322 research outputs found
RR Lyrae - Theory vs Observation
The luminosities, effective temperatures and metallicities that are derived
empirically by Kovacs and Jurcsik from the light curves of a large number of
globular cluster and field RRab and RRc stars are compared to theoretical RR
Lyrae models. The strong luminosity dependence of the empirical blue and red
edges (Log L vs Log Teff diagram) is in disagreement with that of both
radiative and convective models. A reexamination of the theoretical
uncertainties in the modelling leads us to conclude that the disagreement is
irreconcilable.Comment: 6 pages, 5 figures (revised april 2000, revisions relatively minor
Hydrodynamical Survey of First Overtone Cepheids
A hydrodynamical survey of the pulsational properties of first overtone
Galactic Cepheids is presented. The goal of this study is to reproduce their
observed light- and radial velocity curves. The comparison between the models
and the observations is made in a quantitative manner on the level of the
Fourier coefficients. Purely radiative models fail to reproduce the observed
features, but convective models give good agreement.
It is found that the sharp features in the Fourier coefficients are indeed
caused by the P1/P4 = 2 resonance, despite the very large damping of the 4th
overtone. For the adopted mass-luminosity relation the resonance center lies
near a period of 4.2d +/- 0.2 as indicated by the observed radial velocity
data, rather than near 3.2d as the light-curves suggest.Comment: ApJ, 12 pages, (slightly) revise
Turbulent convection: comparing the moment equations to numerical simulations
The non-local hydrodynamic moment equations for compressible convection are
compared to numerical simulations. Convective and radiative flux typically
deviate less than 20% from the 3D simulations, while mean thermodynamic
quantities are accurate to at least 2% for the cases we have investigated. The
moment equations are solved in minutes rather than days on standard
workstations. We conclude that this convection model has the potential to
considerably improve the modelling of convection zones in stellar envelopes and
cores, in particular of A and F stars.Comment: 10 pages (6 pages of text including figure captions + 4 figures),
Latex 2e with AAS Latex 5.0 macros, accepted for publication in ApJ
RR Lyrae Variables in the Globular Cluster M55. The First Evidence for Non Radial Pulsations in RR Lyr Stars
We present the results of a photometric study of RR Lyrae variables in the
field of the globular cluster M55. We have discovered nine new RR Lyrae stars,
increasing the number of known variables in this cluster to 15 objects. Five of
the newly discovered variables belong to Bailey type RRc and two to type RRab.
Two background RRab stars are probable members of the Sagittarius dwarf galaxy.
Fourier decomposition of the light curves was used to derive basic properties
of the present sample of RR Lyrae variables. From an analysis of the RRc
variables we obtain a mean mass of , luminosity , effective temperature K, and helium
abundance . Based on the colors, periods and metallicities
of the RRab stars we estimate the value of the color excess for M55 to be equal
to . Using this value we derive the colors of the blue and
red edges of the instability strip in M55. The blue edge lies at
mag and the red edge lies at mag. We estimate the values of the
visual apparent and dereddened distance moduli to be and
, respectively. The light curves of three of the RRc variables
exhibit changes in amplitude of over 0.1 mag on the time scale of less than a
week, rather short for the Blazhko effect, but with no evidence for another
radial pulsational frequency. However we do detect other periodicities which
are clearly visible in the light curve after removing variations with the first
overtone radial frequency. This is strong evidence for the presence of
non-radial pulsations, a behavior common for Scuti stars but not yet
observed among RR Lyr variables.Comment: submitted to Astronomical Journal, 33 pages with 11 figure
Double-Mode Stellar Pulsations
The status of the hydrodynamical modelling of nonlinear multi-mode stellar
pulsations is discussed. The hydrodynamical modelling of steady double-mode
(DM) pulsations has been a long-standing quest that is finally being concluded.
Recent progress has been made thanks to the introduction of turbulent
convection in the numerical hydrodynamical codes which provide detailed results
for individual models. An overview of the modal selection problem in the HR
diagram can be obtained in the form of bifurcation diagrams with the help of
simple nonresonant amplitude equations that capture the DM phenomenon.Comment: 34 pages, to appear as a chapter in Nonlinear Stellar Pulsation in
the Astrophysics and Space Science Library (ASSL), Editors: M. Takeuti & D.
Sasselov (prints double column with pstops
'2:[email protected](22.0cm,-2cm)[email protected](22.0cm,11.0cm)' in.ps out.ps
Association between adenovirus viral load and mortality in pediatric allo-hct recipients. the multinational advance study
This multivariable analysis from the AdVance multicenter observational study assessed adenovirus (AdV) viremia peak, duration, and overall AdV viral burdenâmeasured as time-averaged area under the viremia curve over 16 weeks (AAUC0-16)âas predictors of all-cause mortality in pediatric allo-HCT recipients with AdV viremia. In the 6 months following allo-HCT, 241 patients had AdV viremia â„ 1000 copies/ml. Among these, 18% (43/241) died within 6 months of first AdV â„ 1000 copies/ml. Measures of AdV viral peak, duration, and overall burden of infection consistently correlate with all-cause mortality. In multivariable analyses, controlling for lymphocyte recovery, patients with AdV AAUC0-16 in the highest quartile had a hazard ratio of 11.1 versus the lowest quartile (confidence interval 5.3â23.6); for peak AdV viremia, the hazard ratio was 2.2 for the highest versus lowest quartile. Both the peak level and duration of AdV viremia were correlated with short-term mortality, independent of other known risk factors for AdV-related mortality, such as lymphocyte recovery. AdV AAUC0-16, which assesses both peak and duration of AdV viremia, is highly correlated with mortality under the current standard of care. New therapeutic agents that decrease AdV AAUC0-16 have the potential of reducing mortality in this at-risk patient population
V440 Per: the longest period overtone Cepheid
V440 Per is a Population I Cepheid with the period of 7.57 day and low
amplitude, almost sinusoidal light and radial velocity curves. With no reliable
data on the 1st harmonic, its pulsation mode identification remained
controversial. We obtained a radial velocity curve of V440 Per with our new
high precision and high throughput Poznan Spectroscopic Telescope. Our data
reach the accuracy of 130 m/s per individual measurement and yield a secure
detection of the 1st harmonic with the amplitude of A_2= 140+/- 15 m/s. The
velocity Fourier phase \phi_21 of V440 Per is inconsistent at the 7.25 \sigma
level with those of the fundamental mode Cepheids, implying that the star must
be an overtone Cepheid, as originally proposed by Kienzle et al.(1999). Thus,
V440 Per becomes the longest period Cepheid with the securely established
overtone pulsations. We show, that the convective nonlinear pulsation hydrocode
can reproduce the Fourier parameters of V440 Per very well. Requirement to
match the observed properties of V440 Per constrains free parameters of the
dynamical convection model used in the pulsation calculations, in particular
the radiative losses parameter.Comment: Submitted to MNRA
A two-columns formalism for time-dependent modelling of stellar convection. I. Description of the method
Despite all advances in multi-dimensional hydrodynamics, investigations of
stellar evolution and stellar pulsations still depend on one-dimensional
computations. The present work devises an alternative to the mixing length
theory or turbulence models usually adopted for the modelling of convective
transport in such studies. Assuming that the largest convective patterns
generate the majority of convective transport, the convective velocity field is
described using two parallel radial columns to represent up- and downstream
flows. Horizontal exchange in the form of fluid flow and radiation over their
connecting interface couples the two columns and allows a simple circulating
motion. The main parameters of this convective description have a
straightforward geometrical meaning, namely the diameter of the columns
(corresponding to the size of the convective cells) and the ratio of cross
section between up- and downdrafts. For this geometrical setup, the
time-dependent solution of the equations of radiation hydrodynamics is computed
from an implicit scheme which has the advantage of being not affected by the
Courant-Friedrichs-Lewy time step limit. In order to demonstrate the approach,
results for the example of convection zones in Cepheids are presented
Near-IR spectra of ISOGAL sources in the Inner Galactic Bulge
In this work we present near-IR spectra (HK-band) of a sample of 107 sources
with mid-IR excesses at 7 and 15 m detected during the ISOGAL survey.
Making use of the DENIS interstellar extinction map from Schultheis et al.
(1999) we derive luminosities and find that the vs.~
and diagrams are powerful tools for identifying
supergiants, AGB stars, giants and young stellar objects. The majority of our
sample are AGB stars (~ 80%) while we find four good supergiant candidates,
nine young stellar objects and 12 RGB candidates. We have used the most recent
relation by Jeong et al. (2002) based on recent theoretical
modeling of dust formation of AGB stars to determine mass-loss rates. However,
the uncertainties in the mass-loss rates are rather large. The mass-loss rates
of the supergiants are comparable with those in the solar neighbourhood while
the long-period Variables cover a mass-loss range from . The red giant candidateslie at the lower end of the
mass-loss rate range between . We used the
equivalent width of the CO bandhead at 2.3 , the NaI doublet and the
CaI triplet to estimate metallicities using the relation by Ram\'{\i}rez et al.
(\cite{Ramirez2000}). The metallicity distribution of the ISOGAL objects shows
a mean [Fe/H] -0.25 dex with a dispersion of which is
in agreement with the values of Ram\'{i}rez et al. (\cite{Ramirez2000}) for
Galactic Bulge fields between and . A
comparison with the solar neighbourhood sample of Lan\c{c}on & Wood (LW) shows
that our sample is ~ 0.5 dex more metal-rich on average.Comment: 23 pages, 9 figures, 2 appendix with IR spectra. accepted for A&
Genomeâwide offâtarget analyses of CRISPR/Cas9âmediated Tâcell receptor engineering in primary human T cells
Objectives
Exploiting the forces of human T cells for treatment has led to the current paradigm of emerging immunotherapy strategies. Genetic engineering of the T-cell receptor (TCR) redirects specificity, ablates alloreactivity and brings significant progress and off-the-shelf options to emerging adoptive T-cell transfer (ACT) approaches. Targeted CRISPR/Cas9-mediated double-strand breaks in the DNA enable knockout or knock-in engineering.
Methods
Here, we perform CRISPR/Cas9-mediated TCR knockout using a therapeutically relevant ribonucleoprotein (RNP) delivery method to assess the safety of genetically engineered T-cell products. Whole-genome sequencing was performed to analyse whether CRISPR/Cas9-mediated DNA double-strand break at the TCR locus is associated with off-target events in human primary T cells.
Results
TCRα chain and TCRÎČ chain knockout leads to high on-target InDel frequency and functional knockout. None of the predicted off-target sites could be confirmed experimentally, whereas whole-genome sequencing and manual Integrative Genomics Viewer (IGV) review revealed 9 potential low-frequency off-target events genome-wide. Subsequent amplification and targeted deep sequencing in 7 of 7 evaluable loci did not confirm these low-frequency InDels. Therefore, off-target events are unlikely to be caused by the CRISPR/Cas9 engineering.
Conclusion
The combinatorial approach of whole-genome sequencing and targeted deep sequencing confirmed highly specific genetic engineering using CRISPR/Cas9-mediated TCR knockout without potentially harmful exonic off-target effects
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