Augmented space recursion for partially disordered systems

Off-stoichiometric alloys exhibit partial disorder, in the sense that only some of the sublattices of the stoichiometric ordered alloy become disordered. This paper puts forward a generalization of the augmented space recursion (ASR) (introduced earlier by one of us (Mookerjee et al 1997(*))) for systems with many atoms per unit cell. In order to justify the convergence properties of ASR we have studied the convergence of various moments of local density of states and other physical quantities like Fermi energy and band energy. We have also looked at the convergence of the magnetic moment of Ni, which is very sensitive to numerical approximations towards the k-space value 0.6 $\mu_{B}$ with the number of recursion steps prior to termination.Comment: Latex 2e, 21 Pages, 13 Figures, iopb style file attache

Third-generation muffin-tin orbitals

By the example of sp^3-bonded semiconductors, we illustrate what 3rd-generation muffin-tin orbitals (MTOs) are. We demonstrate that they can be downfolded to smaller and smaller basis sets: sp^3d^10,sp^3, and bond orbitals. For isolated bands, it is possible to generate Wannier functions a priori. Also for bands, which overlap other bands, Wannier-like MTOs can be generated a priori. Hence, MTOs have a unique capability for providing chemical understanding.Comment: 13 pages, 8 eps figure

Voltage Response Measurements for Power Transformer Moisture and Ageing Condition Assessment

A paper moisture conditioning system has been designed and developed to prepare different moisture level samples for voltage response measurement. The moisture conditioning system has good moisture level predetermining ability. The moisture conditioned samples and the artificially aged samples are tested with the voltage response techniques: decay voltage and return voltage measurement (single cycle). The objective was to see if we could use decay voltage measurement and return voltage measurement to separately investigate the moisture and ageing in the oil impregnated paper insulation. Results from these measurements are presented and discussed in the paper

Modeling Metal Oxide Surge Arrester for the Modern Polarization Based Diagnostics

Recently a number of new non-destructive diagnostic techniques have been investigated for the reliable condition assessment of the ageing of metal oxide surge arrester (MOSA). Among them polarizationrdepolarization current and return voltage measurement techniques showed very promising results. This paper presents an insulation polarization model for investigating polarization-based diagnostics for metal oxide surge arrester. The simulations of the proposed model are validated and verified by comparing the data from the polarization/depolarization current measurements. The simulation of return voltage for MOSA is also performed to validate the insulation polarization model. Finally, the usefulness of this model for MOSA diagnostics has been highlighted in this paper

Some Precautions for the Field Users of PDC Measurement for Transformer Insulation Condition Assessment

The need for economic, reliable and effective delivery of electric power has lead to the search for new, efficient and effective methods for diagnosing the insulation of the HV equipments in the industries all over the world. One of the methods currently being investigated as a potential nondestructive diagnostic tool for condition monitoring of the oilpaper insulation of power transformers is the Polarisation and Depolarisation Current (PDC) measurement. This paper starts with a theoretical and physical description of the PDC technique. Several practical aspects of the technique have been discussed in the paper along with corresponding experimental and field test results. These physical considerations can be used as 'precautions' for the potential field users of the PDC technique for insulation condition assessment of transformers

Correlation effects on the electronic structure of TiOCl: a NMTO+DMFT study

Using the recently developed N-th order muffin-tin orbital-based downfolding technique in combination with the Dynamical Mean Field theory, we investigate the electronic properties of the much discussed Mott insulator TiOCl in the undimerized phase. Inclusion of correlation effects through this approach provides a description of the spectral function into an upper and a lower Hubbard band with broad valence states formed out of the orbitally polarized, lower Hubbard band. We find that these results are in good agreement with recent photo-emission spectra.Comment: 4 pages, 3 figure