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Biomedical subjects

D Siegmund

Publications and source records attributed to D Siegmund.

23 records · Page 2Linked to original sources
PubMed1992

A model for penicillin production with and without temperature shift after the growth phase.

A strain of Penicillium chrysogenum producing about 8 milligrams/l of penicillin V, was cultivated in a 10-1 bioreactor. Under carbon (C)-limitation during the production phase a glucose/ammonium sulphate mixture was fed using microprocessor control. When the temperature was shifted from 25 degrees C to 30 degrees C at the end of the active growth phase, the specific penicillin production rate was increased by 30%, while the yield remained constant. Maximal productivity without sporulation was obtained when the net growth rate of the active (respiring and producing) biomass, estimated by measuring the respiration rate under defined conditions, was equal to or higher than 0.004 h-1. A model was developed for penicillin fermentation during C-limitation possessing the following properties: (1) the model is based on ordinary differential equations; (2) the influence of different nutrients is considered; (3) the model recognizes two cell types (active and inactive); (4) the model describes the influence of a temperature shift at the end of the vigorous growth phase.

Fermentation↗
PubMed1982

Continuous intravenous vasopressin in active upper gastrointestinal bleeding.

Sixty patients with active upper gastrointestinal bleeding were randomized to received either continuous intravenous infusions of vasopressin (29 patients) or placebo (31 patients) at a rate of 40 U/h. Six hours after beginning the study, 13 patients in the vasopressin group and 11 in the placebo group] had ceased bleeding (p = 0.46). By 24 hours. 17 patients in the vasopressin group and 14 in the placebo group had stopped bleeding (p = 0.30). Restriction of the analysis to patients bleeding from varices showed no advantage with vasopressin treatment after 6 or 24 hours. No consistent trend favoring use of vasopressin to stop hemorrhage was noted during the 30-month study period. There was little difference between the two groups in the number of patients needing surgery (13 on vasopressin, 18 on placebo; p = 0.30) or the number of deaths (eight on vasopressin, 11 on placebo; p = 0.51); the transfusion requirement was the same. In our patients, a continuous intravenous infusion of vasopressin neither controlled bleeding nor altered outcome.

Clinical Trials as Topic↗
PubMed1980

Sequential medical trials.

A model for sequential clinical trials is discussed. Three proposed stopping rules are studied by the Monte Carlo method for small patient horizons and mathematically for large patient horizons. They are shown to be about equally effective and asymptotically optimal from both Bayesian and frequentist points of view and are markedly superior to any fixed sample size procedure.

Journal Article↗
PubMed1969

Probability distributions related to the law of the iterated logarithm.

Let W(t) denote a standard Wiener process for 0 </= t < infinity. We compute the probability that W(t) >/= t((1/2))A(t) for some t >/= 1 (or for some t >/= 0) for a certain class of functions A(t), including functions which are approximately (2 log log t)((1/2)) as t --> infinity. We also give an invariance principle which states that this probability is the limit as m --> infinity of the probability that s(n) >/= n((1/2))A(n/m) for some n >/= m (or for some n >/= 1), where s(n) is the sum of n independent and identically distributed random variables with mean 0 and variance 1.

Journal Article↗