569 research outputs found
Comparing the Dynamic Global Core Plasma Model with ground-based plasma mass density observations
Correlating microbial community profiles with geochemical data in highly stratified sediments from the Arctic Mid-Ocean Ridge
Microbial communities and their associated metabolic activity in
marine sediments have a profound impact on global biogeochemical
cycles. Their composition and structure are attributed to geochemical
and physical factors, but finding direct correlations has remained a
challenge. Here we show a significant statistical relationship between
variation in geochemical composition and prokaryotic community
structure within deep-sea sediments. We obtained comprehensive
geochemical data from two gravity cores near the hydrothermal
vent field Loki’s Castle at the Arctic Mid-Ocean Ridge, in the Norwegian-
Greenland Sea. Geochemical properties in the rift valley
sediments exhibited strong centimeter-scale stratigraphic variability.
Microbial populations were profiled by pyrosequencing from
15 sediment horizons (59,364 16S rRNA gene tags), quantitatively
assessed by qPCR, and phylogenetically analyzed. Although the
same taxa were generally present in all samples, their relative
abundances varied substantially among horizons and fluctuated
between Bacteria- and Archaea-dominated communities. By independently
summarizing covariance structures of the relative
abundance data and geochemical data, using principal components
analysis, we found a significant correlation between changes in
geochemical composition and changes in community structure.
Differences in organic carbon and mineralogy shaped the relative
abundance of microbial taxa. We used correlations to build hypotheses
about energy metabolisms, particularly of the Deep Sea Archaeal
Group, specific Deltaproteobacteria, and sediment lineages
of potentially anaerobic Marine Group I Archaea. We demonstrate
that total prokaryotic community structure can be directly correlated
to geochemistry within these sediments, thus enhancing our
understanding of biogeochemical cycling and our ability to predict
metabolisms of uncultured microbes in deep-sea sediments
A model of energetic electron precipitation fluxes inside and outside of the plasmasphere during space weather events
Measurements of binary stars with coherent integration of NPOI data
In this paper we use coherently integrated visibilities (see separate paper
in these proceedings, Jorgensen et al. 2008) to measure the properties of
binary stars. We use only the phase of the complex visibility and not the
amplitude. The reason for this is that amplitudes suffer from the calibration
effect (the same for coherent and incoherent averages) and thus effectively
provide lower accuracy measurements. We demonstrate that the baseline phase
alone can be used to measure the separation, orientation and brightness ratio
of a binary star, as a function of wavelength.Comment: 2008 SPIE Astronomical Telescopes and Instrumentatio
Cryptosporidium, Enterocytozoon, and Cyclospora Infections in Pediatric and Adult Patients with Diarrhea in Tanzania.
Cryptosporidiosis, microsporidiosis, and cyclosporiasis were studied in four groups of Tanzanian inpatients: adults with AIDS-associated diarrhea, children with chronic diarrhea (of whom 23 of 59 were positive [+] for human immunodeficiency virus [HIV]), children with acute diarrhea (of whom 15 of 55 were HIV+), and HIV control children without diarrhea. Cryptosporidium was identified in specimens from 6/86 adults, 5/59 children with chronic diarrhea (3/5, HIV+), 7/55 children with acute diarrhea (0/7, HIV+), and 0/20 control children. Among children with acute diarrhea, 7/7 with cryptosporidiosis were malnourished, compared with 10/48 without cryptosporidiosis (P < .01). Enterocytozoon was identified in specimens from 3/86 adults, 2/59 children with chronic diarrhea (1 HIV+), 0/55 children with acute diarrhea, and 4/20 control children. All four controls were underweight (P < .01). Cyclospora was identified in specimens from one adult and one child with acute diarrhea (HIV-). Thus, Cryptosporidium was the most frequent and Cyclospora the least frequent pathogen identified. Cryptosporidium and Enterocytozoon were associated with malnutrition. Asymptomatic fecal shedding of Enterocytozoon in otherwise healthy, HIV children has not been described previously
Evolution of planetary nebulae II. Population effects on the bright cut-off of the PNLF
We investigate the bright cut-off of the [OIII]l5007 planetary nebula
luminosity function (PNLF), that has been suggested as a powerful extragalactic
distance indicator. Theoretical PNLFs are constructed via Monte-Carlo
simulations of populations of PNe, whose individual properties are described
with the aid of recent PN synthetic models (Marigo et al. 2001), coupled to a
detailed photoionisation code (CLOUDY). The basic dependences of the cut-off
magnitude M* are then discussed. We find that: (i) In galaxies with recent or
ongoing star formation, the modelled PNLF present M* values between -4 and -5,
very close to the observationally-calibrated value for the LMC. (ii) In these
galaxies, the PNLF cut-off is produced by PNe with progenitor masses of about
2.5 Msun, while less massive stars give origin to fainter PNe. As a consequence
M* is expected to depend strongly on the age of the last burst of star
formation, dimming by as much as 5 mag as we go from young to 10-Gyr old
populations. (iii) Rather than on the initial metallicity of a stellar
population, M* depends on the actual [O/H] of the observed PNe, a quantity that
may differ significantly from the initial value (due to dredge-up episodes),
especially in young and intermediate-age PN populations. (iv) Also the
transition time from the end of AGB to the PN phase, and the nuclear-burning
properties (i.e. H- or He-burning) of the central stars introduce
non-negligible effects on M*. The strongest indication derived from the present
calculations is a serious difficulty to explain the age-invariance of the
cut-off brightness over an extended interval, say from 1 to 13 Gyr, that
observations of PNLFs in galaxies of late-to-early type seem to suggest.Comment: 22 pages, to appear in Astronomy & Astrophysic
The Prognostic Value of Plasma Small Extracellular Vesicles' Phenotype in Patients With Gastrointestinal Stromal Tumor
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