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

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

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,

Efficiency of New Ethanol Plants in the U.S. North-Central Region

Replaced with revised version of paper 07/29/09.Ethanol, Efficiency, DEA, Production Economics, Resource /Energy Economics and Policy,

Work distribution functions for hysteresis loops in a single-spin system

We compute the distribution of the work done in driving a single Ising spin with a time-dependent magnetic field. Using Glauber dynamics we perform Monte-Carlo simulations to find the work distributions at different driving rates. We find that in general the work-distributions are broad with a significant probability for processes with negative dissipated work. The special cases of slow and fast driving rates are studied analytically. We verify that various work fluctuation theorems corresponding to equilibrium initial states are satisfied while a steady state version is not.Comment: 9 pages, 15 figure

Whales, dolphins, and porpoises of the eastern North Pacific and adjacent Arctic waters: a guide to their identification

This is an identification guide for cetaceans (whales, dolphins, and porpoises), that was designed to assist laymen in identifying cetaceans encountered in eastern North Pacific and Arctic waters. It was intended for use by ongoing cetacean observer programs. This is a revision of an earlier guide with the same title published in 1972 by the Naval Undersa Center and the National Marine Fisheries Service. It includes sections on identifying cetaceans at sea as well as stranded animals on shore. Species accounts are divided by body size and presence or lack of a dorsal fin. Appendices include illustrations of tags on whales, dolphins, and porpoises, by Larry Hobbs; how to record data from observed cetaceans at sea and for stranded cetaceans; and a list of cetacean names in Japanese and Russian. (Document contains 245 pages - file takes considerable time to open

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,

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

Food Security and Poverty, Public Economics,