205 research outputs found
The value of perfect information
Eutrophication from nitrogen and phosphorus has damaged the Baltic Sea, leaving large sea bottom areas without biological life, thus changing the marine ecosystem, and triggering the growth of toxic algae. Despite efforts to curb this pollution, the sea remains eutrophic. We argue that eutrophication management is subject to both uncertainty and irreversibility, and hence could explain why impacted countries may not be willing to enforce load reduction targets. This thesis focuses on the time lag of benefits following nitrogen abatement. The time taken for concentration levels to decrease after abatement is uncertain, leading to uncertain benefits. Using the quasi option value model, we calculate the value of learning this information, and thus find that removing this uncertainty is worth over 8.6 billion EUR, to all bordering countries. This could be of significant importance for actors rationally waiting for more information, before implementing expensive and irreversible policy
Local bone metabolism during the consolidation process of spinal interbody fusion
INTRODUCTION: Although computed tomography (CT) can identify the presence of eventual bony bridges following lumbar interbody fusion (LIF) surgery, it does not provide information on the ongoing formation process of new bony structures. 18F sodium fluoride (18F-NaF) positron emission tomography (PET) could be used as complementary modality to add information on the bone metabolism at the fusion site. However, it remains unknown how bone metabolism in the operated segment changes early after surgery in uncompromised situations. This study aimed to quantify the changes in local bone metabolism during consolidation of LIF. MATERIALS AND METHODS: Six skeletally mature sheep underwent LIF surgery. 18F-NaF PET/CT scanning was performed 6 and 12 weeks postoperatively to quantify the bone volume and metabolism in the operated segment. Bone metabolism was expressed as a function of bone volume. RESULTS: Early in the fusion process, bone metabolism was increased at the endplates of the operated vertebrae. In a next phase, bone metabolism increased in the center of the interbody region, peaked, and declined to an equilibrium state. During the entire postoperative time period of 12 weeks, bone metabolism in the interbody region was higher than that of a reference site in the spinal column. CONCLUSION: Following LIF surgery, there is a rapid increase in bone metabolism at the vertebral endplates that develops towards the center of the interbody region. Knowing the local bone metabolism during uncompromised consolidation of spinal interbody fusion might enable identification of impaired bone formation early after LIF surgery using 18F-NaF PET/CT scanning
Islands of linkage in an ocean of pervasive recombination reveals two-speed evolution of human cytomegalovirus genomes
Human cytomegalovirus (HCMV) infects most of the population worldwide, persisting throughout the host's life in a latent state with periodic episodes of reactivation. While typically asymptomatic, HCMV can cause fatal disease among congenitally infected infants and immunocompromised patients. These clinical issues are compounded by the emergence of antiviral resistance and the absence of an effective vaccine, the development of which is likely complicated by the numerous immune evasins encoded by HCMV to counter the host's adaptive immune responses, a feature that facilitates frequent super-infections. Understanding the evolutionary dynamics of HCMV is essential for the development of effective new drugs and vaccines. By comparing viral genomes from uncultivated or low-passaged clinical samples of diverse origins, we observe evidence of frequent homologous recombination events, both recent and ancient, and no structure of HCMV genetic diversity at the whole-genome scale. Analysis of individual gene-scale loci reveals a striking dichotomy: while most of the genome is highly conserved, recombines essentially freely and has evolved under purifying selection, 21 genes display extreme diversity, structured into distinct genotypes that do not recombine with each other. Most of these hyper-variable genes encode glycoproteins involved in cell entry or escape of host immunity. Evidence that half of them have diverged through episodes of intense positive selection suggests that rapid evolution of hyper-variable loci is likely driven by interactions with host immunity. It appears that this process is enabled by recombination unlinking hyper-variable loci from strongly constrained neighboring sites. It is conceivable that viral mechanisms facilitating super-infection have evolved to promote recombination between diverged genotypes, allowing the virus to continuously diversify at key loci to escape immune detection, while maintaining a genome optimally adapted to its asymptomatic infectious lifecycle
Twitter Flood Mapping Scripts: First Release
The increasing number and severity of floods, driven by phenomena
such as urbanization, deforestation, subsidence and climate change, create a
growing need for accurate and timely flood maps. In this paper we present and
evaluate a method to create deterministic and probabilistic flood maps from
Twitter messages that mention locations of flooding. A deterministic flood
map created for the December 2015 flood in the city of York (UK) showed good
performance (F(2) = 0.69; a statistic ranging from 0 to 1,
with 1 expressing a perfect fit with validation data). The probabilistic
flood maps we created showed that, in the York case study, the uncertainty in
flood extent was mainly induced by errors in the precise locations of flood
observations as derived from Twitter data. Errors in the terrain elevation
data or in the parameters of the applied algorithm contributed less to flood
extent uncertainty. Although these maps tended to overestimate the actual
probability of flooding, they gave a reasonable representation of flood
extent uncertainty in the area. This study illustrates that inherently
uncertain data from social media can be used to derive information about
flooding
Overwegingen bij een boerka verbod. Zienswijze van de deskundigen inzaken een verbod op gezichtsbedekende kleding
Modernity (Religion and Modernity
Excitation of the molecular gas in the nuclear region of M82
We present high resolution HIFI spectroscopy of the nucleus of the
archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4
fine-structure lines are detected. Besides showing the effects of the overall
velocity structure of the nuclear region, the line profiles also indicate the
presence of multiple components with different optical depths, temperatures and
densities in the observing beam. The data have been interpreted using a grid of
PDR models. It is found that the majority of the molecular gas is in low
density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and
a relatively low UV radiation field (GO = 10^2). The remaining gas is
predominantly found in clouds with higher densities (n=10^5 cm^-3) and
radiation fields (GO = 10^2.75), but somewhat lower column densities
(N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1%
relative surface filling) component, with an even higher density (n=10^6 cm^-3)
and UV field (GO = 10^3.25). These results show the strength of multi-component
modeling for the interpretation of the integrated properties of galaxies.Comment: Accepted for publication in A&A Letter
An investigation of the structural requirements for ATP hydrolysis and DNA cleavage by the EcoKI Type I DNA restriction and modification enzyme
Type I DNA restriction and modification enzym
Herschel observations of water vapour in Markarian 231
The Ultra Luminous InfraRed Galaxy Mrk 231 reveals up to seven rotational
lines of water (H2O) in emission, including a very high-lying (E_{upper}=640 K)
line detected at a 4sigma level, within the Herschel/SPIRE wavelength range,
whereas PACS observations show one H2O line at 78 microns in absorption, as
found for other H2O lines previously detected by ISO. The absorption/emission
dichotomy is caused by the pumping of the rotational levels by far-infrared
radiation emitted by dust, and subsequent relaxation through lines at longer
wavelengths, which allows us to estimate both the column density of H2O and the
general characteristics of the underlying far-infrared continuum source.
Radiative transfer models including excitation through both absorption of
far-infrared radiation emitted by dust and collisions are used to calculate the
equilibrium level populations of H2O and the corresponding line fluxes. The
highest-lying H2O lines detected in emission, with levels at 300-640 K above
the ground state, indicate that the source of far-infrared radiation
responsible for the pumping is compact (radius=110-180 pc) and warm
(T_{dust}=85-95 K), accounting for at least 45% of the bolometric luminosity.
The high column density, N(H2O)~5x10^{17} cm^{-2}, found in this nuclear
component, is most probably the consequence of shocks/cosmic rays, an XDR
chemistry, and/or an "undepleted chemistry" where grain mantles are evaporated.
A more extended region, presumably the inner region of the 1-kpc disk observed
in other molecular species, could contribute to the flux observed in low-lying
H2O lines through dense hot cores, and/or shocks. The H2O 78 micron line
observed with PACS shows hints of a blue-shifted wing seen in absorption,
possibly indicating the occurrence of H2O in the prominent outflow detected in
OH (Fischer et al., this volume).Comment: 5 pages, 3 figure
Black hole accretion and star formation as drivers of gas excitation and chemistry in Mrk231
We present a full high resolution SPIRE FTS spectrum of the nearby
ultraluminous infrared galaxy Mrk231. In total 25 lines are detected, including
CO J=5-4 through J=13-12, 7 rotational lines of H2O, 3 of OH+ and one line each
of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels
up to J=8 can be accounted for by UV radiation from star formation. However,
the approximately flat luminosity distribution of the CO lines over the
rotational ladder above J=8 requires the presence of a separate source of
excitation for the highest CO lines. We explore X-ray heating by the accreting
supermassive black hole in Mrk231 as a source of excitation for these lines,
and find that it can reproduce the observed luminosities. We also consider a
model with dense gas in a strong UV radiation field to produce the highest CO
lines, but find that this model strongly overpredicts the hot dust mass in
Mrk231. Our favoured model consists of a star forming disk of radius 560 pc,
containing clumps of dense gas exposed to strong UV radiation, dominating the
emission of CO lines up to J=8. X-rays from the accreting supermassive black
hole in Mrk231 dominate the excitation and chemistry of the inner disk out to a
radius of 160 pc, consistent with the X-ray power of the AGN in Mrk231. The
extraordinary luminosity of the OH+ and H2O+ lines reveals the signature of
X-ray driven excitation and chemistry in this region.Comment: 5 pages, 2 figures, accepted for publication in Astronomy &
Astrophysics Special Issue on Herschel first result
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