8,472 research outputs found
Modification of the biological intercept model to account for ontogenetic effects in laboratory-reared delta smelt (Hypomesus transpacificus)*
We investigated age, growth, and ontogenetic effects on
the proportionality of otolith size to fish size in laboratory-reared delta smelt (Hypomesus transpacificus)
from the San Francisco Bay estuary. Delta smelt larvae were reared from hatching in laboratory mesocosms for 100 days. Otolith increments from known-age fish were enumerated to
validate that growth increments were deposited daily and to validate the age of fish at first ring formation. Delta smelt were found to lay down daily ring increments; however, the first increment did not form until six days after hatching. The relationship between otolith size and fish size was not biased by age or growth-rate effects but did exhibit an interruption in linear growth owing to an ontogenetic shift at the postflexon stage. To back-calculate the size-at-age of individual fish, we modified the biological intercept (BI) model to account for ontogenetic changes in the otolith-size−fish-size relationship and compared the results to the time-varying
growth model, as well as the modified Fry model. We found the modified BI model estimated more accurately the
size-at-age from hatching to 100 days after hatching. Before back-calculating size-at-age with existing models,
we recommend a critical evaluation of the effects that age, growth, and ontogeny can have on the otolith-size−fish-size relation
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Chemistry and valency spectra of Chromite in SNC meteorites
Shergottite chromite core mantle sources were Al-poor, Fe-rich, low Fe^{3+}/Fe^{2+}, fO_{2} 1 to 4 unit
Enhancement of the Benjamin-Feir instability with dissipation
It is shown that there is an overlooked mechanism whereby some kinds of
dissipation can enhance the Benjamin-Feir instability of water waves. This
observation is new, and although it is counterintuitive, it is due to the fact
that the Benjamin-Feir instability involves the collision of modes with
opposite energy sign (relative to the carrier wave), and it is the negative
energy perturbations which are enhanced.Comment: 15 pages, 2 figures To download more papers, go to
http://www.cmla.ens-cachan.fr/~dias. Physics of Fluids (2007) to appea
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Stardust microcrater residue compositional groups
Compositional groups are defined in residue from Stardust craters (1-9 Dc) by qualitative EDS. These compositional groups are being further studied by a FIB-SEM technique to determine representative residue compositions
SCUBA Observations of NGC 1275
Deep SCUBA observations of NGC 1275 at 450 micron and 850 micron along with
the application of deconvolution algorithms have permitted us to separate the
strong core emission in this galaxy from the fainter extended emission around
it. The core has a steep spectral index and is likely due primarily to the AGN.
The faint emission has a positive spectral index and is clearly due to extended
dust in a patchy distribution out to a radius of 20 kpc from the
nucleus. These observations have now revealed that a large quantity of dust,
6 10 , 2 orders of magnitude larger than that
inferred from previous optical absorption measurements, exists in this galaxy.
We estimate the temperature of this dust to be 20 K (using an emissivity
index of = 1.3) and the gas/dust ratio to be 360. These values are
typical of spiral galaxies. The dust emission correlates spatially with the hot
X-ray emitting gas which may be due to collisional heating of broadly
distributed dust by electrons. Since the destruction timescale is short, the
dust cannot be replenished by stellar mass loss and must be externally
supplied, either via the infalling galaxy or the cooling flow itself.Comment: 13 pages, 4 figures. Figure 4 is colou
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