Modeling currents at satellite altitudes

A mathematical formalism for modeling the poloidal magnetic field and current density at satellite altitudes is presented

Unofficial Development Assistance: A Dynamic Model of Charities' Donation Income

The empirical literature on the determinants of charities donation income, distinguishing the charitable cause, is small. We extend the literature in several ways. First, we focus on overseas development charities allowing us to give more consideration to the particular characteristics of this cause. Second, we look at the impact of macroeconomic change over a quarter century including changes in household income and in government spending on ODA, as well as 'charity level' variables that earlier authors have considered. Third, we use a general dynamic model and rigorous testing procedures to arrive at our specification. Using a newly assembled long panel of data, we find evidence of a strong, but diminishing fundraising effect. We find no evidence of crowding out by either grants made directly to charities or by changes in the public provision of development funding.overseas development, charitable giving

Gibrat’s law and legacy for non-profit organisations: a non-parametric analysis

Gibrat’s Law of proportional effect (i.e. growth is independent of initial size) has been tested for firms for several decades. In this paper I test Gibrat’s Law for charities in England and Wales through time. Using a data set based on the population of registered charities from 1998 to 2009, I am able to test the ‘ex ante’ hypothesis that Gibrat’s Law holds over the long run for a sample of charities as well as testing Gibrat’s Legacy (that Gibrat’s Law holds for large and mature organisations), the ‘ex post’ hypothesis. I use nonparametric local polynomial smoothing techniques which are more robust to the issues of autocorrelation, sample selection and truncation that make the conventional parametric approaches to testing Gibrat’s Law difficult in practice. Results suggest that the dynamic processes driving growth in the charitable sectors may differ from those driving the growth of firms. Unlike for-profit firms Gibrat’s Law is found to generally hold when controlling for selection both ‘ex ante’ and ‘ex post’. Results may be driven by the absence of a minimum efficient scale which charities must achieve to survive and the different funding profiles of charities

Does the geoid drift west?

In 1970 Hide and Malin noted a correlation of about 0.8 between the geoid and the geomagnetic potential at the Earth's surface when the latter is rotated eastward in longitude by about 160 degrees and the spherical harmonic expansions of both functions are truncated at degree 4. From a century of magnetic observatory data, Hide and Malin inferred an average magnetic westward drift rate of about 0.27 degrees/year. They attributed the magnetic-gravitational correlation to a core event at about 1350 A.D. which impressed the mantle's gravity pattern at long wavelengths onto the core motion and the resulting magnetic field. The impressed pattern was then carried westward 160 degrees by the nsuing magnetic westward drift. An alternative possibility is some sort of steady physical coupling between the magnetic and gravitational fields (perhaps migration of Hide's bumps on the core-mantle interface). This model predicts that the geoid will drift west at the magnetic rate. On a rigid earth, the resulting changes in sea level would be easily observed, but they could be masked by adjustment of the mantle if it has a shell with viscosity considerably less than 10 to the 21 poise. However, steady westward drift of the geoid also predicts secular changes in g, the local acceleration of gravity, at land stations. These changes are now ruled out by recent independent high-accuracy absolute measurements of g made by several workers at various locations in the Northern Hemisphere

Self-consistent simulations of a von K\'arm\'an type dynamo in a spherical domain with metallic walls

We have performed numerical simulations of boundary-driven dynamos using a three-dimensional non-linear magnetohydrodynamical model in a spherical shell geometry. A conducting fluid of magnetic Prandtl number Pm=0.01 is driven into motion by the counter-rotation of the two hemispheric walls. The resulting flow is of von K\'arm\'an type, consisting of a layer of zonal velocity close to the outer wall and a secondary meridional circulation. Above a certain forcing threshold, the mean flow is unstable to non-axisymmetric motions within an equatorial belt. For fixed forcing above this threshold, we have studied the dynamo properties of this flow. The presence of a conducting outer wall is essential to the existence of a dynamo at these parameters. We have therefore studied the effect of changing the material parameters of the wall (magnetic permeability, electrical conductivity, and thickness) on the dynamo. In common with previous studies, we find that dynamos are obtained only when either the conductivity or the permeability is sufficiently large. However, we find that the effect of these two parameters on the dynamo process are different and can even compete to the detriment of the dynamo. Our self-consistent approach allow us to analyze in detail the dynamo feedback loop. The dynamos we obtain are typically dominated by an axisymmetric toroidal magnetic field and an axial dipole component. We show that the ability of the outer shear layer to produce a strong toroidal field depends critically on the presence of a conducting outer wall, which shields the fluid from the vacuum outside. The generation of the axisymmetric poloidal field, on the other hand, occurs in the equatorial belt and does not depend on the wall properties.Comment: accepted for publication in Physical Review

Risk aversion and inequity aversion in demand for unemployment benefits

This paper is an empirical study of what motivates net contributors to support redistributive policies. While studies in the area have tended to consider broad measures of inequality and support for redistribution in general, we focus on a single, salient relationship between local unemployment rates and demand for spending on unemployment benefits. Using a particularity of the Spanish labour market, we estimate how workers' stated preferences for unemployment benefits spending respond to changes in the local unemployment rate. We then decompose this response into the part explained by risk aversion, and thus demand for insurance, and the part explained by inequity aversion. Our results suggest that increases in local unemployment rates lead to increased demand by workers for unemployment benefits spending. Moreover, our results are consistent with an insurance motive driving this relationship but provide little support for inequity aversion. Our results suggest that studies of the relationship between inequality and demand for redistribution might benefit from considering both the source and measure of the inequality and the instrument of redistribution

Is income redistribution a form of insurance, a public good or both?

This paper is an empirical study of redistributive preferences. Our interest is what motivates net contributors to support redistributive policies. Using instrumental variable estimation and exploiting a particularity of the Spanish labour market we estimate how workers’ declared preferences for unemployment benefits spending respond to changes in the local unemployment rate. We then decompose this response into the part explained by risk aversion, and thus demand for insurance, and the part explained by the public goods nature of redistribution. Our results suggest that the declared preferences of workers for unemployment benefits spending are driven by demand for insurance rather than any public goods component. We show how these results suggest that preferences for redistribution in the form of unemployment benefits are driven by Insurance considerations rather than by any public goods consideration

Charitable Giving for Overseas Development: UK trends over a quarter century

Charitable giving is an important source of funding for overseas development and emergency relief. Donations in the UK are about a quarter of the size of government development aid. There has been strong growth over time, reflecting the activities of development charities and the public response to humanitarian emergencies. The paper examines how this charitable giving has changed since 1978, using a newly constructed panel data set on donations to individual UK charities. When did the increase take place? Did the public respond to events such as Live Aid or has there been a steady upward trend? What has been the relationship with changes in household income? Which charities have grown fastest? Have new charities displaced old? How do changes in giving for overseas compare with changes in giving for other causes?charitable giving, overseas development