1,185 research outputs found
Earthshine observation of vegetation and implication for life detection on other planets - A review of 2001 - 2006 works
The detection of exolife is one of the goals of very ambitious future space
missions that aim to take direct images of Earth-like planets. While
associations of simple molecules present in the planet's atmosphere (,
, etc.) have been identified as possible global biomarkers, we
review here the detectability of a signature of life from the planet's surface,
i.e. the green vegetation. The vegetation reflectance has indeed a specific
spectrum, with a sharp edge around 700 nm, known as the "Vegetation Red Edge"
(VRE). Moreover vegetation covers a large surface of emerged lands, from
tropical evergreen forest to shrub tundra. Thus considering it as a potential
global biomarker is relevant. Earthshine allows to observe the Earth as a
distant planet, i.e. without spatial resolution. Since 2001, Earthshine
observations have been used by several authors to test and quantify the
detectability of the VRE in the Earth spectrum. The egetation spectral
signature is detected as a small 'positive shift' of a few percents above the
continuum, starting at 700 nm. This signature appears in most spectra, and its
strength is correlated with the Earth's phase (visible land versus visible
ocean). The observations show that detecting the VRE on Earth requires a
photometric relative accuracy of 1% or better. Detecting something equivalent
on an Earth-like planet will therefore remain challenging, moreover considering
the possibility of mineral artifacts and the question of 'red edge'
universality in the Universe.Comment: Invited talk in "Strategies for Life Detection" (ISSI Bern, 24-28
April 2006) to appear in a hardcopy volume of the ISSI Space Science Series,
Eds, J. Bada et al., and also in an issue of Space Science Reviews. 13 pages,
8 figures, 1 tabl
The Convergence of Digital-Libraries and the Peer-Review Process
Pre-print repositories have seen a significant increase in use over the past
fifteen years across multiple research domains. Researchers are beginning to
develop applications capable of using these repositories to assist the
scientific community above and beyond the pure dissemination of information.
The contribution set forth by this paper emphasizes a deconstructed publication
model in which the peer-review process is mediated by an OAI-PMH peer-review
service. This peer-review service uses a social-network algorithm to determine
potential reviewers for a submitted manuscript and for weighting the relative
influence of each participating reviewer's evaluations. This paper also
suggests a set of peer-review specific metadata tags that can accompany a
pre-print's existing metadata record. The combinations of these contributions
provide a unique repository-centric peer-review model that fits within the
widely deployed OAI-PMH framework.Comment: Journal of Information Science [in press
Public health impact of low-dose aspirin on colorectal cancer, cardiovascular disease and safety in the UK – Results from micro-simulation model
Background: Low-dose aspirin therapy reduces the risk of cardiovascular disease and may have a positive effect on the prevention of colorectal cancer. We evaluated the population-level expected effect of regular low-dose aspirin use on cardiovascular disease (CVD), colorectal cancer (CRC), gastrointestinal bleeding, symptomatic peptic ulcers, and intracranial hemorrhage, using a microsimulation study design. Methods: We used individual-level state transition modeling to assess the impact of aspirin in populations aged 50–59 or 60–69 years old indicated for low-dose aspirin usage for primary or secondary CVD prevention. Model parameters were based on data from governmental agencies from the UK or recent publications. Results: In the 50–59 years cohort, a decrease in incidence rates (IRs per 100 000 person years) of non-fatal CVD (-203 and -794) and fatal CVD (-97 and-381) was reported in the primary and secondary CVD prevention setting, respectively. The IR reduction of CRC (-96 and -93) was similar for primary and secondary CVD prevention. The IR increase of non-fatal (116 and 119) and fatal safety events (6 and 6) was similar for primary and secondary CVD prevention. Similar results were obtained for the 60–69 years cohort. Conclusions: The decrease in fatal CVD and CRC events was larger than the increase in fatal safety events and this difference was more pronounced when low-dose aspirin was used for secondary compared to primary CVD prevention. These results provide a comprehensive image of the expected effect of regular low-dose aspirin therapy in a UK population indicated to use aspirin for CVD prevention. © 202
Electronic structure and ferroelectricity in SrBi2Ta2O9
The electronic structure of SrBi2Ta2O9 is investigated from first-principles,
within the local density approximation, using the full-potential linearized
augmented plane wave (LAPW) method. The results show that, besides the large
Ta(5d)-O(2p) hybridization which is a common feature of the ferroelectric
perovskites, there is an important hybridization between bismuth and oxygen
states. The underlying static potential for the ferroelectric distortion and
the primary source for ferroelectricity is investigated by a lattice-dynamics
study using the Frozen Phonon approach.Comment: 17 pages, 7 figures. Phys. Rev. B, in pres
Charged lepton electric dipole moments with the localized leptons and the new Higgs doublet in the two Higgs doublet model
We study the lepton electric dipole moments in the split fermion scenario, in
the two Higgs doublet model, where the new Higgs scalars are localized around
the origin in the extra dimension, with the help of the localizer field. We
observe that the numerical value of the electron (muon, tau) electric dipole
moment is at the order of the magnitude of 10^{-31} (10^{-24}, 10^{-22}) (e-cm)
and this quantity is sensitive the new Higgs localization in the extra
dimension.Comment: 20 pages, 7 figure
Spin-Charge Separation in the Model: Magnetic and Transport Anomalies
A real spin-charge separation scheme is found based on a saddle-point state
of the model. In the one-dimensional (1D) case, such a saddle-point
reproduces the correct asymptotic correlations at the strong-coupling
fixed-point of the model. In the two-dimensional (2D) case, the transverse
gauge field confining spinon and holon is shown to be gapped at {\em finite
doping} so that a spin-charge deconfinement is obtained for its first time in
2D. The gap in the gauge fluctuation disappears at half-filling limit, where a
long-range antiferromagnetic order is recovered at zero temperature and spinons
become confined. The most interesting features of spin dynamics and transport
are exhibited at finite doping where exotic {\em residual} couplings between
spin and charge degrees of freedom lead to systematic anomalies with regard to
a Fermi-liquid system. In spin dynamics, a commensurate antiferromagnetic
fluctuation with a small, doping-dependent energy scale is found, which is
characterized in momentum space by a Gaussian peak at (, ) with
a doping-dependent width (, is the doping
concentration). This commensurate magnetic fluctuation contributes a
non-Korringa behavior for the NMR spin-lattice relaxation rate. There also
exits a characteristic temperature scale below which a pseudogap behavior
appears in the spin dynamics. Furthermore, an incommensurate magnetic
fluctuation is also obtained at a {\em finite} energy regime. In transport, a
strong short-range phase interference leads to an effective holon Lagrangian
which can give rise to a series of interesting phenomena including linear-
resistivity and Hall-angle. We discuss the striking similarities of these
theoretical features with those found in the high- cuprates and give aComment: 70 pages, RevTex, hard copies of 7 figures available upon request;
minor revisions in the text and references have been made; To be published in
July 1 issue of Phys. Rev. B52, (1995
Dynamical mean-field approach to materials with strong electronic correlations
We review recent results on the properties of materials with correlated
electrons obtained within the LDA+DMFT approach, a combination of a
conventional band structure approach based on the local density approximation
(LDA) and the dynamical mean-field theory (DMFT). The application to four
outstanding problems in this field is discussed: (i) we compute the full
valence band structure of the charge-transfer insulator NiO by explicitly
including the p-d hybridization, (ii) we explain the origin for the
simultaneously occuring metal-insulator transition and collapse of the magnetic
moment in MnO and Fe2O3, (iii) we describe a novel GGA+DMFT scheme in terms of
plane-wave pseudopotentials which allows us to compute the orbital order and
cooperative Jahn-Teller distortion in KCuF3 and LaMnO3, and (iv) we provide a
general explanation for the appearance of kinks in the effective dispersion of
correlated electrons in systems with a pronounced three-peak spectral function
without having to resort to the coupling of electrons to bosonic excitations.
These results provide a considerable progress in the fully microscopic
investigations of correlated electron materials.Comment: 24 pages, 14 figures, final version, submitted to Eur. Phys. J. for
publication in the Special Topics volume "Cooperative Phenomena in Solids:
Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom
Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
Nearby clusters and groups of galaxies are potentially bright sources of
high-energy gamma-ray emission resulting from the pair-annihilation of dark
matter particles. However, no significant gamma-ray emission has been detected
so far from clusters in the first 11 months of observations with the Fermi
Large Area Telescope. We interpret this non-detection in terms of constraints
on dark matter particle properties. In particular for leptonic annihilation
final states and particle masses greater than ~200 GeV, gamma-ray emission from
inverse Compton scattering of CMB photons is expected to dominate the dark
matter annihilation signal from clusters, and our gamma-ray limits exclude
large regions of the parameter space that would give a good fit to the recent
anomalous Pamela and Fermi-LAT electron-positron measurements. We also present
constraints on the annihilation of more standard dark matter candidates, such
as the lightest neutralino of supersymmetric models. The constraints are
particularly strong when including the fact that clusters are known to contain
substructure at least on galaxy scales, increasing the expected gamma-ray flux
by a factor of ~5 over a smooth-halo assumption. We also explore the effect of
uncertainties in cluster dark matter density profiles, finding a systematic
uncertainty in the constraints of roughly a factor of two, but similar overall
conclusions. In this work, we focus on deriving limits on dark matter models; a
more general consideration of the Fermi-LAT data on clusters and clusters as
gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo,
minor revisions to be consistent with accepted versio
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