

Cover illustration: Polar mode GM6 (left) and antiferrodistortive mode M31q (right) present in the monoclinic structure of SrAl_{2}O_{4}, together with a graph of maximal subgroups showing their isotropy subgroups. The amplitude of mode GM6 is much larger, and ab initio calculations confirm its soft character, while distortion M31q is a hard mode frozen as an induced secondary distortion [PerezMato et al. (2010). Acta Cryst. A66, 558590]. The mode figures were drawn using FullProf Studio [RodriguezCarvajal (1993). Physica B, 192, 5569]. 
Acta Cryst. (2011). A67, 491506 [ doi:10.1107/S0108767311029825 ] A Fourier transform method for powder diffraction based on the Debye scattering equationN. W. ThomasSynopsis: A novel fast Fourier transform method is described for calculating powder diffraction patterns from crystal structural data. By also taking the Patterson symmetry of crystal structures into account, computational times can be reduced by an order of magnitude, thereby facilitating the application of the Debye scattering equation to microcrystallites. Online 13 October 2011 
Acta Cryst. (2011). A67, 507511 [ doi:10.1107/S0108767311034039 ] Structure of ice Ih and ice Ic as described in the language of Delaunay simplicesY. I. Naberukhin and V. P. VoloshinSynopsis: A full classification of the Delaunay simplex forms has been performed which involve the structure of ice Ih and ice Ic. Online 13 October 2011 
Acta Cryst. (2011). A67, 512516 [ doi:10.1107/S0108767311034350 ] Some B_{eq} are more equivalent than othersE. A. MerrittSynopsis: B_{eq} is a well defined entity that represents one property, meansquare displacement, of the anisotropic atomic displacement parameter tensor from which it is derived. B_{eq} is not, however, the best estimate of the B factor that would result from isotropic model refinement. A new entity B_{est} is proposed to serve this purpose. Online 13 October 2011 
Acta Cryst. (2011). A67, 517520 [ doi:10.1107/S0108767311035513 ] Form, symmetry and packing of biomacromolecules. IV. Filled capsids of cowpea, tobacco, MS2 and pariacoto RNA virusesA. JannerSynopsis: The molecular crystallographic properties of four RNA viruses are discussed. Online 13 October 2011 
Acta Cryst. (2011). A67, 521532 [ doi:10.1107/S010876731103577X ] Form, symmetry and packing of biomacromolecules. V. Shells with boundaries at antinodes of resonant vibrations in icosahedral RNA virusesA. JannerSynopsis: Periodic shells in icosahedral RNA viruses are interpreted in terms of a resonator model. Online 13 October 2011 
Acta Cryst. (2011). A67, 533543 [ doi:10.1107/S0108767311036269 ] Common arc method for diffraction pattern orientationG. Bortel and M. TegzeSynopsis: An orientation method based on the intersection arcs of continuous diffraction patterns is described and is shown to perform well on simulated patterns of singleparticle diffraction experiments performed at Xray freeelectron laser sources. Online 13 October 2011 
Acta Cryst. (2011). A67, 544549 [ doi:10.1107/S0108767311037469 ] A multidataset datacollection strategy produces better diffraction dataZ.J. Liu, L. Chen, D. Wu, W. Ding, H. Zhang, W. Zhou, Z.Q. Fu and B.C. WangSynopsis: Theoretical analysis and experimental validation prove that a multidataset datacollection strategy produces better diffraction data. The readiness test is a simple and sensitive method for Xray datacollection system evaluation and a benchmark. Online 18 October 2011 
Acta Cryst. (2011). A67, 550556 [ doi:10.1107/S0108767311037238 ] Polarizationdependent Xray sixbeam pinhole topographs for a channelcut silicon crystalK. Okitsu, Y. Yoda, Y. Imai and Y. UejiSynopsis: Experimentally obtained and computersimulated Xray sixbeam pinhole topographs based on the nbeam TakagiTaupin (TT) equation are reported for a channelcut silicon crystal. It has been clarified that the algorithm to integrate the nbeam TT equation can calculate the Xray wavefield in a crystal of complex shape. Online 18 October 2011 
Acta Cryst. (2011). A67, 557558 [ doi:10.1107/S010876731103724X ] On the polarization state of Xrays generated using a rotating fourquadrant Xray phase retarder systemK. OkitsuSynopsis: A method of calculating the polarization state of Xrays transmitted through a rotating fourquadrant Xray phase retarder system is described using Jones calculus. Online 18 October 2011 
Acta Cryst. (2011). A67, 559560 [ doi:10.1107/S0108767311037251 ] Computersimulated Xray threebeam pinhole topographs for spherical silicon crystalsK. OkitsuSynopsis: Computersimulated pinhole topographs for spherical silicon crystals are reported and compared with those for parallelplate crystals. Online 18 October 2011 
Acta Cryst. (2011). A67, 561563 [ doi:10.1107/S0108767311039523 ] Fundamentals of CrystallographyOnline 18 October 2011 
Acta Cryst. (2011). A67, 564565 [ doi:10.1107/S010876731104298X ] Prices of IUCr journalsOnline 18 October 2011 
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