92 research outputs found
An Exploratory Investigation of Public Perceptions Towards Key Benefits and Concerns from the Future Use of Flying Cars
The imminent introduction of flying cars in the traffic fleet is anticipated to modify the mobility patterns of urban commuters. Flying cars' hybrid operation on the ground and in the air, in conjunction with their (semi-) automated capabilities, may lead to more appealing trip considerations, such as travel time, fuel consumption, or environmental emissions, as well as to the emergence of new sources of concerns for the potential users. In this context, the future adoption of flying cars is directly associated with individuals' perceptions of the benefits and concerns arising from the use of flying cars. This paper aims to identify the perceptual patterns of individuals towards travel time, cost and environmental benefits, as well as towards challenges arising from key flying cars operational characteristics. To that end, grouped random parameters bivariate probit models of individuals' perceptions are estimated using data collected from an online survey of 692 individuals. The statistical analysis shows that a number of socio-demographic, behavioral, and attitudinal characteristics affect respondents' expectations and concerns towards the adoption and implementation of flying cars. Even though individuals' perceptions are anticipated to undergo substantial changes until the introduction of flying cars in the traffic fleet, the findings of this work may shed more light on perceptual nuances with critical effect on public interest about the adoption of flying cars
Precision asteroseismology of the pulsating white dwarf GD 1212 using a two-wheel-controlled Kepler spacecraft
We present a preliminary analysis of the cool pulsating white dwarf GD 1212,
enabled by more than 11.5 days of space-based photometry obtained during an
engineering test of the two-reaction-wheel-controlled Kepler spacecraft. We
detect at least 19 independent pulsation modes, ranging from 828.2-1220.8 s,
and at least 17 nonlinear combination frequencies of those independent
pulsations. Our longest uninterrupted light curve, 9.0 days in length,
evidences coherent difference frequencies at periods inaccessible from the
ground, up to 14.5 hr, the longest-period signals ever detected in a pulsating
white dwarf. These results mark some of the first science to come from a
two-wheel-controlled Kepler spacecraft, proving the capability for
unprecedented discoveries afforded by extending Kepler observations to the
ecliptic.Comment: 8 pages, 4 figures, accepted for publication in The Astrophysical
Journa
An exploratory empirical analysis of willingness to hire and pay for flying taxis and shared flying car services
A new transportation mode that can simultaneously operate on land and in the air, namely the flying cars, is anticipated to penetrate the automobile fleet between 2020 and 2025. Due to their flexible mobility patterns and automated operational characteristics, flying taxi and shared flying car services are expected to expand the existing shared mobility services (such as Uber, Lyft, and similar services) of the urban transportation network. Despite their forthcoming introduction in the shared mobility market, public perceptions and expectations about these services have not been investigated in travel demand literature. This study aims to provide an exploratory analysis of public willingness to hire and pay for flying taxis and shared flying car services, and to identify the determinants of the willingness to hire and pay for such services. Using data collected from an online survey, individuals’ willingness to hire and to pay for flying taxi and shared flying car services are statistically modeled within a correlated grouped random parameters bivariate probit framework. The analysis shows that various socio-demographic characteristics and individuals’ opinions towards the perceived benefits and challenges of flying cars affect public willingness to hire and pay for flying taxi and shared flying car services. Even though the awareness about the operation of flying taxis and shared flying car services is possibly limited in the public sphere, the findings of this study can provide insights into the challenges that policymakers, manufacturing companies, and shared mobility providers will face with the introduction of such flying car services in the transportation networks
Analysis of Safety Benefits and Security Concerns from the Use of Autonomous Vehicles: A Grouped Random Parameters Bivariate Probit Approach with Heterogeneity in Means
This paper investigates public perceptions towards potential safety benefits, and safety- and security-related concerns from the future use of autonomous vehicles by utilizing data collected from an online survey. The survey includes responses from 584 individuals from the United States, who responded to a varying range of questions related to autonomous vehicles and their usage. The subsequent exploratory statistical analysis is conducted by employing a novel method, namely the grouped random parameters bivariate probit model with heterogeneity in means. The proposed method accounts for the challenges stemming from the presence of multiple layers of unobserved heterogeneity in the data, and simultaneously offers more insightful results. From the analysis, several socio-demographic characteristics, and driving attitude related characteristics and opinions were found to affect the perceptions towards the safety and security related aspects of autonomous vehicles. The heterogeneity in means approach revealed distinct individual-specific characteristics that affect the peak of the distribution of the parameter density function of the random parameters, adding further clarity to the understanding of the factors affecting individuals’ perceptions towards autonomous vehicles. The findings from this study suggest the ongoing evaluation of public perceptions, and reinforce the requirement of analyzing temporal variations in public perceptions. This can, in turn, aid regulatory and governance entities and autonomous vehicle manufacturers to adapt their strategies and implementation plans accordingly
Terrestrial Planet Occurrence Rates for the Kepler GK Dwarf Sample
We measure planet occurrence rates using the planet candidates discovered by
the Q1-Q16 Kepler pipeline search. This study examines planet occurrence rates
for the Kepler GK dwarf target sample for planet radii, 0.75<Rp<2.5 Rearth, and
orbital periods, 50<Porb<300 days, with an emphasis on a thorough exploration
and identification of the most important sources of systematic uncertainties.
Integrating over this parameter space, we measure an occurrence rate of F=0.77
planets per star, with an allowed range of 0.3<F<1.9. The allowed range takes
into account both statistical and systematic uncertainties, and values of F
beyond the allowed range are significantly in disagreement with our analysis.
We generally find higher planet occurrence rates and a steeper increase in
planet occurrence rates towards small planets than previous studies of the
Kepler GK dwarf sample. Through extrapolation, we find that the one year
orbital period terrestrial planet occurrence rate, zeta_1=0.1, with an allowed
range of 0.01<zeta_1<2, where zeta_1 is defined as the number of planets per
star within 20% of the Rp and Porb of Earth. For G dwarf hosts, the zeta_1
parameter space is a subset of the larger eta_earth parameter space, thus
zeta_1 places a lower limit on eta_earth for G dwarf hosts. From our analysis,
we identify the leading sources of systematics impacting Kepler occurrence rate
determinations as: reliability of the planet candidate sample, planet radii,
pipeline completeness, and stellar parameters.Comment: 19 Pages, 17 Figures, Submitted ApJ. Python source to support Kepler
pipeline completeness estimates available at
http://github.com/christopherburke/KeplerPORTs
Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems
The Kepler mission has discovered over 2500 exoplanet candidates in the first
two years of spacecraft data, with approximately 40% of them in candidate
multi-planet systems. The high rate of multiplicity combined with the low rate
of identified false-positives indicates that the multiplanet systems contain
very few false-positive signals due to other systems not gravitationally bound
to the target star (Lissauer, J. J., et al., 2012, ApJ 750, 131). False
positives in the multi- planet systems are identified and removed, leaving
behind a residual population of candidate multi-planet transiting systems
expected to have a false-positive rate less than 1%. We present a sample of 340
planetary systems that contain 851 planets that are validated to substantially
better than the 99% confidence level; the vast majority of these have not been
previously verified as planets. We expect ~2 unidentified false-positives
making our sample of planet very reliable. We present fundamental planetary
properties of our sample based on a comprehensive analysis of Kepler light
curves and ground-based spectroscopy and high-resolution imaging. Since we do
not require spectroscopy or high-resolution imaging for validation, some of our
derived parameters for a planetary system may be systematically incorrect due
to dilution from light due to additional stars in the photometric aperture.
None the less, our result nearly doubles the number of verified exoplanets.Comment: 138 pages, 8 Figures, 5 Tables. Accepted for publications in the
Astrophysical Journa
Planetary Candidates Observed by Kepler IV: Planet Sample From Q1-Q8 (22 Months)
We provide updates to the Kepler planet candidate sample based upon nearly
two years of high-precision photometry (i.e., Q1-Q8). From an initial list of
nearly 13,400 Threshold Crossing Events (TCEs), 480 new host stars are
identified from their flux time series as consistent with hosting transiting
planets. Potential transit signals are subjected to further analysis using the
pixel-level data, which allows background eclipsing binaries to be identified
through small image position shifts during transit. We also re-evaluate Kepler
Objects of Interest (KOI) 1-1609, which were identified early in the mission,
using substantially more data to test for background false positives and to
find additional multiple systems. Combining the new and previous KOI samples,
we provide updated parameters for 2,738 Kepler planet candidates distributed
across 2,017 host stars. From the combined Kepler planet candidates, 472 are
new from the Q1-Q8 data examined in this study. The new Kepler planet
candidates represent ~40% of the sample with Rp~1 Rearth and represent ~40% of
the low equilibrium temperature (Teq<300 K) sample. We review the known biases
in the current sample of Kepler planet candidates relevant to evaluating planet
population statistics with the current Kepler planet candidate sample.Comment: 12 pages, 8 figures, Accepted ApJ Supplemen
Two Earth-sized planets orbiting Kepler-20
Since the discovery of the first extrasolar giant planets around Sun-like
stars, evolving observational capabilities have brought us closer to the
detection of true Earth analogues. The size of an exoplanet can be determined
when it periodically passes in front of (transits) its parent star, causing a
decrease in starlight proportional to its radius. The smallest exoplanet
hitherto discovered has a radius 1.42 times that of the Earth's radius (R
Earth), and hence has 2.9 times its volume. Here we report the discovery of two
planets, one Earth-sized (1.03R Earth) and the other smaller than the Earth
(0.87R Earth), orbiting the star Kepler-20, which is already known to host
three other, larger, transiting planets. The gravitational pull of the new
planets on the parent star is too small to measure with current
instrumentation. We apply a statistical method to show that the likelihood of
the planetary interpretation of the transit signals is more than three orders
of magnitude larger than that of the alternative hypothesis that the signals
result from an eclipsing binary star. Theoretical considerations imply that
these planets are rocky, with a composition of iron and silicate. The outer
planet could have developed a thick water vapour atmosphere.Comment: Letter to Nature; Received 8 November; accepted 13 December 2011;
Published online 20 December 201
Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates
We present the discovery of the Kepler-20 planetary system, which we
initially identified through the detection of five distinct periodic transit
signals in the Kepler light curve of the host star 2MASSJ19104752+4220194. We
find a stellar effective temperature Teff=5455+-100K, a metallicity of
[Fe/H]=0.01+-0.04, and a surface gravity of log(g)=4.4+-0.1. Combined with an
estimate of the stellar density from the transit light curves we deduce a
stellar mass of Mstar=0.912+-0.034 Msun and a stellar radius of
Rstar=0.944^{+0.060}_{-0.095} Rsun. For three of the transit signals, our
results strongly disfavor the possibility that these result from astrophysical
false positives. We conclude that the planetary scenario is more likely than
that of an astrophysical false positive by a factor of 2e5 (Kepler-20b), 1e5
(Kepler-20c), and 1.1e3 (Kepler-20d), sufficient to validate these objects as
planetary companions. For Kepler-20c and Kepler-20d, the blend scenario is
independently disfavored by the achromaticity of the transit: From Spitzer data
gathered at 4.5um, we infer a ratio of the planetary to stellar radii of
0.075+-0.015 (Kepler-20c) and 0.065+-0.011 (Kepler-20d), consistent with each
of the depths measured in the Kepler optical bandpass. We determine the orbital
periods and physical radii of the three confirmed planets to be 3.70d and
1.91^{+0.12}_{-0.21} Rearth for Kepler-20b, 10.85 d and 3.07^{+0.20}_{-0.31}
Rearth for Kepelr-20c, and 77.61 d and 2.75^{+0.17}_{-0.30} Rearth for
Kepler-20d. From multi-epoch radial velocities, we determine the masses of
Kepler-20b and Kepler-20c to be 8.7\+-2.2 Mearth and 16.1+-3.5 Mearth,
respectively, and we place an upper limit on the mass of Kepler-20d of 20.1
Mearth (2 sigma).Comment: accepted by ApJ, 58 pages, 12 figures revised Jan 2012 to correct
table 2 and clarify planet parameter extractio
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