Miao J, Kirz J, Sayre D
Department of Physics and Astronomy, State University of New York at Stony Brook, New York 11794, USA.
Acta Crystallogr D Biol Crystallogr. 2000 Oct;56(Pt 10):1312-5. doi: 10.1107/s0907444900008970.
Sampling the diffraction pattern of a finite specimen more finely than the Nyquist frequency (the inverse of the size of the diffracting specimen) corresponds to surrounding the electron density of the specimen with a no-density region. When the no-density region is bigger than the electron-density region, sufficient information is recorded so that the phase information can be retrieved from the oversampled diffraction pattern, at least in principle. By employing an iterative algorithm, the phase information from the oversampled diffraction pattern of a micrometre-sized test specimen has been successfully retrieved. This method is believed to be able to open a door for high-resolution three-dimensional structure determination of complex and non-crystalline biological specimens, i.e. whole cells and sub-micrometre molecular clusters and micrometre-sized protein crystals. With the possible appearance in the future of X-ray free-electron lasers, it may become possible to image single molecules by recording diffraction patterns before radiation damage manifests itself.
以高于奈奎斯特频率（衍射样本尺寸的倒数）更精细地采样有限样本的衍射图案，相当于在样本的电子密度周围设置一个无密度区域。当无密度区域大于电子密度区域时，就会记录到足够的信息，这样至少在理论上可以从过采样的衍射图案中检索相位信息。通过采用迭代算法，已经成功地从微米级测试样本的过采样衍射图案中检索到了相位信息。人们认为，这种方法能够为确定复杂的非晶态生物样本（即全细胞、亚微米级分子簇和微米级蛋白质晶体）的高分辨率三维结构打开一扇门。随着未来可能出现的X射线自由电子激光器，在辐射损伤显现之前通过记录衍射图案对单分子进行成像或许将成为可能。
