998 resultados para pit crater


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Esitelmä pidetty Suomalaisen lakimiesyhdistyksen Lapin osaston kokouksessa Rovaniemellä 9.10.1997

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A recent study of a pair of sympatric species of cichlids in Lake Apoyo in Nicaragua is viewed as providing probably one of the most convincing examples of sympatric speciation to date. Here, we describe and study a stochastic, individual-based, explicit genetic model tailored for this cichlid system. Our results show that relatively rapid (<20,000 generations) colonization of a new ecological niche and (sympatric or parapatric) speciation via local adaptation and divergence in habitat and mating preferences are theoretically plausible if: (i) the number of loci underlying the traits controlling local adaptation, and habitat and mating preferences is small; (ii) the strength of selection for local adaptation is intermediate; (iii) the carrying capacity of the population is intermediate; and (iv) the effects of the loci influencing nonrandom mating are strong. We discuss patterns and timescales of ecological speciation identified by our model, and we highlight important parameters and features that need to be studied empirically to provide information that can be used to improve the biological realism and power of mathematical models of ecological speciation.

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A report on the ultrastructural observations of the pit connections in three species of Gelidiocolax (G. margarifoides (Martin and Pocock) Fan and Papenfus, G. christianae Feldmann and G. deformans Seoane-Carnba) has been carried out. As has been described in other species, electrondense elements and myelinic figures, possibly formed by the endoplasmic reticulum, were condensed in a mass. This mass became a diabolos-shaped structure before the cytoplasm had finished its division and the septum had reached its complete development. Myelinic figures were usually found in the core of well formed pit plugs, but such figures were apparently substituted by granular material during the ontogeny. Key words: Gelidiocolax ultrastructure, Pit connection, Pit connection ultrastructure, Pit connection Ontogeny.

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In November of 1966, an investigation of the rigid Class I asphalt treated base specification, requiring 70 per cent crushed limestone, was initiated. It was felt that it might be possible to modify the need for crushed particles, in the construction of basis on heavy duty roads, at a savings, by using more local materials, without sacrificing strength and/or durability. This is a short study on typical sources of pit run gravel, with various percentages of limestone. It is conducted with an eye open to the possibility that our specifications may be modified. The possibility that further investigation may be desirable is not ignored.

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