25,993 research outputs found
Revealing the dynamics of Class 0 protostellar discs with ALMA
We present synthetic ALMA observations of Keplerian, protostellar discs in
the Class 0 stage studying the emission of molecular tracers like CO,
CO, HCO, HCO, NH, and HCO. We model the
emission of discs around low- and intermediate-mass protostars. We show that
under optimal observing conditions ALMA is able to detect the discs already in
the earliest stage of protostellar evolution, although the emission is often
concentrated to the innermost 50 AU. Therefore, a resolution of a few 0.1"
might be too low to detect Keplerian discs around Class 0 objects. We also
demonstrate that under optimal conditions for edge-on discs Keplerian rotation
signatures are recognisable, from which protostellar masses can be inferred.
For this we here introduce a new approach, which allows us to determine
protostellar masses with higher fidelity than before. Furthermore, we show that
it is possible to reveal Keplerian rotation even for strongly inclined discs
and that ALMA should be able to detect possible signs of fragmentation in
face-on discs. In order to give some guidance for future ALMA observations, we
investigate the influence of varying observing conditions and source distances.
We show that it is possible to probe Keplerian rotation in inclined discs with
an observing time of 2 h and a resolution of 0.1", even in the case of moderate
weather conditions. Furthermore, we demonstrate that under optimal conditions,
Keplerian discs around intermediate-mass protostars should be detectable up to
kpc-distances.Comment: 17 pages, 17 figures, accepted for publication by MNRA
Highly synchronized noise-driven oscillatory behavior of a FitzHugh-Nagumo ring with phase-repulsive coupling
We investigate a ring of FitzHugh--Nagumo elements coupled in
\emph{phase-repulsive} fashion and submitted to a (subthreshold) common
oscillatory signal and independent Gaussian white noises. This system can be
regarded as a reduced version of the one studied in [Phys. Rev. E \textbf{64},
041912 (2001)], although externally forced and submitted to noise. The
noise-sustained synchronization of the system with the external signal is
characterized.Comment: 7 pages, 15 figures, uses aipproc.cls, aip-6s.clo and aipxfm.sty.
"Cooperative Behavior in Neural Systems: Ninth Granada Lectures'', edited by
J. Marro, P. L. Garrido, and J. J. Torre
Soy protein enzymatic hydrolysis and polysaccharides interactions: differential performance on kinetic adsorption at air-water interface
The objective of the work was to study the impact of soy protein hydrolysis on kinetic adsorption to the air-water interface and the effect
of polysaccharides addition. Was used soy protein (SP) and theirs hydrolysates of 2% (H1) and 5.4% (H2) degree of hydrolysis. The
polysaccharides (PS) used were a surface active one called E4M and a non-surface active one, lamda carrageenan (C). The dynamic
surface pressure of interfacial films was evaluated with a drop tensiometer. In this contribution, we have determined the kinetic
parameters of adsorption to the air-water interface which determined the penetration (Kp) and rearrangement (Kr) rates of SP, H1, H2
and PS, as well as their mixed systems. It was observed an increase of Kp and Kr when the protein were hydrolyzed (from SP to H1),
however, when degree of hydrolysis progresses to H2 the parameters decreased again. In other hand, considerable differences were not
found between these two PS studied concerning the Kp to air-water interface at these conditions. In spite of the different surface active
nature of the PS, the proteins seem to control the behavior of the protein-PS interactions. However, when Kr of mixed systems was
analyzed, the degree of hydrolysis and PS nature started to have a huge importance. Hence, it could be observed synergic or antagonic
effects on Kr of biopolymers at liquid interface depending to the degree of hydrolysis of protein analyzed and the type of PS selected.CYTED through project 105PI0274CYCYT through grant AGL2007-60045Junta de Andalucía through grant PO6-AGR-01535Universidad de Buenos Aires, Agencia Nacional de Promoción Científica y Tecnológica (PICT 2008-1901) and Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentin
Directly Indecomposables in Semidegenerate Varieties of Connected po-Groupoids
We study varieties with a term-definable poset structure, "po-groupoids". It
is known that connected posets have the "strict refinement property" (SRP). In
[arXiv:0808.1860v1 [math.LO]] it is proved that semidegenerate varieties with
the SRP have definable factor congruences and if the similarity type is finite,
directly indecomposables are axiomatizable by a set of first-order sentences.
We obtain such a set for semidegenerate varieties of connected po-groupoids and
show its quantifier complexity is bounded in general
First-principles study of the atomic and electronic structure of the Si(111)-(5x2-Au surface reconstruction
We present a systematic study of the atomic and electronic structure of the
Si(111)-(5x2)-Au reconstruction using first-principles electronic structure
calculations based on the density functional theory. We analyze the structural
models proposed by Marks and Plass [Phys. Rev. Lett.75, 2172 (1995)], those
proposed recently by Erwin [Phys. Rev. Lett.91, 206101 (2003)], and a
completely new structure that was found during our structural optimizations. We
study in detail the energetics and the structural and electronic properties of
the different models. For the two most stable models, we also calculate the
change in the surface energy as a function of the content of silicon adatoms
for a realistic range of concentrations. Our new model is the energetically
most favorable in the range of low adatom concentrations, while Erwin's "5x2"
model becomes favorable for larger adatom concentrations. The crossing between
the surface energies of both structures is found close to 1/2 adatoms per 5x2
unit cell, i.e. near the maximum adatom coverage observed in the experiments.
Both models, the new structure and Erwin's "5x2" model, seem to provide a good
description of many of the available experimental data, particularly of the
angle-resolved photoemission measurements
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