New approach to diffraction pattern calculation

1993 ◽  
Vol 43 (1-4) ◽  
pp. 67-72
Author(s):  
J. Wolny ◽  
L. Pytlik
Keyword(s):  
Diffraction Pattern ◽  
New Approach

Quantitative XRD Analysis by Partial Least Squares Application in a Commercial Product

1991 ◽  
Vol 35 (A) ◽  
pp. 117-126
Author(s):  
Arthur G. Mateos
Keyword(s):  
Data Compression ◽  
Least Squares ◽  
Diffraction Pattern ◽  
Partial Least Squares ◽  
Latent Variables ◽  
Xrd Analysis ◽  
Commercial Product ◽  
Calibration Model ◽  
New Approach ◽  
Data Points

AbstractA new approach to quantitative XRD by Partial Least Squares (PLS) used region(s) or the entirety of the diffraction pattern of calibration standards (also called a training set) in the model. The basic concept of this approach states that the information in many observed variables, expressed as matrix I = (i1, i2 … , ik,) is concentrated onto a few underlying latent variables, called factors, by the process of data compression. In XRD, the data points of the diffraction pattern are compressed to few factors T, computed according to their ability to explain the variation in the diffraction pattern or matrix I. The procedure incorporates into the model that part of I that is correlated to C concentrations. Data compression preserves the redundancy between variables due to collinearity and stabilizies the predictions against noise in I. The resulting calibration model allows for detection of outliers. Another important effect of data reduction is the ability to analyze muticomponent systems even when lines of the components are overlapped, Examples of quantitative analysis by PLS are demonstrated in the analysis of a commercial product.

scholarly journals Shift-field refinement of macromolecular atomic models

2020 ◽  
Vol 76 (12) ◽  
pp. 1192-1200
Author(s):  
K. Cowtan ◽  
S. Metcalfe ◽  
P. Bond
Keyword(s):  
Diffraction Pattern ◽  
Crystallographic Structure ◽  
Model Parameters ◽  
Molecular Replacement ◽  
Macromolecular Crystallography ◽  
Initial Model ◽  
New Approach ◽  
Structure Solution ◽  
Uncertainty Parameters ◽  
Key Parameter

The aim of crystallographic structure solution is typically to determine an atomic model which accurately accounts for an observed diffraction pattern. A key step in this process is the refinement of the parameters of an initial model, which is most often determined by molecular replacement using another structure which is broadly similar to the structure of interest. In macromolecular crystallography, the resolution of the data is typically insufficient to determine the positional and uncertainty parameters for each individual atom, and so stereochemical information is used to supplement the observational data. Here, a new approach to refinement is evaluated in which a `shift field' is determined which describes changes to model parameters affecting whole regions of the model rather than individual atoms only, with the size of the affected region being a key parameter of the calculation which can be changed in accordance with the resolution of the data. It is demonstrated that this approach can improve the radius of convergence of the refinement calculation while also dramatically reducing the calculation time.

Some further considerations in powder diffraction pattern indexing with the dichotomy method

2014 ◽  
Vol 29 (S2) ◽  
pp. S7-S12 ◽  
Author(s):  
Daniel Louër ◽  
Ali Boultif
Keyword(s):  
Computer Program ◽  
Diffraction Pattern ◽  
Powder Diffraction ◽  
Input Data ◽  
Zero Point ◽  
New Approach ◽  
Detailed Review

Some improvements have been introduced in the current computer program for powder diffraction pattern indexing using the dichotomy algorithm. The resulting version, DICVOL14, includes optimizations and extension of scanning limits for triclinic cases, a detailed review of the input data from the indexing solutions, cell centering tests and a new approach for zero-point offset evaluation. The performance of the new version is illustrated with many examples, such as triclinic cases with long axes and dominant zones. Some important parameters in pattern indexing based on the dichotomy algorithm are commented upon, e.g. the precision of data and spurious lines.

scholarly journals High-throughput powder diffraction. I. A new approach to qualitative and quantitative powder diffraction pattern analysis using full pattern profiles

2004 ◽  
Vol 37 (2) ◽  
pp. 231-242 ◽  
Author(s):  
Christopher J. Gilmore ◽  
Gordon Barr ◽  
Jonathan Paisley
Keyword(s):  
Diffraction Pattern ◽  
Powder Diffraction ◽  
High Throughput ◽  
Pattern Analysis ◽  
Statistical Tests ◽  
Integrated Approach ◽  
Data Sets ◽  
New Approach ◽  
Qualitative And Quantitative ◽  
Value Decomposition

A new integrated approach to full powder diffraction pattern analysis is described. This new approach incorporates wavelet-based data pre-processing, non-parametric statistical tests for full-pattern matching, and singular value decomposition to extract quantitative phase information from mixtures. Every measured data point is used in both qualitative and quantitative analyses. The success of this new integrated approach is demonstrated through examples using several test data sets. The methods are incorporated within the commercial software programSNAP-1D, and can be extended to high-throughput powder diffraction experiments.

New Approach to Improve X-Ray Diffraction Pattern of Protein Crystal Using UV-Laser Ablative Processing

2004 ◽  
Vol 43 (No. 2B) ◽  
pp. L297-L299 ◽  
Author(s):  
Hiroshi Kitano ◽  
Hiroaki Adachi ◽  
Atsutoshi Murakami ◽  
Hiroyoshi Matsumura ◽  
Kazufumi Takano ◽  
...  
Keyword(s):  
Diffraction Pattern ◽  
Protein Crystal ◽  
Uv Laser ◽  
X Ray Diffraction ◽  
New Approach ◽  
X Ray

The O–C diagrams of minor planets − a new approach to modelling the rotation

1999 ◽  
Vol 173 ◽  
pp. 185-188
Author(s):  
Gy. Szabó ◽  
K. Sárneczky ◽  
L.L. Kiss
Keyword(s):  
Error Analysis ◽  
Time Dependence ◽  
Theoretical Work ◽  
Minor Planet ◽  
Minor Planets ◽  
New Approach ◽  
Preliminary Results ◽  
Ccd Observations

AbstractA widely used tool in studying quasi-monoperiodic processes is the O–C diagram. This paper deals with the application of this diagram in minor planet studies. The main difference between our approach and the classical O–C diagram is that we transform the epoch (=time) dependence into the geocentric longitude domain. We outline a rotation modelling using this modified O–C and illustrate the abilities with detailed error analysis. The primary assumption, that the monotonity and the shape of this diagram is (almost) independent of the geometry of the asteroids is discussed and tested. The monotonity enables an unambiguous distinction between the prograde and retrograde rotation, thus the four-fold (or in some cases the two-fold) ambiguities can be avoided. This turned out to be the main advantage of the O–C examination. As an extension to the theoretical work, we present some preliminary results on 1727 Mette based on new CCD observations.

Analysis of electron-diffraction intensity profiles using a photodiode-array detection system

1983 ◽  
Vol 41 ◽  
pp. 322-323
Author(s):  
J. B. Warren
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Detection System ◽  
High Energy ◽  
Photographic Emulsion ◽  
Diffraction Intensity ◽  
Silicon Photodiode ◽  
Photodiode Array Detection ◽  
Analog To Digital ◽  
Photodiode Array

Electron diffraction intensity profiles have been used extensively in studies of polycrystalline and amorphous thin films. In previous work, diffraction intensity profiles were quantitized either by mechanically scanning the photographic emulsion with a densitometer or by using deflection coils to scan the diffraction pattern over a stationary detector. Such methods tend to be slow, and the intensities must still be converted from analog to digital form for quantitative analysis. The Instrumentation Division at Brookhaven has designed and constructed a electron diffractometer, based on a silicon photodiode array, that overcomes these disadvantages. The instrument is compact (Fig. 1), can be used with any unmodified electron microscope, and acquires the data in a form immediately accessible by microcomputer.Major components include a RETICON 1024 element photodiode array for the de tector, an Analog Devices MAS-1202 analog digital converter and a Digital Equipment LSI 11/2 microcomputer. The photodiode array cannot detect high energy electrons without damage so an f/1.4 lens is used to focus the phosphor screen image of the diffraction pattern on to the photodiode array.

Light Optical Diffraction Studies of Macromolecular Ultrastructure

1970 ◽  
Vol 28 ◽  
pp. 258-259
Author(s):  
Glen B. Haydon
Keyword(s):  
High Resolution ◽  
Diffraction Analysis ◽  
Diffraction Pattern ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
Electron Micrograph ◽  
Its Analysis ◽  
Resolution Electron ◽  
Diffraction Patterns

Analysis of light optical diffraction patterns produced by electron micrographs can easily lead to much nonsense. Such diffraction patterns are referred to as optical transforms and are compared with transforms produced by a variety of mathematical manipulations. In the use of light optical diffraction patterns to study periodicities in macromolecular ultrastructures, a number of potential pitfalls have been rediscovered. The limitations apply to the formation of the electron micrograph as well as its analysis.(1) The high resolution electron micrograph is itself a complex diffraction pattern resulting from the specimen, its stain, and its supporting substrate. Cowley and Moodie (Proc. Phys. Soc. B, LXX 497, 1957) demonstrated changing image patterns with changes in focus. Similar defocus images have been subjected to further light optical diffraction analysis.

Electron Diffraction Analysis of Microtwin Structures in Regrown (III) Silicon

1982 ◽  
Vol 40 ◽  
pp. 460-461
Author(s):  
P. Ling ◽  
R. Gronsky ◽  
J. Washburn
Keyword(s):  
Electron Diffraction ◽  
Ion Implantation ◽  
Diffraction Analysis ◽  
Diffraction Pattern ◽  
Direct Consequence ◽  
The Other ◽  
Electron Diffraction Analysis ◽  
Defect Microstructures ◽  
Ion Implanted

The defect microstructures of Si arising from ion implantation and subsequent regrowth for a (111) substrate have been found to be dominated by microtwins. Figure 1(a) is a typical diffraction pattern of annealed ion-implanted (111) Si showing two groups of extra diffraction spots; one at positions (m, n integers), the other at adjacent positions between <000> and <220>. The object of the present paper is to show that these extra reflections are a direct consequence of the microtwins in the material.

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