2,167,825 research outputs found
Glycerol as an Energy Source for Ruminants: a Meta-Analysis of in Vitro Experiments
Glycerol or glycerin is generally recognized as a safe compound to be used in animal feed, especially for ruminants. A number of in vitro studies related to glycerol supplementation in ruminant ration have been published but to date the results have not been summarized. The objective of this study was, therefore, to evaluate in vitro digestibility, ruminal fermentation characteristics, total gas and methane production through the meta-analysis approach. Meta-analysis was applied to 13 experiments and 42 treatments dealing with glycerol supplementation in ruminants. Data were analyzed by general linear model procedure in which the glycerol levels and the different studies were treated as fixed effects. Results revealed that glycerol supplementation did not affect the in vitro digestibility and total VFA production, but significantly decreased molar proportion of acetate and iso-valerate (P<0.05). In contrast, molar proportion of propionate, butyrate, and valerate significantly increased, and thus the ratio of acetate to propionate declined linearly (P<0.05). Methane production decreased linearly and accompanied with an increase of total gas production with increasing levels of glycerol supplementation (P<0.05). It is concluded that the use of glycerol as an energy substitution in animal feed has no detrimental effects in the rumen and environmentally friendly
Semileptonic decays of pseudoscalar mesons to scalar "f_0" meson
The transition form factors of (D_s -> f_0 l nu), (D -> f_0 l nu) and (B_u ->
f_0 l nu) decays are calculated in 3-point QCD sum rule method, assuming that
"f_0" is a quark-antiquark state with a mixture of strange and light quarks.
The branching ratios of these decays are calculated in terms of the mixing
angle.Comment: 12 pages, 4 figures, LaTeX formatte
Expansions of the solutions of the general Heun equation governed by two-term recurrence relations for coefficients
We examine the expansions of the solutions of the general Heun equation in
terms of the Gauss hypergeometric functions. We present several expansions
using functions, the forms of which differ from those applied before. In
general, the coefficients of the expansions obey three-term recurrence
relations. However, there exist certain choices of the parameters for which the
recurrence relations become two-term. The coefficients of the expansions are
then explicitly expressed in terms of the gamma functions. Discussing the
termination of the presented series, we show that the finite-sum solutions of
the general Heun equation in terms of generally irreducible hypergeometric
functions have a representation through a single generalized hypergeometric
function. Consequently, the power-series expansion of the Heun function for any
such case is governed by a two-term recurrence relation
Semi-direct Gauge Mediation in Conformal Windows of Vector-like Gauge Theories
Direct gauge mediation models using the Intriligator-Seiberg-Shih (ISS)
metastable vacua suffer from the Landau pole problem of the standard model
gauge couplings and the existence of R symmetry forbidding gaugino masses.
These problems may be solved by using the recently proposed SUSY breaking
models in a conformal window of the vector-like gauge theory with
gauge singlets. In this paper we propose a model of gauge mediation based on
the SUSY-breaking model in the conformal window, and study the dynamics for the
SUSY breaking. In the model, there are massive vector-like bifundamental fields
charged under both and the standard model gauge group, and our model
can be regarded as a semi-direct gauge mediation model. The color number
can be small to avoid the Landau pole problem, and the R symmetry is also
broken under a reasonable assumption on the strong dynamics of the model. The
model possesses only one free parameter, and the gaugino and sfermion masses
are naturally of the same order.Comment: 21 pages, 1 figur
Quantum chaos with spin-chains in pulsed magnetic fields
Recently it was found that the dynamics in a Heisenberg spin-chain subjected
to a sequence of periodic pulses from an external, parabolic, magnetic field
can have a close correspondence with the quantum kicked rotor (QKR). The QKR is
a key paradigm of quantum chaos; it has as its classical limit the well-known
Standard Map. It was found that a single spin excitation could be converted
into a pair of non-dispersive, counter-propagating spin coherent states
equivalent to the accelerator modes of the Standard Map. Here we consider how
other types of quantum chaotic systems such as a double-kicked quantum rotor or
a quantum rotor with a double-well potential might be realized with spin
chains; we discuss the possibilities regarding manipulation of the one-magnon
spin waves.Comment: 10 pages, 4 figures. Submitted to PTP special issue for QMC200
Multiexciton molecules in the hexaborides
We investigate multiexciton bound states in a semiconducting phase of
divalent hexaborides. Due to three degenerate valleys in both the conduction
and valence bands the binding energy of a 6-exciton molecule is greatly
enhanced by the shell effect. The ground state energies of multiexciton
molecules are calculated using the density functional formalism. We also show
that charged impurities stabilize multiexciton complexes leading to
condensation of localized excitons. These complexes can act as nucleation
centers of local moments.Comment: RevTEX, 7 pages with 3 figure
Near-infrared spectroscopy of AGB star candidates in Fornax, Sculptor and NGC 6822
Context: The Asymptotic Giant Branch (AGB) phase is characterised by
substantial mass loss that is accompanied by the formation of dust. In extreme
cases this will make the star no longer visible in the optical. For a better
understanding of AGB evolution it is important to identify and characterise
these very red AGB stars.
Aims: The first aim of this article is to improve the census of red AGB stars
in three Local Group galaxies, based on near-IR spectroscopic observations of
new candidates with red 2MASS (J-K) colours. The opportunity is taken to
compare the near-IR spectra with those of Milky Way stars.
Methods: We used ISAAC on the ESO VLT to take J and H-band spectra of 36
targets in Fornax, Sculptor and NGC 6822.
Results: Twelve new C-stars are found in Fornax, and one is confirmed in
Sculptor. All C-stars have (J-K) > 1.6, and are brighter than -3.55 in
bolometric magnitude. Ten new oxygen-rich late-type giant stars are identified
in Fornax, but none is extremely red or very luminous. Five luminous O-rich AGB
stars are identified in NGC 6822, of which 3 show water absorption, indicative
of spectral type M. Again, none is as red as Milky Way OH/IR stars, but in this
galaxy the list of candidate AGB stars is biased against very red objects. In
some C-stars with (J-K)>2 an extremely strong 1.53 m absorption band is
found. These stars are probably all Mira variables and the feature is related
to the low temperature, high density chemistry that is a first step towards
dust formation and mass loss.Comment: A&A accepte
Baade-Wesselink distances to Galactic and Magellanic Cloud Cepheids and the effect of metallicity
(abridged) The aim of this paper is to investigate the metallicity dependence
of the PL relation in V and K, based on a sample of 128 Galactic, 36 LMC, and 6
SMC Cepheids with individual Baade-Wesselink (BW) distances and individually
determined metallicities from high-resolution spectroscopy. The p-relation
finally adopted is 1.50 -0.24log P. The slope of this relation is based on the
condition that the distance to the LMC does not depend on period or (V-K)
colour and that the slope of the PL relation based on the BW distances agrees
with that based on apparent magnitude. The zero point of the relation is tight
to the Cepheids with HST and revised Hipparcos parallaxes as well as to
Cepheids in clusters. The slope of the Galactic and LMC K-band relation
formally agrees within the errors, and combining all Cepheids (including the
SMC) results in a negligible metallicity dependence. A similar conclusion is
found for the reddening-free Wesenheit relation. In the V-band the situation is
more complex. The slope of the LMC and the Galactic PL relation differ at the
3sigma level. Combining the sample nevertheless results in a metallicity term
significant at the 2sigma level. The details of the comparison of BW-based
distances and Cepheids with HST and revised Hipparcos parallaxes also play a
role. The method used by Storm et al. would lead to larger DM of 18.37 and
18.81 for the LMC and SMC, respectively. The LMC DM is shorter than the
currently accepted value, which is in the range 18.42 to 18.55 (Walker 2012),
and it is speculated that the p-factor may depend on metallicity.Comment: Accepted for A&
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