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In-pipe robots provide inspection and maintenance services to various pipelines. This article proposes an algorithm to calculate the required radial variations for in-pipe robots to pass through pipeline elbows smoothly. It first gives a full overview of a robot passing through a U-shaped elbow and identifies the problem location where the radial dimension changes the most. It then presents a detailed analysis on the focused stage and deduces the algorithm. Based on the obtained algorithm, a realizing Matlab program is written to calculate all possible lengths of front and rear legs at every moment during the process. Finally, the calculation results are presented to precisely describe the track of movement, the length deformations during the whole process, and different contributions of structural variables. This article provides the design and the control of an in-pipe robot with an algorithm to calculate the lengths of its legs at every moment and to what extent the deformations of elastic legs are required. [ABSTRACT FROM AUTHOR]

Zhu B-P (Department of Epidemiology, Division of Social Medicine and Public Health, Peking Union Medical College, Beijing, People's Republic of China), Liu M, Wang S-Q, He G-Q, Chen D-H, Shi J-H and Shang J-Z. Cigarette smoking among junior high school students in Beijing, China, 1988. 1992; 21: 854–861. Prevalence, behavioural patterns and risk factors of cigarette smoking were studied in a sample of 8437 junior high school students in Beijing in 1988. Smoking at least occasionally was reported by 34.4% of boys and 3.9% of girls, though the intensity tended to be low. Smoking prevalence increased with age among boys. Inhaling smoke into the lungs was practised by 68.2% of the boys who smoked and 37.3% of the girls. ‘Believing that one looks elegant when smoking’, ‘trying to be fashionable’ and ‘seeking stimulation’ were the most important reasons for smoking. Of the boys 83.5% and of the girls 86.5% usually smoked with friends or schoolmates. Many more boys (19.2%) than girls (1.7%) smoked at home. Examinations of risk factors for teenage smoking showed that it was associated with a combination of familial, psychological and socio-school factors, with peer group pressure being the most important one. [ABSTRACT FROM PUBLISHER]