127 research outputs found
Estimating carbon dioxide fluxes from temperate mountain grasslands using broad-band vegetation indices
The broad-band normalised difference vegetation index (NDVI) and the simple ratio (SR) were calculated from measurements of reflectance of photosynthetically active and short-wave radiation at two temperate mountain grasslands in Austria and related to the net ecosystem CO<sub>2</sub> exchange (NEE) measured concurrently by means of the eddy covariance method. There was no significant statistical difference between the relationships of midday mean NEE with narrow- and broad-band NDVI and SR, measured during and calculated for that same time window, respectively. The skill of broad-band NDVI and SR in predicting CO<sub>2</sub> fluxes was higher for metrics dominated by gross photosynthesis and lowest for ecosystem respiration, with NEE in between. A method based on a simple light response model whose parameters were parameterised based on broad-band NDVI allowed to improve predictions of daily NEE and is suggested to hold promise for filling gaps in the NEE time series. Relationships of CO<sub>2</sub> flux metrics with broad-band NDVI and SR however generally differed between the two studied grassland sites indicting an influence of additional factors not yet accounted for
Gap-filling strategies for annual VOC flux data sets
Up to now the limited
knowledge about the exchange of volatile organic compounds (VOCs) between the
biosphere and the atmosphere is one of the factors which hinders more
accurate climate predictions. Complete long-term flux data sets of several
VOCs to quantify the annual exchange and validate recent VOC models are
basically not available. In combination with long-term VOC flux measurements
the application of gap-filling routines is inevitable in order to replace
missing data and make an important step towards a better understanding of the
VOC ecosystem–atmosphere exchange on longer timescales.
<br><br>
We performed VOC flux measurements above a mountain meadow in Austria during
two complete growing seasons (from snowmelt in spring to snow reestablishment
in late autumn) and used this data set to test the performance of four
different gap-filling routines, mean diurnal variation (MDV), mean gliding
window (MGW), look-up tables (LUT) and linear interpolation (LIP), in terms
of their ability to replace missing flux data in order to obtain reliable VOC
sums. According to our findings the MDV routine was outstanding with regard
to the minimization of the gap-filling error for both years and all
quantified VOCs. The other gap-filling routines, which performed gap-filling
on 24 h average values, introduced considerably larger uncertainties. The
error which was introduced by the application of the different filling
routines increased linearly with the number of data gaps. Although average
VOC fluxes measured during the winter period (complete snow coverage) were
close to zero, these were highly variable and the filling of the winter
period resulted in considerably higher uncertainties compared to the
application of gap-filling during the measurement period.
<br><br>
The annual patterns of the overall cumulative fluxes for the quantified VOCs
showed a completely different behaviour in 2009, which was an exceptional
year due to the occurrence of a severe hailstorm, compared to 2011. Methanol
was the compound which, at 381.5 mg C m<sup>−2</sup> and 449.9 mg
C m<sup>−2</sup>, contributed most to the cumulative VOC carbon emissions in
2009 and 2011, respectively. In contrast to methanol emissions, however,
considerable amounts of monoterpenes (−327.3 mg C m<sup>−2</sup>) were
deposited onto the mountain meadow during 2009 caused by a hailstorm. Other
quantified VOCs had considerably lower influences on the annual patterns
<i>Candida tropicalis</i> is the most prevalent yeast species causing candidemia in Algeria:The urgent need for antifungal stewardship and infection control measures
Bohmian trajectories and Klein's paradox
We compute the Bohmian trajectories of the incoming scattering plane waves
for Klein's potential step in explicit form. For finite norm incoming
scattering solutions we derive their asymptotic space-time localization and we
compute some Bohmian trajectories numerically. The paradox, which appears in
the traditional treatments of the problem based on the outgoing scattering
asymptotics, is absent.Comment: 14 pages, 3 figures; minor format change
An ecosystem-scale perspective of the net land methanol flux: Synthesis of micrometeorological flux measurements
Integrated management of a Swiss cropland is not sufficient to preserve its soil carbon pool in the long term
Croplands are involved in the exchange of carbon dioxide (CO2)
between the atmosphere and the biosphere. Furthermore, soil carbon (C) stocks
play an important role in soil fertility. It is thus of great interest to
know whether intensively managed croplands act as a net source or sink of
atmospheric CO2 and if soil C stocks are preserved over long
timescales. The FluxNet site CH-Oe2 in Oensingen, Switzerland, has been
operational since the end of 2003. This cropland is managed under the Swiss
framework of the Proof of Ecological Performance (PEP, a variant of
integrated management) with a crop rotation centred on winter wheat, which
also includes winter barley, winter rapeseed, peas, potato and intermediate
cover crops. In addition to eddy covariance measurements, meteorological and
soil measurements were available along with information on C imports and
exports from organic fertilisation, sowing and harvesting. This study
investigates cropland C budgets over 13Â years and assesses whether the PEP
regulations resulted in a balanced C budget. The strongest CO2 uptake was
observed during cereal seasons. C export through harvest, however, offset the
strong uptake of the cereal crops. The largest net CO2 emissions to
the atmosphere were observed during pea and cover crop seasons. Net biome
production, representing the overall C budget (assuming carbon leaching to
groundwater to be negligible), typically ranged between close to C neutral to
C losses of up to 407 g C m−2 per season, with peas being the largest
source. Overall, the field lost 1674 g C m−2 over 13 years
(129 g C m−2 yr−1), which was confirmed by soil C stock
measurements at the beginning and the end of the study period. Although
managing the field under the regulations of PEP did not result in an overall
C sink, model simulations showed that the use of cover crops reduced the C
losses compared to leaving the field bare. The use of solid manure improved
the C budget by importing substantial amounts of C into the soil, while liquid
manure had only a small effect. We thus conclude that additional efforts are
needed to bring Swiss management practices closer to the goal of preserving
soil C in the long term.</p
Preclinical evaluation of two 68Ga-siderophores as potential radiopharmaceuticals for Aspergillus fumigatus infection imaging
PURPOSE: Invasive pulmonary aspergillosis is mainly caused by Aspergillus fumigatus, and is one of the major causes of morbidity and mortality in immunocompromised patients. The mortality associated with invasive pulmonary aspergillosis remains high, mainly due to the difficulties and limitations in diagnosis. We have shown that siderophores can be labelled with (68)Ga and can be used for PET imaging of A. fumigatus infection in rats. Here we report on the further evaluation of the most promising (68)Ga-siderophore candidates, triacetylfusarinine (TAFC) and ferrioxamine E (FOXE). METHODS: Siderophores were labelled with (68)Ga using acetate buffer. Log P, protein binding and stability values were determined. Uptake by A. fumigatus was studied in vitro in cultures with high and low iron loads. In vivo biodistribution was determined in normal mice and an infection model was established using neutropenic rats inoculated with A. fumigatus. Static and dynamic muPET imaging was performed and correlated with CT images, and lung infection was evaluated ex vivo. RESULTS: (68)Ga-siderophores were labelled with high radiochemical purity and specific activity. (68)Ga-TAFC and (68)Ga-FOXE showed high uptake by A. fumigatus in iron-deficient cultures. In normal mice, (68)Ga-TAFC and (68)Ga-FOXE showed rapid renal excretion with high metabolic stability. In the rat infection model focal lung uptake was detected by muPET with both compounds and increased with severity of the infection, correlating with abnormal CT images. CONCLUSION: (68)Ga-TAFC and (68)Ga-FOXE displayed excellent in vitro stability and high uptake by A. fumigatus. Both compounds showed excellent pharmacokinetics, highly selective accumulation in infected lung tissue and good correlation with severity of disease in a rat infection model, which makes them promising agents for A. fumigatus infection imaging
- …