Effect of nearby Pearl vortices upon the IcI_c vs BB characteristics of planar Josephson junctions in thin and narrow superconducting strips

In this paper I show how to calculate the effect of a nearby Pearl vortex or antivortex upon the critical current $I_c(B)$ when a perpendicular magnetic induction $B$ is applied to a planar Josephson junction in a long, thin superconducting strip of width $W$ much less than the Pearl length $\Lambda = 2\lambda^2/d$, where $\lambda$ is the London penetration depth and $d$ is the thickness ($d < \lambda$). The theoretical results provide a qualitative explanation of unusual features recently observed experimentally by Golod {\it et al.}\cite{Golod10} in a device with a similar geometry.Comment: 8 pages, 11 figure

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.

Self-field effects upon the critical current density of flat superconducting strips

We develop a general theory to account self-consistently for self-field effects upon the average transport critical current density Jc of a flat type-II superconducting strip in the mixed state when the bulk pinning is characterized by a field-dependent depinning critical current density Jp(B), where B is the local magnetic flux density. We first consider the possibility of both bulk and edge-pinning contributions but conclude that bulk pinning dominates over geometrical edge-barrier effects in state-of-the-art YBCO films and prototype second-generation coated conductors. We apply our theory using the Kim model, JpK(B) = JpK(0)/(1+|B|/B0), as an example. We calculate Jc(Ba) as a function of a perpendicular applied magnetic induction Ba and show how Jc(Ba) is related to JpK(B). We find that Jc(Ba) is very nearly equal to JpK(Ba) when Ba > Ba*, where Ba* is the value of Ba that makes the net flux density zero at the strip's edge. However, Jc(Ba) is suppressed relative to JpK(Ba) at low fields when Ba < Ba*, with the largest suppression occurring when Ba*/B0 is of order unity or larger.Comment: 9 pages, 4 figures, minor revisions to add four reference

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

Self-fields in thin superconducting tapes: implications to the thickness effect in coated conductors

Most applications of superconductors, such as power transmission lines, motors, generators, and transformers, require long cables through which large currents circulate. Impressive progress has recently been achieved in the current-carrying capability in conductors based on high-temperature superconductors. Coated conductors are likely the best examples, consisting of very good quality thin layers of YBCO superconductor grown on top of a metallic tape with some intermediate layers. However, there is an important problem for achieving large currents: a large decrease in transport critical-current density Jc when increasing film thickness has been observed in coated conductors made by all available techniques. Here, we theoretically explain the nature and the ubiquitous presence of this so-called thickness effect by analyzing the self-field created by the transport currents in the superconductor, assuming a realistic field-dependent Jc. This knowledge can help finding new ways to improve transport current in thick superconducting films.Comment: 7 pages, 3 figure