1,797 research outputs found
The Influence of Non-Uniform Cloud Cover on Transit Transmission Spectra
We model the impact of non-uniform cloud cover on transit transmission
spectra. Patchy clouds exist in nearly every solar system atmosphere, brown
dwarfs, and transiting exoplanets. Our major findings suggest that fractional
cloud coverage can exactly mimic high mean molecular weight atmospheres and
vice-versa over certain wavelength regions, in particular, over the Hubble
Space Telescope (HST) Wide Field Camera 3 (WFC3) bandpass (1.1-1.7 m). We
also find that patchy cloud coverage exhibits a signature that is different
from uniform global clouds. Furthermore, we explain analytically why the
"patchy cloud-high mean molecular weight" degeneracy exists. We also explore
the degeneracy of non-uniform cloud coverage in atmospheric retrievals on both
synthetic and real planets. We find from retrievals on a synthetic solar
composition hot Jupiter with patchy clouds and a cloud free high mean molecular
weight warm Neptune, that both cloud free high mean molecular weight
atmospheres and partially cloudy atmospheres can explain the data equally well.
Another key find is that the HST WFC3 transit transmission spectra of two well
observed objects, the hot Jupiter HD189733b and the warm Neptune HAT-P-11b, can
be explained well by solar composition atmospheres with patchy clouds without
the need to invoke high mean molecular weight or global clouds. The degeneracy
between high molecular weight and solar composition partially cloudy
atmospheres can be broken by observing the molecular Rayleigh scattering
differences between the two. Furthermore, the signature of partially cloudy
limbs also appears as a 100 ppm residual in the ingress and egress of the
transit light curves, provided the transit timing is known to seconds.Comment: Accepted to ApJ Feb. 8, 201
An Observational Diagnostic for Distinguishing Between Clouds and Haze in Hot Exoplanet Atmospheres
The nature of aerosols in hot exoplanet atmospheres is one of the primary
vexing questions facing the exoplanet field. The complex chemistry, multiple
formation pathways, and lack of easily identifiable spectral features
associated with aerosols make it especially challenging to constrain their key
properties. We propose a transmission spectroscopy technique to identify the
primary aerosol formation mechanism for the most highly irradiated hot Jupiters
(HIHJs). The technique is based on the expectation that the two key types of
aerosols -- photochemically generated hazes and equilibrium condensate clouds
-- are expected to form and persist in different regions of a highly irradiated
planet's atmosphere. Haze can only be produced on the permanent daysides of
tidally-locked hot Jupiters, and will be carried downwind by atmospheric
dynamics to the evening terminator (seen as the trailing limb during transit).
Clouds can only form in cooler regions on the night side and morning terminator
of HIHJs (seen as the leading limb during transit). Because opposite limbs are
expected to be impacted by different types of aerosols, ingress and egress
spectra, which primarily probe opposing sides of the planet, will reveal the
dominant aerosol formation mechanism. We show that the benchmark HIHJ,
WASP-121b, has a transmission spectrum consistent with partial aerosol coverage
and that ingress-egress spectroscopy would constrain the location and formation
mechanism of those aerosols. In general, using this diagnostic we find that
observations with JWST and potentially with HST should be able to distinguish
between clouds and haze for currently known HIHJs.Comment: 10 pages, 4 figures, accepted to ApJ Letter
Bayesian numerical inference for Markovian models -- Application to tropical forest dynamics
International audienceBayesian modelling is fluently employed to assess natural ressources. It is associated with Monte Carlo Markov Chains (MCMC) to get an approximation of the distribution law of interest. Hence in such situations it is important to be able to propose N independent realiza- tions of this distribution law. We propose a strategy for making N parallel Monte Carlo Markov Chains interact in order to get an approximation of an independent N -sample of a given target law. In this method each individual chain proposes candidates for all other chains. We prove that the set of interacting chains is itself a MCMC method for the product of N target measures. Compared to independent parallel chains this method is more time consuming, but we show through example that it possesses many advantages. This approach will be applied to a forest dynamic model
Food Sharing Initiatives and Food Democracy: Practice and Policy in Three European Cities
Calls for greater food democracy in Europe have emerged as the limitations of urban food systems dominated by commercial organisations are documented, but little attention has been paid to how policy arrangements affect attempts to transition to more democratic food futures. This article examines food sharing initiatives - increasingly facilitated by the use of information and communication technologies - as a potential means to enhance urban food democracy, and explores the role of policy in shaping those practices in three European capital cities: Berlin, London, and Dublin. We pose two related questions: To what extent are diverse food sharing initiatives exemplars of food democracy, and to what extent do policy arrangements affect food sharing practices and the nature of any food democracy they might embody? Our empirical evidence demonstrates where the goals and impacts of food sharing initiatives align with key dimensions of food democracy. We also consider how food sharing initiatives - and any food democracy dimensions that they support - are affected by the policy environment in which they operate. The food sharing initiatives examined revealed to be agents of pro-democratic change, at least within the boundaries of their spheres of influence, despite policies rarely having their activities and aspirations in mind
Osteoporosis in men: its pathophysiology and the role of teriparatide in its treatment
As the population ages, the burden of osteoporosis in men is expected to rise. Implementation of preventive measures such as falls prevention strategies, exercise and adequate calcium and vitamin D intake is recommended. However, when the diagnosis of osteoporosis is made, effective treatments need to be initiated to prevent fractures. As opposed to postmenopausal women, reduced bone formation is the predominant mechanism of age-related bone loss in men, making anabolic agents a logical treatment option for men with osteoporosis. Teriparatide is the only anabolic agent currently approved for treatment of osteoporosis in men. This paper summarizes the mechanism of action of teriparatide, as well as its tolerability and safety. Furthermore, the evidence supporting the efficacy of teriparatide treatment in men with osteoporosis is reviewed and its current role in the management of osteoporosis in men is discussed
Mesure de durées de vie au moyen de champs hyperfréquences
Des champs électriques synchrones pulsent le faisceau, puis modulent en énergie des électrons K, ou bien modulent les deux électrons K d'une cascade
A novel role for granzymes in anti-tumor immunity
The cytotoxic properties of granzymes are well established, though recent publications suggest additional roles for granzymes in immunity. We demonstrated that granzymes can act as regulators of cross-presentation by dendritic cells by inducing critical “eat-me” signals on the dying tumor cell, resulting in efficient phagocytosis of cell-associated tumor antigen
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