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2 Janelia Publications

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    Grigorieff Lab
    08/28/15 | Evaluation of super-resolution performance of the K2 electron-counting camera using 2D crystals of aquaporin-0.
    Chiu P, Li X, Li Z, Beckett B, Brilot AF, Grigorieff N, Agard DA, Cheng Y, Walz T
    Journal of Structural Biology. 2015 Aug 28:. doi: 10.1016/j.jsb.2015.08.015

    The K2 Summit camera was initially the only commercially available direct electron detection camera that was optimized for high-speed counting of primary electrons and was also the only one that implemented centroiding so that the resolution of the camera can be extended beyond the Nyquist limit set by the physical pixel size. In this study, we used well-characterized two-dimensional crystals of the membrane protein aquaporin-0 to characterize the performance of the camera below and beyond the physical Nyquist limit and to measure the influence of electron dose rate on image amplitudes and phases.

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    Grigorieff Lab
    08/13/15 | CTFFIND4: Fast and accurate defocus estimation from electron micrographs.
    Rohou A, Grigorieff N
    Journal of Structural Biology. 2015 Aug 13;192(2):216-21. doi: 10.1016/j.jsb.2015.08.008

    CTFFIND is a widely-used program for the estimation of objective lens defocus parameters from transmission electron micrographs. Defocus parameters are estimated by fitting a model of the microscope's contrast transfer function (CTF) to an image's amplitude spectrum. Here we describe modifications to the algorithm which make it significantly faster and more suitable for use with images collected using modern technologies such as dose fractionation and phase plates. We show that this new version preserves the accuracy of the original algorithm while allowing for higher throughput. We also describe a measure of the quality of the fit as a function of spatial frequency and suggest this can be used to define the highest resolution at which CTF oscillations were successfully modeled.

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