4,368 research outputs found
Calculating three thermal coefficients from one data set
© 2019 Academic Publications. We study the problem of determining three thermal coefficients from one set data of a model problem rising in thermodynamics. This is an inverse problem, that is to coincide the solution of the differential equation with actual experimental results. The used method is based on minimizing the solution of the problem with the experimental data. Both the direct and inverse problems are described and numerical results are given
A multiwavelength radial velocity search for planets around the brown dwarf LP 944-20
The nearby brown dwarf LP 944-20 has been monitored for radial velocity
variability at optical and near-infrared wavelengths using the VLT/UVES and the
Keck/NIRSPEC spectrographs, respectively. The UVES radial velocity data
obtained over 14 nights spanning a baseline of 841 days shows significant
variability with an amplitude of 3.5 km s. The periodogram analysis of
the UVES data indicates a possible period between 2.5 hours and 3.7 hours,
which is likely due to the rotation of the brown dwarf. However, the NIRSPEC
data obtained over 6 nights shows an rms dispersion of only 0.36 km s
and do not follow the periodic trend. These results indicate that the
variability seen with UVES is likely to be due to rotationally modulated
inhomogeneous surface features. We suggest that future planet searches around
very low-mass stars and brown dwarfs using radial velocities will be better
conducted in the near-infrared than in the optical.Comment: accepted by ApJ Letter
A Physical Limit to the Magnetic Fields of T Tauri Stars
Recent estimates of magnetic field strengths in T Tauri stars yield values
--. In this paper, I present an upper limit to the
photospheric values of by computing the equipartition values for different
surface gravities and effective temperatures. The values of derived from
the observations exceed this limit, and I examine the possible causes for this
discrepancy
Observations of Cepheids with the MOST satellite: Contrast between Pulsation Modes
The quantity and quality of satellite photometric data strings is revealing
details in Cepheid variation at very low levels. Specifically, we observed a
Cepheid pulsating in the fundamental mode and one pulsating in the first
overtone with the Canadian MOST satellite. The 3.7-d period fundamental mode
pulsator (RT Aur) has a light curve that repeats precisely, and can be modeled
by a Fourier series very accurately. The overtone pulsator (SZ Tau, 3.1 d
period) on the other hand shows light curve variation from cycle to cycle which
we characterize by the variations in the Fourier parameters. We present
arguments that we are seeing instability in the pulsation cycle of the overtone
pulsator, and that this is also a characteristic of the O-C curves of overtone
pulsators. On the other hand, deviations from cycle to cycle as a function of
pulsation phase follow a similar pattern in both stars, increasing after
minimum radius. In summary, pulsation in the overtone pulsator is less stable
than that of the fundamental mode pulsator at both long and short timescales.Comment: accepted in MNRAS, 11 pages, 10 figure
Occurrence of Blarina brevicauda in Arkansas and Notes on the Distribution of Blarina carolinensis and Cryptotis parva
We provide an update on the species and distribution of shrews occurring in Arkansas. Shrews were collected within Arkansas Game and Fish Commission Wildlife Management Areas and along the Buffalo National River. We also searched mammal collections at several institutional museums to provide additional locality records for Cryptotis parva. Specimens of Blarina were identified to species by DNA sequencing of the mitochondrial cytochrome b gene. Previously, Blarina hylophaga was believed to occur in the northwest corner of Arkansas and B. carolinensis throughout the rest of the state. However, our genetic analysis revealed that it is B. brevicauda that occupies the northwestern portion of the state. We also document several new county records for B. carolinensis and C. parva in Arkansas
MOST photometry of the enigmatic PMS pulsator HD 142666
We present precise photometry of the pulsating Herbig Ae star HD 142666
obtained in two consecutive years with the MOST (Microvariability & Oscilations
of STars) satellite.
Previously, only a single pulsation period was known for HD 142666. The MOST
photometry reveals that HD 142666 is multi-periodic. However, the unique
identification of pulsation frequencies is complicated by the presence of
irregular variability caused by the star's circumstellar dust disk. The two
light curves obtained with MOST in 2006 and 2007 provided data of unprecedented
quality to study the pulsations in HD 142666 and also to monitor the
circumstellar variability.
We attribute 12 frequencies to pulsation. Model fits to the three frequencies
with the highest amplitudes lie well outside the uncertainty box for the star's
position in the HR diagram based on published values.
The models suggest that either (1) the published estimate of the luminosity
of HD 142666, based on a relation between circumstellar disk radius and stellar
luminosity, is too high and/or (2) additional physics such as mass accretion
may be needed in our models to accurately fit both the observed frequencies and
HD 142666's position in the HR diagram.Comment: 10 pages, 11 figures, accepted for publication by Astronomy and
Astrophysic
Effects of RAF inhibitors on PI3K/AKT signalling depend on mutational status of the RAS/RAF signalling axis
Targeted therapies within the RAS/RAF/MEK/ERK signalling axis become increasingly popular, yet cross-talk and feedbacks in the signalling network lead to unexpected effects. Here we look systematically into how inhibiting RAF and MEK with clinically relevant inhibitors result in changes in PI3K/AKT activation. We measure the signalling response using a bead-based ELISA, and use a panel of three cell lines, and isogenic cell lines that express mutant forms of the oncogenes KRAS and BRAF to interrogate the effects of the MEK and RAF inhibitors on signalling. We find that treatment with the RAF inhibitors have opposing effects on AKT phosphorylation depending on the mutational status of two important oncogenes, KRAS and BRAF. If these two genes are in wildtype configuration, RAF inhibitors reduce AKT phosphorylation. In contrast, if BRAF or KRAS are mutant, RAF inhibitors will leave AKT phosphorylation unaffected or lead to an increase of AKT phosphorylation. Down-regulation of phospho-AKT by RAF inhibitors also extends to downstream transcription factors, and correlates with apoptosis induction. Our results show that oncogenes rewire signalling such that targeted therapies can have opposing effects on parallel pathways, which depend on the mutational status of the cell
MOST photometry of the roAp star 10 Aql
Context: We present 31.2 days of nearly continuous MOST photometry of the
roAp star 10Aql. Aims:The goal was to provide an unambiguous frequency
identification for this little studied star, as well as to discuss the detected
frequencies in the context of magnetic models and analyze the influence of the
magnetic field on the pulsation. Methods: Using traditional Fourier analysis
techniques on three independent data reductions, intrinsic frequencies for the
star are identified. Theoretical non-adiabatic axisymmetric modes influenced by
a magnetic field having polar field strengths Bp = 0-5kG were computed to
compare the observations to theory. Results: The high-precision data allow us
to identify three definite intrinsic pulsation frequencies and two other
candidate frequencies with low S/N. Considering the observed spacings, only one
(50.95microHz) is consistent with the main sequence nature of roAp stars. The
comparison with theoretical models yields a best fit for a 1.95Msun model
having solar metallicity, suppressed envelope convection, and homogenous helium
abundance. Furthermore, our analysis confirms the suspected slow rotation of
the star and sets new lower limits to the rotation period (Prot>1 month) and
inclination (i>30\pm10deg.). Conclusions:The observed frequency spectrum is not
rich enough to unambiguously identify a model. On the other hand, the models
hardly represent roAp stars in detail due to the approximations needed to
describe the interactions of the magnetic field with stellar structure and
pulsation. Consequently, errors in the model frequencies needed for the fitting
procedure can only be estimated. Nevertheless, it is encouraging that models
which suppress convection and include solar metallicity, in agreement with
current concepts of roAp stars, fit the observations best.Comment: accepted by A&
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