Confinement of rotating convection by a laterally varying magnetic field

Spherical shell dynamo models based on rotating convection show that the flow within the tangent cylinder is dominated by an off-axis plume that extends from the inner core boundary to high latitudes and drifts westward. Earlier studies explained the formation of such a plume in terms of the effect of a uniform axial magnetic field that significantly increases the lengthscale of convection in a rotating plane layer. However, rapidly rotating dynamo simulations show that the magnetic field within the tangent cylinder has severe lateral inhomogeneities that may influence the onset of an isolated plume. Increasing the rotation rate in our dynamo simulations (by decreasing the Ekman number $E$) produces progressively thinner plumes that appear to seek out the location where the field is strongest. Motivated by this result, we examine the linear onset of convection in a rapidly rotating fluid layer subject to a laterally varying axial magnetic field. A cartesian geometry is chosen where the finite dimensions $(x,z)$ mimic $(\phi,z)$ in cylindrical coordinates. The lateral inhomogeneity of the field gives rise to a unique mode of instability where convection is entirely confined to the peak-field region. The localization of the flow by the magnetic field occurs even when the field strength (measured by the Elsasser number $\varLambda$) is small and viscosity controls the smallest lengthscale of convection. The lowest Rayleigh number at which an isolated plume appears within the tangent cylinder in spherical shell dynamo simulations agrees closely with the viscous-mode Rayleigh number in the plane layer linear magnetoconvection model. The localized excitation of viscous-mode convection by a laterally varying magnetic field provides a mechanism for the formation of isolated plumes within Earth's tangent cylinder.Comment: 12 figures, 3 table

Are agricultural markets location-optimal? A case study of Gaya District (Bihar)

The thesis of efficiency and optimality of Indian agricultural system has several facets that have called for attention of a number of scholars. Some have proved allocative optimality of resource utilization, the others have proved optimality of distribution of gains from agriculture, while still others have come up with the cases of marketing optimality. However, there is hardly any work that studies location optimality of market centers in any region of India. In this paper we examine if the empirically observed market locations are optimal and as a case study take up the agricultural markets located in Gaya district of Bihar. We have used the location-allocation model for optimality analysis. Our findings reveal that existing locations and arrivals of merchandise at the agricultural markets of Gaya are very close to what might have been if they had been located on the principle of optimality. There are minor deviations, of course. However, as the existing markets have developed in an open region, unlike our cost-optimal locations searched out in a closed region, a discount must be made in favour of the existing locations, and we do not have enough reasons and evidence to conclude that the existing markets are sub-optimally located. We conclude, therefore, that market forces automatically establish location optimality and assert that the existing agricultural markets in Gaya district are location-optimal

Information, Candidate Selection, and the Quality of Representation: Evidence from Nepal

How do we improve the quality of representation in new democracies? This paper studies candidate selection by party leaders and asks whether poor information about public preferences can lead elite choices to diverge from mass opinion. Working with a political party in Nepal, we show that while elites value voter preferences, these preferences only explain one third of elite candidate selection. Next, we embed an experiment in actual candidate selection deliberations for this party and find that party leaders not only select different candidates when polling data are presented to them, but that their updated decisions also improve the party’s vote share. By opening the black-box of candidate selection, this paper demonstrates that closing the information gap between elites and voters has the power to improve the quality of representation

Polarized non-abelian representations of slim near-polar spaces

In (Bull Belg Math Soc Simon Stevin 4:299-316, 1997), Shult introduced a class of parapolar spaces, the so-called near-polar spaces. We introduce here the notion of a polarized non-abelian representation of a slim near-polar space, that is, a near-polar space in which every line is incident with precisely three points. For such a polarized non-abelian representation, we study the structure of the corresponding representation group, enabling us to generalize several of the results obtained in Sahoo and Sastry (J Algebraic Comb 29:195-213, 2009) for non-abelian representations of slim dense near hexagons. We show that with every polarized non-abelian representation of a slim near-polar space, there is an associated polarized projective embedding