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Seven dicarboxylates of calcium were synthesized. The effect of dicarboxylate on the formation of ␤-form polypropylene was investigated by X-ray diffraction. Calcium pimelate, calcium suberate, calcium phthalate, and calcium terephthalate have been found to be an effective ␤-nucleator.The K x values of the isotatic propylene samples with 0.5 wt % of the nucleators above are 0.95, 0.96, 0.93, and 0.62, respectively. Calcium succinate, calcium adipate, and calcium sebacate behave invalidly on the nucleating of the ␤-phase. We conducted an investigation on the affect of particle shape, crystal form, and crystallinity upon the level of the ␤-form. The X-ray diffraction of the effective nucleators reveals a common character that their first reflection locate at the d-spacing between 10 to 13 Å, indicating structural similarity of the nucleators with ␤-polypropylene. The nucleation mechanism is explained by the cooperative effect of the nonpolar and polar part of nucleating agents in the crystallization of polypropylene.

We present an analysis of the meteorological data collected at Dome A, Antarctica by the Kunlun Automated Weather Station, including temperatures and wind speeds at eight elevations above the snow surface between 0 m and 14.5 m. The average temperatures at 2 m and 14.5 m are −54 • C and −46 • C, respectively. We find that a strong temperature inversion existed at all heights for more than 70% of the time, and the temperature inversion typically lasts longer than 25 hours, indicating an extremely stable atmosphere. The temperature gradient is larger at lower elevations than higher elevations. The average wind speed was 1.5 m/s at 4 m elevation. We find that the temperature inversion is stronger when the wind speed is lower and the temperature gradient decreases sharply at a specific wind speed for each elevation. The strong temperature inversion and low wind speed results in a shallow and stable boundary layer with weak atmospheric turbulence above it, suggesting that Dome A should be an excellent site for astronomical observations. All the data from the weather station are available for download.

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Seeing, the angular size of stellar images blurred by atmospheric turbulence, is a critical parameter used to assess the quality of astronomical sites. Median values at the best midlatitude sites are generally in the range of 0.6-0.8 arcsec 1-3 . Sites on the Antarctic plateau are characterized by comparatively-weak turbulence in the free-atmosphere above a strong but thin boundary layer 4-6 . The median seeing at Dome C is estimated to be 0.23-0.36 arcsec 7-10 above a boundary layer that has a typical height of 30 m 10-12 . At Dome A and F, the only previous seeing measurements were made during daytime 13, 14 . Here we report the first direct measurements of night-time seeing at Dome A, using a Differential Image Motion Monitor 15 . Located at a height of just 8 m, it recorded seeing as low as 0.13 arcsec, and provided seeing statistics that are comparable to those for a 20 m height at Dome C. It indicates that the boundary layer was below 8 m 31% of the time. At such times the median seeing was 0.31 arcsec, consistent with free-

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