3,909 research outputs found
Splice variants in apoptotic pathway
Elimination of superfluous or mutated somatic cells is provided by various mechanisms including apoptosis, and deregulation of apoptotic signaling pathways contributes to oncogenesis. 40 years have passed since the term “apoptosis” was introduced by Kerr et al. in 1972; among the programmed cell death, a variety of therapeutic strategies especially targeting apoptotic pathways have been investigated. Alternative precursor messenger RNA splicing, by which the process the exons of pre-mRNA are spliced in different arrangements to produce structurally and functionally distinct mRNA and proteins, is another field in progress, and it has been recognized as one of the most important mechanisms that maintains genomic and functional diversity. A variety of apoptotic genes are regulated through alternative pre-mRNA splicing as well, some of which have important functions as pro-apoptotic and anti-apoptotic factors. In this article we summarized splice variants of some of the apoptotic genes including BCL2L1, BIRC5, CFLAR, and MADD, as well as the regulatory mechanisms of alternative splicing of these genes. If the information of the apoptosis and aberrant splicing in each of malignancies is integrated, it will become possible to target proper variants for apoptosis, and the trans-elements themselves can become specific targets of cancer therapy as well. This article is part of a Special Issue entitled “Apoptosis: Four Decades Later”
Time-dependent Turbulence in Stars
Three-dimensional (3D) hydrodynamic simulations of shell oxygen burning
(Meakin and Arnett 2007) exhibit bursty, recurrent fluctuations in turbulent
kinetic energy. These are shown to be due to a global instability in the
convective region, which has been suppressed in calculations of stellar
evolution which use mixing-length theory (MLT). Quantitatively similar behavior
occurs in the model of a convective roll (cell) of Lorenz (1963), which is
known to have a strange attractor that gives rise to random fluctuations in
time.An extension of the Lorenz model, which includes Kolmogorov damping and
nuclear burning, is shown to exhibit bursty, recurrent fluctuations like those
seen in the 3D simulations. A simple model of a convective layer (composed of
multiple Lorenz cells) gives luminosity fluctuations which are suggestive of
irregular variables (red giants and supergiants, Schwarzschild 1975).
Apparent inconsistencies between Arnett, Meakin, and Young (2009) and
Nordlund, Stein, and Asplund (2009) on the nature of convective driving have
been resolved, and are discussed.Comment: 8 pages, 2 figures, IAU Symposium 271 "Astrophysical Dynamics: From
Galaxies to Stars", Nice, FR, 201
Improved Fokker-Planck Equation for Resonance Line Scattering
A new Fokker-Planck equation is developed for treating resonance line
scattering, especially relevant to the treatment of Lyman alpha in the early
universe. It is a "corrected" form of the equation of Rybicki & Dell'Antonio
that now obeys detailed balance, so that the approach to thermal equilibrium is
properly described. The new equation takes into account the energy changes due
to scattering off moving particles, the recoil term of Basko, and stimulated
scattering. One result is a surprising unification of the equation for
resonance line scattering and the Kompaneets equation. An improved energy
exchange formula due to resonance line scattering is derived. This formula is
compared to previous formulas of Madau, Meikson, & Rees (1997) and Chen &
Miralda-Escud\'e (2004).Comment: 10 pages, no figures, submitted to Ap
Crustal Oscillations of Slowly Rotating Relativistic Stars
We study low-amplitude crustal oscillations of slowly rotating relativistic
stars consisting of a central fluid core and an outer thin solid crust. We
estimate the effect of rotation on the torsional toroidal modes and on the
interfacial and shear spheroidal modes. The results compared against the
Newtonian ones for wide range of neutron star models and equations of state.Comment: 15 page
Impact of neutron star oscillations on the accelerating electric field in the polar cap of pulsar: or could we see oscillations of the neutron star after the glitch in pulsar?
Pulsar "standard model", that considers a pulsar as a rotating magnetized
conducting sphere surrounded by plasma, is generalized to the case of
oscillating star. We developed an algorithm for calculation of the
Goldreich-Julian charge density for this case. We consider distortion of the
accelerating zone in the polar cap of pulsar by neutron star oscillations. It
is shown that for oscillation modes with high harmonic numbers (l,m) changes in
the Goldreich-Julian charge density caused by pulsations of neutron star could
lead to significant altering of an accelerating electric field in the polar cap
of pulsar. In the moderately optimistic scenario, that assumes excitation of
the neutron star oscillations by glitches, it could be possible to detect
altering of the pulsar radioemission due to modulation of the accelerating
field.Comment: 7 pages, 8 figures. Presented at the conference "Isolated Neutron
Stars: from the Interior to the Surface", London, April 24-28, 2006; to
appear in Astrophysics and Space Scienc
Porto Oscillation Code (POSC)
The Porto Oscillation Code (POSC) has been developed in 1995 and improved
over the years, with the main goal of calculating linear adiabatic oscillations
for models of solar-type stars. It has also been used to estimate the
frequencies and eigenfunctions of stars from the pre-main sequence up to the
sub-giant phase, having a mass between 0.8 and 4 solar masses.
The code solves the linearised perturbation equations of adiabatic pulsations
for an equilibrium model using a second order numerical integration method. The
possibility of using Richardson extrapolation is implemented. Several options
for the surface boundary condition can be used. In this work we briefly review
the key ingredients of the calculations, namely the equations, the numerical
scheme and the output.Comment: Accepted for publication in Astrophysics and Space Science
On the transfer of resonant-line radiation in mesh simulations
The last decade has seen applications of Adaptive Mesh Refinement (AMR)
methods for a wide range of problems from space physics to cosmology. With the
advent of these methods, in which space is discretized into a mesh of many
individual cubic elements, the contemporary analog of the extensively studied
line radiative transfer (RT) in a semi-infinite slab is that of RT in a cube.
In this study we provide an approximate solution of the RT equation, as well as
analytic expressions for the probability distribution functions (pdfs) of the
properties of photons emerging from a cube, and compare them with the
corresponding slab problem. These pdfs can be used to perform fast
resonant-line RT in optically thick AMR cells where, otherwise, it could take
unrealistically long times to transfer even a handful of photons.Comment: 5 two-column pages, 2 figures; matches accepted version, to appear on
Ap
The chaotic behavior of the black hole system GRS 1915+105
A modified non-linear time series analysis technique, which computes the
correlation dimension , is used to analyze the X-ray light curves of the
black hole system GRS 1915+105 in all twelve temporal classes. For four of
these temporal classes saturates to which indicates that
the underlying dynamical mechanism is a low dimensional chaotic system. Of the
other eight classes, three show stochastic behavior while five show deviation
from randomness. The light curves for four classes which depict chaotic
behavior have the smallest ratio of the expected Poisson noise to the
variability () while those for the three classes which depict
stochastic behavior is the highest (). This suggests that the temporal
behavior of the black hole system is governed by a low dimensional chaotic
system, whose nature is detectable only when the Poisson fluctuations are much
smaller than the variability.Comment: Accepted for publication in Astrophysical Journa
Oscillations of rapidly rotating relativistic stars
Non-axisymmetric oscillations of rapidly rotating relativistic stars are
studied using the Cowling approximation. The oscillation spectra have been
estimated by Fourier transforming the evolution equations describing the
perturbations. This is the first study of its kind and provides information on
the effect of fast rotation on the oscillation spectra while it offers the
possibility in studying the complete problem by including spacetime
perturbations. Our study includes both axisymmetric and non-axisymmetric
perturbations and provides limits for the onset of the secular bar mode
rotational instability. We also present approximate formulae for the dependence
of the oscillation spectrum from rotation. The results suggest that it is
possible to extract the relativistic star's parameters from the observed
gravitational wave spectrum.Comment: this article will be published in Physical Review
Radiative Transfer Effects in He I Emission Lines
We consider the effect of optical depth of the 2 ^{3}S level on the nebular
recombination spectrum of He I for a spherically symmetric nebula with no
systematic velocity gradients. These calculations, using many improvements in
atomic data, can be used in place of the earlier calculations of Robbins. We
give representative Case B line fluxes for UV, optical, and IR emission lines
over a range of physical conditions: T=5000-20000 K, n_{e}=1-10^{8} cm^{-3},
and tau_{3889}=0-100. A FORTRAN program for calculating emissivities for all
lines arising from quantum levels with n < 11 is also available from the
authors.
We present a special set of fitting formulae for the physical conditions
relevant to low metallicity extragalactic H II regions: T=12,000-20,000 K,
n_{e}=1-300 cm^{-3}, and tau_{3889} < 2.0. For this range of physical
conditions, the Case B line fluxes of the bright optical lines 4471 A, 5876 A,
and 6678 A, are changed less than 1%, in agreement with previous studies.
However, the 7065 A corrections are much smaller than those calculated by
Izotov & Thuan based on the earlier calculations by Robbins. This means that
the 7065 A line is a better density diagnostic than previously thought. Two
corrections to the fitting functions calculated in our previous work are also
given.Comment: To be published in 10 April 2002 ApJ; relevant code available at
ftp://wisp.physics.wisc.edu/pub/benjamin/Heliu
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