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Search Results: 1 - 10 of 401124 matches for " M. Muether "
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Vanishing Gamow-Teller Transition Rate for A=14 and the Nucleon-Nucleon Interaction in the Medium
M. S. Fayache,L. Zamick,H. Muether
Physics , 1999, DOI: 10.1103/PhysRevC.60.067305
Abstract: The problem of the near vanishing of the Gamow-Teller transition ($GT$) in the A=14 system between the lowest $J=0^+~ T=1$ and $J=1^+~ T=0$ states is revisited. The model space is extended from the valence space $(p^{-2})$ to the valence space plus all 2$\hbar \omega$ excitations. The question is addressed as to what features of the effective nucleon-nucleon interaction in the medium are required to obtain the vanishing $GT$ strength in this extended space. It turns out that a combination of a realistic strength of the tensor force combined with a spin-orbit interaction which is enhanced as compared to the free interaction yields a vanishing $GT$ strength. Such an interaction can be derived from a microscopic meson exchange potential if the enhancement of the small component of the Dirac spinors for the nucleons is taken into account.
Comparison of the Effective Interaction to Various Orders in Different Mass Regions
M. Hjorth-Jensen,H. Muether,A. Polls,E. Osnes
Physics , 1995, DOI: 10.1088/0954-3899/22/3/006
Abstract: The convergence of the perturbation expansion for the effective interaction to be used in shell-model calculations is investigated as function of the mass number $A$, from $A=4$ to $A=208$. As the mass number increases, there are more intermediate states to sum over in each higher-order diagram which contributes to the effective interaction. Together with the fact that the energy denominators in each diagram are smaller for larger mass numbers, these two effects could largely enhance higher-order contributions to the effective interaction, thereby deteriorating the order-by-order convergence of the effective interaction. This effect is counterbalanced by the short range of the nucleon-nucleon interaction, which implies that its matrix elements are weaker for valence single-particle states in ``large'' nuclei with large mass number as compared to those in light nuclei. These effects are examined by comparing various mean values of the matrix elements. It turns out that the contributions from higher-order terms remain fairly stable as the mass number increases from $A=4$ to $A=208$. The implications for nuclear structure calculations are discussed.
Self-energy of Lambda in finite nuclei
M Hjorth-Jensen,A Polls,A Ramos,H Muether
Physics , 1996, DOI: 10.1016/0375-9474(96)00190-X
Abstract: The self--energy of the strange baryon $\Lambda$ in $^{17}$O is calculated using a microscopic many--body approach which accounts for correlations beyond the mean--field or Hartree--Fock approximation. The non-locality and energy-dependence of the $\Lambda$ self--energy is discussed and the effects on the bound and scattering states are investigated. For the nucleon--hyperon interaction, we use the potential models of the J\"{u}lich and Nijmegen groups.
Interferometer-Type Structures for Guided Atoms
R. Dumke,T. Muether,M. Volk,W. Ertmer,G. Birkl
Physics , 2002, DOI: 10.1103/PhysRevLett.89.220402
Abstract: We experimentally demonstrate interferometer-type guiding structures for neutral atoms based on dipole potentials created by micro-fabricated optical systems. As a central element we use an array of atom waveguides being formed by focusing a red-detuned laser beam with an array of cylindrical microlenses. Combining two of these arrays, we realize X-shaped beam splitters and more complex systems like the geometries for Mach-Zehnder and Michelson-type interferometers for atoms.
High-momentum proton removal from 16O and the (e,e'p) cross section
A. Polls,M. Radici,S. Boffi,W. H. Dickhoff,H. Muether
Physics , 1996, DOI: 10.1103/PhysRevC.55.810
Abstract: The cross section for the removal of high-momentum protons from 16O is calculated for high missing energies. The admixture of high-momentum nucleons in the 16O ground state is obtained by calculating the single-hole spectral function directly in the finite nucleus with the inclusion of short-range and tensor correlations induced by a realistic meson-exchange interaction. The presence of high-momentum nucleons in the transition to final states in 15N at 60-100 MeV missing energy is converted to the coincidence cross section for the (e,e'p) reaction by including the coupling to the electromagnetic probe and the final state interactions of the outgoing proton in the same way as in the standard analysis of the experimental data. Detectable cross sections for the removal of a single proton at these high missing energies are obtained which are considerably larger at higher missing momentum than the corresponding cross sections for the p-wave quasihole transitions. Cross sections for these quasihole transitions are compared with the most recent experimental data available.
Modern nucleon-nucleon potentials and symmetry energy in infinite matter
L. Engvik,M. Hjorth-Jensen,R. Machleidt,H. Muether,A. Polls
Physics , 1997, DOI: 10.1016/S0375-9474(97)00496-X
Abstract: We study the symmetry energy in infinite nuclear matter employing a non-relativistic Brueckner-Hartree-Fock approach and using various new nucleon-nucleon (NN) potentials, which fit np and pp scattering data very accurately. The potential models we employ are the recent versions of the Nijmegen group, Nijm-I, Nijm-II and Reid93, the Argonne $V_{18}$ potential and the CD-Bonn potential. All these potentials yield a symmetry energy which increases with density, resolving a discrepancy that existed for older NN potentials. The origin of remaining differences is discussed.
Microoptical Realization of Arrays of Selectively Addressable Dipole Traps: A Scalable Configuration for Quantum Computation with Atomic Qubits
R. Dumke,M. Volk,T. Muether,F. B. J. Buchkremer,G. Birkl,W. Ertmer
Physics , 2001, DOI: 10.1103/PhysRevLett.89.097903
Abstract: We experimentally demonstrate novel structures for the realisation of registers of atomic qubits: We trap neutral atoms in one and two-dimensional arrays of far-detuned dipole traps obtained by focusing a red-detuned laser beam with a microfabricated array of microlenses. We are able to selectively address individual trap sites due to their large lateral separation of 125 mu m. We initialize and read out different internal states for the individual sites. We also create two interleaved sets of trap arrays with adjustable separation, as required for many proposed implementations of quantum gate operations.
Quantum Information Processing with Microfabricated Optical Elements
F. B. J. Buchkremer,R. Dumke,M. Volk,T. Muether,G. Birkl,W. Ertmer
Physics , 2001,
Abstract: We discuss a new direction in the field of quantum information processing with neutral atoms. It is based on the use of microfabricated optical elements. With these elements versatile and integrated atom optical devices can be created in a compact fashion. This approach opens the possibility to scale, parallelize, and miniaturize atom optics for new investigations in fundamental research and applications towards quantum computing with neutral atoms. The exploitation of the unique features of the quantum mechanical behavior of matter waves and the capabilities of powerful state-of-the-art micro- and nanofabrication techniques lend this approach a special attraction.
Dependence of the Shell-Model Single-Particle Energies on Different Components of the Nucleon-Nucleon Interaction
Y. Y Sharon,M. S. Fayache,Y. Durga Devi,L. Zamick,H. Muether
Physics , 1999,
Abstract: The spin-orbit splittings in the spectra of nuclei with mass numbers 5, 15 and 17 are studied within the framework of shell-model configuration mixing calculations including 2$\hbar \omega$ excitations. The contributions of the two-body spin-orbit and tensor components of the nucleon-nucleon interaction are studied in various model spaces. It is found that the effects of the two-body spin-orbit interaction are dominant and quite sensitive to the size of the model-space considered. The effects of the tensor interaction are weaker. The correlations effects which are included in the larger (0+2) $\hbar \omega$ shell-model space reduce the spin-orbit splitting in the case of A=5 by 20%, and enhance it for A=15 by about the same 20%. However, it is found that the correlations have a very small effect on the $d_{3/2} - d_{5/2}$ splitting in A=17.
Overexpression of HTRA1 Leads to Ultrastructural Changes in the Elastic Layer of Bruch's Membrane via Cleavage of Extracellular Matrix Components
Sarah Vierkotten, Philipp S. Muether, Sascha Fauser
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0022959
Abstract: Variants in the chromosomal region 10q26 are strongly associated with an increased risk for age-related macular degeneration (AMD). Two potential AMD genes are located in this region: ARMS2 and HTRA1 (high-temperature requirement A1). Previous studies have suggested that polymorphisms in the promotor region of HTRA1 result in overexpression of HTRA1 protein. This study investigated the role of HTRA1 overexpression in the pathogenesis of AMD. Transgenic Htra1 mice overexpressing the murine protein in the retinal pigment epithelium (RPE) layer of the retina were generated and characterized by transmission electron microscopy, immunofluorescence staining and Western Blot analysis. The elastic layer of Bruch's membrane (BM) in the Htra1 transgenic mice was fragmented and less continuous than in wild type (WT) controls. Recombinant HTRA1 lacking the N-terminal domain cleaved various extracellular matrix (ECM) proteins. Subsequent Western Blot analysis revealed an overexpression of fibronectin fragments and a reduction of fibulin 5 and tropoelastin in the RPE/choroid layer in transgenic mice compared to WT. Fibulin 5 is essential for elastogenesis by promoting elastic fiber assembly and maturation. Taken together, our data implicate that HTRA1 overexpression leads to an altered elastogenesis in BM through fibulin 5 cleavage. It highlights the importance of ECM related proteins in the development of AMD and links HTRA1 to other AMD risk genes such as fibulin 5, fibulin 6, ARMS2 and TIMP3.
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