526 research outputs found
Reproductive capacity of the red cusk-eel genypterus chilensis (Guichenot, 1848) in captivity
Indexación: Scopus.This work was supported by the FONDEF Project D06I 1024 “Development of technologies for the production of red cusk-eel fingerlings (Genypterus chilensis)”.Genypterus chilensis is a marine fish of high gastronomic demand, whose capture has declined in recent years due to overfishing. In the development of the farming technology, high mortalities were obtained during egg incubation. The objective of this study is to contribute to the knowledge of fecundity and eggs viability of G. chilensis in captivity. The spawns of G. chilensis were analyzed over a period of 2 years and 3 months. The total fecundity was estimated by counting the masses and eggs produced monthly throughout the period. The results confirm that G. chilensis is a partial spawner, since a female may more than two masses of eggs per day, due to a large amount of mass spawned per season (621 average). The total production of masses of the Farming Centre during the period was 2,290; of these, only 7% (166) corresponding to 15,330,517 eggs were incubated. Because of its high fecundity, G. chilensis produces numerous masses of eggs, of which only a small percentage reaches incubation, as well as it occurs in other marine fish. © 2018, Escuela de Ciencias del Mar. All rights reserved.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-560X201800020048
Dynamics of a Massive Binary at Birth
Almost all massive stars have bound stellar companions, existing in binaries
or higher-order multiples. While binarity is theorized to be an essential
feature of how massive stars form, essentially all information about such
properties is derived from observations of already formed stars, whose orbital
properties may have evolved since birth. Little is known about binarity during
formation stages. Here we report high angular resolution observations of 1.3 mm
continuum and H30alpha recombination line emission, which reveal a massive
protobinary with apparent separation of 180 au at the center of the massive
star-forming region IRAS07299-1651. From the line-of-sight velocity difference
of 9.5 km/s of the two protostars, the binary is estimated to have a minimum
total mass of 18 solar masses, consistent with several other metrics, and
maximum period of 570 years, assuming a circular orbit. The H30alpha line from
the primary protostar shows kinematics consistent with rotation along a ring of
radius of 12 au. The observations indicate that disk fragmentation at several
hundred au may have formed the binary, and much smaller disks are feeding the
individual protostars.Comment: Published in Nature Astronomy. This is author's version. Full article
is available here (https://rdcu.be/brENk). 47 pages, 10 figures, including
methods and supplementary informatio
ALMA Cycle 1 Observations of the HH46/47 Molecular Outflow: Structure, Entrainment and Core Impact
We present ALMA Cycle 1 observations of the HH46/47 molecular outflow using
combined 12m array and ACA observations. The improved angular resolution and
sensitivity of our multi-line maps reveal structures that help us study the
entrainment process in much more detail and allow us to obtain more precise
estimates of outflow properties than previous observations. We use 13CO(1-0)
and C18O(1-0) emission to correct for the 12CO(1-0) optical depth to accurately
estimate the outflow mass, momentum and kinetic energy. This correction
increases the estimates of the mass, momentum and kinetic energy by factors of
about 9, 5 and 2, respectively, with respect to estimates assuming optically
thin emission. The new 13CO and C18O data also allow us to trace denser and
slower outflow material than that traced by the 12CO maps, and they reveal an
outflow cavity wall at very low velocities (as low as 0.2km/s with respect to
the cores central velocity). Adding with the slower material traced only by
13CO and C18O, there is another factor of 3 increase in the mass estimate and
50% increase in the momentum estimate. The estimated outflow properties
indicate that the outflow is capable of dispersing the parent core within the
typical lifetime of the embedded phase of a low-mass protostar, and that it is
responsible for a core-to-star efficiency of 1/4 to 1/3. We find that the
outflow cavity wall is composed of multiple shells associated with a series of
jet bow-shock events. Within about 3000AU of the protostar the 13CO and C18O
emission trace a circumstellar envelope with both rotation and infall motions,
which we compare with a simple analytic model. The CS(2-1) emission reveals
tentative evidence of a slowly-moving rotating outflow, which we suggest is
entrained not only poloidally but also toroidally by a disk wind that is
launched from relatively large radii from the source.Comment: Accepted for publication in ApJ. 26 pages, 20 figure
Implicancias ambientales de la deslignificación de pulpas kraft de eucalipto utilizando perácidos
Because of great environmental pressures, the cellulose industry has studied the potential of use of new bleaching agents among which peroxymonosulfuric acid and peracetic acid stand out. This survey summarizes the results of various laboratory investigations using peracids to delignify eucalyptus kraft pulps. The effect of a step using peroxymonosulfuric acid followed by a D-Eo-D sequence [free of elemental chlorine] was studied and compared with the use of peracetic acid and mixtures of these two acids. It was shown that a mixture of peroxymonosulfuric acid and peracetic acid reduced more lignin (measured as kappa index) than the individual peracids, and reduced more hexenuronic acid than peracetic acid with less degradation of the cellulose than with peroxymonosulfuric acid. This was explained on the basis of the electrophilic and nucleophilic properties of these acids that improved the delignification of eucalyptus kraft pulp. The effluents generated in these steps involving the peracids had greater color, chemical oxygen demand (COD), and total phenols correlating with the amount of lignin removed and the analyses of bioassays did not show acute toxicity from effluents coming from a peroxymonosulfuric acid step. The delignification with peracids may possibly reduce the use of chlorine dioxide in a sequence involving bleaching with elemental free chlorine (ECF), in this way reducing the concentration of organic chlorides (AOX) in the bleaching effluent
Internal Motions in Starless Dense Cores
This paper discusses the statistics of internal motions in starless dense
cores and the relation of these motions to core density and evolution. Four
spectral lines from three molecular species are analyzed from single-pointing
and mapped observations of several tens of starless cores. Blue asymmetric
profiles are dominant, indicating that inward motions are prevalent in
sufficiently dense starless cores. These blue profiles are found to be more
abundant, and their asymmetry is bluer, at core positions with stronger line emission or higher column density. Thirty three starless cores are
classified into four types according to the blue and red shifts of the lines in
their molecular line maps. Among these cores, contracting motions dominate: 19
are classified as contracting, 3 as oscillating, 3 as expanding, and 8 as
static. Contracting cores have inward motions all over the core with
predominance of those motions near the region of peak density. Cores with the
bluest asymmetry tend to have greater column density than other cores and all
five cores with peak column density are found
to be contracting. This suggests that starless cores are likely to have
contracting motions if they are sufficiently condensed. Our classification of
the starless cores may indicate a sequence of core evolution in the sense that
column density increases from static to contracting cores: the static cores in
the earliest stage, the expanding and/or the oscillating cores in the next, and
the contracting cores in the latest stage.Comment: Accepted for publication in The Astrophysical Journal, 34 pages, and
14 figure
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