168 research outputs found
Taurine metabolism and effects of inclusion levels in rotifer (Brachionus rotundiformis, Tschugunoff, 1921) on Atlantic bluefin tuna (Thunnus thynnus, L.) larvae
Taurine appears to be a crucial nutrient for teleosts, especially top predator species such as Atlantic bluefin tuna (Thunnus thynnus, L.; ABT). While dietary taurine supplementation has been highly recommended, there is a lack of studies on taurine assimilation and biosynthesis for this iconic species. The present study aims to provide insight into the molecular mechanisms involved in taurine biosynthesis and transport in ABT by studying tissue distribution and ontogenetic development of expression of cysteine dioxygenase (cdo), cysteine sulfinic acid decarboxylase (csad), 2-aminoethanethiol dioxygenase (ado) and taurine transporter (tauT) in response to graded levels of dietary taurine supplementation. The full open reading frame (ORF) for cdo and partial sequences for csad, ado and tauT were obtained, with the translated polypeptides being 202, 176, 166 and 324 amino acids, respectively. All three showed characteristics such as cupin motifs in Cdo and predicted N-glycosylation sites in Taut that are common to these genes in other species. Phylogenetic analysis showed that the ABT sequences clustered with sequences of other teleosts, and separately from mammals and molluscs. Tissue distribution varied, with adipose tissue, kidney, white muscle and testis/brain showing highest expression of cdo, csad, ado and tauT, respectively. Whole larvae expression of csad peaked at 15 dah, whereas the other genes generally increased throughout development to show highest expression at 25 dah. The nutritional trial was carried out by feeding ABT larvae from mouth opening to 14 days after hatching (dah) with rotifers (Brachionus rotundiformis) enriched with 4 different levels of taurine: 0.0 (tau0), 0.5 (tau0.5), 1.0 (tau1), and 2.0 g taurine per 106 rotifers (tau2). Rotifers effectively accumulated taurine with ABT larvae fed on treatment tau2 attaining the highest concentration of taurine. However, ABT larvae fed tau1 displayed higher growth and survival, and flexion index at 14 dah, than larvae fed the other taurine levels. Larvae fed tau1 also showed generally higher expression of tauT and cdo and digestive and antioxidant enzyme genes. While this study showed that larval ABT express taurine metabolism genes, suggesting possible synthesis that could contribute to the taurine pool in the fish, larval performance was enhanced by a level of dietary taurine (3.7 mg taurine g−1 rotifer) supplied by enrichment of rotifers at 1 g taurine per 106 rotifers.En prensa2,04
Branonium
We study the bound states of brane/antibrane systems by examining the motion
of a probe antibrane moving in the background fields of N source branes. The
classical system resembles the point-particle central force problem, and the
orbits can be solved by quadrature. Generically the antibrane has orbits which
are not closed on themselves. An important special case occurs for some
Dp-branes moving in three transverse dimensions, in which case the orbits may
be obtained in closed form, giving the standard conic sections but with a
nonstandard time evolution along the orbit. Somewhat surprisingly, in this case
the resulting elliptical orbits are exact solutions, and do not simply apply in
the limit of asymptotically-large separation or non-relativistic velocities.
The orbits eventually decay through the radiation of massless modes into the
bulk and onto the branes, and we estimate this decay time. Applications of
these orbits to cosmology are discussed in a companion paper.Comment: 34 pages, LaTeX, 4 figures, uses JHEP
de Sitter String Vacua from Supersymmetric D-terms
We propose a new mechanism for obtaining de Sitter vacua in type IIB string
theory compactified on (orientifolded) Calabi-Yau manifolds similar to those
recently studied by Kachru, Kallosh, Linde and Trivedi (KKLT). dS vacuum
appears in KKLT model after uplifting an AdS vacuum by adding an anti-D3-brane,
which explicitly breaks supersymmetry. We accomplish the same goal by adding
fluxes of gauge fields within the D7-branes, which induce a D-term potential in
the effective 4D action. In this way we obtain dS space as a spontaneously
broken vacuum from a purely supersymmetric 4D action. We argue that our
approach can be directly extended to heterotic string vacua, with the dilaton
potential obtained from a combination of gaugino condensation and the D-terms
generated by anomalous U(1) gauge groups.Comment: 17 pages, 1 figur
Non-linear absorption of InN/InGaN multiple-quantum-well structures at optical telecommunication wavelengths
We report on the nonlinear optical absorption of InN/ InxGa1−xN x=0.8, 0.9
multiple-quantum-well structures characterized at 1.55 m by the Z-scan method in order to obtain
the effective nonlinear absorption coefficient 2 of the samples at high repetition rate. Saturable
absorption is observed for the sample with x=0.9, with an effective 2 −9 103 cm/GW for the
studied optical regime. For lower In content in the barrier, reverse saturable absorption is observed,
which is attributed to two-photon absorption.Ministerio de Ciencia e InnovaciónComunidad de Madri
Kahler Moduli Inflation
We show that under general conditions there is at least one natural
inflationary direction for the Kahler moduli of type IIB flux
compactifications. This requires a Calabi-Yau which has h^{2,1}>h^{1,1}>2 and
for which the structure of the scalar potential is as in the recently found
exponentially large volume compactifications. We also need - although these
conditions may be relaxed - at least one Kahler modulus whose only
non-vanishing triple-intersection is with itself and which appears by itself in
the non-perturbative superpotential. Slow-roll inflation then occurs without a
fine tuning of parameters, evading the eta problem of F-term inflation. In
order to obtain COBE-normalised density perturbations, the stabilised volume of
the Calabi-Yau must be O(10^5-10^7) in string units, and the inflationary scale
M_{infl} ~ 10^{13} GeV. We find a robust model independent prediction for the
spectral index of 1 - 2/N_e = 0.960 - 0.967, depending on the number of
efoldings.Comment: 17 pages, 1 figure; v2. references adde
Brane-Antibrane Inflation in Orbifold and Orientifold Models
We analyse the cosmological implications of brane-antibrane systems in
string-theoretic orbifold and orientifold models. In a class of realistic
models, consistency conditions require branes and antibranes to be stuck at
different fixed points, and so their mutual attraction generates a potential
for one of the radii of the underlying torus or the 4D string dilaton. Assuming
that all other moduli have been fixed by string effects, we find that this
potential leads naturally to a period of cosmic inflation with the radion or
dilaton field as the inflaton. The slow-roll conditions are satisfied more
generically than if the branes were free to move within the space. The
appearance of tachyon fields at certain points in moduli space indicates the
onset of phase transitions to different non-BPS brane systems, providing ways
of ending inflation and reheating the corresponding observable brane universe.
In each case we find relations between the inflationary parameters and the
string scale to get the correct spectrum of density perturbations. In some
examples the small numbers required as inputs are no smaller than 0.01, and are
the same small quantities which are required to explain the gauge hierarchy.Comment: 30 pages, 2 figures. Substantial changes on version 1. New
cosmological scenarios proposed including the dilaton as the inflaton. Main
conclusions unchange
Analysis of bioactivities and chemical composition of Ziziphus joazeiro Mart. using HPLC–DAD
AbstractThe aim of this study was to evaluate the chemical profile and antioxidant, antimicrobial and antiparasitic activities of the hydroalcoholic extract of the leaves of Ziziphus joazeiro Mart. (HELZJ). The antioxidant DPPH and FRAP assays and chemical profile were determined by colorimetric methods and HPLC/DAD. The antiparasitic, antibiotic and antibiotic-modifying activity were evaluated by microdilution assays. The HPLC–DAD assay showed the presence of mostly tannins and flavonoids, such as caffeic acid and quercetin. The levels of polyphenols and flavonoids were 183.136mg/g extract and 7.37mg/g extract, respectively. DPPH and FRAP showed low antioxidant activity for the extract. The antibacterial and antifungal activities were not of clinical relevance, showing MIC>1024μg/mL. However, synergism was observed between HELZJ and the antibiotics amikacin and gentamicin, which resulted in decreased bacterial drug resistance. EHFZJ showed low toxicity in fibroblasts in vitro, while antiparasitic results against Trypnosoma cruzi, Leishmania braziliensis and Leishmania infantum were not clinically relevant. Thus, our results indicate that Z. joazeiro Mart. (HELZJ) could be a source of plant-derived natural products that could lead to the development of promising new antibiotic compounds for infectious diseases
Metastable SUSY Breaking, de Sitter Moduli Stabilisation and K\"ahler Moduli Inflation
We study the influence of anomalous U(1) symmetries and their associated
D-terms on the vacuum structure of global field theories once they are coupled
to N=1 supergravity and in the context of string compactifications with moduli
stabilisation. In particular, we focus on a IIB string motivated construction
of the ISS scenario and examine the influence of one additional U(1) symmetry
on the vacuum structure. We point out that in the simplest one-Kahler modulus
compactification, the original ISS vacuum gets generically destabilised by a
runaway behaviour of the potential in the modulus direction. In more general
compactifications with several Kahler moduli, we find a novel realisation of
the LARGE volume scenario with D-term uplifting to de Sitter space and both
D-term and F-term supersymmetry breaking. The structure of soft supersymmetry
breaking terms is determined in the preferred scenario where the standard model
cycle is not stabilised non-perturbatively and found to be flavour universal.
Our scenario also provides a purely supersymmetric realisation of Kahler moduli
(blow-up and fibre) inflation, with similar observational properties as the
original proposals but without the need to include an extra (non-SUSY)
uplifting term.Comment: 38 pages, 8 figures. v2: references added, minor correction
SUSY Breaking and Moduli Stabilization from Fluxes in Gauged 6D Supergravity
We construct the 4D N=1 supergravity which describes the low-energy limit of
6D supergravity compactified on a sphere with a monopole background a la Salam
and Sezgin. This provides a simple setting sharing the main properties of
realistic string compactifications such as flat 4D spacetime, chiral fermions
and N=1 supersymmetry as well as Fayet-Iliopoulos terms induced by the
Green-Schwarz mechanism. The matter content of the resulting theory is a
supersymmetric SO(3)xU(1) gauge model with two chiral multiplets, S and T. The
expectation value of T is fixed by the classical potential, and S describes a
flat direction to all orders in perturbation theory. We consider possible
perturbative corrections to the Kahler potential in inverse powers of
and , and find that under certain circumstances, and when taken together
with low-energy gaugino condensation, these can lift the degeneracy of the flat
direction for . The resulting vacuum breaks supersymmetry at moderately
low energies in comparison with the compactification scale, with positive
cosmological constant. It is argued that the 6D model might itself be obtained
from string compactifications, giving rise to realistic string
compactifications on non Ricci flat manifolds. Possible phenomenological and
cosmological applications are briefly discussed.Comment: 32 pages, 2 figures. Uses JHEP3.cls. References fixed and updated,
some minor typos fixed. Corrected minor error concerning Kaluza-Klein scales.
Results remain unchange
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