4,088 research outputs found
A Detailed Investigation of the Proposed NN Serpentis Planetary System
The post-main sequence eclipsing binary NN Serpentis was recently announced
as the potential host of at least two massive planetary companions. In that
work, the authors put forward two potential architectures that fit the
observations of the eclipsing binary with almost identical precision. In this
work, we present the results of a dynamical investigation of the orbital
stability of both proposed system architectures, finding that they are only
stable for scenarios in which the planets are locked in mutual mean motion
resonance. In the discovery work, the authors artificially fixed the orbital
eccentricity of the more massive planet, NN Ser(AB) c, at 0. Here, we reanalyse
the observational data on NN Serpentis without this artificial constraint, and
derive a new orbital solution for the two proposed planets. We detail the
results of further dynamical simulations investigating the stability of our new
orbital solution, and find that allowing a small non-zero eccentricity for the
outer planet renders the system unstable. We conclude that, although the
original orbits proposed for the NN Serpentis planetary system prove
dynamically feasible, further observations of the system are vital in order to
better constrain the system's true architecture.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society; 5 figures, 2 table
(1173) Anchises - Thermophysical and Dynamical Studies of a Dynamically Unstable Jovian Trojan
We have performed detailed thermophysical and dynamical modelling of Jovian
Trojan (1173) Anchises. Our results reveal a most unusual object. By examining
observational data taken by IRAS, Akari and WISE between 11.5 and 60 microns,
along with variations in its optical lightcurve, we find Anchises is most
likely an elongated body, with an axes-ratio of ~1.4. This yields calculated
best-fit dimensions of 170x121x121km (an equivalent diameter of 136+18/-11km).
We find the observations are best fit by Anchises having a retrograde sense of
rotation, and an unusually high thermal inertia (25 to 100 Jm-2s-0.5K-1). The
geometric albedo is found to be 0.027 (+0.006/-0.007). Anchises therefore has
one of the highest published thermal inertias of any object larger than 100km
in diameter, at such large heliocentric distances, and is one of the lowest
albedo objects ever observed. More observations are needed to see if there is a
link between the very shallow phase curve, with almost no opposition effect,
and the derived thermal properties for this large Trojan asteroid. Our
dynamical investigation of Anchises' orbit has revealed it to be dynamically
unstable on timescales of hundreds of Myr, similar to the unstable Neptunian
Trojans 2001 QR322 and 2008 LC18. Unlike those objects, we find that Anchises'
dynamical stability is not a function of its initial orbital elements, the
result of the exceptional precision with which its orbit is known. This is the
first time that a Jovian Trojan has been shown to be dynamically unstable, and
adds weight to the idea that planetary Trojans represent a significant ongoing
contribution to the Centaur population, the parents of the short-period comets.
The observed instability does not rule out a primordial origin for Anchises,
but when taken in concert with the result of our thermophysical analysis,
suggest that it would be a fascinating target for future study.Comment: 5 figures, 3 tables, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
MAGSAT data processing: A report for investigators
The in-flight attitude and vector magnetometer data bias recovery techniques and results are described. The attitude bias recoveries are based on comparisons with a magnetic field model and are thought to be accurate to 20 arcsec. The vector magnetometer bias recoveries are based on comparisons with the scalar magnetometer data and are thought to be accurate to 3 nT or better. The MAGSAT position accuracy goals of 60 m radially and 300 m horizontally were achieved for all but the last 3 weeks of Magsat lifetime. This claim is supported by ephemeris overlap statistics and by comparisons with ephemerides computed with an independent orbit program using data from an independent tracking network. MAGSAT time determination accuracy is estimated at 1 ms. Several errors in prelaunch assumptions regarding data time tags, which escaped detection in prelaunch data tests, and were discovered and corrected postlaunch are described. Data formats and products, especially the Investigator-B tapes, which contain auxiliary parameters in addition to the basic magnetometer and ephemeris data, are described
A Dynamical Analysis of the Proposed Circumbinary HW Virginis Planetary System
In 2009, the discovery of two planets orbiting the evolved binary star system
HW Virginis was announced, based on systematic variations in the timing of
eclipses between the two stars. The planets invoked in that work were
significantly more massive than Jupiter, and moved on orbits that were mutually
crossing - an architecture which suggests that mutual encounters and strong
gravitational interactions are almost guaranteed. In this work, we perform a
highly detailed analysis of the proposed HW Vir planetary system. First, we
consider the dynamical stability of the system as proposed in the discovery
work. Through a mapping process involving 91,125 individual simulations, we
find that the system is so unstable that the planets proposed simply cannot
exist, due to mean lifetimes of less than a thousand years across the whole
parameter space. We then present a detailed re-analysis of the observational
data on HW Vir, deriving a new orbital solution that provides a very good fit
to the observational data. Our new analysis yields a system with planets more
widely spaced, and of lower mass, than that proposed in the discovery work, and
yields a significantly greater (and more realistic) estimate of the uncertainty
in the orbit of the outermost body. Despite this, a detailed dynamical analysis
of this new solution similarly reveals that it also requires the planets to
move on orbits that are simply not dynamically feasible. Our results imply that
some mechanism other than the influence of planetary companions must be the
principal cause of the observed eclipse timing variations for HW Vir. If the
sys- tem does host exoplanets, they must move on orbits differing greatly from
those previously proposed. Our results illustrate the critical importance of
performing dynamical analyses as a part of the discovery process for
multiple-planet exoplanetary systems.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Origin and Dynamical Evolution of Neptune Trojans - II: Long Term Evolution
We present results examining the fate of the Trojan clouds produced in our
previous work. We find that the stability of Neptunian Trojans seems to be
strongly correlated to their initial post-migration orbital elements, with
those objects that survive as Trojans for billions of years displaying
negligible orbital evolution. The great majority of these survivors began the
integrations with small eccentricities (e < 0.2) and small libration amplitudes
(A < 30 - 40{\deg}). The survival rate of "pre-formed" Neptunian Trojans (which
in general survived on dynamically cold orbits (e < 0.1, i < 5 - 10{\deg}))
varied between ~5 and 70%. By contrast, the survival rate of "captured" Trojans
(on final orbits spread across a larger region of e-i element space) were
markedly lower, ranging between 1 and 10% after 4 Gyr. Taken in concert with
our earlier work, we note that planetary formation scenarios which involve the
slow migration (a few tens of millions of years) of Neptune from an initial
planetary architecture that is both resonant and compact (aN < 18 AU) provide
the most promising fit of those we considered to the observed Trojan
population. In such scenarios, we find that the current day Trojan population
would number ~1% of that which was present at the end of the planet's
migration, with the bulk being sourced from captured, rather than pre-formed
objects. We note, however, that even those scenarios still fail to reproduce
the currently observed portion of the Neptune Trojan population moving on
orbits with e 20{\deg}. Dynamical integrations of the currently
observed Trojans show that five out of the seven are dynamically stable on 4
Gyr timescales, while 2001 QR322, exhibits significant dynamical instability.
The seventh Trojan object, 2008 LC18, has such large orbital uncertainties that
only future studies will be able to determine its stability.Comment: 24 pages, 6 figures, accepted for publication in MNRAS (The abstract
was shortened. Original version can be found in the pdf file
New Area Recommendations For Oats
Beginning in the fall of 1957, Iowa State College oat variety recommendations will be made on the basis of four state areas. Who determined the areas? Why, none other than the oat varieties themselves
InP/Ga0.47In0.53As monolithic, two-junction, three-terminal tandem solar cells
The work presented has focussed on increasing the efficiency of InP-based solar cells through the development of a high-performance InP/Ga(0.47)In(0.53)As two-junction, three-terminal monolithic tandem cell. Such a tandem is particularly suited to space applications where a radiation-hard top cell (i.e., InP) is required. Furthermore, the InP/Ga(0.47)In(0.53)As materials system is lattice matched and offers a top cell/bottom cell bandgap differential (0.60 eV at 300 K) suitable for high tandem cell efficiencies under AMO illumination. A three-terminal configuration was chosen since it allows for independent power collection from each subcell in the monolithic stack, thus minimizing the adverse impact of radiation damage on the overall tandem efficiency. Realistic computer modeling calculations predict an efficiency boost of 7 to 11 percent from the Ga(0.47)In(0.53)As bottom cell under AMO illumination (25 C) for concentration ratios in the 1 to 1000 range. Thus, practical AMO efficiencies of 25 to 32 percent appear possible with the InP/Ga(0.47)In(0.53)As tandem cell. Prototype n/p/n InP/Ga(0.47)In(0.53)As monolithic tandem cells were fabricated and tested successfully. Using an aperture to define the illuminated areas, efficiency measurements performed on a non-optimized device under standard global illumination conditions (25 C) with no antireflection coating (ARC) give 12.2 percent for the InP top cell and 3.2 percent for the Ga(0.47)In(0.53)As bottom cell, yielding an overall tandem efficiency of 15.4 percent. With an ARC, the tandem efficiency could reach approximately 22 percent global and approximately 20 percent AMO. Additional details regarding the performance of individual InP and Ga(0.47)In(0.53)As component cells, fabrication and operation of complete tandem cells and methods for improving the tandem cell performance, are also discussed
Formation and Dynamical Evolution of the Neptune Trojans - the Influence of the Initial Solar System Architecture
In this work, we investigate the dynamical stability of pre-formed Neptune
Trojans under the gravitational influence of the four giant planets in compact
planetary architectures, over 10 Myr. In our modelling, the initial orbital
locations of Uranus and Neptune (aN) were varied to produce systems in which
those planets moved on non-resonant orbits, or in which they lay in their
mutual 1:2, 2:3 and 3:4 mean-motion resonances (MMRs). In total, 420
simulations were carried out, examining 42 different architectures, with a
total of 840000 particles across all runs. In the non-resonant cases, the
Trojans suffered only moderate levels of dynamical erosion, with the most
compact systems (those with aN less than or equal 18 AU) losing around 50% of
their Trojans by the end of the integrations. In the 2:3 and 3:4 MMR scenarios,
however, dynamical erosion was much higher with depletion rates typically
greater than 66% and total depletion in the most compact systems. The 1:2
resonant scenarios featured disruption on levels intermediate between the
non-resonant cases and other resonant scenarios, with depletion rates of the
order of tens of percent. Overall, the great majority of plausible
pre-migration planetary architectures resulted in severe levels of depletion of
the Neptunian Trojan clouds. In particular, if Uranus and Neptune formed near
their mutual 2:3 or 3:4 MMR and at heliocentric distances within 18 AU (as
favoured by recent studies), we found that the great majority of pre-formed
Trojans would have been lost prior to Neptune's migration. This strengthens the
case for the great bulk of the current Neptunian Trojan population having been
captured during that migration.Comment: 17 pages, 2 figures, MNRAS (in press). Abstract slightly reduced in
size, but in original form in the PDF fil
Differential negative reinforcement of other behavior to increase compliance with wearing an anti-strip suit
Using a changing-criterion design, we replicated and extended a study (Cook, Rapp, & Schulze,
2015) on differential negative reinforcement of other behavior (DNRO). More specifically,
educational assistants implemented DNRO to teach a 12-year-old boy with autism spectrum
disorder to comply with wearing an anti-strip suit to prevent inappropriate fecal behavior in a
school setting. The duration for which the participant wore the suit systematically increased from
2 s at the start of treatment to the entire duration of the school day at the termination of the study.
Moreover, these effects were generalized to a new school with novel staff and persisted for more
than a year. These findings replicate prior research on DNRO and further support the use of the
intervention to increase compliance with wearing protective items, or medical devices, in
practical settings
History of the Department of Agricultural Leadership, Education and Communication
Names of the Department Administrators Location of Headquarters The Formative Years Practice Teaching Centers Cooperation with Teachers College Present Administration Organization Teaching: A Unique Role The Graduate Program Vocational Agriculture Contests Student Club Research Related Organizations Staff Recognition Reference
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