25,162 research outputs found
[Review of] Sidner J. Larson. Catch Colt. American Indian Lives
Catch Colt describes Gros Ventre writer Sidner J. Larson\u27s experience as a mixed-blood Native American looking for his heritage, identity, and personal direction. Although minority fiction writers (such as Rudolfo A. Anaya and Leslie Marmon Silko) have addressed this theme, non-fiction discussions of mixed-blood Native American lives are lacking. Larson\u27s autobiography, however, is only moderately successful because he fails to make readers identify with his struggle as a member of “two different worlds at the same time...with a degree of non-acceptance by both
Parametric Instabilities in Resonantly-Driven Bose-Einstein Condensates
Shaking optical lattices in a resonant manner offers an efficient and
versatile method to devise artificial gauge fields and topological band
structures for ultracold atomic gases. This was recently demonstrated through
the experimental realization of the Harper-Hofstadter model, which combined
optical superlattices and resonant time-modulations. Adding inter-particle
interactions to these engineered band systems is expected to lead to
strongly-correlated states with topological features, such as fractional Chern
insulators. However, the interplay between interactions and external
time-periodic drives typically triggers violent instabilities and
uncontrollable heating, hence potentially ruling out the possibility of
accessing such intriguing states of matter in experiments. In this work, we
study the early-stage parametric instabilities that occur in systems of
resonantly-driven Bose-Einstein condensates in optical lattices. We apply and
extend an approach based on Bogoliubov theory [PRX 7, 021015 (2017)] to a
variety of resonantly-driven band models, from a simple shaken Wannier-Stark
ladder to the more intriguing driven-induced Harper-Hofstadter model. In
particular, we provide ab initio numerical and analytical predictions for the
stability properties of these topical models. This work sheds light on general
features that could guide current experiments to stable regimes of operation.Comment: 15 pages, 6 figures, one appendi
The planetary nebula IC 5148 and its ionized halo
Many round or nearly roundish Planetary Nebulae (PNe) show multiple shells
and halo structures during their evolutionary stage near the maximum
temperature of their central star. Controversial debate is currently ongoing if
these structures are recombination halos, as suggested by hydrodynamic
modelling efforts, or ionized material. Recently we discovered a halo with even
somewhat unusual structures around the sparsely studied PN IC~5148 and present
for the first time spectroscopy going out to the halo of such a PN.} resolution
spectroscopy is used to derive dust chemistry and mineralogy. We investigate
the spatial distribution of material and its ionization state from the center
of the nebula up to the very outskirts of the halo. We obtained long-slit low
resolution spectroscopy (FORS2@VLT) of the nebula in two position angles, which
we used to investigate the nebular structure and its halo in the optical range
from 450 to 880\,nm. In addition we used medium resolution spectra taken with
X-SHOOTER@VLT ranging from 320 nm to 2.4 mu to derive atmospheric parameters
for the central star. We obtained the distance and position in the Galaxy from
various methods combined with GAIA DR2 data. We also applied Cloudy models to
the nebula in order to derive physical parameters of the various regions. We
obtained spatially resolved structures and detailed descriptions of the
outrunning shock front and a set of unusual halo structures denoted to further
shock. The halo structures appears clearly as hot ionized material. Furthermore
we derived a reliable photometric value for the central star at a GAIA distance
of D=1.3kpc. Considering the large distance \,kpc from the galactic
plane together to its non-circular motion in the galaxy and, a metallicity only
slightly below that of typical disk PNe, most likely IC 5148 originates from a
thick disk population star.Comment: 12 pages, 17 figures, accepted for publication in Astronomy &
Astrophysic
QED Penguin Contributions To Isospin Splittings of Heavy-Light Quark Systems
Recent experiments show that the isospin-violating mass splitting of the B
mesons is very small, but the best fits with a QCD sum rule analysis give a
splitting of at least 1.0 MeV. The isospin-violating mass splittings of the
charmed mesons, on the other hand, are in agreement with experiment. In this
letter we show that the inclusion of 2 kind QED penguin diagrams can
account for this discrepancy within the errors in the QCD sum rule method.Comment: 9 pages, latex, 2 figure
SN1987A - a Testing Ground for the KARMEN Anomaly
We show, that SN1987A can serve as an astrophysical laboratory for testing
the viability of the assertion that a new massive neutral fermion is implied by
the KARMEN data. We show that a wide range of the parameters characterizing the
proposed particle is ruled out by the above constraints making this
interpretation very unlikely.Comment: 12 pages, 1 eps figure embedded, to appear in Phys. Lett.
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