344 research outputs found
Surfactant control of gas transfer velocity along an offshore coastal transect: results from a laboratory gas exchange tank
Understanding the physical and biogeochemical controls of air–sea gas
exchange is necessary for establishing biogeochemical models for predicting
regional- and global-scale trace gas fluxes and feedbacks. To this end we
report the results of experiments designed to constrain the effect of
surfactants in the sea surface microlayer (SML) on the gas transfer velocity
(<i>k</i><sub>w</sub>; cm h<sup>−1</sup>), seasonally (2012–2013) along a 20 km
coastal transect (North East UK). We measured total surfactant activity (SA),
chromophoric dissolved organic matter (CDOM) and chlorophyll <i>a</i> (Chl <i>a</i>) in
the SML and in sub-surface water (SSW) and we evaluated corresponding
<i>k</i><sub>w</sub> values using a custom-designed air–sea gas exchange tank.
Temporal SA variability exceeded its spatial variability. Overall, SA varied
5-fold between all samples (0.08 to 0.38 mg L<sup>−1</sup> T-X-100), being
highest in the SML during summer. SML SA enrichment factors (EFs) relative to
SSW were ∼ 1.0 to 1.9, except for two values (0.75; 0.89: February
2013). The range in corresponding <i>k</i><sub>660</sub> (<i>k</i><sub>w</sub> for CO<sub>2</sub> in
seawater at 20 °C) was 6.8 to 22.0 cm h<sup>−1</sup>. The film factor
<i>R</i><sub>660</sub> (the ratio of <i>k</i><sub>660</sub> for seawater to <i>k</i><sub>660</sub> for “clean”,
i.e. surfactant-free, laboratory water) was strongly correlated with SML SA
(<i>r</i> ≥ 0.70, <i>p</i> ≤ 0.002, each <i>n</i> = 16). High SML SA typically
corresponded to <i>k</i><sub>660</sub> suppressions ∼ 14 to 51 % relative to
clean laboratory water, highlighting strong spatiotemporal gradients in gas
exchange due to varying surfactant in these coastal waters. Such variability
should be taken account of when evaluating marine trace gas sources and
sinks. Total CDOM absorbance (250 to 450 nm), the CDOM spectral slope ratio
(<i>S</i><sub>R</sub> = <i>S</i><sub>275 − 295</sub>∕<i>S</i><sub>350 − 400</sub>), the 250 : 365 nm CDOM
absorption ratio (<i>E</i><sub>2</sub> : <i>E</i><sub>3</sub>), and Chl <i>a</i> all indicated spatial
and temporal signals in the quantity and composition of organic matter in the
SML and SSW. This prompts us to hypothesise that spatiotemporal variation in
<i>R</i><sub>660</sub> and its relationship with SA is a consequence of compositional
differences in the surfactant fraction of the SML DOM pool that warrants
further investigation
Jet quenching pattern at LHC in PYQUEN model
The first LHC data on high transverse momentum hadron and dijet spectra in
PbPb collisions at center-of-mass energy 2.76 TeV per nucleon pair are analyzed
in the frameworks of PYQUEN jet quenching model. The presented studies for the
nuclear modification factor of high-pT hadrons and the imbalance in dijet
transverse energy support the supposition that the intensive wide-angular
("out-of-cone") medium-induced partonic energy loss is seen in central PbPb
collisions at the LHC.Comment: 5 pages including 4 figures as EPS-files; prepared using LaTeX
package for publication in the European Physical Journal
Discrimination of Juvenile Red Snapper Otolith Chemical Signatures from Gulf of Mexico Nursery Regions
Age-0 red snapper Lutjanus campechanus from the 2005-2007 year-classes were sampled in six regions across the Gulf of Mexico (Gulf) to develop nursery signatures from otolith element : Ca ratios (Ba:Ca, Mg:Ca, Mn:Ca, Sr:Ca, and Li:Ca) and stable isotope delta values (delta C-13 and delta O-18). Element : Ca ratios were analyzed with sector field inductively coupled plasma mass spectrometry on dissolved right sagittae; isotope ratio mass spectrometry was employed to analyze pulverized left otoliths for delta C-13 and delta O-18. Otolith chemical signatures were significantly different among regions in each year. Year-class-specific quadratic discriminant function analysis (QDFA) distinguished nursery regions with an accuracy of 82% for 2005, 70% for 2006, and 72% for 2007. However, samples were not obtained from all six study regions in 2005 and 2006. A QDFA of all year-classes combined produced an overall classification accuracy of 70%, thus indicating that region-specific otolith chemical signatures from adjacent sampling years could be used as surrogates for regions where samples were not obtained in a given year
Application of Otolith Chemical Signatures to Estimate Population Connectivity of Red Snapper In the Western Gulf of Mexico
Otolith chemical signatures of Red Snapper Lutjanus campechanus from six nursery regions were used to estimate the sources of recruits to four sampling regions in the western Gulf of Mexico (Gulf) and to estimate whether postsettlement mixing of Red Snapper occurs between the U.S. and Mexican portions of the western Gulf. In a previous study, region-specific otolith signatures (element : Ca ratios: Ba:Ca, Mg:Ca, Mn:Ca, Sr:Ca, and Li:Ca; stable isotope delta values: δ13C and δ18O) were developed based on age-0 Red Snapper (2005–2007 year-classes) sampled from the six nursery areas. In the present study, subadult and adult Red Snapper (ages 1–3) belonging to those same year-classes were collected from four sampling regions within the western Gulf (two regions in U.S. waters; two regions along the Mexican continental shelf) during summer in 2006–2008. Left sagittal otoliths were used to age subadults and adults to the corresponding nursery year-classes, and right sagittal otoliths were cored for chemical analysis. Off the southwestern U.S. coast, the sampled age-1–3 Red Snapper included locally derived recruits as well as recruits from the northwestern Gulf nursery region. However, analytical results were inconclusive with respect to estimating the connectivity between Red Snapper populations in U.S. and Mexican waters of the western Gulf
Transport Theoretical Description of Collisional Energy Loss in Infinite Quark-Gluon Matter
We study the time evolution of a high-momentum gluon or quark propagating
through an infinite, thermalized, partonic medium utilizing a Boltzmann
equation approach. We calculate the collisional energy loss of the parton,
study its temperature and flavor dependence as well as the the momentum
broadening incurred through multiple interactions. Our transport calculations
agree well with analytic calculations of collisional energy-loss where
available, but offer the unique opportunity to address the medium response as
well in a consistent fashion.Comment: 12 pages, updated with additional references and typos correcte
Monte Carlo Tools for Jet Quenching
A thorough understanding of jet quenching on the basis of multi-particle
final states and jet observables requires new theoretical tools. This talk
summarises the status and propects of the theoretical description of jet
quenching in terms of Monte Carlo generators.Comment: proceedings of the 22nd International Conference on
Ultra-Relativistic Nucleus Nucleus Collisions (Quark Matter 2011
MEM-BRAIN gas separation membranes for zero-emission fossil power plants
The aim of the MEM-BRAIN project is the development and integration of gas separation membranes for zero-emission fossil power plants. This will be achieved by selective membranes with high permeability for CO2, O2 or H2, so that high-purity CO2 is obtained in a readily condensable form. The project is being implemented by the “MEM-BRAIN” Helmholtz Alliance consisting of research centres, universities and industrial partners.\ud
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The MEM-BRAIN project focuses on the development, process engineering, system integration and energy systems analysis of different gas separation membranes for the different CO2 capture process routes in fossil power plants
Characterization of cytochrome P450 CYP109E1 from Bacillus megaterium as a novel vitamin D3 hydroxylase
In this study the ability of CYP109E1 from Bacillus megaterium to metabolize vitamin D3 (VD3) was investigated. In an in vitro system using bovine adrenodoxin reductase (AdR) and adrenodoxin (Adx4-108), VD3 was converted by CYP109E1 into several products. Furthermore, a whole-cell system in B. megaterium MS941 was established. The new system showed a conversion of 95% after 24h. By NMR analysis it was found that CYP109E1 catalyzes hydroxylation of VD3 at carbons C-24 and C-25, resulting in the formation of 24(S)-hydroxyvitamin D3 (24S(OH)VD3), 25-hydroxyvitamin D3 (25(OH)VD3) and 24S,25-dihydroxyvitamin D3 (24S,25(OH)2VD3). Through time dependent whole-cell conversion of VD3, we identified that the formation of 24S,25(OH)2VD3 by CYP109E1 is derived from VD3 via the intermediate 24S(OH)VD3. Moreover, using docking analysis and site-directed mutagenesis, we identified important active site residues capable of determining substrate specificity and regio-selectivity. HPLC analysis of the whole-cell conversion with the I85A-mutant revealed an increased selectivity towards 25-hydroxylation of VD3 compared with the wild type activity, resulting in an approximately 2-fold increase of 25(OH)VD3 production (45mgl(-1)day(-1)) compared to wild type (24.5mgl(-1)day(-1))
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