19,280 research outputs found
SATURN'S INNER SATELLITES: ORBITS, MASSES, AND THE CHAOTIC MOTION OF ATLAS FROM NEW CASSINI IMAGING OBSERVATIONS
We present numerically-derived orbits and mass estimates for the inner
Saturnian satellites, Atlas, Prometheus, Pandora, Janus and Epimetheus from a
fit to 2580 new Cassini ISS astrometric observations spanning February 2004 to
August 2013. The observations are provided in a supplementary table. We
estimate GM_ Atlas=0.384+/-0.001 x 10^(-3)km^3s^(-2), a value 13% smaller than
the previously published estimate but with an order of magnitude reduction in
the uncertainty. We also find GM_ Prometheus=10.677+/-0.006x10(-3)km^3s^(-2),
GM_Pandora=9.133+/-0.009x10^(-3)km^3s^(-2),
GM_Janus=126.51+/-0.03x10^(-3)km^3s^(-2) and
GM_Epimetheus=35.110+/-0.009x10^(-3)km^3s^(-2), consistent with previously
published values, but also with significant reductions in uncertainties. We
show that Atlas is currently librating in both the 54:53
co-rotation-eccentricity resonance (CER) and the 54:53 inner Lindblad (ILR)
resonance with Prometheus, making it the latest example of a coupled CER-ILR
system, in common with the Saturnian satellites Anthe, Aegaeon and Methone, and
possibly Neptune's ring arcs. We further demonstrate that Atlas's orbit is
chaotic, with a Lyapunov time of ~10 years, and show that its chaotic behaviour
is a direct consequence of the coupled resonant interaction with Prometheus,
rather than being an indirect effect of the known chaotic interaction between
Prometheus and Pandora. We provide an updated analysis of the second-order
resonant perturbations involving Prometheus, Pandora and Epimetheus based on
the new observations, showing that these resonant arguments are librating only
when Epimetheus is the innermost of the co-orbital pair, Janus and Epimetheus.
We also find evidence that the known chaotic changes in the orbits of
Prometheus and Pandora are not confined to times of apse anti-alignement.Comment: 23 pages, 16 figures. Accepted for publication in The Astronomical
Journal 23 September 2014 (corrected Fig. 11
How Brexit could harm African economies that trade with the UK and disrupt regional integration
The UK must pay urgent attention to the complexities of African trade in order to avoid Brexit having damaging effects, explains Peg Murray-Evans. Failure to do so could mean new barriers to trade from vulnerable African economies and disruption to regional integration
The Levy Institute Measure of Economic Well-Being: Estimates for Canada, 1999 and 2005
This report presents estimates of the Levy Institute Measure of Economic Well-Being (LIMEW) for a representative sample of Canadian households in 1999 and 2005. The results indicate that there was only modest growth in the average Canadian household’s total command over economic resources in the six years between 1999 and 2005. Although inequality in economic well-being increased slightly over the 1999-2005 period, the LIMEW was more equally distributed across Canadian households than more common income measures (such as after-tax income) in both 1999 and 2005. The median household’s economic well-being was lower in Canada than in the United States in both years.LIMEW, well-being, income, earnings, wealth, public consumption, government expenditure, household production, inequality
"The Levy Institute Measure of Economic Well-Being: Estimates for Canada, 1999 and 2005"
This report presents estimates of the Levy Institute Measure of Economic Well-Being (LIMEW) for a representative sample of Canadian households in 1999 and 2005. The results indicate that there was only modest growth in the average Canadian household’s total command over economic resources in the six years between 1999 and 2005. Although inequality in economic well-being increased slightly over the 1999–2005 period, the LIMEW was more equally distributed across Canadian households than more common income measures (such as after-tax income) in both 1999 and 2005. The median household’s economic well-being was lower in Canada than in the United States in both years.Well-being, Inequality, Income, Wealth, Government Expenditure, Household Production, LIMEW, (Canada)
How to Find Young Massive Cluster Progenitors
We propose that bound, young massive stellar clusters form from dense clouds
that have escape speeds greater than the sound speed in photo-ionized gas. In
these clumps, radiative feedback in the form of gas ionization is bottled up,
enabling star formation to proceed to sufficiently high efficiency so that the
resulting star cluster remains bound even after gas removal. We estimate the
observable properties of the massive proto-clusters (MPCs) for existing
Galactic plane surveys and suggest how they may be sought in recent and
upcoming extragalactic observations. These surveys will potentially provide a
significant sample of MPC candidates that will allow us to better understand
extreme star-formation and massive cluster formation in the Local Universe.Comment: 5 pages, 1 figure, 1 table, accepted for publication in ApJ
The timing of maternal depressive symptoms and child cognitive development: a longitudinal study.
Background: Maternal depression is known to be associated with impairments in child cognitive development, although the effect of timing of exposure to maternal depression is unclear. Methods: Data collected for the Avon Longitudinal Study of Parents and Children, a longitudinal study beginning in pregnancy, included self-report measures of maternal depression the Edinburgh Postnatal Depression Scale, completed on 6 occasions up to 3 years of age, and IQ of the index child (WISC) measured at aged 8 years. We used these data to assign women to 8 groups according to whether depression occurred in the antenatal, postnatal, preschool period, any combination of these times, or not at all. We compared a model comprising all patterns of depression (saturated model) with models nested within this to test whether there is a relationship between depression and child cognitive development and, if so, whether there is a sensitive period. We then investigated the relationship with child IQ for each model, following adjustment for confounders. Results: Six thousand seven hundred and thirty-five of 13,615 children from singleton births (49.5%, of eligible core sample) attended a research clinic at 8 years and completed a WISC with a score ≥ 70. A total of 5,029 mothers of these children had completed mood assessments over the 3 time periods. In unadjusted analyses, all three sensitive period models were as good as the saturated model, as was an accumulation model. Of the sensitive period models, only that for antenatal exposure was a consistently better fit than the accumulation model. After multiple imputation for missing data (to n = 6,735), there was no effect of postnatal depression on child IQ independent of depression at other times [-0.19 IQ points, 95% confidence interval (CI) -1.5 to 1.1 points]. There was an effect of antenatal depression (-3.19 IQ points, 95% CI: -4.33 to -2.06) which attenuated following adjustment (-0.64 IQ points, 95% CI: -1.68 to 0.40). Conclusions: The postnatal period is not a sensitive one for the effect of maternal depression on child cognitive development. © 2011 The Authors. Journal of Child Psychology and Psychiatry
Chemotactic Collapse and Mesenchymal Morphogenesis
We study the effect of chemotactic signaling among mesenchymal cells. We show
that the particular physiology of the mesenchymal cells allows one-dimensional
collapse in contrast to the case of bacteria, and that the mesenchymal
morphogenesis represents thus a more complex type of pattern formation than
those found in bacterial colonies. We finally compare our theoretical
predictions with recent in vitro experiments
The present-day star formation rate of the Milky-Way determined from Spitzer detected young stellar objects
We present initial results from a population synthesis model aimed at
determining the star formation rate of the Milky-Way. We find that a total star
formation rate of 0.68 to 1.45 Msun/yr is able to reproduce the observed number
of young stellar objects in the Spitzer/IRAC GLIMPSE survey of the Galactic
plane, assuming simple prescriptions for the 3D Galactic distributions of YSOs
and interstellar dust, and using model SEDs to predict the brightness and color
of the synthetic YSOs at different wavelengths. This is the first Galaxy-wide
measurement derived from pre-main-sequence objects themselves, rather than
global observables such as the total radio continuum, Halpha, or FIR flux. The
value obtained is slightly lower than, but generally consistent with previously
determined values. We will extend this method in the future to fit the
brightness, color, and angular distribution of YSOs, and simultaneously make
use of multiple surveys, to place constraints on the input assumptions, and
reduce uncertainties in the star formation rate estimate. Ultimately, this will
be one of the most accurate methods for determining the Galactic star formation
rate, as it makes use of stars of all masses (limited only by sensitivity)
rather than solely massive stars or indirect tracers of massive stars.Comment: 12 pages, 3 figures, Published in the Astrophysical Journal Letter
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