Symbolic parametrization of curves

If algebraic varieties like curves or surfaces are to be manipulated by computers, it is essential to be able to represent these geometric objects in an appropriate way. For some applications an implicit representation by algebraic equations is desirable, whereas for others an explicit or parametric representation is more suitable. Therefore, transformation algorithms from one representation to the other are of utmost importance.We investigate the transformation of an implicit representation of a plane algebraic curve into a parametric representation. Various methods for computing a rational parametrization, if one exists, are described. As a new idea we introduce the concept of working with classes of conjugate (singular or simple) points on curves. All the necessary operations, like determining the multiplicity and the character of the singular points or passing a linear system of curves through these points, can be applied to such classes of conjugate points. Using this idea one can parametrize a curve if one knows only one simple point on it. We do not propose any new method for finding such a simple point. By classical methods a rational point on a rational curve can be computed, if such a point exists. Otherwise, one can express the coordinates of such a point in an algebraic extension of degree 2 over the ground field.     

XV. Yeast sequencing reports. Isolation and DNA sequence of the STE13 gene encoding dipeptidyl aminopeptidase

We have isolated a mutant which exhibits partial constitutivity for a -specific gene expression in α cells. The wild-type gene was cloned and demonstrated to be allelic to the STE13 gene, which encodes the dipeptidyl aminopeptidase involved in processing of the α-factor prepropheromone. Thus, the mating defect of the ste13 mutations in α cells may result both from the production of incompletely processed α-factor and from the increased expression of a -specific genes. The STE13 open reading frame of 931 amino acids contains a putative membrane-spanning segment near its amino terminus and is 31% identical to a second yeast dipeptidyl aminopeptidase (DAP2). A null mutant of STE13 has been constructed: it is viable and sporulation-proficient. The sequence has been deposited in the GenBank data library under Accession Number L21944.     

Hypertension and pulmonary edema associated with subconjunctival phenylephrine in a 2-month-old child during cataract extraction

We have analysed trends in male:female ratios among newborns between 1950 and 1990 in 29 countries from five continents. The numbers of liveborn males and females over the period 1950-1994 were derived from the World Health Organization (WHO) database. Countries for which reliable data were available included 20 major European countries (excluding the former Soviet Union, Albania and a few small countries), Canada, the USA, selected countries of Central and South America, Japan, Australia and New Zealand. From the original numbers of males and females, we computed the proportion of males among liveborns for each country and for selected broader areas within Europe. In most countries the proportion of male liveborns was constant during the study period. In particular, the proportion of male newborns in the European Union was 0.515 in 1950-1954, 0.514 in 1970-1974 and 0.514 in 1990-1994. In the USA, corresponding values were 0.513, 0.513 and 0.512. In Japan the ratios were 0.513 in 1950-1954, 0.516 and 1970-1974 and 0.514 in 1990-1994. Decreasing ratios were observed in some northern and eastern European countries plus Greece and Portugal and, particularly, in Mexico. In contrast, the proportion of male liveborns tended to increase in southern Europe and Australia. Overall, among the 29 countries considered, the proportion of males declined in 16, increased in six, and remained stable in seven.     

Distribution of diethylstilboestrol in pigs

The synthetic growth promoter diethylstilboestrol (DES) administered orally to pigs can be detected by radioimmunoassay (RIA) analysis of kidney, liver, faeces, bile and urine from animals fed continuously to slaughter, but not in muscle, fat or plasma. If treated animals are fed on material not containing DES for 72 h prior to slaughter, then the levels of parent compound and metabolite in all products decrease to become not significantly greater than those in control animals. The gross metabolism of DES in pigs and bovines appears to be similar.