66 research outputs found
An evolutionary study of the pulsating subdwarf B eclipsing binary PG1336-018 (NY Vir)
The formation of subdwarf B (sdB) stars is not well understood within the
current framework of stellar single and binary evolution. In this study, we
focus on the formation and evolution of the pulsating sdB star in the very
short-period eclipsing binary PG1336-018. We aim at refining the formation
scenario of this unique system, so that it can be confronted with observations.
We probe the stellar structure of the progenitors of sdB stars in short-period
binaries using detailed stellar evolution calculations. Applying this to
PG1336-018 we reconstruct the common-envelope phase during which the sdB star
was formed. The results are interpreted in terms of the standard
common-envelope formalism (the alpha-formalism) based on the energy equation,
and an alternative description (the gamma-formalism) using the angular momentum
equation. We find that if the common-envelope evolution is described by the
alpha-formalism, the sdB progenitor most likely experienced a helium flash. We
then expect the sdB mass to be between 0.39 and 0.48 Msun, and the sdB
progenitor initial mass to be below ~2 Msun. However, the results for the
gamma-formalism are less restrictive, and a broader sdB mass range (0.3 - 0.8
Msun) is possible in this case. Future seismic mass determination will give
strong constraints on the formation of PG1336-018 and, in particular, on the CE
phase.Comment: 9 pages, 7 figures, 2 tables, accepted for publication in A&
A splicing isoform of TEAD4 attenuates the Hippo–YAP signalling to inhibit tumour proliferation
Aberrant splicing is frequently found in cancer, yet the biological consequences of such alterations are mostly undefined. Here we report that the Hippo–YAP signalling, a key pathway that regulates cell proliferation and organ size, is under control of a splicing switch. We show that TEAD4, the transcription factor that mediates Hippo–YAP signalling, undergoes alternative splicing facilitated by the tumour suppressor RBM4, producing a truncated isoform, TEAD4-S, which lacks an N-terminal DNA-binding domain, but maintains YAP interaction domain. TEAD4-S is located in both the nucleus and cytoplasm, acting as a dominant negative isoform to YAP activity. Consistently, TEAD4-S is reduced in cancer cells, and its re-expression suppresses cancer cell proliferation and migration, inhibiting tumour growth in xenograft mouse models. Furthermore, TEAD4-S is reduced in human cancers, and patients with elevated TEAD4-S levels have improved survival. Altogether, these data reveal a splicing switch that serves to fine tune the Hippo–YAP pathway
Slowing down atomic diffusion in subdwarf B stars: mass loss or turbulence?
Subdwarf B stars show chemical peculiarities that cannot be explained by
diffusion theory alone. Both mass loss and turbulence have been invoked to slow
down atomic diffusion in order to match observed abundances. The fact that some
sdB stars show pulsations gives upper limits on the amount of mass loss and
turbulent mixing allowed. Consequently, non-adiabatic asteroseismology has the
potential to decide which process is responsible for the abundance anomalies.
We compute for the first time seismic properties of sdB models with atomic
diffusion included consistently during the stellar evolution. The diffusion
equations with radiative forces are solved for H, He, C, N, O, Ne, Mg, Fe and
Ni. We examine the effects of various mass-loss rates and mixed surface masses
on the abundances and mode stability. It is shown that the mass-loss rates
needed to simulate the observed He abundances (10^{-14}<=Mdot
[Msun/yr]<=10^{-13}) are not consistent with observed pulsations. We find that
for pulsations to be driven the rates should be Mdot<=10^{-15} Msun/yr. On the
other hand, weak turbulent mixing of the outer 10^{-6} Msun can explain the He
abundance anomalies while still allowing pulsations to be driven. The origin of
the turbulence remains unknown but the presence of pulsations gives tight
constraints on the underlying turbulence model.Comment: 12 pages, 8 figures, 1 table, accepted for publication in MNRA
Gravitational settling in pulsating subdwarf B stars and their progenitors
Diffusion of atoms can be important during quiescent phases of stellar
evolution. Particularly in the very thin inert envelopes of subdwarf B stars,
diffusive movements will considerably change the envelope structure and the
surface abundances on a short timescale. Also, the subdwarfs will inherit the
effects of diffusion in their direct progenitors, namely giants near the tip of
the red giant branch. This will influence the global evolution and the
pulsational properties of subdwarf B stars. We investigate the impact of
gravitational settling, thermal diffusion and concentration diffusion on the
evolution and pulsations of subdwarf B stars. Our diffusive stellar models are
compared with models evolved without diffusion. We constructed subdwarf B
models with a mass of 0.465 Msun from a 1 and 3 Msun ZAMS progenitor. The low
mass star ignited helium in an energetic flash, while the intermediate mass
star started helium fusion gently. For each progenitor type we computed series
with and without atomic diffusion. Atomic diffusion in red giants causes the
helium core mass at the onset of helium ignition to be larger. We find an
increase of 0.0015 Msun for the 1 Msun model and 0.0036 Msun for the 3 Msun
model. The effects on the red giant surface abundances are small after the
first dredge up. The evolutionary tracks of the diffusive subdwarf B models are
shifted to lower surface gravities and effective temperatures due to outward
diffusion of hydrogen. This affects both the frequencies of the excited modes
and the overall frequency spectrum. Especially the structure and pulsations of
the post-non-degenerate sdB star are drastically altered, proving that atomic
diffusion cannot be ignored in these stars.Comment: 10 pages, 6 figures, accepted for publication in A&
A seismic approach to testing different formation channels of subdwarf B stars
There are many unknowns in the formation of subdwarf B stars. Different
formation channels are considered to be possible and to lead to a variety of
helium-burning subdwarfs. All seismic models to date, however, assume that a
subdwarf B star is a post-helium-flash-core surrounded by a thin inert layer of
hydrogen. We examine an alternative formation channel, in which the subdwarf B
star originates from a massive (>~2 Msun) red giant with a non-degenerate
helium-core. Although these subdwarfs may evolve through the same region of the
log g-Teff diagram as the canonical post-flash subdwarfs, their interior
structure is rather different. We examine how this difference affects their
pulsation modes and whether it can be observed.
Using detailed stellar evolution calculations we construct subdwarf B models
from both formation channels. The iron accumulation in the driving region due
to diffusion, which causes the excitation of the modes, is approximated by a
Gaussian function. The pulsation modes and frequencies are calculated with a
non-adiabatic pulsation code. A detailed comparison of two subdwarf B models
from different channels, but with the same log g and Teff, shows that their
mode excitation is different. The excited frequencies are lower for the
post-flash than for the post-non-degenerate subdwarf B star. This is mainly due
to the differing chemical composition of the stellar envelope. A more general
comparison between two grids of models shows that the excited frequencies of
most post-non-degenerate subdwarfs cannot be well-matched with the frequencies
of post-flash subdwarfs. In the rare event that an acceptable seismic match is
found, additional information, such as mode identification and log g and Teff
determinations, allows us to distinguish between the two formation channels.Comment: 10 pages, 8 figures, 2 tables, accepted for publication in A&
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
Output Pulse Characteristics of a Mamyshev Fiber Oscillator
The dependence of the output pulse characteristics of a Mamyshev fiber oscillator on cavity parameters is investigated in detail. We analyze the change in pulse spectrum bandwidth, pulse duration, dechirped pulse duration and chirp with the change in fiber group velocity dispersion, fiber nonlinearity, gain, and filters by putting forward a numerical model. In particular, as one of the most important components, the effect of filters bandwidth and the central wavelength interval between them is discussed. The passive fibers are classified into two kinds according to their locations in the cavity, which are the one before the gain fiber and the one after the gain fiber. Numerical simulation results show that a wide spectrum can be obtained by increasing the nonlinearity of the second passive fiber, while the change in nonlinearity of the first passive fiber has a weak effect on spectrum broadening. A wide spectrum could also be obtained by increasing the nonlinearity or the small-signal gain coefficient of the gain fiber. A Yb-doped Mamyshev fiber oscillator is demonstrated. The results show the increase in pump power, which agrees reasonably well with the numerical simulation results
Deformation Detection Method of Mine Tunnel Based on Mobile Detection System
Subway structure safety detection is an important method to ensure the safe operation of trains. Efficient, high-precision, and automatic tunnel clearance detection is the key to ensure safe operations. This study introduces a mobile tunnel scanning system that integrates a scanner, an inertial measurement unit (IMU), and a rail car. Global Navigation Satellite System (GNSS) time and system hardware calibration are used to synchronize time and space information of the system; the attitude and speed are corrected using the control points from the tunnel to improve the accuracy of absolute positioning. The section coordinate system is converted using the control points and system calibration parameters to complete the tunnel clearance inspection, and the distance between the nearest point of the section and the clear height of the vault is given. Taking Fengxi Road’s Bashan tunnel section of Chongqing Metro Line 5 as an example, the overall system accuracy was tested. The accuracy of chord line measurements was within 1 mm, the internal coincidence accuracy of repeated measurements of the vault clear height was 1.1 mm, the internal coincidence accuracy of repeated measurements of the closest gauge point was 4.8 mm, and the system calibration accuracy was approximately 2 mm. Compared with the existing scheme, the system combines absolute measurement and relative measurement mode to judge the structural safety of tunnel section from multiple angles, high precision, and high efficiency
- …