757 research outputs found
Mercury-T: a new code to study tidally evolving multi-planet systems: applications to Kepler-62
A large proportion of observed planetary systems contain several planets in a compact orbital configuration, and often harbor at least one close-in object. These systems are then most likely tidally evolving. We investigate how the effects of planet-planet interactions influence the tidal evolution of planets. We introduce for that purpose a new open-source addition to the Mercury N-body code, Mercury-T, which takes into account tides, general relativity and the effect of rotation-induced flattening in order to simulate the dynamical and tidal evolution of multi-planet systems. It uses a standard equilibrium tidal model, the constant time lag model. Besides, the evolution of the radius of several host bodies has been implemented (brown dwarfs, M-dwarfs of mass 0.1 M-circle dot, Sun-like stars, Jupiter). We validate the new code by comparing its output for one-planet systems to the secular equations results. We find that this code does respect the conservation of total angular momentum. We applied this new tool to the planetary system Kepler-62. We find that tides influence the stability of the system in some cases. We also show that while the four inner planets of the systems are likely to have slow rotation rates and small obliquities, the fifth planet could have a fast rotation rate and a high obliquity. This means that the two habitable zone planets of this system, Kepler-62e ad f are likely to have very different climate features, and this of course would influence their potential at hosting surface liquid water
Economic Evaluation of Conservation Concepts for Municipal Water Systems
Five concepts for conservation of municipal water supply are analyzed from an economic efficiency perspectice. They include: 1) seasonal pricing (for reduction of peak period water use), 2) dual water systems (separate high quality drinking water and untreated outdoor irrigation systems), 3) imported water transmission facility capacity optimization, 4) flow restricting devices, and 5) short-term rationing concepts. Optimization models, including generalized model generators, were developed for analysis of the first three concepts and demonstrated by applications to cities in Utah. The flow restricting device and short-term rationsing concept analyses applied approaches taken from the literature to example sites in Utah. The final chapter is a comparison of results and summary of conditions which favor each approach to conservation. Conclusions include: Seasonal pricing was demonstarted to reduce peak period water use but is not justified in Salt Lake City because the added cost of metering exceeds the additional benefits. Dual water systems are potentially an important concept for matching various qualities of water with appropriate uses and producing net economic benefits. Determination of capacity of an imported water facility is dominated more by the decision maker\u27s attitude toward risk than by pricing policy. Flow restricting devices produce economic benefits only if the change in quality of service is ignored. Price elasticity is much lower during a drought than during normal conditions
Quantum Transport in Chemically-modified Two-Dimensional Graphene: From Minimal Conductivity to Anderson Localization
An efficient computational methodology is used to explore charge transport
properties in chemically-modified (and randomly disordered) graphene-based
materials. The Hamiltonians of various complex forms of graphene are
constructed using tight-binding models enriched by first-principles
calculations. These atomistic models are further implemented into a real-space
order-N Kubo-Greenwood approach, giving access to the main transport length
scales (mean free paths, localization lengths) as a function of defect density
and charge carrier energy. An extensive investigation is performed for epoxide
impurities with specific discussions on both the existence of a minimum
semi-classical conductivity and a crossover between weak to strong localization
regime. The 2D generalization of the Thouless relationship linking transport
length scales is here illustrated based on a realistic disorder model.Comment: 14 pages, 18 figures, submitte
Efecto de la inoculación al cultivo antecesor sobre la nodulación de la soja, en suelos de desmonte.
En los suelos de Chaco y Corrientes recién desmontados o bien en suelos de muchos años de agricultura sin cultivo de soja, la nodulación de esta leguminosa es deficiente. Por lo expuesto se necesitan buscar tecnologías económicamente rentables para el aumento de la infectividad de soja con Bradyrhizobium japonicum en estas situaciones problemas. El objetivo del presente trabajo fue determinar si la nodulación de plantas de soja es afectada por la inoculación del cultivo antecesor con B .japonicum. El ensayo se realizó en condiciones de invernadero, utilizando como sustrato el suelo de un lote recién desmontado ubicado en el Dorsal Agrícola Chaqueño. Se sembró maíz como antecesor. Los tratamientos fueron: 1– antecesor sin inocular– soja sin inocular; 2– antecesor sin inocular – soja inoculada; 3– antecesor inoculado– soja sin inocular; 4– antecesor inoculado – soja inoculada; 5– antecesor doble inoculación– soja sin inocular; 6– antecesor doble inoculación – soja inoculada. Luego de cincuenta días, las plantas de soja inoculadas en las que el cultivo antecesor no fue inoculado (tratamiento 2) presentaron los mayores valores de peso seco aéreo, mientras que las plantas de soja no inoculadas cuyo cultivo antecesor fue inoculado dos veces (tratamiento 5) presentaron los menores valores de peso seco aéreo y peso seco radicular. Los tratamientos inoculados en soja presentaron mayor infectividad, independientemente de la inoculación del cultivo anterior. Si bien son necesarios posteriores ensayos, en el presente trabajo la inoculación del cultivo antecesor no afectó las variables analizadas relacionadas con la nodulación de la soja
Increased insolation threshold for runaway greenhouse processes on Earth like planets
Because the solar luminosity increases over geological timescales, Earth
climate is expected to warm, increasing water evaporation which, in turn,
enhances the atmospheric greenhouse effect. Above a certain critical
insolation, this destabilizing greenhouse feedback can "runaway" until all the
oceans are evaporated. Through increases in stratospheric humidity, warming may
also cause oceans to escape to space before the runaway greenhouse occurs. The
critical insolation thresholds for these processes, however, remain uncertain
because they have so far been evaluated with unidimensional models that cannot
account for the dynamical and cloud feedback effects that are key stabilizing
features of Earth's climate. Here we use a 3D global climate model to show that
the threshold for the runaway greenhouse is about 375 W/m, significantly
higher than previously thought. Our model is specifically developed to quantify
the climate response of Earth-like planets to increased insolation in hot and
extremely moist atmospheres. In contrast with previous studies, we find that
clouds have a destabilizing feedback on the long term warming. However,
subsident, unsaturated regions created by the Hadley circulation have a
stabilizing effect that is strong enough to defer the runaway greenhouse limit
to higher insolation than inferred from 1D models. Furthermore, because of
wavelength-dependent radiative effects, the stratosphere remains cold and dry
enough to hamper atmospheric water escape, even at large fluxes. This has
strong implications for Venus early water history and extends the size of the
habitable zone around other stars.Comment: Published in Nature. Online publication date: December 12, 2013.
Accepted version before journal editing and with Supplementary Informatio
Tidal decay and orbital circularization in close-in two-planet systems
The motion of two planets around a Sun-like star under the combined effects
of mutual interaction and tidal dissipation is investigated. The secular
behaviour of the system is analyzed using two different approaches. First, we
solve the exact equations of motion through the numerical simulation of the
system evolution. In addition to the orbital decay and circularization, we show
that the final configuration of the system is affected by the shrink of the
inner orbit. Our second approach consist in the analysis of the stationary
solutions of mean equations of motion based on a Hamiltonian formalism. We
consider the case of a hot super-Earth planet with a more massive outer
companion. As a real example, the CoRoT-7 system is analyzed solving the exact
and mean equations of motion. The star-planet tidal interaction produces
orbital decay and circularization of the orbit of CoRoT-7b. In addition, the
long-term tidal evolution is such that the eccentricity of CoRoT-7c is also
circularized and a pair of final circular orbits is obtained. A curve in the
space of eccentricities can be constructed through the computation of
stationary solutions of mean equations including dissipation. The application
to CoRoT-7 system shows that the stationary curve agrees with the result of
numerical simulations of exact equations. A similar investigation performed in
a super-Earth-Jupiter two-planet system shows that the doubly circular state is
accelerated when there is a significant orbital migration of the inner planet,
in comparison with previous results were migration is neglected.Comment: Accepted for publication in MNRAS; 10 pages, 13 figure
Analysis of new high-precision transit light curves of WASP-10 b: starspot occultations, small planetary radius, and high metallicity
The WASP-10 planetary system is intriguing because different values of radius
have been reported for its transiting exoplanet. The host star exhibits
activity in terms of photometric variability, which is caused by the rotational
modulation of the spots. Moreover, a periodic modulation has been discovered in
transit timing of WASP-10 b, which could be a sign of an additional body
perturbing the orbital motion of the transiting planet. We attempt to refine
the physical parameters of the system, in particular the planetary radius,
which is crucial for studying the internal structure of the transiting planet.
We also determine new mid-transit times to confirm or refute observed anomalies
in transit timing. We acquired high-precision light curves for four transits of
WASP-10 b in 2010. Assuming various limb-darkening laws, we generated best-fit
models and redetermined parameters of the system. The prayer-bead method and
Monte Carlo simulations were used to derive error estimates. Three transit
light curves exhibit signatures of the occultations of dark spots by the planet
during its passage across the stellar disk. The influence of stellar activity
on transit depth is taken into account while determining system parameters. The
radius of WASP-10 b is found to be no greater than 1.03 Jupiter radii, a value
significantly smaller than most previous studies indicate. We calculate
interior structure models of the planet, assuming a two-layer structure with
one homogeneous envelope atop a rock core. The high value of the WASP-10 b's
mean density allows one to consider the planet's internal structure including
270 to 450 Earth masses of heavy elements. Our new mid-transit times confirm
that transit timing cannot be explained by a constant period if all literature
data points are considered. They are consistent with the ephemeris assuming a
periodic variation of transit timing...Comment: Accepted for publication in A&
Atmospheric Evolution
Earth's atmosphere has evolved as volatile species cycle between the
atmosphere, ocean, biomass and the solid Earth. The geochemical, biological and
astrophysical processes that control atmospheric evolution are reviewed from an
"Earth Systems" perspective, with a view not only to understanding the history
of Earth, but also to generalizing to other solar system planets and
exoplanets.Comment: 34 pages, 3 figures, 2 tables. Accepted as a chapter in
"Encyclopaedia of Geochemistry", Editor Bill White, Springer-Nature, 201
A binary merger origin for inflated hot Jupiter planets
We hypothesize that hot Jupiters with inflated sizes represent a separate
planet formation channel,the merging of two low-mass stars. We show that the
abundance and properties of W UMa stars and low mass detached binaries are
consistent with their being possible progenitors. The degree of inflation of
the transiting hot Jupiters correlates with their expected spiral-in life time
by tidal dissipation, and this could indicate youth if the stellar dissipation
parameter Q'* is sufficiently low. Several Jupiter-mass planets can form in the
massive compact disk formed in a merger event. Gravitational scattering between
them can explain the high incidence of excentric, inclined, and retrograde
orbits. If the population of inflated planets is indeed formed by a merger
process, their frequency should be much higher around blue stragglers than
around T Tauri stars.Comment: Accepted for publication in A&
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