Comment on "Energies of the ground state and first excited 0+0^{+} in an exactly solvable pairing model"

We comment on a recent application of the RPA method and its extensions to the case of the two-level pairing model by N. Dinh Dang [1].Comment: 5 pages, 1 figure, submitted to EPJ

Self-consistent theory of large amplitude collective motion: Applications to approximate quantization of non-separable systems and to nuclear physics

The goal of the present account is to review our efforts to obtain and apply a ``collective'' Hamiltonian for a few, approximately decoupled, adiabatic degrees of freedom, starting from a Hamiltonian system with more or many more degrees of freedom. The approach is based on an analysis of the classical limit of quantum-mechanical problems. Initially, we study the classical problem within the framework of Hamiltonian dynamics and derive a fully self-consistent theory of large amplitude collective motion with small velocities. We derive a measure for the quality of decoupling of the collective degree of freedom. We show for several simple examples, where the classical limit is obvious, that when decoupling is good, a quantization of the collective Hamiltonian leads to accurate descriptions of the low energy properties of the systems studied. In nuclear physics problems we construct the classical Hamiltonian by means of time-dependent mean-field theory, and we transcribe our formalism to this case. We report studies of a model for monopole vibrations, of $^{28}$Si with a realistic interaction, several qualitative models of heavier nuclei, and preliminary results for a more realistic approach to heavy nuclei. Other topics included are a nuclear Born-Oppenheimer approximation for an {\em ab initio} quantum theory and a theory of the transfer of energy between collective and non-collective degrees of freedom when the decoupling is not exact. The explicit account is based on the work of the authors, but a thorough survey of other work is included.Comment: 203 pages, many figure

Trust, Organizational Controls, Knowledge Acquisition from the Foreign Parents, and Performance in Vietnamese International Joint Ventures

Successful adaptation in strategic alliances "calls for a delicate balance between the twin virtues of reliability and flexibility" [Parkhe 1998]. On one hand, the joint venture must be flexible enough to respond to the uncertainties of competitive business environments because it is not feasible to plan for every possible contingency. Yet, on the other hand, unfettered flexibility invites dysfunctional behavior, such as opportunism and complacency. This delicate balance accompanies a parallel balance between trust and control of the joint venture. The primary goal of this study is to empirically examine this relationship in the context of Vietnamese international joint ventures (IJVs) by building on the model of knowledge acquisition and performance in IJVs established by Lyles and Salk [1996]. This study makes three major contributions to the literature. First it confirms several findings of the original Lyles and Salk study [1996]. Second, we strengthen Lyles and Salk's original model by incorporating multiple measures of both interorganizational trust and control as independent variables. Finally, this study represents one of the first in-depth examinations of business in the emerging Vietnamese economy.http://deepblue.lib.umich.edu/bitstream/2027.42/39713/3/wp329.pd

Covalency and the metal-insulator transition in titanate and vanadate perovskites

A combination of density functional and dynamical mean-field theory is applied to the perovskites SrVO$_3$, LaTiO$_3$ and LaVO$_3$. We show that DFT+DMFT in conjunction with the standard fully localized-limit (FLL) double-counting predicts that LaTiO$_3$ and LaVO$_3$ are metals even though experimentally they are correlation-driven ("Mott") insulators. In addition, the FLL double counting implies a splitting between oxygen $p$ and transition metal $d$ levels which differs from experiment. Introducing into the theory an \textit{ad hoc} double counting correction which reproduces the experimentally measured insulating gap leads also to a $p$-$d$ splitting consistent with experiment if the on-site interaction $U$ is chosen in a relatively narrow range ($\sim 6\pm 1$ eV). The results indicate that these early transition metal oxides will serve as critical test for the formulation of a general \textit{ab initio} theory of correlated electron metals.Comment: 5 pages, 3 figure