6,848 research outputs found
Angular momentum evolution of young low-mass stars and brown dwarfs: observations and theory
This chapter aims at providing the most complete review of both the emerging
concepts and the latest observational results regarding the angular momentum
evolution of young low-mass stars and brown dwarfs. In the time since
Protostars & Planets V, there have been major developments in the availability
of rotation period measurements at multiple ages and in different star-forming
environments that are essential for testing theory. In parallel, substantial
theoretical developments have been carried out in the last few years, including
the physics of the star-disk interaction, numerical simulations of stellar
winds, and the investigation of angular momentum transport processes in stellar
interiors. This chapter reviews both the recent observational and theoretical
advances that prompted the development of renewed angular momentum evolution
models for cool stars and brown dwarfs. While the main observational trends of
the rotational history of low mass objects seem to be accounted for by these
new models, a number of critical open issues remain that are outlined in this
review.Comment: 22 pages, 8 figures, accepted for publication in Protostars & Planets
VI, 2014, University of Arizona Press, eds. H. Beuther, R. Klessen, K.
Dullemond, Th. Hennin
Thermal States as Convex Combinations of Matrix Product States
We study thermal states of strongly interacting quantum spin chains and prove
that those can be represented in terms of convex combinations of matrix product
states. Apart from revealing new features of the entanglement structure of
Gibbs states our results provide a theoretical justification for the use of
White's algorithm of minimally entangled typical thermal states. Furthermore,
we shed new light on time dependent matrix product state algorithms which yield
hydrodynamical descriptions of the underlying dynamics.Comment: v3: 10 pages, 2 figures, final published versio
Analysis of the relationship between seismic moment and fault length for large crustal strike-slip earthquakes between 1977-92
Photoemission of a doped Mott insulator: spectral weight transfer and qualitative Mott-Hubbard description
The spectral weight evolution of the low-dimensional Mott insulator TiOCl
upon alkali-metal dosing has been studied by photoelectron spectroscopy. We
observe a spectral weight transfer between the lower Hubbard band and an
additional peak upon electron-doping, in line with quantitative expectations in
the atomic limit for changing the number of singly and doubly occupied sites.
This observation is an unconditional hallmark of correlated bands and has not
been reported before. In contrast, the absence of a metallic quasiparticle peak
can be traced back to a simple one-particle effect.Comment: 4 pages, 4 figures, related theoretical work can be found in
arXiv:0905.1276; shortene
Observations of Mira stars with the IOTA/FLUOR interferometer and comparison with Mira star models
We present K'-band observations of five Mira stars with the IOTA
interferometer. The interferograms were obtained with the FLUOR fiber optics
beam combiner, which provides high-accuracy visibility measurements in spite of
time-variable atmospheric conditions. For the M-type Miras X Oph, R Aql, RU
Her, R Ser, and the C-type Mira V CrB we derived the uniform-disk diameters
11.7mas, 10.9mas, 8.4mas, 8.1mas, and 7.9mas (+/- 0.3mas), respectively.
Simultaneous photometric observations yielded the bolometric fluxes. The
derived angular Rosseland radii and the bolometric fluxes allowed the
determination of effective temperatures. For instance, the effective
temperature of R Aql was determined to be 2970 +/- 110 K. A linear Rosseland
radius for R Aql of (250 +100/-60) Rsun was derived from the angular Rosseland
radius of 5.5mas +/- 0.2mas and the HIPPARCOS parallax of 4.73mas +/- 1.19mas.
The observations were compared with theoretical Mira star models of Bessel et
al. (1996) and Hofmann et al. (1998). The effective temperatures of the M-type
Miras and the linear radius of R Aql indicate fundamental mode pulsation.Comment: 12 pages, 4 postscript figure
Monitoring online biomass with a capacitance sensor during scale-up of industrially relevant CHO cell culture fed-batch processes in single-use bioreactors
In 2004, the FDA published a guideline to implement process analytical technologies (PAT) in biopharmaceutical processes for process monitoring to gain process understanding and for the control of important process parameters. Viable cell concentration (VCC) is one of the most important key performance indicator (KPI) during mammalian cell cultivation processes. Commonly, this is measured offline. In this work, we demonstrated the comparability and scalability of linear regression models derived from online capacitance measurements. The linear regressions were used to predict the VCC and other familiar offline biomass indicators, like the viable cell volume (VCV) and the wet cell weight (WCW), in two different industrially relevant CHO cell culture processes (Process A and Process B). Therefore, different single-use bioreactor scales (50–2000 L) were used to prove feasibility and scalability of the in-line sensor integration. Coefficient of determinations of 0.79 for Process A and 0.99 for Process B for the WCW were achieved. The VCV was described with high coefficients of determination of 0.96 (Process A) and 0.98 (Process B), respectively. In agreement with other work from the literature, the VCC was only described within the exponential growth phase, but resulting in excellent coefficients of determination of 0.99 (Process A) and 0.96 (Process B), respectively. Monitoring these KPIs online using linear regression models appeared to be scale-independent, enabled deeper process understanding (e.g. here demonstrated in monitoring, the feeding profile) and showed the potential of this method for process control. © 2019, The Author(s)
Synthetic Spectra and Color-Temperature Relations of M Giants
As part of a project to model the integrated spectra and colors of elliptical
galaxies through evolutionary synthesis, we have refined our synthetic spectrum
calculations of M giants. After critically assessing three effective
temperature scales for M giants, we adopted the relation of Dyck et al. (1996)
for our models. Using empirical spectra of field M giants as a guide, we then
calculated MARCS stellar atmosphere models and SSG synthetic spectra of these
cool stars, adjusting the band absorption oscillator strengths of the TiO bands
to better reproduce the observational data. The resulting synthetic spectra are
found to be in very good agreement with the K-band spectra of stars of the
appropriate spectral type taken from Kleinmann & Hall (1986) as well. Spectral
types estimated from the strengths of the TiO bands and the depth of the
bandhead of CO near 2.3 microns quantitatively confirm that the synthetic
spectra are good representations of those of field M giants. The broad-band
colors of the models match the field relations of K and early-M giants very
well; for late-M giants, differences between the field-star and synthetic
colors are probably caused by the omission of spectral lines of VO and water in
the spectrum synthesis calculations. Here, we present four grids of K-band
bolometric corrections and colors -- Johnson U-V and B-V; Cousins V-R and V-I;
Johnson-Glass V-K, J-K and H-K; and CIT/CTIO V-K, J-K, H-K and CO -- for models
having 3000 K < Teff < 4000 K and -0.5 < log g < 1.5. These grids, which have
[Fe/H] = +0.25, 0.0, -0.5 and -1.0, extend and supplement the color-temperature
relations of hotter stars presented in a companion paper (astro-ph/9911367).Comment: To appear in the March 2000 issue of the Astronomical Journal. 60
pages including 15 embedded postscript figures (one page each) and 6 embedded
postscript tables (10 pages total
Resolving asymmetries along the pulsation cycle of the Mira star X Hya
The mass-loss process in Mira stars probably occurs in an asymmetric way
where dust can form in inhomogeneous circumstellar molecular clumps. Following
asymmetries along the pulsation cycle can give us clues about these mass-loss
processes. We imaged the Mira star X Hya and its environnement at different
epochs to follow the evolution of the morphology in the continuum and in the
molecular bands. We observed X Hya with AMBER in J-H-K at low resolution at two
epochs. We modelled squared visibilities with geometrical and physical models.
We also present imaging reconstruction results obtained with MiRA and based on
the physical a priori images. We report on the angular scale change of X Hya
between the two epochs. 1D CODEX profiles allowed us to understand and model
the spectral variation of squared visibilities and constrain the stellar
parameters. Reconstructed model-dependent images enabled us to reproduce
closure phase signals and the azimuthal dependence of squared visibilities.
They show evidence for material inhomogeneities located in the immediate
environment of the star.Comment: Accepted for publication in A&A, 17 pages, 16 figure
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