55 research outputs found
Long-term Photometric Analysis of the Active W UMa-type System TU Bootis
We present multi-color light curves for the W UMa-type eclipsing binary TU
Boo for two epochs separated by 22 years. An analysis of the O-C diagram
indicates the earlier observations took place right in the middle of a major
period change, thus allowing for a unique study on mass transfer and period
changes in this W UMa-type system. We compute model fits to our light curves,
along with the only other published set, using the Wilson-Devinney program, and
find temporally correlated changes in the size of the secondary component with
anomalies in the O-C diagram. We investigate the cause of these changes and
find support for the existence of rapid, large-scale mass transfer between the
components. We postulate that this interaction allows them to maintain nearly
equal surface temperatures despite having achieved only marginal contact. We
also find support for the evolutionary scenario in which TU Boo has undergone a
mass ratio reversal in the past due to large-scale mass transfer so that what
is presently the secondary component of TU Boo is in an advanced evolutionary
state, oversized due to a helium-enriched core, with a total system age of
10 Gyr.Comment: Accepted to AJ, 9 pages of text, 6 Figure
Clinical and parasitological evaluation of pour-on fluazuron and ivermectin for treating canine demodicosis
Redescription and phylogenetic position of the enigmatic Neotropical electric fish Iracema caiana Triques (Gymnotiformes: Rhamphichthyidae) using x-ray computed tomography
Peixes da Estação Ecológica Serra Geral do Tocantins, bacias dos Rios Tocantins e São Francisco, com observações sobre as implicações biogeográficas das "águas emendadas" dos Rios Sapão e Galheiros
Ontogeny of the Electric Organs in the Electric Eel, Electrophorus electricus: Physiological, Histological, and Fine Structural Investigations
This study attempts to clarify the controversy regarding the ontogenetic origin of the main organ electrocytes in the electric eel, Electrophorus electricus. The dispute was between an earlier claimed origin from a skeletal muscle precursor [Fritsch, 1881], or from a distinct electrocyte-generating matrix, or germinative zone [Keynes, 1961]. We demonstrate electrocyte formation from a metamerically organized group of pre-electroblasts, splitting off the ventralmost tip of the embryonic trunk mesoderm at the moment of hatching from the egg. We show details of successive stages in the development of rows of electric plates, the electrocytes, by means of conventional histology and electron microscopy. The membrane-bound pre-electroblasts multiply rapidly and then undergo a specific mitosis where they lose their membranes and begin extensive cytoplasm production as electroblasts. Electrical activity, consisting of single and multiple pulses, was noticed in seven-day-old larvae that began to exhibit swimming movements. A separation of discharges into single pulses and trains of higher voltage pulses was seen first in 45-mm-long larvae. A lateralis imus muscle and anal fin ray muscles, implicated by earlier investigators in the formation of electrocytes, begin developing at a time in larval life when eight columns of electrocytes are already present. Axonal innervation is seen very early during electrocyte formation.Peer Reviewe
Archolaemus blax Korringa (Pisces, Gymnotiformes, Sternopygidae); a redescription with notes on ecology
Volume: 8Start Page: 231End Page: 24
Tidal migration and patterns in feeding of the four-eyed fish Anableps anableps L. in a north Brazilian mangrove
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