1,192 research outputs found
On the variational distance of two trees
A widely studied model for generating sequences is to ``evolve'' them on a
tree according to a symmetric Markov process. We prove that model trees tend to
be maximally ``far apart'' in terms of variational distance.Comment: Published at http://dx.doi.org/10.1214/105051606000000196 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Infection of cultured and freshwater fishes with monogeneans in Syria
During a survey made in 2004 and 2005 in Syrian fish farms of the Orontes valley and on natural water fishes harvested in the Orontes River and in Lake Assad (a water reservoir of the Euphrates River), 145 specimens of fish belonging to 15 fish species were examined for monogenean infections. Eleven monogenean species (8 Dactylogyrus spp., 1 Silurodiscoides sp. and 2 Cychlidogyrus spp.) were found in the gills. Monogeneans infecting farm-cultured fishes were the same as those commonly occurring in cyprinids (Dactylogyrus anchoratus, D. extensus, D. lamellatus) and filapia (Cychlidogyrus tilapiae, C. arthracan thus) cultured in Europe and in tropical countries. Among monogeneans found in fishes of natural waters, typical representatives of the Tigris-Euphrates Basin (Dactylogyrus carassobarbi, D. holciki) and species common in the Holoarctic zoogeographical zone (D. alatus, D. carpathicus, D. distinguendus and Silurodiscoides vistulensis) were equally found
First description of myxozoans from Syria: novel records of hexactinomyxon, triactinomyxon and endocapsa actinospore types
Oligochaete worms collected in late March and early April 2005 from 3
freshwater biotopes in Syria were surveyed over an 11 wk period for
myxosporean parasites (Myxozoa). Three types of novel actinospore
stages were identified from 1 host species, Psammoryctides albicola. A
hexactinomyxon was found in 6 P. albicola (7.5%) collected from a
branch of the River Orontes, north of the city of Hama. A
triactinomyxon and an endocapsa were found in single P. albicola
specimens from the Al-Thaurah region of the Euphrates River (Lake
Assad). No oligochaetes collected from Al-Ghab fish farm (Orontes
region) released actinospores during the observation period. The
present study is the first description of myxosporeans, including
actinospore stages, from Syria. The 3 types described herein differ
morphologically and molecularly (18S rDNA) from published records
Development of Myxobolus dispar (Myxosporea : Myxobolidae) in an oligochaete alternate host, Tubifex tubifex
The development of Myxobolus dispar Thelohan, 1895, a myxosporean parasite of the gills of common carp (Cyprinus carpio L.) was studied in experimentally infected oligochaetes Tubifex tubifex Muller. After infection of uninfected tubificids with mature spores of M. dispar development of actinosporean stages was first observed light microscopically 21 days after initial exposure. In histological sections, early pansporocysts were located in the gut epithelium of experimental oligochaetes, while advanced stages occupied mostly the outer layers of the gut and the coelozoic space. Mature pansporocysts, each containing 8 raabeia spores, appeared 199 days after initial exposure. Following damage of the intestinal wall and rupture of the pansporocysts, free actinosporean stages were found in the gut lumen of the oligochaetes. Actinospores of M. dispar emerged from the worms after 217 days of intra-oligochaete development. They were floating in the water and showed a unique raabeia form. Each raabeia sport had three pyriform polar capsules and a cylindrical-shaped sporoplasm with approximately 32 secondary cells. The spore body joined the three caudal projections without a style. Caudal projections were bifurcated at the end and the two main branches had further small bifurcations. The total length of the raabeia sport was approximately 158 mu m. The prevalence of infection in 240 experimentally infected Tubifex specimens was 99.2%. No infection was found in the control oligochaetes
Wiener Index and Remoteness in Triangulations and Quadrangulations
Let be a a connected graph. The Wiener index of a connected graph is the
sum of the distances between all unordered pairs of vertices. We provide
asymptotic formulae for the maximum Wiener index of simple triangulations and
quadrangulations with given connectivity, as the order increases, and make
conjectures for the extremal triangulations and quadrangulations based on
computational evidence. If denotes the arithmetic mean
of the distances from to all other vertices of , then the remoteness of
is defined as the largest value of over all vertices
of . We give sharp upper bounds on the remoteness of simple
triangulations and quadrangulations of given order and connectivity
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