In our previous work we demonstrated an unusual crystallite aggregate in which the crystallites correlate in crystallographic orientation and form a fractal pattern with strong anisotropy (Wang, M.; et al. Phys. ReV. Lett. 1998, 80, 3089. Liu, X. Y.; et al. J. Cryst. Growth 2000, 208, 687.). Yet it remains unanswered why each crystallite appears with specific orientation and obeys a strict order. Here we report an in-depth study of the origin of the long-range correlation of the crystallographic orientations in the aggregate investigated by means of micro-X-ray-diffraction, atomic force microscopy, and in-situ optical observation. The experimental data suggest that the topographic regularity of the aggregate arises from the consecutive rotation of the crystallographic orientation in the nucleation-mediated growth. This effect may occur when nucleation takes place in a region with inhomogeneous surface tension, and may help us to understand the long-range ordering effect in aggregating crystallites.

To reduce the discharge of the standard bulk Micromegas and GEM detector, the GEM-Micromegas detector was developed at the Institute of High Energy Physics. Taking into account the advantages of the two detectors, one GEM foil was set as a preamplifier on the mesh of Micromegas in the structure and the GEM preamplification decreased the working voltage of Micromegas to reduce the effect of the discharge significantly. At the same gain, the spark probability of the GEM-Micromegas detector can be reduced to a factor 0.01 compared to the standard Micromegas detector, and even the higher gain could be obtained. In the paper, the performance of the detector in X-ray beam was studied at 1W2B Laboratory of Beijing Synchrotron Radiation Facility. Finally, the result of the energy resolution under various X-ray energies was given in different working gases. It indicates that the GEM-Micromegas detector has the energy response capability in the energy range from 6 keV to 20 keV and it could work better than the standard bulk-Micromegas.

Current methods of characterizing electromagnetic(EM)-pulse can be divided into two classes,one is based on photons replica of the EM-pulse under test and the other on electrons replica. Methods in first class, such as interferometry and spectrography, are difficult to be competent for characterization of EM-pulse with attosecond(AS)-level duration due to too short duration or too broad bandwidth. Methods in second class, such as streak camera method, is competent but demands the pulse to have a peak strength high enough for efficiently producing X-ray photons. We propose a simple, universal method without special demand on the peak strength. It uses conventional optics method to sample, in AS-level step, wavefronts of the EM-pulse under test. Phase information carried by each sampled wavefront is fixed into, as a long-life trace, solid-state circuit and hence allow recording raw measurement data to be conducted over a feasible longer time scale.

We present an improvement of short term frequency stability of the integrating sphere cold atom clock after increasing the intensities of clock signals and optimizing the feedback loop of the clock. A short term frequency stability of 13 1/2 5.0 10     has been achieved and the limiting factors have been analyzed.