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N Nikolaidis

Publications and source records attributed to N Nikolaidis.

8 recordsLinked to original sources
PubMed1996

Non-linear algorithms for processing biological signals.

This paper illustrates different approaches to the analysis of biological signals based on non-linear methods. The performance of such approaches, despite the greater methodological and computational complexity is, in many instances, more successful compared to linear approaches, in enhancing important parameters for both physiological studies and clinical protocols. The methods introduced employ median filters for pattern recognition, adaptive segmentation, data compression, prediction and data modelling as well as multivariate estimators in data clustering through median learning vector quantizers. Another approach described uses Wiener-Volterra kernel technique to obtain a satisfactory estimation and causality test among EEG recordings. Finally, methods for the assessment of non-linear dynamic behaviour are discussed and applied to the analysis of heart rate variability signal. In this way invariant parameters are studied which describe non-linear phenomena in the modelling of the physiological systems under investigation.

Algorithms↗
PubMed1996

The Drosophila montium subgroup species. Phylogenetic relationships based on mitochondrial DNA analysis.

Mitochondrial DNA (mtDNA) restriction site maps for three Drosophila montium subgroup species of the melanogaster species group, inhabiting Indian and Afrotropical montium subgroup territories, were established. Taking into account previous mtDNA data concerning six oriental montium species, a phylogeny was established using distance-matrix and parsimony methods. Both genetic diversity and mtDNA size variations were found to be very narrow, suggesting close phylogenetic relationships among all montium species studied. The phylogenetic trees that were constructed revealed three main lineages for the montium subgroup species studied: one consisting of the Afrotropical species Drosophila seguyi, which is placed distantly from the other species, one comprising the north-oriental (Palearctic) species, and one comprising the southwestern (south-oriental, Australasian, Indian, and Afrotropical) species. The combination of the mtDNA data presented here with data from other species belonging to the melanogaster and obscura subgroups revealed two major clusters: melanogaster and obscura. The melanogaster cluster is further divided into two compact lineages, comprising the montium subgroup species and the melanogaster complex species; the species of the other complex of the melanogaster subgroup, yakuba, disperse among the obscura species. The above grouping is in agreement with the mtDNA size variations of the species. Overall, among all subgroups studied, the species of the montium subgroup seem to be the most closely related.

Animals↗
PubMed1995

Three computer methods to reconstruct pulpal blood vessels and nerves.

This study describes three methods of computerized three-dimensional reconstruction of the main neurovascular pulpal bundle of human teeth, using serial cross-paraffin sections, digital image processing, and three-dimensional computer graphics. These methods are surface representation, representation by means of a stack of slices, and volume representation.

Adolescent↗
PubMed1995

Computerized reconstruction of TEM examined pulpal blood vessels and nerves.

Five healthy premolars were used for transmission electron microscopy examination and three-dimensional (3D) reconstruction of pulpal blood vessels and their surrounding nerves. Serial Epon thin sections were taken from specimens. After a series of preprocessing steps that included digitization, contrast enhancement, slice alignment, segmentation and interpolation, three dimensional surface representation was performed using the triangulation method. The findings showed that vessels were usually accompanied by a number of myelinated and unmyelinated nerves. The nerves shared a more or less common course with the vessels. Small arteries presented greater number of nerves in their vicinity, compared to small veins. In the sections examined, no direct contact between the nerve trunks and the wall of the vessels was found; the closest distance measured was approximately 67 microns. The common course of vessels and nerves suggested autonomic innervation on part of the myelinated axons.

Adult↗
PubMed1993

[Trichobezoar as a rare cause of ileus of the small intestine].

For several weeks a 15-year-old girl had complained of increasing abdominal pain with vomiting. On admission to hospital the bloated abdomen was diffusely sensitive to pressure and the bowel sounds were high pitched and loud. Erythrocyte sedimentation rate was increased to 23/40 mm and the white cell count to 12,000/microliters. Ultrasound examination revealed an echo-dense area with dorsal echo loss at the gastric side of the pylorus. X-ray films of the stomach showed fluid levels and a soft-tissue mass in the left upper abdomen. At laparotomy a large (12 x 6 cm) trichobezoar was found in the middle of the small intestine and two smaller ones at the pylorus. Subsequently the patient admitted to trichophagia but refused any psychological treatment.

Adolescent↗