An FPGA Architecture for Extracting Real-Time Zernike Coefficients from Measured Phase Gradients

Zernike modes are commonly used in adaptive optics systems to represent optical wavefronts. However, real-time calculation of Zernike modes is time consuming due to two factors: the large factorial components in the radial polynomials used to define them and the large inverse matrix calculation needed for the linear fit. This paper presents an efficient parallel method for calculating Zernike coefficients from phase gradients produced by a Shack-Hartman sensor and its real-time implementation using an FPGA by pre-calculation and storage of subsections of the large inverse matrix. The architecture exploits symmetries within the Zernike modes to achieve a significant reduction in memory requirements and a speed-up of 2.9 when compared to published results utilising a 2D-FFT method for a grid size of 8×8. Analysis of processor element internal word length requirements show that 24-bit precision in precalculated values of the Zernike mode partial derivatives ensures less than 0.5% error per Zernike coefficient and an overall error of <1%. The design has been synthesized on a Xilinx Spartan-6 XC6SLX45 FPGA. The resource utilisation on this device is <3% of slice registers, <15% of slice LUTs, and approximately 48% of available DSP blocks independent of the Shack-Hartmann grid size. Block RAM usage is <16% for Shack-Hartmann grid sizes up to 32×32

Reasons for regional integration agreements

Regional integration agreements are commonplace in the world today. In 1996 there were 88 such agreements worldwide, covering a variety of forms from declarations of intent to unilateral preferential trade agreements, free trade treaties, customs unions, and the common market with its freedom of movement for labour and capital. Which factors have contributed to the great popularity of regional integration agreements

Betreute Praktika - Anforderungen an Praktikumslehrerinnen und -lehrer

Ziel des Projekts "Lernen im Praktikum" (vgl. Hascher & Moser, 1999; Moser & Hascher, 2000) war, die Lernprozesse im Praktikum während der Ausbildung am Sekundarlehramt der Universität Bern differenzieren und erklären zu können. Ein zentrales, wenn auch nicht überraschendes Ergebnis dabei war, dass die Betreuung durch die Praktikumslehrer/innen für die Lernprozesse von Studierenden sehr wichtig ist. Im nachfolgenden Beitrag werden nun die Rollen der Praktikumslehr- Personen und ihre Unterstützungsformen näher beleuchtet. Dazu wird sowohl auf die quantitative als auch die qualitative Studie, sowohl auf die Sicht der Studierenden als auch auf die Perspektive der Praktikumsleiter/innen Bezug genommen. Ebenso werden schwierige Aspekte der Betreuung im Praktikum diskutiert

Editorial

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The Effects of depth on microplastics distribution and ingestion by a biological indicator species: Mytilus galloprovincialis

Global plastic production rates are currently at the highest that they have ever been and are projected to continue to increase over the next 20 years. Models that have only accounted for surface plastics have severely underestimated actual plastic loads in the world’s oceans, largely due to the distribution of microplastics below the water’s surface. Despite being ingested by organisms at nearly every trophic level and observed in virtually every ocean environment, the complex nature of microplastics’ distribution patterns remains poorly understood. Recent studies have observed distinct depth profiles of microplastics, thereby implying differential bioavailability to biotic communities depending on their position in the water column. To date, depth profiles of microplastics have only been characterized in open ocean environments and gyres, and no study of depth profiles has directly, quantitatively linked vertical distribution of microplastics in the water column to ingestion by marine organisms. This study has aimed to further our understanding of microplastic depth profiles and the implications for biological communities by (1) determining the vertical distribution of microplastics in a stratified marine habitat in Puget Sound and (2) relating that distribution to ingested plastic loads in a biological indicator species at different depths. In both water samples and mussel samples taken from our study site in Totten Inlet, 99% of plastics found were filamentous. No distinct patterns of distribution were observed in either water samples or mussel samples from 0-4 m depths