Abstracts 255

We discuss the chemical potential of a non-zero temperature electron gas embedded in a strong

magnetic field and the effect of the field on the electron screening potential. 33S is taken as a specific

example. It is shown that a sufficiently strong field can decrease the capture rate significantly at

low temperatures and densities, but for the fields (10s-10’3 G) on the surface of neutron stars, the

effect on electron capture is almost nil. (AA& 1966, 3’7, 430-436)

Separators in the solar magnetic field and the flare sites Li Bi-qiang, Song Mu-tao & Hu

Fu-min Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008

Using Ha filtergrams of the active region NOAA 6309 taken on 1990 Ott 13-16 at Ganyu

Observing Station of Purple Mountain Observatory and solar magnetic field data of the former

Soviet Union, we determined the field separator in the daily magnetic maps. We found that the

bright plages and flare knots are located at, or close to the separator, thus confirming the close link

between separator, flares and magnetic field reconnection. (AAnS 1996, 37, 437442).

El nifio events and the 50 d oscillation in solar activity Li Zhi-an, Lin Qiao, Han Yan-ben

and Zhao Juan Department of Astronomy, Beijing Normal University, Beijing 100875

We analysed the 50d oscillation in the data of solar flux, relative sunspot number, atmospheric

angular momentum and changes in the length of day for the years 1981-1994. We found the

oscillation period varied between 40 and 60d. We point out that the three el nifio events in these

years all happened when the oscillation period was low. (AAnS 1996, 37, 443-448).

On the periodicity in the redshift distribution of QSOs Wang Jia-qing Department of

Physics, Anhui Normal University, Wuhu, 241001

It is pointed out that the restriction of the redshifted spectral lines by the optical window is

at least one of the major factors that cause the observed periodicity in the redshift distribution of

QSOs. (AAnS 1996, 37, 449-454).

On relativistic beam models &in Yi-ping, Xie Guang-zhong & He Miao-than Yunnan Obserua-

tory, Chinese Academy of Sciences, Kunming 650011

Relativistic beams models can be classified according as the apparent transverse velocity is or

is not redshift-dependent. A statistical test is proposed using the numbers of superluminal sources

with low and high redshifts. The result of the test is tentative, because of severe observational

selection effects. AApS 1997, 17, 13-20.

The size distribution of r-ray bursts Wu Mei, Song Li-ming, Yu Wen-fei, Li Ti-pei & Li Yi

Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039

It is shown that the size (photon count) distribution of y-ray bursts calculated on assuming

standard candle and uniform density in space in a simple cosmological model does not deviate

significantly from the observed BATSE data, corrected for trigger efficiency and dead time. (AApS

1997, 17, 29-36).

The effect of spiral structure on the formation of giant molecular clouds Zhang Tong-jie

& Song Guo-xuanshanghai Observatory, Chinese Academy of Sciences, Shanghai 200030

We follow the evolution of 120 000 basic clouds of mass 10’ MO each in a Toomre galactic

disk for 300Myr and note their aggregation into larger clouds. We find that the spiral structure

promotes the formation of giant clouds in the arms, but these may subsequently disintegrate in the

inter-arm region. Compared to the case of no spiral structure, the effect of the spiral arms is an

increase in the number of very massive clouds, while the number of clouds with masses in the range

105-lo6 MO is hardly affected. (AApS 1197, 17, 50-56.

A set of simple and accurate formulae for gyrosynchrotron radiation Zhou Ai-hua,

Ma Chun-yun, Zhang Jie & Wang Xin-dongPurple Mountain Observatory, Chinese Academy of

Sciences, Nanjing 210008

For two of the three indices that figure in usual approximate formulae for emissivity and