3,388 research outputs found
Discussion on the paper “Real-Time Prediction of Clinical Trial Enrollment and Event Counts: A Review”, by DF Heitjan, Z Ge, and GS Ying
No abstract available
Electronic Structure and Exchange Interactions of NaVO
We have performed first-principle calculations of the electronic structure
and exchange couplings for the nanotube compound NaVO using
the LDA+U approach. Our results show that while the intra-ring exchange
interactions are mainly antiferromagnetic, the inter-ring couplings are {\it
ferromagnetic}. We argue that this is a consequence of the strong hybridization
between filled and vacant 3d vanadium orbitals due to the low symmetry of
NaVO, which results into strong - and often dominant -
ferromagnetic contributions to the total exchange interaction between vanadium
atoms. A comparison with results of previous works is included.Comment: 6 pages, 5 figure
Averaging methods for transient regimes in overloading retrial queueing systems
Cataloged from PDF version of article.A new approach is suggested to study transient and stable regimes in overloading retrial queueing systems. This approach is based on limit theorems of averaging principle and diffusion approximation types for so-called switching processes. Two models of retrial queueing systems of the types h?/G/i/w.r (multidimensional Poisson input flow, one server with general service times, retrial system) and M/M/m/w.r (m servers with exponential service) are considered in the case when the intensity of calls that reapply for the service tends to zero. For the number of re-applying calls, functional limit theorems of averaging principle and diffusion approximation types are proved.
@ 1999 Elsevier Science Ltd. All rights reserved
Single Mott Transition in Multi-Orbital Hubbard Model
The Mott transition in a multi-orbital Hubbard model involving subbands of
different widths is studied within the dynamical mean field theory. Using the
iterated perturbation theory for the quantum impurity problem it is shown that
at low temperatures inter-orbital Coulomb interactions give rise to a single
first-order transition rather than a sequence of orbital selective transitions.
Impurity calculations based on the Quantum Monte Carlo method confirm this
qualitative behavior. Nevertheless, at finite temperatures, the degree of
metallic or insulating behavior of the subbands differs greatly. Thus, on the
metallic side of the transition, the narrow band can exhibit quasi-insulating
features, whereas on the insulating side the wide band exhibits pronounced
bad-metal behavior. This complexity might partly explain contradictory results
between several previous works.Comment: 8 pages, 11 figure
Symplectic Cobordism in Small Dimensions and a Series of Elements of Order Four
We present the structure of symplectic cobordism ring in dimensions
up to 51 and give a construction of an infinite series of elements ,
, of order four in this ring, where . The key element of the series is in dimension 103.Comment: 117 pages, 18 table
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