63 research outputs found
The role of multiple marks in epigenetic silencing and the emergence of a stable bivalent chromatin state
We introduce and analyze a minimal model of epigenetic silencing in budding
yeast, built upon known biomolecular interactions in the system. Doing so, we
identify the epigenetic marks essential for the bistability of epigenetic
states. The model explicitly incorporates two key chromatin marks, namely H4K16
acetylation and H3K79 methylation, and explores whether the presence of
multiple marks lead to a qualitatively different systems behavior. We find that
having both modifications is important for the robustness of epigenetic
silencing. Besides the silenced and transcriptionally active fate of chromatin,
our model leads to a novel state with bivalent (i.e., both active and
silencing) marks under certain perturbations (knock-out mutations, inhibition
or enhancement of enzymatic activity). The bivalent state appears under several
perturbations and is shown to result in patchy silencing. We also show that the
titration effect, owing to a limited supply of silencing proteins, can result
in counter-intuitive responses. The design principles of the silencing system
is systematically investigated and disparate experimental observations are
assessed within a single theoretical framework. Specifically, we discuss the
behavior of Sir protein recruitment, spreading and stability of silenced
regions in commonly-studied mutants (e.g., sas2, dot1) illuminating the
controversial role of Dot1 in the systems biology of yeast silencing.Comment: Supplementary Material, 14 page
An 11 Earth-mass, Long-period Sub-Neptune Orbiting a Sun-like Star
Although several thousands of exoplanets have now been detected and
characterized, observational biases have led to a paucity of long-period,
low-mass exoplanets with measured masses and a corresponding lag in our
understanding of such planets. In this paper we report the mass estimation and
characterization of the long-period exoplanet Kepler-538b. This planet orbits a
Sun-like star (V = 11.27) with M_* = 0.892 +/- (0.051, 0.035) M_sun and R_* =
0.8717 +/- (0.0064, 0.0061) R_sun. Kepler-538b is a 2.215 +/- (0.040, 0.034)
R_earth sub-Neptune with a period of P = 81.73778 +/- 0.00013 d. It is the only
known planet in the system. We collected radial velocity (RV) observations with
HIRES on Keck I and HARPS-N on the TNG. We characterized stellar activity by a
Gaussian process with a quasi-periodic kernel applied to our RV and cross
correlation function full width at half maximum (FWHM) observations. By
simultaneously modeling Kepler photometry, RV, and FWHM observations, we found
a semi-amplitude of K = 1.68 +/- (0.39, 0.38) m s^-1 and a planet mass of M_p =
10.6 +/- (2.5, 2.4) M_earth. Kepler-538b is the smallest planet beyond P = 50 d
with an RV mass measurement. The planet likely consists of a significant
fraction of ices (dominated by water ice), in addition to rocks/metals, and a
small amount of gas. Sophisticated modeling techniques such as those used in
this paper, combined with future spectrographs with ultra high-precision and
stability will be vital for yielding more mass measurements in this poorly
understood exoplanet regime. This in turn will improve our understanding of the
relationship between planet composition and insolation flux and how the rocky
to gaseous transition depends on planetary equilibrium temperature
Planet Hunters TESS III: Two transiting planets around the bright G dwarf HD 152843
We report on the discovery and validation of a two-planet system around a
bright (V = 8.85 mag) early G dwarf (1.43 , 1.15 , TOI
2319) using data from NASA's Transiting Exoplanet Survey Satellite (TESS).
Three transit events from two planets were detected by citizen scientists in
the month-long TESS light curve (sector 25), as part of the Planet Hunters TESS
project. Modelling of the transits yields an orbital period of \Pb\ and radius
of for the inner planet, and a
period in the range 19.26-35 days and a radius of for the outer planet, which was only seen to transit once. Each
signal was independently statistically validated, taking into consideration the
TESS light curve as well as the ground-based spectroscopic follow-up
observations. Radial velocities from HARPS-N and EXPRES yield a tentative
detection of planet b, whose mass we estimate to be , and allow us to place an upper limit of
(99 per cent confidence) on the mass of planet c. Due to the
brightness of the host star and the strong likelihood of an extended H/He
atmosphere on both planets, this system offers excellent prospects for
atmospheric characterisation and comparative planetology
Radial velocity confirmation of K2-100b: A young, highly irradiated, and low-density transiting hot Neptune
We present a detailed analysis of HARPS-N radial velocity observations of
K2-100, a young and active star in the Praesepe cluster, which hosts a
transiting planet with a period of 1.7 days. We model the activity-induced
radial velocity variations of the host star with a multi-dimensional Gaussian
Process framework and detect a planetary signal of , which matches the transit ephemeris, and translates to a planet
mass of . We perform a suite of validation tests to
confirm that our detected signal is genuine. This is the first mass measurement
for a transiting planet in a young open cluster. The relatively low density of
the planet, , implies that K2-100b
retains a significant volatile envelope. We estimate that the planet is losing
its atmosphere at a rate of due to the high
level of radiation it receives from its host star.O.B. and S.Ai. acknowledge support from
the UK Science and Technology Facilities Council (STFC) under grants
ST/S000488/1 and ST/R004846/1. J.K., S.G. and A.P.H acknowledges support by Deutsche Forschungsgemeinschaft (DFG) grants PA525/18-1 and
PA525/19-1 and HPA 3279/12-1 within the DFG Schwerpunkt SPP 1992,
Exploring the Diversity of Extra-solar Planets. L.M. acknowledges support from PLATO ASI-INAF agreement n.2015-019-R.1-2018. S.Al. acknowledges the support from the Danish Council for Independent Research through the DFF Sapere Aude Starting Grant No. 4181-00487B, and
the Stellar Astrophysics Centre which funding is provided by The Danish National Research Foundation (Grant agreement no.: DNRF106). This
work is partly supported by JSPS KAKENHI Grant Numbers JP18H01265,
JP18H05439, 15H02063, and 18H05442 and JST PRESTO Grant Number
JPMJPR1775. M.C.V.F. and C.M.P. gratefully acknowledge the support of
the Swedish National Space Agency (DNR 174/18)
Measurement of the cross-section for Z → e<sup>+</sup>e<sup>-</sup> production in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV
A measurement of the cross-section for pp → Z → e+e− is presented using data at s√=7 TeV corresponding to an integrated luminosity of 0.94 fb−1. The process is measured within the kinematic acceptance p T > 20 GeV/c and 2 < η < 4.5 for the daughter electrons and dielectron invariant mass in the range 60–120 GeV/c 2. The cross-section is determined to be σ(pp→Z→e+e−)=76.0±0.8±2.0±2.6pb where the first uncertainty is statistical, the second is systematic and the third is the uncertainty in the luminosity. The measurement is performed as a function of Z rapidity and as a function of an angular variable which is closely related to the Z transverse momentum. The results are compared with previous LHCb measurements and with theoretical predictions from QCD
Study of eta-eta ' mixing from measurement of B-(s)(0) -> J/psi eta((')) decay rates
A study of B and Bs meson decays into J/ψ η and J/ψ η′ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fb−1 of integrated luminosity. The decay B0 → J/ψ η′ is observed for the first time. The following ratios of branching fractions are measured:
B(B0→J/ψη′)B(B0s→ J/ψη′)=(2.28±0.65 (stat)±0.10 (syst)±0.13 (fs/fd))×10−2,B(B0→ J/ψη)B(B0s→ J/ψη)=(1.85±0.61 (stat)±0.09 (syst)±0.11 (fs/fd))×10−2, where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a Bs or a B0 meson. The branching fraction ratios are used to determine the parameters of η − η′ meson mixing. In addition, the first evidence for the decay Bs → ψ(2S)η′ is reported, and the relative branching fraction is measured,
B(B0s→ ψ(2S)η′)B(B0s→ J/ψη′)=(38.7±9.0 (stat)±1.3 (syst)±0.9(B))×10−2, where the third uncertainty is due to the limited knowledge of the branching fractions of J/ψ and ψ(2S) mesons
Precise measurements of the properties of the B-1(5721)(0,+) and B-2*(5747)(0,+) states and observation of B-+,B-0 pi(-,+) mass structures
Invariant mass distributions of B+pi- and B0pi+ combinations are investigated
in order to study excited B mesons. The analysis is based on a data sample
corresponding to 3.0 fb-1 of pp collision data, recorded by the LHCb detector
at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses
and widths of the B_1(5721)^(0,+) and B_2*(5747)^(0,+) states are reported.
Clear enhancements, particularly prominent at high pion transverse momentum,
are seen over background in the mass range 5850--6000 MeV in both B+pi- and
B0pi+ combinations. The structures are consistent with the presence of four
excited B mesons, labelled B_J(5840)^(0,+) and B_J(5960)^(0,+), whose masses
and widths are obtained under different hypotheses for their quantum numbers.Comment: 29 pages, 5 Figures, 8 Table
- …