduction is introduced, and preliminary analysis presented

VALIDATION OF REMOTE MEASUREMENT OF RAIN CHARACTERISTICS BY THE METHOD OF DOUBLE FREQUENCY RADAR SENSING

Subject and Purpose. The development of radar methods for measuring liquid-drop precipitation characteristics is of great importance for studying physical processes in the atmosphere and for lots of applied problems to be solved. At the same time, an expe­rimental research of these methods in situ is essential to determine their frames and scope and estimate retrieval errors of the rain parameters. The purpose of the work is to evaluate effectiveness of the previously proposed method that is based on the parametrization of the distribution function of drops by size, uses averaged touch-probing data of the three-parameter gamma distribution of the parameters versus the rain intensity, and employs the double-frequency method of precipitation remote sensing. For its validation, the rain intensity results obtained by the radar sensing are compared with the data taken from the ground raingauge. Methods and Methodology. The measurement results gained by the proposed method are compared with the measurement results obtained by the standard technique. Results. An experimental study using the previously developed algorithm and with a refined double-frequency weather radar MRL-1 has been given to the double-frequency sensing of liquid-drop precipitation. The obtained results show that the proposed data processing algorithm for double-frequency sensing of liquid-drop precipitation is good at the rain intensity retrieval and makes it possible to estimate liquid precipitation amounts over long periods of time. Conclusion. The rain intensity measured with the use of meteo radar almost completely coincides, both qualitatively and quantitatively, with the data from the ground raingauge. The algorithm proposed by the authors for processing double-frequency radar sensing data on liquid-drop precipitation retrieves the rain intensity and, also, evaluates liquid-drop precipitation amounts