8,879 research outputs found
Updated bathymetry of the Anegada-Jungfern Passage complex and implications for Atlantic inflow to the abyssal Caribbean Sea
Recent bathymetric, hydrographic and direct velocity measurements indicate that a previously unexplored deep passage in the northeastern Caribbean Sea may play a significant role in the abyssal ventilation of this basin. The Anegada-Jungfern Passage complex has long been recognized as the sole pathway for deep Atlantic inflow to the eastern Caribbean. The Anegada Passage (sill depth 1915 m) connects the Atlantic Ocean with the small Virgin Islands Basin, while Jungfern Passage (sill depth 1815 m) connects the latter with the large and deep Venezuela Basin comprising the eastern third of the Caribbean Sea. In the region of Jungfern Passage recent bathymetric measurements reveal additional, shallower routes for Atlantic inflow at depths between 1710 and 1630 m. Despite the relatively shallow controlling depths of these passages, direct measurements of velocity and watermass properties reveal an active inflow of water of Atlantic origin. Bathymetric and other oceanographic observations indicate that the previously unexplored Grappler Channel (sill depth 1710 m; located just west of Jungfern Passage) is responsible for up to 20% of the total inflow to the abyssal Caribbean from the mid-depth Atlantic (about 0.2 Sv)
Follow-Up Observations of PTFO 8-8695: A 3 MYr Old T-Tauri Star Hosting a Jupiter-mass Planetary Candidate
We present Spitzer 4.5\micron\ light curve observations, Keck NIRSPEC radial
velocity observations, and LCOGT optical light curve observations of
PTFO~8-8695, which may host a Jupiter-sized planet in a very short orbital
period (0.45 days). Previous work by \citet{vaneyken12} and \citet{barnes13}
predicts that the stellar rotation axis and the planetary orbital plane should
precess with a period of days. As a consequence, the observed
transits should change shape and depth, disappear, and reappear with the
precession. Our observations indicate the long-term presence of the transit
events ( years), and that the transits indeed do change depth, disappear
and reappear. The Spitzer observations and the NIRSPEC radial velocity
observations (with contemporaneous LCOGT optical light curve data) are
consistent with the predicted transit times and depths for the $M_\star = 0.34\
M_\odot$ precession model and demonstrate the disappearance of the transits. An
LCOGT optical light curve shows that the transits do reappear approximately 1
year later. The observed transits occur at the times predicted by a
straight-forward propagation of the transit ephemeris. The precession model
correctly predicts the depth and time of the Spitzer transit and the lack of a
transit at the time of the NIRSPEC radial velocity observations. However, the
precession model predicts the return of the transits approximately 1 month
later than observed by LCOGT. Overall, the data are suggestive that the
planetary interpretation of the observed transit events may indeed be correct,
but the precession model and data are currently insufficient to confirm firmly
the planetary status of PTFO~8-8695b.Comment: Accepted for publication in The Astrophysical Journa
The Transit Light Curve Project. IX. Evidence for a Smaller Radius of the Exoplanet XO-3b
We present photometry of 13 transits of XO-3b, a massive transiting planet on
an eccentric orbit. Previous data led to two inconsistent estimates of the
planetary radius. Our data strongly favor the smaller radius, with increased
precision: R_p = 1.217 +/- 0.073 R_Jup. A conflict remains between the mean
stellar density determined from the light curve, and the stellar surface
gravity determined from the shapes of spectral lines. We argue the light curve
should take precedence, and revise the system parameters accordingly. The
planetary radius is about 1 sigma larger than the theoretical radius for a
hydrogen-helium planet of the given mass and insolation. To help in planning
future observations, we provide refined transit and occultation ephemerides.Comment: To appear in ApJ [22 pages
Biodiversity Gains? The Debate on Changes in Local- vs Global-Scale Species Richness
Editorial: Do changes in biodiversity at local scales reflect the declines seen at global scales? This debate dates back at least 15 years..
Tri-Rotor Aircraft Capable of Vertical Takeoff and Landing and Transitioning to Forward Flight
Systems, methods, and devices provide a vehicle, such as an aircraft, with rotors configured to function as a tri-copter for vertical takeoff and landing ("VTOL") and a fixed-wing vehicle for forward flight. One rotor may be mounted at a front of the vehicle fuselage on a hinged structure controlled by an actuator to tilt from horizontal to vertical positions. Two additional rotors may be mounted on the horizontal surface of the vehicle tail structure with rotor axes oriented vertically to the fuselage. For forward flight of the vehicle, the front rotor may be rotated down such that the front rotor axis may be oriented horizontally along the fuselage and the front rotor may act as a propeller. For vertical flight, the front rotor may be rotated up such that the front rotor axis may be oriented vertically to the fuselage, while the tail rotors may be activated
White-light flares on cool stars in the Kepler Quarter 1 Data
We present the results of a search for white light flares on the ~23,000 cool
dwarfs in the Kepler Quarter 1 long cadence data. We have identified 373
flaring stars, some of which flare multiple times during the observation
period. We calculate relative flare energies, flare rates and durations, and
compare these with the quiescent photometric variability of our sample. We find
that M dwarfs tend to flare more frequently but for shorter durations than K
dwarfs, and that they emit more energy relative to their quiescent luminosity
in a given flare than K dwarfs. Stars that are more photometrically variable in
quiescence tend to emit relatively more energy during flares, but variability
is only weakly correlated with flare frequency. We estimate distances for our
sample of flare stars and find that the flaring fraction agrees well with other
observations of flare statistics for stars within 300 pc above the Galactic
Plane. These observations provide a more rounded view of stellar flares by
sampling stars that have not been pre-selected by their activity, and are
informative for understanding the influence of these flares on planetary
habitability.Comment: 42 pages, 10 figures, 2 tables; Accepted for publication in the
Astronomical Journa
X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics
We study the spectral and temporal behavior of X-ray flares from the active
M-dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare
parameters by fitting an empirical function which characterizes the amplitude,
shape, and scale. The flares range from very short (<1 ks) to long (10 ks)
duration events with a range of shapes and amplitudes for all durations. We
extract spectra for composite flares to study their mean evolution and to
compare flares of different lengths. Evolution of spectral features in the
density-temperature plane shows probable sustained heating. The short flares
are significantly hotter than the longer flares. We determined an upper limit
to the Fe K fluorescent flux, the best fit value being close to what is
expected for compact loops.Comment: 9 pages; 9 figures; latex/emulateapj style; Submitted to The
Astrophysical Journa
Disk Imaging Survey of Chemistry with SMA: II. Southern Sky Protoplanetary Disk Data and Full Sample Statistics
This is the second in a series of papers based on data from DISCS, a
Submillimeter Array observing program aimed at spatially and spectrally
resolving the chemical composition of 12 protoplanetary disks. We present data
on six Southern sky sources - IM Lup, SAO 206462 (HD 135344b), HD 142527, AS
209, AS 205 and V4046 Sgr - which complement the six sources in the Taurus star
forming region reported previously. CO 2-1 and HCO+ 3-2 emission are detected
and resolved in all disks and show velocity patterns consistent with Keplerian
rotation. Where detected, the emission from DCO+ 3-2, N2H+ 3-2, H2CO 3-2 and
4-3,HCN 3-2 and CN 2-1 are also generally spatially resolved. The detection
rates are highest toward the M and K stars, while the F star SAO 206462 has
only weak CN and HCN emission, and H2CO alone is detected toward HD 142527.
These findings together with the statistics from the previous Taurus disks,
support the hypothesis that high detection rates of many small molecules depend
on the presence of a cold and protected disk midplane, which is less common
around F and A stars compared to M and K stars. Disk-averaged variations in the
proposed radiation tracer CN/HCN are found to be small, despite two orders of
magnitude range of spectral types and accretion rates. In contrast, the
resolved images suggest that the CN/HCN emission ratio varies with disk radius
in at least two of the systems. There are no clear observational differences in
the disk chemistry between the classical/full T Tauri disks and transitional
disks. Furthermore, the observed line emission does not depend on measured
accretion luminosities or the number of infrared lines detected, which suggests
that the chemistry outside of 100 AU is not coupled to the physical processes
that drive the chemistry in the innermost few AU.Comment: accepted for publication in ApJ, 41 pages including 7 figure
Key influences to cost modelling and analysis in off-site construction: research trends and GAP analysis
The last decade has witnessed a proliferation of Off-Site Construction (OSC) operations and systems in the UK in response to persistent performance challenges in the construction industry. However, understanding the real influences of cost modelling for accurate project costing and cost performance remains limited. Consequently, this systematic literature review aims to identify the key parameters associated with effective cost modelling in OSC systems. Using literature in the last 10 years (i.e. 2011–2021) and keyword search terms, the review covers OSC aspects such as cost modelling and models, life cycle costing, cost analysis and taking off. Knowledge gaps are identified within literature and practice in cost modelling despite a backdrop of a proliferation of OSC systems and concomitant literature. Emergent findings uncover thematic clusters in analysed literature with the role of design, 88%, costs, 69% and modelling, 74% dominating the literature reviewed. Moreover, key influences to cost modelling in OSC (e.g. abnormal costs, factory-based preliminaries, and contractor’s overheads) do not feature prominently in any published research. This paper provides a cross-sectional snapshot of contemporary developments in the field and highlights the need for new research to support integrated cost modelling to support current OSC practice
The effect of the dispersion of microfibrillated cellulose on the mechanical properties of melt-compounded polypropylene–polyethylene copolymer
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