56,048 research outputs found
Possible multiple evolution of indirect telencephalo-cerebellar pathways in teleosts: studies in Carassius auratus and Pantodon buchholzi
Among vertebrates, telencephalo-pontine systems exist only in birds and mammals. However, three nuclei in the diencephalon and mesencephalon of teleost fishes have been indicated — analogous to the pons — to represent relay stations between telencephalon and cerebellum. Since two of these nuclei (dorsal preglomerular nucleus, dorsal tegmental nucleus) have only been described in the highly derived, electrosensory mormyrids, we investigated telencephalic connections in two nonelectrosensory teleosts, the goldfish Carassius auratus and the freshwater butterflyfish Pantodon buchholzi, and cerebellar connections only in the latter species, since for C. auratus these connections are already established. Horseradish peroxidase tracing reveals that C. auratus has a dorsal tegmental nucleus and a paracommissural nucleus both of which are telencephalo-recipient and project to the cerebellum, and that P. buchholzi has a dorsal preglomerular nucleus with such connections. These results extend our knowlegde of the distribution and, therefore, the phylogeny of telencephalo-cerebellar systems in teleosts. Similar to tetrapods, teleosts appear to have developed telencephalo-cerebellar systems several times independently
Phylogeny of putative cholinergic visual pathways through the pretectum to the hypothalamus in teleost fish
Phased models for evaluating the performability of computing systems
A phase-by-phase modelling technique is introduced to evaluate a fault tolerant system's ability to execute different sets of computational tasks during different phases of the control process. Intraphase processes are allowed to differ from phase to phase. The probabilities of interphase state transitions are specified by interphase transition matrices. Based on constraints imposed on the intraphase and interphase transition probabilities, various iterative solution methods are developed for calculating system performability
The valvula cerebelli of the spiny eel, Macrognathus aculeatus, receives primary lateral-line afferents from the rostrum of the upper jaw
In the spiny eel, Macrognathus aculeatus, anterodorsal and (to a lesser degree) anteroventral lateralline nerves project massively to the granular layer of the valvula cerebelli, throughout its rostrocaudal extent. The posterior lateral-line nerve terminates in the corpus cerebelli. Thus, valvula and corpus cerebelli are supplied with mechanosensory input of different peripheral origins. An analysis of the taxonomic distribution of experimentally determined primary lateral-line input to the three parts of the teleostean cerebellum reveals that the eminentia granularis always receives such input, and that the corpus cerebelli is the recipient of primary lateral-line input in many teleosts. The valvula, however, receives primary lateral-line afferents in only two examined species. In M. aculeatus, the massive lateral-line input to the valvula probably originates in mechanoreceptors located in the elongated rostrum of the upper jaw, a characteristic feature of mastacembeloid fishes. This projection to the valvula may therefore represent a unique specialization that arose with the evolution of the peculiar rostrum
Histochemical, connectional and cytoarchitectonic evidence for a secondary reduction of the pretectum in the European eel Anguilla anguilla
Morphological operators for very low bit rate video coding
This paper deals with the use of some morphological tools for video coding at very low bit rates. Rather than describing a complete coding algorithm, the purpose of this paper is to focus on morphological connected operators and segmentation tools that have proved to be attractive for compression.Peer ReviewedPostprint (published version
A formal method for identifying distinct states of variability in time-varying sources: SgrA* as an example
Continuously time variable sources are often characterized by their power
spectral density and flux distribution. These quantities can undergo dramatic
changes over time if the underlying physical processes change. However, some
changes can be subtle and not distinguishable using standard statistical
approaches. Here, we report a methodology that aims to identify distinct but
similar states of time variability. We apply this method to the Galactic
supermassive black hole, where 2.2 um flux is observed from a source associated
with SgrA*, and where two distinct states have recently been suggested. Our
approach is taken from mathematical finance and works with conditional flux
density distributions that depend on the previous flux value. The discrete,
unobserved (hidden) state variable is modeled as a stochastic process and the
transition probabilities are inferred from the flux density time series. Using
the most comprehensive data set to date, in which all Keck and a majority of
the publicly available VLT data have been merged, we show that SgrA* is
sufficiently described by a single intrinsic state. However the observed flux
densities exhibit two states: a noise-dominated and a source-dominated one. Our
methodology reported here will prove extremely useful to assess the effects of
the putative gas cloud G2 that is on its way toward the black hole and might
create a new state of variability.Comment: Submitted to ApJ; 33 pages, 4 figures; comments welcom
Development of advanced fuel cell system, phase 3
A multiple task research and development program was performed to improve the weight, life, and performance characteristics of hydrogen-oxygen alkaline fuel cells for advanced power systems. Gradual wetting of the anode structure and subsequent long-term performance loss was determined to be caused by deposition of a silicon-containing material on the anode. This deposit was attributed to degradation of the asbestos matrix, and attention was therefore placed on development of a substitute matrix of potassium titanate. An 80 percent gold 20 percent platinum catalyst cathode was developed which has the same performance and stability as the standard 90 percent gold - 10 percent platinum cathode but at half the loading. A hybrid polysulfone/epoxy-glass fiber frame was developed which combines the resistance to the cell environment of pure polysulfone with the fabricating ease of epoxy-glass fiber laminate. These cell components were evaluated in various configurations of full-size cells. The ways in which the baseline engineering model system would be modified to accommodate the requirements of the space tug application are identified
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