1,412 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
Unit organization of the subject: child care and development with laboratory experience in nursery school, secondary level.
Thesis (Ed.M.)--Boston Universit
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
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&
More haste, less speed: Could public-private partnerships advance cellular immunotherapies?
Cellular immunotherapies promise to transform cancer care. However, they must overcome serious challenges, including: (1) the need to identify and characterize novel cancer antigens to expand the range of therapeutic targets; (2) the need to develop strategies to minimize serious adverse events, such as cytokine release syndrome and treatment-related toxicities; and (3) the need to develop efficient production/manufacturing processes to reduce costs. Here, we discuss whether these challenges might better be addressed through forms of public-private research collaborations, including public-private partnerships (PPPs), or whether these challenges are best addressed by way of standard market transactions. We reviewed 14 public-private relationships and 25 underlying agreements for the clinical development of cancer cellular immunotherapies in the US. Most were based on bilateral research agreements and pure market transactions in the form of service contracts and technology licenses, which is representative of the commercialization focus of the field. We make the strategic case that multiparty PPPs may better advance cancer antigen discovery and characterization and improved cell processing/manufacturing and related activities. In the rush toward the competitive end of the translational continuum for cancer cellular immunotherapy and the attendant focus on commercialization, many gaps have appeared in our understanding of cellular biology, immunology, and bioengineering. We conclude that the model of bilateral agreements between leading research institutions and the private sector may be inadequate to efficiently harness the interdisciplinary skills and knowledge of the public and private sectors to bring these promising therapies to the clinic for the benefit of cancer patients
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
Nematicity as a route to a magnetic field-induced spin density wave order; application to the high temperature cuprates
The electronic nematic order characterized by broken rotational symmetry has
been suggested to play an important role in the phase diagram of the high
temperature cuprates. We study the interplay between the electronic nematic
order and a spin density wave order in the presence of a magnetic field. We
show that a cooperation of the nematicity and the magnetic field induces a
finite coupling between the spin density wave and spin-triplet staggered flux
orders. As a consequence of such a coupling, the magnon gap decreases as the
magnetic field increases, and it eventually condenses beyond a critical
magnetic field leading to a field-induced spin density wave order. Both
commensurate and incommensurate orders are studied, and the experimental
implications of our findings are discussed.Comment: 5 pages, 3 figure
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