4,939 research outputs found
Comparative chemistry of diffuse clouds III: sulfur-bearing molecules
Using data from IRAM's Plateau de Bure Interferometer and 30 m Telescope, we
discuss the mm-wave absorption lines of CS, SO, H2S and HCS+ which arise in
diffuse clouds occulting several extragalactic continuum sources. Typical
relative abundances are X(CS)/X(HCO+) ~ 2, X(CS)/X(SO) ~ 2, X(CS)/X(H2S) ~ 6
and X(CS)/X(HCS+) ~ 13.Comment: Accepted by A&A 2002-Jan-1
Imaging galactic diffuse gas: Bright, turbulent CO surrounding the line of sight to NRAO150
To understand the environment and extended structure of the host galactic gas
whose molecular absorption line chemistry, we previously observed along the
microscopic line of sight to the blazar/radiocontinuum source NRAO150 (aka
B0355+508), we used the IRAM 30m Telescope and Plateau de Bure Interferometer
to make two series of images of the host gas: i) 22.5 arcsec resolution
single-dish maps of 12CO J=1-0 and 2-1 emission over a 220 arcsec by 220 arcsec
field; ii) a hybrid (interferometer+singledish) aperture synthesis mosaic of
12CO J=1-0 emission at 5.8 arcsec resolution over a 90 arcsec-diameter region.
CO components that are observed in absorption at a moderate optical depth (0.5)
and are undetected in emission at 1 arcmin resolution toward NRAO 150 remain
undetected at 6 arcsec resolution. This implies that they are not a
previously-hidden large-scale molecular component revealed in absorption, but
they do highlight the robustness of the chemistry into regions where the
density and column density are too low to produce much rotational excitation,
even in CO. Bright CO lines around NRAO150 most probably reflect the variation
of a chemical process, i.e. the C+-CO conversion. However, the ultimate cause
of the variations of this chemical process in such a limited field of view
remains uncertain.Comment: 18 pages, 22 PostScript files giving 14 figures. Accepted for
publication in Astronomy & Astrophysics in the letter section. Uses aa LaTeX
macro
Severe malaria - a case of fatal Plasmodium knowlesi infection with post-mortem findings: a case report.
BACKGROUND: Zoonotic malaria caused by Plasmodium knowlesi is an important, but newly recognized, human pathogen. For the first time, post-mortem findings from a fatal case of knowlesi malaria are reported here.
CASE PRESENTATION: A formerly healthy 40 year-old male became symptomatic 10 days after spending time in the jungle of North Borneo. Four days later, he presented to hospital in a state of collapse and died within two hours. He was hyponatraemic and had elevated blood urea, potassium, lactate dehydrogenase and amino transferase values; he was also thrombocytopenic and eosinophilic. Dengue haemorrhagic shock was suspected and a post-mortem examination performed. Investigations for dengue virus were negative. Blood for malaria parasites indicated hyperparasitaemia and single species P. knowlesi infection was confirmed by nested-PCR. Macroscopic pathology of the brain and endocardium showed multiple petechial haemorrhages, the liver and spleen were enlarged and lungs had features consistent with ARDS. Microscopic pathology showed sequestration of pigmented parasitized red blood cells in the vessels of the cerebrum, cerebellum, heart and kidney without evidence of chronic inflammatory reaction in the brain or any other organ examined. Brain sections were negative for intracellular adhesion molecule-1. The spleen and liver had abundant pigment containing macrophages and parasitized red blood cells. The kidney had evidence of acute tubular necrosis and endothelial cells in heart sections were prominent.
CONCLUSIONS: The overall picture in this case was one of systemic malaria infection that fit the WHO classification for severe malaria. Post-mortem findings in this case were unexpectedly similar to those that define fatal falciparum malaria, including cerebral pathology. There were important differences including the absence of coma despite petechial haemorrhages and parasite sequestration in the brain. These results suggest that further study of knowlesi malaria will aid the interpretation of, often conflicting, information on malaria pathophysiology in humans
The shaping effect of collimated fast outflows in the Egg nebula
We present high angular resolution observations of the HCN J=5--4 line
from the Egg nebula, which is the archetype of protoplanetary nebulae. We find
that the HCN emission in the approaching and receding portion of the
envelope traces a clumpy hollow shell, similar to that seen in normal carbon
rich envelopes. Near the systemic velocity, the hollow shell is fragmented into
several large blobs or arcs with missing portions correspond spatially to
locations of previously reported high--velocity outlows in the Egg nebula. This
provides direct evidence for the disruption of the slowly--expanding envelope
ejected during the AGB phase by the collimated fast outflows initiated during
the transition to the protoplanetary nebula phase. We also find that the
intersection of fast molecular outflows previously suggested as the location of
the central post-AGB star is significantly offset from the center of the hollow
shell. From modelling the HCN distribution we could reproduce qualitatively
the spatial kinematics of the HCN J=5--4 emission using a HCN shell
with two pairs of cavities cleared by the collimated high velocity outflows
along the polar direction and in the equatorial plane. We infer a relatively
high abundance of HCN/H 3x10 for an estimated mass--loss
rate of 3x10 M yr in the HCN shell. The high
abundance of HCN and the presence of some weaker J=5--4 emission in the
vicinity of the central post-AGB star suggest an unusually efficient formation
of this molecule in the Egg nebula.Comment: 22 pages, 6 figures, submitted to the Astrophysical Journa
Time-dependent H2 formation and protonation
Methods: The microscopic equations of H2-formation and protonation are
integrated numerically over time in such a manner that the overall structures
evolve self-consistently under benign conditions. Results: The equilibrium H2
formation timescale in an H I cloud with N(H) ~ 4x10^{20}/cm^2 is 1-3 x 10^7
yr, nearly independent of the assumed density or H2 formation rate constant on
grains, etc. Attempts to speed up the evolution of the H2-fraction would
require densities well beyond the range usually considered typical of diffuse
gas. The calculations suggest that, under benign, quiescent conditions,
formation of H2 is favored in larger regions having moderate density,
consistent with the rather high mean kinetic temperatures measured in H2, 70-80
K. Formation of H3+ is essentially complete when H2-formation equilibrates but
the final abundance of H3+ appears more nearly at the very last instant.
Chemistry in a weakly-molecular gas has particular properties so that the
abundance patterns change appreciably as gas becomes more fully molecular,
either in model sequences or with time in a single model. One manifestation of
this is that the predicted abundance of H3+ is much more weakly dependent on
the cosmic-ray ionization rate when n(H2)/n(H) < 0.05. In general, high
abundances of H3+ do not enhance the abundances of other species (e.g. HCO+)
but late-time OH formation proceeds most vigourously in more diffuse regions
having modest density, extinction and H2 fraction and somewhat higher
fractional ionization, suggesting that atypically high OH/H2 abundance ratios
might be found optically in diffuse clouds having modest extinction
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