358 research outputs found
Effects of dietary vitamin D3 levels on survival, mineralization, and skeletal development of gilthead seabream (Sparus aurata) larvae
Vitamin D is an essential fat soluble micronutrient that helps in growth, bone development, calcium homeostasis and other metabolic process. The study on effect of vitamin D3 in marine fish larvae were very scarce irrespective of species. The present study determines the impacts of dietary vitamin D3 on growth performance, calcium absorption, mineralization, and skeletal anomalies during the development of gilthead seabream (Sparus aurata) larvae was assessed until 47 days post hatching. Diets containing four levels of vitamin D3 (0, 25, 30, 384 ÎŒg kgâ1 or 11.6, 1000, 1200, 15,360 IU kgâ1) were formulated to determine the effect of vitamin D3 at deficient, excess, and optimum levels. The gilthead seabream larvae in the present study fed with this wide range of vitamin D3 presented a constant growth with all the diets but presented signs of toxicity in excess level, affecting the survival, calcium uptake, and bone biomarker mechanism in larvae, which resulted in increased skeletal anomalies and mortality. An increase of dietary vitamin D3 up to 384 ÎŒg kgâ1 significantly raised the whole body vitamin D3 content, calcium, and phosphorus intake and increased the incidence of skeletal anomalies, particularly cranial anomalies. The appearance of skeletal anomalies in larvae fed 384 ÎŒg kgâ1 vitamin D3 was in association with the upregulation of bmp2, alp, and oc gene expression. However, larvae fed 0, 25, 30 ÎŒg kgâ1 vitamin D3 showed higher survival than the group fed 384 ÎŒg kgâ1 vitamin D3. Meanwhile vitamin D3 deficient diet 0 ÎŒg kgâ1 presented with lower mineralization rate and increase incidence of maxillary anomaly. Thus, the current study revealed the evidence of vitamin D3 deficiency as well as toxicity in gilthead seabream larvae during the developmental process and conclude that the recommended dietary vitamin D3 level for gilthead seabream larvae may range between 25 and 30 ÎŒg kgâ1 which improves larval survival, calcium and phosphate level and vertebral mineralization with reduced incidence of skeletal anomalies in gilthead seabream larva
Dynamical mass generation of a two-component fermion in Maxwell-Chern-Simons QED_3: The lowest ladder approximation
Dynamical mass generation of a two-component fermion in with a
Chern-Simons term is investigated by solving the Schwinger-Dyson equation
formulated in the lowest ladder approximation. Dependence of the dynamical
fermion mass on a gauge-fixing parameter, a gauge coupling constant, and a
topological mass is examined by approximated analytical and also numerical
methods. The inclusion of the Chern-Simons term makes impossible to choose a
peculiar gauge in which a wave function renormalization is absent. The
numerical evaluation shows that the wave function renormalization is fairly
close to 1 in the Landau gauge. It means that this gauge is still a specific
gauge where the Ward-Takahashi identity is satisfied approximately. We also
find that the dynamical mass is almost constant if the topological mass is
larger than the coupling constant, while it decreases when the topological mass
is comparable to or smaller than the coupling constant and tends to the value
in without the Chern-Simons term.Comment: 22 pages, 9 figures, Version to appear in Phys. Rev.
Universal de Sitter solutions at tree-level
Type IIA string theory compactified on SU(3)-structure manifolds with
orientifolds allows for classical de Sitter solutions in four dimensions. In
this paper we investigate these solutions from a ten-dimensional point of view.
In particular, we demonstrate that there exists an attractive class of de
Sitter solutions, whose geometry, fluxes and source terms can be entirely
written in terms of the universal forms that are defined on all SU(3)-structure
manifolds. These are the forms J and Omega, defining the SU(3)-structure
itself, and the torsion classes. The existence of such universal de Sitter
solutions is governed by easy-to-verify conditions on the SU(3)-structure,
rendering the problem of finding dS solutions purely geometrical. We point out
that the known (unstable) solution coming from the compactification on SU(2)x
SU(2) is of this kind.Comment: 20 pages, 3 figures, v2: added reference
Higher-Derivative Quantum Cosmology
The quantum cosmology of a higher-derivative derivative gravity theory
arising from the heterotic string effective action is reviewed. A new type of
Wheeler-DeWitt equation is obtained when the dilaton is coupled to the
quadratic curvature terms. Techniques for solving the Wheeler-DeWitt equation
with appropriate boundary conditions shall be described, and implications for
semiclassical theories of inflationary cosmology will be outlined.Comment: 11 pages TeX. A term has been removed from equation (13
Polarization and magnetization dynamics of a field-driven multiferroic structure
We consider a multiferroic chain with a linear magnetoelectric coupling
induced by the electrostatic screening at the ferroelectric/ferromagnet
interface. We study theoretically the dynamic ferroelectric and magnetic
response to external magnetic and electric fields by utilizing an approach
based on coupled Landau- Khalatnikov and finite-temperature
Landau-Lifshitz-Gilbert equations. Additionally, we compare with Monte Carlo
calculations. It is demonstrated that for material parameters corresponding to
BaTiO3/Fe the polarization and the magnetization are controllable by external
magnetic and electric fields respectively
Metastable de Sitter vacua in N=2 to N=1 truncated supergravity
We study the possibility of achieving metastable de Sitter vacua in general
N=2 to N=1 truncated supergravities without vector multiplets, and compare with
the situations arising in N=2 theories with only hypermultiplets and N=1
theories with only chiral multiplets. In N=2 theories based on a quaternionic
manifold and a graviphoton gauging, de Sitter vacua are necessarily unstable,
as a result of the peculiar properties of the geometry. In N=1 theories based
on a Kahler manifold and a superpotential, de Sitter vacua can instead be
metastable provided the geometry satisfies some constraint and the
superpotential can be freely adjusted. In N=2 to N=1 truncations, the crucial
requirement is then that the tachyon of the mother theory be projected out from
the daughter theory, so that the original unstable vacuum is projected to a
metastable vacuum. We study the circumstances under which this may happen and
derive general constraints for metastability on the geometry and the gauging.
We then study in full detail the simplest case of quaternionic manifolds of
dimension four with at least one isometry, for which there exists a general
parametrization, and study two types of truncations defining Kahler
submanifolds of dimension two. As an application, we finally discuss the case
of the universal hypermultiplet of N=2 superstrings and its truncations to the
dilaton chiral multiplet of N=1 superstrings. We argue that de Sitter vacua in
such theories are necessarily unstable in weakly coupled situations, while they
can in principle be metastable in strongly coupled regimes.Comment: 40 pages, no figure
The Boundary Multiplet of N=4 SU(2)xU(1) Gauged Supergravity on Asymptotically-AdS_5
We consider N=4 SU(2)xU(1) gauged supergravity on asymptotically-AdS_5
backgrounds. By a near-boundary analysis we determine the boundary-dominant
components of the bulk fields from their partially gauge-fixed field equations.
Subdominant components are projected out in the boundary limit and we find a
reduced set of boundary fields, constituting the N=2 Weyl multiplet. The
residual bulk symmetries are found to act on the boundary fields as
four-dimensional diffeomorphisms, N=2 supersymmetry and (super-)Weyl
transformations. This shows that the on-shell N=4 supergravity multiplet yields
the N=2 Weyl multiplet on the boundary with the appropriate local N=2
superconformal transformations. Building on these results we use the AdS/CFT
conjecture to calculate the Weyl anomaly of the dual four-dimensional
superconformal field theories in a generic bosonic N=2 conformal supergravity
background.Comment: 23 pages; to appear in JHE
Accelerating Universes in String Theory via Field Redefinition
We study cosmological solutions in the effective heterotic string theory with
-correction terms in string frame. It is pointed out that the
effective theory has an ambiguity via field redefinition and we analyze
generalized effective theories due to this ambiguity. We restrict our analysis
to the effective theories which give equations of motion of second order in the
derivatives, just as "Galileon" field theory. This class of effective actions
contains two free coupling constants. We find de Sitter solutions as well as
the power-law expanding universes in our four-dimensional Einstein frame. The
accelerated expanding universes are always the attractors in the present
dynamical system.Comment: 22 pages, 3 figures, some additional formulae adde
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