174 research outputs found
The outflow in Mrk 509: A method to calibrate XMM-Newton EPIC-pn and RGS
We have analyzed three XMM-Newton observations of the Seyfert 1 galaxy Mrk
509, with the goal to detect small variations in the ionized outflow
properties. Such measurements are limited by the quality of the
cross-calibration between RGS, the best instrument to characterize the
spectrum, and EPIC-pn, the best instrument to characterize the variability. For
all three observations we are able to improve the relative calibration of RGS
and pn consistently to 4 %. In all observations we detect three different
outflow components and, thanks to our accurate cross-calibration we are able to
detect small differences in the ionization parameter and column density in the
highest ionized component of the outflow. This constrains the location of this
component of the outflow to within 0.5 pc of the central source. Our method for
modeling the relative effective area is not restricted to just this source and
can in principle be extended to other types of sources as well.Comment: 11 pages, 9 figure
Internal Motility in Stiffening Actin-Myosin Networks
We present a study on filamentous actin solutions containing heavy meromyosin
subfragments of myosin II motor molecules. We focus on the viscoelastic phase
behavior and internal dynamics of such networks during ATP depletion. Upon
simultaneously using micro-rheology and fluorescence microscopy as
complementary experimental tools, we find a sol-gel transition accompanied by a
sudden onset of directed filament motion. We interpret the sol-gel transition
in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain
the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure
The warm absorber in NGC 5548: The lean years
We study the variability of the warm absorber and the gas responsible for the
emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the
location and physical properties of these components. Using X-ray spectra taken
with the \textit{Chandra}LETGS in 2002 and 2005, we study variability in the
ionic column densities and line intensities. We find a lower \ion{O}{vii}
forbidden emission line flux in 2005, while the Fe K line flux stays
constant. The warm absorber is less ionized in 2005, allowing us to constrain
its location to within 7 pc of the central source. Using both the observed
variability and the limit on the FWHM of the \ion{O}{vii} f line, we have
constrained the location of the narrow line region to a distance of 1 pc from
the central source. The apparent lack of variability of the Fe K line
flux does not allow for a unique explanation.Comment: 6 pages, 6 figures, accepted by A&
A phenomenological model for the X-ray spectrum of Nova V2491 Cygni
The X-ray flux of Nova V2491 Cyg reached a maximum some forty days after
optical maximum. The X-ray spectrum at that time, obtained with the RGS of
XMM-Newton, shows deep, blue-shifted absorption by ions of a wide range of
ionization. We show that the deep absorption lines of the X-ray spectrum at
maximum, and nine days later, are well described by the following
phenomenological model with emission from a central blackbody and from a
collisionally ionized plasma (CIE). The blackbody spectrum (BB) is absorbed by
three main highly-ionized expanding shells; the CIE and BB are absorbed by cold
circumstellar and interstellar matter that includes dust. The outflow density
does not decrease monotonically with distance. The abundances of the shells
indicate that they were ejected from an O-Ne white dwarf. We show that the
variations on time scales of hours in the X-ray spectrum are caused by a
combination of variation in the central source and in the column density of the
ionized shells. Our phenomenological model gives the best description so far of
the supersoft X-ray spectrum of nova V2491 Cyg, but underpredicts, by a large
factor, the optical and ultraviolet flux. The X-ray part of the spectrum must
originate from a very different layer in the expanding envelope, presumably
much closer to the white dwarf than the layers responsible for the
optical/ultraviolet spectrum. This is confirmed by absence of any correlation
between the X-ray and UV/optical observed fluxes.Comment: 11 pages, 6 figure
Isolation of a novel aquaglyceroporin from a marine teleost (Sparus auratus) Function and tissue distribution
The aquaporins (formerly called the major intrinsic
protein family) are transmembrane channel proteins. The
family includes the CHIP group, which are functionally
characterised as water channels and the GLP group,
which are specialised for glycerol transport. The present
study reports the identification and characterisation of a
novel GLP family member in a teleost fish, the sea bream
Sparus auratus. A sea bream aquaporin (sbAQP) cDNA of
1047·bp and encoding a protein of 298·amino acids was
isolated from a kidney cDNA library. Functional
characterization of the sbAQP using a Xenopus oocyte
assay revealed that the isolated cDNA stimulated osmotic
water permeability in a mercury-sensitive manner and
also stimulated urea and glycerol uptake. Northern
blotting demonstrated that sbAQP was expressed at high
levels in the posterior region of the gut, where two transcripts were identified (1.6·kb and 2·kb), and in
kidney, where a single transcript was present (2·kb). In
situ hybridisation studies with a sbAQP riboprobe
revealed its presence in the lamina propria and smooth
muscle layer of the posterior region of the gut and in
epithelial cells of some kidney tubules. sbAQP was also
present in putative chloride cells of the gill. Phylogenetic
analysis of sbAQP, including putative GLP genes from
Fugu rubripes, revealed that it did not group with any of
the previously isolated vertebrate GLPs and instead
formed a separate group, suggesting that it may be a novel
GLP member.This work was supported by project PRAXIS
XXI/2/2.1/BIA/211/94 from the Portuguese National Science
and Technology Foundation (FCT), co-financed by EU
structural funds, DG-Fisheries Project Q5RS-2002-00784
(CRYOCYTE) and an EU Biotech grant (QLRT2000-00778).
C.R.A.S., J.C.R.C. and J.F. were in receipt of FCT
fellowships PRAXIS XXI/BPD/22040/99, PRAXIS
XXI/BD/19925/99BPD/22033/99, respectively
Inverse modeling of GOSAT-retrieved ratios of total column CH4 and CO2 for 2009 and 2010
This study investigates the constraint provided by greenhouse gas measurements from space on surface fluxes. Imperfect knowledge of the light path through the atmosphere, arising from scattering by clouds and aerosols, can create biases in column measurements retrieved from space. To minimize the impact of such biases, ratios of total column retrieved CH4 and CO2 (Xratio) have been used. We apply the ratio inversion method described in Pandey et al. (2015) to retrievals from the Greenhouse Gases Observing SATellite (GOSAT). The ratio inversion method uses the measured Xratio as a weak constraint on CO2 fluxes. In contrast, the more common approach of inverting proxy CH4 retrievals (Frankenberg et al., 2005) prescribes atmospheric CO2 fields and optimizes only CH4 fluxes. The TM5–4DVAR (Tracer Transport Model version 5–variational data assimilation system) inverse modeling system is used to simultaneously optimize the fluxes of CH4 and CO2 for 2009 and 2010. The results are compared to proxy inversions using model-derived CO2 mixing ratios (XCO2model) from CarbonTracker and the Monitoring Atmospheric Composition and Climate (MACC) Reanalysis CO2 product. The performance of the inverse models is evaluated using measurements from three aircraft measurement projects. Xratio and XCO2model are compared with TCCON retrievals to quantify the relative importance of errors in these components of the proxy XCH4 retrieval (XCH4proxy). We find that the retrieval errors in Xratio (mean = 0.61 %) are generally larger than the errors in XCO2model (mean = 0.24 and 0.01 % for CarbonTracker and MACC, respectively). On the annual timescale, the CH4 fluxes from the different satellite inversions are generally in agreement with each other, suggesting that errors in XCO2model do not limit the overall accuracy of the CH4 flux estimates. On the seasonal timescale, however, larger differences are found due to uncertainties in XCO2model, particularly over Australia and in the tropics. The ratio method stays closer to the a priori CH4 flux in these regions, because it is capable of simultaneously adjusting the CO2 fluxes. Over tropical South America, comparison to independent measurements shows that CO2 fields derived from the ratio method are less realistic than those used in the proxy method. However, the CH4 fluxes are more realistic, because the impact of unaccounted systematic uncertainties is more evenly distributed between CO2 and CH4. The ratio inversion estimates an enhanced CO2 release from tropical South America during the dry season of 2010, which is in accordance with the findings of Gatti et al. (2014) and Van der Laan et al. (2015). The performance of the ratio method is encouraging, because despite the added nonlinearity due to the assimilation of Xratio and the significant increase in the degree of freedom by optimizing CO2 fluxes, still consistent results are obtained with respect to other CH4 inversions
Biomass burning fuel consumption rates: a field measurement database
Landscape fires show large variability in the amount of biomass or fuel consumed per unit area burned. Fuel consumption (FC) depends on the biomass available to burn and the fraction of the biomass that is actually combusted, and can be combined with estimates of area burned to assess emissions. While burned area can be detected from space and estimates are becoming more reliable due to improved algorithms and sensors, FC is usually modeled or taken selectively from the literature. We compiled the peerreviewed literature on FC for various biomes and fuel categories to understand FC and its variability better, and to provide a database that can be used to constrain biogeochemical models with fire modules. We compiled in total 77 studies covering 11 biomes including savanna (15 studies, average FC of 4.6 t DM (dry matter) ha 1 with a standard deviation of 2.2),tropical forest (n = 19, FC = 126 +/- 77),temperate forest (n = 12, FC = 58 +/- 72),boreal forest (n = 16, FC = 35 +/- 24),pasture (n = 4, FC = 28 +/- 9.3),shifting cultivation (n = 2, FC = 23, with a range of 4.0-43),crop residue (n = 4, FC = 6.5 +/- 9.0),chaparral (n = 3, FC = 27 +/- 19),tropical peatland (n = 4, FC = 314 +/- 196),boreal peatland (n = 2, FC = 42 [42-43]),and tundra (n = 1, FC = 40). Within biomes the regional variability in the number of measurements was sometimes large, with e. g. only three measurement locations in boreal Russia and 35 sites in North America. Substantial regional differences in FC were found within the defined biomes: for example, FC of temperate pine forests in the USA was 37% lower than Australian forests dominated by eucalypt trees. Besides showing the differences between biomes, FC estimates were also grouped into different fuel classes. Our results highlight the large variability in FC, not only between biomes but also within biomes and fuel classes. This implies that substantial uncertainties are associated with using biome-averaged values to represent FC for whole biomes. Comparing the compiled FC values with co-located Global Fire Emissions Database version 3 (GFED3) FC indicates that modeling studies that aim to represent variability in FC also within biomes, still require improvements as they have difficulty in representing the dynamics governing FC
Distribution and biological role of the oligopeptide-binding protein (OppA) in Xanthomonas species
In this study we investigated the prevalence of the oppA gene, encoding the oligopeptide binding protein (OppA) of the major bacterial oligopeptide uptake system (Opp), in different species of the genus Xanthomonas. The oppA gene was detected in two Xanthomonas axonopodis strains among eight tested Xanthomonas species. The generation of an isogenic oppA-knockout derivative of the Xac 306 strain, showed that the OppA protein neither plays a relevant role in oligopeptide uptake nor contributes to the infectivity and multiplication of the bacterial strain in leaves of sweet orange (Citrus sinensis) and Rangpur lime (Citrus limonia). Taken together these results suggest that the oppA gene has a recent evolutionary history in the genus and does not contribute in the physiology or pathogenesis of X. axonopodis
Hyponatremia revisited: Translating physiology to practice
The complexity of hyponatremia as a clinical problem is likely caused by the opposite scenarios that accompany this electrolyte disorder regarding pathophysiology (depletional versus dilutional hyponatremia, high versus low vasopressin levels) and therapy (rapid correction to treat cerebral edema versus slow correction to prevent osmotic demyelination, fluid restriction versus fluid resuscitation). For a balanced differentiation between these opposites, an understanding of the pathophysiology of hyponatremia is required. Therefore, in this review an attempt is made to translate the physiology of water balance regulation to strategies that improve the clinical management of hyponatremia. A physiology-based approach to the patient with hyponatremia is presented, first addressing the possibility of acute hyponatremia, and then asking if and if so why vasopressin is secreted non-osmotically. Additional diagnostic recommendations are not to rely too heavily of the assessment of the extracellular fluid volume, to regard the syndrome of inappropriate antidiuresis as a diagnosis of exclusion, and to rationally investigate the pathophysiology of hyponatremia rather than to rely on isolated laboratory values with arbitrary cutoff values. The features of the major hyponatremic disorders are discussed, including diuretic-induced hyponatremia, adrenal and pituitary insufficiency, the syndrome of inappropriate antidiuresis, cerebral salt wasting, and exercise-associated hyponatremia. The treatment of hyponatremia is reviewed from simple saline solutions to the recently introduced vasopressin receptor antagonists, including their promises and limitations. Given the persistently high rates of hospital-acquired hyponatremia, the importance of improving the management of hyponatremia seems both necessary and achievable. Copyrigh
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