2,949 research outputs found
Advances of plasma diagnostics with high-resolution spectroscopy of stellar coronae
X-ray emission from cool stars is an important tracer for stellar activity.
The X-ray luminosity reflects different levels of activity and covers four
orders of magnitude in stars of spectral types M-F. Low spectral resolution
provided by X-ray observations of stellar coronae in the past allowed the
determination of temperature distributions and elemental abundances making use
of atomic databases (listing line emissivities and bremsstrahlung continuum for
a given temperature structure). The new missions XMM-Newton and Chandra carry
X-ray gratings providing sufficient spectral resolution to measure the fluxes
of strategic emission lines. I describe the different approaches applicable to
low-resolution and high-resolution spectra, especially focusing on the new
grating spectra with X-ray lines. From only a few lines it is possible to
determine plasma temperatures and associated densities, to check for any
effects from resonant scattering, and to identify particular abundance
anomalies. Line-based temperature- and density measurements represent only a
fraction of the total plasma, but the pressure environment of different
fractions can be probed simply by selection of specific lines. Selected results
are presented covering all aspects of line-based analyses.Comment: 11 pages, 2 figures; Advances in Space Research, Proceedings for
COSPAR meeting in Paris July 200
Longitudinal Assessment of Dementia Measures in Down Syndrome
Introduction: Early detection of dementia symptoms is critical in Down syndrome (DS) but complicated by clinical assessment barriers. The current study aimed to characterize cognitive and behavioral impairment using longitudinal trajectories comparing several measures of cognitive and behavioral functioning.
Methods: Measures included global cognitive status (Severe Impairment Battery [SIB]), motor praxis (Brief Praxis Test [BPT]), and clinical dementia informant ratings (Dementia Questionnaire for People with Learning Disabilities [DLD]). One-year reliability was assessed using a two-way mixed effect, consistency, single measurement intraclass correlation among non-demented participants. Longitudinal assessment of SIB, BPT, and DLD was completed using linear mixed effect models.
Results: One‐year reliability (n = 52; 21 male) was moderate for DLD (0.69 to 0.75) and good for SIB (0.87) and BPT (0.80). Longitudinal analysis (n = 72) revealed significant age by diagnosis interactions for SIB (F(2, 115.02) = 6.06, P = .003), BPT (F(2, 85.59) = 4.56, P = .013), and DLD (F(2, 103.56) = 4.48, P = .014). SIB progression (PR) had a faster decline in performance versus no‐dementia (ND) (t(159) = −2.87; P = .013). Dementia had a faster decline in BPT performance versus ND (t(112) = −2.46; P = .041). PR showed quickly progressing scores compared to ND (t(128) = −2.86; P = .014).
Discussion: Current measures demonstrated moderate to good reliability. Longitudinal analysis revealed that SIB, BPT, and DLD changed with age depending on diagnostic progression; no change rates were dependent on baseline cognition, indicating usefulness across a variety of severity levels in DS
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