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ISSN: 2053-2733

March 2000 issue

Highlighted illustration

Cover illustration: Unit cell of a self-intersecting minimal surface with symmetry I432. The surface subdivides R3 into two congruent three-periodic mutually interpenetrating labyrinths with symmetry P4232. Lines of self-intersection are marked in red. See Koch [Acta Cryst. (2000), A56, 15-23].

research papers


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Phase extension in protein molecules is presented. `Super-resolution' extension and a new figure of merit based on crystallographic symmetry are discussed.

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False minima occurred frequently during Shake-and-Bake applications to large P1 data sets. These minima can be recognized and avoided with proper choice of parameter-shift conditions.

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A method to obtain the crystal potential from the scattering matrix in dynamical electron diffraction, which takes absorption into account, is proposed.

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Simulated annealing can be used to solve the Sayre equation for ab initio structure determination. Trial calculations involving as many as 126 light atoms in the asymmetric unit are presented.

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Geometrical criteria to identify the twins and allotwins of the four basic polytypes of mica from their diffraction patterns are derived and expressed by means of the `minimal rhombus' unit in reciprocal space.

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The phase (M2Cu2O3)(Cu1+δO2+γ) described as the member m/n = 1/1 in the series (M2Cu2O3)m(CuO2)n can be considered as an individual `Cu-deficient ladder-type' structure intermediate between SrCu2O3 and incommensurate phases (M2Cu2O3)m(CuO2)n (mn).

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A method to expand conventional scalar validation statistics to three dimansions is described.

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Reflection and transmission coefficients of X-rays by a single atomic plane are obtained in the general case where the plane consists of any two-dimensional Bravais lattice and the incident and exit X-ray beams take any direction with respect to the plane. A formula obtained for the coefficients is written in simple form.

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A cylindrically symmetric model is proposed for the distribution of atomic coordinate errors in helical structures. Formulas for likelihood functions in fiber difraction are presented.

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A method for the classification of crystal structures is proposed, which is based on the representation of the interatomic bond system in a crystal as a finite `reduced' graph. The computer program IsoTest realizing this method is described.

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An effective quantitative CBED method was used to obtain the Debye–Waller factors of Co and Ti atoms in Co3Ti. The results are BCo = 0.20–0.24 and BTi = 0.41–0.43 Å2 at room temperature.

international union of crystallography


books received


Acta Cryst. (2000). A56, 226
doi: 10.1107/S0108767399012374

Acta Cryst. (2000). A56, 226
doi: 10.1107/S0108767399014014

Acta Cryst. (2000). A56, 226
doi: 10.1107/S0108767300000908
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