12,561 research outputs found
Variability and nature of the binary in the Red Rectangle Nebula
We present new observations of the central binary inside the Red Rectangle
nebula. The detection of zinc in the optical spectrum confirms that the
peculiar photospheric abundances are due to accretion of circumstellar gas.
Grey brightness variations with the orbital period are observed. They are
interpreted as being due to the variation of the scattering angle with orbital
phase. The small orbital separation of the system is not compatible with
previous normal evolution of the primary on the AGB. We point out the
similarity of the orbital history of this and other similar systems with those
of some close Barium stars and suggest that the nonzero eccentricity of the
orbit is the result of tidal interaction with the circumbinary disk.Comment: 4 pages, 3 figures, A&A Letters accepte
One-second coherence for a single electron spin coupled to a multi-qubit nuclear-spin environment
Single electron spins coupled to multiple nuclear spins provide promising
multi-qubit registers for quantum sensing and quantum networks. The obtainable
level of control is determined by how well the electron spin can be selectively
coupled to, and decoupled from, the surrounding nuclear spins. Here we realize
a coherence time exceeding a second for a single electron spin through
decoupling sequences tailored to its microscopic nuclear-spin environment. We
first use the electron spin to probe the environment, which is accurately
described by seven individual and six pairs of coupled carbon-13 spins. We
develop initialization, control and readout of the carbon-13 pairs in order to
directly reveal their atomic structure. We then exploit this knowledge to store
quantum states for over a second by carefully avoiding unwanted interactions.
These results provide a proof-of-principle for quantum sensing of complex
multi-spin systems and an opportunity for multi-qubit quantum registers with
long coherence times
The Vector Meson Form Factor Analysis in Light-Front Dynamics
We study the form factors of vector mesons using a covariant fermion field
theory model in dimensions. Performing a light-front calculation in the
frame in parallel with a manifestly covariant calculation, we note the
existence of a nonvanishing zero-mode contribution to the light-front current
and find a way of avoiding the zero-mode in the form factor calculations.
Upon choosing the light-front gauge (\ep^+_{h=\pm}=0) with circular
polarization and with spin projection , only the
helicity zero to zero matrix element of the plus current receives zero-mode
contributions. Therefore, one can obtain the exact light-front solution of the
form factors using only the valence contribution if only the helicity
components, , and , are used. We also compare our
results obtained from the light-front gauge in the light-front helicity basis
(i.e. ) with those obtained from the non-LF gauge in the instant form
linear polarization basis (i.e. ) where the zero-mode contributions to
the form factors are unavoidable.Comment: 33 pages; typo in Eq.(15) is corrected; comment on Ref.[9] is
corrected; version to appear in Phys. Rev.
Infrared High-Resolution Spectroscopy of Post-AGB Circumstellar Disks. I. HR 4049 - The Winnowing Flow Observed?
High-resolution infrared spectroscopy in the 2.3-4.6 micron region is
reported for the peculiar A supergiant, single-lined spectroscopic binary HR
4049. Lines from the CO fundamental and first overtone, OH fundamental, and
several H2O vibration-rotation transitions have been observed in the
near-infrared spectrum. The spectrum of HR 4049 appears principally in emission
through the 3 and 4.6 micron region and in absorption in the 2 micron region.
The 4.6 micron spectrum shows a rich 'forest' of emission lines. All the
spectral lines observed in the 2.3-4.6 micron spectrum are shown to be
circumbinary in origin. The presence of OH and H2O lines confirm the
oxygen-rich nature of the circumbinary gas which is in contrast to the
previously detected carbon-rich material. The emission and absorption line
profiles show that the circumbinary gas is located in a thin, rotating layer
near the dust disk. The properties of the dust and gas circumbinary disk and
the spectroscopic orbit yield masses for the individual stars, M_AI~0.58 Msolar
and M_MV~0.34 Msolar. Gas in the disk also has an outward flow with a velocity
of 1 km/s. The severe depletion of refractory elements but near-solar
abundances of volatile elements observed in HR 4049 results from abundance
winnowing. The separation of the volatiles from the grains in the disk and the
subsequent accretion by the star are discussed. Contrary to prior reports, the
HR 4049 carbon and oxygen isotopic abundances are typical AGB values:
12C/13C=6^{+9}_{-4} and 16O/17O>200.Comment: 42 pages, 14 figures, Accepted by Ap
Neutrophil gelatinase-associated lipocalin as an early indicator for mortality in adult critically ill patients with acute kidney injury
Thomson scattering in a low-pressure neon mercury positive column
The electron density and the electron temperature in a low-pressure neon mercury positive column are determined using Thomson scattering. Special attention has been given to the stray light reduction in the Thomson scattering setup. The results are obtained in a discharge tube with a 26 mm diam, 10 mbar of neon, a mercury pressure inbetween 0.14 and 0.85 Pa, and an electric current ranging from 100 to 400 mA. The systematic error in the electron density is 15%–45%, the statistical error is 25%–35%. The total error in the electron temperature is 15%–35%. ©2001 American Institute of Physics
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