16 research outputs found
Revisiting the Rigidly Rotating Magnetosphere model for Ori E - II. Magnetic Doppler imaging, arbitrary field RRM, and light variability
The initial success of the Rigidly Rotating Magnetosphere (RRM) model
application to the B2Vp star sigma OriE by Townsend, Owocki & Groote (2005)
triggered a renewed era of observational monitoring of this archetypal object.
We utilize high-resolution spectropolarimetry and the magnetic Doppler imaging
(MDI) technique to simultaneously determine the magnetic configuration, which
is predominately dipolar, with a polar strength Bd = 7.3-7.8 kG and a smaller
non-axisymmetric quadrupolar contribution, as well as the surface distribution
of abundance of He, Fe, C, and Si. We describe a revised RRM model that now
accepts an arbitrary surface magnetic field configuration, with the field
topology from the MDI models used as input. The resulting synthetic Ha emission
and broadband photometric observations generally agree with observations,
however, several features are poorly fit. To explore the possibility of a
photospheric contribution to the observed photometric variability, the MDI
abundance maps were used to compute a synthetic photospheric light curve to
determine the effect of the surface inhomogeneities. Including the computed
photospheric brightness modulation fails to improve the agreement between the
observed and computed photometry. We conclude that the discrepancies cannot be
explained as an effect of inhomogeneous surface abundance. Analysis of the UV
light variability shows good agreement between observed variability and
computed light curves, supporting the accuracy of the photospheric light
variation calculation. We thus conclude that significant additional physics is
necessary for the RRM model to acceptably reproduce observations of not only
sigma Ori E, but also other similar stars with significant stellar
wind-magnetic field interactions.Comment: 16 pages, 17 figures, accepted for publication in MNRA
Nuclear inclusions of pathogenic ataxin-1 induce oxidative stress and perturb the protein synthesis machinery
Spinocerebellar ataxia type-1 (SCA1) is caused by an abnormally expanded polyglutamine (polyQ) tract in ataxin-1. These expansions are responsible for protein misfolding and self-assembly into intranuclear inclusion bodies (IIBs) that are somehow linked to neuronal death. However, owing to lack of a suitable cellular model, the downstream consequences of IIB formation are yet to be resolved. Here, we describe a nuclear protein aggregation model of pathogenic human ataxin-1 and characterize IIB effects. Using an inducible Sleeping Beauty transposon system, we overexpressed the ATXN1(Q82) gene in human mesenchymal stem cells that are resistant to the early cytotoxic effects caused by the expression of the mutant protein. We characterized the structure and the protein composition of insoluble polyQ IIBs which gradually occupy the nuclei and are responsible for the generation of reactive oxygen species. In response to their formation, our transcriptome analysis reveals a cerebellum-specific perturbed protein interaction network, primarily affecting protein synthesis. We propose that insoluble polyQ IIBs cause oxidative and nucleolar stress and affect the assembly of the ribosome by capturing or down-regulating essential components. The inducible cell system can be utilized to decipher the cellular consequences of polyQ protein aggregation. Our strategy provides a broadly applicable methodology for studying polyQ diseases
Antenna Arrays for Tactical Communication Systems: A Comparative Study
In this paper, we give a comparative study of several planar antenna concepts for reliable long range links in a tactical environment. The antenna elements are studied in terms of their electrical properties (bandwidth, reflection coefficient and radiation characteristics) and construction (robustness and material consumption). First, we model single antenna elements to investigate if they meet the requirements. Second, we arrange the elements with the best features into 2x2 arrays. Computer simulations of the arrays are verified by measurements. Finally, we formulate recommendations for large array (8x8 or 16x16 elements) synthesis to achieve the required properties
The roAp star α
We report on an analysis of high-precision, multi-colour photometric
observations of the rapidly-oscillating Ap (roAp) star Cir. These
observations were obtained with the BRITE-Constellation, which is a coordinated
mission of five nanosatellites that collects continuous
millimagnitude-precision photometry of dozens of bright stars for up to 180
days at a time in two colours (Johnson B and R). BRITE stands for BRight Target
Explorer. The object Cir is the brightest roAp star and an ideal
target for such investigations, facilitating the determination of oscillation
frequencies with high resolution. This star is bright enough for complementary
interferometry and time-resolved spectroscopy. Four BRITE satellites observed
Cir for 146 d or 33 rotational cycles. Phasing the photometry
according to the 4.4790 d rotational period reveals qualitatively different
light variations in the two photometric bands. The phased red-band photometry
is in good agreement with previously-published WIRE data, showing a light curve
symmetric about phase 0.5 with a strong contribution from the first harmonic.
The phased blue-band data, in contrast, show an essentially sinusoidal
variation. We model both light curves with Bayesian Photometric Imaging, which
suggests the presence of two large-scale, photometrically bright (relative to
the surrounding photosphere) spots. We also examine the high-frequency
pulsation spectrum as encoded in the BRITE photometry. Our analysis establishes
the stability of the main pulsation frequency over the last 20 years, confirms
the presence of frequency f7, which was not detected (or the mode not excited)
prior to 2006, and excludes quadrupolar modes for the main pulsation frequency.Comment: 10 pages, 11 figures, accepted by Astronomy & Astrophysic