2 resultados para Bellingshausen Sea, steep slope east of TMF
em CaltechTHESIS
Resumo:
After artificial activation or fertilization of non-nucleate fragments or eggs of the sea urchin, the mitochondria actively synthesize RNA. The RNA made in non-nucleate fragments is shown to be mostly single stranded and to be associated primarily with the low speed pellet of centrifuged cellular homogenates.
Protein synthesis is observed in non-nucleate fragments in the presence or absence of the mitochondrial RNA synthesis: it is found to be qualitatively similar but quantitatively less in the absence of the RNA synthesis. The continued syntheses of proteins in the non-nucleate fragments in the absence of mitochondrial RNA synthesis provides additional evidence for the presence of a stable messenger RNA component in the unfertilized sea urchin egg.
Since the uptake or actinomycin D was found to be inhibited by the presence of a fertilization membrane, ethidium bromide, at 10 μgs/ml, is used as an effective inhibitor of RNA synthesis in non-nucleate fragments and in early cleavage stage embryos. However, this same concentration of ethidium bromide is found to be only partially effective in blocking RNA synthesis at the mesenchyme blastula stage of development.
Low concentrations of ethidium bromide (2 and 5 μgs/ml) are found not to be lethal but to be capable of producing moderate developmental defects. In the presence of concentrations of ethidium bromide adequate to inhibit all the mitochondrial RNA synthesis (10 μgs/ml of ethidium bromide), from fertilization on, the embryos do not cleave beyond the 4-8 cell stages. When similar concentrations of ethidium bromide are added at an early mesenchyme blastula stage, the embryos do not gastrulate but continue to swim for more than 24 additional hours (adequate for control embryos to develop to a late prism stage). These results lead to the conclusion that mitochondrial RNA synthesis may be very essential for normal development to occur.
DNA is synthesized in the non-nucleate fragments of sea urchin eggs. None of the newly synthesized DNA is found in the closed circular form. When phenol extracted directly from the fragments, the DNA is found to sediment at approximately 38 and 27s in sucrose gradients but neither of these size classes could be found associated with the isolated mitochondria. The template for the synthesis of DNA in non-nucleate fragments remains unknown.
Resumo:
This study is concerned with some of the properties of roll waves that develop naturally from a turbulent uniform flow in a wide rectangular channel on a constant steep slope . The wave properties considered were depth at the wave crest, depth at the wave trough, wave period, and wave velocity . The primary focus was on the mean values and standard deviations of the crest depths and wave periods at a given station and how these quantities varied with distance along the channel.
The wave properties were measured in a laboratory channel in which roll waves developed naturally from a uniform flow . The Froude number F (F = un/√ghn, un = normal velocity , hn = normal depth, g =acceleration of gravity) ranged from 3. 4 to 6. 0 for channel slopes So of . 05 and . 12 respectively . In the initial phase of their development the roll waves appeared as small amplitude waves with a continuous water surface profile . These small amplitude waves subsequently developed into large amplitude shock waves. Shock waves were found to overtake and combine with other shock waves with the result that the crest depth of the combined wave was larger than the crest depths before the overtake. Once roll waves began to develop, the mean value of the crest depths hnmax increased with distance . Once the shock waves began to overtake, the mean wave period Tav increased approximately linearly with distance.
For a given Froude number and channel slope the observed quantities h-max/hn , T' (T' = So Tav √g/hn), and the standard deviations of h-max/hn and T', could be expressed as unique functions of l/hn (l = distance from beginning of channel) for the two-fold change in hn occurring in the observed flows . A given value of h-max/hn occurred at smaller values of l/hn as the Froude number was increased. For a given value of h /hh-max/hn the growth rate of δh-max/h-maxδl of the shock waves increased as the Froude number was increased.
A laboratory channel was also used to measure the wave properties of periodic permanent roll waves. For a given Froude number and channel slope the h-max/hn vs. T' relation did not agree with a theory in which the weight of the shock front was neglected. After the theory was modified to include this weight, the observed values of h-max/hn were within an average of 6.5 percent of the predicted values, and the maximum discrepancy was 13.5 percent.
For h-max/hn sufficiently large (h-max/hn > approximately 1.5) it was found that the h-max/hn vs. T' relation for natural roll waves was practically identical to the h-max/hn vs. T' relation for periodic permanent roll waves at the same Froude number and slope. As a result of this correspondence between periodic and natural roll waves, the growth rate δh-max/h-maxδl of shock waves was predicted to depend on the channel slope, and this slope dependence was observed in the experiments.