883 research outputs found
Ammonia exposure promotes algal biomass in an ombrotrophic peatland
Nitrogen pollution affects many peatlands with consequences for their biodiversity and ecosystem function. Microorganisms control nutrient cycling and constitute most of the biodiversity of peatlands but their response to nitrogen is poorly characterised and likely to depend on the form of deposition. Using a unique field experiment we show that ammonia exposure at realistic point source levels is associated with a general shift from heterotrophic (bacteria and fungi) to autotrophic (algal) dominance and an increase in total biomass. The biomass of larger testate amoebae increased, suggesting increased food supply for microbial predators. Results show the widespread impacts of N pollution and suggest the potential for microbial community-based bioindicators in these ecosystems
Hydrological dynamics and fire history of the last 1300years in western Siberia reconstructed from a high-resolution, ombrotrophic peat archive
International audienceSiberian peatlands provide records of past changes in the continental climate of Eurasia. We analyzed a core from Mukhrino mire in western Siberia to reconstruct environmental change in this region over the last 1300 years. The pollen analysis revealed little variation of local pine-birch forests. A testate amoebae transfer function was used to generate a quantitative water-table reconstruction; pollen, plant macrofossils, and charcoal were analyzed to reconstruct changes in vegetation and fire activity. The study revealed that Mukhrino mire was wet until the Little Ice Age (LIA), when drought was recorded. Dry conditions during the LIA are consistent with other studies from central and eastern Europe, and with the pattern of carbon accumulation across the Northern Hemisphere. A significant increase in fire activity between ca. AD 1975 and 1990 may be associated with the development of the nearby city of Khanty-Mansiysk, as well as with the prevailing positive Arctic Oscillation
Impacts of tropospheric ozone exposure on peatland microbial consumers
Tropospheric ozone pollution is recognised as an important threat to terrestrial ecosystems but impacts on peatlands are little understood despite the importance of peat as a global carbon store. Here we investigate the impacts of three levels of elevated exposure to tropospheric ozone on peatland microbial communities with a particular focus on testate amoebae, the dominant microbial consumers. We found that in the intermediate (ambient + 25 ppb O3) and high treatments (ambient +35 ppb summer, +10 ppb year round) there were significant changes in testate amoeba communities, typified by an increase in abundance of Phyrganella spp. and loss of diversity. Phyrganella is often suggested to feed on fungi so the community change identified in our experiment might suggest that the testate amoeba response is at least partially mediated by interactions with other microbial groups. We do not find evidence for changes in numbers of undifferentiated microalgae, nematodes or rotifers but do find weak evidence for an increase in flagellates and ciliates. Our results provide the first direct data to show the impact of ozone on microbial consumers in peatlands
The 21 cm Signature of Cosmic String Wakes
We discuss the signature of a cosmic string wake in 21cm redshift surveys.
Since 21cm surveys probe higher redshifts than optical large-scale structure
surveys, the signatures of cosmic strings are more manifest in 21cm maps than
they are in optical galaxy surveys. We find that, provided the tension of the
cosmic string exceeds a critical value (which depends on both the redshift when
the string wake is created and the redshift of observation), a cosmic string
wake will generate an emission signal with a brightness temperature which
approaches a limiting value which at a redshift of is close to 400
mK in the limit of large string tension. The signal will have a specific
signature in position space: the excess 21cm radiation will be confined to a
wedge-shaped region whose tip corresponds to the position of the string, whose
planar dimensions are set by the planar dimensions of the string wake, and
whose thickness (in redshift direction) depends on the string tension. For
wakes created at , then at a redshift of the
critical value of the string tension is , and
it decreases linearly with redshift (for wakes created at the time of equal
matter and radiation, the critical value is a factor of two lower at the same
redshift). For smaller tensions, cosmic strings lead to an observable
absorption signal with the same wedge geometry.Comment: 11 pages, 4 figures; a couple of comments added in the discussion
sectio
Microstructural evolution and transmutation in tungsten under ion and neutron irradiation
This study aims to compare the effects of neutron and self-ion irradiation on the mechanical properties and microstructural evolution in W. Neutron irradiation at the HFR reactor to 1.67 dpa at 800 °C resulted in the formation of large Re and Os rich clusters and voids. The post-irradiation composition was measured using APT and verfified against FISPACT modelling. The measured Re and Os concentration was used to create alloys with equivalent concentrations of Re and Os. These alloys were exposed to self-ion irradiation to a peak dose of 1.7 dpa at 800 °C. APT showed that self-ion irradiation leads to the formation of small Os clusters, wheras under neutron irradiation large Re/Os clusters form. Voids are formed by both ion and neutron irradiation, but the voids formed by neutron irradiation are larger. By comparing the behaviour of W-1.4Re and W-1.4Re-0.1Os, suppression of Re cluster formation was observed. Irradiation hardening was measured using nanoindentation and was found to be 2.7 GPa, after neutron irradiation and 1.6 GPa and 0.6 GPa for the self-ion irradiated W-1.4Re and W-1.4Re-0.1Os. The higher hardening is attributed to the barrier strength of large voids and Re/Os clusters that are observed after neutron irradiation
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
Novel insights on diagnosis, cause and treatment of diabetic neuropathy: Focus on painful diabetic neuropathy
Diabetic neuropathy is common, under or misdiagnosed, and causes substantial morbidity with increased mortality. Defining and developing sensitive diagnostic tests for diabetic neuropathy is not only key to implementing earlier interventions but also to ensure that the most appropriate endpoints are employed in clinical intervention trials. This is critical as many potentially effective therapies may never progress to the clinic, not due to a lack of therapeutic effect, but because the endpoints were not sufficiently sensitive or robust to identify benefit. Apart from improving glycaemic control, there is no licensed treatment for diabetic neuropathy, however, a number of pathogenetic pathways remain under active study. Painful diabetic neuropathy is a cause of considerable morbidity and whilst many pharmacological and nonpharmacological interventions are currently used, only two are approved by the US Food and Drug Administration. We address the important issue of the âplacebo effectâ and also consider potential new pharmacological therapies as well as nonpharmacological interventions in the treatment of painful diabetic neuropathy
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