8,436 research outputs found
Spin selective transport through helical molecular systems
Highly spin selective transport of electrons through a helically shaped
electrostatic potential is demonstrated in the frame of a minimal model
approach. The effect is significant even in the case of weak spin-orbit
coupling. Two main factors determine the selectivity, an unconventional Rashba-
like spin-orbit interaction, reflecting the helical symmetry of the system, and
a weakly dispersive electronic band of the helical system. The weak electronic
coupling, associated with the small dispersion, leads to a low mobility of the
charges in the system and allows even weak spin-orbit interactions to be
effective. The results are expected to be generic for chiral molecular systems
displaying low spin-orbit coupling and low conductivity.Comment: 9 pages, 4 figures v2 (misprints corrected, new figures
Kinematics of gas and stars in circumnuclear star-forming regions of early type spirals
(Abbr.) We present high resolution (R~20000) spectra in the blue and the far
red of cicumnuclear star-forming regions (CNSFRs) in three early type spirals
(NGC3351, NGC2903 and NGC3310) which have allowed the study of the kinematics
of stars and ionized gas in these structures and, for the first time, the
derivation of their dynamical masses for the first two. In some cases these
regions, about 100 to 150 pc in size, are seen to be composed of several
individual star clusters with sizes between 1.5 and 4.9 pc estimated from
Hubble Space Telescope (HST) images. The stellar dispersions have been obtained
from the Calcium triplet (CaT) lines at 8494,8542,8662 \AA,
while the gas velocity dispersions have been measured by Gaussian fits to the
H and [OIII] 5007 \AA lines on the high dispersion
spectra. Values of the stellar velocity dispersions are between 30 and 68 km/s.
We apply the virial theorem to estimate dynamical masses of the clusters,
assuming that systems are gravitationally bounded and spherically symmetric,
and using previously measured sizes. The measured values of the stellar
velocity dispersions yield dynamical masses of the order of 10 to 10
solar masses for the whole CNSFRs. Stellar and gas velocity dispersions are
found to differ by about 20 to 30 km/s with the H emission lines being
narrower than both the stellar lines and the [OIII] 5007 \AA
lines. The twice ionized oxygen, on the other hand, shows velocity dispersions
comparable to those shown by stars, in some cases, even larger. We have found
indications of the presence of two different kinematical components in the
ionized gas of the regions...Comment: 4 pages, proceeding of the meeting "Young massive star clusters -
Initial conditions and environments", Granada, Spain, 200
PPAK Wide-field Integral Field Spectroscopy of NGC 628: II. Emission line abundance analysis
In this second paper of the series, we present the 2-dimensional (2D)
emission line abundance analysis of NGC 628, the largest object within the PPAK
Integral Field Spectroscopy (IFS) Nearby Galaxies Survey: PINGS. We introduce
the methodology applied to the 2D IFS data in order to extract and deal with
large spectral samples, from which a 2D abundance analysis can be later
performed. We obtain the most complete and reliable abundance gradient of the
galaxy up-to-date, by using the largest number of spectroscopic points sampled
in the galaxy, and by comparing the statistical significance of different
strong-line metallicity indicators. We find features not previously reported
for this galaxy that imply a multi-modality of the abundance gradient
consistent with a nearly flat-distribution in the innermost regions of the
galaxy, a steep negative gradient along the disc and a shallow gradient or
nearly-constant metallicity beyond the optical edge of the galaxy. The N/O
ratio seems to follow the same radial behaviour. We demonstrate that the
observed dispersion in metallicity shows no systematic dependence with the
spatial position, signal-to-noise or ionization conditions, implying that the
scatter in abundance for a given radius is reflecting a true spatial physical
variation of the oxygen content. Furthermore, by exploiting the 2D IFS data, we
were able to construct the 2D metallicity structure of the galaxy, detecting
regions of metal enhancement, and showing that they vary depending on the
choice of the metallicity estimator. The analysis of axisymmetric variations in
the disc of NGC 628 suggest that the physical conditions and the star formation
history of different-symmetric regions of the galaxy have evolved in a
different manner.Comment: Accepted for publication in MNRAS, 40 pages, 22 figures, online data:
http://www.ast.cam.ac.uk/ioa/research/ping
The role of gas infall in the evolution of disc galaxies
Spiral galaxies are thought to acquire their gas through a protracted infall
phase resulting in the inside-out growth of their associated discs. For field
spirals, this infall occurs in the lower density environments of the cosmic
web. The overall infall rate, as well as the galactocentric radius at which
this infall is incorporated into the star-forming disc, plays a pivotal role in
shaping the characteristics observed today. Indeed, characterising the
functional form of this spatio-temporal infall in-situ is exceedingly
difficult, and one is forced to constrain these forms using the present day
state of galaxies with model or simulation predictions. We present the infall
rates used as input to a grid of chemical evolution models spanning the mass
spectrum of discs observed today. We provide a systematic comparison with
alternate analytical infall schemes in the literature, including a first
comparison with cosmological simulations. Identifying the degeneracies
associated with the adopted infall rate prescriptions in galaxy models is an
important step in the development of a consistent picture of disc galaxy
formation and evolution.Comment: 12 pages, 12 figures, MNRAS, accepte
Self-similar transmission properties of aperiodic Cantor potentials in gapped graphene
We investigate the transmission properties of quasiperiodic or aperiodic
structures based on graphene arranged according to the Cantor sequence. In
particular, we have found self-similar behaviour in the transmission spectra,
and most importantly, we have calculated the scalability of the spectra. To do
this, we implement and propose scaling rules for each one of the fundamental
parameters: generation number, height of the barriers and length of the system.
With this in mind we have been able to reproduce the reference transmission
spectrum, applying the appropriate scaling rule, by means of the scaled
transmission spectrum. These scaling rules are valid for both normal and
oblique incidence, and as far as we can see the basic ingredients to obtain
self-similar characteristics are: relativistic Dirac electrons, a self-similar
structure and the non-conservation of the pseudo-spin. This constitutes a
reduction of the number of conditions needed to observe self-similarity in
graphene-based structures, see D\'iaz-Guerrero et al. [D. S. D\'iaz-Guerrero,
L. M. Gaggero-Sager, I. Rodr\'iguez-Vargas, and G. G. Naumis,
arXiv:1503.03412v1, 2015]
Study of complexes of Poly(9-vinylcarbazole) with copper, cobalt and chromium on solid state
In this paper we have studied the synthesis and characterization in solution and on solid state of different poly(9-vinylcarbazole) with some transition metal chlorides suchas CuCl2ă»2H2O, CoCl2ă»6H2O and CrCl3ă»6H2O. The polymermetal complexes were characterized by FTIR and the result revealed that the infrared spectra of the complexes show significant shift with respect to that of PNVC, indicating that linking between the polymer and metal may be tacking place only through the tertiary nitrogen of the carbazole side group. The thermal stability and glass transition temperature of the polymer-metal complexes were found to be higher than that of the polymer. The pores of the polymer are filled after interaction with cation with polymeric ligand
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