Kurt Bräuer

Hyperon-nucleon interaction in the quark cluster model☆

Abstract The lambda-nucleon and sigma-nucleon interaction is described in the nonrelativistic quark cluster model. The SU(3) flavor symmetry breaking due to the different quark masses is taken into account, i.e. different wavefunctions for the light (up, down) and heavy (strange) quarks are used in flavor and orbital space. The six-quark wavefunction is fully antisymmetrized. The model hamiltonian contains gluon exchange, pseudoscalar meson exchange and a phenomenological σ-meson exchange. The six-quark scattering problem is solved within the resonating group method. The experimental lambda-nucleon and sigma-nucleon cross sections are well reproduced.

Binding energy of the dihyperon in the quark cluster model

Abstract The dihyperon is described in the non-relativistic quark cluster model. The SU(3) flavor symmetry breaking due to the different quark masses is taken into account not only in the hamiltonian, but also in the quark wave functions. The interaction contains the one-gluon-exchange potential, pseudoscalar-meson exchange between quarks plus an additional phenomenological σ-meson exchange. The mass of the dihyperon is predicted to be (2211 ± 5) MeV, i.e. a binding energy of the dihyperon of (−20 ± 5) MeV below the ΛΛ threshold is found.

On one pion exchange potential with quark exchange in the resonating group method

The effect of quark exchange between different nucleons on the one pion exchange potential is studied in the framework of the resonating group method. The calculated phase shifts including the one pion exchange potential with quark exchange in addition to the one gluon plusσ meson exchange are shown to be consistent with experiments. Especially thep-wave phase shifts are improved by taking into account the quark exchange on the one pion exchange potential.

Influence of six-quark bags on the NN interaction in a resonating group scattering calculation☆

Abstract The influence of six-quark bags on the nucleon-nucleon (NN) interaction is studied in a dynamical calculation of the NN scattering process. The NN interaction is described by the exchange of gluons and pions between quarks and a phenomenological σ-meson exchange between nucleons. The quark wave functions are harmonic oscillators and the relative wave function between the two nucleons is determined by the resonating group method. At short distances the NN system is allowed to fuse to a six-quark bag where all six quarks are in a ground state or where two quarks are in excited Op states. The sizes of these six-quark bags are dynamical parameters in the resonating group calculation allowing for spatial polarisation effects during the interaction. The S-wave NN scattering data can be reproduced by adjusting the σ-coupling strength. The main result is that the six-quark bags with an increased radius have a large influence on the NN scattering process.

Nucleon-nucleon interaction in a quark model with pions

Abstract We investigate a constituent quark model, where pions are coupled directly to quarks. Special attention is given to non-central forces due to pion and gluon exchange between the quarks. Therefore we calculate S-, P- and D-wave scattering of nucleons. The new features of the pion exchange in this model agree well with scattering data. The fit to the intermediate-range attraction between nucleons supports arguments for deformed six-quark bags. The spin-orbit force of the gluon exchange is too weak.

Wavelet analysis of skin perfusion in healthy volunteers.

Objective: Rhythmical changes in microvascular perfusion of the skin depend on various influences, which appear continuously but not in a predictable manner. For identifying and quantifying different physiological influences the authors used wavelet transformation, analyzing continuously and simultaneously measured data.

Nonlinear analysis of blood flux in human vessels

Laser Doppler fluxmetry (LDF) is frequently used in research on microcirculation of blood. Usually LDF time series are analysed by conventional linear methods, mainly Fourier analysis. These methods may not be optimal for the investigation of nonlinear effects of vasomotion, heartbeat or vessels. Nonlinear methods are based on a reconstruction of the system trajectory in an embedding space describing not only the measured time series but the behaviour of the whole system. The fill factor is a tool for displaying the main properties of this attractor in two dimensions and for determining diverse parameters for further analysis. A quantitative characterization of the system is possible by the distribution of correlation dimensions in the embedding space. The singular value decomposition (SVD) can be used to display and characterize individual degrees of freedom. These methods were applied to LDF time series from nine healthy controls and nine patients with Raynauds phenomenon due to connective tissue disease. The fill factor and the SVD indicate qualitatively that in the controls vasomotion and heartbeat are the main influences on blood flow and act fairly independently of each other. In the patients there was a mixture of strong but irregular degrees of freedom. The mean and the maximal local correlation dimensions were significantly higher in the patient group. Nonlinear analysis of LDF time series provides additional information which cannot be detected using conventional approaches.

A small-size neural network for computing with strange attractors

A small-size model for a chaotic neural network is proposed using strange attractors for computation. This network has a chaotic ground state and is capable of responding to external stimuli by constraining the network dynamics to specific parts of the ground state attractor. For parameter optimization, bifurcation diagrams are evaluated.

Hyperon-nucleon interaction and the H-dibaryon in the quark cluster model

Abstract The non-relativistic cluster model is used to describe the hyperon-nucleon (ΛN, ΣN) and hyperon-hyperon (H-dibaryon) interaction. Including central and tensor parts of the one-gluon exchange, pseudoscalar-meson exchange plus an additional phenomenological σ-meson exchange, a very good fit of the experimental hyperon-nucleon cross-sections is achieved. Applying this model to the H-dibaryon, a bound state with a binding energy of (−15 ± 5) MeV below the ΛΛ threshold is found, i.e. the mass of the H-dibaryon is predicted to be around 2216 MeV.

Wavelet analysis of cutaneous blood flow in melanocytic skin lesions.

Laser Doppler flowmetry (LDF) is frequently used to study the microcirculation. Usually LDF time series are analyzed by conventional linear methods, mainly Fourier analysis. The aim of this study was to observe dynamic blood perfusion of the skin in malignant and benign melanocytic skin lesions. Wavelet transformation was performed on each LDF time series in order to calculate a vasomotion field. First, the differences in vasomotion between healthy and pigmented skin were evaluated visually on six different time scales of the vasomotion field. In order to quantify the findings, vasomotion scale variance (VSV) was calculated for each scale plane of the vasomotion field. These VSV were compared using contrast ΔVSV to determine the difference between healthy skin and a pigmented skin lesion in the same patient. After the measurements, the skin lesions were excised and examined histologically. We found that wavelet analysis of LDF time series is a specific, sensitive method for the in vivo identification of malignant melanoma. It is a non-invasive procedure and takes minimal time to be carried out.