Pancake vortices

I describe the magnetic-field and current-density distributions generated by two-dimensional (2D) pancake vortices in infinite, semi-infinite, and finite-thickness stacks of Josephson-decoupled superconducting layers. Arrays of such vortices have been used to model the magnetic structure in highly anisotropic layered cuprate high-temperature superconductors. I show how the electromagnetic forces between pancake vortices can be calculatated, and I briefly discuss the effects of interlayer Josephson coupling.Comment: 16 pages, 4 figures, accepted in J. Supercond. for the Special Issue celebrating Michael Tinkham's 75th birthday, typos [notably in Eq. (67)] correcte

Does The Economic Value Of The Asian Elephant To Urban Dwellers Exceed Their Cost To The Farmers? A Sri Lankan Study

Urban dwellers and farmers in the areas affected by human-elephant conflict in Sri Lanka are often in discord about the conservation of wild elephant in Sri Lanka. The urban dwellers regard this species as a valued resource but farmers in these areas consider it as an agricultural pest that interferes with their farming practices. This dual character of the elephant as both an agricultural pest and an economic asset reflects a difficulty in classifying it as a pest or as a resource. However, it seems that compensating farmers for the damages caused by elephants is essential, if this endangered species is to survive in the long run. This paper uses the results from contingent valuation survey of a sample of urban residents in Colombo in order to examines whether the urban dwellers' willingness to pay for the conservation of elephants is sufficient to compensate farmers for the damage caused by elephants and to raise farmers' tolerance of the present elephants on their farming fields. We find that the annual return for the total extrapolated WTP of urban residents (Rs. 2012.43 million) in Sri Lanka is nearly twice the extent of crop and property damage caused to farmers by elephants (Rs. (Rs.1121.42 million) per annum. This indicates that the policy of compensating farmers by urban dwellers for elephant damage so the farmers will tolerate elephants on their farming fields might be viable. Furthermore, this also suggests that there is a strong economic case for the conservation of the wild elephant population in Sri Lanka, at least at their current population level.

Field and current distributions and ac losses in a bifilar stack of superconducting strips

In this paper I first analytically calculate the magnetic-field and sheet-current distributions generated in an infinite stack of thin superconducting strips of thickness d, width 2a >> d, and arbitrary separation D when adjacent strips carry net current of magnitude I in opposite directions. Each strip is assumed to have uniform critical current density Jc, critical sheet-current density Kc = Jc d, and critical current Ic = 2a Kc, and the distribution of the current density within each strip is assumed to obey critical-state theory. I then derive expressions for the ac losses due to magnetic-flux penetration both from the strip edges and from the top and bottom of each strip, and I express the results in terms of integrals involving the perpendicular and parallel components of the magnetic field. After numerically evaluating the ac losses for typical dimensions, I present analytic expressions from which the losses can be estimated.Comment: 8 pages, 9 figure

Metastability and uniqueness of vortex states at depinning

We present results from numerical simulations of transport of vortices in the zero-field cooled (ZFC) and the field-cooled (FC) state of a type-II superconductor. In the absence of an applied current $I$, we find that the FC state has a lower defect density than the ZFC state, and is stable against thermal cycling. On the other hand, by cycling $I$, surprisingly we find that the ZFC state is the stable state. The FC state is metastable as manifested by increasing $I$ to the depinning current $I_{c}$, in which case the FC state evolves into the ZFC state. We also find that all configurations acquire a unique defect density at the depinning transition independent of the history of the initial states.Comment: 4 pages, 4 figures. Problem of page size correcte