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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.

A two years experiment was conducted using maize inbred line Qi 319 with different nitrogen fertilization levels and exogenous hormone 6 benzyl adenine (6-BA) treatments. The results demonstrated that the chlorophyll content and net photosynthetic rate (P n ) were gradually decreased after anthesis. In treatments of 6-BA without nitrogen fertilizer, chlorophyll contents were increased significantly, but P n showed no significant increase, and the activity of PSII reaction center was not increased. Under the condition of applying nitrogen fertilizer, P n and the activity of PSII reaction center were increased significantly, and based on nitrogen fertilizer used, the 6-BA could improve the response of P n and performance of PSII to nitrogen fertilizer effectively. Under the nitrogen fertilizer and 6-BA interaction conditions, the chlorophyll content and P n were increased significantly (P<0.05), the activities of donor site and acceptor site of PSII were increased significantly, and the donor site was improved more than that of acceptor site. The most obvious improvement of the activity of PSII reaction center was appeared at the 10th day after anthesis. The improvement of photosynthetic performance significantly improved the single plant dry matter accumulation and grain yield (P<0.05). In conclusion, spraying plant with 6-BA under suitable application of nitrogen fertilizer can significantly improve the photosynthetic performance of maize leaf.

The preparation of the key intermediate 4 of the methyl isosartortuoate is described. Methyl isosartortuoate 1 was a marine natural product with unique and complex architectures, which was first disclosed in 1986.' The presence of eleven stereogenic centers and the four rings heighten the challenge of synthesis for the target compound. Su and co-workers' have presented a provocative hypothesis to explain the biogenetic path of methyl isosartortuoate , involving an intermolecular Diels-Alder cycloaddition between the dienophile 2 and diene 3 (Scheme 1 ) . This interesting possibility as well as scheme 1 the unusual structure features of methyl isosartortuoate promoted us to initiate a research project aimed at its total synthesis. Herein we report the full results of the enantioselective synthesis of 1Cmembered carbocyclic nucleus 4, in which all of the chiral centers in the diene unite 3 have been established.Our retrosynthesis is shown in Scheme 1. Although carbocyclization has been successfully employed in several total syntheses,3 we chose to employ a [ 2,3]-Wittig ring contraction of the 17-membered cyclic propargyl allylic ether, leading to the 14-membered carbocyclic nucleus 4.The synthetic work first focused on the construction of the chiral tetrahydrofuran ring by using of twice Sharpless AE reactions and epoxide-opening process (Scheme 2 ) . The commercially available geraniol was first converted into the secondary allylic alcohol 8 as a known procedure ,4 2 3 u 6 4