587 research outputs found
Enhanced photosensitivity in tin-codoped germanosilicate optical fibres
Enhanced photosensitivity is found in Tin-codoped germanosilicate optical fibers. A photo-induced refractive index change (~1.4 x 10-3 times larger than that observed in pure germanosilicate fibers has been demonstrated. Unlike the technique of using Boron-codoping to enhance the photosensitivity of germanosilicate fibers, Tin-doping does not have a significant effect on fiber loss at the important telecommunication window of 1.55µm. High temperature stability of the gratings in Tin-codoped germanosilicate fibers is also much over Boron-codoped fibers
Effects of dietary Aloe vera crude extracts on digestive enzyme activities and muscle proximate composition of GIFT tilapia juveniles
This study investigated the effects of dietary Aloe vera powder extract on the activities of digestive enzymes and muscle composition of Oreochromis niloticus (GIFT strain) juveniles. Five dietary groups were formulated in which A. vera powder was added into a tilapia feed at 0.5%, 1.0%, 2.0%, and 4%/kg feed, and fed for eight weeks. Amylase, trypsin, and lipase activities in the liver and along the alimentary canal (stomach, midgut, and hindgut) varied significantly between dietary groups. Amylase activity was significantly enhanced in the liver of fish fed 0.5, 1, and 2% dietary A. vera, and in the stomach of those fed 1%. Total amylase activity in the gastrointestinal tract (total gut) was significantly enhanced in fish fed 0.5% and 1% compared with control and those fed 4% dietary A. vera. Trypsin activity was significantly enhanced in the stomach of fish supplemented with 0.5% dietary A. vera and in the duodenum of those supplemented with 1%, 2%, and 4% dietary A. vera when compared with the control. Lipase activity was increased in the duodenum of fish fed 1.0% dietary A. vera when compared with the control. Muscle moisture content was significantly lower in all A. vera-supplemented fish, whereas protein was lower in those fed 2% and 4% A. vera diet when compared with the control. Based on second-order polynomial regression analysis, dietary A. vera inclusion level less than or equal to 1.76%, 1.82%, 2.10%/kg feed was determined to be suitable in enhancing carbohydrate, protein and lipid digestion, respectively, in GIFT tilapia in this study.Keywords: Aquaculture, digestion enhancers, freshwater fish, medicinal herb
Has the nonlinear Meissner effect been observed?
We examine recent high-precision experimental data on the magnetic field,
, dependence of the penetration depth in
(YBCO) for several field directions in the
plane. In a new theoretical analysis that incorporates the effects of
orthorhombic symmetry, we show that the data at sufficiently high magnetic
fields and low temperatures are in quantitative agreement with the theoretical
predictions of the nonlinear Meissner effect.Comment: 4 text pages plus 3 postscript figure
Revisiting Generalized Chaplygin Gas as a Unified Dark Matter and Dark Energy Model
In this paper, we revisit generalized Chaplygin gas (GCG) model as a unified
dark matter and dark energy model. The energy density of GCG model is given as
,
where and are two model parameters which will be constrained by
type Ia supernova as standard candles, baryon acoustic oscillation as standard
rulers and the seventh year full WMAP data points. In this paper, we will not
separate GCG into dark matter and dark energy parts any more as adopted in the
literatures. By using Markov Chain Monte Carlo method, we find the result:
and .Comment: 6 pages, 4 figure
Constraints on accelerating universe using ESSENCE and Gold supernovae data combined with other cosmological probes
We use recently observed data: the 192 ESSENCE type Ia supernovae (SNe Ia),
the 182 Gold SNe Ia, the 3-year WMAP, the SDSS baryon acoustic peak, the X-ray
gas mass fraction in clusters and the observational data to constrain
models of the accelerating universe. Combining the 192 ESSENCE data with the
observational data to constrain a parameterized deceleration parameter,
we obtain the best fit values of transition redshift and current deceleration
parameter , .
Furthermore, using CDM model and two model-independent equation of
state of dark energy, we find that the combined constraint from the 192 ESSENCE
data and other four cosmological observations gives smaller values of
and , but a larger value of than the combined
constraint from the 182 Gold data with other four observations. Finally,
according to the Akaike information criterion it is shown that the recently
observed data equally supports three dark energy models: CDM,
and .Comment: 18 pages, 8 figure
Large photo-induced index changes in Sn-doped germanosilicate fibres
Index change (~1.4 x 10-3) of 3 times larger than in germanosilicate fibres is demonstrated. Both fibre loss at 1.55µm and high temperature stability of the gratings are much improved comparing to those in B-codoped germanosilicate fibres
Acceleration of the universe, vacuum metamorphosis, and the large-time asymptotic form of the heat kernel
We investigate the possibility that the late acceleration observed in the
rate of expansion of the universe is due to vacuum quantum effects arising in
curved spacetime. The theoretical basis of the vacuum cold dark matter (VCDM),
or vacuum metamorphosis, cosmological model of Parker and Raval is revisited
and improved. We show, by means of a manifestly nonperturbative approach, how
the infrared behavior of the propagator (related to the large-time asymptotic
form of the heat kernel) of a free scalar field in curved spacetime causes the
vacuum expectation value of its energy-momentum tensor to exhibit a resonance
effect when the scalar curvature R of the spacetime reaches a particular value
related to the mass of the field. we show that the back reaction caused by this
resonance drives the universe through a transition to an accelerating expansion
phase, very much in the same way as originally proposed by Parker and Raval.
Our analysis includes higher derivatives that were neglected in the earlier
analysis, and takes into account the possible runaway solutions that can follow
from these higher-derivative terms. We find that the runaway solutions do not
occur if the universe was described by the usual classical FRW solution prior
to the growth of vacuum energy-density and negative pressure (i.e., vacuum
metamorphosis) that causes the transition to an accelerating expansion of the
universe in this theory.Comment: 33 pages, 3 figures. Submitted to Physical Review D15 (Dec 23, 2003).
v2: 1 reference added. No other change
Generalized Chaplygin gas model: Cosmological consequences and statefinder diagnosis
The generalized Chaplygin gas (GCG) model in spatially flat universe is
investigated. The cosmological consequences led by GCG model including the
evolution of EoS parameter, deceleration parameter and dimensionless Hubble
parameter are calculated. We show that the GCG model behaves as a general
quintessence model. The GCG model can also represent the pressureless CDM model
at the early time and cosmological constant model at the late time. The
dependency of transition from decelerated expansion to accelerated expansion on
the parameters of model is investigated. The statefinder parameters and
in this model are derived and the evolutionary trajectories in plane are
plotted. Finally, based on current observational data, we plot the evolutionary
trajectories in and planes for best fit values of the parameters of
GCG model. It has been shown that although, there are similarities between GCG
model and other forms of chaplygin gas in statefinder plane, but the distance
of this model from the CDM fixed point in diagram is shorter
compare with standard chaplygin gas model.Comment: 10 pages, 5 figures, accepted in Astrophys Space Sci. (2011
Magnetic field effects on the density of states of orthorhombic superconductors
The quasiparticle density of states in a two-dimensional d-wave
superconductor depends on the orientation of the in-plane external magnetic
field H. This is because. in the region of the gap nodes, the Doppler shift due
to the circulating supercurrents around a vortex depend on the direction of H.
For a tetragonal system the induced pattern is four-fold symmetric and, at zero
energy, the density of states exhibits minima along the node directions. But
YBa_2C_3O_{6.95} is orthorhombic because of the chains and the pattern becomes
two-fold symmetric with the position of the minima occuring when H is oriented
along the Fermi velocity at a node on the Fermi surface. The effect of impurity
scattering in the Born and unitary limit is discussed.Comment: 24 pages, 11 Figure
Statefinder and Om Diagnostics for Interacting New Holographic Dark Energy Model and Generalized Second Law of Thermodynamics
In this work, we have considered that the flat FRW universe is filled with
the mixture of dark matter and the new holographic dark energy. If there is an
interaction, we have investigated the natures of deceleration parameter,
statefinder and diagnostics. We have examined the validity of the first
and generalized second laws of thermodynamics under these interactions on the
event as well as apparent horizon. It has been observed that the first law is
violated on the event horizon. However, the generalized second law is valid
throughout the evolution of the universe enveloped by the apparent horizon.
When the event horizon is considered as the enveloping horizon, the generalized
second law is found to break down excepting at late stage of the universe.Comment: 9 pages, 13 figure
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