52,200 research outputs found
Circumstellar environment of the M-type AGB star R Dor. APEX spectral scan at GHz
Our current insights into the circumstellar chemistry of asymptotic giant
branch (AGB) stars are largely based on studies of carbon-rich stars and stars
with high mass-loss rates. In order to expand the current molecular inventory
of evolved stars we present a spectral scan of the nearby, oxygen-rich star R
Dor, a star with a low mass-loss rate (/yr). We
carried out a spectral scan in the frequency ranges 159.0-321.5GHz and
338.5-368.5 GHz (wavelength range 0.8-1.9mm) using the SEPIA/Band-5 and SHeFI
instruments on the APEX telescope and we compare it to previous surveys,
including one of the oxygen-rich AGB star IK Tau, which has a high mass-loss
rate (/yr). The spectrum of R Dor is dominated by
emission lines of SO and the different isotopologues of SiO. We also detect
CO, HO, HCN, CN, PO, PN, SO, and tentatively TiO, AlO, and NaCl.
Sixteen out of approximately 320 spectral features remain unidentified. Among
these is a strong but previously unknown maser at 354.2 GHz, which we suggest
could pertain to HSiO, silanone. With the exception of one, none of these
unidentified lines are found in a similarly sensitive survey of IK Tau
performed with the IRAM 30m telescope. We present radiative transfer models for
five isotopologues of SiO (SiO, SiO, SiO, SiO,
SiO), providing constraints on their fractional abundance and radial
extent. We derive isotopic ratios for C, O, Si, and S and estimate that R Dor
likely had an initial mass in the range 1.3-1.6, in agreement with
earlier findings based on models of HO line emission. From the presence of
spectral features recurring in many of the measured thermal and maser emission
lines we tentatively identify up to five kinematical components in the outflow
of R Dor, indicating deviations from a smooth, spherical wind.Comment: 66 pages, 25 figures, Accepted for publication in Astronomy &
Astrophysics. Fully reduced FITS spectrum made available through CD
Parity-violating electron scattering and nucleon structure
The measurement of parity violation in the helicity dependence of electron-nucleon scattering provides unique information about the basic quark structure of the nucleons. This review presents the general formalism of parity-violating electron scattering, with emphasis on elastic electron-nucleon scattering. The physics issues addressed by such experiments are discussed, and the major goals of the presently envisioned experimental program are identified. Results from a recent series of experiments are summarized and the future prospects of this program are discussed
Bank efficiency, ownership and market structure: Why are interest spreads so high in Uganda?.
Antiferromagnetism and Superconductivity in a Model with Extended Pairing Interactions
The competition between antiferromagnetism and the superconducting
state is studied in a model with near and next near neighbour interactions in
the absence of any on-site repulsion. A mean field study shows that it is
possible to have simultaneous occurrence of an antiferromagnetic and a singlet
superconducting state in this model. In addition, such a coexistence
generates a triplet superconducting order parameter with centre of mass
momentum {\it dynamically} having the same orbital symmetry as
the singlet superconductor. Inclusion of next nearest neighbour hopping in the
band stabilises the superconducting state away from half filling, the
topology of the phase diagram, though, remains similar to the near neighbour
model. In view of the very recent observation of a broad region of coexistence
of antiferrmagnetic and unconventional superconducting states in organic
superconductors, the possibility of observation of the triplet state has been
outlined.Comment: 12 pages(tex file), 7 figures (ps files
Designers manual for circuit design by analog/digital techniques Final report
Manual for designing circuits by hybrid compute
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