104 research outputs found
Environmental impact of combined ITS traffic management strategies
Transport was responsible for 20% of the total greenhouse gas emissions in Europe during 2011 (European Environmental Agency 2013) with road transport being the key contributor. To tackle this, targets have been established in Europe and worldwide to curb transport emissions. This poses a significant challenge on Local Government and transport operators who need to identify a set of effective measures to reduce the environmental impact of road transport and at the same time keep the traffic smooth. Of the road transport pollutants, this paper considers NOx, CO2 and black carbon (BC). A particular focus is put on black carbon, which is formed through incomplete combustion of carboneous materials, as it has a significant impact on the Earth’s climate system. It absorbs solar radiation, influences cloud processes, and alters the melting of snow and ice cover (Bond et al. 2013). BC also causes serious health concerns: black carbon is associated with asthma and other respiratory problems, heart attacks and lung cancer (Sharma 2010; United States Environmental Protection Agency 2012). Since BC emissions are mainly produced during the decelerating and accelerating phases (Zhang et al. 2009), ITS actions able to reduce stop&go phases have the potential to reduce BC emissions. This paper investigates the effectiveness of combined ITS actions in urban context in reducing CO2 and BC emissions and improving traffic conditions
Discovery of a Transiting Planet Near the Snow-Line
In most theories of planet formation, the snow-line represents a boundary
between the emergence of the interior rocky planets and the exterior ice
giants. The wide separation of the snow-line makes the discovery of transiting
worlds challenging, yet transits would allow for detailed subsequent
characterization. We present the discovery of Kepler-421b, a Uranus-sized
exoplanet transiting a G9/K0 dwarf once every 704.2 days in a near-circular
orbit. Using public Kepler photometry, we demonstrate that the two observed
transits can be uniquely attributed to the 704.2 day period. Detailed light
curve analysis with BLENDER validates the planetary nature of Kepler-421b to >4
sigmas confidence. Kepler-421b receives the same insolation as a body at ~2AU
in the Solar System and for a Uranian albedo would have an effective
temperature of ~180K. Using a time-dependent model for the protoplanetary disk,
we estimate that Kepler-421b's present semi-major axis was beyond the snow-line
after ~3Myr, indicating that Kepler-421b may have formed at its observed
location.Comment: 14 pages, 10 figures, 3 tables. Accepted in Ap
Nitrogen sequestration under long-term paddy management in soils developed on contrasting parent material
All Six Planets Known to Orbit Kepler-11 Have Low Densities
The Kepler-11 planetary system contains six transiting planets ranging in
size from 1.8 to 4.2 times the radius of Earth. Five of these planets orbit in
a tightly-packed configuration with periods between 10 and 47 days. We perform
a dynamical analysis of the system based upon transit timing variations
observed in more than three years of \ik photometric data. Stellar parameters
are derived using a combination of spectral classification and constraints on
the star's density derived from transit profiles together with planetary
eccentricity vectors provided by our dynamical study. Combining masses of the
planets relative to the star from our dynamical study and radii of the planets
relative to the star from transit depths together with deduced stellar
properties yields measurements of the radii of all six planets, masses of the
five inner planets, and an upper bound to the mass of the outermost planet,
whose orbital period is 118 days. We find mass-radius combinations for all six
planets that imply that substantial fractions of their volumes are occupied by
constituents that are less dense than rock. The Kepler-11 system contains the
lowest mass exoplanets for which both mass and radius have been measured.Comment: 39 pages, 10 figure
Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone
We present an investigation of twelve candidate transiting planets from
Kepler with orbital periods ranging from 34 to 207 days, selected from initial
indications that they are small and potentially in the habitable zone (HZ) of
their parent stars. Few of these objects are known. The expected Doppler
signals are too small to confirm them by demonstrating that their masses are in
the planetary regime. Here we verify their planetary nature by validating them
statistically using the BLENDER technique, which simulates large numbers of
false positives and compares the resulting light curves with the Kepler
photometry. This analysis was supplemented with new follow-up observations
(high-resolution optical and near-infrared spectroscopy, adaptive optics
imaging, and speckle interferometry), as well as an analysis of the flux
centroids. For eleven of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01,
3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the
likelihood they are true planets is far greater than that of a false positive,
to a confidence level of 99.73% (3 sigma) or higher. For KOI-4427.01 the
confidence level is about 99.2% (2.6 sigma). With our accurate characterization
of the GKM host stars, the derived planetary radii range from 1.1 to 2.7
R_Earth. All twelve objects are confirmed to be in the HZ, and nine are small
enough to be rocky. Excluding three of them that have been previously validated
by others, our study doubles the number of known rocky planets in the HZ.
KOI-3284.01 (Kepler-438b) and KOI-4742.01 (Kepler-442b) are the planets most
similar to the Earth discovered to date when considering their size and
incident flux jointly.Comment: 27 pages in emulateapj format, including tables and figures. To
appear in The Astrophysical Journa
An ancient extrasolar system with five sub-Earth-size planets
The chemical composition of stars hosting small exoplanets (with radii less
than four Earth radii) appears to be more diverse than that of gas-giant hosts,
which tend to be metal-rich. This implies that small, including Earth-size,
planets may have readily formed at earlier epochs in the Universe's history
when metals were more scarce. We report Kepler spacecraft observations of
Kepler-444, a metal-poor Sun-like star from the old population of the Galactic
thick disk and the host to a compact system of five transiting planets with
sizes between those of Mercury and Venus. We validate this system as a true
five-planet system orbiting the target star and provide a detailed
characterization of its planetary and orbital parameters based on an analysis
of the transit photometry. Kepler-444 is the densest star with detected
solar-like oscillations. We use asteroseismology to directly measure a precise
age of 11.2+/-1.0 Gyr for the host star, indicating that Kepler-444 formed when
the Universe was less than 20% of its current age and making it the oldest
known system of terrestrial-size planets. We thus show that Earth-size planets
have formed throughout most of the Universe's 13.8-billion-year history,
leaving open the possibility for the existence of ancient life in the Galaxy.
The age of Kepler-444 not only suggests that thick-disk stars were among the
hosts to the first Galactic planets, but may also help to pinpoint the
beginning of the era of planet formation.Comment: Accepted for publication in ApJ; 42 pages, 10 figures, 4 table
KOI-3158: The oldest known system of terrestrial-size planets
The first discoveries of exoplanets around Sun-like stars have fueled efforts
to find ever smaller worlds evocative of Earth and other terrestrial planets in
the Solar System. While gas-giant planets appear to form preferentially around
metal-rich stars, small planets (with radii less than four Earth radii) can
form under a wide range of metallicities. This implies that small, including
Earth-size, planets may have readily formed at earlier epochs in the Universe's
history when metals were far less abundant. We report Kepler spacecraft
observations of KOI-3158, a metal-poor Sun-like star from the old population of
the Galactic thick disk, which hosts five planets with sizes between Mercury
and Venus. We used asteroseismology to directly measure a precise age of
11.2+/-1.0 Gyr for the host star, indicating that KOI-3158 formed when the
Universe was less than 20% of its current age and making it the oldest known
system of terrestrial-size planets. We thus show that Earth-size planets have
formed throughout most of the Universe's 13.8-billion-year history, providing
scope for the existence of ancient life in the Galaxy.Comment: Submitted to EPJ Web of Conferences, to appear in the Proceedings of
the 3rd CoRoT Symposium, Kepler KASC7 joint meeting; 4 pages, 1 figur
Masses, radii, and orbits of small Kepler planets : The transition from gaseous to rocky planets
We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).Peer reviewedFinal Accepted Versio
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