Construction of Localized Basis for Dynamical Mean Field Theory

Many-body Hamiltonians obtained from first principles generally include all possible non-local interactions. But in dynamical mean field theory the non-local interactions are ignored, and only the effects of the local interactions are taken into account. The truncation of the non-local interactions is a basis dependent approximation. We propose a criterion to construct an appropriate localized basis in which the truncation can be carried out. This involves finding a basis in which a functional given by the sum of the squares of the local interactions with appropriate weight factors is maximized under unitary transformations of basis. We argue that such a localized basis is suitable for the application of dynamical mean field theory for calculating material properties from first principles. We propose an algorithm which can be used for constructing the localized basis. We test our criterion on a toy model and find it satisfactory

The chaotic nature of healthcare information systems: The need for transdisciplinary collaboration

Copyright @ 2013 EMCIS.This paper demonstrates one of the challenges of the healthcare information systems development, namely the chaotic nature of healthcare systems. Although the reliable evidence demonstrating the positive effects of health information systems on safety and quality remains inconclusive (a growing body of research revealing the unintended consequences and potentially error producing effects of health information systems’ implementation. Different arguments from the literature concerning the chaotic nature of healthcare, including but not limited to the nature of patients and disease have been presented. The requirements of new ways of systems design and the need for transdisciplinary dynamic teams within the requirements engineering phase as a start has been discussed. These arguments have been investigated in the context of an exploratory case addressing one of the advanced oncology centres in the US. This paper concludes that there is an important need to rethink healthcare information systems development method, which has to be in a dynamic ongoing manner for some major issues

Magneto-elastic quantum fluctuations and phase transitions in the iron superconductors

We examine the relevance of magneto-elastic coupling to describe the complex magnetic and structural behaviour of the different classes of the iron superconductors. We model the system as a two-dimensional metal whose magnetic excitations interact with the distortions of the underlying square lattice. Going beyond mean field we find that quantum fluctuation effects can explain two unusual features of these materials that have attracted considerable attention. First, why iron telluride orders magnetically at a non-nesting wave-vector $(\pi/2, \pi/2)$ and not at the nesting wave-vector $(\pi, 0)$ as in the iron arsenides, even though the nominal band structures of both these systems are similar. And second, why the $(\pi, 0)$ magnetic transition in the iron arsenides is often preceded by an orthorhombic structural transition. These are robust properties of the model, independent of microscopic details, and they emphasize the importance of the magneto-elastic interaction.Comment: 4 pages, 3 figures; minor change

Controlled fabrication of single electron transistors from single-walled carbon nanotubes

Single electron transistors (SETs) are fabricated by placing single walled carbon nanotubes (SWNTs) on a 100 nm wide local Al/Al2O3 bottom gate and then contacting with Pd electrodes. Coulomb oscillations up to 125 K were observed and charging energies of 12-15 meV with level spacing of ~5 meV were measured from the Couloumb diamond, in agreement with a dot size of ~100 nm, implying that the local gate defines the dot size by bending SWNT at the edges and controls its operation. This "mechanical template" approach may facilitate large scale fabrication of SET devices using SWNT.Comment: 5 pages, 3 figure