7,435 research outputs found
On the Stability of Compactified D=11 Supermembranes
We prove D=11 supermembrane theories wrapping around in an irreducible way
over on the target manifold, have a
hamiltonian with strict minima and without infinite dimensional valleys at the
minima for the bosonic sector. The minima occur at monopole connections of an
associated U(1) bundle over topologically non trivial Riemann surfaces of
arbitrary genus. Explicit expressions for the minimal connections in terms of
membrane maps are presented. The minimal maps and corresponding connections
satisfy the BPS condition with half SUSY.Comment: 15 pages, latex. Added comments in conclusions and more reference
Tracing shocks and photodissociation in the Galactic center region
We present a systematic study of the HNCO, C18O, 13CS, and C34S emission
towards 13 selected molecular clouds in the Galactic center region. The
molecular emission in these positions are used as templates of the different
physical and chemical processes claimed to be dominant in the circumnuclear
molecular gas of galaxies. The relative abundance of HNCO shows a variation of
more than a factor of 20 amo ng the observed sources. The HNCO/13CS abundance
ratio is highly contrasted (up to a factor of 30) between the shielded
molecular clouds mostly affected by shocks, where HNCO is released to gas-phase
from grain mantles, and those pervaded by an intense UV radiation field, where
HNCO is photo-dissociated and CS production favored via ion reactions. We
propose the relative HNCO to CS abundance ratio as a highly contrasted
diagnostic tool to distinguish between the influence of shocks and/or the
radiation field in the nuclear regions of galaxies and their relation to the
evolutionary state of their nuclear star formation bursts.Comment: 25 pages, 5 figures, Accepted for publication in Ap
Abundant Z-cyanomethanimine in the interstellar medium: paving the way to the synthesis of adenine
We report the first detection in the interstellar medium of the Z-isomer of
cyanomethanimine (HNCHCN), an HCN dimer proposed as precursor of adenine. We
identified six transitions of Z-cyanomethanimine, along with five transitions
of E-cyanomethanimine, using IRAM 30m observations towards the Galactic Center
quiescent molecular cloud G+0.693. The Z-isomer has a column density of
(2.00.6)10 cm and an abundance of
1.510. The relative abundance ratio between the isomers is
[Z/E]6. This value cannot be explained by the two chemical formation
routes previously proposed (gas-phase and grain surface), which predicts
abundances ratios between 0.9 and 1.5. The observed [Z/E] ratio is in good
agreement with thermodynamic equilibrium at the gas kinetic temperature
(130210 K). Since isomerization is not possible in the ISM, the two species
may be formed at high temperature. New chemical models, including surface
chemistry on dust grains and gas-phase reactions, should be explored to explain
our findings. Whatever the formation mechanism, the high abundance of Z-HNCHCN
shows that precursors of adenine are efficiently formed in the ISM.Comment: Accepted in Monthly Notices of the Royal Astronomical Society Letter
Complex organic molecules in the Galactic Centre: the N-bearing family
We present an unbiased spectral line survey toward the Galactic Centre (GC)
quiescent giant molecular cloud (QGMC), G+0.693 using the GBT and IRAM 30
telescopes. Our study highlights an extremely rich organic inventory of
abundant amounts of nitrogen (N)-bearing species in a source without signatures
of star formation. We report the detection of 17 N-bearing species in this
source, of which 8 are complex organic molecules (COMs). A comparison of the
derived abundances relative to H is made across various galactic and
extragalactic environments. We conclude that the unique chemistry in this
source is likely to be dominated by low-velocity shocks with X-rays/cosmic rays
also playing an important role in the chemistry. Like previous findings
obtained for O-bearing molecules, our results for N-bearing species suggest a
more efficient hydrogenation of these species on dust grains in G+0.693 than in
hot cores in the Galactic disk, as a consequence of the low dust temperatures
coupled with energetic processing by X-ray/cosmic ray radiation in the GC.Comment: 24 pages, 23 figures, 7 tables, accepted for publication in MNRA
PPl 15: The First Brown Dwarf Spectroscopic Binary
PPl 15 is the first object to have been confirmed as a brown dwarf by the
lithium test (in 1995), though its inferred mass was very close to the
substellar limit. It is a member of the Pleiades open cluster. Its position in
a cluster color-magnitude diagram suggested that it might be binary, and
preliminary indications that it is a double-lined spectroscopic binary were
reported by us in 1997. Here we report on the results of a consecutive week of
Keck HIRES observations of this system, which yield its orbit. It has a period
of about 5.8 days, and an eccentricity of 0.4+/-0.05. The rotation of the stars
is slow for this class of objects. Because the system luminosity is divided
between 2 objects with a mass ratio of 0.85, this renders each of them an
incontrovertible brown dwarf, with masses between 60-70 jupiters. We show that
component B is a little redder than A by studying their wavelength-dependent
line ratios, and that this variation is compatible with the mass ratio. We
confirm that the system has lithium, but cannot support the original conclusion
that it is depleted (which would be surprising, given the new masses). This is
a system of very close objects which, if they had combined, would have produced
a low mass star. We discuss the implications of this discovery for the theories
of binary formation and formation of very low mass objects.Comment: Latex, 18 pages, 4 figures, submitted to Astron.
Diferenciación de carnes de jabalí europeo (Sus scrofa scrofa) y cerdo doméstico (Sus scrofa domestica) mediante el análisis por PCR de la región mitocondrial D-loop y el gen nuclear MC1R
En este trabajo se describe la diferenciación de carnes procedentes de jabalí europeo (Sus scrofa scrofa) y cerdo doméstico (Sus scrofa domestica) mediante el análisis por PCR de la región mitocondrial D-loop y del gen nuclear que codifica para el receptor 1 de la melanocortina (MC1R). La discriminación por PCR-RFLP de jabalí y cerdo en la región D loop no fue posible. Sin embargo, la técnica de PCR-RFLP desarrollada en el gen MC1R determinó perfiles de bandas característicos que permitieron la diferenciación de jabalí y cerdo mediante el empleo de las endonucleasas BspHI y BstUI.This work describes the differentiation of European wild boar (Sus scrofa scrofa) and domestic swine (Sus scrofa domestica) meats by PCR targeting sequences from the mitochondrial displacement loop (D-loop) region and the nuclear melanocortin receptor 1 (MC1R) gene. Detailed analysis of every D-loop sequence obtained indicated that PCR RFLP differentiation between wild and domestic Sus scrofa meats was not possible. Nevertheless, the PCR-RFLP technique developed targeting the MC1R gene generated characteristic PCR–RFLP profiles that allowed discrimination among meats from wild and domestic swine specimens using BspHI and BstUI endonucleases
Chiral condensate thermal evolution at finite baryon chemical potential within Chiral Perturbation Theory
We present a model independent study of the chiral condensate evolution in a
hadronic gas, in terms of temperature and baryon chemical potential. The
meson-meson interactions are described within Chiral Perturbation Theory and
the pion-nucleon interaction by means of Heavy Baryon Chiral Perturbation
Theory, both at one loop, and nucleon-nucleon interactions can be safely
neglected within our hadronic gas domain of validity. Together with the virial
expansion, this provides a systematic expansion at low temperatures and
chemical potentials, which includes the physical quark masses. This can serve
as a guideline for further studies on the lattice. We also obtain estimates of
the critical line of temperature and chemical potential where the chiral
condensate melts, which systematically lie somewhat higher than recent lattice
calculations but are consistent with several hadronic models. We have also
estimated uncertainties due to chiral parameters, heavier hadrons and higher
orders through unitarized Chiral Perturbation Theory.Comment: 15 pages, 15 figures, 3 tables, ReVTeX. Version to appear in Phys.
Rev. D. References added. More conservative estimate of applicability domain,
with new figure. More detailed explanation of final results with two more
figures. Results unchange
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