958 research outputs found
Resonance breaking due to dissipation in planar planetary systems
We study the evolution of two planets around a star, in mean-motion resonance
and undergoing tidal effect. We derive an integrable analytical model of
mean-motion resonances of any order which reproduce the main features of the
resonant dynamics. Using this simplified model, we obtain a criterion showing
that depending on the balance of the tidal dissipation in both planets, their
final period ratio may stay at the resonant value, increase above, or decrease
below the resonant value.
Applying this criterion to the two inner planets orbiting GJ163, we deduce
that the current period ratio (2.97) could be the outcome of dissipation in the
3:1 MMR provided that the innermost planet is gaseous (slow dissipation) while
the second one is rocky (faster dissipation). We perform N-body simulations
with tidal dissipation to confirm the results of our analytical model.
We also apply our criterion on GJ581b, c (5:2 MMR) and reproduce the current
period ratio (2.4) if the inner planet is gaseous and the outer is rocky (as
for GJ163).
Finally, we apply our model to the Kepler mission's statistics. We show that
the excess of planets pairs close to first order MMR but in external
circulation, i.e., with period ratios P_out/P_in > (p+1)/p for the resonance
(p+1):p, can be reproduced by tidal dissipation in the inner planet. There is
no need for any other dissipative mechanism, provided that these systems left
the resonance with non-negligible eccentricities.Comment: 14 pages, 9 figures, submitted for publicatio
Planets in Mean-Motion Resonances and the System Around HD45364
In some planetary systems, the orbital periods of two of its members present
a commensurability, usually known by mean-motion resonance. These resonances
greatly enhance the mutual gravitational influence of the planets. As a
consequence, these systems present uncommon behaviors, and their motions need
to be studied with specific methods. Some features are unique and allow us a
better understanding and characterization of these systems. Moreover,
mean-motion resonances are a result of an early migration of the orbits in an
accretion disk, so it is possible to derive constraints on their formation.
Here we review the dynamics of a pair of resonant planets and explain how their
orbits evolve in time. We apply our results to the HD 45365 planetary system.Comment: invited review, 17 pages, 6 figure
PrĂ©diction de lâinsulino-rĂ©sistance par les ratios de lipoprotĂ©ines chez les adultes bĂ©ninois
Des controverses subsistent sur force prĂ©dictive de lâinsulino-rĂ©sistance par les ratios de lipoprotĂ©ines chez les Afro-amĂ©ricains. Lâobjectif est de dĂ©terminer la force prĂ©dictive de lâinsulino-rĂ©sistance (IR) par les ratios triglycĂ©rides-par-HDL-cholestĂ©rol (TG/HDL-C) et cholestĂ©rol total-par-HDL-cholestĂ©rol (CT/HDL-C) chez des adultes bĂ©ninois. LâĂ©tude est de type transversal, issue dâune enquĂȘte longitudinale sur le risque cardiomĂ©tabolique et a inclut 416 sujets ĂągĂ©s de 29 Ă 69 ans. Les mesures anthropomĂ©triques et les dosages de la glycĂ©mie Ă jeun, de lâinsulinĂ©mie, du CT, du HDL-C et des TG sont rĂ©alisĂ©s. LâIR est dĂ©finie par le 75Ăšme percentile des valeurs de « lâindice dâĂ©valuation de modĂšle d'homĂ©ostasie pour lâinsulino-rĂ©sistance» (HOMA IR). Les valeurs prĂ©dictives de lâIR par les ratios TG/HDL-C et CT/HDL-C sont dĂ©terminĂ©es par les aires sous les courbes (AUC) de la « fonction dâefficacitĂ© du rĂ©cepteur» (ROC). Les concentrations plasmatiques moyennes des lipides ont Ă©tĂ© en gĂ©nĂ©ral plus Ă©levĂ©es chez les IR que chez les non IR sauf pour les triglycĂ©rides : 0,9±0,5 mmol/L versus 0,8±0,4 mmol/L (p=0,138) chez les femmes, le cholestĂ©rol total : 4,7±1,7 mmol/L versus 4,3±1,2 mmol/L (p=0,161) et le HDL-CholestĂ©rol : 1,2±0,5 mmol/L versus 1,34±0,5 mmol/L (p=0,105) chez les hommes. Les AUC ROC de prĂ©diction de lâIR par le TG/HDL-C sont infĂ©rieures Ă Â 0,70 chez les femmes et les hommes, les obĂšses et les non obĂšses. LâAUC ROC de prĂ©diction de lâIR par le CT/HDL-C est supĂ©rieure Ă 0,70 seulement chez les femmes : 0,71 (0,64-0,78). Le ratio TG/HDL-C nâest pas un prĂ©dicteur de lâIR dans la population dâĂ©tude alors que le ratio CT/HDL-C prĂ©dit lâIR chez les femmes seulement. Ces rĂ©sultats contribueront au dĂ©pistage prĂ©coce de lâIR chez les femmes aux fins de la mise en place de mesures prĂ©ventives.Mots clĂ©s : PrĂ©diction, insulino-rĂ©sistance, lipoprotĂ©ines, dyslipidĂ©mies, BĂ©nin
Dissipation in planar resonant planetary systems
Close-in planetary systems detected by the Kepler mission present an excess
of periods ratio that are just slightly larger than some low order resonant
values. This feature occurs naturally when resonant couples undergo dissipation
that damps the eccentricities. However, the resonant angles appear to librate
at the end of the migration process, which is often believed to be an evidence
that the systems remain in resonance.
Here we provide an analytical model for the dissipation in resonant planetary
systems valid for low eccentricities. We confirm that dissipation accounts for
an excess of pairs that lie just aside from the nominal periods ratios, as
observed by the Kepler mission. In addition, by a global analysis of the phase
space of the problem, we demonstrate that these final pairs are non-resonant.
Indeed, the separatrices that exist in the resonant systems disappear with the
dissipation, and remains only a circulation of the orbits around a single
elliptical fixed point. Furthermore, the apparent libration of the resonant
angles can be explained using the classical secular averaging method. We show
that this artifact is only due to the severe damping of the amplitudes of the
eigenmodes in the secular motion.Comment: 18 pages, 20 figures, accepted to A&
Structural and dynamical properties of liquid Si. An orbital-free molecular dynamics study
Several static and dynamic properties of liquid silicon near melting have
been determined from an orbital free {\em ab-initio} molecular dynamics
simulation. The calculated static structure is in good agreement with the
available X-ray and neutron diffraction data. The dynamical structure shows
collective density excitations with an associated dispersion relation which
closely follows recent experimental data. It is found that liquid silicon can
not sustain the propagation of shear waves which can be related to the power
spectrum of the velocity autocorrelation function. Accurate estimates have also
been obtained for several transport coefficients. The overall picture is that
the dynamic properties have many characteristics of the simple liquid metals
although some conspicuous differences have been found.Comment: 12 pages, 11 figure
Stability of resonant configurations during the migration of planets and constraints on disk-planet interactions
We study the stability of mean-motion resonances (MMR) between two planets during their migration in a protoplanetary disk. We use an analytical model of resonances and describe the effect of the disk by a migration timescale (T-m,T-i) and an eccentricity damping timescale (T-e,T-i) for each planet (i = 1; 2 for the inner and outer planets, respectively). We show that the resonant configuration is stable if T-e,T-1/T-e,T-2 > (e(1)/e(2))(2). This general result can be used to put constraints on specific models of disk-planet interactions. For instance, using classical prescriptions for type-I migration, we show that when the angular momentum deficit (AMD) of the inner orbit is greater than the outer's orbit AMD, resonant systems must have a locally inverted disk density profile to stay locked in resonance during the migration. This inversion is very atypical of type-I migration and our criterion can thus provide an evidence against classical type-I migration. That is indeed the case for the Jupiter-mass resonant systems HD 60532b, c (3: 1 MMR), GJ 876b, c (2: 1 MMR), and HD 45364b, c (3: 2 MMR). This result may be evidence of type-II migration (gap-opening planets), which is compatible with the high masses of these planets
A 12-month follow-up of a mobile-based (mHealth) obesity prevention intervention in pre-school children: the MINISTOP randomized controlled trial
Background: To date, few mobile health (mHealth) interventions aimed at changing lifestyle behaviors have
measured long term effectiveness. At the 6-month follow-up the MINISTOP trial found a statistically significant
intervention effect for a composite score comprised of fat mass index (FMI) as well as dietary and physical activity
variables; however, no intervention effect was observed for FMI. Therefore, the aim of this study was to investigate
if the MINISTOP intervention 12-months after baseline measurements: (i) improved FMI and (ii) had a maintained
effect on a composite score comprised of FMI and dietary and physical activity variables.
Methods: A two-arm parallel randomized controlled trial was conducted in 315 healthy 4.5 year old children
between January 2014 and October 2015. Parentsâ of the participating children either received the MINISTOP
intervention or a basic pamphlet on dietary and physical activity behaviors (control group). After 6 months,
participants did not have access to the intervention content and were measured again 6 months later (i.e. the
12-month follow-up). The Wilcoxon rank-sum test was then used to examine differences between the groups.
Results: At the 12-month follow-up, no statistically significant difference was observed between the intervention
and control groups for FMI (p = 0.57) and no maintained effect for the change in composite score was observed
(mean ± standard deviation for the intervention and control group: + 0.53 ± 1.49 units and + 0.35 ± 1.27 units
respectively, p = 0.25 between groups).
Conclusions: The intervention effect observed at the 6-month follow-up on the composite score was not
maintained at the 12-month follow-up, with no effect on FMI being observed at either follow-up. Future studies
using mHealth are needed to investigate how changes in obesity related markers in young children can be
maintained over longer time periods.The MINISTOP project was funded by the Swedish Research Council (project
no. 2012â2883), the Swedish Research Council for Health, Working Life and
Welfare (2012â0906), Bo and Vera Axson Johnsons Foundation, and
Karolinska Institutet (M.L.). C.D.N was supported by the Swedish Nutrition
Foundation and S.S was funded by the Seaver Foundation. None of the
funding bodies had any contributions or influence in the design of the
study, data collection, analysis, interpretation of the data, or the writing of
the manuscript
Essential requirement for sphingosine kinase activity in eNOS-dependent NO release and vasorelaxation
Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that acts both as an extracellular ligand for endothelial differentiation gene receptor family and as an intracellular second messenger. Cellular levels of S1P are low and tightly regulated by sphingosine kinase (SPK). Recent studies have suggested that eNOS pathway may function as a downstream target for the biological effects of receptor-mediated S1P. Here we have studied the possible interplay between intracellular SIP generation and the eNOS activation pathway. S1P causes an endothelium-dependent vasorelaxation in rat aorta that is PTX sensitive, inhibited by L-NAME that involves eNOS phosphorylation, and mainly dependent on hsp90. When rat aorta rings were incubated with the SPK inhibitor DL-threo-dihydrosphingosine (DTD), there was a concentration-dependent reduction of Ach-induced vasorelaxation, implying a consistent contribution of sphingolipid pathway through intracellular sphingosine release and phosphorylation. Co-immunoprecipitation experiments consistently showed increased association of hsp90 with eNOS after exposure of cells to S1P as well to BK or calcium ionophore A-23187. Interestingly, as opposite to A-23187, BK and S1P effect were significantly inhibited by pretreatment with the SPK inhibitor DTD. In conclusion, our data demonstrate that an interplay exists among eNOS, hsp90, and intracellularly generated S1P where eNOS coupling to hsp90 is a major determinant for NO release as confirmed by our functional and molecular studies
- âŠ