A highly miniaturized electron and ion energy spectrometer prototype for the rapid analysis of space plasmas.

MEMS (Micro Electro-Mechanical Systems) plasma analyzers are a promising possibility for future space missions but conventional instrument designs are not necessarily well suited to micro-fabrication. Here, a candidate design for a MEMS-based instrument has been prototyped using electron-discharge machining. The device features 10 electrostatic analyzers that, with a single voltage applied to it, allow five different energies of electron and five different energies of positive ion to be simultaneously sampled. It has been simulated using SIMION and the electron response characteristics tested in an instrument calibration chamber. Small deviations found in the electrode spacing of the as-built prototype were found to have some effect on the electron response characteristics but do not significantly impede its performance

A Centered Index of Spatial Concentration: Axiomatic Approach with an Application to Population and Capital Cities

We construct an axiomatic index of spatial concentration around a center or capital point of interest, a concept with wide applicability from urban economics, economic geography and trade, to political economy and industrial organization. We propose basic axioms (decomposability and monotonicity) and refinement axioms (order preservation, convexity, and local monotonicity) for how the index should respond to changes in the underlying distribution. We obtain a unique class of functions satisfying all these properties, defined over any n-dimensional Euclidian space: the sum of a decreasing, isoelastic function of individual distances to the capital point of interest, with specific boundaries for the elasticity coefficient that depend on n. We apply our index to measure the concentration of population around capital cities across countries and US states, and also in US metropolitan areas. We show its advantages over alternative measures, and explore its correlations with many economic and political variables of interest.

A Centered Index of Spatial Concentration : Axiomatic Approach with an Application to Population and Capital Cities

We construct an axiomatic index of spatial concentration around a center or capital point of interest, a concept with wide applicability from urban economics, economic geography and trade, to political economy and industrial organization. We propose basic axioms (decomposability and monotonicity) and renement axioms (order preservation, convexity, and local monotonicity) for how the index should respond to changes in the underlying distribution. We obtain a unique class of functions satisfying all these properties, defined over any n-dimensional Euclidian space : the sum of a decreasing, isoelastic function of individual distances to the capital point of interest, with specifc boundaries for the elasticity coecient that depend on n. We apply our index to measure the concentration of population around capital cities across countries and US states, and also in US metropolitan areas. We show its advantages over alternative measures, and explore its correlations with many economic and political variables of interest.Spatial Concentration, Population Concentration, Capital Cities, Gravity, CRRA, Harmonic Functions, Axiomatics

A Centered Index of Spatial Concentration: Axiomatic Approach with an Application to Population and Capital Cities

We construct an axiomatic index of spatial concentration around a center or capital point of interest, a concept with wide applicability from urban economics, economic geography and trade, to political economy and industrial organization. We propose basic axioms (decomposability and monotonicity) and refinement axioms (order preservation, convexity, and local monotonicity) for how the index should respond to changes in the underlying distribution. We obtain a unique class of functions satisfying all these properties, defined over any n-dimensional Euclidian space: the sum of a decreasing, isoelastic function of individual distances to the capital point of interest, with specific boundaries for the elasticity coefficient that depend on n. We apply our index to measure the concentration of population around capital cities across countries and US states, and also in US metropolitan areas. We show its advantages over alternative measures, and explore its correlations with many economic and political variables of interest.Spatial Concentration, Population Concentration, Capital Cities, Gravity, CRRA, Harmonic Functions, Axiomatics.

Instability and Incentives for Corruption

We investigate the relationship between corruption and political stability, from both theoretical and empirical perspectives. We propose a model of incumbent behavior that features the interplay of two effects : A horizon effect, whereby greater instability leads the incumbent to embezzle more during his short window of opportunity; and a demand effect, by which the private sector is more willing to bribe stable incumbents. The horizon effect dominates at low levels of stability, since firms are unwilling to pay high bribes and unstable incumbents have strong incentives to embezzle, whereas the demand effect gains salience in more stable regimes. Together, these two effects generate a nonmonotonic, U-shaped relationship between total corruption and stability. On the empirical side, we find a robust U-shaped pattern between country indices of corruption perception and various measures of incumbent stability, including historically-observed average tenures of chief executives and governing parties : Regimes that are very stable or very unstable display higher levels of corruption when compared to those in an intermediate range of stability. These results suggest that minimizing corruption may require an electoral system that features some reelection incentives, but with an eventual term limit.corruption, Political Stability, Incumbent Tenure, Term Limits

Phase diagram of a model for a binary mixture of nematic molecules on a Bethe lattice

We investigate the phase diagram of a discrete version of the Maier-Saupe model with the inclusion of additional degrees of freedom to mimic a distribution of rodlike and disklike molecules. Solutions of this problem on a Bethe lattice come from the analysis of the fixed points of a set of nonlinear recursion relations. Besides the fixed points associated with isotropic and uniaxial nematic structures, there is also a fixed point associated with a biaxial nematic structure. Due to the existence of large overlaps of the stability regions, we resorted to a scheme to calculate the free energy of these structures deep in the interior of a large Cayley tree. Both thermodynamic and dynamic-stability analyses rule out the presence of a biaxial phase, in qualitative agreement with previous mean-field results

Toward in vitro fertilization in Brachiaria spp.

Brachiaria are forage grasses widely cultivated in tropical areas. In vitro pollination was applied to accessions of Brachiaria spp. by placing pollen of non-dehiscent anthers on a solid medium near isolated ovaries. Viability and in vitro germination were tested in order to establish good conditions for pollen development. Comparing sexual to apomictic plants, apomictic pollen has more abortion after meiosis during the microspore stage and a lower viability and, of both types, only some plants have sufficient germination in a high sugar concentration. Using in vitro pollination with the sexual plant, the pollen tube penetrates into the nucellus and micropyle, but the embryo sac degenerates and collapses. In the apomictic B. decumbens, in vitro pollination leads to the transfer of the sperm nuclei into the egg cell and the central cell. The results are discussed according to normal fertilization and barriers in sexual and apomictic plants

Monetary policy as a source of uncertainty

This paper proposes a model in which control variations induce an increase in the uncertainty of the system. The aim of our paper is to provide a stochastic theoretical model that can be used to explain under which uncertainty conditions monetary policy rules should be less or more aggressive, or, simply, applied or not.