386 research outputs found
A comparison of satellite- and ground-based measurements of SO<inf>2</inf> emissions from tungurahua volcano, Ecuador
Satellite-measured SO2 mass loadings and ground-based measurements of SO2 emission rate
are not directly comparable, with ∼40% differences between mean emissions reported by each technique
from Tungurahua volcano, Ecuador, during late 2007. Numerical simulations of postemission processing and
dispersal of Tungurahua’s SO2 emissions enable more effective comparison of ground- and satellite-based
SO2 data sets, reducing the difference between them and constraining the impact of plume processing on
satellite SO2 observations. Ground-based measurements of SO2 emission rate are used as the model input,
and simulated SO2 mass loadings are compared to those measured by the Ozone Monitoring Instrument
(OMI). The changing extent of SO2 processing has a significant impact on daily variation in SO2 mass loading
for a fixed volcanic emission rate. However, variations in emission rate at Tungurahua are large, suggesting
that overall volcanic source strength and not subsequent processing is more likely to be the dominant
control on atmospheric mass loading. SO2 emission rate estimates are derived directly from the OMI
observations using modeled SO2 lifetime. Good agreement is achieved between both observed and
simulated mass loadings (∼21%) and satellite-derived and ground-measured SO2 emission rates (∼18%),
with a factor of 2 improvement over the differences found by simple direct comparison. While the balance
of emission source strength and postemission processing will differ between volcanoes and regions, under
good observation conditions and where SO2 lifetime is ∼24 hours, satellite-based sensors like OMI may
provide daily observations of SO2 mass loading which are a good proxy for volcanic source strength.B.T.M. acknowledges funding from the
National Centre for Earth Observation,
part of the UK’s Natural Environment
Research Council, and latterly the
Deep Carbon Observatory and
the Smithsonian Institution. B.T.M.,
M.E., and T.A.M. are supported by
and contribute to the NERC NCEO
Dynamic Earth and Geohazards group.
S.A.C. acknowledges funding from
NASA through grants NNX09AJ40G
(Aura Validation), NNX10AG60G
(Atmospheric Chemistry Modeling and
Analysis Program), and NNX11AF42G
(Aura Science Team). J.Y. was funded
by the Isaac Newton Trust at the
University of Cambridge for the
duration of this project. The authors
thank Anja Schmidt and two anonymous
reviewers for their thorough
and constructive comments. We
acknowledge the Goddard Earth
Sciences Data and Information
Services Center for making OMI SO2
data publicly available.This is the final published version. It first appeared at http://onlinelibrary.wiley.com/doi/10.1002/2013JD019771/abstract
Identification of fetal DNA and cells in skin lesions from women with systemic sclerosis
BACKGROUND: Systemic sclerosis is a disease of unknown origin which often occurs in women after their childbearing years. It has many clinical and histopathological similarities to chronic graft-versus-host disease. Recent studies indicate that fetal stem cells can survive in the maternal circulation for many years post partum. This finding suggests that fetal cells persisting in the maternal circulation or tissues could be involved in the pathogenesis of systemic sclerosis by initiating a graft-versus-host reaction.
METHODS: We used the polymerase chain reaction (PCR) to identify Y-chromosome sequences in DNA extracted from peripheral-blood cells and skin lesions from women with systemic sclerosis of recent onset. To confirm the PCR findings, we used fluorescence in situ hybridization of peripheral-blood cells and cells within chronic inflammatory-cell infiltrates in biopsy specimens of affected skin.
RESULTS: Y-chromosome sequences were found in DNA from peripheral-blood cells in 32 of 69 women with systemic sclerosis (46 percent), as compared with 1 of 25 normal women (4 percent, P\u3c0.001), and in T lymphocytes from 3 women with systemic sclerosis who had male offspring. Furthermore, Y-chromosome sequences were identified in skin-biopsy specimens from 11 of 19 women with systemic sclerosis (58 percent); 9 of the 11 were known to have carried male fetuses. Nucleated cells containing Y chromosomes were detected by fluorescence in situ hybridization in paraffin-embedded sections of skin lesions from all seven women we tested whose skin-biopsy specimens contained Y-chromosome sequences.
CONCLUSIONS: Fetal antimaternal graft-versus-host reactions may be involved in the pathogenesis of systemic sclerosis in some women
Structural insights into RNA processing by the human RISC-loading complex.
Targeted gene silencing by RNA interference (RNAi) requires loading of a short guide RNA (small interfering RNA (siRNA) or microRNA (miRNA)) onto an Argonaute protein to form the functional center of an RNA-induced silencing complex (RISC). In humans, Argonaute2 (AGO2) assembles with the guide RNA-generating enzyme Dicer and the RNA-binding protein TRBP to form a RISC-loading complex (RLC), which is necessary for efficient transfer of nascent siRNAs and miRNAs from Dicer to AGO2. Here, using single-particle EM analysis, we show that human Dicer has an L-shaped structure. The RLC Dicer's N-terminal DExH/D domain, located in a short 'base branch', interacts with TRBP, whereas its C-terminal catalytic domains in the main body are proximal to AGO2. A model generated by docking the available atomic structures of Dicer and Argonaute homologs into the RLC reconstruction suggests a mechanism for siRNA transfer from Dicer to AGO2
Looking through the QCD conformal window with perturbation theory
We study the conformal window of QCD using perturbation theory, starting from the perturbative upper edge and going down as much as we can towards the strongly coupled regime. We do so by exploiting the available five-loop
computation of the -function and employing Borel resummation techniques both for the ordinary perturbative series and for the Banks-Zaks conformal expansion. Large- results are also used. We argue that the perturbative series for the -function is most likely asymptotic and non-Borel resummable, yet Borel resummation techniques allow to improve on ordinary perturbation theory. We find
substantial evidence that QCD with flavours flows in the IR to a conformal field theory. Though the evidence is weaker, we find indications that also might sit within the conformal window. We also compute the value
of the mass anomalous dimension at the fixed point and compare it with the available lattice results. The conformal window might extend for lower values of , but our methods break down for n_f<11, where we expect that non-perturbative effects become important. A similar analysis is performed in the Veneziano limit
Stochastic Gravity: Theory and Applications
Whereas semiclassical gravity is based on the semiclassical Einstein equation
with sources given by the expectation value of the stress-energy tensor of
quantum fields, stochastic semiclassical gravity is based on the
Einstein-Langevin equation, which has in addition sources due to the noise
kernel. In the first part, we describe the fundamentals of this new theory via
two approaches: the axiomatic and the functional. In the second part, we
describe three applications of stochastic gravity theory. First, we consider
metric perturbations in a Minkowski spacetime, compute the two-point
correlation functions of these perturbations and prove that Minkowski spacetime
is a stable solution of semiclassical gravity. Second, we discuss structure
formation from the stochastic gravity viewpoint. Third, we discuss the
backreaction of Hawking radiation in the gravitational background of a black
hole and describe the metric fluctuations near the event horizon of an
evaporating black holeComment: 100 pages, no figures; an update of the 2003 review in Living Reviews
in Relativity gr-qc/0307032 ; it includes new sections on the Validity of
Semiclassical Gravity, the Stability of Minkowski Spacetime, and the Metric
Fluctuations of an Evaporating Black Hol
The forgotten smoker: a qualitative study of attitudes towards smoking, quitting, and tobacco control policies among continuing smokers
Although research suggests that the majority of smokers want to quit smoking, the uptake of Stop Smoking Services, designed to assist smokers with quitting, remains low. Little is known about continuing smokers who do not access these services, and opportunities to influence their motivation and encourage quit attempts through the uptake of services. Using PRIME theory, this study explored differences between continuing smokers who had varying levels of motivation to quit, in terms of their plans to quit, evaluative beliefs about smoking, cigarette dependence, and attitudes towards tobacco control policies and services
Truth after post-truth: for a Strong Programme in Discourse Studies
Contemporary post-truth discourses put the constructivist foundations of Discourse Studies to a test. According to critical observers, discourse analysts have been playing into the hands of Trump, Brexit and right-wing populists by politicising scientific knowledge and undermining the idea of scientific truth. In order to respond to these concerns, this article outlines a Strong Programme in Discourse Studies. While the Strong Programme insists on truths as discursive constructions, in no way does it claim that all ideas have the same truth value or that an idea can become true because somebody wants it to be true. The Strong Programme makes the case for discourse research that is constructivist (it asks how truths are constructed practically) without being relativist (all ideas do not have the same normative quality). Taking inspiration from debates in Science and Technology Studies of the 1970s, the Strong Programme formulates principles for discourse researchers dealing with conflicting truth claims. Discourse analytical explanations of truths of first-order participants and of second-order observers should be symmetrical, heterogeneous, multi-perspectival and reflexive. The Strong Programme discourse research is grounded in the founding traditions of ?French? and ?Critical? Discourse Studies, which have struggled over questions of truth and reality since the beginning. While critically interrogating the structuralist heritage of these strands, the Strong Programme insists on the practices of making and unmaking ideas through language use no matter whether they appear as true or false to participants and observers. Discourse Studies are encouraged to critically reflect on how hierarchies between knowledges are not only represented but, through their representation, also constituted through discursive practices
Epigenetic tethering of AID to the donor switch region during immunoglobulin class switch recombination
A complex of KAP1 and HP1 is needed to tether AID to the H3K9me3-marked donor switch region during CSR
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