Determination of nuclear shielding tensor orientations in polycrystalline materials by dipolar modulation. The diluteI2Ssystem

1987 ◽  
Vol 86 (8) ◽  
pp. 4362-4368 ◽  
Author(s):  
M. Munowitz ◽  
T.‐H. Huang ◽  
R. G. Griffin
Keyword(s):  
Polycrystalline Materials ◽  
Nuclear Shielding ◽  
Shielding Tensor ◽  
Dipolar Modulation

The [sup 129]Xe nuclear shielding tensor surfaces for Xe interacting with rare gas atoms

2003 ◽  
Vol 118 (6) ◽  
pp. 2575 ◽  
Author(s):  
Cynthia J. Jameson ◽  
Devin N. Sears ◽  
Angel C. de Dios
Keyword(s):  
Rare Gas ◽  
Rare Gas Atoms ◽  
Nuclear Shielding ◽  
Shielding Tensor

New Method of Modeling Infrared Spectra of Non-Cubic Single-Phase Polycrystalline Materials with Random Orientation

2002 ◽  
Vol 56 (9) ◽  
pp. 1194-1205 ◽  
Author(s):  
Thomas G. Mayerhöfer
Keyword(s):  
Single Phase ◽  
Common Factor ◽  
Dispersion Analysis ◽  
Polycrystalline Materials ◽  
Implicit Assumption ◽  
Resolution Limit ◽  
Random Orientation ◽  
New Approach ◽  
Arithmetic Average

A new approach has been used to model optical properties of noncubic single-phase polycrystalline materials with random orientation and crystallites small compared to the resolution limit of light. This method has been applied to fresnoite (Ba2TiSi2O8) and proved to provide widely adequate results to effective medium approximation (EMA) and an excellent correspondence between simulated and measured spectra. In contrast to EMA, the new theory predicts that the deviation between damping constants of polycrystalline and single crystal fresnoite can be adjusted by one common factor for all damping constants. Based on EMA and the new model, much smaller damping constants have been determined for polycrystalline fresnoite compared to conventional dispersion analysis; the latter is able to provide a relevant dielectric function, but seems to be of little reliability concerning the determination of meaningful oscillator parameters due to the implicit assumption of an arithmetic average of the principal dielectric functions. This approximation, which can be derived in a similar form from EMA and is of widespread use, is shown to be inferior to an approximation based on the arithmetic average of the principal refractive indices.

The Generalisation and Refinement of the Vector Method for the Texture Analysis of Polycrystalline Materials

1979 ◽  
Vol 23 ◽  
pp. 349-360 ◽  
Author(s):  
Daniel Ruer ◽  
Albert Vadon ◽  
Raymond Baro
Keyword(s):  
Experimental Data ◽  
Texture Analysis ◽  
Orientation Distribution ◽  
Polycrystalline Materials ◽  
Crystallite Orientation ◽  
Vector Method ◽  
Cubic Materials ◽  
First Time

AbstractA so-called “Vector Method” for the texture analysis of cubic materials was presented for the first time at this conference in 1976. Since then this method has been refined and applied successfully to non cubic-materials. It is shown in this paper that the Vector Method provides several advantages over series methods of texture analysis, the most important of which being the relatively small amount of experimental data which are needed for the determination of the entire crystallite orientation distribution.

Diffraction determination of stress field and elastic constants in polycrystalline materials

1997 ◽  
Vol 231 (1-2) ◽  
pp. 10-16 ◽  
Author(s):  
N Freri ◽  
A Tintori ◽  
L.E Depero ◽  
L Sangaletti ◽  
F Cernuschi
Keyword(s):  
Stress Field ◽  
Elastic Constants ◽  
Polycrystalline Materials ◽  
Diffraction Determination

scholarly journals Analysis of Microstructure Images Referred to Percolation Theory

2015 ◽  
Vol 15 (1) ◽  
pp. 109-112 ◽  
Author(s):  
W. Trzaskowski ◽  
W. Sobaszek ◽  
D. Myszka ◽  
S. Świłło
Keyword(s):  
Percolation Theory ◽  
Spatial Arrangement ◽  
Polycrystalline Materials ◽  
Practical Implementation ◽  
Material Structure ◽  
Two Phase ◽  
Modern Computer ◽  
Planar Images ◽  
Metallographic Image Analysis

Abstract The paper discusses possible applications of the percolation theory in analysis of the microstructure images of polycrystalline materials. Until now, practical use of this theory in metallographic studies has been an almost unprecedented practice. Observation of structures so intricate with the help of this tool is far from the current field of its application. Due to the complexity of the problem itself, modern computer programmes related with the image processing and analysis have been used. To enable practical implementation of the task previously established, an original software has been created. Based on cluster analysis, it is used for the determination of percolation phenomena in the examined materials. For comparative testing, two two-phase materials composed of phases of the same type (ADI matrix and duplex stainless steel) were chosen. Both materials have an austenitic - ferritic structure. The result of metallographic image analysis using a proprietary PERKOLACJA.EXE computer programme was the determination of the content of individual phases within the examined area and of the number of clusters formed by these phases. The outcome of the study is statistical information, which explains and helps in better understanding of the planar images and real spatial arrangement of the examined material structure. The results obtained are expected to assist future determination of the effect that the internal structure of two-phase materials may have on a relationship between the spatial structure and mechanical properties.

Generation and applications of structure envelopes for porous metal–organic frameworks

2013 ◽  
Vol 46 (2) ◽  
pp. 346-353 ◽  
Author(s):  
Andrey A. Yakovenko ◽  
Joseph H. Reibenspies ◽  
Nattamai Bhuvanesh ◽  
Hong-Cai Zhou
Keyword(s):  
Electron Density ◽  
Structural Characteristics ◽  
Metal Organic Frameworks ◽  
Porous Metal ◽  
Polycrystalline Materials ◽  
X Ray Diffraction ◽  
Structure Solution ◽  
Metal Organic ◽  
A Charge

The synthesis of polycrystalline, as opposed to single-crystalline, porous materials, such as zeolites and metal–organic frameworks (MOFs), is usually beneficial because the former have shorter synthesis times and higher yields. However, the structural determination of these materials using powder X-ray diffraction (PXRD) data is usually complicated. Recently, several methods for the structural investigation of zeolite polycrystalline materials have been developed, taking advantage of the structural characteristics of zeolites. Nevertheless, these techniques have rarely been applied in the structure determination of a MOF even though, with the electron-density contrast between the metal-containing units and pore regions, the construction of a structure envelope, the surface between high- and low-electron-density regions, should be straightforward for a MOF. Herein an example of such structure solution of MOFs based on PXRD data is presented. To start, a Patterson map was generated from powder diffraction intensities. From this map, structure factor phases for several of the strongest reflections were extracted and a structure envelope (SE) of a MOF was subsequently constructed. This envelope, together with all extracted reflection intensities, was used as input to theSUPERFLIPsoftware and a charge-flipping (CF) structure solution was performed. This structure solution method has been tested on the PXRD data of both activated (solvent removed from the pores;dmin= 0.78 Å) and as-synthesized (dmin= 1.20 Å) samples of HKUST-1. In both cases, our method has led to structure solutions. In fact, charge-flipping calculations using SE provided correct solutions in minutes (6 min for activated and 3 min for as-synthesized samples), while regular charge flipping or charge flipping with histogram matching calculation provided meaningful solutions only after several hours. To confirm the applicability of structure envelopes to low-symmetry MOFs, the structure of monoclinic PCN-200 has been solvedviaCF+SE calculations.

Variational estimates for the creep behaviour of polycrystals

1995 ◽  
Vol 448 (1932) ◽  
pp. 121-142 ◽  
Keyword(s):  
Heterogeneous Media ◽  
Creep Behaviour ◽  
The Self ◽  
Polycrystalline Materials ◽  
Variational Procedure ◽  
Constitutive Behaviour ◽  
Effective Potentials ◽  
Self Consistent ◽  
Geometric Arrangements

A variational procedure is developed for estimating the effective constitutive behaviour of polycrystalline materials undergoing high-temperature creep. The procedure is based on a new variational principle allowing the determination of the effective potential function of a given nonlinear polycrystal in terms of the corre­sponding potential for a linear comparison polycrystal with an identical geometric arrangements of its constituent single-crystal grains. As such, it constitutes an extension, to locally anisotropic behaviour, of the variational procedure devel­oped by Ponte Castañeda (1991) for nonlinear heterogeneous media with locally isotropic behaviour. By way of an example, the procedure is applied to the de­termination of bounds of the Hashin-Shtrikman type for the effective potentials of statistically isotropic nonlinear polycrystals. The bounds are computed for the special class of untextured FCC polycrystals with isotropic pure power-law viscous behaviour, first considered by Hutchinson (1976), in the context of a calculation of the self-consistent type. The new bounds are found to be more restrictive than the corresponding classical Taylor-Bishop-Hill bounds, and also more re­strictive, if only slightly so, than related bounds of the Hashin-Shtrikman type by Dendievel et al . (1991). The new procedure has the advantage over the self-consistent procedure of Hutchinson (1976) that it may be applied, without any essential complications, to aggregates of crystals with slip systems exhibiting dif­ferent creep rules - with, for example, different power exponents - and to general loading conditions. However, the distinctive feature of the new variational proce­dure is that it may be used in conjunction with other types of known bounds and estimates for linear polycrystals to generate corresponding bounds and estimates for nonlinear polycrystals.

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