Modeling and removal of optical ghosts in the PROBA-3/ASPIICS externally occulted solar coronagraph

Context: ASPIICS is a novel externally occulted solar coronagraph, which will be launched onboard the PROBA-3 mission of the European Space Agency. The external occulter will be placed on the first satellite approximately 150 m ahead of the second satellite that will carry an optical instrument. During 6 hours per orbit, the satellites will fly in a precise formation, constituting a giant externally occulted coronagraph. Large distance between the external occulter and the primary objective will allow observations of the white-light solar corona starting from extremely low heights 1.1RSun. Aims: To analyze influence of optical ghost images formed inside the telescope and develop an algorithm for their removal. Methods: We implement the optical layout of ASPIICS in Zemax and study the ghost behaviour in sequential and non-sequential regimes. We identify sources of the ghost contributions and analyze their geometrical behaviour. Finally we develop a mathematical model and software to calculate ghost images for any given input image. Results: We show that ghost light can be important in the outer part of the field of view, where the coronal signal is weak, since the energy of bright inner corona is redistributed to the outer corona. However the model allows to remove the ghost contribution. Due to a large distance between the external occulter and the primary objective, the primary objective does not produce a significant ghost. The use of the Lyot spot in ASPIICS is not necessary.Comment: 14 pages, 13 figure

An analysis of reconnection dynamics in an eruptive flare model

This dissertation develops a one-dimensional, analytic model for current sheets that form during solar flares. The model uses a method developed by B. V. Somov & V. S. Titov for Petschek-type reconnection. The first part of this dissertation provides a detailed analysis of the Somov-Titov model, its assumptions, strengths and weaknesses. We consider the role of both the diffusion region and nonuniform resistivity in the generation of Petschek-type solutions. The second part of this dissertation extends the averaging method to the dynamics of an asymmetric current sheet during a solar flare. We determine the location of the x-line and the distribution of incoming Poynting flux into upward and downward directed reconnection jets. We find that, except at the very beginning of a flare when the current sheet is most symmetric, the x-line is generally located near the lower tip of the sheet. We predict that it should be low enough in the corona to be observed by X-ray and EUV telescopes. We find that in most cases the majority of incoming flux exits the current sheet through the upward jet, in contrast to previous studies that assumed as much as 50% of the incoming flux is directed into the downward jet and flare ribbons. In the third part, we integrate thermal conduction into the Somov-Titov framework using a slow-shock model that includes conduction, and allows us to describe the thermal halo that surrounds the current sheet because of heat flow across the current sheet boundary. We find that thermal conduction has a significant effect on the fast-mode mach number of the reconnection outflow, producing mach numbers as high as 7 for solar-flare conditions, three times greater than previously calculated. We conclude that these termination shocks are considerably more efficient at producing particle acceleration than previously thought since the efficiency of particle acceleration at shocks increases dramatically with Mach number. We compare this model with numerical simulations by T. Yokoyama & K. Shibata and find good agreement

Optical investigation of a hybrid system of plasmonic structures and semiconductor quantum dots

Next generation integrated nanophotonic devices must fabricate large numbers of nanoscaled light coupling structures onto a single wafer: emitters such as quantum dots, resonators such as nanocavities and plasmonic nanoparticles, photonic crystal and nano-plasmonic waveguides, among others. Before precision planning and engi- neering will be possible a thorough understanding of the interaction between these structures must be documented. We present in this work an investigation of the interaction between quantum dots and plasmonic structures in the weak coupling regime. We found that surface plasmon supporting silver structures placed about 100nm from InGaAs quantum dots enabled an all optical polarization dependent switching mechanism between different exciton charge states when exciting above the band gap energy of the encapsulating GaAs. Furthermore, when exciting below the band gap of GaAs, we found a reduction in the photoluminescence intensity due to the launching of surface plasmon polaritons (SPPs) on the silver surfaces

Yield and chemical composition of soybeans as affected by Molybdenum and lime

In 1975 and 1976, two experiments involving Molybdenum (Mo) and soybean production were conducted in Tennessee on Collins silt loam. One experiment was a Mo source study which consisted of treatments of a check with no Mo fertilizer or lime, 280 kg/ha of lime banded in the row and no Mo, 35 g/ha of Mo applied as a slurry seed treatment. Mo plus Captan applied to the seed as a powder in the hopper box at planting time, and 6.7 metric tons/ha of lime broadcast. The other experiment was a Mo rate study which consisted of slurry seed treatments of Mo at the rates of 0, 7, 14, 21, 28, and 35 g/ha. In 1977, a separate study of lime and Mo rates was conducted on Loring silt loam using two varieties of soybeans, Essex and Bragg. The lime was applied at three rates to produce three soil pH levels with average pH values near 5.2, 5.9, and 6.5. The Mo rates were 0, 200, and 800 g/ha. The objective of this research was to determine the effects of the selected rates of lime and the selected rates and sources of Mo on the availability of soil Mo and the yield and chemical composition of soybeans. The data from the two earlier experiments consisted of leaf Mo and N concentrations and soybean yields, while the data of the second consisted of these variables plus leaf Mn concentrations, available soil Mo and exchangeable soil Mn concentrations, and soil pH values. The data from the Mo source study revealed that in both years, only the broadcast lime and the slurry seed treatments produced higher leaf N values than the check, but were not different from each other at the 0.05 probability level. With regard to soybean yield, all of the Mo sources tested, with the exception of the banded lime treatment in 1975, produced higher yields than the check, with the slurry seed treatments being responsible for the highest yields in both years. The Mo rate study revealed that in 1975, only the 21 and 35 g/ha Mo rates resulted in leaf Mo values that were higher than the check. It was also found that all of the rates tested in 1975 produced higher leaf N concentrations than the check, with the 14, 28, and 35 g/ha rates yielding the highest values, In both years, all Mo rates produced higher soybean yields than the check. Both varieties from the 1977 lime and Mo rate study revealed that of the variables tested, only the lime treatments produced differences. With the Essex variety, the highest lime rate produced the largest leaf N, soil Mo, and soil pH values and the lowest leaf and soil Mn values. With regard to the Essex soybean yields, all lime rates produced increases in soybean yields over the no lime rate. With the Bragg variety, the highest lime rate resulted in higher leaf N and soil pH values and lower leaf and soil Mn values than were produced by the zero and medium lime rates. An attempt was also made to correlate plant Mo and N concentrations with soybean yields. Results of these experiments indicate that the slurry seed application of Mo at any of the rates tested increased soybean yields on some unlimed acid soils in Tennessee. It was concluded that soybean yields responded little to soil applied Mo where lime was also added. In addition, leaf content of Mo was found to be an inaccurate indicator of the Mo needs of soybeans

Fact Checking and Information in the Age of Covid

The Covid‐19 pandemic has revealed and accelerated an information crisis as well as a health one. What we discover about Covid 19, how it spreads, to whom and why and how best to mitigate it—all depend on information. The essays in this special section, which this article introduces, explore the importance of information and the fundamental role of fact checkers in understanding how information flows, why mistakes are made, and how to counteract them. Fact checking as an idea and a practice emerged in the early twenty‐first century, developed as a positive beacon to counteract a growing sense that information could no longer be trusted. Now, more than a decade after its creation, fact checking sits within a far more complex and chaotic media context, and its expertise and understanding has never been so important. We need to understand what fact checkers do because they are grappling with how to tether us to reality