2,965 research outputs found
On the Formation of Multiple-Shells Around Asymptotic Giant Branch Stars
Two types of models for the formation of semi-periodic concentric multiple
shells (M-shells) around asymptotic giant branch (AGB) stars and in planetary
nebulae are compared against observations. Models that attribute the M-shells
to processes in an extended wind acceleration zone around AGB stars result in
an optically thick acceleration zone, which reduces the acceleration efficiency
in outer parts of the extended acceleration zone. This makes such models an
unlikely explanation for the formation of M-shells. Models which attribute the
M-shell to semi-periodic variation in one or more stellar properties are most
compatible with observations. The only stellar variation models on time scales
of 50-1500 years that have been suggested are based on an assumed solar-like
magnetic cycle. Although ad-hoc, the magnetic cycle assumption fits naturally
into the increasingly popular view that magnetic activity plays a role in
shaping the wind from upper AGB stars.Comment: 8 pages, Submitted to Ap
Tissue holder for experimental and Demonstration Surgery
Development of device for holding anatomical tissues during operations is discussed. Device consists of plastic dish with hemispherical recess in center to hold excised eyes. Low vacuum applied to underside of recess insures holding of part
Distance Dependent Offsets between Parallaxes for Nearby Stars and Gaia DR1 Parallaxes
We use 612 single stars with previously published trigonometric parallaxes
placing them within 25 pc to evaluate parallaxes released in Gaia's first data
release (DR1). We find that the Gaia parallaxes are, on average, mas smaller than the weighted mean trigonometric parallax values for
these stars in the solar neighborhood. We also find that the offset changes
with distance out to 100 pc, in the sense that the closer the star, the larger
the offset. We find no systematic trends in the parallax offsets with stellar
magnitude, color, or proper motion. We do find that the offset is
roughly twice as large for stars south of the ecliptic compared to those that
are north.Comment: 14 pages, 2 figures, 3 tables, accepted for publication in ApJ
Letter. The table 1 is available in its entirety in a machine-readable form
in the online journa
Mapping Metal Distributions in Thin Cryosections without Scanning Transmission Electron Microscope with the Philips Electron Beam and Image Deflection (EBID) Unit
The purpose of the present paper was to describe the use of a commercially-available, and relatively inexpensive, beam and image deflection unit that can facilitate digital X-ray (element) mapping in a standard transmission electron microscope not furnished with a STEM attachment. The test specimen was a thin freeze-dried section of the metal-sequestering chloragogenous tissue from the earthworm, Lumbricus rubellus, inhabiting a soil naturally contaminated with Pb, Zn and Cd. Qualitative maps obtained from this material confirmed the efficacy of the deflection unit, and revealed the presence of three compositionally distinct metal-accumulating compartments within the chloragocytes: (i) ovoid, electron-dense, phosphate-bearing and Ca-, Pb-and Zn-containing chloragosomes; (ii) relatively electron lucent, morphologically featureless, Cd-and S-rich cadmosomes ; an extremely electron-dense compartment lying close to individual chloragosomes, containing high concentrations of Ca, Pb and Zn but deficient in P. Azo dye histochemistry indicated that the chloragogenous tissue did not contain either diffuse or focal acid phosphatase activity. The possible relationships of the three metal-sequestering compartments to each other and to the lysosomal system was discussed
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