Excitability in liquid crystal.

The spiral waves observed in a liquid crystal submitted to a vertical electric field and a horizontal rotating magnetic field are explained in the framework of a purely mechanical description of the liquid crystal. The originality of the experiment described in this paper is the presence of the vertical electric field which allows us to analyze the spiral waves in the framework of a weakly nonlinear theory.

Evolution of alpha-fetoprotein serum levels throughout life in humans and rats, and during pregnancy in the rat.

PIP: A radioimmunoassay method (RIA) with specific antisera for human and rat alpha fetoprotein (AFP) was used to study the evolution of AFP levels in humans and rats, respectively, throughout the life span. Sera of 66 rats, aged 3-70 weeks, as well as sera of 201 clinically well children, 192 healthy blood donors, and 16 persons aged 70-98 were assayed. In humans, AFP levels decreased steeply during the 1st year of life, reaching a low basal range by the end of the 2nd year which is maintained throughout adulthood. Rats showed a similar pattern, but concentrations were higher at every stage of life. Puberty occurs in rats while AFP is still decreasing, whereas in humans the adult basal level is stabilized long before puberty. Maternal serum AFP was studied in 29 rats, and the levels were found to begin a sharp increase on the 10th-13th day of gestation. From Day 13-19, a deceleration of AFP increase was observed which led to a decrease between Day 17 and 19. From Day 19-21, AFP levels increased sharply again. A significant correlation was observed on Day 21 of pregnancy between the number of rat fetuses and the maternal AFP level. Hemihysterectomy led to a reduction of AFP level that was grossly proportional to the number of remaining fetuses. The stable level of AFP that persists throughout adult life is attributed to the stability of this protein's synthesis. Conversely, in pregnancy the evolution of serum AFP curve is dependent on the fetal synthesis, maternal and fetal catabolism, and permeability of the placental barrier.^ieng

Influence of age on the physiological serum alpha-fetoprotein levels in man and rat.

PIP: The physiological serum alpha fetoprotein (AFP) levels in humans and rats throughout the life cycle were characterized from 201 blood smaples from children (0-15 years); 192 sera from blood donors aged 20-60 years; and 16 samples from people aged 60-98 years. Males and females were about equally divided. Radioimmunoassay was used for determinations, and its sensitivity was .1 ng for human and 1 ng/ml for rat AFP. A table gives normal AFP levels as determined by different workers. The results led to the following conclusions: 1) AFP levels declined steeply during the 1st year of life, with normal adult levels reached by the end of the 2nd year; 2) 1st year values were highly scattered, but this was unrelated to prematurity; 3) normal adult levels were stable from 20-60 years of age, and no significant change during this period was observed by other workers (average level: 2.6+ or -l.6 ng/ml); 4) AFP level was not influenced by sex nor puberty; 5) the average level in a group of 15 normal people aged 60-98 years was 2 ng/ml (+or-l.l ng), whereas for people over 74 years it was l.4 ng (+ or-.5), which is significantly different (P .05); 6) rat AFP behaved differently, varying by weight more than age though these 2 factors may be correlated, suggesting that the decrease of AFP levels reflected the influence of age rather than weight. This study confirms that the postnatal reduction of AFP biosyntheses is not complete and shows that it is a gradual process both in the rat and humans.^ieng