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SPQK-Symposium:
Diffraction - Theory and Practice
(DIFTP)
Max-Planck-Institute
for Physics of Complex Systems
December 19.-21. 1999
Diffraction - Theory and Practice
(DIFTP)
Max-Planck-Institute
for Physics of Complex Systems
December 19.-21. 1999
REPORT
(program,
references)
(program, references)
The last SPQK-symposium in 1999 took place at the Max-Planck-Institute for Physics of Complex Systems (MPIPKS) in Dresden on December, 19-21. It was sponsored by the DFG-Schwerpunkt "Quasicrystals: Structure and Physical Properties" (SPQK) and the MPIPKS. Due to the funds of the MPIPKS it was possible to invite many guests from outside the SPQK. The topic of the Symposium, "Diffraction -- Theory and Practice", brought together 33 researchers from both sides, theory and experiment. The program consisted mainly of longer plenary talk. Most of them were devided into two parts. In the first part, an introduction was given for the non-speciallists. The second (bigger) part was devoted to the state of the art knowledge of the field. The length of the talks gave enough time for questions and detailed discussions, and both, the speakers and the audience, used this freedom during and after the talks.
The program started with a theory session on Sunday morning. Michael Baake (Tuebingen) discussed the current state of knowledge about the question: "Which state of matter diffracts". Although this question was posted (by Bomberi and Taylor) shortly after the discovery of quasicrystals by Dan Shechtman in 1984, the answer is far more complicated than expected. We have to be aware that there are many (more or less) ordered structures even beyond quasiperiodicity that can give rise to Bragg oder Bragg-like diffraction spectra. And we have to take into account that their contribution can spoil our interpretation of present day data. Afterwards, Veit Elser (Cornell) gave an intuitive approach to the diffraction properties of random tiling structures focussing on the additional non Bragg-like part of the spectra. The theory session was closed by Moritz Hoeffe (Tuebingen). He showed diffraction properties of several examples, with focus on the diffuse background.
In the first experimental session, Conradin Beeli (Zuerich) gave a review about electron microscopy. After an introdution to several technical aspects, he focused on the achievements and the problems of electron imaging. The monday morning session was opend by Eveline Weidner (Muenchen) who gave the introduction to the different aspects of X-ray scattering. She supplied the audiance with knowledge about the experimental setups, the experimental data collection and the usual approximations. Afterwards Fritz Frey (Muenchen) spoke about what we know and what we can do with X-ray scattering concerning the structure analysis of quasicrystals. In the afternoon, Marc de Boissieu (Grenoble) summarized the knowledge about neutron scattering, the state of the art and the problems. All three big experimental sessions were brought into one line by the speakers so that the audience could follow the advantages and disadvantages of the different techniques.
On Tuesday morning, Stephen Pennycook (Oak Ridge) spoke about Z-contrast imaging in general and its application to aperiodic crystals in particular. He introduced the audience to this relatively new technique and outlined its potential power. But he also clearly marked the possible pitfalls. The second morning talk was given by Veit Elser who gave an overview about his method of phase-reconstruction called "Principle of Minimum Charge". This method can become an alternative approach (compared with e.g. the maximum entropy method) in structure analysis. The end of the official program was a talk of Dr. Takakura (Tsukuba) about "Modelling and Structure Refinement of Quasicrystals".
All talks were embedded into lively discussions so that the timeslots for the individual talks were filled out. But because all participants were accomodated in the guest-houses of the MPIPKS there was enough time for discussions even after the talks. The familiar ambiente of the MPIPKS is for sure a major factor for every meeting of this kind. For the organizers it is an easy and pleasant job to be responsible for a symposium which is supported by the professional conference team of this institute. So it is our pleasure to thank the MPIPKS for the additional funding of our meeting and Mrs. Katrin Lantsch for her organisational work before and during the conference.
Last but not least we want to thank the speakers who did a real good (and sometimes exhausting) job and the audience who contributed with comments, questions and answers. We hope that the SPQK can continue to support meetings like this.
Dresden,
Dieter Joseph (joseph@mpipks-dresden.mpg.de )
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