The Unitary Correlation Operator Method from a Similarity Renormalization Group Perspective

We investigate how the Unitary Correlation Operator Method (UCOM), developed to explicitly describe the strong short-range central and tensor correlations present in the nuclear many-body system, relates to the Similarity Renormalization Group (SRG), a method to band-diagonalize Hamiltonians by continuous unitary transformations. We demonstrate how the structure of the UCOM transformation, originally motivated from the physically intuitive picture of correlations in coordinate space, arises naturally from the SRG flow equation. Apart from formal considerations we show that the momentum space matrix elements of the effective interactions obtained in both schemes agree extremely well.Comment: 5 pages, 2 figures, using REVTEX4; v2: references adde

Quasiparticle Random Phase Approximation with Interactions from the Similarity Renormalization Group

We have developed a fully consistent framework for calculations in the Quasiparticle Random Phase Approximation (QRPA) with $NN$ interactions from the Similarity Renormalization Group (SRG) and other unitary transformations of realistic interactions. The consistency of our calculations, which use the same Hamiltonian to determine the Hartree-Fock-Bogoliubov (HFB) ground states and the residual interaction for QRPA, guarantees an excellent decoupling of spurious strength, without the need for empirical corrections. While work is under way to include SRG-evolved 3N interactions, we presently account for some 3N effects by means of a linearly density-dependent interaction, whose strength is adjusted to reproduce the charge radii of closed-shell nuclei across the whole nuclear chart. As a first application, we perform a survey of the monopole, dipole, and quadrupole response of the calcium isotopic chain and of the underlying single-particle spectra, focusing on how their properties depend on the SRG parameter $\lambda$. Unrealistic spin-orbit splittings suggest that spin-orbit terms from the 3N interaction are called for. Nevertheless, our general findings are comparable to results from phenomenological QRPA calculations using Skyrme or Gogny energy density functionals. Potentially interesting phenomena related to low-lying strength warrant more systematic investigations in the future.Comment: 18 pages, 17 figures, 3 tables (RevTeX 4.1), v2: fixed typos & figures, as publishe

Treatment of the Intrinsic Hamiltonian in Particle-Number Nonconserving Theories

We discuss the implications of using an intrinsic Hamiltonian in theories without particle-number conservation, e.g., the Hartree-Fock-Bogoliubov approximation, where the Hamiltonian's particle-number dependence leads to discrepancies if one naively replaces the particle-number operator by its expectation value. We develop a systematic expansion that fixes this problem and leads to an a posteriori justification of the widely-used one- plus two-body form of the intrinsic kinetic energy in nuclear self-consistent field methods. The expansion's convergence properties as well as its practical applications are discussed for several sample nuclei.Comment: 6 pages, 5 figure

From nucleon-nucleon interaction matrix elements in momentum space to an operator representation

Starting from the matrix elements of the nucleon-nucleon interaction in momentum space we present a method to derive an operator representation with a minimal set of operators that is required to provide an optimal description of the partial waves with low angular momentum. As a first application we use this method to obtain an operator representation for the Argonne potential transformed by means of the unitary correlation operator method and discuss the necessity of including momentum dependent operators. The resulting operator representation leads to the same results as the original momentum space matrix elements when applied to the two-nucleon system and various light nuclei. For applications in fermionic and antisymmetrized molecular dynamics, where an operator representation of a soft but realistic effective interaction is indispensable, a simplified version using a reduced set of operators is given

Ab Initio Description of Open-Shell Nuclei: Merging No-Core Shell Model and In-Medium Similarity Renormalization Group

We merge two successful ab initio nuclear-structure methods, the no-core shell model (NCSM) and the multi-reference in-medium similarity renormalization group (IM-SRG) to define a new many-body approach for the comprehensive description of ground and excited states of closed and open-shell nuclei. Building on the key advantages of the two methods---the decoupling of excitations at the many-body level in the IM-SRG and the access to arbitrary nuclei, eigenstates, and observables in the NCSM---their combination enables fully converged no-core calculations for an unprecedented range of nuclei and observables at moderate computational cost. We present applications in the carbon and oxygen isotopic chains, where conventional NCSM calculations are still feasible and provide an important benchmark. The efficiency and rapid convergence of the new approach make it ideally suited for ab initio studies of the complete spectroscopy of nuclei up into the medium-mass regime.Comment: 5 pages, 4 figures, v2: update to published versio

Student Perceptions Of The Value Of Internships In Business Education

Internships are an increasingly popular element of higher education in business and provide many potential benefits to students.  An internship experience can help students make the connection between their academic studies and the world of business.  They can also create valuable connections and networking opportunities to improve the employment and career prospects for students.  This study analyzes the internships of 114 undergraduate and graduate students to determine what factors account for the most valuable internship experience.  The results show a strong statistical correlation between the perceived value of the internship and the student’s demographic profile, the structure of the internship, and the connection to the students’ career plans.  These findings provide a basis for designing successful internship programs in business education

Shareholder Value In The Third Wave Of Acquisitions

Acquisition activity in the United States has occurred in three distinct waves.  During the 1960s, acquisitions were predominantly made in areas unrelated to the acquiring firms.  Later analysis of this conglomerate boom generally indicated that little or no shareholder value was created in this process.  A second wave of acquisition and divestiture activity in the 1980s was characterized by the unwinding of the conglomerates and a search for synergy between the buyer and the acquired firm.  The evidence on value creation for this period is somewhat more encouraging, although most studies indicate that firms did not succeed in creating profits through acquisitions.  A third wave of acquisitions occurred in the late 1990s.  This was an unprecedented era of merger and acquisition activity.  Nearly $4 trillion worth of mergers occurred from 1998-2000.  This represents a volume of activity greater than the previous 30 years put together.  This study examines the returns to acquiring firms during this period and compares them to previous studies of acquisition performance.  Was it different this time?  This study indicates that shareholder value was generally reduced in making acquisitions, although some factors can mitigate the degree of poor performance.  On average, acquiring firms lost 4-7% from making acquisitions.  There is evidence to support the conventional wisdom that firms often overpay making acquisitions and that the size of the stock premium can be tied to firm performance.  However, after controlling for the price premium, there is significant evidence of wealth creation (synergy) from the transaction

Numerical modelling of the absolute stress state in the Marmara region - a contribution to seismic hazard assessment

The kinematics and dynamics of the Sea of Marmara region are addressed using 3D geomechanical numerical modelling. The velocity field and absolute stress in the crust are modelled both in the long-term and during the interseismic period. A number of quantities relevant for seismic hazard assessment are derived

Nuclear Structure and Response based on Correlated Realistic NN Interactions

Starting from the Argonne V18 nucleon-nucleon (NN) interaction and using the Unitary Correlation Operator Method, a correlated interaction v_UCOM has been constructed, which is suitable for calculations within restricted Hilbert spaces. In this work we employ the v_UCOM in Hartree-Fock, perturbation-theory and RPA calculations and we study the ground-state properties of various closed-shell nuclei, as well as some excited states. The present calculations provide also important feedback for the optimization of the v_UCOM and valuable information on its properties. The above scheme offers the prospect of ab initio calculations in nuclei, regardless of their mass number. It can be used in conjunction with other realistic NN interactions as well, and with various many-body methods (Second RPA, QRPA, Shell Model, etc.).Comment: 3 pages, incl. 2 figures; Proc. Int. Conf. on Frontiers in Nuclear Structure, Astrophysics and Reactions (FINUSTAR), Kos, Greece, Sept.200