Analysis of a Long-term Experiment with Repeated-measurement Models

Long‐term experiments are a classical case of repeated measurements. Traits are measured on the same experimental unit over many years so that correlations arise between the observations made on the same plot in consecutive years. This paper describes the analysis of a three‐crop‐rotation long‐term experiment. We analysed the yields of the crops and the organic carbon content in the topsoil over 30 consecutive years. Several variance–covariance approaches are discussed and the trait‐specific best fit is interpreted. Mixed models are used to describe the structure of the experiment. Both yields and soil organic carbon show a more or less pronounced variance heterogeneity. Especially for yields, the heterogeneity of cycles and years is dominant. The consideration of correlations results in a better model fit in all cases.     

Annual sex hormonal profiles, gonad development and age determination of the Mekong giant catfish (Pangasianodon gigas, Chevey)

Annual sex hormonal profiles, gonad development and age determination of 18 (13–14 kg body weight) and three (145–226 kg body weight) Mekong giant catfish (MGC) (Pangasianodon gigas, Chevey) reared in earthen ponds in Chiang Mai and from the Mekong River in Chiang Rai, Thailand, respectively, were investigated. The hormonal profiles were determined from blood samples of the fish by electrochemiluminescence immunoassay during May to August in 2000. The highest testosterone levels of 0.06 ng mL^?1 in both sexes and the highest oestradiol of 47.8 and 14.23 pg mL^?1 in females and males, respectively, were observed in May. The gonadosomatic index was found to be 0.07 for males and 0.38 for females from ponds in comparison with 2.27 for males and 8.29 for females from the Mekong River. Higher development stages of spermatocytes and oocytes of the cultured fish in May than in February and November were demonstrated. No mature germ cells were obtained from either the males or females, indicating no sexual maturity. The average age of fish was determined from the annual rings of the cross‐section of the pectoral fins by a stereomicroscope. The average age of fish in earthen pond determined from the annual ring was 8 years, which agreed with the actual culture records, while those from the Mekong River were 21 years. This information will be beneficial for the breeding programmes and conservation of the MGC.     

Agrogis: a computer‐based program for collecting information on pests of plants in Poland*

A computer system Agrogis has been developed to record information on pest infestation of plants in different regions of Poland. Data can be entered manually or from disks, and can be displayed in the form of charts and maps. Agrogis will be made available on the Internet.     

糖类寄生螨快速分离检验方法

本文对糖类寄生螨的快速分离检验方法进行了改进。将糖类溶解后，经过500目/英寸标准检验筛进行过筛分离。此方法对各种可溶性糖类中的寄生螨类能取得100％的快速分离检验结果。     

浙江淳安新安江开发公司封山育林效益研究

浙江省淳安县新安江开发公司所属16个国营林场22475.53hm~3荒山迹地,封山育林30年,现有天然次生林总蓄积量135万m~3,年总生长率8.07％,活立木直接经济价值2.25亿元。到1987年止公司已获中间利用净收入2135万元。近20年累计天然次生林比无林地多涵蓄水10亿m~3,每年进入水库的泥沙量减少80％,对调节水库水源、延长发电年限、纯洁水质都起到良好作用。公司长期实施的5项管护技术,把封山育林提高到科学经营水平,在千岛湖区成功地建立了森林生态屏障。     

Developmental biology of T cell receptors

T cell receptors are the antigen-recognizing elements found on the effector cells of the immune system. Two isotypes have been discovered, TCR-gamma delta and TCR-alpha beta, which appear in that order during ontogeny. The maturation of prothymocytes that colonize the thymic rudiment at defined gestational stages occurs principally within the thymus, although some evidence for extrathymic maturation also exists. The maturation process includes the rearrangement and expression of the T cell receptor genes. Determination of these mechanisms, the lineages of the cells, and the subsequent thymic selection that results in self-tolerance is the central problem in developmental immunology and is important for the understanding of autoimmune diseases.