High dynamic range imaging with a single-mode pupil remapping system : a self-calibration algorithm for redundant interferometric arrays

The correction of the influence of phase corrugation in the pupil plane is a fundamental issue in achieving high dynamic range imaging. In this paper, we investigate an instrumental setup which consists in applying interferometric techniques on a single telescope, by filtering and dividing the pupil with an array of single-mode fibers. We developed a new algorithm, which makes use of the fact that we have a redundant interferometric array, to completely disentangle the astronomical object from the atmospheric perturbations (phase and scintillation). This self-calibrating algorithm can also be applied to any - diluted or not - redundant interferometric setup. On an 8 meter telescope observing at a wavelength of 630 nm, our simulations show that a single mode pupil remapping system could achieve, at a few resolution elements from the central star, a raw dynamic range up to 10^6; depending on the brightness of the source. The self calibration algorithm proved to be very efficient, allowing image reconstruction of faint sources (mag = 15) even though the signal-to-noise ratio of individual spatial frequencies are of the order of 0.1. We finally note that the instrument could be more sensitive by combining this setup with an adaptive optics system. The dynamic range would however be limited by the noise of the small, high frequency, displacements of the deformable mirror.Comment: 11 pages, 7 figures. Accepted for publication in MNRA

Effect of picosecond strain pulses on thin layers of the ferromagnetic semiconductor (Ga,Mn)(As,P)

The effect of picosecond acoustic strain pulses (ps-ASP) on a thin layer of (Ga,Mn)As co-doped with phosphorus was probed using magneto-optical Kerr effect (MOKE). A transient MOKE signal followed by low amplitude oscillations was evidenced, with a strong dependence on applied magnetic field, temperature and ps-ASP amplitude. Careful interferometric measurement of the layer's thickness variation induced by the ps-ASP allowed us to model very accurately the resulting signal, and interpret it as the strain modulated reflectivity (differing for $\sigma_{\pm}$ probe polarizations), independently from dynamic magnetization effects.Comment: 6 pages, 5 figure

TECHNOLOGICAL CHANGE AND WELFARE IN AN ECONOMY WITH DISTORTIONS

Traditional measures of the benefits of technological change use producer prices. Consumer-oriented measures are more appropriate but they require knowledge of price impacts. They may diverge in the presence of distortions. This paper shows that in general equilibrium they are interrelated differing by the price effect of the technological change.Demand and Price Analysis, Research and Development/Tech Change/Emerging Technologies, Research Methods/ Statistical Methods,

Have Price Policies Damaged LDC Agricultural Productivity?

This paper examines agricultural policies in 18 developing countries over the period 1961-1985. We measure productivity with both a nonparametric Malmquist index and a production function, confirming previous findings of declining agricultural productivity, but with sufficident inconsistencies as to raise concern about the adequacy of the methods. We nontehless find considerable support for the hypothesis that unfavorable price policies have damaged agricultural performance in these countries.Agricultural productivity, developing countries, price policies

FOOD STAMP PROGRAM IMPACT ON RESOURCE USE: TEXAS COMPARED WITH THE U.S., FISCAL YEAR 1974

Food Security and Poverty, Public Economics,

DYNAMIC PRICING OF GENETICALLY MODIFIED CROP TRAITS

This paper considers the time path of prices for crop traits such as herbicide resistance, specifically whether they conform to Coase's conjecture that monopoly prices can't be sustained on durables. While property rights determine whether such traits are durables, prices for RR soybeans and Bt corn are consistent with Coase.Crop Production/Industries,

INTERVENTIONS AND PRODUCTION SECTOR WASTE IN LDC AGRICULTURE

Recent studies have revealed that less developed countries (LDCs) have been taxing their agricultural sectors at rates of 40-50%. This study uses quantity-based general equilibrium measures of deadweight loss to evaluate the cost of these distortions in 18 of these countries. The Allais-Debreu loss measures indicate that from 7-16% of either output or of the agricultural resource base has been wasted due to the associated misallocation of agricultural inputs across these countries.Production Economics,

Dynamic pricing of Genetically Modified Crop Traits

The issue considered here is the retail pricing of patented crop traits such as Roundup Ready herbicide resistance or Bt insect resistance. Our concern is not with the price of the seeds in which the traits are embodied, but rather with the implicit or explicit price for the traits themselves. Intellectual property rights are now available for traits, and while monopoly pricing of them has received some limited consideration in theeconomics literature1, no one has yet examined the possible implications of the durability of these traits as a factor in determining such monopolists' pricing behavior.Coase, dynamic monopoly, traits.

INSTITUTIONS AND AGRICULTURAL PRODUCTIVITY IN SUB-SAHARA AFRICA

Agricultural productivity in 41 Sub-Saharan Africa (SSA) countries from 1960 to 1999 is examined by estimating a semi-nonparametric Fourier production frontier. Over the four decades the estimated rate of productivity change was 0.83% per year, although the average rate from 1985-99 was a strong 1.90% per year. Former UK colonies exhibited significantly higher productivity gains than others, while Liberia and countries that had been colonies of Portugal or Belgium exhibited net reductions in productivity. We measure a significant reduction in productivity during political conflicts and wars, and a significant increase in productivity among those countries with a measure of political rights and civil liberties.Institutional and Behavioral Economics, Productivity Analysis,

Institutions and Agricultural Productivity in Sub-Saharan Africa

Agricultural productivity in 41 Sub-Saharan Africa (SSA) countries from 1960 to 1999 is examined by estimating a semi-nonparametric Fourier production frontier. Over the four decades the estimated rate of productivity change was 0.83% per year, although the average rate from 1985-99 was a strong 1.90% per year. Former UK colonies exhibited significantly higher productivity gains than others, while Liberia and countries that had been colonies of Portugal or Belgium exhibited net reductions in productivity. We measure a significant reduction in productivity during political conflicts and wars, and a significant increase in productivity among those countries with higher levels of political rights and civil liberties.Sub-Saharan Africa, agricultural productivity, institutions, stochastic frontier, Fourier functional form.