119,867 research outputs found
An overview of the focus of the International Gap Junction Conference 2017 and Future Perspectives
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Quantum phase transition in capacitively coupled double quantum dots
We investigate two equivalent, capacitively coupled semiconducting quantum
dots, each coupled to its own lead, in a regime where there are two electrons
on the double dot. With increasing interdot coupling a rich range of behavior
is uncovered: first a crossover from spin- to charge-Kondo physics, via an
intermediate SU(4) state with entangled spin and charge degrees of freedom;
followed by a quantum phase transition of Kosterlitz-Thouless type to a
non-Fermi liquid `charge-ordered' phase with finite residual entropy and
anomalous transport properties. Physical arguments and numerical
renormalization group methods are employed to obtain a detailed understanding
of the problem.Comment: 4 pages, 3 figure
Constraints to the Masses of Brown Dwarf Candidates from the Lithium Test
We present intermediate dispersion (0.7-2.2 \AA ~pix) optical
spectroscopic observations aimed at applying the ``Lithium Test'' to a sample
of ten brown dwarf candidates located in the general field, two in young open
clusters, and two in close binaries. We find evidence for strong Li depletion
in all of them, and thus infer lower mass limits of 0.065~M, depending
only slightly (0.005~M) on the interior models. None of the field
brown dwarf candidates in our sample appears to be a very young (age
~10~yr) substellar object. For one of the faintest proper motion
Pleiades members known (V=20.7) the Li test implies a mass greater than
0.08~M, and therefore it is not a brown dwarf. From our spectra
we estimate spectral types for some objects and present measurements of Halpha
emission strengths and radial velocities. Finally, we compare the positions in
the H-R diagram of our sample of brown dwarf candidates with the theoretical
region where Li is expected to be preserved (Substellar Lithium Region). We
find that certain combinations of temperature calibrations and evolutionary
tracks are consistent with the constraints imposed by the observed Li depletion
in brown dwarf candidates, while others are not.Comment: 20 pp.; 4 figs, available under request; plain LaTeX, ApJ in press,
OACatania-94-00
Extragalactic CS survey
We present a coherent and homogeneous multi-line study of the CS molecule in
nearby (D10Mpc) galaxies. We include, from the literature, all the available
observations from the to the transitions towards NGC 253, NGC
1068, IC 342, Henize~2-10, M~82, the Antennae Galaxies and M~83. We have, for
the first time, detected the CS(7-6) line in NGC 253, M~82 (both in the
North-East and South-West molecular lobes), NGC 4038, M~83 and tentatively in
NGC 1068, IC 342 and Henize~2-10. We use the CS molecule as a tracer of the
densest gas component of the ISM in extragalactic star-forming regions,
following previous theoretical and observational studies by Bayet et al.
(2008a,b and 2009). In this first paper out of a series, we analyze the CS data
sample under both Local Thermodynamical Equilibrium (LTE) and non-LTE (Large
Velocity Gradient-LVG) approximations. We show that except for M~83 and Overlap
(a shifted gas-rich position from the nucleus NGC 4039 in the Antennae
Galaxies), the observations in NGC 253, IC 342, M~82-NE, M~82-SW and NGC 4038
are not well reproduced by a single set of gas component properties and that,
at least, two gas components are required. For each gas component, we provide
estimates of the corresponding kinetic temperature, total CS column density and
gas density.Comment: 17 pages, 16 figures, 3 tables, Accepted to Ap
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