3,636 research outputs found
The effectiveness of using carbonate isotope measurements of body tissues to infer diet in human evolution: Evidence from wild western chimpanzees (Pan troglodytes verus)*
Changes in diet throughout hominin evolution have been linked with important evolutionary changes. Stable carbon isotope analysis of inorganic apatite carbonate is the main isotopic method used to reconstruct fossil hominin diets; to test its effectiveness as a paleodietary indicator we present bone and enamel carbonate carbon isotope data from a well-studied population of modern wild western chimpanzees (Pan troglodytes verus) of known sex and age from Taï, Cote d'Ivoire.We found a significant effect of age class on bone carbonate values, with adult chimpanzees being more 13C- and 18O-depleted compared to juveniles. Further, to investigate habitat effects, we compared our data to existing apatite data on eastern chimpanzees (P. troglodytes schweinfurthii) and found that the Taï chimpanzees are significantly more depleted in enamel d13Cap and d18Oap compared to their eastern counterparts. Our data are the first to present a range of tissue-specific isotope data from the same group of wild western chimpanzees and, as such, add new data to the growing number of modern non-human primate comparative isotope datasets providing valuable information for the interpretation of diet throughout hominin evolution. By comparing our data to published isotope data on fossil hominins we found that our modern chimpanzee bone and enamel data support hypotheses that the trend towards increased consumption of C4 foods after 4 Ma (millions of years ago) is unique to hominins
Fluorogenic Membrane Overlays to Enumerate Total and Fecal Escherichia coli and Total Vibrionaceae in Shellfish and Seawater
Three assays were developed to enumerate total and fecal Escherichia coli and total Vibrionaceae in shellfish, seawater, and other foods and environmental samples. Assays involve membrane overlays of overnight colonies on nonselective agar plates to detect β-glucuronidase and lysyl aminopeptidase activities for E. coli and Vibrionaceae, respectively. Cellulose membranes containing the substrates 4-methylumbeferyl-β-D-glucuronide (MUG) produced a bright blue fluorescence when overlaid onto E. coli, while L-lysyl-7-amino-4-trifluoromethylcoumarin produced green fluorescent foci when overlaid onto Vibrionaceae family members. A multiplex assay was also developed for simultaneously enumerating total E. coli and total Vibrionaceae in oysters and seawater. Overall, 65% of overlaid E. coli (non-O157:H7) were MUG-positive, compared with 62% as determined by the most-probable-number-MUG assay. The overlays are rapid, simple, and cost effective for quantification purposes. This research provides practical alternatives for monitoring bacterial indicators and potential pathogens in complex samples, including molluscan shellfish
New Sources for the Hot Oxygen Geocorona: Solar Cycle, Seasonal, Latitudinal, and Diurnal Variations
This paper demonstrates the variability of thermospheric sources of hot oxygen atoms. Numerical calculations were performed for day and night, high and low solar activity, summer and winter, and low- and middle-latitude conditions. Under most conditions, reactions involving metastable species are more important hot O sources than previously considered dissociative recombination of O2+ and NO+. All the hot O sources are an order of magnitude lower at midnight than at noon. At night, dissociative recombination of O2+and NO+ are the most important sources. Quenching of vibrationally excited N2 (N2*) by O is the most important metastable source at night. Above 300 km, hot O sources increase by an order of magnitude between solar minimum and solar maximum. For a given level of solar activity, the high-altitude total production rate of hot O kinetic energy is greater during winter than during summer, indicating a dominance of cooler hot O sources during summer. The N2* source dominates at low altitudes. At high altitudes it is almost negligible at solar minimum, but increases to become the dominant source at solar maximum. Atomic oxygen quenching of N(²D) is a large source at solar minimum and is still important at solar maximum. Overall, seasonal variations are small compared to solar cycle, diurnal and latitudinal variations. While quenching of metastable species is more important at midlatitudes than at low latitudes, there is little latitudinal variation in hot O production due to dissociative recombination of NO+ and O2+
The X-ray Spectral Properties and Variability of Luminous High-Redshift Active Galactic Nuclei
We perform a detailed investigation of moderate-to-high quality X-ray spectra
of ten of the most luminous active galactic nuclei (AGNs) known at z>4 (up to
z~6.28). This study includes five new XMM observations and five archived X-ray
observations (four by XMM and one by Chandra). We find that the X-ray power-law
photon indices of our sample, composed of eight radio-quiet sources and two
that are moderately radio loud, are not significantly different from those of
lower redshift AGNs. The upper limits obtained on intrinsic neutral hydrogen
column densities, N_H<~10^{22}-10^{23} cm^{-2}, indicate that these AGNs are
not significantly absorbed. A joint fit performed on our eight radio-quiet
sources, with a total of ~7000 photons, constrains the mean photon index of z>4
radio-quiet AGNs to Gamma=1.97^{+0.06}_{-0.04}, with no detectable intrinsic
dispersion from source to source. We also obtain a strong constraint on the
mean intrinsic column density, N_H<~3x10^{21} cm^{-2}, showing that optically
selected radio-quiet AGNs at z>4 are, on average, not more absorbed than their
lower-redshift counterparts. All this suggests that the X-ray production
mechanism and the central environment in radio-quiet AGNs have not
significantly evolved over cosmic time. The mean equivalent width of a putative
neutral narrow Fe Ka line is constrained to be <~190 eV, and similarly we place
constraints on the mean Compton reflection component (R<~1.2). None of the AGNs
varied on short (~1 hr) timescales, but on longer timescales (months-to-years)
strong variability is observed in four of the sources. In particular, the X-ray
flux of the z=5.41 radio-quiet AGN SDSS 0231-0728 dropped by a factor of ~4
over a rest-frame period of 73 d. This is the most extreme X-ray variation
observed in a luminous z>4 radio-quiet AGN.Comment: 10 pages (emulateapj), 5 figures. Accepted by Ap
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