364 research outputs found
Exploring the Venus global super-rotation using a comprehensive General Circulation Model
The atmospheric circulation in Venus is well known to exhibit strong
super-rotation. However, the atmospheric mechanisms responsible for the
formation of this super-rotation are still not fully understood. In this work,
we developed a new Venus general circulation model to study the most likely
mechanisms driving the atmosphere to the current observed circulation. Our
model includes a new radiative transfer, convection and suitably adapted
boundary layer schemes and a dynamical core that takes into account the
dependence of the heat capacity at constant pressure with temperature.
The new Venus model is able to simulate a super-rotation phenomenon in the
cloud region quantitatively similar to the one observed. The mechanisms
maintaining the strong winds in the cloud region were found in the model
results to be a combination of zonal mean circulation, thermal tides and
transient waves. In this process, the semi-diurnal tide excited in the upper
clouds has a key contribution in transporting axial angular momentum mainly
from the upper atmosphere towards the cloud region. The magnitude of the
super-rotation in the cloud region is sensitive to various radiative parameters
such as the amount of solar radiative energy absorbed by the surface, which
controls the static stability near the surface. In this work, we also discuss
the main difficulties in representing the flow below the cloud base in Venus
atmospheric models.
Our new radiative scheme is more suitable for 3D Venus climate models than
those used in previous work due to its easy adaptability to different
atmospheric conditions. This flexibility of the model was crucial to explore
the uncertainties in the lower atmospheric conditions and may also be used in
the future to explore, for example, dynamical-radiative-microphysical
feedbacks.Comment: Accepted for publication in Planet. Space Sc
Analytical Models of Exoplanetary Atmospheres. II. Radiative Transfer via the Two-stream Approximation
We present a comprehensive analytical study of radiative transfer using the
method of moments and include the effects of non-isotropic scattering in the
coherent limit. Within this unified formalism, we derive the governing
equations and solutions describing two-stream radiative transfer (which
approximates the passage of radiation as a pair of outgoing and incoming
fluxes), flux-limited diffusion (which describes radiative transfer in the deep
interior) and solutions for the temperature-pressure profiles. Generally, the
problem is mathematically under-determined unless a set of closures (Eddington
coefficients) is specified. We demonstrate that the hemispheric (or
hemi-isotropic) closure naturally derives from the radiative transfer equation
if energy conservation is obeyed, while the Eddington closure produces spurious
enhancements of both reflected light and thermal emission. We concoct recipes
for implementing two-stream radiative transfer in stand-alone numerical
calculations and general circulation models. We use our two-stream solutions to
construct toy models of the runaway greenhouse effect. We present a new
solution for temperature-pressure profiles with a non-constant optical opacity
and elucidate the effects of non-isotropic scattering in the optical and
infrared. We derive generalized expressions for the spherical and Bond albedos
and the photon deposition depth. We demonstrate that the value of the optical
depth corresponding to the photosphere is not always 2/3 (Milne's solution) and
depends on a combination of stellar irradiation, internal heat and the
properties of scattering both in optical and infrared. Finally, we derive
generalized expressions for the total, net, outgoing and incoming fluxes in the
convective regime.Comment: Accepted by ApJS. 23 pages, 11 figures, 3 tables, 158 equations. No
change from previous version except for title (to match ApJS convention
Modelling the 3D Climate of Venus with OASIS
Flexible 3D models to explore the vast diversity of terrestrial planets and
interpret observational data are still in their early stages. In this work, we
present OASIS: a novel and flexible 3D virtual planet laboratory. With OASIS we
envision a platform that couples self-consistently seven individual modules
representing the main physical and chemical processes that shape planetary
environments. Additionally, OASIS is capable of producing simulated spectra
from different instruments and observational techniques. In this work we focus
on the benchmark test of coupling four of the physical modules: fluid dynamics,
radiation, turbulence and surface/soil. To test the OASIS platform, we produced
3D simulations of the Venus climate and its atmospheric circulation and study
how the modeled atmosphere changes with various cloud covers, atmospheric heat
capacity, and surface friction. 3D simulations of Venus are challenging because
they require long integration times with a computationally expensive radiative
transfer code. By comparing OASIS results with observational data, we verify
that the new model is able to successfully simulate Venus. With simulated
spectra produced directly from the 3D simulations, we explore the capabilities
of future missions, like LUVOIR, to observe Venus analogs located at a distance
of 10 pc. With OASIS, we have taken the first steps to build a sophisticated
and very flexible platform capable of studying the environment of terrestrial
planets, which will be an essential tool to characterize observed terrestrial
planets and plan future observations.Comment: MNRAS published versio
THOR 2.0: Major Improvements to the Open-Source General Circulation Model
THOR is the first open-source general circulation model (GCM) developed from
scratch to study the atmospheres and climates of exoplanets, free from Earth-
or Solar System-centric tunings. It solves the general non-hydrostatic Euler
equations (instead of the primitive equations) on a sphere using the
icosahedral grid. In the current study, we report major upgrades to THOR,
building upon the work of Mendon\c{c}a et al. (2016). First, while the
Horizontally Explicit Vertically Implicit (HEVI) integration scheme is the same
as that described in Mendon\c{c}a et al. (2016), we provide a clearer
description of the scheme and improved its implementation in the code. The
differences in implementation between the hydrostatic shallow (HSS),
quasi-hydrostatic deep (QHD) and non-hydrostatic deep (NHD) treatments are
fully detailed. Second, standard physics modules are added: two-stream,
double-gray radiative transfer and dry convective adjustment. Third, THOR is
tested on additional benchmarks: tidally-locked Earth, deep hot Jupiter,
acoustic wave, and gravity wave. Fourth, we report that differences between the
hydrostatic and non-hydrostatic simulations are negligible in the Earth case,
but pronounced in the hot Jupiter case. Finally, the effects of the so-called
"sponge layer", a form of drag implemented in most GCMs to provide numerical
stability, are examined. Overall, these upgrades have improved the flexibility,
user-friendliness, and stability of THOR.Comment: 57 pages, 31 figures, revised, accepted for publication in ApJ
Theory vs practice: synthesis of red lead following ancient recipes
The synthesis of red lead pigment (chemically lead oxide, Pb3O4) was carried out considering different starting lead compounds. The experimental procedure followed was established according to some recipes of ancient painting treatises and the knowledge of the phase transformation of lead oxides. The samples transformation was monitored by X-ray powder diffraction and selected samples were also characterized by scanning electron microscopy. The pure Pb3O4 phase was obtained for the transformation of PbO2 and 2PbCO3·Pb(OH)2. Morphological studies revealed that the material obtained from PbO2 presented the more homogeneous grain size distribution. The transformation of white lead Kremer Pigment resulted in a mixture of Pbr3O4 (major phase) and cerussite (PbCO3), leading to a sample with low crystallinity.info:eu-repo/semantics/publishedVersio
Revisiting the Phase Curves of WASP-43b: Confronting Reanalyzed Spitzer Data with Cloudy Atmospheres
Recently acquired Hubble and Spitzer phase curves of the short-period hot
Jupiter WASP-43b make it an ideal target for confronting theory with data. On
the observational front, we re-analyze the 3.6 and 4.5 m Spitzer phase
curves and demonstrate that our improved analysis better removes residual red
noise due to intra-pixel sensitivity, which leads to greater fluxes emanating
from the nightside of WASP-43b, thus reducing the tension between theory and
data. On the theoretical front, we construct cloudfree and cloudy atmospheres
of WASP-43b using our Global Circulation Model (GCM), THOR, which solves the
non-hydrostatic Euler equations (compared to GCMs that typically solve the
hydrostatic primitive equations). The cloudfree atmosphere produces a
reasonable fit to the dayside emission spectrum. The multi-phase emission
spectra constrain the cloud deck to be confined to the nightside and have a
finite cloud-top pressure. The multi-wavelength phase curves are naturally
consistent with our cloudy atmospheres, except for the 4.5 m phase curve,
which requires the presence of enhanced carbon dioxide in the atmosphere of
WASP-43b. Multi-phase emission spectra at higher spectral resolution, as may be
obtained using the James Webb Space Telescope, and a reflected-light phase
curve at visible wavelengths would further constrain the properties of clouds
in WASP-43b.Comment: Accepted for publication in Ap
Multiple model adaptive control of neuromuscular blockade: Design guidelines and clinical cases
The high level of uncertainty of the dynamic response of patients subject to anaesthesia motivates the use of adaptive control methods. This paper proposes an approach based on Switched Multiple Model Adaptive Control (SMMAC) to tackle this problem in what concerns the control of the neuromuscular blockade level. It is shown how to design the different elements of the SMMAC controller, enhancing the importance of the observer polynomial, that is shown to be instrumental to stabilize the loop. Clinical results using atracurium as blocking agent are reported, thereby illustrating the application of the proposed approach in actual clinical practice
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The new Oxford planetary unified model system for Venus (OPUS-V)
We present a new version of the Oxford Venus GCM, which using our new parameterisations produce a realistic Venus mesosphere atmospheric circulation. We present results that give hints to the formation of global super-rotation
HELIOS-Retrieval: An Open-source, Nested Sampling Atmospheric Retrieval Code, Application to the HR 8799 Exoplanets and Inferred Constraints for Planet Formation
We present an open-source retrieval code named HELIOS-Retrieval (hereafter
HELIOS-R), designed to obtain chemical abundances and temperature-pressure
profiles from inverting the measured spectra of exoplanetary atmospheres. In
the current implementation, we use an exact solution of the radiative transfer
equation, in the pure absorption limit, in our forward model, which allows us
to analytically integrate over all of the outgoing rays (instead of performing
Gaussian quadrature). Two chemistry models are considered: unconstrained
chemistry (where the mixing ratios are treated as free parameters) and
equilibrium chemistry (enforced via analytical formulae, where only the
elemental abundances are free parameters). The nested sampling algorithm allows
us to formally implement Occam's Razor based on a comparison of the Bayesian
evidence between models. We perform a retrieval analysis on the measured
spectra of the HR 8799b, c, d and e directly imaged exoplanets. Chemical
equilibrium is disfavored by the Bayesian evidence for HR 8799b, c and d. We
find supersolar C/O, C/H and O/H values for the outer HR 8799b and c
exoplanets, while the inner HR 8799d and e exoplanets have substellar C/O,
substellar C/H and superstellar O/H values. If these retrieved properties are
representative of the bulk compositions of the exoplanets, then they are
inconsistent with formation via gravitational instability (without late-time
accretion) and consistent with a core accretion scenario in which late-time
accretion of ices occurred differently for the inner and outer exoplanets. For
HR 8799e, we find that spectroscopy in the K band is crucial for constraining
C/O and C/H. HELIOS-R is publicly available as part of the Exoclimes Simulation
Platform (ESP; www.exoclime.org).Comment: 27 pages, 21 figures, 3 tables, published in A
Low Adherence to the Mediterranean Diet Is Associated with Poor Socioeconomic Status and Younger Age: A Cross-Sectional Analysis of the EpiDoC Cohort
Funding: This research was funded by Fundação Ciência e Tecnologia, IP national support through CHRC (UIDP/04923/2020) and through FrailcareAI (DSAIPA/AI/0106/2019).The Mediterranean diet (MD) is recognized as one of the healthiest dietary patterns as it has been consistently associated with several beneficial health outcomes. Adherence to the MD pattern has been decreasing in southern European countries for the last decades, especially among low socioeconomic groups. The aim of this study was to assess the adherence to the MD in Portugal, to evaluate regional differences, and explore associated factors (sociodemographic, economic, and lifestyles behaviors). This study used the third data collection wave of the Epidemiology of Chronic Diseases Cohort Study (EpiDoC 3). MD adherence was assessed using the Portuguese-validated MD adherence score (MEDAS) questionnaire. Non-adjusted and adjusted logistic regression models were used to assess the risk factors for low MD adherence and individual MEDAS items. In this cross-sectional evaluation of the EpiDoC 3 cohort study (n = 5647), 28.8% of the Portuguese population had low adherence to a MD. Azores and Madeira had lower adherence to the MD than the rest of the country. Younger individuals in lower income categories (e.g., ORfinding it very difficult = 1.48; 95% CI 1.16–1.91) and with a lower educational level (e.g., OR0–4 years = 2.63; 95% CI 2.09–3.32) had higher odds of having a lower adherence to the MD. Portuguese adults have a high prevalence of low adherence to the MD, especially among those who are younger and have lower socioeconomic status. Public health policies to promote adherence to the MD should pay special attention to these groups.publishersversionpublishe
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