1,638 research outputs found
Peatlands and the carbon cycle: from local processes to global implications - a synthesis
Peatlands cover only 3% of the Earth's land surface but boreal and subarctic peatlands store about 15-30% of the world's soil carbon ( C) as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling. This paper synthesizes the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands in the context of climate change. The main drivers controlling most are related to some aspects of hydrology. Despite high spatial and annual variability in Net Ecosystem Exchange ( NEE), the differences in cumulative annual NEE are more a function of broad scale geographic location and physical setting than internal factors, suggesting the existence of strong feedbacks. In contrast, trace gas emissions seem mainly controlled by local factors. Key uncertainties remain concerning the existence of perturbation thresholds, the relative strengths of the CO2 and CH4 feedback, the links among peatland surface climate, hydrology, ecosystem structure and function, and trace gas biogeochemistry as well as the similarity of process rates across peatland types and climatic zones. Progress on these research areas can only be realized by stronger co-operation between disciplines that address different spatial and temporal scales
A new lab facility for measuring bidirectional reflectance/emittance distribution functions of soils and canopies
Recently, a laboratory measurement facility has been realized for assessing the anisotropic reflectance and emittance behaviour of soils, leaves and small canopies under controlled illumination conditions. The facility consists of an ASD FieldSpec 3 spectroradiometer covering the spectral range from 350 – 2500 nm at 1 nm spectral sampling interval. The spectroradiometer is deployed using a fiber optic cable with either a 1°, 8° or 25° instantaneous field of view (IFOV). These measurements can be used to assess the plant pigment (chlorophyll, xanthophyll, etc.) and non-pigment system (water, cellulose, lignin, nitrogen, etc.). The thermal emittance is measured using a NEC TH9100 Infrared Thermal Imager. It operates in a single band covering the spectral range from 8 – 14 mm with a resolution of 0.02 K. Images are 320 (H) by 240 (V) pixels with an IFOV of 1.2 mrad. A 1000 W Quartz Tungsten Halogen (QTH) lamp is used as illumination source, approximating the radiance distribution of the sun. This one is put at a fixed position during a measurement session. Multi-angular measurements are achieved by using a robotic positioning system allowing to perform either reflectance or emittance measurements over almost a complete hemisphere. The hemisphere can be sampled continuously between 0° and 80° from nadir and up to a few degrees from the hot-spot configuration (depending on the IFOV of the measurement device) for a backscattering target. Measurement distance to targets can be varied between 0.25 and 1 m, although with a distance of more than 0.6 m it is not possible to cover the full hemisphere. The goal is to infer the BRDF (bidirectional reflectance distribution function) and BTDF (bidirectional thermal distribution function) from these multi-angular measurements for various surface types (like soils, agricultural crops, small tree canopies and artificial objects) and surface roughness. The steering of the robotic arm and the reading of the spectroradiometer and the thermal camera are all fully automated
Gene induction during differentiation of human monocytes into dendritic cells: an integrated study at the RNA and protein levels
Changes in gene expression occurring during differentiation of human
monocytes into dendritic cells were studied at the RNA and protein levels.
These studies showed the induction of several gene classes corresponding to
various biological functions. These functions encompass antigen processing and
presentation, cytoskeleton, cell signalling and signal transduction, but also
an increase in mitochondrial function and in the protein synthesis machinery,
including some, but not all, chaperones. These changes put in perspective the
events occurring during this differentiation process. On a more technical
point, it appears that the studies carried out at the RNA and protein levels
are highly complementary.Comment: website publisher:
http://www.springerlink.com/content/ha0d2c351qhjhjdm
Accelerating global parameter estimation of gravitational waves from Galactic binaries using a genetic algorithm and GPUs
The Laser Interferometer Space Antenna (LISA) is a planned space-based
gravitational wave telescope with the goal of measuring gravitational waves in
the milli-Hertz frequency band, which is dominated by millions of Galactic
binaries. While some of these binaries produce signals that are loud enough to
stand out and be extracted, most of them blur into a confusion foreground.
Current methods for analyzing the full frequency band recorded by LISA to
extract as many Galactic binaries as possible and to obtain Bayesian posterior
distributions for each of the signals are computationally expensive. We
introduce a new approach to accelerate the extraction of the best fitting
solutions for Galactic binaries across the entire frequency band from data with
multiple overlapping signals. Furthermore, we use these best fitting solutions
to omit the burn-in stage of a Markov chain Monte Carlo method and to take full
advantage of GPU-accelerated signal simulation, allowing us to compute
posterior distributions in 2 seconds per signal on a laptop-grade GPU.Comment: 13 pages, 11 figure
Bayesian parameter-estimation of Galactic binaries in LISA data with Gaussian Process Regression
The Laser Interferometer Space Antenna (LISA), which is currently under
construction, is designed to measure gravitational wave signals in the
milli-Hertz frequency band. It is expected that tens of millions of Galactic
binaries will be the dominant sources of observed gravitational waves. The
Galactic binaries producing signals at mHz frequency range emit quasi
monochromatic gravitational waves, which will be constantly measured by LISA.
To resolve as many Galactic binaries as possible is a central challenge of the
upcoming LISA data set analysis. Although it is estimated that tens of
thousands of these overlapping gravitational wave signals are resolvable, and
the rest blurs into a galactic foreground noise; extracting tens of thousands
of signals using Bayesian approaches is still computationally expensive. We
developed a new end-to-end pipeline using Gaussian Process Regression to model
the log-likelihood function in order to rapidly compute Bayesian posterior
distributions. Using the pipeline we are able to solve the Lisa Data Challange
(LDC) 1-3 consisting of noisy data as well as additional challenges with
overlapping signals and particularly faint signals.Comment: 12 pages, 10 figure
Nanogranular MgB2 thin films on SiC buffered Si substrates prepared by in-situ method
MgB2 thin films were deposited on SiC buffered Si substrates by sequential
electron beam evaporation of B-Mg bilayer followed by in-situ annealing. The
application of a SiC buffer layer enables the maximum annealing temperature of
830 C. The Transmission Electron Microscopy analysis confirms the growth of a
nanogranular MgB2 film and the presence of a Mg2Si compound at the surface of
the film. The 150-200 nm thick films show a maximum zero resistance critical
temperature TC0 above 37 K and a critical current density JC ~ 106 A/cm2 at
11K.Comment: 7 pages, 6 figures, submitted to Applied Physics Letter
Correction Mesoporous thin film WO3 photoanode for photoelectrochemical water splitting a sol gel dip coating approach
Correction for Mesoporous thin film WO3 photoanode for photoelectrochemical water splitting a sol gel dip coating approach by Samantha Hilliard et al., Sustainable Energy Fuels, 2017, 1, 145 15
Nucleic Acids Res
Type II topoisomerases are essential enzymes that regulate DNA topology through a strand-passage mechanism. Some type II topoisomerases relax supercoils, unknot and decatenate DNA to below thermodynamic equilibrium. Several models of this non-equilibrium topology simplification phenomenon have been proposed. The kinetic proofreading (KPR) model postulates that strand passage requires a DNA-bound topoisomerase to collide twice in rapid succession with a second DNA segment, implying a quadratic relationship between DNA collision frequency and relaxation rate. To test this model, we used a single-molecule assay to measure the unlinking rate as a function of DNA collision frequency for Escherichia coli topoisomerase IV (topo IV) that displays efficient non-equilibrium topology simplification activity, and for E. coli topoisomerase III (topo III), a type IA topoisomerase that unlinks and unknots DNA to equilibrium levels. Contrary to the predictions of the KPR model, topo IV and topo III unlinking rates were linearly related to the DNA collision frequency. Furthermore, topo III exhibited decatenation activity comparable with that of topo IV, supporting proposed roles for topo III in DNA segregation. This study enables us to rule out the KPR model for non-equilibrium topology simplification. More generally, we establish an experimental approach to systematically control DNA collision frequency
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