摘要:

It is shown that inhomogeneous electron density distribution as represented either by a spherical model containing smaller spheres or by a sphere with radially periodic density does not produce positive slope in Soulé–Porod plots (Ih4versush4) of protein small‐angle scattering data. It is found that the introduction of small particles into the scattering population can produce the zero or positive slope commonly seen. It is also shown that intersubunit interference is able to account for the low 2θ minimum or dip often observed inIh4vsh4plots of the scattering from multisubunit pro

ISSN:1600-5767    

DOI:10.1107/S0021889877013120

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

An analysis of thickness variances from an electron‐microscope cross‐section of myelin sheath shows that the standard deviation varies proportionally to the square root of the number of intervening lamellae. This result implies that the lamellar irregularities are additive and that a paracrystalline stacking model is an appropriate representation for the myelin structure. The X‐ray diffraction data from myelin exhibit the characteristics of a paracrystalline material. Both electron microscope and X‐ray diffraction evidence suggest that myelin is paracrystalline rather than crys

ISSN:1600-5767    

DOI:10.1107/S0021889877013132

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

It is shown that to determine the quantitative phase composition ofnsamples each of which contains n phases it is sufficient to obtain a set ofn2intensities values of analytical lines,Iij, where 1 ≤i≤nis the phase number in a sample of number 1 ≤j≤n. It is supposed that in every sample the complete phase composition is determined. To calculate concentrations in one sample a system of consisting ofnlinears equations was obtained:wheresis the number of the sample, the mass absorption coefficient of the phase to be determined,x_isthe weight fraction of theith phase in the analysed sample. This system is modified if there are additional data on the samples,e.g.values of mass absorption coefficients. The use of this method excludes measurement of analytical line intensity in the pure phase or mixture of pure phases. Experimental verification of the method with two‐ and three‐phase artificial mixtures gave satisfactory results. The necessary conditions for the application of this method are essential differences in the quantitative phase composition of the sampl

ISSN:1600-5767    

DOI:10.1107/S0021889877013144

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

The aim of this paper is to show the influence of a small addition of Mg on the two mechanisms of precipitation that were previously pointed out on the Al–6–8% Zn alloy by Junqua, Delafond, Mimault&Grilhé [Scripta Met. (1974),8, 317–322]. The comparison between the binary and the ternary alloy (with the same Zn content) indicates that the addition of Mg increases the spinodal temperature by several degrees. The influence of Mg is discussed here in more detail with kinetics studies and quantitative values obtained by small‐angle X‐ray scattering with the help of a position‐lin

ISSN:1600-5767    

DOI:10.1107/S0021889877013156

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

By allowing the axis of the film cylinder to intersect the rotation axis of the crystal at 45°, it is possible to design a compact camera which can be place into a Dewar vessel of diameter 115 mm that can be made of glass. This feature allows the diffraction study of single crystals to be carried out at liquid‐helium temperature. A modified equi‐inclination method is used and distorted Weissenberg patterns are obtained. The geometrical analyses lead to a comprehensive interpretation of the resulting patterns. Reflections can be indexed by graphical methods. Diagrams for indexing rotation, zero and nth‐layer photographs a

ISSN:1600-5767    

DOI:10.1107/S0021889877013168

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

The lattice parameters, bond lengths and bond angles of Si2N2O have been determined at pressures up to 23 kbar by time‐of‐flight neutron diffraction. The average compressibility coefficients of the orthorhombic structure areKa= 21 (2),Kb= 34 (2),Kc= 25 (2) andKν= 79 (4) x 10−5 kbar−1, though the anisotropy is more pronounced at lower pressures with Ka (at zero pressure) estimated to be 10 (8) × 10–5 kbar−1. The major contribution to the compression is a cooperative rotation of adjacent SiN3O tetrahedra brought about by a decrease in the Si–O–Si bond angle. The shortening of one Si–N bond within each tetrahedron further enhances the compress

ISSN:1600-5767    

DOI:10.1107/S002188987701317X

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

It is shown that the neutron small‐angle scattering of pure polycrystalline metals is strongly connected with surface imperfections in the samples (surface irregularities and oxide layers) rather then with the grain boundaries. It is also shown that the asymptotic form of the scattering cross section of the surface imperfections isq−4like the Porod

ISSN:1600-5767    

DOI:10.1107/S0021889877013181

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

The overlapping of reflections during the intensity measurement of a polycrystal (grown‐together single crystals) can be checked by formulae given in this paper. These formulae are based on scan mode, scan width and detector apertur

ISSN:1600-5767    

DOI:10.1107/S0021889877013193

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

Precision strain‐gauge measurements of the basal‐plane lattice asymmetry (a−b)/[(a+b)/2] in gallium metal have been made in the temperature range 190 K

ISSN:1600-5767    

DOI:10.1107/S002188987701320X

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY

摘要:

A new method for unfolding X‐ray diffraction profiles is reported. The procedure is based on the minimization of an economical function defined as the sum of the squared relative differences between the experimental function and a calculated profile. The latter is numerically computed from the convolution equation by fitting the pure diffraction profile with a damped polynomial. The influence of the truncation and the width of the instrumental function is studied; some results are given concerning the evaluation of a constant background for both the experimental and instrumental functions and its influence on the precision of the results. Finally, the perturbation produced by the simulation of statistical noise is discusse

ISSN:1600-5767    

DOI:10.1107/S0021889877013211

出版商:International Union of Crystallography    

年代:1977

数据来源: WILEY