Ewald Sphere Iterative Refinement Algorithm for Single Particle Reconstructions

2007 ◽  
Vol 13 (S02) ◽  
Author(s):  
P Leong ◽  
ZH Zhou ◽  
G Jensen
Keyword(s):  
Single Particle ◽  
Iterative Refinement ◽  
Ewald Sphere ◽  
Refinement Algorithm

Double shear layer evolution on the non-uniform computational mesh

2021 ◽  
Author(s):  
Yu M. Kulikov ◽  
E. E. Son
Keyword(s):  
Shear Layer ◽  
Iterative Refinement ◽  
The Novel ◽  
Original Sequence ◽  
Double Shear ◽  
Computational Mesh ◽  
Mesh Resolution ◽  
Initial Vorticity ◽  
High Resolution Technique ◽  
Refinement Algorithm

Abstract This paper considers the canonical problem of a thin shear layer evolution at Reynolds number Re = 400000 using the novel Compact Accurately Boundary Adjusting high-Resolution Technique (CABARET). The study is focused on the effect of the specific mesh refinement in the high shear rate areas on the flow properties under the influence of the developing instability. The original sequence of computational meshes (256^2, 512^2, 1024^2, 2048^2 cells) is modified using an iterative refinement algorithm based on the hyperbolic tangent. The properties of the solutions obtained are discussed in terms of the initial momentum thickness and the initial vorticity thickness, viscous and dilatational dissipation rates and also integral enstrophy. The growth rate for the most unstable mode depending on the mesh resolution is considered. In conclusion the accuracy of calculated mesh functions is estimated via L1, L2, L∞ norms.

An Iterative Refinement Algorithm for the Minimum Branch Vertices Problem

2011 ◽  
pp. 421-433 ◽  
Author(s):  
Diego M. Silva ◽  
Ricardo M. A. Silva ◽  
Geraldo R. Mateus ◽  
José F. Gonçalves ◽  
Mauricio G. C. Resende ◽  
...  
Keyword(s):  
Iterative Refinement ◽  
Refinement Algorithm

Research on the Repeater Optimization Based on Voronoi Model

2012 ◽  
Vol 588-589 ◽  
pp. 802-805
Author(s):  
Ban Teng Liu ◽  
Xi Lin Hu ◽  
Zheng Yu Xu ◽  
Yao Lin Liu ◽  
You Rong Chen
Keyword(s):  
Cellular Networks ◽  
Voronoi Diagram ◽  
Iterative Refinement ◽  
Local Optimum ◽  
Limited Capacity ◽  
Circular Area ◽  
Absolute Minimum ◽  
Voronoi Regions ◽  
Refinement Algorithm ◽  
Better Than

This paper propose a two-tiered network in which lower-power users communicate with one another through repeaters, which amplify signals and retransmit them, have limited capacity, and may interfere with one another if their transmitter frequencies are close and they share the same private-line tone. Motivated by cellular networks, this paper gives a naive solution where the number of repeaters and their positions can be obtained analytically. In a circular area with radius 40 miles, 12 repeaters can accommodate 1,000 simultaneous users. This paper further propose an iterative refinement algorithm consisting of three fundamental modules that draw the Voronoi diagram, determine the centers of the circumscribed circles of the Voronoi regions, and escape the local optimum by using external optimization. The algorithm obtains a solution with 11 repeaters, which we prove to be the absolute minimum. For 10,000 users, it uses 104 repeaters, better than the naive solution's 108.

scholarly journals ACCURATE OPTICAL TARGET POSE DETERMINATION FOR APPLICATIONS IN AERIAL PHOTOGRAMMETRY

2016 ◽  
Vol III-3 ◽  
pp. 257-262 ◽  
Author(s):  
D. A. Cucci
Keyword(s):  
Target Position ◽  
Iterative Refinement ◽  
Target Size ◽  
Geometric Invariant ◽  
Pose Determination ◽  
Aerial Photogrammetry ◽  
Circle Center ◽  
Position And Orientation ◽  
Orientation Determination ◽  
Refinement Algorithm

We propose a new design for an optical coded target based on concentric circles and a position and orientation determination algorithm optimized for high distances compared to the target size. If two ellipses are fitted on the edge pixels corresponding to the outer and inner circles, quasi-analytical methods are known to obtain the coordinates of the projection of the circles center. We show the limits of these methods for quasi-frontal target orientations and in presence of noise and we propose an iterative refinement algorithm based on a geometric invariant. Next, we introduce a closed form, computationally inexpensive, solution to obtain the target position and orientation given the projected circle center and the parameters of the outer circle projection. The viability of the approach is demonstrated based on aerial pictures taken by an UAV from elevations between 10 to 100 m. We obtain a distance RMS below 0.25 % under 50 m and below 1 % under 100 m with a target size of 90 cm, part of which is a deterministic bias introduced by image exposure.

scholarly journals Defocus-dependent Thon-ring fading

2020 ◽  
Author(s):  
Robert M. Glaeser ◽  
Wim J.H. Hagen ◽  
Bong-Gyoon Han ◽  
Richard Henderson ◽  
Greg McMullan ◽  
...  
Keyword(s):  
Structural Biology ◽  
Single Particle ◽  
Electron Beams ◽  
Spatial Coherence ◽  
Field Of View ◽  
Electron Cryomicroscopy ◽  
Data Collection Strategy ◽  
Clear Explanation ◽  
Ewald Sphere ◽  
Very High

ABSTRACTThe brightness of modern Schottky field-emission guns can produce electron beams that have very high spatial coherence, especially for the weak-illumination conditions that are used for single-particle electron cryo-microscopy in structural biology. Even so, many users have observed defocus-dependent Thon-ring fading that has led them to restrict their data collection strategy to imaging with relatively small defocus values. In this paper, we reproduce the observation of defocus-dependent Thon-ring fading and produce a quantitative analysis and clear explanation of its causes. We demonstrate that a major cause is the delocalization of high-resolution Fourier components outside the field of view of the camera. We also show that it is important to make a correction for linear magnification anisotropy, even if it is quite small, before circular averaging of the Thon rings, as is also true before merging data from particles in many orientations. Under the conditions used in this paper, which are typical of those used in single-particle electron cryomicroscopy, fading of the Thon rings due to source coherence is negligible. The principal conclusion is that much higher values of defocus can be used than is currently thought to be possible. This increased understanding should give electron microscopists the confidence to use higher amounts of defocus to allow, for example, better visibility of their particles and Ewald sphere correction.

scholarly journals ACCURATE OPTICAL TARGET POSE DETERMINATION FOR APPLICATIONS IN AERIAL PHOTOGRAMMETRY

2016 ◽  
Vol III-3 ◽  
pp. 257-262 ◽  
Author(s):  
D. A. Cucci
Keyword(s):  
Target Position ◽  
Iterative Refinement ◽  
Target Size ◽  
Geometric Invariant ◽  
Pose Determination ◽  
Aerial Photogrammetry ◽  
Circle Center ◽  
Position And Orientation ◽  
Orientation Determination ◽  
Refinement Algorithm

We propose a new design for an optical coded target based on concentric circles and a position and orientation determination algorithm optimized for high distances compared to the target size. If two ellipses are fitted on the edge pixels corresponding to the outer and inner circles, quasi-analytical methods are known to obtain the coordinates of the projection of the circles center. We show the limits of these methods for quasi-frontal target orientations and in presence of noise and we propose an iterative refinement algorithm based on a geometric invariant. Next, we introduce a closed form, computationally inexpensive, solution to obtain the target position and orientation given the projected circle center and the parameters of the outer circle projection. The viability of the approach is demonstrated based on aerial pictures taken by an UAV from elevations between 10 to 100 m. We obtain a distance RMS below 0.25 % under 50 m and below 1 % under 100 m with a target size of 90 cm, part of which is a deterministic bias introduced by image exposure.

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