5,216 research outputs found
Brazil, the bomb and the poet: Cecilia Meireles and the Gandhian Seminar (1953)
In 1953, a group of nine delegates (from non-communist countries)
met in New Delhi to discuss Gandhiâs âoutlooks and techniquesâ as a creative
means to resolve Cold War nuclear tensions. This article mainly focuses on the
politics and lyrical impressions as observed by the Brazilian poet CecĂlia
Meireles in the Seminar proceedings and the DiĂĄrio de NotĂcias. As the only
Latin American delegate to attend the Seminar, she sheds new light on the ways
emerging countries such as India and Brazil cope with racism, war, hunger, and
violence. One pressing Gandhian issue Meireles and other delegates address is
the ethical role of âmachinesâ in modern society. Problems faced by postcolonial cultures, such as industrialization, poverty, and racial strife, seem to
take a different (and more dangerous) perspective when thought of in terms of
machines and progress. To elucidate this âmachine-likeâ rhetoric, the ideas of
Deleuze and Guattari have been applied throughout. Other participant comments
such as those by Ralph Bunche and John Boyd Orr allow for additional insight
into topics still relevant today
Characterization of the known T type dwarfs towards the Sigma Orionis cluster
(Abridged) A total of three T type candidates (SOri70, SOri73, and
SOriJ0538-0213) lying in the line of sight towards Sigma Orionis were
characterized by means of near-infrared photometric, astrometric, and
spectroscopic studies. H-band methane images were collected for all three
sources and an additional sample of 15 field T type dwarfs using LIRIS/WHT.
J-band spectra of resolution of ~500 were obtained for SOriJ0538-0213 with
ISAAC/VLT, and JH spectra of resolution of ~50 acquired with WFC3/HST were
employed for the spectroscopic classification of SOri70 and 73. Proper motions
with a typical uncertainty of +/-3 mas/yr and a time interval of ~7-9 yr were
derived. Using the LIRIS observations of the field T dwarfs, we calibrated this
imager for T spectral typing via methane photometry. The three SOri objects
were spectroscopically classified as T4.5+/-0.5 (SOri73), T5+/-0.5
(SOriJ0538-0213), and T7 (SOri70). The similarity between the
observed JH spectra and the methane colors and the data of field ultra-cool
dwarfs of related classifications suggests that SOri70, 73, and
SOriJ053804.65-021352.5 do not deviate significantly in surface gravity in
relation to the field. Additionally, the detection of KI at ~1.25 microns in
SOriJ0538-0213 points to a high-gravity atmosphere. Only the K-band reddish
nature of SOri70 may be consistent with a low gravity atmosphere. The proper
motions of SOri70 and 73 are measurable and are larger than that of the cluster
by >3.5 sigma. The proper motion of SOriJ0538-0213 is consistent with a null
displacement. These observations suggest that none of the three T dwarfs are
likely Sigma Orionis members, and that either planetary-mass objects with
masses below ~4 MJup may not exist free-floating in the cluster or they may lie
at fainter near-infrared magnitudes than those of the targets (this is H>20.6
mag), thus remaining unidentified to date.Comment: Accepted for publication in A&A (2014), corrected typo
Ionic polaron in a Bose-Einstein condensate
The ground state properties of a degenerate bosonic gas doped with an ion are
investigated by means of quantum Monte Carlo simulations in three dimensions.
The system features competing length and energy scales, which result in vastly
different polaronic properties compared to neutral quantum impurities.
Depending on whether a two-body bound state is supported or not by the atom-ion
potential, we identify a transition between a polaron regime amenable to a
perturbative treatment in the limit of weak atom-ion interactions and a
many-body bound state with vanishing quasi-particle residue composed of
hundreds of atoms. In order to analyze the structure of the corresponding
states we examine the atom-ion and atom-atom correlation functions. Our
findings are directly relevant to experiments using hybrid atom-ion setups that
have recently attained the ultracold regime.Comment: 11 pages, 6 figures, 1 tabl
Search and characterization of T-type planetary mass candidates in the sigma Orionis cluster
(Abridged) We aim to: i) confirm the presence of methane absorption in S Ori
73 (a T-type member candidate of the sig Orionis cluster, 3 Myr, 352 pc)
through methane imaging; ii) study S Ori 70 and 73 cluster membership via
photometric colors and accurate proper motion analysis; iii) perform a new
search to identify additional T-type sig Orionis member candidates with likely
masses below 7 Mjup. We obtained HAWK-I (VLT) J, H, and CH4off photometry of an
area of 119.15 sq. arcmin in sig Orionis down to Jcomp = 21.7 and Hcomp = 21
mag. Near-infrared data were complemented with optical photometry using images
acquired with OSIRIS (GTC) and VISTA as part of the VISTA Orion survey. We
derived proper motions by comparison of the new HAWK-I and VISTA images with
published near-infrared data taken 3.4 - 7.9 yr ago. S Ori 73 has a red
H-CH4off color indicating methane absorption in the H-band and a spectral type
of T4 +/- 1. S Ori 70 displays a redder methane color than S Ori 73 in
agreement with its latter spectral classification. Our proper motion
measurements are larger than the motion of sig Orionis, rendering S Ori 70 and
73 cluster membership uncertain. We identified one new photometric candidate
with J = 21.69 +/- 0.12 mag and methane color consistent with spectral type
greater than T8. S Ori 73 has colors similar to those of T3-T5 field dwarfs,
which in addition to its high proper motion suggests that it is probably a
field dwarf located at 170-200 pc. The origin of S Ori 70 remains unclear: it
can be a field, foreground mid- to late-T free-floating dwarf with peculiar
colors, or an orphan planet ejected through strong dynamical interactions from
sig Orionis or from a nearby star-forming region in Orion.Comment: Accepted for publication in A&
Trigonometric parallaxes of young field L dwarfs
(Abridged) We aim to determine the trigonometric parallaxes and proper
motions of a sample of ten field L0-L5 dwarfs with spectroscopic evidence for
low-gravity atmospheres. We obtained J and Ks imaging data using 2-4-m class
telescopes with a typical cadence of one image per month between 2010 January
and 2012 December. We also obtained low resolution optical spectra (R~300,
500-1100 nm) using the 10-m GTCs to assess the presence of lithium absorption
in four targets and confirm their young age. Trigonometric parallaxes and
proper motions were derived to typical accuracies of 1 mas and +/-10 mas/yr.
All ten L dwarfs have large motions, and are located at distances between 9 and
47 pc. They lie above and on the sequence of field dwarfs in the absolute J and
K_s magnitude versus spectral type and luminosity versus Teff diagrams,
implying ages similar to or smaller than those typical of the field. The
detection of atomic lithium in the atmosphere of 2MASS J00452143+1634446 is
reported for the first time. Three dwarfs have locations in the HR diagram
indicative of old ages and high masses consistent with the observed lithium
depletion previously published. We did not find evidence for the presence of
astrometric companions with minimum detectable masses typically >=25 Mjup and
face-on, circular orbits with periods between 60-90 d and 3 yr around eight
targets. The astrometric and spectroscopic data indicate that about 60-70% of
the field L-type dwarfs in our sample with evidence for low-gravity atmospheres
are indeed young-to-intermediate-age brown dwarfs of the solar neighborhood
with expected ages and masses in the intervals 10-500 Myr and 11-45 Mjup. The
peaked-shape of the H-band spectra of L dwarfs, a signpost of youth, appears to
be present up to ages of 120-500 Myr and intermediate-to-high gravities.Comment: Accepted for publication in A&
Segal-Bargmann-Fock modules of monogenic functions
In this paper we introduce the classical Segal-Bargmann transform starting
from the basis of Hermite polynomials and extend it to Clifford algebra-valued
functions. Then we apply the results to monogenic functions and prove that the
Segal-Bargmann kernel corresponds to the kernel of the Fourier-Borel transform
for monogenic functionals. This kernel is also the reproducing kernel for the
monogenic Bargmann module.Comment: 11 page
Effect of Co, Ni, and Cu substitution on the electronic structure of hexagonal YMnO3 studied by x-ray absorption spectroscopy
[[abstract]]X-ray absorption spectroscopy measurements have been performed to elucidate local electronic and atomic structures of orthorhombic 3d-transition metal-doped yttrium manganites (YMnO3) with chemical formulae YMn2/3Me1/3O3 (Me = Co, Ni, and Cu). The MnâL3- and K-edges x-ray absorption near-edge structure (XANES) demonstrate the direct substitution of Me2+ for Mn3+, so that the positive effective charge of Mn ions are increased. Me-doping is also found to induce substantial broadening of the MnâL3-edge feature, which suggests enhancement of the delocalization of Mnâ3d eg subbands and conductivity. Local spin density approximation (LSDA)+U (Hubbard U parameter) calculations were used to understand their electronic structures.[[notice]]èŁæŁćźçą[[incitationindex]]SCI[[booktype]]çŽæŹ[[booktype]]é»ć
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