The Effect of Ramsauer Type Transmission Resonances on the Conductance Modulation of Spin Interferometers

We use a mean field approach to study the conductance modulation of gate controlled semiconductor spin interferometers based on the Rashba spin-orbit coupling effect. The conductance modulation is found to be mostly due to Ramsauer type transmission resonances rather than the Rashba effect in typical structures. This is because of significant reflections at the interferometer's contacts due to large potential barriers and effective mass mismatch between the contact material and the semiconductor. Thus, unless particular care is taken to eliminate these reflections, any observed conductance modulation of spin interferometers may have its origin in the Ramsauer resonances (which is unrelated to spin) rather than the Rashba effect.Comment: 3 figure

The dominant spin relaxation mechanism in compound organic semiconductors

Despite the recent interest in "organic spintronics", the dominant spin relaxation mechanism of electrons or holes in an organic compound semiconductor has not been conclusively identified. There have been sporadic suggestions that it might be hyperfine interaction caused by background nuclear spins, but no confirmatory evidence to support this has ever been presented. Here, we report the electric-field dependence of the spin diffusion length in an organic spin-valve structure consisting of an Alq3 spacer layer, and argue that this data, as well as available data on the temperature dependence of this length, contradict the notion that hyperfine interactions relax spin. Instead, they suggest that the Elliott-Yafet mechanism, arising from spin-orbit interaction, is more likely the dominant spin relaxing mechanism.Comment: Accepted for publication in Physical Review

Fiscal health of selected Indian cities.

The paper aims to assess the fiscal health of five urban agglomerations (UAs) in India viz. Delhi, Hyderabad, Kolkata, Chennai, and Pune. Our sample consists of five corporations and sixty three smaller Urban Local Bodies (ULBs) dispersed in thirteen districts of five major states. The main objective of the paper is twofold. First, to review the status of revenue generation and expenditure responsibilities of the constituent ULBs. Second, to assess the magnitudes of their fiscal gaps by estimating the expenditure needs and revenue capacities and give some useful recommendations to reduce these gaps. Data on ULB finances for the financial year 2004-05 collected through surveys are used for the analysis. For estimation of expenditure needs the updated financial norms on the selected services specified by Zakaria Committee are used as benchmarks. For revenue capacity estimations Gross City Products (GCPs) are estimated from non-agricultural components of the District Domestic Products (DDPs). Revenue capacities are estimated by applying a tax-to-GCP ratio, which is higher than that existing in a ULB by a politically feasible margin, on the estimated GCPs. The main findings suggest that excepting five small ULBs in Hyderabad, the others are not in a position to cover their expenditure needs by their present revenue collections. All the UAs have unutilised potentials for revenue generations but with the exception of one UA i.e, Hyderabad, all the others would fail to cover their expenditure needs, even if they realise their revenue potentials. In all the UAs, except Chennai, bigger corporations are more constrained than the smaller ULBs. Besides, concrete evidence in support of the efficiency of parastatal agencies in sharing the burden of responsibilities cannot be established. The paper recommends better utilisation of 'own revenue' handles of the cities, by improved administration of the property taxes, implementation of other taxes, and collection of user charges. The option of state governments to allow the local bodies piggybacking a small proportion on their VAT collections can also be explored. Another way to reduce the fiscal gap would be to earmark a portion of the sales proceeds from land and housing by state governments sold through their development agencies for improvement in the infrastructure of the cities. The paper also recommends that the State Finance Commissions (SFCs) should develop appropriate norms for estimating expenditure needs based on which transfers from the state to local governments can be decided.Expenditure needs ; Revenue capacity ; Fiscal gap