(IUCr) Contents for Acta Crystallographica Section A Vol. 58 Part 2 (March 2002)

Acta Cryst. (2002). A58, 125-132 [ doi:10.1107/S0108767301019134 ]

Homogeneous cubic cylinder packings revisited

M. O'Keeffe, J. Plévert and T. Ogawa

Synopsis: A method of systematically enumerating homogeneous (i.e. symmetry-related) packings of equal cylinders is developed.

Online 7 February 2002

Acta Cryst. (2002). A58, 133-137 [ doi:10.1107/S0108767301017986 ]

Excited-state structure by time-resolved X-ray diffraction

C. D. Kim, S. Pillet, G. Wu, W. K. Fullagar and P. Coppens

Synopsis: A time-resolved stroboscopic study of the photo-induced triplet excited state of the [Pt₂(pop)₄]^4- ion (pop = pyrophosphate), performed at He temperatures with synchrotron radiation, is reported.

Online 7 February 2002

Acta Cryst. (2002). A58, 138-145 [ doi:10.1107/S0108767301017718 ]

One-dimensional scattering in K-hollandite: theory and experiment

L. A. Brussaard, H. Boysen, A. Fasolino and T. Janssen

Synopsis: Calculations using the Frenkel-Kontorova and double-chain models lead to new results explaining the experimental diffraction pattern of K-hollandite. The use of a deformable host chain and a Lennard-Jones-like interchain interaction gives the best results. It is concluded that the guest as well as the host are deformed and that the system is pinned. The inclusion of Debye-Waller factors as fitting parameters is also discussed, with the conclusion they should not be used in the case of the double-chain model.

Online 7 February 2002

Acta Cryst. (2002). A58, 146-154 [ doi:10.1107/S0108767301019766 ]

X-ray four-quadrant diamond phase-retarder system to compensate for off-axis and chromatic aberrations

K. Okitsu, Y. Ueji, K. Sato and Y. Amemiya

Synopsis: A new type of X-ray phase-retarder system that can compensate for aberrations (phase-shift inhomogeneity) not only due to angular divergence of incident X-rays (off-axis aberration) but also due to energy spread (chromatic aberration) has been developed. The principle of this new X-ray optical system, which consists of four transmission-type diamond X-ray phase retarders whose planes of incidence are inclined with respect to the horizontal plane by 45, 135, 225 and 315°, is described together with experimental results revealing its advantage over a single phase retarder.

Online 7 February 2002

Acta Cryst. (2002). A58, 155-161 [ doi:10.1107/S0108767301020219 ]

On the auxiliary lattices and dislocation reactions at triple junctions

V. Y. Gertsman

Synopsis: The coincidence site lattice theory of triple junctions is applied to grain-boundary dislocation interactions.

Online 7 February 2002

Acta Cryst. (2002). A58, 162-170 [ doi:10.1107/S0108767301020256 ]

Modeling chemical bonding effects for protein electron crystallography: the transferable fragmental electrostatic potential (TFESP) method

S. Zhong, V. M. Dadarlat, R. M. Glaeser, T. Head-Gordon and K. H. Downing

Synopsis: The use of different atomic and molecular fragments is analyzed for reproducing the electrostatic potential of proteins in order to enhance structure refinement in electron crystallography.

Online 7 February 2002

Acta Cryst. (2002). A58, 171-179 [ doi:10.1107/S0108767301020311 ]

Analysis of polynuclear aromatic hydrocarbons via the Voronoi tessellation approach: classification of atom types using artificial neural networks

S. W. Christensen

Synopsis: It is shown how Voronoi polyhedra for C and H atoms in polynuclear aromatic hydrocarbons display characteristic differences that allow perfect atom-type prediction from knowledge of the atomic coordinates alone.

Online 7 February 2002

Acta Cryst. (2002). A58, 180-184 [ doi:10.1107/S0108767301021195 ]

General periodic average structures of decagonal quasicrystals

A. Cervellino and W. Steurer

Synopsis: A general method for obtaining periodic average structures of a decagonal quasicrystal is presented. New insights into the concept of periodic average structure are revealed. The method, based on reciprocal space, allows an easy comparison between quasicrystals and related periodic phases.

Online 7 February 2002

Acta Cryst. (2002). A58, 185-189 [ doi:10.1107/S0108767301021249 ]

Wavelength extrapolation to zero extinction: a -ray case. The quantitative effect of the extrapolation function on the kinematical limit value

A. McL. Mathieson and A. W. Stevenson

Synopsis: For imperfect crystals, a discontinuous physical model is suggested in relation to [gamma] -ray diffraction. On this basis, a close dependence of the extrapolation procedure on the experimental measurements is demonstrated.

Online 7 February 2002

Acta Cryst. (2002). A58, 190-200 [ doi:10.1107/S0108767301021298 ]

Whole powder pattern modelling

P. Scardi and M. Leoni

Synopsis: A new approach for the modelling of diffraction patterns without using analytical profile functions is described and tested on ball milled f.c.c. Ni powder samples. The proposed whole powder pattern modelling (WPPM) procedure allows a one-step refinement of the most relevant microstructure parameters (including those of domain size and lattice defects) by a direct modelling of the experimental pattern.

Online 7 February 2002

Acta Cryst. (2002). A58, 201-207 [ doi:10.1107/S0108767302000624 ]

Direct methods and isomorphous replacement. The triplet invariant estimate when heavy atoms are located

C. Giacovazzo, D. Siliqi and L. De Caro

Synopsis: Triplet invariants of the native protein are estimated when diffraction amplitudes of the derivative and of the heavy-atom structure are available.

Online 7 February 2002

addenda and errata

Acta Cryst. (2002). A58, 208 [ doi:10.1107/S0108767301020414 ]

A finite group that derives all the 14 Bravais lattices as its subgroups. Erratum

M. Hosoya

Synopsis: Erratum to Acta Cryst. (2000), A56, 259-263.

Online 7 February 2002

letters to the editor

Acta Cryst. (2002). A58, 209 [ doi:10.1107/S0108767301018633 ]

Comments on quasicrystalline phases and examples of quasicrystalline phase nomenclature in Nomenclature of magnetic, incommensurate, composition-changed morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr Working Group on Phase Transition Nomenclature by J.-C. Tolédano et al. (2001). Acta Cryst. A57, 614-626

K. H. Kuo

Synopsis: The definition of quasicrystals suggested by the International Union of Crystallography Ad Interim Commission on Aperiodic Crystals is recommended.

Online 7 February 2002

Acta Cryst. (2002). A58, 210 [ doi:10.1107/S0108767301021341 ]

Response to K. H. Kuo's Comments on quasicrystalline phases and examples of quasicrystalline phase nomenclature in Nomenclature of magnetic, incommensurate, composition-changed morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr Working Group on Phase Transition Nomenclature by J.-C. Tolédano et al. (2001). Acta Cryst. A57, 614-626

J.-C. Tolédano, R. S. Berry, P. J. Brown, A. M. Glazer, R. Metselaar, D. Pandey, J. M. Perez-Mato, R. S. Roth and S. C. Abrahams

Synopsis: Responses are made to K. H. Kuo's three comments in the previous paper concerning quasicrystalline phases and the examples of quasicrystalline phases in the recommendations presented earlier.

Online 7 February 2002

Acta Crystallographica Section A

Foundations of Crystallography

Volume 58, Part 2 (March 2002)

research papers

Homogeneous cubic cylinder packings revisited

M. O'Keeffe, J. Plévert and T. Ogawa

Excited-state structure by time-resolved X-ray diffraction

C. D. Kim, S. Pillet, G. Wu, W. K. Fullagar and P. Coppens

One-dimensional scattering in K-hollandite: theory and experiment

L. A. Brussaard, H. Boysen, A. Fasolino and T. Janssen

X-ray four-quadrant diamond phase-retarder system to compensate for off-axis and chromatic aberrations

K. Okitsu, Y. Ueji, K. Sato and Y. Amemiya

On the auxiliary lattices and dislocation reactions at triple junctions

V. Y. Gertsman

Modeling chemical bonding effects for protein electron crystallography: the transferable fragmental electrostatic potential (TFESP) method

S. Zhong, V. M. Dadarlat, R. M. Glaeser, T. Head-Gordon and K. H. Downing

Analysis of polynuclear aromatic hydrocarbons via the Voronoi tessellation approach: classification of atom types using artificial neural networks

S. W. Christensen

General periodic average structures of decagonal quasicrystals

A. Cervellino and W. Steurer

Wavelength extrapolation to zero extinction: a -ray case. The quantitative effect of the extrapolation function on the kinematical limit value

A. McL. Mathieson and A. W. Stevenson

Whole powder pattern modelling

P. Scardi and M. Leoni

Direct methods and isomorphous replacement. The triplet invariant estimate when heavy atoms are located

C. Giacovazzo, D. Siliqi and L. De Caro

addenda and errata

A finite group that derives all the 14 Bravais lattices as its subgroups. Erratum

M. Hosoya

letters to the editor

K. H. Kuo

J.-C. Tolédano, R. S. Berry, P. J. Brown, A. M. Glazer, R. Metselaar, D. Pandey, J. M. Perez-Mato, R. S. Roth and S. C. Abrahams


	Cover illustration: Electrostatic equilibrium of simultaneous Coulomb attraction and core repulsion for an ensemble ${\cal F}=(X_1^-,X_2^-)$ ; the conjoint centroids, shown in yellow, characterize force-free positions of the fragment inside the unit cell. For comparison, the pure Coulomb equilibrium is shown in the background. See Mädler, Behrends & Knorr [Acta Cryst. (2001). A57, 20-23].