Jovian dust streams: Probes of the Io plasma torus

Jupiter was discovered to be a source of high speed dust particles by the Ulysses spacecraft in 1992. These dust particles originate from the volcanic plumes on Io. They collect electrostatic charges from the plasma environment, gain energy from the co-rotating electric field of the magnetosphere, and leave Jupiter with escape speeds over $\rm 200 km s^{-1}$. The dust streams were also observed by the Galileo and Cassini spacecraft. While Ulysses and Cassini only had a single encounter with Jupiter, Galileo has continuously monitored the dust streams in the Jovian magnetosphere since 1996. The observed dust fluxes exhibit large orbit-to-orbit variability due to both systematic and stochastic changes. By combining the entire data set, the variability due to stochatic processes can be approximately removed and a strong variation with Jovian local time is found. This result is consistent with theoretical expectations and confirms that the majority of the Jovian dust stream particles originate from Io rather than other potential sources.Comment: 4 pages, 1 b/w figure, 2 color figures, accepted for Geophysical Research Letter

A BSDE approach to stochastic differential games with incomplete information

We consider a two-player zero-sum stochastic differential game in which one of the players has a private information on the game. Both players observe each other, so that the non-informed player can try to guess his missing information. Our aim is to quantify the amount of information the informed player has to reveal in order to play optimally: to do so, we show that the value function of this zero-sum game can be rewritten as a minimization problem over some martingale measures with a payoff given by the solution of a backward stochastic differential equation

Racial and Gender Wage Differentials in South Africa: What can Cohort Data tell?

Three subsequent years of the October Household Survey data are used to construct a synthetic panel. Preparing cross sectional data that way allows to better utilise individual information and to address temporal developments also in the absence of genuine panel data. This paper focuses on gender and race specific cohort wages. Average earnings of birth cohorts of African and White workers employed full-time in formal sector jobs are followed over time and wage differentials as well as the mobility of cohort wages are studied in detail. A decomposition of African cohort wages into age, cohort, and year effects gives information about the existence of cohort effects. Results suggest that especially for African women such generational trends may differ from the theoretical expectation. However, to arrive at assured results a greater number of periods is needed

Aspects of the Mass Distribution of Interstellar Dust Grains in the Solar System from In-Situ Measurements

The in-situ detection of interstellar dust grains in the Solar System by the dust instruments on-board the Ulysses and Galileo spacecraft as well as the recent measurements of hyperbolic radar meteors give information on the properties of the interstellar solid particle population in the solar vicinity. Especially the distribution of grain masses is indicative of growth and destruction mechanisms that govern the grain evolution in the interstellar medium. The mass of an impacting dust grain is derived from its impact velocity and the amount of plasma generated by the impact. Because the initial velocity and the dynamics of interstellar particles in the Solar System are well known, we use an approximated theoretical instead of the measured impact velocity to derive the mass of interstellar grains from the Ulysses and Galileo in-situ data. The revised mass distributions are steeper and thus contain less large grains than the ones that use measured impact velocities, but large grains still contribute significantly to the overall mass of the detected grains. The flux of interstellar grains with masses $> 10^{-14} {\rm kg}$ is determined to be $1\cdot 10^{-6} {\rm m}^{-2} {\rm s}^{-1}$. The comparison of radar data with the extrapolation of the Ulysses and Galileo mass distribution indicates that the very large ($m > 10^{-10} {\rm kg}$) hyperbolic meteoroids detected by the radar are not kinematically related to the interstellar dust population detected by the spacecraft.Comment: 14 pages, 11 figures, to appear in JG

Racial and gender wage differentials in South Africa: What can cohort data tell?

High poverty rates as well as a very unequal distribution of income and wealth are distinctive features of post Apartheid South Africa. Studies analysing the extent of income inequality show that since the end of Apartheid the distribution of income has at best not changed at all, but depending on the measure, might also have worsened in the last decade. The data used in most of these studies are repeated cross sections, allowing a snapshot of the extent of income inequality at several points in time. Analysing temporal changes at an individual level is not possible. This paper proceeds differently. By using subsequent waves of the October Household Surveys and Labour Force Surveys a synthetic panel will be constructed. Preparing cross sectional data that way allows us to better utilise individual information and to address temporal developments also in the absence of genuine panel data. The paper focuses on gender and population group specific cohort wages to get a more detailed description of wage inequality. Average earnings of birth cohorts of African and White workers employed full-time in formal sector jobs are followed over time and wage differentials as well as the mobility of cohort wages are studied in detail. A decomposition of African cohort wages into age, cohort, and year effects gives information about the existence of cohort effects. Results suggest that especially for young African women such generational trends may differ from the theoretical expectation. --cohort data,wage differentials,generational trends

Zero-sum stopping games with asymmetric information

We study a model of two-player, zero-sum, stopping games with asymmetric information. We assume that the payoff depends on two continuous-time Markov chains (X, Y), where X is only observed by player 1 and Y only by player 2, implying that the players have access to stopping times with respect to different filtrations. We show the existence of a value in mixed stopping times and provide a variational characterization for the value as a function of the initial distribution of the Markov chains. We also prove a verification theorem for optimal stopping rules which allows to construct optimal stopping times. Finally we use our results to solve explicitly two generic examples

Growth, Income Distribution, And well-Being In Transition Countries

In this paper we use several well-being measures that combine average income with a measure of inequality to undertake international and intertemporal well-being comparisons in transition countries. Our well-being measures drastically change the impression of levels and changes in well-being from a traditional reliance on income measures. They also significantly affect the ranking of countries, when compared to rankings based on real incomes. Due to low inequality and moderate income levels, socialist countries enjoyed relatively high levels of economic well-being. In the transition process, rising inequality and falling incomes have led to a dramatic decline in well-being in many transition countries, and a corresponding worsening in rank when compared to other countries. There is great variance in the income and inequality performance of transition countries. We find a close correlation between income losses and inequality increases suggesting the ability of appropriate policies to reduce the income losses and reduce rising inequality. While the political dimension of transformation remains largely successful, our indicators suggest that most transition countries have yet to reach the level of economic well-being enjoyed in the late 1980s

Techniques for Galactic Dust Measurements in the Heliosphere

Galactic interstellar dust (ISD) is the major ingredient in planetary formation. However, information on this important material has been extremely limited. Recently the Ulysses dust detector has identified and measured interstellar dust outside 1.8~AU from the Sun at ecliptic latitudes above $50^{\circ}$. Inside this distance it could not reliably distinguish interstellar from interplanetary dust. Modeling the Ulysses data suggests that up to 30 % of dust flux with masses above $10^{-16}\rm kg$ at 1~AU is of interstellar origin. From the Hiten satellite in high eccentric orbit about the Earth there are indications that ISD indeed reaches the Earth's orbit. Two new missions carrying dust detectors, Cassini and Stardust, will greatly increase our observational knowledge. In this paper we briefly review instruments used on these missions and compare their capabilities. The Stardust mission [{\em Brownlee et al.}, 1996] will analyze the local interstellar dust population by an in-situ chemical analyzer and collect ISD between 2 and 3~AU from the Sun. The dust analyzer on the Cassini mission will determine the interstellar dust flux outside Venus' orbit and will provide also some compositional information. Techniques to identify the ISD flux levels at 1~AU are described that can quantify the interstellar dust flux in high-Earth orbit (outside the debris belts) and provide chemical composition information of galactic dust.Comment: Accepted for Journal of Geophysical Research, 6 figures, Late