61 research outputs found
Trajectory Design from GTO to Near-Equatorial Lunar Orbit for the Dark Ages Radio Explorer (DARE) Spacecraft
The trajectory design for the Dark Ages Radio Explorer (DARE) mission concept involves dropping the DARE spacecraft off in a generalized geosynchronous transfer orbit (GTO) as a secondary payload. From GTO, the spacecraft is then required to enter a near-equatorial lunar orbit that is stable (i.e., no station-keeping maneuvers are required) and yields the required number of cumulative hours (1,000) for science measurements while in the lunar farside radio quiet cone over a span of three years. Preliminary and expected results of the corresponding trajectory design are presented herein
Trajectory Design from GTO to Near-Equatorial Lunar Orbit for the Dark Ages Radio Explorer (DARE) Spacecraft
The trajectory design for the Dark Ages Radio Explorer (DARE) mission concept involves launching the DARE spacecraft into a geosynchronous transfer orbit (GTO) as a secondary payload. From GTO, the spacecraft then transfers to a lunar orbit that is stable (i.e., no station-keeping maneuvers are required with minimum perilune altitude always above 40 km) and allows for more than 1,000 cumulative hours for science measurements in the radio-quiet region located on the lunar farside
Deconstructing the galaxy stellar mass function with UKIDSS and CANDELS: the impact of colour, structure and environment
We combine photometry from the Ultra Deep Survey (UDS), Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) UDS and CANDELS the Great Observatories Origins Deep Survey-South (GOODS-S) surveys to construct the galaxy stellar mass function probing both the low- and high-mass end accurately in the redshift range 0.326.0), affording us robust measures of structural parameters. We construct stellar mass functions for the entire sample as parametrized by the Schechter function, and find that there is a decline in the values of ϕ and of α with higher redshifts, and a nearly constant M* up to z∼3. We divide the galaxy stellar mass function by colour, structure, and environment and explore the links between environmental overdensity, morphology, and the quenching of star formation. We find that a double Schechter function describes galaxies with high Sérsic index (n>2.5), similar to galaxies which are red or passive. The low-mass end of the n>2.5 stellar mass function is dominated by blue galaxies, whereas the high-mass end is dominated by red galaxies. This shows that there is a possible link between morphological evolution and star formation quenching in high mass galaxies, which is not seen in lower mass systems. This in turn suggests that there are strong mass-dependent quenching mechanisms. In addition, we find that the number density of high-mass systems is elevated in dense environments, suggesting that an environmental process is building up massive galaxies quicker in over densities than in lower densitie
Deconstructing the Galaxy Stellar Mass Function with UKIDSS and CANDELS: the Impact of Colour, Structure and Environment
We combine photometry from the UDS, and CANDELS UDS and CANDELS GOODS-S
surveys to construct the galaxy stellar mass function probing both the low and
high mass end accurately in the redshift range 0.3<z<3. The advantages of using
a homogeneous concatenation of these datasets include meaningful measures of
environment in the UDS, due to its large area (0.88 deg^2), and the high
resolution deep imaging in CANDELS (H_160 > 26.0), affording us robust measures
of structural parameters. We construct stellar mass functions for the entire
sample as parameterised by the Schechter function, and find that there is a
decline in the values of phi and of alpha with higher redshifts, and a nearly
constant M* up to z~3. We divide the galaxy stellar mass function by colour,
structure, and environment and explore the links between environmental
over-density, morphology, and the quenching of star formation. We find that a
double Schechter function describes galaxies with high Sersic index (n>2.5),
similar to galaxies which are red or passive. The low-mass end of the n>2.5
stellar mass function is dominated by blue galaxies, whereas the high-mass end
is dominated by red galaxies. This hints that possible links between
morphological evolution and star formation quenching are only present in
high-mass galaxies. This is turn suggests that there are strong mass dependent
quenching mechanisms. In addition, we find that the number density of high mass
systems is elevated in dense environments, suggesting that an environmental
process is building up massive galaxies quicker in over densities than in lower
densities.Comment: 26 pages, 14 figures, Accepted for publication in MNRA
A randomized controlled trial of nonoperative treatment versus open reduction and internal fixation for stable, displaced, partial articular fractures of the radial head: The RAMBO trial
Background: The choice between operative or nonoperative treatment is questioned for partial articular fractures of the radial head that have at least 2 millimeters of articular step-off on at least one radiograph (defined as displaced), but less than 2 millimeter of gap between the fragments (defined as stable) and that are not associated with an elbow dislocation, interosseous ligament injury, or other fractures. These kinds of fractures are often classified as Mason type-2 fractures. Retrospective comparative studies suggest that operative treatment might be better than nonoperative treatment, but the long-term results of nonoperative treatment are very good. Most experts agree that problems like reduced range of motion, painful crepitation, nonunion or bony ankylosis are infrequent with both nonoperative and operative treatment of an isolated displaced partial articular fracture of the radial head, but determining which patients will have problems is difficult. A prospective, randomized comparison would help minimize bias and determine the balance between operative and nonoperative risks and benefits. Methods/Design. The RAMBO trial (Radial Head - Amsterdam - Amphia - Boston - Others) is an international prospective, randomized, multicenter trial. The primary objective of this study is to compare patient related outcome defined by the \u27Disabilities of Arm, Shoulder and Hand (DASH) score\u27 twelve months after injury between operative and nonoperative treated patients. Adult patients with partial articular fractures of the radial head that comprise at least 1/3rd of the articular surface, have ≥ 2 millimeters of articular step-off but less than 2 millimeter of gap between the fragments will be enrolled. Secondary outcome measures will be the Mayo Elbow Performance Index (MEPI), the Oxford Elbow Score (OES), pain intensity through the \u27Numeric Rating Scale\u27, range of motion (flexion arc and rotational arc), radiographic appearance of the fracture (heterotopic ossification, radiocapitellar and ulnohumeral arthrosis, fracture healing, and signs of implant loosening or breakage) and adverse events (infection, nerve injury, secondary interventions) after one year. Discussion. The successful completion of this trial will provide evidence on the best treatment for stable, displaced, partial articular fractures of the radial head. Trial registration. The trial is registered at the Dutch Trial Register: NTR3413. © 2014Bruinsma et al.; licensee BioMed Central Ltd
A randomized controlled trial of nonoperative treatment versus open reduction and internal fixation for stable, displaced, partial articular fractures of the radial head: The RAMBO trial
Background: The choice between operative or nonoperative treatment is questioned for partial articular fractures of the radial head that have at least 2 millimeters of articular step-off on at least one radiograph (defined as displaced), but less than 2 millimeter of gap between the fragments (defined as stable) and that are not associated with an elbow dislocation, interosseous ligament injury, or other fractures. These kinds of fractures are often classified as Mason type-2 fractures. Retrospective comparative studies suggest that operative treatment might be better than nonoperative treatment, but the long-term results of nonoperative treatment are very good. Most experts agree that problems like reduced range of motion, painful crepitation, nonunion or bony ankylosis are infrequent with both nonoperative and operative treatment of an isolated displaced partial articular fracture of the radial head, but determining which patients will have problems is difficult. A prospective, randomized comparison would help minimize bias and determine the balance between operative and nonoperative risks and benefits. Methods/Design. The RAMBO trial (Radial Head - Amsterdam - Amphia - Boston - Others) is an international prospective, randomized, multicenter trial. The primary objective of this study is to compare patient related outcome defined by the 'Disabilities of Arm, Shoulder and Hand (DASH) score' twelve months after injury between operative and nonoperative treated patients. Adult patients with partial articular fractures of the radial head that comprise at least 1/3rd of the articular surface, have ≥ 2 millimeters of articular step-off but less than 2 millimeter of gap between the fragments will be enrolled. Secondary outcome measures will be the Mayo Elbow Performance Index (MEPI), the Oxford Elbow Score (OES), pain intensity through the 'Numeric Rating Scale', range of motion (flexion arc and rotational arc), radiographic appearance of the fracture (heterotopic ossification, radiocapitellar and ulnohumeral arthrosis, fracture healing, and signs of implant loosening or breakage) and adverse events (infection, nerve injury, secondary interventions) after one year. Discussion. The successful completion of this trial will provide evidence on the best treatment for stable, displaced, partial articular fractures of the radial head. Trial registration. The trial is registered at the Dutch Trial Register: NTR3413
Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star
Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining1. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability2,3,4,5. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required
Can Kozai-Lidov cycles explain Kepler-78b?
Kepler-78b is one of a growing sample of planets similar, in composition and
size, to the Earth. It was first detected with NASA's \emph{Kepler} spacecraft
and then characterised in more detail using radial velocity follow-up
observations. Not only is its size very similar to that of the Earth (), it also has a very similar density ( g cm). What makes
this planet particularly interesting is that it orbits its host star every
hours, giving it an orbital distance of only au. What we
investigate here is whether or not such a planet could have been perturbed into
this orbit by an outer companion on an inclined orbit. In this scenario, the
outer perturber causes the inner orbit to undergo Kozai-Lidov cycles which, if
the periapse comes sufficiently close to the host star, can then lead to the
planet being tidally circularised into a close orbit. We find that this process
can indeed produce such very-close-in planets within the age of the host star
( Myr), but it is more likely to find such ultra-short-period
planets around slightly older stars ( Gyr). However, given the size of the
Kepler sample and the likely binarity, our results suggest that Kepler-78b may
indeed have been perturbed into its current orbit by an outer stellar
companion. The likelihood of this happening, however, is low enough that other
processes - such as planet-planet scattering - could also be responsible.Comment: 10 pages, 9 figures, accepted for publication in MNRA
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