Local Er(iii) environment in luminescent titanosilicates prepared from microporous precursorsElectronic supplementary information (ESI) available: Er LIII-edge k3-weighted EXAFS spectra and Fourier transforms. See http://www.rsc.org/suppdata/jm/b1/b107136j/

2002 ◽  
Vol 12 (4) ◽  
pp. 1162-1168 ◽  
Author(s):  
José P. Rainho ◽  
Martyn Pillinger ◽  
Luís D. Carlos ◽  
Sidney J. L. Ribeiro ◽  
Rui M. Almeida ◽  
...  
Keyword(s):  
Fourier Transforms ◽  
Supplementary Information ◽  
Exafs Spectra

ON THE NATURE OF NONSTRUCTURAL LOW-R PEAK IN FOURIER TRANSFORMS OF SOME EXAFS-SPECTRA

1986 ◽  
Vol 47 (C8) ◽  
pp. C8-83-C8-87 ◽  
Author(s):  
A. G. KOCHUR ◽  
A. M. NADOLINSKY ◽  
V. F. DEMEKHIN
Keyword(s):  
Fourier Transforms ◽  
Exafs Spectra

EXAFS Spectroscopy with Amorphous Transition Metal-Metalloid Alloys

1982 ◽  
Vol 37 (6) ◽  
pp. 572-580 ◽  
Author(s):  
Friedrich Schmückle ◽  
Peter Lamparter ◽  
Siegfried Steeb
Keyword(s):  
Local Structure ◽  
Thermal Effects ◽  
Amorphous Alloys ◽  
Fourier Transforms ◽  
Great Similarity ◽  
X Ray ◽  
Similar Chemical ◽  
Pure Metals ◽  
Co Alloys ◽  
Exafs Spectra

Abstract EXAFS measurements were performed with amorphous T80M20 (T=Fe,Co, Ni; M=B,P). For the interpretation of the EXAFS spectra it was necessary also to compare them with spectra obtained from crystalline specimes with known atomic arrangement and with similar chemical composition such as the alloys Fe2B, CO3B, Ni3B as well as Fe3P, CO3P, and Ni3P. As a radiation source the Ag-target of a rotating anode X-ray generator (6 kW) was used. The spectra were obtained using a flat LiF-(220) monochromator. The specimens were kept at 80 K and thus thermal effects could be reduced. The EXAFS spectra of the amorphous alloys and those of the corresponding crystalline compounds of the type T3M show among each other a relatively great similarity. The greatest similarity exists in the case of the Ni-and Co-alloys. The amorphous alloys based on iron however show larger discrepancies with respect to the corresponding crystalline ones, where the greatest deviation occurs with the compound Fe2B. The Fourier transforms show such similarities too. The EXAFS spectra of the crystalline elements Fe. Co, and Ni as well as their Fourier transforms evidently show differences compared to the amorphous specimens and to the T3M compounds.The similarities observed between the amorphous alloys and the corresponding crystalline specimens of the T3M-type together with their large discrepancies with respect to the pure metals led to the conclusion that the local structure in the amorphous alloys is in considerable accordance with that of the corresponding T3M-compound.

Computer processing of high-resolution images of periodic specimens

1986 ◽  
Vol 44 ◽  
pp. 2-5
Author(s):  
W. Chiu ◽  
M.F. Schmid ◽  
T.-W. Jeng
Keyword(s):  
High Resolution ◽  
Fourier Transforms ◽  
Complex Structure ◽  
Distribution Functions ◽  
Multiple Image ◽  
Cryo Electron Microscopy ◽  
Structure Factors ◽  
Unit Cells ◽  
High Resolution Images ◽  
Phase Probability Distribution

Cryo-electron microscopy has been developed to the point where one can image thin protein crystals to 3.5 Å resolution. In our study of the crotoxin complex crystal, we can confirm this structural resolution from optical diffractograms of the low dose images. To retrieve high resolution phases from images, we have to include as many unit cells as possible in order to detect the weak signals in the Fourier transforms of the image. Hayward and Stroud proposed to superimpose multiple image areas by combining phase probability distribution functions for each reflection. The reliability of their phase determination was evaluated in terms of a crystallographic “figure of merit”. Grant and co-workers used a different procedure to enhance the signals from multiple image areas by vector summation of the complex structure factors in reciprocal space.

The extended Fourier algorithm: Application in discrete optics and electron holography

1994 ◽  
Vol 52 ◽  
pp. 918-919
Author(s):  
E. Voelkl ◽  
L. F. Allard
Keyword(s):  
Fourier Transform ◽  
Fourier Transforms ◽  
Sampling Rate ◽  
Electron Holography ◽  
Optical Bench ◽  
Fourier Space ◽  
Ccd Cameras ◽  
Simulated Image ◽  
Initial Sampling ◽  
Fourier Algorithm

The conventional discrete Fourier transform can be extended to a discrete Extended Fourier transform (EFT). The EFT allows to work with discrete data in close analogy to the optical bench, where continuous data are processed. The EFT includes a capability to increase or decrease the resolution in Fourier space (thus the argument that CCD cameras with a higher number of pixels to increase the resolution in Fourier space is no longer valid). Fourier transforms may also be shifted with arbitrary increments, which is important in electron holography. Still, the analogy between the optical bench and discrete optics on a computer is limited by the Nyquist limit. In this abstract we discuss the capability with the EFT to change the initial sampling rate si of a recorded or simulated image to any other(final) sampling rate sf.

Observations of Frozen-Hydrated Microtubules

1990 ◽  
Vol 48 (1) ◽  
pp. 504-505
Author(s):  
D. Chrétien ◽  
D. Job ◽  
R.H. Wade
Keyword(s):  
Fourier Transforms ◽  
Structural Complexity ◽  
Image Contrast ◽  
Phase Behaviour ◽  
Experimental Conditions ◽  
Thin Sections ◽  
Surface Lattice ◽  
Cilia And Flagella ◽  
Outstanding Question

Microtubules are filamentary structures found in the cytoplasm of eukaryotic cells, where, together with actin and intermediate filaments, they form the components of the cytoskeleton. They have many functions and show various levels of structural complexity as witnessed by the singlet, doublet and triplet structures involved in the architecture of centrioles, basal bodies, cilia and flagella. The accepted microtubule model consists of a 25 nm diameter hollow tube with a wall made up of 13 paraxial protofilaments (pf). Each pf is a string of aligned tubulin dimers. Some results have suggested that the pfs follow a superhelix. To understand how microtubules function in the cell an accurate model of the surface lattice is one of the requirements. For example the 9x2 architecture of the axoneme will depend on the organisation of its component microtubules. We should also note that microtubules with different numbers of pfs have been observed in thin sections of cellular and of in-vitro material. An outstanding question is how does the surface lattice adjust to these different pf numbers?We have been using cryo-electron microscopy of frozen-hydrated samples to study in-vitro assembled microtubules. The experimental conditions are described in detail in this reference. The results obtained in conjunction with thin sections of similar specimens and with axoneme outer doublet fragments have already allowed us to characterise the image contrast of 13, 14 and 15 pf microtubules on the basis of the measured image widths, of the the image contrast symmetry and of the amplitude and phase behaviour along the equator in the computed Fourier transforms. The contrast variations along individual microtubule images can be interpreted in terms of the geometry of the microtubule surface lattice. We can extend these results and make some reasonable predictions about the probable surface lattices in the case of other pf numbers, see Table 1. Figure 1 shows observed images with which these predictions can be compared.

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