Hartree-Fock Many-Body Perturbation Theory for Nuclear Ground-States

We investigate the order-by-order convergence behavior of many-body perturbation theory (MBPT) as a simple and efficient tool to approximate the ground-state energy of closed-shell nuclei. To address the convergence properties directly, we explore perturbative corrections up to 30th order and highlight the role of the partitioning for convergence. The use of a simple Hartree-Fock solution to construct the unperturbed basis leads to a convergent MBPT series for soft interactions, in contrast to, e.g., a harmonic oscillator basis. For larger model spaces and heavier nuclei, where a direct high-order MBPT calculation in not feasible, we perform third-order calculation and compare to advanced ab initio coupled-cluster calculations for the same interactions and model spaces. We demonstrate that third-order MBPT provides ground-state energies for nuclei up into tin isotopic chain that are in excellent agreement with the best available coupled-cluster results at a fraction of the computational cost.Comment: 6 pages, 5 figures, 1 tabl

Ab Initio Path to Heavy Nuclei

We present the first ab initio calculations of nuclear ground states up into the domain of heavy nuclei, spanning the range from 16-O to 132-Sn based on two- plus three-nucleon interactions derived within chiral effective field theory. We employ the similarity renormalization group for preparing the Hamiltonian and use coupled-cluster theory to solve the many-body problem for nuclei with closed sub-shells. Through an analysis of theoretical uncertainties resulting from various truncations in this framework, we identify and eliminate the technical hurdles that previously inhibited the step beyond medium-mass nuclei, allowing for reliable validations of nuclear Hamiltonians in the heavy regime. Following this path we show that chiral Hamiltonians qualitatively reproduce the systematics of nuclear ground-state energies up to the neutron-rich Sn isotopes.Comment: 5 pages, 5 figure

Ab Initio Calculations of Medium-Mass Nuclei with Explicit Chiral 3N Interactions

We present the first ab initio coupled-cluster calculations of medium-mass nuclei with explicit chiral three-nucleon (3N) interactions. Using a spherical formulation of coupled cluster with singles and doubles excitations including explicit 3N contributions, we study ground states of 16,24-O, 40,48-Ca and 56-Ni. We employ chiral NN plus 3N interactions softened through a similarity renormalization group (SRG) transformation at the three-body level. We investigate the impact of all truncations and quantify the resulting uncertainties---this includes the contributions from triples excitations, the truncation of the set of three-body matrix elements, and the omission of SRG-induced four-body interactions. Furthermore, we assess the quality of a normal-ordering approximation of the 3N interaction beyond light nuclei. Our study points towards the predictive power of chiral Hamiltonians in the medium-mass regime.Comment: 6 pages, 3 figures, 2 table

Extension of coupled-cluster theory with a non-iterative treatment of connected triply excited clusters to three-body Hamiltonians

We generalize the coupled-cluster (CC) approach with singles, doubles, and the non-iterative treatment of triples termed $\Lambda$CCSD(T) to Hamiltonians containing three-body interactions. The resulting method and the underlying CC approach with singles and doubles only (CCSD) are applied to the medium-mass closed-shell nuclei O16, O24, and Ca40. By comparing the results of CCSD and $\Lambda$CCSD(T) calculations with explicit treatment of three-nucleon interactions to those obtained using an approximate treatment in which they are included effectively via the zero-, one-, and two-body components of the Hamiltonian in normal-ordered form, we quantify the contributions of the residual three-body interactions neglected in the approximate treatment. We find these residual normal-ordered three-body contributions negligible for the $\Lambda$CCSD(T) method, although they can become significant in the lower-level CCSD approach, particularly when the nucleon-nucleon interactions are soft.Comment: 21 pages, 3 figure

Modelling of the temperature distribution of spot-weldable composite/metal joints

Resistance spot welding is the most economical joining method for the production of automotive steel bodies. In modern car body construction, however, its future applicability is limited due to the growing mix of materials in multi-material design. In response to increasing weight reduction requirements to protect the environment and natural resources, lightweight materials, and fibre-reinforced plastics (FRP) in particular, are more and more used in modern vehicle bodies. To facilitate the future joining of FRP/steel structures with resistance spot welding, spot-weldable force-introduction elements may be embedded in the laminate as a joining interface. When welding the so-called inserts, thermal damage to the surrounding polymer should be avoided, as this is the only way to calculate the strength of the joint correctly. For this purpose, the paper presents a numerical model that allows the prediction of the temperature propagation during spot welding of FRP/steel joints with embedded inserts. The simulative approach is subsequently validated by comparison with experimentally determined temperature curves and in doing so, an excellent model prediction can be noted

Sprachkritik – Eine unlösbare Aufgabe? Ergebnisse einer Befragung unter Linguisten

Während Sprachkritik in der Öffentlichkeit derzeit wieder einen (nicht unbedenklichen) Popularitätsschub erlebt, ist es innerhalb der Linguistik um das Thema seltsam still geworden. Nach den vielversprechenden Ansätzen in den Achtzigerjahren, sie als linguistische Methode zu etablieren, spielt Sprachkritik derzeit – wenn überhaupt – nur noch als Objekt eine Rolle. Ist das Unterfangen, Sprachkritik als linguistische Methode, als Form »angewandter Linguistik« innerhalb des Fachs zu etablieren, gescheitert, bevor es ein methodisches Fundament erhalten konnte? Dieser Frage gehen eine Reihe von Doktorandinnen und Doktoranden und Studierenden an der Freiburger Universität seit dem Wintersemester 2000/2001 innerhalb eines Arbeitskreises nach. In diesem Zusammenhang entstand die Idee, Vertreter der Sprachwissenschaft nach ihrer Meinung zum Thema Sprachkritik direkt zu befragen. Die Ergebnisse dieser Befragung sollen im Folgenden kurz vorgestellt werden