120 research outputs found
Internal tree cycling and atmospheric archiving of mercury: examination with concentration and stable isotope analyses
Trees predominantly take up mercury (Hg) from the atmosphere via stomatal assimilation of gaseous elemental Hg (GEM). Hg is oxidised in leaves/needles and transported to other tree anatomy including bole wood where it can be stored long-term. Using Hg associated with growth rings facilitates archiving of historical GEM concentrations. Nonetheless, there are significant knowledge gaps on the cycling of Hg within trees. We investigate Hg archived in tree rings, internal tree Hg cycling, and differences in Hg uptake mechanisms in Norway spruce and European larch sampled within 1 km of a HgCl2 contaminated site using total Hg (THg) and Hg stable isotope analyses. Tree ring samples are indicative of significant increases in THg concentrations (up to 521µg·kg-1) from background period (BGP; facility closed; 1992—present) to secondary industrial period (2ndIP; no HgCl2 wood treatment; 1962–1992) to primary industrial period (1stIP; active HgCl2 wood treatment; ≈1900–1962). Mass dependent fractionation (MDF) Hg stable isotope data are shifted negative during industrial periods (δ202Hg: 1stIP: 4.32±0.15 ‰; 2ndIP: 4.04±0.32 ‰; BGP: 2.83±0.74 ‰; 1SD). Even accounting for a ≈ 2.6 ‰ MDF shift associated with stomatal uptake, these data are indicative of emissions derived from industrial activity being enriched in lighter isotopes associated with HgCl2 reduction and Hg0 volatilisation. Similar MDF (δ202Hg: 3.90±0.30 ‰; 1SD) in bark Hg (137±105µg·kg-1) suggests that stomatal assimilation and downward transport is also the dominant uptake mechanism for bark Hg (reflective of negative stomatal uptake MDF shift) rather than deposition to bark. THg was enriched in sapwood of all sampled trees across both tree species. This may indicate long-term storage of a fraction of Hg in sapwood or xylem solution. These data advance our understanding of the physiological processing of Hg within trees and provide critical direction to future research into the use of trees as archives for historical atmospheric Hg.</p
From aptamer-based biomarker discovery to diagnostic and clinical applications: an aptamer-based, streamlined multiplex proteomic assay
Recently, we reported an aptamer-based, highly multiplexed assay for the purpose of biomarker identification. To enable seamless transition from highly multiplexed biomarker discovery assays to a format suitable and convenient for diagnostic and life-science applications, we developed a streamlined, plate-based version of the assay. The plate-based version of the assay is robust, sensitive (sub-picomolar), rapid, can be highly multiplexed (upwards of 60 analytes), and fully automated. We demonstrate that quantification by microarray-based hybridization, Luminex bead-based methods, and qPCR are each compatible with our platform, further expanding the breadth of proteomic applications for a wide user community
A Post-AGB Star in the Small Magellanic Cloud Observed with the Spitzer Infrared Spectrograph
We have observed an evolved star with a rare combination of spectral
features, MSX SMC 029, in the Small Magellanic Cloud (SMC) using the
low-resolution modules of the Infrared Spectrograph on the Spitzer Space
Telescope. A cool dust continuum dominates the spectrum of MSX SMC 029. The
spectrum also shows both emission from polycyclic aromatic hydrocarbons (PAHs)
and absorption at 13.7 micron from C2H2, a juxtaposition seen in only two other
sources, AFGL 2688 and IRAS 13416-6243, both post-asymptotic giant branch (AGB)
objects. As in these sources, the PAH spectrum has the unusual trait that the
peak emission in the 7-9 micron complex lies beyond 8.0 micron. In addition,
the 8.6 micron feature has an intensity as strong as the C-C modes which
normally peak between 7.7 and 7.9 micron. The relative flux of the feature at
11.3 micron to that at 8 micron suggests that the PAHs in MSX SMC 029 either
have a low ionization fraction or are largely unprocessed. The 13-16 micron
wavelength region shows strong absorption features similar to those observed in
the post-AGB objects AFGL 618 and SMP LMC 11. This broad absorption may arise
from the same molecules which have been identified in those sources: C2H2,
C4H2, HC3N, and C6H6. The similarities between MSX SMC 029, AFGL 2688, and AFGL
618 lead us to conclude that MSX SMC 029 has evolved off the AGB in only the
past few hundred years, making it the third post-AGB object identified in the
SMC.Comment: 4 figures, Fig. 4 color; to appear in the 20 November 2006
Astrophysical Journal Letter
R CrB Candidates in the Small Magellanic Cloud: Observations of Cold, Featureless Dust with the Spitzer Infrared Spectrograph
We observed 36 evolved stars in the Small Magellanic Cloud (SMC) using the
low-resolution mode of the Infrared Spectrograph (IRS) on the Spitzer Space
Telescope. Two of these stars, MSX SMC 014 and 155, have nearly featureless
spectral energy distributions over the IRS wavelength range (5.2-35 um) and
F_nu peaking at ~8-9 um. The data can be fit by sets of amorphous carbon shells
or by single 600-700 K blackbodies. The most similar spectra found in extant
spectral databases are of R CrB, although the spectral structure seen in R CrB
and similar stars is much weaker or absent in the SMC sources. Both SMC stars
show variability in the near-infrared. Ground-based visual spectra confirm that
MSX SMC 155 is carbon-rich, as expected for R CrB (RCB) stars, and coincides
with an object previously identified as an RCB candidate. The temperature of
the underlying star is lower for MSX SMC 155 than for typical RCB stars. The
strength of the C_2 Swan bands and the low temperature suggest that it may be a
rare DY Per-type star, only the fifth such identified. MSX SMC 014 represents a
new RCB candidate in the SMC, bringing the number of RCB candidates in the SMC
to six. It is the first RCB candidate discovered with Spitzer and the first
identified by its infrared spectral characteristics rather than its visual
variability.Comment: Accepted by ApJ Letters 25 August, 2005, 4 pages (emulateapj), 5
figure
Controlling a magnetic Feshbach resonance with laser light
The capability to tune the strength of the elastic interparticle interaction
is crucial for many experiments with ultracold gases. Magnetic Feshbach
resonances are a tool widely used for this purpose, but future experiments
would benefit from additional flexibility such as spatial modulation of the
interaction strength on short length scales. Optical Feshbach resonances offer
this possibility in principle, but suffer from fast particle loss due to
light-induced inelastic collisions. Here we show that light near-resonant with
a molecular bound-to-bound transition can be used to shift the magnetic field
at which a magnetic Feshbach resonance occurs. This makes it possible to tune
the interaction strength with laser light and at the same time induce
considerably less loss than an optical Feshbach resonance would do
From SOMAmer-Based Biomarker Discovery to Diagnostic and Clinical Applications: A SOMAmer-Based, Streamlined Multiplex Proteomic Assay
Recently, we reported a SOMAmer-based, highly multiplexed assay for the purpose of biomarker identification. To enable seamless transition from highly multiplexed biomarker discovery assays to a format suitable and convenient for diagnostic and life-science applications, we developed a streamlined, plate-based version of the assay. The plate-based version of the assay is robust, sensitive (sub-picomolar), rapid, can be highly multiplexed (upwards of 60 analytes), and fully automated. We demonstrate that quantification by microarray-based hybridization, Luminex bead-based methods, and qPCR are each compatible with our platform, further expanding the breadth of proteomic applications for a wide user community
Magnitude and Mechanism of Siderophore-Mediated Competition at Low Iron Solubility in the Pseudomonas aeruginosa Pyochelin System
A central question in microbial ecology is whether microbial interactions are predominantly cooperative or competitive. The secretion of siderophores, microbial iron chelators, is a model system for cooperative interactions. However, siderophores have also been shown to mediate competition by sequestering available iron and making it unavailable to competitors. The details of how siderophores mediate competition are not well understood, especially considering the complex distribution of iron phases in the environment. One pertinent question is whether sequestering iron through siderophores can indeed be effective in natural conditions; many natural environments are characterized by large pools of precipitated iron, and it is conceivable that any soluble iron that is sequestered by siderophores is replenished by the dissolution of these precipitated iron sources. Our goal here was to address this issue, and investigate the magnitude and mechanism of siderophore-mediated competition in the presence of precipitated iron. We combined experimental work with thermodynamic modeling, using Pseudomonas aeruginosa as a model system and ferrihydrite precipitates as the iron source with low solubility. Our experiments show that competitive growth inhibition by the siderophore pyochelin is indeed efficient, and that inhibition of a competitor can even have a stronger growth-promoting effect than solubilization of precipitated iron. Based on the results of our thermodynamic models we conclude that the observed inhibition of a competitor is effective because sequestered iron is only very slowly replenished by the dissolution of precipitated iron. Our research highlights the importance of competitive benefits mediated by siderophores, and underlines that the dynamics of siderophore production and uptake in environmental communities could be a signature of competitive, not just cooperative, dynamics
Adsorption of hydroxamate siderophores and EDTA on goethite in the presence of the surfactant sodium dodecyl sulfate
Siderophore-promoted iron acquisition by microorganisms usually occurs in the presence of other organic molecules, including biosurfactants. We have investigated the influence of the anionic surfactant sodium dodecyl sulfate (SDS) on the adsorption of the siderophores DFOB (cationic) and DFOD (neutral) and the ligand EDTA (anionic) onto goethite (α-FeOOH) at pH 6. We also studied the adsorption of the corresponding 1:1 Fe(III)-ligand complexes, which are products of the dissolution process. Adsorption of the two free siderophores increased in a similar fashion with increasing SDS concentration, despite their difference in molecule charge. In contrast, SDS had little effect on the adsorption of EDTA. Adsorption of the Fe-DFOB and Fe-DFOD complexes also increased with increasing SDS concentrations, while adsorption of Fe-EDTA decreased. Our results suggest that hydrophobic interactions between adsorbed surfactants and siderophores are more important than electrostatic interactions. However, for strongly hydrophilic molecules, such as EDTA and its iron complex, the influence of SDS on their adsorption seems to depend on their tendency to form inner-sphere or outer-sphere surface complexes. Our results demonstrate that surfactants have a strong influence on the adsorption of siderophores to Fe oxides, which has important implications for siderophore-promoted dissolution of iron oxides and biological iron acquisition
K0s K0s Final State in Two-Photon Collisions and Implications for Glueballs
The K0s K0s final state in two-photon collisions is studied with the L3
detector at LEP. The mass spectrum is dominated by the formation of the
f_2'(1525) tensor meson in the helicity-two state with a two-photon width times
the branching ratio into K Kbar of 76 +- 6 +- 11 eV. A clear signal for the
formation of the f_J(1710) is observed and it is found to be dominated by the
spin-two helicity-two state. No resonance is observed in the mass region around
2.2 GeV and an upper limit of 1.4 eV at 95% C.L. is derived for the two-photon
width times the branching ratio into K0s K0s for the glueball candidate
xi(2230)
Classification of 2.4-45.2 Micron Spectra from the ISO Short Wavelength Spectrometer
The Infrared Space Observatory observed over 900 objects with the Short
Wavelength Spectrometer in full-grating-scan mode (2.4-45.2 micron). We have
developed a comprehensive system of spectral classification using these data.
Sources are assigned to groups based on the overall shape of the spectral
energy distribution (SED). The groups include naked stars, dusty stars, warm
dust shells, cool dust shells, very red sources, and sources with emission
lines but no detected continuum. These groups are further divided into
subgroups based on spectral features that shape the SED such as silicate or
carbon-rich dust emission, silicate absorption, ice absorption, and
fine-structure or recombination lines. Caveats regarding the data and data
reduction, and biases intrinsic to the database, are discussed. We also examine
how the subgroups relate to the evolution of sources to and from the main
sequence and how this classification scheme relates to previous systems.Comment: 91 pages (40 for Table 6), 6 figures, accepted by ApJS. Figures 1-5
have degraded resolution due to astro-ph size limits. For full-resolution
figures see: http://isc.astro.cornell.edu/~sloan/library/swsclass.html and
for the classification table (Table 6) in ASCII format, see:
http://isc.astro.cornell.edu/~sloan/library/cat.htm
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