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H Thijs

Publications and source records attributed to H Thijs.

5 recordsLinked to original sources
PubMed2001

Sensitivity analysis for nonrandom dropout: a local influence approach.

Diggle and Kenward (1994, Applied Statistics 43, 49-93) proposed a selection model for continuous longitudinal data subject to nonrandom dropout. It has provoked a large debate about the role for such models. The original enthusiasm was followed by skepticism about the strong but untestable assumptions on which this type of model invariably rests. Since then, the view has emerged that these models should ideally be made part of a sensitivity analysis. This paper presents a formal and flexible approach to such a sensitivity assessment based on local influence (Cook, 1986, Journal of the Royal Statistical Society, Series B 48, 133-169). The influence of perturbing a missing-at-random dropout model in the direction of nonrandom dropout is explored. The method is applied to data from a randomized experiment on the inhibition of testosterone production in rats.

Animals↗
PubMed1996

Measurement of transepidermal water loss in Tanzanian cot-nursed neonates and its relation to postnatal weight loss.

In healthy cot-nursed Tanzanian neonates (n = 92, gestation 26-42 weeks) measurements of trans-epidermal water loss (TEWL) and weight change were performed during the first 24 h after birth at an average ambient humidity of 70% and an environmental temperature of 32 degrees C. Urine production on day 1 (ml/kg per 24 h) was documented for a subgroup of 13 preterm and 8 term infants. In a limited group of preterm infants (n = 5) TEWL measurements, weight and 24 h urine volume measurements were repeated daily for 7 days. Maximum weight loss was determined in 7 preterm (gestational age 30-36 weeks) and 6 term infants. TEWL was estimated by measuring the evaporation rate at three sites of the body using the water vapour pressure gradient method. On day 1, TEWL was highest in the most preterm infants, whereas TEWL and urine production were higher in large for gestational age infants as compared to appropriate for gestational age (AGA) infants of the same gestational age (31-36 weeks). For the whole group, weight loss on day 1 was correlated with TEWL (r = 0.49, p < 0.05). At follow-up TEWL in preterm infants remained almost constant during the first 4 days and decreased after the fourth day, at which time weight gain commenced. Preterm AGA infants (gestational age 24-37 weeks) showed a mean postnatal weight loss of 4.4% of the birth weight, while in term infants this loss was only 2.6%. A reduced postnatal weight loss as compared to Caucasian infants may be explained by a lower water loss during the first days after birth, through both skin evaporation and urine excretion.

Body Water↗
PubMed1995

Polarity of meiotic gene conversion is 5' to 3' within the niaD gene of Aspergillus nidulans.

We have examined polarity of meiotic gene conversion in the niiA-niaD gene cluster of Aspergillus nidulans in two-point crosses. The type and position of the mutations represented by the niaD alleles and the correlation between the relative frequency of gene conversion and the physical position of these mutations were determined. We show that polarity of meiotic gene conversion is 5' to 3' (transcribed strand) within the niaD gene. Additional crosses involving a niiA allele and a niaD allele show little polarity of gene conversion, which suggests that the recombination events leading to restoration of the niaD gene are initiated upstream of the coding region of the niaD gene but within the niiA-niaD gene cluster, possibly within the intergenic promoter region.

Alleles↗
PubMed1995

A basic serine protease from Paecilomyces lilacinus with biological activity against Meloidogyne hapla eggs.

Scanning electron micrographs of the nematode-egg-parasitic fungus Paecilomyces lilacinus infecting eggs of the root-knot nematode Meloidogyne spp. suggested the involvement of lytic enzymes. When grown on a liquid mineral salts medium, supplemented with different substrates as the sole N- and C-source, the fungus produced an extracellular protease. Colloidal chitin, vitellin and intact eggs of the root-knot nematode Meloidogyne hapla induced proteolytic activity that was repressed by glucose. The protease was partially purified from the culture filtrate by affinity chromatography. It has a molecular mass of 33.5 kDa, a pH optimum of 10.3, a temperature optimum of 60 degrees C and an isoelectric point above pH 10.2. The enzyme was completely inhibited by PMSF. The amino acid sequence, as derived from the nucleotide sequence of a cDNA clone, had high homology with several subtilisin-like serine proteases. It was shown that the purified enzyme degrades vitellin. The protease quantitatively bound to nematode eggs, and eggs incubated with the purified protease eventually floated. Incubation of the purified protease with nematode eggs significantly influenced their development as demonstrated by time-lapse microscopy. Immature eggs were highly vulnerable to protease treatments, whereas those containing a juvenile were more resistant. In addition, hatched larvae were not visibly affected by the protease. It can be concluded that the serine protease might play a role in penetration of the fungus through the egg-shell of nematodes.

Amino Acid Sequence↗