9,376 research outputs found
Dietary Phytase: an ideal approach for a cost effective and low-polluting aquafeed
Global fishmeal production from wild-catch sources cannot continue to increase indefinitely; suitable alternatives have to be found for sustainable aquaculture. Plant-based aquafeed seems to be the ideal alternative to this, but has its own limitations. Plant ingredients are rich in phytic acid, which reduces the bioavailability of nutrients like minerals and protein to the fish, thereby causing aquaculture pollution. Dietary phytase treatment reduces the aquaculture pollution by improving the bioavailability of nutrients, and reduces the feed cost as evident from poultry and piggery. Phytase activity is highly dependent upon the pH of the gut. Unlike mammals, fish are either gastric or agastric, and hence, the action of dietary phytase varies from species to species. In this article, the authors attempt to summarise various effects of phytase on nutrient utilization, growth of fish and aquatic pollution
Neutrino dispersion relation in a magnetized multi-stream matter background
We study the propagation of a neutrino in a medium that consists of two or
more thermal backgrounds of electrons and nucleons moving with some relative
velocity, in the presence of a static and homogeneous electromagnetic field. We
calculate the neutrino self-energy and dispersion relation using the linear
thermal Schwinger propagator, we give the formulas for the dispersion relation
and discuss general features of the results obtained, in particular the effects
of the stream contributions. As a specific example we discuss in some detail
the case of a magnetized two-stream electron, i.e., two electron backgrounds
with a relative velocity in the presence of a magnetic field. For a
neutrino propagating with momentum , in the presence of the stream the
neutrino dispersion relation acquires an anisotropic contribution of the form
in addition to the well known term , as
well as an additional contribution proportional to . We
consider the contribution from a nucleon stream background as an example of
other possible stream backgrounds, and comment on possible generalizations to
take into account the effects of inhomogeneous fields. We explain why a term of
the form does not appear in the dispersion
relation in the constant field case, while a term of similar form can appear in
the presence of an inhomogeneous field involving its gradient.Comment: Title changed, 21 pages, 1 figur
Optical observations of the fast declining type Ib supernova iPTF13bvn
We present optical UBVRI photometry and medium resolution spectroscopy of the
type Ib supernova iPTF13bvn, spanning a phase of d to d
with respect to -band maximum. The post maximum decline rates indicate a
fast decline with . Correcting for a galactic
extinction and host galaxy extinction of
, the absolute -band magnitude peaks at
M. The bolometric light curve indicates that M of Ni was synthesized in the explosion. The earliest
spectrum (d) shows the presence of He~{\sc i} 5876 \AA\ feature at a
velocity of 15000 km s, which falls rapidly by the time the SN
approaches the epoch of B-band maximum. The photospheric velocity near maximum
light, as indicated by the Fe~{\sc ii} 5169~\AA\ feature, is km
s. The estimate for the Ni mass, together with the estimates for
the ejected mass () and kinetic energy of the explosion
() indicate that iPTF13bvn is a low luminosity type Ib supernova,
with a lower than average ejected mass and kinetic energy. Our results suggest
that the progenitor of iPTF13bvn is inconsistent with a single Wolf-Rayet star.Comment: Accepted for publication in MNRAS, 11 pages, 12 figure
One year of monitoring of the Type IIb supernova SN 2011dh
Optical photometry and low resolution spectroscopy of the type IIb
supernova SN 2011dh in M51 are presented, covering the first year after the
explosion. The light curve and spectral evolution are discussed. The early
phase light curve evolution of SN 2011dh is very similar to SN 1993J and SN
2008ax. In the late phase, however, SN 2011dh declines faster than SN 1993J.
The late phase decline in the -band is steeper than in the and
bands, indicating the possibility of dust formation. With a peak -band
absolute magnitude of mag, SN 2011dh is a marginally
faint type IIb event. The reddening corrected colour curves of SN 2011dh are
found to be redder than other well studied type IIb supernovae. The bolometric
light curve indicates 0.09 M of Ni is synthesized during
the explosion. The HeI lines were detected in the spectra during the rise to
maximum. The nebular spectra of SN 2011dh show a box shaped emission in the red
wing of the [OI] 6300-6363 \AA\ feature, that is attributed to H
emission from a shock excited circumstellar material. The analysis of nebular
spectra indicates that M of oxygen was ejected during the
explosion. Further, the [CaII]/[OI] line ratio in the nebular phase is
0.7, indicating a progenitor with a main sequence mass of 10-15 M.Comment: Accepted for publication in MNRA
Supernova SN 2012dn: A spectroscopic clone of SN 2006gz
We present optical and UV analysis of the luminous type Ia supernova SN
2012dn covering the period 11 to +109 days with respect to the band
maximum, that occurred on JD 2456132.89 0.19, with an apparent magnitude
of = 14.38 0.02. The absolute magnitudes at maximum in
and bands are and
, respectively. SN 2012dn is marginally
luminous compared to normal type Ia supernovae. The peak bolometric luminosity
of erg s suggests that
M of Ni was synthesized in the explosion. The
decline rate mag is lower than
that of normal type Ia supernovae, and similar to the luminous SN 1991T.
However, the photometric and spectroscopic behaviour of SN 2012dn is different
from that of SN 1991T. Early phase light curves in and bands are very
broad. The band peak has a plateau-like appearance similar to the
super-Chandra SN 2009dc. Pre-maximum spectra show clear evidence of C\,{\sc ii}
6580 \AA\, line, indicating the presence of unburned materials. The velocity
evolution of C\,{\ sc ii} line is peculiar. Except for the very early phase
(13 d), the C\,{\sc ii} line velocity is lower than the velocity
estimated using the Si\,{\sc ii} line. During the pre-maximum and close to
maximum phase, to reproduce observed shape of the spectra, the synthetic
spectrum code {\sc syn++} needs significantly higher blackbody temperature than
those required for normal type Ia events. The photospheric velocity evolution
and other spectral properties are similar to those of the carbon-rich SN
2006gz.Comment: Accepted for publication in MNRAS, 19 pages, 20 figure
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