摘要:

The surface quality of copper whiskers grown by the hydrogen reduction of cuprous iodide has been investigated by measuring Bragg‐case diffraction curves by means of X‐ray triple‐crystal diffractometry with CuKα1radiation. The observed half‐widths vary from whisker to whisker, probably owing to the existence of a very thin surface layer contaminated with oxygen and/or impurity atoms. When the surface is good in quality, the observed diffraction curves clearly show the asymmetry of the intensity profile and fit well with the convoluted curve calculated with the dynamical theory of X‐ray diffraction for a perfect single‐crystal. From the half‐width of the diffraction curve showing the best fitting with the calculated curve, thef0220value has been determined as 16.75 ± 0.08 with a dispersion correctionf′ = −2.019, in excellent agreement with the theoretical value 16.76 given by Freeman&Watson [Acta Cryst.

ISSN:1600-5767    

DOI:10.1107/S0021889879012085

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

An algorithm, suitable for small computers with low memory capacity, is presented and applied to the diffractograms of graphite lamellar compounds crystallizing in the hexagonal, orthorhombic or monoclinic systems. The basic input data consist of the Bragg angleθand its uncertaintyΔθ, andn, the ratio of graphite atoms to intercalated molecules. All possible lattices corresponding to a given value ofnare investigated and means are also provided to explore lattices with 2n, 3n,etc. (centered lattices) or with a value for the parameter c equal to 2Ic, 3Ic,etc. (whereIcis the so‐called identity period) should there exist a screw axis parallel to thec

ISSN:1600-5767    

DOI:10.1107/S0021889879012097

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

Static strain‐gauge extensometry and ultrasonic velocity measurements have been carried out on CuAl2single‐crystal samples of known orientation in order to determine the value of the six elastic constants. The apparent Young's modulus over all the space directions is derived. Young's modulus and Poisson's ratio of the nearest isotropic body are also calcula

ISSN:1600-5767    

DOI:10.1107/S0021889879012103

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

Transformations equations between reciprocal space and X‐ray film are derived. With the use of these equations `resolution curves' representing the instrument resolution of a Buerger's precession camera can be defined. A point on the X‐ray photographic film taken by the precession camera is proved to correspond to two resolution curves in the shape of the character `X' in reciprocal space. As an example, equi‐intensity contours of thermal diffuse scattering from NaCl on an X‐ray film were calculated on the basis of known elastic constant data, taking account of the resolution of the camera, and were compared with those in reciprocal space. Equi‐intensity contours were found to be deformed considerably due to instrument resolution, unless the width of the layer‐line screen was grea

ISSN:1600-5767    

DOI:10.1107/S0021889879012115

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

Mutual orientations of different lattices in haematite crystals have been recognized by studying the relationship between the shapes of the etch figures and the crystal structure. The twinning law based on the most stable face being the composition plane, therefore having two directions of strongest bonds in common, has been generalized. We show as an example that the only way of reconstructing the observed etch figures leads to the three directions of strongest bonding being nearly parallel.

ISSN:1600-5767    

DOI:10.1107/S0021889879012127

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

The distance distribution function contains all the accessible information about the scattering medium. It is possible to determine the following particle parameters from this function: maximum dimension of the particle, radius of gyration, and zero‐angle intensity (molecular weight). The shape of the distance distribution function enables one to distinguish and to recognize directly and rationally the following types of particles: compact globular particles; particles elongated in one dimension, with constant and with variable cross‐section; spherical vesicles. The thickness of flat particles as well as the inner and outer diameter of spherical vesicles can be determined from the distance distribution function. Inhomogeneous particles with at least two regions of electron densities differing in their signs show typical features in the distance distribution. These characteristics can be found without further assumptions, independently of the shape of the particle. For concentric shells with different electron densities it is possible to obtain some general information about their structure. Residual concentration effects cannot be overlooked in real space. The formation of dimers can be analyzed with the aid of the distance distribution funct

ISSN:1600-5767    

DOI:10.1107/S0021889879012139

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

In all organisms the multi‐subunit enzyme DNA‐dependent RNA polymerase catalyses the first basic step in gene expression, the transcription of DNA into RNA. The neutron small‐angle scattering effects were studied in the Guinier region by applying the contrast‐matching technique. Isotopic labelling was realised by culturing fully deuteratedE. colicells in a heavy‐water medium containing deuterated substrates. One or two completely deuterated components (subunits) of polymerase holoenzyme (composition formulaα2ββ′σ, molecular weight 497000) were recombined with the remaining natural (`hydrogenated') subunits for these neutron measurements. Measurements are presented of radii of gyrationR, overall shapes, and pair distancesd, of three components (subunitsα2β,β′) in RNA polymerase ofE. coli. The subunitsβ′,βandα2are obviously rather elongatedin situand exhibit (as scattering‐equivalent prolate ellipsoids) axial ratios of about 7:1 up to 9:1. The intersubunit centre of gravity distances were analysed to be 7.3 ± 0.8 nm forβ−β′, 8.2 ± 1.2

ISSN:1600-5767    

DOI:10.1107/S0021889879012140

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

It is demonstrated experimentally that the well known spin‐selective deflection of neutrons transmitted through a static magnetic field region with triangular geometric boundaries combined with the high angular resolution of a non‐dispersive double‐crystal arrangement can be used to polarize a thermal neutron beam to a degree close to unity at reasonably low laboratory fields of 1.0 to

ISSN:1600-5767    

DOI:10.1107/S0021889879012152

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

A long‐wavelength neutron scattering facility at the SAFARI‐1 reactor is described. Neutrons of wavelength between 5 and 15 Å can be selected. Features of the facility are the use of microwave guides as neutron conductors, flexible guide‐pipe configuration and automatic sequential sample changing. Examples are given of measurements on radiation‐induced voids in copper, aluminium, Al‐0.4%Si and Al‐0.1%In after neutron irradiation and magnetic scattering in US and in 8

ISSN:1600-5767    

DOI:10.1107/S0021889879012164

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

The development is critical in recording X‐ray topographs since it takes a long time and determines the final quality of the pictures. It is shown that, in most cases, it is possible to decrease both exposure time and development time and still obtain pictures of good quality. Standard conditions of development should be used to achieve higher resolution only. This new standard may be of great use with the modern high‐power sour

ISSN:1600-5767    

DOI:10.1107/S0021889879012176

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY