224 research outputs found
An Empirically Derived Three-Dimensional Laplace Resonance in the Gliese 876 Planetary System
We report constraints on the three-dimensional orbital architecture for all
four planets known to orbit the nearby M dwarf Gliese 876 based solely on
Doppler measurements and demanding long-term orbital stability. Our dataset
incorporates publicly available radial velocities taken with the ELODIE and
CORALIE spectrographs, HARPS, and Keck HIRES as well as previously unpublished
HIRES velocities. We first quantitatively assess the validity of the planets
thought to orbit GJ 876 by computing the Bayes factors for a variety of
different coplanar models using an importance sampling algorithm. We find that
a four-planet model is preferred over a three-planet model. Next, we apply a
Newtonian MCMC algorithm to perform a Bayesian analysis of the planet masses
and orbits using an n-body model in three-dimensional space. Based on the
radial velocities alone, we find that a 99% credible interval provides upper
limits on the mutual inclinations for the three resonant planets
( for the "c" and "b" pair and for
the "b" and "e" pair). Subsequent dynamical integrations of our posterior
sample find that the GJ 876 planets must be roughly coplanar
( and ), suggesting the amount of
planet-planet scattering in the system has been low. We investigate the
distribution of the respective resonant arguments of each planet pair and find
that at least one argument for each planet pair and the Laplace argument
librate. The libration amplitudes in our three-dimensional orbital model
supports the idea of the outer-three planets having undergone significant past
disk migration.Comment: 19 pages, 11 figures, 8 tables. Accepted to MNRAS. Posterior samples
available at https://github.com/benelson/GJ87
The 55 Cancri Planetary System: Fully Self-Consistent N-body Constraints and a Dynamical Analysis
We present an updated study of the planets known to orbit 55 Cancri A using
1,418 high-precision radial velocity observations from four observatories
(Lick, Keck, Hobby-Eberly Telescope, Harlan J. Smith Telescope) and transit
time/durations for the inner-most planet, 55 Cancri "e" (Winn et al. 2011). We
provide the first posterior sample for the masses and orbital parameters based
on self-consistent n-body orbital solutions for the 55 Cancri planets, all of
which are dynamically stable (for at least years). We apply a GPU
version of Radial velocity Using N-body Differential evolution Markov Chain
Monte Carlo (RUN DMC; B. Nelson et al. 2014) to perform a Bayesian analysis of
the radial velocity and transit observations. Each of the planets in this
remarkable system has unique characteristics. Our investigation of high-cadence
radial velocities and priors based on space-based photometry yields an updated
mass estimate for planet "e" ( M), which affects its
density ( g cm) and inferred bulk composition.
Dynamical stability dictates that the orbital plane of planet "e" must be
aligned to within of the orbital plane of the outer planets (which we
assume to be coplanar). The mutual interactions between the planets "b" and "c"
may develop an apsidal lock about . We find 36-45% of all our model
systems librate about the anti-aligned configuration with an amplitude of
. Other cases showed short-term perturbations in the
libration of , circulation, and nodding, but we find the
planets are not in a 3:1 mean-motion resonance. A revised orbital period and
eccentricity for planet "d" pushes it further toward the closest known Jupiter
analog in the exoplanet population.Comment: 12 pages, 5 figures, 4 tables, accepted to MNRAS. Figure 2 (left) is
updated from published version. Posterior samples available at
http://www.personal.psu.edu/ben125/Downloads.htm
CALHM3 Is Essential for Rapid Ion Channel-Mediated Purinergic Neurotransmission of GPCR-Mediated Tastes
Binding of sweet, umami, and bitter tastants to G protein-coupled receptors (GPCRs) in apical membranes of type II taste bud cells (TBCs) triggers action potentials that activate a voltage-gated nonselective ion channel to release ATP to gustatory nerves mediating taste perception. Although calcium homeostasis modulator 1 (CALHM1) is necessary for ATP release, the molecular identification of the channel complex that provides the conductive ATP-release mechanism suitable for action potential-dependent neurotransmission remains to be determined. Here we show that CALHM3 interacts with CALHM1 as a pore-forming subunit in a CALHM1/CALHM3 hexameric channel, endowing it with fast voltage-activated gating identical to that of the ATP-release channel in vivo. Calhm3 is co-expressed with Calhm1 exclusively in type II TBCs, and its genetic deletion abolishes taste-evoked ATP release from taste buds and GPCR-mediated taste perception. Thus, CALHM3, together with CALHM1, is essential to form the fast voltage-gated ATP-release channel in type II TBCs required for GPCR-mediated tastes. Ma et al. identify a CALHM1/CALHM3 hetero-hexameric ion channel as the mechanism by which type II taste bud cells release ATP as a neurotransmitter to gustatory neurons in response to GPCR-mediated tastes, including sweet, bitter, and umami substances. © 2018 Elsevier Inc
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Construction and analysis of tag single nucleotide polymorphism maps for six human-mouse orthologous candidate genes in type 1 diabetes.
BACKGROUND: One strategy to help identify susceptibility genes for complex, multifactorial diseases is to map disease loci in a representative animal model of the disorder. The nonobese diabetic (NOD) mouse is a model for human type 1 diabetes. Linkage and congenic strain analyses have identified several NOD mouse Idd (insulin dependent diabetes) loci, which have been mapped to small chromosome intervals, for which the orthologous regions in the human genome can be identified. Here, we have conducted re-sequencing and association analysis of six orthologous genes identified in NOD Idd loci: NRAMP1/SLC11A1 (orthologous to Nramp1/Slc11a1 in Idd5.2), FRAP1 (orthologous to Frap1 in Idd9.2), 4-1BB/CD137/TNFRSF9 (orthologous to 4-1bb/Cd137/Tnrfrsf9 in Idd9.3), CD101/IGSF2 (orthologous to Cd101/Igsf2 in Idd10), B2M (orthologous to B2m in Idd13) and VAV3 (orthologous to Vav3 in Idd18). RESULTS: Re-sequencing of a total of 110 kb of DNA from 32 or 96 type 1 diabetes cases yielded 220 single nucleotide polymorphisms (SNPs). Sixty-five SNPs, including 54 informative tag SNPs, and a microsatellite were selected and genotyped in up to 1,632 type 1 diabetes families and 1,709 cases and 1,829 controls. CONCLUSION: None of the candidate regions showed evidence of association with type 1 diabetes (P values > 0.2), indicating that common variation in these key candidate genes does not play a major role in type 1 diabetes susceptibility in the European ancestry populations studied.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are
Discovery and Follow-up of ASASSN-19dj: An X-ray and UV Luminous TDE in an Extreme Post-Starburst Galaxy
We present observations of ASASSN-19dj, a nearby tidal disruption event (TDE)
discovered in the post-starburst galaxy KUG 0810+227 by the All-Sky Automated
Survey for Supernovae (ASAS-SN) at a distance of d 98 Mpc. We observed
ASASSN-19dj from 21 to 392 days relative to peak UV/optical emission using
high-cadence, multi-wavelength spectroscopy and photometry. From the ASAS-SN
-band data, we determine that the TDE began to brighten on 2019 February 6.8
and for the first 25 days the rise was consistent with a flux
power-law. ASASSN-19dj peaked in the UV/optical on 2019 March 6.5 (MJD =
58548.5) at a bolometric luminosity of . Initially remaining roughly constant in X-rays and slowly fading
in the UV/optical, the X-ray flux increased by over an order of magnitude
225 days after peak, resulting from the expansion of the X-ray emitting
surface. The late-time X-ray emission is well-fit by a blackbody with an
effective radius of and a temperature of
. Analysis of Catalina Real-Time Transient
Survey images reveals a nuclear outburst roughly 14.5 years earlier with a
smooth decline and a luminosity of erg
s, although the nature of the flare is unknown. ASASSN-19dj occurred in
the most extreme post-starburst galaxy yet to host a TDE, with Lick
H = \AA.Comment: 25 pages, 14 figures. Will be submitted to MNRAS. For a short video
description please see https://youtu.be/WjTZwO7vcF
Neurosteroids and Self-Reported Pain in Veterans Who Served in the U.S. Military after September 11, 2001
Nearly half of Operation Enduring Freedom / Operation Iraqi Freedom (OEF/OIF) veterans experience continued pain post-deployment. Several investigations report analgesic effects of allopregnanolone and other neurosteroids in animal models, but few data are currently available focusing on neurosteroids in clinical populations. Allopregnanolone positively modulates GABAA receptors and demonstrates pronounced analgesic and anxiolytic effects in rodents, yet studies examining the relationship between pain and allopregnanolone in humans are limited. We thus hypothesized that endogenous allopregnanolone and other neurosteroid levels may be negatively correlated with self-reported pain symptoms in humans
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