4,374 research outputs found
Puzzling out the coexistence of terrestrial planets and giant exoplanets. The 2/1 resonant periodic orbits
Hundreds of giant planets have been discovered so far and the quest of
exo-Earths in giant planet systems has become intriguing. In this work, we aim
to address the question of the possible long-term coexistence of a terrestrial
companion on an orbit interior to a giant planet, and explore the extent of the
stability regions for both non-resonant and resonant configurations. Our study
focuses on the restricted three-body problem, where an inner terrestrial planet
(massless body) moves under the gravitational attraction of a star and an outer
massive planet on a circular or elliptic orbit. Using the Detrended Fast
Lyapunov Indicator as a chaotic indicator, we constructed maps of dynamical
stability by varying both the eccentricity of the outer giant planet and the
semi-major axis of the inner terrestrial planet, and identify the boundaries of
the stability domains. Guided by the computation of families of periodic
orbits, the phase space is unravelled by meticulously chosen stable periodic
orbits, which buttress the stability domains. We provide all possible stability
domains for coplanar symmetric configurations and show that a terrestrial
planet, either in mean-motion resonance or not, can coexist with a giant
planet, when the latter moves on either a circular or an (even highly)
eccentric orbit. New families of symmetric and asymmetric periodic orbits are
presented for the 2/1 resonance. It is shown that an inner terrestrial planet
can survive long time spans with a giant eccentric outer planet on resonant
symmetric orbits, even when both orbits are highly eccentric. For 22 detected
single-planet systems consisting of a giant planet with high eccentricity, we
discuss the possible existence of a terrestrial planet. This study is
particularly suitable for the research of companions among the detected systems
with giant planets, and could assist with refining observational data.Comment: Accepted for publication in A&
Origin and continuation of 3/2, 5/2, 3/1, 4/1 and 5/1 resonant periodic orbits in the circular and elliptic restricted three-body problem
We consider a planetary system consisting of two primaries, namely a star and
a giant planet, and a massless secondary, say a terrestrial planet or an
asteroid, which moves under their gravitational attraction. We study the
dynamics of this system in the framework of the circular and elliptic
restricted TBP, when the motion of the giant planet describes circular and
elliptic orbits, respectively. Originating from the circular family, families
of symmetric periodic orbits in the 3/2, 5/2, 3/1, 4/1 and 5/1 mean-motion
resonances are continued in the circular and the elliptic problems. New
bifurcation points from the circular to the elliptic problem are found for each
of the above resonances and thus, new families, continued from these points are
herein presented. Stable segments of periodic orbits were found at high
eccentricity values of the already known families considered as whole unstable
previously. Moreover, new isolated (not continued from bifurcation points)
families are computed in the elliptic restricted problem. The majority of the
new families mainly consist of stable periodic orbits at high eccentricities.
The families of the 5/1 resonance are investigated for the first time in the
restricted three-body problems. We highlight the effect of stable periodic
orbits on the formation of stable regions in their vicinity and unveil the
boundaries of such domains in phase space by computing maps of dynamical
stability. The long-term stable evolution of the terrestrial planets or
asteroids is dependent on the existence of regular domains in their dynamical
neighbourhood in phase space, which could host them for long time spans. This
study, besides other celestial architectures that can be efficiently modelled
by the circular and elliptic restricted problems, is particularly appropriate
for the discovery of terrestrial companions among the single-giant planet
systems discovered so far.Comment: Accepted for publication in Celestial Mechanics and Dynamical
Astronom
Sandplay with children in the school setting
Sandplay therapy, developed by Margaret Lowenfeld, is a technique where children choose miniature objects to place in a sand tray to create a concrete representation of their internal struggles. The counselor\u27s role is to create a safe and protected environment and does not impose personal suggestions or ideas. The counselor can choose to facilitate different types of sandplay with a child: directed, nondirected, static, moving, or interactive. Sandplay therapy offers techniques such as hide and seek, family sand trays, mazes, and self-figures. Sandplay therapy is effective with children in the school setting. Teachers report that students return to class more relaxed, calm, happy, and focused after doing a sand tray (Allan & Berry, 1987). Mental health professionals should consider the limitations of sandplay
Sub-2 cm/s passivation of silicon surfaces by aprotic solutions
Minimizing recombination at semiconductor surfaces is required for the accurate determination of the bulk carrier lifetime. Proton donors, such as hydrofluoric acid and superacids, are well known to provide highly effective short-term surface passivation. We demonstrate here that aprotic solutions based on bis(trifluoromethanesulfonyl)methane (TFSM) in hexane or pentane can also result in excellent passivation of (100)-orientation silicon surfaces. We show that the optimized TFSM-pentane passivation scheme can measure effective lifetimes up to 20 ms, with a surface recombination velocity of 1.7 cm s1 at an excess carrier density of 1015 cm3 . Fitting injection-dependent lifetime curves requires chemical passivation and field effect passivation from a negatively charged layer with a charge density of 1010–1011 q cm2 . The slightly higher recombination velocity of 2.3 cm s1 measured with TFSM-hexane can be explained by a lower charge density in the passivating layer, suggesting that the steric hindrance associated with the solvent size could play a role in the passivation mechanism. Finally, phosphorus nuclear magnetic resonance experiments confirm that TFSM-based solutions have Lewis acidity without being superacids, which opens up opportunities for them to be used in materials systems sensitive to superacidic environments
RNA-seq reveals post-transcriptional regulation of Drosophila insulin-like peptide dilp8 and the neuropeptide-like precursor Nplp2 by the exoribonuclease Pacman/XRN1
Ribonucleases are critically important in many cellular and developmental processes and defects in their expression are associated with human disease. Pacman/XRN1 is a highly conserved cytoplasmic exoribonuclease which degrades RNAs in a 5' - 3' direction. In Drosophila, null mutations in pacman result in small imaginal discs, a delay in onset of pupariation and lethality during the early pupal stage. In this paper, we have used RNA-seq in a genome-wide search for mRNAs misregulated in pacman null wing imaginal discs. Only 4.2% of genes are misregulated ±>2-fold in pacman null mutants compared to controls, in line with previous work showing that Pacman has specificity for particular mRNAs. Further analysis of the most upregulated mRNAs showed that Pacman post-transcriptionally regulates the expression of the secreted insulin-like peptide Dilp8. Dilp8 is related to human IGF-1, and has been shown to co-ordinate tissue growth with developmental timing in Drosophila. The increased expression of Dilp8 is consistent with the developmental delay seen in pacman null mutants. Our analysis, together with our previous results, show that the normal role of this exoribonuclease in imaginal discs is to suppress the expression of transcripts that are crucial in apoptosis and growth control during normal development
Exploiting periodic orbits as dynamical clues for Kepler and K2 systems
Many extrasolar systems possessing planets in mean-motion resonance or
resonant chain have been discovered to date. The transit method coupled with
transit timing variation analysis provides an insight into the physical and
orbital parameters of the systems, but suffers from observational limitations.
When a (near-)resonant planetary system resides in the dynamical neighbourhood
of a stable periodic orbit, its long-term stability, and thus survival, can be
guaranteed. We use the intrinsic property of the periodic orbits, namely their
linear horizontal and vertical stability, to validate or further constrain the
orbital elements of detected two-planet systems. We computed the families of
periodic orbits in the general three-body problem for several two-planet Kepler
and K2 systems. The dynamical neighbourhood of the systems is unveiled with
maps of dynamical stability. Additional validations or constraints on the
orbital elements of K2-21, K2-24, Kepler-9, and (non-coplanar) Kepler-108
near-resonant systems were achieved. While a mean-motion resonance locking
protects the long-term evolution of the systems K2-21 and K2-24, such a
resonant evolution is not possible for the Kepler-9 system, whose stability is
maintained through an apsidal anti-alignment. For the Kepler-108 system, we
find that the stability of its mutually inclined planets could be justified
either solely by a mean-motion resonance, or in tandem with an inclination-type
resonance. Going forward, dynamical analyses based on periodic orbits could
yield better constrained orbital elements of near-resonant extrasolar systems
when performed in parallel to the fitting of the observational data.Comment: Accepted for publication in A&
Mass spectrometry of the white adipose metabolome in a hibernating mammal reveals seasonal changes in alternate fuels and carnitine derivatives
Mammalian hibernators undergo substantial changes in metabolic function throughout the seasonal hibernation cycle. We report here the polar metabolomic profile of white adipose tissue isolated from active and hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus). Polar compounds in white adipose tissue were extracted from five groups representing different timepoints throughout the seasonal activity-torpor cycle and analyzed using hydrophilic interaction liquid chromatography-mass spectrometry in both the positive and negative ion modes. A total of 224 compounds out of 660 features detected after curation were annotated. Unsupervised clustering using principal component analysis revealed discrete clusters representing the different seasonal timepoints throughout hibernation. One-way analysis of variance and feature intensity heatmaps revealed metabolites that varied in abundance between active and torpid timepoints. Pathway analysis compared against the KEGG database demonstrated enrichment of amino acid metabolism, purine metabolism, glycerophospholipid metabolism, and coenzyme A biosynthetic pathways among our identified compounds. Numerous carnitine derivatives and a ketone that serves as an alternate fuel source, betahydroxybutyrate (BHB), were among molecules found to be elevated during torpor. Elevated levels of the BHB-carnitine conjugate during torpor suggests the synthesis of beta-hydroxybutyrate in white adipose mitochondria, which may contribute directly to elevated levels of circulating BHB during hibernation
Mass spectrometry of the white adipose metabolome in a hibernating mammal reveals seasonal changes in alternate fuels and carnitine derivatives
Mammalian hibernators undergo substantial changes in metabolic function throughout the seasonal hibernation cycle. We report here the polar metabolomic profile of white adipose tissue isolated from active and hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus). Polar compounds in white adipose tissue were extracted from five groups representing different timepoints throughout the seasonal activity-torpor cycle and analyzed using hydrophilic interaction liquid chromatography-mass spectrometry in both the positive and negative ion modes. A total of 224 compounds out of 660 features detected after curation were annotated. Unsupervised clustering using principal component analysis revealed discrete clusters representing the different seasonal timepoints throughout hibernation. One-way analysis of variance and feature intensity heatmaps revealed metabolites that varied in abundance between active and torpid timepoints. Pathway analysis compared against the KEGG database demonstrated enrichment of amino acid metabolism, purine metabolism, glycerophospholipid metabolism, and coenzyme A biosynthetic pathways among our identified compounds. Numerous carnitine derivatives and a ketone that serves as an alternate fuel source, betahydroxybutyrate (BHB), were among molecules found to be elevated during torpor. Elevated levels of the BHB-carnitine conjugate during torpor suggests the synthesis of beta-hydroxybutyrate in white adipose mitochondria, which may contribute directly to elevated levels of circulating BHB during hibernation
Influence of periodic orbits on the formation of giant planetary systems
The late-stage formation of giant planetary systems is rich in interesting
dynamical mechanisms. Previous simulations of three giant planets initially on
quasi-circular and quasi-coplanar orbits in the gas disc have shown that highly
mutually inclined configurations can be formed, despite the strong eccentricity
and inclination damping exerted by the disc. Much attention has been directed
to inclination-type resonance, asking for large eccentricities to be acquired
during the migration of the planets. Here we show that inclination excitation
is also present at small to moderate eccentricities in two-planet systems that
have previously experienced an ejection or a merging and are close to resonant
commensurabilities at the end of the gas phase. We perform a dynamical analysis
of these planetary systems, guided by the computation of planar families of
periodic orbits and the bifurcation of families of spatial periodic orbits. We
show that inclination excitation at small to moderate eccentricities can be
produced by (temporary) capture in inclination-type resonance and the possible
proximity of the non-coplanar systems to spatial periodic orbits contributes to
maintaining their mutual inclination over long periods of time.Comment: 13 pages, 7 figures, Published in Celestial Mechanics and Dynamical
Astronomy, 02/201
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