October 1996 issue
Cover illustration: Neutron scattering pattern in the (hk0) reciprocal-lattice plane from alpha-AgI at 520 K. The portion shown extends from 0 to 5.4 reciprocal-lattice units in both h and k. Courtesy of D. A. Keen, V. M. Nield and R. L. McGreevy.
It is shown that a simple interpretation of diffuse and specular reflectivity is possible if the resolution function is separable for two directions in the scattering plane.
The von Mises–Fisher matrix distribution on SO(3) provides a versatile mathematical model for both analysis and component-fit methods in texture analysis, even though a theoretical justification is missing.
Sintering of Pt on NaY zeolite support during processing is examined via in situ small-angle X-ray scattering, which indicates that the particle-size distribution of Pt in the reduced and finished catalyst is determined during the earliest stages of calcination.
Intensity corrections are described when the textures of thin layers are studied in low-incidence geometry. These corrections are applied to aluminium and iron thin films or bilayers deposited on steel or silicon.
The specific influence of the asymmetric diffraction geometry on peak position, profile shape and intensity determination is studied when a curved position-sensitive detector and a conventional pseudoparallel incident beam are used.
With the a priori assumption of a special type of structure model, the unknown parameters are calculated using analytical real- space functions and slit-distorted small-angle scattering curves.
The indirect-transformation method in reciprocal space (ITR) and the indirect-transformation method are used in the analysis of small-angle X-ray scattering (SAXS) curves from semidilute aqueous solutions of fragmented DNA. In particular, the ITR method is used to desmear those SAXS curves where interparticle interference effects are present, with the aim of obtaining the interference function.
The absorption behaviour of X-rays scattered by samples in transmission geometry is analyzed and a correction procedure is proposed. The given expressions were tested by their application in Rietveld analysis.
Measurements of refractive index and thermal expansion as a function of temperature, which were conducted using a new Kösters prismn interferometer, are described and presented for quartz, barium sodium niobate and indium-doped potassium titanyl arsenate.
Measurement has been made of the minimum glycerol concentration required to cryoprotect 50 typical protein crystallization solutions for use in macromolecular cryocrystallographic diffraction data collection at around 100 K.
By use of the Rietveld method and the formation-reaction equations as constraint, a straightforward numerical procedure to improve the quantitative analysis of a compound was obtained.
A simple general argument is given showing the independence of the asymptotic behaviour of small-angle scattering from any amount of multiple scattering. The argument is valid as long as the intensity drops faster than 1/q2.
Correction to J. Appl. Cryst. (1996), 29, 164–169.
A program (XPACK.PL) written in Perl that transforms Brook- haven Protein Data Bank structure files into three-dimensional crystal packing Virtual Reality Modelling Language (VRML) world files is discussed.
CIFtbx2 is a new version of a Fortran subroutine library for programmers developing CIF applications. The functions for reading and writing CIF data in CIFtbx have been expanded and facilities for handling macromolecular CIF data and dictionaries have been added.
Implementation into the control program of very flexible scans in hkl and angular space is presented. With the analysing tool, it can be used for determination of real structures in thin films, superstructures etc.
Apparatus for investigating air-sensitive powder samples with a flat sample holder fitting in an Enraf-Nonius FR552 Guinier camera is described.
A simple device for studying crystalline samples under moderate gaseous pressure has been used to produce several xenon derivatives of proteins providing useful phasing information.