NEUROSPORA MUTANT LACKING AN ARGININE-SPECIFIC CARBAMYL PHOSPHOKINASE

An arginine-requiring mutant of Neurospora lacks the carbamyl phosphokinase activity present in other strains. Although carbamyl phosphate, the product of this enzyme, is required in both arginine and pyrimidine synthesis, the enzymne appears to serve only the arginine pathway. A pyrimidine specific mode of carbamyl phosphate synthesis is inferred, although it has not yet been demonstrated.     

管道涂敷施工前表面处理研究

通常情况下,管道涂敷商在涂敷新涂层之前,都要将管道表面处理到Sa 2.5级或者近白级,但是在施工现场却很难达到这一标准.讨论了旧涂层去除的常规方法、表面处理以及可预见的结果,并讨论了当前在表面处理方面的研究成果以及在涂层涂敷过程中二次生锈的各种影响.     

Fossil Evidence for a Late Cretaceous Origin of "Hoofed" Mammals

Seventeen of eighteen orders of living placental mammals are not known before 65 million years ago. The monophyly of each order is well established, but interrelations have been less certain. A superordinal grouping of up to seven extant orders plus a variety of extinct orders, all included within Ungulata ("hoofed" mammals), can be linked to Late Cretaceous mammals from the 85-million-year-old Bissekty Formation, Uzbekistan (and, less certainly, North America and Europe), thus pushing the origin of this major clade back by 20 million years. Ungulatomorphs are not closely related to primates, rodents, or rabbits.     

Behavioural determinants of distribution and survival in early stages of walleye pollock, Theragra chalcogrammai a synthesis of experimental studies

This review summarizes results of an extensive series of laboratory studies on the behavioural responses of early life stages of walleye pollock, Theragra chakogramma to key environmental factors including light, temperature, gravity, turbulence, food availability and predator presence. Experiments focused on vertical distribution of egg through 0-age stages, and social interactions of age-0 juveniles. Key factors were modified either singly or in concert to determine their direct and indirect influence on fish behaviour. The observed results suggest that the behaviour of individual fish depends on the integration of a continually changing hierarchy of both intrinsic and extrinsic factors, with the relative importance of a specific factor varying with ontogeny and over time and space. The broad range of responses displayed by early life stages suggests that behaviour plays an important role in determining the consequences of environmental variability on walleye pollock populations. In general, results from our laboratory experiments are consistent with patterns observed in field studies, supporting the efficacy of using experimental behavioural research to define some of the underlying mechanisms controlling distribution and survival in the field, and eventual recruitment to adult populations.     

The enhancement of resistance of the American eel, Anguilla rostrata Le Sueur, to a pathogenic bacterium, Aeromonas hydrophila, by an extract of the tunicate, Ecteinascidia turbinata

Abstract. Extracts of the tunicate Ecteinascidia turbinate were used in preventing Aeromono hydrophila infection in the American eel, Anguilla rostrata. Intraperitoneal injection of the extract 2 days after bacterial challenge was shown to increase dramatically eel phagocytic activity and resistance to disease. Intravenous injection of the extract 2 days post-bacterial injection was shown to increase antibody titres. This study helps to substantiate the possible use of E. turbinata extract in treating eel diseases. The exact nature of its protective effect will be dependent on the time and route of its delivery.