Memory impairment in flowing suspensions. I. Some theoretical considerations

1978 ◽  
Vol 56 (22) ◽  
pp. 2815-2823 ◽  
Author(s):  
A. Okagawa ◽  
G. J. Ennis ◽  
S. G. Mason
Keyword(s):  
Numerical Calculation ◽  
Experimental Verification ◽  
Memory Impairment ◽  
Orientation Distribution ◽  
Newtonian Liquid ◽  
Initial Orientation ◽  
Initial State ◽  
Damped Oscillations ◽  
Orientation Distributions ◽  
Theoretical Considerations

When a suspension of nearly monodisperse rigid axisymmetric particles in a Newtonian liquid is sheared, the orientation distributions of the particle undergo damped oscillations of frequency twice that of the rotating particles. If the flow is stopped and then reversed, the oscillations regrow under certain restricted conditions until the initial state is fully restored: the system has perfect memory. Removing some of the restrictions causes imperfect recovery of the initial orientation distribution, so that when the flow is reversed cyclically back and forth, the orientation distribution eventually becomes time-independent: the system has lost all of its memory. A number of sources of memory impairment are considered theoretically, several of which are amenable to experimental verification and are illustrated by numerical calculation.

Texture Development in a Model Al-Li Alloy Subjected to Severe Plastic Deformation

2006 ◽  
Vol 114 ◽  
pp. 337-344 ◽  
Author(s):  
Bogusława Adamczyk-Cieślak ◽  
Jaroslaw Mizera ◽  
Krzysztof Jan Kurzydlowski
Keyword(s):  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Equal Channel Angular Extrusion ◽  
Orientation Distribution ◽  
X Ray Diffraction ◽  
Technological Parameters ◽  
Initial State ◽  
Texture Characteristic ◽  
X Ray ◽  
Ultrafine Grained

The texture of Al – 0.7 wt. % Li alloy processed by two different methods of severe plastic deformation (SPD) has been investigated by X-ray diffraction, and analyzed in terms of the orientation distribution function (ODF). It was found that severe plastic deformation by both Equal Channel Angular extrusion (ECAE) and Hydrostatic Extrusion (HE) resulted in an ultrafine grained structure in an Al – 0.7 wt. % Li alloy. The microstructure, grain shape and size, of materials produced by SPD strongly depend on the technological parameters and methods applied. The texture of the investigated alloy differed because of the different modes of deformation. In the initial state the alloy exhibited a very strong texture consisting of {111} fibre component. A similar fibrous texture characteristic was also found after HE whereas after the ECAE the initial texture was completely changed.

scholarly journals Tools for Visualizing and Analyzing Fourier Space Sampling in Cryo-EM

2020 ◽  
Author(s):  
Philip R. Baldwin ◽  
Dmitry Lyumkis
Keyword(s):  
Graphical User Interface ◽  
Signal To Noise Ratio ◽  
Orientation Distribution ◽  
Geometrical Factor ◽  
Fourier Space ◽  
Complete Understanding ◽  
Spherical Surfaces ◽  
Compensation Factor ◽  
Spectral Signal ◽  
Orientation Distributions

AbstractA complete understanding of how an orientation distribution contributes to a cryo-EM reconstruction remains lacking. It is necessary to begin critically assessing the set of views to gain an understanding of its effect on experimental reconstructions. Toward that end, we recently suggested that the type of orientation distribution may alter resolution measures in a systematic manner. We introduced the sampling compensation factor (SCF), which incorporates how the collection geometry might change the spectral signal-to-noise ratio (SSNR), irrespective of the other experimental aspects. We show here that knowledge of the sampling restricted to spherical surfaces of sufficiently large radii in Fourier space is equivalent to knowledge of the set of projection views. Moreover, the SCF geometrical factor may be calculated from one such surface. To aid cryo-EM researchers, we developed a graphical user interface (GUI) tool that evaluates experimental orientation distributions. The GUI returns plots of projection directions, sampling constrained to the surface of a sphere, the SCF value, the fraction of the empty region of Fourier space, and a histogram of the sampling values over the points on a sphere. Finally, a fixed tilt angle may be incorporated to determine how tilting the grid during collection may improve the distribution of views and Fourier space sampling. We advocate this simple conception of sampling and the use of such tools as a complement to the distribution of views to capture the different aspects of the effect of projection directions on cryo-EM reconstructions.

Reliability criteria in quantitative texture analysis with experimental and simulated orientation distributions

2005 ◽  
Vol 38 (4) ◽  
pp. 603-611 ◽  
Author(s):  
Daniel Chateigner
Keyword(s):  
Texture Analysis ◽  
Orientation Distribution ◽  
Point Of View ◽  
Real Sample ◽  
Experimental Point ◽  
Orientation Distributions ◽  
Counting Statistics ◽  
New Criterion

Quantitative texture analysis reliability factors are examined from an experimental point of view, using real-sample and modelled orientation distribution refinements. The classicalRPfactors of texture analysis are shown to depend on the texture strength, and their representation of the various textures is not homogeneous. The surface-weightedRPwhomologues exhibit lower texture strength dependency and better homogeneities, but still do not allow for comparison of refinements operated on samples with different textures. New factors,Rw, weighted by the counting statistics, show the lowest dependency and best homogeneity. FromRw1(Rw0) curves a new criterion is established, which allows the detection of poorly refined orientation distributions. This study highlights a unique entropy-to-texture index relationship, which also gives a new criterion for testing refinement reliability, and proposes two different ranges in which to apply the texture index and the entropy factors.

Memory impairment in flowing suspensions. II. Experimental results

1978 ◽  
Vol 56 (22) ◽  
pp. 2824-2832 ◽  
Author(s):  
G. J. Ennis ◽  
A. Okagawa ◽  
S. G. Mason
Keyword(s):  
Memory Loss ◽  
Orientation Distribution ◽  
Particle Orientation ◽  
Light Transmittance ◽  
Particle Interactions ◽  
Electrical Shock ◽  
Cyclic Shear ◽  
Rigid Rods ◽  
Gradual Loss ◽  
Orientation Distributions

Experiments on the reversibility of particle orientation distributions in suspensions of nearly monodisperse rigid rods and hardened red blood cells (HRBC) subjected to cyclic shearing are described.The orientation distributions of initially aligned rods measured by direct observation exhibited a gradual loss in memory as flow was reversed back and forth which was attributed mainly to non-reversible particle interactions. When an electric field was applied continuously during cyclic shear flow, the rate of memory loss was increased. However, if an electrical shock was applied momentarily between each reversal of flow, the suspension maintained some memory. These results are generally in agreement with the theory presented in the preceding paper.With suspensions of HRBC, the particles were initially randomly oriented and the light transmittance across the planes of shear was used to measure changes in orientation distribution. Since HRBC are small enough to exhibit appreciable rotary Brownian motion, memory loss was inevitable and increased with the duration of each shear cycle and the cell concentration.Memory loss was also observed for rods and HRBC in non-Newtonian media and was attributed to drift in the rotational orbit constants of the particles.

scholarly journals Texture, Piezoelectricity and Ferroelectricity

1995 ◽  
Vol 23 (4) ◽  
pp. 221-236 ◽  
Author(s):  
L. Fuentes ◽  
O. Raymond
Keyword(s):  
Distribution Function ◽  
Barium Titanate ◽  
Texture Analysis ◽  
Technological Process ◽  
Orientation Distribution Function ◽  
Orientation Distribution ◽  
Odd Order ◽  
Order Expansion ◽  
Orientation Distributions ◽  
Expansion Coefficients

A Quantitative Texture Analysis approach to polycrystal piezoelectric and ferroelectric phenomena is given. Monocrystal longitudinal piezoelectric moduli are expanded in Bunge's symmetry- adapted functional bases. Suitable expansion coefficients are given. Orientation Distribution Function based algorithms for polycrystal piezo-moduli prediction are presented. Significant odd-order expansion terms are calculated and their relation to ghost phenomena is commented. Polycrystal ferroelectricity is characterized. Quantitative describers associated to crystallographic and electric orientation distributions are presented and related. Their evolution during heat and poling processes is discussed. Two computer-simulated examples are analyzed: (a) Texture-modulated longitudinal piezo-modulus is calculated for an ideal quartz single-component texture. (b) Barium titanate fibre texture transformation during a hypothetical technological process is investigated.

scholarly journals Calculation of Texture Volume Fractions by Integration and Gaussian Fitting

1997 ◽  
Vol 29 (3-4) ◽  
pp. 155-183 ◽  
Author(s):  
M. B. Cortie
Keyword(s):  
Distribution Function ◽  
Harmonic Function ◽  
Texture Component ◽  
Volume Fraction ◽  
Orientation Distribution ◽  
Volume Fractions ◽  
Gaussian Fitting ◽  
Orientation Distributions ◽  
Function Integration ◽  
The Ideal

The concept of texture volume fractions has proved useful in the assessment of the orientation distributions of polycrystalline samples. Unfortunately, there is more than one method of calculating volume fractions, and the different techniques may give rather different answers. The three most commonly used methods appear to be calculation from the coefficients of the harmonic function, integration over a selected portion of an orientation distribution function (ODF), or decomposition of an ODF into component Gaussian ideal textures by a least squares fitting. The integration and Gaussian fitting methods are examined further here. In particular, the nature of the errors or differences arising from the method of integration or fitting chosen, the differing interpretations of the shape and ‘spread’ of the ideal texture, and the effect of neglecting texture components lying outside of the H0 subspace are considered. Integration of a volume enclosed by one or more cylinders defined in Eulerian space seems the most robust technique. It is usually, but not always, acceptable to neglect the effect of texture components lying outside of H0. However, it is vital that the ‘spread’ of the ideal texture component be precisely defined, and the texture volume fraction is very sensitive to the magnitude of the spread as well as to the geometric shape assumed for it.

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