204 research outputs found
Shape and spin distributions of asteroid populations from brightness variation estimates and large databases
Context. Many databases on asteroid brightnesses (e.g. ALCDEF, WISE) are
potential sources for extensive asteroid shape and spin modelling. Individual
lightcurve inversion models require several apparitions and hundreds of data
points per target. However, we can analyse the coarse shape and spin
distributions over populations of at least thousands of targets even if there
are only a few points and one apparition per asteroid. This is done by
examining the distribution of the brightness variations observed within the
chosen population.
Aims. Brightness variation has been proposed as a population-scale rather
than individual-target observable in two studies so far. We aim to examine this
approach rigorously to establish its theoretical validity, degree of
ill-posedness, and practical applicability.
Methods. We model the observed brightness variation of a target population by
considering its cumulative distribution function (CDF) caused by the joint
distribution function of two fundamental shape and spin indicators. These are
the shape elongation and the spin latitude of a simple ellipsoidal model. The
main advantage of the model is that we can derive analytical basis functions
that yield the observed CDF as a function of the shape and spin distribution.
The inverse problem can be treated linearly. Even though the inaccuracy of the
model is considerable, databases of thousands of targets should yield some
information on the distribution.
Results. We establish the theoretical soundness and the typical accuracy
limits of the approach both analytically and numerically. Using simulations, we
derive a practical estimate of the model distribution in the (shape,
spin)-plane. We show that databases such as Wide-field Infrared Survey Explorer
(WISE) yield coarse but robust estimates of this distribution, and as an
example compare various asteroid families with each other.Comment: 16 pages, 21 figures, manuscript accepted in Astronomy &
Astrophysics, to be published in section 10. Planets and planetary system
Probing a regular orbit with spectral dynamics
We have extended the spectral dynamics formalism introduced by Binney &
Spergel, and have implemented a semi-analytic method to represent regular
orbits in any potential, making full use of their regularity. We use the
spectral analysis code of Carpintero & Aguilar to determine the nature of an
orbit (irregular, regular, resonant, periodic) from a short-time numerical
integration. If the orbit is regular, we approximate it by a truncated Fourier
time series of a few tens of terms per coordinate. Switching to a description
in action-angle variables, this corresponds to a reconstruction of the
underlying invariant torus. We then relate the uniform distribution of a
regular orbit on its torus to the non-uniform distribution in the space of
observables by a simple Jacobian transformation between the two sets of
coordinates. This allows us to compute, in a cell-independent way, all the
physical quantities needed in the study of the orbit, including the density and
in the line-of-sight velocity distribution, with much increased accuracy. The
resulting flexibility in the determination of the orbital properties, and the
drastic reduction of storage space for the orbit library, provide a significant
improvement in the practical application of Schwarzschild's orbit superposition
method for constructing galaxy models. We test and apply our method to
two-dimensional orbits in elongated discs, and to the meridional motion in
axisymmetric potentials, and show that for a given accuracy, the spectral
dynamics formalism requires an order of magnitude fewer computations than the
more traditional approaches.Comment: 13 pages, 18 eps figures, submitted to MNRA
Brief communication "Application of mobile laser scanning in snow cover profiling"
We present a snowmobile-based mobile mapping system and its first application to snow cover roughness and change detection measurement. The ROAMER mobile mapping system, constructed at the Finnish Geodetic Institute, consists of the positioning and navigating systems, a terrestrial laser scanner, and the carrying platform (a snowmobile sledge in this application). We demonstrate the applicability of the instrument to snow cover roughness profiling and change detection by presenting preliminary results from a mobile laser scanning (MLS) campaign. The results show the potential of MLS for fast and efficient snow profiling from large areas in a millimetre scale
Modelling of laboratory data of bi-directional reflectance of regolith surface containing Alumina
Bidirectional reflectance of a surface is defined as the ratio of the
scattered radiation at the detector to the incident irradiance as a function of
geometry. The accurate knowledge of the bidirectional reflection function (BRF)
of layers composed of discrete, randomly positioned scattering particles is
very essential for many remote sensing, engineering, biophysical applications
and in different areas of Astrophysics. The computations of BRF's for plane
parallel particulate layers are usually reduced to solve the radiative transfer
equation (RTE) by the existing techniques. In this work we present our
laboratory data on bidirectional reflectance versus phase angle for two sample
sizes of 0.3 and 1 of Alumina for the He-Ne laser at 632.8 nm (red) and
543.5nm(green) wavelength. The nature of the phase curves of the asteroids
depends on the parameters like- particle size, composition, porosity, roughness
etc. In our present work we analyse the data which are being generated using
single scattering phase function i.e. Mie theory considering particles to be
compact sphere. The well known Hapke formula will be considered along with
different particle phase function such as Mie and Henyey Greenstein etc to
model the laboratory data obtained at the asteroid laboratory of Assam
University.Comment: 5 pages, 5 figures [accepted for publication in Publications of the
Astronomical Society of Australia (PASA) on 8 June, 2011
Physical properties of ESA Rosetta target asteroid (21) Lutetia: Shape and flyby geometry
Aims. We determine the physical properties (spin state and shape) of asteroid
(21) Lutetia, target of the ESA Rosetta mission, to help in preparing for
observations during the flyby on 2010 July 10 by predicting the orientation of
Lutetia as seen from Rosetta.
Methods. We use our novel KOALA inversion algorithm to determine the physical
properties of asteroids from a combination of optical lightcurves,
disk-resolved images, and stellar occultations, although the latter are not
available for (21) Lutetia.
Results. We find the spin axis of (21) Lutetia to lie within 5 degrees of
({\lambda} = 52 deg., {\beta} = -6 deg.) in Ecliptic J2000 reference frame
(equatorial {\alpha} = 52 deg., {\delta} = +12 deg.), and determine an improved
sidereal period of 8.168 270 \pm 0.000 001 h. This pole solution implies the
southern hemisphere of Lutetia will be in "seasonal" shadow at the time of the
flyby. The apparent cross-section of Lutetia is triangular as seen "pole-on"
and more rectangular as seen "equator-on". The best-fit model suggests the
presence of several concavities. The largest of these is close to the north
pole and may be associated with large impacts.Comment: 17 pages, 5 figures, 3 tables, submitted to Astronomy and
Astrophysic
Barriers to the management of Heart Failure in Ontario Long-Term Care Homes: an Interprofessional Care perspective
Background: With population aging, the prevalence of heart failure (HF) is risingin long-term care (LTC) homes. Given this burden, there is an urgent need to establish effective HF management programs.Methods and Findings: To understand what barriers would need to be addressed to develop such a program, we conducted a series of consultations among various LTC staff, as well as residents and their family caregivers. This article uses data obtained from the consultations to describe the interprofessional (IP) barriers that exist among the various LTC staff roles. Consultation methods included a Delphi survey followed by focus group interviews of LTC staff, and then personal interviews with LTC residents with HF and their family caregivers. Data were interpreted using an IP care framework in which interpersonal relationships among LTC staff provide the most direct influence on collaborative resident-centred practice, within the broader context of conditions within the LTC home, which in turn are housed in the broader context of systemic determinants.Conclusion: Across all data sets, the most consistently mentioned determinant was communication between the resident and the healthcare team, between different healthcare providers, between shifts, between medical specialists, and between the long-term care home and the hospital
The nucleus of Comet 67P/Churyumov-Gerasimenko: a new shape model and thermophysical analysis
Context. Comet 67P/Churyumov-Gerasimenko is the target of the European Space Agency Rosetta spacecraft rendez-vous mission. Detailed physical characteristation of the comet before arrival is important for mission planning as well as providing a test bed for ground-based observing and data-analysis methods.
Aims. To conduct a long-term observational programme to characterize the physical properties of the nucleus of the comet, via ground-based optical photometry, and to combine our new data with all available nucleus data from the literature.
Methods. We applied aperture photometry techniques on our imaging data and combined the extracted rotational lightcurves with data from the literature. Optical lightcurve inversion techniques were applied to constrain the spin state of the nucleus and its broad shape. We performed a detailed surface thermal analysis with the shape model and optical photometry by incorporating both into the new Advanced Thermophysical Model (ATPM), along with all available Spitzer 8–24 μm thermal-IR flux measurements from the literature.
Results. A convex triangular-facet shape model was determined with axial ratios b/a = 1.239 and c/a = 0.819. These values can vary by as much as 7% in each axis and still result in a statistically significant fit to the observational data. Our best spin state solution has Psid = 12.76137 ± 0.00006 h, and a rotational pole orientated at Ecliptic coordinates λ = 78◦(±10◦), β = +58◦(±10◦). The nucleus phase darkening behaviour was measured and best characterized using the IAU HG system. Best fit parameters are: G = 0.11 ± 0.12 and HR(1,1,0) = 15.31 ± 0.07. Our shape model combined with the ATPM can satisfactorily reconcile all optical and thermal-IR data, with the fit to the Spitzer 24 μm data taken in February 2004 being exceptionally good. We derive a range of mutually-consistent physical parameters for each thermal-IR data set, including effective radius, geometric albedo, surface thermal inertia and roughness fraction.
Conclusions. The overall nucleus dimensions are well constrained and strongly imply a broad nucleus shape more akin to comet
9P/Tempel 1, rather than the highly elongated or “bi-lobed” nuclei seen for comets 103P/Hartley 2 or 8P/Tuttle. The derived low thermal inertia of −2 K−1 s−1/2 is comparable with that measured for other comets scaled to similar heliocentric distances, and implies a surface regolith finer than lunar surface material
Understanding organizational context and heart failure management in long term care homes in Ontario, Canada
This study examined the prevalence of Control Intervention (CI) use in adult in-patient psychiatric units/hospitals in Ontario and developed a profile of those patients who had CI use during their admission between April 2006 and March 2010. Control intervention types included mechanical/physical, chair prevents rising, acute control medications, and seclusion. The profiles of patients with control intervention use included an examination of sociodemographic, mental health service use, and mental health clinical characteristics.Supported by an unrestricted grant-in-aid from the Heart and Stroke Foundation of Ontari
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