815 research outputs found
Asteroid Models from Multiple Data Sources
In the past decade, hundreds of asteroid shape models have been derived using
the lightcurve inversion method. At the same time, a new framework of 3-D shape
modeling based on the combined analysis of widely different data sources such
as optical lightcurves, disk-resolved images, stellar occultation timings,
mid-infrared thermal radiometry, optical interferometry, and radar
delay-Doppler data, has been developed. This multi-data approach allows the
determination of most of the physical and surface properties of asteroids in a
single, coherent inversion, with spectacular results. We review the main
results of asteroid lightcurve inversion and also recent advances in multi-data
modeling. We show that models based on remote sensing data were confirmed by
spacecraft encounters with asteroids, and we discuss how the multiplication of
highly detailed 3-D models will help to refine our general knowledge of the
asteroid population. The physical and surface properties of asteroids, i.e.,
their spin, 3-D shape, density, thermal inertia, surface roughness, are among
the least known of all asteroid properties. Apart for the albedo and diameter,
we have access to the whole picture for only a few hundreds of asteroids. These
quantities are nevertheless very important to understand as they affect the
non-gravitational Yarkovsky effect responsible for meteorite delivery to Earth,
or the bulk composition and internal structure of asteroids.Comment: chapter that will appear in a Space Science Series book Asteroids I
High-overtone Bulk-Acoustic Resonator gravimetric sensitivity: towards wideband acoustic spectroscopy
In the context of direct detection sensors with compact dimensions, we
investigate the gravimetric sensitivity of High-overtone Bulk Acoustic
Resonators, through modeling of their acoustic characteristics and experiment.
The high frequency characterizing such devices is expected to induce a
significant effect when the acoustic field boundary conditions are modified by
a thin adlayer. Furthermore, the multimode spectral characteristics is
considered for wideband acoustic spectroscopy of the adlayer, once the
gravimetric sensitivity dependence of the various overtones is established.
Finally, means of improving the gravimetric sensitivity by confining the
acoustic field in a low acoustic-impedance layer is theoretically established.Comment: 9 pages, 10 figures in J. Appl. Phys. 201
Near-infrared spatially resolved spectroscopy of (136108) Haumea's multiple system
The transneptunian region of the solar system is populated by a wide variety
of icy bodies showing great diversity. The dwarf planet (136108) Haumea is
among the largest TNOs and displays a highly elongated shape and hosts two
moons, covered with crystalline water ice like Hamuea. Haumea is also the
largest member of the sole TNO family known to date. A catastrophic collision
is likely responsible for its unique characteristics. We report here on the
analysis of a new set of observations of Haumea obtained with SINFONI at the
ESO VLT. Combined with previous data, and using light-curve measurements in the
optical and far infrared, we carry out a rotationally resolved spectroscopic
study of the surface of Haumea. We describe the physical characteristics of the
crystalline water ice present on the surface of Haumea for both regions, in and
out of the Dark Red Spot (DRS), and analyze the differences obtained for each
individual spectrum. The presence of crystalline water ice is confirmed over
more than half of the surface of Haumea. Our measurements of the average
spectral slope confirm the redder characteristic of the spot region. Detailed
analysis of the crystalline water-ice absorption bands do not show significant
differences between the DRS and the remaining part of the surface. We also
present the results of applying Hapke modeling to our data set. The best
spectral fit is obtained with a mixture of crystalline water ice (grain sizes
smaller than 60 micron) with a few percent of amorphous carbon. Improvements to
the fit are obtained by adding ~10% of amorphous water ice. Additionally, we
used the IFU-reconstructed images to measure the relative astrometric position
of the largest satellite Hi`iaka and determine its orbital elements. An orbital
solution was computed with our genetic-based algorithm GENOID and our results
are in full agreement with recent results.Comment: Accepted for publication in A&
SsODNet: The Solar system Open Database Network
The sample of Solar system objects has dramatically increased over the last
decade. The amount of measured properties (e.g., diameter, taxonomy, rotation
period, thermal inertia) has grown even faster. However, this wealth of
information is spread over a myriad of articles, under many different
designations per object. We provide a solution to the identification of Solar
system objects from any of their multiple names or designations. We also
compile and rationalize their properties to provide an easy access to them. We
aim to continuously update the database as new measurements become available.
We built a Web Service, SsODNet, that offers four access points, each
corresponding to an identified necessity in the community: name resolution
(quaero), compilation of a large corpus of properties (datacloud),
determination of the best estimate among compiled values (ssoCard), and
statistical description of the population (ssoBFT). The SsODNet interfaces are
fully operational and freely accessible to everyone. The name resolver quaero
translates any of the ~5.3 million designations of objects into their current
official designation. The datacloud compiles about 105 million parameters
(osculating and proper elements, pair and family membership, diameter, albedo,
mass, density, rotation period, spin coordinates, phase function parameters,
colors, taxonomy, thermal inertia, and Yarkovsky drift) from over 3,000
articles (and growing). For each of the known asteroids and dwarf planets (~1.2
million), a ssoCard providing a single best-estimate for each parameter is
available. The SsODNet service provides these resources in a fraction of second
upon query. Finally, the large ssoBFT table compiles all the best-estimates in
a single table for population-wide studies
The triaxial ellipsoid dimensions, rotational pole, and bulk density of ESA Rosetta target asteroid (21) Lutetia
We seek the best size estimates of the asteroid (21) Lutetia, the direction
of its spin axis, and its bulk density, assuming its shape is well described by
a smooth featureless triaxial ellipsoid, and to evaluate the deviations from
this assumption. Methods. We derive these quantities from the outlines of the
asteroid in 307 images of its resolved apparent disk obtained with adaptive
optics (AO) at Keck II and VLT, and combine these with recent mass
determinations to estimate a bulk density. Our best triaxial ellipsoid
diameters for Lutetia, based on our AO images alone, are a x b x c = 132 x 101
x 93 km, with uncertainties of 4 x 3 x 13 km including estimated systematics,
with a rotational pole within 5 deg. of ECJ2000 [long,lat] = [45, -7], or
EQJ2000 [RA, DEC] = [44, +9]. The AO model fit itself has internal precisions
of 1 x 1 x 8 km, but it is evident, both from this model derived from limited
viewing aspects and the radius vector model given in a companion paper, that
Lutetia has significant departures from an idealized ellipsoid. In particular,
the long axis may be overestimated from the AO images alone by about 10 km.
Therefore, we combine the best aspects of the radius vector and ellipsoid model
into a hybrid ellipsoid model, as our final result, of 124 +/- 5 x 101 +/- 4 x
93 +/- 13 km that can be used to estimate volumes, sizes, and projected areas.
The adopted pole position is within 5 deg. of [long, lat] = [52, -6] or[RA DEC]
= [52, +12]. Using two separately determined masses and the volume of our
hybrid model, we estimate a density of 3.5 +/- 1.1 or 4.3 +/- 0.8 g cm-3 . From
the density evidence alone, we argue that this favors an enstatite-chondrite
composition, although other compositions are formally allowed at the extremes
(low-porosity CV/CO carbonaceous chondrite or high-porosity metallic). We
discuss this in the context of other evidence.Comment: 9 pages, 8 figures, 5 tables, submitted to Astronomy and Astrophysic
Revising the age for the Baptistina asteroid family using WISE/NEOWISE data
We have used numerical routines to model the evolution of a simulated
Baptistina family to constrain its age in light of new measurements of the
diameters and albedos of family members from the Wide-field Infrared Survey
Explorer. We also investigate the effect of varying the assumed physical and
orbital parameters on the best-fitting age. We find that the physically allowed
range of assumed values for the density and thermal conductivity induces a
large uncertainty in the rate of evolution. When realistic uncertainties in the
family members' physical parameters are taken into account we find the
best-fitting age can fall anywhere in the range of 140-320 Myr. Without more
information on the physical properties of the family members it is difficult to
place a more firm constraint on Baptistina's age.Comment: 27 pages, 16 figures, accepted to Ap
Involving children in creating a healthy environment in low Socioeconomic Position (SEP) neighborhoods in The Netherlands:A Participatory Action Research (PAR) project
To ensure that health behavior interventions for children living in low socioeconomic position (SEP) neighborhoods are in line with childrenâs wishes and needs, participation of the children in the development, implementation, and evaluation is crucial. In this paper, we show how children living in three low SEP neighborhoods in the Netherlands can be involved in Participatory Action Research (PAR) by using the photovoice method, and what influences this research process. Observations, informal chats, semi structured interviews, and focus group discussions with children and professionals were done to evaluate the research process. The photovoice method provided comprehensive information from the childrenâs perspectives. With the help of the community workers, the children identified feasible actions. We found that it is important to constantly discuss the research process with participants, start with a concrete question or problem, and adapt the project to the local context and skills of participants
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
Mechanisms and contextual factors related to key elements of a successful integrated community-based approach aimed at reducing socioeconomic health inequalities in the Netherlands:A realist evaluation perspective
Background Reducing health inequalities is a challenge for policymakers and civil society. A multisectoral and multilevel approach is most promising to reduce those inequalities. Previous research showed what key elements of Zwolle Healthy City, an integrated community-based approach aimed at reducing socioeconomic health inequalities, are. To fully understand approaches that are complex and context dependent, questions as 'how does the intervention work' and 'in what context does it work' are just as important as 'what works'. The current study aimed to identify mechanisms and contextual factors associated with the key elements of Zwolle Healthy City, using a realist evaluation perspective. Methods Transcripts of semi-structured interviews with a wide range of local professionals were used (n = 29). Following realist evaluation logic in the analysis of this primary data, context-mechanism- outcome configurations were identified and thereafter discussed with experts (n = 5). Results How mechanisms (M) in certain contexts (C) were of influence on the key elements (O) of the Zwolle Healthy City approach are described. For example, how, in the context of the responsible aldermen embracing the approach (C), regular meetings with the aldermen (M) increased support for the approach among involved professionals (O). Or, how, in the context of available financial resources (C), assigning a program manager (M) contributed positively to coordination and communication (O). All 36 context-mechanism-outcome configurations can be found in the repository. ConclusionThis study showed what mechanisms and contextual factors are associated with the key elements of Zwolle Healthy City. By applying realist evaluation logic in the analysis of primary qualitative data we were able to disentangle the complexity of processes of this whole system approach and show this complexity in a structured manner. Also, by describing the context in which the Zwolle Healthy City approach is implemented, we contribute to the transferability of this approach across different contexts.</p
Children's Attention-Deficit/Hyperactivity Disorder Symptoms Predict Lower Diet Quality but Not Vice Versa:Results from Bidirectional Analyses in a Population-Based Cohort
BACKGROUND: As an adjuvant for medication, dietary changes focused on specific nutrients have been proposed to prevent or reduce attention-deficit/hyperactivity disorder (ADHD) symptoms. However, whether an overall healthy dietary pattern is associated with ADHD symptom severity during childhood remains unclear. Furthermore, it is not clear what the direction of this association is. OBJECTIVES: We aimed to examine the association between dietary patterns and ADHD symptoms in school-aged children. In addition, we aimed to identify the temporal direction of this association-that is, whether dietary patterns predict ADHD symptoms or vice versa. METHODS: We analyzed data from 3680 children participating in the Generation R Study, a prospective cohort in Rotterdam, Netherlands. ADHD symptoms were assessed with parent-report questionnaires at ages 6 and 10 y using the Child Behavior Checklist. Dietary intake was assessed at the age of 8 y with a validated food-frequency questionnaire. We computed a diet quality score reflecting adherence to dietary guidelines. We examined bidirectional associations of diet quality with ADHD symptom scores using multivariable linear regression analysis and cross-lagged modeling. RESULTS: Linear regressions showed that more ADHD symptoms at age 6 y were associated with a lower diet quality score at age 8 y (SD score = -0.08; 95% CI: -0.11, -0.05) but that diet quality at age 8 y was not associated with ADHD symptoms at age 10 y. Cross-lagged models confirmed a unidirectional relation from ADHD symptoms to diet quality but not vice versa. Associations did not differ by overweight status or between boys and girls. CONCLUSION: Our study suggests that children with more ADHD symptoms may be at higher risk of an unhealthy diet but that overall diet quality does not affect ADHD risk
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