15,735 research outputs found
Integral Inequalities and their Applications to the Calculus of Variations on Time Scales
We discuss the use of inequalities to obtain the solution of certain
variational problems on time scales.Comment: To appear in Mathematical Inequalities & Applications
(http://mia.ele-math.com). Accepted: 14.01.201
The largest oxigen bearing organic molecule repository
We present the first detection of complex aldehydes and isomers in three
typical molecular clouds located within 200pc of the center of our Galaxy.
We find very large abundances of these complex organic molecules (COMs) in
the central molecular zone (CMZ), which we attribute to the ejection of COMs
from grain mantles by shocks. The relative abundances of the different COMs
with respect to that of CH3OH are strikingly similar for the three sources,
located in very different environments in the CMZ. The similar relative
abundances point toward a unique grain mantle composition in the CMZ. Studying
the Galactic center clouds and objects in the Galactic disk having large
abundances of COMs, we find that more saturated molecules are more abundant
than the non-saturated ones. We also find differences between the relative
abundance between COMs in the CMZ and the Galactic disk, suggesting different
chemical histories of the grain mantles between the two regions in the Galaxy
for the complex aldehydes. Different possibilities for the grain chemistry on
the icy mantles in the GC clouds are briefly discussed. Cosmic rays can play an
important role in the grain chemistry. With these new detections, the molecular
clouds in the Galactic center appear to be one of the best laboratories for
studying the formation of COMs in the Galaxy.Comment: 20 pages, 4 figures, accepted in Ap
VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter?
We present long-slit spectroscopy, continuum and [OIII]5007 imaging data
obtained with the Very Large Telescope and the Gran Telescopio Canarias of the
type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich
environment. It appears to be physically connected by a tidal bridge to another
galaxy at a projected distance of ~100 kpc, which suggests this is an
interacting system. Ionized gas is detected to a distance of at least ~133 kpc
from the nucleus. The nebula has a total extension of ~180 kpc. This is one of
the largest ionized nebulae ever detected associated with an active galaxy.
Based on the environmental properties, we propose that the origin of the nebula
is tidal debris from a galactic encounter, which could as well be the
triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that
giant, luminous ionized nebulae can exist associated with type 2 quasars of low
radio luminosities, contrary to expectations based on type 1 quasar studies.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letter
How does breakup influence the total fusion of Li at the Coulomb barrier?
Total (complete + incomplete) fusion excitation functions of Li on
Co and Bi targets around the Coulomb barrier are obtained using
a new continuum discretized coupled channel (CDCC) method of calculating
fusion. The relative importance of breakup and bound-state structure effects on
total fusion is particularly investigated. The effect of breakup on fusion can
be observed in the total fusion excitation function. The breakup enhances the
total fusion at energies just around the barrier, whereas it hardly affects the
total fusion at energies well above the barrier. The difference between the
experimental total fusion cross sections for Li on Co is notably
caused by breakup, but this is not the case for the Bi target.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Shape of the spatial mode function of photons generated in noncollinear spontaneous parametric downconversion
We show experimentally how noncollinear geometries in spontaneous parametric
downconversion induce ellipticity of the shape of the spatial mode function.
The degree of ellipticity depends on the pump beam width, especially for highly
focused beams. We also discuss the ellipticity induced by the spectrum of the
pump beam
Chemical Features in the Circumnuclear Disk of the Galactic Center
The circumnuclear disk (CND) of the Galactic Center is exposed to many
energetic phenomena coming from the supermassive black hole Sgr A* and stellar
activities. These energetic activities can affect the chemical composition in
the CND by the interaction with UV-photons, cosmic-rays, X-rays, and shock
waves. We aim to constrain the physical conditions present in the CND by
chemical modeling of observed molecular species detected towards it. We
analyzed a selected set of molecular line data taken toward a position in the
southwest lobe of the CND with the IRAM 30m and APEX 12-meter telescopes and
derived the column density of each molecule using a large velocity gradient
(LVG) analysis. The determined chemical composition is compared with a
time-dependent gas-grain chemical model based on the UCL\_CHEM code that
includes the effects of shock waves with varying physical parameters. Molecules
such as CO, HCN, HCO, HNC, CS, SO, SiO, NO, CN, HCO, HCN,
NH and HO are detected and their column densities are obtained.
Total hydrogen densities obtained from LVG analysis range between and cm and most species indicate values around
several cm, which are lower than values corresponding to
the Roche limit, which shows that the CND is tidally unstable. The chemical
models show good agreement with the observations in cases where the density is
cm, the cosmic-ray ionization rate is high, s, or shocks with velocities km s have occurred.
Comparison of models and observations favors a scenario where the cosmic-ray
ionization rate in the CND is high, but precise effects of other factors such
as shocks, density structures, UV-photons and X-rays from the Sgr A* must be
examined with higher spatial resolution data.Comment: 17 Pages, 13 figures, accepted for publication in A&
Positive cross-correlations induced by ferromagnetic contacts
Due to the Fermionic nature of carriers, correlations between electric
currents flowing through two different contacts attached to a conductor present
a negative sign. Possibility for positive cross-correlations has been
demonstrated in hybrid normal/superconductor structures under certain
conditions. In this paper we show that positive cross-correlations can be
induced, if not already present, in such structures by employing ferromagnetic
leads with magnetizations aligned anti-parallel to each other. We consider
three-terminal hybrid structures and calculate the mean-square correlations of
current fluctuations as a function of the bias voltage at finite temperature.Comment: 6 pages, 5 figures; accepted version by PRB, figures replace
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